THE ELECTRIC RAILWAY McGraw-Hill DookCompany Electrical World The Engineering and Mining Journal Engineering Record Engineering News Railway Age Gazette American Machinist Signal E,ngin 10000 ^< ^ <*.. --- i > 10 15 TO 25 30 35 40 Speed, M. P. H. FIG. 1. Characteristics of typical steam locomotives. to the cylinders. Since the number of strokes, and hence the quantity of steam used, varies directly with the speed, a point must be reached where the boiler cannot keep up its pressure against the increasing demand for steam. To reach higher speeds the cut-off must be advanced, so that the amount of steam taken per stroke is reduced. The higher the speed, the earlier must be the cut-off, and hence the less the mean effective pressure and the tractive effort. This is shown graphically in Fig. 1, which gives a tractive effort-speed curve of a modern passenger engine and of a modern freight engine. In the high-speed portion of the curve the locomotive is virtually a constant power machine, since the tractive effort varies almost inversely as the speed. INTRODUCTION 7 The performance of the cylinders is hampered, since they rely for their steam on a boiler of limited capacity. The boiler in turn is dependent on the fire-box and the ability of the fireman to keep it properly supplied with fuel. Owing to the necessity of getting maximum capacity per unit of weight, the performance is forced beyond the most efficient operating point. The draft is so great that a large portion of the fuel (in case coal is used) is thrown out of the stack in the form 'of cinders. Tests show that approximately one-tenth of the total weight of coal fired is dis- charged in this manner. Although it may be possible, by the use of special precautions, to operate the steam locomotive with- out smoke or dirt, it is in general impractical to do so. Since the entire power plant, and also a supply of fuel and water, must be hauled in addition to the train, there is a distinct loss of efficiency due to that cause. The steam locomotive is most efficient when built in the larger sizes, since many of the losses are nearly constant, or increase more slowly than in proportion to the weight. The limit is reached only by the ability of the fireman to handle the necessary amount of coal. In some recent locomotives mechan- ical stokers are used, resulting in some increase in capacity over hand firing. In the smallest sizes, the steam locomotive is decidedly inefficient, and in many respects is not the excellent machine that has been developed by the designers of modern large engines. Other Motive Powers. Gasoline and other fuel oils have been used in connection with internal combustion engines. While these combinations are, in common with the steam locomotive, complete power plants, they are considerably simpler, and are lighter than it per unit of output. They also operate with but a small fraction of the smoke and dirt incident to the steam locomotive. The internal combustion motor is in- herently a constant-speed machine, and special means must be employed to reduce speeds at starting and for slow running. In the automobile this is brought about by changes of gearing, and variations in the amount of charge and the time of its ignition. At best these methods give an imperfect speed control; and they are not very practical for heavy train service. Compressed air and stored steam have also been tried for motive powers. The engines are similar to the ordinary loco- motive steam engine, but are supplied from tanks on the loco- 8 THE ELECTRIC RAILWAY motive containing either steam or air compressed to a high pressure. Owing to the high storage capacity necessary, and to the low thermodynamic efficiency of the complete cycle, they have not been successful. A few locomotives of these types are used in mines, where the fire of the steam locomotive would be liable to cause explosions of the mine gases. The cable has already been mentioned. It was never suited to any class of service except in congested city districts,- and even there its limitations forced its retirement as soon as a better motive power was available. At the present time the only roads operated by cable are in a few places where the grades are so steep that some form of positive drive is necessary. Electric Systems. For railway service, there is available a number of combinations of motors and electric circuits, giving an almost unlimited flexibility, and enabling the engineer to choose the best type of equipment for each case. In fact, this wide range of choice is one of the factors which has prevented earlier consideration of electrification by steam railroad managers, who are to a certain extent awaiting the standardization of one or another of the principal systems of electric operation. Although practically every type of electric motor ever built has been used or suggested for traction at one time or another, there are in use three systems which have driven out all others for practical service: 1 . The direct-current system, using series-wound motors. 2. The single-phase alternating-current system, using (a) Single-phase commutator motors, or (6) Three-phase induction motors operated through a " split-phase converter." 3. The three-phase alternating-current system, using three-phase induction motors. It is beyond the scope of the present chapter to present an extended discussion and comparison of the different electric systems. They will be taken up part by part in later chapters, with a summary under " Systems of Electrification." In general, the direct-current series motor and some of the alternating- current commutator motors possess characteristics quite similar to those of the steam locomotive engine, with even better performance at starting; while the induction motors operate at substantially constant speed throughout their working range. The speed of each type may be reduced for starting or slow run- INTRODUCTION 9 ning by purely electrical means, thus obviating the necessity of change gears, as with the internal combustion engines. The efficiency of each is high, and, including all losses in genera- tion and distribution, is at least as good as that of the steam locomotive. Of the three systems, the direct-current has been in use the longest time. All of the early experiments were made with direct-current motors ; and for about 20 years alternating current was not even thought of in connection with railway operation. It is evident that the direct-current motor, having passed through a long stage of experimentation and development, has reached the highest state of perfection at the present time. All railways of the first class (street railways) are operated by this system; and in this kind of service it has proved eminently satisfactory. Whether it will maintain its excellent reputation in the heavier classes of traction remains to be proved. Advantages of Electric Systems. As compared with other motive powers, electric motors possess a number of marked advantages. They may be enumerated as follows: (a) The heavy overloads that may be imposed on the electric motor for a short time. (b) The great starting ability due to the economical distri- bution of weight. (c) The absence of reciprocating parts, giving a uniform torque. (d) The cleanliness and noiselessness of this method of operation. (e) The ease and economy of control of the motors. (/) The high efficiency of the electric motor and distribu- tion systems as applied to traction. Electric motors of the types used for traction are capable of withstanding heavy overloads. In fact, if properly designed for its continuous capacity, a motor may be loaded until stopped without harm to it, unless the overload be too prolonged. This characteristic is of great value when there is difficulty in starting a train due to any cause. The weight-distribution of electric motive powers is excellent. In the case of motor cars, all of the train weight may be made available for adhesion, by placing a motor on each axle. This maximum adhesion is seldom demanded; although for a number of reasons single cars are often equipped with four motors. In 10 THE ELECTRIC RAILWAY steam locomotives, a considerable proportion of the total weight is in the tender with its load of fuel and water. Not only is this feature absent in the electric locomotive, but a larger portion of the weight of the locomotive proper may be placed on the drivers. The effect of this is that the electric engines will be much the lighter for the same hauling power. In the steam locomotive, the tractive effort in one revolution of the drivers varies over a considerable range, due to the non- uniform effort of the steam during the stroke of the piston. In some cases this will cause slipping of the wheels before the average value of the maximum tractive effort is reached. In the electric locomotive the torque may be applied up to the slipping point of the wheels without difficulty, since, due to the symmetrical design of the motor armature, it gives the same torque in any position; which is also true in those machines where the force is transmitted through cranks and side-rods, if the cranks be " quartered," as is the usual practice. The cleanliness of electric motors, as compared with steam engines, is unquestioned. In fact, this feature is one of those that have made rapid transit on city streets satisfactory, and is the one thing that has made subway and tunnel operation possible. The absence of smoke, dust and cinders is a great argument, especially since a measurable financial loss is in- volved in the dirt incident to steam operation. The view has been taken by the courts that persons living along the line of a steam road in a city can recover for damage due to these causes. Noise may be reduced to an almost negligible amount by the use of properly maintained electrical equipment, something impossible with steam; for the sharp blast of the exhaust through the nozzle is necessary to provide sufficient draft in the fire-box. Electric motors of the various types may be controlled by electrical means to operate at various speeds; and the speed may be reduced to zero for starting or coupling purposes. Although there are some losses incident to greatly reduced speeds which do not appear with steam locomotives, they do not compare unfavorably with losses in the control of other motive powers. Traction motors are usually designed, not for high efficiency, but for ruggedness and reliability. Commercial machines have very good efficiencies, however. The overall efficiency of the complete electric system will vary from 50 per cent, to 75 per cent, in ordinary cases. Although at first sight these values may INTRODUCTION 11 appear low, they are in reality excellent, and better than those of other motive power systems employed in similar service. The advantages enumerated above are most marked in the first and second classes of roads; but nearly all of them are applicable to the third class also. They are likewise greater in the case of motor car operation than when the power is con- centrated in locomotives, though the use of the latter introduces certain compensating advantages which often more than offset the detriments. In general, the superiority of electric power is great enough to warrant its consideration for any class of railway service; and its use is the more desirable almost in proportion to the density of the traffic, either freight or passenger. The Railway Problem. In a broad sense, the railway has much in common with other engineering works. Speaking generally, what is desired is to perform certain functions for the benefit of the public, at the same time making a reasonable profit on the invested capital. In attacking any problem of this character, it is necessary to consider all phases of it in determining whether a project is attractive for the investor. To do this, certain engineering points must be considered in detail, and assumptions made and proved correct. In the following chapters the engineering methods are discussed sepa- rately; but the main object, as given in this paragraph, must not be lost sight of. CHAPTER II THE MECHANICS OF TRACTION Fundamental Principles. The fundamental relations govern- ing the motion of railway trains are derived directly from the laws of motion of any material bodies. For convenience in calculation a number of secondary units have been derived for the solution of railway problems. Since these units are almost universally employed in the literature of the subject, a brief review of their derivation is desirable. Work and Energy. When a material body is moved over a given distance, mechanical energy is expended and work is done. By the principle of the conservation of energy, the two must be equal, and the numerical measure of either is the product of the force employed into the distance over which the body has moved, or W = Fs (1) where W is the energy or work, F is the force employed, and s is the distance over which the body is moved. The above equation expresses the potential energy of the body. If we consider a body in motion, especially if the force be a vari- able one, the equation must be made to express momentary changes of distance covered, or dW = Fds (2) From equation (2) may be derived the total energy or work done, by the integration, W = fFds (3) In order to apply equation (3), it is necessary to estimate the change in the distance covered at each portion of the motion. This is most readily done by means of the velocity, which is the rate of change of position with respect to time, or ds 12 THE MECHANICS OF TRACTION 13 This may also be written ds = vdt (4a) where v is the velocity, and t the time. If we use this last value in the above equation for energy, (2), it becomes dW = Fvdt (5) From elementary mechanics we have W = %-Mv* (6) where M is the mass of the body in motion. A differentiation of this last equation, (6), with respect to Vj gives dW = Mvdv (7) Acceleration. We may now equate the two expressions for differential energy, (5) and (7), or Fvdt = Mvdv (8) whence F = M -j- (8a) In this equation, -77, the rate of change of velocity with respect to time, is better known as the acceleration, a, or F = Ma (9) Equation (9) holds good in any system of notation. In countries where the English system of units is employed, the force F and the mass M are usually measured in pounds, and acceleration a in feet per second per second. Since masses are usually estimated by gravity-measure, it is customary to restate equation (9) as '-? (10) where G is the weight of the moving body and g the acceleration due to gravity. In the English system the " gravitation con- stant" g has a value of approximately 32.2, whence F = 3^2 a (10tt) and a = ' 14 THE ELECTRIC RAILWAY In equations (10a) and (106) acceleration a is expressed in feet per second per second, and force, F, and weight, G, in pounds. For use in railway problems these units are inconvenient, the speeds being more readily determined in miles per hour and the accelera- tions in miles per hour per second ; and the weights are of such magnitude that they are better expressed in tons (in the United States the short ton of 2000 Ib. is now universally used). Formula (10a) and (106) must therefore be modified for prac- tical use. A mile contains 5280 feet, and an hour 60 X 60 = 3600 seconds; hence a velocity of l.mile per hr. is equal to O 1.467 ft. per sec. If we express accelerations in miles per hour per second by A, then a = 1.467A (11) or ' A = 0.682a (llo) Employing T to represent weight in short tons, and A to denote accelerations in miles per hr. per sec., as given in equations (11) and (Ha), equation (10a) becomes 1.467 A 2000 T whence A = 0.01098 ~ (12) or, solving for F, F = 91.097 TA (13) or, in other words, a force of 91.1 Ib. applied to a body weighing 1 ton will produce in it an acceleration of 1 mile per hr. per sec. Equations (12) and (13) are the ones usually employed in discussing acceleration of railway trains. Rotational Acceleration. Besides the rectilinear acceleration as determined above, it is also necessary to impart to the wheels, axles, gears and motor armatures a motion of rotation. To produce this rotational acceleration an additional amount of force must be employed. This may be determined as follows: Referring to Fig. 2, consider a particle of mass dM, of any of the rotating parts of a car, situated at a distance p from the center of rotation. If the angular acceleration of the rotating part be 0, the tangential acceleration of the mass dM at any instant will be \ THE MECHANICS OF TRACTION 15 p0, and, from equation (9), the force /i to produce that accelera- tion is pddM. Since the force /i acts at a distance p from the center of rotation, its moment is pBdM X p = p 2 BdM The total moment of the whole rotating mass is fp*edM = KB (14) where K is the moment of inertia of the body about its axis of rotation. It may also be expressed by the relation K = k 2 M (15) where k is the radius of gyration and M the total rotating mass. Also re = a (16) or a Accel.6 r (16a) where r is the radius of the rotating part considered, and a its tangential acceleration. FlG - 2. Determination of rotational acceleration. Hence Total moment = k 2 M (17) k 2 = -Ma (17o) and Moment Ma (18) For a pair of ordinary cast iron car wheels and axle the weight is approximately 1950 lb., and the ratio- =0.64. Substituting in equation (18), 1Q50 /i = (0.64) 2 X 32-2 a = 24 ' 80a This gives the force /i Ib. to produce a corresponding acceleration in feet per second per second. To transform the equation to our 16 THE ELECTRIC RAILWAY railway system of units, it is only necessary to multiply by the constant 1.467. Since there are four axles and pairs of wheels on an ordinary car, the value thus found should be multiplied by 4, making the complete expression for the force to produce angular acceleration for a car without electrical equipment / = 24.80 X 1.467 X 4^ = 145.52 A When motor cars are considered, an additional, amount of force must be employed besides that for angular acceleration of wheels and axles. It may be determined in the same manner as outlined above. 1 The values will vary with the type and number of motors per car or per locomotive. The following figures are representative of American practice: 2 PER CENT. OF TOTAL ACCELERATING FORCE REQUIRED FOR ROTATING PARTS Per cent. Steam locomotive and train 2-5 Electric locomotive and heavy freight train 5 Electric locomotive and high-speed passenger train. . 7 High-speed electric motor cars 7 Low-speed electric motor cars 10 Total Accelerating Force. The total force required to pro- duce acceleration both of translation and rotation is F = 91.1 TA + 145.52A or F = 91.1 A(!T + 145.52) (19) for a car without electrical equipment. In the particular case of a 27.5 ton car equipped with four 38 kw. motors, and geared for a speed of 50 miles per hr., the force required for producing rotational acceleration is 9.55 per cent, of that necessary for rectilinear, making the total force for an acceleration of 1 mile per hr. per sec. equal to 91.1 XI. 0955, or 99.8 Ib. per ton. In general, a value of 100 Ib. per ton may be used with a fair degree of accuracy as the total force required for unit ac- celeration for electric motor cars, so that equation (19) may be rewritten : F =100 A (19a) iSee also Chapter VIII, "Effect of Rotational Inertia." 2 Standard Handbook for Electrical Engineers, Sec. 13, par. 88, Third Edition. THE MECHANICS OF TRACTION 17 which is widely used in practice where extreme accuracy is not required. In this book it will be used as a correct approximation. Train Resistance. When a train is in motion, a number of forces are always at work tending to reduce its velocity. Some of them are always present; others occur only under certain conditions. It is therefore necessary to state just what is meant by the term " train resistance." As ordinarily defined, it is understood to include those forces which oppose the motion of a train when running on a straight level track at constant speed, and in still air. This portion of the train resistance, which is inherent to operation under the stated conditions, may be divided into the following components: 1. Journal friction. 2. Rolling resistance. 3. Flange friction. 4. Oscillatory resistances. 5. Air resistance. 6. Friction of motor gears and bearings (in motor cars only). The above resistances are always acting to retard the motion of a train when operating under the conditions stated. In addi- tion to these components, there are others not inherent to the motion of the train itself, but which depend on special condi- tions of operation. They are: 7. Grade resistance. 8. Curve resistance. 9. Wind resistance. These additional components may frequently exceed the in- herent resistance in amount; and in the operation of freight trains at slow speeds they are usually the more important. They may be grouped under the head "incidental resistances." Journal Friction. Friction in the journals of ordinary rolling stock follows the laws of bearing friction in general. A common form of car bearing is shown in Fig. 3, which is a section through the standard 5 X 9 in. journal adopted by the American Electric Railway Engineering Association. The axle is extended to form the journal, /, which rotates in the journal bearing or "brass," B. Lubrication is provided by placing a quantity of oil-soaked wool waste in the oil cellar, C. This packing carries oil from the cellar to the journal by capillary attraction, and so serves to 18 THE ELECTRIC RAILWAY lubricate the bearing. The principle of lubrication in such a bearing depends on sufficient oil being drawn between the journal and the brass to form a film of lubricant separating the two metal surfaces. When this is done, the friction is that of the molecules of oil against one another, which is comparatively small. If, for any reason, the oil film is broken, the molecular friction of the lubricant is replaced by rubbing friction of metal on metal. The force required is then much increased, and the work done appears in the bearing as heat. If the action is J, Journal; B, bearing brass; W, wedge; C, oil cellar. FIG. 3. Standard A. E. R. E. A. Journal and Bearing. allowed to continue for any great time, the temperature is raised to a point where any oily waste in the bearing cellar will catch fire, and a "hot-box" results. When a train is standing still, the static pressure of the bearing on the journal will squeeze all the oil out from between the bearing surfaces, so that when the train is started the friction is quite large. As the speed increases, oil is drawn into the bearing, and the friction reduced. The minimum resistance is reached at a speed of about 30 miles per hr. for any given temperature and journal pressure; and beyond this point it becomes greater with in- creased speed. THE MECHANICS OF TRACTION 19 Experiments have shown that the friction falls as the pressure per unit area is increased, within the ordinary range of bearing pressures; and it also grows less with rise in temperature up to the point where the viscosity has been reduced so that the oil film cannot be maintained. This is beyond the ordinary range of working temperatures. If the oil is too fluid, it will not have sufficient viscosity to form a film; and if too thick, not enough will be drawn into the bearing to make the film complete. It is necessary to have oil of the proper viscosity if the lubrication is to be good. Since the viscosity varies with the temperature, a heavier oil is needed in summer than in winter. Variations in the character of the oil used will cause greater differences in the friction than any of the other items considered, and hence it is not possible to give absolute figures for journal friction unless the characteristics of the lubri- cant used are known. Flange Friction, Rolling and Oscillatory Resistances. These resistances are so intermingled that no attempt to separate them has been successful. The causes producing one of them usually gives rise to the others. Rolling resistance is due to several things. The loaded wheel produces a deflection of the rail, and also compresses it, so that in effect the car is always climbing a small grade. The bending of the rail is augmented by deflections and compression of the ties and the roadbed, and by yielding at the rail joints. Flange friction is produced by the rubbing of the wheel flanges against the rail heads. This varies with the speed of the train, condition of the trucks, shape of the wheel and the rail and other causes; and also depends to some extent on the track construction and methods of suspension. Oscillatory resistances are quite indefinite. If the train sways from side to side of the track, it is evident that a certain amount of energy must be absorbed by such motion. They cannot be determined separately, and are usually considered to be those resistances remaining after the other items have been accounted for. They are necessarily closely related to the rolling friction. It is certain that they increase rapidly with the speed, since the force of impact varies as the square of the velocity. The sum of the flange friction, rolling and oscillatory re- sistances make up a, not inconsiderable portion of the total train resistance. Although the above discussion would indicate that 20 THE ELECTRIC RAILWAY these items should increase more rapidly than the speed, they are considered by some writers to vary directly with it. Air Resistance. In high-speed operation the air resistance is the most important factor of train resistance. This may be divided into three components: 1. Head end resistance. 2. Side friction. 3. Rear suction. The head end resistance is due to the displacement of the air caused by the passage of the train through it. It is the largest 30 40 50 Miles per Hour FIG. 4. Head end air resistance. 20 30 40 50 Miles per Hour FIG. 5. Rear end air suction. part of the air resistance. It depends on the projected area of the front of the train, the shape of the front, and the speed. A number of tests have been made to quantitatively determine its value. Prominent among these are the ones made by the Electric Railway Test Commission, formed by the electric railway interests in connection with the Louisiana Purchase Exposition in 1904, 1 and the so-called " Berlin-Zossen " tests, conducted in 1 Report of the Electric Railway Test Commission, McGraw Publishing Co., 1906. THE MECHANICS OF TRACTION 21 1901 and 1902-03 by a committee working in conjunction with the German government 1 . The conclusions of both these investigations indicate that the head end air resistance varies as the square of the speed, and has materially different values for various shapes of front end. The results obtained by the Electric Railway Test Commission are summarized in Fig. 4. It appears that a wedge-shaped front offers much less resistance than the ordinary forms used on electric cars. The rear suction is quite similar to the front end resistance, being due to filling the partial vacuum formed by the passage of a train with air at atmospheric pressure. It follows the same laws, but is less in amount, than the front end resistance. Values of rear suction are shown in Fig. 5. It may be noted that the resistance of the parabolic shaped rear end is less than that of the wedge, which at the front end gives the lowest value. The side friction is caused by the rubbing of the air against the sides of the car. It also varies approximately as the square of the speed, and for a single car is about one-tenth the sum of the front and rear resistances. Motor and Gearing Friction. In the case of electrically driven cars, there is a certain loss due to the friction of the motor armature bearings, the motor axle bearings, and, in the case of geared motors, of the gears. The motor bearing friction is ordinarily included in the losses of the motor, but that of the axle is omitted. It follows the general laws of friction, as in that of the car journals. The gear friction is sometimes included in the motor losses, and in others must be taken with the train resistance. The loss incurred in the transmission of power through a pair of spur gears such as are commonly used in transferring the torque from the armature shaft to the axle, generally runs between 3 per cent, and 9 per cent., depending on the pitch line speed and the condition of the teeth. New gears show a higher loss than those which have worn enough to remove the irregularities due to cutting. The loss again increases considerably after the teeth have become badly worn. For gears in good condition and for moderate pitch line speeds, the loss is about 3J^ per cent, of the power transmitted. 1 Berlin-Zossen Electric Railway Tests of 1902-03, McGraw Publishing Co., 1905. 22 THE ELECTRIC RAILWAY It should be noted that the losses in the gears, and also the mechanical losses in the motors, while supplied electrically when power is being drawn from the electric circuit, must be taken from the momentum of the train when it is coasting. This causes some difference in the values ef train resistance in the two cases. The gear loss while the train is coasting is, how- ever, small, since the power transmitted is only sufficient to drive the armature while running light. In case the motors are used for any form of dynamic braking, the loss will of course be larger in proportion to the power drawn from them. The gear losses occur only in cars and locomotives driven by motors acting through gearing, being of course entirely absent in the case of gearless machines. Determination of Train Resistance. A number of methods have been employed for the determination of the resistance of cars and trains, the practice depending to some extent on the motive power employed. The resistance of steam trains may be obtained by any one of three methods. The first of these is to place a dynamometer directly behind the tender of the locomotive, and record the drawbar pull. This pull, if obtained with uniform conditions as outlined in the definition at the beginning of the discussion, is a direct measure of the resistance for the speed at which the observation is taken. Results deter- mined in this manner are inaccurate in that the head end re- sistance is omitted. In the case of long freight trains operating at relatively slow speeds, this is unimportant; but with high- speed passenger trains it may lead to considerable error. In steam locomotive work the inaccuracy is corrected by includ- ing the head end resistance in the "machine friction" of the locomotive. If tests made in this way are to be used for deter- mining electric train resistance, care must be taken in interpret- ing them. The second method of obtaining the resistance of steam trains consists in taking indicator diagrams at various constant speeds, and from the cylinder performance determining the force supplied to overcome train resistance. This method is liable to all the defects encountered when indicating steam engines under the disadvantages inherent to road tests, and also intro- duces an error by including the locomotive friction. The third method consists in allowing a train to coast, and finding the time required to retard from one given speed to THE MECHANICS OF TRACTION 23 another. This method would appear to be of at least as great accuracy as the last, although it has never met with much favor in the eyes of steam railroad men. The resistance of electrically equipped trains may be deter- mined readily by operating at constant speed under the proper conditions, and determining the input to the motors. If the efficiency of the motors be determined by a separate test, the corresponding output can be found at once, giving the value of the train resistance directly. This method has met with the greatest favor of late years, and the best and most consistent results have been obtained by its use. Train Resistance Formulae. Ever since the subject of train resistance began to be understood, attempts have been made to render the results of tests universally applicable by presenting them in the form of equations involving the constants of the equipment and the speed. A large number of such formulae have been published; but their great divergence would indicate either that they are inaccurate or that they are inapplicable over a wide range of conditions of operation. Of these formulae there are two distinct types: those applying to steam trains, which omit head end resistance, and those applying to electric trains, which include this item. Although the resistance of either kind of train is essentially the same for similar conditions, the above difference will cause considerable variation in the train re- sistance equation. Unfortunately, investigators do not always specify the class of trains to which their formulae are applicable. In obtaining a rational formula for train resistance, it is obvious that several of the components can be grouped together. A portion is sensibly constant at all speeds, a part varies as the speed, and still another as its square. If there are functions of higher powers of the speed, they have not as yet been segregated, and they must be quite unimportant. A rational train resistance formula should then be of the type R = A + BV + C7 2 (20) where R is the resistance in pounds per ton, V the speed of the train in miles per hour, and A, B and C coefficients determined experimentally. A formula of the semi-rational type has been developed by Mr. A. H. Armstrong, as follows: (21) 24 THE ELECTRIC RAILWAY in which R is the resistance in Ib. per ton, T is the weight of the train in tons, V is the speed of the train in miles per hr., a is the area of cross-section of the train in sq. ft., n is the number of cars in the train. The first term represents largely the bearing friction, the second the rolling resistance, flange friction and a portion of the oscillatory resistance, and the third term the remainder of the oscillatory resistance and the air resistance. The last factor of the third term is to allow for the side air friction if there be more than one car in the train. This formula has given fairly 30 40 50 Speed, Miles per Hour FIG. 6. Train resistance for cars of different weights. consistent results, and may be safely used in predetermining the train resistance for ordinary American passenger rolling stock. In Fig. 6 is shown the application of Armstrong's equation for cars of different weights. The curves are of the same general type, and differ only in the first and third terms. In Fig. 7 is shown a series of curves for the resistance of different trains made up of cars of the same weight. The lower resistance per ton as the number of cars in the train is increased is clearly shown. It should be noted that none of the formulae for train resistance in the form of equation (20) make allowance for the starting resistance. This will usually be much greater than the resistance after even a very low speed has been attained, on account of the high bearing friction at starting. This has already been referred THE MECHANICS OF TRACTION 25 to, and accounts for some discrepancies which appear in the application of train resistance equations. It is more difficult to determine the resistance of freight trains than that of passenger trains, since the former are made up of 8. \n T5 I ^ ! 10 60 70 30 40 SO Speed, M.P.H. FIG. 7. Train resistance for different numbers of cars. 80 cars of widely varying weight and different design. There is moreover a difference in resistance between that found for loaded cars and for empties. The expense of making up complete trains 10 25 30 35 40 15 20 Speed, M.P.H. FIG. 8. Freight train resistance. of freight cars of one weight and type would be great; and the cost would not be justified, since such trains are not to be found in practice. A better method is to make tests on ordinary trains 26 THE ELECTRIC RAILWAY of any make-up, and base the resistance on the average car weight. The result of such a series of tests on trains in regular service is shown in Fig. 8, which is from results obtained by Professor Edward C. Schmidt. 1 These curves were taken with a dynamometer car, and do not include the head end resistance. Incidental Resistances. Grades. In surmounting a grade a train has to be lifted through a definite vertical distance. To do this a certain amount of force is required, sufficient to balance the tendency of the train to run down the grade. The measure of this is the value of the gradient, which may be expressed either in FIG. 9. Determination of grade resistance. per cent, rise, or in feet rise per mile. The surveyor, in laying out the track, measures the horizontal distance, I (Fig. 9), and the vertical height h. If a train weighing T tons be on the grade, this weight may be resolved into two components, N normal to the track and F along the track. It is this latter force which must be balanced by the force F f to keep the train in equilibrium. The value of the force F is T sin a. Since N and T are respectively perpendicular to t and I, and angles BCA and bca are right angles, the triangles ABC and abc are similar, and angle B AC = angle bac. Therefore, F' = - F = T sin a = T - (22) L It is usually inconvenient to determine - directly; but the * tangent of the angle a, j, may be readily found. For ordinary grades the error is negligible in assuming the sine equal to the C. SCHMIDT, "Freight Train Resistance," Bulletin 43, Engi- neering Experiment Station, University of Illinois. THE MECHANICS OF TRACTION 27 tangent. For example, the error for a 4 per cent, grade, which is about the practical limit, is one-fourth of 1 per cent., and for a 10 per cent, grade, one-half of 1 per cent. For a rise of 1 ft. per 100, and a train weight of 1 ton, F = 2000 X ^ = 20 Ib. (23) For a rise of 1 ft. per mile, and a weight of 1 ton, F = 2000 X -^77 = 0.3788 Ib. (24) The force necessary to maintain motion on a grade is there- fore 20 Ib. per ton for each per cent, of rise, or 0.3788 Ib. per ton for each foot per mile. If the train is going down the grade, the force is in the opposite direction, and aids the tractive effort of the motive power. Virtual Grades. When the speed of a train is changing, it may be considered that it is virtually on a slope whose resistance is equal to the sum of the resistance of the actual grade and that of one which is equivalent in its effect to the acceleration. A grade of this character is called a " virtual" or "velocity" grade, and the total resistance of a train on it is always equal to that on the actual grade and the resistance corresponding to the force required for acceleration. The virtual grade may be either greater or less than the actual one, depending on whether the train speed is increasing or decreasing; or, in other words, whether the acceleration is positive or negative. When trains, especially those making infrequent stops, such as heavy freight trains, are operated on roads having a broken profile, it is often possible to approach the up-grades at higher speeds than can be maintained to the summit. The stored kinetic energy will be reduced as the ascent progresses, and be liberated. This energy will aid in lifting the train, thus being converted into potential energy. In effect, the resistance will be less than that due to the actual grade; and, in deter- mining the weight of train that can be hauled by a given loco- motive, the virtual grade should preferably be used. It is then important to find the value of the latter, which may readily be done by calculating the liberated kinetic energy due to the difference in speeds between that of approach and at the summit. The length of the grade being known, the average velocity dur- 28 THE ELECTRIC RAILWAY ing ascent can be found, and the force equivalent to the con- verted energy determined. This force, subtracted from the re- sistance of the actual grade, gives that corresponding to the virtual grade. From this the resistance in pounds per ton, and the equivalent rise in feet per mile or in per cent, may be found directly by equations (23) or (24). It is evident that virtual grades are always limited in length. The Ruling Grade. In any given section of track, the maxi- mum gradient encountered is known as the " ruling grade," whether it be an actual or a virtual one. The maximum load which a given motive power can haul on a certain division of a road is determined by the greatest tractive effort it can exert on the ruling grade. In general, ruling grades are not of such great importance in the case of electric roads as in steam roads, since the electric motors can usually be forced beyond their normal rating for a short time, as in climbing the ruling grade; whereas the maximum output of the steam locomotive is practically a fixed quantity, which cannot be exceeded for even a short period. Curves. In American railway practice it is customary to rate curves in degrees of central angle subtended by a chord of 100 ft. This method follows from the ordinary procedure in laying out curves with a transit. At the point of curvature, A, Fig. 10, the instrument is set up, and angles DAB, FAC, etc., laid off, each equal to one-half the "degree" of the curve. In the case of a 1 curve, the angle A OB is 1 and DAB is 30'. Referring to Fig. 10, if AB = 100 ft., then AK . a /0 _, AO = Sm 2 (25) = sin 30' = 0.00873, from which AO = 5730 ft. In general, if D is the degree of the curve, and r its radius, sin y 2 D = ~ (26) and r = 50 esc % D (26a) Approximately, the radius for ordinary curves may be taken as ~~f\~ ft. In curves of large degree and correspondingly small THE MECHANICS OF TRACTION 29 radius this assumption leads to considerable error; and when laying them out chords of 50 ft. or less are used in place of the 100 ft. which is employed for those of longer radius. In street railway work, where the radii are extremely short, being from 35 ft. to 100 ft., the curves are ordinarily designated by the radius in feet. In such cases they are not usually laid out with instruments; but the rails are shaped and assembled by the manufacturer before shipment and are installed as a complete unit. Such track is referred to under the general term "special work." FIG. 10. Method of laying out curves. In high-speed railway work an abrupt change of direction from a tangent to a circular curve would cause difficulty in operation, and might even make a train leave the track. To obviate this difficulty the first portion of a curve is some form of spiral which makes an easy transition from the tangent to the circular arc. A number of such curves are in use and methods of construction may be found in any good handbook on railway location. Since a body in motion tends to travel in a straight line, a force must be introduced in order to cause it to change its direction. The value of this force depends on the speed and weight of the train and the amount of curvature; it may be supplied by pres- 30 THE ELECTRIC RAILWAY sure of the wheel flanges against the outer rail of the track or by gravity. In the latter case the force is obtained by locating the outer rail of the track at a higher level than the inner. This is known as the superelevation of the outer rail. In Fig. 11 consider a car of weight G = Mg on a curve of radius r, the superelevation of the outer rail being such that the track makes an angle with the horizontal. The force G due to the weight of the car will have a tendency to pull the train toward the center of the curve. The centrifugal force has a value of - FIG. 11. Centrifugal effect of curves. exerted in a horizontal direction. From the figure it may be seen that the resultant of these forces will be normal to the track when tan = - rg (27) It is evident from the above discussion that the superelevation of a curve is correct for one speed, and for that speed only. If the velocity be greater than this value, the reaction from the track will not supply all of the directive force required; the remainder must be furnished by pressure of the flanges against the outer rail; if less than the balancing speed, the force supplied by the track reaction will be greater than necessary, and the train will fall toward the inner rail, the pressure being taken by the flanges of the inner wheels. In either of these cases there will be an amount of flange friction additional to that occurring on straight track. Since the tracks of ordinary railroads must be used in common by fast and by slow trains, it is not possible to compensate the curves for all of them. A compromise is usually effected so that THE MECHANICS OF TRACTION 31 the superelevation is too great for the freight trains and too small for the passenger trains. The general result will be to reduce the resistance on curves for all of them, and to make operation safe at speeds up to the maximum used. The proper choice of a mean velocity for which the compensation should be calculated depends on the relation between the speeds of different classes of trains and the relative numbers operated. A certain amount of friction is also present due to swinging the trucks from their normal position under the cars. The total effect is to increase the train resistance. Experiments indicate that this increase in train resistance averages from 0.5 Ib. to 1.5 Ib. per ton per degree of curvature. Wind Resistance. Natural winds a#ect the operation of trains by changing the relative velocity of the train with respect to the air, and hence vary the air resistance. For example, a train operating at 40 miles per hr. against a head wind blowing at the rate of 20 miles per hr. will have the same wind resistance as though it were moving through still air at 60 miles per hr. If operating in the opposite direction (i.e., with the wind) the effect will be the same as the air resistance met by moving through still air at 20 miles per hr. Quartering and side winds also affect train resistance by introducing additional flange friction, the wheels being crowded against the rails on the " lee ward" side. In general these results are indeterminate in amount. The Speed-Time Curve. In order to make a rational com- parison of train performance under varying conditions of opera- tion it is necessary to adopt some standard method of reporting results. This need has led to the use of a series of curves, all plotted with time as their abscissae. The ordinates of this group of curves may be any of the factors which vary with the time, and include the distance covered, the speed, the acceleration, the tractive effort, and the electrical quantities current, e.m.f. and power. Of the mechanical values, distance is the fundamental one; in the equations at the beginning of this chapter some of those which depend on the distance are derived. It is seen that velocity is the rate of change of distance with respect to time, or ds v = dt (4) Acceleration is the rate of change of velocity with respect to time, or 32 THE ELECTRIC RAILWAY -* (28) From the relations of these two equations it may be seen that ac- celeration is the second derivative of the distance with respect to time, or a = J (29) In certain problems involving excessive acceleration and retardation, it has been found that a high rate of change of velocity can be maintained without discomfort if it is reached gradually. This brings into use the rate of change of the ac- celeration, giving the relation da d 2 v d*s w :: w "" w In a similar manner, the velocity is the first integral of the acceleration, as v = fadt (31) The distance is the first integral of the velocity, and the second integral of the acceleration. s = fvdt = f fadt (32) The use of graphical methods for the representation of train motion brings in these relations, and the performance may be shown by means of the distance-time, speed-time, or accelera- tion-time curves, as desired. If a distance-time curve be dif- ferentiated with respect to time, the first differential curve will be that between speed and time, and the second differential curve that between acceleration and time. Similarly, the first integral curve of the acceleration-time curve is the speed-time curve, and the second integral curve the distance time curve. If any one of the three curves be plotted, it is a simple matter to derive the other two. Since the area enclosed between a curve and its axis of abscissae is a measure of the integral, a fairly definite idea of that value may be found by inspection. In like manner, the slope of a curve is a measure of its derivative, and the general form of the differential curve may be approxi- mated. For this reason, more information can be obtained by the use of the speed-time curve than by employing either the distance-time curve or the acceleration-time curve for depict- ing the motion of a train. THE MECHANICS OF TRACTION 33 Components of the Speed-Time Curve. In ordinary railway operation, a train starts from rest, and its speed is increased with a rapid acceleration, which will usually fall off as the speed is increased, until the train operates at constant speed. The train may then be allowed to coast without the use of power, after which it is stopped rapidly by application of the brakes. Acceleration Curve. In order to produce motion, a certain force must be used, which can be calculated quantitatively if the weight of the train and the required acceleration are known; or the acceleration can be determined if the force and the train weight are given. The method of calculation is that indicated by equations (12) and (19). If the force remains constant, the train will be accelerated at a uniform rate; but if the force is variable, the acceleration will fluctuate correspond- ingly. If the law of variation of the accelerating force (tractive effort) can be stated in the form of an equation, then the resulting acceleration and the speed at any instant can be determined analytically. Ordinarily, the relation between tractive effort and time is so intricate that no exact expression for it can be found. In any case it is too complex for easy mathematical analysis. Recourse is usually had to a graphical method of treatment, which facilitates the calculation materially. As the speed of the train increases, the train resistance be- comes greater, while at the same time the tractive effort, as supplied by nearly all motive powers, diminishes. A speed will be reached where the train resistance will have increased to a point where it just equals the tractive effort. It is evident that there can then be no further acceleration, and that the speed must become constant at this limiting value. This is often referred to as the " balancing speed." It is always the same for constant conditions, but varies with the grade and the other incidental resistances which may occur. The train will continue to run at this speed until the conditions change, or until power is cut off. Coasting Curve. When no power is supplied to the moving train, it will continue in motion, but will be retarded at a rate which depends on the value of the train resistance. This re- tardation becomes less as the speed decreases, since the train resistance diminishes with reduction in speed. In case the train is on a down grade which gives a force great enough to equal or 34 THE ELECTRIC RAILWAY exceed the train resistance, the train will coast at constant or even increasing speed. Braking Curve. To stop a train by allowing it to coast to a standstill would be impractical, and in some cases impossible; hence a retarding force additional to the train resistance must be introduced to cause more rapid stopping. This force is ordinarily supplied by some form of brake. In ordinary railway practice the force supplied is due to the friction of metallic shoes pressing against the treads of the wheels, although other methods are sometimes employed. A discussion of this topic is given in Chapter VII. The dynamic relations while braking are precisely the same as those existing during acceleration, except that the main force is reversed in direction. The acceleration is therefore negative. Its value may be determined quantitatively by the applica- tion of the same equations as used for a consideration of ac- celeration, care being taken that the algebraic signs are correctly interpreted. Calculation of Speed-Time Curves. The problem of plotting the speed-time curve from given data is one which is constantly recurring in railway work; and it is desirable to have at hand a simple and accurate means of making the determination. An inspection of equations (28) to (32) gives the basis of the method available for making the calculation. The most convenient way of determining the graphical repre- sentation of the speed-time relation is to locate points on a sheet of coordinate paper for a number of values lying along the curve, these points being taken sufficiently close together to give the required accuracy, and the curve plotted through them. The closer they are taken together, the more accurate is the curve. The data given in the statement of the problem usually are the tractive effort and the speed to which it corresponds. In other words, the information is that derived from the characteristic curve of the motive power, such as the curve of the series railway motor, Fig. 19. From equations (13), (19) or (19a) the accelera- tion produced by the motor tractive effort may be found at once. This gives us the speed and the corresponding value of accelera- tion, from which the time must be calculated. The means of doing this is to use the relation a - * (28) THE MECHANICS OF TRACTION 35 which may be rewritten *-* a (28a) This shows at once that there is no easy way of getting the summation of the time increments for a given run, since it is not possible to have a simple equation expressing the relation between speed and tractive effort of the motive power. The total elapsed time from any reference point must be the summation of a large number of increments; and the result obtained depends to a large extent on the accuracy of the method employed for de- termining the successive time increments. Any graphical method for plotting speed-time curves thus consists of approxi- mating the value of time corresponding to a definite acceleration. FIG. 12. Determination of time increments. In this figure the increments dy and dx are assumed to be infinitesimal. Mr. C. O. Mailloux 1 has resolved the problem into the follow- ing form : " Given the ordinate, y, and the slope of the curve, '-p, at any point of a curve, to find the abscissa, x, corresponding to the ordinate, or the distance of the ordinate from the F-axis." Two cases exist the first where the slope is positive, comprising all acceleration curves; and the second where the slope is negative, which includes all retardation curves. In the former case the curves are usually concave to the X-axis, and in the latter may be either concave or convex to it. In Fig. 12 the curve OEF represents any portion of a speed-time 1 C. O. MAILLOUX, "Notes on the Plotting of Speed- Time Curves," Transactions A. I. E. E., Vol. XIX, p. 984 (1902). The following discussion is based on this paper. 36 THE ELECTRIC RAILWAY curve with a positive slope (i.e., an acceleration curve). Consider lines drawn tangent to the curve at various points, as ab, cd, ef. Also take two ordinates y and y', which are very close together, and which may be assumed to include the portion of the speed- time curve at the point of tangency, E, of the line cd. The difference between these is dy, and we may write dy = y' - y (33) The corresponding difference between the abscissae, dx, is dx = x' - x (34) In order that the two ordinates may be considered to be at the same point of tangency, E, the distance between them must be infinitely small. The application of similar triangles to Fig. 12 gives the relation ^ = d / (35) cx dx which expresses the well-known fact that the ordinate y at the point of tangency, divided by the sub-tangent cx, is a measure of the differential at that point. From this relation the value of -/ can be determined. ax The assumption that has been made, that the increment of ordinate, dy, is infinitesimal, makes it of no value in the plotting of curves. For ordinary purposes it must be increased to some finite value. This makes necessary a re-statement of equa- tions (33) and (34) as follows (see Fig. 13) : x' - x = Ax (36) y' - y = by (37) in which Ai/ is the increment of ordinate which corresponds to the increment of abscissa Ax. The essential difference between the infinitesimal and the finite statements, as given in equations (33) and (34), and (36) and (37), is that while in the former case the ordinates are taken so close together that there is no appreciable difference in dy the values of -/- whether measured by the tangent at the point of the curve having the ordinate y, or that with the ordinate y', it may not hold true in the latter. This is shown in Fig. 13, THE MECHANICS OF TRACTION 37 which is purposely exaggerated. At the point E, the differential is dy = V_ dx ex while at the point F it is dy' j/_ dx' ' ex' (38) (39) It may thus be seen that the differential coefficient cannot be represented by any single value when the increment of ordinate is large enough that a material change in the slope of the curve is included. The correct value of the differential coefficient will, in general, correspond to some intermediate point, such as D. Drawing c FIG. 13. Practical method for estimating acceleration. In this figure the speed increment. Ay, and the corresponding time increment, Ax, are taken as finite values. Compare with Fig. 12. the line gh parallel to the tangent g'h' through this point, the differential triangle EFH is produced, which is similar to the differential triangle corresponding to the point D. We can therefore write dx (40 ) where XQ, y , are the coordinates of the point D. An inspection of the triangles EmI, EFH and EnJ shows the difference in the magnitude of Arc as obtained when using the values of differential corresponding to x, X Q and x', respectively. In a majority of curves, the point D is approximately midway between E and F. When y and y' are taken sufficiently close 38 THE ELECTRIC RAILWAY together, the error made by assuming this condition to be true becomes negligible. The value of the differential may then be taken as that corresponding to the average point between those of y and y', so that V" = -^/ (41) The closer the values of y and y' are taken together, the smaller will be the error introduced by making this approximation. Total Force for Train Operation. A study of the foregoing paragraphs indicates that a number of forces are always pres- ent, which govern the total amount of power which must be supplied to the moving train. If a train is moving at constant speed through still air on a straight level track, the only force required is that to overcome the normal train resistance; but if it is on a grade, or on a curve, or in the presence of a natural wind, a variation in the force becomes necessary if the train is to maintain its speed. If the speed of the train is changing, still other forces act. The laws of motion show that the resultant of all forces act- ing on a body is their algebraic or vector sum. Since all the forces which concern the movement of trains act parallel to the track, the algebraic sum gives a correct representation of the total. Using the following notation: R = force for overcoming train resistance, G = force for overcoming (up) grades, C = force for overcoming curves, P = force for producing (positive) acceleration, F = total force to be supplied by the motive power, we may then state as an equation the value of total force F = R G + C P (42) In this statement the value of P must be taken to include both force for linear and for rotational acceleration. The value of G is positive on up grades, since it acts as a resistance, or opposes the force F' } on down grades it is negative. The value of P is positive when the speed is increasing (i.e., when the accelera- tion is positive), and becomes negative when the speed is de- creasing from any cause. In other words, the kinetic energy increases directly with the (square of) speed. At the end of every practical run, it is necessary to bring the train to rest by the application of an external retarding force. THE MECHANICS OF TRACTION 39 This phenomenon is known as braking, and will be taken up in detail in a later chapter. The necessary value of braking force may, however, be determined by an equation similar to the one above. Using the same notation, and calling the external brak- ing force B, we have, B = - R + G - C +P (43) It is to be noted that the signs of R, G and C are reversed; during retardation these resistances hasten the change of velocity. P is always positive, i.e., the change in motion is always in the same direction as the retarding force, in normal braking. Plotting Speed-Time Curves. The relations outlined above give a practical method of plotting speed-time curves. The arrangement involving the least complication is to make an analytical calculation of the time increments (Az), assuming speed increments (Ai/) sufficiently close together to keep the error within the required limits. The accuracy will depend on the conditions of the individual problem, so that no definite limits for the speed increments can be stated. It must be re- membered that the calculations are somewhat tedious, and need considerable care, to prevent inaccuracy. Since the time incre- ments must be added together to give the total time, the errors are likely to be cumulative, and cannot be expected to annul one another. In the practical calculation, the tractive effort curve of the motor is used to get the values of acceleration corresponding to various speeds. From this the average acceleration during the increment is found, and from it the time increment. The total elapsed time is obtained by adding together these latter. To reduce the labor incident to a large number of such calcula- tions, several methods have been advanced to determine the speed-time curve graphically. Of these, the one most used is that proposed by Mailloux. 1 In his method the tractive effort of the motor is replaced by the acceleration which it will produce on th given equipment, and is plotted against speed, as shown in Fig. 14. This is termed the " gross acceleration." The "net acceleration," which is the one actually produced on the train, is determined by subtracting the equivalent negative acceleration due to the train resistance. This is the result on straight level track. When 1 C. O. MAILLOUX, "Notes on the Plotting of Speed-Time Curves," Transactions A. I. E. E., Vol. XIX, p. 984 (1902). 40 THE ELECTRIC RAILWAY grades are encountered, a constant force is introduced, amounting to 20 Ib. per ton for each per cent, of grade. It is evident that the ordinate of the net acceleration curve will be increased or diminished by the corresponding amount, as shown by the figures at the right of the chart. This has the effect of raising or lowering the base line to the place indicated by the value of grade. Curves may be similarly treated, except that their effect is always opposed to the direction of motion. Having determined the acceleration at any particular speed from a chart similar to Fig. 14, the corresponding time increment may be found from equation (28o), which may be re-stated -1 a (286) 2.0 ! 40 i Sjjeed , Miles per Hour FIG. 14. Chart of accelerations. This normally involves the calculation of -; but if a curve is plotted between natural numbers and their reciprocals, the values of a may be taken from the chart of accelerations with dividers, or by other convenient methods, and the corresponding result for - read from the reciprocal chart. If the speed incre- ment is unity, it is evident that the time will be given directly THE MECHANICS OF TRACTION 41 by this method. If it is desired to use other speed increments, a series of curves may be drawn between natural numbers and one- half, one-tenth, twice, ten times, etc., the actual values of recip- rocals. With such a chart the determination of the speed-time curve is relatively quite simple, and the detailed calculations are all dispensed with. It is evident that a new curve of accelera- tions must be made for each different motor, or for the same motor with different equipments; while the chart of reciprocals is equally good for all cases. Power for Train Movement. Having determined the force necessary for train propulsion, as in equation (42), it is easy to calculate the power required at any instant if the speed be known. This is, in horsepower, HP = (44) where F is the total tractive effort in pounds, and v the speed in feet per second. If the speed is stated in miles per hour, F, the equation becomes UD 5280 ffF ,. . . HP = 60X33,000 (44a) To express the power in kilowatts, we have KW = where F is in pounds and v in feet per second. Using speed in miles per hour, this reduces to _ 5280^7 ,._ , KW = 60 X 44,256.7 (45a) CHAPTER III MOTORS FOR TRACTION Functions of Motive Powers. Any motive power for railway service has two definite functions: 1. To accelerate a train from rest. 2. To maintain it in motion at a predetermined speed. These functions may be performed by almost any form of electric motor now known; but a few types possess inherent characteristics so much better suited to the purpose than the others that they are used almost exclusively. Electric Distribution Systems. Electrical apparatus is usu- ally operated on one of two well-defined systems: the constant- current or the constant-potential. Although it is not im- possible to operate motors on a moving vehicle from a constant- current supply, the difficulties are so great that after a few trials it has been entirely abandoned for this service. The constant-potential system, on the other hand, readily lends it- self to the purpose of distributing, energy in large or small amounts, and is especially adapted for serving moving cars or locomotives. Its use has been so very successful that at the present time it is the only system of distribution employed on electric railways. The entire discussion of electrical equip- ment in this book will be confined to a consideration of constant- potential systems. The systems for supply of electrical energy may be further classified according to the kind of current: alternating or direct. With the latter there can be but one variation in the conditions of the supply the line pressure. The former may be of any commercial potential, frequency or phase; for railway service a comparatively limited number of potentials and frequen- cies have been standardized, and the three-phase and single- phase systems are used exclusively when alternating current is employed. Classification of Electric Motors. Electric motors of all 42 MOTORS FOR TRACTION 43 types may be classified either according to the kind of circuit on which they may be operated, or to their inherent char- acteristics. In the former classification, the natural divisions are alternating current and direct current. The most im- portant types of motors are listed below. I. MOTORS FOR OPERATION ON ALTERNATING-CURRENT CIRCUITS: Single-phase Polyphase (three-phase) Synchronous Synchronous Asynchronous Asynchronous Induction Induction Squirrel-cage Squirrel-cage Wound secondary Wound secondary Commutator Commutator Series Various types Plain Compensated Conductive Inductive Repulsion II. MOTORS FOR OPERATION ON DIRECT-CURRENT CIRCUITS: Series Shunt Compound Cumulative winding Differential winding. The principal characteristics of the various types of motors are those of torque and speed. Of the tw,o, it is much more useful to classify them as regards the latter. In this table only two speed classifications are given: constant and variable. Several of the motors may have performance which is inter- mediate between true constant speed and what is known as " variable speed." Such types have either been omitted or included with one or the other class. III. CLASSIFICATION AS REGARDS SPEED CHARACTERISTICS: Constant speed Variable speed Shunt direct current Series direct current Synchronous Series alternating current Induction Repulsion Differential Cumulative compound 44 THE ELECTRIC RAILWAY Consider first the two principal types of direct-current motors, the shunt-wound and the series-wound machines. The entire difference between them lies in the connections of the field windings, in the former the field being connected in series with the armature, and in parallel with it in the latter type. The shunt motor, having its field excited by a winding connected to the supply circuit independent of the armature, has a field of sensibly constant magnetic strength ; while in the series machine the field strength is directly dependent on the current drawn through the armature. Torque Characteristics. In any electric motor, the torque developed by the armature is proportional to the product of the 1200 1000 D-- 800 ft: 400 200 1200 1000:5 a 800 600 400 200 50 250 100 150 200 Current, Amperes. . FIG. 15. Characteristic curves of shunt motor. field flux, the number and arrangement of conductors on the armature, and the current through them. In the case of a motor having a constant field strength, the torque is directly pro- portional to the armature current, since for any particular design the number of armature conductors is fixed. This is sub- stantially the condition which exists in the shunt motor. Al- though there is a small reduction of field flux with increase of armature current, the field strength may be considered sensibly constant, hence a curve drawn between armature current and torque will be practically a straight line, as shown in Fig. 15. MOTORS FOR TRACTION 45 Consider a motor whose field current is proportional to its armature current, the permeability of the magnetic circuit re- maining constant. The field flux is then directly proportional to the armature current ; and the torque, depending as it does on the product of the field flux and the armature current, varies as the square of the latter (see curved, Fig. 16). Such a relation would exist in the case of a series motor with an unsaturated magnetic circuit. Practically, it is not attainable, due to variations in the permeability of magnetic materials with changes in magnetizing force. 1400 SO 100 . 150 200 250 Current, Amperes FIG. 16. Characteristic curves of series motor. In the last example, if the area of the magnetic circuit be re- stricted, the field will become "saturated" with large values of current. As ordinarily used, the term " saturation" does not imply that there is no gain in flux with increase of magnetizing current. Even though the magnetic material were incapable of carrying any further induction than a certain maximum value, the flux would vary with the magnetizing current at the same rate as it would with a magnetic circuit composed wholly of air. This condition is far beyond any magnetic densities used in 46 THE ELECTRIC RAILWAY practice. Since, however, the change in flux is not proportional to the variation of field current, the torque will be less than in the case of the unsaturated motor. The torque-current curve will thus lie between those for the shunt motor and the unsaturated series motor (curve J5, Fig. 16). Speed Characteristics. The counter e.m.f. of a direct-current motor is proportional to the product of field flux, the number and arrangement of conductors on the armature, and its speed; hence 50 100 150 200 250 Current, Amperes. FIG. 17. Comparison of series and shunt motors. the latter varies directly with the counter e.m.f. and inversely with the field flux. Since the fall of potential due to resistance of the motor windings is a comparatively small amount, the counter e.m.f. to be developed is nearly constant, and it follows that the speed of a motor with a constant field strength varies but little with the armature current. This is practically the case of the shunt motor, the drop in speed from no load to full load being quite small in a well-designed machine (Fig. 15). In a motor whose field strength is proportional to the armature current, such as the hypothetical "unsaturated" series motor, the MOTORS FOR TRACTION 47 speed must fall in inverse proportion to the armature current, for it varies inversely with the field flux. The speed curve of such a machine is an equilateral hyperbola, as shown at A' , Fig. 16. For the practical series motor, with saturated field, the decrease of speed with load is less rapid (B f , Fig. 16). It will, however, fall much more than is the case with the shunt motor of equal rating. From the preceding discussion it may be noted that for values of current below full load the shunt motor -gives more torque per ampere than the series motor, while above this point the con- ditions are reversed. Where a large amount of torque is needed at reduced speeds, as in the case of starting a train, the series motor gives a certain tractive effort with less load on the line than the shunt motor. If the shunt motor and the series motor are of equal capacity, the former will be able to accelerate the train at the maximum rate practically up to its full speed; but this is considerably lower than the maximum speed of the cor- responding series machine. In case a comparison is desired on the basis of motors having the same " balancing" or free-running speed, they will be as shown in Fig. 17. Here the series motor is the same as in the preceding comparison, but the characteristics of the shunt motor are changed, by gearing or otherwise, to increase the speed without changing the horsepower output. The torque is correspondingly lowered. It will be seen at once that this shunt motor cannot possibly give the same accelerating torque as the series motor without imposing an excessive overload on the former ; and the torque corresponding to a given value of current is much less than for the series motor. The shunt motor has one advantage, in that it can accelerate the train at the maximum rate up to practically full speed. This partially, but not wholly, compensates for the lower acceleration, since the series motor can only produce its maximum torque up to about half speed. This advantage is slight, as may be seen from Fig. 18, which shows speed-time curves produced by the applica- tion to the starting of a particular train of each of the three motors considered. The speed-time curves are based on the ap- plication of a maximum value of one and one-half times full- load current during the acceleration period. The series motor gives the highest acceleration, but this falls off from about half speed up to full speed, which is reached only after a long time. The shunt motors, on the other hand, give maximum accelera- 48 THE ELECTRIC RAILWAY tion until the full running speed is reached, after which the speed is constant. The advantage of the series motor is greatest where the run is relatively short. In many railways, especially those of the first and second classes mentioned in Chapter I, the motors are not allowed to accelerate up to the point where full speed is attained, but the car is stopped after a relatively short period of operation. With long runs, the time spent in acceleration is comparatively unimportant, and a lower rate is permissible. For this latter service the shunt motor would have the advantage of operating at practically constant speed under all conditions of track. The 50 60 70 80 90 100 110 120 130 Time, Seconds 10 20 30 40 FIG. 18. Comparative speed-time curves with series and shunt motors. advantages of the series type of motor so far outweigh those of the shunt, that up to the present time the latter has not been seriously considered for traction. Its counterpart for alternating- current operation, the polyphase induction motor, has not only received favorable attention, but is actually used in a large number of equipments operating in Europe. This success is partly due to the fact that it is the most rugged and efficient type of alternating-current motor yet designed. The Direct-Current Series Motor. The direct-current series motor has been used for traction ever since the first practical electric roads were built. Other types of motor have been used from time to time, but none has the excellent operating charac- teristics of the series machine. Since about 97 per cent, of all the MOTORS FOR TRACTION 49 electric railway mileage in the United States is operated with direct-current series motors, a careful study of their characteristics is necessary. The general performance of this type of motor has already been discussed briefly. The salient characteristics are a torque which increases with the load at a rate greater than the first power of the current, and a speed which falls off rapidly with it, especially at the smaller loads. These curves may be seen in Fig. 19, which gives the performance of a 56 kw. (1 hr. rating) railway motor. 4-000 I 100 150 ZOO 250 Current, Amperes. FIG. 19. Curves for typical series railway motor. Variation of Speed Characteristic. It must be noted that although the series motor is usually referred to as a "variable speed" machine, there is for any given value of torque a cor- responding definite speed at which the motor will operate; so that, if the tractive effort is constant, the motor will run at one fixed speed. If it is necessary that a train be propelled at varying speeds when the track alignment is uniform, some means must be introduced into the equipment by which the motor speed will be altered to suit the conditions. One possible method of doing this 50 THE ELECTRIC RAILWAY is by changing the gear ratio. This means is actually employed in the gasoline automobile. It is not, however, necessary to use such a method with the series motor, since a variation in the e.m.f. supplied the motor will cause a change in the speed for a given tractive effort. The speed characteristic may be readily altered by varying the potential at the motor terminals; this may be accomplished directly by changing the e.m.f. supplied the motor, or by placing resistance in series with it. Details of methods for securing these results will be taken up in Chapter V. The counter e.m.f. developed by a direct-current motor operating on a constant -potential circuit must be equal to the impressed e.m.f. less the IR drop in the windings. Since the resistance of a well-designed motor is quite low, the IR drop will be but a small portion of the impressed potential ; it is rarely more than one-tenth of this value even at heavy loads. The counter e.m.f. must therefore be nearly constant. Its value depends on two factors: the speed of the armature, and the field flux. For the e.m.f. developed in any conductor varies directly as the flux density, the speed, the length of the con- ductor, and its arrangement with respect to the field and the direction of motion. Where several conductors are connected together, the e.m.f. also depends on the number of them and their arrangement. In the case of an armature these factors are fixed for a particular design, and may be included in a general constant. We may therefore write: E c = k$n (1) where E c is the counter (or direct) e.m.f. developed by an arma- ture, k is a constant depending on the design of the winding, is the field flux cut by the conductors and n is the speed of revolu- tion. This equation may also be written = f; a-) or, in other words, the speed of a motor varies directly with the counter e.m.f. and inversely with the field flux. Since the counter e.m.f., E c , may be represented in terms of the impressed potential, or E c = E - Ir (2) MOTORS FOR TRACTION 51 where E is the impressed e.m.f., / the armature current, and r the resistance through which that current has to pass, equation (la) may be rewritten 50 100 150 200 250 Current, Amperes'. FIG. 20. Speed curves for series motor with reduced potentials. Consider any definite value of current, I\. In the series motor this determines both the IR drop and the field flux, 3>. For various values of applied e.m.f., EI, E z , the speed may be found by direct proportion. E l - I,r k - J 2 r whence E, - (4) (4a) This latter expression (4a) may be conveniently used for determining the speed of the motor when any potential other 52 THE ELECTRIC RAILWAY than normal is impressed on its terminals. The curves of speed for the 56 kw. motor shown in Fig. 19 are redrawn in Fig. 20 at one-half potential (250 volts) and at one-fourth potential (125 volts). It may be seen from these curves that the speed is slightly less than half its normal value when the potential is reduced to one-half, and somewhat less than one-fourth the normal value when the potential is reduced to one-fourth. This is because the IR drop is a larger proportion of the total, the lower the impressed e.m.f. 50 100 150 200 250 Amperes FIG. 21. Speed curve for series motor with external resistance. Variation of Speed with Resistance. The other method of changing the speed by variation in potential is by the insertion of resistance in series with the motor. Its action may be deter- mined by application of the method of equation (3), as shown by the following relation: Ei-hr where n\ is the normal speed at current /i, n 2 the speed with an external resistance R introduced into the circuit, and the other values as before. In Fig. 21 is shown the speed curve for the motor of Fig. 19 with an external resistance of four times the motor MOTORS FOR TRACTION 53 resistance added in series with it. It may be noted that the effect of this added resistance is quite small at light loads; but at heavy loads the speed is reduced until the motor is brought to a standstill. In order to obtain the same speed reduction at light loads the external resistance would need to be considerably greater. Torque Characteristic. It is also necessary to determine the effect of the above changes on the torque characteristic of the motor. The production of torque depends on the funda- mental principle that a conductor carrying a current tends to be pushed sidewise out of any magnetic field in which it is situated. The value of this push varies directly with the current, with the flux density, and with the length of the armature con- ductors and their number and arrangement. For any par- ticular motor they are permanently arranged, so that we have D = k$I (6) where D is the torque produced by the motor, k the winding con- stant, 3> the field flux, and I the current through armature and field. It may be seen at once that for a given value of current, the torque of the series motor is fixed, since the armature current also determines the field strength. Changes in potential have no effect on the torque characteristic of the series motor, and only serve to vary the speed at which any torque is produced. 1 Variation of Field Strength. In certain cases it may be found desirable to vary the field strength of the series motor. Since the field and armature draw their current through the same series circuit, it is necessary to divert a portion of it from the field winding or to actually reduce the number of turns on the coils, in order to diminish the flux. Either of these methods may be used in practice, as is explained in Chapter V. The two methods have the same effect on the characteristic performance. Referring to equation (la), it may be seen that the speed of a motor varies inversely with the field flux. This latter depends on the field current; but the relation is not a direct one. The magnetic circuit is made up of a number of materials with 1 A small change in losses and in the magnetic relations will cause a slight difference in the torque produced under different conditions, but these changes are so small as to have little effect on the general form and value of the torque characteristic. 54 THE ELECTRIC RAILWAY different magnetic characteristics and widely varying area of cross-section, so that the flux densities are quite different in various parts of the circuit. The ability of a material to carry flux depends on its permeability, and this varies widely with different values of magnetizing force and with the physical and chemical composition of the material. To determine the re- lation between the magnetizing force and the flux produced by it would necessitate taking the saturation curve of the machine. In the series motor, however, there is a method for determining relative values of flux from the performance curves. Equation 50 50 100 150 200 Current, Amperes. FIG. 22. Flux curve for series motor. The torque (or approximately the tractive effort) per ampere is a direct measure of the field flux in the series motor. (6) gives the relation between torque, flux and current. If the torque and current are known (as for example, they are given in the curves of Fig. 19) a result may be obtained pro- portional to the values of flux: 7= fc * (7) A curve plotted between torque per ampere and amperes (Fig. 22) will then represent the variation in flux with magnetizing MOTORS FOR TRACTION 55 force. This relation only holds true in the case of motors whose field current is the same as or varies directly with the load current. If the field flux of a motor remain constant, as in the shunt motor, the torque varies directly with the load current, according to equation (6). To determine the performance of a motor whose field strength has been changed from the normal value, the torque should be taken corresponding to the normal field strength, and its varia- tion found from the ratio of values of field flux. If the armature current is the same in both cases, the torque will be in direct proportion to the flux. That is: D 2 * 2 B;-*; where DI and D 2 are values of torque corresponding to normal field flux $1 and changed field flux 3> 2 respectively. We may then write > 2 = f^i (8a) Since only the relative values of flux are needed, they may be found from the values of torque per ampere, as indicated in equation (7). The effect on the speed of weakening the field may be seen from equation (3). The speed will vary inversely with the flux, so that for a decrease in flux the speed will be correspondingly greater. If n\ be the speed with normal field flux, and n 2 the speed with changed field flux, then we have - = lr 0) ni 3> 2 where n\ and n z are the values of speed corresponding to normal field flux 3>i and changed field flux < 2 respectively. From this we may write $1 w 2 = ni (10) As with the torque, only relative values of the flux, which may be found from equation (7), are needed for the solution of the equation. The effect on the characteristic curves of the series motor of reducing the field ampere turns to one-half the normal value is shown in Fig. 23. It should be noted that although the magneto- 56 THE ELECTRIC RAILWAY motive force has been reduced to one-half, the flux is not lowered in anything like the same proportion, and the curves are not so widely different as might be anticipated. Reduction of field ampere turns was used for controlling the performance of series motors in the early days of electric railways, but was abandoned on account of the increased tendency to sparking with the weak field. Modern designs of railway motors, using interpole construction, have made possible a return to the early method of control. It is especially advantageous for 4000 500 100 150 BOO Z50 Current, Amperes. FIG. 23. Characteristic curves of series motor with half field. trains which have to operate at slow schedule speed with rapid acceleration for a portion of the run, and for the remainder operate at high schedule speed with few stops. Losses in the Series Motor. The losses which occur in the series motor, while of the same character as for any electric machine, differ in that the speed and the flux density both vary with the armature current. None of the losses are constant, but all change with the load. They may be classified as follows : MOTORS FOR TRACTION 57 Resistance losses (copper losses) Armature PR Field PR Compensating (interpole) winding PR Brush loss Iron losses Hysteresis Eddy currents Mechanical losses Bearing friction Brush friction Windage. Copper loss, being the product of the current squared and the resistance, is readily found for the series motor. The windings being all in series, the total resistance of the motor may be taken and the entire loss calculated at once. The only precaution is to remember that when the field is weakened either by reducing the number of turns, or by shunting the winding, the resistance is thereby lessened. Brush loss is a function of the current through the brush and the drop of potential in it and in the contact between it and the commutator. This drop is largely independent of the current, being a definite amount at no load and increasing at a lower rate than in proportion thereto. The loss may be determined with various degrees of accuracy by the application of empirical for- mulae to be found in electrical handbooks. Iron loss consists of two distinct components : hysteresis loss and eddy currents. The former varies approximately as the 1.6 power of the flux density, and directly as the frequency; the latter as the square of the flux density and as the square of the speed. Since the speed decreases as the current and flux in- crease, the variation of iron Loss with load is quite involved. It is usually determined for different current values at various potentials, as shown in Fig. 24. Ordinarily the determination of iron loss is made experimentally, and it is not readily possible to formulate an equation expressing the theoretical conditions of its variation. The mechanical losses depend only on the speed of the machine. Brush friction varies directly as the speed, and bearing friction and windage as a power of the speed between the first and second. Their separation is difficult, and is not ordinarily 58 THE ELECTRIC RAILWAY attempted. The total value of these losses is quite small unless the armature is specially constructed to circulate air through the windings for cooling. Efficiency of the Series Motor. In any machine, the effi- ciency is the ratio of output to input. It may also be stated as the ratio of output to output plus losses, or the ratio of in- put minus losses to input. Hence if any two of the quantities 400 100 500 200 300 400 E.M.F., Volts. FIG. 24. Iron loss curves for series motor. output, input, losses or efficiency be given, the other two may be found by a simple calculation. The efficiency of the series motor may be determined by any of the methods outlined in the last paragraph. In testing series motors, it is difficult and somewhat unsatisfactory to load them with a prony brake, as is necessary to determine efficiency by the input-output method. Ordinarily the separate losses are obtained, and the performance found therefrom. For methods of calculating efficiency from losses, reference may be made to any text-book on electrical testing. Alternating-Current Commutator Motors. For many years attempts were made to produce motors which would operate MOTORS FOR TRACTION 59 satisfactorily on single-phase circuits, and have characteristics suitable for railway purposes. When the alternating-current system of transmission was first brought out, motors were designed which were practically the same as the direct-current series motor. None of them was successful, since an incorrect understanding of the nature of iron loss led to the use of a solid iron structure for carrying the alternating magnetic flux. In 1902 a new type of single-phase motor was announced, which was the exact counterpart of the direct-current series motor, modified for use on alternating current by having a number of special features. In order to understand the operation of this type of motor, it will be well to trace its development from the direct-current machine. Consider a motor operating on direct current, the field and armature being in series. If, for any reason, the current through the motor is reversed, there will be no permanent result what- ever on the operation. This can be repeated as often as desired, provided it is not done more than a few times a minute. In case an attempt is made to reverse the motor too frequently, several effects are to be observed: (1) the amount of current that can be forced through its circuits will be reduced, owing to the inductance of the field windings; (2) due to this inductance, the current will lag behind the electromotive force; (3) the iron in the magnetic circuit will heat up on account of the hysteresis and eddy currents caused by the variable flux; (4) there will be severe sparking at the commutator. It is possible to reduce the iron loss to a reasonable amount by using a good grade of electrical steel and by lamination of the metal. This is one of the first requirements of any good alternating-current motor. The inductance of the field can be lessened by cutting down the number of field turns. A con- siderable reduction may be made in the field ampere turns without a great diminution in the flux, since in modern direct- current motors the iron is worked at a high degree of saturation (see Fig. 22). This will reduce the inductance of the field wind- ing, and hence diminish the lag of the motor current. The power factor can be still further improved by the insertion in the circuit of compensating coils, of the general nature of an inter- pole winding, with a number of ampere turns sufficient to neu- tralize the magnetomotive force of the armature. This will both tend to lessen the reactance and to improve commutation. 60 THE ELECTRIC RAILWAY The use of these devices will in some cases produce a motor which may operate on frequencies up to about 25 cycles. In general, however, additional means must be taken to reduce the sparking to a point where it is not objectionable. Reference to Fig. 25 will show the reasons for the excessive sparking of the single-phase motor. Consider an armature ro- tating in the field produced by current drawn from the line through the field winding. Whether the flux be constant or not, there will be an e.m.f. developed in the armature, its maximum value per turn being induced in the conductors directly under the poles. The maximum total appears at the brushes B } B. If the flux be varying in value (i.e., alternating) there will be an e.m.f. produced due to the change in flux, which will have its maximum per turn in the conductors between the poles, and its total maxi- mum at the brushes A, A. It may be seen that these two e.m.f.'s are entirely inde- pendent, the former, which we may call the " speed e.m.f.," depending on the mechanical rate of cutting the flux with the armature con- ductors, due to the speed of FIG. 25.-Single-phase series motor, rotation; while the latter, which may be termed the " transformer e.m.f.," depends on the rate of change of the field flux caused by the cyclic variation in the magnetizing current. To operate as a normal series motor, the speed e.m.f. is the one which must be commutated, and the transformer e.m.f. must be entirely disregarded. The brushes should therefore be placed in the positions B, B. It is evident that the turns which are short-circuited by the brushes are the very ones which are generating the maximum e.m.f. due to transformer action, and there is a tendency toward severe sparking, even when the distortion of the field due to the cross ampere turns of the armature has been entirely removed by a suitable interpole or MOTORS FOR TRACTION 61 compensating winding. Reducing the number of armature turns per commutator bar will dimmish the current in the short-circuit, but not as a rule to a satisfactory value. An additional method which has been employed by one of the large manufacturers in this country is to introduce between each commutator bar and the armature winding, a fixed resistance of proper amount, sufficient to limit the current in the short- circuited coil to a safe value. The action of such resistance may be seen in Fig. 26. It will be noticed that only those resistance leads which connect to the coils undergoing commutation are in circuit, and that the ones carrying current are in parallel with each other, so that if the brush covers several bars, the resistance inserted in the path of the main current can be in- Brush Commutator Res. Leads Arm. Winding FIG. 26. Use of resistance leads in single-phase motor. considerable, and yet the resistance in the local short-circuit may be sufficient to reduce the sparking materially. The proper proportioning of these resistance leads is a question of con- siderable importance in making a successful single-phase motor of the series type. Frequencies for Single-Phase Motors. The general theory of the single-phase series motor, as developed above, would indi- cate that its performance will be better the lower the frequency. This leads to the logical conclusion that the best number of cycles is zero, or in other words, that the perfomance of the machine is best on direct current. While this is not strictly true, it does apply to a certain extent; and it is possible to operate the same motor both on alternating- and direct-current circuits. The highest frequency which can be used for a particular machine depends on the reactance of the windings, the iron losses, and the commutation. All these quantities vary as functions of 62 THE ELECTRIC RAILWAY the number of cycles. Commercial designs of single-phase series motors have been made to operate on circuits up to 25 cycles per second; but the limitations make it exceedingly difficult to produce motors of this type for higher frequencies. When designed for operation on a 25-cycle circuit, the series motor will weigh from 10 per cent, to 25 per cent, more than a machine of equal rating for direct current. The auxiliary equipment, such as transformers and regulators, shows an increase of capacity at the higher frequencies. This tends to offset the gains made in the motor performance when the number of cycles is reduced. Manufacturers of single- phase equipment consider that the best compromise is the use of 15 to 17 cycles, which gives a marked increase in motor capacity over that at 25 cycles, while at the same time the auxiliary equipment is not excessively heavy. The electrical performance of the series motor at this lower frequency is considerably improved. While the reduction in frequency is entirely beneficial to the series motor, the effect on the repulsion motor is not so good. As is shown in the following paragraphs, motors of the repulsion type have some of the characteristics of the transformer, and a reduction in frequency therefore tends to. increase the weight somewhat. The commutation is also better at high frequencies, since the speed e.m.f. is disregarded to a considerable extent and the transformer e.m.f. commutated. The general char- acteristics of the repulsion motor are not, however, so good for traction as those of the series type. Variations of the Alternating-Current Series Motor. Due to the inductive effects of alternating currents, the arrangement of circuits in the single-phase motor is open to considerable varia- tion without interfering with the . performance to any marked extent. Leaving out of consideration the plain series motor, consisting of only an armature and a set of field coils, and which is not an operative success, we can have three different types of series motor. Fig. 27 shows the ordinary type of series motor, described above, which is commonly known as the " conductively com- pensated" type. In this, as in the direct-current series motor with interpoles, all the windings are in series. Since the armature winding is a source of magnetic flux, the current for the compensating coils may be obtained by trans- MOTORS FOR TRACTION 63 former action from this flux, without connection to the main circuit. Such a motor, known as the " inductively compen- sated" type, is shown diagrammatically in Fig. 28. Compensating Winding UUUU Field FIG. 27. Conductively compensated single-phase series motor. In this machine the armature, compensating winding and field are all in series. It will operate either on alternating or on direct current. Compensating Winding JLQJU Field. FIG. 28. Inductively compen- sated single-phase series motor. In this machine the compensating winding is short-circuited, the current in it being produced by induction from the armature. It is possible to go a step further, and let the armature flux excite both the compensating coil and the main field, as shown in Fig. 29, which illustrates the " induction series" motor. Of the three types, the former two are used in practice, the conductively FIG. 29. Induction series motor. In this machine both the field and the com- pensating winding are short-circuited, the cur- rent in them being induced from the arma- ture, which is connected to the line. FIG. 30. Atkinson repulsion motor. This machine is electrically the re- verse of the induction series motor, the armature being short-circuited and the other windings connected to the line. compensated motor finding its use principally where it is neces- sary to operate the same machine on both alternating and direct current. 64 THE ELECTRIC RAILWAY Repulsion Motor. As it is possible to make either coil of a transformer the primary, so the connections of the induction series motor may be reversed to make the field and compensating windings the primary, and the armature the secondary, circuit. In this form, shown in Fig. 30, the machine is known as the Atkinson repulsion motor. It may also be considered as a development of the plain repulsion motor, which is shown in Fig. 31. In the latter type use is made of the transformer e.m.f., which is entirely disregarded in the series motor. The brushes are placed at an angle with the field, so as to utilize portions of both the transformer e.m.f. and of the speed e.m.f. in order to obtain variable speed characteristics. The repulsion motor has a great advantage over the series motor, in that the primary, being the stationary member, can be con- nected to the supply circuit without mov- able contacts, as when the current must be led through a commutator; the primary can therefore be wound for relatively high potentials. It is also possible, since the coils generating the maximum trans- former e.m.f. are not short-circuited, to FIG. 31. Plain repulsion operate it on somewhat higher frequencies m tor. than with the series motor. At starting This differs from the motor . . . , . , , shown in Fig. 30 in that the the short-circuit current is lower than in compensating and the exciting , . 1,1 , < windings are combined. For the series motor, and the necessity of that reason the brushes are . . . , , , , . , placed at an angle with the using resistance leads much less, so that by careful design they may be omitted. But in general the characteristics of the repulsion motor are not so well suited for railway work as are those of the series motor, and it never has become popular for this class of service. Compensated Repulsion Motor. A modification of the repulsion motor, known as the compensated repulsion motor, or the Latour-Winter-Eichberg motor, has been developed to obtain the advantages of both the series and the repulsion types. This motor (Fig. 32), has two separate sets of brushes, one set short-circuited, the other connected in series with the field. In this way it combines the characteristics of both the series and the repulsion types. It has been used to some extent in electrifica- tion work in Europe, but has not been applied in the United States. MOTORS FOR TRACTION 65 Performance of the Alternating-Current Series Motor. Referring to the vector diagram of the e.m.f.'s in the series motor, Fig. 33, it may be seen that the total potential at the motor terminals is divided into three components: the drop OB across the field, the drop BD across the armature, and the speed e.m.f. DE. For any given current value, the two drops are constant, no matter what the speed. 1 If the motor is at a standstill, these drops will consti- tute the entire potential OD at the motor terminals. As the speed of the motor is increased to give a counter e.m.f. DE } it must be accompanied by an increase in the terminal potential, as given by the vector OE. Since the speed e.m.f. must be in phase with the current, while the armature and field drops are always ahead of it, it may be seen that an increase of ^ j . : FIG. 32. Compensated speed will improve the power factor of repulsion motor. the motor. By keeping the reactances in the circuit down to reasonable values, the normal operating power factor of the motor may be made very satisfactory; that is, it can be made as good as or better than the power factor of induction motors of similar capacity. c hJrac\eScs ne f FIG. 33. E. m. f. and current relations in single-phase series motor. The characteristics of a typical single-phase series motor are shown in Fig. 34. The speed curve is more dropping than with the direct-current series motor, due to the lower saturation of the magnetic circuit. For the same reason the tractive effort 1 The armature and field drops are each equal to the product of the current by the impedance of the circuit. Since the frequency is constant, the reactances are practically constant in any particular machine. They will be changed slightly by variations in iron loss at different speeds. 5 66 THE ELECTRIC RAILWAY approximates more nearly the parabolic form than in the com- mercial direct-current series motor. The power factor approaches unity at zero current, and decreases from this value almost uni- formly in proportion to the load. 120 60 200 400 600 800 Current, Amperes. 1000 FIG. 34. Characteristics of single-phase series motor. Note that the speed curve is more dropping than for the normal direct-current series motor, on account of the lower saturation in the magnetic field. Variation of Single-Phase Motor Characteristics. The charac- teristics of the alternating-current series motor may be varied in much the same manner as with the direct-current series motor. The three methods which may be used are: 1. Variation of terminal potential. 2. Insertion of series resistance. 3. Variation of field strength independently of armature strength. The first method is more readily applicable than with the direct- current motor, since alternating e.m.f.'s of any desired value may be secured with the aid of a stationary transformer. The ease in obtaining change of motor potential makes the other methods of control unnecessary. The use of series resistance is uneco- nomical, and persists with direct-current motors only as a matter of necessity. The variation of field flux in the alternating- MOTORS FOR TRACTION 67 current motor is undesirable, since to make a good commercial machine the flux has to be cut down normally to a minimum, and further reduction is unwise. When the terminal e.m.f. is lowered, it is evident that the power factor will be reduced, since the quadrature component of potential remains about constant, while that in phase is diminished, due to the lessened speed. As with the direct- current series motor, a reduction in potential does not change the torque to any great degree. Since the potential in an alternating- current circuit may be varied at will either by means of a station- ary transformer with a number of taps on the secondary, or by a transformer with a rotatable secondary (induction regulator), it is easy to obtain a wide variation in potential without the need for re-connecting the motors, as in a series-parallel combination, and without the loss inherent to the use of resistance in the armature circuit. Commutation in Single-Phase Motors. A comparison of the circuits of the series and the repulsion motors makes it evident that the series motor has its brushes placed in such a position that the transformer e.m.f. is short-circuited at starting; while the repulsion motor short-circuits the speed e.m.f. The re- pulsion motor should therefore have better commutation when starting, while the performance of the series motor in this respect will be superior at speeds above synchronism. At synchronous speed the e.m.f. developed by transformer action is equal to that produced by the conductors of the armature cutting the field flux, so that the potential is uniform at all points around the commutator. At this speed the sparking will be the same no matter where the brushes are placed. The various methods used for improving the commutation make the series motor satis- factory at starting; but so far the repulsion motor has not given good results as regards sparking at speeds much above synchro- nism. Since the power factor of the series motor is better as the speed increases, it has a considerable advantage in performance for high-speed work. The Polyphase Induction Motor. The polyphase induction motor is so well known, and its characteristics have been so fully described, that no general treatment will be entered into here. It is sufficient to understand that the motor possesses performance characteristics similar to those of the shunt motor, as shown in Fig. 35. If the machine is well designed, the drop in speed from 68 THE ELECTRIC RAILWAY no load to full load is but a small amount, rarely over 5 per cent. The normal speed-torque curve of such a motor is given a " Notch 7." It will be noticed that the effort available at start- ing is considerably less than the maximum running torque. It may further be shown that to produce this starting torque requires a relatively large current, and at a low power factor. If the secondary resistance of the motor be greater, a curve such as " Notch 6" may be obtained. Here the starting torque is increased; but in order to accomplish this result, the efficiency over the entire working range has to be sacrificed. By con- siderably increasing the secondary resistance, as by the use of 250 500 750 1000 Torque, Pounds at One Foot Radius. FIG. 35. Characteristics of polyphase induction motor. external resistors, the starting torque may be increased to the maximum possible value, as at " Notch 5;" or, if it be desired to reduce the starting current further, and the maximum torque is not needed at starting, additional resistance will give curves such as Notches 1, 2, etc. In all of these cases, however, the efficiency is very much reduced, being in no case as great as the speed in per cent, of synchronism. It is evident, then, that to get efficient operation, the resistance must be inserted only during the starting period, it being gradually cut out of the circuit as the speed increases, until the motor is operating with short-circuited secondary. With this connection the motor will operate at practically constant speed. MOTORS FOR TRACTION 69 Another method of reducing the speed at starting is to lower the potential applied to the terminals. Since the motor receives its magnetizing current and the working current in the same winding, any reduction of the potential will decrease the field strength as well as the load current. In normal induction motors, the field iron is practically unsaturated, so that the flux is lessened nearly in proportion to the reduction of potential. The decrease in primary potential causes a similar reduction in the secondary induced e.m.f., so that the secondary current is lessened. It follows that the torque produced at any given value of load current varies as the square of the applied potential. When the primary potential is reduced the power factor and the efficiency are also lowered, so that the performance is poor. A further effect, due to the larger proportion of losses in the motor, is that the heating at any given primary current is increased and the capacity of the motor reduced. If the induction motor is used for starting heavy trains, this method of speed control is not to be recommended; and in any case it is far inferior to the first method, by insertion of resistance in the secondary circuit. The induction motor inherently must operate at a speed somewhat below synchronism; and we have seen that the normal curve does not fall far below this value. It is possible to change the speed of the motor if the synchronous speed can be changed ; and this can be done without any great sacrifice of power factor or efficiency. There are two methods by which the synchronous speed may be altered: by variation of the frequency, and by a change in the number of poles on the primary and secondary. No variation in frequency can be expected in the supply circuit, so any change made must be in the control of the motor. This is usually done by " cascade control" or " concatenation," in which the secondary current from one induction motor is fed into the primary of another motor, the two being mechanically connected together so that they must run at the same speed. This will be described more in detail in connection with methods of control. The number of poles on an induction motor may be changed much more readily than on a direct-current motor, since the field is usually constructed with a distributed winding. The inclusion of more or less coils in a group makes it possible to re-connect the winding to give two or more sets of poles with the same field coils. To get more than two sets of poles with the same coils 70 THE ELECTRIC RAILWAY complicates the winding to an extent where it is not practical; so for such cases the primary and secondary parts of the motor are each supplied with two or more separate windings, in case more than two speeds in the ratio of 2 : 1 are desired. This method of speed control has been worked satisfactorily in a con- siderable number of European locomotives; but is too cumber- some for use with individual motor cars, especially where train operation is desirable on the multiple-unit system. Induction Motor Performance. Under normal conditions, the efficiency of the induction motor can be made at least as high as that of the best direct-current series motors, and with a some- what smaller weight per unit of output. The efficiency is some- what better than that of the single-phase series motor, being about equal to the efficiency of the direct-current series motor. The power factor is at least as low as, or often lower than, that of the single-phase motors, so that the line current required is equal to or somewhat greater than that required for the series motor. Further than this, it must be remembered that the induction motor operates only on a polyphase circuit, so that at least two trolley wires are necessary, using the track for the third con- ductor. If it is possible to install a rotating phase changer on the locomotive, polyphase motors may be used on a single-phase supply system. This is actually being done on one American railroad at the present time. CHAPTER IV RAILWAY MOTOR CONSTRUCTION Motor Development. Although the first experimental electric railway was built in 1835, and various inventors were from time to time developing model electric locomotives, it was not until the year 1879 that anything resembling a practical electric road was produced. From that time the improvement was rapid, and it was only a comparatively few years until the essentials of the modern electric railway had been invented and applied. The motors used during the first or experimental period, from 1835 to 1879, were mere toys, and had no practical operating value. In the latter year, the great engineering firm of Siemens and Halske exhibited an electric locomotive designed to draw a light train of passenger cars. This train was displayed at the Berlin exposition. It marked the change from a scientific' toy to a practical means of train propulsion. The Siemens loco- motive was equipped with a single stationary type motor, mounted on the platform, and belted to the axle. In the next few years a large number of inventors, both in America and in Europe, produced electric locomotives and motor cars which were more or less successful. In all of the earlier types the motors were the ordinary stationary machines, usually applied to the work without any change whatever. In some cases even arc-light generators were used as motors. It must be understood that the equipment in these early roads was exceedingly crude. This was not surprising, since the applica- tion of electrical machinery in general had just begun, and practically none of the present theory had been developed. Early Motors. In the early electric railways in this country the practice mentioned in the first road (that of the Siemens and Halske firm) of using a motor placed on the platform of the car or locomotive was adhered to. This was almost necessary, since the performance of the motors was so poor that it was absolutely essential to keep a close watch on the motor operation, 71 72 THE ELECTRIC RAILWAY especially of the commutator and brushes. It was considered the best practice to shift the brushes to give good commutation; and if the car was reversed, a considerable brush displacement was called for. With the road installed in Richmond in 1888 by Frank J. Sprague came the recognition that the railway motor is a special piece of machinery, and should be designed to perform its work in the best possible manner. In this installation the motors were hung on the car axles, and were inaccessible from the floor of the car for constant inspection and adjustment. Since these motors were designed to be reversible, it was necessary to place the brushes in the neutral position, making no allowance for shifting them to obtain good commutation. This practice has FIG. 36. Sprague motor. This is the type of motor which was used on the Richmond road in 1888. forms were used, but the general appearance of all was quite similar. Several different persisted to the present time, and the design of modern motors has always been made with this feature as a necessary detail. The early motors were all bipolar, following the stationary practice of that time. It was not until about ten years after the first electric railways were operated that it was considered more economical to use multipolar designs, in order to get better distribution of the active material and to obtain improved per- formance. When it was found possible to build multipolar rail- way motors, an attempt was made to use a comparatively large number of poles. This arrangement was also abandoned in favor of motors with four poles, which number has become standard for all direct-current railway motors of the ordinary types. The first railway motors, being a direct adaptation of the stationary types, were entirely open. While this type of ma- chine had better facilities for getting rid of the heat generated by the losses, the exposure of an open motor under a car, to all RAILWAY MOTOR CONSTRUCTION 73 sorts of dirt, mud, and water, led to grounding of the insulation, pitting of the commutators, and rapid destruction of the bear- ings. The logical remedy was to totally enclose the working parts of the motor, extending the field frame to make a casing around the field and armature. The first attempts of this sort did not aim at total enclosure of the working parts. While the partial enclosing did some good, there was still difficulty from splashing water and dust. The successive designs went further, until no openings whatever to the interior of the motor were left. Access to the commutator was had by means of a hand-hole with removable cover; but since by that time the commutation had been improved to a point where constant inspection was unnecessary, this caused no disadvantage. Armature Construction. The early armatures were of the smooth core, hand wound drum type, usually with one turn per commutator bar, with either a lap or a ring winding. Such a construction requires as many brush arms as the motor has poles. It was found that by the use of the two-circuit wave wind- ing but two brush arms were required, irrespective of the number of poles on the motor. This was an important improvement, since it became possible to place both brush arms on the upper part of the commutator, where they could be easily inspected through the hand-hole. Better knowledge of the phenomena of commutation led to the use of slotted cores for the armatures. This was more of an advance than may appear at first, for the heavy torque required at starting had the effect of stripping the windings off the smooth cores. With the slotted type, the wires had a solid wall of iron against which to exert the push. The knowledge of commutation also made it possible to wind the armatures with more than one turn per commutator bar, thus making a cheaper and more rigid construction, and facilita- ting repairs. These changes in armature construction were coincident with improvements in the brushes and brush rigging. The early machines used brushes of leaf copper, such as are some- times employed at the present time on electrolytic machines. The use of brushes of this type, with inherently low resistance, made a small number of turns between bars necessary to prevent excessive sparking. In the history of the Richmond road, brushes of solid bronze were used at one period. Replacement 74 THE ELECTRIC RAILWAY of all these types of brush with those of carbon made possible the changes in armature design noted above. Armature Speeds. In nearly all of the pioneer designs of railway motors, the armatures were of large diameter. This construction was adopted to get the necessary high peripheral speed without having an extremely great angular velocity. Even with the large armatures the speeds were excessive in many instances. The use of multipolar motors made possible a lower peripheral speed, and, at the same time, a reduction in speed of rotation. This effect was aided by lengthening the core somewhat parallel to the shaft. The large diameter arma- ture, especially when rotating at a high speed, possessed a great deal of inertia. We have already seen that the inertia of the rotating parts of the equipment is a comparatively im- portant part of the total for a moving car. The still larger amount of inertia caused the consumption of additional energy, and considerable extra brake wear, besides increasing the time for stopping the cars. In most of the early motors, the armature speeds were so high that single-reduction gears could not be used, and it was necessary to have back-geared or double-reduction motors. This caused an extra loss, and an added complication that did not seem warranted. The slower armature speeds obtained in the later designs brought at the same time the single-reduction gearing which has persisted to the present time except for certain large locomotive motors. Field Frames. Motors of the old horseshoe type were almost invariably made with field yokes of wrought iron. While this material has excellent electrical properties, it is entirely too expensive for use on a large scale, as in railway motors. The alternative material which was developed in the early history of electric motors is cast iron. This is much cheaper, but requires approximately twice the weight for the same field strength. On the other hand, it lends itself better to the totally enclosed designs which were coming into vogue at the time it was intro- duced. Cast iron, in its turn, was found too heavy, and in some cases not strong enough. It was gradually superseded by cast steel, which has been the accepted material for railway motor frames for over fifteen years. Cast steel is more expensive per unit of weight than cast iron; but its superior magnetic properties RAILWAY MOTOR CONSTRUCTION 75 allow the manufacture of a frame weighing about half that for a cast-iron one, and at approximately the same cost. If there is a sufficient .demand for motors of a certain type, it is possible that cast steel may in its turn be superseded by frames of rolled and pressed open-hearth steel. Although the first cost of a pressed-steel frame is exceedingly high, the manufacture of large quantities of a certain single design will make it an active competitor of the cast steel. One design has already been made using pressed steel, and which is superior in many ways to the ordinary type of cast-steel motor. The changes outlined above mark the development of the rail- way motor from a crude device, upon which little reliance could be placed, to one that can be used without difficulty, and will perform its work satisfactorily under the severe conditions of service inherent to railway operation. The structural develop- ment outlined was carried along with an improvement of con- struction details both electrical and mechanical. The result is an increase in efficiency from quite low values, to fairly high ones over the entire operating range. In a railway system, efficiency of the traction motor is but a small item; but the saving in cost due to the increase in efficiency is worth considerable to the railway operator, since it has come with other improvements of a desirable nature. Modern Direct-Current Railway Motors. The development we have just traced has been entirely in the direct-current series motor. The greater part of it took place prior to the year 1893; since that time the changes have been more in the nature of minor refinements than in radical developments. Modern Motor Frames. The frames of modern motors are made of cast steel, and include the magnetic circuit of the field, with the protecting casing. There are two types of frame in general use solid and split. The split frames are the earlier development. It was formerly the universal practice to inspect the motors without removing them from the car axles. This is done in one of two ways. The motor is split in a horizontal plane through the shaft in such a manner that the lower half can be dropped down, thus permitting inspection from a pit beneath the track; or else the upper half can be raised, allowing inspection on the shop floor after the truck has been run out from under the car. This latter method was used only on a few 76 THE ELECTRIC RAILWAY of the largest systems, the former being much more widely employed. With the refinements which have been made in modern motors, the need for inspection has diminished, so that it is possible to make a far greater mileage between overhaulings of the motors than previously. This has made possible the use of motors with solid frames, the armatures being removed from the end. This latter construction is more rigid and somewhat cheaper; but it makes it impossible to remove an armature unless the entire motor is first taken off the truck. To determine the clearance between the armature and poles, it is customary to have small hand-holes for inspection in the lower portion of the motor case. The choice of solid or split frames depends largely on the shop equipment avail- able for handling the motors. In some small shops it is quite difficult to remove and replace the armatures of solid^frame motors; but in the larger shops, especially those equipped with cranes, the employment of this type has proved entirely saisfactory; and their use seems to be grow- ing at the present time. In the first designs of railway motors, the poles were made integral with the main horseshoe forgings for the field. This was fairly successful, since a high-grade magnetic material of prac- tically uniform permeability was used. The first machines with cast-iron frames had the poles cast in the frames. This design was not successful, since neither the control over the quality of the metal, nor the dimensions of the poles, was complete. In a few types, an attempt was made to correct this trouble by build- ing up poles of laminated steel, and casting them into the motor frame. While this was an improvement, it did not meet all the demands of a satisfactory pole structure. In all modern motors the poles are made of steel laminations, built up and riveted together. They are fastened into the field frame with bolts, and FIG. 37. Modern direct-current rail- way motor. This is the solid-frame type of motor. The armature is removed by taking off the end-bell after the motor has been removed from the car. The axle gear and the gear case are not shown. RAILWAY MOTOR CONSTRUCTION 77 are so designed that they may be removed without taking the armature out of the case. The use of the laminated pole makes it possible to shape the pole tips to aid commutation, and they can be properly spaced in the frame to ensure correct alignment. This feature, although perhaps not fully appreciated, is one of the factors in the splendid performance of modern direct-current motors. Use of Interpoles. Within the past few years the use of interpoles has become quite general. Of all types of commutator electric motors, the series machine has the least inherent tendency to spark, since the field strength automatically increases with the armature current. The sud- den and heavy overloads, how- ever, make the very best com- mutation a necessity for con- tinued successful operation. In all cases where constant attention cannot be given the commutator, the destructive results of sparking are cumula- tive; and even though the sparking of well-designed non- interpole railway motors was formerly considered negligible, the wear of both commutator and brushes is considerable. The use of interpoles has re- duced sparking to a point where it is practically absent; and with its decrease a great gain has been realized in the life of commutators and brushes. In form the interpoles are practically the same as those for stationary direct-current machinery. The turns are, so far as possible, concentrated near the armature surface, to increase their effectiveness. The supporting cores are of steel, bolted into the field frame between the main poles. The inter pole coils are connected directly in series with the armature and field windings, and are arranged so that they may be reversed along with the armature, in order that the current through the commutating coils may be in the proper direction to assist the commutation and not hinder it. FIG. 38. Arrangement of interpoles. The main poles, a, and the interpoles, b, have windings which are placed in series with the armature. Usually the main field winding is reversed to change the direction of rotation. 78 THE ELECTRIC RAILWAY Modern Armature Construction. The armatures of modern motors are invariably of the slotted drum type, and are wound with two complete coils per slot. The early armatures of this class were designed with a comparatively large number of small slots, each with one or two single coils in it. This practice causes weak, narrow teeth, and is wasteful of space, since the major coil insulation must necessarily be of a definite thickness whether one or a number of separate coils are assembled together. Inci- dentally the cost of punching the iron with a large number of teeth is greater, and the commutation is poorer. Modern practice is to include from three to five single coils in each com- plete coil, so that the total number of slots is considerably less than in the early armatures, even though the number of commutator bars has been increased. In some motors the armature punchings are assembled directly on the shaft, and in others they are mounted on a spider of cast iron. In the larger machines the use of the spider is universal. Its employment depends on the amount of iron which needs to be left back of the teeth for carrying the flux, and on the arrangements made for ventilation. Armature windings of direct-current railway motors are almost invariably of the two-circuit type. The use of two-circuit wind- ings, as has already been stated, results in the need for only two brush arms, no matter how many poles the motor has. On the other hand, if the current capacity is large, a brush-arm can be supplied for each pole of the motor, thus making possible a short commutator. The maximum currents to be handled with direct-current motors are usually well within the limits of the two-circuit winding. Armature coils are made of wire only in the small sizes. For the larger motors, strap-wound coils are the universal practice. The strap gives a better space-factor i.e., the proportion of the slot occupied by copper is greater, and that taken up by insula- tion is less. Generally, the individual armature coils are wound complete in one piece ; but in some types the coils are separated into two parts, and are connected together at the back end of the armature. This makes replacement of damaged coils easier, but increases the number of soldered joints. Commutator Construction. Modern commutators are gener- ally built of rolled or drop-forged copper. Uniformity of the surface has much to do with long life of the commutator and RAILWAY MOTOR CONSTRUCTION 79 brushes in service. Another factor is the material employed for insulation between bars. Although a number of materials have been used, the only one which has been satisfactory is mica. At the present time it is exceedingly difficult to obtain mica of uniform quality, and in consequence the practice has been adopted of using insulation built up from small sheets of this material held together with some form of binder, such as shellac. To get good service from a commutator, the insula- tion and the copper must wear down at the same rate. If the mica is too soft, it will wear away faster than the copper, and leave low spots at the edges of the bars. On the contrary, if the mica is too hard, it will not wear away as rapidly as the copper. The result will be that the brushes will have a tend- ency to jump away from the surface of the commutator, causing sparking and flashing which will conduce to further pitting and wearing down of the copper, until turning is necessary. Prac- tically all the mica which is available for commutator insula- tion at the present day is harder than the copper surface, giving the latter effect. The remedy for this is the practice, which is being quite generally adopted, of " under cut ting" the mica, or removing it to a depth of about Jfg m - below the surface. This permits the brushes to bear evenly on the commutator, and allows uniform wear of the copper. With the aid of corn- mutating poles and undercut mica the commutation of modern motors is well-nigh perfect. Motor Lubrication. It is in the mechanical parts of the motor that the most radical changes have been made since the beginnings of electric railway operation. In the early machines, lubrication was commonly effected with grease. Grease as a lubricant is theoretically inefficient, since it re- quires the bearing to overheat before acting. It has been re- placed by the use of oil, carried to the rotating part by capillary attraction through the medium of wool waste, which rubs against the shaft, and thus ensures a constant supply of oil under all conditions. Both armature bearings and axle bearings are lubricated in the same manner. Bearing Housings and Bearings. As the early motors were of the open type, there was little difficulty in removing the armatures for inspection or for repair. When the enclosed motors became standard, provision for removing the armatures was made by splitting the frames, as already explained. With 80 THE ELECTRIC RAILWAY the modern solid-frame motors, the armatures must be removed from the ends of the casing. To do this, the opening in the end of the frame must be at least as large as the diameter of the armature. The accepted method of closing this opening is to use a bearing bracket, turned to fit a bored hole in the frame, and containing the bearing and bearing housing, to- gether with the oil receptacle. The same type of end bracket has been adopted with split-frame motors, on account of the rigid support it gives the bearing, and its excellent arrangement for oiling. The bearings proper are made of brass or bronze, with the wearing surface of babbitt metal. This construction is good, since the use of a soft metal reduces the friction to a minimum under normal conditions; and if anything happens to melt out the babbitt, the bronze itself furnishes a good bearing to run on until the motor can be removed from the car at the end of the trip. Without such a safeguard the melting of the babbitt would cause the armature to strike the pole faces, resulting in damage to the winding and possibly destruction of the core itself. Ventilation of Motors. The oldest railway motors, being open, were ventilated entirely by natural circulation of the sur- FIG. 39. Method of forced ventilation. The air is circulated through the motor case by means of fans carried on the armature. A number of other arrangements of air-paths are in use to obtain a passage of air through the motor case. rounding air. With the advent of the enclosed motor, a different condition was confronted. The outside air no longer had access to the armature, commutator and field coils; but all the heat generated had to be transferred to the frame and dissipated from the outside surface of the case. The result was that the capacity of a motor of given weight was much smaller than in RAILWAY MOTOR CONSTRUCTION 81 the case of the corresponding open machine. But it has been found necessary, on account of the bad effects of dust and moisture, to keep the motors almost completely enclosed. A number of years ago an attempt was made to force air into the motor by means of ducts leading to the front of the car. This was not entirely successful; but it led the way to the use of fans on the motor armature, by means of which a circulation is established, drawing air in from the outside, and passing it through the motor, finally discharging it again. By this method, shown in Fig. 39, the temperature of the motor may be reduced materially for the same load, or the rating of a given motor may be increased. The result is to lighten the equipment. In the large locomotive motors such ventilation would not be sufficient, especially since the greatest generation of heat occurs when starting. At this time the efficiency of any fan driven by the armature is least, and the cooling effect small, since the speed is low. To give an adequate supply of cooling air to such motors, they are provided with ventilating ducts, the air being furnished from an independent motor-driven blower located in the cab. Single-Phase Commutator Motors. In the case of single- phase motors, the field flux is alternating. A solid field structure is inadmissible, and it is necessary to provide a complete lami- nated core for the magnetic flux. This leads to a quite different arrangement from that of the standard direct-current motors. The field is built up of a set of punchings, which are held rigidly in a frame of cast steel that also serves as the enclosing case of the motor. The poles are made integral with the core, for it is impossible to remove them on account of the compensating winding. The field coils of alternating-current series motors are not essentially different from those of direct-current motors, except that they have less turns. The compensating windings, instead of being concentrated, as in the direct-current interpoles, are distributed over nearly the entire pole-face. By this means the neutralizing ampere turns are placed very near the armature conductors whose inductance it is desired to oppose, and their effectiveness is increased. On account of the compensating winding, it is not possible to split the frame; and, since the majority of single-phase motors are of comparatively large rating, and are used on roads with 6 82 THE ELECTRIC RAILWAY adequate shop equipment, there is not a great demand for that construction. In most modern machines, the external appear- ance is not essentially different from that of direct-current motors of similar capacity. The armatures of alternating-current series motors are very nearly the same as those for direct-current motors, the principal apparent difference being the greater number of commutator bars on the former. In the type manufactured in the United States, there is a difference, not readily discernible, due to the interposition of resistance leads between the armature coils and the commutator. These leads are placed in the bottoms of the slots in the smaller sizes of motors; and in the larger ones are FIG. 40. Interior of single-phase series motor. The pole faces are slotted, and have the conductors of the compensating winding em- bedded in them. placed in the core in separate slots located beneath the path of the flux. This method of construction makes repairs and replacements comparatively easy. In distinction to the direct-current armatures, those of single- phase motors are ordinarily lap wound. Since there is a possi- bility of uneven distribution of the magnetic flux, due to in- equalities in the air gap, it is customary to supply them with balancing rings such as are used on large generators. The use of these rings permits equalizing currents to flow in the armature, thus compensating for variations in the magnetic strength of different poles. The use of lap- wound armatures makes obligatory the use of as many brush arms as there are poles. In order to improve the performance of the motors, there is a tendency to increase the RAILWAY MOTOR CONSTRUCTION 83 number of poles, which requires an additional number of brush arms. For this reason it is somewhat more difficult to maintain the brushes on single-phase motors. None of the purely mechanical parts of the alternating-current series motors are essentially different in any particular from those of direct-current motors. In fact, the external appearance is nearly identical for the two types of machines. Since the alternat- ing-current motors are used to a considerable extent on large locomotives, the design of individual units may lead to a material difference in appearance. Induction Motors. The design of induction motors for railway service calls for more radical departures from the ordinary direct- current designs than is the case with the series motor. The field or primary winding is usually placed on the stator; but it must be distributed, and resembles an armature winding. This calls for a different type of construction. The enclosing frame, however, may be made to resemble that of the direct-current motor quite closely, and the mechanical parts may be the same. The secondary is generally made the rotor; and, for the forms ordinarily used in traction work, the winding is of the definite type, similar to that of the primary. There is this essential difference : no commutator is required, and the ends of the wind- ings are brought out to collector rings, through which the current is led to the resistors by means of brushes. The secondary has no connection whatever with the supply circuit, and can be wound for any convenient potential. The secondary windings are nearly always made three-phase, since this allows of the minimum number of rings and brushes. The location of the collector rings is a matter of some impor- tance. If the size of the motor is not excessive, the rings can be located inside the frame, in a position similar to that of the com- mutator in a series motor. If the capacity of the motor is large, it may be difficult to find room for the collector. In some designs it is mounted inside the spider; in at least one, the leads from the winding are taken through the bearing in a duct bored in the shaft, the collector being placed outside the crank. While this may be considered an extreme design, it was necessitated by the demands made on the motor for space. CHAPTER V CONTROL OF RAILWAY MOTORS Need for Control. If an electric motor of any type, with its armature at rest, were connected directly to the line, an excessive current would flow, limited only by the impedance of the motor and the supply circuit. In case the protective devices failed to open the circuit, the torque produced would in general be so great as to slip the driving wheels; or, failing to do that, to start the train with a severe jerk. Since a fairly uniform acceleration of moderate amount is desirable, some form of control which limits the torque to a proper value is an absolute essential to satisfactory operation. Available Methods. There are two general methods for obtaining the desirable changes in characteristics, which are applicable to nearly all types of electric motors: 1. Variations in potential. 2. Changes in relative strength of armature and field. For certain types of alternating-current motors, the characteris- tics may be varied by the following additional methods: 3. Changes in the number of poles. 4. Changes in frequency. Change of Potential. The effect of changes in the terminal potential is different with various types of motors. In the case of "constant field" machines, such as the direct-current shunt motor, or the alterating-current induction motor, a change of potential at the terminals varies the field or magnetizing current and hence affects the field flux. The variation in the flux cor- responding to a given change in the terminal e.m.f . depends on the characteristic of the magnetic circuit; and in general is different for individual machines. If the magnetic circuit is practically unsaturated, as in most alternating-current induction motors, the torque produced by a given current varies approximately as the square of the e.m.f. In this type of motor a reduction in the terminal potential has a comparatively small effect on the speed, 84 CONTROL OF RAILWAY MOTORS 85 that being determined principally by the frequency of the supply circuit. In the direct-current shunt motor, a change of potential will not have quite so much effect on the torque as in the induction motor, since the field is normally saturated to some extent; but the change in torque will be considerably greater than in direct proportion to the applied potential. At the same time the speed will be varied somewhat by a change in e.m.f. These effects may be obviated by placing the field winding in a separate circuit and keeping it connected to a source of constant potential. The field flux will then remain constant, and the torque will be the same for any value of terminal e.m.f. The speed will vary practically in proportion to the applied potential. In the series motor, a change in the terminal e.m.f. has no effect on the field flux for a given current; but the speed will vary nearly in proportion to the e.m.f. applied to the terminals (see Chapter III). Methods of Potential Variation. The possible methods by which the potential may be varied in railway motor control are: 1. Change of e.m.f. supplied the motor. 2. Combinations of motors (e.g., series and parallel). 3. Insertion of resistance in motor circuits. Changing the e.m.f. supplied the motor is difficult of ac- complishment in ordinary direct-current equipments, since some form of rotating apparatus is necessary to produce the desired result. Although this method has been suggested in one type of control, it has never been introduced practically. For alternating-current motors, changes in potential may be easily accomplished by taking taps from a transformer or an auto-transformer to give the desired values. A simple and efficient means of varying the e.m.f. applied at the motor terminals is available when an equipment consists of two or more motors, by placing them either in series or in parallel with one another. Two-motor equipments can thus be arranged to take full potential and half potential at their terminals; three- motor equipments (if such were used) could have full potential and one-third potential ; and four-motor equipments full, one-half and one-quarter potential. This method of reducing the pressure is used in nearly all direct-current equipments. When this method of reducing potential is used, it is necessary that all the motors in 86 THE ELECTRIC RAILWAY 600 the combination have identical characteristics, since otherwise they will not divide the line e.m.f . equally when in series, or the current equally when in parallel. No troubles of this sort are to be anticipated from modern motors as received from the manufacturer, provided only machines of the same type and rating are used together. In case motors have been repaired by unskilled workmen, it may be necessary to test them in order to be sure that the performance has not been changed. If these precautions be taken, the motors will divide the pressure equally among themselves at all loads when in series (see Fig. 41). Since the current taken by motors in series is the same, the load imposed on them must in that case be equal. The only con- dition which can then cause trouble is that one motor may revolve faster than the other, due to slipping of the wheels. When this happens, the motor whose driving wheels are slip- ping will develop a greater counter e.m.f. than the other, which will then tend to run at a reduced speed, until it finally stops, the first motor revolv- ing with but a small load due to the sliding friction of the wheel on the rail. To overcome this difficulty the motors must be stopped and the rail sanded. With direct-current motors, the insertion of series resistance has a similar effect to a forced reduction of potential. Since such an added resistance increases the IR drop, the amount of reduc- tion in pressure at the motor terminals varies directly wtih the current. A resistance which will reduce the terminal po- tential of a motor to a low value -with a heavy current will have but little effect on it at light loads (see Fig. 21). The effect of series resistance is quite different in the various types of direct- current motors. In the series motor it serves merely to reduce the pressure at the armature terminals, without affecting the field strength for a given armature current; but in the shunt motor, it reduces the field current as well. The result in this case is similar to that already noted for forced changes in motor potentials; and, if it is desired to control the shunt motor in this manner, the resistance should be placed in the arma- Ho+or No. 2 FIG. 41. Division of e.m.f. with motors in series. CONTROL OF RAILWAY MOTORS 87 ture circuit alone, the field being permanently connected to the line. A reduction in the potential supplied an induction motor- affects it in much the same way as with the shunt motor. Since the armatures of several machines cannot be placed in series, as with direct-current shunt motors, this method of control has but little application. Changes in Armature and Field Strength. Since the torque of a motor depends on the product of field flux and armature current, a change in the flux will cause a proportional variation in the torque for a constant value of armature current. Likewise, since the speed depends directly on the counter e.m.f. and in- versely on the field flux, a change in flux at any value of armature current will cause an inverse effect on the speed. In the shunt motor the field strength may be readily varied by insert- ing resistance in series with the field windings; but in the series motor it is less easy to make the TViprp nrp frmr mpthnrk , This method of field weakening has ^ie are lOUr IlietllUUb b een abandoned on account of inductive Resistance FIG. 42. Field weakening by diverting resistor. which may be employed to vary the field strength in series motors, as follows: 1. Placing resistance in parallel with the field winding. 2. Short-circuiting portions of the field winding. 3. Cutting out of circuit portions of the field winding. 4. Placing halves of the field coils in series and in parallel. Of these methods, the first, shown diagrammatically in Fig. 42, was used in the early days of electric railways. It was soon abandoned on account of the severe sparking occasioned with the weakened field. In the motors of that period the problem of commutation was not understood so well as it is at the present time, and the margin of field strength was not great enough to permit this practice. With modern motors, equipped with interpoles, the commutation is so much better that a certain amount of field weakening is permissible without any trouble 88 THE ELECTRIC RAILWAY from sparking. Further, in the designs arranged for this method of control, the flux with the full field in circuit is considerably greater than for the ordinary motor not arranged for field weakening. The use of a resistance in parallel with the field is, however, open to several objections. It places a non-inductive path for the current in parallel with a highly inductive one. If the load is suddenly varied, the resulting change in current will at first be practically all made through the resistance, on account of the inductive effect of the field winding. The current will after- ward gradually build up in the field coils; but sometimes not FIG. 43. Field weakening by short- circuiting turns. Field FIG. 44. Field weakening by cutting out turns. This method and that shown in Fig. 43 are in general use where field control motors are employed. The reduction in the number of turns is usually from 20 to 30 per cent. until considerable damage has been done due to sparking or flashing at the commutator under the abnormal conditions. The second method is to be preferred to the first. In this, as shown in Fig. 43, all the current must pass through the field winding, no matter what momentary variations in current strength there may be. This is a marked advantage over the use of par- allel resistance. The third method, illustrated in Fig. 44, is electrically the same as the second, and gives precisely the same results. The only difference is that the portion of the winding not in use is entirely cut out, instead of being merely short-circuited. CONTROL OF RAILWAY MOTORS 89 In the fourth method, Fig. 45, the turns which are removed from the circuit in the second and third methods, are connected in parallel with the other portion of the winding. This arrange- ment will only allow of two combinations, with full and half ampere turns. It has the advantage over the second and third methods of loading all parts of the field winding equally. The efficiencies of the first three connections are identical, if the amount of field weakening is the same. Consider the field strength reduced to one-half its normal value by each method. In the first this will be accomplished by placing a resistor in parallel with the field whose resistance is equal to that of the field winding. The total resistance of the combination is one- half that of the field alone, and the am- pere turns in the field coils one-half the normal value for the same armature cur- rent. With the second or third methods of connection, the resistance is reduced to one-half the normal value, since one-half of the winding is removed from the circuit. The efficiency of either connection is, there- fore, the same as for the first. In the fourth connection it is greater, since, when the two halves of the field are connected in parallel, the resistance of the combination is but one-quarter the normal value. In any of the four methods of connection, the ampere turns on the field will be the same, if the parallel resistance is equal to that of the field, if one-half of the field turns are short-circuited or cut out of the circuit, or if the halves of the winding are connected in parallel instead of in series. The one to be used in any particular case depends on the size of the motor and the conditions of operation. For small machines, either the second or third method of connection may be used to advantage. For large locomotive motors, the additional com- plication of the winding and connections in the fourth method is warranted on account of the lower loss and the smaller heating. Changes in Number of Poles, and in Frequency. These methods of control are only applicable to induction motors. They will be considered in detail in connection with the con- trol of motors of this type. FIG. 45. Field 3akening tn fields in para! weakening by placing This method is usually applicable only to the larger locomotive motors. 90 THE ELECTRIC RAILWAY Practical Combinations of Control Methods. In the practical control of railway motors, one or more of the methods outlined in the preceding" paragraphs may be used to give the proper varia- tion in characteristics desired. The simplest method is to con- trol the potential; for alternating current this may be readily done with the aid of a transformer. For direct current, no simple, and at the same time efficient, method is available. For small equipments, or those which are infrequently started, the plain rheostatic method is the simplest and most rugged combination that can be used. The chief disadvantage lies in the waste of energy in the resistors. The method in most general use is a combination of the rheostatic control with changes in arrange- ment of the motors, placing them in series and in parallel. Since there are several methods of accomplishing the results sought, they will be taken up more in detail in the succeeding paragraphs. Rheostatic Control. The simplest way of controlling the per- formance of one or more series motors is by the rheostatic method. Resistance is placed in series with the motor or motors, the value being determined by the current desired through the motor at starting. Taps are taken from the resistors at certain points, so that the resistance may be varied from the maximum value to zero in a fixed number of steps. The proportioning of the resis- tance values is done in the same way as for series-parallel control- lers, and may be determined as in the example under that heading. It must be remembered that since there is usually only one motor, the full line potential will be impressed on the motor circuit at the start, and the values of resistance must be determined accordingly. A number of practical controllers have been designed using the rheostatic principle. All of the early ones were of this type, the series-parallel connection not being widely adopted at first. The best known modern controllers of this kind are the Type R, which are sold by the leading electrical manufacturers in this country. A number of sizes are built, the main difference being in the capacity of the motors which can be handled. A controller of this type consists essentially of a rotatable drum carrying a number of copper segments arranged to make the proper sequence of con- nections. A set of fingers, connected to the various external circuits, are brought to bear on the segments as the drum is revolved beneath them. CONTROL OF RAILWAY MOTORS 91 The development of a rheostatic controller, known as the type R-17, is shown in Fig. 46. This controller is suited for use with one 40 kw. motor. The operation may be readily traced from the diagram, the maximum resistance being connected in series on the first point and cut out in steps until the motor is working on the full line potential. With this type of controller, as with any rheostatic control, there is but one running point, that where the motor is connected directly to the line. On that point all the resistance is short-circuited, and the loss in the controller is simply that of any closed switch. (Qroundedj FIG. 46. Development of type R controller. This form of controller is used principally for the control of single motors for mining and industrial work. It is seldom employed for railway cars. Rheostatic controllers are also made for operation with sev- eral motors, permanently connected in series or in parallel; and in some others of this type, provision is made for connecting motors in series or in parallel by means of a commutating switch located in the same case, and sometimes on the same shaft with the reversing drum. Limitations of Rheostatic Control. Controllers of the rheo- static type, while they are of the greatest simplicity, and are extremely rugged, are limited in their present application almost entirely to mining locomotives. Practically none are used on electric railways of any description, having been superseded entirely by series-parallel controllers. The reason for this is 92 THE ELECTRIC RAILWAY found in their low efficiency of operation. During the period while resistance is connected in series with a motor or a set of motors, a portion of the electrical input is being consumed in the 800 400 40 600 300 30 45 Time, Seconds. FIG. 47. Energy loss with rheostatic control. The shaded area represents the energy wasted in resistance. It is nearly one-half of the entire input while the controller is being turned to the full-on position. 800 400 40 45 FIG. 48. Energy loss with series-parallel control. In this control the wasted energy is but one-half as great as in the rheostatio control. Approximately one-fourth the input shown in Fig. 47 has been saved. resistors. The input to the motors is therefore less than the input to the train by the amount consumed in the wiring and in the resistors. For short runs this may amount to a very consid- erable part of the total input if rheostatic controllers are used. CONTROL OF RAILWAY MOTORS 93 In Fig. 47 is shown a curve between power input and time for a certain run, using four motors in parallel with rheostatic control. The shaded area is a measure of the energy used in the resistors. This shaded portion represents approximately one-half the total input during the period while the controller is being turned to the full-speed position. The same motors may be connected in groups of two in parallel, and operated with a series-parallel control to give the same acceleration. In Fig. 48 is shown the curve of input for this form of control. The shaded area, representing the loss, is only one- 800 400 40 600 300 30 400 200 ZO - 200 100 10 * I < t" FIG. 49. Energy loss with series, series-parallel control. The energy saving over the series-parallel control is much less than that of the latter over the rheostatic. For this reason it has not a very wide application for light railway service. half as large as in Fig. 47. This saving amounts to one-fourth of the total energy input during the time of operating the controller, and is a considerable portion of the entire input for the run. Following the same line of argument, it may be seen that a controller can be arranged to put all four motors in series, re-con- nect them in series-parallel at the proper time, and finally place them in full parallel. The power curve for such a control is shown in Fig. 49. It may be noted that the saving in energy is about one-half of that lost in the series connection of the single series-parallel control, and one-eighth of the loss by the rheostatic method. It is only one-sixteenth of the input during the ac- celeration period, and a much smaller portion of the entire energy input for the run. While any saving of energy is a good 94 THE ELECTRIC RAILWAY thing, the resulting complication of the controller is so great that it usually overbalances the gain. The saving incident to the series-parallel over the rheostatic control is so much larger that the complication is thereby justified. Another advantage may be gained by the use of series-parallel control. With the rheostatic method, there is only one efficient operating point, that being the position with all resistance cut out of circuit. For reduced speeds it is necessary to waste a large amount of the input in the resistors. By the use of single series-parallel control, a second efficient operating speed becomes available when the motors are connected in series. The efficiency of the motors on half-potential is slightly less than under normal conditions, but it is quite high compared with the efficiency when half-speed is obtained by rheostatic control. Even without the saving in energy during acceleration, the complication of the con- trol is justified to obtain the second operating point, which gives approximately half the full speed. By the use of the series, series-parallel control, an additional operating speed of about one-fourth the normal may be obtained. This is not needed in ordinary car operation; but in the case of locomotives which must do a certain amount of switching and slow-speed yard work, the extra efficient speed will justify the added complication. It is only used on a few of the larger loco- motives which are designed for normal high speeds. Generally speaking, all of the controllers for direct-current series motors are of the single series-parallel type, either with two-motor or four- motor equipments. Series -Parallel Control. Practically all direct-current railway motor equipments consist of two, or multiples of two, series motors, controlled by the series-parallel method. The basic principle of this control is, as has already been stated, to first put the two motors in series with resistance, next to cut it out of the circuit in a few steps, then to change the connections to parallel with a certain amount of resistance, and finally to cut it out again in steps. In some types of series-parallel control, the additional feature is included of reducing the field turns on the parallel con- nection after the external resistance is short-circuited. The main differences in the arrangements of series-parallel controllers are occasioned by the methods of changing from the series to the parallel connection. It may be easily seen that the change from series to parallel can be made by one of two methods CONTROL OF RAILWAY MOTORS 95 to open the motor circuits entirely while re-connecting, or to short-circuit one of the motors. Small platform or "hand" controllers are usually of the latter type, and are made in various sizes, as required by equipments of different capacity. Type K Controllers. The best known series-parallel control- lers in America are the "Type K." This type (see Fig. 50, which represents the K-ll controller) consists of a drum carrying a number of copper segments, the connections to the circuits being made through corresponding stationary fingers which press against the segments as the drum is rotated beneath them. The general arrangement is quite simi- lar to that of the Type R rheo- static control lers. The small drum at the right is for the pur- pose of reversing the direction of rotation of the motors, this being accomplished by interchanging either the field or the armature connections. To prevent the de- struction of the segments and fingers by arcing when breaking the circuits, the well-known action of the magnetic field on an arc is employed in the so-called "mag- netic blow-out." A coil carrying the main motor current is wound on an iron core fastened to the cast-iron back of the controller case, which thus becomes one pole of an electromagnet. The other pole is of such a shape that the flux produced must pass across the places where arcing will occur, and tend to break the arc before it has damaged the con- tacts. Since the front cover of the controller is of sheet iron, a certain amount of flux passes through it instead of across the contacts, reducing the efficiency of the magnetic blow-out by as much as one-half. The contacts on the reverse drum are not made sufficiently heavy to stand arcing, and they are not protected by a magnetic blow-out. It is hence necessary to prevent the reverse drum being thrown while current is passing through the contacts. This is accomplished by interlocking the two drums together FIG. 50. Type K-ll controller. The type K controllers are very widely used in America for the control of fairly small motors by the series-parallel method. Practically all street cars use this form of controller. 90 THE ELECTRIC RAILWAY by a dog, which prevents motion of the reverse lever except when the main controller handle is in the "off" position. Since it is inadvisable for the motorman to leave his car in such condition that there is any possibility of irresponsible persons operating the controller, an interlock is arranged so that the reverse lever cannot be removed except when the drum is in the "off" position, i.e., midway between the "forward" and "re- verse" positions. When the reverse lever is removed, another interlock will prevent the rotation of the main drum; hence the I 2 FIG. 51 Development of Type K-10 controller. The Type K controllers are made in a number of different models. The one shown is suitable for the control of two series motors. The difference is principally in the number of resistance steps, and in the number of motors which may be connected to the reverse drum. reverse drum cannot be improperly operated under any condi- tions that may arise. In case of emergencies it may be necessary to operate the car with only one motor or pair of motors. Switches are provided (near the base of the controller) to cut out of the circuit either one. When one of the motors is out of the circuit, there is no object in turning the controller drum beyond full series, since that position will place the motor on the line without resistance. The switches for cutting out the motors are provided with interlocks preventing CONTROL OF RAILWAY MOTORS 97 the drum from being turned beyond the last series notch when either switch is closed. A development of the K-10 controller is shown in Fig. 51. From this diagram the sequence of connections may be clearly traced. The points which are suitable for continuous operation are designated as " running points." It is obvious that it would be unwise to operate continuously with external resistance in the cir- cuit on account of the reduction in efficiency. Moreover, the resistors are not designed to carry the motor current for more than a few minutes without overheating. When it is desired to use a controller of this type with an equipment of four motors, the main drum is exactly similar to that of a two-motor controller. The motors are permanently ar- ranged in groups of two ; and the only difference in the controller is the extension of the reverse drum to provide additional con- tacts for the field and armature circuits of the four motors. Gen- erally, the two machines of a group are placed in parallel; but if the equipment consists of four 600-volt motors to be operated on a 1200-volt circuit, the pairs will be arranged in series. On some roads, where a portion of the line is at 1200 volts and another portion at 600 volts, the motor connections may be changed by an independent switch, which is interlocked with the controller to prevent improper operation. Type L Controller. The "Type L" controller, which was formerly much used for the heavier equipments, is similar in its general mechanical design to the Type K. The main difference is in the method of changing from the series to the parallel connec- tion, which is accomplished by opening the motor circuits while making the change, as shown in Fig. 52. This type of controller has been practically superseded by various forms of so-called "multiple-unit" control. A few years ago, considerable trouble was experienced on ac- count of controllers being used for' handling heavier currents than they were designed for. This sometimes resulted in the contacts being completely burned out, or at least rendered useless tempo- rarily. This became so serious that the leading manufacturers have placed on the market an improvement in providing an auto- matic switch for closing and opening the main circuit so that the controller drum is relieved of this duty. This switch is operated electrically from the main controller, but is mechanic- ally independent of it, usually being placed beneath the car. 98 THE ELECTRIC RAILWAY Some of the ordinary types of platform controller have been modified by being provided with an auxiliary trip on the main drum, which prevents the contactor from closing until the operat- ing handle has been turned to the first notch, after which the circuit operating the switch is closed. This prevents burning of the fingers on closing the main circuit. When the drum is turned backward to cut off the current, the operating circuit is opened before the drum has been returned to the off position, so that in this case the arc is also taken by the contactor. This system may be further developed by using the switch under the car as an auxiliary circuit breaker, whose tripping coil is in the trolley cir- cuit, and whose jaws are in the operating circuit of the contactor. Series Parallel r-VWWVi \y^ LA/VWW Full Parallel ''Circuif Open- 1 FIG. 52. Circuits of Type L Controller. This controller was formerly much used for large equipments, but has now been superseded by the various forms of multiple-unit control, as shown in Figs. 53 and 54. It can be set to open at any desired value of current within its operating limits. When the current reaches this value, the tripping coil breaks the operating circuit, thus opening the main contacts. Multiple-Unit Control. When it is desired to operate a number of cars in a train, there are two general methods of procedure. The cars may be left without electrical equipment, and the power concentrated in a locomotive; or each car, or as many of them as required, may be equipped with electric motors and controllers. There are many arguments against the use of locomotives in this type of service, and in general the use of motor cars is preferred. The successful operation of a train of motor cars depends to a great extent on having the motors divide the work equally. CONTROL OF RAILWAY MOTORS 99 To do this the controllers must all be moved at the same rate. This cannot be done satisfactorily by having a motorman on each car, since it is practically out of the question to have them syn- chronize their movements. Further, this would increase the cost of platform labor to a prohibitive amount. The ideal system is one in which all the motor cars are controlled by one motorman, who can be located at any convenient position on the train, as at the front of the leading car, whether that be a motor car or a trailer. In addition, it is desirable to be able to change the number of cars in a train at will, depending on the amount of traffic. All these advantages may be obtained with any one of the forms of multiple-unit control now in use on the large electric roads in all parts of the country. Sprague System. The earliest method of control of the multi- ple-unit type Was the Sprague system, invented by Lieut. Frank J. Sprague, and first used on the South Side Elevated Railway in Chicago. In this system the main or motor controller was a drum similar to that of the Type K platform controller, but differing from it in being operated by a " pilot motor." This latter was under the control of the motorman, who could cause its armature to rotate, thus revolving the main control cylinder and making the proper connections for the acceleration of the car motors. A number of novel devices were incorporated in this type of control. In order to start the car, all that was necessary was for the motorman to start the pilot motor in operation, which would begin the revolution of the main controller drum. The rate of movement of this drum was limited by the propulsion cur- rent. A relay was interposed in the main control circuit, and so arranged that if the live current exceeded a predetermined amount, the circuit of the pilot motor would be broken, stopping the movement of the main drum until the live current fell below the limiting value. Then the pilot motor would again be con- nected to its circuit and the cylinder be revolved further. This action would continue until the propulsion motors were in the full parallel connection. A number of other relays were introduced to make the operation more certain, and to prevent abuse of the equipment. Magnetic blow-outs similar to those used on the platform controllers were employed. In general, its operation was quite satisfactory for fairly small cars, taking not over about 150 kw. total capacity. 100 THE ELECTRIC RAILWAY Type M Control. When the original Sprague controller was used for heavy equipments it was found inadequate; so when the Sprague patents were purchased by the General Electric Company the manufacture of the original Sprague control was abandoned, the "Type M" control being substituted for it. This latter, shown diagram mat ically in Fig. 53, utilizes the princi- ple mentioned in connection with the heavy Type K controllers of breaking the circuit in specially designed contactors. A set of magnetically operated switches is substituted for the drum. FIG. 53. Circuits of type M controller. This type of controller is very widely used on elevated and interurban cars. Motors of practically any capacity may be handled. These are actuated by a small current from the trolley, and their movement is governed by the motorman through a " master controller," whose function is to admit current to the proper switches and secure the correct sequence of closing and opening them to obtain the desired combinations. The location of the master controller may thus be practically independent of the main controller, the only connection being through the small wires for supplying current to the magnets for operating the main switches of the control. Two types of operation are standard: that providing manual control of the switches, and that in which CONTROL OF RAILWAY MOTORS 101 the movement of the switches is automatically governed by the motor current, as in the original Sprague system. The essential element of the system, the "unit switch" or " contactor," is a switch actuated by an electromagnet. Each of these units may be considered as replacing a finger and its corre- sponding segment in the hand-operated controllers, and consists of a pair of contacts, one of which is fixed, and the other moved by the action of the solenoid. The pair of contacts operate in an arc chute of moulded insulation with an individual magnetic blow- out. To insure the proper sequence of closing and opening the switches, interlocks are provided for making the necessary con- nections. All of the contactors are placed in a covered metal box mounted on an insulated support beneath the car, or in the cab of the locomotive. Since each contactor is independent of the others, the capacity of the switch may be made as large as required for the particular case. The size of motors which can be handled is not limited, as with the drum type of controller. In case the desired capacity is too great for a single switch, two or more may be placed in parallel to subdivide the current. The automatic control provides for the acceleration of the train at a predetermined value of motor current, although it does not prevent manual operation of the controller at a lower rate if de- sired. The arrangement is quite similar to that described for the original Sprague control. The operation of the contactors is governed by a limit switch in the motor circuit, so that the motor current while accelerating is confined within a definite range. This is accomplished by having interlocking contacts on certain of the switches, the movement of each connecting the magnet coil of the next succeeding contactor to the control circuit. Under all conditions the contactors are energized in a definite order, as described in the general paragraph on the series-parallel controller. The progression of switches can be arrested at any point by the master controller, and is also governed by the limit switch, so that the rate of movement is never beyond that which will keep the motor current within the prescribed range. Unit Switch Control. The system used by the Westinghouse Company is quite similar to that just described, differing mainly in the means used to operate the individual "unit switches" or contactors. While in the Type M system the switches are operated electrically by means of current taken from the line, in the Westinghouse control they are actuated by means of com- 102 THE ELECTRIC RAILWAY pressed air supplied from the air-brake reservoirs. The admission of air to the operating cylinders is controlled by electrically oper- ated needle valves. The current for them may be obtained either from a low-potential storage battery or from the line. The main claims in favor of this type of control are that a more positive action of the switches may be obtained on account of the greater pressures possible between the contact fingers. The general features of operation are quite similar to those of the Type M control; in fact, both equipments may be arranged to be oper- Master Controller Grounded on frame B.O. ( Cutout Snitches a,b&.c are \ Connected to No. I Handle \ Cutout Switches dc,&fare Connected fo No. ? Handle Sequence of Switches LS Q P Ei 1 U a JUUUUL. ll" FIG. 55. Bridge method of transition. This method makes the change from series to parallel without breaking the circuit through either motor, and without causing any great disturbance on the line. It is widely used in connection with controllers of the multiple-unit type. Pneumatically-Operated Drum Control. The drum controller is at present the most compact and the most flexible device for producing a number of different combinations in electric circuits, and it is still the most suitable method of control for small equip- ments. With remote operation of the drum, and protection against arcing, it makes a satisfactory apparatus for multiple- unit control. A type of controller has been developed, primarily for single-car service on the New York City railways, but which is applicable for multiple-unit operation of any cars which are not too heavy. Mechanically, it consists of an ordinary drum con- troller, which is actuated by a pair of compressed-air cylinders 104 THE ELECTRIC RAILWAY arranged to turn the main shaft through a rack and pinion. The reverse drum is also moved by air cylinders. Admission and re- lease of air are governed by magnetically-operated needle valves, as in the unit switch control. A current limit relay is introduced in the control circuit to keep the motor current within a pre- scribed range. This device operates in the same manner as the limit switches already described with multiple-unit control. 1 Jones Type Control. A novel type of series-parallel control, suitable for use with four-motor equipments, has been brought out by Messrs. P. N. Jones and J. W. Welsh of the Pittsburgh Railways Co. It operates with a permanent series connection between all of the motors, and employs a minimum of resistance for securing the desired steps. At least three of the motors are in circuit at all times. The connections on the different steps are shown in Fig. 56. The controller has seven points, of which three, numbered 2, 4 and 7, are operating positions. The current in some of the mo- tors is reversed in making the changes; but since both armature and field are reversed together, the direction of motion is not changed. The first position places all the motors in series with a suitable resistance, which is cut out on the second point. One motor is completely short-circuited on the third notch, after which it is connected to the line through resistance. On the next transition point a second motor is reversed, thus placing it in series with the other and the resistance. On the fourth notch the re- sistance is cut out, leaving the motors in the series-parallel connection. The next transition point is similar to the other transition connections, except that but three motors are in circuit. The fifth and sixth positions are really transition steps; and the motors are placed in full parallel on the seventh notch. This type of control has been employed with success on the cars of the Pittsburgh Railways, which are equipped ' with motors having small diameter armatures on account of the small-sized wheel. It is stated that the control will work equally well with stand- ard motors. For further details of the apparatus and arrange- ments of the circuits reference may be made to U. S. Patent No. 1,109,338, issued September 1, 1914. Proportioning of Resistances. In any of the methods so far devised for the control of direct-current series motors, it is not 1 For a detailed description of this type of control see Electric Journal, October, 1913. CONTROL OF RAILWAY MOTORS 105 sufficient to reduce the potential at the motor terminals by the use of different combinations of motors. To prevent an excessive flow of current, and to keep the torque within rather narrow lim- its, it is necessary to introduce a certain amount of resistance into the circuit in series with the motors. The amount of this resistance should be just enough to reduce the starting current tr ^^r- -/4V- FIG. 56. Jones type control. In this control combination of the motors are used instead of the usual resistance, reducing the energy loss while starting, and giving a greater number of running points. and the torque to the desired limiting values allowable for the equipment. As the motors gain speed, the amount of resistance must be lessened, until it is all removed from the circuit. This may constitute the entire control, or it may be done in conjunc- tion with changes in the arrangement of the motors, such as connections in series and in parallel. 106 THE ELECTRIC RAILWAY At standstill, the current flowing through the motors is lim- ited only by the resistance of the windings of the machines con- nected in series, unless sufficient external resistance be inserted to cut the current down to some specified value. As an example, take the 56 kw. railway motor, curves for which are shown in Fig. 19. It is desired to accelerate a certain car by using a pair of such motors with series-parallel control at such a rate that the current will vary between the limits of 200 amp. and 150 amp. while resistance is included in the circuit. The actual determination of the limiting values of current depends on the weight of the car, the desired acceleration, and the allowable load on the motors. The difference between the maximum and minimum values of current is determined by the number of steps on the controller, which in its turn depends on the permissible variation from the mean acceleration. At standstill the current will have the maximum value, and the necessary resistance to be used will be found by Ohm's law: 7/ = ' where /' is the maximum current, E is the line e.m.f., Ri the ex- ternal resistance, and r the motor resistance. In the example cited, r = 0.232 ohm, hence 200 - + 2 X 0.232 whence R\ = 2.036 ohms. This represents the total resistance which must be added to the motor circuit to keep the first rush of current down to the desired limit. With current passing through the motors, a torque will be de- veloped, which will cause the car to accelerate. As the car gains speed, the motors develop a counter e.m.f., the production of which causes a decrease in the motor current, and hence in the tractive effort and the acceleration. In order to keep the trac- tive effort within the limits desired, the resistance should be re- duced when the current has fallen to the minimum value decided on. When the current has fallen to some value I", the counter e.m.f. developed by the two motors in series, 2E C , will be 2E C = E - I"(R l + 2 r) (2). CONTROL OF RAILWAY MOTORS 107 It is then necessary to determine the new value of external re- sistance, R z , which will cause the current through the motors to increase to the maximum value /'. The reduction in resistance will be made instantaneously, so that there will be no opportunity for the speed to change during the operation of the controller from one notch to the next. If the field flux remained constant with variations in armature current, as in a shunt motor, the counter e.m.f. would be the same after the resistance had been reduced, except for the small change in IR drop in the motor windings. But with the series motor, an increase in armature current carries with it a corresponding increase in field flux, so that the counter e.m.f. will also be greater. In order to find the amount of this rise in counter e.m.f., the saturation curve of the motor may be used, and the two values of flux corresponding to the currents /' and I" determined from it. The ratio of increase can also be found from the curve of torque per ampere, Fig. 22. In obtaining the rise of counter e.m.f. when the resistance is reduced so that the current increases from I" amp. to I' amp., it is only necessary to determine the ratio of tractive effort per ampere for the two values of current. That is, 777 T/ J-^C\ 1 1? = TV' V"/ xl/c2 U w where E c i and E c2 are the counter e.m.f. 's at currents /' and I" respectively, and D' and D" the corresponding tractive efforts. The value of E ei having been found already by equation (2), that of E c2 can be determined from equation (3). The new amount of resistance will have to be such as to give the counter e.m.f. E e z when a current /' flows through the circuit, which will satisfy the equation i' = trf 5 (4) This equation is similar in form to equation (1), but takes ac- count of any value of counter e.m.f. which may exist at the moment. Applying these equations to the example cited, we have, from equation (2), 2E cl = 500 - 150 (2.036 + 2 X 0.232) = 125 volts 108 THE ELECTRIC RAILWAY This is the counter e.m.f . existing the instant before the resistance is reduced. The instant following the reduction, this becomes 1O A Q 2E C2 = 125 X J^Q = 135 volts The necessary value of resistance is determined from the relation 500 ~ 135 R 2 + 2 X 0.232 from which R 2 is found to be 1.361 ohms. The same reduction in torque as the speed of the motor in- creases will be noted, and, when the current has fallen to 150 amp. the counter e.m.f. may be calculated by equation (2) as before. A new value of resistance may then be found by the use of equa- tions (3) and (4). This process will be continued until all the resistance is cut out, and the motors are connected in series di- rectly across the line. To obtain further acceleration, it is necessary to reconnect the motors in parallel. The counter e.m.f. per motor will be the same; but when the connections are changed to parallel the two e.m.f.'s will not add. Equation (2) will have to be rewritten as follows : E el = #-27"fl + (5) Having obtained the new value for E c i, that of E c2 may be found by equation (3). By this method the magnitude of all the par- allel resistances may be determined. Table I shows these values as computed for the problem out- lined. In the columns for counter e.m.f., the upper values are for each motor (E c ), and the lower for the two motors when they are in series. In the columns for resistance, the upper values are per motor, and the lower for two motors in parallel. It may be seen that on points 5 and 9, on which all resistance has been cut out, the current will not rise to quite 200 amp. This is unavoidable with the assumptions made. Graphical Method of Calculating Resistances. This method of calculation lends itself very readily to a graphical solution. Referring to Fig. 57 a diagram has been plotted between motor amperes and motor volts. If the line e.m.f. is 500, then when the two motors are in series, each will be taking 250 volts, less what is consumed in the resistance. The lines SE and PJ have been CONTROL OF RAILWAY MOTORS TABLE I 109 Point of Controller Speed Counter e.m.f. IR Drop Resistance 200 amp. 150 amp. 200 amp. 150 amp. 200 amp. 150 amp. Total Motor External 1 0.0 2.35 0.0 62.5 125.0 500.0 375.0 2.5 0.464 2.036 2 2.35 4.26 67.5 113.0 135.0 226.0 365.0 274.0 1.825 0.464 1.361 3 4.26 5.82 122.2 154.5 244.4 309.0 255.6 191.0 1.278 0.464 0.814 4 5.82 7.06 167.0 188.5 334.0 377.0 166.0 123.0 0.830 0.464 0.366 5 7.06 1 8.09 203. 6 1 215.2 407. 2 ] 430.4 92.8 69.6 0.464 0.464 0.0 6 8.09 11.24 232.0 299.0 268.0 201.0 1.340 0.232 1.108 0.670 0.116 0.554 7 11.24 13.8 322.5 366.7 177.5 133.3 0.887 0.232 0.655 0.443 0.116 0.327 8 13.8 15.8 395.0 421.0 105.0 79.0 0.525 0.232 0.293 0.262 0.116 0.146 9 15. S 1 453. 6 1 46.4 0.232 0.232 0.0 drawn at an angle such that the ordinate, as S f E f or P'J' repre- sents the IR drop in one motor at any current /. The line SA has been drawn to represent the IR drop per motor for any value of current, when the resistance is so chosen as to bring the motor to a standstill at 200 amp. When the current has fallen to 150 amp., the total IR drop is represented by the ordinate S'A', and the drop in external resistance by E'A'. If the resistance is then reduced so as to bring the current to 200 amp., the counter e.m.f. will be increased by the ratio given in equation (5). The curve TYWT' between tractive effort per ampere and current has been plotted to the same base, although, if the current limits are to be those decided on, the points Y and W are all that need to be lo- cated. The straight line WYX is then drawn through F and W, intersecting the current axis prolonged at X. It will be seen at once, from similar triangles, that any line drawn through X will produce intersections on the lines UP' and AP" that are propor- tional. That is, UA' UY AB ~ AW 1 At 196 amperes. 110 THE ELECTRIC RAILWAY and so on, for any possible line drawn through X. If then the line XA'B is drawn through X and A' intersecting AP" at B, the ordinate AB will represent the counter e.m.f . developed when the current has been increased from 150 to 200 amp. without changing the speed. The ordinate S"B gives the total IR drop and EB that external to the motor; this latter, divided by the current, determines the new value of resistance. The IR drop will then decrease along the line BB f as the current falls off, until, 500 100 EOO Motor Amperes. FIG. 57. Volt -ampere diagram for determining resistance. at point B' ', the current must be increased again. The same construction is repeated until the two motors are in series without resistance. The current which will be obtained when the last point of resistance is cut out may be readily determined, since the IR drop in the motor alone is plotted as SE. When the last line radiating from X is drawn it will intersect this line at some point as E". The abscissa determines the current. In changing to parallel, it is only necessary to move the axis of reference for IR drop to the proper point, in this case the ordi- nate for 500 volts, and continue the construction from that place. The remainder of the diagram is exactly the same as before. As explained, the diagram is theoretically correct, and a com- parison of the values found graphically for resistances with those calculated in Table I shows how closely they agree. Further, CONTROL OF RAILWAY MOTORS 111 the diagram may be used for any value of line potential without other change than shifting the origin for the IR drop. For different current limits it is necessary to take other points on the tractive effort per ampere curve, thus getting a new location for X. The shape of the curve, as drawn on the diagram, shows that a small variation may be made without relocating this point, and the error will not be great. In general, as the resistors are used both for the series and the parallel connections, a certain amount of adjustment must be made of the values deter- mined for definite current limits. The method of doing this may be seen at once from the construction. It is only necessary to continue the IR lines either above or below the limits set, and the proper values can be found directly. If a controller is to be used with four motors, the changes in the method to allow for sets of two motors perma- nently connected in series or in parallel may easily be de- termined. Time for Operating Con- troller. In Fig. 58 is given a diagram between motor speed and motor current for each of the points on the control, as computed in the preceding problem. From methods already outlined, the time when the controller handle should be moved from one point to the next may be obtained, if the car weight be known. For a given equipment, the time for operation of the controller has been found, and the relations be- tween current and time are given in Fig. 59. It is noticeable that the length of time of operation on each point of the control is different, the time on the parallel points being considerably greater. Current. Amperes FIG. 58. Speed curves for resistance points. These curves, \vith the exception of the "Full Series" and the "Full Parallel" positions, are similar to that in Fig. 21, and may be calcu- lated in the same manner. 112 THE ELECTRIC RAILWAY With a controller arranged for automatic acceleration, the resistance will be reduced at the proper time, and no attention need be given this phase of its action. With hand controllers the tendency is for the motorman to rotate the operating handle at a uniform rate. Should he do this, the resistances having been calculated for definite current limits, as outlined in the preceding 400 300 I f 200 Curre nt per Ca r \ \ \ \ \ \ \ \ Cu r rent per Motor \ -^ 1 3 100 c \ \ \ \ \ \ \ \ \ \ x \ | \i \< % \ \ V \ \ . 2 4 > Time 8 , Second^ 10 12 FIG. 59. Current-time curve for starting a car. This is the form of curve obtained when the resistances and the time of moving the con- troller handle have been correctly determined. Note that the time on the various points is not uniform. paragraphs, the results will be quite different. Fig. 60 gives the values of current obtained when the controller, with resistances as determined previously, is rotated at a uniform rate such that all the resistance will be removed from the circuit at the same time as in the proper operation. The conclusion is obvious. Either the controller should be notched up at the proper rate, or the resistance should be re-calculated for a uniform length of time on each point. CONTROL OF RAILWAY MOTORS 113 Resistors for Railway Service. In connection with the types of control already considered, it is essential that proper resistors be employed. The amount of energy to be dissipated is compara- tively large, and the current-carrying capacity must be consider- able. Further, the materials of which the resistors are made should be such that continual service, calling for repeated heating and cooling, will not cause injury to them. 400 16 350 14 300 12 fe 3: r 250 JO -' *S s s. ^200 "8 150 6 100 4 50 2 Current ren Car i Current 4 6 a Time, Seconds. 10 FIG. 60. Starting current with improper operation of controller. The time increments on the successive points are uniform. Note that while the average value of the current is practically the same as in Fig. 59, it varies over a wider and non-uni- form range; and the speed-time curve is not smooth. In early equipments the resistors were chosen merely to give the proper resistance, without regard to their other qualities. A favorite type consisted of strips of German silver, interlaid with strips of mica, and rolled up into spirals. These were expensive, and heavy overloads would tend to burn them out. An improve- ment was introduced by ventilating the coils; but this did not make them very successful. They have been entirely superseded 114 THE ELECTRIC RAILWAY for regular service by resistors of the cast grid type. The grids are made of cast iron, or of iron alloys, and are assembled in light frames in units of the proper capacity, as shown in Fig. 61. The grids are entirely open to the air, and if placed under the car or locomotive in such positions as will allow currents of air to reach them, they are entirely satisfactory. They are cheap and reliable, and, although the temperature coefficient is not negligible, it makes little difference, for it can be determined and allowed for. A recent variation of the grid resistors is in making them of steel bar, bent to the proper shape and afterward case-hardened, in- stead of cast iron. This removes the greatest objection to the cast grid brittleness while not changing the other properties to any extent. FIG. 61. Assembled frame of grid resistors, and separate unit. The resistors used with railway motor control are of this or similar types. They are made of cast iron in the form of grids, and assembled in frames, as shown. A type which has found some favor, especially in connection with polyphase induction motor control, is the liquid or electrolytic resistor. A tank of the proper size and shape is provided with two metal electrodes and is filled with brine or other electrolyte. One of the electrodes is movable, so that the distance between them, and hence the resistance, may be changed by fine grada- tions. The acceleration does not have abrupt variations, such as must necessarily be occasioned when a limited number of fixed resistances are used. The water resistor is cheap, and is capable of getting rid of a large amount of heat, since the temperature of the electrolyte cannot increase beyond the boiling point, the generation of heat at that point causing ebullition of the electro- lyte, releasing energy in the vapor. CONTROL OF RAILWAY MOTORS 115 Control of Single -Phase Motors. Single-phase series motors can be controlled by the ordinary series-parallel method just described. Owing to the fact that the main justification for the single-phase motor is in the high trolley potentials which may be employed, it is necessary to use a stationary transformer on the car or locomotive to reduce the pressure to a value suitable for operation of the motors. This makes it possible to get an efficient Trolley FIG. 62. Transformer control for single-phase motors. The motor performance is varied by connecting the machines to the different taps, 1, 2, 3, etc. in turn. method of potential variation simply by bringing out from the secondary of the transformer a number of taps which may be con- nected in turn to the motors. A controller of this type is shown diagrammatically in Fig. 62. Owing to the high efficiency of the transformer, each step on the controller may be used as an operating point, there being no loss due to the use of resistance, as with direct-current con- trol. The motors are ordinarily placed permanently in parallel 116 THE ELECTRIC RAILWAY or in series-parallel, and the entire variation in potential is ob- tained by changing the transformer taps to which the motors are connected. In order to obviate breaking the circuit in shifting from one tap to the next, connection is made through a " preventive coil," which is a coil of wire on a magnetic core, designed to have approximately the same e.m.f. as the portion of the transformer winding it short-circuits. The lower terminal of the coil may then be disconnected and reconnected to the next higher tap without causing any disturbance in the system. The method is shown in detail in Fig. 63. For the heavier equipments a double To Trolley To Motors FIG. 63. Use of the preventive coil. By the use of the preventive coil the motors may be connected to the various taps on the transformer without breaking the circuit, and without any wide variation in tractive effort set of preventive coils is used, making the operation still more smooth. An induction regulator can be employed for varying the po- tential on the motors of a single-phase equipment, as shown in Fig. 64. This allows an absolutely uniform acceleration. Its use was proposed when the single-phase system was first projected; but experience has proved that the acceleration obtained with taps from the main transformer is smoother than in series-parallel control of direct-current motors with the same number of steps, and the use of the regulator has been unnecessary. In some of the larger European single-phase locomotives it has been em- ployed with considerable satisfaction. Combination Systems for Single Phase and Direct Current. Since the single-phase series motor, when conductively compen- sated, is also an excellent direct-current motor, it may be oper- CONTROL OF RAILWAY MOTORS 117 ated equally well on a single-phase alternating-current circuit or on a direct-current circuit, provided the line pressure be correct. A number of the heavier single-phase equipments are arranged for both methods of operation. All that is necessary is to have proper controllers for each kind of current, and switches for changing circuits as the train passes from one source of supply to the other, as shown in Fig. 65. It is essential to guard against the possibility of wrong connections on the car, for an accidental FIG. 64. Induction regulator control for single-phase motors. The transformer taps are replaced by an induction regulator, by means of which the motor potential may be varied by infinitesimal steps. contact of the high-tension alternating circuit with the series- parallel controller would be disastrous. To prevent this, the main switch of the car equipment is provided with a retaining coil so arranged that it will open when the circuit is interrupted. Where the alternating- and the direct-current sections adjoin, a dead space is left between the two for a distance not exceeding a car length. A car may then pass from one section to the other at full speed, in which case the main switch opens on the insulated space through lack of power to operate the retaining coil, resetting auto- matically for the other form of power after passing the breaker. Control of Three -Phase Motors. Three-phase motors require entirely different forms of control from those previously described. 118 THE ELECTRIC RAILWAY D.C. Trolley FIG. Q5. Combined single-phase and direct-current control. A combination of the transformer control for the single-phase circuit with rheostatic for the direct current. On account of the complication, it is not used so much now as formerly. FIG. 66. Three-phase motor control. The leads from the secondary winding are brought out to collector rings, and short cir- cuited through a set of variable resistors. CONTROL OF RAILWAY MOTORS 119 Three Phase Supply It has already been shown that reductions in the primary poten- tial are inadvisable, since the torque of an induction motor varies approximately as the square of the applied pressure. The motor speed may be decreased without diminution of torque by placing resistance in the secondary circuits, as shown in Fig. 66. The effect of such resistance is approximately the same as when used in the armature circuit of the direct-current shunt motor, the torque for a given value of current being obtained at a lower speed when resistance is introduced. This method is open to the same objec- tions as the rheostatic control for direct- current motors, in that the loss is great at reduced speeds. The efficiency of an induction motor is always slightly less than the speed in terms of syn- chronism. A reduction of the speed to one-half normal therefore decreases the efficiency to something less than 50 per cent. For classes of service where one operating speed is sufficient, and where stops are infrequent, rheostatic control is applicable; for other cases one or another of the methods described below may be used. Changes in Number of Poles. The only type of motor which can be readily arranged to operate with varying num- bers of poles is the alternating-current induction motor. The machine usually has a distributed primary winding; and it is possible, by proper interconnection of the coils, to change their grouping to give two definite numbers of poles, one of which is twice the other. One method of doing this is shown in Fig. 67. Also, on account of the construction of the primary, the coils being distributed in slots around the periphery, two or more distinct windings, each giving any desired number of poles, may be placed on the machine. Each of these may have its coils grouped to give two sets of poles in the ratio of 2 :1, so that two windings may be arranged to give four sets of poles. The speed of an induction motor de- pends almost entirely on the frequency of the supply and the FIG. 67. Arrangement of induction motor for two sets of poles. This is used to give two effi- cient operating speeds for the in- duction motor. 120 THE ELECTRIC RAILWAY number of poles, so that this combination would give four oper- ating speeds. In order to make the arrangement available, it is also necessary to wind the secondary of the motor with the same numbers of poles as the primary. On account of the com- plication when several different windings are placed on the sec- ondary, the usual limit is two numbers of poles. In case a squir- rel-cage secondary winding is used, this ' restriction does not apply, and the same secondary will work fairly well for any com- bination. The squirrel-cage rotor is not very satisfactory for traction, and is seldom used. Changes in Frequency. The speed of an induction motor may readily be varied by changing the frequency of the supply circuit. This can be done only through the medium of a rotat- ing frequency changer, so that it is not employed directly. It is possible, however, to use the induction motor itself in this ca- pacity; and when there are two motors in the equipment this permits a method which is used to some extent for controlling the speed of induction motors for railway service. In this form the connection is known as " cascade control," " concatenation," or " tandem control." Concatenation of Induction Motors. If the rotor of an induc- tion motor be held still, and an e.m.f. be impressed on the pri- mary, an e.m.f. will be induced in the secondary in the same manner as in a stationary transformer. The frequency in the sec- ondary will then be the same as that of the supply circuit. This secondary e.m.f. may be used for any purpose, the same as with the ordinary types of polyphase transformer. If the rotor be revolved in the same direction as the magnetic field, it will cut the flux at a lower rate, and the secondary frequency will be corre- spondingly reduced. If the speed of the rotor be increased to synchronism, the flux will not be cut at all by the conductors on the rotor, and its frequency will be zero. Between the limits of synchronous speed and standstill the frequency will vary directly as the drop in speed below synchronism, or the "slip." The e.m.f. generated in the secondary may be used to furnish a second motor with electric power. If the first motor be run at half speed, the frequency of its secondary circuit will be exactly one-half that of the supply; and if the secondary have the same number of turns as the primary, its e.m.f. will be one-half the line potential. The two motors being electrically similar, and mechan- ically coupled together, so that they are forced to run at the CONTROL OF RAILWAY MOTORS 121 same speed (as, for example, two motors on axles of the same car) the power will be delivered by the secondary of the first motor at the synchronous speed of the second. Since an induction motor cannot deliver any power at synchronous speed, the second machine will not take any current from the first save for excita- tion, and the first motor in turn, having no current in its second- ary but the magnetizing current for the second, will not deliver any power. The system is then in the same state of equilibrium as would be the case were the first motor running alone in syn- chronism. The speed of the combination in this condition is, FIG. 68. Connections for concatenation control of three-phase induction motors. The secondary circuit of motor No. 1 is connected to the primary of motor No. 2, whose secondary is short-circuited through resistors. This arrangement gives an efficient half- speed running point, in which respect it is similar to the arrangement shown in Fig. 67. however, exactly one-half the normal synchronous speed of the single motor. If the speed of the motors falls a trifle, the frequency in the secondary of the first one is then slightly greater than one-half that of the primary, and the second will be operating below synchron- ism. The value of the slip of the second motor is the difference between the speed corresponding to the secondary frequency and the actual speed. Conditions are therefore right for producing torque in the second machine. This will cause a power current to flow in the rotor of the second motor, which in turn must be transformed from its primary. This power current must of course be drawn through the first motor, and the current in the second- ary of the latter, reacting against its field flux, will produce a torque. It may be shown that approximately one-half the torque 122 THE ELECTRIC RAILWAY is furnished from each machine. In order to obtain still lower speeds, as for starting, resistance may be introduced into the rotor circuit of the second motor. This will have the same effect as the insertion of resistance in the secondary of a single motor. When it is desired to operate above the half-speed obtained with the two motors in tandem, the second one may be cut out of the circuit and the secondary of the first short-circuited, either on itself or through resistance, as necessary. The second motor, if wound for the correct potential, may be connected to the line in parallel with the first ; but since the amount of power required for constant-speed running is considerably less than that for acceleration, the second motor is ordinarily left entirely out of the circuit, the power factor and efficiency of the single motor being higher than when the load is divided. This arrangement also makes possible a simpler form of controller. In any case when motors are connected in cascade, the syn- chronous speed of the set may be determined from the fact that the effective number of poles of the combination is the sum of those of the two motors. For instance, if a four pole motor is con- catenated with one having six poles, the result is the same as though a single motor with ten poles were used, whichever ma- chine is connected to the line. Split-Phase Control. If a polyphase induction motor be con- nected to a single-phase supply, it will not have any starting torque, and will therefore remain stationary. If, however, the motor be started by any external means, it will continue to run and may be used in the same way as though it were operating on a poly- phase circuit. Experiment has shown that this effect is due to a transforming action in the motor changing the single-phase supply to polyphase. If the terminals of the idle phase be tested, an e.m.f. will be found, substantially of the same value and in the same phase position as in regular polyphase operation. This e.m.f. may be utilized to furnish, with the single-phase e.m.f. of the supply, a true polyphase circuit on which may be operated standard polyphase apparatus. If an induction machine of the type described in the last para- graph be placed on a locomotive, it is evident that a single-phase contact line may be used to supply polyphase motors for propul- sion, as shown diagrammatically in Fig. 69. This method is used in one important installation in this country. The three-phase CONTROL OF RAILWAY MOTORS 123 induction motors may be of standard types, controlled by any of the means which have been described above. Special Systems. A number of special systems of operation have been tried at one time or another. All of them possess points of superiority, and may be used to advantage in certain installations. The most valuable of them are: 1. The " Ward-Leonard" system. 2. Permutator system. 3. Mechanical rectifier. 4. Mercury vapor rectifier. Resistors FIG. 69. Split-phase control for operation of three-phase motors from a single-phase trolley. By this means three-phase induction motors may be employed for railway service through the medium of the rotating phase-converter. Ward-Leonard System. This system of control, invented by the late H. Ward Leonard, is in its widest application suitable for use on any kind of supply circuit whatever. The current from the contact line is used to operate a constant-speed motor- generator set (Fig. 70), consisting of a motor suitable for the supply system, a separately excited direct-current generator, and an exciter, all mounted on the same shaft. The propulsion mo- tors are permanently connected to the generator through the reverser, and operation is controlled by varying the potential. This may be done either by changing the resistance in the gen- erator field circuit, or by varying the field current of the exciter. 124 THE ELECTRIC RAILWAY The latter is the method usually recommended, since the loss is less. This form of control can be operated to give absolutely uni- form acceleration, and is applicable to any form of supply circuit. The efficiency during acceleration is high, since the rheostatic losses are practically eliminated. No contacts carrying heavy currents have to be broken or closed while the train is in opera- tion, since the motor current can be reduced to zero by opening the exciter field circuit. The objection to the system is its great weight and cost. For this reason it never has been used in prac- tice, and only a few locomotives have been equipped with it. Some recently adopted types of control would indicate that the Feverser Traction Motvr, FIG. 70. Ward-Leonard system of control. This method is suitable for the operation of standard direct-current railway motors from a single-phase trolley, no matter what the frequency. A motor for operation on any com- mercial circuit may be substituted for the single-phase machine. weight and cost of the Ward-Leonard system are not so excessive as would appear from the opinions of different engineers. It should be stated in this connection that the Ward-Leonard control is used somewhat extensively for mine hoists and simi- lar stationary service. Permutator Control. A special form of induction machine, known as the "permutator," has been brought out for transfor- mation from alternating to direct current. l It consists essentially of an induction motor primary and secondary winding held stationary. The secondary winding is similar to a direct- current generator armature, and has leads brought out to a com- mutator. Since the secondary is held still with reference to the 1 A more complete description of this machine is given in Chapter XIII. CONTROL OF RAILWAY MOTORS 125 primary, the e.m.f. generated by the former has a direct ratio to the line potential, as in an ordinary transformer. If a set of brushes be rotated on the commutator at synchronous speed, direct current can be taken off, and used to operate ordinary series railway motors. Any standard type of direct-current control may be employed, or the primary potential may be varied by taking different taps from the lowering transformer. A locomotive constructed on this principle has been operated in France for some time, and is said to be very satisfactory. Mechanical Rectifier. 1 In place of the permutator, a mechan- ical rectifier may be employed for furnishing the means of chang- Trolley Lowering Trans Traction Motors FIG. 71. Mercury rectifier control. With the mercury vapor rectifier, standard direct-current motors may be satisfactorily operated from a single-phase trolley. As shown, two 600-volt machines are placed in series, with the middle point grounded. ing from alternating to direct current for supplying the propulsion motors. The rectifier is in effect a two-part commutator, ro- tated at synchronous speed by means of a small motor. The two main segments of the commutator are divided into several sections, and connected through reactance. This prevents the e.m.f. from dropping to zero while passing from one pole to the other. A locomotive has been built, using this method of opera- tion, but no figures have been published which would indicate whether it has proved satisfactory or not. Mercury Vapor Rectifier. Still another system proposed for railway operation is to change from high-tension single-phase cur- 1 See also Chapter XIII. 126 THE ELECTRIC RAILWAY rent to direct current through the medium of a mercury vapor rectifier. Rectifiers of this type have been built commercially in large sizes, and are not by any means the delicate contrivances of several years ago. During the year 1914, a trial equipment was placed in operation for the Pennsylvania Railroad on the single-phase line of the New York, New Haven and Hartford Railroad. This locomo- tive was equipped with standard direct-current motors, operated from a mercury vapor rectifier. The connections are shown in Fig. 71. Although detailed reports are not yet available, the equipment has been in revenue service for several months, and it is stated that the performance is exceedingly satisfactory. It is evident that this form of control is a commercial possibility; and if adopted will remove some of the limitations imposed on the single-phase system on account of its inability to use standard direct-current motors. CHAPTER VI POWER REQUIREMENTS AND ENERGY CONSUMPTION Requirements of Train Operation. In the engineering work necessary in connection with the design and operation of a rail- road, it is essential that the amount of power demanded from the system, and also the amount of energy required for train move- ment, be accurately determined, whatever the character of the motive power. For any type of motive power, there are certain fundamental relations which determine these quantities; and from them the proper selection of equipment may be made. The consideration of these relations has already been made in Chapter II ; they must now be brought together to see their connection in the solution of the problems at hand. The quantities which have the greatest effect on train operation are its weight, the train resistance, both inherent and incidental, the acceleration and the maximum speed. These are the essen- tial ones; but the length of run has a marked effect, since it may change the maximum speed or the acceleration. The maximum speed attained affects the power required prin- cipally by the difference it makes in the train resistance, but its effect on the energy consumed is much greater, since it is a measure of the energy input. The train weight is a determining factor in both power and energy, since the value of either varies directly with it. It will be shown that the acceleration has a great influence on the power required, but its effect on the total energy is very small, save in an indirect way. This must be so, since the energy im- parted to the train depends so much on the maximum speed attained during the run. The inherent train resistance, while it has some effect on both the power and the energy, is in most cases small in comparison with other variables. The incidental resistance, especially that due to grades, may affect the requirements more than any other factor. This is seen most in operation of slow-speed freight trains, in which case the acceleration is relatively low. 127 128 THE ELECTRIC RAILWAY In order to ascertain the power demand, then, for any specific case, it is necessary to know the values given above. The deter- mination can be made by the methods outlined in Chapter II. "Straight Line" Speed-Time Curves. It is difficult to deduce an analytical relation between the variables entering into the power problem. The characteristic curves of motive powers vary in a manner difficult to express in a simple equation; and the same is true of train resistance. In a large number of prob- lems a need is felt for a simple and reasonably accurate deter- mination of power requirements. By making a number of approximate assumptions it is possible to use a graphical treat- ment which is comparatively simple. 80 60 f 20 20 40 60 80 100 IZO Time. Seconds. FIG. 72. Simple straight-line speed-time curve. If we consider the motive power to be such that it can supply a constant tractive effort over a limited range of operation, and assume uniform rates of coasting and of braking, the problem is reduced to a point where a solution becomes practical. The simplest run of this type (A, Fig. 72) consists of acceleration at a constant rate until it is necessary to cut off the power and apply the brakes. It is evident that if the rate of braking is the same for all runs, this gives the minimum possible acceleration. Fur- ther than this, an inspection of the diagram shows that the maxi- mum speed is exactly twice the average speed. Comparing this run with the ideal run K, at average speed, it will be seen that the distance covered is the same in each, the area of the two dia- grams being the same. POWER REQUIREMENTS 129 If a higher rate of acceleration than the minimum be used, it will be necessary, in order to cover the same distance in the same time, to introduce a period of coasting (Fig. 73, run B). Such a high maximum speed as in run A (which is reproduced from Fig. 72) will not be attained, since the train is propelled at nearly the maximum speed for some time by coasting. With still higher rates of acceleration (runs C and D) the maximum speed is further reduced. In certain runs, if 'the amount of drifting is too great, the velocity which the train must reach will again be increased, on account of the great reduction of speed while coasting. In gen- eral, the efficiency of the motive powe,r remaining the same, the most effective run for covering the given distance is that in which lowest value of crest or maximum speed is attained. The method outlined in the last paragraph shows a way of determining the most economical acceleration for any given run. ZO 4Q. 60 &0 100 IZO Time, Seconds. FIG. 73. Influence of acceleration on speed-time curve. If a succession of identical runs is taken as the required service, one acceleration can be found which is most efficient for all of them. When the runs differ, the best average rate can be used. This acceleration having been chosen, it should be used for all runs, no matter what their length. Speed-Time Curves with Electric Motors. When we consider applications of the straight line speed-time curve, we find that in most cases of practical motive powers, the assumed conditions cannot be exactly met. In using electric motors, the uniform acceleration can be adhered to only while the potential is being- raised. After the motors are operating directly on the line there is no possibility of continuing the maximum acceleration; but the tractive effort will fall off as determined by the characteristic curve of the particular machine used. If the run is short, this 130 THE ELECTRIC RAILWAY will not make a marked deviation from the straight line curve, so that for preliminary estimates or for analytical study the approxi- mate method remains useful. For the actual selection of equip- ment for any individual case the motor characteristics must be employed. The method used for determining the speed-time curve is that described in Chapter II, page 39, or any other accurate way of plotting it. In order to estimate the distance covered by the run, the distance-time curve may be obtained by the use of the integraph, by successive partial integrations, or by determination of the distance increments from the data used to plot the speed-time diagram. Curves of this character are of the greatest value, since they show the exact distance covered by the train at any portion of the run. Current-Time Curves. After the speed-time curve for any run has been plotted, the current-time curve may be found directly, since there is a definite relation between the speed of a motor and the current passing through it, which is invariable. This may be seen at once by an inspection of Fig. 19. It must be remem- bered, however, that while the motors of an equipment are run- ning at reduced potentials, or under other abnormal conditions, the relation between speed and current will not be the same as for normal operation, although easily found at such times by the methods already given. The current-time curve may then be plotted. This curve is of value, as indicating the load which is being demanded from the line, as well as that which is being imposed on the motors. Power-Time Curves. If the line potential is constant, the current curve gives a measure of the power drawn from the line at any instant, and its integral measures the amount of energy used for the run. By this means the performance of different trains or of different runs may be compared. If the line pressure is vari- able, the power-time curve must be obtained as the product of the current curve and the pressure. In that case a graph of the latter should be plotted against time. Use of the Current and Power Curves. This series of curves is of great use to the engineer in determining the size of equipment necessary for the generating and substations of a road, and for the size of transmission and feeder wires. For this purpose current- time or power-time curves must be plotted for a day, or such other period as covers the entire range of load. The sum of the instantaneous current values gives the total demand on the POWER REQUIREMENTS 131 power plant at any given instant; so by a process of summation the actual load curve for an entire day's run or any desired time is determined. A study of the territory in which the road is located will, in conjunction with the current or power curves for individual trains, give an opportunity for dividing the line into proper sections for the location of substations. This will be considered at greater detail in a later chapter. Motor Capacity. The other great use of the current-time curve is in the determination of the capacity of the motors to be used for a particular purpose. There are several different methods of doing this. Of these, the most direct is that in which the motor heating is ascertained from the current and potential carried by the motor during the period which the rating covers. The ability of a motor to carry load depends on several differ- ent things: the form of the characteristic curves must be correct, and operation not extended beyond their proper range; the temperature must not exceed some maximum value, as deter- mined by the materials of which the machine is constructed, and the motor must not be worked beyond the limits of commuta- tion. In modern, well-built motors, the characteristic curves continue of proper shape beyond the ordinary range of operation, and the commutation, both in direct-current and single-phase railway motors, is so good that it need not be a determining factor. The heating of the motor parts stands as the practical limit, both for instantaneous and for sustained loads. Modern motors are usually constructed of fireproof material, the only non-metallic parts being the insulation, which consists very largely of mica, asbestos and other heat-resisting substances. Heating Limits. Heating of the motor imposes limits of two kinds to its capacity: instantaneous or momentary, and con- tinuous. If a sudden load is placed on a motor, there is a rush of current, with a consequent PR loss in all portions of the circuit. If the loss is sufficient, it may cause overheating of some part, and burn out the winding at that place. Or it may be great enough to melt one or more of the soldered connections and open the circuit, with the possible formation of an arc. Even though the joints in modern motors are all made with high-grade tin solder, it sometimes happens that an overload is so heavy as to melt the solder at the commutator necks. The natural safeguard against such damage is to place in the motor 132 THE ELECTRIC RAILWAY circuit an automatic circuit-breaker, or a fuse, set so as to open before the motor is damaged. The other heating limit is the one on which the normal rating is based. Any electrical apparatus has a certain loss in convert- ing energy from one form to another; and it is this which, occur- ring within the machine, causes heating. Motor losses have already been discussed in Chapter III. Some of them are de- pendent on the current, others on the potential, and still others on the speed of rotation. In general, however, the losses may be grouped into two classes: those which are a function of the current, and those dependent on other relations. Those losses due to the current vary nearly as its square; the remainder about as the first power of the terminal pressure. To get the average loss for a given run will be to determine the corresponding rate of heat generation, and hence gives a means of finding the capacity of the motor. In this country, railway and other motors for intermittent service are rated in two ways: by the load they can carry for one hour or other stated time with a given temperature rise, under specified conditions, and by that which they can carry continu- ously with the same temperature rise, under other stated condi- tions. Either method assumes that the load will be uniform during the period for which the rating is made. 1 Character of Railway Motor Load. In general, it is not possible to maintain the load on any machine at a constant value in service. In the case of a railway motor, its function is to start a train from rest, accelerate it to some operating speed, arid run it at that speed for a greater or less time. After this the power is cut off, the train allowed to coast and finally come to rest under the action of the brakes. An inspection of the load curve shows that the current through the motor is never constant, unless the run is so long that the speed continues at the maximum for some time. It is not possible to assign any average value to it offhand. Further- more, there is a period in every run where the motors are not in operation, a portion of it being while the train is in motion and the remainder while it is standing still. After making a stop of limited duration, a similar cycle ensues; and this will be repeated indefinitely during the entire time of 1 The accepted method of rating railway motors is given in the Standard- ization Rules of the American Institute of Electrical Engineers, 1914 edition. POWER REQUIREMENTS 133 operation, as for a round trip, or more frequently a whole day's run. The succeeding cycles of current may not be precisely the same, since the length of individual runs, the maximum speeds possible, and the physical limitations of grades, curves and wind may vary. But the general nature of the cycle re- mains the same in all cases. If it is desired to depict the per- formance of a railway motor, it is necessary to plot a series of current-time curves for a long period of operation, say for a round trip. Such a current-time curve is shown in Fig. 74. Methods of Equating Motor Load. In order to use the data from the actual operation of the motors, as determined by the current-time and power-time curves, it is necessary to find some basis on which they may be equated to constantly applied loads. This is essential both for purposes of testing and for the proper selection of motors for a given service. The oldest way was by comparison, an equipment being selected for a proposed road be- cause it had given satisfaction in a similar service, possibly in another locality. Although this method is crude, it was used for want of a better, and it must be admitted that very good results have been obtained. The scientific method of getting the equivalent rating is to determine the potential and current which, constantly applied, will produce the same load on the motor as the variable one ob- tained in service. Since heating is the principal condition which determines motor capacity, it is evident that at the equivalent load it must be the same as that in service. The determination of this load depends on the use of a method which will find the proper relations between the variable current and potential and their equivalent constant values to give the same heating in the motor. Heating Value of the Current. 1 In any electric circuit, there is a certain loss due to the passage of the current through resis- tance. This loss is a function of the current, the time, and the resistance. It is always proportional to the square of the in- stantaneous value of current, i, into the resistance in ohms, r, being numerically equal to i z r. With the current remaining constant at a value I for any definite interval of time, as 1 This discussion follows the method of C. O. MAILLOUX, "Methode de determination du courant constant produisant le meme echauffement qu'un courant variable," International Electrical Congress, Turin, 1911. 134 THE ELECTRIC RAILWAY t = ti - t Q the amount of energy, W, dissipated as heat in the resistance r is . W = Pr (^ - t ) = Prt (1) When the current varies during the time considered the loss becomes, calling the instantaneous value of current i, W = I i Jo i 2 rdt (2) Jo If the resistance loss is the same in the two cases, we may equate the expressions (1) and (2): W = Prt = I Prdt (3) from which we may determine pt = fm (4) (6) Equations (5) and (6) give the important relations between the equivalent constant and variable currents producing the same heating in the same time interval. From equation (5) it may be seen that their squares are equal, and equation (6), that the so-called "effective" current is equal to the square root of the mean of the squares of instantaneous values. The problem of equating a variable current to a constant one thus resolves itself into finding an effective value which is numer- ically equal to the square root of the mean of the successive ordinates of the curve representing the function i 2 = f(t). If the equation of this function is known, the determination is simple; but if, as is usually the case, it cannot be obtained, some approximate construction must be resorted to. Determination of Effective Current from I 2 Curve. The gen- eral form of the graph of current as a function of time is shown in Fig. 74, which represents a curve of this character. Such a chart may be drawn by a recording ammeter, or by taking a large number of successive readings and plotting the curve therefrom. POWER REQUIREMENTS 135 To apply the method indicated by equation (6) for getting the equivalent current, the values of i in the current-time curve must be squared and re-plotted, as shown in Fig. 75. The more rapid the fluctuations of the original curve, the closer together the 800 SJ600 400 200 40 120 160. ZOO 240 2?>0 320 Time, Seconds. FIG. 74. Typical current-time curve. This represents the actual form of curve obtained in rapid-transit service with frequent stops. points should be taken, since the effect of squaring is to greatly magnify the differences between succeeding values. The area under the curve, as Fig. 75, must next be found by some form of mechanical integration, as the use of a planimeter. 80,000 ; 60,000 \S) g 40,000 '20,000 40 80 120 160 200 240 2&0 320 360 Time, Seconds. FIG. 75. Current squared-time curve. This curve is produced by squaring the values of the current shown in Fig. 74. This area, divided by the total length of the diagram, gives the mean ordinate, P. It is necessary to use the same units of linear and square measure, for, if the planimeter gives the area in square 136 THE ELECTRIC RAILWAY inches, the length of the base should be taken in inches, and the quotient will give the average height in inches. This is some- times forgotten in interpreting the results. The square root of this mean ordinate, when reduced to the scale of the curve, is the effective value desired, as / in equation (6). Determination by Polar Method. The second method, which was elaborated by Mr. Mailloux in the paper above referred to 45 00 3--oo 45 S.-oo 4:00 45 FIG. 76. Polar current-time diagram. This represents the same function as Fig. 74, but replotted in polar coordinates. obviates the necessity of plotting a curve of values of current squared, replacing it by a polar diagram of current, Fig. 76, which, while giving the same final result, is simpler to construct. The use of the polar curve for finding the heating due to a current originated with Dr. Fleming, 1 who employed it for de- termining the effective value of the alternating current. The method of Mr. Mailloux is based on the same principles, but is wider in scope, including the evaluation of any currents, as indi- cated in equation (6). 1 J. A. FLEMING, "The Alternate Current Transformer," 1896, Vol. I, 32, pp. 190-194, "Representation of Periodic Currents by Polar Diagrams." POWER REQUIREMENTS 137 The first step in this method consists in plotting the current- time curve on a polar basis, as shown in Fig. 76. In doing this the current, i, being the independent variable, is made the radius vector, and the time, t, becomes the angle. To make the transformation of coordinates complete, the following condition must be met, and that only: f(nAt) = f(nAO) (7) for all values of n included between the limits n = 0, and n = > At when t is the total length of the diagram in rectangular (or any form of Cartesian) coordinates. If this requirement is met, an ordinate y of the rectangular curve, at any distance from the origin along the X-axis and represented by nAt, will always be equal to the radius vector, p, of a polar curve, situated at a pro- portional angular distance, by nA0. It may be seen at once that this relation is independent of the values given to AZ or to A0, proportional changes in these affecting only the scale of the curve. The polar curve has different properties from the rectangular curve; since it is this difference which is utilized, the character- istics of the polar curve must be determined. Of these, the most important for the present purpose is the area included by the curve. An element of the polar diagram contained between two radii vectores, OP and OQ (Fig. 76), has an area dA, dA = Y 2P ds = %P 2 d8 (8) p being the radius vector, dO the vectorial angle, and ds = pdd any element of the curve. When the entire vectorial angle in- cluded is /j i i = ad ~~~ 4 A comparison of equations (13) and (14) shows that the result of applying the brakes is to reduce the rail pressure on each pair of wheels of the rear truck by an amount -^r [equa- zgi tions (5) and (6)]; and has also transferred from the rear to the forward wheels of the truck an amount equal to ahWi adW z 2gb gb If the car is to be operated only in one direction, the values of all forces may be determined and all pressures on the brake shoes modified accordingly. Ordinarily cars must be suitable for operation in either direction; in which case the maximum pres- t - t u i Wi + 2W 2 ^ sure for any pair of wheels must be reduced from - j - to the value given in equation (13). Solving equation (12) for a we have Since TFi + 2TF 2 is the total weight of the car the equations above may be simplified by designating by W the total weight, or W = W l + 2W 2 (16) Equation (15) then becomes T\ + Ti a = 2(, - l -^- (17) The equations for the rail pressures RI and R 2 hold for any values of TI and 7 7 2 that may exisjt. If the coefficient of adhesion be represented by /i, then T, = /A (18) and T, = f,R 2 (19) We may now re-arrange the expressions for rail pressures, solv- ing them for TI and T 2 from equations (18) and (19), and re- ducing by the substitution of values of W and a from equations (16) and (17). Then BRAKING OF ELECTRIC RAILWAY TRAINS 177 fiW Wb + 2f,(Wih Wb - Under normal conditions, with the direction of motion re- versible, the greatest pressure that can be applied to any pair of wheels and will slide none of them may be determined by making T, = T 2 = f,R 2 (22) Substituting this value in the equation for R 2 , and simplifying V _ 4- X - ^- (23) Wb + 2f l [Wi(h + ) + 2W 2 d] From the dimensions of standard passenger cars without electrical equipment, and assuming a coefficient of adhesion fiW fi = 0.25, it is found that, instead of having a value of j- for fiW each pair of wheels, the adhesion is only 0.834 T Another way of looking at this is that if the brake-shoe pressures are equal on all wheels, the available adhesion for obtaining re- tardation is only 83.4 per cent, of the total weight of the car. If these pressures can be adjusted to allow for this transfer of weight the effectiveness can be increased over 16 per cent. Although it is not practical to properly alter the shoe pressures between the two trucks without changing the fixed leverages of the brake rigging, it is possible to make a readjustment of the forces acting on each to compensate for the weight transfer from the forward to the rear wheels of that truck. In common practice, the brake shoes may bear on the wheels either on the inside or the outside of the truck frame. Ordina- rily, they are placed on the inside, as shown in Fig. 87. When this arrangement is used, it is possible, by varying the angu- larity of the hanger link, to introduce a force which will equalize to any desired degree the transfer of weight from the rear to the forward axle. In Fig. 87 are shown the forces acting on the truck during an application of the brakes. The forces P and P are those supplied 12 178 THE ELECTRIC RAILWAY from the brake beam, and are really equally divided between the two wheels at opposite ends of an axle; while the other forces occur separately, but generally in equal amount, at the individual contact points. As mentioned before, it is simpler to treat the pair of wheels on a single axle as one unit. Opposed to the brake-shoe pressure are the reactions Qi and Q 2 from the wheels, and the frictional forces FI and F 2 result from these. The reac- tions on the brake shoes from the hanger links are represented by FI and F 2 . The middle of the brake shoes is usually located a small distance below the center of the wheels; the angle between the direction of Qi and Q 2 and the horizontal, is represented by 6 (by similar triangles). The mean values of the frictional FIG. 87. Equalization of brake-shoe pressure. By properly offsetting the brake hangers, the weight transfer between the wheels of the truck may be compensated, allowing a greater total braking force. forces FI and F 2 must therefore be inclined from the vertical at the same angle. In the particular example of brake rigging shown, the hanger links are inclined to the tangential direction of the friction by the angle . Resolving the forces into rectangular components, referred to the axes of the hanger links for each pair of wheels, we have Qi cos - FI sin - P cos (0 + 0) = (24) Q 2 cos + F 2 sin - P cos (0 + )= (25) Now, designating the coefficient of brake-shoe friction by / 2 , Fi = f 2 Qi (26) F 2 = / 2 Q 2 (27) and Re-writing equations (24) and (25) with these values and solving for and P BRAKING OF ELECTRIC RAILWAY TRAINS 179 tan = lT (28) /2 ri + /*2 p= (Fi + ^) cos - / 2 (/?! - /? 8 ) sin (fr 2/ 2 cos Effect of Rotational Inertia. In addition to destroying the energy of translation existing in the moving car, the brake-shoe friction must also absorb the rotational energy of the wheels and axles, and in the case of motor cars or locomotives, of the motors. This inertia is entirely independent of that due to translation; and in destroying it the coefficient of adhesion between wheels and track does not enter. Practically, a greater braking force must be used to produce a given retardation when the rotation of the wheels and other parts is taken into consideration. 1 Letting r represent the radius of the wheel, the retardation a of the car is also accompanied by a retardation - in the motion of the wheel. Calling the weight of one wheel and one-half of its axle w\, and the radius of gyration of this part about its axis kij the retarding force necessary to be applied at the wheel tread is for a truck without electrical equipment. For a motor truck this force must be increased by the amount 55 /*)/*!)' g \r I \n z / where w 2 is the weight and k z the radius of gyration of the armature, and n\ and n^ the respective numbers of teeth on the axle gear and on the motor pinion. The total retarding forces necessary are, therefore, for a trailer truck, ' (30) a (31) or, for a truck equipped with two motors, 1 Compare Chapter II, "Rotational Acceleration." 180 THE ELECTRIC RAILWAY a (32) (33) For an ordinary pair of cast-iron wheels and axle, ~ = 0.64, and ( j = 0.41; using these values in equations (30) and (31), and replacing TI and T 2 by their values found in equations (20) and (21), we have (W + 3.28wi) b + 2/i (Wih (34) /iTT (Tf + 3.28u)i) 6 - 2/i (TTife 4 (IF + ^,-3 6 (35) Substituting these values in equation (28), we have 2/, WA * * = - Equation (29) may likewise be simplified by substituting the value of Fi F% from equation (28) : Fi - F 2 = / 2 (Fi + F 2 ) tan (37) whence /! W W + 3.28^! (1 - / 2 2 tan 2 ) cos = /24 Tf + 2/ 1 TF 1 ^ COS( ^ + in.) 186 THE ELECTRIC RAILWAY and the length 6 is 30 - 17% = 12% in. For the cylinder lever, the length d is 4920 X 30 11,880 and c is therefore 12.41 in. (in practice in.) 30 - 12% = 17% in. With a force of 1200 Ib. acting on the hand-brake rod, which To Hand drake "KoeTiS. 7, R*cd ; \ J \'" &".' \ 67801k 2>3901b. k- Fixtd-rf ** %* u /? \r \ J K800lb\ l\l I \l7000ik 24601k Fixed Ib. 20 " 20\9SOOIk 2460 Ib. Fixed 9500 Ib ho" 20\ 9500 Ib. 7* 70401k FIG. 90. Distribution of forces in foundation brake rigging. must be increased to 6780 Ib., the force required at the end of the multiplying lever is The length from the fulcrum to the point of connection is therefore 1200 X 36 10 _. , ,. 1oqx . , 339Q = 12.74 (practically 12% in.) In order that the levers may be parallel when the slack ad- juster is half way out, and the piston is at the end of its normal stroke, the length of the cylinder rod must be 20 + 5 + 5 = 30 in. BRAKING OF ELECTRIC RAILWAY TRAINS 187 A movement of J in. at each shoe on the motor truck will give a movement at the push rod of 27 1 2 "37 ^0 (M X 2) X y X - X jy^ = L393 in ' A similar movement of Y in. at each shoe on the trailer truck will give a movement at the push rod of 1 fi 12 88 (MX 2) X y X ~^ = 0.86 in. The total movement of the push rod is 1.393 + 0.86 = 2.25 in. and, adding % in. for lost motion, the travel necessary for the push rod to apply the maximum braking force is approximately Automatic Slack Adjuster. The amount of air needed for producing a certain cylinder pressure depends on the piston travel, so that it is desirable to keep this as short as possible. With the automatic brake, where the cylinder is supplied from an auxiliary reservoir of small capacity, excessive piston travel will result in reduced cylinder pressure, and consequently smaller braking effort. The best operation is obtained when the piston travel is just sufficient to allow proper clearance of the shoes when the brakes are released. On standard equipments this calls for a running travel of about 8 in. Any greater movement simply calls for more air or for less efficient braking. Various forms of automatic slack adjusters are on the market. The best known of these is shown in Fig. 89. A small connec- tion is made through the brake-cylinder wall at a point deter- mined by the maximum desirable piston travel. When this is exceeded air is admitted to the tap, and serves to operate a ratchet, changing the position of the lever, as indicated in the diagram. Each time the brakes are applied when the travel is greater than the desired amount, the ratchet will move one notch, until the excess has all been taken up, after which no further action of the slack adjuster will take place until the slack has again passed the limiting value, and the piston travel has become too great. Methods of Supplying Braking Force. Hand Brakes. The brake rigging described will work equally well with any available 188 THE ELECTRIC RAILWAY force that can be applied in the proper amount, and with proper control. Two methods of operation have been suggested manual and air pressure being used. With hand brakes, the force is applied to a brake staff by means of a cranked handle or hand-wheel turned by the motorman. The staff carries at its lower end a chain which is attached to the pull rod connecting to the foundation brake rigging. By rotating the brake staff the chain is wrapped about it, thus applying the braking force to the rigging. If the car is heavy, and the necessary retarding force is large, it is sometimes impossible to get sufficient leverage with this arrangement. To increase the pull, the bottom of the brake staff may carry a gear, the chain connection to the pull rod being made through the meshing gear. The force may thus be increased to any desired value. A limitation may be seen in various forms of high-ratio hand brakes, in that, if designed to give the maximum braking force when applied by the average motorman, there is a great risk of skidding the wheels when operated by a stronger man. This is something which cannot be taken care of in the design, and may result in the use of hand brakes of less power merely to obviate this danger. In the operation of hand brakes, it is necessary, as in any case, to have a certain amount of " slack" in the rigging. This is needed to keep the shoes away from the wheels when the brakes are released. The ordinary motorman, in making a stop, de- sires to apply the brakes as soon as possible after the signal has been given, or the proper place for their operation has been reached. In order to prevent loss of time in making the appli- cation, it is often the custom among motormen to run the cars with the slack all taken out of the brake rigging, the shoes being as near the wheels as possible without applying the brakes. This is done by winding the spare chain on the brake staff, and holding the handle in that position continually. When operating in this manner, it is almost impossible to keep from having some friction of the shoes on the wheels. This, in effect, is the same as increasing the train resistance; and it requires additional power from the electric circuit. In certain cases where air brakes have been added to cars already in use with hand brakes only, it has been found that there has been a marked decrease in the power consumption, sometimes amounting to as much as 15 to 20 per cent. BRAKING OF ELECTRIC RAILWAY TRAINS 189 Air Brakes. Of all the forms of power brakes which have been developed, the one which has met with the greatest success and has been most widely adopted, is that in which the braking force is produced by means of compressed air. Generally speaking, compressed air is admitted to the brake cylinder, and the piston operates a push rod connected to the rigging. The principal difference in various types of brakes is in the methods by which the admission and release of air to the cylinder is controlled. The two methods in general use are the " straight " and the " auto- matic" systems. In the former, air is applied directly to the brake cylinder from a main reservoir; in the second, it is supplied to the cylinder from an auxiliary reservoir, the main air pressure being used to control the admission of air to and from the latter, and the release of the air from the brake cylinder to the outside atmosphere. Methods of Compressing the Air. Another way in which systems of air brakes differ is due to the methods in use for sup- plying the compressed air. The simplest arrangement is to provide large stationary compressors at suitable points along the railroad. These plants continuously charge stationary reser- voirs of large capacity. Each car is provided with a storage tank, which may be charged from the stationary reservoirs as needed, the operation taking but a few minutes as the car reaches the charging station. In order to reduce the size of the car reservoir, the air is stored at high pressure (about 300 Ib. per sq. in.). For use in the cylinders, this is reduced to about 45 Ib. per sq. in., which causes a certain loss in efficiency. The more common method of supplying the compressed air is by means of individual compressors, located on the cars or locomotives. For steam service, the compressors are driven directly by steam from the boiler, there being one or more installed on each locomotive, depending on the capacity required. For service on electric roads, the steam pump is replaced by one driven either from gearing connected to the axle, or by an individual elec- tric motor. The axle-driven compressors were favored in the early period of air-brake operation on electric roads; but, owing to a number of difficulties in construction, and high maintenance costs, they have been almost entirely susperseded by motor- driven compressors. The motor-driven compressor may be either a simple or a two- stage air pump of the reciprocating type, operated direct or 190 THE ELECTRIC RAILWAY through gearing by a small series motor, in the case of direct- current or single-phase roads; or by an induction motor on three- phase lines. In systems using individual compressors, where the reservoir can be charged as often as required, the pressure range is between 50 and 90 lb. ; the limits between the maximum and the minimum values usually being about 20 Ib. (e.g., between 70 and 90 Ib. is the range on many systems). To keep the pressure in the reservoir within the proper limits, intermittent operation of the air compressor is necessary. The action is controlled automatically by some form of governor which connects the motor to the line when the pressure has fallen to the minimum limit, and opens the circuit when it has been increased to the maximum. Various types of governor are in use, but the basic principle, as stated above, is the same in all. Straight Air Brakes. The simplest method of supplying the air to the brake cylinder is obviously that in which it is admitted directly from the main reservoir. The control for this type of brake consists essentially of a valve operated by the motorman, which can connect the cylinder to the main reservoir, can dis- connect it and retain the air, or can release the air completely from the cylinder by connecting it with the atmosphere. For single-car operation, the straight air brake is ideal, for the motorman can graduate the amount of air admitted to the cylinder and thereby adjust the braking force to obtain uniform retardation in spite of the variable coefficient of friction. As the length of the train is increased, difficulty is experienced in getting uniform application of the brakes. All the air which enters the cylinders must flow from the main reservoir on the forward car or locomo- tive, through the controlling valve, and then through a train pipe to the brake cylinders on the individual cars. It is evident that the pressure will build up at the front end of the train first ; and that a considerable time will elapse before the brakes are applied with full force on the last car of the train. This variation in force at the instant when the brakes are applied may cause trains to break in two, resulting in serious accidents; and at best imposes severe strains on the drawbars. Automatic Air Brakes. To obviate the troubles incident to the use of straight air brakes on trains of considerable length, the automatic air brake was developed. In this system the train pipe does not feed directly into the brake cylinders, but is used to charge a main reservoir on the locomotive and a set of auxiliary BRAKING OF ELECTRIC RAILWAY TRAINS 191 reservoirs, one of which is located on each car. In the normal running position, all of the latter are fully charged to the train pipe pressure, and the brake cylinders are open to the outside atmosphere. These relations are controlled by a device known as the " triple valve," shown in Fig. 91, which automatically makes the proper connections between the train pipe, the auxiliary reservoir, the brake cylinder, and the outside atmosphere. It is evident that a triple valve is a necessary part of the equip- ment of each car in the train. To Auxiliary Reservoir A Jo drake Cylinder Jo rain FIG. 91. Plain triple valve. As shown, the brake cylinder is exhausting to the outside atmosphere, and the auxiliary reservoir is being charged from the train pipe. This is the release or running position. A reduction in train pipe pressure causes the slide valve to move to the left, closing the connec- tion between the train pipe and the auxiliary reservoir, and connecting the latter to the brake cylinder, the exhaust being closed at the same time. To apply the brakes, the train pipe pressure is suddenly re- duced, which causes a movement of the triple valve, disconnect- ing the auxiliary reservoir from the train pipe, and connecting it with the brake cylinder, meanwhile closing the exhaust con- nection. This causes the air to flow from the auxiliary reservoir to the brake cylinder, applying the brakes. Various improve- ments have been made from time to time to increase the rapidity with which the train-pipe pressure is lowered, and to make the movement of the triple valve with a minimum reduction in pressure. In the well-known " quick-action " brake, which is in use on a large proportion of the steam roads, the train pipe is vented directly into the brake cylinder by the movement of 192 THE ELECTRIC RAILWAY the triple valve. In this way the reduction in train-pipe pressure can be made in a very short time, requiring only a few seconds for the longest freight trains in operation. In making an ordinary or " service" application, the full pressure available from the auxiliary reservoir is not needed. When the desired amount of air has been admitted to each brake cylinder, its triple valve is closed. To produce this effect the train-pipe pressure need only be lessened a small amount; in the standard types of brake this reduction must not exceed about 15 Ib. With a greater drop in the train pipe the " emergency" applica- tion occurs, in which the train pipe is fully vented to the atmos- phere or to the cylinders, and the full pressure from the auxiliary reservoir is applied to the brakes. To release the brake, the engineer's valve is moved to such a position as to admit air from the main reservoir to the train pipe. This increase in train-pipe pressure changes the position of the triple valve so as to close the connection between the auxiliary reservoir and the brake cylinder, connecting the former to the train pipe. This recharges the auxiliary reservoir. At the same time the brake cylinder is connected to the atmosphere, which releases all the air and removes the pressure from the piston and from the brakes. A modification of the quick-action brake, known as the " high-speed" brake, has been developed for use on fast passenger trains. In the design of this brake, account is taken of the fact that the coefficient of friction is less at high speeds. The train-pipe pressure in this type is higher than in the quick-action brake, being in the neighborhood of 110 Ib. When the emergency application is made, the full pressure is applied from the auxiliary reservoirs to the cylinders, producing a braking force which, although not sufficient to cause sliding of the wheels at the high speed, would almost certainly do it before stopping the train. To prevent such a result, the pressure is lowered gradually, by means of an automatic reducing valve on the car, to the emergency standard of 60 Ib. Electropneumatic Brake. Although the quick-action and the high-speed brakes have been very satisfactory in general serv- ice, conditions arise in connection with the operation of heavy, fast trains, where the control they exercise is not sufficient. Even with the quick-actiori brake, there is a certain time lag between the movement of the engineer's valve and the application of the BRAKING OF ELECTRIC RAILWAY TRAINS 193 brakes on the rear car of the train. Where the trains are short, or where the speeds are low, this will cause no difficulty in opera- tion. With long, high-speed trains there is considerable surging of the cars, and strain on the draft rigging. Further than this, the time required for the full application of the brakes makes the total distance from the braking signal to a stop materially longer than if the brakes were all set simultaneously. A certain time element is unavoidable, for the air cannot flow from the auxiliary reservoir to the brake cylinder instantaneously; but beyond this, it is de- sirable to eliminate the lag. This is accomplished by the use of the electropneumatic brake. In this type, the ordinary features of the automatic brake are retained, but the application of the pressure is governed by an electric circuit, in a manner somewhat similar to that of the electropneumatic control of the motor circuits in multiple-unit operation. A special form of triple valve is used, in which the admission of air to the brake cylinders is governed by electromagnetic valves. By proper combinations of electric circuits the brake cylinder pressure may be built up to the maximum, may be held in the cylinders, or may be wholly or partially exhausted. This latter feature is of great impor- tance, since with the ordinary automatic brake there is little oppor- tunity to provide a graduated release. A comparison of the action of the two types of brake is shown in Fig. 92. 1 In the pneumatically controlled brake, the stop is made in 40 seconds from the time the brake application was be- gun, bringing the train to rest in a distance of 1290 ft. In this operation a graduated action was obtained by increasing the train-pipe pressure to release the brakes and then partially re- applying them. In comparison, with this, the electrically con- trolled brakes brought the train to rest after 20 seconds, or one- half the time required for the pneumatic, the distance taken being 700 ft. In the operation of the electrically controlled brake, a much more effective graduation of the release was obtained, there being two partial reductions of pressure. The result can be seen in the more uniform slope of the speed-time curve. Due to this feature, the maximum braking effort can be increased to a value which would be dangerous for the ordinary automatic brake. It should be noted that the final pressure at the end of the stop is 1 Figs. 92 and 93 are from an article by W. V. TURNER, Electric Journal, Vol. VIII, p. 905, Oct., 1911. 13 194 THE ELECTRIC RAILWAY 1500 36 4Z 24 30 Time, Seconds. FIG. 92. Service stops with automatic and electropneumatic brakes. Note that the pressure builds up much more rapidly in the electropneumatic application; also that the release is gradual, while in the automatic application the brakes were released and then re-applied to reduce the pressure. bis fa nee, Automatic store Elec. Pneu. 18 24 30 Time, Seconds FIG. 93. Emergency stops with automatic and electropneumatic brakes. In addition to using a higher braking force, it is possible to build up the pressure more rapidly with the electropneumatic brake, resulting in a considerable reduction both in time and distance required for stopping a train. BRAKING OF ELECTRIC RAILWAY TRAINS 195 less with the electropneumatic control than with the common type. In emergency stops the advantage of simultaneous action of the brakes on all the cars is much greater than for service applica- tions. A typical comparison of emergency stops is shown in Fig. 93, which has been plotted to the same scales as Fig. 92. It may be seen that the total distance for the stop is 300 ft. less for the electric brake, or only slightly over half that for the pneumatic. The time for stopping the train is likewise decreased from 22 seconds to 11 seconds. The use of the electric con- trol makes possible a considerable reduction in the distance interval which must be allowed between trains for safety, so that track capacity may be materially increased. Combined Straight and Automatic Brake. Many electric roads operate their cars singly for the greater portion of the time, but occasionally run trains of two or three cars. For single-car service the straight air brake gives all the desired features and is easier to manipulate than the automatic. But when cars are coupled together, the use of the straight air brake, even on com- paratively short trains, leads to the difficulties due to slow trans- mission of the braking force to the rear of the train. For such cases it is possible to have a combined equipment, which for normal operation acts as a straight air brake, but may be quickly converted into an automatic brake by the change in a few valve connections. A number of variations in the arrangement of the valves is possible, and several types of combination brake are in use. Vacuum Brake. Although the air brake is in almost universal use in this country, it has a competitor in Europe in the vacuum brake. In this type the principle of operation is almost identical with that of the air brake, but the compressed air is replaced by a partial vacuum, produced by a pump somewhat similar to the ordinary air-compressor. Since the pressure in the brake cylinder depends on the unbalanced action of the external air on the piston, it follows that the maximum force which can be obtained is 15 Ib. per sq. in. In order to get the same brake-shoe pressures as are ordinarily in use, the size of cylinders must be consider- ably increased. In general, the operation of .this brake is infe- rior to the modern air brakes described above. Electric and Magnetic Brakes. A number of attempts to utilize electric energy for the braking of trains have been made 196 THE ELECTRIC RAILWAY from time to time. The simplest of these consists of a disc, fastened to the axle, and a circular electromagnet attached to the truck. The magnet, when energized with current from the trolley wire, may be made to bear against the disc. This type of brake was developed a number of years ago; but it never was very successful, and is now obsolete. A much simpler arrangement is to reverse the car motors and connect them to the line. This produces a counter torque, giving a powerful retarding effort. Both of these methods of braking require the use of electric energy from the line, and the second increases the duty of the motors. It has already been shown that a moving car possesses a considerable amount of stored energy, due to its velocity. It would seem desirable to utilize this in stopping the car in some other way than to waste it in heating the brake shoes and wheels. If the motors can be made to reverse their usual functions and act as generators, they will convert the kinetic energy of the moving train into electricity, which may be returned to the line or used for some other purpose. The greatest obstacle in the way of returning energy with ordinary equipments is that the series motor does not readily lend itself to this use. If allowed to operate without change of connections, it cannot be made to exert a counter-torque, since the speed increases indefinitely as the load is reduced. On the other hand, if the field is reversed, the counter e.m.f. will be in the same direction as the line e.m.f., so that the motor will give a counter-torque, but with additional current from the line. To make the series motor available for this kind of braking, and to return energy to the constant-poten- tial trolley circuit, it is necessary to add a shunt field. This complicates the construction of the motor and of the controller to a point where it is not ordinarily considered feasible. It is possible to short-circuit the motor on itself, after the line circuit has been disconnected. In this case the machine acts as an ordinary series generator, and will deliver a current de- pendent on its characteristic and the resistance in the external circuit. By properly choosing the resistance, the power delivered can be adjusted as desired, with a corresponding retardation of the train. To adapt this method of braking to a set of motors with series- parallel control, it is necessary to reverse the motor fields so the e.m.f. will be generated in the proper direction. The resistance BRAKING OF ELECTRIC RAILWAY TRAINS 197 may be chosen to give the desired retardation. This is a method of emergency braking which is always available on any car equipped with two or more motors and series-parallel control. The machines may be disconnected from the line, reversed and thrown to the parallel position. They will then generate e.m.f.'s in the same direction; but, since the magnetic circuits are never absolutely identical, there will be more residual magnetism in one or the other machine, so that it will overpower the other and operate it as a motor. The two e.m.f.'s will then be in series, and a considerable current will flow around the local circuit, whose value will be determined by the speed of the car and the resist- ance. The power required for this action is taken from the momentum of the car, and tends to reduce the speed. In the case of a four-motor equipment, with the ordinary platform con- troller, it is unnecessary to throw the handle to the parallel position, for the pairs of motors are placed in parallel through the reverser. All that is needed is to change the connections by throwing the reverse lever. It is obvious that if the car is moving backward, the braking effect will be produced with the controller thrown to the forward position. With some types of controller the only resistance will be that of the motors and the wiring, so that the current and the braking effort will be large, but if the method is used for emergency stops only, this will not occasion any difficulty. If the torque de- veloped is so great as to cause the wheels to slide, the e.m.f. generated by the motors falls to zero, and the torque conse- quently disappears. The motors will then revolve, again producing a braking effort. Newell Magnetic Brake. A form of brake, depending on the same principle, but using it much more effectively, was developed about ten years ago, and placed on the market under the name of the "Newell" brake, from its inventor. In this type, shown in Fig. 94, the current from the motors, acting as gen- erators, is passed through the coil a of the magnet, 6, pulling it against the track and providing a powerful braking effort. The movement of the magnet downward has also the effect of operat- ing the lever system, thus applying the brake shoes to the wheels. The effect of the magnets is twofold; in addition to producing a braking effort in themselves, they pull the entire truck down on the track with increased force so that a greater total braking effort may be applied to the wheels. 198 THE ELECTRIC RAILWAY An ingenious feature of the Newell brake is that the energy wasted in resistance, instead of being dissipated to the air be- neath the car, is utilized for heating by having the resistors put inside the car body in place of the ordinary electric heaters. Both the loss at starting and while braking are used to heat the resistors; and the material of which they are made is such as to store the heat and give it out at a nearly uniform rate. With city cars making frequent stops, the amount generated in this manner is ordinarily more than sufficient to keep the tem- perature as high as is usual with the ordinary methods of heat- ing. While there is no reason why the starting loss should not be used in the same way, when this system of braking is not employed, it is not customary to do so. For service in summer FIG. 94. Newell electromagnetic brake. Current delivered by the car motors acting as generators is passed through the coil a of the electromagnet b, causing a braking effort. a duplicate set of resistors is placed beneath the car in the usual position. With this type of brake it is entirely practical to obtain retar- dations of 3 miles per hr. per sec. and over. The greatest operating difficulty with the Newell brake, as with all types utilizing the motors to generate current in a local circuit, is that when the rotation of the wheels ceases the braking effort stops. It is, therefore, necessary to use the hand brake, or some other form of power brake, to hold the train after it has been brought to rest, which is an undesirable feature. Another objection is that the motors are working a greater portion of the time, so that the effective heating (r.m.s.) current is increased. If they are of more than sufficient capacity to make the schedule, this will have but little effect; but if already worked to the heating limit, the imposition of the added load will force them beyond their continuous capacity and cause damage. This point should be given careful study in case any such form of brake is to be applied. BRAKING OF ELECTRIC RAILWAY TRAINS 199 Momentum Brakes. The inertia of the train may also be used to operate a mechanical brake. Momentum brakes have been designed in which the shoes or drums are brought in con- tact by means of some form of friction clutch. This type has never been very successful, and its use has been extremely limited. It is difficult to make any such form of brake operable for more than a single car, which limits its application at once. It is extremely doubtful whether any such device can ever find a wide use. CHAPTER VIII CARS AND CAR EQUIPMENT Classification. Cars for railway operation may be very broadly divided into two main groups: those for freight or ex- press service and those for the transportation of passengers. Cars of the former type have been standardized to a large de- gree, and their design must conform to certain rules adopted by the Interstate Commerce Commission and the Master Car Builders' Association. Passenger cars, on the contrary, are not subject to such rigid supervision; and, especially in the case of electric roads, there is wide divergence in their design. It is with those of the latter type that this chapter treats. The development of car design for electric railway service has very closely followed the growth of the different classes of roads, as enumerated in Chapter I. Passenger cars for electric railways may therefore be roughly classified as follows: 1. Cars for city and suburban service. 2. Rapid transit cars (elevated and subway). 3. Interurban cars. 4. Trunk-line coaches. 5. Special service cars. The latter two types need not differ in any particular from standard cars for steam railway service. On such trunk lines as have been or may be electrified, our present experience indi- cates that all motive power will be supplied by independent locomotives, so that no electrical equipment on the cars is needed for successful operation. In case a general electrification of any railroad is made, it may be desirable to include such minor details as electric light and heat, and possibly bus lines and control cables so that the motive power may be subdivided and placed at intervals throughout the length of the train, and handled with multiple-unit control. Such changes are of minor importance, and need not be considered, since they do not require any modification of the design. 200 CARS AND CAR EQUIPMENT 201 Cars of the types for operation on city surface railways (" tram ways") have undergone a gradual development from the same beginnings as the steam railroad coach; but the neces- sities of the service have produced a radically different structure. Although street cars have been passing through a process of evolution for the last 60 years, there is today less uniformity in design than ever before. This is largely due to the changing conditions of operation on large city roads, which are forcing them to provide increased facilities and at the same time receive less return on the investment. In order to meet this situation, car builders and railway companies are today developing radical designs with the object of better and more economical operation. Since they run almost exclusively on private right-of-way, cars for elevated and subway service are not subject to the same limiting conditions as to size and weight as are surface cars. Their design approaches more nearly that of standard steam coaches. The main difference lies in the fact that to secure rapid movement the doors must be specially designed to facilitate passenger interchange. For interurban service the cars may be quite similar to standard railway coaches. Since they are ordinarily operated in one- or two-car trains, it is often essential that a single unit combine the functions of coach, smoker, baggage car, and sometimes express and mail. As the traffic on roads of this class is largely local, more attention should be paid to the design of doors than in cars for through trunk-line traffic. Structural Classification and Development. Considering cars from a structural standpoint, they may be classified according to form or type, to material, or to framing and construction. They naturally divide themselves into two types: closed or "box" cars, and open or "summer" cars. The early designs of street cars were of the closed body or "box car" type; and most of the more recent developments have been in this class. The first cars were direct adaptations of the stage coach for service on railways or tramways. While those for steam roads were soon increased in size, and before long crystallized into standard designs of considerable capacity, the street cars, due to the limitations of animal power, tended toward extremely light construction. The one-horse "bobtail" car was the first development for purely city service. Cars of this type were usually about 12 ft. long, were single ended, and 202 THE ELECTRIC RAILWAY were arranged for operation by one man, the driver. The floor plan of a car of this type is given in Fig. 95. With the growth of cities and the corresponding development of the street railway business, came a demand for designs of increased capacity. This led to the construction of cars of about 18 to 20 ft. length of body (Fig. 96), usually drawn by two horses. In some cases these were handled by the driver alone, but more frequently they were arranged for two- man operation. Due to .^ the necessity of light weight, no further de- velopment was possible so H - - it' >i long as animal power was FIG. 95. Floor plan one horse car. retained. The use of the This type of car was in use in a large number of cable did not change the American cities from about 1850 to as late as 1900. situation to any extent, since its strength was limited, and the car weight had to be kept a minimum. The advent of electric power changed the entire situation. Although most of the early electric cars were the same ones that had previously been used with horses, it was almost immediately seen that the limit to size had been removed. A gradual increase began at once; but before long the limit of capacity for a single - -20 -- FIG. 96. Single-truck horse car, or early electric car. A later model than that shown in Fig. 95, designed to be drawn by two horses. Many of them were remodeled and fitted with electric motors between 1890 and 1900. truck caused the adoption of longer bodies, supported by two swiveling or " bogie" trucks. This has become the standard for nearly all classes of service, the small single-truck car having now been superseded in all important cities, except for special service or on lines of extremely light traffic. The open car, Fig. 97, has always been a favorite with the riding public. It is only applicable for city service, being unsuited for high speeds or for long runs. It usually consists of CARS AND CAR EQUIPMENT 203 a wooden underframe, supporting a skeleton side framing with a light roof. On account of the lack of side bracing, it is struc- turally weak. The seats are ordinarily transverse benches extending the entire width of the car, and access is obtained by a step or running board at either side. Such an arrangement is dangerous for the passengers. It may be shown that it is slower to load and unload than the modern types. While the open car may be justified in southern climates, where it can be in service the entire year, its use in northern cities is limited to a season seldom over six months long. This requires FIG. 97. Single-truck open car. This type of car has been in use, both with horses and with electric motors, from the early days of street railways up to the present time. a duplication of equipment. Some of the smaller roads reduce the capital expense by using the same trucks under both open and closed cars, transferring them at stated dates. This prac- tice is open to considerable objection. In order to meet the demand for the open car, and at the same time reduce the total cost of equipment, a new type was designed about ten years ago, known as the "convertible" car. In this the window sash and side paneling could be removed or else stored in the roof, so that the same body was available for either summer or winter service. Due to the inherent structural weakness and the difficulty of getting a tight con- struction for winter service, this car never had a great popularity with the street railways. A compromise between the closed and the open types was finally made in the so-called " semi-convertible' 7 car. This is 204 THE ELECTRIC RAILWAY practically a closed car, but with larger windows than ordinary. The sash are either stored in the roof or in pockets in the side walls beneath the window sill. With the use of transverse seats, this type meets most of the demands of the riding public, and is adaptable to any of the methods of fare collection which have become standard in the last few years. In the larger cities, the demand for units of very great capacity has become pressing in the past few years. Double-truck cars of the largest types have been unable to meet the needs where street congestion is great. At the present time, several cities are making experiments with double-deck cars to obtain maximum capacity with minimum space in the street. These have not been in service for a sufficient length of time to demonstrate their worth, but it is probable that their use will be extended where congestion is a maximum. Another attempt to increase capacity has been made by the use of articulated cars. In the types which have been brought out, two small car bodies have their platforms removed and are joined by a flexible unit, so that the combination forms a single car. The entrance is placed in the flexible platform, and the exits are at the ends. 1 Still another method for getting increased car capacity is the use of trains of two or more units. These may consist of one motor car and trailers, or two or more motor cars, operated by multiple-unit control. Exceptional 'conditions have from time to time brought forth special designs of cars. Among these may be mentioned the " California" type. This car is a combination of closed and open car. In most of the designs the center portion of the body is enclosed while the end portions of the car are open. It is a favorite where the climate is mild, but is changeable, as in California. It is not likely to ever have a very wide field of application, since in localities where the weather changes are sudden and severe the car has practically one-half its capacity idle at all times. Materials of Car Construction. All the earlier cars for every class of service were built exclusively of wood. This is the cheapest available material, and its fabrication does not call for expert design. Within the last ten years the price of wood has 1 For a more complete description, see Electric Railway Journal, Vol. XLI, p. 583; Mar. 29, 1913. CARS AND CAR EQUIPMENT 205 risen considerably, so that the advantage of low cost is less than formerly. Steel as a material for cars has been making rapid progress, for, although the first cost is greater, the de- preciation is less. Steel cars are more reliable and are nearly free from fire risk. In collisions they stand up better than those built of wood. The advantages of wood as an interior finish are obvious; and some roads seek to retain the good points of both materials by adopting a semi-steel construction, in which the main framing is of steel, the details and finish being of wood. This makes a cheaper structure than the all-steel car, but the fire risk is greater and the depreciation usually more. The use of the all-steel car is increasing rapidly, and it is quite possible that it will be required by law on all main line passenger roads within a few years. Framing. There are three general methods of supporting the car body. The oldest and most used is to build a heavy underframe or platform, which is strong enough and sufficiently rigid to carry the entire superstructure. This construction pro- duces a very satisfactory car, whether the framing is of steel or of wood, but it is often unnecessarily heavy and correspondingly costly. The expense incident to hauling needless dead weight may be a large amount on a road operating many cars; and the framing should be so designed as to reduce this extra weight to a minimum. This can be done by carefully determining the stresses in all parts and designing the members only sufficiently heavy to give a proper factor of safety. When the entire strength is in the floor or bottom framing, the vertical stiffness is not great, and must be supplied either by making the longitudinal members heavy, or by providing tension members beneath the sills. A second method of framing was invented by George Gibbs, and first used in the design of the original steel cars for the New York subway. 1 The principal difference in this design is that the main longitudinal members are located at the top of the car, the weight being carried by the sills through the medium of the window posts. The floor framing is light, having only enough strength to support itself. The window posts are heavy enough to transmit the load to the bolsters. By the adoption of this construction, the total weight of the members may be less than 1 A complete description of the original subway cars is given in American Engineer and Railroad Journal, October, 1904. 206 THE ELECTRIC RAILWAY with the rigid underframe. It is obvious that this is only appli- cable to cars built wholly or partially of steel; but with this type of framing they may be made nearly as light as those of wood. A third method of construction makes the side sheathing of the car furnish a large portion of the vertical stiffness, the de- sign being quite similar to the familiar plate girder bridge. By thus utilizing the side sheathing, a maximum weight efficiency may be obtained. Cars of this type have been designed for a considerable number of city roads, for a few interurbans, and for nearly all of the elevated and subway lines. The excellence of this framing, and the comparatively small amount of dead weight, is increasing its popularity; so that it is likely to become stand- ard for many types of cars for different classes of service. Roof Framing. In the early designs of cars, the roofs were made independent of the bodies, and were of the lightest con- struction, often being flimsy. Operation by electric power with an overhead trolley made it necessary to considerably strengthen the roof framing. At the same time, it was felt that the flat roof design of the old standard horse car did not permit good ventilation. A somewhat radical change was made by the addition of the ''monitor deck," the type which is familiar on steam railroad coaches. After a long period of use, it has been found that the monitor roof, with movable sash, does not offer a satisfactory solution of the ventilation problem, and that the break in the roof framing inherent to the design makes a weak structure. Ventilation has been taken care of -by various systems, some dependent on the motion of the car to draw the used air out through special ventilators, while in others air is circulated by means of motor-driven blowers. The application of these devices has removed the primary need for the monitor deck; and the secondary purpose, to furnish light, has been all but defeated through the use of colored glass. A solution of the roof problem which has been satisfactory was advanced a few years ago, and is being adopted in many of the new designs. The monitor is omitted entirely, the roof being made in the form of a flat arch, rounded at the ends to form a platform hood. The use of steel angles, bent to the proper shape, for carlines, results in stiffening the roof to a marked degree, and with a reduction in weight over the monitor design. The natural lighting of the car need not be interfered with, since the form of the roof allows the windows to be made somewhat CARS AND CAR EQUIPMENT 207 higher. A further development is to continue the window posts upward, bending them in a complete arch, and making them serve for carlines. This still further strengthens the framing, making the entire structure more nearly one complete unit. In any of the arch-roof cars the ventilation must be taken care of by some form of forced air circulation. Careful design has given much better results in this respect than were possible with the monitor roof; and the general appearance of the car, both interior and exterior, is at least as good as that of the earlier type. Door Arrangement. Where the stops are infrequent, as in trunk-line service, the arrangement of the car interior is generally for the comfort of the passengers during the journey, any extra time consumed at stops being of minor importance. With city surface lines and rapid transit roads, however, the main object is to obtain a fair schedule speed with a maximum number of stops. In such cases the length of ride per passenger is compara- tively short, and a certain amount of comfort may be sacrificed in order to reduce the duration of the trip. For this class of traffic the arrangement of the car, both as regards the seating and the doors, should be made to facilitate the movement of passengers when entering and leaving. The earliest types of car for this service were on the same general plan as the ordinary steam coach, having doors at each end, and seats arranged either trans- versely, or longitudinally, as in Fig. 96. In the older cars, the platforms were entirely open ; but owing to public demands, most of them have been enclosed with permanent vestibules for the past ten years. The first effect of this change was to attract a large number of passengers to the platforms, where they rode by preference. Naturally this tended to congest the entrances, and to make rapid loading and unloading difficult. In some cities, such use of the platforms by passengers has been prohibited. Although this aids to some extent it still is not the best arrange- ment for rapid interchange. A simple expedient is to use one end of the car for entrance only, and the other for exit. This establishes regular paths for the movement of the passengers, and aids greatly in reducing the time of stops. Many objections to this method of operation have been raised, the principal one being that passengers must either get on or off the car quite a distance from the street crossing, which may necessitate walking through mud or snow. In some cities a compromise is made by regularly 208 THE ELECTRIC RAILWAY employing the scheme mentioned above, but allowing passengers to use either platform as an exit at the discretion of the con- ductor. With this modification, the efficiency of the method is reduced considerably. The proper design and location of the entrance and exit doors has a marked effect on the rapidity of loading and unloading. r ^> L. ' - i i FIG. 98. Accelerator car. An early attempt to prevent crowding of the entrance and exit, and to reduce the time of stops. Suitable for single-end operation only. The single, narrow swinging door of the steam coach limits the speed with which passengers can enter or leave the car. If doors of this type are used for street cars, a long time will b,e needed at stops. An early attempt to aid the passenger distribution is the r FIG. 99. Semi-accelerator car. A modification of the type shown in Fig. 98, arranged to allow double-end operation. Brownell " accelerator " car, shown diagrammatically in Fig. 98, In this the doors were placed at one side of the center, nearest the entrance step. This prevented any persons who might be stand- ing on the platform from interfering with the movement of pas- Q D FIG. 100. Center-door car. A recent type which, with a few minor modifications, has been adopted in a number of large American cities. sengers boarding the car. Such a design is only applicable where the cars always run in one direction. Where they must run either way, the "semi-accelerator" car, Fig. 99, could be substituted. As a further aid to rapid movement, center doors may be used, either alone, as in Fig. 100, or in conjunction with the end doors. CARS AND CAR EQUIPMENT 209 The former possess many practical advantages, due to the fact that the passenger movement may always be under the eye of the conductor, and he may be held responsible for any accidents. The great operating objection to the center-door car is that it is more difficult to establish regular paths for the passengers than in the end-door cars. By careful training of the conductors it is possible to largely prevent this trouble. Seating Arrangement. The influence of the seating plan on the rapidity of loading and unloading is quite marked. The older JUUUUUUUL innnnnnnr FIG. 101. Cross-seat car. A design widely used about 1900; an adaptation from steam railroad coach designs. types of street cars were nearly all equipped with longitudinal seats on either side of the center aisle, running the entire length of the car body (Figs. 95, 96, 98, 99). While this plan is fairly satisfactory when there is no crowding, it becomes bad with a standing load. It is unplesant for the seated passengers, and inconvenient for those standing. The use of transverse seats, as in Fig. 101, provides greater comfort for the former, but uuuuuu u nnnnnnn FIG. 102. Modified type of cross-seat car. A development from the design shown in Fig. 101, to overcome objectionable crowding at the doors, and to permit of a wider opening. restricts the amount of space available for the latter. The stand- ing space is more comfortable than with longitudinal seats, since grab handles may be placed on the seat backs for support. The worst trouble is that the congestion near the entrance and exit doors is much greater than with side seats. A compromise is usually adopted in city cars by having longitudinal seats near the doors, and cross seats in the center of the car, when designed for end entrance, as in Fig. 102. With center entrance cars the 210 THE ELECTRIC RAILWAY trouble is not so marked, and the seats can all be placed trans- versely without much danger of congestion. Other combina- tions may be made advantageously for particular cases. A more logical study of both seating arrangements and door design has been made in conjunction with the prepayment of fares. The further consideration of both these topics will be taken up in that connection. Fare Collection. Certain roads, especially rapid transit lines, collect fares before the passengers enter the cars. This obviates any need of conductors, guards or brakemen being the only employees needed on the trains in addition to the mot or men. Practically all surface roads, both city and interurban, are so situated that fares must be collected after the passengers have boarded the car. According to the older methods, the conductor passed through, collecting fares from passengers after they had entered and become seated. Often he would be in the interior doing this during a stop. This practice has two disadvantages: the conductor is not in a good position to know whether the steps are clear before signaling the motorman to start, nor can he see the passengers who are entering or leaving the car. Besides mak- ing operation dangerous, this makes fare collection difficult, and in some cases almost impossible. It also gives dishonest conductors a chance to "miss" fares, or to fail in registering them. A number of schemes to make fare collection easier and more cer- tain, and to reduce accidents, have been tried within the past few years. Of the various ones advocated, the prepayment plan has met with the most success in the United States. It has been adopted in nearly every large city in the country, and in many of the smaller ones. The basic principle of all methods of fare prepayment is to have the conductor at or near the entrance, and to prevent any person from going into the car without first tendering his fare. By this means the conductor does not have to depend on his memory to ensure collection of fares ; and he may be located in such a position that he can be sure the steps are clear before giving the signal to go ahead. In the later types of pre- payment cars, various forms of doors, operated by the conductor from his fixed position, make it impossible for passengers to enter or leave after the starting signal has been given. This reduces the boarding and alighting accidents by a marked degree. CARS AND CAR EQUIPMENT 211 If the fares were collected at the instant of boarding the car, the time taken in loading would be materially increased. This is obviated by using the entrance platform for holding a certain number of passengers while they are getting their fares ready to present to the conductor, the door being closed and the car started immediately after they have boarded the platform. In some of the types of prepayment cars, as many as ten to twelve passengers may be accommodated in this manner, so that no more time is consumed in the ordinary stop than where fare collection is made in the old way. Types of Prepayment Cars. Practically any standard type of car may be arranged for fare prepayment. The success of any particular design depends to a considerable degree on the amount of space available for passengers before presenting fares. This requires special design of platforms in most cases. FIG. 103. Original Pay-As-You-Enter car. The conductor is stationed in the fixed position shown, and receives the fares from the passengers as they pass him on entering the car. The seating arrangement is not an essential feature of this type of car. The first type of prepayment car, which was introduced in Montreal in 1905, is shown diagrammatically in Fig. 103. In this the platforms are lengthened somewhat from the standard de- sign, and a railing divides the rear one into two portions, one for entering passengers, and the other for the conductor and leaving passengers. The conductor remains in his position at all times, and each passenger, on entering the car, tenders his fare or deposits it in a special fare box. The conductor is then in a position where he can collect all fares, and where he can watch the movements of the entering and leaving passengers. The front door is used for exit only, and is under the observation of the motorman. In the original design, the steps were not movable, and no en- closing doors for the vestibules were provided. No special at- tempt was made to prevent passengers from leaving or boarding the car while in motion. Although this type considerably re- 212 THE ELECTRIC RAILWAY duced the number of accidents from such causes, it did not en- tirely prevent them. Another type of prepayment car, known as the "Pay- Within" car, was brought out soon after the " Pay-As- You-Enter " car, but by a rival concern. In the original form, shown in Fig. 104, the bulkheads are entirely removed, the conductor is stationed in the middle of the end entrance, and provided with an operating stand. The vestibule has sliding doors which are worked either by compressed air or by a system of hand-operated levers, worked from the operating stand. The outside steps are also arranged to fold up and disappear when the vestibule doors are closed. In this design the entire platform is made available for entering passengers waiting to pay their fares. Exit is usually made by Conductor 'UUUUUU 1 .nnnnnnr FIG. 104. Original Pay- Within car. A type developed soon after the P-A-Y-E car. The principal distinguishing feature is the system of doors and folding steps. the front platform, the door being the same as that for entrance, but controlled by the motorman. With this type of car boarding and alighting accidents are practically eliminated, since the con- ductor is instructed not to give the starting signal until the en- trance door is closed; and the motorman must not start the car, after receiving the signal, unless the exit door is closed. The distinctive feature of this car is the system of doors and folding steps. After a few years the manufacturers of these two forms of prepayment cars combined, incorporating the good features of both. Generally speaking, the platform construction of the original P-A-Y-E car was combined with the door arrangement of the Pay- Within car, producing a design considerably in advance of either. With cars of the prepayment type, it is essential to rapid opera- tion that the space near the doors be as little restricted as possible. For this reason the seating arrangements have been developed from that shown in Fig. 102, since in most cities the cross seats have been found more desirable. CARS AND CAR EQUIPMENT 213 A further development of the door-operating principle is to have the doors arranged so that the starting signal is given auto- matically when all of them are closed. This may be accomplished very simply with a bell or light circuit, giving the indication to the motorman without signal from the conductor. The scheme may be carried still further, in cars equipped with multiple-unit control, by including the doors in the master control circuit. With this arrangement the car cannot be started until they have all been closed. It then becomes possible to increase the speed of operation, for as soon as the car has come to a stop and the doors have been opened, the motorman can throw his controller to the first operating position. Then, as soon as they have been closed, the car will start without signals of any sort and the motorman can at once turn his controller further as desired. If the doors are opened while the car is running, power will imme- diately be cut off. Center Entrance Cars. The prepayment principle has been extended to center side-door cars. As already mentioned, the side door has many operating advantages. It decreases the average distance the passenger must go from the entrance to find a place; and since the platforms are unnecessary, they may be entirely omitted, being replaced with seats, thus adding materi- ally to the capacity of the car. It is also possible, by inclining the floor, to make a car with lower steps than the standard. In New York, a design has been produced in which, by having the floor inclined upward both ways from the center door, and by the use of special features, the step has been entirely eliminated, the car floor at the entrance being only 10 in. above the street level 1 (see Fig. 105). Near-Side Car. A special type of car has been designed for prepayment of fares in connection with the near-side stop, which is being required in many cities on account of safety. In the " Near-Side" car, Fig. 106, the entrance and exit are both on the front platform, the rear platform being entirely eliminated un- less the car is designed for double-end service. The conductor is relieved of all operating duties, since the passengers enter and leave the car under the eye of the motorman. The latter, having control of both the entrance and exit doors, can start the car when he is satisfied that the steps are clear. It is possible to 1 A complete description of this car may be found in Electric Railway Journal, Vol. XXXIX, p. 418, Mar. 16, 1912. 214 THE ELECTRIC RAILWAY interlock the controller with the doors, so as to prevent opera- tion of the motors unless the doors are closed. The conductor, then, acts merely as cashier, his function being to make change and assure himself that the proper fare has been deposited in the fare box by the passenger. In small cities with light traffic, the UUUI IUUU n'nni innn FIG. 105. New York stepless car. The floor level is but 10 in. above the ground, and there are no steps inside the car. Note the arrangement of seats to clear the pony wheels, and the position of the motors at the outer ends of the trucks. conductor may even be dispensed .with, the motorman perform- ing the duties of both. In the latter case, the time consumed in stops is liable to be somewhat longer than where a conductor is employed. Conductor. Motorman uuuuuuu nnnnnnn I I I I I I I I I I I M FIG. 106. Near-side car. The entrance and exit doors are under the control of the motorman; the conductor is not required tc give starting signals. Rapid Transit Cars. The design of cars for service on elevated and subway roads is not limited as for use on surface lines, prin- cipally because the problem of fare collection does not enter. In all roads of this class prepayment of fares is an essential part; but, on account of the physical features, making it possible to CARS AND CAR EQUIPMENT 215 operate entirely on private right-of-way, payment is made in the stations before the passengers enter, so that the cars can be designed entirely for comfort and rapidity of operation. The doors of the earliest type of rapid transit car were modeled closely after those of the open platform steam coach of the same period, but the cars ordinarily had longitudinal seats in- stead of the cross seats of standard railroad designs. Such a car is shown diagrammatically in Fig. 107. Cab || \ ^ RemoYablc /' * Seat \_^.^ // n / ///^///////////^^^^ Fie. 107. Early rapid-transit car. This type, with open platforms, has been widely used on all of the earlier elevated roads. Note the position of the motorman's cab. It is to be noted in connection with all cars for operation on elevated and subway lines that, since the platforms must be specially designed in any case, there is no advantage in having them near the level of the rail. Much more rapid loading and unloading can be obtained with them at the level of the car floor, since this obviates any need of steps. This arrangement also simplifies the car framing to some extent, since the sills can be made continuous from one end of the body to the other. U UU U FIG. 108. Rapid-transit car, used in New York, Chicago, Brooklyn, etc. A medication of the open-platform car shown in Fig. 108. Another type of rapid transit car, shown in Fig. 108, is the same in general design, but includes a few cross seats near the middle of the car. These seats are invariably of the non-reversible type. Cars such as shown in these two diagrams have been operated on the principal elevated lines for many years. The general demand for the enclosed vestibule car led to the type shown in Fig. 109, which is the one used on several of the elevated lines of Chicago. The principal operating advantage in this design is that, since the passengers are protected from the 216 THE ELECTRIC RAILWAY weather, they are better lined up at the exits when the car comes to a station. Since the principal problem in the design of rapid transit cars is to secure swift movement of the passengers, it would appear that the addition of doors in the middle of the sides would add to ] U LU U n Ck FIG. 109. Rapid-transit enclosed vestibule car. A later type than those shown in Figs. 107 and 108. the speed of unloading and loading. A car of this type, shown in Fig. 110, was first used on the Boston Elevated Railroad. On that road the scheme is to have the passengers enter by the end doors and leave by the center doors. If this plan is adhered to by all the passengers, it increases the rapidity of operation con- flab N U U "A / FIG. 110. Side-entrance rapid-transit-car, New York. A modification of the type shown in Fig. 109, to give greater facilities for rapid loading and unloading. siderably. Unfortunately, it is not possible to completely train the American riding public to move in fixed channels, so that the advantage of establishing regular directions of movement is but partially realized. Even a partial establishment of a regular 1 II 1 1 1 Ui i 1 i U U n n u n n, 1 il LI i M it i - FIG. 111. Side-entrance rapid-transit car, Philadelphia. This differs from the New York car principally in the seating arrangement. direction of motion helps to some extent; and it would seem that, even if no general adherence to the rule were made, the extra doors should aid in loading and unloading. Cars of a similar design have been adopted on a number of rapid transit roads. CARS AND CAR EQUIPMENT 217 A slight modification consists in the addition of a few cross seats on either side of the center doors, as shown in Fig. Ill, which represents the type of car used on the Philadelphia elevated road. Practically the same results in rapidity of passenger inter- change should be accomplished by combining the center and end j u n uwu nmn umu nmn u n FIG. 112, Rapid-transit car, Metropolitan Railroad of Paris. Note the short distance from the doors to the seats in any part of the car. doors, placing two side doors some distance from the ends of the car, as in Fig. 112, which represents a design used in Paris. In this the maximum distance from a seat to a door is no greater than when center and end doors are used in a car of equal length. u u ' fi n i u u an u FIG. 113. Cambridge subway car. A recent type of rapid-transit car, arranged for large capacity. A movement has been growing in the past few years for longer cars for this class of service, since the passenger capacity can be increased to some extent without adding to the platform labor. Recent cars designed for the Boston-Cambridge subway (Fig. 113) and for the New York Municipal Railway (Fig. 114) are nn -T--4-.rr m, FIG. 114. Rapid-transit car, New York Municipal Railway. A very recent car, designed after a comprehensive study, to give maximum passenger capacity. examples of this. In both types, the principle mentioned in the last paragraph has been used to reduce the distance from the doors to the seats; but both cars are so long (69 ft. 6J in. and 67 ft. 4 in., respectively) that it is necessary to combine these side doors with center side doors, as used in some of the earlier designs. In 218 THE ELECTRIC RAILWAY this way the distance to the seats is no more than in the end- and side-door cars; and is actually less than in much shorter end- door cars. While it is desirable to seat every passenger, it is generally recognized that in congested business districts it is not possible to provide enough cars to furnish seats for all; and, when many business houses close at the same time, it taxes to the limit the ordinary rapid transit road to provide accommodations of any kind. This has been recognized in the car for the New York Municipal Railway. While a large door capacity is needed for rush-hour service, it is not so necessary at other times; and some of the doors are arranged to be used only when needed, folding seats being placed in front of them as desired. The effect on operation due to the use of different rapid transit cars is very marked. For instance, it has been estimated that the new New York Municipal Railway cars will increase the capacity of the track by 20 to 25 per cent, over what it would be if the latest type of cars now in use on other roads of its class in New York City were employed; and it will also save about $200,000 a year in platform costs, and between $1,000,000 and $2,000,000 in power system capacity because of the decreased energy consumption per passenger carried. 1 Interurban Cars. The interior arrangement of cars for inter- urban roads is subject to more conflicting elements of design than in city or rapid transit service. The collection of fares must be considered to some extent, but the problem is not so serious as in city cars; for the number of passengers entering is not very large at any one stop, and the rides are longer. Further, some system of fare receipts may be used for indemnification. It is more essen- tial to provide facilities for the comfort of the passengers, and this need increases with the average length of ride. On roads operat- ing trains for runs exceeding about two hours in length, the con- veniences should be about the same as those standard for steam coaches. A car which has been adopted by one of the larger interurban roads of the Middle West is shown in Fig. 115. In this are combined the functions of standard passenger coach, smoker, and baggage car. The smoking and baggage rooms are merged, in order to save space. This compartment has a num- ber of folding seats which are normally used for passengers, but 1 See Electric Railway Journal, June 6, 1914, Vol. XLIII, p. 1261. CARS AND CAR EQUIPMENT 219 which can be folded back against the walls in case there is an extra amount of baggage. The use of the center entrance car for interurban service has made but little headway so far; but it is likely to have a wider application in the future on account of its excellent qualities. The main compartment may be separated by the entrance from the smoking and baggage rooms, while the distance from any part to the doors may be reduced. Fig. 116 shows a car of this type which has been successfully used in high-speed service. j FoidingSeaf I Baggage, Exp. and \ '" | Smoker v** .n \^ Folding 5e,&00 *o a 6 000 ^ 600 1 4000^400 2000 ZOO \ \ \ x \ ^r \^ X ^ v ^ ^ X 10 50 60 ZO 30 40 Miles cer Hour. FIG. 118. Effect of speed on current collecting capacity of wheel trolleys. is too small, the wheel may leave the wire entirely at times. This latter condition is especially bad, since it causes a succession of arcs which pit the wire and the wheel. Pitting the wheel has the further effect of roughening the surface of the wire at other points. These various factors cause a rapid decrease in the amount of current which a trolley wheel can collect, as the speed is raised. Although the capacity of the contact is quite large at low speeds, the current which can be successfully delivered to the car is much less when the maximum speeds reached in ordinary interurban service are attained. The relation between speed and current collecting capacity is shown in Fig. 118. Coincident with the reduction in current capacity as the speed is increased, there is a marked diminution in the life of the trolley CARS AND CAR EQUIPMENT 227 wheels. The relation between the life of wheels and the maxi- mum speeds attained is also shown in Fig. 118. For high-speed roads, other forms of contact have been tried. Of the ones for use on overhead lines, the best are those which replace the wheel with some form of sliding contact. The two principal types of sliding collector are the bow trolley and the pantograph. Their successful operation depends to a large ex- FIQ. 119. Bow trolley. This design is better suited than the wheel trolley for current collection at high speeds, on account of i ts smaller inertia. It is widely used in Europe. tent on making a structure of such light weight and small inertia that heavy blows will not be delivered to the wire as the car passes beneath. At the same time it has become customary to use a form of construction in which the trolley wire is held more nearly in a horizontal plane. 1 The bow contact is made in two entirely different forms. The bow trolley proper, Fig. 119, replaces the trolley pole and heavy wheel with a light framework supporting a horizontal contact piece of steel or aluminum, which is held against the wire by means of a spring, or, in high-potential equipments, by a com- pressed air cylinder. With the latter arrangement it is unneces- 1 See Chapter XII, "Catenary Suspension." 228 THE ELECTRIC RAILWAY FIG. 120. Pantograph trolley. This type is in use for current collection in fast, heavy service, such as on trunk lines. FIG. 121. Over-running third rail shoe. This type is in use on practically all the elevated roads of the country. It is only suited to the unprotected top-contact rail. CARS AND CAR EQUIPMENT 229 sary for the operator to come in contact with the live portion of the circuit in any way, since the air may be applied by remote control, usually being worked by the motorman from a connection on the master controller. The pantograph trolley, Fig. 120, consists of a light diamond- shaped framework carrying at its top the contact piece, which is similar in form to that used with the bow trolley. This type is almost invariably operated by compressed air. On third-rail roads, a special form of collector must be used. Since the rail is carefully aligned with the track, there is no varia- tion in level, and the need of a heavy spring to insure contact is unnecessary. For over-running 1 rails a very simple type of col- lector may be employed. One of the commonly used forms is shown in Fig. 121. It consists of a loosely jointed pantograph of FIG. 122. Slipper shoe for under-running third rail. This type is standard for bottom-contact rails, or for protected top-contact rails. small dimensions, carrying at the bottom a contact shoe which is held on the rail by gravity or by a light spring. Connection is made to the car wiring by a flexible cable. When the under- running third rail is used, a different form of shoe is employed, a common type being shown in Fig. 122. This shoe, known as the " slipper type," has a hinged contact piece carried from a light framework attached to the truck. Its action is obvious from the diagram. This shoe is also excellent for over-running rails; and it is possible to arrange it so that it may be used inter- changeably for either top or bottom contact. Car Painting. No matter what the materials of which the car is built, it is necessary to provide some sort of protective coating, usually paint for the outside, and varnish for the interior over the natural wood. The proper finishing of cars is a subject which has 1 See Chapter XII, "Over-running Third Rail." 230 THE ELECTRIC RAILWAY received less attention than it merits, for on it depends to a con- siderable extent the life and general appearance of the equipment, whether the material be wood or steel. A description of the methods employed is out of place in this book, but may be found by reference to the files of the railway periodicals. Miscellaneous Details of Car Equipment. In addition to the apparatus already considered, there are many minor parts of the car equipment which are essential to successful operation. Seats, curtains, ventilators, door-operating mechanism, destination and route signs, headlights, markers, and a number of other parts are all necessary to make the equipment complete. While a detailed discussion of these parts of the car is unwarranted, it must not be forgotten that there is more or less latitude in their selection, and FIG. 123. Single truck, 7-ft. wheel base. Trucks of this and similar types are in use on practically all of the single-truck cars in operation. that considerable care should be taken to obtain proper and satisfactory material. Trucks and Running Gear. The operation of railway vehicles makes necessary some adequate form of running gear, which will carry the body in such a manner as to prevent objectionable shocks and vibration. The method of support differs widely, the principal variation depending on whether the car is mounted on a single rigid framework, or has two swiveling trucks. Single Truck Cars. The smaller cars for city service, having bodies not more than about 20 ft. long, can be carried with sat- isfaction on a single rigid-frame truck. The construction is of the simplest character, consisting of a support for the car body and pedestal bearings for the axles. In general, a rigid mounting of the car on the truck is undesirable, so that some form of spring is interposed; and the truck proper is supported on the journals by helical springs over the pedestals or by an arrangement of elliptical or semi-elliptical springs. The single trucks produced by different manufacturers vary widely in their details, but all are quite similar in general appearance. A typical single truck is shown in Fig. 123. CARS AND CAR EQUIPMENT 231 When the car body is too long, difficulties arise in the design of single trucks. In order to operate satisfactorily on city track, where the curves are almost invariably of short radius, the rigid wheel base must be kept to a minimum length, or bind- ing of the flanges, and in some cases more serious trouble, will result. If the wheel base is short, there will be a large overhang FIG. 124. Brill radial axle truck. Note the action of the hangers. By this means a longer wheel base can be used on a gingle- truck car than is possible with the design shown in Fig. 123. at the ends of the car, giving a weak structure, and causing longi- tudinal oscillations if the car is operated at high speeds. The ordinary methods of spring mounting of the body do not remove this difficulty, but at certain speeds may aggravate it. The sim- plest solution is to use two swiveling trucks under the car; but this increases the expense, and may appear undesirable if the car is only slightly above the limiting length. Another solution which 232 THE ELECTRIC RAILWAY has been developed is to carry the axles on hangers which may be swung at an angle with the car body when rounding curves. With proper design, the hangers can provide for throwing the axles in a radial direction as the curve is reached, restoring them to the parallel relation after getting back on tangent track. One form of hanger and the method of operation are shown in Fig. 124. Swiveling Trucks. For long cars, and for some locomotive service, it is necessary to use two swiveling trucks to provide for operation around curves. The trucks are independent structures, and are each connected to the car body by a single heavy pin, or " king-bolt." They are then free to turn, and allow the wheels to align themselves on any track. This construction is appli- cable to cars of any length. In order to prevent dangerous sway- ing of the car body, it is customary to provide bearings at the FIG. 125. Rigid bolster truck. Suitable for slow-speed locomotive service only. sides of the truck to limit the oscillation of the car at high speeds. These may be either flat plates or ball bearings. For the latter it is claimed that the friction is reduced materially, since the trucks are more free to align themselves with the track. The principal differences in trucks are in the methods by which the car body is hung. The simplest way is to support the bolster rigidly from the truck frame. The only spring possible is then that over the pedestal. Trucks of this type, as shown in Fig. 125, are only suitable for slow-speed locomotive service, the cush- ioning being insufficient even for freight cars. The floating bolster construction, shown in Fig. 126, detaches the bolster from the rigid connection with the side frames, and supports it through elliptical springs acting in a vertical plane transverse to the direction of motion of the truck, the bolster being allowed to move in ways provided for that purpose. While CARS AND CAR EQUIPMENT 233 the cushioning is better than with the rigid bolster construction, it is not sufficient for high-speed passenger operation, but is chiefly confined to freight-car and locomotive service. A further development is the swinging bolster truck. In this type the bolster is mounted on springs traveling in a guide, as with the floating bolster; but the springs, instead of resting di- rectly on the side frames, are carried by a saddle or series of hang- FIG. 126. Floating bolster (arch bar) truck. Suitable for freight cars, but not flexible enough for passenger cars. ers which allow the bolster to swing in a transverse direction. This permits the car body to roll or sway on curves and at high speeds, reducing the shock to a minimum. Trucks of this kind are standard for all steam and electric railway passenger cars, and are built in a multitude of forms for every class of service. A widely used type is shown in Fig. 127. FIG. 127. Swinging bolster truck. Suitable for high-speed passenger cars. Trucks of this general type are made in a wide range of forms. Maximum Traction Trucks. It has been shown that it is desirable to use a minimum number of motors consistent with obtaining the necessary tractive effort for car operation. For city service this generally calls for two motors per car. If the car body is too long for a single truck, ordinary swiveling types can be used ; and the motors may either be mounted both on one truck, the other being without electrical equipment, or one may be 234 THE ELECTRIC RAILWAY mounted on each. When the cars are to be operated in either direction the latter method of mounting is preferable, since the weight transfer between the trucks is then equalized for both directions of motion. In cases where the acceleration demanded is high, the use of two motors may not give sufficient adhesion, since only about 60 per cent, of the total weight is carried on the motor-equipped axles (a portion of the motor weight is carried directly, accounting for the increase over the 50 per cent, which might be expected). The weight distribution may be changed to throw a greater portion on the driving wheels by placing the bolster nearer the driving axle. In this way the available ad- hesion may be increased to between 70 per cent, and 85 per cent, of the total car weight. Since the trailer wheels are not carrying FIG. 128. Maximum traction truck. Used for city cars, in order to employ two-motor equipments with high accelerations. as much weight as the others, their size may be considerably re- duced without difficulty, and without affecting the riding qual- ities. In this form the " maximum traction'' truck has been standardized, and is used on a number of roads. One style is shown in Fig. 128. A feature of trucks of this class is that the small wheels may be allowed to extend under the drop platforms of city cars, thus increasing the total wheel base beyond what would be possible with standard trucks. This tends to make the car easy riding. All maximum traction trucks are subject to one objection. Since a large portion of the total weight has been transferred to the driving wheels, there may not be enough weight on the small ones to keep them on the rails at sharp curves, especially at high speeds. For this reason maximum traction trucks are considered unsafe at speeds over about 30 miles per hr. If higher- speeds are desired, standard trucks should be used, and the accelera- tion kept down to a point where there will be no danger of CARS AND CAR EQUIPMENT 235 exceeding the adhesion; or, if the high accelerations are neces- sary, four-motor equipments should be used. Motor Suspensions. In adapting trucks for electric opera- tion, it is essential to make provision for mounting the motors on them. It has become the universal practice to gear the motors directly to the axles without intermediate flexible connections, so that it is necessary to maintain the gear centers at a constant dis- FIG. 129. Nose suspension (outside hung motor). This method of support makes it possible to carry a portion of the motor weight on springs. There are several variations from this arrangement. tance to ensure their correct operation. This practically means that a portion of the motor weight must be carried directly on the axle. Generally, bearings are provided on the motor case, to give the necessary support for the machine and for the purpose of aligning the gears. The remainder of the motor weight may be spring borne by any available means. FIG. 130. Gibbs cradle suspension. With this arrangement, the motors mutually support each other. equipments. Used for heavy The simplest and oldest arrangement consists in using a lug or nose cast directly on the side of the motor case opposite the axle bearings, and which is connected to the side frames of the truck by a transverse bar, the support being through helical springs. A number of variations in this form of construction may be made. One standard type of mounting is shown in Fig. 129. Another method of spring support consists in the use of a cradle in which the two motors are hung. This allows them to mutually 236 THE ELECTRIC RAILWAY carry each other through springs. A suspension of this type is shown in Fig. 130. The motors may be placed either between the axles of the truck or outside. In general, it is better to place them inside, since this decreases the over all length of the truck and gives better weight distribution while accelerating; but in some cases the wheel base required is so short that there is not sufficient room for the motors. It is then necessary to place one or both motors out- side of the axles. The mounting of a motor in this way is shown in Fig. 129. This construction is ordinarily used with the nose suspension, and is adopted only for light trucks, since long, heavy cars are not well suited for operation around curves of extremely short radius. Motor Gearing. Ever since the direct form of drive has been used for railway motors, it has been the custom to use high speeds for the motor armatures with considerably lower axle speeds. This reduces the weight of the motor for a given output, and permits a more efficient construction. The early motors were designed for extremely high speeds, 1000 to 1500 r.p.m. being about the range employed. Since the axles of street cars with 30-in. wheels rotate at 100 to 200 r.p.m., it follows that the speed ratio is in the nature of 10 : 1. The space limitations make the greatest practical ratio for railway service with a pair of spur gears about 3J/2 :1, so that these high motor speeds call for a double reduction. After a few years' experience with this ar- rangement, it was found better to reduce the motor speeds some- what, so that a single pair of gears could be used. The present street railway motors have armature speeds of from 500 to 750 r.p.m., making a single reduction entirely practical. The early gears were of cast iron or malleable iron, and the pinions of rawhide or soft steel. After a comparatively short trial, it was found that rawhide could not stand the severe service demanded, and steel was employed exclusively. The use of steel pinions with cast-iron gears caused the most of the wear to fall on the latter; and to prevent rapid destruction malle- able iron was substituted for cast iron. This material was more economical, but it was soon found that a better gear could be made of cast steel, with greater strength and longer life than from malleable iron. Although cast steel has given considerable satisfaction, it has not proved uniform enough in quality to allow of its CARS AND CAR EQUIPMENT 237 being worked up to its limit of strength. More recent designs of gears have been made of forged or rolled steel, which has at once greater uniformity of composition and a chance for varying the ingredients to meet the needs of a particular service. Harder steels have been used; but it has been found that with the hard steels there is more tendency to brittleness, which may cause the teeth to break before their limit of wear is reached. To obviate this difficulty two methods have been employed. In the first the gears have been made of a low- carbon steel which is tough. After the teeth are cut the gear is treated to a case-hardening process, giving a surface which is flinty and wear-resisting, while the interior remains fibrous and tough. The other method is to make the gears of a metal which will allow surface tempering. This requires a steel which is somewhat higher in carbon, but it is claimed that the heat treatment leaves a hard wearing surface with a tough core. Both types of gear are in common use now, and are giving greatly increased life in many cases equaling the life of the axle itself. The increased life with the improved forms of gear- ing is from three to five times that with the cast-steel gear and machinery-steel pinion, while the cost is from one and one-half to two times as great. In figures, the life has been increased from about 100,000 miles for a cast-steel gear, to 350,000 miles for a tempered one and 500,000 miles when case-hardened. While the wear on gears is severe, that on pinions is still worse, since the number of teeth is smaller. Some of the pinions are made of case-hardened steel, and others of heat-treated steel. A recent development is the use of tempered tool steel for pin- ions. It must not be overlooked, however, that a great increase in hardness of one of the meshing gears above that of the other may cause wear of the softer metal. The early gears were cast in halves, and held on the axle with bolts. This construction makes it easy to replace damaged gears, but results in a structural weakness, with corresponding liability to breakage. With the later high-grade gears, lasting about as long as the axles, the need for having them split for easy removal has disappeared, so that it is preferable to make them solid and press them permanently on the axles. To lengthen the life of the gearing, it is always enclosed in a special dust-proof case. The cases supplied by the manu- facturers are ordinarily of malleable iron, but in some instances 238 THE ELECTRIC RAILWAY they are made of pieces of sheet steel riveted or welded together. Since the principal function of the case is to protect the gears from dirt and it does not carry any other parts, its mechanical strength is of secondary importance. The bottom of the case comes within a few inches of the top of the rail; and if there is not sufficient strength there, it may be crushed or broken when obstructions are encountered projecting above the level of the rails. An important point is the width of face and the thickness of tooth. It is on these factors that the size of gearing is deter- mined. Since the space available for the motor is limited to the distance btween the wheel hubs, less that taken by the gears, it is imperatve that the width of face be kept a minimum. Since the only other dimension which is capable of change is the thick- ness of tooth, the pitch must be kept a maximum. This has re- sulted in diametral pitches of 2J^ to 3, which are common for motor gearing. Once this value has been fixed, the total number of teeth which can be placed on the gear and pinion is determined by the distance between centers. When a motor is designed, it is necessary, in order to prevent extra cost of patterns and special machining, to keep the axle centered at a fixed distance from the armature shaft for all motors with the same frame. Since the force exerted at the pitch line is approximately constant for all gear ratios, the diametral pitch should be kept uniform for all changes in speed of the motor. The various possibilities for speed reduction lie in the gears whose teeth total the same. For example, if a certain motor is designed for a normal gear reduction of 20 : 59, the only allowable changes from this are such as will give the same total of 79 teeth on the gear and the pinion. Pos- sible ratios are then 22:57; 21:58; 19:60, and so on; and in all these combinations the strength of tooth will be constant. The limits in gear reduction are, on the one hand, the mini- mum diameter of pinion or the maximum size of gear that can be used; and on the other, the dimensions of the gear case which can be employed. The smallest number of teeth which can be used on a pinion without undercutting the teeth to a point where they are materially weakened varies with the form of tooth, but will generally be about 12 to 15. This gives an absolute min- imum size to the pinion, and a limit to the reduction in speed. The gear, on the other hand, must not be so large that there will be no clearance beneath it, or there will be danger of the gear case CARS AND CAR EQUIPMENT 239 striking the track. This limit is a real one, for the ordinary minimum clearance beneath the gear case is only 3 to 4 in. The other limit is seldom reached, for the maximum-speed equipments are not nearly so much in demand, and a very low reduction can be made without encroaching on the clearance limits. CHAPTER IX ELECTRIC LOCOMOTIVES Development. The early experimental applications of electric power to traction all contemplated the use of locomotives. This was undoubtedly due largely to the example set by the steam loco- motive, which was at that time the accepted motive power for all classes of railways, except street-car lines. When the possibilities of the electric motor were better known, it was seen that superior results could be obtained by placing the entire equipment on the cars, thus eliminating the unnecessary dead weight incident to locomotive operation. This arrangement has become standard for all street cars, and for rapid-transit lines, so that there is no field for the electric locomotive in these classes of service. Advantages of Motor Car Trains. For such roads as those mentioned above, there are several advantages to the use of motor cars, which cannot be obtained when locomotives are employed. Where exceedingly high acceleration is a prime requisite, the drawbar pull of a locomotive would be so great as to make it a practical impossibility. For instance, the express trains in the New York subway, consisting of seven motor cars and three trail cars, weigh approximately 360 tons. These trains are accelerated at a rate of 1.4 miles per hr. per sec. up to a speed of about 20 miles per hr., the maximum running speed being in the neighborhood of 40 miles per hr. This service calls for a tractive effort at start- ing, on straight level track, of approximately 53,000 lb., which must be maintained up to about 20 miles per hr. ; at the maximum speed the tractive effort is roughly 4400 lb. While the drawbar pull at starting is approximately that of a consolidation locomo- tive of standard steam railroad design, there are none in service which can maintain it up to the high speed required. Another advantage of the motor-car train is its extreme flex- ibility, when operated with multiple-unit control. The number of cars may be adjusted to suit the traffic, since each can be made an independent unit. The motor equipment is just sufficient 240 ELECTRIC LOCOMOTIVES 241 to give the desired tractive effort, so that there is no ques- tion of underloading or overloading, as often happens with locomotives. Field of the Electric Locomotive. When cost is considered, motor cars do not compare so favorably with locomotives; for the large number of comparatively small motors, with their complicated wiring and control, will usually cost considerably more than when the same power is concentrated in a few locomo- tive units. The flexibility due to multiple-unit control can be obtained to some degree with the latter, for these can be built in sizes of, say, one-half the normal capacity. Such units can be operated singly or in groups, so as to give approximately the cor- rect power for any train in use. The example cited above is one in which the locomotive could not be used to advantage. This is generally the case where the service is severe, and the acceleration is high. But where the schedule does not call for so great tractive effort, the obvious advantage of the locomotive may make it desirable instead of the motor-car train. Such operation is that of trunk line through trains in ordinary passenger service, and, in general, of all freight trains. Although the use of individual motor cars for freight service has been proposed, there is no doubt but that any elec- trification involving the haulage of large amounts of freight will call for locomotives, operated as single units or in groups. It is in such service that the electric locomotive has its field. As compared with the steam, the electric locomotive possesses the great advantage of capacity. Since the boiler, with its weight of water, and the tender, with a considerable load, are absent, the entire equipment may if desired be used for adhesion. The locomotive being essentially a pulling machine, any weight which is not used for adhesion is a dead loss; and this weight should be kept a minimum. It must be remembered that while the steam locomotive is com- plete in itself, the electric engine is but one part of the electric power system. While the output of the former is limited to what it can develop, the latter has behind it a source of power which is much greater; so that the electric locomotive can carry overloads for a short period which would be quite beyond the capacity of the engine and boiler of the ordinary steam locomotive. Due to the inherent characteristics of electric motors, the lo- comotive is better adapted to haul trains at high speeds when 16 242 THE ELECTRIC RAILWAY developing maximum tractive effort, than is the steam locomotive. For this reason it has the ability to pull large loads at consider- ably higher speeds, which tends to increase the capacity of the track. The possibility of subdivision makes the proper selection of units easy to give the best combination for any class of service. On account of the power-plant apparatus being concentrated, the stand-by losses incident to steam operation are largely elimi- nated. In a system of moderate size the average load at any period of the day can be made fairly constant, so that the boilers and generating equipment are loaded near their maximum capac- ity; and the losses due to coal consumption while locomotives are ready for service, but not actually in use, are very small. There is no need for long periods of rest, such as those due to cleaning out flues, washing boilers, and other incidents to steam operation; nor is there i>he waste of fuel in starting fires at the beginning, and dumping them at the end of the run. These characteristics materially increase the amount of time the locomotive can be in service, so that the total number of units required is less than for steam traction. Wheel Classification. There are two methods of notation in use for representing the arrangement of wheels on locomotives. The method most used in America is to give the numbers of wheels, first for the leading truck, then for the drivers, and finally for the trailers. A locomotive of the familiar " American " type is shown by the symbol 4-4-0, there being a four-wheeled leading truck, four driving wheels, and no trailers. In the European classifica- tion system the numbers of axles are referred to, the leading and trailing wheels by number, and the driving wheels by letter, A being equivalent to a single axle, and so on. Thus the American type engine would be represented in the European notation as 2-B-Q. Since this method of designation is so much more ex- pressive, differentiating between driving and idle axles, it will be used in this chapter. The table on page 243 shows the classification of standard American steam locomotives. While the wheel arrangements of electric locomotives differ somewhat from those given for steam engines, the latter are use- ful for reference and comparison. ELECTRIC LOCOMOTIVES CLASSIFICATION OF STEAM LOCOMOTIVES 243 Name Wheel arrangement Classification Per cent, weight on drivers Service American European Single Z oo Oo 4-2-2 2-A-l 45 Light passenger driver (obsolete). American . : Z o o O O 4-4-0 2-B-Q 65 Light passenger. Columbia. ZoOOo 2-4-2 l-B-l 65 Light passenger (obsolete). Atlantic. . . Z oo O Oo 4-4-2 2-5-1 55 High-speed pas- senger. Forney 1 ... Z COoo 0-4-4 0-J5-2 50-65 Suburban (obso- lescent). Switcher 1 .. Z OOO . 0-6-0 0-C-O 100 Switching and helper. Mogul .... ZoOOO 2-6-0 1-C-O 86 Light freight (obsolescent). Ten-wheel. Zoo OOO 4-6-0 2-C-O 75 Passenger and freight. Prairie .... ZoOOOo 2-6-2 1-C-l 75 Heavy passenger and freight. Pacific. . . . ZooOOOo 4-6-2 '2-C-l 60 Fast, heavy pas- senger. Consolida- ZoOOOO 2-8-0 jl-D-0 88 Freight. tion. Mastodon. Zoo 0000 4-8-0 2-D-O 80 Freight. Mikado.. .IZoOOOOo 2-8-2 1-D-l 75 Heavy freight. Mountain .ZooOOOOo 4-8-2 2-D-l 70 Very heavy pas- senger. Decapod.. ZoOOOO 2-10-0 l-E-0 90 Heavy freight. Santa Fe. .,' Z o O O OO Oo 2-10-2 l-E-l 80 Heavy freight. Mallet 1 . . . : ZoOOO-OOOo 2-6-6-2 1-C + C-l 85-100 Mountain service. Electric Locomotive Types. The early electric locomotives were nearly all direct adaptations of motor cars, the motor capac- ity being increased so that one or more trailers could be hauled by a car, usually of the baggage type. This practice developed until it was found that the equipment could be more advantageously disposed by limiting the duty of the motor vehicle to pulling only. This led to considerable variation in the design of the superstructure; but the fundamental part, the trucks and running gear, remained the same as in ordinary double-truck cars. Since the object is to develop the greatest possible tractive effort with 1 The wheel arrangements of locomotives under these same names vary somewhat. Those given are typical. 244 THE ELECTRIC RAILWAY the available weight, such locomotives are invariably equipped with four motors. The general arrangement is shown in Fig. 131. The motors are of the ordinary type, with single reduction gears. It is also possible to use gearless motors on this type of locomo- M aster ^ asts s=(s^ s ^' n ' f ' o 9 ra P^ Trolley Controller^ Main Switch Blower , Compressor Flexible Blowe Connection* ^Main Reservoir FIG. 131. B+B geared locomotive, Southern Pacific. Locomotives of this general type are in use on many interurban railroads. Note the com- pact arrangement of the equipment. tive, but the advantage is small and the weight and cost consider- ably greater for the same output. It is mechanically well suited for slow operation; but when run at high speeds, the weight sup- ported directly on the axles without springs is so great as to cause pounding of the track. FIG. 132. 0-B-B-O geared locomotive, Baltimore and Ohio. This locomotive is well suited for slow -speed, heavy freight service. It is evident that the entire draw-bar pull of the swiveling-truck locomotive must be transmitted through the center plates. This renders the design unsuitable for heavy loads, and a modi- fication has been made by articulating the trucks together and mounting the draft gear directly on them, as shown in Fig. 132. ELECTRIC LOCOMOTIVES 245 The cab is light in construction, and serves principally to house the control apparatus. Locomotives of the above types can be modified for high-speed operation by the addition of leading and trailing wheels, which serve to guide the heavy rigid structure, and prevent "nosing," !*_}__.] 3fo=4---------~4 J H- - ,.-.~'..~,3*r--7-- -. I!. 1 FIG. 133. 1-B + B-l gearless locomotive New York, New Haven and Hartford. This design has proved excellent for high-speed, heavy passenger trains in trunk-line service. especially on curves. A locomotive of this type is shown in Fig. 133. This represents a gearless locomotive built for the New York, New Haven and Hartford single-phase line. A somewhat similar design, in service on the New York Central, is shown in Fig 134. In this design a four-wheeled leading and a similar trailing truck are used. 36' 0"- 4f'o" -- over Couplers FIG. 134. 2-D-2 gearless locomotive, New York Central. This type has been used for heavy terminal passenger service. The dead weight on the axles is rather large for successful operation at high speeds. For heavy service, especially at high speed, the above types have not proved entirely satisfactory. Many attempts have been made to improve the transmission by the use of cranks and side rods. These designs have been employed to a considerable ex- tent in Europe, and to a much smaller degree in America. The 246 THE ELECTRIC RAILWAY most successful one in the United States is that of the Pennsyl- vania Railroad, for service at its New York terminal. This en- gine is shown in Fig. 135. The motors are spring-supported on the running gear, and are connected to jackshafts which in turn drive the wheels through parallel rods. When the motor speed is too high for direct connection, the motor may be geared to a jackshaft. A locomotive of this class 55 II ! 64' II"- over Couplers FIG. 135. 2-B+B-2 gearless locomotive, Pennsylvania Railroad. A high-speed passenger locomotive, with crand and side rod drive. Note that the motors are mounted high above the driving wheels, raising the center of gravity. is shown in Fig. 136. This represents the latest design used on the Lotschberg Railway in Switzerland. Flexibility is accom- plished by connecting the motors to the driving wheels through "Scotch yokes," which permit a certain amount of vertical move- ment, while there is no horizontal play save that required for the bearings. FIG. 136. 1-E-l geared locomotive, Swiss Federal Railways. In this design the necessary play between the cranks and the side-rods is obtained by the use of "Scotch yokes." Application of Locomotive Types. For slow-speed service, such as freight and switching, the principal requirement is to get the maximum tractive effort from the available weight. For this purpose the entire mass should be mounted on the drivers, leading to the swiveling truck or articulated types, such as are shown in Fig. 131 and Fig. 132. These designs have proved entirely sat- isfactory in service of this kind. ELECTRIC LOCOMOTIVES 247 For fast operation, it appears almost essential to place a por- tion of the total weight on leading trucks, in order that the main mass may be guided along the track. In addition, there seems to be ground for believing that the center of gravity of the locomo- tive should be made as high as possible. When the mass is low, there is little cushioning of the oscillations as the locomotive moves from side to side of the track, due to irregularities in the alignment of the rails. The parts rigidly mounted on the axles are especially destructive in their action. The result is excessive maintenance costs; and, since the force of the blow depends on the kinetic energy of the moving parts, the effect increases as the square of the speed. On the contrary, if the mass of the locomo- tive is high above the track, the result of variations in the align- ment is to cause the superstructure to. sway, while the wheels follow the small irregularities of the rails. The locomotive is not so easy riding; but, since its function is to develop tractive effort, this does not cause any operating difficulty, while the wear on the track is reduced. For this reason, designs of the general form shown in Figs. 135 and 136 have been developed for high-speed passenger service. In general, to secure a high center of gravity, it is necessary to place the motors on the superstructure of the locomotive, which causes difficulty in making a mechanical connection with the driv- ing wheels. This inevitably leads to a design embodying cranks and side rods. One of the early arguments made in favor of electric locomotives as compared with steam was the absence of reciprocating parts; and it now appears that it may be impossible to eliminate them from electric engines. The effect of the rods is, however, not so destructive in the latter case, for the motor has a rotary motion, giving uniform torque at all points in the revo- lution. In order to transmit the motion without severe twisting strains, it is essential that cranks be placed on both ends of the armature shaft. By placing them 90 apart, the torque will be transmitted uniformly at any position; for the action is compar- able to the addition of two sine waves in quadrature, as in a two- phase electric circuit. The sum of the two is always a constant quantity. On account of this uniformity in turning effort, the strains on the track are not so severe as in steam practice, and the wear on the reciprocating parts is less. A mechanical difficulty is introduced by the crank and side- rod construction which does not exist in steam locomotives. Both 248 THE ELECTRIC RAILWAY cranks are attached to the same armature shaft and driving wheels. If the parts are not in perfect alignment, the torsional strains in the shafts and connecting rods will be great. In some cases they have been so severe as to shear off the cranks or to break the shafts, while in others the bearings have excessive wear. The obvious remedy is extreme accuracy in alignment of the cranks and bearings; but this calls for careful maintenance, which cannot always be obtained in the ordinary railroad repair shop. 700 til 600 I 500 1 200 & JOO .24 36 48 60 72 Diameter of Wheel, Inches. FIG. 137. Revolutions of driving wheels per mile. Geared and Gearless Motors. The proper speed of the motor armature and of the driving wheels has an important bearing on the design of the mechanical transmission in the locomotive. The electric motor is, in general, essentially a high-speed machine. If it is to be directly connected to the drivers the wheel diameter should be chosen to give the proper armature speed for econom- ical operation. In locomotives for fast service, this is not very difficult. The relation between the diameter of drivers and the revolutions per mile is shown in Fig. 137. At a speed of 60 miles per hr., the revolutions per mile and per minute will be the same. ELECTRIC LOCOMOTIVES 249 With 44-in. drivers, as are used on the New York Central gearless locomotives, the armature revolves at 460 r.p.m. at this train speed. This is a fair value for motors of the size used. Even with 72-in. drivers, as on the Pennsylvania locomotives, the speed is 280 r.p.m., which is not excessively low, since the entire loco- motive capacity is concentrated in two machines. But if similar gearless locomotives were to be used for normal speeds of 20 to 30 miles per hr., the armature speeds would be so low as to be electrically inefficient, and the weight would be excessive for the output. It is apparent that if the normal speeds are to be low, the wheel diameter must be reduced for a gearless locomotive. If the mo- tors are mounted directly on the axles, this will probably be im- possible, since the armature diameter with the high-speed motors is so large that there is little excess clearance above the track. For motors driven through cranks, the wheel size may be reduced somewhat; but since one of the advantages to be obtained by crank connection is the raising of the center of mass, this will lead to an awkward design. The difficulty can be overcome by gear- ing the motors, for then the motor speed may be chosen to give good efficiency, while the wheel diameter may be such as de- manded by the operating characteristics. There are many rea- sons why large drivers are to be preferred. They give more surface of contact between wheel and rail, with consequently greater adhesion. The shocks while climbing small inequalities in the rails, and in passing bad joints, are materially less, and the wear on the wheels themselves is smaller. A gear ratio of 2 : 1 makes possible the use of a motor of, say, 500 r.p.m. with 40-in. drivers at a normal speed of 30 miles per hr. This is within the limits of economy. The application of geared motors for low speeds may be made easily in the swiveling truck designs; or, if it is desired to concen- trate the power in one or two large motors, a combination of gears and side rods may be made, as in Fig. 136. By this means the advantages of high center of gravity may be obtained. While the complication is somewhat greater, it appears to be justified, if one may judge by recent European designs. Number and Coupling of Drivers. An examination of existing designs of locomotives, both electric and steam, shows a wide range in the number of drivers, length of wheel base, and methods of coupling wheels together. The primary limitation of the track 250 THE ELECTRIC RAILWAY is the maximum load which can be safely imposed by a single wheel. The best American practice, with first-class roadbed and track, limits the load per axle to from 50,000 Ib. to 57,000 Ib. These values are extreme, and should be used only when the track construction is the best. This limit will then determine at once the number of driving wheels necessary to give the desired tract- ive effort, if the adhesion coefficient is known. This latter is usually assumed, for purposes of design, at 22 per cent, to 25 per cent. A driving axle load of 50,000 Ib. will then give a maximum tractive effort of 12,500 Ib.; so that the weight on the drivers may be determined. The weight to be carried on the idle axles depends largely on the maximum speed, character of the roadbed, and method of equalization. An inspection of the table on p. 243 shows the American practice for steam locomotives. For electric service the proportion of the weight on drivers may be somewhat greater, since there is no necessity for trailing wheels, which have been introduced in steam locomotive designs to allow an increase in the size of fire-box for large capacities. The number of driving wheels which can be coupled together is limited by the total rigid wheel base permitted. This is deter- mined by the radius of the maximum curves encountered, since the side play in the axle bearings is restricted. The length of rigid wheel base may be increased somewhat for slow-speed serv- ice by making some of the intermediate drivers without flanges; but, on account of danger of derailment at high speeds, this is not to be commended for passenger locomotives. In steam practice, the rigid wheel base will be from 10 ft. to 13 ft. for passenger locomotives, and from 10 ft. to 17 ft. for freight engines. Longer rigid wheel bases have been found destructive, both to the track and to the drivers. In steam service longer wheel bases have been made possible by the use of Mallet articulated locomotives, in which the driving wheels are assembled in two separate units, the forward engine being mounted on a swiveling truck. In electric locomotives, the result may be attained more simply by the use of separate units, operated together by multiple-unit control. Evidence has been introduced to show that the tractive effort which can be developed by a locomotive will be increased if sev- eral driving axles are coupled together. 1 This is to be expected, since there is a certain amount of weight transfer between the 1 ELMER A. SPERRY, Transactions A. I. E. E., Vol. XXIX, p. 1453. ELECTRIC LOCOMOTIVES 251 driving axles during acceleration and retardation. This point has already been considered in connection with train braking. For this reason it would seem advisable, if several axles are mounted on a rigid frame, to couple the wheels together, by means of side rods or by gearing. This action becomes ap- parent only while accelerating or retarding, so that for certain classes of service it may not be of great importance. Interchangeability of Locomotives. In many cases it is de- sirable to be able to use the same locomotive units for both freight and passenger service. When this can be done, the total in- vestment in motive power is decreased, and the necessary repair work Is simplified. The factors affecting the design, as it has been pointed out in this chapter, make it somewhat difficult to build a "universal" locomotive. If satisfactory for slow speed, it may not have the proper riding qualities for fast service; and if properly designed for high speed, it will be excessive in weight and cost when applied to slow-speed work. When geared motors are used, it may be possible to approach the desired condition by using different gear ratios for high-speed and low-speed service, the mechanical design being otherwise the same. This reduces the number of separate parts, but does not make the equipment interchangeable. A compromise may be made in some cases by operating the motors at different potentials for the various classes of service. For instance, on a 600-volt direct-current locomotive, the motors may be placed in parallel for high-speed passenger operation, and in series-parallel for freight service. It must be remembered that the current capac- ity of the motors is not increased by this procedure, so that when running in series each motor is only giving about one-half its normal rating. On roads where most of the trains are in passenger or fast freight service, this method may give satis- factory results. The fact remains that, for the best operating efficiency, the locomotives should be designed particularly for the service they are to be used on; and if a compromise is necessary it must be effected at some loss. Tractors. A recent development in electric locomotive prac- tice is to increase the capacity of the equipment by the use of auxiliary tractors. These, as used on one American railroad, 1 are four-wheeled motor trucks, which are operated in conjunc- 1 Tractor Trucks and Additional Locomotives for Butte 2400- Volt Railway, Electric Railway Journal, Vol. XLIII, p. 1349, June 13, 1914. 252 THE ELECTRIC RAILWAY tion with the locomotives. There is no control equipment on the trucks, but the motors are placed in series with those on the locomotive. The four main motors are wound for 1200 volts, and are operated two in series in normal service. When the tractors are used, the additional motors are connected one in series in each circuit, making three motors in series, and operat- ing at approximately two-thirds normal speed in parallel, and one-third speed when all the motors are placed in series. Each tractor weighs approximately one-half as much as a standard locomotive, so that the drawbar pull is increased 50 per cent, by its addition. Using this method the flexibility of the equip- ment and its total capacity may be considerably extended at a fairly low cost. No operating data have been published to show the success of this arrangement. Locomotive Equipment. The equipment required for electric locomotives is, in general, the same as that in use on motor cars. The principal difference is in the capacity of the motors. The location of the motors determines largely the position of the auxiliary apparatus on the locomotive. When geared or gearless motors are used, mounted directly on the axles, there is the entire space above the main frame available for control equipment. This does not ordinarily take up all the space, so that many locomotives of this class are designed with the so- called " steeple' 7 cabs, as shown in Figs. 131, 132 and 134. When the motors are mounted on the frame, and coupled to the driving wheels with connecting rods, the space left for the apparatus is much less, and the cab is usually built over the en- tire locomotive frame. Such designs are shown in Figs. 133, 135 and 136. The auxiliary equipment which is necessary on the ordinary locomotive consists of the controller, the resistors (if used), air compressor and governor, transformer (for alternating-current locomotives), and the miscellaneous apparatus needed for ease in operation. For use in connection with standard passenger cars, a boiler for supplying steam for heating is a necessity. All of this equipment is comparatively bulky; and in the latest designs the entire cab is filled with it, there being only a narrow passageway on each side. Locomotive Control. Due to the demand for independent units which may be operated together for increased output, practically all locomotives are provided with multiple-unit ELECTRIC LOCOMOTIVES 253 control. On account of the large amounts of power handled, controllers of this type are almost essential in any case, since the capacities of hand-operated ones are not by any means ade- quate. It is interesting to note that in a recent European design, the controller is of the drum type; but this is an exception to the usual arrangement. For heavy locomotive service, the variations in tractive effort which are allowable with motor cars would cause de- structive jerking during acceleration. For this reason the number of steps on the controller is invariably greater. Since the acceleration may need to be varied to suit the requirements of each particular train, automatic control is seldom used, it being considered better practice to place the operation entirely in command of the motorman. With high-class employees, this method gives consistently good results. Choice of Locomotives. It may appear, at first sight, that the selection of the proper type of locomotive for a particular service is subject to exact rules. Such does not appear to be the case. The locomotives of competing manufacturers for almost identical service are so widely at variance that there can be no general agreement; and in some cases the same manufacturer has used entirely different designs for similar conditions. Electric locomotives are still subject to great development; and it is quite possible that they may be standardized. It must be remembered that practically all of them in service have been designed within the past ten years, while the steam locomotives are the development of a century's study. It will not be re- markable if many years pass before the electric locomotive reaches the same condition of standardization as its steam competitor; and it is doubtful if this is desirable, for standardiza- tion on a large scale is liable to mean stagnation. CHAPTER X SELF-PROPELLED CARS Field of Self -Propelled Cars. Any railroad, whether steam or electric, has a comparatively high cost of construction. The gross receipts must be sufficient to cover the operating expenses, and leave enough margin to pay interest on the investment, be- fore any profit can be realized. A certain class of roads exists in which operation by any of the ordinary methods, such as steam locomotives, or electric motors fed from a central power station, will not cover the expense. The steam locomotive, as has been shown, is at its best only in large units; and, if several trains per day are to be run, the cost of operating inefficient small locomotives may be prohibitive. On the other hand, the electric distributing circuit will be as expensive, in many cases, when but one car is run as when service is given every hour. The interest on the investment and maintenance charges will in this case prohibit successful operation. It is for this class of roads that some form of low-cost, fairly efficient service must be given if a railway is to operate at all. Such is the case of many steam-road branches where, in order to develop traffic, the line has been built without sufficient knowl- edge of local conditions. Another instance is that where a rail- road is desired to develop a new territory, but where the return may, for several years, be inadequate to pay expenses. Such a line is usually a feeder to a large steam or electric railway system. In other cases the cost of construction may be excessive. An example of this is the cross-town surface lines in New York City, where the overhead trolley is prohibited by law. To build underground conduit roads of the type used on the main through routes would cost much more than the traffic would justify. In each of these cases the demand is for a cheaply constructed track, and a motive power which will give satisfactory service at comparatively low cost. It is for this reason that the various self-propelled cars have been developed. 254 SELF-PROPELLED CARS 255 Self-propelled cars can also be used during hours of light load, such as at night. With infrequent operation of this sort it may prove economical to shut down the electric power plant entirely, giving the required service with self-propelled cars. In this way the no-load losses incident to a large system may be eliminated, while at the same time an opportunity is presented for inspection and repair to the power plant and substation apparatus. At the present time, there are in use three different types of self-propelled cars, which cover the entire range of service needed. They are the gasoline type with mechanical drive, gasoline with electric drive, and the storage battery car. Gasoline Cars. All of the straight gasoline cars in the United States are of the same general class, being the product of one builder. The first of them were introduced about eleven years ago for use on unprofitable branch lines of the Union Pacific oooooooooo CJ ^-nnnnnnnhFir FIG. 138. 55-ft. gasoline car, mechanical transmission. In this car the front axle is the driver, the engine being mounted directly above. Note the form of the car to reduce air resistance. Railroad. The success met with in this service was so great that cars of similar type have been built for a number of roads in various parts of the country. The gasoline driven cars are of somewhat special construction, as shown in Fig. 138. The forward end is reserved for the power plant, which consists of a 200-hp. internal combustion engine, directly geared to the front axle of the forward truck. Speed control is obtained in the same manner as in the gasoline automobile, by means of gears and a free engine clutch. Varia- tions in the charge and the ignition allow still further .range in the control. 256 THE ELECTRIC RAILWAY The cars which are in operation are from 55 ft. to 70 ft. in length, and are somewhat similar to those for standard electric interurban railways. It is interesting to note that this design of car is the only one in regular service which has taken advantage of the experimental results found in connection with air resistance at high speeds. The front is wedge shaped, while the rear end is rounded. The roof is of the plain arch type, and all of the fittings, such as windows and doors, are so designed as to give the most regular contour possible. The builders claim a mater- ially reduced train resistance due to the construction. Gas-Electric Cars. There are two distinct types of gasoline- electric cars in use in America, both of which embody the same general features. One of the cars of the General Electric Com- pany is shown in Fig. 139, and a similar one, manufactured by the * -v L J L__J L_l L_J l__i LJ LJ 1 J L_J L_J 1 1 L 1 I Kinnnnnnnnnnn? > tooooM l^^ z*\_J 00 FIG. 139. 70-ft. General Electric gas electric car. The gasoline engine drives a direct-current generator from which current is obtained for operating the railway motors. Drake Railway Automotrice Company, is shown in Fig. 140. In either the power plant consists of an internal combustion en- gine, driving a direct-current generator, current from which is used to operate standard 600-volt motors. A special form of series-parallel controller is used, which, instead of inserting re- sistance in series with the motors, varies the field strength of the generator. By this method the control is made more efficient than with the direct mechanical drive; and, since the motors are able to deliver maximum tractive effort at low speeds with corre- spondingly reduced power input, the total capacity of the power plant can be less than for the direct drive. This allows a lighter gasoline engine; but the weight of the entire equipment must necessarily be somewhat heavier for the electric transmission, since a generator and a set of motors must be added. SELF-PROPELLED CARS 257 In practice, the operating costs for the three types of gasoline cars are approximately the same, varying with the severity of the service and the weight of the equipment. Either type is fully capable of hauling one or more trailers when required, so that the apparatus is exceedingly flexible. Storage Battery Cars. The storage battery car is one of the oldest developments in the history of electric traction, being antedated only by those driven by primary batteries. In the early experiments, batteries of the types obtainable at that time were tried and abandoned, largely on account of the great weight of the equipment. The recent improvements in storage battery design and manufacture, due largely to the advent of the electric automobile, have made it possible to obtain batteries having :Ei ,R -UUUUUUUU L V Coach -nnnnnnnrt? UUL \>5moker Baggage Cab FIG. 140. 70-ft. Drake "automotrice." This car is similar to that shown in Fig. 139, but is of somewhat lighter construction. much greater output per pound of weight, with increased life. This development has made their use practical for propelling railway cars with a reasonable efficiency. There are several different kinds of storage battery car in use at the present time, differing principally in the type of cells em- ployed. Both the lead and the Edison nickel-iron batteries are used, and appear to be giving satisfaction. One type of car, following largely the double-truck stepless design of the New York Railways, and in use on the same road, is shown in Fig. 141. In any of the storage battery cars, successful operation depends on having the body as light as possible, since the size of battery to be used is a direct function of the weight hauled. Much at- tention has been paid to this feature, and exceedingly low weights per seat have been attained. In addition, the bearings are of the anti-friction types, such as roller or ball bearings. Since the 17 258 THE ELECTRIC RAILWAY car speeds in the service for which storage battery cars are best fitted are low, the train resistance consists largely of journal fric- tion; and by the use of such bearings it may be diminished con- siderably. Some of the makers go a step further and use a rigid axle with two independent wheels, as in ordinary wagons. It is claimed that this reduces the friction still more, especially on curves. No extended experiments have been made to prove this, and it is possible that the lower friction on curves may be offset by increased oscillatory resistance. There are two different methods of operating the batteries. One maker advises that they be of sufficient capacity to give a D U J i T FIG. 141. Stepless storage battery car. The batteries are placed under the seats. The motors are connected independently to the wheels by chain drive. Friction is reduced by using ball- or roller-bearings. whole day's run without recharging, while others recommend a smaller battery, with a full charge once a day, and short ''boost- ing charges" at the end of each trip. While this latter method allows the use of a battery of less capacity, it does not give such flexibility in service. For instance, if a car is late in arriving at the charging station, it will not receive sufficient charge, and the battery may be exhausted before the day is over, or else the schedule will be disarranged. Trouble has resulted in a number of cases from this cause, and has made it an open question as to which is the better method of operation. The motors for storage battery cars are much smaller than those for standard electric railway service with equipment of equal weight. This is largely due to the fact that the acceleration SELF-PROPELLED CARS 259 and the maximum speeds are low. With high acceleration the size of battery required becomes so great as to render its use impractical. Storage battery cars are controlled by series-parallel connec- tions of the batteries, instead of the motors, although by com- bining the two methods three economical running speeds may be obtained. Otherwise the arrangement is the same as for standard railway equipment. The cars may easily be arranged for multiple-unit control; and in some cases are so operated. Comparison of Self-Propelled Cars. It is evident that the various types of self-propelled cars have different fields of service. Any of the gasoline-driven cars are capable of operation over any length of line, and are limited only by the requirements of ob- taining fuel and having sufficient time at terminals for inspection and repair. Storage battery cars, on the other hand, are re- stricted in action by the amount of charge, and must run only between points where electric current is available. There must be a certain time of inaction during charging, whether it is for a single long period per day, or at the end of each trip. The gasoline drive may be suited to the weight hauled, so that there is no limitation to the size of car which can be equipped with this type of motive power, while the storage battery increases in bulk quite rapidly with the weight. This condition is inherent, and cannot be overlooked in any comparison. It appears that the gasoline drive is best suited to units of comparatively large weight, which must run over considerable distances, and at fairly high speeds. The choice between the mechanical and the electric drives depends on the need for smooth acceleration, and efficient operation over a wide range of speeds. The running expenses are nearly the same for both types; but the first cost of the gas-electric cars is somewhat higher, owing to the greater amount of equipment. They are also slightly heavier for the same capacity. The wide use of gas-electric cars at the present time would indicate that the smoother operation is of sufficient value to warrant the extra cost and weight. Storage battery cars are better for local service where traffic is sparse, or where conditions are such as to prohibit the use of overhead trolleys. It is not to be expected that the use of independent units will ever supersede the ordinary electric railway with a central power plant for general service, for a limit to the field of the self- 260 THE ELECTRIC RAILWAY propelled car is reached with a comparatively low traffic density. This can be determined by calculating the fixed charges and run- ning expenses of the two methods. On comparison it will be seen that the operating cost of any form of self-propelled car is higher than that for standard electric equipment; and the first cost is also greater. As the number of cars in use increases, the fixed charges on the power plant and distribution system become proportionally less ; and when the total cost becomes equal in the two cases, the advantage of the independent units disappears. Actual comparisons show the field of this class of vehicle to be limited to that stated at the beginning of the chapter. For these special forms of service the self-propelled car furnishes a valuable auxiliary to a large railway system, and may increase the earnings or decrease the expense by a considerable amount. Gasoline and Special Locomotives. The arguments in favor of self-propelled cars do not apply with equal force to locomotives, since the steam locomotive is quite satisfactory for nearly all classes of service. The success of the internal combustion motor has led engineers to believe that there is a field for engines of this class, and several designs have been made. At present a few locomotives with internal combustion motors are in service. A road having a small amount of freight business, and operated either by the electric system or by self-propelled cars, may have need of such a unit. The mechanical and the electric drive have both been applied to internal combustion locomotives. One type of the latter, in conjunction with the Diesel crude oil engine, has been used in Europe for some time. In connection with the electrification of the railroads entering Chicago, a proposition was made several years ago to use storage battery locomotives. While there is no question but that such equipment is a possibility, it is extremely doubtful whether it could show sufficient economy in operation to justify itself. Un- doubtedly the total running cost would be much greater than for any standard form of electric system working on a distributing circuit from a central power plant. CHAPTER XI ELECTRIC RAILWAY TRACK Track Construction. Although the requirements of all rail- way track are essentially the same, there are two distinct types of construction used, depending on whether the railroad is laid on private right-of-way or in paved streets. A large portion of all interurban roads are built on private property; and in all such cases the ordinary construction adopted by steam roads can be used to advantage. The rails are of standard T-section, the size being chosen with regard to the amount of traffic and weight of trains. In track construction the primary consideration is good drainage. There should be a well-settled foundation of the natural soil, above which is placed a layer of broken stone or ? /.rj (*- -4-0%-- >f 8p /b. /fair 2 TiesS'xe'xS' FIG. 142. Standard interurban track construction. gravel ballast, from 8 to 12 in. in thickness. On this are placed the cross-ties, and the space between them filled with the ballast, which should be well tamped beneath the ties to secure them firmly in place. With this construction, the porous stone ballast will allow surface water to drain off readily, and so keep the foundation dry. It is necessary to provide ditches along the side of the roadbed, at a level below the bottom of the ballast, in order to drain off the water which has collected on the track. In this way the entire structure will be more permanent and will require less maintenance than where the roadbed has been poorly built. A typical form of railway roadbed is shown in Fig. 142. The ties in use are generally of hard wood, such as cedar, oak or chestnut. At the present time it is somewhat difficult 261 262 THE ELECTRIC RAILWAY to secure a good grade of such materials; and the practice of using soft wood ties, such as pine and hemlock, but impregnated with some preservative compound, has spread rapidly. The chemicals in general use are creosote and zinc chloride. These are applied in liquid form, the ties being treated either in the open air or in vacuum tanks. While the latter process is more expensive, it gives a more uniform application of the preservative, and causes it to sink much deeper into the fiber of the wood. Treated ties are considerably more expensive than untreated ones; but the soft wood, when properly impregnated, has at least as good life as the natural hard wood, and the cost is no greater. When hard wood is treated in the same manner, its life may also be proportionally pro- longed at a comparatively low cost. Indeed, it has been possible to prevent decay to such an extent that the life of the tie is determined by mechanical wear from the chafing of the rails, and the destruction of the fibers by driving spikes. In the older track construc- tion the rails are laid directly on the ties, and are fastened in place by common spikes. The mechanical wear on the ties in such construction is severe, and even untreated ones may be rendered unfit for further service before they have decayed. With the use of preservatives, and the consequent increase in life, many roads have adopted the practice of placing tie plates under the rails to take the wear. Another advance is in the use of screw spikes instead of the common driving spikes. This further increases the life of the ties. Track Rails. The rails in use are of the standard sections adopted by the American Society of Civil Engineers, the American Railway Association, or the American Electric Railway Engineer- ing Association. A section of the standard 100-lb. rail adopted by the latter is shown in Fig. 143. The weights used vary FIG. 143. Standard 100-lb. T-rail. This is the standard T-rail adopted by the American Electric Railway Association. Other sizes are quite similar in shape. ELECTRIC RAILWAY TRACK 263 from about 60 Ib. per yd. to 100 lb., the majority of rails being from 70 to 80 lb. for interurban construction. The chemical composition of rails has a marked effect on their physical properties, and on the results which may be obtained from them in service. Where the roadbed construction possesses sufficient flexibility, the composition may be such that the metal is tough, but fairly soft. For use in paved streets, where the sub- base of the track is rigid, as when laid with concrete, a harder rail, possessing greater resistance to wear, is desirable. The hardness depends to a large degree on the content of carbon, although a number of different elements, such as manganese, titanium, nickel, chromium, silicon, etc., may be added to vary the properties of the steel. In general, since the wheel loads on electric railroads are much less than for steam trunk lines, the composition may be selected to give greater hardness, even though the metal may be more brittle. The recommendations of the American Electric Railway Engineering Association for rail metal are as follows: 1 Elements Per cent. Class A Class B Carbon . 60 to . 75 0.60 to 0.90 Not over . 20 Not over . 04 0.70 to 0.85 0.60 to 0.90 Not over 0.20 Not over . 04 Manganese Silicon Phosphorus Rail Joints. The connection between rails is of vital im- portance. Rail joints are either suspended or supported, de- pending on whether the joint is placed between two adjacent ties or on top of one tie. The forms in common use are numer- ous, and both methods of support are used. The connection between rails is made by means of two plates, known severally as " joint plates," " splice bars," " angles" or "fish plates." These are of special rolled sections and are placed one on either side of the rail ends, being bolted to each rail. The simpler forms, such as shown at (a) in Fig. 144, consist of a pair of plates which are drawn in against the base and head of the rail by bolts. This form of joint may be either suspended or sup- 1 Engineering Manual, American Electric Railway Engineering Associa- tion, Section Wr 2c. 264 THE ELECTRIC RAILWAY ported. The " continuous" rail joint is shown in Fig. 144 (6). In this the plate is continued down beneath the base of the rail, forming a chair. A number of joints of this general design are in use both on steam and on electric roads. Track Construction on Paved Streets. In cities, where the streets are paved, it is necessary to build the track in such a manner as to interfere as little as possible with the surface of the paving. The standard T-rail construction may be used, the paving being laid on top of the ties so as to bring it flush with the head of the rails. Since it is necessary to allow space for the wheel flanges on the inside of the track, special paving blocks FIG. 144. Types of rail joints. (a) Common fish-plate joint. (&) Continuous rail joint. are sometimes used to give the necessary groove. While this is satisfactory where the travel is not very heavy, it is not so good on streets which are much used for heavy teaming. The height of the ordinary T-rails is not sufficient to use standard paving blocks with a cushion of sand deep enough to give good wear. This defect may be remedied to some extent by using special rails with a high web, and having the head and base the same as the standard T-section. In many of the large cities provision is made that the street railway tracks must be available for wagon traffic; in some it is provided by law that a rail of a tram sec- tion, such as that shown in Fig. 145, must be used. In others, where such regulations are not in effect, the railroads have some- times laid rails with a grooved head, as in Fig. 146. This pro- vides no path for vehicles, which is a good thing from the standpoint of the railway. When the tram section of rail is used, it makes an excellent roadway for vehicles, the wheel treads running on the projecting lips of the rails. The difficulty in its use is that if the lip is below the rail head a ELECTRIC RAILWAY TRACK 265 U s" A I- s% 4 FIG. 145. Tram section FIG. 146. Grooved section girder rail. girder rail. Both of these sections have been used to a considerable extent for street railway track, but re now almost entirely superseded by rails of the general type shown in Fig. 147. FIG. 147. 9-in. Girder rail and joint plates. Used in city construction on paved streets. 266 THE ELECTRIC RAILWAY sufficient distance to allow the use of a standard wheel flange, it is hard to get vehicles out of the path of cars, thus delaying traffic. A compromise has been effected by the use of the grooved rail in such a form that the lip is far enough below the head to provide a runway for vehicles, and at the same time make it easy for them to leave the tracks. The design for a 9-in. girder rail with joint plates, as standardized by the American Electric Railway Engineering Association, is shown in Fig. 147. This or similar designs have been adopted in many of the large cities of the country, and have proved satisfactory. Special Forms of Rail Joints. While the various forms of mechanical joints made by splice bars and joint plates are entirely satisfactory in open construction, they must be care- fully maintained and tightened as the bolts wear loose. This requires constant inspection. It is evident that where the track is laid in city streets, and completely surrounded with paving, such care is impossible. It is essential that the joints remain in good condition with no inspection whatever, and that the repairs be very few, since each time one is made it means to tear up and replace the paving around the joint. A method which has been used in many cities is to weld the rail ends together, thus forming a continuous structure. This arrangement cannot be used in open track, since the expansion and contraction will tear the track loose from the ballast with every change in temperature; but in city streets it can be em- ployed to advantage, since the rails can be anchored firmly by the paving, so that the temperature changes can only place the rails in tension or compression. As the rails are usually laid in the hottest days of summer, the track will be in tension for nearly the entire year, and there will be practically no tend- ency to buckle. It is evident that this construction cannot be used to advantage on curves. Cast Welded Joints. There are three methods of track weld- ing which are in general use. The oldest is the cast weld. In this construction, shown in Fig. 148, the rail ends are joined by a mass of cast iron surrounding them. The iron is melted at a high temperature and poured into iron moulds around the rail ends. This chills the outside surface of the cast metal, so that the in- terior has its temperature raised to a welding heat, and an actual weld is made with the steel of the rails. This form of joint is quite satisfactory, the principal objection being that extreme cold ELECTRIC RAILWAY TRACK 207 weather may strain the cast metal beyond its tensile limit and crack the weld. From one to two per cent, fail in this manner. Thermit Weld. Another method of rail welding is by the use of "Thermit." This is a patented mixture consisting of metallic aluminum and iron oxide in proper proportions, with other materials added to obtain a metal of the required composition. This is supplied in the form of a powder, which, when ignited, undergoes a chemical reaction, the aluminum combining with the oxygen to produce alumina and metallic iron at a high tempera- ture. The powder is placed in crucibles directly above the rail joints, which have been previously heated by some external means. The mixture is ignited, and when the reaction is complete the molten iron is tapped into moulds around the rail ends. The weld FIG. 148. Cast weld. FIG. 149. Thermit weld. produced is not unlike the cast weld; but the metal is of a different character, being of the composition of wrought iron or steel, depending on the ingredients of the mixture employed. The temperature of the molten metal is much higher, so that a more perfect weld is obtained, and the amount of iron required is considerably less than for the ordinary cast weld. The appear- ance of a thermit weld is shown in Fig. 149. Electric Welding. The third way of welding is with the aid of the electric current. There are two distinct methods which may be used. In the first, which has the widest application, joint plates are welded to the sides of the rail ends by the incandescent or resistance process. This consists in taking current from the contact line, converting it to alternating current by a rotary converter or motor-generator set, and changing to a low potential through a stationary transformer, whose secondary winding con- sists of a single turn of heavy bar and terminates in jaws which are placed against the parts to be welded. The diagram of con- 268 THE ELECTRIC RAILWAY nections is shown in Fig. 150. The resistance in the secondary circuit is practically all concentrated at the junction between the rail and the joint plate; so that a considerable amount of heat is generated there, and the temperature is raised to the welding point. By applying a suitable pressure to the jaws, an actual union of the metals is obtained. The entire rail section is not welded; but two or three places on the end of each rail suffice to make a more permanent connection than is possible with any of the usual forms of mechanical joints. D.C. Trolley m- I U U Primary f I /^^4~X X~f the contact rail varies somewhat. the contact surface is the top of the rail. In this type of con- struction, Fig. 164, the rail is mounted on insulators of porcelain, reconstructed granite, or other suitable material. An ordinary rail section is most often employed, although in a few cases special designs have been used to reduce the cost of manufacture and to give a rail more readily mounted. Many persons look on the third rail as a source of danger, due to the possibility of accidental contact from persons working along the track. To prevent such occurrence, it has become customary to "protect" the rail by making the metal inaccessible. At the same time, the contact surface must be kept free for the passage of the collector. It is quite difficult to effectively protect the third rail where the top contact is used. A number of devices, such as the mounting of boards parallel to the rail, at one side and above it, have been tried with indifferent success. Forms of THE DISTRIBUTING CIRCUIT 289 protection are shown in Fig. 165. A trouble with the unpro- tected rail is that it is liable to have a thin coat of ice form over its contact surface during sleet storms. This film, although some- times very thin, is a good insulator, and occasionally prevents train movements entirely. Various methods have been tried to combat the difficulty. Some roads use steel scrapers attached to the trucks, passing over the rail surface ahead of the contact shoes. Others spray the rail with an ice-resisting liquid, such as FIG. 165. Forms of protection for over-running third rail. These are used to prevent accidental contact of persons walking along the track with the live conductor. salt or calcium chloride solution. The first expedient is not entirely successful, and the second may affect the insulation. Under-Running Third Rail. In order to more completely protect the third rail, and at the same time to lessen trouble from snow and sleet, the under-running contact has come into use in the last few years. The rail is suspended from hangers, as shown in Fig. 166, with insulation at the supports. It is a simple matter to protect against ordinary accidents by cover- FIG. 166. Under-running third-rail construction. ing the top surface with a wooden trough, or with a special clay tile. Sleet does not form so easily on the under surface of the rail, and little or no trouble has been experienced from this source. The principal objection to the under-running third rail is that it encroaches more on the clearance limits of ordinary rolling stock; so that, unless special care is taken to eliminate cars having parts outside the clearance limits, fouling will re- sult, with consequent interruption of service. 19 290 THE ELECTRIC RAILWAY In some cases rails of the same chemical composition as the track rails are employed; but frequently they are made of a special composition selected to give maximum conductivity. The principal point is to have a soft steel, with a minimum amount of impurity. Such a composition would be too soft for a running rail, but its conductivity can be increased from one-third to one-half above that of the rail steel; and its hardness is sufficient to stand the wear that is produced by the rubbing of the contact 0-02. 50 60 70 80 90 Weight, Pounds per Yard 100 no FIG. 167. Resistance of rails with bonds. shoes on its surface. The resistance of rails, complete with bonds, is shown in Fig. 167. With the third rail, the conductivity, even for comparatively light cross-sections, is so great that little additional feeding capacity is needed, except on very heavy systems. Underground Conduit Systems. In a few cities, the opposi- tion to the overhead trolley for esthetic reasons has been so great that it has been absolutely prohibited. In the United States the only instances are New York and Washington. In these cities it has been necessary to furnish electric street railway service without the use of overhead construction. The third rail, as THE DISTRIBUTING CIRCUIT 291 ordinarily used, is of course out of the question for use on city streets. Two alternatives remain : to place the conductors under- ground, contact being made through a slotted conduit, or else by a system of surface contact. Both have been tried, but the former has been used to the entire exclusion of the other. Plaster / 7 Girder Rail Scoria Block Plaster l &T Class ..- Concrete Section A- 5 Section C-D FIG. 168. Underground conduit system. In the underground conduit system, as installed in the two cities named, the conductors are placed in a continuous trough or conduit, as shown in Fig. 168. They consist of two T-rails, one positive and one negative, the track not being used for a con- ductor. These rails are entirely insulated from the ground by 292 THE ELECTRIC RAILWAY porcelain insulators. Connection is made to the car equipment through a detachable plow, which is carried on one of the trucks, and has on its lower end a pair of shoes making contact with the two conductor rails. This system has given excellent service where it is used, both in the United States and abroad; the principal objection is the very high cost of installation. Surface Contact Systems. From time to time, experiments have been made with systems of current supply which do not depend on overhead wires, and are less expensive to install than the underground conduit. These " surface contact" systems all operate by having a series of contact studs, insulated from the ground, but placed practically flush with the street surface. These studs are normally not in the feeder circuit; but. may be connected by a series of magnetic or of mechanical switches, operated automatically by the passage of a car in such a manner that only those studs under it are energized. Current is col- lected by some form of shoe or "skate" of metal connected to the car, and rubbing on the contact studs. Owing to the great difficulty of maintaining the insulation of the studs, and keeping in operation a large number of auto- matic switches, the failure of any one of which will either leave the car stalled or else allow a live contact to remain unpro- tected, the systems of this type have never been popular. Al- though there are a few lines of surface contact road in opera- tion, its use is not being extended; and in nearly all of the places where it has been tried it has been abandoned in favor of the overhead trolley or of the underground conduit system. The Return Circuit. In a constant potential circuit, the electrical relations are the same on either side of the line. When the system is ungrounded, the conductors may be made the same in cross-section, and the drop in potential will be evenly dis- tributed. This is the case with the double-trolley construction, which is used in a few places in this country and abroad, and in the underground conduit system as installed in New York and Washington. In these the outgoing and the return circuits are made identical, and the losses are evenly divided on the two sides. There is no reason, save for convenience, why they should be thus distributed. Use of Rails as a Conductor. In any railway, it is necessary to use rails of iron or steel for the track. Even in the lightest section, these form an excellent conductor if properly connected THE DISTRIBUTING CIRCUIT 293 together, and, if there is no objection to operation on a grounded circuit, furnish a simple means of obtaining one of the main conductors of the electric system. The contact between the rail and the electrical apparatus on the car is universally made through the wheels, the motors and other equipment being grounded to the axles. In this way a moving contact at least equal to that between the contact line and the collecting device can be maintained without expense. Track Bonding. In order to utilize the track for one of the main conductors, it is necessary that a complete electric circuit be maintained through it. Although ordinary track, when newly laid, may be a fairly good conductor, it deteriorates rapidly through rusting at the rail joints, and the resistance be- comes so high that the loss is excessive. To prevent this con- FIG. 169. Chicago type unprotected rail bond. dition arising, it is customary to make a permanent electrical connection between the ends of each pair of abutting rails. This process is known as "bonding" the track. The early electric roads were operated without bonding, until it was found that the power stations could not supply enough energy to properly drive the cars. On discovering the cause, bonds of iron wire of light section were used; but these did not make the track resistance low enough for successful operation. They have been superseded by bonds of copper wire or flexible strap, permanently fastened to the rails. The simplest type of bond in use consists of a piece of heavy copper wire, riveted through holes drilled in the rails far enough from the ends to make the connection outside the splice bars. This type of bond is fairly satisfactory, but in practice it has been found better to use a special terminal on the wire, as shown in Fig. 169, which can be expanded into the holes in the rails, instead of riveted. This makes a better mechanical connection, and prevents the entrance 294 THE ELECTRIC RAILWAY of water into the junction, so that there is less liability of rusting and deterioration of the bond. Bonds of this type are open to a serious commercial objection, in that they are a constant tempta- tion to copper thieves. To prevent this trouble, bonds are more frequently installed beneath the splice bars, where they are pro- tected. A bond of this type is shown in Fig. 170. FIG. 170. Protected rail bond. A type which has been used to some extent is the soldered bond. This is held to the rail by soft soldering, so that no drill- ing is required. It is difficult to solder coppper to steel, and there is always danger of imperfect joints, which will break after a short period. On this account it has not been very popular. A method of bonding which has met with considerable favor is to weld the bond terminals directly to the rails, by a method like , ... Electricalfy drated Joints y \ "-. FIG. 171. Electrically welded bond. The soldered type bond is precisely similar in appearance; the difference is that the joints between the rail and the bond are made with soft solder. that used for resistance welding of track. The equipment is almost identical, but is of smaller capacity. The connection is very similar to a brazed joint, and can be made entirely permanent if care is used. This type of bond (Fig. 171) is not subject to deterioration as with the expanded terminal type. It is some- what more expensive to install; and, like the track weld, must be done by special machinery. If a bond fails after the welding THE DISTRIBUTING CIRCUIT 295 equipment has been removed replacement is difficult; otherwise it is exceedingly satisfactory. Resistance of the Return Circuit. When the track is used as the return circuit, it is important to know its electrical qualities. Ordinary steel has a conductivity of about one-twelfth that of copper, so that a rail weighing 100 Ib. per yd. has a resistance of about 0.05 ohms per mile; and, since there are two rails which may be placed in parallel in each track, the total per mile is 0.025 ohms. To this must be added the resistance of the bonds. These are about equivalent in section to a 4-0 copper wire, but there is a certain additional loss in the contact between steel and copper. While the total resistance of bonds varies greatly, being least for the welded type, it may ordinarily be taken as about 0.005 ohms per mile of single rail, with joints every 30 ft. This makes the total resistance per mile of single track, laid with 100-lb. rails, about 0.0275 ohms. For other weights of rail, the values will be proportional, except that the effect of the bonds is con- stant. The resistance of the two rails of a track, with ordinary bonding, as a function of the weight, is shown in Fig. 167. In case the bonding is not well maintained, the track resistance may be materially greater. Reactance of Rails. When alternating current is employed for the propulsion of trains, the track being used for the return conductor, an additional effect is noticed. There is an extra drop in the circuit due to the reactance of the rails. These, being of a magnetic material, have a relatively high inductance, and also cause "skin effect" even with fairly low frequencies. The values which have been obtained in tests on the flow of alternating current in rails are not entirely satisfactory, al- though a great deal of experimental data has been taken. The best results published are probably those of the Electric Railway Test Commission. 1 The reactance changes with the current carried, due largely to variations in permeability. In any case the "apparent resistance" (impedance) is several times the true resistance of the rail when transmitting direct current. Defects in the Return Circuit. The conductivity of good track is so high that there is a comparatively small drop in potential in carrying the current. In a single track with 100-lb. rails this is but 2.75 volts per mile per 100 amp. With this value, 1 Report of the Electric Railway Test Commission, Chapter VI, p. 387; McGraw Publishing Co., New York, 1906. 296 THE ELECTRIC RAILWAY it is evident that very little, if any, additional feeder capacity is required unless the load is exceedingly large. But if there are a few bad bonds in the track, all the current may be forced to flow through one rail, thus increasing the drop. To obviate this difficulty, it is customary to cross-bond the rails at frequent in- tervals by connecting jumpers to them, as shown in Fig. 172. With this arrangement the distance the current will have to flow through one rail alone is limited to the portion between cross- bonds containing the bad connection; and, if there are several open bonds in the track, the chances of its electrical continuity being broken are very much reduced. The result of increased resistance of the track circuit is seen at once in the greater loss. The value of the energy may be measured in dollars and cents; and only a little calculation is needed to show that it is financially the proper thing to keep the return circuit in first-class condition. rCro&s bonding Track Kails \ ^ Copper Feeder Buried in Roadbed ' r * Track Kails ' Cross / Bonding '' FIG. 172. Cross bonding with return feeder. Electrolysis. There is another disadvantage from having a high resistance, which is even more serious, and which cannot be directly measured in the money cost. This is the damage to property caused by electrolytic action. The track is normally partially insulated from the earth, especially in dry weather; but it must be considered as a grounded circuit at all times. Since the track is in connection with the soil, either partially or completely, the latter becomes an electric conductor in parallel with the rails. Its resistance is high, but not enough so to prevent some current flowing through it. If this can be determined, it is possible to calculate the proportion of the current which will flow through the ground; but local condi- tions vary so greatly that it is difficult to compute it accurately. The use of the earth as a conductor in parallel with the track is not inherently a disadvantage, since the effect is to increase the conductivity of the return circuit, but the difficulty lies in controlling the path of the current as it flows through the ground. THE DISTRIBUTING CIRCUIT 297 Earth conduction is electrolytic in its nature. The soil consists of inert matter, holding a certain proportion of metallic salts which may be in solid form, and a content of water, more or less impregnated with solutions of salts. When current enters the earth, the effect is to eat away the metal; and where it leaves the ground, a metal or hydrogen will be deposited. If the earth circuit were made up of an iron salt, the effect would be to dissolve a certain amount of iron from the rail at the point where the current enters the ground, and to deposit an equal quantity of iron where the current leaves. This would result in a certain weight of metal being worn away from the rails at definite points, which, although a serious matter, concerns no one but the railroad company. The deposition of metal on the rail at another place would have but little effect, since it could not aid the rail section to any extent. The main difficulty with earth conduction is that in cities there are many lines of pipe and cable running parallel with the railway tracks, buried beneath the paving of the streets through which the tracks run. Such lines furnish a conducting medium which is superior to the earth; and the effect is for the current to be diverted to them whenever there is any tendency for it to leave the rails. A pipe line lying parallel to the track in- creases the ability to take current from the rails in proportion to its conductivity, so that the tendency to have current flow through outside paths is increased greatly by the presence of such conductors. When the current does flow through them, the same phenomena occur as when it leaves the rail. At the point where the current enters the conductor there is a deposit, usually of hydrogen, and where it leaves, the metal is eaten away. The amount which will be eaten is a function of the current and the time. One ampere, flowing continuously for a year, will dis- solve 13.4 Ib. of iron in the ferric state (trivalent), 20.1 lb. of ferrous (bivalent) iron, or 74.5 lb. of lead. Corrosion is likely to take place to a greater extent than indicated by these values, since the electrolytic action will induce natural corrosion by the salts in the soil. The effect is rendered more serious since the tendency is for the current to cause deep pits in the metal, some- times eating through pipes in a few spots when the remainder of the surface is but slightly affected. Remedies for Electrolysis. Since the track is earthed, and the ground furnishes a path in parallel with the rails, it is not 298 THE ELECTRIC RAILWAY possible to entirely eliminate electrolytic action so long as they are employed for a conductor. The only absolute preventive is to use an insulated return circuit. In that case electrolysis cannot exist. But the excellence of the track as an electric conductor makes it most desirable to employ it for conducting the current. There are several methods for mitigating the effects of electrolysis, while at the same time permitting the use of the rails as part of the electric circuit. The simplest way of preventing electrolysis is to cover the parallel lines of pipe and other conductors with a protective coat- ing, which, if it could be thoroughly applied, and be permanent, would be a most effective remedy. Unfortunately, it is not possible to commercially cover pipe with a perfect coating; and, even if a proper coat could be made, it would be subject to deterioration in contact with the soil. The general method of failure of such a form of protection is by its breaking in a few places. This has the effect of localizing the electrolysis, causing more rapid destruction at such points than if no coating were used. Another method which has been advocated to some extent is to break the pipe into sections by the use of insulated joints. This makes it a much poorer conductor than otherwise. With this arrangement, the current has a tendency to follow the pipe as far as it is a continuous conductor, and to pass into the earth around the insulated joint and back into the pipe, thus causing electrolytic action at such points. These joints are somewhat expensive, and this method of protection is only good in com- bination with others. Since the current inherently seeks the best conductor, and hence tends to follow a pipe line, an effective remedy should be to make the pipe as good a conductor as possible, by bonding the joints, and attaching it to the rail at suitable points. This is often referred to as the "pipe drainage system." This makes the pipe line an integral part of the electric circuit, and eliminates the chance of electrolytic conduction. It leads to much greater currents in the pipes than when no connection is used, and may have injurious effects if, for any reason, a bond is broken. In such an event the electrolysis is locally much worse than if no remedy is used. The effectiveness of the pipe drainage system is considerably improved if a series of negative feeders is installed to aid the THE DISTRIBUTING CIRCUIT 299 rails. This tends to remove the injurious action when a single bond is defective, and to reduce the drop of potential in general, as shown in Fig. 173. In any case it is difficult to determine the proper feeder capacity, since the entire circuit is grounded, and the calculation of the drop through parallel circuits is involved. In order to have this method of protection effective, all pipes which are in the immediate vicinity of the railway track must be connected to it, and must be electrically continuous. If this is done, there is some additional danger to other pipes which are not connected to the return system. Jo Trolley 1 Substation To Negative Bus Track. Kails Pipe Line Cross foncf Track Rails Distance from Substation FIG. 173. Potential drop with pipe drainage system. This arrangement is used for prevention of electrolysis in a number of large city systems. It is evident that any method of protection which reduces to a minimum the difference of potential between points in the track will lessen the tendency for current to flow in paths ex- terior to the regular circuit. Such a condition can be obtained by the use of insulated track feeders, proportioned in a manner similar to the feeding system for the distributing circuit. If the number and resistances of such feeders be properly chosen, the difference of potential between various points can be re- duced to any desired value. In order to have such systems ef- fective, the feeders must be entirely insulated from the rails except at the points of connection. In certain cases, if, the track is tied to the generator at the station with a short, low-resistance cable, it may be necessary to use feeders to other parts of the 300 THE ELECTRIC RAILWAY system which are larger than warranted by the economics of the situation. This may be obviated by removing the direct con- nection at the station entirely, or by increasing its resistance until the desired effect is obtained (see Fig. 174). If some of the feeders are long, boosters may be inserted, as is sometimes done in the distributing circuit. All of the above methods have been used for the mitigation of electrolysis. At the present time there is no general agree- ment that one is decidedly better than the others. The two which have been used to the greatest extent are pipe drainage and To Trolfey Substation Jo Negative Bus Track Raif& Track Raife Insulated Feeder I FIG. 174. Potential drop with insulated negative feeders of correct resistance. This method of electrolysis mitigation is recommended by the United States Bureau of Standards. the insulated feeder system. A possible solution is the com- bination of these two. Polarity of the Direct-Current Circuit. Until now nothing definite has been said about the proper direction of current flow in -direct-current railway systems. So far as electrolytic effects go, either the positive or the negative terminal of the generator may be connected to the distributing circuit; for, if any current goes out of the rails, it must return at some other point; and it is where the current leaves the metallic conductor that the destruc- tive effect occurs. There is this difference: if the distributing circuit is connected to the positive terminal of the generator, the electrolysis of the rail will occur at the point farthest from THE DISTRIBUTING CIRCUIT 301 the station, and of the pipes or other structures nearest it ; while if the distributing circuit is connected to the negative pole, the pipes will be attacked farthest from the station and the rails will be affected at the point near it. Apparently, since the amount of metal dissolved is a function of the current, there is no inherent difference in the two methods of connection. Experience has shown, however, that the current flow to or from the rail at the points far from the station will be distributed over a consider- able distance, while nearby it will be concentrated in a short space. Since electrolysis of the rail only affects the railway com- pany, it is the pipe line which must be protected; and it is easier to inspect a short length of pipe in the vicinity of the station, and renew it when necessary, than to take care of a long sec- tion at an indefinite distance. For this reason, all electric railways have for many years adopted the practice of making the rail circuit negative, thus localizing the damage. With a better understanding of the causes and results of electrolysis, more effective remedies have been developed, so that the need for keeping the same polarity is less; but in the intervening time the practice has been so standardized that it is in universal use where direct current is employed for train propulsion. Alternating Currents and Electrolysis. The above discussion on electrolysis has been confined to a consideration of the effects of direct currents. A number of experiments have been con- ducted to determine whether similar results are obtained when alternating currents are used for train propulsion with a grounded return. Up to date the indications of such tests have been negative, there being no evidence that any electrolysis results from the alternating-current circuit. This would naturally be the case since the reversal of the current is so rapid that, even if metal should be dissolved in one alternation, it would be re- placed on the electrode during the succeeding half cycle. Natural Corrosion. In making tests to determine the exact amount of electrolytic corrosion it is difficult to obtain accurate results. Any practical tests must necessarily mean leaving metal plates in the soil, exposed to the action of the electric current. Under such conditions there is invariably some action due to the natural corrosion of the metal in contact with the earth salts. Some recent tests 1 indicate that the rate of corrosion under such 1 E. M. SCOFIELD and L. A. STENGER: "Corrosion of Metals in Natural Soils," Electric Railway Journal, Vol. XLIV, p. 1092, Nov. 14, 1914. 302 THE ELECTRIC RAILWAY circumstances is much greater than was formerly imagined. Corrosion may be due to impurities in the metals in contact with the soil. Different soils have diverse activities in corroding metals; and sometimes when two kinds of soil are in contact with a single piece of metal the corrosion is increased over that in a homogeneous earth. The corrosion noted in some tests is suffi- cient to explain fully all the phenomena observed in connection with what is supposed to be electrolysis from current passing through metals in contact with the earth. Special Methods of Feeding. At various times, special methods of feeding have been suggested, and some of them have been used in a few cases. A favorite suggestion in the early days of electric railway history was to use the two contact wires of a double-track road as the two outside lines of a three-wire system, the track being the neutral. The arrangement of circuits is Amp ' s ?*?'* Trolley? '"Generators in Series or Three -rtlre Car on '" (xnera-hr Track I \ \ 200 Amp. Car -on. ... Track 2 IT \ 159 Amp Track 1 I < . + 50 Amp. Cross- bond --r^r Track 2 T - ->- 150 Amp. FIG. 175. Three-wire distribution system. In this system the two trolley wires are made the opposite sides of the circuit, and the track the neutral. Note that the current flowing through the track is considerably smaller than that in the trolley wires. shown in Fig. 175. By this means the current flowing in the track would be reduced to that necessary for supplying the unbalance of the system, and electrolytic effects would be eliminated. In a three-wire system, the neutral carries but a small current, and hence its size may be much less than that of the outside wires. The effect of making the rail the neutral is to almost entirely lose the advantage of its high conductivity as an aid to the distributing circuit, so that the decrease in the amount of copper required over the two- wire system with grounded return is quite small. The extra complication of the contact conductors, requiring those of opposite polarity to be insulated from each other, makes cross- ings and switches difficult to lay out, and necessitates the use of THE DISTRIBUTING CIRCUIT 303 special insulators. Further, it makes the connection of all the overhead lines into a single network impossible, and may prevent the operation of a damaged section by feeding from adjacent parts of the circuit. The use of higher working potentials has been advocated for many years, and there has been a notable advance in this respect. The first electric railways were operated on 100 volts, or there- abouts; from that time a rapid increase was made until 450 volts was used on the Richmond road in 1888. That potential was adopted as being the highest for which a practical direct-current generator could be built. Since that time the increase has been slower, but the pressure has gradually been brought up to 600 volts, which is now almost a universal standard. In some few in- stances roads have been built for pressures from 650 to 750 volts, which, until a few years ago, represented the limit of commutator design. Quite recently, the possibility of using two or more commu- tators in series has been exploited in the so-called "1200-volt" system, which in its original conception contemplated the use of two standard railway motors, insulated for the higher potential, connected permanently in series on a 1200-volt circuit. The generating equipment similarly consisted of two standard 600- volt machines in series. The effect of this increase of line poten- tial is to reduce the amount of distribution copper for the same loss in inverse proportion to the square of the potential; so that for two lines of equal capacity, one for 1200 volts would require but one-fourth as much copper in the distributing circuit as the other at 600 volts. Better knowledge of commutation and the use of interpole machines has made possible the construction of motors and generators carrying 1200 volts on a single commu- tator, so that the apparatus has been simplified. Further than this, it has allowed the placing of two of these machines in series on a 2400-volt circuit. Further increases in the contact line potential depend on the development of motors adapted to commutate high pressures. It is interesting to note that the most recent installation, that of the Chicago, Milwaukee and St. Paul, contemplates the use of two direct-current motors in series on a trolley at a potential of 3000 volts. Laboratory tests involving the use of still higher potentials show that such increases are within the limits of possibility. 304 THE ELECTRIC RAILWAY When alternating current is used on the contact line, there is no definite limit to the pressure that can be employed, for lower- ing transformers give any desired potential for the operation of the equipment. The limit is then only in the pressure for which the contact line and the collectors can be insulated. Pressures of 11,000 volts to 20,000 volts are now being used, but there is no reason why they should not be increased if found desirable. CHAPTER XIII SUBSTATIONS FOR ELECTRIC RAILWAYS Historical Sketch of Development. Early electric railways had the simplest of electrical circuits. The generators pro- duced directly the e.m.f. required for operating the car motors, and fed into the contact line, usually without the aid of an auxiliary feeder system. This arrangement has the sole ad- vantage of simplicity. In every other respect it is deficient. With the growth of electric railways, it was soon found that the limitations imposed by this arrangement were serious. At the outset, the efficiency of the distribution became low, on account of the excessive fall of potential in the contact line. The obvious remedy was to increase the area of the conductor, but this has the effect of augmenting the fixed charges on the investment. In the larger systems, an attempt was made to improve the economy without excessive cost of distribution copper by using a number of independent power stations, located at such points as would cut down the length of circuit fed from any one of them to a minimum. While this made a decided improvement in the economy of the system, the result was to have a number of small and relatively inefficient plants, each operating at a low load factor. Various arrangements to better this condition were tried, such as the use of boosters on long feeders; but these remedies did not get to the root of the trouble. The beneficial effects on the distribution circuit of the use of higher potentials was early demonstrated; but it was not found possible to increase the capacity of a single commutator beyond a limiting e.m.f of about 550 to 650 volts. This was (and still is, for some classes of railway service) the maximum potential that could be applied successfully to the contact line. The diffi- culties of distribution were found greatest in interurban roads, where the length of feeder circuits and the concentration of the load in a few scattered units made the problem exceedingly difficult to handle. In order to get away from the limitations imposed by direct generation at the contact line potential, the 20 305 306 THE ELECTRIC RAILWAY use of a separate generating and transmission system working at a pressure considerably higher than that of the distribution circuit was tried fairly early in the history of electric railways. This furnished a solution of the problem which has been entirely satisfactory except for the complications involved, and is now universally used for most classes of electric railways. Complex Distribution Systems. The use of a high-tension transmission circuit with a low-tension distribution system requires the introduction of some form of transforming ma- chinery into the electric circuit, resulting in a great flexibility not possible with direct generation. Generally speaking, there are four possible combinations which may be made, as follows: 1. Generation of alternating current, and distribution as alternating current at the same frequency. 2. Generation of direct current, and distribution as alter- nating current. 3. Generation of direct current, and distribution as direct current. 4. Generation of alternating current, and distribution as direct current. Of these four possible combinations, all except the first re- quire the use of some form of rotating converting machinery (with the exception of the mercury vapor rectifier). The use of the first combination is limited to those roads using alternat- ing-current equipment on the cars and locomotives, and for this class of service is almost universally employed. The second and the third methods contemplate the use of high-tension direct-current transmission. At the present time there is but one system available for this form of transmission, the Thury system. This consists of the use of a number of con- stant-current machines in series, both at the generating and at the receiving ends of the transmission line. The motors at the receiving station drive ordinary generators of the constant- potential type, designed for the distributing circuits on which they are to operate. In Europe, several transmission lines of considerable length, and working at maximum potentials of over 50,000 volts, are in service. The system is extremely simple, but is limited in application on account of its lack of flexibility. The second combination would be available for the operation of alternating-current roads, but on account of the SUBSTATIONS FOR ELECTRIC RAILWAYS 307 ability to employ stationary transformers in the first method, that is invariably used in practice. The third combination is rarely seen. The fourth method of transmission is the one of widest applica- tion, since it allows the use of standard alternating-current machinery for the transmission circuit, and standard direct- current apparatus on the distributing system. The conversion from alternating current to direct can be made in a number of ways, as explained in this chapter. Types of Converters. At the present time, there are several methods available for the conversion of alternating current into direct current. They are: 1. The motor-generator set. (a) Using a synchronous motor. (b) Using an induction motor. 2. The synchronous (rotary) converter. 3. The induction motor-converter. 4. The permutator. 5. The mercury vapor rectifier. 6. Various types of mechanical rectifiers. The motor-generator set, the motor-converter, and the permutator, give direct-current potentials which are inde- pendent of the alternating e.m.f. The alternating-current wind- ing may be constructed for any desired potential within the limits of the machine insulation, while the direct-current side is arranged to give any standard potential desired. The syn- chronous converter, the mercury vapor rectifier, and all the types of mechanical rectifiers, are limited in their design to a fixed ratio between alternating and direct e.m.f. 's. The latter must therefore be used in connection with lowering transformers to give the desired direct potential. Motor-Generator Sets. The simplest and most flexible type of converting machinery is the motor-generator with an induc- tion motor, shown diagrammatically in Fig. 176. The two ma- chines are mounted with their rotating members on a common shaft, but are in all other respects independent. The induction motor is usually of the squirrel-cage type, since the starting duty is not heavy; and it operates at high efficiency and practically constant speed over the entire range of load. The direct- current generator may be of any standard type, and wound 308 THE ELECTRIC RAILWAY for the contact line potential. It can be equipped with a shunt or a compound field winding; and constant potential regulation may be effected either by the compounding of the series field or by the use of an automatic regulator. Three-Phase Supply FIG. 176. Induction motor- generator set. In some cases a shunt-wound generator, with a potential regulator, may be used instead of the compound-wound generator illustrated. The objections to the induction motor-generator are chiefly its high first cost, low efficiency as compared with other forms of converters, and the comparatively large lagging current which is taken by the induction motor. Three -Phase Supply fxcifcr Synchronous Motor D. C. Oenerafor FIG. 177. Synchronous motor-generator set. The synchronous motor is occasionally excited from the direct-current generator when a supply of direct current is available for starting, or when a self-starting motor is used. The synchronous motor-generator, shown in Fig. 177, removes the objection of low power factor, which is inherent to the in- duction motor. Exciting current is most frequently taken from SUBSTATIONS FOR ELECTRIC RAILWAYS 309 a separate direct-current generator, usually mounted on the same shaft with the main machines, although in some cases direct current from the main generator is used for excitation. By varying the exciting current the power factor may be con- trolled within certain limits. The cost, weight and efficiency are approximately the same as for the induction motor generator. Synchronous Converters. The synchronous converter, in effect, combines the armatures of the two machines of the synchronous motor-generator set. By so doing, the e.m.f. obtained at the brushes is a fixed function of that led into the machine from the alternating-current side, making independent regulation of the direct-current pressure impossible. Various devices may be introduced to remedy this defect, the simplest of which is the use of a series-wound synchronous booster, through which the alternating current must pass. By exciting the field of the booster with the line current of the direct-current side, an additional e.m.f. is added to or subtracted from the potential delivered by the transformers. Another method of regulation is the use of the split-pole converter, in which the ratio between alternating and direct e.m.f.'s may be varied by changing the wave from within the converter armature. Neither scheme is used in practice to any extent for railway service, but they are valuable in connection with industrial applications. The usual method of regulation is to put a series winding on the converter field, as shown in Fig. 178, similar to the ordinary series field winding used on compound direct-current generators. In connection with such a winding reactance coils, through which the main current is drawn, are placed on the alternating-current side. The shunt field rheostat is set so that the converter draws slightly lagging current at no load. With increase in load, the series turns of the field winding cause over-excitation, making the current lead the e.m.f. When this leading current is drawn through the inductance of the machine, the transformers and the reactance coils, a reactive drop is produced which adds to the potential delivered from the circuit. By properly pro- portioning the series winding and the reactance coils, the potential on the direct-current side may be regulated. In large systems, where too much leading current is objection- able, the e.m.f. supplied the alternating side of the rotary converter is varied by some standard form of potential regulator, such as the induction regulator. This method may be used alone, or in 310 THE ELECTRIC RAILWAY combination with the series winding on the converter; so that both the direct e.m.f. and the power factor of the alternating- current circuit may be governed at will. The arrangement is similar to that shown in Fig. 178, except that the regulator replaces the reactance coils. The early rotary converters were all built for comparatively low frequencies, most of them being for 25 cycles. Recent im- provements in design, especially the use of interpoles, have made the performance and the cost of 60-cycle synchronous converters practically on a par with those for lower frequencies. Three-Phase Supply FIG. 178. Synchronous converter with regulating reactance. The reactance coils may be replaced with an automatic potential regulator. The Motor-Converter. The motor-converter, or " cascade- converter," is an application of the same principle as that used in cascade control of induction motors. It consists, Fig. 179, of a primary winding like that for an induction motor, and a secondary of a type similar to that of the phase-wound motor, the principal difference being that the converter is ordinarily designed for a larger number of phases. The secondary winding is tapped directly into the armature of a machine electrically the same as the synchronous converter. As in cascade operation of motors, the motor end and the converter end of the set may each have any number of poles; practically they are wound for the same number. For starting, the secondary winding of the induction machine is brought out to collector rings, through which it may be short-circuited with resistance. SUBSTATIONS FOR ELECTRIC RAILWAYS 311 In operation, the set runs at half the speed of the primary field, the frequency in the secondary being half that of the line; while the converter operates as though in synchronism at the secondary frequency. Half of the power is transmitted directly through the secondary winding, while the other half is delivered through the shaft. The size of the set is therefore decidedly less than for a motor-generator of equal rating. The efficiency is considerably better than that of a motor-generator, but slightly less than of the ordinary rotary converter. Synchronizing is extremely simple, consisting in adjusting the starting resistance until the machine falls into step. The starting current is small; but, on the other hand, the magnetizing current is drawn directly from the line, as in an induction motor, so that the power factor Three -Phase Supply FIG. 179. Induction motor-converter. The induction motor end and the converter end of the converter are usually assembled within one frame; this is not shown in the diagram. is not so easily controlled. Over-excitation of the direct-current field will, however, reduce the quadrature component of the primary current. While the motor converter had, at the time of its introduction, considerable superiority over the synchronous converter for operation at high frequencies, recent improvements in the latter have placed the two machines about on a par in this respect. When the motor converter can have its primary wound for the line potential, without the use of lowering transformers, there is little difference in first cost; when transformers are required, the motor-converter will be more expensive. Its greatest advantage is the small amount of attention needed for operation, as compared with the synchronous converter. 312 THE ELECTRIC RAILWAY The Permutator. If the secondary winding of an induction motor is held still, current will be generated in it at the frequency of the primary circuit, and at an e.m.f. equal to that of the pri- mary, multiplied by the ratio of transformation. If the second- ary winding be connected to a commutator of the ordinary type, and a set of brushes rotated thereon at synchronous speed, direct current can be taken off and used for any purpose. A machine embodying this principle, known as the permutator, has been used for several years in Europe for converting alternating cur- rent into direct. In its construction, the parts may be arranged similarly to those of the induction motor; but, since there is no relative motion between them, no air-gap is necessary, and by omitting it the magnetizing current is reduced. Brushes are rotated on the commutator by means of a small synchronous motor wound with the same number of poles as the main machine. The permutator is reported to have excellent operating char- acteristics. The efficiency is high, since the mechanical losses due to rotation are almost entirely absent; and the weight and cost are about the same as those of rotary converters of the same rating. The principal objection is due to rotation of the brushes. This makes necessary a somewhat complicated brush rigging, and precludes any repairs or replacement of brushes while the machine is in operation. The magnetizing current, being the same in character as that for the induction motor, is lagging; and, notwithstanding the quadrature component is less than for a motor of equal rating, it is never possible to eliminate it, although the power factor is very high. The ratio between the alternating and the direct e.m.f. is fixed in any one machine, but is not limited to a definite ratio as with the synchronous converter. It is possible to wind the machine for high potentials, as with the induction motor or the motor-converter. With the im- provement of other forms of converters, it is doubtful whether the permutator will have a wide application. The Mercury Vapor Rectifier. The use of the mercury vapor rectifier, in connection with locomotive equipment, has already been mentioned in Chapter V. This apparatus is equally applicable for substation service. The principle of operation is based on the fact, discovered by Dr. Peter Cooper Hewitt, that a mercury electrode in contact with the vapor of mercury will conduct current in one direction only. SUBSTATIONS FOR ELECTRIC RAILWAYS 313 To utilize the principle for rectification from a single-phase circuit, the terminals of the secondary winding of a transformer (or of an auto-transformer) are connected to two electrodes in a vessel containing a mercury cathode, and vapor of mercury at the proper pressure. The arrangement of circuits is shown in Fig. 180. There is no tendency to cause a flow of current through the vapor under such conditions; but when the current is once started, as may be done by providing a metallic conductor be- tween the electrodes (for instance, by tilting the container until the mercury forms a continuous film between the cathode and Tfrree- Phase Supply Alternating ...- Current ' Transformer Neutral Wire Neutral Wire Steel Case (Insulated Inside) .. -Metallic Mercury _ ' Inductance FIG. 180. Single-phase mer- cury vapor rectifier. The direct potential may be varied by connecting to different taps on the transformer secondary. Steel Case (insulated Inside) Metallic Mercury FIG. 181. Three-phase mercury vapor rectifier. the other electrode), or by means of a motor-generator set, the vapor will continue to conduct current from the anode (electrode connected to the transformer winding) to the cathode as long as the e.m.f. persists in the same direction. When it ceases, the vapor becomes a non-conductor. If, however, current con- tinues to flow until the e.m.f. has established itself in the proper direction through the other electrode connected to the trans- former, the current will be maintained through the vapor in the same direction as before, but from the other anode. With a 314 THE ELECTRIC RAILWAY single-phase source, this can be done if sufficient inductance is inserted in the receiving circuit. If the latter is normally in- ductive, as when supplying motors, no additional reactance is needed. The other lead for the direct current is taken from the neutral point of the transformer; and hence the current flows for one-half of the alternating cycle through one portion, and for the other half through the remainder, of the winding. With a three-phase supply for the alternating current, the arrangement is slightly different, as shown in Fig. 181. There is no need of inductance to maintain the circuit through the vapor, since two currents are always flowing in the same direction. Although the current produced by the rectifier is unidirectional, it is^not uniform in amplitude. If there were no inductance in the circuit, the form of the rectified current would be very nearly the same as that of the alternating, with every other half-wave reversed. The effect of inductance is to smooth out the waves of current until there is only a slight ripple. For similar reasons, the current produced from a polyphase rectifier is more uniform than when a single phase is used. Extensive tests which have been made indicate that the effect of inductance on the wave form is great enough that standard direct-current motors will give entirely satisfactory service. The efficiency of the rectifier is high at commercial potentials. The loss appears to consist mainly of a definite drop which is independent of the current; so that the converter has a constant efficiency at all loads. This drop of potential varies from ap- proximately 14 volts in the small rectifiers used for charging storage batteries, up to 50 volts in some of the larger units which have been tested. The rectifier used on the Pennsylvania Rail- road experimental equipment in 1914 1 showed a constant drop of about 25 volts, when delivering approximately 1200 volts direct current. The efficiency is hence in the neighborhood of 98 per cent. It must be remembered that at the present time (1915) the mercury vapor rectifier is still in the experimental state, but apparatus has been built giving outputs as high as 1000 kw. and 7000 volts. 2 Compared with other forms of converting machin- ery, it is light in weight, low in first cost and in maintenance, and exceptionally high in efficiency. If the development proceeds as rapidly as is at present anticipated, it will certainly place the 1 Electric Railway Journal, Dec. 19, 1914, Vol. XLIV, p. 1343. 2 Electric Journal, January, 1915, Vol. XII, p. 2. SUBSTATIONS FOR ELECTRIC RAILWAYS 315 rectifier in an excellent position, both for operation on locomo- tives or cars, and for permanent location in substations along the line. Mechanical Rectifiers. Some work has been done in perfect- ing various forms of mechanical rectifiers. These devices are practically two-part commutators, driven at synchronous speed, the brushes being placed in such positions that they will reverse the current as the alternating wave is passing through zero. If the current and inductance remain constant, such a device can be made very satisfactory. If, however, the apparent inductance of the direct-current circuit is subject to rapid fluctuations, the position of the wave will shift; and, to secure good commutation, the brushes should be moved correspondingly. This makes the operation of the rectifier unsatisfactory in connection with a motor load. Various attempts to overcome the trouble have been made, and results of tests have been announced from time to time which would indicate that satisfactory rectifiers have been built ; but up to the present none has been used commercially with any large measure of success. It is questionable whether any device of this type can equal the performance of the mercury-vapor rectifier, especially at high potentials and large currents. Comparison of Converters. In the present state of the art, it is exceedingly difficult to give a satisfactory comparison of the different forms of apparatus for converting alternating current into direct. The excellence of the modern synchronous converter has caused its adoption for practically all classes of railway service, so that motor-generator sets, the induction motor-con- verter, and the permutator may not be used to any extent in competition with it. On the other hand, the synchronous con- verter, from its inherent design, is difficult to construct for the extremely high direct potentials which apparently will be neces- sary for future development of heavy railway equipment if direct-current motors are to be employed; and the possibilities of rectifiers, especially of the mercury vapor type, are so attractive that the latter will undoubtedly be a serious competitor of the synchronous converter in this field. It is, therefore, idle to consider converting equipment standardized at the present time; although, where heavy currents at comparatively low potentials are required, the synchronous converter is undoubtedly the best machine at present. 316 THE ELECTRIC RAILWAY Substation Equipment. With the wide diversity in apparatus which may be used for converting one kind of current into another, it is not possible to consider any form of substation equipment as standard. The arrangement of apparatus, using synchronous converters, has, however, been almost completely standardized. What is desired, in order to keep the operating cost low, is a station in which the machinery is most nearly automatic, so that little or no attention is necessary. With modern machines, this is approximated; but with rotating de- vices, there is always need for expert attention. There is one notable exception: the alternating-current trans- former station. If alternating current is to be used on the con- tact line, all the equipment that is required in the substation is the necessary installation of transformers, with proper switching and protective devices. Such a station can be made automatic in operation, requiring no attention whatever after the line switches have been closed, except in case of abnormal conditions. If the mercury vapor converter is developed, as now seems likely, it may be possible to have similar automatic substations for conversion from alternating to direct current. Storage Batteries in Substations. The widely fluctuating loads in ordinary railway service make it impossible to keep the machines operating at the most efficient load at all times. There are two types of fluctuation of load: the regular daily changes, due to the number of trains in operation, and momentary varia- tions from trains starting, ascending grades, etc. The former can be easily taken care of by having the proper number of units in operation, starting and stopping them as the load changes. The latter cannot be cared for in this manner, but will place mo- mentary overloads on the equipment, sometimes amounting to twice the full-load rating of the machines in service. By the use of storage batteries, these rapid momentary fluc- tuations can be smoothed out to a very large extent on roads operating with direct current. For such service the battery is either " floated" on the line, or connected to it through a suitable regulator. A sudden demand for current causes the battery to discharge, so that the additional load is assumed by it instead of by the converters. When the load falls below the average value, the batteries are charged. In this way the substation equipment is kept operating at or near its maximum efficiency, and the regu- lation of the transmission circuit is improved. SUBSTATIONS FOR ELECTRIC RAILWAYS 317 The other principal use of storage batteries in substations is to assume a portion of the total load, so that the excess capacity need not be carried in rotating machines. This has the effect of reducing the cost of the transmission line and of the generating equipment, since the peak is carried by the batteries, and does not affect the power station. A third use of the storage battery is to assume the total load when, for any reason, the generating equipment is out of service. This makes it possible to operate the road for short periods in case of accident to the machinery, so that the damaged apparatus may sometimes be repaired and put back in service before the battery is discharged. The battery may also assume the entire load during hours when the service is light, as at night. It is evident that the same battery can be used to serve all of these purposes; but the capacity required is very different for each of them. To smooth out the momentary variations in load, a comparatively small battery is needed, since the total time of charge and discharge is quite short for a single peak due to starting a car. To assume the daily overloads during the rush hours a larger battery is needed, and to assume the entire load of the station for extended periods takes a still larger battery, the exact size of course depending on the frequency and length of the interruptions to be provided for. It cannot be claimed that the operation of storage batteries is in itself efficient, for the conversion from electric into chemical energy and back again will result in a considerable loss. The efficiency in this service will ordinarily be from 75 to 85 per cent. The effectiveness of the battery comes from equalization of the load, so that the generators, transmission and converters operate with less loss. The use of batteries is not so general at present as it was several years ago. Better design of electrical machinery makes it more able to stand the momentary overloads; and the efficiency of modern equipment is high over the entire range of loads. The main functions of the battery may thus be served by other means, so that there is not the use for it that formerly obtained. Batteries can be applied to alternating-current roads with the interposition of a rotary converter or a motor-generator to con- nect them to the load. While this arrangement is not widely used, there is at least one installation in the United States operat- ing in this manner. It is reported to be entirely satisfactory. 318 THE ELECTRIC RAILWAY Classes of Distribution Systems. Distribution circuits may be classed into two radically different forms: those in which the sub- station may be located at the center of the system, the lines ra- diating from it; and those in which the distribution is linear, there being but one line, along which the substation may be located. The former represents the conditions in city service, or in some kinds of terminal electrification; while the latter represents the case of the interurban road or the trunk line. Naturally, there will be many places in which the two classes will overlap, so that an absolute classification is somewhat difficult. The general principle remains the same in either, and the problems involved are similar. Location and Capacity of Substations. The most difficult problem in connection with the distribution system is the deter- mination of the proper positions for substations to give the maxi- mum efficiency in operation. The problem is complicated by the fact that the location not only affects the amount of feeder copper required for a given efficiency, or the efficiency with a given amount of copper, but also changes the capacity of individual stations, thus influencing the cost. What is desired from the economic standpoint is to determine that arrangement which will give the lowest annual cost for losses, and interest and depreciation on the investment. The most general statement of the proper arrangement of the circuit is that known as Kelvin's law, which was developed by Lord Kelvin in connection with the determination of conductor size for transmission circuits. This law is usually stated as fol- lows: "The most economical conductor is that in which the annual cost of energy wasted (due to line loss) is equal to the interest and depreciation on the capital outlay that is propor- tional to the weight of the conductor." In practice it is not possible to have the conditions of Kelvin's law met at all times. The law holds true, in its strictest sense, only when a given value of current is flowing constantly. It has been seen that the current in an electric railway transmission or distribution circuit is always fluctuating over a wide range. The condition necessary for use in connection with Kelvin's law may be determined for all practical purposes by taking the root mean square value over an extended period of time, which will correctly represent the average loss due to the current, as called for in the statement of the law. SUBSTATIONS FOR ELECTRIC RAILWAYS 319 In the case of roads which are of the radial type, the location of substations is comparatively simple, although the mathematical treatment is much involved. What is required is to have efficient operation, at the same time keeping the maximum drop as small as possible consistent with economy. In such cases, the amount of load is ordinarily sufficiently great that the capacity of a single substation will be large enough to utilize machinery in units that may be operated at or near maximum efficiency. In other words, just enough units may be in service at any one time that the load on each machine is very near its full-load rating. 1 In roads of this type the load is naturally concentrated at a few points. Practically all lines in this class are city systems, or congested parts of trunk lines such as terminals and yards. The substa- tions may therefore be placed at the normal centers of load. In case there is a question of the exact location, it may be deter- mined by assuming the average load at the mean distance on each radial line fed from the station, and finding the electrical center of gravity of the total load. Location of City Substations. The location of substations for city lines is affected to a large extent by the high cost of land at the normal centers of load. For this reason the largest roads have found it economical to concentrate as much capacity in a single station as possible without excessive drop on any of the outlying lines. This concentration has been carried to such a point that synchronous converters of extremely large rating have been built; and in some cases converters of such sizes as 4000 kw. have been constructed to replace units of 1500 kw., the better knowledge of design enabling manufacturers to produce machines of the larger size which can actually replace the smaller units on the same foundations. 2 Location of Substations for Interurban Roads. Interurban roads fall into the class of linear distribution, and generally can be treated in a much simpler manner than city lines. The varia- tion in the number of substations carries with it a considerable difference in the cost of equipment, as well as in that of operation. The total capacity of all the substations must be equal to that of 1 The effect of the proper operation of the individual units on the all-day efficiency of the substation is shown in a paper by L. P. CRECELIUS, Electric Journal, October, 1914, Vol. XI, p. 543. 2 "History of the Rotary Converter in America," F. D. NEWBURY, Electric Journal, January, 1915, Vol. XII, p. 27. 320 THE ELECTRIC RAILWAY the generating station, augmented by whatever reserve equipment is required due to uneven distribution of the load. As the num- ber of substations is increased, the number and total capacity of such reserve units will become greater. Conversely, as the num- ber of stations is decreased, the size of each unit which can be eco- nomically employed will be greater, resulting in less cost of equip- ment. The cost of ground and building will not vary much with the capacity of the station, nor will the attendance; so that a very decided gain can be made from greater spacing. The cost of attendance will also be very nearly constant, no matter what the capacity. Generally, the fixed charges representing the investment in land, buildings and equipment, and the cost of operation, will increase as a function of the number of substations; while the fixed charges on the secondary copper, and the value of the loss in the distribution circuit, vary inversely with it. It should, therefore, be possible to find a condition where the total cost will be a minimum, corresponding to a definite spacing. Two methods of determining the proper spacing of substations have been suggested: the first, calculation of the distance by trial for any particular case, 1 and the second, by an analysis of the variables, with a mathematical solution. 2 It is the opinion of engineers that the exact location of substations cannot be made entirely by mathematical treatment, since the variables which may enter will vitiate the results to a considerable extent. For instance, on interurban roads using direct current, it is necessary to have an attendant at the substation at all times. His duties will not occupy the entire day, so that it is usual to place the sub- stations so far as possible in towns located along the line. The operator may then also perform the duties of freight- and ticket- agent, thus calling for a smaller number of employees, or giving better service, than would otherwise be possible. This practice is nearly universal with interurban roads. Effect of Potential on Substation Spacing. Since the loss in the distributing circuit varies as the square of the pressure, it is evident that the most economical potential is the highest which 1 "Some Considerations Determining the Location of Electric Railway Substations," C. W. RICKER, Transactions A. I. E. E., Vol. XXIV (1905), p. 1097. 2 "The Determination of the Economic Location of Substations in Elec- tric Railways," GERARD B. WERNER, Transactions A. I. E. E., Vol. XXVII; (1908), p. 1201. SUBSTATIONS FOR ELECTRIC RAILWAYS 321 can be practically employed. As has been stated in previous chapters, direct-current motors have been standardized for 600 volts and multiples of this value. If the pressure is increased from 600 volts to 1200 volts on the contact line, the losses in the distribution circuit, for the same amount of copper, will be but one-fourth what they are at the lower potential. On the other hand, with the same loss, the conductor will have but one- fourth the section and hence cost but one-fourth as much. There is another important advantage which can be obtained by the use of higher potentials. The economical distance between sub- stations can be considerably greater with the same total operating cost. This will result in practically doubling the distance be- tween stations. It also has the effect of increasing the capacity of each substation, so that the investment in reserve equipment can be less and the operating efficiency higher. The excellent results of the increase of potential on the effi- ciency of the distribution system have led many interurban roads to adopt higher working pressures than the old standard of 600 volts. It has already been mentioned that the connection of two 600-volt motors in series permits operation on a 1200-volt system, the only difference being that the motors must be insulated for a higher pressure, and the control equipment must be changed accordingly. The advance in the manufacture of railway appa- ratus has made feasible the construction of motors using 1200 volts on a single commutator, and two such machines may be placed in series on a 2400-volt circuit. In one proposed installation, the pressure per commutator is to be increased to 1500 volts, making a distribution potential of 3000 volts. No definite limit is in sight for direct current. If the mercury vapor converter fulfils expectations, the limiting feature will be the commutating capacity of direct-current motors. Alternating-Current Distribution. The advantage of high trolley potential is the one main feature which has led to the alternating-current system. In this case there is no limit to the distributing e.m.f., since stationary transformers along the track and on the cars and locomotives furnish a simple means of obtain- ing any pressure suitable for the apparatus and the transmission. Single-phase motors of the commutator type are all inherently low-potential machines; but the use of a transformer makes prac- tical any pressure on the distributing circuit, so long as the insu- lation can be taken care of. 21 322 THE ELECTRIC RAILWAY The use of stationary transformers removes nearly all the limi- tations from the operating economy of the converting apparatus, since the demand for attendance is reduced to a minimum. There is no need for elaborate controlling devices, as with the syn- chronous converter installations, and the no-load losses are so small that the equipment can be permanently connected for the maximum output. The greater potential possible makes con- centration of the substation equipment feasible, giving higher load factors. Portable Substations. It is not possible to predetermine the load on a railway system under all conditions. The growth of traffic may be different from what was expected in the estimates, or there may be additional service required for portions of the year. High Tension Lead '' Choke Coif Negative and Equalizer Ter FIG. 182. Portable substation. As shown, an outdoor type transformer is used for lowering from the transmission line potential. In some designs, a transformer of the ordinary indoor type is used instead. In such cases it is not desirable to permanently install sufficient substation equipment to meet the maximum demand, since it will be needed for but a few months in the year. On the other hand, operation with too small substation capacity is unsatisfactory, due to the large drop in potential, to say nothing of the excessive loss. In recent years, many interurban roads have adopted the method of using portable substations, which may be moved from point to point as needed. While developed for the purposes mentioned, the portable substation is useful when building a new line or an extension, in which case the transmission line may be installed, the permanent converting equipment being left until the required capacity and the correct location have been determined. It is also useful when repairs have to be made on an existing station, for the portable substation can be placed on a siding near the SUBSTATIONS FOR ELECTRIC RAILWAYS 323 permanent one, which may be entirely disconnected while repairs are being made. For direct-current roads, the converting equipment will consist of a rotary converter of proper size, with suitable transformers and controlling devices. Such a station is shown diagrammatically in Fig. 182. The apparatus is placed on a specially designed car, the transformers being of the indoor or the outdoor type, as desired. No motive power equipment is used, the car being hauled by locomotives from point to point. Converter sub- stations of this type are usually of 300 kw. capacity, although sometimes larger. For alternating-current roads, all that is required is a trans- former of the proper characteristics. This can usually be carried on a car and left at the proper location to aid or replace the per- manent equipment. No special car is required in this case. CHAPTER XIV THE TRANSMISSION CIRCUIT Development. In the preceding chapters the characteristics of the distributing circuit have been considered largely apart from any connection with the transmission system. It is evident that the successful operation of an electric railway does not depend on the use of high-tension transmission with conversion to the proper kind of current for motor service; but the latter as generated may be entirely satisfactory, provided the amount of power to be delivered by one generating station is sufficient to warrant its operation at the potential of the distributing circuit. In most cases the amount of power which can be so concentrated is not enough to justify such an arrangement. The reason for this is entirely because of the economies which can be effected by the use of large generating systems. Improvements in power-plant equipment, coupled with large increase in the commercial capacities of the units, are modifying conditions so that a system correctly laid out in the past with individual generating stations may now be considered inefficient beside a modern one with the power supply concentrated in a single plant. In fact, several large railroads have found it economical to abandon the older individual power stations, replacing them with single large plants and high-tension trans- mission with low-tension secondary distribution. The advan- tages of large generating units will be considered in the next chapter; for the present let it be assumed that such an arrange- ment is the most satisfactory for the ordinary railroad. It then becomes necessary to transmit the power so produced to the point where it is to be utilized with a minimum of loss; or, more strictly, in such a manner that the total cost of transmitting the energy will be least. Types of Transmission Circuits. As already shown, electric energy can be transmitted either by direct current or alternating current. The former is in many ways superior, since but a single pair of conductors is required, and the motors which can be used 324 THE TRANSMISSION CIRCUIT 325 on direct-current circuits are in some respects superior to alter- nating-current motors. Certain effects of the alternating cur- rent, such as inductance and capacity, which are present to a considerable extent in transmission lines, disappear with direct current. But the latter has one insurmountable disadvantage: up to the present time it is impossible to convert it from one potential to another without the use of rotating machinery; while, on the other hand, the transformer provides a simple and efficient means for doing this with alternating current. It is this one thing which has generally prohibited the use of direct current for long-distance transmission. The only way in which direct current has been used for trans- mission is by the so-called "Thury" system, in which a constant current is employed at variable potential. This has already been referred to in the previous chapter. It requires the use of special rotating machinery at each end of the transmission line, and does not possess the flexibility of the constant potential system, so that its application has been exceedingly limited. Alternating current is available at a number of commercial frequencies, and either single-phase or polyphase. It is shown in all text-books on electric transmission that the single-phase and two-phase circuits require a greater weight of conductor than the other polyphase systems; so that, unless there is some other com- pensating advantage, the first-mentioned forms of electric power are inferior to the others. The single-phase requires the simplest machinery, and only two wires are necessary for the electric cir- cuits. It has the disadvantage of more expensive generating equipment; and the motors for operation on a single phase are not so satisfactory for general purposes as polyphase motors. Even when a single-phase contact line is to be employed, there are enough advantages in polyphase transmission that it is sometimes used in that connection. When the distributing circuit is to be arranged for direct current, the use of polyphase transmission is universal, partly on account of the saving in cost of conductor and partly because of the superiority of the machinery. So far as transmission econ- omy goes, the two-phase and the single-phase are on a par; but even though the latter requires four 1 wires against two for the former, it is preferable on account of the better operation of the 1 Three-wire two-phase circuits are practically never used for trans- mission purposes, on account of the lack of symmetry. 326 THE ELECTRIC RAILWAY equipment. The three-phase circuit, for the same transmission loss, requires but three-fourths as much conductor material as either the single-phase or the two-phase; and the machinery is at least as good as, and as cheap as, two-phase apparatus. For this reason the two-phase circuit has become practically obsolete for all kinds of electric transmission and distribution. The arguments in favor of the three-phase circuit apply with equal force to higher numbers of phases; but these require addi- tional wires without a corresponding gain in efficiency. It is true that a larger number increases the capacity of rotating ma- chinery; but these advantages can be obtained with three-phase transmission by a simple arrangement of the raising and lowering transformers. For these reasons the higher polyphase circuits have never been used commercially for this purpose; and today, three-phase is universally adopted whenever transmission with polyphase circuits is desired. Need for High Tension. It has been shown that the loss in the electric circuit, for a given size of conductor and amount of power transmitted, varies inversely as the square of the potential. It is for this reason, and for this reason alone, that the use of high potential is needed for the economical transmission of power. This relation holds true, irrespective of the kind of current, phase or frequency. If there were no limitations, there would be no inherent objections to the use of extremely high potentials for all kinds of power transmission. Practically, the use of high-tension circuits brings a number of disadvantages which must be over- come to make them practical. The most troublesome feature to be taken into account in the use of high tension is the requirement of properly insulating the conductors, both from each other and from the earth. The trouble from this cause is small at low pressures, but when the potential exceeds rather definite limits, the difficulties increase very rapidly. In addition to this, the effects of capacitance in- crease with the potential, so that special precautions must be taken to avoid difficulty from this source. Lightning also re- quires particular attention. It is interesting to note that when extremely high pressure lines are operated, the need for protec- tion against surges due to short circuits or sudden opening of the switches exceeds that against lightning. In such cases lightning has been found to cause little or no disturbance on the line, and sometimes does not even interfere with the continuity of operation. THE TRANSMISSION CIRCUIT 327 Choice of Potential. The proper potential for the transmission circuit, as well as the size of conductor to be used, can be deter- mined with some exactness by the application of well-known en- gineering principles. That potential should be used which will give the lowest total annual cost for wasted energy and interest and depreciation "on the investment. This may be found by Kelvin's law, as in the case of the distributing circuit. Other considerations often affect the result in the determination of the potential and size of conductor, so that the best values, as found theoretically, may not be the ones finally adopted. The use of standard equipment will generally dictate that the pressure adopted be one of a comparatively few for which apparatus is made commercially. This may effect a considerable reduction in first cost, which will overbalance possible saving in energy due to a higher potential. Again, many electric roads are now becoming interconnected through high-tension networks, and it may be better to use the existing potential of the network rather than to connect through transformers. In certain cases the size of conductor, as determined for economy, may be less than that which can be used commercially on a long line. If no saving in cost of conductor is to be effected, there is no advantage in the use of an extremely high potential, since the difficulties in transmission increase with the pressure. The required regulation of the circuit may dictate a wire in ex- cess of the most economical size. A great many interurban roads in the Middle West have practically standardized on potentials of 16,500 and 33,000 volts for transmission systems. While these pressures are not high, according to modern standards, the amounts of power to be trans- mitted are not so large as to occasion excessive loss. As the size of the road increases, the need for higher potentials is more keenly felt, and a readjustment of the circuits may become necessary for the highest economy. When purchasing transforming equipment, it is often possible to anticipate future changes in operating potential by having the transformers wound for a higher pressure than that on which they are used. This may be done by bringing out taps from inter- mediate points on the windings, by connecting the high-tension coils in parallel, or by arranging the primaries in delta. If it is desired to increase the transmission pressure, the transformers will then be ready for the change with no added cost save the work of rearranging the connections. 328 THE ELECTRIC RAILWAY Regulation of the Transmission Line. In all constant poten- tial electric circuits, it is essential that the variation in pressure shall not exceed a certain amount, depending on the character of the apparatus connected to it. While the operation of electric cars and locomotives does not demand a very close regulation in the distributing circuit, the operation of the substation equipment and of the generators is affected injuriously by wide fluctuations in the transmission pressure. In addition to this, the power factor of the alternating-current circuit has a marked effect on the performance and on the line drop. Some form of automatic regulation is very desirable to keep the potential of the transmission circuit at a nearly constant value. This may be obtained in direct-current circuits by compounding the generators, so that the e.m.f. produced will increase enough with load to compensate for the line drop. When alternating current is used, this method of regulation has never met with success, for it requires complication of the machines and does not give entirely satisfactory operation. When synchronous machinery, such as rotary converters, is used at the receiving end of the line, regulation may be effected by over-excitation, and drawing the current through reactance. This combination will cause the leading current taken on account of the over- excitation to produce a negative impedance drop, which has the effect of compounding the transmission line. Where the regula- tion must be closer than can be obtained with this arrangement, or where it is desirable to keep the power factor constant, auto- matic potential regulators can be used. Close regulation is not a prime essential, so far as the successful operation of most types of railway motors is concerned. We have seen that the allowable drop is quite considerable, especially for interurban operation. But in general poor regulation usually carries with it low efficiency, so that the pressure should not be allowed to vary through such wide limits in the transmission line as in the distribution circuit. The total permissible drop must be divided between the different parts of the system, unless some form of automatic pressure control is employed. If synchronous converters are used without any form of regulator, the variation in potential is transmitted through the machines and the trans- formers directly, so that the drop in the transmission line will add to that in the distributing circuit. When an automatic regulator is employed, the drop in the two circuits can be made practically independent. THE TRANSMISSION CIRCUIT 329 Mechanical Arrangements of Transmission Lines. In many cases, the transmission line for an electric railway differs ^from that for general power purposes, mainly because the wire circuit can be placed on the same poles that carry the distributing feeders and furnish the support for the contact conductor. This cheap- ens the construction materially over that used for a separate line, since the only expense incurred above that for the transmission wire, insulators and cross-arms is due to the extra length of poles required for supporting the high-tension circuit. On account of this, it may in certain cases be cheaper to use a fairly low tension, rather than to adopt a type of insulator which will require a separate pole line for the transmission system. These remarks, of course, do not apply to roads operating with the third rail, where any pole lines which may be erected are en- tirely for the transmission and the distribution circuits; nor where conditions are such that it is necessary to use underground con- ductors. In cities, the transmission line can ordinarily be made much more direct than to follow the railway track. The high-tension circuit is usually run with copper wires of the proper size, but occasionally aluminum is employed instead. The relative merits of the two metals have been the subject of considerable discussion, and the final decision usually lies with the metal which is cheaper at the time of purchase. The fluctua- tions of the metal market are so rapid and so erratic that it is not possible to state definitely that the advantage lies with either. In some cases a single transmission circuit is used alone; but in others, to avoid interruption of service, two or more are em- ployed in parallel, either on the same pole line or on entirely sepa- rate structures. The choice depends largely on the conditions of operation. In climates where there are few periods of severe weather, the advantage of duplicate lines is much less than where storms are frequent and violent. This is a question which must be settled independently for each separate case. The determination of mechanical stress in transmission lines can be accomplished by the same method as that given for the dis- tribution circuit. Added load due to ice is of greater importance in this case, on account of the smaller size of conductor ordinarily used, and the longer spans which are often employed. The side strain caused by wind is also of considerable moment, especially when aluminum conductors are used. CHAPTER XV POWER GENERATION Requirements. The requirements of electric railways are in no material way different from those for other users of electric power. The load, it is true, is subject to wide fluctuations, but this can equally well be said of other consumers. There is, there- fore, no inherent reason why the power plants for railway service should differ in any great respect from those for general power purposes. Capacity of the Power Station. After the capacities of the different substations have been determined, as indicated in pre- vious chapters, similar calculations for the power plant are comparatively easy. The all-day load charts for the various substations should be superposed to give the total demand on the power plant. This is a process of summation, the instantaneous loads being added directly together. From the load chart for the power station, obtained in this manner, the total output may be found by integration, and the average load determined by di- viding the energy output by the time used in the integration. The size of individual units depends on the average load, and also on the momentary overload. Their number should be so chosen that, at any period of the day (except, perhaps, when the load is the very lightest), the machines in service will be work- ing at or near full load. This consideration is important if the highest efficiency is to be reached in operation of the plant. In the smallest stations, where only two or three machines will be used, it is not possible to do more than approximate this con- dition; but in the larger systems, the number of units can be chosen with regard to economy in operation. The efficiency of most electric generators is greatest at full load, or at an output slightly less than this point, although the varia- tion in efficiency from half load to load-and-a-quarter is, in mod- ern machines, quite small. Outside these limits, the efficiency falls off quite rapidly; and if generators are to be operated at light load for large portions of the day, the efficiency of the station may 330 POWER GENERATION 331 be reduced materially. Proper choice of units will, therefore, be ineffective unless accompanied by correct operation. A lower limit to the subdivision of the generators also exists. The cost of electrical machinery increases per kilowatt as the size of unit is decreased, and the maximum operating efficiency becomes lower. It is important that the units be as large as is consistent with proper subdivision of the load, that these advan- tages in cost and efficiency of the larger machines may be availed of. In any particular case, the proper selection of apparatus should be carefully considered. The possibility of future ex- tensions to the system should not be overlooked, for this may influence to a considerable degree the selection of generating equipment. Power Plant Location. Abstractly considered, the location of the power plant may be determined in the same way as that of the substations. The center of load can be found, and the station may be built at this point. In general, such a situation will be at a place where it is impractical to build a power plant. For a successful steam plant, the location must be such that coal can be delivered cheaply and easily, and an adequate supply of water for the boilers and condensers must be available. The first con- sideration practically dictates that the station shall be situated on the line of a steam railroad, unless a suitable interchange agree- ment can be made for operating coal trains over the tracks of the electric road. Sometimes it is feasible to place the power plant on the bank of a navigable stream, in which case coal can often be delivered by water at a cost less than possible when rail de- livery is used. The second consideration generally demands that the station be located on or near a river or creek of sufficient size for the water supply. In certain cases it may be cheaper to pipe water considerable distances; as, for example, to use a city water supply, and have some form of water cooling plant in con- nection with the condensing system. Local conditions affect these points so much that it is not possible to formulate any gen- eral rules for location. The most important single thing which will affect the position of the plant, after these primary considerations, is the cost of land. This will practically prohibit the erection of a station in the center of a city, which would be, for example, the ideal place for it in connection with a street railway. It is frequently far cheaper in total operating cost to locate the station outside the 332 THE ELECTRIC RAILWAY city where land is cheap, and where the advantages of coal and water supply may be better than in the more central position. When power is to be transmitted to substations at high poten- tial, the exact location of the plant has but a small effect on the total economy of the system. In such cases there is no great ad- vantage in putting the station at the center of load, and it may be preferable to have it at a point far removed from the ideal posi- tion, if the other factors can be better met. Hydraulic Power. Where water power is available, it is always desirable to consider using this in place of steam. In order to compete with steam power, the total cost of generation with water power must be as small as, or smaller than, that for steam. The operating costs for hydro-electric plants are usually materially lower than those for steam stations; but the construction costs are so much higher that there is often little difference between the total annual expenses. When hydraulic power is used, the location of the plant is, of course, the outcome of natural conditions, and cannot be changed materially. In cases where the hydro-electric development must be placed a long distance from the railroad system, the question may arise whether it would be cheaper to build a steam power plant nearer the center of load, thus doing away with a long transmission line. Such problems must be considered individu- ally on their merits. Choice of Equipment. In the selection of power station ma- chinery, there are many different types which may be used, and considerable engineering judgment is necessary to get the best combination for a particular installation. Aside from those for hydraulic power, the prime movers available are steam turbines, reciprocating steam engines, and internal combustion engines. The choice between them depends to a considerable extent on the size of the plant and the cost of fuel. With large units and fairly low prices for coal, the steam turbine is the most economical prime mover available. With smaller machines, the reciproctaing engine is not at such a great disadvantage. The field of the gas engine is rather uncertain, and it does not appear to be a serious competitor of steam for large sizes. Power Plant Construction. No attempt will be made to con- sider the actual design of power plants. For such information, reference should be made to any good book on power plant design. It should be noted that the type of plant will be influenced to some POWER GENERATION 333 extent by the cost of land available for the station. If it is neces- sary to build in the congested part of a city, where land is ex- pensive, apparatus should be used which is of the greatest com- pactness. This consideration usually calls for the steam turbine in preference to other prime movers. In some cases an attempt has been made to still further reduce the ground required by placing the equipment in two stories. This arrangement has not been uniformly successful. Purchased Power. A movement has been put forward by the large central stations within the last few years to advocate the use of energy purchased from power companies for railroad operal tion. There are several reasons why this should be the idea- arrangement, and why the cost of energy to the railroad should be lower when purchased than when generated in the road's own plant. The power company is specifically in the business of producing and selling energy. The entire staff has been trained to that end; and better results should be obtained with such an organization than by that of a railroad, whose primary business is to furnish transportation. Coal and supplies should be bought at lower prices, both on account of the better organization, and on account of the larger amounts purchased. A large central station generates such great amounts of energy that the railroad load is but a small portion of the total. It is possible to use more efficient prime movers and electric machinery than are available for the railroad alone. The larger size of the units, and the concentration of power in a single station, reduces the cost of producing energy by a not inconsiderable amount. But the greatest argument in favor of this method of operation is the " diversity factor.' 7 If the railroad load came at exactly the same time as the general demand, there would be no advantage in central station power, other than those mentioned. Ex- perience shows, however, that the peaks of the various loads never coincide. For example, in a large city transportation is required in greatest amount at times immediately before the factories and offices open, and just after they close. Even a small diversity in time may make a great difference in the total capacity of generating equipment needed. If the railway peaks could be made to come during light load for other purposes, it might easily be possible that the entire railway service in a large city could be furnished by a central power plant with no addition to the equipment re- quired for other users. This condition cannot be attained, for 334 THE ELECTRIC RAILWAY some railway service is needed at the peak of the general power load, and the maximum railway load coincides very nearly with a large demand for power. But even a slight difference permits a considerable reduction in total plant capacity. Electrified steam roads handling large amounts of freight have found it possible to run many of the freight trains at night, when the gen- eral power demand is a minimum. In this way the maximum railway load may be kept entirely away from the industrial and lighting peaks, so that the best possible utilization of the power plant machinery may be realized. It is this diversity feature which makes it feasible for the power companies to make such attractive prices for energy to railway companies. On the side of the railroad, it is easy to see that, if power can be purchased for what its generation in an independent plant would cost, and no investment is required, it forms a very good way of solving the problem. Even a large trunk line may find it profitable to buy power. As an example of what can be done with purchased power, it may be stated that practically all energy for operation of the electric roads in Chicago, both surface and elevated, is generated in the stations of the Commonwealth Edison Company, and sold to the roads at a price so low that they have found it advanta- geous to shut down their own plants completely. Further than this, the substations are being operated by the power company, and power is distributed from a single station to several different roads. In this way the load factor of the substations is improved, and the total cost of equipment decreased, while the efficiency is raised. Equally good results might be obtained in other cities, both for the city roads, and for interurban lines entering them. In this connection, it is only fair to state that many of the smaller central stations have been built to accommodate both the railway load and the lighting load, and have been so operated for years. The older plants, especially in small cities, have usually been equipped with separate units for the railway and the lighting and industrial loads. The development of potential regulators has changed the situation so that there is no reason why power for railway service and for lighting should not come from the same machine. In fact, the use of larger units has the effect of minimizing the bad results due to the sudden fluctuations of load which are incident to railway operation, while not affecting to any extent the control of potential for the lighting circuits. CHAPTER XVI SIGNALS FOR ELECTRIC ROADS Uses of Signals. The early railroads were operated without signals of any sort. This was possible because the speeds were low and the trains light. When higher speeds and heavier trains became common, it was found necessary to introduce devices to prevent attempts to use the same track for more than one train at a time. This became more and more necessary as traffic in- creased, and the tracks became more fully occupied. Expressed in modern terms, the primary use for signals is to obtain "Safety First.'* The need for some form of protection to prevent acci- dents increases rapidly as the traffic develops, and more particu- larly as higher speeds are employed. Another legitimate reason for the employment of signals is to promote, through intelligent use of the track, a greater capacity than is otherwise possible. To accommodate the maximum traffic, trains should follow one another as rapidly as can be done with safety, and speeds should be as high as practical without requiring too great spacing between them to permit stopping in case the track is found to be occupied. The various forms of automatic block signals, when properly applied, will increase by a considerable amount the number of trains which can be run over a given track, and at the same time make the operation decidedly more safe than when other forms of control are employed. Kinds of Signals. A number of devices, which are often over- looked in modern operation, constitute the backbone of the signal system on any road. It is well to know which of these are avail- able, and which are used, since they form a valuable adjunct to the better-known types of signals which the public ordinarily considers. Signals are of two main kinds : audible and visible. The former usually consist of the bell, the whistle and the torpedo. These may be operated by the engineer of the train, or by some other member of the train crew, or in certain cases by members of the operating force not directly connected with the train service. 335 336 THE ELECTRIC RAILWAY The use of these devices is invaluable in many critical situations, and must not by any means be overlooked. Visible signals are of two types : movable and fixed. The movable signals are the trainman's lantern or flag, the fusee, and other devices of the same general character. Their use is largely the same as that of the audible signals, and the two are often employed in conjunction. The fixed signals are those which are placed in permanent loca- tions ^along the track, where they may be observed by the engi- neers of passing trains. The simplest of them have one aspect only, and the indication given is to be observed invariably. Such are the whistle post, drawbridge signs, and slow or stop signs. These signals have the effect of warning the engineman of the character of the track ahead, or to remind him of a duty he must invariably perform. Fixed signals having more than one aspect are often employed ; and it is this type which is brought before the public most often in connection with train operation. In this class fall switch targets, train order signals, block signals and interlocking signals. Methods of Displaying Indications. In the use of signals of any sort, a great deal depends on the methods employed for imparting their meaning to the train crew. In general, the indica- tion is displayed at a fixed point along the right-of-way, whether for a train-order system, an interlocking signal or a block signal, and regardless of whether the system is manual or automatic in character. A marked variation in signal indications may be possible when they are to be viewed by day; but for night operation, colored lights are almost invariably employed. The difference between the night signals is due to the methods for changing the color of light displayed. Where electric lamps are used, the most general method for displaying the indication is to have a number of lamps behind colored lenses, the controlling circuits being so arranged that one or more lamps may be lighted to convey different information. With oil lamps, the signal is usually given by a single lamp, the change in color being accomplished by mov- ing a sector with different colored glasses in front of the light. For daylight indications, the oldest and most widely used device is the semaphore. This consists of a blade, mounted on a suitable support, and in a vertical plane perpendicular to the track. It is rotatable about a fixed point near one end, and the indication is given by its position. There are four possible arrangements of SIGNALS FOR ELECTRIC ROADS 337 the semaphore blade, depending on which quadrant is used for the rotation. The maximum rotation used is never more than 90, one of the positions being horizontal. The American Electric Railway Engineering Association has adopted as stand* ard the following with relation to the use of semaphore signals: 1 "Where semaphore signals are used they shall be so ar- ranged as to indicate three positions in the upper left- hand quadrant." It is rather expensive to install and maintain semaphore sig- nals, so that electric roads have been trying to find other types of indicators which will be satisfactory at a lower cost. Within the last few years, great progress has been made in the use of lamps for daylight signaling. To be satisfactory in this service, the lamp must be equipped with a lens which will properly direct the rays, and be carefully shaded so that it will not be interfered with by direct sunlight. From the excellent results which have been obtained with lamp signals, it seems that they are entirely adequate for day use. On the other hand, there is a large advertising value in any kind of signal system, and the more prominent the indication, the greater the advertisement. Semaphores are without question more readily observed by the traveling public, and their indications are plainer than those of any other form of signal in use; so that from this standpoint they have received more favorable attention in comparison to other forms. Colored discs have been used to a small extent for day indica- tions, but they possess no advantage over the semaphore and, like it, require colored lights at night. They are now nearly obsolete on all railroads. Signal Indications. A signal is to give certain information to the enginemen, and the more certain it is, the better the system. The most usual indications to be given are " stop " and " proceed." In some methods of signaling, a third indication, " proceed with caution," is also used. The standard American Electric Railway Engineering Association's indications are: (a) Stop, (6) Proceed with caution, (c) Proceed. These may be interpreted in somewhat different ways, depend- ing on the type of signal system used. The " stop " signal usually 1 Engineering Manual, American Electric Railway Engineering Association, Section Ss 2a. 22 338 THE ELECTRIC RAILWAY conveys the additional information that there is a train directly ahead, or that some abnormal condition makes it essential that the train should not proceed. It may mean merely that the train crew should report for orders. The " proceed with caution" indicates that, while it is not safe to go ahead at full speed, it is possible to do so at reduced speed, prepared to stop short of any obstruction. Where the signal Stop Stop and Sfay Stop and Proceed Red Proceed with Caution Proceed, Next Signal erf- Stop Proceed Under Corrtrol felfow Yellow Yellow Proceed Green Green Lighted Lamps Shown mite, Colors Indicated FIG. 183. Aspects in three-position signaling. These indications have been adopted as standard by the American Electric Railway Engineering Association. is used as a preliminary to a stop signal ahead, it may mean to proceed, prepared to stop before reaching the next signal. The " proceed" indication shows that the track is clear, at least as far as the next signal, and that full speed may safely be maintained. SIGNALS FOR ELECTRIC ROADS 339 In America, the "stop" signal is invariably given by a hori- zontal semaphore, or by a red light. There are two possible locations of the semaphore for this indication, with the blade in a horizontal position, either to the right or to the left of the mast; but the left-hand position is being adopted more at the present time. When semaphore signals are employed for day use, it is customary to have a series of colored lenses mounted on a pro- jection of the blade, so that they will appear in front of a lamp to give the night and the day indications simultaneously. The " proceed with caution " indication is given by a semaphore inclined at an angle of 45, or by a yellow light, a combination of lights, or a light and semaphore. The "proceed" signal is a semaphore in a vertical position in three-position signaling, or 60 from the horizontal in two-position signaling, or a green light. The former use of a white light for "proceed" has been almost entirely abandoned, since there is great danger of confusion with other lights along the road, which might give false indications to the enginemen. The standard aspects in three-position signaling, as adopted by the American Electric Railway Engineering Association, are shown in Fig. 183. Methods of Train Spacing. The fundamental principle of train operation, which is almost universally used on railroads, is to have successive trains separated by such an interval that, in the event of an accident to any train, the one following will have sufficient distance to stop before colliding with the first. This has been rigidly adhered to in all systems of train dispatching, and is naturally the only one which will prevent frequent colli- sions; for conditions may arise at any time which make it neces- sary for a train to stop at an unexpected place. The exact dis- tance which must be allowed between trains depends largely on the maximum speeds attained, as may be seen by referring to Chapter VII. Time Interval Operation. The earliest method of keeping the proper distance between trains was to separate them by a fixed time interval. Provided the train speeds are the same, this will keep them at a constant distance apart, so the proper interval for allowing an emergency stop will always be maintained. But if the first train is delayed, there is no way, after the second one has passed the last station before the forward one is reached, to warn the engineer of the following train that the track is occupied. This deficiency is presumably taken care of by sending back a 340 THE ELECTRIC RAILWAY flagman from the delayed train, who signals the second one to proceed under control, prepared to find the other train ahead of him. If the first again moves forward at its usual speed, the proper distance will be maintained. The correct time interval can be regained when the next station is reached. This method is open to serious objections. The first train may not be stopped, but may be forced to run at a lower speed than normal. No flagman will be sent back in such a case, so that there will be no protection for the following train as in the first example. On a curved track, where the engineman of the follow- ing train cannot see the rear of the for ward one, there is great dan- ger of a collision. Such troubles have been so frequent that the method has fallen entirely into disfavor. Train Order Dispatching. A modification of the method consists in placing the entire division under the control of a dis- patcher, who is responsible for the proper movement of all trains. By his direction, orders are issued to the crews, specifying meeting points and trains liable to be encountered. Under no circum- stances is a crew to proceed without obtaining an order. This procedure gives the dispatcher knowledge of the location of all trains at all times, and should prevent any possibility of accident. The system is usually worked in connection with a published time- table, in which case the regular trains, when running on schedule time, may be relieved from receiving special orders. The train- order method of dispatching is in very wide use in this country, and may be termed the standard method of operation for Ameri- can trains. The principal objection to it is the danger of a slip occurring in the dispatcher's office, or between him and the crew. Two methods of transmitting train orders are in general use: the telegraph and the telephone. The former is quite satis- factory, and has been in use for many years. The telephone, while it has only been tried in the last few years, appears to have the same superiority over the telegraph that it has in commercial work. It is more rapid, does not require expert operators, and gives a better chance for direct communication with the train crews, and so informing them of details which may be overlooked with the telegraphic train order. The Space Interval. The maintenance of a proper distance between trains, rather than a fixed time, is evidently the scientific method of protection. Each train carries in front of it a danger zone, determined by the distance required for stopping. The SIGNALS FOR ELECTRIC ROADS 341 ideal way would be to have this zone marked in front of the train, arranging that if an obstruction should be encountered, the engineman would be warned, so that he could stop his train within the protected space. This is obviously impossible; but the converse of the method, to provide a danger zone behind, with an arrangement to warn the following train, can be provided in a number of different ways. It is not necessary to make the danger zone absolutely the smallest stopping distance, unless the traffic is so dense as to render it essential. Any distance above this minimum can be employed, and the safety will be even greater. The simplest method of providing the proper spacing is to di- vide the track into a number of sections, which must be at least as long as the minimum stopping distance. These sections are ordinarily known as " blocks." Telegraphic Block. The easiest way to divide the track into blocks is to place signalmen at the proper points, providing them with telegraphic connection to the signalmen on either side. The general method of operation is to allow but one train in a block at one time. Where it enters, the signalman reports to the operator at the other end that he has admitted the train, and the block is then closed to further traffic until it is reported out by the opera- tor at the far end. The block is then clear for a train from either direction, if the road is operated as a single-track line. The condition of the track is reported to the engineman by word of mouth, by a flag or lantern, or more commonly by a fixed sig- nal, consisting of a semaphore or target by day, and a colored light at night. The signal can be operated by hand or by some mechanical method under control of the signalman. Controlled Manual System. It is possible to interlock the sig- nals at the two ends of the block, so that, after the signal has been set to protect a train, it cannot be changed until the train has been reported out at the other end of the block. This is accomplished by having an electric interlock in the operating mechanism, which can be released only by a movement of the controlling switch at the other end of the block. In this form, it is known as the " con- trolled manual system." Automatic Block Signals. Both the plain telegraphic block and the controlled manual depend on the ability of the operators. Although man-failure is fortunately quite rare, there have been enough serious accidents from neglect of duty, misunderstanding, and other similar causes to make it desirable to have some form 342 THE ELECTRIC RAILWAY of control entirely independent of the human factor. The most logical arrangement is to have the signals operated by the action of the train itself, in which case the reliability depends on the excellence of the mechanical devices used for transmitting the information supplied by the movement of the train. All the successful forms of automatic block signals use elec- tricity for transmitting the indications. The differences between various systems depend on the means used for the transmission, and for operating the signals. There are two entirely distinct methods of controlling signals electrically: by the use of a separate wire circuit, and by making the rails the conductors of the signal system. In the latter method a wire circuit may be run as an auxiliary. Wire Circuit Signals. Signals employing a wire circuit are used to a considerable extent on the shorter interurban roads, and also on city roads. The principle is about the same as that of the two-way switch for operating incandescent lamps. This ._ Trolley ~T~ & ina , Wn ~T~ Lamps ^Lamp$\ Track FIG. 184. Manually operated wire circuit signal. This contains the essential elements of the widely used types of trolley-contact signals. arrangement has actually been applied to railway signaling. It may be employed as a manually operated device, as shown in Fig. 184. Here a single wire has in its circuit a number of incan- descent lamps, sufficient to burn at about normal brilliancy on trolley pressure. Each end of the signal wire terminates in a single-pole, double-throw switch, which, as shown, may be connected either to the trolley or to the track. In the position given, with both ends of the signal circuit grounded, the lamps will not light, and the same result occurs if both are connected to the trolley. When a train enters the block at either end, throwing the switch to the opposite position will light the lamps at both ends of the block. On leaving, throwing the switch will extinguish the lamps. The only difference will then be that the lamp circuit is connected to the trolley at each end, while origi- nally it was grounded. It is in the proper position that when a train enters the block at either end, the lamps can again be SIGNALS FOR ELECTRIC ROADS 343 lighted. This arrangement is suitable for single- or double-track roads, with traffic in one or both directions, and it is used in this form on a number of electric roads, being operated by hand. The greatest objection to the manual signal is that the car must come to a stop, and one of the crew must leave his position on the train to throw the signals. A development of this simple signal is to have the switch thrown automatically, which may be accomplished by a mechan- ical trip, but better by a magnet operated from the trolley circuit. When desired, a semaphore can be used in place of the lamps as an indicator. A modification of the trolley contact signal is made in which it not only indicates whether a block is occupied or not, but also records the number of cars therein, so that the signals are not cleared until all the cars have been counted out. This is accom- plished by having the cars pass two trolley contacts, motion in one direction notching up a ratchet, and in the other direction returning it toward its normal position. With one such system as many as fifteen cars can be recorded in this manner. In signal operation, it is not sufficient to have the " proceed" indication given whenever the block is clear, and the "stop" signal when it is occupied. Conditions may arise when there is no train in the block and yet it is unsafe for one to proceed. Such, for example, are the presence of a broken rail, an open switch, or a train on a siding which is so near the main line that it will foul the track. If any of these be present, the signals should give the "stop" indication. In general, such abnormal condi- tions are not indicated by signals of the trolley contact type. The use of this type should therefore be limited to places where the liability of danger from such sources is a minimum. Further, there is a prevalent opinion among railway men that the action of the trolley contactors is not entirely satisfactory at high speeds, although the manufacturers claim that their operation is perfect at speeds up to about 60 miles per hr. Continuous Track Circuit Signals. To care for protection from conditions such as are mentioned in the above paragraph, an entirely different method of controlling the signals may be used. This is by the use of the track rails as the conductors of the signal system. The American Electric Railway Engineering Associa- tion makes the following recommendation: 1 1 Engineering Manual, American Electric Railway Engineering Asso- ciation, Section Ss 7a. 344 THE ELECTRIC RAILWAY "For high-speed interurban service, where automatic sig- nals are controlled by continuous track circuits, that expenditures be concentrated on the form of indication in preference to a more expensive form of signal, and a less reliable form of control." The original patent covering the use of the track circuit as a control for the signal system was granted to William Hobinson in 1872. The fundamental parts of this system are shown in Fig. 185. The track is divided into sections at the ends of the blocks, the rails being electrically separated from each other at these points by insulating joints. At the end of the block where the train enters is placed a relay, similar to the ordinary telegraph relay; while at the opposite end is a closed-circuit battery of the proper size. When there is no train in the block, and the continuity of the track circuit is perfect, a current will Track Rails' Battery 'firoceeer FIG. 185. Simple track circuit. In this form, the track circuit signals have been installed on a great many lines of double- track steam railroad. flow from the battery through the rails, energizing the relay. This operates a local circuit at the signal to give the "proceed" indication. If a train enters the block, the wheels and axles place a short-circuit on the battery, and the relay is de-energized. This causes the auxiliary circuit to open, giving the "stop" indication. It is evident that the same result is obtained if a broken rail exists in the block. By including all switches in the circuit, and connecting the rails of sidings back to a point beyond the fouling limits, protection is obtained from these sources of danger. The original Robinson device is suitable for the protection of steam roads, on which the traffic is always in one direction. It is the basis of all modern signal systems using the track for the con- trol circuit. There are a number of objections to the system, none of which is particularly serious. The operation depends on SIGNALS FOR ELECTRIC ROADS 345 the insulation between the rails being maintained at a fairly high value, since the fundamental idea is to have sufficient current reach the relay to energize it when the block is clear. Although but a few volts are used, the leakage of current during wet weather is considerable. A larger number of cells in series does not aid much, since the leakage is increased somewhat faster than in pro- portion to the e.m.f. Of the total output of the battery, about 40 per cent, is used to operate the relay, the remainder being used to overcome the resistance of the track circuit and to supply leakage. Track Circuits for Electric Railways. The direct-current track circuit, as described, is not suitable for electric railways if the rails are to be used for carrying the propulsion current, since even a small current due to train operation may be enough to give false indications of the signals. In order to make the track circuit applicable for electric railway signaling, it is necessary to make a radical change in some of the details. The difficulty due to the presence of current in the track can be overcome by using a different kind in the signal circuit, and employing a relay which responds only to that. For instance, on roads having direct current for propulsion, alternating current is suitable for signaling, and a relay of the induction type, which does not respond to direct current, may be employed. Single Rail System. Another difficulty in the use of track circuits for electric railway signaling is that the rails must be made continuous if they are to carry the main current. If condi- tions are such that the conductivity of one rail is sufficient for the purpose, or if auxiliary conductors can be installed, one of the track rails can be used for carrying the line current, while the other is cut into insulated sections to form the signal blocks. The arrangement of circuits is shown in Fig. 186. It may be seen that a lowering transformer replaces the battery of the direct- current signal circuit, a supply of alternating current being furnished by the signal mains. To limit the current which can flow when a large difference of potential exists in the return con- ductor rail between the ends of the block, a certain amount of non-inductive resistance is inserted in the circuit. To prevent any magnetizing action from what direct current does pass through the signal apparatus, the transformer is made with an air-gap, and a reactance coil, also with an air-gap, is shunted across the terminals of the relay. The action of the latter is like that in the direct-current signal system, but the type is 346 THE ELECTRIC RAILWAY different, being similar to a single-phase induction motor. The action of the signal mechanism may be the same as with direct- current track circuits; but, since a supply of alternating current is present for the track circuit, it is simpler to use it throughout, induction motors being employed for operating semaphores. When lamps are used for the indications, they can be supplied from the signal mains through lowering transformers. It is evident that the same protection is given with this system as with the direct-current track circuit. A broken rail or a fouled switch can be made to indicate equally well. The principal objection is that only one of the track rails is available for the return circuit; and in some cases additional feeders must be installed. For an elevated or a subway line, this defect is not Re f urn Current Rail FIG. 186. Single-rail alternating-current signal circuit. This type of track-circuit signal is suitable for electric roads using direct current, or for eteam roads where there is danger of interference from stray current in the rails. serious, since the metal structure can be used to supplement the track; but for an interurban road the cost of additional copper may be prohibitive. For steam roads, the alternating-current system is finding more favor at present than the direct, since stray direct currents due to leakage from electric lines are liable to derange the signal circuits. This may be obviated by the use of alternating current for operat- ing the signals, as described above. In this case both rails may be divided into insulated sections. Double Rail Alternating-Current System. If the propulsion current can be prevented from interfering with the action of the signal mechanism, it will do no harm in the rails; but to keep the blocks separate is a more difficult matter. The method already SIGNALS FOR ELECTRIC ROADS 347 described sacrifices the conductivity of one rail. Another way is to use a form of bond which will pass direct current, but will not allow alternating current to flow through. Such a bond may be made by the use of balanced inductances. The arrangement is shown in Fig. 187. The insulated joints are retained, as with the direct-current track circuit, but the two rails in each block are connected by inductance coils, which are joined together at their middle points. The obstruction to the flow of direct current is small, since the resistance of the bonds is low; but there is no tendency for the alternating current to pass such a bond, for the two sides of the track in the adjacent block are balanced. If the direct current is evenly divided between the two rails, the unbalancing in the inductive bonds is negligible; but when the Insulated FIG. 187. Double-rail alternating-current signal circuit. Suitable for use with direct or alternating propulsion current. difference between the currents carried by the rails is large, it is necessary to introduce an air-gap into the core of the bond to lower the inductance. The more perfect balancing of the potential drop between the two rails renders the use of an air-gap in the magnetic circuit of the lowering transformer unnecessary, and makes it pos- sible to dispense with the regulating resistance and with the re- actance shunting the relay, as used in the single-rail system. A similar induction relay, which responds only to alternating cur- rent, is employed. The other parts of the apparatus can be the same as for any form of track circuit signals. As described, the alternating-current track circuit signal system is suitable for use in connection with roads employing direct current for propulsion. It is equally applicable to single- 348 THE ELECTRIC RAILWAY phase or three-phase lines, provided the frequency of the signal circuit is so chosen that the inductive bonds will pass the pro- pulsion current, while holding back that for operating the signals. This can be accomplished by using a higher frequency for the signal system, with an amount of inductance in the bonds which has a small effect at the line frequency. For 25-cycle roads, 60- cycle signaling current is entirely satisfactory in actual service. Methods of Operating Semaphores. When semaphores are used for the daylight indication, it is necessary to have a more complicated mechanism for operating them than is employed with lights alone. The semaphore usually consists of a wooden blade, pivoted at one end, and counterweighted so that the un- balanced mass is small. When arranged for use in an upper quad- rant, the blade is slightly heavier than the counterweight, so that it will fall to the "stop" indication if the mechanism fails to hold it at " proceed" for any reason, whether in the normal operation of the system, or through failure of the signal apparatus. On the other hand, semaphores for indication in the lower quad- rant have the counterweight the heavier, producing the same result. The great advantage of the upper quadrant signal is that if the blade is weighted with a coating of ice sufficient to prevent operation, the blade will fall to the "stop" indication rather than to " proceed." This is a safety precaution which has great value, and is extending the use of upper quadrant signals. The semaphore is ordinarily moved to the " proceed " indication by a small electric motor, driven by batteries in direct-current signaling, and by a transformer from the signal mains in the alter- nating-current systems. After the proper movement is made, the motor is automatically disconnected, and the blade held in posi- tion by an electromagnet. In all types of signals the appa- ratus is so arranged that a failure of the operating current, or of any part of the mechanism, will cause the signal to give the "stop " indication. Permissive Operation. The signals discussed so far are of the absolute type. That is, the indication is either "stop" or "pro- ceed." There may be many instances where it is not necessary for the train to stop and remain at the signal, but where movement with extreme caution will be sufficient to guard against accident. In any of the absolute systems, such as those described, permis- sion may be given by the operating rules to disregard the signal indication under certain conditions. When a train is halted by SIGNALS FOR ELECTRIC ROADS 349 a signal set against it, the indication may be due to an open switch, a broken rail, or a train on a siding within the fouling limits. To save time, the engineman is allowed, after having waited a reasonable length of time, to enter and proceed slowly, being prepared to stop short of any obstruction. If a train is in the block, it is still protected by the slow speed of the second train, and if one of the accidental conditions is encountered, or the signal mechanism is out of order, it can be reported by the train crew. When operated in this manner the signal system becomes permissive to a limited extent. Preliminary Signals. It is not always possible to locate the signals at such points that they may be seen for great distances Home Distant Horns Distant Home FIG. 188. Use of distant signals. The home signal is repeated at a point far enough ahead that the engineer can get his train under control, prepared to stop when necessary before reaching the home signal. along the track. In order to be effective, the distance which a signal can be observed by the engineman must be sufficient to permit stopping the train before passing it. If there are obstruc- tions along the track, it may be necessary to repeat the indication at some point in advance of the signal. The arrangement is shown in Fig. 188. The indication of the home signal js merely FIG. 188. Combined home and distant signals. The operation is the same as shown in Fig. 188; this arrangement is used when the blocks are short enough to warrant it. repeated, but it is read differently. The distant signal in the forward block shown may be read: " Proceed at full speed; ex- pect to find the next home signal in 'proceed' position.'' The distant signal in the rear block indicates: " Proceed, prepared to stop at the next honie signal.'' If the distant signal is placed at least as far as the stopping distance ahead of the home signal, ample warning is given the engineman to get his train under control. If, in the meanwhile, the train occupying the block 350 THE ELECTRIC RAILWAY ahead has passed out of it, the engineman of the second train can resume full speed as soon as he sees the " proceed" indication of the home signal. When the blocks are. necessarily short, it becomes more eco- nomical to mount the two semaphores on a single mast, or to com- bine them in a single three-position signal. In the latter case, the arrangement is shown in Fig. 189. The indications are as before; but the same semaphore may give both the distant indi- cation for the block ahead, and the home indication for its own. Signals for Operation in Two Directions. The signals so far considered are all designed for normal operation in one direction only, or, in other words, for double-track roads. To provide an absolute block system for a single track does not present much FIG. 190. Single-track signaling. Positions of semaphores for following cars. additional difficulty, requiring principally that arrangement be made to show the proper indication at each end of the block, instead of at one end only. A simple method of accomplishing this is to place the battery or transformer supplying the track circuit at the center of the block with relays at each end. The conductance of the train is so much greater than that of the relay, that if the size of battery or transformer is properly chosen, the presence of a train will prevent enough current reaching the relay to operate it, so that the signals at both ends of the block will give the "stop" indication. While this arrangement will give protection, and can be used with or without preliminary signals, it limits the capacity of the block to one train at a time. It is possible to operate several trains in the same direction in one block, provided the signals will give proper protection; but, with SIGNALS FOR ELECTRIC ROADS 351 the ordinary types controlled by the track circuit, it is not easy to do this. A recent type of track circuit signal is arranged to give control so that two cars may be in a block between sidings, if moving in the same direction, while they must be spaced a distance apart at least one-half of the total block length. The arrangement of signals in this system is given in Fig. 190, the progression of two following cars through the blocks being shown, while in Fig. 191 the movement of two opposing trains is seen. Details of the equipment and methods of operation are given in recent issues of the Electric Railway Journal. 1 FIG. 191. Single-track signaling. Positions of semaphores for opposing Cab Signals. In bad weather, there is always difficulty in observing the indications given by roadside signals. This condi- tion calls for extreme care on the part of the engineman to pre- vent running past them. In extremely bad weather, it may be necessary to reduce the running speed; and some serious acci- dents have occurred through inability of the engineman to ob- serve the signals. *A New System for Track Circuit Signaling Without Preliminaries; Electric Railway Journal, Vol. XLIII, p. 199, January 24, 1914. A New Method of Traffic Acceleration on the Scranton & Binghamton; Electric Railway Journal, Vol. XLIV, p. 602, October 3, 1914. 352 THE ELECTRIC RAILWAY If the signal indications can be given in the locomotive cab, instead of at a fixed point along the track, it is evident that run- ning conditions will be considerably improved, especially in bad weather. This has been accomplished in at least one system. The operation is quite similar to that of a trolley contact signal, the connection being made by a ramp alongside the track, which presses against a shoe on the car or locomotive. By this means an indication is given which is the same as the corresponding one at the fixed signal. It may be operated by a track circuit, the action of the ramp being controlled thereby; or the ramp may be used in connection with a trolley contact. Cab signals possess the advantage of presenting the indication to the engineman at all times, so that there is no valid excuse for running past a "stop' 7 signal. This feature is one which is worthy of considerable attention from railway operators. The Automatic Stop. For many years it has been desired to have a suitable means of absolutely preventing disregard of the signal indications. On all railroads some form of surprise test is made at irregular intervals to determine whether the indica- tions are being obeyed. This arrangement, while getting better service, is a crude way of checking the effectiveness of the signal system. A method which absolutely prevents improper opera- tion is the best, and next to that is the determination of every infringement of the rules. Methods of stopping trains which run past danger signals have usually been confined to devices for applying the emergency brakes. The earliest arrangement consisted of a glass tube con- nected to the air-brake system, and mounted on the roof of the car or locomotive in such a position that it would strike an arm projecting from the semaphore blade, and moved therewith. Passing of a "stop" signal breaks the glass, and applies the emer- gency brake. If a tube has been broken, it must be replaced with a good one in order that the train may proceed. A duplicate tube is furnished each train crew; but the fact that one has been broken is an indication in itself that the signal has been disobeyed. A modification of the system, in use in the subways and tunnels around New York City, is identical in principle, but employs a mechanical trip projecting from the roadbed, which opens a valve on the train. It is usually desirable to make the automatic stop permissive, in the same way that the fixed signal is permissive. To do this, SIGNALS FOR ELECTRIC ROADS 353 an arrangement must be made so that the train crew can unlock the stop, and proceed by it, when allowed under the rules. This may readily be done; and it prevents loss of time in case a false indication is given, or if any of the abnormal conditions which may exist are present. Automatic Train Control. It is but a short step from the auto- matic stop to the entire automatic control of train operation. The former, as described, will stop a train only when it has already passed a " stop " signal. It is possible that the train which causes the indication is directly ahead of the signal, in which case there would be no additional protection due to the automatic stop. To make the latter effective in such emergencies, the stop should be located at the distant or preliminary signal. This, again, has the disadvantage that if the block should be cleared before the train reaches the home signal, the operation of the stop will cause an unwarranted delay. The ideal control is to have a form of trip operated in such a manner that it will cause the train to reduce speed on passing a distant signal giving the " proceed with caution" indication, but not forcing a stop unless the train over- runs a home signal displaying " stop." By this method the speed of the train will be under control from the time the distant signal is passed, whether the engineman obeys the indication or not. Up to the present time, no system has been developed which has proved entirely satisfactory. In a prize competition held by the New Haven road a few years ago, no less than 1800 entries were made. From the amount of interest in the subject, as evidenced by this large number of competitors, it would seem that a satis- factory solution of the problem may be made within the next few years. Interlocking. At points where several lines of railroad track diverge, or where roads intersect, there is an exceptionally dangerous situation. In many cities, where the lines cross steam railroad tracks at grade, it is customary to have a flagman, or to have one of the train crew flag the car across the tracks. This slows down the schedule speed considerably, and is not absolutely safe, especially where there are but few steam trains. Interurban and steam railroads usually guard their tracks against collisions by the use of interlocking plants at the points of intersection. The interlocking plant consists of a set of "stop" signals, so interconnected that it is impossible to give the "proceed" in- dication on conflicting routes. Combined with this is a set of 23 354 THE ELECTRIC RAILWAY derailing switches to prevent the progress of trains which might disregard the "stop" signals. Detector bars are usually em- ployed to prevent a rearrangement of the signals while a train is in the act of passing the intersection. By these precautions, a collision is impossible, even when the indications are disregarded, unless the apparatus is out of order. The operation of the interlocking apparatus may be accom- plished by several methods. The simplest of these is the plain mechanical interlocking machine, which has been in service on many roads for years. The power for operation is supplied by a signalman, who is located in a tower where he can see the entire set of tracks under his supervision. The levers of the mechanical machine are somewhat heavy, and require a considerable amount of force to operate. The movement is necessarily slow. Improvements on the mechanical interlocking machine have been mainly in the substitution of some easily controlled power for manual. The most successful forms of power interlocking machines are the electric and the electropneumatic. The methods of operation of the two are almost identical, the main difference being that in one compressed air is employed for throw- ing the switches and signals, while in the other electric motors and electromagnets are used. In both the movement is con- trolled electrically. The principal advantages of power interlocking of the two kinds mentioned are that the time of operation is reduced by about one- half, that the space required in the interlocking tower is but about one-fourth, that the number of operators is materially reduced, and the space needed for connections between the tower and the signals and switches is much less. These advantages are suffi- cient to justify the use of power apparatus in any but the smallest plants. CHAPTER XVII SYSTEMS FOR ELECTRIC RAILWAY OPERATION As was stated in the first chapter, there are several possible combinations of electric circuits and motors for the operation of railway trains. The various elements have been considered separately, and it now remains to bring together the details which make up the complete systems. Of the possible combina- tions, the direct-current, the three-phase, and the single-phase circuits have been used for supplying the propulsion current to the cars. These will be taken up in order, so that the merits of each can be discussed. 6oo-Volt Direct-current System. This is the oldest type of electric railway distribution at present in use. As has been mentioned in previous chapters, it is a gradual development from the low-pressure circuits with which the early roads were equipped and represents about the safe limit of potential for continuous operation of motors without interpoles. The motors used are almost invariably of the series type. Due to the long period of development, they are well standard- ized, and the minor defects have been eliminated to a large extent. No more reliable and satisfactory motors are known for use on railway circuits. The direct-current series motor, when adapted for railway operation, is as light as any, and, since the parts are comparatively simple, it is one of the cheapest motors avail- able. Furthermore, the standard machines are quite effi- cient, although no attempts have been made to attain the very highest efficiency. Ruggedness and freedom from breakdowns have been considered more desirable than refinements. The series motor has a great advantage over other types, in that it automatically protects itself against overloads. Since the same current flows through both armature and field, a sudden load thrown on the machine cannot cause a great increase in armature current without a corresponding gain in field strength, so that the motor slows down when an overload is encountered, and does not draw such a great rush of current as do other types under similar conditions. With the addition of interpoles, the 355 356 THE ELECTRIC RAILWAY troubles due to overload and to variation of the supply potential are minimized to a point where they have practically no effect on the satisfactory operation of the machines. If a need arises, as for instance to get characteristics suitable for regeneration, the shunt motor can be used; and if desired, the compound motor is also available for operation on the direct- current circuit. In this way, speed characteristics of any form whatever may be obtained with this system, although up to the present time the series motor has fulfilled all requirements. The control of direct-current motors, while quite satisfactory, is scarcely up to the standard set by the motors themselves. It has been shown that there is a considerable loss of energy in the resistors while starting, which is an inherent defect, and which cannot be remedied without the use of very special methods which are so complicated as to have but limited application. With the ordinary forms of series-parallel control, there are but two, or at best three, efficient operating speeds. By the use of field control, as many more speeds may be added at the cost of a slight complication of the circuits. Field control also reduces the energy consumption when direct-current motors are used for mixed service, such as combined city and interurban lines. The contact line is extremely simple. Either the third rail or the overhead trolley may be used, or, if special conditions de- mand it, the underground conduit or perhaps surface contact can be satisfactorily employed. While these special forms of contact conductor might be used with other distribution circuits, they are not suited to higher potentials, which form the basis of all the other systems. The low-tension distribution, which is responsible for the ex- treme simplicity of the 600-volt system, is in itself the great source of inefficiency. The loss in the distributing circuit is necessarily large, whether in energy when a small expenditure for copper is made, or in overhead cost when a larger conductor is used. This is the great drawback to the universal application of the system. It is so serious that, even for city roads of compara- tively great congestion and short length, it is necessary to gener- ate alternating current for the economy it offers in high-tension transmission, and to add the somewhat complicated and inefficient link of lowering transformers and rotating converting equipment. An incidental disadvantage, which is exceedingly difficult to completely combat, is the trouble caused other corporations who SYSTEMS FOR ELECTRIC RAILWAY OPERATION 357 have metal structures buried in the soil, by electrolysis. The low-potential distribution is a great contributing factor in this, since it calls for large currents to be transmitted through the rails, unless an insulated return circuit is provided. While it is con- ceded that, with great care, electrolysis can be prevented, it is difficult to maintain the grounded return circuit in such ex- cellent condition that trouble is not liable to arise almost without warning. In spite of the disadvantages, the excellence of the 600-volt system is such that it has been universally used for city service, and for this class of operations it is unquestionably without an equal. It is not probable that any other method of distribution will be advanced which will drive the 600-volt system out of this field. For interurban service it has been in the past nearly always adopted; but the use of higher potentials will probably supersede the low-tension system more and more where the length of dis- tribution is great. High-Tension Direct-Current Systems. The use of direct current at higher potentials has followed the need for a reduction of the loss in the distributing circuit, especially for long lines. Motors of the interpole type must be employed, and the use of higher potentials has been entirely dependent on the development of this kind of machine. They possess the same excellent char- acteristics as the 600-volt motors; and, in fact, where a 1200-volt contact line is used, there is no difference in their construction save the need for more insulation. On account of this, the out- put of a given motor must be somewhat less when wound for use on the higher pressure, so that the motors are not so light, so cheap, or so efficient when so arranged. The difference for 1200- volt operation is comparatively small, so that no great effect due to this cause is apparent. When the motors are wound directly for the 1200-volt circuit, the difference is greater; but since this change is usually made to permit the use of a contact line at 2400 volts, it is entirely justified. The control for the higher potentials is more expensive than for 600-volt equipment. The arcs are more difficult to break, so that greater distances between the switch blades, better magnetic blowouts, and longer arc chutes are required. It is sometimes even necessary to place two breaks in series to prevent damage from the arcs. On account of the smaller current, when the energy to be dissipated remains the same, the resistors used must 358 THE ELECTRIC RAILWAY be of smaller cross-section and greater length. This leads to a more expensive and less rugged design. The great advantage in the high-tension system lies in the sav- ing in cost of the contact line, either of the conductor or of the energy lost in it. This is the cause of the adoption of the higher potentials. In the lines so far constructed, it has not been found practical to generate direct current at the contact line potential; but alternating-current generation, with high-tension transmis- sion and conversion to direct current through rotating machinery, has been adhered to. The highest potential at present in use on the contact line is 2400 volts, while one installation for operation at 3000 volts is now being constructed. These values are still far less than those which have been considered suitable for trans- mission; and even if decidedly higher contact line pressures are used, it does not. seem likely that this link in the electric system can be eliminated. One possibility, which has been increasing in importance in the past few years, is the use of mercury vapor converters for pro- ducing a unidirectional current for the contact line and motor operation. While it is yet too early to make any definite state- ments, it may improve the efficiency of conversion by a large amount. A minor disadvantage in all the high-tension direct-current systems is the difficulty of obtaining suitable current for the operation of auxiliaries, such as air compressors, lights, heaters and minor apparatus. In some cases the pressure has been cut down directly by the use of resistance, while in others special dynamotors and motor-generators have been used to transform to a lower potential. None of the solutions thus far advanced seems entirely satisfactory. In any of the direct-current systems, the return of energy to the electric circuit is difficult, unless motors with a shunt char- acteristic are employed. Since one of the advantages which has always been claimed for direct current is the use of motors of the series type, it would mean an entire revolution in operating methods to make the complete change to shunt motors. By the use of separate windings or by special connections of the series fields, it may be possible to provide this feature in direct- current equipments. It must be admitted, however, that the use of coasting will reduce by a considerable amount the advan- tage to be gained by regeneration. SYSTEMS FOR ELECTRIC RAILWA Y OPERATION 359 Three -Phase System. The use of alternating current was introduced in Europe about 15 years ago, the distribution being by the three-phase system. At that time the only motor which could be used for traction on such a circuit was the polyphase induction motor. Although other types of polyphase machines, employing commutators, have been developed since then, none of them has characteristics which would be suitable for rail- way service, or would give better results than the induction type. Three-phase distribution may be said to call for the use of the latter as a necessity. The induction motor is one of the most rugged machines built. In the squirrel-cage type, the secondary is a compact structure, not connected in any way to the external circuit, so that no commutator or collector is required. The secondary winding is exceedingly simple, consisting of heavy copper bars short-cir- cuited to resistance rings at the ends of the core. The primary winding is not complicated, being comparable to that of a direct- current armature without the commutator. When it is necessary to employ a wound secondary, as is usually the case, a regular phase winding similar to that on the primary is used, and the terminals are connected to a short-circuiting resistance through collector rings. In this form the motor is slightly more compli- cated than the squirrel-cage machine, but the difference is small, and the simplicity of the design is still much greater than that of any motor using a commutator. The induction motor is probably the lightest of any built for railway service, and is correspondingly cheap. The efficiency is quite high, and the power factor may be made satisfactory- for commercial purposes. The difference in performance between the induction motor and the direct-current series motor is slight; but if there is any advantage, it is on the side of the alternating- current machine. The disadvantage of the induction motor lies in the fact that it is a constant-speed machine. Although the advocates of the three-phase system claim that constant speeds are preferable, rail- way operators in the United States are not convinced that it would be desirable to change from the variable speed which has characterized the operation by steam locomotives for nearly a century. On the other hand, it may be argued that there are but a few speeds available with direct-current series motors, although these few, unlike those of the induction motor, are not constant 360 THE ELECTRIC RAILWAY over a wide range of load. It is difficult to make a fair decision between the two methods, for the data at hand with regard to constant-speed operation of large railroad systems is entirely inadequate for a comparison. The method of control used for induction motors is somewhat similar to that for direct-current motors, in that the speed is lowered at starting by the use of resistance in the motor circuits. If concatenation of motors, or other means to give a reduced run- ning speed, be used, the losses in the control resistors are not much greater than when direct-current motors are operated with series- parallel control. In many ways there is but little choice between the two. The alternating-current control has one marked ad- vantage, in that the potential to be handled is low, and is in a local circuit, where disarrangement of the resistor connections can do but little damage; while the resistors in the direct-current control are inserted in the main circuit between the contact line and the motors. With induction motors the main circuit need not be opened at all when power is being drawn from the line, so that the danger from arcing at the controller contacts is re- duced to a minimum. The great disadvantage of the three-phase system is the com- plicated contact line. Using the track rails as one conductor, two additional lines are necessary, so that two parallel trolley wires, each carrying the full potential, must be supported above the track. The greatest difficulty is found in maintaining the insulation between these conductors. This is especially true where there are many turnouts, crossovers, and other special work, since the wires of opposite potential must be insulated from each other. These difficulties have limited the pressure in most cases to about 3300 volts, so that the primary purpose of the three-phase distribution, to allow a high working potential, is in part defeated. Aside from this, the distribution is quite flexible, since the e.m.f. can be changed by stationary transform- ers placed along the track, and, if the motors are wound for lower pressures than the trolley, reducing transformers can be placed on the locomotives and cars. The economy of the distribution system is quite high, for in spite of the fairly low potential, there is a considerable saving in loss due to the inherent property of the three-phase circuit, that three conductors give the same loss as four of the same cross- section in the two-phase system, or two of double section in the S Y STEMS FOR ELECTRIC RAILWA Y OPERA TION 361 single-phase or direct-current systems, for the same effective pressure. With the three-phase system, using induction motors, regenera- tion of energy on down grades can be obtained automatically without any modification of the control circuits. All that is re- quired is to leave the motors connected to the line. This is especially useful when heavy freight trains must be handled on long down grades, in which case the control of the train without the use of brakes is safer, and gives considerable saving in brake- shoe wear. The Single-Phase Alternating-Current System. This is much more flexible than the three-phase system in the range of equip- ment which can be applied. Most of the installations up to the present time have used machines of the commutator types, with characteristics nearly the same as those of the direct-current series motor. While these are quite satisfactory from an operat- ing standpoint, they are considerably more complicated, are from 10 to 20 per cent, heavier for the same output, and correspond- ingly more expensive than direct-current series motors of the same rating. This disadvantage is partially overcome by oper- ating the single-phase machines at higher speeds, although this has in itself some objections. Single-phase commutator motors have full-load efficiencies from one to two per cent, lower at full load than direct-current motors. By the use of a " phase-splitter, " three-phase induction motors may be operated on the single-phase distribution circuit, thus giving a performance identical with that of the three-phase sys- tem. In some cases the use of this combination may be justified; and it is actually being applied in one instance in America. If the mercury vapor rectifier fulfills the present expectations, it will make the single-phase circuit available for use in connec- tion with a suitable type of direct-current motor, giving any required range of characteristics. The control of single-phase series motors, or of direct-current motors through a rectifier, is quite simple, and is much more effi- cient than the series-parallel control used with direct-current cir- cuits. If three-phase motors are employed, the control must be effected with resistance alone, or in combination with concatena- tion or pole-changing connections, in which case the efficiency is about the same as for the direct-current system. The single-phase contact line is simple, and in this respect is 362 THE ELECTRIC RAILWAY on a par with direct current. The principal argument in favor of the single-phase system is in the high tension which can be used effectively on the contact line; and it is in this respect that it is ahead of all the other methods. With the aid of lowering trans- formers on the cars or locomotives, the motors can be wound for any suitable pressure, irrespective of the distribution potential. There has been no serious difficulty in maintaining good insulation of the contact line at pressures as high as 20,000 volts. This high potential reduces the current to a point where the conductor section can be very small; in fact, the size of the trolley wire for mechanical strength is in practically every case great enough that no supplementary feeders are necessary, even for heavy traffic. The distribution circuit as a whole is the simplest in character of that for any system, and the converting equipment consists only of single-phase transformers of the proper rating, spaced along the track. The high distribution potential makes possible the use of long distances between substations, so that the load- factor is improved over that obtained with any system operating at a lower pressure. In addition, the use of a control consisting of taps from the secondary of the car transformer makes the actual value of the potential drop of very little importance, and high accelerating current or high speed may be maintained under practically all conditions. Rotating machinery is required in the distributing circuit only when it is necessary to change the frequency; and, as satisfactory motors can be designed for 25 cycles, there is little difficulty in using standard apparatus, without frequency changers. If it is found desirable to generally adopt motors designed for operation on a frequency of 15 cycles, either a separate generating and distributing system must be provided, or else rotating frequency changers must be used. But the recent developments, men- tioned in the preceding paragraphs, in the use of different types of motors on the single-phase contact line may make such an arrangement unnecessary. With the use of the rectifier, it would even be possible to operate the system at the commercial fre- quency of 60 cycles. So far as can be determined, there is no danger of electrolysis with alternating current, although this advantage is slight, since the single-phase system is best suited to cross-country work, where the danger to other metallic structures in the surrounding earth is a minimum. S Y 'STEMS FOR ELECTRIC RAILWA Y OPERA TION 363 If induction motors are used, regeneration of electric energy is automatic; but while it is easily possible to recover energy with single-phase commutator motors, it is questionable whether the complication in the control would not offset the advantages to be gained. Field of the Systems. Up to the present time, the use for city service of the 600-volt, direct-current system is universal in America, and practically so all over the world. While this may be due largely to its early application in all important installations, there is no conclusive argument to be made against it. The series motor has the characteristics required for rapid accelera- tion; and, although the direct-current control is somewhat ineffi- cient, the loss due to the extra weight of apparatus for single- phase operation leaves a wide margin in favor of the former. The use of the low-tension distributing circuit is to some extent a disadvantage, but the distances through which the direct current must be transmitted are relatively quite short, so that the total loss is not excessive. One of the worst features incident to direct current in city service is the necessity for locating substations at central points where the cost of real estate is high. Another disadvantage is the danger of damage from electrolysis. This latter trouble can be overcome to a great extent by the proper maintenance of the return circuit, and it is seldom necessary to resort to the heroic remedy of using two trolley wires. For suburban and interurban service, where a portion of the run must be made over city streets, a combination system which will allow the same motors to be used for all parts of the road is desirable. The earlier lines of this class are all equipped with the 600-volt system, as it was the only one available at the time they were installed. A few roads, built about ten years ago, were equipped with single-phase series motors, with a duplicate control so arranged that they could run either on alternating or direct current. In practically every case such operation has been to a large degree unsuccessful, mainly on account of the great com- plication and excessive weight of the equipment. For this class of service the use of 1200 volts direct current has been a more satisfactory solution of the power supply problem, since the added complication to adapt the motors and control for both circuits is comparatively small. A large number of roads, for- merly using 600 volts, have rearranged their distribution circuits to admit of 1200-volt operation, with satisfactory results. 364 THE ELECTRIC RAILWAY For heavy service, any of the systems are available, and all of them are used. There is no general agreement as to which is the best suited for all-around railroad work; but it is quite evident that for long-distance lines a high-tension distribution circuit is a prime necessity. This of course rules out the 600-volt system from consideration for such roads, although where it has been installed for terminal service, it has in all cases given good satisfaction. In America, the choice seems to lie between the single-phase and high-tension direct current. Developments are taking place so rapidly at the present time that it is impossible to predict that one or the other system will prove greatly supe- rior. There is no immediate prospect of the use of direct poten- tials comparable with those for single-phase circuits; but the lower distribution losses incident to direct current put it more nearly on a par with its competitor than it otherwise would be Three-phase distribution has not been a serious factor in this country, although it has been very successful abroad in several important installations. In view of recent developments, it is doubtful whether the straight three-phase system with induction motors will meet the needs of American railroads. Single-phase operation has the greatest possibilities for heavy service. The ability to use any known type of propulsion motor, with the converting equipment on the locomotive, makes it as near a universal system as can be obtained. Even if some roads should adopt other methods of distribution, it is still possible to design single-phase locomotives so that they can be run efficiently on such circuits. With induction motors, the same locomotive could be operated on three-phase circuits with a comparatively slight complication of the control; and the same is true of direct- current motors if used on the single-phase circuit through some form of converter. Recent developments make it seem doubtful whether the alternating-current commutator motor will survive, at least in its present form; but the use of this machine is only an incident to the successful development of the single-phase system. CHAPTER XVIII ENGINEERING PRELIMINARIES Electric Railway Location. The proper location of an electric rail way is a problem involving a considerable number of variables, all of which must be given consideration if the best possible result is to be obtained. The quantities entering are so numerous and so diverse that it is almost impossible to determine absolutely in all cases the best location, equipment and schedule. The last quantity is one which can be modified at will, within the limits of the rolling stock and the electric system; but the first two, when once chosen, are quite difficult to modify without incurring a large additional cost. It is, therefore, exceedingly important that the preliminary engineering be very carefully done, since the final success of a road may be seriously jeopardized if mistakes are made at this point. City Roads. The requirements of nearly all cities of large or moderate size for purely urban transportation have been largely met at the present time, so that a study of the requirements for such lines is almost entirely academic. The method of deter- mining the proper equipment is of some value, as it gives a means of checking existing installations as to their adequacy. In some cases, where the present facilities are insufficient, such a study may lead to the extension of the lines to meet the needs of the inhabitants. The length of track which a city can support is, to a large extent, a function of the population. The relation of population to length of track per thousand inhabitants for a number of American cities is shown in Fig. 192. It will be seen that the proportional length of track which a city can support decreases as the density of population increases up to a certain point, after which it becomes sensibly constant. This would be expected, since the smaller cities, in order to give any kind of service, must provide relatively large amounts of track, even though the num- ber of passengers carried is comparatively small. As the size of cities increases, the use which is made of the existing track is 365 366 THE ELECTRIC RAILWAY greater, so that the additional amount of line which has to be installed per inhabitant becomes decidedly less in the larger urban centers. A saturation point is finally reached, beyond which the increase in necessary track is practically in proportion to the population. The place where this condition occurs de- pends largely on the compactness of the city and the number of independent centers which exist within the community. The more concentrated the population, the less is the ultimate limit for the amount of track per inhabitant. Boston ^Portland, Ore. Manta < )?rovidence ^Washing-fan^ Jersey City -Newark neapolis-Sf-.Haul st.lou ltimore OIZ34567& Population in Hundreds of Thousands. FIG. 192. Relation of urban track to population. In some cities the amount of track which can be used is much greater than the average. Boston, for instance, has a much greater length per inhabitant than any other American city of similar size. This difference is more apparent than real, for a large population in the immediate vicinity of the metropolitan district is served by the same system, so that additional facilities for the adjacent cities are not required. The extra demand for transportation from the surrounding suburbs will increase the use of the city railway tracks, so that the earnings may be exceedingly high when a line is located in such a center. Another cause for ENGINEERING PRELIMINARIES 367 extensive use of the road is when the physical location of the city is such that it is impossible or difficult for the inhabitants to walk to and from their homes. An example of such a city is New York, where the business district is of such a character that very few persons can live within easy walking distance of any point in it. For this reason, an adequate transportation system must be pro- vided to permit the further development of the city. In fact, in New York the growth of the city railroads is decidedly behind the increase in population, so that the existing facilities are strained to the utmost. Similar conditions exist in many other places, but the results cannot be so clearly seen as in the former city. Future Requirements. In addition to determining the present need for railway facilities, it is necessary to make some provision for future growth, if the requirements of the city are to be served for any length of time. In certain cases it is possible to make such provision merely by the extension of the existing tracks farther into the suburbs, as these develop; while in others the growth of the urban section may make a complete rearrangement of the entire road necessary. Careful design of this part of the system may add considerably to the growth which can be taken care of without extending the existing tracks. In a number of the smaller cities it has been customary to route all cars past a central point, such as an important street intersection or a civic center. Although this practice makes the transfer of passengers simple while the traffic is light, it is likely to cause serious congestion when the city has developed to a larger size. In some places where this arrangement has been used, considerable objection by the public has developed to the re-routing of cars on different thoroughfares. This condition can only be overcome by careful publicity work on the part of the railroad company. It is impossible to make an accurate estimate of the future growth; but consideration should be had of the variable condi- tions which may enter to change the final result, and the lines laid out in such a way as to make them of the greatest present use, while later they may be extended to meet the future needs. Even at the present time such precautions may be taken in planning extensions to existing lines, and in this way the improvements will be of greater value to the community than if changes are made to meet the present requirements only. The second important factor in determining the adequacy of a street railway is the use made of it by the public. Again statis- 368 THE ELECTRIC RAILWAY tics may be employed to show the probable value of a road to a city. The number of rides which each inhabitant is liable to take increases with the size of the place in which the road is located, the growth being very rapid in the smaller towns and much less after a certain size is reached. A curve between the annual num- ber of rides per inhabitant and the size of the city is shown in Fig. 193. This information is valuable in connection with estimates of probable growth in population to prevent making the assump- 600 OIZ3456 Population in Hundreds of Thousands. FIG. 193. Relation of rides per inhabitant to population. tion that the use of the road will increase as a direct function of this gain. Since the rate of fare in most cities is fixed by law, the values determined above give at once the gross earnings from trans- portation. The fare on practically all urban lines is five cents, so the number of passengers is a direct measure of the receipts. It should be noted that transfer passengers must be omitted from this estimate, since they do not add anything to the revenue, although it is the usual practice to include them in the total num- ber of passengers carried. On this point there is a great deal of misunderstanding, since many railway officials look on transfers ENGINEERING PRELIMINARIES 369 as an unmitigated evil. This is largely a misapprehension, for the use of transfers often permits the routing of cars to give a much more efficient service than were through routes used exclu- sively. In such cases the use of transfers is a positive benefit to the company. Number of Cars. The number of cars and the frequency with which they are operated are quite difficult to estimate properly. They have a direct effect on the cost of the service and an indirect one on the number of passengers carried. Other things being equal, the number of persons who will ride increases with the frequency of operation up to the point where cars are run every two or three minutes. Beyond this there is no great possibility of obtaining more passengers in this way. The worst feature in modern city operation comes from the excessive congestion of traffic at certain times during the day. By far the greatest num- ber of the regular passengers begin work at approximately the same hour, and stop at the same time. This means that facilities for handling a great number of passengers must be provided, while they are only in use for a few hours, twice a day. Even with the best and most modern equipment, it is hard to provide even standing room for all the passengers, while at other times the cars will be nearly empty. This condition is inherent to Ameri- can business methods, and can be avoided only by a large amount of educational work. A variation of only a few minutes in the time for closing stores, factories and offices would make a great reduction in the peak of the load, with a corresponding improve- ment in the service. This point has already been considered in connection with the determination of power requirements. It is erroneous to suppose that the greatest earnings of the railways come from the crowded cars run during the rush hours. As a matter of fact, the congestion calls for the operation of cars additional to those on the regular schedule. Although these special cars are used but a few hours a day, their first cost, and the cost of the entire system necessary for their operation, is as great as though they were in continuous service. In addition the platform men must be given a living wage, and this must be done even if the amount of time of actual service is but two or three hours a day. It is not often possible to arrange schedules to provide continuous employment for these men. Size and Type of Cars. The proper determination of the type of car to use for any urban road is largely a matter of individual 24 370 THE ELECTRIC RAILWAY taste. Many kinds are in use on such lines, and the apparent lack of agreement indicates that no single type is entirely satisfactory for all classes of service. It would appear that for street railways in the smaller cities, cars with bodies about 20 ft. in length, mounted on single trucks and equipped with two motors of from 20 to 30 kw. each, will meet the average requirements. Cars of this type will seat about twenty passengers and will provide standing room for as many more. For the larger cities, addi- tional capacity must be provided, which can be done only by the use of units of greater size. This naturally calls for double- truck cars, since a 20-ft. body is about the longest which can be mounted on a single truck, unless some form of non-parallel axle is used. The details of cars for this class of service have been discussed in Chapter VIII. Schedule and Maximum Speeds. In many cities, the maxi- mum speed of cars is defined by law. While this has some effect on the schedule speed, it can be offset by the acceleration which is used. It has been shown in previous chapters that the latter has as great an effect on the schedule speed in short runs as does the maximum velocity attained. When a great many stops are made, the schedule speed which can be reached is usually very low, often not more than 10 miles per hr., unless the motor equipment is entirely abnormal. It is advisable not to attempt high speeds under such conditions, since the cost is out of all proportion to the advantage gained. Where the run includes a certain distance in suburban territory, in which the speed can be materially increased, it is frequently the custom, as has already been mentioned, to use motors for the entire division geared so that the cars may operate at high maxi- mum speeds in the suburban district. The result of this is to overload the motors, while the schedule speed which can be main- tained is frequently less than could be reached were the same motors used with a higher gear ratio, giving a lower maximum speed. The most desirable arrangement is to use motors geared for the maximum acceleration, but obtaining the high speeds needed by the use of field control. This will give the advantages of the low and the high gear ratios, and will reduce the power and energy requirements by a marked degree. Tests which have been conducted on such equipments show considerable savings over the normal single-speed motors. ENGINEERING PRELIMINARIES 371 Interurban Roads. The probable earning power of interurban railways is much more difficult to estimate than for city lines. A great deal depends on the kind of service given and the facilities which are offered farmers residing along the road for light freight service. Generally, high schedule speeds are less important than frequent service, since a large part of the passenger traffic is local. Since the revenue of the normal interurban railway is so largely from passenger traffic, a careful analysis of the population served, and the number and length of rides per inhabitant, must be made in order to get a close estimate of the probable gross earnings. The factors which enter are so materially different from those which govern the earnings of urban roads that very little aid can be had from a comparison with such properties. The sources of passenger traffic for interurban roads depend to a large extent on the location of the principal cities along the line. Usually an interurban railway is constructed with one city of considerable size as a primary terminal. The road may operate from this point entirely through rural territory, serving this and the small towns located along the line; or it may connect the prin- cipal city with one or more of smaller size. The greatest source of passenger traffic is ordinarily travel from the rural districts to the main terminal; but if the road exceeds a certain length, the traffic from this source will not increase greatly with additional distance. For such roads a second terminal is necessary, and the greater the length of road, the more intermediate cities are essen- tial to give the earnings requisite to make a successful property. The estimation of the city population served is apparently quite simple; but to obtain figures which have any direct value is much more difficult. The travel which will be obtained between a terminal city and the surrounding territory does not depend to any material extent on the size of the city, but rather on the re- lations which exist between the urban and the rural populations. For example, a county seat will have considerable traffic from the surrounding country, but very little to it; while a manufac- turing center will probably develop both classes of travel, espe- cially if the territory surrounding it is largely of the same general character. The estimation of the rural population served by the proposed road is usually made by considering a section of territory from one to four miles wide, on each side of and contiguous to the track. Some objection may be found to this method, in that the amount 372 THE ELECTRIC RAILWAY of travel to be expected depends perhaps more on the size and character of the towns along the line than on the farming popula- tion served by the road. An alternative method is to adopt a fac- tor for use in connection with the population of the intermediate towns located along the line. A very important consideration is that of the probable future growth of the territory served, and an estimation of the effect this will have on the earnings of the road. A good interurban service does, without question, develop the country through which it passes; but the amount of such growth may be a vital factor in determining the success or failure of the property. It is usually impossible to build roads before the population is great enough to allow them to earn operating expenses, although in the past many such lines have been built; but, if the probable increase in revenue due to the presence of the road is sufficient, it may pay to install it before the traffic is enough to pay dividends on the stock. Such a determination is very difficult to make, and great care should be taken to prevent loss of capital. In general, the prob- able earnings from a projected line are subject to so many vari- ables that the best procedure in such preliminary estimating is to secure the services of the best engineering talent available. Operating Expenses. Of equal importance to the expected revenue is the probable expense of operation of the road. The principal items under this classification are maintenance of way, maintenance of equipment, and expenses directly concerned in conducting transportation. Maintenance charges depend to a very considerable extent on the excellence of the construction and the equipment; but if these are assumed to be at least of average quality, the estimation of maintenance costs can be made with a fair degree of accuracy by comparison with existing roads of the same general character. The cost of conducting transportation is a function of the amount of service given, although not directly dependent on it. The cost of operating a car-mile or a ton-mile depends very largely on the number of such units hauled, although such items as the overhead charges for production of power and platform labor are very nearly constant regardless of the use which is made of the road. If the line is to be successful, the regular schedules must be maintained whether any traffic appears or not; and the cost of hauling empty trains is very nearly as great as when they are loaded to their maximum capacity. ENGINEERING PRELIMINARIES 373 Estimation of Construction Cost. The estimation of the cost of construction is not difficult, once the components have been correctly determined. Having the power demands, the capacity of the generating and substations may be found at once, the num- ber of units being selected to give the desired subdivision of load, with a proper number of reserve machines. By the application of the principles of transmission and distribution circuits, the proper size of the conductors may be determined. The methods of estimating the number of cars are various, but if a certain standard of service has been decided on, as, for ex- ample, the operation of one train in each direction per hour, the required number may be found at once from an inspection of the graphical time-table. A certain allowance must be made for extra service, for repairs, etc. Generally it is best to purchase at the beginning the minimum number which will give the desired service, and add to them as the traffic develops and the use of additional cars becomes necessary. In this way the latest im- provements in design may be taken advantage of. The methods of estimating the probable amount of power re- quired have been taken up in the preceding chapters. Once the schedule is determined, the proper speed-time curves to give the desired performance may be laid out, and the motors selected to meet this requirement. From the current-time and potential curves, the power demands on the substations- and on the gen- erating station may be determined. The amount of energy needed for the operation of the desired schedule is found at once by an integration of the power-time curve; and if the efficiency of the various elements of the equip- ment be known, the output of the generators at the bus bars and the quantity of coal to be burned on the grates can be calculated. The cost of platform labor can be found at once from the number of car-hours operated, if the average wage has been established. Other labor is more difficult to determine, depend- ing as it does on a variety of factors. The number of power- plant operators, repair shop men, and similar employees is largely independent of the size of the road, until it reaches con- siderable proportions. The office force required to handle the business is quite variable, and depends not so much on the number of units operated as on the individual ideas of the management. 374 THE ELECTRIC RAILWAY Having determined the various items which enter into the operating cost, the total may now be found as their sum. Net Receipts. The difference between the gross receipts and the operating expense gives the net income. If the operating expense is found to be greater than the receipts, the investigation may properly end at this point, unless it is found possible in some way to predict an increase of the one or a reduction in the other. If the estimate indicates a net return, further study will show whether this income is sufficient to pay taxes, fixed charges, and other legitimate overhead costs, and after doing this leave a balance available for dividends. This is, of course, the final measure of success or failure of a road. It is essential that the greatest care be taken to make the preliminary estimate accurate, especially if any doubt exists as to the ability of the projected line to pay dividends; and it is better to leave alone a project rather than run the risk of sustaining material loss. Steam Road Electrification. A type of problem which is becoming of increasing importance is the electrification of trunk lines. Such roads are usually old and well-established properties, which have already developed a good traffic. The problem is here much simpler, since the preliminary determinations of traffic and equipment are wholly or partially solved before beginning the estimates. In many cases, all that is desired is to replace the existing steam locomotives with electric, keeping substantially the same sched- ules and train weights. This is the simplest statement of the problem, and requires the least preliminary engineering. Once the system for the contact line has been decided on, the size and equipment of the locomotives is comparatively easy to determine, since they will be of the same rating as the steam engines they replace. Having found the locomotive capacity, the motor char- acteristics must next be selected to give correct operation. The speed-time and power and energy curves may now be drawn, giving the demand on the substations and on the power plant. The equipment for these parts of the system, and for the trans- mission and distribution circuits, may be selected, and the total operating cost peculiar to the electric installation found. The criterion of excellence which must be met is that the oper- ating cost of the electric equipment must be less than that for steam, after including a proper allowance for the increased cost of construction. If the total annual cost is less than for steam op- ENGINEERING PRELIMINARIES 375 eration, the project is feasible and may be recommended; other- wise it is necessary to look toward other reasons for the adoption of electricity. Even though the electric operation of a division may not show a decreased cost directly, there may be other conditions which modify the problem to make electrification desirable. It may be possible to haul trains at a higher speed, thus permitting the pas- sage of a greater number of tons in a given time; or it may be possible to give more frequent passenger service by operating more and lighter trains. Many such considerations must be looked into and may give excellent reasons for electrification, even though the direct saving to be obtained is small. In some cases, the change from steam to electric operation has caused an increase in passenger receipts. This is sometimes due to the fact that competing lines have been taking a large share of the traffic, which can be regained by better service; and in other cases to an increased desire to travel, on account of the improved accommodations. It is impossible to do more than hint at the possibilities of this sort, and they must be determined for each individual case. An instance of the successful application of electricity is in mountain-grade operation. Here the limiting conditions usually depend on the weight of trains which can be handled by steam locomotives. Some roads have found the capacity of an entire railway system limited by that of a single short division. If light trains are run, the requirements of safe operation limit materially the capacity of the track; and if long trains are used, the speeds which are feasible with steam are decidedly low. Elec- tric operation makes possible the running of heavy trains at fairly high speeds, so that the number of tons which can be hauled may be materially increased. This is due to the prac- ticability of concentrating larger amounts of power in the equip- ment than can be done with steam. Choice of System. Reference to Chapter XVII will show that of the three systems of secondary distribution, any one will fulfill the requirements of ordinary trunk-line operation. No general agreement has been reached as to the complete superiority of any one; but for a particular installation there may be a solution of the motive-power problem which will be the most satisfactory. If any doubt exists, the best way is to prepare separate estimates based on the use of each of the three systems, obtaining the 376 THE ELECTRIC RAILWAY relative costs of installation and operation. Except in rare cases, one of them will show a lower total operating cost than either of the others; and, unless there are separate considerations to be met, this is the one which should be adopted. It would be exceedingly desirable to adopt for an entire rail- road system, or for all the railroads of the country, a single uni- versal plan for electrification. This would permit standardiza- tion of equipment, and would reduce the cost of the various parts of the electrical apparatus. Until this is done, the cost of installations for electric lines will be considerably higher than if such standardization is brought about. It would be a poor policy, however, to postpone the electrification of such lines as warrant the change until such a condition has been realized; for, with the systems all possessing points of excellence, any one of them may show operating economies which will make the sav- ing sufficient to warrant its adoption, even with the possibility of a future change in case some universal or superior type of equipment is adopted later. In the final analysis, it may be seen that the use of electric power presupposes a certain traffic density before it becomes a paying investment, so that the lines of heavy travel are certain to be electrified first, except that where coal is expensive and electricity is cheap a comparatively light traffic may make the change desirable. Such conditions exist in the Mountain states, where water power is available; and at the present time at least one important road is equipping its main line for electric opera- tion in the interest of economy, there being no other basic reason for the adoption of electricity. Apart from such special installa- tions, it is quite probable that the Eastern roads will be the first to use electric power for the operation of long divisions, since they are the ones which will receive the greatest benefits from so doing. INDEX Accelerating force for rotating parts total Acceleration, chart of . . curve effect on power curve mechanics of rotational units of Accelerator car Adhesion coefficient Adjuster, slack Advantages of motor car trains. of series motor Air brakes see Brakes cylinders, sizes compressed, power for compressors resistance Alternating-current distribution electrolysis signals single-phase system field of three-phase system field of American Electric Railway En- gineering Association . Standard bearing car wiring signal aspects indications track rails trolley wire American Institute of Electrical Engineers 132, Angle of inclination for brake beams Angular acceleration Application of electric loco- motive types Arch roof for cars . . Arcing in controllers 97 Armature construction 73 13 speeds 74 14 winding for single-phase 16 motors 82 40 modern 78 33 Armstrong, A. H 23 128 Armstrong's equation 23 13 Arrangement of drivers on 14 electric locomotives. . . 249 14 on steam locomotives 243 208 Articulated cars 204 166 Atkinson repulsion motor 64 187 Automatic air brake 190 240 block signals 341 48 control 101 189 slack adjuster '. 187 181 stop 352 157 train control 353 189 Auxiliary equipment, car 220 20 effect of frequency on 62 321 energy for 157 301 Average motor potential 140 345 361 B 364 359 Banking of curves see Super- 363 elevation 30 Battery, storage, in substations. 316 Bearing friction of d.c. motor . . 57 18 car 18 224 motor 79 338 Block signals, automatic 341 337 telegraphic 341 262 Blow-out, use of 95 287 Bobtail cars 201 Bolsters, truck 232 141 Bond, rail, Chicago type 293 electric welded 294 180 inductive 347 14 protected 294 resistance of 295 246 soldered 294 206 Bonding, track 293 377 378 INDEX Boosters, use of 277 Bow trolley 227 Bracket construction 285 Brakes, air 189 automatic 190 combined straight and automatic 195 electropneumatic 192 high-speed 192 quick action 191 straight 190 tests of 193 Brake beams, angle of incli- nation 181 cylinders, sizes 181 electric 195 emergency 196 hand 187 magnetic 195 magnetic, Newell 197 momentum 199 power, need for 165 rigging 181 calculation of 184 foundation 183 truck 182 shoe wear, effect of regen- eration on 161 vacuum 195 Braking 164 curve 34 forces, distribution of on car 172 rotational inertia 179 total 180 transmission of 172 importance of 164 methods available 164 phenomena, nature of 166 Brazed bonds 294 Bridge connection 102 for supporting contact line . 286 Brush rigging, development of . . 73 loss . . 58 Cab signals 351 California type cars 204 Capacity, motor 131, 143 substation 132 Car, cars 200 accelerator 208 articulated 204 auxiliary equipment of .... 220 bearings 17 bobtail 201 braking see Braking 164 California type 204 center door 208, 213 classification 200 structural 201 collectors 225 construction 204 framing 205 materials of 204 roof framing 206 convertible 203 development 201 door arrangement 207 double-truck 204 electric 201 elevated 214 equipment, miscellaneous 230 fare collection 210 framing 205 freight 219 gasoline 255 heaters 222 electric 223 hot air 222 hot water 222 stove 222 heating 222 power for 158 horse 201 interurban 218 lighting 220 power for 157 -mile, as basis for energy consumption 151 near side 213 number of for city system . 369 one man 214 open 202 painting 229 parlor 219 P-A-Y-E.. 211 INDEX 379 Car, pay-within 212 prepayment 211 rapid transit 214 seating arrangement .. 209, 218 self-propelled 254 comparison 259 gas-electric 256 gasoline 255 storage battery 257 semi-accelerator 208 semi-convertible 203 side door 207, 209 single-truck 230 sleeping 220 storage battery 257 street 201 subway 214 trucks see Trucks 230 wiring 224 Cascade control 120 Cast-iron motor frames 74 welded rail joints 266 Catenary, equation of 279 suspension 282 Center door, cars 208, 213 Center of gravity of electric locomotives 247 Changes in frequency 120 in poles 119 Characteristics of motors see Motors 42 Choice of equipment 332 of locomotives 253 of potential 327 Circuit, distributing see Dis- tributing Circuit 270 return see Return Circuit 292 transmission see Trans- mission 324 City railways 365 substations 319 Classes of distribution systems 318 Classification of cars 200 of electric motors 42 of signals 335 Coasting curve 33 Coefficient of adhesion. : 166 of friction 168 Coils, armature 78 Collection of fares . 210 Collectors, current 225 of induction motors 83 Combination systems of control 116 Commutating poles 77 Commutation in single-phase motors 67 Commutator construction 78 motors, a.c. see Motors. 58 Comparison of converters 315 of control methods 91 of self-propelled cars 259 of shunt and series motors. 46 Compensated repulsion motor. . 64 Compensating winding, use of . . 59 Compensation of a.c. motors. 62 of brake hangers 180 of curves 29 Compound motor 43 Compounding of transmission circuit 328 Compressed air see Motive Powers, Air Brakes Compressors for air brakes .... 189 Concatenation control 120 Conductive compensation for a.c. series motor 62 Conductor, contact 286 position in prepayment cars 210 use of rails as 292 Conduit system 290 Constant-current system 42 Constant-potential system 42 Construction, car 204 cost of 373 power plant 332 railway motor '. 71 track 261 Contact conductor, size of .... 286 line 278 construction 284 forms of 279 methods of supporting . . 284 requirements of 278 three-phase 360 surface 292 Contactors, use of 97 in multiple-unit control.. . 101 380 INDEX Continuous rating of motors. . 142 track circuit signals 343 Control 84 automatic 101 calculations for 104 cascade 120 changes in armature strength 87 combined a.c. and d.c 116 concatenation 120 Jones type 104 locomotive 252 methods of 84 practical combinations. . 90 multiple-unit 98 Sprague system 99 Type M 100 unit switch type 101 need for 84 permutator 124 potential variation 85 proportioning of resistances 104 railway motor 84 rectifier 125 resistors 113 rheostatic 90 limitations of 91 principle 86 series-parallel 94 advantages of 93 comparison with rheo- static 91 comparison 356, 357 principle 85 series, series-parallel 94 single-phase 115 special systems 123 split-phase 122 tandem 120 three-phase 117 comparison 360 train, automatic 353 transformer 115 unit-switch 101 Ward Leonard 123 Controlled manual system 341 Controller, drum type 95 Jones type 104 operating Ill Controller, pneumatically oper- ated 103 rheostatic 90 type HL 102 typeK 95 type L 97 type M.... 100 type R 90 Converters 307 comparison of 315 mercury vapor 312 motor- 310 synchronous 309 types of 307 Convertible cars 203 Copper loss in d.-c. motor 57 Corrosion by current 297 natural 301 Cost, construction 373 of stops 153 Counter e.m.f 50 Cradle suspension 236 Crecelius, L.P 319 Current, heating value of 133 limits for control 106 rectified 314 root mean square 134 -squared curve 136 time curves 135 Curves, measurement of 28 D Defects in return circuit 295 Determination of train resist- ance 22 Development of car design 201 of railway motors 71 of substations 305 Differential coefficient 36 Direct-current circuit, polarity of 300 motors see Motors 42 system, field of 363 high-tension 357 600-volt 355 signals 342, 343 Distant signals 349 Dispatching, train 340 INDEX 381 Distributing circuit 270 contact line 278 equations of 272 high-tension d.c 303 limiting drop 273 methods of feeding 275 simple 271 single-phase 304 three-wire 302 use of boosters 277 use of graphical time-table 273 systems : 270 classes of 318 complex 306 d.c., comparison 357 a.c., comparison 360, 362 single-phase, comparison.. . 362 three-phase, comparison. . . 360 Distribution, a.c 321 of braking forces on car. . . 172 on truck 174 of energy consumption. ... 156 systems, electric 42 Diversity factor 333 Doors, car 207 Double-rail signals 346 -trucks 232 -truck cars 204 Drivers, coupling of 105 speed of 248 Drop in distributing circuit .... 272 in return circuit . . . 295 E Early motors 71 Earnings, net 374 Earth conduction 296 Effect of potential on substation spacing 320 Effective current 134 Efficiency of series motor 58 Electric brakes 195 cars 200 distributing circuit 270 distribution systems 42 heaters 223 locomotives see Locomo- tives.. . 240 Electric motors see Motors. . . 42 railway track see Track. 110 systems, advantages of .... 9 direct-current 8 single-phase 8 three-phase 8 traction, advantages of ... 11 welded bonds 294 rail joints 267 Electrification, scope of 4 steam road 374 Electrolysis 296 alternating currents and . . 301 remedies for 297 Electropneumatic brake 192 Elevated railway cars 214 Emergency stops 194 E.m.f . method of speed variation 50 counter 50 of single-phase motor 60 Energy consumption 147 distribution of 156 effect of gear ratio on ... 151 of grades on 155 of length of run on . . 153 of train resistance on . 152 for auxiliaries 157 methods of comparing .. 151 for train operation 147 kinetic 148 mechanical 12 potential 12 regeneration of 158 effects on equipment. . . . 161 objections 162 Engineering preliminaries 365 Equating motor load 133 Equipment of locomotives 252 power plant, choice of .... 332 substation 316 Estimation of construction cost 373 Expenses, operating 372 Fare collection 210 rate of 368 Feeding, methods of 275 special methods of 302 382 INDEX Field control motors 144 principle of 87 of electric locomotive 241 of railway systems 363 frames 74 strength, control by 87 variation of 53 weakening, methods of. ... 87 Flange friction 19 Floating bolster trucks 232 Flux curve of series motor 54 Force for acceleration 13 for train operation 38 mechanics of 12 Forces, braking see Braking. . 172 Forms of contact line 279 Formula, train resistance 23 Foundation brake rigging 183 Four-motor equipments 145 Frames, motor 74 Framing, car 205 Freight train resistance 25 Frequency, changes in 89, 120 changers, use of 362 for single-phase motors ... 61 Friction 168 effect of sliding wheels. ... 170 flange 19 journal 17 of motors and gears 21 rolling 166 sliding 168 effect of variations in ... 171 of distance on 169 of pressure on 170 variation with speed. ... 168 Functions of motive powers ... 42 Future requirements for city roads. . . 367 Gas-electric cars 256 Gasoline cars 255 Gears, choice of 143 friction of 21 motor 236 ratio, effect on energy con- sumption 150 Gears ratio, limits to 238 of early motors 74 Generation, power see Power. 330 Generators, efficiency of 330 subdivision of 331 Grades 26 effect on energy consump- tion 155 ruling 28 velocity 27 virtual 27 Graphical time table 273 Grid resistors 114 Growth, future, of population. 371 Hand brakes 187 Head-end resistance 20 Heaters, electric 223 Heating, car 222 of motors 131 power for 158 value of current 133 High-speed brake , . 192 -tension d.c. system 357 transmission 326 Horse cars 201 Horsepower for train movement 41 Hot box, cause of 18 Hydraulic power 332 Hysteresis loss 58 IR drop, effect on motor speed 50 in distributing circuit .... 272 in return circuit 295 PR loss in series motor 57 Ice load, effect on trolley wire . . 282 on third rail 289 Incidental resistances 26 Inclination of brake hangers. . . 180 Indications, signal 336 Inductance of single-phase motor 59 Induction motor see Motors . . 67 -generator 307 regulator control 116 series motor . . 63 INDEX 383 Inductive bonds 347 Inertia, rotational, in braking. . 179 Interlocking signals 353 Interpoles, motor 77 Interurban cars 218 railways 371 substations 819 Interval, space 340 Iron loss of series motor . . 58 Joints, rail 263, 266 Jones, P. N 104 Journal friction. . 17 K Kelvin, Lord 275, 318 Kelvin's law 275, 318 Kilowatt hours per car mile. ... 151 Kilowatts for train movement. 41 Kinds of signals 335 Kinetic energy 148 Lamps, car 220 signals 336, 342 Latour-Winter-Eichberg motor. 64 Length of run, effect on energy consumption 153 Leonard, H. Ward 123 Leverage in brake rigging 181 Light signals 336 Lighting, car 220 power for 157 Limitations of rheostatic control 91 Lines, transmission see Trans- mission 324 Location of power plant 331 of substations 318 of third rail 288 Locomotives, electric 240 applications of 246 center of gravity 247 choice of 253 comparison with steam.. 241 control . . . 252 Locomotive, electric, coupling of drivers 249 development 240 equipment 252 field of 241 geared 244 gearless 245 interchangeability of. ... 251 motors 248 motor speeds 245 number of drivers 249 tractors 251 types '. 243 weight on drivers 250 wheel base 250 gasoline 260 special 260 steam 6 characteristics 6 comparison with electric. 241 development of 1 dirt incident to 7 efficiency of . . . 7 types 243 storage battery 260 wheel classification 243 Longitudinal car seats 209 Losses in series motor 56 Lubrication of motors . . 79 M Magnetic brakes 195 Magnetic field of d.c. motor.. . . 54 'Mailloux, C. 35, 39, 133 Manual signal systems 341 Materials for car construction. . 204 Maximum traction trucks 233 Mechanical arrangements of transmission lines. . . . 329 losses of d.c. motor 57 rectifier 315 Mechanics, fundamental prin- ciples 12 of traction 12 Mercury vapor rectifier. . .125, 312 Methods of displaying signal indications 336 of feeding 275 384 INDEX Methods of operating sema- phores 348 of suspending trolley wire.. 279 of train spacing 339 Momentum brakes 199 Monitor roof 206 Motion, equations of 31 Motive powers 6 cable 2, 8 compressed air 7 electricity 8 functions of 42 gasoline 7 steam locomotive 6 stored steam 7 Motor, Motors 42 a.c. commutator 58 induction 67 induction series 63 power required 146 series 58 conductively c o in - pensated 62 inductively c o m p e n - sated 63 performance 65 single-phase, variation of characteristics 66 armature construction 73 speeds 74 bearings 79 capacity 131, 143 -car trains 240 classification of 42 commutator construction. . 78 -compressors 189 construction 71 control. see Control 84 -converter 310 development 71 d.c 42 classification 42 compound 43 series 48 comparison 355 efficiency 58 flux curve 54 losses 56 for regeneration 160 Motor, d.c. series, speed char- acteristics 46 variation of 49 torque characteristic . . 53 shunt 44 for regeneration 159 early 71 energy consumption 150 field control 144 for traction 42 frames 74 friction 21 gearing 74, 143, 236 -generator, induction . . . 307 sets 307 synchronous 308 heating of 131 induction 83 comparison 359 interpoles 77 load, character of 132 equating of 133 lubrication 80 modern 75 armatures 78 number of 144 open type 72 polyphase induction 67 number of poles 69 on single-phase circuit . . 122 performance of 70 speed control 67 potential, average 140 pressed steel 75 railway 10 rating 132, 141 repulsion 64 Atkinson 64 compensated 64 selection of 143 series, advantages of 48 single-phase 81 commutation of 67 frequency for 61 sparking in 60 variations of 62 speeds of 143 calculation of 50 variation with resistance 52 INDEX 385 Motor, Sprague suspensions ventilation windings Multiple-unit control N Near-side car Net receipts Newbury, F. D Newell magnetic brake . . . Nominal rating of motors Nose suspension Number of motors Oil for car journals Open cars Operating expenses Operation of semaphores permissive systems of time-interval Order, train Oscillatory resistance .... Overhead trolley Over-running third rail . . Polar method current 72 Polarity of d.-c. circuit 300 235 Poles, changes in 89, 119 80 of induction motor 69 78 Polyphase induction motor see 98 Motors 67 system 359 Population, estimation of 371 relation to track 365 213 Portable substations 322 374 Potential, change of 84 319 effect on polyphase induc- 197 tion motor 69 141 on substation spacing. . 320 235 method of speed variation . 51 144 motor 140 variation of 85 Power factor of single phase motors 59, 65 19 for a.-c. motors 146 202 for train movement 41 372 generation 330 348 requirements of 330 348 hydraulic 332 355 plant, capacity of 330 339 construction 332 340 equipment, choice of .... 332 19 location 331 279 purchased 333 288 required for auxiliaries .... 157 requirements 127 time curves 130 Preliminaries, engineering. ..... 365 Preliminary signals 349 Prepayment cars 211 Pressures, brake shoe 177 Preventive coil, use of 116 Protected rail bond 294 Protection from electrolysis 297 of third rail 288 Pumps, air 189 Purchased power 333 Q Quick action brake 191 R of equating Rail bonding 293 136 composition 263 Painting, car 229 Pantograph trolley 229 Parabolic equation of trolley wire 283 Paving, track 264 Pay-as-you-enter car 211 Pay-within car 212 Performance, motor see Motors 42 Permissive operation 348 Permutator 312 control 124 Phase splitter, use of 361 Pinions, motor 237 Pipe drainage system 298 Plotting speed-time curves .... 39 386 INDEX Rail joints 263 cast weld 266 cost of welding 269 electric weld 267 special 266 Thermit weld 267 welded 266 reactance of 295 resistance of 295 sections 263 signals 343 third see Third Rail 287 track 262 resistance of 295 Railway, cable 2 cost of 3 city 365 adequacy of 367 future requirements 367 number of cars 369 schedule speeds 370 size of cars 369 type of cars 369 ' use of 367 classification of 5 electric, scope of 4 electrification 374 interurban 3, 371 motor control 84 problem 11 street 2 electric, development of. 3 suburban 5, 370 track see Track 261 trunk line 2 Rapid-transit cars 214 Rating of motors 132, 141 Reactance of rails 295 Receipts, net 374 Reciprocal method for speed- time curves 39 Rectifier, efficiency of 314 mechanical 125, 315 mercury vapor 125, 312 application to d.-c. system 358 application to single- phase system 362 Regeneration, effects on equip- ment.. . 161 Regeneration of energy 158 with d.-c. system 358 with single-phase system.. 363 with three-phase system . . 361 Regulation of transmission circuit 328 Regulator, induction 116 Remedies for electrolysis 297 Repulsion motor see Motors. 64 Requirements, future, for city roads 367 of contact line 278 of train operation 127 Resistance, air 20 control 86, 90 effect on induction motor. . 68 for controllers, proportion- ing of 104 incidental see Train Re- sistance 26 leads in single-phase motor 61 losses of d.c. motor 57 method of speed variation 52 of return circuit 295 oscillatory 19 rolling 19 train-see Train Resistance 17 used for weakening motor field 88 Resistors 113 Retardation see Braking 164 determination of correct. . 171 methods for 164 Retarding force for braking. . . . 180 Return circuit 292 defects in 295 resistance of 295 use of rails as 292 Revenue of interurban roads. . 371 Reverser, controller 95 Revolutions of drivers 248 Rheostatic control 90 Richer, C. W 320 Rigging, brake 181 Rigid bolster trucks 232 Roads, city 365 Robinson, Wm 344 Rolling friction 166 resistance . . 19 INDEX 387 Roof framing of cars 206 Root mean square current 134 Rotary converter 309 Rotational acceleration 14 inertia in braking 179 Ruling grade 28 Run, length of, effect on energy consumption 153 Running gear, car 230 S in contact wire 280 effect of temperature on. . . 281 method of calculation 280 Saturation of magnetic circuit. 45 effect of speed character- istic 47 effect on torque character- istic 45 Schedule speeds for city rail- ways 370 Schmidt, E. C 26 Scofield, E. M 301 Seating arrangement of cars . . . 209 Self-propelled cars see Cars. . 254 Semaphores, methods of operat- ing 348 signals 336 Semi-accelerator car 208 Semi-convertible car 203 Series motor see Motors 48 Series-parallel c o n t r o 1 s e e Control 94 Service stops 194 Shunt motor see Motors 44 Side air resistance 20 -door cars 208, 213 friction 20 Signals 335 automatic block 341 cab 351 car counting 343 controlled manual 341 for a.-c. roads 347 for d.-c. roads 345 for operation in two direc- tions 350 indications 336, 337 Signals, interlocking. 353 kinds of 335 light 337 manual 341 preliminary 349 semaphore 336 single-rail 345 telegraphic 341 track-circuit 343 alternating current 345 double rail a.-c 346 single rail a.-c 345 trolley contact 343 uses of 335 wire circuit 342 Single-phase motor s s e e Motors 58 system 361 transmission 325 Single rail signal 345 Size of contact conductor 286 Slack adjuster 187 Sliding friction 168 Soldered rail bonds 294 Solid frames for motors 75 Space interval 340 Spacing of trains 339 Span, length of 280 wire construction 285 Sparking of single-phase motor . 60 Special methods of feeding .... 302 work, track 269 Speed characteristics of motors 46 control by field weakening. 56 of induction motor 68 e.m.f . of single-phase motor 60 maximum, effect on power consumption 127 motor 49, 143 of a.c. series motor 65 of drivers 248 schedule, for city railways 370 -time curve 31 acceleration curve 33 braking curve 34, 194 calculation of 34 coasting curve 33 components 33 plotting 39 388 INDEX Speed-time,* curve, shunt and series motors... 48 straight-line 128, 149 with electric motors .... 129 Sperry, E. A 250 Spikes, track 262 Split frames for motors 75 -phase control 122 Sprague, F. J 72, 99 Station, power see Power. . . 330 Steam locomotive see Loco- motive 6 road electrification 374 Steel motor frames 74 Stenger, L. A 301 Stop, automatic 352 Stops, cost of 153 Storage battery cars 257 in substations 316 system of air brakes 189 Straight air brakes 190 -line speed- time curves.. . . 128 Street cars 201 Substations. 305 alternating-current 321 capacity of 318 city 319 development of 305 equipment 316 interurban 319 location of 318 portable 322 spacing 320 storage battery in 316 Suburban railways 370 Subway cars 214 Suction, rear 20 Superelevation of outer rail. ... 30 Supports for trolley wire 284 Supporting bridges for contact wire 286 Surface contact system 292 Suspension, bracket 285 by bridges 286 catenary 282 motor 235 span-wire 285 Swinging bolster trucks 233 Switches, track 269 Synchronous converters 309 motor-generator 307 Systems, distribution 42 Systems, electric see Electric for electric railway opera- tion 355 railway 355 a.-c. single-phase 361 a.-c. three-phase 359 choice of 375 d.-c. 600-volt 355 d.-c. high-tension 357 field of 363 three-phase 359 Tandem speed control 120 Telegraphic block 341 Temperature, effect on sags in wire 281 Tension in trolley wire 281 Tests of air brakes 193 Thermit weld 267. Third rail 287 collectors 229 location of 288 over-running 288 protection of 289 removal of ice 289 resistance of 290 under-running 289 Three-phase control. 119 motors see Motors 67, 83 system 359 transmission 325 Thury system 306, 325 Ties, track 261 treated 262 Time element in controller operation Ill increment, determination of 34 interval operation 339 -table, graphical 273 Ton-mile, as basis for energy consumption 151 Torque characteristic of motors. 44 of series motor 53 per ampere 54 INDEX 389 Track 261 bonding 293 -circuit signals 343 for electric railways 345 construction 261 in paved streets 264 length of, relation to popu- lation 366 rails 262 reactance of 295 resistance of . 295 special work 269 ties 261 Traction, mechanics of 12 Tractive effort 38 of single-phase motor ... 65 of steam locomotive. .6, 10 force, calculation of 38 Tractors 251 Traffic of city roads 365 of interurban roads 371 Train control 353 movement, power for 41 operation, force for 38 -order dispatching 340 resistance 17 components 17 determination of 22 effect of curves on 30 of winds 31 on energy consump- tion 152 on power consumption 127 on speed-time curve . . 33 formulae 23 incidental 26 motor-car 240 spacing, methods of 339 Transfers, use of 368 Transformer e.m.f. of single- phase motor 60 Transformers, choice of 327 control with 115 Transmission circuit 324 development 324 regulation 328 types of 324 Transmission, direct-current . . . 306 high-tension 326 Transmission lines, mechanical arrangement of 329 lines, stress in 329 of braking forces 172 potentials 327 Transportation, requirements of 1 Transverse car seats 209 Triple valve 191 Trolley, bow 227 contact signals 343 overhead 279 pantograph 228 wheel 225 wire, grooved 287 length 280 methods of supporting. . 284 of suspending 279 stresses in 281 Truck brake rigging 182 Trucks and running gear 230 bogie 232 braking of 174 double - 232 floating bolster 232 maximum traction 233 rigid bolster 232 single 230 swinging bolster 233 swiveling 232 Two-direction signals 350 Two-motor equipments 144 Types of transmission circuits. . 324 U Underground conduit system.. . 290 Under-running third-rail 289 Uses of signals 335 Vacuum brake. 195 Valve, triple 191 Variation of performance in single-phase motors. . . 66 Vector diagram for single-phase motor . . 65 390 INDEX Velocity grades 27 Ventilation of motors 80 Virtual grades 27 W Ward Leonard control 123 Water power 332 rheostat 114 Watt-hours per ton-mile 151 Weakening of field for control. . 87 of motor field on speed. ... 53 Weight distribution of electric motive powers 9 Welded rail-bonds 294 rail joints 266 Welsh, J.W 104 Werner, G. B 320 Wheel trolley 225 Windage of motor 58 Winds, natural 31 Wire circuit signals 342 Wire, trolley see Trolley Wire . 287 Wiring, car 224 Work, mechanical 12 THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. L> Jun24'51 LIBRARY USE II || 9 iqKA JUL w I30*r Jill 21354LU fi^~ $S\ *C.t^J^ , \\ \ ^eco ^ n *t /_ *dA-^^J >H t,l? , LD 21-100m-8,'34 313776 r UNIVERSITY OF CALIFORNIA LIBRARY