UNIVERSITY OF CALIFORNIA ANDREW SMITH HALLIDIL: Long -Distance Electric Power Transmission Being a Treatise on the Hydro-Electric Generation of Energy; Its Transformation, Transmission, and Distribution BY ROLLIN W. HUTCHINSON, JR. CONSULTING ELECTRICAL ENGINEER ; ASSOCIATE MEMBER AMERICAN INSTITUTE OF ELECTRICAL ENGINEERS, AND MEMBER OF THE AMERICAN ELECTROCHEMICAL SOCIETY NEW YORK: D. VAN NOSTRAND COMPANY 23 MURRAY AND 27 WARREN STS. 1907 HAUIE'E Copyright, 1907, BY D. VAN NOSTRAND COMPANY PREFACE SINCE the beginning of the twentieth century the devel- opment .of water-powers for long-distance transmission which began with the famous Frankfort-Lauffen trans- mission in Germany, in 1891, has been so rapid, and has been marked by such startling feats of engineering skill, that it is almost impossible, except to those who have been intimately connected with this field of engineering, to have more than a vague knowledge of the physical features of such plants. The author has been encouraged to write the book by the demand of engineers and students for information in concise and convenient form, on the kinds of machinery and apparatus used in hydro-electric, high-tension engineer- ing, and the construction and operation of high-potential transmission properties. While primarily intended as a book of reference for engineers and a text-book for students, it is believed that with the exception of some portions it can be intelligently read by those educated persons who are seriously looking for information on this fascinating branch of applied science. The book does not claim to present anything new, nor does it claim to be an exhaustive treatise on the subject. Indeed, the field of high-tension power transmission is so large that it is impossible to give more than a resume of the subject within the compass of this work. The first three chapters are devoted to a brief discussion of the salient principles involved in the construction and iii 158898 iv PREFACE operation of the hydraulic end of high-tension generating plants. Elementary mathematics is employed, and fre- quent reference has been made to the classic of Merriman, "Hydraulics." In the chapters on generators and the laws involved in transmission, the treatment is rather succinct, and presup- poses a knowledge of alternating currents and polyphase machinery. The art is undergoing such a rapid evolution that the author will warmly appreciate any suggestions from readers on improvements in apparatus treated since the material was prepared. To those manufacturers who have courteously given information on, and loaned electrotypes of, their apparatus, the author desires to express his hearty thanks. Chicago, August, 1906. ERRATA PAGE 114. Read "several curves of an i85o-k.w. machine.' 1 PAGE 164. Read L = ^, L = d ~ - PAGE 208. Read " five kilobits," " fifty kilovolts." PAGE 258. " Three kilovolts " should read '. " thirty kilovolts." PAGE 317. Omit " per annum," second line from bottom of page. PAGES 322, 323, 324. All values expressed in kilovolts should read ten times larger; thus, "four kilovolts" should be "forty kilovolts," "five kilovolts" should be "fifty kilovolts," etc. CONTENTS CHAPTER PAGE I. LAWS OF HYDRAULICS ...... i II. APPLIED HYDRAULICS 23 III. HYDRAULIC MACHINES AND ACCESSORY APPARATUS..... 65 IV. GENERATORS, SWITCHES, AND PROTECTIVE DEVICES 109 V. LAWS GOVERNING TRANSMISSION OF ENERGY 159 VI. THE TRANSMISSION LINE 178 VII. TRANSFORMERS 239 VIII. MOTORS 266 IX. CONVERTERS 291 X. PRACTICAL PLANTS 311 XI. DISTINCTIVE FEATURES OF PROMINENT LONG-DISTANCE TRANSMISSIONS 326 LONG-DISTANCE ELECTRIC POWER TRANSMISSION CHAPTER I LAWS OF HYDRAULICS THE energy of water is usually expressed in two ways ; namely, potential energy and kinetic energy. Water weighing W pounds raised to a height h contains an amount of potential energy equal to the product of the two com- ponents, thus, Wh = Potential energy. When a volume of water is dropped from a known height, it acquires an amount of kinetic energy proportional to the square of the velocity attained by it in falling ; thus, v 2 W = Kinetic energy *g in which W = the weight of the water and v = the ve- locity of its descent in feet per second. According to the laws of the conservation of energy the potential energy must equal the kinetic energy, or Wh= W', hence h = - 2g 2g Head and Pressure. The surface of calm water is perpendicular to the direction of gravitational force. For 2 LONG-DISTANCE ELECTRIC POWER TRANSMISSION bodies of water of small area, this surface may be conven- iently regarded as a plane. Any distance or depth meas- ured below this plane is termed a " head." The head upon any point is its perpendicular depth below the level surface. Call h the head and w the weight of a cubic foot of water. At a depth h each horizontal square unit has upon it a pressure equal to the weight of a column of water of a height //, and a cross-section of one square unit, or wh. But since the pressure at this point is exerted in all direc- tions with the same intensity, the unit pressure at the depth h is wh. Conversely, the head for a unit pressure / is ~ , w hence 7 , , P p = wh and h = w When h is given in feet and / in pounds per square foot these equations reduce to / = 62.5 h, and // = 0.016 / (62.5 being the mean value of w}. It is obvious that head and pressure are readily convert- ible, one into the other. It is a common error to use one term as synonymous in meaning with the other : in reality, each is proportional to the other. It is convenient to re- member that one foot head is equivalent to a pressure of 0.434 pounds per square inch ; and that a pressure of one pound per square inch is equivalent to a head of 2.304 feet. Laws of Falling Bodies.- In a perfectly smooth, in- clined channel or conduit, water would flow with a con- stantly increasing velocity, and would, therefore, obey the same laws which govern a body moving down an inclined plane. A flow under such conditions is never realized in practice, since all surfaces over which water moves are more or less LAWS OF HYDRAULICS 3 rough. The motion due to gravity is retarded by the fric- tion between the water and the irregular surfaces over which it flows ; hence the theoretical velocities developed by the following equations cannot be equaled by the true or actual velocities. If a body of water or any other substance, at rest above the surface of the earth and contained in a vacuum, is allowed to fall, its velocity at the end of one second will be g feet (the mean value of g being 32.16) ; and at the end of t seconds its velocity will be the product of the two, or V=gt. The distance through which the body passes in the time t, is the product of the mean velocity J Fand the number of seconds, or h (the distance) = \ gf. Transposing to eliminate t, the relations between dis- tance h and velocity V become, y* V= V2i and h = -- If a body is falling with a velocity V^ at the commence- ment of a period of time t t its velocity at the expiration of this time will be v* = Vi+gt, and the distance through which it will fall in that time is h = vj+\gp. Eliminating t in the equations, the relations become r 2 = Pi and which equations hold good irrespective of the direction of the initial velocity V r 4 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Flow from Orifices. If an opening or orifice is made at any point in the base or sides of a vessel filled with water, the water issues from the orifice with a velocity which depends on the head, the velocity increasing with increase of head. The law of the theoretical velocity of flow is that enun- ciated by Torricelli in 1664, viz : The theoretical velocity of flow from an orifice is that which will be attained by a body falling from rest in a vacuum through a height equal to the head of water on the orifice. Hence, regardless of the plane in which the orifice lies, whether it be vertical, horizontal or inclined, if the head be sufficiently large to exert practically a uniform pressure on all sections of the orifice, the equations ex- pressing the relations are and h V * h = ; 2g the first of which applies to the theoretical velocity of flow that will be given by a definite head ; the second, to the theoretical head which will be produced by a given velocity. The latter expression is usually designated the "velocity head." Discharge from Small Orifices. In hydromechanics the word "discharge" is defined as the quantity of water which flows in one second from an orifice, or pipe. The theoretical discharge is commonly represented by the letter Q, and is the discharge as calculated by ignoring the retardation due to frictional resistance. If every filament of water composing the issuing jet has LAWS OF HYDRAULICS 5 the same velocity, the quantity of water which issues in one second is equivalent to the volume of a prism having a base of the same dimension as the cross-section of the stream, and a length equal to its velocity. Representing this area by a and the theoretical velocity by V, the theo- retical discharge is given by the equation If a be taken in square feet and V in feet per second, the value of Q will be in cubic feet per second. If the orifice be of small area, and the head h the same at all points of the opening, the discharge will be (theoreti- cally) Q = a V = a \/2gh. This equation is strictly applicable only to orifices which lie in a horizontal plane and on which the head is constant. The error involved by applying it to vertical orifices, how- ever, is less than one-half of I per cent if h be greater than twice the depth of the orifice. When the equation is applied to a vertical orifice, h must be taken as the vertical distance from the center of the orifice to the free water surface. The Energy of a Jet. If a stream of water has a ve- locity V, and if W be the weight of water per second which passes any given cross-section, the kinetic energy possessed by this moving water is the same as will be stored up by a body falling freely under the influence of gravity through a height //, and attaining thereby a ve- locity V. Calling E its kinetic energy, V 2 E = Wh = W~ . 6 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Hence, if the quantity of water passing through any given cross-section of the jet be constant, the energy of the jet is (theoretically) proportional to the square of its velocity. It is evident that the weight W of the water may be expressed in terms of the area or cross-section of the jet and its velocity. Designating the cross-section of the jet in square feet by the letter a, and the weight of a cubic foot of water by w t WaV* & = , from which it is obvious that the energy or work which a jet is capable of performing (theoretically) varies as the cube of its velocity. The energy of a jet is always the same, irrespective of the direction in which it is moving whether horizontal, vertical, or inclined. Its energy per second is under all conditions Wk, in which // is the velocity head correspond- ing to the actual velocity V, and W the weight of water discharged per second. Since the theoretical velocity V generally exceeds the actual velocity, the energy of a jet should never be calculated from the theoretical velocity. Impulse and Dynamic Reaction of a Jet. If a jet delivers W pounds of water per second at a uniform velocity F, the motion of such a stream may be considered as due to a constant force F, which acts for one second on the weight IV, and is then withdrawn. During this inter- val of time the velocity of the water W increases from zero to a value F, and the average velocity is -J F Therefore, the work F- J F is given to the water by the force F. The kinetic energy of the flowing water is W ; and LAWS OF HYDRAULICS 7 by the law of the conservation of energy, the magnitude of the constant force is which reduces to / It is apparent that the expression W - is the same as o that for momentum; and as W may be written WaV (w being the weight of a unit of water and a the area of the orifice), the equation resolves into the form : _ WaV* ~~ and since in which the value of F is termed the impulse of the jet. Since the values of W, V, and g are in pounds and feet per second respectively, the value of F is also expressed in pounds. In hydromechanics the word " impulse " has a different meaning from its definition in mechanics as the product of force and time. Since W in hydraulic computations is expressed in pounds per second, the impulse will also be expressed in pounds. If any surface, as, for instance, the vanes of a water- wheel, be placed in the path of the jet, the impulse may be considered as a pressure which sets up a rotation of the wheel. 8 LONG-DISTANCE ELECTRIC POWER TRANSMISSION If a jet is caused to impinge normally on a plane it pro- duces a pressure on the plane which corresponds to the im- pulse F, because the force necessary to stop W pounds of water in one second is the same as that which was required to produce its motion. Likewise, if a jet, which is moving with a velocity v v suffers a retardation by which its velocity is reduced to v 2 within one second, the impulse in the first second of time is W > and in the next second, it is W - g g The difference between these two, or is the dynamic pressure developed. Upon this principle de- pends the operation of turbines or other hydraulic machines. Constant Flow in Smooth Pipes. When water flows through a pipe of irregular cross-section, every section of which is filled with water, a like quantity of water passes each section per second. Designating the quantity of water by q and the mean velocities by v lt v# and v s in sections having areas a v a , and a s respectively, the flow is given by the equation, q av rtj t\ + a 2 v 2 + a 3 v s ... (The velocities in different sections vary inversely as the areas of the sections.) Call W the weight of water which flows per second through the sections of the pipe a l and a 2 , and let i\ and v 2 be the mean velocities in these sections. In the section #! the potential energy possessed by the water when at rest is Wh. When motion is imparted to it, the energy in that LAWS OF HYDRAULICS 9 section is the potential energy Wh, due to the head pres- sure plus the kinetic energy Ignoring the losses due to impact or friction, the energy in both cases is the same, hence, ff l = ^ + ^ and H z = h z + ^-> H being the hydrostatic head at no flow. The law repre- sented by this equation was first established by Bernouilli, and may be stated as follows : At any section of a tube or pipe, in which the flow is steady and frictionless, the pressure head plus the velocity head equals the hydrostatic head which exists when there is no flow. In applied hydraulics this theorem is of very great im- portance. Definitions of Coefficients of Contraction, Velocity, and Discharge. A jet of water issuing from an orifice suffers a contraction of area, due to the fact that the filaments of water approaching the orifice move along constantly converging lines. This convergence continues for a slight distance beyond the plane of the orifice. The contraction of the jet causes only the inner corner of the orifice to be struck by the issuing water. (It is this phenomenon which causes a jet issuing from a cylin- drical orifice to have the appearance of a clear crystal bar.) A contraction of the issuing stream also takes place when an irregular or triangular orifice is used 10 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The coefficient of contraction may be defined as the number by which the area of the orifice must be multiplied to give the area of a section of the jet at a distance from the plane of the orifice equal to approximately one-half its diameter. Denoting the coefficient of contraction by c c and the area of the contracted section of the issuing jet by a c , then a c = c c a, the value of which is always less than unity. The coefficient of contraction can be directly determined by measuring with calipers the dimensions of the least Fig. i. Measurement of Coefficient of Contraction cross-section of the jet. Fig. i shows the method of mak- ing the measurement. For a circular orifice having diam- eters for sections a and a c , d and d c respectively, where D is the total depth of the stream, and /X the depth of water below the end of the rod. APPLIED HYDRAULICS 2/ A more accurate method than floats for determining the velocities of streams is the use of the current meter. This device is operated from a bridge in the case of small streams or from an anchored boat in a river. This method of gaug- ing the discharge gives more accurate results than can^ be obtained by any formula. For making a gauging, a section of channel should be selected where a uniform flow exists. Several sections at right angles to the direction of flow are then chosen, and soundings made upon them at a number of points across the stream, the water gauge being read at each sounding. The distance between sounding points is measured by means of a cord stretched across the stream. The information is now at hand for obtaining the areas shown in Fig. 9. The sum of these areas is the total area a. In Order to obtain Fig. 9. Method of Determining Total Area of .-, i T, . ! a Stream the additional areas for a rise of stream, levels should be run beyond the water edge to high-water marks. When a current meter can be used, it is necessary to make readings only in one section : when floats are used, two or more sections should be selected. The next step is the determination of the mean velocities v i> v v 7; s' etc -> m eac h f tne sub-areas. When a current meter is employed, this is accomplished by commencing at one side of a sub-division and slowly moving the meter until bottom is nearly touched ; then moving it a few feet in a horizontal plane and drawing it to the surface ; again mov- ing it a short distance longitudinally and lowering it, and so 28 LONG-DISTANCE ELECTRIC POWER TRANSMISSION on until the entire sub-area has been gone over. The velocity obtained from the total number of revolutions dur- ing the time the meter is submerged is the mean velocity for the sub-area. A common method of making this determination consists in merely raising and lowering the meter in the middle of the sub-area and taking a reading. This gives a fair approxima- tion to the mean velocity. The areas and velocities having been found, the discharge q is computed by the equation q = a^ + a 2 v 2 + a B v B + . . . . J dividing this by the total area, a, the mean velocity in the entire section is ascertained. Rough determinations of velocity can be found* by one or several measurements by the use of floats. This method is much less expensive than the other methods given, and where quick and only approximate results are desired is to be recommended. Experimental work has shown that the ratio of the mean velocity, v, to the maximum surface velocity, V, lies between 0.7 and 0.85 ; calling it 0.8 v = 0.08 V. This assumption gives an error in the value of v which rarely exceeds 1 8 per cent ; usually the error is much less than this value. The selection of the particular method to be used in determining the energy of streams should depend upon the conditions. It will be usually found that measurements which give the most accurate results irrespective of expense are the most satisfactory in the long run. APPLIED HYDRAULICS 2Q Types of Dams. Five general types of dams are em- ployed in hydraulic engineering practice : masonry dams, rock-Jill dams, hydraulic-fill dams, timber dams, and earthen dams. The type of dam suitable for any given condition depends on the character of the foundation which can be secured, the size and importance of the structure which is necessary, the topography of the country, the degree of imperviousness required, and the permissible cost. The character of structure best adapted to withstand water pressure and the destructive action of the elements is unquestionably the masonry dam founded on solid rock, and built up in the form of a monolith between natural rock buttresses on a gorge, with Portland cement mortar. Masonry dams, however, cannot be erected on every site where it is desired to impound water, since the founda- tions are not always suitable, and the conditions which must be met render their cost prohibitive. The general requirements to be met in the design of a masonry dam are : (i) It must not fail by overturning ; (2) it must not slide on its foundations or any horizontal points ; (3) it must not fail by the crushing of the masonry or by the settlement of its foundations ; (4) it must be safe from excessive pressure upon the masonry whether the reservoir be full or empty ; (5) certain known safe limits to crushing of the masonry of the class to be used should not be exceeded. Masonry dams are generally built in the form of a sim- ple triangle with certain modifications, such as a definite width of top to enable the dam to resist wave action and ice thrust. Masonry dams may resist the thrust of water pressure 3O LONG-DISTANCE ELECTRIC POWER TRANSMISSION either by their weight alone or by being built in the form of an arch which will transmit the pressure to the abut- ments. The first of these two types is called the " gravity " dam. The second is termed the " arch " dam ; and it may be either of the gravity type in arched form, or it may depend upon its arched form alone. In either case, the weight of the dam must be borne by foundations which must be of the best quality of solid bed rock. Every masonry dam should be built in the form of an arch in order to avoid cracks or fissures in its surface due to changes of temperature. Another advantage of a curved arch dam is that the pressure of the water tends to close all small cracks that occur, and also takes up the move- ment due to temperature changes without producing cracks. Wilson says that the pressure on the back of an arched dam is perpendicular to the up-stream face and is decomposed into two components, one perpendicular to the span of the arch and the other parallel to it. Rock-fill dams find application at the present time in cases where economy is the main consideration. They are largely used in the Western States for reservoir dams when a large supply of stone is available. They are built in six forms : (i) With a facing of asphalt concrete laid on a sloping wall ; (2) with a central core of steel plates and hand-laid facing walls; (3) with facing of Portland cement laid on a dry wall ; (4) with facing of masonry built verti- cally and covered on the lower side with blocks of stone laid in mortar ; (5) with facing of steel-plates laid on a sloping interior surface on a dry hand-laid wall ; (6) with a facing of earth. Hydraulic-fill dams are the cheapest to construct, and are used in regions where the adoption of a different type APPLIED HYDRAULICS 31 would be prohibitive on account of the topography of the country and the cost of transporting material to the site. The conditions required for the practical employment of hydraulic-fill dams are: (i) An abundance of water at a proper elevation to form a "sluicing head " ; (2) sufficient deposits of materials to form the dam, convenient to either end and high enough above the top to permit of the requi- site grade for transporting the suspended matter to the desired point ; (3) a good foundation, which is requisite for all dams. Hydraulic-fill dams are constructed by tearing down loosely attached rock, earth, and other organic matter by means of a jet of water under high pressure and allowing it to float to the point where the dam is to be constructed. They are commonly employed in some sections of the West for storage reservoirs. They have been built as cheaply as 65 cents per acre-foot of storage capacity. Wooden dams are frequently employed when the stream is small, and a supply of timber is readily available. Their chief recommendation is cheapness. Earthen dams, pure and simple, are seldom used at the present time. Six forms exist: (i) A homogeneous em- bankment of earth in which all material is alike through- out ; (2) an embankment with a central core of puddle con- sisting generally of a mixture of sand, gravel, and concrete of clay ; (3) embankment in which the central core is a wall of masonry or concrete ; (4) embankment with "puddle" or concrete placed on the water face ; (5) embankment of earth resting against an embankment of loose earth ; (6) embankment " sluiced" into position by high pressure. The most popular of these forms is the masonry core wall with "puddle " facing. 32 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Pressure on Dams. Causes of Failure. In construct- ing a dam to impound water one of two possible cases exists : In the first the masonry may extend to a con- siderable distance above the level of the water behind it, the discharge being effected by means of a waste weir. The water pressure against its surface is then in a direc- tion normal to the horizon- tal plane (Fig. 10). Such Fife. 10. Direction of Pressures , , . . , , . on Dams pressure may be divided into two composite parts, one part of which lies in a horizontal and the other in a vertical plane. For all practical purposes the horizontal component is the only one which need be considered. Representing this by J/and its height above the base of the dam by h, the magnitude of these two quantities for one linear foot becomes M=wh where w represents the weight of a cubic foot of water. It is obvious that the horizontal component of water pressure does not depend on the slope of the dam. In the more common case where the water n is discharged over the top of the dam (Fig. n), let //, as before, be the height of the dam and d the depth of water on the crest of APPLIED HYDRAULICS 33 the dam. Then the horizontal pressure against its back will be M= wh (d + $X) = J wh (h + 2d). Dams burst or fail from the following causes: (i) By sliding ; (2) by rotation of the toe ; (3) by overturning ; (4) by crushing of the material (if of masonry); (5) by settling of the foundations. The first two are the most common causes of failure. A dam will slide when the horizontal pressure against its surface equals or exceeds its frictional resistance. Calling M the horizontal pressure against a dam, f the coefficient of friction and W a its weight, sliding occurs when Rotation of the toe of a dam occurs when the moment of M equals the moment of fFwith respect to the toe. Or, fail- ure from this cause occurs when Ml = W a a, in which / and a are the lever arms let fall from the toe in the direction of M and W a respectively. For masonry dams the maximum permissible pressure should not exceed 1 5 tons per square foot. In some cases it should not exceed 6 tons per square foot. A frequent cause of failure in dams where the surplus water is not discharged over the crest is lack of sufficient spillway or waste weirs. The most notable instance of the failure of a high dam for hydro-electric power development is that of the Austin, Texas, municipal dam. The dam proper was 1,091 feet long and 68 feet high. It was built perfectly straight and con- 34 LONG-DISTANCE ELECTRIC POWER TRANSMISSION tained about 88,000 cubic yards of masonry, of which 70,000 cubic yards was of rough rubble and 18,000 cubic yards of cut stone. The cost of the dam, with the head- gate masonry, was $608,000. It was situated on the Colorado River, two and a half miles above the city. In a severe flood early in April, 1900 (the highest in the history of the dam), about 500 feet of the structure was pushed bodily down stream, sliding, apparently, on its base. Storage Reservoirs. In regions particularly the Western States where the supply of water from the primary source is not constant throughout the year, means must be resorted to for furnishing the deficit from a secondary source, or reservoir, during the season of low water. .Storage reservoirs are of two kinds natural and arti- ficial. Natural reservoirs are found principally in the West, east of the Rocky Mountains. These natural basins, or depressions, collect the water run off in the wet season from the surrounding watershed, and retain it in ponds until it is partly or wholly lost by evaporation. Such natural basins are frequently utilized for storage reservoirs by con- ducting water into them from adjacent streams, and pro- viding them with outlets, by means of which they are connected with the primary source of supply. Moreover, they are frequently found at elevations sufficiently high to enable high heads to be secured by leading the pipe or conduit line down the gradient into the valley or canyon, wherein is located the power plant. Artificial reservoirs are generally formed by erecting a dam across a valley at a point where the topography of the country is such as to obviate any loss of water into another APPLIED HYDRAULICS 35 watershed, or by leakage from the dam. The reservoir should also be formed sufficiently high up in the valley to permit the water to flow freely to the place of utilization, or not infrequently to furnish the desired head of water at this point. It is quite desirable that the valley be narrow and the surrounding hills be steep at the point where the dam is located, so as to prevent both expensive construction and shallow water. However, a basin or valley with slight longitudinal slope will afford a given amount of storage with less height of dam than one with a precipitous channel. The location of a reservoir, or system of reservoirs, for supplying a hydraulic plant depends on the particular con- ditions which must be met, such as the quantity of water which the auxiliary source of supply must furnish in the drought season ; the length of the low season ; the area of the supplying watershed, and the quantity of water which can be impounded in the rainy season. ' Aside from the water-impounding area afforded by the contour of the country, the capacity of storage reservoirs depends on the annual precipitation and the climatic con- ditions in the particular region ; the size of the watershed drained, and the losses from leakage and evaporation. The latter loss generally ranges from 8 per cent to 12 percent of the consumption. In dry, arid regions of the West, the loss by evaporation amounts to 75 per cent or more of the consumption per annum. Waste Weirs or Spillways. Waste weirs find appli- cation in discharging surplus water from reservoirs or dams. They are usually constructed in the sides of a reservoir, and have no end contractions. When a waste weir is made with a narrow crest and a vertical front, the dis- 36 LONG-DISTANCE ELECTRIC POWER TRANSMISSION charging stream of water will have air beneath it, and the quantity of water discharged is, by Francis's formula, q = 3-33 W5T*, where b represents the length of the crest, and H the head measured at a definite distance back of the crest. The equation is modified by a wide crest and sloping approach, the discharge in such cases being slightly less. For a crest with inclined approach and about three feet wide, the formula of Francis becomes q = 3.01 Since it. is extremely difficult to determine the exact dis- charge which is to pass over a waste weir, the accurate determination of its length is unimportant ; but a large factor of safety should be allowed in order to obviate the dangers from exceptional floods. When, as in the case of dams, the water flows over an apron of timber or masonry, the inclination of the material, as well as the inclination of the approach to the crest, changes the form of the equation, which then becomes q = in which //"is the head due to velocity of approach, and m is a constant, the value of which ranges between 2.5 to 4-3- Several forms of waste weirs exist: (i) Waste weirs excavated in natural soil at one or both ends of the dam. (This type is not safe unless the foundation is of rock.) (2) Spillways channeled through some low point in the dividing ridge and the water conducted to another valley. (3) A portion of the dam (if of masonry) is designed as a spillway, and is located at about the axis of the valley. APPLIED HYDRAULICS 37 When spillways of the latter type are used, their con, struction should be so substantial that the strains of over- flow from floods will not affect them. The tops of spillways should also be so designed as to resist the blows of, and pass over, logs, ice, or debris, brought down by floods. Loss of Head in Pipe Lines. The principal sources of loss which occur in pipe lines are due to (i) Friction ; (2) contraction of the area ; (3) constriction of the orifice ; (4) curvature. The first and principal loss is caused by the resistance to flow offered by the interior surface of the pipe. In very long pipes it becomes quite prominent, so that the dis- charge may be but a small percentage of that due to the head. The loss of head by friction may be ascertained for any particular case by measurement of the head //, the area a of the cross-section of the pipe, and the discharge q per second. Five approximate laws govern the friction loss in pipe lines: (i) The loss by friction is proportional to the length of the pipe. (2) It varies nearly as the square of the velocity. (3) It decreases as the diameter of the pipe increases. (4) It increases with the roughness of the inside surface. (5) It is independent of the pressure of the water. Or stated in the form of an equation : / V* fi f =-c , d 2g where c is the coefficient of friction, / the length of the pipe in feet, d its diameter in the same units, and v the 38 LONG-DISTANCE ELECTRIC POWER TRANSMISSION velocity of flow. The equation is but an empirical one since the theoretical expression for h f has not as yet been determined. The friction factor is governed by the character of the interior surface of the pipe, diminishing with smoothness of surface. A value commonly employed is 0.02. While our knowledge of the internal frictional resistances of flowing water is still in a very unsettled state, it appears that the energy transformed by friction into heat is lost in two ways : by direct friction along the inside surface, and by impact caused by the varying motion of the particles of water. Loss of head, due to the contraction of the cross-section of a pipe, also causes a contraction of the water stream, and its tendency to expand to fill the diminished section causes loss in head. In the case of a gradual contraction in the cross-section of a pipe, which is the more common one, the loss in head can be determined for any definite velocity by noting the difference in height between two pressure columns, one of which is inserted just above the point where the cross- section changes, and the other, slightly below the point where the contracted section commences. Having determined the values for the velocities v, and z> 2 > and the heads k, and h^ in the respective cross-sections, the loss in head, occasioned by a contraction of cross- section, becomes If there is no subsequent increase of cross-section, the loss of head from this cause is not appreciable, since it is due to loss of velocity caused by abrupt expansion. APPLIED HYDRAULICS 39 Loss of head in a pipe line may also be caused by a sud- den constriction of the orifice of the pipe. It is explained by the fact that the particles of water, as they approach the orifice, move in converging directions ; hence such contraction of the stream causes only the inner corner of the orifice to be touched by the water in its outward pas- sage. When a pipe line is laid on a curve the water flow is changed in direction, which causes an increase of pressure in the direction of the radius of the curve and away from its center. The increase of pressure sets up eddying movements in the water, causing impacts against the wall of the pipe. Such impacts dissipate some of the energy of the head by transforming it into heat. It is obvious that the loss of head h c , caused by a curve in a pipe line, in- creases with its length. It is also larger for small pipes than for large ones. The loss of head, caused by a curve in a pipe line, is expressed by the following equation, in which f c is a number termed the curve factor, the value of which depends upon the ratio of the radius of the pipe to its diameter ; / is the length of the curve ; d the diam- eter of the pipe, and v the mean velocity of flow. Repre- senting by R the radius of the circle in which the center r> line of the pipe is laid, as the ratio decreases, the value d of f c increases. Owing to a lack of sufficient experimental data to deter- mine accurate values for the curve factor f c , the equation 40 LONG-DISTANCE ELECTRIC POWER TRANSMISSION can only be considered as a rough guide. For cast iron pipe, Messrs. Hubbell and Frenkell determined the follow- ing values of the curve factor for 3O-inch pipe laid with a curve of 90 degrees : = 24 16 10 6 4 2.4 a f- c = 0.036 0.037 0.047 0.060 0.062 0.072. When there are several bends or curves in a pipe line, the value of f c is computed for each curve ; and the sum of these values is taken in order to find the total loss of head due to the curvatures. The equation then becomes in which k represents the sum of these values for all the curves. The loss in head caused by curves in a pipe or flume line is generally small compared with that lost in friction, as the curves are made as few and as slight as possible. Mean Velocity of Flow in Pipes. Assuming that the pipe is running full, the formula for mean velocity of flow can be deduced from the factors which have been 9 V thus far stated. Let Ji be the maximum head, the v 2 effective velocity head of the issuing stream, and h -- the lost head. The lost head is equal to the sum of its component parts, which may be called //' -f hj -f- h c . APPLIED HYDRAULICS Loss of Head in Pipe by Friction The following tables show the loss of head by friction in each 100 feet in length of different- diameters of pipe, when discharging the following quantities of water per minute : INSIDE DIAMETER OF PIPE IN INCHES. 13 14 15 16 18 20 Vel. Loss of 1 Cubic Loss of Cubic Loss of Cubic Loss of Cubic Loss of Cubic Loss of Cubic in ft. head feet head feet head feet head feet head feet head feet per per in per in per in per in per in per sec. feet. min. feet. min. feet. feet. min. feet. min. feet. mm. 2.0 .183 110. .169 128. .158 147. 147 167. .132 212. .119 262. 2.2 .216' 121. .200 141. .187 162. 175 184. .156 233.- .140 288. 2.4 .252 133. .234 154. .2tf 176.. .205 201. .182 254. .164 314. 2.6 .290 144. .270 167. .252 191. .236 218. .210 275 .189 340. 2.8 .332 156. .308 179 .288 206. .270 234. .240 297. .216 366. 3.0 .375 166, .349 192. .325 221. .306 251. .271 318. .245 393. 3.2 .422 177. .392 205. .366 235. .343 268. .305 339. .275 419 3.4 .471 188. .438 218. .408 250. .383 284. .339 360. .306 445. 3.6 .522 199 .485 231. .452 265. .425 301. .377 382- ,339 471. 3.8 .576 210. .535 243. .499 280.' .468 318. .416 403, .374 497. 4.0 .632 221. .587 256. .548 294. .513 335. .456 424. .410 523. 4.2 .691 232. .641 269. .598 309. .561 352. .499 445. .449 550. 4.4 .751 243. .698 282. .651 324. .611 368. .542 466. .488 576. 4.6 .815 254. .757 295. .707 339. .662 385. .588 488. .529 602. 4.8 .881 265. .818 308. .763 353. .715 402. .636 509 .572 628. 5.0 .949 276. .881 321. .822 368. .770 419. .685 530. .617 654. 5.2 1.020 287. .947 333. .883 383. .828 435. .736 551. .662 680. 5.4 1.092 298. 1.014 346. ;947 397. .888 452. .788 572. .710 707. 5.6 1.167 309. 1.083 359. 1.011 412. .949 469. .843 594. .758 733. 5.8 1.245 321. 1.155 372. 1.078 427. 1.011 486. .899 615. .809 759. 60 1.325 332. 1.229 385. 1.148 442. 1.076 502. .957 636 .861 785. 7.0 1.75 387. 1.630 449. '1.520 515. 1.430 586. 1.270 742. 1.143 9.16. INSIDE DIAMETER OF PIPE IN INCHES. 22 24 26 23 30 36 Vel. Loss o Cubic Loss of Cubic Loss of Cubic Loss of Cubic Loss of Cubic Loss o( Cubic In ft. head feet head feet head feet head feet head feet head feet per per in per in per in per in per in per .sec. feet. min. feet. min. feet. feet. min. feet. min. feet min. 2.0 .108 316. .098 377. .091 442. 084 513. .079 589: .066 '848. 2.2 .127 348. .116 414. .108 486. .099 564 .093 648. .078 933. 2.4 .149 380. .136 452. .126 531. .116 616. .109 707. .091 1018. 2.6 .171 412. .157 490. .145 575. .134 667. .126 766. .104 1100. 2.8 .195 443 .180 528. .165 619. .153 718. .144 824. .119 1188. 30 .222 475. .204 565. .188 663. .174 770. .163 883. .135 1273. 8.2 .249 507. .229 603. .211 708. .195 821. .182 942. .152 1357. 3.4 .278 538 .255 641. .235 752. .218 872. .204 1001. .169 1442. 3.6 .308 570. .283 678. .261 796. .242 923. .226 1060. .188 1527. 3.8 .340 601. .312 716. .288 840. .267 974. .249 1119. .207 1612. 4.0 .373 633. .342 754. .315 885. .293 1026. .273 1178. .228 1697. 42 .408 665. .374 791. .345 929 .320 1077. .299 1237. .249 1782. 4.4 .444 697. .407 829. .375 973. .348 1129. .325 1296. .271 1866. 4.6 .482 728. .441 867. .407 1017 .378 1180. .353 1355. .294 1951. 48 .521 760. .476 905. .440 1062. .409 1231. .381 1414. .318 2036. 6.0 .561 792. .513 942. .474 1106. .440 1283. .411 1472. .342 2121. 5.2 .602 823. .552 980. .510 1150. .473 1334. .441 1531. .368 2206. 54 .645 855. .591 1018. .546 1194. .507 1385. .473 1590. .394 2291. 56 .690 887. .632 1055. .533 1239. .542 1437. .506 1649. .421 2376. 5.8 .735 918. .674 1093. .622 1283. .578 1488. .540 1708. .450 2460. 6.0 782 950. .717 1131. .662 1327. .615 1539. .574 1767. .479 2545. 7.0 1.040 1109. .953 1319. .879 1548. .817 1796. .762 2061. .636 2968. The following formula, deduced by Wm. Cox, gives practically the same results as the above table and will be found useful in many instances. F = -^-^ (4 V 2 + 5 V-2). Where F friction head, L length of pipe in feet; D diameter of pipe in inches; V velocity in feet per second. Table I 42 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Substituting the values of //, h p and h c , from the pre- vious paragraphs, 1? V* I 7? tf h = h m h c . t- , 2^ 2g (t 2g 2g V 2 where m is the loss of head at the entrance (negligible & 72 2 for long pipes) \c-,* , the loss by friction, and n , the d 2g 2g loss due to curvature. Solving for v, the equation becomes -v/ i + m + C-, + // a which is applicable satisfactorily to pipes of moderate length. Determination of Discharge from Pipes. The dis- charge per second from any pipe of a given diameter is found by multiplying the area of its cross-section by the velocity of discharge, which, stated as a formula, is Determination of the Diameter of Pipe to Discharge a Given Quantity of Water. Let d represent the diameter, / the required length of the pipe line, q the quantity of water to be discharged, h the head, and f the coefficient of friction (0.02). Neglecting the influence of curvature, an equation for diameter is d = o.479 in which the values of //, /, and d are taken in feet, and that APPLIED HYDRAULICS 43 of q in cubic feet per second. In applying this formula two computations are generally made. In the first calcu- lation, d in the right-hand side is disregarded and a rough value for the diameter is calculated. Then determining the velocity from the equation the friction coefficient for this velocity is looked up in a table of coefficients. A second calculation of d is then made, using in the right-hand side of the equation the rough value of d first derived. To arrive at the value of d with a fair degree of accu- racy, several computations are generally made, using each time the approximate value of d obtained by the preceding computation. Long Pipes. A pipe is said to be long when its length is approximately 4,000 times its diameter, or more. In the West, particularly in California, the pipe or flume lines which conduct the impounded water to the hydraulic machines range in length from a few hundred feet up to seven miles or more, and it is with this class of pipes that we are principally concerned. In long pipes the friction loss predominates, the velocity head being usually small. The expression for velocity, when a long pipe is running full, is in which the letters have the significance assigned in previous paragraphs. 44 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The discharge per second through a long pipe is given by the expression * * f**k 6 - 3 V^r Maximum Energy Transmitted by a Water Pipe. Let Q = total cubic feet of water. D = diameter of the pipe. h = total head. / = length. The relation between these quantities becomes A cubic foot of water falling through a distance of one foot develops 62.5 x 60 = 0.1135 horse-power. 33,000 Then H. P. =0.1135 Q H > where H equals the distance of fall in feet and Q = quan- tity of water in cubic feet per second. Hence if h f is the loss of head due to friction, the horse-power delivered at any distance L feet away is H. P. = 0.1135 Q ( H ~ h f)- By substituting the value of Q the relation becomes H. P. = 0.1135 X 38.5 D \ ( H ~ fa Calling the value of h f equal to kH (where k equals APPLIED HYDRAULICS 45 the sum of all the curve factors) we get by substituting and reducing H. P. = The first formula gives the horse-power that can be transmitted for any definite fraction of the head lost in friction ; and the second, the length of pipe which will transmit a given amount of power with a given loss. Loss of head is proportional to F 2 and loss of power to V, hence the maximum power is transmitted when one- third of the head is dissipated in friction. Mean Velocity of Flow in Canals and Conduits. The general empirical formula of Chezy for the mean velocity of flow in streams is also applicable to conduits and canals, and, with some modifications, to all forms of chan- nels. For a circular conduit running full or half full, the hydraulic radius r \d ; hence the mean velocity is v = c \rs = c . where c is the friction coefficient, the value of which depends upon the roughness of the conduit and its curva- ture, and s is the slope. The discharge from the same kind of channel is then given by the equation q = av = c . \a v5jr, in which a is either one-half of the area of the cross- section, or the entire circular cross-section. 46 LONG-DISTANCE ELECTRIC POWER TRANSMISSION For a rectangular conduit, the velocity and discharge are given by the equations v = c *\frs and q = av = c a *Jrs, the values of c being taken from a table of coefficients for circular conduits. In case the depth of water is greater or less than one- half the diameter of the pipe, the value of c increases with r. It also increases greatly with the degree of roughness. The empirical formula of Kutter (derived from the experiments conducted by Ganguillet and Kutter in 1869) is now universally employed for determining the value of c in the Chezy formula, since it is applicable to all kinds of surfaces. In fact, it may be said in general, that no design for channels is now made without its employment in the preliminary investigations. The formula of Kutter for c is i.8n , c = - -- h 41.65 + 0*00 n I _( 4I . 6s where r is expressed in feet, and v in feet per second ; n is an abstract number of a value depending upon the charac- ter of the surface. In Kutter's formula the value of c is expressed in terms of the hydraulic radius r, slope s, and the degree of rough- ness of surface. The Contruction of Flumes. Flumes are frequently employed for conveying water to hydro-electric plants, but are not considered as economical as pipe systems or con- duits, since the loss in leakage is greater; and they are APPLIED HYDRAULICS 47 also more liable to damage or destruction from snow- storms, wind, and decay. In mountainous regions, how- ever, where timber is abundant, and the cost of transport- ing the pipe system prohibitive, their use may be more advantageous than other forms of water-conducting sys- tems. A flume can be made much smaller than a canal on account of the high permissible velocity of water in it, which is usually about 6 or 8 feet per second. Flumes also offer much less resistance to the flow of water than canals, which give a smaller loss of head for the same capacity. Flumes are generally constructed in rectangular form of durable timber, and are supported either on trestles, or stone or concrete blocks. When a flume system is sup- ported on level benches, cut in the hillside or soil, the flume is termed a bench flume. Bench flumes are sup- ported on concrete brick or solid stone. In crossing a rough section of country, or a valley or divide, flumes are supported on trestles. The timber used 'in the construction of flumes should be of a variety which does not easily decay, and which is also plentiful in the neighborhood. When a flume line is laid near the base of a hillside or mountain, the bed on which it rests should be excavated in the side of the elevation, and the flume laid very close to the bank, as a precaution against damage from snow or wind storms. In exposed places, flumes are covered with planks and timber from two to six inches in thickness, as a protection against roll- ing bowlders and landslides. In California, where flumes are extensively used as water- conducting systems for hydro-electric plants, the flume boxes are generally constructed of clear, surfaced redwood, placed in position longitudinally to the flow of water. The 48 LONG-DISTANCE ELECTRIC POWER TRANSMISSION trestle caps, stringers, and yokes are usually made of Ore- gon pine. Fig. 12 shows a type of California flume constructed of the materials as stated above. Flumes are braced at intervals of several feet by diag- onal scantlings nailed to horizontal timbers or sills, fas- tened to the bottom. The construction employed when the loss in leakage is desired ,wire Naiis to be kept as small as possible, consists of a double thickness of planking, the inner one being sometimes coated with tar or asphaltum to prevent any seepage of water, and also to pro- long its life. The length of life of a flume is f 9'- 9 If fc I 4 Batten ^Boxes 12 Ft.Long \\ Bottom & Sides * X A Cut Nail? 34 to Lb. l^Gtln. "'SO Nails 4" Long about 35 to Lb. Two SetB of Three Intermediate Poets Fig. 12. Type of Flume used in Some California Plants greatly prolonged by creosoting the timber, but the construction is rendered much more expensive thereby. A type of flume used principally on the Pacific coast is known as the stave and binder flume. In this type the bottom is constructed like the lower half of wood stave pipe, but vertical sides are used instead of the closed top. A binding rod is passed around the flume, its ends passing through the two ends of a cross-head, and provided with nuts by means of which the staves are forced together. Flumes of this shape are supported on T-shaped frames made of T-iron, and resting on wooden bolsters, spaced UNIVERSITY or HYDRAULICS 49 about 8 feet apart ; each frame resting on concrete blocks. Trestles for supporting flume lines are made of either wood or steel, with footings constructed of a cement con- Fig. 13. Flume Supported on Trestle crete. Fig. 1 3 shows a flume line carried on a wooden trestle. Waste flumes are designed to carry away the overflow from forebays, and are similar in design to conducting flumes. When a flume or water-conducting channel runs through a forest, means must be adopted to prevent leaves and twigs which fall in the water from entering the connecting pipe line or penstock. Figs. 14 and 15 illustrate a device employed in the flume line of the Mill Creek Plant of the California Edison Company, to free the water of such 50 LONG-DISTANCE ELECTRIC POWER TRANSMISSION matter before it reaches the connecting pipe line. It com- prises an endless wire screen, wound over two drums, the lower end of the screen being immersed in the water, thus catching and removing the floating matter from the water, and depositing it in a mass underneath the upper end. Movement of the screen drum is effected by means of a Fig. 14. Device for Removing Leaves and Twigs from Flume Lines sprocket chain actuated by an undershot wheel, which is operated by the current in the flume. Precautions are also adopted to prevent the sand which enters the flume line from the supplying stream, from getting, into the connecting line, where it would quickly abrade the metal and cause serious damage to the nozzles and buckets of the wheel, APPLIED HYDRAULICS 5 I Circumferential Pressure in Pipes. Let / = intensity of strain, r = radius of pipe, p = pressure-head, / = thickness of shell. Then / = ^T For stresses in riveted steel pipe : Let / = intensity of strain, e == modulus of elasticity, / = change of temperature, k coefficient of expansion. Then i=etk. The Construction of Pipe Lines. The method of con- veying water to hydraulic machines by means of pipe lines has become almost universal practice on the Pacific coast, and in mountainous sections of the West. The material used in the construction of pipe lines is either wood, cast iron, wrought iron, or steel, the latter being generally used in the riveted form. The use of wood stave pipe as a conveying medium for water is quite general in some sections of the West. It is constructed of redwood, fir, cypress, pine, or other durable woods with wooden tongue-butt joints, the sections being bound with steel bands, and held together with clips or shoes made of cast iron. The pressure which a wooden stave pipe can safely withstand depends upon the hardness of the saturated wood a working head of 200 feet having been shown by experience to be a safe practical limit in the case of redwood and Douglass fir. 52 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Among the advantages claimed for wooden stave pipe are: (i) Greater discharging capacity than metal pipe of the same diameter, due to the fact that the friction factor does not increase with age i.e., they do not become rougher with age. (2) The materials for constructing a stave pipe can be easily transported to the region through Fig. 15. Undershot Wheel which Actuates Device Shown in Fig. 14 which a pipe line must be laid, and the pipe system con- structed on the site. This is an important advantage when the water-conducting medium traverses a rough and moun- tainous country where it would be very difficult or impos- sible to transport heavy metal pipe. (3) It is cheaper than metal pipe. The cost of a 30 inch redwood pipe laid and buried was $3.90 per foot for 200 feet head. * * Adams, Transactions American Society Civil Engineers, 1898, p. 676. APPLIED HYDRAULICS 53 The disadvantages of stave pipe are : (i) It is shorter lived than metal pipe. It is manifest that changes of temperature and wind will cause a steady movement back and forth of the limit of saturation within the staves, thus leaving the outer skin of the wood in a condition which in- vites decay. Adams claims, however, that there are some stave pipe lines in New England that are constructed of pine and have lasted from 20 to 40 years. Evidently, redwood pipe lines should last much longer. (2) It is Fig. 16. Construction of Stave. Pipe Line subject to attack from insects, rodents, etc. (3) Evapora- tion losses from wood pipe are considerable. To prevent evaporation losses it has been proposed to put a protective coating of asphalt or paint on the outside of the pipe. Fig. 1 6 shows the construction of a Wheeler continuous stive pipe, made by the National Wood Pipe Co., of Los 54 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Angeles, and Fig. 17 shows a completed pipe line. Stave pipe is used in sizes ranging from a few inches up to 10 feet in diameter. When iron pipe is used, cast iron is preferable to wrought iron, since it rusts materially less than wrought iron, and its life is practically unlimited. It is also non- Fig. 17. Completed Wooden Pipe Line collapsible and capable of withstanding as high hydrostatic pressures as wrought iron. In some Western transmission practice the pipe lines are constructed of steel or wrought iron in one part of their length, and cast iron in the other ; and are graduated in thickness, being of heaviest metal near the receivers. The joints used on continuous metal pipe are usually of the flange type, the sections being bolted together. Fig. i Sa shows a type of joint used on the cast iron pipe line of a APPLIED HYDRAULICS 55 Fig. i8a. A Type of Joint for High-head Pipe Lines California transmission company. A groove extends round the flange, into which is forced a circular rubber gasket of a slightly smaller diameter than the groove in the flange. It is placed in the groove, and when the rivets are inserted and the flanges drawn to- gether, the sections of pipe are united metal to metal. Water press- ure tends to force the gasket more firmly into the recess of the flange and insures absolute water tightness. Iron pipe for conveying water to hydro-electric plants is rarely used in sizes larger than 3 or 4 feet in diameter. Riveted pipe is more widely used for a water-conducting medium than any other kind of metal pipe. It is made from iron or sheet steel plates of the thickness required to withstand the pressure, these being rolled to the desired diameter. The plates or sheets are held together by a double or triple row of rivets along the longitudinal seam, and a single row of rivets along the circular seams. As a protection against corrosion and in order to decrease the frictional resistance, each section of pipe is immersed in a vat of hot asphaltum, which gives it a smooth finish on the interior. The sections of riveted pipe are joined together either by means of slip joints, if the head of water on the line does not exceed 350 feet; or by means of collar and sleeve joints, when the head is not much over 750 feet ; or by flanged joints, when the head is considerably above 750 feet. On most riveted pipe, joints are made by means of a 56 LONG-DISTANCE ELECTRIC POWER TRANSMISSION single row of rivets commonly called " round seams." In this style of riveting, holes are accurately punched by a multiple punching machine, and the joints of the sections riveted with cold rivets on light gauges, and hot rivets on the heavier gauges. The pipe is then chipped and caulked to insure a water-tight joint, metal to metal, around the joint. At points where the lap in the joint occurs, the Fig. i8b Fig. i8c Size and Spacing of Rivets on Pipe Lines metal of the overlapping joint is likewise chipped and caulked. Finally, the inside and outside of the joint are painted with asphaltum as a protection against corrosion by the action of water and chemicals in the soil. Pipe ranging from 24 inches in diameter upward is gen- erally continuous-riveted, and varies in thickness from No. 14 to oooo B. W. G. Lap welded pipe for heavier gauges is also quite common. On lighter gauge pipes "bump" joints are generally APPLIED HYDRAULICS 57 used. These are constructed by expanding one end of a section enough to permit the other near end of the next sec- tion to enter it. Then holes are punched through both the sections of pipe, at the ends to be joined together, and the riveting done by means of hot rivets in a similar manner to that employed on round seams. Usually, on very light gauges of pipe of the bump joint IXB.W.%. SHEET. Fig. i8d Fig. i8e Size and Spacing of Rivets on Pipe Lines type, a single row of rivets is used on the joint. On pipes of from one-half to three-fourths inch diameter, double rivets are generally used, and the rivets staggered as on straight seams on riveted pipe. Figs. i8, iSc, i8d, and 1 8^, show the size and spacing of rivets used in many Western pipe lines. Figs. 19, 20, and 21 show the three methods of connec- tion employed on riveted pipe, and also illustrate riveted steel pipe made by the Pelton Wheel Company. Riveted 58 LONG-DISTANCE ELECTRIC POWER TRANSMISSION section pipe has been satisfactorily employed to convey water under heads up to 2,000 feet. The material used in some pipe lines is open hearth, box- annealed steel of a tensile strength, ranging from 40,000 to 6o,OOO pounds per square inch, and with riveted joints. The preference for steel over iron is to some extent a SLIP JOINT SUP JOINT PIPE LEAD JOINT .COLLAR AND SLEEVE LEAD JOINT ... FLANGED JOINT SECTIONS SHOWiNG GASKETS Figs. 19, 20, 21. Methods of Connecting Riveted Pipe matter of cost. Pipes are calculated to resist a certain pressure, and the greater tensile strength of steel is an important factor ; in order to resist the same pres- sure an iron pipe of much greater weight would be required. On the other hand, steel pipe is much more liable to be damaged by electrolytic action when laid on alkali soils. Under such conditions iron and carbon form the two ele- APPLIED HYDRAULICS 59 ments, differing in the electrochemical series, while alkali is the electrolyte. With iron pipe very little electrolytic action ensues, since iron contains very little carbon. Pipe lines for conveying water to hydro-electric plants are generally laid on the surface of the ground, and when the gradient is steep they are securely anchored by embedding them in cement blocks spaced 10 or 15 feet apart. Fig. 22 shows the pipe line and method of anchoring adopted by the Bay Counties Power Com- pany of California. In some cases pipe sys- tems are laid in trenches from 3 to 6 feet deep and back-filled with earth and rock. At various points along the line heavy anchors of concrete are placed, ex- tending all around the pipe. These anchorages are generally dovetailed into the solid rock in the sides and bottom of the trench, and hold the pipe rigidly. All curves on pipe lines should be made with a long radius to reduce the loss of head. At points near the receiver, and where inverted siphons are used, blow-offs, air valves, or other safety devices should be installed in order to prevent accidents from bubbles, water hammer, and vacuum. A standpipe for the escape of air bubbles is sometimes Fig. 22. Method of Anchoring Pipe Lines on Steep Grades 6O LONG-DISTANCE ELECTRIC POWER TRANSMISSION Table of Riveted Hydraulic Pipe Showing price and weight, with safe head for various sizes of double riveted pipe. ( Revised ) Diameter of pipe (n || inches Thickness of material U. S. standard gauge Equivalent thickness in inches. Head itrfeet pipe will safely stand. 1 Weight per lineal foot in pounds. % 8 *c a, Diameter of pipe in inches. Thickness of material U. S. standard gauge. Equivalent thickness in Miches. 'i t| II f Weight per lineal foot in pounds. 1 Price, per foot. 1 3 4 4 18 18 16 .05 .05 .062 810 607 760 2.25 3.00 3.75 *0.20 5 .35 18 18 18 12 11 10 .109 .125 .14 295 337 378 25.25 29.00 32.50 $1.90 2.10 2.40 5 18 .05 485 3.75 .30 5 5 16 14 .062 .078 605 757 4.50 5.75 .45 .50 20 20 16 14 .062 .078 151 189 16.00 19.75 1.26 154 6 6 6 18 16 14 .05 -062 .078 405 505 630 ' 4.25 .5.25 6.50 .44 .50 .56 20 20 20 11 10 8 .125 .14 .171 304 340 415 31.50 35.00 45.50 2.25 2.50 3.40 7 7 7 18 16 14 05 .062 .'078 346 433 540 4.75 6.00 7.50 .50 .56 .63 22 22 22 16 14 12 .062 .078 109 "138" 172 240 17.75 22.00 30.50 1.40 1.70 2.25 8 8 8 16 14 12 .062 .078 .109 378 472 660 7.00 8.75 12.00 .65 .75 .94 22 22 22 11 10 8 .125 .14 171 276 309 376 34.50 39.00 50.00 2.40 . 2.80 3.75 9 9 9 16 14 12 .062 .078 .109 336 420 587 7.50 9.25 12.75 .69 .88 1.06 24 24 24 14 12 11 .078 .109 .125 Idtf 220 253 23.75 32.00 37.50 1.80 2.35 2.70 10 10 10 16 14 12 .062 .078 .109 307 378 530 8.25 10.25 14.25 .72 .82 1.00 24 24 24 10 8 6 .14 .171 .20 283 346 405 42.00 50.00 59.00 2.95 3.50 4.30 10 10 11 10 .125 .14 607 680 16 25 18.25 1.25 1.50 26 26 14 12 .078 .109 145 203 25.50 35.50 2.00 2.59 11 11 11 11 16 14 12 11 .062 .078 109 .125 275 344 480 553 9.00 1100 15.25 17.50 .75 .94 1.25 1.44 26 26 26 26 11 10 8 6 .125 .14 .171 .20 233 261 319 373 39.50 44.25 54.00 64.00 2.87 3.10 3.85 4.75 11 10 .14 617 19.50 1.62 28 14 .078 135 27.25 2.12 12 12 12 12 12 16 14 12 11 10 .062 .078 .109 .125 .14 252 316 442 506 567 10.00 12125 17.00 19.50 21.75 .82 1.00 1.38 1.50 1.69 28 28 28 28 28 12 11 10 8 6. .109 .125 .14 .171 .20 188 216 242 295 346 38.00 42.25 47.50 58.00 6900 2.75 3.00 3.20 4.15 5.00. 13 13 13 13 13 16 14 12 11 10 .062 .078 .109 .125 .14 233 291 407 467 522 10.50 13.00 18.00 20.50 23.00 .90 1.12 1.50 1.65 1.80 30 30 30 30 30 12 11 10 8 6 .109 .125 .14 .171 .20 176 202 226. 276 323 39.50 45.00 50.50 61.75 73.00 2.90 3.15 350 4.30" 5.25 14 16 .062 216 11.25 .98 30 V* .25 404 9000 6.50 14 14 14 14 14 12 11 10 .078 .109 .125 .14 271 878 433 485 14.00 19.50 22.25 25.00 1.17 1.57 1.72 1.95 36 36 36 36 11 10 fe .125 .14 .187 25 168 189 252 337 54.00 60.50 81.00 109 00 3.80 4.30 5.75 7.60 15 15 16 .062 078 202 252 11.75 14 75 .96 1 28 36 */:* .312 420 135.00 9.50 15 15 15 12 11 10 .109 .125 .14 352 405 453 20.50 23.25 26.00 1.75 1.95 2.10 40 40 40 10' : .14 .187 .25 170 226 303 67.50 90.00 12000 4.75 640 8.40 16 16 16 14 .062 .078 190 237 13.00 16.00 1.05 1.20 40 IK .375 455 180.00 12.00 16 16 16 12 11 10 .109 ' .125 14 332 379 425 22.25 24.50 28.50 .1.70 1.85 2.00 42 42 42 10 fe .14 M7 .25 162 216 289 71.00 94.50 126.00 5.05 700 9.50 is IS 16 14 . .062 .078 168 210 14.75 18.50 1.20 1.40 42 1 42 Vie / .312 .375 360 435 158.00 190.00 12.00 15.00 Table II APPLIED HYDRAULICS 61 located a few feet below the forebay for counteracting water hammer near the power house. The factor of safety for nearly all material used in pipe lines under high heads ranges from five to six, and it is occasionally eight. (Table II. ) Auxiliaries of Pipe Systems: Fore bays, Sand Boxes, and " Grizzles." Forebays have two functions ; namely, to Fig. 23. Type of Sand Box used in Western Practice allow the water to settle before it is admitted to the press- ure pipe, so that sand and silt will be deposited, and to permit submerging the intake of the pressure pipe. Fore- bays are constructed either of concrete masonry or a natural basin is sometimes taken advantage of by constructing an earthen dam across a canyon or ravine, the bottom of which is sometimes paved with cement. 62 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Sand boxes are placed at the ends of water-conducting systems to prevent sand from entering the nozzles and buckets of water wheels. They usually consist of chambers, or box-like compartments, having a considerable slope from the point where the water enters. Each of the dividing walls of the chambers except the middle one is designed to be several feet below the surface of the water. The middle wall is slightly higher than the water surface, and thus allows the water to pass through a gate into the connecting pipe line. Fig. 23 shows a sand box of this construction. At the lower end of the com- partments is a plug valve provided with a stem that runs up through the water to a board walk above. The valve is lifted by a block and tackle, which opens the orifice in the bottom of a compartment, and by turning water into each compartment the box can be quickly cleared of sand. Sand boxes are sometimes made of two parallel hoppers with sluice gates in the bottom through which accumulated sand and silt can be expelled. Water is passed through one hopper while the other is being emptied. " Grizzles " are devices for removing leaves, debris, etc., from water-conducting systems. Conduits and Canals. The term " conduit " as generally applied in hydraulics means a channel of any shape, open or closed, and lined with masonry, concrete, or timber. The word is also applicable to large pipes made of metal or wood. The term "canal" is applied to a conduit excavated in the earth and without masonry or other artificial lining. A common name for a supply canal is " head-race" Conduits and canals are more generally employed for APPLIED HYDRAULICS 63 conveying water to hydraulic plants than any other form of conducting medium. Their usual shape is rectangular, but they may be of either trapezoidal or triangular cross- section. In regions where the geological formation or character of the soil would occasion considerable loss of water through seepage into the soil, it is considered more advan- tageous, especially if the conducting channel is long, to line it with concrete or timber. When a canal pure and simple is used to convey water, the sides and bottom are generally puddled with clay to prevent percolation of the water through the soil. In some cases this is accomplished by sending through a sediment of clay with the water. This is continued until the walls and bottom of the canal are well plastered with the clay. Concrete pipe or conduit is usually constructed of Port- land cement in sections two or three feet long and from one and a half to two and a half inches thick. In the con- ducting systems of some Pacific coast hydro-electric plants, the material used in the construction of concrete conduits is the natural gravel and sand taken from the wash of the stream, with Portland cement as the binding material. When the sections of pipe are completed they are cured for a season on the spot. And when the pipe is made in ravines or canyons, as is frequently the case, the sectio'ns are hoisted by means of a steel cable to the trench grade on the mountain side above. Conduits and canals should receive the water from the reservoir in a way that will occasion no loss by leakage, and so that the mouth of the channel can be tightly closed if desired. Means must also be adopted to prevent leaves, trash, gravel, or sand from entering the channel. 64 LONG-DISTANCE ELECTRIC POWER TRANSMISSION BIBLIOGRAPHY Water Power. Frizell. Third Edition. Wiley & Sons. New York. 1903. Design and Construction of Dams. Wegmann. Fourth Edition. Wiley & Sons. 1899. Reservoirs for Irrigation, Water Power, etc. Schuyjer. Wiley & Sons. New York. 1901. A Treatise on Masonry Construction. Baker. Ninth Edition. Wiley & Sons. New York. 1899. A Method for Determining the Supply from a Given Watershed. Greenleaf. Engineering News. Volume 33. Page 238. A Form of Mass Diagram for Studying the Yield of Watersheds. Horton. Engineering Record. 1897. Volume 36. Page 285. Instructions for Installing Weirs, Measuring Flumes and Water Registers. Johnson. Engineering News. August 29, 1901. Page 131. Commercial Value of Water Power per Horse Power per Annum. Transactions American Society Mechanical Engineers. . Abstracted in En- gineering News. January 22, 1903. Stave-Pipe. A. L. Adams. . Transactions American Society Civil Engineers. 18.98. Page 676. Diagram Giving Discharge of Pipes by Kutter's Formula. Greg- ory. Engineering' Record. Volume 42. Manufacture and Inspection of Cast-iron Pipe. Wiggen. Journal Association of Engineering Societies. May, 1899. Page 209. Design of American Dams. Engineering Record. February 20, 1902. Wooden Stave vs. Riveted Pipe. Journal Association of Engineering Societies. Pages 239-262. Philadelphia. 1898. CHAPTER III HYDRAULIC MACHINES AND ACCESSORY APPARATUS Hydraulic Machines. Distinction between a Turbine and a Water Wheel. When water is admitted to only one part of the circumference of a hydraulic motor the machine is termed a water wheel. When water is admitted around the entire periphery of a hydraulic motor the ma- chine is termed a turbine. In either case the rotation of the wheel is produced by the weight of water falling from a higher to a lower level, or by dynamic reaction due to a change in velocity and direction -of a stream. According to the manner in which they operate, turbines are divided into two general classes, namely, "impulse" and "reaction " turbines. The essential difference between the two is that in an impulse turbine water enters the machine with a velocity due to the head at the point of entrance in the same manner that it does from the nozzle which actuates the impulse wheel, whereas in a reaction turbine the velocity of the entering water may be greater or less than that due to the head on the entrance orifices ; like the reaction wheel it is influenced by the speed of the water. The reason for this is that the hydrostatic pressure of the water is largely transmitted to the rotating wheel that is, if the spaces between the vanes or buckets are entirely filled. It is feasible to make any turbine work either as a reaction or as an impulse machine. By actuating it so that the 6s 66 LONG-DISTANCE ELECTRIC POWER TRANSMISSION water passes through the vanes without entirely filling them, the turbine becomes an impulse machine. If, on the other hand, the entering water is obliged to fill all the buckets, the turbine becomes a reaction machine. It is manifest from the foregoing definitions that the buckets of an impulse turbine are considerably smaller than those of the reaction type. In order that the entire energy of the water be utilized, MOVING WHEEL Fig. 24. Outward-Flow Turbine F1XK) Gl/JPE PASSAGES Fig. 25. Inward-Flow Turbine the vanes or buckets of turbines are curved tangentially, so that the water may react upon the surfaces and deliver as much energy as possible. Kinds of Turbines. Turbines are classified according to the way in which water is passed through them into " outward-flow," " inward-flow," and " downward-flow " tur- bines. In an outward-flow turbine water enters around the complete inner periphery of the runner and is discharged around the entire outer periphery. In an inward-flow tur- bine the motion of the water is exactly opposite. In the downward-flow turbine water is admitted around HYDRAULIC MACHINES 67 all the upper annular openings, and is shot downward between the rotating vanes, passing out through the lower annulus. The normal speed of an impulse turbine is somewhat lower than that of a corresponding reaction turbine oper- ating under the same head, but the entrance velocity of the water is considerably greater in the impulse type, which means that consider- , , , . , , FIXED GUIDE PASSAGES ably more energy is liable ~T j T h T T T- to be wasted by shock and \ \ \ \ \ \ \ foam. \\\V\ \ \ MOVING WHEEL Fig. 24 shows an out- Fie ^ Downward . Flow ward-flow turbine, Fig. 25 an inward-flow turbine, and Fig. 26 a downward-flow turbine. Conditions to which Impulse and Reaction Turbines are Adapted. The type of hydraulic machine which should be adopted in any particular case depends upon the height of head which is to be utilized. In general, for low heads, i.e., up to 45 feet, the impulse or " American " type of turbine, mounted on a horizontal or vertical shaft, with open flume (and usually with draft tube), should be employed. For moderate heads, ranging from 45 to 400 feet, the reaction turbine (with radial inward flow), mounted on a horizontal shaft and fitted with a cast-iron case and draft tube, should be employed. For high heads, i.e., those ranging from 400 to 2,000 feet or over, the Pelton type of wheel or the radial out- ward-flow machine, mounted on a vertical shaft and con- tained in a cast or wrought iron case, with draft tube, should be used 68 LONG-DISTANCE ELECTRIC POWER TRANSMISSION A reaction turbine, as stated previously, is rotated by the dynamic pressure of moving water, which may also be more or less under static pressure. Hence, the particular sphere of work to which the reaction machine is suited is under conditions where a large quantity of water under a moderate head must be handled. As regards the conditions for which the impulse wheel is well adapted, it may be said in general that for heads ranging from 100 feet upwards this type of wheel is the only practical form, capacity and size being equal. When a hydraulic machine is driving an electric gene- rator it becomes imperative to maintain a practically con- stant speed irrespective of changes in the load. In this respect a reaction turbine cannot compare with an impulse water wheel, since a change in its speed involves a consid- erable loss in efficiency. In an impulse wheel water can be admitted through a part of the guides, which with a reaction turbine is manifestly infeasible. The efficiency of an impulse wheel is not appreciably diminished by a partial closing of the admission gates, but with a reaction turbine the abrupt increase of cross-section beyond the partly closed gates causes a considerable diminu- tion of efficiency. The normal speed of an impulse wheel is constant for all positions of the gate. With a reaction turbine the speed is considerably less at partial than at maximum gate. Efficiencies of Hydraulic Machines. The efficiency of hydraulic motors depends upon the following conditions : (i) The water should enter the machine without producing appreciable shock. (2) It should be discharged from the machine at a low velocity. (In general the lower the velocity in the tail race, the greater the amount of useful HYDRAULIC MACHINES 6 9 work which the motor has abstracted from it.) Or the water should enter the buckets without shock and leave without velocity. (3) The buckets or vanes of the turbine should be so curved as to receive the full impact of the nozzle jet. (4) The water supply should be free from sediment, sand, leaves, or other organic matter. (5) The rotating member of the turbine should revolve in its bear- ings with the minimum of friction. The efficiencies of American-made hydraulic machines range from 65 to 85 per cent, depending upon the design, EFFICIENCY TEST OF RISDON WATER WHEEL AT COLGATE STATION Tl C > c > c c ' c 5 d 1 I 1 ^ > tf H ^ 1 L t ? s ; t i < i ? i ? s S \ \ J I S S ? 1 a s 3 1 S 9 < l 1 8 Ho N SO ,. . - , __ -* .^n * . * ^ -* > __ Id ^ ^ ^^^ fA Fig. 27 output, and conditions of operation. The majority of machines of moderate output will not exceed 70 per cent in efficiency. Fig. 27 shows the efficiency curve of a 3,000 horse-power Risdon impact wheel. The importance and desirability of employing the most efficient turbine commensurate with the permissible outlay cannot be over-estimated. In cases where the water supply is uncertain or limited it becomes almost imperative to 70 LONG-DISTANCE ELECTRIC POWER TRANSMISSION adopt a machine which will transform the kinetic energy of the water into the maximum mechanical power. Es- pecially is this true in cases where the water is bought or power sold. In the Engineering News of December 4, 1902, Mr. John W. Thurso admirably shows the great importance Fig. 28. Samson Niagara Type Turbine of using an efficient turbine. He says, " Supposing that power is sold at $15 per year for an effective mechani- cal horse-power at the turbine shaft, and that the water supply is limited. The amount of water required to de- velop one effective horse-power with 70 per cent efficiency will give 1.143 horse-power, worth $17. 14 per year, with 80 per cent efficiency. " The difference of $2.14 in favor of the turbine with higher efficiency is equal to an interest of 1 5 per cent as HYDRAULIC MACHINES 7 1 above on $14.27 ; or a 1,000 horse-power turbine giving 80 per cent efficiency could cost $14,267 more than a tur- bine giving 70 per cent efficiency witliout being more ex- pensive." Types of American Turbines. Fig. 28 shows one form of the Samson turbine made by the James Leffel Com- pany. It is of the double-discharge horizontal form, and is BB^*1 , . i Fig. 29. High-Head Heavy Duty Turbine called the Niagara design. This type is usually fitted with one runner and two similar sets of buckets. The entering water is equally divided between the two sets of guides and is discharged in opposite horizontal directions. This form of turbine is fitted with an outer casing, thus afford- ing an easy circulation of water around the guides on the runner. Water is admitted to the casing either from below or at any desired angle from a horizontal or vertical line on top. The shafts revolve in ring-oiled bearings supported by 72 LONG-DISTANCE ELECTRIC POWER TRANSMISSION heavy iron -bridge-trees. The illustration shows a 2,400 horse-power machine for direct connection. Fig. 29 shows a high head, heavy duty, center dis- charge, horizontal shaft Samson turbine. It consists of two 56-inch turbines mounted on a bronze shaft and fitted with bronze runners and balanced steel gates. The type of runner used on Samson turbines is shown in Fig. 30, which is an illustration of the vertical shaft type. The runner is made up of two distinct forms of wheels which have different diameters. Each set of buckets comprising a wheel receives its separate quantity of water from the same set of guides, and discharges to the outlet ; the water does not act twice upon the combined wheel. . Fig. $ia shows a 5 5 -inch Vic- tor high pressure turbine made by the Platt Iron Works. This turbine develops 8,000 horse- power under a 63O-foot head and is controlled by a Lombard gov- ernor. The illustration shows the water supply connection below the floor level, also the by-pass valve. Fig. 31^ shows this type of turbine coupled to an alternator. The Victor machine is a mixed-flow type, water entering radially inward at the circumference and discharging downwards and outwards. The whole depth of the wheel Fig. 30. Runner of Samson Turbine HYDRAULIC MACHINES 73 proper is occupied by the buckets, which are deep axially, thus giving large capacity for its size. Water supply to turbines is regulated by two types of gate, one of which is termed the register gate and the other the cylinder gate. The former admits water to the turbine by turning about the axis of the wheel, thus Fig. sia. Victor High-Pressure Turb-'ne opening the passage wider and wider as it is turned more and more, and at the same time giving direction to the water. The cylinder gate is the preferable form when the water supply is variable or when the work is variable : the cylinder gate is also better adapted to low and medium heads. Fig. 32 shows a pair of 42-inch McCormick turbines made by the S. Morgan Smith Company. The machines are 74 LONG-DISTANCE ELECTRIC POWER TRANSMISSION designed for direct connection to an electric generator, and develop 4,000 horse-power at 300 revolutions per minute under a 72-foot head. The illustration also shows a single 400 horse-power turbine for driving the generator exciter. Water Wheels Principles of Operation : Features upon which Speed and Power Depend. A hydraulic machine, as has been already stated, is known as a " water wheel" Fig. 3ib. A 1,000 Horse-Power Turbine Coupled to Alternator when water is admitted to one part of its circumference. Since this type is driven by the impact of a jet or jets of water against buckets mounted on the periphery of a wheel it is termed an " impulse wheel." In general the impulse wheel is the most practical form of machine that can be employed when the head is above 100 feet, and for very high heads it is the only type of machine that can be employed. The buckets of water HYDRAULIC MACHINES 75 wheels are curved tangentially or ellipsoidally, the object in either case being to oblige the water to react upon the bucket surfaces so as to give up the maximum amount of its energy. Water is conducted to an impulse wheel through the various types of artificial channels described in the preceding chapter, and is delivered to the buckets through a nozzle, the end of which is fitted with a cylindrical tip, the diameter jj L Fig. 32. A Pair of 4,000 Horse-Power McCormick Turbines of which is proportional to the head of water and the amount of power to be developed. Since tips of different diameters can be screwed into the nozzle it is thus possible to vary the power of the wheel from the maximum (limited by the size of the buckets) down to a small percentage of the rated capacity. The use of varying sizes of nozzles thus permits of maintaining a nearly uniform efficiency at all stages of load. When it is desired to double or treble the output of a water wheel without increasing its diameter, two or three nozzles are employed, the consumption of water being correspondingly increased, of course. 76 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The power of a water wheel, strictly speaking, does not depend upon its dimensions, but upon the head and quantity of water supplied to it. The speed of a water wheel depends upon its diameter, and when operating under a given head the number of revolutions which it maintains should be constant, regardless of the amount of power it is developing. Water wheels are constructed to operate in either a vertical or horizontal plane, the horizontal type, however, being more commonly employed. In the horizontal type the wheel is supported on a shaft running in journal boxes, the entire running mechanism being inclosed in an iron casing divided in a horizontal plane. When the wheel is mounted in a vertical plane the shaft is provided with a step and thrust bearing. The buckets of water wheels are constructed of phosphor bronze, cast steel, or cast iron, depending upon the conditions under which the wheel must operate, i.e., the head of water and the character of the water supply, its freedom or non- freedom from abrasive material in suspension. Power of a Water- Fall Utilized by a Hydraulic Machine. Representing the pounds of water delivered per second to a hydraulic machine by W, and considering // as its effective head in feet as it enters the machine (the head // may be due to either pressure or velocity or to pressure and velocity combined), then the theoretical power in foot-pounds per second of the water is K=Wh, and the theoretical horse-power of the water as it enters the machine is 55 HYDRAULIC MACHINES 77 On account of losses in impact, friction, etc., the actual horse-power of a hydraulic machine is considerably less than the theoretical horse-power of the water. Using k to indicate the work delivered by a hydraulic machine, and e its efficiency, then, k k h.p. e = =-TTTT, and e = K ~ Wti H.P? a fair average for wheels of moderate output being 75 per cent. The average efficiency of wheels of even compara- tively large output is rarely over 78 per cent, and their all- day efficiency will barely exceed 60 per cent. Effective Head on an Impulse Wheel. When water is conducted through a nozzle or a pipe line to a water wheel, the head h is not the maximum head, since a con- siderable portion of this latter head is lost in friction in the pipe system. Hence the head on the turbine or water F 2 wheel is really the velocity head, , of the jet. Having determined the value of V from the discharge q, and the area of the cross-section of the stream, the effec- tive .head on an impulse wheel is 2g 2ga v in which q is the discharge, and a the area of its cross- section. Speed Regulation of Water Wheels and Turbines. The three general methods for regulating the speed of water wheels are : (i) By means of a deflecting nozzle; (2) by a plug nozzle; and (3) by the use of a cut-off hood. In each 78 LONG-DISTANCE ELECTRIC POWER TRANSMISSION method the controlling device is always actuated by some form of automatic governor, the function of which is to adjust the position of the device to suit the demands of the load. The deflecting nozzle is usually of cast iron and fitted with a ball and socket joint, which permits of its being raised or lowered, thereby throwing the nozzle on or off the buckets. Thus the power output of the wheel is in- creased or decreased to meet a change of load, and the Fig. 33. Deflecting Nozzle speed is kept uniform. A modification of this speed-regu- lating device consists of a plate which deflects the stream, the nozzle being kept stationary. Fig. 33 shows a deflect- ing nozzle. A plug nozzle is a nozzle body fitted with a concentric tapered plug. By changing the position of this plug a change is produced in the discharge area of the nozzle, thereby varying the amount of water consumed by the wheel, the power output being governed accordingly. A cut-off hood consists of a spherical plate fitted tightly over the end of the nozzle. Variation in the position of the HYDRAULIC MACHINES 79 hood produces a change in the discharge area of the nozzle, thus varying the power of the wheel. The speed regulation of turbines is accomplished almost universally by means of gate valves controlled by some form of governor, the function of the governor being to open or close the water supply orifice to an extent corresponding to the increased or decreased demand for power. Perfect speed regulation of hydraulic machines is im- possible, owing to two limitations : (i) Such limitations as are imposed by the governor itself, and (2) those imposed by the inertia of the masses upon which the governor acts to control the speed. Governors Requisites of a Good Governor. The most important desiderata which a good governor should possess are simplicity, ability to regulate closely the speed of the hydraulic machine, freedom from racing and hence avoidance of unnecessary movements of the gate, freedom from all shocks and jerky movements, adaptability to all kinds of plants, reliability of operation, and low cost of maintenance. The chief limitations possessed by all forms of governors are due to the fact that there must be a speed variation to some degree before the governor can begin to operate, and a definite time is required to adjust the gate to its new position. Moreover, the initial change must become ap- preciable before the governor operates the gate at its maximum speed, but the appliances used to prevent the overspeeding of the gate invariably exercise a dampening effect upon the speed of the gate movement while it is motive. The secondary limitations, or those due to the inertia of the masses to be moved, are far more complex. These are 80 LONG-DISTANCE ELECTRIC POWER TRANSMISSION due to the sluggishness of movements of the various com- ponents of the gate, such as the shafts and the rigging, and to the inertia of the water to be controlled. Kinds of Governors Principles of Operation. Gover- nors for regulating hydraulic machines are, (i) those oper- ated by the pressure of a fluid, which may be oil or water ; (2) mechanically operated ; (3) electro-mechanical, or (4 induction motor governors. Governors of the first kind are generally termed "hy- draulic " governors. The fluid used for operation depends on the conditions which must be met, as well as considera- tions of cost and maintenance. In general oil-pressure governors are used for low heads, while the water-pressure form is employed for heads above 100 feet. The essential elements of a hydraulic governor are, a cylinder fitted with a shaft or piston which actuates the water gate ; a hydraulic valve or valves working in a chamber, and con- trolling the pressure applied to the hydraulic cylinder ; a centrifugal governor for controlling the movements of the main valve ; an auxiliary controlling device which deter- mines the amount of the gate opening for any definite variation of load ; some form of anti-racing mechanism ; some form of controller for determining the rate of speed at which the governor shall operate, and a power pump (if the governor is of the oil-pressure form). Mechanically operated governors usually consist of a train of gear wheels, driven by the governed unit and fitted with a centrifugal speed-regulating device which permits the governor to trip some mechanical device for moving the water gates. Electro-mechanical governors operate by means of electro-magnets which throw reciprocating pawls into oper- HYDRAULIC MACHINES 8l ation, these pawls being so arranged that they actuate the regulating mechanism of the wheel. Governing by electric (induction) motors has been suc- cessfully applied in one or two Western hydro-electric plants to small impulse wheels driving exciter dynamos. The speed regulation of the turbo-generator unit in this case depends upon the principle of the induction motor in running below synchronism normally, and of giving no mechanical output of power when driven at synchronous speed. When driven above synchronous speed by extra- neous means current is delivered instead of consumed. In the case under discussion the motor is run above syn- chronism, and thus absorbs the surplus energy of the water wheel over that demanded by the exciter dynamo. But when the load on the exciter becomes of such a value that the water wheel is unable to take care of it, the motor ceases to generate current and performs its function of motor, thus helping the water wheel. When the water supply of the wheel is accidentally or purposely cut off, the motor can be used to drive the exciter dynamo. Thus it can be made to perform the function both of a water wheel governor and a prime mover. In the cases where the electric motor has been employed as a governor it is mounted on the same shaft with the water wheel. Switchboard Control of Governors. The control of governors from the switchboard greatly reduces the time and labor necessary to effect a variation in the speed of a hydraulic machine, and also simplifies the method of speed regulation considerably. This plan of governor operation readily enables the switchboard attendant to start, .stop, or alter the speed of a single machine or of all the machines under his care, from one central point. 82 LONG-DISTANCE ELECTRIC POWER TRANSMISSION In this method of operation a small alternating current motor performs the work of shortening or lengthening the valve stem, instead of the attendant's fingers. Hence this dispenses with the practice of having one man to watch the synchronizing lamps and an- other to attend the governor and vary its speed in accordance with the signals given from the switch- board, so that the switchboard at- tendant can per- form any or all of the operations of starting or stop- ping or synchro- nizing machines thrown in paral- Fig. 34. Electric Speed Controller for Governors lei, without Ollt- side assistance. Fig. 34 shows the electric speed controller of the Lom- bard Governor Company. In this type of controller a small fan motor of about one sixteenth horse-power is attached to a bracket, which is clamped to the governor regulating valve. The armature shaft of the motor carries a small worm, which drives a worm gear on a vertical pinion shaft. HYDRAULIC MACHINES 83 The pinion imparts a rotary motion to another gear which is threaded through its hub, and so acts as a right and left coupling to force together or push apart the two portions of a valve stem upon which it rotates. The pinion is made of sufficient length so as not to interfere with the up and down travel of the gear. Current for operation is obtained either from the exciter circuit or from batteries. The controlling apparatus consists of a small reversible motor connected by double reduction worm gearing to the bracket supporting the controlling lever of the governor. The motor imparts an endwise thrust to this bracket, which in turn shifts the position of the controlling lever, and thus causes a variation of the speed at which the governor has been maintaining the turbine. The switch which controls the motor, and which may be located at any point desired, such as a switchboard, has two buttons for raising and lowering the speed, and a small thumb switch for entirely cutting out the apparatus when it is not in use. The thumb switch is fitted with three contacts, one of which is employed for quickly stopping the unit without requiring the attendant to depress the push button while this is being done. Automatic cut-outs are used on the motor to prevent its overrunning when the lever has reached its limit of movement. Types of American Governors. A type of fluid pressure governor quite extensively used in hydro-electric plants is the Lombard, made by the Lombard Governor Company, of Boston. Fig. 35 shows the type " D " Lombard oil pressure governor. The cylindrical tank which is contained under the bed of the governor is divided into two compartments, the dividing partition being located at the point indicated by the row of rivets. 84 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The larger part of the cylinder (to the left) is filled about half full of oil, while the upper part of the larger compart- ment of the pressure tank is filled with air under a pressure of approximately 200 pounds per square inch. The smaller compartment of the cylinder contains a Fig- 35- Oil Pressure Governor for Moderate Sized Turbines vacuum. Both pressure and vacuum are constantly main- tained by means of a pump placed on the farther side of the governor bed and driven by the larger pulley, this being belted so as to revolve continuously when the governor is in operation. The movement of the water wheel gates takes place HYDRAULIC MACHINES when oil from the pressure tank is let in on one side of the piston. Immediately this occurs, oil on the other side of the piston is discharged into the vacuum tank, from whence Fig. 36. Governor for Impulse Water Wheels it is at once pumped into the pressure tank. The piston rod is terminated in a rack which is geared positively to the gate shaft. A full stroke of the piston rod completely opens or closes the water wheel gates ; intermediate or 86 LONG-DISTANCE ELECTRIC POWER TRANSMISSION partial motions of the piston causes correspondingly smaller movements of the gates. The oil pressure type of governor is coming into greater use in American hydraulic plants, as it has been found from practical experience that it is more certain and positive in its operation than the water pressure type, owing to the fact that it is extremely difficult to prevent grit, sediment, or other organic matter from entering the governor supply pipe, thereby clogging up and hindering the quick operation of its mechanism. The frequent cleanings thus required in some cases render the use of the oil pump far more satisfactory, notwithstand- ing it is troublesome to maintain. The type "L" Lombard water pressure governor shown in Fig. 36 is primarily designed to regulate large tangential water wheels, but is also applied to the regulation of tur- bines of moderate size under high head. The general construction of the governor can be clearly seen in the illustration. The terminal shaft in this type makes 1.52 revolutions to open the water wheel gates and rotates clockwise to open them. As in the oil pressure type, the small hand wheel actuates a pin clutch, which permits of the operation of the water wheel gates by means of the hand wheel if desired. The piston is terminated in a rack which rotates a gear sector, the central shaft of which is geared or coupled directly to the rock shaft which controls the deflecting nozzle. As the piston travels in or out the nozzle deflects the water on to or off from the water wheel, or opens or closes the gates of the turbine, as may be the case to which the governor is applied. HYDRAULIC MACHINES F.g. 37. Type N, Lombard Water Wheel Governor Some American water wheel governors embody the relay principle of operation, which permits the governed unit to run at a slower speed when loaded than when running empty. 88 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The object of this is to gradually and systematically use the stored energy in the rotating parts of the hydraulic motor. The Lombard Type " N " oil pressure governor shown in Fig. 37 is equipped with the relaying valve mechanism and is especially adapted to the requirements of large water wheel units. One large casting forms the main cylinder and -the bearings for the terminal shaft. The base forms the lower cylinder head and the upper cylinder head is integral with the cylinder; the object of this con- struction being to obtain maximum strength with least weight of metal and to obviate the possibility of joints loosening under the great stresses involved. The linear motion of the piston is transformed by racks and pinions to rotary motion at the terminal shaft. In order to reduce the vertical height of the governor and also to transmit the force of the piston to the rotating shaft efficiently, double racks and pinions are used, the racks being connected to an equalizing yoke, and the racks 'are placed alongside of the cylinder instead of beyond it. The steel terminal shaft is 2^| inches in diameter and is supported by bearings on both sides of the piston. The main piston rod gland cap is cup-shaped so as to prevent leakage over the machine. The usual form of hand wheel is employed which is thrown out of gear when the governor is in regular operation. The main valve of the governor consists of a large double hollow piston contained in the horizontal cylindrical case back of the rim of the hand wheel at the left of the figure. The valve is perfectly balanced so as to require a very slight force to move it, but in order to insure absolute reliability of movement hydraulic plungers are also provided. These plungers are simultaneously actuated by a small primary HYDRAULIC MACHINES 8 9 valve secured to the stem of the centrifugal balls, and a small valveless displacement pump in the slender vertical cylinder at the left of the illustration (Fig. 37). The piston Fig. 38. Duplex or Differential Relay Governor of this pump is attached to and moves with the main piston of the governor. These parts are so disposed with respect QO LONG-DISTANCE ELECTRIC POWER TRANSMISSION to each other that the slightest displacement of the primary valve by the centrifugal balls causes an instantaneous and positive movement of the large main valve. The main valve is instantly restored to its closed position by the action of the dis- placement pump as soon as the primary valve is again closed. The movement of the primary valve results in an instanta- neous magnification and insures accurate speed regulation. Fig. 39. A Relay Returning Governor The working fluid for this governor is a special oil kept un- der pressure in a vertical draw steel tank. Oil is forced into this tank by a powerful pump which is an accessory of the governor. The normal pressure under which the governor works is 200 pounds per square inch, at which pressure it exerts the powerful force of 31,000 foot-pounds per stroke. HYDRAULIC MACHINES A duplex relay governor made by the Replogle Gover- nor Works is shown in Fig. 38. The operation of this governor is on the principle that a movement of the gate automatically cuts the governor out of action, to obviate racing or hunting when the load is varied. Or stated otherwise, there is a rapid movement of the wheel gates to correspond with the variation in load at the time of its variation ; the gate movement being ar- rested in time to permit gravitation to correct momentum and inertia effects. It is claimed that this governor is geared to swing a gate completely in from 15 to 25 seconds. A relay returning governor, made by the Replogle Com- pany, is shown in Fig. 39. The re- turning principle when added to the relay governor is claimed to restore the speed always to normal, leaving it identical with the speed at no load. A type of governor of the hydraulic class, made by the Sturgess Governor Engineering Company, is shown in Fig. 40. This form is designated type "A," and is designed for operation by oil pressure. The main elements of the governor consists of (i) a shaft and Fig. 40. Sturgess Oil Pressure Governor 92 LONG-DISTANCE ELECTRIC POWER TRANSMISSION piston working in an hydraulic cylinder and actuating the gate; (2) a main valve, hydraulically operated, for admitting pressure to the hydraulic cylinder; (3) a cen- trifugal governor for controlling the motions of the main valve ; (4) a secondary controller for gauging the amount of gate movement for any given variation in load. The governor here shown has a power factor of 35,000 pounds, and is designed for units above 2,000 horse-power. Lyndon "Rapid" Water Wheel Governor. A water wheel governor which embodies some novel features has recently been invented by Mr. Lamar Lyndon. This machine is claimed to give very close regulation in ordinary power plants where economy of water is im- portant ; and in such plants where the flow of water exceeds the amount of water used in the water wheels, regulation approaching that of high-speed engines is said to be possible. The governor is of the electrical type and consists essen- tially of a solenoid controller with an electrical contacting device which energizes magnetic clutches ; a small dynamo ; a compensating valve ; a manually operated speed changer; and an arrangement of resistances which prevent over-run- ning of the gates. The compensating device is a simple butterfly valve working in a by-pass pipe which is tapped into the flume or penstock of the hydraulic machine. Its location and operation are indicated in Fig. 41. As is obvious, all water by-passed through the valve and auxiliary pipe goes around the turbine and does no work. In such plants where the quantity of water exceeds that admitted to the turbines, the compensating valve is adjusted HYDRAULIC MACHINES 93 to half-way position and a continual flow through it results. Increase of load on the turbine, which causes the turbine Fig. 41. Arrangement of Compensating Valve, Lyndon Governor gate to suddenly open, causes the compensating valve to close at the same rate of speed as the turbine gate 94 LONG-DISTANCE ELECTRIC POWER TRANSMISSION opens. This admits an increased amount of water into the turbine, without necessitating any change in the velocity of water in the feed pipe; which permits a very quick speed regulation. After the turbine gate has found its new position and regulation is completed, the compensating valve returns slowly to its normal half- Fig. 42. Side Elevation of Lyndon Governor way position while the velocity of the column of water in the feed pipe also changes slowly to furnish the increased supply. Should the load on the turbine decrease, and the gate thereby suddenly close, the compensating valve will open, the movement occurring inversely to the movement of the main gate. The outlet for the water from the feed pipe being increased, a less amount will pass to the water wheel, HYDRAULIC MACHINES 95 and therefore the suddenly decreased gate opening does not mean that the velocity of -water in the feed pipe is suddenly arrested and great pressure set up. The velocity and pressure remain practically unchanged. In such plants where all the available water must be converted into work, this governor will not afford so accu- rate regulation but will give a very uniform speed. When used in such plants the compensating valve is normally fully closed. A side elevation of the Lyndon Governor is shown in Fig. 42. Fig. 43 is a diagrammatic representation of the parts and connections. It consists of a shaft G driven from the turbine to be controlled. Keyed on it are two iron plates E and F, which rotate with the shaft and mag- netically are clutched with plates 30 and 31 respectively. The plates 30 and 31 are secured to miter gears B and C respectively, which are also loose on the shaft. When either electric clutch is energized, the miter gear connected to the clutch plate will turn with the shaft. Meshing with the miter gears B and C is a third gear D, which is keyed on to shaft H, turning at right angles to shaft G. If clutch plate 30 is energized, shaft H will be caused to rotate in one direction by the gear B, while if clutch plate 3 1 be energized, the shaft H will be made to rotate in an opposite direction by gear C. On shaft //is mounted a worm K, which meshes with a worm wheel L, the latter being mounted on a third shaft M, which is parallel to shaft G. This shaft M is the gate shaft, and any movement of it will cause opening or closing of the water wheel gate. It is obvious that the gate will be opened or closed according to whether E or Fis energized. On shaft M is 96 LONG-DISTANCE ELECTRIC POWER TRANSMISSION HYDRAULIC MACHINES 97 a third magnetic clutch consisting of the plates A'' and 32, N being a sheave wheel, having two grooves in it in which lie the wire ropes 28, 29. These ropes are attached to the compensating valve. When the clutch N is energized, 32 will be caused to rotate in one direction or the other accord- ing to the direction of motion of the gate shafts, while the ropes will move the compensating valve in one direction or the other at the same time that the gates are moved. Passing over the hub of N is a heavy leather strap 33 which has its lower ends attached to spring 34. Obviously this spring is extended whenever N rotates in either direc- tion (rotation is limited to about 80 degrees). The small dynamo which supplies the energizing current is driven from the shaft G by means of gears, and therefore varies its speed with that of the water wheel. It is shunt wound with laminated fields and the magnetic density is low ; therefore the voltage will vary as the square of the speed. The controller consists of a plain solenoid W which is connected with the dynamo having inside it an iron core X. The passage of current through the solenoid tends to draw down the core, such pull varying as the square of the voltage. Since the voltage varies as the square of the speed, the pull on the solenoid will vary with the fourth power of the speed. The governor is electrically operated in the following manner. Referring to Fig. 43, when the speed is normal the lever 23 is in a horizontal position, none of the contacts touching the mercury in the cups except point 22, which is longer than the others. When the core is pulled down by increase of voltage, contacts 13 and 15 will connect the dynamo circuit with clutch 30 which will cause the gate 98 LONG-DISTANCE ELECTRIC POWER TRANSMISSION shaft to move in a direction to close the gate. At the same time clutch 32 will be connected to the dynamo circuit by contacts 14 and 16 and the sheave wheel will also turn with the gate shaft. If a drop in voltage occurs, causing the core to rise, the gate opening clutch will be energized by contacts 18 and 20, while the sheave wheel will turn in a direction opposite to that in which it rotates when the gate closes, its clutch now being energized by contacts 17 and 19. Thus the compensating valve is always moved in its proper direction whenever the main gate is moved. When governing is completed and the speed becomes normal, the lever 23 takes a horizontal position, thereby opening the clutch circuits, and the compensator sheave N is drawn by the spring 34 back to its normal position. The water flowing through and surrounding the valve gives a dash pot action and makes this return movement take place slowly. Contacts 21 and 22 change the amount of resistance in the dynamo field with movement of lever 23 and thereby tend to restore the dynamo voltage to normal before the dynamo speed has come to its proper value ; and this arrangement prevents "overrunning" or " hitching" of the gates. Since the gate movement in this type of governor takes place quickly, these machines are made very heavy and powerful. Testing of Turbines and Water Wheels. The data on the output, efficiency, and behavior of their wheels are usually obtained by makers of hydraulic machines from tests conducted at the Holyoke testing flumes. As it is generally too expensive for the purchaser of a wheel to fit up the necessary apparatus for checking up the manufac- turer's data, it is often specified in the contract that the HYDRAULIC MACHINES 99 wheel be sent to a place where all the special facilities for the test are available. The purposes of the tests are usu- ally the determination of effective energy and power of the wheel ; the determination of efficiency ; the determination of the speed which gives the maximum power and effi- ciency. The wheel is mounted in the testing flume, and run at different speeds, in order to ascertain the speed which gives the maximum efficiency and also the effective power output at each speed. Since the efficiency of hydraulic machines varies appreciably with the position of the gate, tests are conducted with the water gate completely opened, as well as at various intermediate positions. Such tests afford the necessary information as to effec- tive power and efficiency under various conditions of oper- ation, and also the consumption of water under different heads. The measurement of effective power is usually made by means of a Prony brake, but is sometimes deter- mined by coupling the wheel to an electric generator and absorbing the power in a water rheostat. Although the tests at the Holyoke flumes are accurately made, they may be quite untrustworthy to the turbine user, since the data obtained at the standard flume may be con- siderably altered under different conditions of wheel set- tings, flumes, and chamber proportions. Thus, the actual working conditions to which the user must adapt his wheel often cause the machine to fall short considerably of con- firming the manufacturer's data. Faults of Turbines and Water Wheels. The principal faults of hydraulic machines are those in design and con- struction, and such faults as arise from bad settings and improper wheel cases. The result of such errors is a 100 LONG-DISTANCE ELECTRIC POWER TRANSMISSION machine of low efficiency and short life, as well as abnor- mal cost of maintenance. Until recently the turbine was not regarded as a machine of the highest importance; hence its design has been badly neglected and nicety of construc- tive details disregarded. Moreover, the material and work- manship were, and are still in many cases, of a very low Fig. 44. Pelton Wheel, Showing Bucket Construction grade. Improvements in efficiency and in the design of turbine settings still leave much to be desired. Types of American Water Wheels. The Pelton water wheel shown in Fig. 44 is of the impulse type, and operates by direct pressure. It is constructed in its simplest form of a cast iron or steel center, to the periphery of which are attached tangential vanes or buckets. The illustration HYDRAULIC MACHINES IOI shows the standard type wheel mounted in a wooden frame, and clearly shows the bucket construction, the nozzle, and gate valve. The buckets are constructed of steel, phos- phor bronze, or cast iron, as the conditions may require. The wheel centers are made of steel and cast iron, and for very high powers are of the disc type. The wheels are driven on the shaft by hydraulic pressure and rigidly keyed. Bearings are of the ring-oiling type, the barrels being lined with a special babbitt metal. Fig. 45- A 3,030 Horse-Power Pelton Wheel Direct Connected to Generator The housings of the wheel are usually constructed of sheet steel or cast iron, riveted and caulked, and have cast iron planed flanges for joints. In order to prevent leakage of water along the shaft and into the journals, a device known as a "centrifugal disc " is employed. It consists of a cast iron disc attached to the shaft of the wheel and revolving within the wall chambers, being secured to the interior of the wheel housing. Water collecting on the IO2 LONG-DISTANCE ELECTRIC POWER TRANSMISSION shaft is caught by the disc and thrown into the centrifugal chamber, from which it is drained away through a tube into the tail race. The Pelton wheel is also designed for several nozzles, in order to increase the power of the wheel without propor- tionately increasing its diameter. The wheel is constructed with a free discharge, in order to prevent leaves, trash, or matter in suspension from choking up the buckets. Fig. 45 shows a 3,000 horse-power Pelton wheel of the iron-mounted type, direct connected to a 1,500 kilo- watt generator through a leather link coupling. The runner of the Risdon wheel made by the Risdon Iron Works, San Francisco, is shown in Fig. 46, which also shows the bucket con- struction employed. The vanes are of the tangential form, and designed to pre- vent the water from reacting from a bucket in a way which will cause it to strike against a succeeding bucket. The water is thus deflected in a clear and free direction. The buckets are made interchangeable, and are bolted to the rim or center by heavy, square-headed bolts with lock nuts ; each bucket bolting closely with dovetails to the one on each side of it, thus making a continuous ring when all are placed in position. Buckets of different size may Fig. 46. Bucket Construction of Risdon Wheel HYDRAULIC MACHINES IO3 be adapted to conform with nearly every size or diameter of wheel, so that the proportion of revolutions to power may be designed to suit various conditions of operation. Fig. 47 illustrates a 3,000 horse-power, double unit Ris- don wheel for direct connection to an electric generator. The unit consists of two wheels of disc form, eight and a half feet in diameter, mounted on the same shaft, each wheel being driven by a single jet, at 240 revolutions per minute. The buckets and centers of the wheels are made of cast steel. Bucket wings are milled out on an Ingersoll Fig. 47. Double Unit 3,000 Horse-Power Risdon Wheel slabbing machine, and driven on the edge of the turned disc. Through wings and disc, holes are drilled to tem- plate, and fitted with driven-in, turned steel forged bolts. Under normal load the bolts securing the buckets to the periphery of the wheel may be under a strain of 65,000 pounds each. To obviate any danger from this source, it is claimed that the bolts are each made to undergo a strain of 700,000 pounds without breaking, or at normal load, the bolts have the exceedingly high factor of safety of sixty. The discs on which the buckets are mounted are bored 104 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Fig. 48. Bucket Construction of the Doble Wheel and shrunk on a heavy shaft, the factor of safety of which against torque and weight is claimed to be over fifteen. The bearings are of the adjustable, ring- oiling ball and socket type, with very large surfaces, which are lined with anti-friction metal. The Doble Water Wheel. The Doble wheel, made by the Abner Doble Com- pany, of San Fran- cisco, is also of the tangential ellipsoidal type. Fig. 48 shows the bucket construc- tion of the wheel, and Fig. 49 shows the runner of a 3,700 horse-power wheel designed for operation under a head of 1,531 feet. The wheel proper or body is constructed of a nickel steel forging, 10 feet 5 inches in diameter, and weighing over io,ooopounds. The buckets are made of open-hearth steel castings, and are designed for a jet of water four and a half inches in diameter. Each bucket is fastened to the periphery of the wheel by two fitted bolts in reamed holes. Fig. 49. Runner of 3,700 Horse-Power Doble Wheel HYDRAULIC MACHINES 105 Fig. 50. Needle-Regulating Nozzle The nozzle used on the Doble wheel is of the needle-regulating type; the adjustment being effected by moving a core axially within the nozzle, thereby vary- ing the annular area of the orifice. Fig. 50 shows a jet issu- ing from a needle- regulating nozzle under a high head. Accessories of Tur- bines and Water Wheels. In regulat- ing the supply of water to a hydraulic machine a gate valve or several gate valves are used. Such valves are arranged to work in a ver- tical plane by partially or entirely closing the admis- sion orifice through the me- dium of a hand wheel or by means of gearing or rig- ging operated electrically or hydraulically. Various forms of gate valves are in use in Amer- ican hydro-electric plants. Fig. 51 shows the Pelton gate valve. It belongs to the straight-way single disc type of valve, and is designed for pressure on one side Fig. 51. A Straight-way Single Disc Gate-Valve IO6 LONG-DISTANCE ELECTRIC POWER TRANSMISSION only. The spindle of the valve can be so manipulated by means of the hand wheel as to bring the disc entirely clear of the opening, thus allowing free passage-way for the water. When the valve is used on pipe systems in which the pressure is very high it is fitted with ball- bearings or some form of gearing. Fig. 52. Battery of Relief Valves for High-Pressure Pipe Lines Fig. 53. The Lombard Water- Balanced Relief Valve Safety Relief Valves become necessary on pipe or con- duit systems working under very high pressure. They are generally placed at the lower end of the pipe line, in close proximity to the nozzle. Their operating pressure slightly exceeds the normal working pressure, and in case of a sudden stopping of the water flow by the closure of the gate valve or some accident to the governor, the safety valves open for an instant to relieve the pressure. This safeguards the pipe system against the serious dangers HYDRAULIC MACHINES ID/ resulting from water hammer. If the pipe line is of very large size and the pressure extremely high, a battery of safety relief valves is used. Fig. 52 shows a battery of such valves, made by the Pelton Wheel Company. Fig. 53 shows the Lombard water-balanced relief valve. In this type of safeguarding appliance the pressure of the water against the gate valve is opposed by the hydrostatic pressure at the point where the valve is fitted to the flume or casing of the wheel. The valve remains closed so long as the operating pressure does not exceed the static pressure. But when the normal pressure is exceeded in the flume the valve at once opens and dis- charges water until the press- ure is restored to the normal condition. Fig. 54 shows a Ludlow high-pressure valve of the double-gate type, constructed of iron and bronze. The valve is operated by means of bevel gearing, the position of the' gates being adjustable with center bearings to prevent the sticking of the parts. The type shown is fitted with an indicating device to show the position of the gate, and also a by-pass outlet. Fig. 54. Mechanically Operated Gate Valve 108 LONG-DISTANCE ELECTRIC POWER TRANSMISSION BIBLIOGRAPHY Mechanics of Engineering. Volume 2. Hydraulics and Hydraulic Motors. Weisbach-Du Bois. The Theory of Impulse Wheels. Kingsford. Engineering News. July 21, 1898. Turbines. Wood. Second Edition. Wiley & Sons. New York. 1901. The Need of Turbine Standards of Measurement. Replogle. Engineering News. October 23, 1902. Page 339. Water-Wheel Regulation. Garrett. Gassier* s Magazine. New York. May, 1901. Report of a Turbine Test. Webber. Engineering News. New York. April 20, 1903. Page 386. Tangential Water- Wheel Efficiencies. Henry. Transactions Pacific Coast Electric Transmission Association. June 16, 1903. Modern Turbine Practice and Water-Power Plants. Thurso. D. Van Nostrand Company, New York. 1906. CHAPTER IV GENERATORS, SWITCHES, AND PROTECTIVE DEVICES Kinds of Generators Used. Three distinct types of alternating-current machines are used in generating current for long-distance transmission, namely, the revolving arma- ture generator, the revolving field generator, and the inductor generator. Of these types the revolving field generator is most used, and is rapidly supplanting the other two types. The revolving armature alternator is generally used in outputs up to 800 kilowatts. The field magnet of this type of machine is constructed of either laminated or solid steel, either cast into the frame of the machine or bolted to it radially. In some few cases cast-iron poles are used. The magnet coils are in nearly every case form wound on collapsible mandrels, and the conductor is copper wire, bar, or strap, depending on the output of the machine. Field magnet coils are insulated with oiled muslin or linen, fuller board, micabeston, vulcabeston, etc., and the sepa- rate layers are sometimes protected by coatings of shellac. The armature of this type of generator is generally drum or barrel wound, and the core is usually of the toothed type. The armature coils are almost invariably form wound and of substantially rectangular outline ; in machines of considerable output the conductors are copper 109 110 LONG-DISTANCE ELECTRIC POWER TRANSMISSION straps or bars, each insulated from its neighbor by layers of fiber impregnated with a bituminous compound and varnished with a heavy coating of shellac, or by micanite and oiled linen, or some similar combination. The separate conductors belonging in one slot are assem- bled into a bundle and tightly bound together with insu- lating tape coated with a moisture-proof compound. The bundles of bars are then laid in the slots around the pe- riphery of the armature coils, which are insulated by troughs of insulating material ; after the coils are secured in place they are connected up to each other and the complete winding is connected to the " collector rings." The revolving field generator is built in two general forms : one in which the field magnet surrounds the arma- ture, as in the case of the Niagara Falls machines, and the other in which the armature surrounds the field magnet ; the latter is the more generally used. External field ma- chines with revolving magnets are used only in special work, such as that at Niagara Falls. In construction they are generally similar to revolving armature machines, except that the shaft is usually vertical, for coupling to a water turbine, and the field magnet is of the overhung or umbrella type. The revolving field generator with the armature sur- rounding the field magnet comprises an annular armature core, mounted in a cast-iron housing, and a wheel or spider mounted on the shaft and carrying radial field mag- net poles on its periphery. The armature winding is laid in slots around the inside of the armature core. In machines of large output this mode of construction has much to recommend it, its especial advantage being that with a given peripheral speed of the moving element there is more GENERATORS, SWITCHES, PROTECTIVE DEVICES I I I room for the disposition of the armature coils. More- over, since the coils are stationary, they admit of a higher degree of insulation than is possible with moving windings. The frame of the revolving field type being provided with air ducts, the rotating field maintains a better circula- tion of air through the coils than is the case with the stationary field type The absence of moving contacts for taking off currents of large value is also highly advan- tageous. The only moving terminals are those for estab- lishing connection with the field winding, and which have to carry but small currents at low voltages. The Inductor Generator. In this type both field and armature windings are stationary, the rotating member con- sisting of bare, soft iron fitted with projections termed "in- ductors." The projections receive their magnetization from an annular field coil, which also magnetizes the stationary part of the magnetic circuit. The frame surrounding the inductor has radial projections which correspond to the inductors both in number and proportions, and on these are mounted the generating coils. (See Figs. $6a and 56^.) When the inductors in rotation come immediately op- posite to the faces of the stationary poles, the magnetic re- luctance is at its lowest value, consequently the flux through the generating coils is at its maximum value. Conversely, when the inductors are at intermediate positions, the mag- netic flux interlinked with the generator coils is smallest, and consequently the E.M.F. is at its lowest value. Hence, at the various polar points around the frame of the generator the flux is varying from maximum to mini- mum, and back again, but does not alter its direction or polarity. 112 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Inductor generators are wound to deliver single and poly- phase currents, the armature windings being usually of the concentrated type. It will be apparent from the shape of the pole pieces that the instantaneous value of the E.M.F. in a coil is proportional to the strength of the magnetic field which it is cutting at that instant. Hence, with a fairly uniform magnetic density over the pole face, the curve of instantaneous E.M.F. during a cycle will not be a sine curve, but a flat-topped curve with an abrupt approach to a zero value. An approximate sine curve in an inductor generator may be obtained by a distribution of the windings in two or more slots per pole per phase, or else by such shaping of the pole faces as will vary the density in the air gap, so as to carry the E.M.F. wave up gradually instead of suddenly. Since all the poles on one side of the inductor generator have the same polarity, the magnetization of the armature teeth and iron is approximately in the same direction. The advantages claimed for the inductor generator are, that the iron is worked through only half a cycle, which makes the iron losses quite small, if the machine is worked at low magnetic densities ; freedom from moving wire, which reduces the liability to breakdown by the chafing of insu- lation ; ample space for insulation, due to stationary wire ; absence of moving current-collecting devices, and hence no losses due to sparking and brush friction. The Regulation of Generators. The inherent regulation of an alternating-current generator is usually defined as the percentage rise of voltage when the total non-inductive load is thrown off, both generator speed and field excita- tion being kept constant. GENERATORS, SWITCHES, PROTECTIVE DEVICES 113 According to the Standardization Committee of the American Institute of Electrical Engineers, "The regu- lation of an apparatus intended for the generation of a potential, current, speed, etc., varying in a definite manner between full load and no load, is to be measured by the maximum variation of potential, current, speed, etc., from the satisfied condition under such constant conditions of operation as give the required full load values." In apparatus which transforms, generates, or transmits alternating currents, regulation refers to non-inductive load, i.e., load in which the current is in phase with the E.M.F. at the outside of the apparatus, and is expressed in per- centage of the full load value. The inherent regulation of standard American alter- nators varies from sixteen per cent to six per cent on non-inductive load, depending on the output and type of machine. On inductive load the regulation of standard machines varies from twenty to ten per cent according to the output and the kind of machine. The fundamental factor involved in securing high inher- ent regulation in a generator is good inductive load regu- lation, which means the use of large amounts of copper and high magnetic densities in the iron. High inherent regulation is obtained at the expense of output per pound of material. Generators for long-distance power transmission work should have good inherent regulation, because machines under such conditions of operation cannot be compounded, for the reason that compounding would only compensate for the losses at one definite power factor. 114 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Moreover, in the majority of high-tension stations the machines are worked in parallel, in which case compound- ing becomes impractical. Efficiency of Generators. The efficiency of an alternat- ing-current machine is the ratio of its net power output to its gross power output. The determination of the efficiency of an alternator is made by measuring the electric power when the current is in phase with the E.M.F., unless otherwise specified. In case a generator has an exciter or other auxiliary apparatus the power consumed by the auxiliary apparatus should not be charged to the machine, but to the entire plant comprising machine and auxiliaries taken together. Plant efficiency is then to be distinguished from machine efficiency. Efficiencies of generators used in long-distance power plants vary rom 90 to 97.5 per cent (at full load). Fig. 55 shows th(^fliJM0MB curve,.,of an 1^850 kilowatt machine. The table below gives efficiencies of several Bullock generators. LOAD. i $ 1 1 H ii AK 14-9,015|, 1,000 kw., 11,000 v., 257 rev AK 18-7,517, 1,200 k\v , 2,300 v., 400 rev 86. 87. 92.2 93 94.2 95. 95.2 96. 95.7 96.6 96 AI 50-180 14|, 1,500 kw., 2,400 v., 120 rev A K 26-130-20 2 000 kw 2200 v. 231 rev. 87.8 87.4 93.4 92.9 95. 95. 96. 96. 96.5 96.5 96.7 96.9 AI 96-36,011, 2,500 kw., 4,500 v., 75 rev " " 3,000 k w., 4,500 v., 75 rev AK 16-6,519, 800 kw., 2,300 v., 450 rev AK 36-l,207|, 750 kw., 2,400 v., 200 rev AH 18-7,512, 600 kw., 2,400 v., 400 rev AI 60-1,807, 400 kw., 2,400 v., 120 rev 90. 91. 85. 86. 80. 80.3 94.2 95. 91.5 92. 89. 88.6 95.6 96.2 94. 94.2 92. 91.7 96.3 97. 95. 95. 93.5 93.2 96.6 97.4 95.5 95.4 94.3 94. 96.8 97.6 95.7 95.4 95. 94.3 Parallel Operation of Generators. The parallel operation of generators in hydro-electric plants is absolutely essential to economical operation in cases where large powers are GENERATORS, SWITCHES, PROTECTIVE DEVICES 115 developed, in order to reduce the number of circuits and transmission lines. Generators of standard make and proper design, coupled to water wheels, operate in parallel 1 850 K.W 1 4,500 VOLTS., 180 REV.,28 POLES 100 AMPERES EXCIJATION 200 Fig. 55 with absolute reliability and simplicity, because of the per- fectly uniform angular motion of water wheels. The most important requirement of a generator intended for parallel operation is a reasonable amount of armature reactance. If the reactance is too small, an enormous Il6 LONG-DISTANCE ELECTRIC POWER TRANSMISSION exchange of current between the machines is liable to occur when there is even a slight difference in their field excitation, or if the machines are thrown in parallel when there is a slight phase difference between them. Parallel operation of machines with an excessive amount of arma- ture reactance can also be effected, but their operation Fig. 560. Construction of 2,000 K. W. Water-Wheel Type Inductor Generator under such conditions is not stable, and " hunting " fre- quently occurs, due to the exchange of a small synchron- izing current between them. In cases where a number of generators are operated in parallel the field excitation of each machine is individually adjusted to enable it to supply its share of the total GENERATORS, SWITCHES, PROTECTIVE DEVICES I I/ current, which prevents an exchange of current between the machines. The fly-wheel effect obtained from the large masses of metal in revolving field generators conduces greatly to stability of operation in parallel, and tends to produce uni- formity ,of angular motion. Figs. $6a and 56^ show a 2,000 kilowatt high-speed Fig. 566. A a, ooo K. W. Water-Wheel Type Inductor Generator Completed water-wheel type inductor alternator, made by the Stanley Electric Manufacturing Company. The stationary part of the machine nearest the air gap is built up of laminated iron, the coils being wound and insulated separately and laid in slots in this part, in the shape in which they are wound. IlS LONG-DISTANCE ELECTRIC POWER TRANSMISSION The single field coil is stationary and is form wound on a brass spool from which it is thoroughly insulated. The secondary action of the brass spool tends to obviate danger from the breaking down of the insulation of the coil when the field circuit is broken. The revolving part consists of bare cast steel, keyed to the shaft, and is filled with laminated iron projections or Fig. 57. A Bullock 3,000 K. W. Water-Wheel Type Generator inductors on its surface. The bearings are of the self- oiling, self-aligning type- Fig. 57 shows a 3,000 kilowatt, 4,400 volt, 3 phase, 60 cycle Bullock revolving field generator of the water-wheel type. The armature is built up of mild annealed steel of high permeability, the laminae being japanned to reduce GENERATORS, SWITCHES, PROTECTIVE DEVICES I 19 eddy currents. The armature coils are wound on cast-iron forms, the conductors being carefully insulated from each other and from the core. The field coils are constructed of copper strap bent edgewise. The difference of potential between the turns is but a fraction of a volt, which insures freedom from in- sulation breakdown. The bearings are of the self-adjusting, self -oiling type. Fig. 58 shows a 3,750 kilowatt water-wheel type Westing- house revolving field generator. The illustration shows the machine during erection in a hydro-electric plant. The field magnet is constructed of laminated steel punchings fastened together by bolts and dovetailed into a cast-iron spider. This spider does not form a part of the magnetic circuit, the lines of force going only through the lamina- tions. The construction is designed to give the rim sufficient strength to resist the strains caused by cen- trifugal force without straining the central spider. The field magnet coils are form wound with copper strap bent on edge. Wedges of copper serve to retain the coils in place and also act as "dampers" to reduce the shifting of the flux across the pole faces due to armature reaction. The armature is built up of slotted steel punchings dovetailed within a cast-iron frame. The winding consists of copper strap bent into the required shape and held in open slots by hard fiber wedges. Switchboards for High-Tension .Current. The switch- board being virtually the heart of a transmission system, its design and equipment are of vital importance in the safe and trustworthy operation of a plant. Switchboards for high-tension plants are made of care- 120 LONG-DISTANCE ELECTRIC POWER TRANSMISSION GENERATORS, SWITCHES, PROTECTIVE DEVICES 121 fully selected marble and built up of panels, or units, which are bolted to structural steel frames. The majority of high-tension boards in stations of large output are provided with a separate panel for each gener- ator as well as a p'anel for each exciter unit ; and in plants where two different pressures are generated there are gen- erally panels for the feeders. A main junction panel in the middle of the board is sometimes provided by means of which it is possible to divide the board electrically into two parts, either of which may be closed down for repairs while the other is in service. A high-tension generator panel is usually equipped with one or more circuit breakers ; single-pole, double-throw main switches ; two or three long-scale alternating-current ammeters ; a dead-beat direct-current ammeter for the field circuit; a double-pole, single-throw, quick-break field switch, with shunt resistance and discharge attachment ; series and shunt transformers \ m synchronizing devices ; indicat- ing and integrating wattmeters, etc. In many cases the rheostats in high-tension stations are mounted under the gallery floor (or the main floor of the station), and are controlled by hand wheels on pedestals located directly in front of their respective generator panels. On some high-tension boards there is provided a mul- tiplying panel for duplicating the bus-bars. Multiplying panels are provided with a double-pole, hand-operated circuit breaker ; single-pole, single-throw multiplying switches ; a synchronizing device and double-throw switch for throwing the synchronizing device on any of the several sets of bus-bars. Each panel for the raising transformers is usually 122 LONG-DISTANCE ELECTRIC POWER TRANSMISSION equipped with a single-pole automatic overload circuit- breaker, with time-limit relays ; a long scale am- meter ; a double-throw, double-pole main switch ; light- ning arresters and static interrupters, together with various auxiliary devices depending on the size of the unit. For each group or bank of transformers there is provided an integrating wattmeter and several shunt transformers. In some high-tension stations the high potential board is arranged so that either of the two transmission lines may be operated on either bank of the transformers, so that either half of the switchboard may be " dead- ened " for cleaning or repairs while the other is in operation. Switches for Handling High Voltages. No apparatus employed in high-tension electric power transmission is of more vital importance than the switches used in controlling the circuits. The severe demands imposed on this part of the electrical equipment necessitate the highest skill and familiarity with the requirements which circuit-controlling appliances must fulfill. Switches used in American high-tension practice are of several general types, namely, air-break switches, com- bined air-break switches and fuses, oil-break switches, com- bined oil-break switches and circuit breakers. Oil-Break Switches. For circuits operating under a pressure of a few thousand up to 60,000 volts, the oil- break type of switch has adequately demonstrated its reli- ability. A type of oil-break switch extensively used in plants of moderate pressure i.e., up to 15,000 volts is shown in Fig. 59. It consists of two or three double-pole single-phase elements or switches (the number depending GENERATORS, SWITCHES, PROTECTIVE DEVICES 123 on whether the circuit is two phase or three phase) inclosed each in a fire- proof cell, but arranged for simultane ous operation. Each element of the switch is usually made up of two brass cylinders, one cylinder per pole. The in- coming terminal of one phase is attached to one cylinder, and the outgoing termi- nal of the same phase to the other cylinder. Each cylinder is filled about two thirds full of oil and is covered over with a metal cap, to which is attached a long insulatingsleeve. Two copper rods forming vertical spindles and united by Fig. 59. Oil-Break Switch for Moderate Pressures 124 LONG-DISTANCE ELECTRIC POWER TRANSMISSION a metallic cross-head at the top slide through the insulating sleeve and fit into tubular contacts at the bottom of the cylinder when operating to close the circuit. To the Fig. 60. Type of Oil-Break Switch for High Pressures cross-head of the copper rods is attached a wooden rod extending through the top of the cell which incloses the switch. This rod is attached to a metallic cross-head, which is actuated by either electric or pneumatic devices. When the rod conductors of the switch are raised the GENERATORS, SWITCHES, PROTECTIVE DEVICES 125 circuit is broken under the oil in two places in each phase. The range through which the cross-head can be actuated varies with the pressure which the switch has to handle. In order to keep the arc from jumping from the copper rod to the cylinder when it is drawn through the oil, the cylinders are lined on the inside with fiber. The isolation of the composite poles of the switch in separate fireproof compartments is to prevent a burn-out in one cell from spreading to the others, and thus causing a complete breakdown of the switch. Another type of oil switch in successful operation on high-tension circuits is shown in Fig. 60. The switch mechanism comprises two or more metallic contact pieces depending upon whether the switch is of single, double, or triple pole type. The contact pieces are attached to sepa- rate rods of chemically treated wood, which in turn are attached to a cross-head actuated in a vertical "plane by a system of levers. Each contact piece makes electric con- nection by means of a clip, which is supported from the frame by porcelain insulators, so as to insulate all live parts. When the contact pieces are brought to their upper position, the switch is closed. On opening, the contacts fall into the bottom of the oil cylinder. The live parts of the switch, such as clips, contact pieces, etc., are entirely immersed in oil when the cylinder is fitted in place. A switch of this type is not intended to break loads under extreme emergencies, such as a short circuit just beyond the switch on the load side. Nor is its use advisable directly on panels which in extreme instances can exceed 2,500 kilowatts, three-phase, or 1,500 kilowatts, single-phase power. Under such conditions, single-pole, single-phase switches of the type shown in Fig. 59 are 126 LONG-DISTANCE ELECTRIC POWER TRANSMISSION generally employed. The type of switch here shown is automatic in its operation and is designed to perform all of the functions of a circuit breaker. Two kinds of Fig. 61. Switchboard Tripping Mechanism of Oil Switch mechanism are used to actuate it, these differing from each other according to whether the switch is mounted directly on the switchboard or is placed in cells at some distance away. The mechanism of the first or the switchboard tripping mechanism is shown in Fig. 61. It GENERATORS, SWITCHES, PROTECTIVE DEVICES 1 2/ is made up of a series of coils placed on the face of the board and energizing armatures which operate to release a latch on the interconnecting link between switch and handle. Connected in series with the main switch are the secondaries of current transformers which energize the coils of the tripping device. When the switch is auto- matically opened by this tripping device, the handle on Fig. 62. Portion of Circuit Breaker on Face of Switchboard the face of the board remains closed, and. the link moves forward through the handle, giving unmistakable indica- tion that the switch has automatically opened. Combined Oil-Break Switch and Circuit Breaker. A radically different type of oil-break switch with attached circuit breaker is shown in Figs. 62 and 63. Fig. 63 shows the portion of the switch behind the board. Fig. 62 is 128 LONG-DISTANCE ELECTRIC POWER TRANSMISSION an illustration of the portion of the mechanism which is on the face of the board. Each pole of the switch is immersed in oil in a separate compartment lined with procelain ; the object of this arrangement being the pre- vention of current leakage and short circuits from pole to Fig. 63. Portion of Circuit Breaker Behind Switchboard pole. Each contact is tipped with zinc in order to obviate pitting action on the blades. By means of the four screws fitted in the marble cover of each compartment of the switch the tank may be removed without disturb- ing the switch mechanism, even while it is carrying current. This form of oil switch is used in either the single or GENERATORS, SWITCHES, PROTECTIVE DEVICES 1 29 double throw type with single, double, triple, or quadruple poles. Its capacity ranges from 4,000 volts and 1,000 amperes to 15,000 volts and 100 amperes. The circuit- breaker attachment is operated by means of the disc shown at "the lower part of the illustration, Fig. 62. The circuit breaker is adjusted to open at different loads by set- ting the dial hand at the points corresponding to the loads. Air-Break Switch with Fuse. A very ingenious air- break switch, with fuse attachment, is shown in Fig. 64. This type of switch is in use in the plants of the Bay Counties Power Company and the Standard Electric Com- pany, of California, and deals with potentials as high as 60,000 volts. The elements of the switch consist of a main arm, an auxiliary arm, a fuse holder, and two contact pins. The main arm consists of a wooden rod hinged at the lower end to a bracket mounted on the switchboard. On the top of the main arm are mounted two zinc jaws which hold one end of the fuse. The arm also carries two blades which make contact with the terminal jaws. The blade near the free end is electrically connected to the zinc jaws, while the lower one is connected by means of a cable to the aux- iliary arm. The auxiliary arm is a hollow wooden rod hinged at its lower end to the main arm. Attached to its free end are two zinc plates forming the holders for the other end of the fuse. A copper rod attached to the auxiliary arm forms the connection be- tween these plates and the cable which connects the lower blade on the main arm. In the event of the fuse becoming unlatched or blowing' 130 LONG-DISTANCE ELECTRIC POWER TRANSMISSION out, the auxiliary arm is quickly pulled, the jar of its fall being absorbed by a dash pot attached by a bracket to a main arm. The fuse holder comprises a hollow insulating tube fitted at each end with perforated corks, and filled with a non- fusible and non-conducting powder through which the fuse is drawn. When it is not supported by the fuse it is tied to the main arm in order to prevent its falling out of position. The fuse is maintained in its posi- tion between the main and auxiliary arms by the zinc jaws on the top end of the main arm and the zinc plates on the auxiliary arm. The jaws which form the terminals are car- ried by separate blocks of marble, and are fur- ther insulated from the marble of the switch- board by means of porce- lain strips and bush- Fig. 64. A High-Potential Air-Break Switch ingS. There IS also mounted on the upper marble blocks the latch which opens the zinc jaws on the main arm. This latch is operated to release the fuse by means of the rope shown in the engraving. / h^m GENERATORS, SWITCHES, PROTECTIVE DEVICES 131 The operation of the switch to rupture a loaded circuit is as follows : With the switch in its normal position, cur- rent is led to the upper terminal, passing thence to the zinc jaws on the main arm, from which it passes through the fuse to the auxiliary arm, down the auxiliary arm, and through the cable to the lower blade on the main arm ; thence it passes out through the bottom terminal. A pull on the latch rope forces the jaws open and thereby releases one end of the fuse, which is then rapidly drawn through the non-conducting powder in the holder tube by the fall SECTION OF SWITCH JAW ROUND BRASS c LU Ei z < I I Fig. 65. A " Ram's Horn, ' ' Pole-Line Switch of the auxiliary arm to its horizontal position, thus ruptur- ing the circuit and blowing out the arc which is formed. The main arm is then unlocked from the catch, and the mechanism of the switch swung down to an accessible posi- tion, and the fuse replaced. When this is accomplished, the mechanism is returned to its normal position by means of 132 LONG-DISTANCE ELECTRIC POWER TRANSMISSION the rope on the main arm. In order to prevent the fuse from rupturing under medium load and instantaneous over- loads, it is made heavier than it would be were the device intended for automatic fuse action rather than a switch. Air-Break Switches. In many long-distance trans- mission plants in the West the high-tension switches employed are simply long-break "stick" switches in which the length of the break is depended on for opening the line. A common home-made switch of this kind has an inclosed fuse attached to the stick on which the switch jaw is carried. When the fuse is blown the switch stick is pulled out and replaced by a similar fused stick, as in the case of an ordinary low-tension removable fuse holder. Another type of home-made switch contains a short fuse mounted between carbon blocks under more or less ten- sion. When the fuse is blown or when a trigger device which holds the switch closed is tripped, the blocks are instantly thrown apart. These types of combined stick switches and fuses are generally made interchangeable so as to admit of easy replacement. A type of switch largely used in Pacific coast high- tension practice is a " ram's horn," air-break, pole-line switch. Fig. 65 illustrates a switch of this kind which has proven quite reliable in handling a potential of 33,000 volts. The jaws of the switch are placed side by side, only thirteen inches apart. Just above the switch-jaws are two curved conducting strips made of line wire. The switch jaws are normally connected together by means of a cylindrical brass rod, attached to a long wooden handle. The jaws have a bayonet clip on their ends which engages GENERATORS, SWITCHES, PROTECTIVE DEVICES 133 the brass rod and prevents it from falling out when the switch handle is released. When the circuit is broken by pulling the brass rod out of the switch jaws by means of the attached handle, the arc which ensues is blown up between the horns by the heated air currents until it passes the point where its length is the maximum that the voltage behind it will maintain, and it breaks. Conditions which Render Switching Necessary. A care- ful consideration of the conditions under which it becomes imperative to open high-tension transmission lines will lead to the conclusion that such instances are indeed few. The opening of high-voltage lines on the high-tension side of transformers is one of the most fruitful causes of trouble in the operation of transmission lines. Hence, for very high pressures, switching either should not be done at all or, if it must be done, it should be accomplished on the low- voltage side of transformers. There is, however, one catastrophe which renders it unavoidable. If a transformer is in any way set on fire, and it becomes necessary to cut it out without bringing about an interruption of service, the high-tension switch must be opened regard- less of line conditions. It is for such infrequent emer- gencies that a stanch and trustworthy switch is most needed. The major part of the switching done under load can be equally well carried out from the low-voltage side of trans- formers as from the high-tension side. The most common switching operation is that of cutting out a bank of trans- formers. This operation can be best done first on the low- voltage side, thus leaving only the transformer exciting current to be cut off on the high-voltage side. In most 134 LONG-DISTANCE ELECTRIC POWER TRANSMISSION cases it is better to leave the transformers in circuit rather than break the high-tension side under no load. In the event of a persistent short circuit on the high-tension line, it is quite feasible, and generally best, to break the low- voltage circuits first. Automatic Station Protective Devices. Perhaps no part of the subject of long-distance transmission has re- ceived more attention than the protection of high-voltage apparatus from damage due to abnormal conditions. The proper design and installation of protective appliances is a matter of far-reaching importance in the laying out of a high-tension line, since the insertion of safety apparatus at the proper point in the line will obviate an endless amount of trouble. The several kinds of protective appliances used in high- tension practice are fuses, circuit breakers (either separate or as composite parts of oil-break switches), overload re- lays, time-limit relays, and reverse-current relays. Of these widely different devices, as regards the function each is designed to exercise, the fuse is the simplest means for automatically breaking a circuit. Fuses for high-tension alternating-current circuits are quite different from those in use on direct-current lines, for the reason that when a fuse ruptures on a high- potential circuit, the arc that is drawn tends to persist, owing to the high voltage behind it. The current of a high-potential line thus ruptured tends to maintain the continuity of the circuit by following the path of the heated air; it may also jump to a point on the other side of the line, and short circuit the line between the protective device and the source of supply. The one object in common in the various kinds of fuses used in GENERATORS, SWITCHES, PROTECTIVE DEVICES 135 alternating-current practice is thoroughly to insulate the fuse from the neighboring parts of the line. Thus it is intended that the suppression of the arc shall be from the fuse block into the neighboring air, thereby increasing the length of the break, and so effectively opening the circuit. Fuse blocks are generally mounted on the back of the switchboard, either on separate marble bases or near the top, and are rigidly secured to the board by means of brackets on the rear of the board. A type of fuse holder in use on alternating-current circuits not exceeding 2,500 volts in pressure is called an expulsion-block fuse, Fig. 66. It consists simply of a porce- lain block in which a rectangular hole has been cut. This recess receives a block of lignum-vitae. At each end of the porcelain block there is fitted a copper stud, which extends through the upper surface and is an elongation of the chisel-shaped contact piece. These also hold the cover of the block in place, which is likewise made of Fig. 66. A Type of Lignum-vitae High-Tension Fuse Block lignum-vitae and fitted with an air- vent, and well insu- lated by thumb-screws on the studs. The fuse is placed under the vent in the upper lignum-vitae block and between the two, and is joined to the copper studs. When the fuse blows the arc takes place between non- combustible material, and hence is blown upward into the atmosphere. 136 LONG-DISTANCE ELECTRIC POWER TRANSMISSION When the potential of the circuit exceeds 2,500 volts, a mechanical device is used to sever the fuse when the tensile strength is reduced by the heating produced by overload currents. Rupture of the circuit just before the fusing point is reached reduces the current of hot air bridging the gap, and consequently tends to suppress the ensuing arc. The tendency to emit showers of fused metal is also overcome, and a quicker breaking of the circuit is made possible. The mechanical means adopted to produce this result consists of a spring-expulsion fuse block introduced in the circuit in the same way as the expulsion block already described. It is made up of a base and two side pieces of hard wood, the whole being varnished and fireproofed. On the base is fitted a lignum-vitae block, which goes between the terminals of the circuit. The fuse block is connected to the circuit by means of a chisel-shaped piece, similar to those used in above-described fuses. Each piece goes through the base, and is attached by means of copper strap to a copper plate. The copper plate has mounted on it a stud with a vent and washer, and is in the shape of an inverted U ; the two ends being carried on a pin which rotates in the plane of the chisel piece. A stout spring mounted on the pin holds the copper pin normally in a recumbent position on the base of the block. The set fuse rests on the lignum-vitae block, and is long enough to hold these terminals in a vertical position. Such a fuse is stout enough to overcome the tendency of the terminals to spring back on the base, but when its tensile strength is diminished by heating, the fuse quickly blows, as above described, and breaks the circuit. The current-carrying parts of the device are completely inclosed in fiber strips, and a cover of lignum-vitae with an air vent is fitted over the GENERATORS, SWITCHES, PROTECTIVE DEVICES 137 top. To obviate the tendency to arc over the sides, the side pieces are extended several inches beyond the inclos- ing strips. When this fuse is used for potentials greater than 5,000 volts, the fuse-block connections are thoroughly insulated from the switchboard by tubes of molded rubber. These also support the block and the connections to the circuit behind the board and several inches from it. Expulsion- type blocks are in use to protect circuits operating under tensiyis as high as 20,000 volts and carrying 100 amperes. Although the use of fuses is quite extensive on circuits of moderate voltages and currents, it becomes impractica- ble to employ them on high-tension circuits carrying large power. Under these conditions it becomes imperative to provide devices which will automatically open the circuit mechanically. The overload relay is an apparatus which exercises a function similar to that of a circuit breaker. In its usual form an overload relay consists of a solenoid surrounding a soft iron rod or plunger, which is attracted upwards and causes an auxiliary bar to strike against contacts and close a local circuit, through the tripping magnet of an oil cir- cuit breaker. In order to adjust the position of the plunger for varying current strengths it is supported by a disc in a tube which is fitted to the lower end of the solenoid. By adjusting the position of this disc vertically the plunger can be set to operate at any desired current strength. In the event that it becomes necessary to use current from a single source, to actuate both the relay and the circuit breaker, which means current from the same trans- former, the tripping mechanism on the oil switch is con- nected in series with the relay, and the secondary of the 138 LONG-DISTANCE ELECTRIC POWER TRANSMISSION current transformer. Normally, this connection short cir- cuits the tripping mechanism, and the plunger of the sole- noid in this case breaks the short circuit when it is pulled upwards, and so permits the operation of the tripping magnet. The connections for both cases are shown in Figs. 67 and 68. The overload time-limit relay is a device intended to STATION BUS BARS I I SERIES . J ; : CONNECTIONS O.F OVERLOAD RELAY' Fig. 67 Fig. 68 operate the circuit breaker, should the overload continue for some definite length of time, for which the relay has been set. Overload time relays are designed for two kinds of service, namely, to handle temporary or brief overloads, and to confine the effect of an overload to some local sec- tion of the circuit, and hence restore normal conditions by causing the protective appliance in that section to operate. GENERATORS, SWITCHES, PROTECTIVE DEVICES 139 The first .function it must discharge, sometimes, when lines become crossed or short circuited. In such cases the cir- cuit often relieves itself, however, by burning out the obstruction, and it would be bad practice to open the circuit unless the trouble is prolonged. When overload time relays are used on feeders or sub- feeders fed by an alternating-current generator, a very Fig 69. Mechanism of a Time-Limit Relay efficient method of protection is obtained by proper em- ployment of the adjustable time feature. By using relays in the main feeders designed to open in, say, five or six seconds, relays in the sub-feeders which will open in two or three seconds, and instantaneously operating relays in 140 LONG-DISTANCE ELECTRIC POWER TRANSMISSION local circuits, an overload or short circuit in the main feeders would not be relieved unless it continued for the time mentioned ; the same trouble would not be relieved in the sub-feeder for two or three seconds; while in the local circuit relief would occur instantly. Time-limit re- lays are operated by clockwork mechanism. Fig. 69 shows the mechanism of a time-limit relay. Fig. 70, two discs of wood, which are carried by slowly rotating shafts. Mounted on the periphery of each disc is a piece of copper strip, against which is pressed a contact piece of spring brass. A companion piece of brass is so fastened as to be just Copper Piece l| A 1 B Fig 70. Detail of Time-Limit Relay out of contact with the top of block A. On the shaft which carries the wooden discs is also mounted a notched brass wheel, which engages with a detent, presenting the movement of the clockwork. On a parallel shaft which revolves at a higher rate of speed are four aluminum vanes at right angles to each other ; these are adjustable to vary the time interval by regulating the speed of the clock- work, which in turn controls the speed of rotation of the wooden discs. In most apparatus of this kind the time per revolution of the discs varies from three to ten sec- onds. The contact points are always connected in an aux- iliary circuit, which generally carries a direct current at low pressure ; they are in series with the tripping magnets of GENERATORS, SWITCHES, PROTECTIVE DEVICES 141 the oil-break switch, and therefore control the operation of that switch. Underneath a lever attached to the ratchet above mentioned is a cylindrical iron piece, about an inch in length, which is supported by a spring that has a vertical motion. Another similar iron piece and joined to it is mounted underneath the spring contact over the disc A. A solenoid which is excited by current transformers forces the two iron pieces upwards, whereupon one of them pulls down the ratchet. The iron pieces which are thus attracted by their cores are designed as levers. The time-limit relay operates on the following principle : Assuming a short cir- cuit to have occurred, both of the coils are magnetized ; one of them releases the clockwork, and the other forces the con- tact against the disc A. So long as the short circuit con- tinues the magnets remain energized and maintain the parts in this condition. Should the short circuit continue during the time necessary for the discs to rotate far enough, both contact pieces will impinge against the copper facings, and so close the auxiliary line. If the trouble is relieved before contact is made, the iron pieces are drawn back into their normal position by retractile springs, thereby pulling the contact pieces away from the disc A, and allowing the detent to bring the mechanism to a stop after it has made one revolution, without tripping the circuit breaker. Since the solenoids operate the magnetic plugs or cores against the resistance of adjustable springs, the calibration of the solenoids is accomplished through the medium of these springs. In order to protect all working parts from injury the mechanism of the time-limit relay is inclosed in a cylin- drical glass case. It is generally located on the panel from which all outgoing circuits radiate. 142 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Reverse-Current Relays. The reverse-current relay usually consists of a direct-current motor of about one sixteenth or one eighth horse-power, with its field energized by a current transformer inserted in series with the line, while its armature is supplied with current from a poten- tial transformer in parallel with the line. Mounted on the motor frame are two contacts, to which are connected the terminals of the local circuit which energizes the tripping mechanism on the oil switch in the main circuit, which is protected by the relay. The shaft of the motor carries a pair of U-shaped carbon pieces which slide against these contacts. When the current in the line is flowing nor- mally, the motor tends to rotate away from them ; but if the line current is reversed the field current of the motor is also reversed, while the direction of flow in the armature remains the same. Hence the motor rotates in the opposite direction, approximately an eighth of a revolution. This is sufficient to bring the U-shaped strips against the contacts, which closes the magnetizing circuit and trips the circuit breaker, or indicates the condition of the circuit by a visual signal. The reverse-current relay finds use on feeders between central and sub-stations in high-tension practice ; these are generally tied together by parallel lines protected by automatic circuit breakers at both ends. In the central station are two sets of bus-bars, from each of which one circuit leaves, but the lines are frequently connected to a common set of bus-bars when they reach the sub-station. Consequently, heavy overloads, or short circuits on either circuit, will affect the protective apparatus on that circuit in the same way that a short circuit on both circuits through the sub-station bus-bars would. It is for this especial GENERATORS, SWITCHES, PROTECTIVE DEVICES 143 condition that a reverse-current relay is designed. The incoming leads to the sub-station are protected by reverse- current relays, while the outgoing leads of the generating station are protected by overload relays. If trouble occurs on either circuit such as to cause the operation of its pro- tecting circuit breaker at the central station end, power will be fed back to the trouble over this line from the sub-station ; this reverse flow of power affects the opera- tion of the reverse-current relay, thereby opening the circuit at the sub-station end also. The other line is, MAGNET COIL ON CIRCUIT BREAKER CIRCUIT CONNECTIONS OF REVERSE-CURRENT RELAY Fig. 71 of course, unaffected. The reverse-current relay also finds especial application in connection with rotary con- verters working in parallel with other apparatus for the purpose of preventing the inverted operation of the rotaries occasioned by cutting off the alternating-current supply. Fig. 71 shows the circuit connections of the reverse- current relay. A reverse-current time-element relay is a protective appliance which combines the functions of all three pieces of apparatus just described, and operates to break the cir- 144 LONG-DISTANCE ELECTRIC POWER TRANSMISSION cuit when a reverse current of definite strength continues to flow for a predetermined length of time. The circuit breaker is actuated by differentially wound solenoids, the winding of one being taken from a potential transformer and that of the other from a series transformer. When the circuit is working under normal conditions the force exerted by the solenoid windings is negligible, each winding prac- tically neutralizing the other. Should the current attain the value for which the mechanism has been set, the clock- work is released and opens the circuit, if the trouble con- tinues for a definite period of time. A reversal of the current with respect to its normal flow also releases the clockwork, but regardless of the current strength because the influence of the two solenoids is now cumulative instead of differential. Circuit Breakers. Circuit breakers designed for use on high-tension lines are of materially different construction from their direct-current progenitors. In direct-current practice a circuit breaker is generally used in conjunction with the main switch ; in alternating-current practice it becomes the main switch itself, and may be either operated by hand or tripped automatically by electromagnetic means. A type of electro-mechanical circuit breaker in which the breaking takes place in oil is shown in Fig. 72. It is of the three-pole, double-break form, and is actuated by electro- magnets. Like the oil switches previously described, each element of the switch portion is contained in a separate brick cell filled with oil. Each pole or element has two stationary contacts, one of which is connected to the in- coming and one to the outgoing leads of the same phase. All live parts are mounted on porcelain insulators attached to a frame made of cast iron, which also carries the oil GENERATORS, SWITCHES, PROTECTIVE DEVICES 145 tanks. Across the top of the masonry structure is placed a soapstone slab in which strain insulators >are fitted to support the cast-iron frame. Fig. 72. A Type of Oil Circuit Breaker for High Voltages The contact for each pole is made up of a U-shaped piece ot copper attached to the end of a strong wooden rod. 146 LONG-DISTANCE ELECTRIC POWER TRANSMISSION When the switch is closed, one of the U-shaped copper pieces electrically connects the two contacts of each ele- ment. A common cross-bar is attached to the wooden bars at their upper ends. This cross-bar is manipulated by a system of levers to work in a vertical plane. The cross- bar is lifted -by the force of the magnet which incloses it, aided at the commencement of the motion by a pair of ^bal- ancing springs. The breaker is fitted with a toggle joint (which can be seen at the left of the illustration) which automatically locks the levers when the breaker is closed. The toggle joint is released by a blow from a tripping mag- net, allowing the cross-bar to drop by gravity and open the contacts, its fall being expedited by a pair of stout springs. The first break occurs at the main contact, and immediately afterward at the removable plug fastened to the rigid con- tact ; and immediately afterward at the removable contact set in a hole on the movable contact. The object of this plug is to dissipate the effects of the possible arcing. The electromagnets are energized by current derived from any convenient low-pressure direct-current source. It is also feasible to operate the circuit breaker by hand. The oil tanks are made of thick sheet metal, lined with insulating cement. The level of the oil in the tanks is shown by a small sight gauge. The controlling and indicat- ing apparatus of the circuit-breaker comprise a master- switch, a telltale indicator working on the electro-mechan- ical principle, and an incandescent lamp. Such apparatus is carried on a convenient panel. To make the circuit breaker automatic, there is provided a polyphase overload relay, which is energized from series transformers in the main circuit. The master switch, which is of the drum type, has marked on it three positions viz. " off," " closed," and GENERATORS, SWITCHES, PROTECTIVE DEVICES 147 position it will remain Fig. 73. A Type of Concentric Cyl- inder Arrester "open." If it is put to the " open so when the operator's hand is removed. If, however, it is thrown to the " closed" posi- tion, it will instantly turn to the " off " position, when the handle is released. When in the "off" position, it connects the controlling circuit in such a way that if the oil circuit breaker is opened by any of the automatic appli- ances the operator's lamp on the stand will be lighted and thus call attention to the condition of the cir- cuit. The lamp, however, is not lighted if the operator should throw the switch to the " open " posi- tion. The electro- mechanical telltale indicator consists of an electromagnet, with its armature so pivoted that it can be attracted through an angle of 90 degrees. Each switch is fitted with an overload relay operating on the principle of a single-phase induction motor. VERTICAL SECTION OF LIGHTNING ARRESTE.R Fig. 74 148 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Types of Lightning Arresters. Fig. 73 shows an arrester for high-tension circuits made by the Stanley Electric Manufacturing Company. Fig. 74 shows a vertical section of the arrester. It consists of two nests of concentric cylinders with diverging ends, which are held in position by perforated porcelain caps at the top and bottom, the caps being rigidly attached to an insulated support of either marble or porce- lain. The line is grounded through the innermost cylinder. The porcelain caps are so grooved as to make all spark gaps about one sixteenth of an inch in width. The pur- pose of the vents in the caps is to provide a good circula- tion of air. Between the line terminal and ground connection there are three spark gaps of one sixteenth inch width, thus making a total of three sixteenths of an inch air gap between either line wire and ground. With commercial frequen- cies, it requires a pressure of 5,000 volts to jump the gaps of the arrester, but the very high frequency of a lightning dis- charge reduces the arcing potential to one half this value. The area of the discharge gap is considerably increased by the use of concentric cylinders, a large discharging area being desirable to take care of heavy discharges. For circuits of 1,000 volts, a double-pole arrester connected together by a metallic strip is used. Circuits of high po- tential are protected by a number of the arresters connected in series, the proper number for a given high-tension circuit being arrived at by experiment. A choke coil is connected between each arrester and the apparatus to be protected. This choke coil is made up of parts so disposed relatively to one another that the coefficient of mutual induction is very high. The coil comprises two parallel coils of insu- GENERATORS, SWITCHES, PROTECTIVE DEVICES 149 lated copper strip, connected in series and wound so that the current passes through them in opposite directions. The proximity of the coils makes the coefficient of mutual induction very high ; hence with commercial currents the self-induction approaches zero. The operation of the arrester is as follows : Lightning enters from the line to the middle cylinder and jumps the gaps in the narrow parts of the arrester; it then passes N.D GRCfOND Fig- 75- Circuit Connections of Arrester shown in Fig. 73 from the outer cylinders to the ground connection. Should the generator current follow the discharge, an air current is immediately set in circulation through the vents of the porcelain caps and between the cylinders ; this air current blows the arc upwards into the spaces between the horn- shaped ends of the cylinders, thereby rupturing it. With this type of arrester there is used a line discharger, the function of which is to remove static charges from the line. 150 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The line discharger consists of a very small air gap in series with one or several tubes containing oxidized metallic particles. The tubes are about 18 inches long, and have a Fig. 76. Westinghouse "Low-Equivalent" Lightning Arrester resistance of about 50 megohms practically infinite. The small air gap is put in series with the tubes as an added precaution against grounding the line. A line dis- charger behaves as a selective lightning arrester. It pre- GENERATORS, SWITCHES, PROTECTIVE DEVICES 151 6 CHOKE COILS, 17 TURNS PER COIL vents dynamic currents from passing, but readily allows static discharges of low potential to pass through the tubes and over the minute air gaps and thence to ground. The number of tubes necessary for a circuit is governed by the line pressure. Fig. 75 shows the way in which a high-tension arrester and line discharger are connected in circuit. Fig. 76 shows a type of "low equivalent" arrester made by the Westinghouse Company and used on one of the Niagara Falls transmis- sion lines. The circuit, after passing through a 36 inch fuse composed of No. 28 German silver wire, inclosed in a hard fiber tube of approxi- mately seven eighths inch diameter, is led through an adjustable spark gap between small metallic balls to a bank of ten arresters, each of which has seven cylin- ders of non-arcing metal. The gaps are one thirty-second of an inch in length. The diagram of the connections (Fig. 77) is self-explana- tory. The discharge first takes place over the adjustable gap of three eighths inch between the balls and then over i . 36 IN. ENCLOSED FUSE NO. 28 GERMAN SILVER WIRE ADJUSTABLE GAP 3 /g r O O ^^ - N rOOOOOOO ^-OOOOOOCh LOOOOOOO roooooool 60 GAPS IN 0000000 HDOOOOOCh SERIES ooooooo rOOOOOOOJ XD O O O O O O boooooO] ^___ LOOOOOOOO ^^ oooooooi z -=^1__^ oooooooo J5 ^^ OOOOOOOO^ GAPS \N BE ^~~~^.^ oooooooo SERIES I ^^ oooooooA O 8 ^~~- -^ oooooooo ^^ oooooooo 1 DIAGRAM OF ARRESTER CONNECTIONS Fig. 77- 152 LONG-DISTANCE ELECTRIC POWER TRANSMISSION the 60 gaps, and through the resistance to ground. The illustration (Fig. 76) shows the frame on which the three sets of arresters for the three high-tension lines are mounted. The containing panels are made of marble and are placed on three sides of the frame. The frame is placed on rollers, so that in the event a set of arresters becomes defective, the frame can be trundled away and another set mounted in its place. Line connection is made through the fuses hooking into flexible spring con- tacts at their upper ends. The object of the springs is to permit of changing the position of the arrester slightly should this become necessary. Ground Detectors. A reliable ground detector is an essential part of the protective apparatus of an alternating- current plant. As the name indicates, it is a device for indicating an earthed or grounded condition of a line. In its usual form the device consists of four fixed vanes arranged around a movable vane made of aluminum and contained in a suitable case. The movable vane is supported on jew- eled bearings and is attached to a pointer. The stationary vanes are connected in pairs, each pair by one of the line conductors through the medium of a condenser. The fixed vanes act inductively upon the mov- able vanes, and the stresses exerted by the two pairs is equal but opposite under normal conditions. Hence the movable vane assumes a position midway between the fixed vanes, and remains thus whether the device is charged or not, and the pointer remains at zero, denoting freedom from ground. When a ground occurs, the primary strip of a condenser and the movable vane become electrically connected, thus causing the pair of fixed vanes which lead to that condenser GENERATORS, SWITCHES, PROTECTIVE DEVICES 153 Fig. 78. General Electric Ground Detector to become of like polarity with the movable vane, repelling it and causing the other fixed vane to be attracted by it. The action of the two forces in the same direction tends to make the movable vane assume a position completely within the vanes charged oppositely to it ; hence the pointer deflects in a direction which indicates a ground on that side of the circuit. In the best practice, the condensers for charging the fixed vanes are inde- pendent of the instrument, which obvi- ates all danger of damage to the device by high potentials and also allows it to be installed wherever it is convenient. Fig. 78 shows a static ground detector for high-potential circuits. Fig. 79 shows the connections of a ground detector to a three-phase three-wire circuit. Synchronizing Devices. When generators are operated in parallel some device is ne- cessary to indicate whether or not the machines are in step or synchronism. The ideal synchronizing device should indicate whether the machine being synchronized is running too fast or too slow ; it should indicate the amount of differ : ence in frequency, and should also indicate the condition of synchronism with exactness. The use of lamps to indi- cate synchronism is a very unsatisfactory method because GROUND Fig- 79' Connection of Ground De- tector to Three-Phase Circuit 154 LONG-DISTANCE ELECTRIC POWER TRANSMISSION X (L tf x Fig. 80. Relative Positions of Coils of the Synchroscope they do not perform the first function. They discharge the second function splendidly and the third function approximately. In the best modern central-station practice the only synchronizing devices employed are the Lincoln Synchroscope and the Synchronism Indicator. The principle upon which the operation of these two synchronizing devices depends is the relative change in posi- tion assumed by a movable coil suspended in the axis of a station- ary coil when the phase-relations of the currents in the two coils differ. Thus for instance beginning with a phase difference between a mova- ble coil A and a fixed coil F of zero, a phase difference of 90 degrees will be followed by a corresponding mechanical change in the movable system of 90 degrees, and each suc- cessive change of 90 de- grees in phase will be fol- lowed by a corresponding mechanical change of 90 degrees. The movable system comprises a second coil B (Fig. 80) which is securely fastened to coil A, with its phase 90 degrees from that of coil A, and the axis of A passing through ,. r r> -ri Fig- 81. The Synchroscope. a diameter of B. There- fore, when a current passes through B the difference in phase relation to that in A will always be 90 degrees. GENERATORS, SWITCHES, PROTECTIVE DEVICES 155 Under such conditions it is obvious that with a difference of phase between A and F of 90 degrees, the movable sys- tem will assume such a position as will bring B parallel to F since the force between A and Fis zero, and the force between B and .Fis a maximum : likewise, when the phase between B and F is 90 degrees, A will be parallel to F. For intermediate phase relations it can be shown that under certain conditions the position of equilibrium assumed by the movable system will exactly represent the phase relations. In the Lincoln Synchroscope (Fig. 81), the coil F con- Fig. 82. The Synchronism Indicator sists of a small laminated iron field provided with a winding whose terminals are connected with the lower binding posts. The coils A and B are windings practically 90 degrees apart on a laminated iron armature pivoted between the poles of the above field. These two windings are joined and a tap from the junction is brought out through a slip ring to one of the upper binding posts. The two remain- ing ends are brought out through two more slip rings, one of which is connected to the remaining top binding post, 156 LONG-DISTANCE ELECTRIC POWER TRANSMISSION through a non-inductive resistance, and the other to the same binding post through an inductive resistance. A light aluminum hand attached to the armature shaft marks the position assumed by the armature, the pointer moving around a dial like the hands of a clock. If the speed of the incoming machine is too fast the pointer rotates in the CONNECTIONS WITH GROUNDED SECONDARIES ON POTENTIAL TRANSFORMERS ftes/stance-ffeactance Box To corresponding phases of machines or buses being synchronized Fig. 83. Circuit Connections of Synchronism Indicator direction marked Fast, and if too slow, in the opposite direction marked Slow. The non-inductive resistance, which consists of an incan- descent lamp, and the inductive resistance, or choke coil, are mounted within the case, thus making the instrument self-contained, no external resistance being necessary. GENERATORS, SWITCHES, PROTECTIVE DEVICES 157 The current taken by this instrument is approximately one-half an ampere from each circuit. The Synchronism Indicator (Fig. 82) is similar in con- struction to a small motor ; the field winding being ener- gized from the synchronizing bus-bars excited by the machine that is being operated. The armature is drum-wound and consists of two coils securely fastened at right angles to each other and connected in series. Fig. 83 shows the connections of the Synchronism Indi- cator in a circuit with grounded secondaries on potential transformers. A and B are binding posts through which the field connections are made. The binding post E is the connection of the armature coils through a collector ring. The other two terminals are conducted to two additional collector rings, one of which is connected to the binding post D, thence through reactance to binding post F; the other terminal is connected to binding post C through a resistance to the same binding post F. The synchronizing . bus-bars excited by the machine to be synchronized are then connected to the binding posts E and F. The resist- ance and reactance are placed behind the board, the latter being contained in a metal case, to the outside of which is secured a socket containing an incandescent lamp which serves as a resistance. Synchronism is indicated when the lamps are dark. BIBLIOGRAPHY Alternating Current Machines. Sheldon and Mason. D. Van Nos- trand Co., New York, 1903. Standard Polyphase Apparatus and Systems. Oudin. 2d Edition. Van Nostrand Co., New York, 1903. Speed Regulation of Prime Movers and Parallel Operation of Alter- nators. Steinmetz. Trans. Amer. Inst. Elect. Engrs., Vol. 18, p. 741. LONG-DISTANCE ELECTRIC POWER TRANSMISSION The Experimental Basis for the Theory of the Regulation of Alter- nators. Behrend. Trans. Amer. Inst. Elect. Engrs., Vol. 20, p. 739. A Contribution to the Theory of the Regulation of Alternators. Hobart and Punga. Trans. Amer. Inst. Elect. Engrs., Vol. 21, p. 183. The Determination of Alternator Characteristics. Herdt. Trans. Amer. Inst. Elect. Engrs., Vol. 19, p. 1092. Compounding of Self-Excited Alternating Current Generators for Variation in Load and Power Factor. Garfield. Trans. Amer. Inst. Elect. Engrs., Vol. 20, p. 811. Parallel Operation of Alternators. Lincoln. Jour. Franklin Inst., April, 1902. Management of Alternators. Hanchett, Central Station, August, 1903. Mechanical Construction of Revolving Field Generators. Rushmore. Trans. Amer. Inst. Elect. Engrs., Vol. 21, p. 145. An Improved Method of Testing Large Alternators Under Full Load Conditions. Behrend. Elect. World and Engineer, New York, Oct. 31, I93P- 7i5- The Use of Group Switches in Large Power Plants. Stillwell. Trans. Amer. Inst. Elect. Engrs., Vol. 21, p. 9. Oil-Switches for High Pressures. Hewlett. Trans. Amer. Inst . Elect. Engrs., Vol. 21, p. u. The Control of High-Potential Systems. Rice. Trans. Amer. Inst. Elect. Engrs., Vol. 18, p. 407. Synchronism and Frequency Indicators. Lincoln. Trans. Amer. Inst . Elect. Engrs., Vol. 18, p. 255. Notes on Synchronizing. Roman. Elect. World and Engineer, New York, June 14, 1902, p. 1044. CHAPTER V LAWS GOVERNING ELECTRICAL TRANSMISSION OF ENERGY Power in an Alternating-Current Circuit Power Factor. In a direct-current circuit the power in the circuit equals the product of the E.M.F. in volts and current strength in amperes. In an alternating-current circuit the instantaneous power equals the product of the instantaneous values of current strength and voltage. When current and voltage are not in phase, which is the usual condition in alternating-current circuits, there are moments when the pressure has a positive sign and the current a negative sign, and vice versa. The instantaneous power at such moments is of negative value, or power is be- ing sent back into the generator by the diminishing mag- netic field which had previously been set up by the cur- rent. Hence the circuit is receiving power from the generator and returning it in pulsations, the frequency of which is double that of the generator frequency. Therefore the power in an alternating-current circuit is not the product of voltage and current but depends on the angle of current lag (j>. Denoting instantaneous values by ('): When the current lags by the angle E f = E m sin a and for convenience a = 2 IT ft 159 160 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Then /' = 7 m sin (a - <) and since E = -^ vr vi the instantaneous power P f = E' 2' = 2EI sm a sin (a ). But sin (a <) = sin a cos < cos a sin <, thus P' = 2^7 (sin 2 a cos sin a cos a sin ). Since < is a constant the average power through 180 is 2^7 cos C n 2EI sin 7^ = Sin z a a a TT Jo T 2^*7 COS . Sin a COS ado. ["I 71 " 2,5'7sin f "I 77 J a I sm 2 d; ^ sm" a Jo TT J which gives P = ^"7 cos = power or energy in an alternat- ing-current circuit. When the current leads the voltage by < the sign of the power equation given above becomes -h, thus P' = 2 fsin a sin (a + ), which equals the expression P = El cos <. The quantity cos < depends upon the angle of lag or lead of the current, and is termed the power factor of the cir- cuit. The power factor is the ratio of the true watts to the apparent watts or volt-amperes. When the current and E.M.F. are 'in exact phase, there is no angle of lag, of course, and is zero ; the power factor of the circuit is then unity. LAWS GOVERNING TRANSMISSION OF ENERGY l6l Frequency. The E.M.F. wave of an alternator goes through a series of positive values during the interval when a given coil on its armature passes from a south to a north pole of the field magnet, and through a series of negative values during the interval when the coil passes from a north to a south pole, or vice versa, according to the coil connec- tions. When the E.M.F. (or current) passes from zero to maximum in one direction, falls back to zero, rises to maxi- mum in the other direction, and returns to zero again, it has passed through a complete " cycle," or two "alterna- tions." A cycle is usually designated by the tilde (^). The number of cycles which an alternating current passes through in unit time i.e., one second is termed its frequency, and is usually denoted by the letter/. The term "alternations" is sometimes employed, and means the number of alternations per minute, unless stated to the contrary. Frequencies in use for power transmission are generally low, ranging from 25 to 60 ~ ; the lower value being con- sidered preferable when converters are used on the circuit. The higher the frequency of transmission the smaller be^ comes the weight and cost of transformers and the greater their efficiencies. Electrical Factors of Power Transmission. In the transmission of electrical energy over long distances, the following factors enter into the design of the system and, in the various ways peculiar to each, modify the character of the energy from that which it possessed at the transmit- ting end, or interfere with the regulation of the line : (i) inductance; (2) capacity or condensance ; (3) resist- ance ; (4) resonance, which results from a certain com- bination of inductance and capacity. 162 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Inductance. Around every conductor carrying a cur- rent of electricity there is set up a magnetic field of force. This field of force is assumed to commence its growth at the axis of the wire at the instant when current begins to flow, and in its inception it is assumed every line of force composing it has been cut once by the conductor. As the current in the conductor grows, this ring-shaped field of force grows proportionally. Conversely, when the current decreases, the field of force decreases or collapses correspondingly, but the diameter of the field may reach zero value without absolute cessation of the current. With a definite strength of current a conductor is en- circled by lines of varying diameter. If the current is decreased, the lines of smaller diameter immediately col- lapse on the conductor, cut it, and disappear to a point on the axis of the conductor an instant before it is cut by those of larger diameter. It is obvious that the number of lines of force, or, what is equivalent, the strength of the field of force, is greater for larger than for smaller currents. The cutting of the conductor by these lines of force sets up an E.M.F. in the opposite direction to that of the E.M.F. causing the current flow ; this is termed self-induction, and the E.M.F. of self-induction is always a counter E.M.F. Self-induction or inductance tends to prevent the start- ing, stopping, or change in strength of an electric current. On starting up a current, the pressure of self-induction retards its flow and so prevents it from attaining an in- stantaneous maximum value. On stopping a current, the E.M.F. of self-induction retards its diminution and tends to keep up the flow in its original direction, LAWS GOVERNING TRANSMISSION OF ENERGY 163 The coefficient of self-induction is that number by which the time rate of change of current in a circuit must be multiplied in order to give the E.M.F. induced in that cir- cuit. Its numerical value equals the number of magnetic lines of force linked with a circuit per absolute unit of cur- rent flowing in the circuit. The definition of "leakage" is the total number of lines inclosing each portion of the circuit. The absolute unit of self-induction being too small for most determinations, a practical unit called the henry is used, the value of which is io 9 times the absolute unit. A circuit has an inductance of one henry induced in it when a uniform rate of change of current of one ampere per second produces a counter E.M.F. of one volt. The physical effect of inductance in an alternating-cur- rent circuit is not only to oppdse the current flow, but also to make the current lag behind the E.M.F., producing it, in the successive rising and falling between zero and maximum. The inductance of a circuit may be made up of two components : self and mutual inductance. The former occurs when the circuit is entirely isolated, the latter when the circuit is influenced magnetically by an adjacent circuit. Mutual inductance is due to lines of force which sur- round one conductor cutting a second conductor in the neighborhood of it and thus setting up an E.M.F. in the second conductor. Such an E.M.F. may either oppose or assist the current already flowing, accord- ing to the relative directions of the currents in the two circuits. 164 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Inductance is represented by the letter L. Mutual inductance is represented by the letter M. Inductance may be expressed in three ways, thus, _ ~ /10 8 where 4> t is the instantaneous value of the flux through a coil of wire, / the number of turns of wire in the coil, and / the instantaneous value of the current in amperes ; again, where e = instantaneous value of the induced E.M.F. in volts and/ /the time rate of change of current; and I a* once more, where J is the energy, in joules or watt-seconds. Mutual Inductance of Circuits. The conductors of an overhead circuit strung on the same pole line exercise a mutually inductive action upon each other, an alternating current in one tending to induce an alternating E.M.F. in the other, and the direction of the induced E.M.F. being opposite to that of the inducing current. Hence if two alternating currents flowing in parallel conductors have the same phase relation they tend to oppose each other; but if they differ in phase by 1 80, which means that they flow in exactly opposite directions at any given instant, their action will be a mutually aiding one. LAWS GOVERNING TRANSMISSION OF ENERGY 165 Assuming the angles of lag of the currents in two or more parallel conductors coming from the same leads of an alternating-current source of supply to be approximately equal, their phase relations will be the same, and they will exercise an opposing action upon each other. Such oppo- sition tends to increase the voltage drop in a manner sim- ilar to self-induction. Under practical conditions two alternating currents coming from separate generators do not continue exactly in phase except for short intervals of time, hence their mutually inductive action produces an opposing effect upon the currents at one4nstant, and an aiding effect at another instant, the character of the inductive effect changing with each change of phase relation. Inductive Reactance. Reactance is the effect of either self-induction or capacity, and is expressed/!^ ohms. In- ductive reactance is numerically equal to 2 irfL t /repre- senting the frequency of the alternating current in cycles per second. The symbol is X t . The effect of inductive reactance in a transmission circuit, or in the apparatus con- nected therein, is to increase the angle of lag and also the wattless component of the current. This component of the current is in quadrature with the energy current and does no useful work in a circuit. The effect of the wattless component is to increase the total current, and thus increase the heating of the con- ductors. In aerial wires of small resistance reactance becomes relatively very prominent. Hence it is important in some cases that conductors of moderate cross-section be adopted for transmission purposes. Since inductance is proportional to the number of mag- 166 LONG-DISTANCE ELECTRIC POWER TRANSMISSION netic lines linked with a circuit, the farther apart the cir- cuit conductors the greater will be the inductance, because the number of magnetic lines is greater. When the inter- axial distance between wires is very slight, the lines of force which encircle each wire are neutralized by those of the other wire ; therefore the effect of inductance can be reduced by placing the wires close together. With high-tension overhead wires, however, this remedy is entirely impracticable, owing to the possibility of short circuits between the conductors, and also the losses which would ensue from leakage and electrostatic induc- tion between the wires. In high-tension practice the three general methods used to reduce line inductance are : subdividing the conductors or using stranded con- ductors of the same total cross-section as the solid con- ductor which would be required : or balancing the effect of inductance with artificial capacity (condensers or con- densive apparatus introduced in the circuit at definite intervals). The simplest means of decreasing mutual inductance is to increase the inter-axial distance between the conductors. The practical limitation of this method is the necessity of carrying the circuits on the same pole, so that mutual in- ductance can only be reduced in practice either by placing the conductors equidistant from each other, so that any one wire will be affected equally by the wires of the other circuit, or else by transposition of the conductors with respect to each other at symmetrical intervals along the line. Fig. 84 shows the latter method diagrammatically as applied to a three-phase circuit. In this method, which is also used in high-tension practice, an equal length LAWS GOVERNING TRANSMISSION OF ENERGY l6/ or distance of one conductor neutralizes the action of an equal length of conductor of another circuit. Thus the inductive action of one circuit upon the other is nugatory. Capacity or Condensance. The capacity of a con- ductor is the property which it possesses of being able to receive a "charge" of electricity. The capacity of a conductor through which an alternating current is flowing is analogous to the electrostatic capacity of a Leyden jar or a condenser ; the unit of capacity is the farad, but actual capacity values are so small that they are commonly expressed in microfarads. A condenser would possess a Fig. 84. Method of Transposing a Three-Phase Circuit capacity of one farad if it were capable of taking a charge of one coulomb at a potential of one volt ; or the numeri- cal value of the capacity of a condenser in farad measure is equal to the quantity of electricity which must be de- livered to it in order to increase the difference of potential between its terminals from zero to one volt. The farad is io~ 9 times the absolute unit. The micro- farad is y-Q^iro Q~O ^ a f ara d> or IO ~~ 15 times the absolute unit of electrostatic capacity. The charging or discharging current of a condenser attains its maximum value when the rate of variation of effective pressure is maximum, or when the E.M.F. is of zero value at the instant of passing from negative to positive value, or vice versa. Hence the physical effect 168 LONG-DISTANCE ELECTRIC POWER TRANSMISSION of capacity is exactly opposite to that of inductance and may entirely neutralize it. Under certain conditions the effect of capacity may cause the current to lead the E.M.F. in phase. In long-distance transmission lines the capacity of the circuits is often of very great magnitude, and may require a large reserve in the kilowatt capacity of the gen- erators to charge the line before working current can be gotten through. Capacity in an alternating-current circuit produces an effect measured in ohms and termed " capacity reactance." Thus in a circuit having capacity, the flow of current in- creases in direct proportion with it and the frequency ; hence the reactance due to capacity is inversely propor- tional to these quantities. Capacity reactance has the nu- merical value expressed by the equation "C f/~i ' 2 TT/C C representing the capacity in parts of a farad. The ef- fect of capacity in transmission lines can be overcome in two different ways : (i) by increasing the distance between the conductors and their distance from the earth ; the de- crease in capacity by doubling the distance between con- ductors may amount to as much as 15 per cent; (2) by the use of inductive apparatus in circuit. Artificial regu- lating impedance coils may be used to accomplish this result. The effect of line capacity-current varies only with the voltage and frequency. As the load decreases its influence decreases, for when the load is light, it is not only entirely neutralized by inductance, but also becomes negligible on LAWS GOVERNING TRANSMISSION OF ENERGY 169 account of the presence of a considerable current in phase with the E.M.F. At periods when both capacity and inductive loads of a line are reduced, the line capacity-current causes the most disturbance to regulation, and on such occasions attempts to neutralize the capacity effect with inductive apparatus which is thrown off at the same time acts only to augment the disturbance. Resistance. An alternating-current circuit possesses resistance just as does a direct -current circuit. The resist- ance of an alternating-current circuit, though usually insig- nificant in comparison with the other characteristics, is not always negligible. If the cross-section of a conductor through which an al- ternating current is flowing be divided into numerous par- allel components or filaments, it is apparent that those components nearer the center suffer greater inductive effects than the components nearer the interior. Hence the streams of current near the surface meet with less opposition and attain their maximum value sooner than those in the central portions of the conductor. In case the conductor is of large area and is carrying large currents of high frequency, a condition may be attained in which the central section of a conductor may not only have no current flowing through it, but under certain circumstances the flow of current may be in the opposite direction. The reduction of the effective cross-section of a conduc- tor due to this phenomenon causes an increase of effective resistance, so that a current of slightly smaller value will flow than would be the case if only the true resistance and inductance of the conductor be considered. LONG-DISTANCE ELECTRIC POWER TRANSMISSION This apparent increase in resistance is termed the " skin- effect." For all practical purposes it is the same as true resistance, and is expressed in ohms. In most practical cases it is negligible. Impedance. The resistance and reactance of an alter- nating-current circuit combined constitute its impedance. Impedance is the total opposition to the flow of current in a conductor and is expressed in ohms, so that with a defi- nite impressed E.M.F. the impedance fixes the maximum current that can flow. The numerical value of impedance is expressed by the equation, z = Resultant Impedance of Several Impedances in Series. When a circuit includes two or more pieces of apparatus in series, each of which may or may not have resistance, in- ductance, and capacity, the current which flows under any impressed E.M.F. has the same phase throughout. The E.M.F.'s at the terminals of the different pieces of appa- ratus may be of different phases, depending upon the in- ductance and capacity of each, and the magnitude of each E.M.F. will depend on the impedance of the device. The determination of the E.M.F. necessary to force a definite current through a series circuit of the kind men- tioned is analytically expressed by the equation, and since E = f Z, the total impedance of the several impedances in series is, LAWS GOVERNING TRANSMISSION OF ENERGY I/I from which it is obvious that the total impedance is not the arithmetical sum of the individual impedances. When a circuit has impedances in series and in parallel, or a series-parallel combination, the' equivalent impedance is determined by calculating the joint impedances of each parallel group and combining them in series. Admittance, Susceptance, and Conductance. The ad- mittance of a circuit is the reciprocal of the impedance, in formula shape, The equivalent admittance of several admittances in parallel is equal to V(S Inductances) 2 + (2 Susceptances) 2 The susceptance of a circuit is the quantity by which E must be multiplied in order to give the component of / perpendicular to E. Its numerical value equals in which $ is the "angle of lag," sin is the "induc- tance factor " of the circuit. The susceptance may also be numerically expressed by b = X 2 ' X being the equivalent reactance, or the difference be- tween the inductive and capacity reactances. The conductance of a circuit is a quantity by which E 1/2 LONG-DISTANCE ELECTRIC POWER TRANSMISSION must be multiplied in order to give the power component of the current, or the component in phase with the im- pressed E.M.F. The symbol is G, and the numerical value is given by the equations and Lr = + X 2 From the latter expression it is evident that conduc- tance is not the reciprocal of resistance, although the two properties are opposite in character. Resonance. Resonance in an alternating-current cir- cuit is that condition which enables a definite E.M.F. to produce maximum current flow at a critical frequency. Resonance takes place when the total inductive reactance equals the total capacity reactance ; or, stated differently, when then the two reactances entirely neutralize each other; the electrostatic energy in the condensive part being given back to the line when the electromagnetic energy of induc- tance is being stored in the line. When this occurs the circuit is said to be " tuned " for the definite periodicity shown by the equation i " / * 2 7T Hence at that particular periodicity the impedance equals the resistance, and a given E.M.F. will send through the circuit the maximum current possible. LAWS GOVERNING TRANSMISSION OF ENERGY 173 Injury to the circuit from electrical resonance may occur when the inductance and capacity are in parallel, or are balanced, thus causing currents of enormous values to flow between the two, because each is always prepared to receive the energy discharged by the other, with the result that a see-sawing or surging action is set up between the two, and this constantly increases, due to the receipt of energy from the line. This surging or resonance effect is liable to overload the conductors between the capacity and induc- tance, and may sometimes destroy them by the heating produced. If the inductance and capacity be in series, the effect of resonance may raise the potential to such a value as to break down the insulation of the generator or of apparatus along the line. In most long-distance lines the inductances and capaci- ties are connected in parallel, and a resonant or distortion- less condition seldom occurs. Mr. Paul M. Lincoln has expressed the opinion (Trans. A. I. E. E., Vol. 20) that " Considerations of voltage regu- lation at the receiving end of a line limits the voltage drop due to resistance in that line to about 15 per cent as a maximum, and the same consideration should keep the inductance volts within a maximum of 20 per cent. With a power factor of 85 per cent this means a line regulation of 24 per cent." He also states that "since the charging current depends directly upon the frequency and the press- ure, the apparent energy at 60 cycles, which is represented in charging a two-hundred-mile three-phase line, is almost equal to the maximum capacity of that line limited by the 20 per cent inductance volts consideration. At 25 cycles the effect of charging current is not appreciable." LONG-DISTANCE ELECTRIC POWER TRANSMISSION ELECTRICAL CONSTANTS OF CERTAIN TRANSMISSION LINES. STANDARD ELECTRIC Co. OF CALIFORNIA. Data : Length of line approximately ...................... 150 miles Aluminum conductors of .................... 75 in diameter Area of conductors ............................ 471,034 C.M. Maximum resistance per mile at 70 ................ " >2O5 ohms Frequency ......................................... 6o^w Voltage of transmission ............................. 60,000 Distance between centres of conductors ................... 42' Inductance of 150 mile line, or 300 mile transmission ......... 0.48 henry Inductive reactance per mile of conductor, or \ mile of transmission at 6o^/ ......................................... ... .634 ohms (If 30-^ were used the inductive reactance would be nearly halved, or ........................................... -3775 ohms) Impedance factor of line (impedance -r- resistance) at 6o^w ..... 3.25 ohms (If 30^ were used the impedance factor would be ........... 1.84 ohms) Resistance of 300 miles of conductor (2 wires of 150 mile transmission) ................................................. 61 .5 ohms Inductive reactance of 300 miles of line at 6o- (2 wires of 150 mile transmission) ...................................... 190.2 ohms (If 30^ were used the inductance reactance of the line would be ............... .................................. 95. i ohms) Impedance of 300 miles of wire at 6o--' ..................... 200 ohms (If 30^ were used the impedance would be ................ 1 13.2 ohms) Capacity of the 1 50 mile transmission or 300 miles wire (considered as two parallel cylinders) .................................... i .43 m.f . Capacity per mile of transmission line ..................... 0.0095 m.f. Capacity reactance between 2 wires, per mile of transmission at 60^ ............................................... 279,000 ohms (If 30^ were used, the capacity reactance between 2 wires per mile of transmission would be ........................... 558,000 ohms) Capacity reactance between two wires of 1 50 mile transmission at 60 ^ ................................................ 1,855 ohms (If 3O>-w were used the capacity reactance between two wires of 150 mile transmission would be ............................... 37 2 ohms) Capacity or charging current between two wires of 1 50 mile transmission at 6o^< and 60,000 volts ......................... 3 2 - 2 5 amperes If 30^ were used, the charging current (at the same voltage) between two wires of 150 mile transmission would be ............. 16,125 am P e res LAWS GOVERNING TRANSMISSION OF ENERGY 175 Apparent power required to charge the line at 6o~w and 60,000 volts 3>348 kilowatts Real energy to charge line at 6o^w and 60,000 volts 32 kilowatts Apparent energy to charge line if 30^' cycles and 60,000 volts were used 1,674 kilowatts Real energy to charge line at 3**^ and 60,000 volts 16 kilowatts 10,000 kw. at 60,000 volts and unity power factor requires 96.3 amperes per wire. The loss in 150 mile transmission is 855.5 kilowatts Per cent loss in transmission 8.55 Volts loss, per pair of wires in 150 mile transmission at 60^* . . 19,260 volts Per cent volts loss, per pair of wires in 150 mile transmission at 6o-^ 32.1 per cent Volts loss, per pair of wires, in 150 mile transmission at 30^ . . 10,901 volts Per cent volts loss, per pair of wires, in 150 mile transmission at 30^ 18.2 The capacity effect on a 150 mile transmission line was demonstrated by considering a single-phase transmission of 3,000 kilowatts at the distributing end, the pressure 50,000 volts being kept constant at the sub-station. The fairly correct supposition was used by considering the line as shunted at the generator and at the sub-station by two condensers each of one sixth the capacity of the line, and in the middle by a condenser of two thirds the line capacity. With the line open at the sub-station, the generator pressure is only 47,676 volts, the line capacity causing the rise at the sub-station to 50,000 volts. With 3,000 kilowatts at unity power factor at the receiv- ing end, the current required is 60 amperes at 50,000 volts. The 32.25 amperes charging current when combined at right angles with the 60 amperes power current, requires 69.2 amperes at the generator, the resulting generator pressure being 58,800 volts. With 3,000 kilowatts at a power factor of 80 per cent at the receiving end, the cur- 1/6 LONG-DISTANCE ELECTRIC POWER TRANSMISSION rent required is 75 amperes at 50,000 volts, or 60 amperes power current and 45 amperes inductive current. The 32.25 amperes of charging current, when combined with the 60 amperes power current and 45 amperes inductive current, requires but 62.1 amperes at the generator, the resulting generator pressure being 60,000 volts. 1 The following quantities are a few of the constants of the Bay Counties Power Company's line Capacity of 150 mile circuit = 3 microfarads. Under a working potential of 40,000 volts there are : i X (3 X io- 6 ) (40,000 X V2) 2 = 4,800 watt-seconds = 4,800 joules, or 3, 500 foot-pounds of energy in electrostatic capacity stored in the circuit when it is fully charged. Charging current at 40,000 volts and 6o~~ = 45 am- peres. The rate of supply of energy to the circuit by the gen- erators and absorption from the circuit by the generators is 45 X 40,000 X 2 . = 1,150,000 watts = 1,150,000 joules per second =843,000 foot-pounds per second. The generator gives out current continuously to the line for one fourth cycle. Hence the received or delivered energy during a half alternation is equivalent to the energy stored in line capacity, 3,500 foot-pounds as. above. To charge the line as a condenser requires the capacity of a 2,000 kilowatt generator. 1 The above data are taken from Professor C. L. Cory's paper on Trans- mission System Regulation, read before the Pacific Coast Transmission Association, June, 1900. LAWS GOVERNING TRANSMISSION OF ENERGY 177 BIBLIOGRAPHY The Theory and Calculation of Alternating Current Phenomena. Steinmetz. McGraw Publishing Company. N*ew York. 1902. Alternating Currents. Franklin & Williamson. Second Edition. Macmillan Co. New York. 1901. Alternating-Current Machines. Sheldon & Mason. Third Edition. D. Van Nostrand Co. New York. 1903. Choice of Frequency for Very Long Lines. Lincoln. Transactions American Institute Electrical Engineers, Vol. 20, p. 1231. Alternating Currents. Hay, D. Van Nostrand Company. New York. 1906. CHAPTER VI THE TRANSMISSION LINE Kinds of Conductors. In electrical transmission plants the line represents a greater financial expenditure than any other part of the electric property. Upon its proper de- sign and installation depend not only the economical and efficient transmission of the developed power, but also the satisfactory operation and regulation of all the apparatus in circuit ; which also means the satisfactory working of the line under different conditions of load. While refinements of design and construction are largely governed by the conditions to be met in each particular case, it is never advisable in the development of electric transmission properties to perfect the generating equipment at the expense of the transmission equipment. The bad regulation and the energy losses which ensue from faulty line construction greatly overbalance the efficiency which is gained by undue attention to the generating end of the problem The design and construction of transmission lines are governed by several factors : ( i ) the amount of energy to be transmitted ; (2) the working potential to be employed; (3) the length of the line; (4) the climatic conditions of the country which it traverses ; and (5) the permissible losses in line drop and leakage. The choice of conductors is confined to two metals, namely, copper and aluminum. Copper, by reason of its high conductivity, mechanical strength, ductility, and free- 178 THE TRANSMISSION LINE 1/9 dom from corrosion is more extensively employed in high- tension practice at the present time than aluminum. It is, however, being largely displaced by aluminum, on account of the superior advantages which the latter metal offers in lightness, and the consequent reduction in the weight to be carried by insulators, pins, and cross-arms. In tensile strength, hard-drawn copper ranges from 60,000 to 70,000 pounds per square inch, while soft-drawn copper has a tensile strength of from 25,000 to 35,000 pounds per square inch. The specific resistance of hard- drawn copper, on the other hand, is from 2 to 4 per cent greater than that of the soft-drawn metal. Hard-drawn copper is also very brittle and inflexible and hence in large sizes is very difficult to handle. The tensile strength of aluminum ranges from 20,000 to 3 3,000 pounds per square inch, and its specific conductivity is only 63% of that of copper of the same purity (com- mercial quality). Hence in wires of equal sizes and lengths aluminum must have a sectional area 1.66 times that of copper to have an equal electrical resistance and transmit a given amount of energy with equal loss. Or, since the cross-sectional areas of round wires vary as the squares of their diameters, the diameter of an aluminum wire must be 1.28 times greater than that of a copper wire of the same length to possess equal conductivity. On the other hand, the specific gravity of copper is 8.89, while that of aluminum is but 2.7, so that a given wire of copper weighs 3.3 times as much as an aluminum wire of equal volume. Hence a copper conductor of the same length and resistance as an aluminum one is approximately twice as heavy. It is quite evident that reduction by one half of the weight on poles, insulators, cross-arms, etc., 180 LONG-DISTANCE ELECTRIC POWER TRANSMISSION becomes of very great advantage in long lines, and espe- cially when the transmission line is projected over rough sections of country. It is also found that the vibration of transmission lines in heavy winds, which tends to make cross-arms, pins, and the fastenings of conductors work loose, is somewhat less with aluminum than with copper conductors, as ordinarily strung, on account of the smaller weight of aluminum, and the greater sag between poles which are given aluminum lines. Since a pound of aluminum made into a conductor of any length has a sectional area 3.33 times greater than an equal weight and length of copper, and for equal resistance has one half its weight, it is obvious that when aluminum can be bought at a lower price per pound than twice the cost of copper, the former metal is the cheaper for trans- mission purposes. As compared with copper, the electrostatic capacity of aluminum is from 5 to 8 per cent greater, depending upon the amount of energy transmitted and the length of the line. (For equivalent conductors, capacity is a logarithmic function of diameter divided by distance apart.) Aluminum, however, possesses several disadvantages which make it ad- visable to observe considerable precaution in the use of it in regions where adverse climatic conditions prevail. Owing to its larger cross-sectional area, as compared with copper, it offers a larger resisting surface to wind storms, which if not actually destructive may permanently elongate it, and so give rise to dangerous sags in the line. Its greater diameter also affords a larger surface for the ac- cumulation of ice, which on account of the low ductility of the metal may cause a breakdown in the line. The very high coefficient of expansion of aluminum with change of THE TRANSMISSION LINE l8l temperature is also a very objectionable feature in regions subject to erratic or wide fluctuations in temperature, and renders line-stringing exceedingly difficult. Aluminum is also greatly subject to electrolytic cor- rosion, and is readily attacked by the fumes from chemical works, especially when they contain sodium. It is a highly electro-positive metal, and when exposed to the atmosphere in contact with any other metal, an insidious electrolytic action ensues in which the electrolyte is the moisture of the air contaminated with chemical impurities. This property of the metal has rendered the proper con- struction of joints in an aluminum transmission line a matter of extraordinary difficulty. Most of the breakdowns and consequent dissatisfaction with aluminum as a conductor are due to a disregard of the electrical character of the metal. If it becomes ab- solutely necessary to solder the joints of an aluminum line, or to use a joint composed of aluminum and another metal, the joint must be waterproofed so thoroughly that not a particle of moisture can come in contact with the metals composing it. The usual joint employed and one which obviates all difficulties from corrosion, consists of an oval aluminum tube (similar to the Mclntire joint), about ten inches in length, which is twisted some three or more times around itself after the ends of the conductors to be united have been introduced. An objectionable feature of aluminum when used in small sizes is the low fusing point of the metal. It melts at 1157 F., while copper melts at 1929 F., and wrought iron at 2800 F. Hence if an iron or copper wire falls across an aluminum line, the latter might readily be melted in two by the current flow through the cross, while the 182 LONG-DISTANCE ELECTRIC POWER TRANSMISSION wire causing the trouble would not be affected. True, this is an easy method of eliminating the trouble, but at the serious expense of interrupting the service. As regards energy losses, there is but little difference between the two metals, the advantage being in favor of copper. As regards cost, the advantage is greatly in favor of aluminum. In fact, one of the main reasons for its use, outside of the physical properties enumerated, is the com- parative cheapness of the metal. Aluminum is used as an aerial conductor only in the stranded or cable form, and only in the bare form. The solid wire shows considerable lack of uniformity of strength, even in the same sample, and breakdowns in lines con- structed of solid metal are not infrequent. When copper is used as the conducting medium for high pressures, it is always in the form of bare, medium hard- drawn, solid, round metal. The experience in American high-tension practice is that copper wires smaller than No. 5 B. & S. gauge should not be used on long-distance lines. Relative Weights of Metal Required for Single- Phase Two-Phase, and Three-Phase Circuits. In long-distance power transmission, a problem of highest importance is the determination of the system which will give the greatest efficiency of transmission with the best economy of ma- terial, and which at the same time will be thoroughly reliable in its operation. Application is made of the general law of copper-conducting circuits, that the weight of copper is inversely proportional to the square of the voltage, other things being equal. The accompanying diagram (Fig. 85), taken from Dr. C. P. Steinmetz's classic " Alternating Current Phenom- ena," shows the relative weights of copper needed for THE TRANSMISSION LINE 183 the various systems. The standard chos.en for comparison is the single-phase two-wire system, for which the percent- age of copper required is 100. Considering first the single-phase three-wire system : If the voltage of the two-wire system is e, the pressure be- WIRING CONNECTIONS PERCENT. DIAGrTMIH Single Phase ', 2 Wire PER CENT. COPPER 100. I Single Phase I 3 Wire <~ Two Phase 4 Wire Two Phase 3 Wire Three Phase 3 Wire Three Phase ihtJ^- 4 Wire ^ I 1 - 1 " 31.6 100. J14B.T 1 72.9 83.8 Fig. 85 4- A A tween the two outside conductors is 2e. But since the amount of copper is inversely proportional to the square of the voltage, the weight of copper is but one quarter when the neutral conductor has no cross-section, or when the system is balanced, thus dispensing with a neutral return conductor. 184 LONG-DISTANCE ELECTRIC POWER TRANSMISSION When the cross-section of the neutral conductor is equal to that of an outside conductor, the maximum amount of copper required for a single-phase three-wire system is 37.5 per cent of that required by a two-wire single-phase system, When the neutral wire has one half the cross-section of each outside conductor, the maximum amount of copper re- quired is 31.25% of that of the standard system. When the neutral has one third the cross-section of the outside wire, the amount of copper needed is 29. 1 5 per cent of the standard system. For a two-phase four-wire system, which is the equiva- lent of two single-phase systems, the amount of copper required is the same as that needed by two single-phase two-wire- lines. When a two-phase three-wire system is used the deter- mination of the necessary copper is more complicated. When a conductor of full cross-section is substituted for two of the leads of the four-wire system, the pressure between the two outside conductors is increased to *^2~e = 1.41 e, e being the voltage bet ween the conductors of either phase. Hence the amount of copper necessary will differ according to whether the basis of comparison is the maximum permissible potential for a given distribution or the minimum potential for low-pressure work. W 7 hen insulation stresses or other causes limit the high- est permissible pressure to e, thus reducing the voltage between the other leads of a two-phase three-wire system e to r-> the amount of copper needed is 145.7 of tnat f the standard system. When limitations of working po- tential do not hold, the basis of comparison is the effective pressure of either phase, or a minimum pressure consider- THE TRANSMISSION LINE 185 ation. The economy in copper over the single-phase system is, under such conditions, 27 per cent, or 72.9 of the copper required by the single-phase standard system. For a three-phase three-wire system the weight of copper necessary for any definite set of conditions is 75 per cent of the copper required by the standard system. With three-phase systems, the comparison of relative weights of copper is easier made if the system be resolved into a number of single-phase systems corresponding with the number of phases. A three-phase system is made up of three single wires with no return conductor, since the maximum current to and from the middle is zero. The voltage of the line is e, and the pressure between any wire and the neutral point e of the system is p- Vs For a three-phase four-wire system with a neutral of full cross-section, the weight of copper necessary is 33^ per cent of the standard single-phase system. If the cross- section of the neutral wire be made one half that of the main wires, the weight of copper necessary is 29.15 per cent of the standard system. A system of this \indis only used for distribution from transformer secondaries ; hence it is compared with other systems only on the basis of equality between phases of minimum voltage. The choice between transmission systems for long-dis- tance lines is practically confined to the two-phase three- wire and the three-phase three-wire systems. The question as to which is preferable is still a mooted one. For all-round service the three-phase three-wire system offers the advantages of simplicity in line construction, greater economy in copper and higher efficiency of trans- l86 LONG-DISTANCE ELECTRIC POWER TRANSMISSION mission. But the two-phase three-wire system gives on the whole a better line regulation and is much more reliable for loads made up entirely of motors. The majority of long-distance power transmission com- panies in the United States employ the three-phase three- wire system for transmitting the energy, and the two-phase four -wire system from step-down transformer secondaries, for distribution, with mixed loads. The accompanying tables from Steinmetz's " Alternating Current Phenomena " show the copper efficiencies of the various systems on the basis of maximum and minimum differences of pressure. Amount of copper required for transmission at a given loss, based on minimum potential. System. No. of Wires Per cent Copper Single-phase 2 100. Single-phase 3 37 5 Two-phase, common return 3 72.9 Two-phase . .... 4 100. Three-phase 3 75. Three-phase, neutral full section. 4 33 3 Three-phase, neutral one-half section 4 29.17 Amount of copper required for transmission at a given loss, based on maxi- mum difference of potential. System. No. of Wires Per cent Copper Single-phase. 2 i on Two-phase, witli common return 3 14^ 7 Two-phase 4 ion Three-phase . . 3 75 Direct Current 2 50. THE TRANSMISSION LINE l8/ Transmission Line Poles. Poles used for supporting long-distance transmission lines are of cedar, chestnut, pine, redwood, fir, or spruce. The use of a particular wood for a pole line depends upon the expenditure allowed for line construction, the factor of safety desired, and the prev- alence of a particular and readily obtained wood in the section of country through which the line passes. Cedar poles are in extensive use, owing to their great durability, but are seldom used in lengths greater than 50 to 5 5 feet, since cedar poles of greater height and having suitable dimensions are difficult to obtain, and if obtain- able their cost is prohibitive. The brittleness of the wood also precludes its use on lines which must be strung at considerable distances above the ground. On account of its cheapness and abundance pine is more widely used for line support than other wood. Although not near so durable nor stout as some of the other woods, such as cedar or redwood, its cheapness and the ease of obtaining it compensate in many cases for these disadvan- tages. Along many of the Western transmission lines which traverse mountainous regions the most abundant woods are several varieties of fir and spruce, which are extensively used in pole lines on account of their straightness and toughness and the readiness with which they can be obtained in the proper sizes. In California transmission circuits, considerable redwood is used, which is always of rectangular section, because of the great size of the redwood tree and the necessity of cut- ting it up into sections for poles. It is advisable to treat poles of soft woods such as spruce and pine with some kind of preservative before they are 188 LONG-DISTANCE ELECTRIC POWER TRANSMISSION set in the ground, but owing to the added expense this treatment is seldom given to poles for high-tension lines. Some Western transmission companies, however, apply hot tar or carbolineum to the butts of the poles or bore into the centers and give them fillings of the latter compound. While the sizes of poles used in long-distance transmis- sion lines vary considerably with the special conditions which must be met, it may be said in general that the length is never under 30 feet and the diameter at the top is never less than 7 inches. In the mountainous sections of the West, the length of pole used is seldom greater than 30 or 35 feet, with a top diameter of 8 inches ; but on level stretches the poles are five or more feet higher as a precaution against mischievous attempts to throw obstruc- tions over the line. The average length of the poles for high-tension transmission lines is about 40 feet, with a butt diameter of 10 inches and tapering to 8| inches at the top. The length of the poles should be so proportioned to the contour of the region that the line may be laid out without any abrupt changes in its level. In crossing other pole lines, such as telegraph and telephone lines, it is customary to use poles of sufficient height to carry the high-tension line at a safe distance above the other line, in order to re- duce the liability to crosses. Poles are generally set in the ground to the following depths : Height of Pole Depth of Setting 35 to 45 feet 5 to 6 feet 50 55 6 7 60 " 80 " ; 8 " The length of life of poles varies quite markedly, being dependent upon the character of the wood, the kind of soil THE TRANSMISSION LINE 189 in which it is set, and the climatic conditions of the region. The life of a cedar pole varies from fifteen to twenty years and not infrequently they last thirty years. The average length of life of a chestnut pole is twelve years, while that of a pine pole is from six to ten years. Redwood and fir poles last almost as long as cedar. Construction of Pole Lines. The construction of the pole line must be carried out with scientific accuracy in order to obtain the highest efficiency of service and freedom from line troubles. Hence in most pole-line construction the line should not only be staked out by a surveyor, but the poles should be set with plumb bobs, and the construc- tion chief should use a thermometer and a set of curves to determine the correct sag to allow the wires at different points along the route. When the section of country through which the line passes is smooth and level, and where the soil is of a character which will hold the pole rigidly in position, no especial difficulties are encountered in the erection of poles. Under such conditions the points for the holes are carefully located and the excavations made to the proper depth. The poles having been distributed at the holes, each pole is set in position by from four to ten men, depending on its dimensions ; the earth is firmly tamped around its butt and the task is finished. In case the line must traverse marshy or "made " ground, it becomes essential to put a concrete mixture around the pole, composed in some instances of one part of cement, three parts of sand, and five parts of broken stone. Where the pole must be set in rock, the butt should be hewn to fit a suitable iron shoe, which is rigidly bolted to the rock. To prevent corrosion of this shoe, it should be painted on the inside with white lead before the pole is in- 1 90 LONG-DISTANCE ELECTRIC POWER TRANSMISSION serted. The outside of the shoe should be left smooth, and hydraulic cement spread over the top surface of the rock on which the shoe is set. It is the general rule in Western practice to place two poles together whenever an angle is made in the line, so that the strain will be equally divided between the two. The absence of guy wires in pole-line construction is quite common on the Pacific coast ; wooden struts are in more general use. Those usually employed average 6 inches by 6 inches, and are attached to a "dead man" buried about 5 or 6 feet in the ground. In cases where it becomes imperative to use a guy, the strut is sometimes used as an anchor, or else a piece of timber about 6 inches by 6 inches by 20 feet long is inserted in the guy to serve as a sort of strain insulator. Transmission lines operating at high potentials are gen- erally run over a private right of way, varying with the conditions from 60 to 300 feet in width. Where the line goes through forests, the trees on each side of it must be cleared away to a distance sufficiently great to prevent trees felled by wind or lumbermen from falling across the line wires. Since the majority of high-tension lines furnish power to enterprises to which an interruption of the service would entail serious loss and inconvenience, it is generally custom- ary to install the lines in duplicate. The first practice was to install both circuits on the same pole line, but induct- ance and short-circuit troubles render it imperative to con- struct a separate and similar transmission line. Although the use of duplicate lines insures continuous service, it is found that unless the most improved form of oil switches are used in the plant that even the brief shut- THE TRANSMISSION LINE IQI downs occasioned by switching from the defective to the duplicate circuit causes some dissatisfaction. This is largely due to the fact that the opening of the line by or- dinary types of switches is rather a slow process, and is at> tended with considerable hazard, as surges of a destructive character may follow. Stresses on Pob-Lin3s. Stresses on pole lines are made up of the following components: (i) Weight of conductors and the force acting downward due to conductor tension. Since the factor of safety of a pole is usually about 90 or above this first component is negligible. (2) Bending mo- ment caused by the pull of the conductors when angles or turns are made in the line. (3) Wind stress on conductors and poles. (4) Wind stress *and the weight of ice on the line. A fairly accurate value of the bending moment may be obtained by the following formula : where J/ 6 = bending moment. C a =area of the pole at the ground. S= strength of pole per unit cross-section. I? = radius at the ground. D = distance between ground and the center of pressure. The bending moment caused by a turn or angle is the angle between the con- ductors at the turn. To find approximately the wind pressure on a line, the following formula may be used : />=o.o 5 192 LONG-DISTANCE ELECTRIC POWER TRANSMISSION in which pressure per square foot. // = average diameter of pole. ^=free length of pole above ground. S c = pressure on conductors, per se. To find the stress due to wind and ice : (ioo) 2 X weight of conductors per foot %d Cross-Arms Methods of Attaching. Cross-arms used in high-tension practice are made of cedar, chestnut, oak, red and yellow pine, and redwood. They are usually rounded or chamfered at the side-top to prevent the ac- cumulation of water in the grain of the wood. Cross-arms vary in length and cross-section with the conditions which must be met, such as the weight of the conductors, the distance apart of the conductors, the size of insulator pins and insulators, and the wind and ice stresses which they must withstand. No special rule applies for the dimensions of cross-arms for a given transmission voltage. It may be said in gen- eral that for pressures ranging from 10,000 to 20,000 volts the length of cross-arm varies from four and a half to eight feet depending upon the distance between wires. Fig. 86 shows the standard 10,000 volt cross-arm used by the California Edison Company, and Fig. 87 shows the dimensions of the cross-arm used on the 3 3,000 volt pole line of the same company from Santa Ana to Los Angeles. Cross-arms in the latest transmission lines in the West are made of carefully selected kiln-dried Oregon pine, 6 inches by 6 inches, and of lengths depending upon the distance between wires. It has now become quite general practice in the West to THE TRANSMISSION LINE 193 give cross-arms one or the other of two kinds of treatment before they are attached to the poles. In the first method, after being thoroughly kiln-dried, they are placed in an Fig. 86. Cross- Arm Used on a 10,000 Volt Line inclosed boiler filled with asphaltum oil, which is main- tained at a temperature of about 220 F. for several hours. This serves two purposes : It preserves the wood, and it fi Fig. 87.1 Cross-Arm Used on a 33,000 Volt Line increases the insulation of the cross-arm and pole top and tends to prevent the burning of the arm when an insulator IQ4 LONG-DISTANCE ELECTRIC POWER TRANSMISSION pin proves defective, or when a short circuit occurs on the line. The second mode of treatment consists in boiling the cross-arm thoroughly in linseed oil. Cross-arms are fastened to poles either by means of lag screws or by through bolts of from five eighths inch to three fourths inch diameter, fitted with cast-iron washers about 3 inches in diameter, under both head and nut. The use of through bolts is somewhat objectionable for the reason that when a cross-arm must be replaced it is fre- quently necessary to use a drift pin to drive out the rusted bolt. Cross-arms for very long pole lines being necessarily very heavy and lengthy require to be stoutly braced. For this purpose single-piece angle iron is quite commonly em- ployed. Fig. 88 shows a bracing frequently employed. The advantage of a single-piece brace lies in the fact that if one of the line conductors should slip from its insulator down on the cross-arm, and thus be burned in two at the middle, the two ends supported by the angle-iron brace may be preserved intact without interrupting the service. In order to overcome the effect of line strains and windage, cross-arms are sometimes braced on both sides of the pole. As a precaution against the splitting of cross-arms, when severe stresses are brought to bear against the pins, car- riage bolts one half inch in diameter are sometimes mounted at a distance of 3 inches from the pin, and approximately 2 inches from the top of the cross-arm. A series of tests conducted by a California transmission company showed that cross-arms could be split without these bolts by a force of 1,200 pounds, whereas with the bolts in place the pin split at the shoulder under a force of 2,200 pounds, THE TRANSMISSION LINE 195 On straight runs of considerable length, cross-arms are set to face each other alternately on adjacent poles, and are placed back to back on the next two poles. This method of construction obviates the danger of a cross-arm being wrenched off if a pole should break, or if a stretch of line is broken. Cross-arms should be doubled at all long stretches and corners, and whenever the line is dead-ended. To accom- Usual Method of Bracing Cross-Arms plish this, a spacing block is used at each end of the cross- arm, and the arm is fastened at the ends by bolts through the spacing blocks. Methods of Prcs^rvinj Wood. The principal causes of the decay of poles and cross-arms are the fermentation of the sap and the alternate wetting and drying to which they 196 LONG-DISTANCE ELECTRIC POWER TRANSMISSION are subjected ; the latter trouble makes the wood crack and split and invites early decay on account of the settling of water in the grain of the timber. Six methods are employed for the preservation of wood, viz. : Creosoting, vulcanizing, burnettizing, kyanizing, car- bolining, and smearing with pitch or tar. In creosoting poles, they are loaded on a flat car, sep- arated by laths or strips of wood ; the cars are then run into an immense cylinder fitted with air-tight iron doors ; with the doors closed, live steam at a temperature of about 250 F. is turned in the cylinder until the heat causes the albumen of the sap to coagulate. The sap is then extracted by forming a vacuum in the cylinder. When this is accomplished coal tar or some variety of dead oil is forced into the cylinder under a pressure of about 125 pounds per square inch. The quantity of oil used varies with the kind of timber and ranges from 1 2 to 24 pounds per cubic foot. Vulcanizing is carried out by subjecting the wood to a temperature of several hundred degrees Fahrenheit in closed chambers, under a pressure of 150 to 200 pounds per square inch. Usually heating for about a half day suffices. The heat so alters the character of the sap that no fermen- tation ensues. Burnettizing is accomplished by forcing a i to 3 per cent solution of chloride of zinc into the pores of the wood. But since this is easily washed out in several methods, as for instance the Thilmay process, it is aimed to prevent this by the use of two different chemical solu- tions which react to form an insoluble salt. In the Thil- may process sulphate of zinc is first injected, followed by barium chloride. The reaction which follows results in THE TRANSMISSION LINE 1 97 zinc chloride and barium sulphate, which latter compound is insoluble. Kyanizing is carried out by immersing the wood for some time in a 3 per cent solution of bichloride of mercury. -The carbolining process is effected either by soaking the timber in carbolineum oil at 200 to 300 F., or else by in- jecting the hot oil into the center of the material by boring small holes into it. This method of preservation is more generally employed in Western pole-line construction than any other. "" Smearing the butts of poles with tar or pitch is quite commonly resorted to, but it is harmful unless the wood is well seasoned. When applied to a wet or unseasoned pole, tar or pitch promotes decay, as it seals the pores of the wood and accelerates the fermentation of the sap. Steel-Supporting Structures for Transmission Lines. The peculiar troubles to which pole lines are liable, such as damage by wind storms, burning of cross-arms, necessity of constant replacing on account of decay, not excepting the need of frequent patrolling, have prompted considerable discussion relative to the advisability of using steel towers instead of poles to carry long-distance high-tension circuits. Fig. 89 shows a type of steel tower used in the seventy-five mile power transmission circuit of the Ontario Power Com- pany, from Niagara Falls to Montreal. The proposition offers many advantages as a means of decreasing the num- ber of breakdowns and the general maintenance of lines, although the initial cost of such construction is somewhat greater than with poles. It has been proposed to use steel towers about ninety feet high and about 1,000 feet apart, the wires to be sus- 198 LONG-DISTANCE ELECTRIC POWER TRANSMISSION pended from tower to tower and about nine feet distant from each other. As regards the advantages and disadvantages of steel Fig. 89. Type of Steel Tower Used in Niagara Falls Montreal Transmission structures and poles for long-distance line construction the following comparison may be made: At least fifty poles per mile are required, necessitating the use of 150 insulators per mile for a three-wire circuit. With steel towers, which can be spaced 500 feet apart or ten spans per mile, the number of insulators required is about thirty per mile. This large reduction in the number THE TRANSMISSION LINE 199 of insulators makes up for the difference in cost of instal- lation, even when poles are cheap. Most of the trouble on high-tension lines is due to break- age or failure of insulators. From the figures cited as to the Guanajuato towers (pages 200-201) it is evident that steel supporting structures reduce such maintenance nearly 80 per cent. Wood poles are liable to damage by lightning, prairie and incendiary fires, and in remote districts may be hacked to pieces by the natives for fuel. Few climates allow wood poles to remain safe at the ground line more than five years. In some semi-tropical and tropical climates eighteen months measure the life of a wood pole, thereby entailing constant expense for main- tenance. With steel-supporting structures this expense is obviated. Lightning does not damage steel towers, and with proper protective devices, the use of which is impossible on pole lines, the insulators and conductors may be pro- jected so as to reduce the lightning damage to a minimum ; this damage in mountainous regions and the tropics is one of the heaviest items in the maintenance account of a pole line. The following prices are current on steel towers (Aermotor Company) : 40 ft. towers weighing approximately 1,400 Ibs. $46.00 5 oft. " " i, 730 Ibs. 57.00 60 ft. " " " 2,000 Ibs. 68.00 70 ft. " " " 2,575 lbs - 8 4- 80 ft. " " " 2,900 lbs. 102.00 90 ft. " " " 3>5 lbs. 123.00 2OO LONG-DISTANCE ELECTRIC POWER TRANSMISSION The approximate cost per mile of constructing a high- tension circuit with a pole line and with steel towers is as follows : 53 wooden poles, 35 ft. with cross-arms and pins, at $6.00 each $318.00 Erection, $1.20 each 63.60 3 x 53 insulators at $1.50 each 238.50 $620.10 9 steel towers, 45 ft. with cross-arms and pins, at $60.00 each $540.00 Assembling and erecting at $7.00 each 63.00 3X9 insulators at $1.50 each 40.50 $643.50 In Mexico several long-distance lines have been pro- jected in which the entire circuits are to be supported on steel structures. Fig. 90 shows the type of tower used on the no mile, 60,000 volt transmission of the Guanajuato Power and Electric Company, and built by the Aermotor Company, of Chicago, 111. Fig. 91 shows the method of erecting the tower. The towers employed on this line are uniformly 40 feet in height, and for particular locations were provided with 20 foot extensions to permit the stringing of the conductors 60 feet above the earth. The weight of the tower is approximately 1,500 pounds. The towers are spaced 440 feet apart, making twelve spans per mile, and carry conductors about -f^ inch in diameter, with 17 or 18 feet sag between insulators. The side strain impressed upon the insulators, should the conductor break between supports, would be about 900 pounds if no slippage occurred at the insulator. THE TRANSMISSION LINE 201 It was found by actual test that the extra heavy pipe which extends six feet above the top of the tower (Fig. 90) and has attached to it a cast-iron in- sulator pin, stood the same press- ure, 900 pounds, without being bent beyond its elastic limit. The cross-arms, which are made of two 4 inch chan- nel irons, weigh- ing 5 1 pounds per foot, clamp to the pipe immediately above the apex of the tower, and are bolted to the two side insulator pins. The maximum side strain which can be impressed upon a tower, should three wires break on one side, is 2,700 pounds. The tower itself, properly anchored, safely stood a strain of 2,500 pounds, which gives it some excess in strength over that of the conductor connections. Fig. 90. Type of Steel Tower Used on a Mexican Long-Distance Line 202 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The tower is put together with bolts, clamps, etc., and is assembled on the site. All parts are thoroughly gal- vanized. A set of ladder steps to attach to one corner post of the tower is provided to enable linemen to ascend the structure, and also a small platform near the apex to form a support for linemen when putting on insulators. Fig. 91. Method of Erecting Steel Tower Shown in Fig. 90 The anchorage of the towers consists of steel anchor posts 6 feet in length, with a stout cross-piece on the higher towers. These anchor posts were set firmly in the ground and weighted with rough stone and rubble, thus forming a secure and solid foundation for the structure. The cost of the towers, including cross-arms and insulator pins, was $53 each. Fig. 92 shows a twin-type steel tower designed to cftrry two high-tension three-phase circuits. THE TRANSMISSION LINE 203 Kinds of Insulator Pins. Pins for carrying high-tension insulators are either wooden or metallic. Wooden pins arfe more extensively employed at the present time, but are being gradually displaced by iron pins on account of the many points of advantage which the latter possess. Wooden pins are made of chestnut, oak, eucalyptus, or locust. In California redwood pins are in quite general use, but locust and eucalyptus offer the largest number of points of superiority. Locust is the toughest and most lasting of woods, but is harder to obtain and much more expensive than some other varieties of timber. Oak pins when properly propor- tioned and carefully treated have given excellent satisfac- tion, but some experience has shown that they have a ten- dency to decay in a few years and break off at the shoulder. On the Pacific coast euca- lyptus wood is almost entirely used for insulator pins on account of its immunity against the attacks of worms and insects. These pins are given the following treatment before they are put into use : The wood is first cut into sticks about 3 inches square, which are then immersed in boiling water for about a day. Fig. 92. Twin-Type Tower for Two Three-Phase Circuits 204 LONG-DISTANCE ELECTRIC POWER TRANSMISSION After this preliminary treatment they are air dried for several months before being cut into the desired sizes for pins. Before being mounted on the cross-arm they are boiled for several hours in linseed oil, at a temperature of about 210 F. (In the best practice wooden pins are al- ways boiled in paraffine or linseed oil before being put into use.) Holes for wooden pins average 2^ inches in diameter and 5 inches deep. In general, holes of these dimensions leave a margin of about I inch of solid wood in the cross- arm on each side of the hole. One of the principal objections to wooden pins is the lia- bility to become charred or to be burnt out entirely by leakage currents over the insulator. Burning generally takes place at the thread of the pin. In some transmis- sion lines, trouble has been experienced by the current arc- ing from the insulators to the pins, and even crossing to cross-arms and pole tops, and forming, supposedly, nitric acid. The elements for the hydrogen and oxygen of the acid are present in water which settles on the wood, while the nitrogen comes from the air. The acid thus formed acts on the wood and makes it quite pulpy. Since nitric acid is also a splendid electrical conductor the tendency of the current to strike from insulator to pin is greatly in- creased ; and hence in time the thread of the pin and other parts become charred and finally break off, or burn out entirely. It is supposed that burning or charring of pins at the threads is due to the high resistance of the pin at this point, which results in the evolution of a high temperature by the leakage current from the insulator. At the lower part burning seldom occurs, as the accumulation of THE TRANSMISSION LINE 205 dust and organic matter affords a fairly good path for the current. Another serious drawback in the use of wooden pins is that a de- fective insulator, or a breakdown of an insulator, usually results in the complete destruction of the pin and not infrequently in the burning of the cross-arm. Metallic pins are generally made of wrought iron, and are constructed with either wooden screw threads and porcelain bases, or else with wooden tops and iron bases, or with wood tops and wood bases. The pin proper, or bolt, which holds the insulator in position varies in dimen- sions from one half inch by i o inches for medium-sized insulators, up to five eighths inch by 1 1 inches for very high pressures and heavy insulators. Fig. 93 shows a Locke iron pin with a porce- lain base, and Fig. 94 shows the same pin with an all wood top. Metallic pins possess the following advan- tages over wooden pins : Greater mechanical strength, greater durability, less liability to cause a breakdown in the line when an insu- lator proves defective. Kinds of Insulators. Advantages and Dis- advantages of Glass and Porcelain. Insulators for high-tension lines are of either glass or porcelain, or Fig. 93. Iron Insulator Pin with Porcelain Base Fig. 94. Iron Pin with Wood Top 206 LONG-DISTANCE ELECTRIC POWER TRANSMISSION a combination of the two. They differ widely from those used in low-tension practice, the essential points of dif- ference being a stouter mechanical construction and special shapes and constructional features employed to enhance the insulating properties. High-tension insulators require to be of larger diameter than low-tension ones for the reason that the striking distance through the air varies from 3.5 to 6.5 inches, so that wide gaps must be provided between the circuit wires and all extraneous objects. The "creeping distance" allowed the current also has to be appreciable. At the present time the ideal insulator for high-tension work does not exist. Some insulators are strong mechani- cally and weak electrically, and vice versa. For mechani- cal strength, high insulating properties, and the greatest degree of reliability under all conditions of operation, the solid porcelain insulator is preeminently superior to any other form that is now used. In point of mechanical strength porcelain of the best grade possesses nearly double the strength of the best glass obtainable, as can be demonstrated by letting a steel ball fall from a given distance on insulators made of the two materials. In point of insulating properties porcelain is fully equal to the best glass, and its non-hygroscopic character insures less liability from surface leakage in damp weather, or on lines near the seacoast. Porcelain is not so brittle as glass, and an insulator may be chipped or struck with a bullet without cracking in such a way as to cause a leak. Porcelain, however, has several disadvantages. It is much more expensive than glass ; de- fects in the construction of porcelain insulators are not THE TRANSMISSION LINE 2O/ apparent to the eye, hence the necessity of making high- voltage tests to determine the quality and condition of the insulators before they are put into use. Such tests are quite tedious and necessitate the use of expensive apparatus. Furthermore, being rather conspicuous in appearance, por- celain insulators offer a fine target to mischievously inclined riflemen and the stone-throwing small boy. The shooting of insulators has become such a frequent source of trouble to some Western transmission companies that statutes have been enacted in a few of the trans-Mississippi States making it a penal offense. For potentials as high as 30,000 volts, glass can in most instances be more advantageously employed for insulators than porcelain. The chief advantage possessed by glass over porcelain is its cheapness. In addition to this, how- ever, glass possesses the advantage that any defects in it are readily visible to the eye, which advantage obviates the expense of testing each insulator before it is mounted on the cross-arm. The transparency of glass confers another practical advantage over porcelain, in that it does not invite insects to build nests within the insulators. Such nests are very liable to form short circuits ultimately. The most important objections urged against glass are its lack of mechanical strength (it averages about half the strength of porcelain of the best grade), and its hygro- scopic character and consequent tendency to promote current leakage through the accumulation of moisture. As an offset to this latter fault, however, it is the con- sensus of opinion among both glass and porcelain advo- cates that the static action of the current tends to dry out any moisture which may collect on either kind of insulator. 208 LONG-DISTANCE ELECTRIC POWER TRANSMISSION In general, glass insulators are better adapted for light lines (aluminum), and under conditions which do not re- quire insulators larger than six or seven inches in diameter. The facUJthat they are giving satisfaction on circuits oper- ating at five kilovolts is sufficient indication that it is by no means a settled question which kind of insulator is supe- rior, everything considered. Combination glass and porcelain and compound insula- tors are now in quite extensive use on high-tension circuits. Combination insulators are built up by cementing an inner glass sheath, which contains the pinhole, to a porcelain body. In a compound insulator constructed entirely of porcelain, the upper part or body is solid, while the porce- lain base is cemented in. Combination insulators have also been constructed by cementing three layers of mate- rial together, two of which are porcelain and the other of glass, or vice versa. Compound and combination insulators are much easier and cheaper to construct than solid insulators, but the die- lectric thus obtained lacks homogeneity, and cannot give the insulating properties of a one-piece dielectric. In combination insulators the current stress is trans- mitted from porcelain to glass, or vice versa, so that a con- centration of the stress occurs where the two surfaces meet, and these being the weakest points in the insulator, a break- down is liable to occur there. Compound and combination insulators also lack mechani- cal strength, since the contraction of the plastic material used to hold the layers together leaves cracks and gives rise to unequal strains. Testing of Insulators. Insulators of all kinds should be free from cracks, bubbles, and pits. THE TRANSMISSION LINE 2O9 The glaze of porcelain should entirely cover the outer surface. Glaze really possesses no insulating value ; its purpose is to prevent the adherence of dirt. Highest grade porcelain exhibits a polished or vitreous fracture. When the insulators are of glass, testing js./usually limited to a visual examination, followed by a few blows from a hammer to determine the soundness of the insulator. When porcelain insulators are used, lengthy and not infrequently expensive tests must be conducted to ascertain whether the material is thoroughly vitrified, of homoge- neous character, absolutely impervious to moisture, and capable of standing the voltage stress without the surface glaze. Final high-potential tests, usually equal to double the line voltage, must also be made. A low grade of porcelain is readily manifest from the character of the fracture. The degree of porosity is most readily determined by soaking the insulators in red ink. After being washed, thoroughly vitrified porcelain shows no traces of the ink, whereas in the low-grade variety the ink is readily absorbed and cannot be washed out. Unless perfectly non-absorbent, porcelain insulators are of no value for high-tension service. High-potential tests to determine the degree of the dielectric properties of insulators are usually made by put- ting a number of the insulators, inverted, in a metallic trough, which is then filled to a depth of two or more inches with brine. The saline solution should also fill the pinholes of the insulators. A metallic rod is set in each pinhole, and all the rods are connected in series to one terminal of a high-tension transformer or group of transformers, and the metallic pan 2IO LONG-DISTANCE ELECTRIC POWER TRANSMISSION to the other terminal. The capacity of the high-tension supply source should be adequate to furnish an appreciable current at a potential approximately double that of the potential which the insulators will normally have to with- stand in practice. Each part of a compound insulator should be capable of withstanding a pressure considerably greater than it will be called upon to withstand when the entire insulator is tested. On closing the circuit, all weak and badly con- structed insulators will be punctured and a shower of intensely luminous sparks will ensue. Wet arcing tests should be carried out in a manner which will give ap- proximately such conditions as exist in rain storms. Such tests can be carried out by directing a stream of water on the insulator, under 50 or 60 pounds pressure, and at an angle of from 25 to 35 degrees from the horizontal. Types of American Insulators. Fig. 95 shows a Locke high-tension insulator. It is of the triple-petticoat type and is constructed entirely of brown porcelain. The diam- eter is 1 1 inches and the height ioj inches. The pinhole is of the ij inch standard, and the side and top grooves are both I inch. Fig. 95. A High-Tension Porcelain Insulator THE TRANSMISSION LINE 211 Fig. 96 shows the Locke " Victor " type of porcelain insulator, which is used on the trans- mission lines of the Bay Counties Power Compahy, the Standard Electric Company, of Cali- fornia, and other high-tension cir- cuits. It is of the triple-petticoat type and is 14 inches in diameter and \2\ Fig. 06. Locke "Victor "Type High-Potential inches in height. insulator The groove at the top in which the conductor is carried is } inch wide. The insulator is designed for 60,000 and 80,000 volts. Fig. 97 illustrates the " Provo " type of glass insulator made by the Hem- ingray Glass Com- pany. This is the first type of glass in- sulator successfully used on a 40,000 volt circuit, and was first applied on the 105 mile line of the Fig. 97. A Type of High-Tension Glass Insulator J Telluride Transmis- sion Company, of Colorado. It is of the triple-petticoat 5^ High IT "Diameter 212 LONG-DISTANCE ELECTRIC POWER TRANSMISSION type and is 7 inches in diameter and 5J inches in height. Fig. 98 shows the "Muncie" type of Hemingray glass in- sulator with sleeve, and Fig. 99 is a sectional sketch of the same insulator with all dimensions appended, as applied to the 57,000 volt circuit of the Missouri River Power Com- pany. This type of in- sulator was designed by Mr. M. H. Gerry, Jr., chief engineer of the Missouri River Company. Devices for Fas- tening Conductors to Insulators. Fig. 100 shows a Clark insulator clamp de- signed for use with standard insulators. It comprises two clamps which are rig- idly secured to the conductor on either Fig. 98. Type of Glass Insulator Used on a 57,ooo s j^ e Q j- Qe i nsu l a tor Volt Circuit by means of a bolt and nut. The projecting ends engage the groove of the insulator and thus transfer the end strain to the insulator. The loop encircling the neck of the insulator holds the clamps firmly in position and prevents the conductor from being lifted from the groove. Fig. 101 shows the Clark interlocking insulator clamp for holding the cable or con- ductor in the groove of the insulator. Insulators designed THE TRANSMISSION LINE 213 for the use of this type of clamp are made with an under- cut recess on either side of the groove in the center of the insulator top, so that when the clamp is in position it is interlocked under the projecting portion in such a manner that the conductor cannot be removed or the clamp separated from the insulator without unlocking the clamp. This type of clamp is made in sizes ranging from No. 2 bare to 500,000 circular mils weather-proof wire. Fig. 1 02 shows the position of the clamp in the insulator. The underlocking insulator clamp (Fig. 103) is employed on transmission lines with long spans or such lines as Fig. 99 . Sectional View of Insulator are subject to the strains shown in Fig. 98 occasioned by high winds or sleet. In this type of clamp the conductor is fastened on each side of the insu- lator. The pro- jections or lips engage a deep Fig. zoo. Clamp for Use on Standard Insulators annular groove in the neck of the insulator which prevents the wire from 214 LONG-DISTANCE ELECTRIC POWER TRANSMISSION being torn from the groove, and transfers the end strain over a wide area of conductor. Two such clamps are required for each insulator. Methods of Stringing Wires. Three methods of stringing wires are employed by American long- distance transmission companies, - parallel, in an isosceles triangle, and in an equilateral triangle. In parallel work the several conduc- tors of the circuit are supported on the same cross-arm. This is the method usually adopted when two or more circuits are carried on a pole line. Fig. 101. An Interlocking Insulator Clamp Fig. 102. Interlocking Clamp in Position When wires are strung at the corners of an isosceles triangle two cross-arms per pole are used. This is the THE TRANSMISSION LINE 215 general method adopted when two separate 'transmission lines are carried on one pole line. In this method of stringing wires the interaxial distance between the upper conductor and each of the two lower ones (assuming a three-wire circuit) is different from that between the two lower wires. This method necessitates frequent spiraling and trans- positions of the two circuits, in order to overcome unequal effects of inductance in the different legs, as well as to neu- tralize the mutual induction and capacity between the two lines. Means must also be adopted to balance the capacity of the separate legs of both circuits with respect to each other. Fig. 104 shows the usual method of string- ing two circuits on the same pole line. In three-phase transmis- sions with common return, which is now generally ac- Fig. 103. An Underlocking Insulator cepted as the most efficient Clamp and economical method of transmitting energy over long distances, the three conductors of a circuit are placed at points of an equilateral triangle and separated from each other by distances varying in practice from 18 to 78 inches. Fig. 105 shows a typical method of stringing conductors in the form of an equilateral triangle. The circuit in question is that of the Missouri River Power Company. Transposition of Wires. When two circuits are strung on one pole line, transpositions of conductors become es- pecially important and somewhat complex, since, as pre- 2l6 LONG DISTANCE ELECTRIC POWER TRANSMISSION viously stated, it then becomes necessary to neutralize the effect of unequal inductance in the different legs of the Fig. 104. Usual Method of Stringing Two Circuits on Same Pole Line circuit (if their interaxial distances vary), and overcome mutual induction between the two lines. The number of transpositions required on long-distance lines vary with the working conditions, such as the distance THE TRANSMISSION LINE 217 apart of the different legs of the circuit, the number of wires on a pole line, the transmission voltage, and the prox- imity of telephone or telegraph wires. In American prac- POLETOP Pig. 105. Equilateral Triangle Arrangement of Conductors Used on 57,000 Volt Line of Missouri River Power Company tice transpositions are made at distances varying from one mile up to fifteen miles. In the equilateral triangle lay-out of wires used on three- phase circuits, the transposition of conductors is not con- 2l8 LONG-DISTANCE ELECTRIC POWER TRANSMISSION sidered absolutely necessary, unless it is impractical to carry the telephone circuit at a distance of, approximately, eight feet below the power line. With steel-supporting struc- tures for carrying lines transpositions may be entirely dis- pensed with. When telephone wires are carried on the same pole line with the power wires, and in close proximity thereto, as is frequently the case on long-distance circuits, special pre- cautions should be taken to prevent inductance troubles. As telephone communication is absolutely necessary be- tween the generating and receiving stations of long-dis- tance lines, and as economical considerations usually require that the telephone circuit be strung on the same pole line with the power circuit, the proper transposition of power and telephone wires is of the highest importance in order to prevent serious disturbances due to both electromagnetic and electrostatic effects. Proper transposition of the telephone wires when they are carried on the same pole line with power wires is more important than the transposition of the power wires them- selves ; for if the telephone wires be properly transposed, the untransposed power circuit cannot set up electromag- netic and electrostatic disturbances in the telephone wires, but will produce such effects only between themselves and the ground. Considerable care must be observed in making transposi- tions to avoid side strains on the line. Fig. 106 shows the usual method of transposing two three-phase circuits. Length of Spans. The length of span which should be used on high-tension circuits varies with the operating conditions and the factor of safety desired. No specific rules are applicable. THE TRANSMISSION LINE 2I 9 Fig. 106. Transposition of Two Three-Phase Circuits 220 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The length of span used on copper transmission lines varies from 90 to 150 feet. Standard practice is now tending towards the use of 106 foot spans on copper lines carried on wooden poles, which makes about fifty poles per mile. On aluminum lines the spans are frequently as long as 176 to 212 feet, requiring from 25 to 30 poles per mile. Much difference of opinion exists as to the advisability of lengthening the span of aluminum lines on account of the appreciable lightening of the weight on cross-arms and insulators secured by the use of aluminum. In most cases the advantage of lightness thus obtained should not be utilized in decreasing the line expense, but should be applied to increase the factor of safety, and the same length of span should be used for both kinds of con- ductors. Protection of Transmission Lines from Lightning. Many of the troubles to which high-tension lines are sub- ject are due to the effects of lightning. The extent to which long-distance circuits suffer from lightning dis- turbances varies with the climatic conditions of the region which a line traverses, being much more severe in semi- tropical, tropical, and mountainous regions than in northerly countries. The problem of effectively protecting high-potential lines from the destructive effects of lightning is one that has not as yet been completely solved. In fact, the capricious action of lightning often entirely sets at naught the safeguards provided to protect the lines. Lightning generally affects an aerial line in three different ways, by direct stroke, by induced charges, and by electrostatic induction. THE TRANSMISSION LINE 221 Disturbances due to direct strokes of lightning are of rare occurrence. In such cases no arrester in existence can completely neutralize the effects of it on the line. Induced discharges caused by the electromagnetic effect of a lightning flash are a frequent source of trouble. Electrostatic charges giving rise to electrostatic induc- tion are due to charges in the surrounding atmosphere. Since a lightning discharge is of enormously high fre- quency, inductance in the line opposes a very high im- pedance to a discharge, and the discharge takes the shortest and most direct passage to ground. This ac- counts in a large measure for the puncturing of transformer coils. Since inductance in the line offers great resistance to the passage of a lightning discharge this fact is sometimes taken advantage of by putting choke coils in series with the line, and between the arrester and the central station. Such choke coils are made of flat copper strip, wound on a non-conducting core, the separate layers being insulated with mica. This combination described works fairly satisfactory as a protecting device for the station apparatus, but its cost makes its use prohibitive on every line arrester unless it is imperative to give the utmost possible protection to the apparatus. Practice differs as regards the use of arresters at various points along high-tension lines. Some transmission com- panies use arresters only in the generating station and at sub-stations. To safeguard a circuit effectively, arresters should be located at the ends of all lines, at sub-stations, and at points where the lines branch off. Many transmission companies rely partly or wholly upon 222 LONG-DISTANCE ELECTRIC POWER TRANSMISSION a grounded wire along the lines as a safeguard against dam- age by lightning. Such wires are made of either smooth galvanized iron in the solid or cable form, or in the shape of barbed wire, and strung parallel to the power wires and grounded at intervals. Such a grounded wire constitutes a short-circuited secondary, which largely absorbs by induc- tion the energy of a lightning discharge to the line. A grounded wire strung near power wires also serves to dis- charge any charged atmosphere which may blow across the line. Another advantage is afforded by a grounded parallel wire in cases where transmission lines run through moun- tainous regions, in which there are marked differences in the altitude of different parts of the line. Under such con- ditions there is an electrostatic effect due to differences in altitude, which produces an appreciably greater difference of potential between conductors and the ground in the low than in the high altitudes. When parallel grounded wires are depended upon for protection, three such wires are usually employed, one wire being strung on top of the pole, and one at each end of the cross-arm. In order to give them reliable mechanical support they are usually mounted on pony insulators. Frequent grounding is necessary in order that the oppo- sition to the flow of current between the grounded wire and the earth will be reduced to a minimum. Surges in Transmission Lines. The chief causes of surges in high-tension circuits are opening a line carrying a load or under a short circuit, closing a high-potential line switch to charge the line, and opening a high-tension switch to make the line dead. THE TRANSMISSION LINE 223 The worst cases of damage to apparatus by surges are those produced by the sudden rupture of a short circuit. This is due to the fact that the current which the line is carrying at the time of the short circuit is considerably in excess of the maximum normal operating current ; the magnitude of alternating-current surging depends upon the value of the current at the instant of rupture. If the interruption takes place at the zero point of the current wave, the surge which follows is slight enough to be considered negligible, but if the interruption occurs at the peak or crest of the current wave the surging has a value which is the same as that which would be produced by a direct current of the same strength. If the conditions of operation render it possible to break the short circuit gradually through external resistance, the surging will not be of appreciable importance. The surg- ing will also be slight if the current wave can be stopped by automatic means at or very near its zero point. When the line switch is first closed on a dead line, charg- ing current at once flows into the line, which is a simple condenser. But this charging current is obliged to flow through the line inductance, and this stores up energy in the shape of a magnetic field. The stored-up energy then discharges into the condensive line and so adds to the charge already in it. The maximum possible E.M.F. from this cause is double the working potential of the line. In opening a line switch to disconnect a circuit, the condenser of the circuit discharges across the terminals of the switch the instant they are separated ; and owing to the charging current of the condenser, the pressure of the circuit rises to its maximum value of operation at the nor- mal frequency of the line. 224 LONG DISTANCE ELECTRIC POWER TRANSMISSION Hence before the switch can be pulled very far apart, the line pressure set up by the oscillating current in the circuit is superposed on the pressure between the switch ter- minals due to the generator. Such increase of potential may cause the arc to oscillate several times between the switch jaws before the circuit becomes absolutely dead. The surge following the opening of a high-tension line may cause a rise of potential equal to double the normal operating pressure. Very great precautions should be exercised in opening a high-potential circuit under load, as destructive voltages are liable to ensue. When an alternating current is suddenly interrupted at the receiving end of a line its natural outlet is sup- pressed. It at once flows into the condenser and charges the circuit, but since the condenser cannot hold the charge, it discharges into the self-inductance of the line, and the energy is converted into magnetic energy. The magnetic field then gives up its energy to the con- denser, and the cyclical exchange of energy is repeated in gradually decreasing amplitude until the line resistance has consumed the energy at first stored in the line self- inductance. The surges or oscillatory currents set up in this way are of a very serious character, and may completely destroy or at least severely strain the insulation of the generating or the transforming apparatus, or both. Losses by Leakage and Electrostatic Induction, Aside from the difficulties of effectively insulating the line, the limitations to the potentials practical for electric power transmission are losses by line leakage and electrostatic induction. THE TRANSMISSION LINE 22 5 Leakage losses take place from wire to wire of the circuit, and with very high potentials may reach enormous values, unless the conductors are made unduly large and are widely separated. A very interesting series of experiments were carried out by Mr. Charles F. Scott, to ascertain the losses by leakage on high-tension circuits and the limitations to long- distance power transmissions. The results of his experi- ments may be thus summed up : The power loss through the air by current leakage between wires increases with the impressed voltage, and after a critical voltage is reached it increases very rapidly. With a given impressed voltage the loss decreases as the distance between wires is increased. The loss is not appreciably affected by atmos- pheric conditions, such as rain, snow, or humidity. Peaked E.M.F. wave shapes give greater losses than flat- topped waves. The loss decreases as the diameter of the wires increases. His results were summed up in a set of curves, repro- duced in Fig. 107, showing the relations between wire distance, operating voltages, and power loss. Fig. 108 shows the loss when the distance between conductors was increased to 48 inches. Dr. Steinmetz found in his experiments on the electric disruptive strength of powerful solid dielectrics that the at- mosphere surrounding the solid dielectric specimen and the electrodes applied thereto would rupture under the strain produced by the flux of electric force through it much easier than the solid dielectric. This produces envelopes of conductive atmosphere around the electrodes and over the surface of the strong dielectric, which phenomenon re- sembles a brush discharge from a static machine, and is 226 LONG-DISTANCE ELECTRIC POWER TRANSMISSION termed the corona. Corona formation depends primarily upon the maximum, and not upon the effective value of the E.M.F. wave, as has been shown by the experiments of Scott, Mershon, Ryan, etc. The experimental work of Steinmetz has also shown that the atmosphere conducts after disruption in two forms, cither arcs or intensely heated streamers at high-current 12.5 60 Fig. 107. Curves Showing Power Losses at Various Voltages and Spacings of Wires density, or coronal or brush discharges at lower current density. The latter begin to appear at pressures above 40,000 volts. Steinmetz further ascertained that the dielectric strength of the atmosphere in bulk requires approximately a potential gradient of 10,000 effective volts per inch, with an E.M.F. wave following the sine law, THE TRANSMISSION LINE 227 The researches of Professor Ryan (Trans. A. I. E. E. Vol. 21) show that the critical voltage of a brush or coronal discharge is a function of the barometric pressure of the air : his equation for this is K v 0.902 b 4- 2.93, where K v effective kilovolts and b = barometric pressure in inches of mercury. 20 30 40 50 60 KILOVOLTS Fig. 108. Curves Showing Losses with Wires 48 Inches Apart Hence on lines crossing high altitudes the pres- sures which are permissible are appreciably less than those which the same line construction admits of at sea level. Danger of brush discharge becomes less as the size of the conductor increases. A large conductor therefore permits the use of higher voltages than a small one, and 228 LONG-DISTANCE ELECTRIC POWER TRANSMISSION aluminum conductors diminish the tendency of coronal discharges. The equation, according to Professor Ryan, which gives the maximum voltage causing corona formation, is, ma x ~. * 2055 (r+d) Iog 10 f-J D' x io 10 where E max = maximum value' of the potential wave impressed upon the line. b = barometric pressure in inches of mercury. / = temperature in degrees Fahr. s = separation of line conductors from center to center, in inches. d = distance from conductor surfaces at which the strain due to the electrostatic field causes rupture of the atmosphere. P' = the dielectric flux density, in coulombs per square inch, that will electrically rupture the atmos- phere at distance d from the surface of the conductor having a radius r. "For wires of 0.25 inch in diameter and upwards, D f and d remain constant at D f = 170 x io~ 10 coulombs per square inch and d = 0.07 inches." Hence for such wires Ryan's equation becomes, Emax = d7 Q 9 + 1 x 35 ' oo ( r + - 7 ) iogi i 3 V ^ \ / Grounding of High-Potential Lines. Grounding the neutral point of a high-tension line is desirable for the fol- lowing reasons : When the neutral point is grounded the voltage between the conductors and the ground is limited to the operating potential of the line. In an ungrounded line, the voltage between phase conductors and ground THE TRANSMISSION LINE 229 may vary between wide limits, and may attain such values that the liability to the breakdown of the line insulation becomes serious. When a high-potential line is grounded, it insures the immediate detection of faults and necessi- tates their immediate removal. One objection to grounding is that it increases the ele- ment of danger to persons and property. It is the general opinion that the fact of the conductor voltages being main- tained at a definite-arid dangerous value above the ground potential is sufficient proof that' the danger to life is greatly augmented by the practice. As an illustration : If the neutral is grounded, the oper- ating Y-pressure of the system is introduced between any line wire and the ground, and on making a contact to ground, a body touching this contact would be subject to this pressure. Hence if capacity were not present, grounding the neu- tral point would augment the element of danger ; but since capacity is always present to a greater or less degree, each wire is really grounded through a condenser. And although the conditions are slightly different from the case of one conductor grounded direct, the results are nearly alike. Thus the action of these capacity connections to ground will be to cause the E.M.F.'s to concentrate themselves about the point of earth potential. And so when the line wires have a capacity effect, there are differences of potentials between them and the ground, even with no part of the system grounded direct. Such differences of potential will not be neutralized by connect- ing the conductor to ground through resistance, since the capacity behaves like an elastic band, and tends to check 230 LONG-DISTANCE ELECTRIC POWER TRANSMISSION the displacement of the conductor E.M.F.'s relative to the earth. However, the difference of potential will be diminished by the flow of current through the resistance, and when the current is of considerable strength, may be reduced to a non-dangerous value. The effect in any particular case will depend upon the value of the capacity in the several wires, and also upon the resistance of the grounding substance. Maintenance of Pole Lines. Patrolling of high-tension lines becomes essential in direct proportion to the potential employed for transmission, and the difficulties of operation. Current practice as regards the patrolling of lines differs quite widely. Some companies have , their lines patrolled daily, some weekly, while others do so only at intervals of one or several months. The character of the country which the line traverses is an important factor in deter- mining the frequency for making inspections. The necessity for patrol trips is considerably obviated by the use of telephone lines on the same poles with the transmission circuits. When a short circuit or a dangerous leakage has occurred on the power circuit, the peculiar sounds given out by the telephone receiver render the fact of its occurrence unmistakable. On circuits where patrolling is carried out the line is divided into sections varying from 10 to 20 miles in length, each of which is assigned to a patrolman. In order to enable the patrolman to make reports to the cen- tral station, taps are brought down from the telephone circuits to booths located a few miles apart, to which the patrolman makes connection with his portable telephone set and informs the station attendants of the condition of THE TRANSMISSION LINE the line. As a precaution against the danger of a high- voltage discharge through the telephone line, each booth is provided with a highly insulated stool upon which the trouble man sits in calling up the central or sub- station. Calculation of a 75 Mile Three-Phase Transmission Line. Data : 2,000 k. w. with line loss of 3 per cent. 25 ~w Frequency. .85 Power Factor. Copper Conductors. Assume 30,000 volts as the pressure of transmission and consider one leg of the circuit. Then * _ = 17320 volts = E.M.F. between any wire and V 3 the neutral point. icooo X 2 A= -- =-- = 17320 V 3 The energy delivered by each leg is 2060 k.w. - = 686.6 k.w. 3 ^ The apparent energy delivered by each leg is 686.6 k.w. = 808,000 watts 8 5 The current in each leg is 808000 - =46.6 amperes. 17320 232 LONG-DISTANCE ELECTRIC POWER TRANSMISSION To determine the size of conductor necessary, assume the limit of the IR drop to be 10 per cent of the voltage in each leg : 10 per cent of 17320 = 1732 volts. Hence, J? = l^ = 37.2 ohms. 46.6 And the ohms per 1,000 feet are, = 0.965 ohms per 1000 ft. S- 2 ^ X 75 . (5.28 is the ohms per mile of wire.) Therefore, we use No. oo wire whose radius R is 0.78 per 1,000 feet by table. And the total resistance of one leg is 0.78 X 75 X 5.28 = 30.9 ohms. The inductance of one leg per mile is r /^\-|io- L (in henrys) = 80.5 + 740 log f - 1 d= 18 inches = 45.8 cms. R = ^5 2.54 = ^462 cms. = (80.5 + 740 log 99.3) 10 - = (80.5 + 740 X 1.996949) W = 80.5 + 1470 = 1550.5 = 1 ,000,000 1 ,000,000 in henrys per wire per mile. THE TRANSMISSION LINE 233 The total inductance of each leg is .00155 x 75 = - IJ 7 henry's. The inductance in ohms is 2 TT/Z = 2 x 3.14 X 25 x .117 = 18.4 ohms. The capacity of the line in microfarads is 2 lo io - where L = length of line in miles. d = distance between wires in inches. r = radius of wire in inches. 5.8* 5-8* 2 X = ~ = 1.46 microfarads. 3-99 C in farads = 1.46 X 10 6 = .00000146. The charging current per wire per leg is _ E x C x 27r x/ * ~ / V3 X io 6 where E = E.M.F. between wires. /= frequency. C = capacity in microfarads between one wire and the neutral point. Hence __ 17,320 x 1.46 x 2 x 3.14 x 25 _ i~ V3 X 1,000,000 .405 amperes per wire per line. 234 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The E.M.F. required to force this charging current through each leg is .-. E c = = 4* co volts. 2 X 3.14 X 25 X .00000146 The charging current drop is 1,760 volts. And the drop due to charging current plus the load cur- rent is JS e+t = 46.3 X 30.9 = 1430 volts drop. The drop due to inductance is E L 2 TrfLI= 18.4 X 46.3 = 852 volts. Explanation : E and / differ in phase by 31, while I c and E c are 90 ahead of E. Taking the resultant of /and 7 C , one gets 7 c + t -, in phase with E c . Finding, by trigonometry, the angle between this E c and E t multiplying this by the cosine and combining the result -with E L . 90 ahead of this E c is E. Finding the angle between E and E L we take its cosine and resolve E L on E. The result is the total E. 179 60' 121 -45 Cos A = 58 -i 5 ' = C + P - 2 ab cos C C=^ 15' a = .405 b = 46.6 Then _ / c +z = V. 1 6402 5 + 2171.56 - 3778 X .5262 2171.56 19.8 = 46.3 amperes for / capacity + load current . Cos 63 = CosZ> = .4540 Cos 27 = Cos^ = .8910 Fig. 109 is a vector diagram showing the magnitude of the various quantities in the above calculation. Combining the volts vectorially one gets (Fig. 1 10) E L X Cos 63 = 852 X .4540 = 3 86 -8 ^capacity + load X COS 27 = 1430 X .89 I = 1274.! ^totai = I 73 20 + 1274.1 H- 386.8 = 18981 y; otal = 46.3 amperes. The above calculations are for one leg of the circuit, and the voltage is considered between one wire and the neutral point. Multiplying this voltage (18,981) by the %/3 we obtain 32,820 as the total line voltage. The true power factor is Cos 27 = .891. The regulation of the line is 32820 -5- 30000 = 9.4 per cent. Then kilowatts at generator = 32820 x 46.3 X 89.1 x 3 -=?- = 2350 + 3 per cent 1000 X V3 = 2450 kilowatts at 89.1 per cent power factor. 236 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Using a I to 6 step-up transformer the E.M.F. of the generator will be 5,500 volts. X 1000 A i ^i ^ And the current, = 445 amperes. OR SOLVING VECTORIALLY ONE GETS I, Fig. 109 Generator specifications : 3 -phase alternator of re- volving field type. 2,450 k.w. or 3,290 h.p. 5,500 volts. I CAPACITY+LOAD Fig. no 445 amperes 25 cycles. 94 r.p.m. 32 poles. To be direct connected to an impulse water-wheel of 3,560 h.p. output, which allows for 92^ generator efficiency. THE TRANSMISSION LINE 237 BIBLIOGRAPHY Electrical Conductors. Perrine. D, Van Nostrand Co. New York. 1902. Data Relating to Electrical Conductors and Cables. Fisher. Pro- ceedings American Institute Electrical Engineers, Vol. 24, p. 687. The Use of Aluminum Line Wire and Some Constants for Transmis- sion Lines. Perrine and Baum. Transactions American Institute Elec- trical Engineers, Vol. 18, p. 391. Mechanical Specifications for a Proposed Insulator Pin. Mershon. Transactions American Institute Electrical Engineers, Vol. 20. Burning of Wooden Pins on High-Tension Transmission Lines. Chesney. Transactions American Institute Electrical Engineers, Vol. 20, P- 435- Testing of Insulators. Blackwell. Transactions American Institute Electrical Engineers, Vol. 20. Overhead High-Tension Distributing Systems in Suburban Districts. Lukes. Transactions American Institute Electrical Engineers, Vol. 21, P-25. Methods of Bringing High-Tension Wires into Buildings. Skinner. Transactions American Institute Electrical Engineers, Vol. 20, p. 1171. Transposition and Relative Location of Power and Telephone Wires. Lincoln. Transactions American Institute Electrical Engineers, Vol. 20. The Protection of Telephone or Telegraph Wires When in Hazardous Proximity to High-Tension Lines. Chetwood. Electrical World and Engineer, New York, May 21, 1904, p. 968. The Prevention of Crosses between Signalling and High- Voltage Cir- cuits. Knowlton. Electrical World and Engineer, New York, April 23, 1904, p 768. The Grounded Wire as a Protection against Lightning. Mershon. Transactions American Institute Electrical Engineers, Vol. 20, p. 1180. Grounding of High-Potential Systems. Nies. Electrical World and Engineer, April 12, 1902, p. 639. Theoretical Investigations of Some Oscillations of Extremely High Potential in Alternating High-Potential Transmissions. Steinmetz. Transactions American Institute Electrical Engineers, Vol. 18, p. 383. The Regulation of Transmission Lines. Lighthipe. Transactions Pacific Coast Transmission Association, San Francisco, July, 1904. 238 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Possibilities of Single-Phase Currents in Electric Power Transmission. Ballard and Sprout. Transactions Pacific Coast Transmission Associa- tion, San Francisco, July, 1904. Medium Span Line Construction. Copeland. Transactions Pacific Coast Transmission Association, San Francisco, July, 1904. Resonance in Aerial Systems. Physical Review, New York, Vol. 18, pp. 200-208. Surges in Transmission Circuits. Kennelly. Electrical World and Engineer, New York, Nov. 23, 1901, p. 847. Atmospheric Losses on High- Voltage Lines. Scott. Transactions American Institute Electrical Engineers, Vol. 15, p. 531. High-Power Surges in Electric Distribution Systems of Great Mag- nitude. Steinmetz. Proceedings American Institute Electrical Engineers, Vol. 24, p. 575. An Experimental Study of the Rise of Potential on Commercial Transmission Lines Due to Static Disturbances. Thomas. Proceedings American Institute Electrical Engineers, Vol. 24, p. 705. The Conductivity of the Atmosphere at High Voltages. Ryan. Transactions American Institute Electrical Engineers, Vol. 21, p. 275. Guard Wires for Transmission Lines. Electrical Review, Jan. 16, 1904. Losses by Electrostatic Discharge on High-Tension Lines. Electrical World and Engineer, July 21, 1900, p. 91. On the Mechanism of Electric Power Transmission. Electrical World and Engineer, New York, Oct. 24, 1903, p. 673. Drop in Alternating-Current Lines. Mershon. American Electrician, New York, June, 1897. CHAPTER VII TRANSFORMERS A TRANSFORMER is an alternating-current device for chang- ing electric energy of one electromotive force into the same electric energy at a different electromotive force. It con- sists of one magnetic circuit and two electric circuits, which are so interlinked with it that current traversing the pri- mary electrical circuit sets up an alternating flux in the mag- netic circuit which induces an alternating E.M.F. in the secondary circuit. The value of the alternating E.M.F. so induced is dependent upon the ratio of the numbers of turns in the primary and secondary windings. Hence, the ratio of transformation is the ratio of the number of turns in the secondary to the number of turns in the primary. If this ratio is greater than unity, the transformer is termed a "step-up" transformer, for the reason that it de- livers energy at a higher potential than it is received. If this ratio is less than unity, the transformer becomes a "step-down" translating device, since it delivers energy at a lower pressure than the primary received pressure. It is obvious that in high-tension transmission of power the step-up transformer finds its principal use at the generating end, owing to the limited potential which alternators are capable of giving, 15,000 volts being the highest pressure for which commercial alternators have been wound up to the time of writing. The step-down type is used at the receiving points in a circuit where currents of particular potentials afe necessary 2 39 240 LONG-DISTANCE ELECTRIC POWER TRANSMISSION for the peculiar characters of apparatus in use on distribu- tion circuits. Losses in Transformers. Transformer losses are made up of (i) Resistance of the electric circuits; (2) hysteresis in the iron ; (3) eddy currents in the iron. These losses are divided into " copper " and " core " losses. The copper loss is due to the resistance of the primary and secondary windings, while core losses are those due" to hysteresis and eddy currents in the iron of the magnetic circuit. Copper losses also properly include eddy current losses, but such losses are in most cases small enough to be considered negligible or else are combined with the eddy current losses in the core. The magnitude of the copper loss is equal to the product of the square of the current times the ohmic resistance of the wire. Calling the copper loss in watts P c ; I p the cur- rent in the primary, and I s the current in the secondary ; and R p and R s the primary and secondary resistances re- spectively, then p / 2 >? -4- np - 1 c J p YV p i J s Yl s from which it is evident that the copper loss varies as the square of the load in amperes. The copper loss also depends largely on the design of the transformer and the conditions of its operation. A well- designed transformer of one kilowatt output will have a copper loss of from 2.5 to 3 per cent. For 100 kilowatt sizes the copper loss is approximately i per cent of the output. Copper losses increase with the resistance, and the re- sistance increasing with rise of temperature makes the. loss larger when the transformer becomes heated by the current or by extraneous sources of heat. The permissible rise in TRANSFORMERS 24! temperature of a transformer is 50 C. above the surround- ing air, according to the American Institute of Electrical Engineers' standard code. The resistance of the windings of a transformer increases about 0.004 ohm for each degree rise of temperature. Copper losses affect a transformer in three ways : (i) The efficiency is reduced ; (2) the resistance gives rise to heat which may damage the insulation ; (3) if of the constant potential type the regulation of the transformer is seriously affected. Hysteresis Loss. A certain number of watts are neces- sary to carry the iron through cyclic changes of magnetiz- ation, causing a loss of energy which by Steinmetz's equation is, in which JP h = loss in watts. V= volume of core in cubic centimeters. f= frequency (cycles per second). jJV= a hysteretic constant. B m = maximum flux density per square centimeter. That component of the impressed E.M.F. which is neces- sary to overcome the hysteretic loss is P F* **=/,' and is in phase with I p . Core losses differ from copper losses in that they are nearly constant for all loads, while the latter vary as the square of the load. (In the constant-current type of trans- former the converse holds true, i.e., the copper loss in the secondary is constant, while the iron loss varies with the load.) 242 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The magnitude of the core loss is also governed by the shape of the impressed E.M.F. wave, a peaked wave form giving a slightly lower core loss than a flat -topped wave. Be- yond a definite limit, however, the wave form may be so flat that the core loss may be greater than that which would be given by a true sine curve E.M.F. In the best types of commercial transformers the core loss for 60 cycles may be about 70 per cent hysteresis and 30 per cent eddy current loss. At 125 cycles it will average 55 per cent hysteresis and 45 per cent eddy cur- rent loss. In most commercial transformers the copper and core losses are almost equal at full load. In cases where constant voltage is imperative, or when the transformer is operated constantly under heavy load, the copper loss is frequently reduced at the expense of the iron loss. Eddy or Foucault Current Losses. These are caused by small currents eddying in the iron of the transformer. The E.M.F. giving rise to eddy currents is in phase with the counter E.M.F. of the primary, since both are due to the same flux. -These eddy currents cause a loss of energy due to the heating which they produce in the iron. To reduce this loss to a minimum the cores of transformers are constructed of thin laminae of iron, which are japanned or lacquered on each side. In the construction of a transformer these laminae are so placed that they are transverse to the direc- tion of flow of the Foucault currents, but are longitudinal to the path of the magnetic flux. The loss in watts from Foucault currents is P. = TRANSFORMERS 243 where P e =5 loss in watts. b = constant depending upon the specific resistance of . A-Tl, the iron. z> == volume of the iron in cubic centimeters. f= frequency (cycles per second). t = thickness of the laminae in centimeters. B m = maximum flux density per square centimeter. Eddy current losses are for all practical considerations independent of the load. Capacity of Transformers. The maximum output for which transformers can be designed is limited by several necessary conditions of operation. When the secondary current is increased the secondary E.M.F. of the trans- former decreases, and the energy output increases with the current, and becomes a maximum. Thus the maximum power output becomes the maximum limit to the capacity of the transformer. But under commercial conditions the capacity of a transformer is limited to a considerably smaller value than this maximum capacity since : (1) If the rise of temperature is not kept within a cer- tain limit, damage to insulation will occur and breakdowns are liable to ensue. (2) In practice it is generally essential that constant secondary E.M.F. be maintained. (3) At excessive outputs transformer efficiencies are greatly reduced. The radiation surface per watt per degree rise of temper- ature of small transformers is relatively large, and their out- put is, in general, limited only by the requirements of close regulation. In large transformers the radiating surface per watt per degree rise of temperature is relatively small, and 244 LONG-DISTANCE ELECTRIC POWER TRANSMISSION their capacity is hence limited by the allowable rise in temperature. The larger the output of transformers up to a certain limit, the closer is their regulation and the higher their efficiency. The capacities of transformers used in high-tension practice vary from a few kilowatts up to as high as 7,500 kilowatts, which is the largest size that has been thus far designed for commercial operation. Efficiencies of Transformers. The efficiency of a trans- former is the ratio of its net power input to the gross power output ; or, in other words, it is the ratio of the power out- put to the power input plus all losses. Hence the efficiency of a transformer is where E s is the difference of potential at the secondary terminals, and I s is the current in the secondary ; and P h , P c , and P e are the losses in watts due to hysteresis, re- sistance, and eddy currents respectively. In large transformers used in high-tension practice, the denominator of the efficiency equation is also increased by the power consumed by the device employed in keeping down its temperature, such as the energy consumed in running blowers for air-blast transformers, and in operating the motor-driven pumps for oil or water-cooled trans- formers. In cases where one blower or other cooling apparatus supplies a bank of transformers, allowance should be made for the percentage of energy supplied to each in keeping it cool. Since transformer losses are largely governed by the TRANSFORMERS 245 temperature, the efficiency can only be accurately deter- mined by bearing in mind some definite temperature (usually 25 C). The all-day efficiency of a transformer is the ratio of the energy output to the energy input during twenty-four hours. In practice this efficiency is calculated on the assumption of nineteen hours of no load and five hours of full load. This applies only to lighting transformers. 90 80 f ^ /' TABLEOF EFFICIENCIES IJfc LOAD = 98. 2% 1 1 /4 ' =98.29% FULL > =98.32% /4 =93.24% 1/2 . =97.88% 1/4 ' =96.43% - / X / ^ c & 30 <^ P x x 1 _ < ^ - -' ^-^ ^ X - =rrr - .. ^. -*^ m" DN LOJ s - ^ ^^ ^^ e.^^ ,0 r-..,- _ .^ ' ^-- > ^^^^ _L 2.5 125 150 50 75 tOO Per Cent Load Fig. in. Efficiency Curves of a 550 K.W. Transformer The efficiency of a transformer is always measured at non-inductive load and at the rated frequency, unless other- wise specified. Fig. in shows efficiency curves of a 550 k.w. transformer. Testing of Transformers. It is generally necessary to make a certain number of tests upon a transformer to ascertain whether it is fulfilling the required specifications and giving its rated efficiency. The tests usually made have for their purpose determination of the following val- 246 LONG-DISTANCE ELECTRIC POWER TRANSMISSION ues : (i) Core Loss and Leakage Currents; (2) Copper Loss; (3) Resistance; (4) Impedance; (5) Heating; (6) Insulation ; (7) Efficiency. In determining the core loss and leakage current, an al- ternating current of the rated secondary pressure and fre- quency is applied to the secondary terminals, and an ammeter and wattmeter are connected in the circuit to read the leakage current and core loss respectively. To ascer- tain the leakage current the reading of the ammeter should be divided by the ratio of transformation. From the data obtained in this test the no-load power factor is readily calculated. D. C. Ammeter Fig. iia. Connections for Scott Method of Hysteresis Measurement Fig. 1 12 shows the connections for applying C. F. Scott's method of measuring the hysteresis loss in large trans- formers. When a direct current is sent through the low- tension winding a magnetic field is set up in the iron. With a gradual increase or decrease of current, the strength of the magnetic field will be proportionately increased or decreased, and this varying field induces an E.M.F. in the transformer winding which is measured by the voltmeter across the high-tension terminals. With a uniform rate of change in the magnetic field there is a constant E.M.F. generated in the winding, and the voltmeter pointer remains stationary. TRANSFORMERS 247 MAXIMUM INDUCTION 1O26O HYSTERESIS LOSS PER CYCLE, PER CD. CM. OF IRON 3958 ERGS HYSTERETIC CONSTANT .00152 Commencing with zero current the resistance is cut out in such steps as will give a steady deflection of the volt- meter. As soon as the maximum desired induction is at- tained the voltmeter is reversed and the current gradually decreased to zero. The current is then reversed and gradu- ally increased to a negative maxi- mum ; then the voltmeter is again reversed and the current decreased to zero, complet- ing the cycle. It is necessary to bring the iron "in- to step " before making readings, by running it through several complete cycles. Fig. 113, hys- teresis curve of a 2,250 kilowatt transformer, shows the curve of hyster- esis loss of a 2,250 kilowatt three-phase twenty-five cycle Westinghouse trans- former, and Fig. 114 shows the efficiencies at various loads of the same transformer. The copper loss is determined from the measured resist- ance, as given by the formula on page 240. The resistance of the coils is most accurately measured Fig. 113. Hysteresis Curve of a 2,250 K.W. Transformer 248 LONG-DISTANCE ELECTRIC POWER TRANSMISSION by the drop in potential method, which consists in measur- ing the volts drop between the terminals of a winding with given currents, from which the resistance is calculated by Ohm's Law. In making this test on large transformers, Peck has modified the drop in potential method to safeguard the measuring instruments against dangerous pressures. When direct current is sent through a transformer winding a magnetic field is induced in the iron ; small current vari- EFFICIENCY AT DIFFERENT LOADS 1 V 2 LOAD 98.5 % 1'/ 4 LOAD 98.59% FULL LOAD 93.63% 3 /4 LOAD 98.6$ 1 /2 LOAD 98.2% V 4 LOAD 97.2% VioLOAD 93.7% REGULATION NON IND. LOAD .76% !0% POWER FACTOR 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 PER CENT OF FULL LOAD Fig. 114. Efficiency Curve of a 2,250 Kilowatt Transformer ations will produce variations in the strength of the mag- netic field, which may set up sufficiently high E.M.F.'s in the transformer windings to injure the measuring instru- ments. In Peck's method one winding is short circuited to obviate this danger. When a sudden change occurs iri the magnetic field a current is induced in the short-circuited winding, which opposes the change in the strength of the field. In other words, the short-circuited winding acts as TRANSFORMERS 249 a choke coil to suppress sudden variations in the magnetic field. But in this method of resistance determination the field does not instantly become stationary, because it is damp- ened by the short-circuited winding ; therefore an appre- ciable length of time elapses before the field reaches its maximum value. During the interval in which the field is increasing, an E.M.F. is induced in the transformer winding, which E.M.F. is in a direction to add itself to the E.M.F. due to the re- sistance ; thus the voltmeter reading is slightly higher than it should be on account of the resistance of the wind- ing alone. The correct drop is only ascertained when the field has become stationary. In making the impedance test the secondary coils of the transformer are first short circuited through an alternating- current ammeter of practically negligible resistance, and a voltage of the rated frequency is impressed upon the primary coils, its value being such as to cause the full-load current to flow. This full-load current can also be meas- ured on the primary side, the secondary being then short circuited. (In this event the small leakage current must be disregarded.) Then the reading of a wattmeter inserted in the primary circuit will almost correspond to the copper loss at full load ; while the reading of the voltmeter repre- sents the impedance drop, which is expressed in per cent of the rated primary pressure. Heating Test. The average temperature of the coils is determined from the formula / (rise in degrees C) = > 0.004^ in which R h = resistance of coils when hot, and R = re- 250 LONG-DISTANCE ELECTRIC POWER TRANSMISSION sistance at room temperature. This is equivalent to divid- ing the per cent increase in resistance by 0.004. For every 10 degrees above 25 C. the above coefficient should be increased by 1 . 5 per cent . Insulation Test. In making an insulation test, a high- voltage transformer is used, and the rated pressure of the transformer is applied between coils and core. The secon- dary should be grounded on the core when making a test between primary and secondary of the core. All primary leads should be connected together as well as all secondary leads to insure against undue stresses in any section of the winding. The requirements of the National Board of Fire Under- writers are : " That the insulation of transformers when heated shall withstand continuously for five minutes a dif- ference of potential of 10,000 volts alternating current be- tween the primary coils and the core, and a no-load run of double voltage for thirty minutes." Efficiency Tests may be made by any one of several methods, namely, the Ryan Method of Instantaneous Curves, the Mordey Method, and Stray Power Methods. In the Ryan Method instantaneous contacts are made to obtain the curves of primary and secondary E.M.F., and primary current, the secondary current being measured by an ammeter. From these curves the power in each circuit is calculated, and the ratio between the two gives the effi- ciency. The principal advantage of this method lies in the fact that both the exact form and phase relations of the waves are sharply brought out. In the Mordey Method of determining efficiency, the transformer is run at a given load until a constant temper, ature is reached, as determined by the thermometer or by TRANSFORMERS 251 resistance tests. Direct current is then passed through the coils, and of such a value that the heating effect keeps the temperature constant. The direct-current power (El), which is readily measured by a wattmeter, is equal to the aggregate losses with the alternating current. Stray Power Methods for determining efficiency are quite accurate, and permit of the individual determination Fig 115. Static Interrupter and Choke Con of the losses. The core losses are found from wattmeter measurements in the primary circuit, the secondary being open circuited. Static Strains in Transformers. When for some rea- son it becomes imperative to perform switching operations on the high-tension side of transformers, such as, for in- 252 LONG-DISTANCE ELECTRIC POWER TRANSMISSION stance, the opening of the line under load or short circuit, the charging of a dead transformer from a live line, or a ground on the line, the surges or oscillating currents which follow may produce a rise of potential over double that of the operating potential of the line. This momen- tary rise of potential will subject the insulation of the primary windings to a severe stress, and may even punc- ture them, due to a concentration of potential in the layers of windings near the terminals. STATIC INTERRUPTER TRANSFORMER LIG'HTNING ARRESTER fTO 50000 > LINE 'TO 50000-VOn ES Fig. 116. WVWW\ .... . . ... ... * SERIES GAPS RESISTANCE VVWWWWWWWVMX/ / SHUNT RESISTANCE Diagram of Connections of Static Interrupter and Lightning Arrester As a protection against the severe static strains to which transformers are subjected a device known as a static inter- rupter is sometimes employed. The high-potential leads of transformers in some examples of high-tension practice are passed first through static inter- rupters, then through fused circuit breakers on one leg, and a plain knife switch on the other leg, connecting thence to three heavy bus wires overhead. Fig. 1 1 5 shows a static interrupter in its containing case. Fig. 116 shows TRANSFORMERS 253 the connection of a static interrupter to protect a trans- former from static strains. Connections of Transformers. The various possible ways of connecting transformers are : Single phase, two- phase, three-phase star or Y, three-phase delta, three-phase T, three-phase V, two-phase, three-phase, three-phase star and delta. Since transmission of electrical power over long distances is practically confined to two-phase and three-phase current, with either one or the other distributing it, only the two- and three-phase connections will here be considered. Fig. 117 shows a delta-connected primary and secondary. Fig. 117. Three-Phase Delta Connection 1,000 to 10,000 Volts. Maximum Strain to Ground 10,000 Volts The use of A or Y connections of transformers is de- pendent upon the peculiar conditions of operation of the transmission line, the use or non-use of grounded neutrals, and the considerations of economy in translating devices and line construction. If three-phase transmission is adopted, with three raising transformers connected in Y fashion, each of the trans- formers must be wound for -~, or approximately 58 per ^3 cent of the line voltage and for total line current. When connected in A each transformer must supply the 254 LONG-DISTANCE ELECTRIC POWER TRANSMISSION full-line pressure, and 58 per cent of the current per line wire. Hence the required number of turns in the winding of a F-connected transformer is only 58 per cent of that required by a A-connected one, with a cross-section of con- ductors proportionately greater. The increased number of turns with their additional quantity of insulation, and the extra care that needs to be carried out in the construction of numerous coils and layers, make a much more expensive transformer for A connection. The dimensions are also somewhat increased when A connection is selected. In general, Y connection possesses the advantage in both size and cost over A, when the transformers are of small output at high potential. But Y connection necessi- tates the employment of three transformers, and if an acci- dent happens to one, the others are also put out of service thereby. If A connected, the disabled transformer can be cut out and the other two made to furnish three-phase energy up to their maximum output, which is two thirds of the maximum capacity of the three. When the neutral or common point of junction of F-con- nected transformers is grounded the potential between coils and core cannot rise above 58 per cent of the line potential, and a possible reduction in insulation between core and coils is feasible. But economy in insulation gained by a grounded neutral is practicable only in the case of small transformers, since with given voltages the space occupied by insulation is relatively larger in a small trans- former. The main advantages offered by A and F connections may be thus summed up: (i) The use of F-connected transformers with grounded neutral is more economical, and is generally selected on this score. Without a grounded TRANSFORMERS 255 neutral its advantage is questionable. (2) If the amount of transmitted energy is large, and the system supplies a large number of widely scattered apparatus, the use of A- connected transformers is preferable, since it obviates the danger of possible rises of voltage from various operating causes. With F-connected transformers greater precau- tions must be adopted, such as, for instance, the use of automatic circuit breakers which will open all legs of the circuits at the same time ; else a serious liability of burn- outs on sound transformers will occur when one transformer is disabled. Many large transmission systems employ F-connected transformers in whole or in part, while others use A connec- tions, or a mixed A and F, and in most instances with equally satisfactory operation. Grounding of Transformer Secondaries. The ground- ing of the secondary or low-tension circuit of transformers possesses the following advantages : (1) If one leg of the circuit is properly grounded, the maximum difference of potential between any secondary lead and ground cannot exceed the voltage required by the apparatus in the secondary circuit, because in the event of a breakdown between primary and secondary the current has a path to ground through the grounded secondary lead. (2) If the secondary circuit is effectively grounded an accidental cross between primary and secondary circuits will result in the blowing of the primary fuse, or fuses of the transformer, and thus serve as a warning to the station attendants of the dangerous conditions of the distributing circuit. Thus, a grounded secondary will protect both life and property. The disadvantages of a grounded secondary are : (i) 256 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Grounding imposes severe strains upon transformer insula- tion in case of static disturbances to the line. Such strains are more pronounced during lightning storms and may cause a complete breakdown of the transformer. (2) Aerial lines grounded on poles are liable to dangers from high-tension crosses. (3) Grounded secondaries are liable to cause fires, especially when a service wire is accidentally grounded or becomes crossed with telegraph or telephone wires, which may be blown down by heavy wind storms. The fire hazard from grounded secondaries is, however, greatly minimized if proper precautions be taken to make an effective ground. The protection to both life and property and other advan- tageous features gained by grounded secondaries are far more important than the admitted objections ; and the best practice in cases where a mixed power and lighting load, or a lighting load only is supplied, is to ground the secondary at its middle or neutral point. Methods of Installation. The method of transformer installation adopted is mainly dependent upon the particu- lar operating conditions, the capacity of the plant, and the potential employed in transmission. American high-tension transformer practice has resolved itself to the following general methods of installation : (1) In the power house on the main floor, or on the gal- lery floor, or in separate masonry or concrete cells. (2) In a separate or transformer house. (3) In a sub-station " step-down" transformers. (4) In the basement of the power house. Practice in high-tension transmission as regards the proper place for locating raising transformers differs considerably, and in addition to the governing factors already mentioned is influenced in large measure by considerations of economy. TRANSFORMERS In cases where only moderate outputs of energy are developed, and when it becomes imperative for reasons of economy to utilize every available inch of floor space, the transforming apparatus should be located on the main floor of the generating station, adequate precautions being taken to thoroughly insulate it from the walls and supporting material. The disadvantage of this method lies principally in the element of danger involved in placing high-tension apparatus in close proximity to the moderate tension gener- ating apparatus. Current practice is now tending towards the installation of the step-up transformers in a building apart from the power house. The transformer house is constructed of either the same or of different material from the central station, and is either an annex of the main building, or is an entirely separate building in close proximity. When transformers are installed in a separate building, the low- pressure leads are usually conducted from the power house to the transformer house in open cable ways the wires being lead covered. In most instances this cable way is on a level with the top of the switchboard. Transformers Used in High-Tension Practice. Two general types of transformers are used in long-distance transmission practice, viz., core type and shell type. According to the method adopted for keeping the tern- perature down, transformers are classified as air-cooled, oil-cooled, water-cooled, and water-cooled, oil-insulated trans- formers. The selection of one or the other of these types is mainly governed by considerations of economy in operation and of floor space. The air-cooled, or air-blast transformer pos- sesses the advantage of being able to quickly and effec- 258 LONG-DISTANCE ELECTRIC POWER TRANSMISSION lively radiate its heat ; and hence all of its coils are kept at a nearly uniform temperature, thus avoiding all danger from charring of insulation and possible burn-outs. The air-cooled type is, however, more expensive to maintain than the oil-cooled kind, except in cases where a bank of trans- formers is supplied by one blower. The air-blast type is principally used on circuits under three kilovolts. The oil- cooled type is more economical of operation than any of the several kinds, since the oil with which it is filled for insula- tion purposes keeps the windings from overheating. On the other hand the oil-cooled type does not radiate its heat Very rapidly, owing to the poor heat-conducting properties of oil, and hence for a given output it must be of larger dimensions than the air-cooled type. The water-cooled, oil-insulated type of transformer is com- ing into extensive use in hydro-electric plants, on account of the easy and effective reduction of temperature which is possible with this form of cooling. The water is kept in constant circulation by means of a pump, the casing of the transformer being provided with a series of pipes run- ning through the coils, or else with a water-jacket between the windings and the outside casing. Since in most in- stances transformers used in high-tension transmission are of sufficient size to permit of the laying of water-pipes in close proximity to the coils, this becomes a highly efficient method of keeping the temperature down to safe limits. In plants where the level of the forebay is about six feet below that of the transformers, recourse is sometimes made to a siphon method of maintaining circulation, instead of pumping it through the pipes. In this method of water- cooling, duplicate main intake pipes equipped with strainers are brought through the canal wall below the low-water TRANSFORMERS 259 level. The transformer coils are bridged between the low- water level and other pipes which lead several feet down to the tail-race. The intake and discharge pipes are con- nected by a valve, which permits water to flow directly through the discharge-pipe vents, and so creates a vacuum. When this valve is closed water is at once siphoned through the transformers. Thiis a constant supply of water can be maintained through the coils, and with no expense other than the initial cost of installing the siphoning apparatus. . A common vacuum gauge is generally used to indicate the condition of the vacuum, the discharge pipe of each trans- former being fitted with a small brass pipe about 12 inches long, and -| inches in diameter at one end and ij inches in diameter at the other end. A single mercury U tube, connected between the central small diameter pipe and its upper end, affords an accurate indication of the water circu- lating through the transformer. The quantity of water required to keep the temperature of transformers down to reasonable limits is about 0.4 gallon per minute for a 75 kw. size, about one gallon per minute for a 500 kw. size, and approximately 1 . 5 gallons per minute for a i ,000 kw. transformer. All types of artificially cooled transformers are open to the objection that if the blowing or pumping apparatus used to cool them should become disabled the transformers would also be put out of commission, or be liable to burn out from overheating. (3) Installation of transformers in sub-stations. When the transmission voltage must be reduced to a value suitable for the operation of motors, converters, lights, or other apparatus along the line or at the main distributing point of the circuit, the step-down transformers are usually in- 260 LONG-DISTANCE ELECTRIC POWER TRANSMISSION stalled in sub-stations, located as near as possible to the apparatus to be supplied. Figo H3. A a, 750 Kilowatt Air-Ulasi Transformer Transformers installed in sub-stations are generally "banked" in parallel, and connected so that when the load TRANSFORMERS 26l is light only one transformer is connected in circuit, the primaries of the others being open circuited. As the load increases the other transformers are gradually cut in ; in Fig. 119. Construction of Air-Blast Transformer this way the core losses are kept in fair proportion to the useful energy. The installation of high-tension transformers in buildings other than those that are intended for electrical apparatus only is now prohibited by the underwriters' rules. 262 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Fig. 118 shows a 2,750 kilowatt Westinghouse air-blast transformer of the shell type, and Fig. 119 illustrates the construction of this transformer, showing the ventilating ducts in the core. The windings of both primary and secondary are divided into a number of flat coils, cotton Pr Fig. 120. An 800 Kilowatt, Oil-Insulated, Water-Cooled Transformer covered. The primary is made up of flat copper strips consisting of one turn per layer. The coils are each separately insulated, and the space between each is filled TRANSFORMERS Fig. iai. A 50,000 Volt Water-Cooled Transformer with heavy insulation. Each layer of coils is separated from the other by a strip of a special, high-resistance insulating material, while the completely assembled coil is incased in a 264 LONG-DISTANCE ELECTRIC POWER TRANSMISSION built-up insulation of high dielectric strength and moisture- proof character. The secondary is wound in a similar manner, of rectangular cross-section copper conductors. In cases where large currents are taken from the secondary, the winding consists of several conductors in parallel. Fig. 1 20 shows an 800 kw. Stanley, oil-insulated, water- cooled transformer of the shell type, and illustrates the method of winding employed. The one here shown is wound to give a secondary E.M.F. of 34,675 volts. The primary is divided into sixteen coils and the secondary into eight coils. Each primary coil is made up of 73.5 turns of copper strip, one turn per layer, with three layers in parallel. Two of the primary coils are placed in position with a sheet of micanite between them on the core, and the groups alternate or are sandwiched in between the secondary coils a secondary between two primaries. The object of this mode of construction is to permit of ample insulation, and also to oblige all of the magnetic flux to interlink with all of the coils. Fig. 121 shows a 950 kilowatt, 50,000 volt, Westinghouse, oil-insulated, water-cooled transformer , with the casing removed. The method of winding is essentially the same as that of the air-blast type, the spread-coil arrangement being characteristic of both types. The coils are spread apart at the ends outside the core to allow the oil to surround each coil. TRANSFORMERS 265 BIBLIOGRAPHY Alternating Current Machines. Sheldon and Mason. D. Van Nos- trand Co. New York. 1903. The Transformer. Bedell. MacMillan Co. New York. 1897. The Alternating Current Transformer. Baum. McGraw Publish- ing Co. New York. 1903. High Tension Transformers. Farley. Central Station, New York. August, 1903. The Relative Fire Risk of Oil and Air-Blast Transformers. Rice. Transactions of American Institute of Electrical Engineers, Vol. 21, p. 5. Terminals and Bushings for High Pressure Transformers. Moody. Transactions of American Institute of Electrical Engineers, Vol. 21, p. 15. Static Strains in High Tension Circuits and the Protection of Appa- ratus. Thomas. Transactions of American Institute of Electrical En- gineers, Vol. 19, p. 213. Reactance Drop and Reactance Factor of Transformers. Kennelly. Electrical World and Engineer, New York, July 20, 1901, p. 92. OF THF I UNIVERSITY / !K'\^X CHAPTER VIII MOTORS SYNCHRONOUS MOTORS Relation Between Generator and Motor Speed, Torque, and Output. IF an excited single-phase or polyphase alternator be brought up to normal speed and then connected to an alter- nating-current circuit of the same periodicity and E M.F. it will run as a motor, and its speed in revolutions per second will equal the quotient of the periodicity by the number of pairs of poles. When operating under these con- ditions the motor is said to be working in synchronism, or its rotor is revolving at synchronous speed. This synchro- nous speed is not literally the speed of the generator which is supplying the motor with energy, but is a speed which if multiplied by the number of poles produces a value equal to the alternations of the generator. Thus a motor with half the number of poles as the generator will have double its speed in revolutions per minute, and vice versa. The speed of a synchronous motor is independent of the pressure, and can be varied by varying the speed of the generator. Hence, closeness of regulation of the prime mover supplying synchronous motors is of prime impor- tance, since the armature of tjie motor possesses a fly-wheel property of sufficient magnitude to consume a relatively large amount of energy without greatly varying its speed. 266 MOTORS 267 Moreover, there will be an interchange of currents between the motor and the generator which will cause troublesome regulation, and also diminish the motor output. The behavior of a synchronous motor on starting is nearly similar to that of the induction motor. Its torque at start- ing may range from zero to 25 or 35 per cent of the full- load running torque, depending mainly on its design. The torque of the synchronous motor is a function of the ter- minal E.M.F. and is limited by it chiefly. The limit to the output of a synchronous motor is the heating of the machine. Polyphase synchronous motors of good design can be made to carry from three to five times full load. With further increase of load they drop out of synchronism, and can only be brought into synchro- nism again by removal of the load. Methods of Starting Synchronous Motors. The starting torque of a synchronous motor being too low to bring it up to speed under load, some extraneous source of power is necessary to perform this task, the auxiliary device being disconnected as soon as synchronism is attained. For this purpose synchronous motors are generally pro- vided with induction motors for starting them, the capacity of the auxiliary being about one-tenth that of the synchro- nous motor. The small motor is usually geared to the shaft of the main motor, as shown in Fig. 122, which is an illustration of a 500 horse-power motor. In connecting a synchronous motor to the mains, it is essential that the motor should not only be running at synchronous speed, but also that the phase difference be- tween the motor E.M.F. and the impressed voltage should be 1 80 degrees. The determination of these points is accomplished by means of a synchronizer. 268 LONG-DISTANCE ELECTRIC POWER TRANSMISSION When synchronous motors are brought up to speed with- out the aid of an auxiliary device, the method of starting is generally as follows : The field circuit is first opened and the armature connected either directly to the source of supply, or to a starting compensator which reduces the supply E.M.F. The armature windings produce a mag- Fig. 122. A Synchronous Motor with Auxiliary Starting Motor netizing effect which sets up enough flux in the poles to furnish a low starting torque. The exciter current is then switched on to the field and the motor gradually brought up to synchronism. The starting current is limited only by the impedance of the armature windings, and may have a value ranging from 150 per cent of full-load current to two or three times nor- MOTORS 269 mal operating current. The external load is subsequently thrown on the motor through the medium of a friction clutch or equivalent appliances which cause the load to be gradually applied to the motor after it has attained synchronous speed. Fig. 123. Synchronous Motor Belted to Shafting Fig. 123 illustrates a synchronous motor belted to a line of shafting on which is mounted a friction coupling. The chief objection to starting the load by means of friction clutches lies in the danger of a break-down in the field-coil insulation, due to the high pressure generated in the field by the varying flux. To obviate this each field 2/0 LONG-DISTANCE ELECTRIC POWER TRANSMISSION coil is provided with a break-up switch to open circuit the coils on starting. The taps or leads from each coil are led to the switch blades, which are mounted on an easily accessible part of the motor frame. When the motor falls into step with the generator, the switch is closed, which puts the field in series and also throws it in circuit with the exciter. The Use of Synchronous Motors as Voltage Regulators on Long-Distance Circuits. On long-distance circuits containing a number of pieces of inductive apparatus in circuit, not only is the power factor of the system appreci- ably lowered thereby, but objectionable lagging currents are produced in certain parts of the system. The great flexi- bility of the synchronous motor is taken advantage of in this class of work to overcome the bad effects caused by apparatus of inductive character. By increasing the ex- citation of a synchronous motor the power factor can be made equal to unity for any load. Likewise an increase of exciting current will give a proportional increase in press- ure produced by the motor, so that by a proper adjust- ment of the excitation, the E.M.F. generated by the motor can be increased considerably above the voltage impressed upon its terminals. When the operating conditions are exactly opposite, i.e., when the field excitation is low, the E.M.F. generated is lower than the impressed volts. Under the first set of conditions, the current will be a leading one, while under the second it will lag behind the impressed volts. Over-exciting a synchronous motor will cause it to behave like a big condenser ; and so operated it will provide for both energy and wattless components of current up to its rated output in amperes. The amount of current absorbed by a synchronous motor MOTORS 271 depends upon its field excitation, there being one value of exciting current for which the current in the armature is a minimum. These properties of the synchronous motor make it a valuable piece of apparatus for regulative purposes, outside of its motor functions, since by producing a phase dis- 2000 1000 5 100 10 200 15 300 TION AND AIR LC ATJION 20 25 400 500 30 EXCITATION 600 KW.fpW.FR I, ABSORBED Fig. 124. Curves of 525 H.P. Three-Phase Synchronous Motor placement between its current and voltage, the reactance caused by the inductance of the line and inductive appara- tus can be wholly or partly neutralized. Hence, by prop- erly distributing such motors along a circuit a low power factor caused by induction motors, or apparatus of like nature, can be corrected to any desirable extent. Another very valuable feature of the synchronous motor 272 LONG-DISTANCE ELECTRIC POWER TRANSMISSION is that in an emergency, such as a failure in the source of current supply, the motor can be made to perform the function of a generator by driving it from some extraneous source of power, and thus become the generator at the sub-stations, supplying energy to induction motors, lamps, or other dead loads in circuit. In many stations this con- venient property of the machine is taken advantage of to such an extent that during day hours synchronous motors discharge their normal functions, while at night, or when- ever the peak of the load occurs, the motors are operated as generators. Troubles of Synchronous Motors. A synchronous motor, both electrically and mechanically, is almost similar to an alternator, and requires the same auxiliary apparatus, such as an exciter and indicating instruments. It is also gen- erally provided with a starting motor or other device. Hence, like the generator, any failure or breakdown of the exciting machine will put the motor out of operation. If the exciting circuit is suddenly ruptured the high E.M.F. induced by the armature may result in a "field discharge," which is liable to puncture the insulation of the coils. Being provided with moving contacts collector rings, commutator, and brushes the usual troubles from this source, such as destructive sparking and short circuiting, are liable to occur. On starting up, trouble or injury is liable to result from improper or unsystematic performance of the various oper- ations. Thus, synchronizing may be attempted before the motor is in exact phase, or when it is below normal speed. Should the load of a synchronous motor (which may possess a large inertia) be thrown on too suddenly, the MOTORS 2/3 motor may not possess a large enough torque and fly-wheel capacity to keep its speed, and will be brought to a standstill. If the motor is stopped by a failure of the source of current supply, it will not start of its own accord when the current is restored, but requires to be put in operation by the starting motor. The electrical connection between generator and motor being rigid and unalterable, the operating current of the mctor depends upon the steadiness or uniformity of the frequency of the supply current, or in other words, upon the constancy or uniformity of the generator speed and other synchronous motors in circuit. The motors endeavor to keep exactly in step with the speed of the supplying generator. Any variation of the latter tends to cause a corresponding variation of motor speed. This sets up a pulsation or vibration on both sides of a mean position which may increase to such an extent as to throw all synchronous apparatus in the circuit out of step. "Pumping" or "hunting" is also liable to occur when the mechanical load on the motor is suddenly changed to a valfee which exceeds the limiting torque and the load has considerable inertia. A synchronous motor is also liable to cause trouble or annoyance by coming to a standstill when the generator quickly speeds up, due to the inability of the motor to increase its speed suddenly without exceeding its maximum torque. In the event of a short circuit in the transmission system, a synchronous motor may turn generator and thus greatly augment the intensity of the short circuit by in- creasing the line current. 274 LONG-DISTANCE ELECTRIC POWER TRANSMISSION THE INDUCTION MOTOR An induction motor closely resembles in its performance a direct-current shunt-wound motor, the main points of dif- ference being that the operating current of the direct-cur- rent motor is conducted into the armature by means of brushes, while the operating current of the induction motor is an induced current, and that the induction motor has no physical field magnet poles. The essential elements of the motor are a primary or stator and a secondary or rotor. The primary winding in most cases is connected to the source of current supply, and in addition to carrying the exciting current it performs the office of inducing the working current in the secondary conductors. Rotation of the secondary member may be regarded as being due to a rapidly varying magnetic field which the revolving member follows. This shifting magnetic field is the resultant of two or more alternating magnetic fields differing in phase. The rotor of an induction motor may be of the squirrel- cage or short-circuited type, or the variable resistance or polar type. Rotors of the squirrel-cage type are generally " wound " with copper bars embedded in slots in a laminated steel core. The windings or inductors, which are of low resist- ance, are all connected in parallel to short-circuited rings placed at each end of the rotor. Since the currents induced in the inductors are obliged to flow parallel with the axis of the motor, the reaction set up by them against the field rlux is in a direction to be most efficient in causing rotation. The short-circuited or squirrel-cage type of motor of small inductance possesses the following features : MOTORS 275 (i) Break-down point of high value; (2) moderately large magnetizing current ; (3) fairly large current for starting and for starting torque ; (4) moderate percentage drop in speed; (5) high power factor ; (6) high efficiency at full and overloads. In induction motors of the variable resistance or polar type the rotor is wound with a definite series of coil wind- ings, which correspond to the polar windings of the stator. The characteristic features of the polar or variable resist- ance type of induction motor are: (i) Moderate break- down point ; (2) small magnetizing current ; (3) low percentage drop in speed ; (4) torque proportional to the starting and running current ; (5) high power factor ; (6) high efficiency at intermediate and full loads. The squirrel-cage type of motor finds its most useful field of application on power circuits where the conditions of oper- ation call for low starting effort and steady full load. It is also particularly adapted to cases where the motor is .required to run overloaded, or on circuits of fluctuating voltage. The particular sphere of usefulness to which the variable resistance type of motor is adapted is on circuits where close regulation is imperative, such as combined power and lighting service, and under conditions where the motors are usually run underloaded. Operation of Induction Motors. Calling the speed at which the magnetic field rotates n^ and the speed of the rotor n 2 , the relative speed between any given inductor on the revolving element and the rotating field will be n^ n^ The ratio of this speed to that of the revolving field is called the slip ; hence the slip is 2/6 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The value of the slip is usually given as a certain per cent of the synchronous speed, ;/ 1% Calling the flux emanating from any given north pole of the primary <1> maxwells, then any single secondary inductor will have an effective E.M.F. induced in it equal to 1. 1 1 /<;/! io~ 8 , in which / represents the number of poles. The E.M.F. so induced has a periodicity which differs from the periodicity of the impressed E.M.F., being s times the frequency of the latter. If the secondary rotated in synchronism with the primary the secondary frequency would be zero; if the secondary remained stationary the frequency of its current would equal that of the current in the primary. In commercial conditions of operation the periodicity of the E.M.F. in the secondary winding is of low value, since the slip of most motors is of small value (from 2 to 15 per cent). In a squirrel-cage secondary the determination of current in a single inductor presents considerable difficulty, since the E.M.F.'s in all the inductors are of different magnitude at any given instant. It is also possible that in some of the windings the current and E.M.F. may be flowing in oppo- site directions. When an induction motor is running without load, the speed of the revolving member is very nearly equal to that of the rotating field, being equal to n^(i s). Hence, the E.M.F. generated is only sufficient to set up a current in the secondary windings large enough to make the elec- trical power equal to the losses in the iron and copper, and those due to windage and friction. A very feeble torque is produced by the magnetic pull of this current. MOTORS 277 On applying a mechanical load to the rotor pulley, a drop in speed occurs due to an increase in the slip. With in- crease of load the speed of the rotor falls further away from synchronism, while the current and E.M.F. therein increase in proportion, and the rotor receives additional increments of energy corresponding to the additions in load. The force exerted by the increased current exerts a torque which is in proportion to the increase of energy that is, up to a critical point. Under varying loads the magnetism of the rotating field which cuts the rotor inductors varies also ; and with in- crease of slip an increasing amount of primary flux passes between primary and secondary windings without cutting them. The tendency of the increased secondary currents to set up a cross-magnetizing action causes the increase in magnetic leakage ; the effect of which is not only to re- duce the torque for an equivalent secondary current, but also requires an increased slip to give the same current. The curves in Fig. 125 exhibit the relation between torque and slip for different secondary resistances. The solid lines represent torque, and the broken lines, current. As the curves show, the greatest torque which a motor can exert is the same for various secondary resistances. But when giving this maximum torque, the rotor speed differs with the difference of resistance in the rotor. This characteristic of the induction motor is employed to keep down the excessive starting current which follows when a motor is connected to its source of supply. In Fig. 126 are shown the relations between the torque, speed, power factor, current, and efficiency of a modern induction motor working under average conditions of prac- tice. With an increase of impressed E.M.F., there is a 2/8 LONG-DISTANCE ELECTRIC POWER TRANSMISSION corresponding increase of magnetic flux interlinked with the secondary, and hence a proportional increase of secon- dary current. The torque exerted by a motor is proportional to the product of the magnetic flux and the ampere-turns of the secondary ; hence, the torque of an induction motor varies 860,000- - 80 40 30 20 10 SYNCHRONISM Fig. 125. Relation Between Torque and Slip in Induction Motors as the square of the impressed voltage. From this it fol- lows that the output of an induction motor varies when it is used on circuits of varying voltages. Speed Regulation of Induction Motors. Variations in the speed of an induction motor can be accomplished either by varying the pressure impressed upon the primary, or by varying the resistance in the rotor, or by changing the MOTORS 279 number of field-polar planes by commutation of the stator windings. The first two methods depend upon the principle that the torque of the motor is proportional to the product of stator flux and rotor current ; hence for a fixed torque the product is a constant. If the voltage impressed upon the ROTOR STATOR AMP. AMP. 1500 150 cos 1000 100 1.00 500 50 100 200 300 400 500 600 700 H. P. Fig. 126. Relations Between Torque, Speed, Power Factor, Current, and Efficiency stator is lowered a reduction of stator flux and also of rotor current ensues. Hence, the speed of the motor de- creases until sufficient E.M.F. is generated to give rise to a current which, when combined with the diminished flux, will afford the original torque. The first method of speed control changing the im- pressed volts at the motor terminals requires the use of 28O LONG-DISTANCE ELECTRIC POWER TRANSMISSION a compensator or external reactance, and the motor should possess high constant rotor resistance. The compensator and its controller are generally separate from the motor. The former is fitted with the requisite number of taps from which leads are conducted to the controller. By manipulation of the controller handle, a gradual variation of the impressed voltage is effected, which causes a cor- responding variation in the speed. Speed variation by altering the resistance is effected by inserting resistance in the rotor circuit, the resistance being varied in graduated steps. This method requires the use of an external rheostat or controller with sufficient resistance to dissipate a goodly amount of energy. Fig. 127 is a diagrammatic representation of the connections of the controlling rheostat of a three-phase motor. When the secondary element revolves, collecting rings are neces- sary to connect the windings electrically with the exter- nal resistance. An increase of rotor resistance lessens the rotor current and necessitates a drop in speed to bring its value up to normal, hence the efficiency of operation is lowered by this method. A reduction in impressed voltage results in a reduction of motor capacity or output, since the output of an induc- tion motor varies as the square of the impressed voltage. Alteration in the speed of an induction motor by chang- ing the number of polar planes is extremely complicated, and requires a complex switching apparatus in addition to a compensator. The variations of speed are also limited to full, one half, and one quarter speeds. This method is occasionally used under conditions which demand half- speed and half-load torque. Efficiency and Power Factor of Induction Motors. - Since the losses in an induction motor are of a similar MOTORS 28l kind to those in a generator, i.e., core, copper, and friction losses, the efficiency can be considerably increased by the generous use of both iron and copper. Efficiencies of modern induction motors range from 70 to 94 per cent, depending upon their size and the conditions of operation. Fig. 137. Connections of Controlling Rheostat of Three-Phase Induction Motor Motors for factory and shop work are frequently de- signed to give their maximum efficiency at about three quarters load. This is due to the fact that such motors are only required to give full load at infrequent intervals, the average working conditions calling for about 20 to 30 per cent less load than their rated output. The power factor of an induction motor is the ratio of 2$2 LONG-DISTANCE ELECTRIC POWER TRANSMISSION the total current received to the energy current, or the current which supplies its losses and does the work at the shaft. The apparent efficiency of an induction motor is the product of the power factor and the actual efficiency. The power factor of modern induction motors at full load ranges from 75 to 92.5 per cent, depending upon their capacity and design. Since a low power factor is caused by magnetic leakage, it is feasible to improve the power factor by making the air-gap as short as is consistent with mechanical clearance ; also by reducing magnetic density in the iron, which reduces the magnetizing current. But applying these methods and maintaining high efficiency greatly increases the cost of the motor. Faults of Induction Motors. The salient objections to the induction motor are : (1) The starting current at full load (with reasonable efficiency) is several times the full-load current. This fault is characteristic, however, only of the squirrel-cage motor. (2) The current consumed in giving full-load starting torque may be from four to six times full-load current. (3) High starting torque with moderate starting cur- rent is obtained at the expense of considerable, and not infrequently cumbersome auxiliary apparatus, such as collector rings, brushes, and rheostat. (4) Low power factor. (5) Inflexibility of speed control. Although in many instances the majority of these ob- jections to the induction motor are valid and tenable, in the majority of cases the faults are due either to the adop- tion of the wrong motor for the conditions desired, or else the use of motors of bad design. In regard to the first fault, let us consider a comparison between the variable resistance in the secondary induction MOTORS 283 motor and the direct-current shunt motor, started by an external rheostat in its armature circuit. There is practi- cally no difference between the two as regards the mode of starting, the purpose of the rheostat in both cases being to prevent the excessive rush of current which always follows when any motor is connected to its supply circuit. It is true, however, that the drop in voltage at the ter- minals of other apparatus (on account of this large starting current), when an induction motor is started up, is some- what greater than the drop which follows the connection of a direct-current motor to its source of supply. In many instances such trouble is brought about by a low power factor, or by faulty design. Regarding the starting torque of the induction motor, it may be said in general that if abnormal means are adopted to secure very high starting torque, the limit will be reached much earlier with the direct-current shunt-wound motor than with the induction motor of the type first considered. Just as the direct -current motor may be started, stopped, reversed, or run at high, low, or intermediate speeds, by means of a rheostat, and with small torque or large torque, so likewise may the induction motor be operated under identically the same conditions. This is equally true of an induction motor which is not provided with slip rings, but has its speed controlled by varying the voltage impressed upon it. In certain kinds of power service, it is highly essential that a motor should act as a constant-speed machine when running at any one of a large number of widely varying speeds. In other words, a varying torque should not appreciably affect the speed. Such a requirement cannot be met by any kind of motor under purely rheostatic control, under the cited con- 284 LONG-DISTANCE ELECTRIC POWER TRANSMISSION ditions, since the torque in connection with the resistance entirely determines the speed of operation, an increase of either lowering it, and a decrease of either raising it. Induction motors of recent manufacture have given a power factor when starting with a given torque of prac- tically the same as when running at that torque; and as the full-load power factor of a well-designed motor of this type may be as high as 90 per cent, the power factor when carrying a load requiring full-load torque may be as high as 90 per cent. With" an induction motor of the squirrel-cage type there is considerable liability of annoying disturbances if the motor is started under load, or run below normal speed, due to the low power factor of this type of motor. At full speed, however, the power factor may be as high as, or higher than, the power factor of an induction motor under rheo- static control. Although the starting up of squirrel-cage induction motors gives rise to more or less line disturbances, their somewhat higher efficiency, and the fact that circumstances often arise when the motor can be started under light load, render the objectionable feature nugatory. The efficiency of an induction motor is not entirely de- pendent upon the power factor of the system, it being quite feasible to design a motor for a low power factor and a high efficiency or vice versa. At medium and light loads the efficiency of the induction motor is slightly in excess of that of the direct-current motor. At such loads, however, the current consumption of the induction motor is slightly greater than that of a direct-current motor of equal output. At full load and equivalent currents consumed at full load, the advantage is held by the direct-current machine. MOTORS 28 S Types of American Induction Motors. Fig. 1 28 shows the primary of a 500 horse-power Westinghouse Type C, Fig. 128. Stator of a 500 H. P. Induction Motor squirrel-cage induction motor designed for constant speed. Fig. 129 shows a completely assembled 150 horse-power Westinghouse motor. The frame of the motor is made 286 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Fig. 129. A 150 H. P. Induction Motor MOTORS 287 of cast iron divided in a horizontal plane. The primary is built up of laminated sheet steel and constitutes a hol- low cylinder with internal slots in which the winding is laid. The laminated rings of which the cylinder con- sists are of segmental design and are dovetailed. These segments fit into corresponding slots in a hollow shell made of cast iron, which is rigidly held in the frame of the motor. The winding consists of copper strap made into coils and bent into the proper form. The terminal blocks through which current is supplied to the motor are located on the side of the frame. The rotor is built up of lami- nated steel discs, mounted on a spider. The rotor induc- tors consist of rectangular copper bars embedded in partially closed slots, all conductors being short circuited. Fig. 130 shows a General Electric squirrel-cage, con- stant-speed motor of 750 horse-power capacity. The Repulsion Motor. The repulsion type of alternat- ing-current motor invented by Professor Elihu Thomson, consists virtually of a direct-current armature revolving in an induction motor field structure. Like an ordinary induction motor there is no electrical connection between primary and secondary. The primary may be wound for a high line potential, while the secondary pressure may be of any value suitable for satisfactory commutation, since it is short circuited on itself through the brushes. The behavior of the repulsion motor is nearly identical with that of the direct-current series motor, i.e., it shows maximum torque at starting, increase of torque with in- crease of speed, with nearly constant efficiency throughout wide variations of speed. Load and impressed voltage limit the maximum speed 288 LONG-DISTANCE ELECTRIC POWER TRANSMISSION of the motor, the maximum speed, however, bearing no relation to the synchronous speed. The motor circuits have a comparatively high reactance, so that the power Fig. 130. A General Electric 750 H.P. Induction Motor factor is low on starting ; but with the repulsion motor a low power factor is not associated with a small torque, the maximum torque occurring simultaneously with the smallest power factor. The power factor increases with increase of load, and MOTORS 289 attains a fairly large value at one third synchronous speed. Power factors of nearly 90 per cent have been obtained throughout wide variations of speed. PERC INT REV. ER IV IN. -90- . ^""""S , A ^ ^== EFF ICIEN 3Y ^ 1 * ~- Sr *<* \ \ ^^ ^ -70- - -700- \ \ FOOT -LB3. -7000 \ \ -60- 600- ' \ \ ym \ / \ ^ f 5000 I */ ? 400 K ^ * 4000- CALCULATED CURVES OF 175-h.p REPULSION MOTOR, AT 1500 VOLTS. \ / / ^x 3000 / \ s 200 IX s \ s 2000- x x \ 100- X ' ^ "too^ - ^ ! ) 4 f AMPER 80 ESAT 1 lo 1B VOLT^ i 1 1! Fig. 131. The high power of the repulsion motor is due to the leading current, which is generated by the conductors of the secondary cutting the primary ftux. This leading cur- 2QO LONG-DISTANCE ELECTRIC POWER TRANSMISSION rent is, however, not of sufficient magnitude at practical speeds to entirely compensate for idle currents, but by the addition of an auxiliary or second circuit a compensated type of motor is produced which may be made to give unity power factor at any load. The efficiency of the repulsion motor ranges from 80 to 85 per cent (including losses in couplings, or gearing), for motors of from 50 to 200 horse-power. Fig. 131 shows the calculated characteristics of a 175 horse-power single-phase 1,500 volt repulsion motor, pre- sented by Mr. W. I. Slichter in a paper before the American Institute of Electrical Engineers. From these curves it can be readily seen " that the repulsion motor is well suited for efficient operation at light loads, and pos- sesses fairly good constants at low speeds." BIBLIOGRAPHY Elements of Electrical Engineering. Steinmetz. McGraw Publishing Company. New York. 1902. Alternating Currents and Alternating Current Machinery. Jackson & Jackson. Macmillan Co. New York. 1901. The Induction Motor. De La Tour-Mailloux. McGraw Publishing Company. New York. 1903. Notes on the Theory of the Synchronous Motor. Steinmetz. Trans- actions American Institute Electrical Engineers, Vol. 19, p. 781. The Repulsion Motor. Steinmetz. Transactions American Institute Electrical Engineers, Vol. 21, p. 75. Speed-Torque Characteristics of the Single-Phase Repulsion Motor. Slichter. Transactions American Institute Electrical Engineers, Vol. 24, p. 6. CHAPTER IX CONVERTERS A CONVERTER is a transforming apparatus consisting of one, field winding and one armature, the latter being con- nected to a direct-current commutator at one end and alternating-current slip rings at the other end. When the machine is designed to transform alternating into direct current it is termed a synchronous converter. When it is designed to transform direct current into alter- nating current the machine is termed an inverted converter^ In high-tension electric transmission the converter finds its chief use in transforming alternating into direct cur- rent suitable for operating railway motors, factory motors, etc. If the brushes which rest on the slip rings be supplied with alternating current of the proper pressure, the armature will rotate like the armature of a synchronous motor, that is, in synchronism with the E.M.F. impressed on the cir- cuit. When rotating in this manner, direct current may be taken from the brushes on the commutator. The power which is delivered to the slip rings of a con- verter must be sufficient to supply the direct-current circuit, and also overcome the losses due to resistance, inductance, hysteresis, friction, windage and eddy currents. The armature winding of a converter is of the closed- coil type, and similar to that of a direct-current dynamo, with the taps leading to the slip rings, 291 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Each slip ring is connected to the armature winding by as many taps as there are pairs of poles on the field magnet, these taps being equidistant from each other. A converter may be fitted with any desirable number of rings. When fitted with ;/ rings the taps are distant from each other by - th of the distance between the centers of n two successive north poles from each other. Fig. 132. Section of Periphery of Commutator of Converter The E.M.F. at the several brushes of a converter may be found in the following manner: Let E d = pressure between successive direct-current brushes. E n = effective pressure between successive rings of an -ring converter. e m = maximum E.M.F. in volts induced in any given arma- ture conductor. (This E.M.F. is generated when the conductor is under the center of a pole.) c = the number of armature conductors in a unit angle (electrical) of its periphery. CONVERTERS 293 The electrical angle subtended by the centers of two suc- cessive poles of like polarity is equal to 2?r. In the dia- grammatical representation of a section of the periphery of the commutator, the pressure set up in a given conductor is considered as varying as the cosine of the angle of its position with respect to a point directly under the center of a given pole, the value of the angle being taken in electrical degrees. Thus at a given angle a in the diagram, Fig. 132, the E.M.F. produced in a conductor is e m cos a volts. Consider an elemental section of the armature. In each section there are cda conductors, in each of which is the above E.M.F. If these conductors are connected in series the pressure which is generated is equal to e m c cos a da volts. If the E.M.F. between any two successive direct-cur- rent brushes be derived by integration and be written equal to this value E d , the magnitude of e m can be determined. r ts Thus, E d = I e m c cos ado. = 2 e m c J The electrical angular distance between the taps of two 27T successive rings 01 an n-nng converter is equal to -- Hence the maximum E.M.F. is generated in the windings between the two taps when the taps are spaced as equal angular distances from the center of a pole. The value of this E.M.F. is equal to I i V2 E n = I J e m c cos eu/a = 2 t m c sn - TT 2 294 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Hence the effective pressure between successive rings is ,5.-^ sin*. V2 To ascertain the maximum value of the alternating current supplied to a converter, assume that after deducting the losses therein the power intake in alternating current equals the direct -current output. Disregard the losses for the moment, and let E n represent the voltage and / represent the alternating current in the armature windings between successive slip rings. Then for the sections of the armature periphery covered by each pair of poles, E d l d = nEJ n where E d represents the quantity assigned to it above, and I d is the current between successive direct-current brushes. Hence, the maximum value of the alternating current is TT n sin - n Ratios of Conversion and Capacity. The effective pressure between the successive rings of a converter is, as has been shown, equal to If the numerical values representing converters with different numbers of rings be substituted in the equation, it is found that the coefficients by which the pressure be, tween direct-current brushes must be multiplied in order CONVERTERS 295 to ascertain the effective pressure between successive rings is as follows : For two-ring converters . . . 0.707 For three-ring converters . . . 0.612 For four-ring converters . . . 0.500 For six-ring converters . . . 0.354 Owing to the non-sinusoidal distribution of flux in the air-gap of commercial converters, however, these coefficients are only approximate. Converters of the synchronous type with closed-coil windings on the armature have the following relative capacities : as a CAPACITY Direct-current generator . . . 100 Single-phase converter ... 85 Three-phase converter . . . 134 Four-phase converter . . . 164 Six-phase converter .... 196 Twelve-phase converter . . . 227 Modern converters can stand overloads which are only limited by satisfactory commutation. Methods of Starting Converters. Since the synchronous converter is a synchronous motor it usually requires some device to bring it up to speed. The three most impor- tant methods used in practice to start up a converter are : (1) The machine may be directly connected to the supply circuit through auto-transformers or impedance coils. (2) By means of a small induction motor. (3) Starting the converter as a shunt-wound motor from the direct- current end. 296 LONG-DISTANCE ELECTRIC POWER TRANSMISSION (1) If an impedance coil is used it is placed between the line and the armature of the converter, its function be- ing to keep down the pressure and thus obviate the exces- sive rush of current and consequent line disturbances which would otherwise occur were the rated voltage im- pressed directly upon the armature when at a standstill. In some instances taps are led out from the windings and the coil is gradually cut out as the armature speeds up, so that when synchronism is attained the coil is completely short circuited. This method of starting may be more or less objectionable, owing to the reaction which follows upon the transmission line. Owing to the fact that the starting current is considerably greater than the full-load running current, and the power factor low, there is but small energy consumption ; hence the line disturbances may be undesirable. If an auto-transformer is used for starting instead of the impedance coil, it is connected in parallel with the line in- stead of in series with it. A number of taps are led out from various parts of the auto-transformer winding to a central point, so that the impressed voltage on the con- verter can be regulated as desired. By means of this con- troller the pressure is gradually raised as the machine comes up to speed. When synchronous speed is attained the rated voltage is impressed on the machine's terminals. Starting a converter through an auto-transformer generally causes less disturbance on the line than the use of an im- pedance coil. This is due to the fact that the auto-trans- former limits the starting current on the line in proportion as the impressed voltage is less than that on the line. (2) Starting a converter by means of an induction motor In this method of starting, a small induction motor with a CONVERTERS synchronous speed higher than that of the converter is mounted on one end of the converter's shaft. To start the converter the motor is connected across the secondaries of the transformer. The converter then gradually comes up to speed, after which the induction motor is disconnected and rims normally without load. (3) Starting the converter as a direct-current shunt motor from the direct-current end is by far the most satis- factory method, as no line disturbances occur. In this case a starting resistance or external rheostat must be provided. The machine is gradually brought up slightly above syn- chronous speed by cutting out resistance, exactly as a direct-current shunt motor is started. The starting motor is then cut out and its field circuit opened ; after which the converter may be connected to the alternating-current mains, the armature quickly falling into synchronism. In cases where several converters are installed in a sub-station, a small motor-generator is sometimes employed to obtain direct current for starting. The apparent power of a converter at starting is approx- imately that which is indicated by the volt-ampere input, for converters with either solid or laminated poles. But in a converter with laminated poles the current is more nearly in phase with the E.M.F. on account of the magnetizing current necessary to set up the field flux being smaller be- cause of the subdivided iron. By subdividing the iron the induction can penetrate farther into the poles. Troubles of Converters. Hunting of Converters on High- Frequency Circuits. The converter being a synchronous apparatus is subject to all the troubles of a synchronous motor. But since no mechanical power is taken off, a con- verter is much more sensitive than a synchronous motor to 298 LONG-DISTANCE ELECTRIC POWER TRANSMISSION slight variations in the supply of electrical energy. The most frequent source of trouble with a converter is a ten- dency to hunt or pump. This phenomenon, which is both a mechanical and electrical oscillation, is due to a variety of causes : (i) Slight variations in the angular velocity of the prime mover. (2) Slight variations in the voltage im- pressed on the converter. (3) Absence of sufficient arma- ture reaction. (4) Sudden changes of speed in the prime mover. (5) Sudden change of load. (i) Variations in the angular velocity of the prime mover are mainly due to faults of design. If the prime mover is a steam engine, the connecting rod may be too short, the governor be over-sensitive, or the flywheel may possess in- sufficient capacity. An increasing angular velocity results in a slight increase in the frequency of the supply circuit. Hence, the current of the converter increases, and the arma- ture tending to come in a more favorable position with re- spect to the field, a powerful force is exerted to increase the speed of the converter. But the armature of the converter by reason of its weight possesses considerable inertia, and a certain time interval is necessary to effect a change in its position. Hence there is liability of the synchronizing im- pulse being oversufficient to bring the armature to the fre- quency which existed at the time of the impulse, so that the armature will be speeded up above synchronism. When the converter armature speeds up, the prime mover may be approaching a part of its cycle where the angular velocity, and likewise the frequency of current, are de- creasing, so that the tendency is to speed the converter ar- mature above synchronism, and so throw it out of step. The action of the prime mover in the opposite direction, or the other half of its cycle, is the same. . Thus the converter is CONVERTERS 299 continually oscillating either above or below its proper phase position, and likewise its instantaneous speed is re- peatedly oscillating above or below synchronous speed. Such pumping or hunting action may also cause seri- ous disturbance to other synchronous machinery in circuit. With water wheels the angular velocity throughout a cycle is constant, and hunting from this cause is of rare occurrence. (2) Hunting caused by variations of impressed voltage. Changes of impressed voltage may result from over-high line constants, such as inductance or resistance. If a sudden change of mechanical load comes on the converter, a drop in its impressed voltage may occur due to high line inductance or resistance. But since both the magnetic circuit and the armature possess more or less inertia, an instantaneous change to a new condition cannot occur. Before a response to altered conditions can take place, the counter E.M.F. may attain a value high enough to exert a pull on the armature sufficient to alter the phase rela- tions of current and E.M.F. Thus an impulse is given to the converter armature to fall out of step, and hunting ensues. (3) Hunting caused by absence of armature reaction. Lack of armature reaction in a converter is the result of an equilibrium between two equal and opposite forces. Since the brushes on the commutator are set at the neu- tral position, the action of the direct current causes a distortion of the field flux in the direction of rotation. The effect of the alternating current (with unity power factor) causes an equal reaction which is opposite in direction. When a change occurs in the values of either or both of 300 LONG-DISTANCE ELECTRIC POWER TRANSMISSION these reactions due to a drop in power factor, the mag- netizing or wattless component of alternating currents ex- erts a demagnetizing action on the field, and thus instable operation of the converter may occur. The effect of a sudden change of load or speed is to cause a displacement in the phase relations of current and E.M.F. in a manner similar to a synchronous motor. In- ertia of the revolving element prevents its instantaneous response to the new conditions. When it does respond the new value is exceeded, and oscillation on both sides of a mean value occurs. Racing of the armature is a common cause of trouble with inverted converters. If from any cause the current of an inverted converter lags behind its E.M.F., the ten- dency of the lagging current is to demagnetize the field. The armature then begins to race in a manner similar to an unloaded shunt motor with weakened fields. Converters operate most successfully on 25 to 40 cycles, although there are a number of Western transmission companies that operate converters on 60 cycle circuits, and with perfect satisfaction. A 60 cycle converter is, however, a very sensitive element on the line, and evinces a decided tendency to hunting. Moreover, a converter designed for use on a 60 cycle circuit must either be run at a very high speed, or else have a large number of poles with brushes set close together. If run at a high speed the brush and commutator wear is quite appreciable, and the humming noise is very objectionable. If the machine is built with a large number of poles the brushes must be set close together to be conveniently handled, and there is danger of flashing or sparking over from one brush to the other on the surface of the commutator. CONVERTERS 301 Types of American Converters. Fig. 133 shows a 750 kilowatt, six-phase, General Electric converter. The field- magnet yoke is made of cast iron, the upper half being fastened to the lower by bolts located in recesses in the sides of the frame. The object of this method of fasten- ing is to avoid the unsightly appearance of external bolts. Fig. 133. A 750 Kilowatt Six-Phase Converter The poles are constructed of solid steel castings and are bolted to the frame to permit of easy removal for repairs. The lower half of the frame is made separate from the bed plate, which permits the entire frame to be slid along the bed plate parallel to the shaft, in case access must be had to the armature. 3O2 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The armature is bar wound, the upper bars being con- nected to the lower bars by means of soldered clips on the collector side of the armature. The collector rings are separated by air spaces to afford sufficient insulation and freedom from short circuits. The brushes on the collector rings are made of copper leaf, while those on the commutator are made of carbon and are held in shank brush holders. In order to insure cool running, the spokes of the arma- ture spider are fitted with small vanes which produce enough centrifugal action to force an air current between the laminae of the armature, over its windings and around the poles. An automatic oscillator or end-play device is used on the shaft to give the armature an occasional to and fro motion parallel to the shaft, and thus give uniform wear on commutator and collectors. Fig. 134 shows a 1,500 kilowatt, three-phase, Westing- house converter, which is the largest converter so far constructed. The armature is wound like an ordinary direct-current generator of large output, the windings being cross- connected so as to facilitate commutation. At regular points around the periphery of the armature, taps are led out to the collector rings on the left side of the armature. The field of the machine is wound with copper strap in a manner similar to a large direct-current generator, and is compounded to compensate for line losses. Motor-Generators versus Converters. The converter as a translating apparatus possesses the advantage of higher efficiency, since there is but one machine instead of two ; consequently machine losses are smaller. Likewise its cost is lower, as but one machine is needed. CONVERTERS 303 304 LONG-DISTANCE ELECTRIC POWER TRANSMISSION A converter may be compounded to compensate for the voltage drop which occurs in the generator and transmis- sion circuit ; hence it exercises no objectionable influence upon the voltage of the transmission system. On the other hand, the voltage which is taken off at the direct-current end bears a fixed relation to the pressure of the received E.M.F. However, by maintaining the E.M.F. of supply reasonably constant, it is possible by means of regulating devices or compounding, so to adjust and control the E.M.F. delivered by a converter that the relation be- tween the pressure of supply and delivery will be close enough to be regarded as negligible. Converters are also about 20 per cent cheaper than motor-generators and from 2 to 8 per cent more economical of power. On low-frequency circuits the operation and behavior of converters are eminently satisfactory, and they require but little attention. But on transmission lines operating at 60 cycles or above, the untrustworthy behavior of converters has led many Western transmission companies to adopt motor-generators as translating devices. A motor-generator consists of a motor, which may be either of the synchronous or induction type, directly coupled to a direct-current generator. The salient points of advantage which a motor-generator possesses over a converter are : ( i ) The E.M.F. of delivery is independent of the E.M.F. of supply and may be adjusted over a wide range to suit any conditions for which direct current may be employed. (2) A motor-generator may be used without putting in a step-down transformer, whereas with a converter the transformer is generally required. (3) If an induction motor is used to drive the generator, peri- odic fluctuations in the speed of the central station gen- CONVERTERS 305 erator will not affect the satisfactory operation of the machines. In other words, hunting or pumping is unknown when an (induction) motor-generator is used as the trans- lating apparatus. Moreover, momentary interruption of the supplying current or a sudden overload on the induction motor may give rise to little if any disturbance, whereas with a converter serious hunting may occur. (4) No highly skilled attendants are required when motor- generators are employed. In American long-distance power transmission practice, the proportion of converters used as translating apparatus is far in excess of motor-generators, which may be consid- ered as indicative of the high state of development which the converter has attained in this country. In Europe the reverse holds true. Efficiencies of Motor- Generator Sets. The following table shows the efficiencies of motor-generator sets of various outputs, and at different loads. Motor -Generator Sets Combined Efficiency. Quarter Load Half Load Three Quarter Load Full Load One and a Quarter Load One and a Half Load 400 kw., 375 revolutions . . 70 8l 85.5 88. 8 9 .2 90 500 kw., 450 revolutions . . 72 83 87 89. 90 9 1 800 kw., 450 revolutions . . 73 83.5 87.5 89-5 9 0.2 91 1 200 kw., 450 revolutions . . 77 86 89.5 91. 91.8 9 2 The figures given apply to Bullock machines. The efficiencies of motor-generator sets of other representative manufacturers will not differ appreciably from these figures. 306 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The following tables are a comparison between the rela- tive efficiencies of static transformers and converters as against motor-generators. The figures apply to 200 kilo- watt units in operation at a sub-station of the Buffalo (N. Y.) Edison Company. Trans- former Con- verter Motor Genera- tor Combined Efficiency Full load 07. C Q^.O nc 92 87.4 Three quarter load . . . 97.1 92.5 94 9 1 85.54 One half load Q6.O QO O 02 88 c' 8l 42 Comparison between the Net Efficiencies of 200 Jfilowatt Units. Motor- Generator Transformers and Converters Difference Full load 87.40 8q 47 2 47 Three quarter load .... 85.54 88.70 3-16 One half load 81.42 84.00 3.48 Frequency Converters. A frequency converter is an apparatus for changing an alternating current of one fre- quency into an alternating-current of another frequency, which may be either higher or lower than the received fre- quency. Its principal use is to transform low frequencies into higher ones. A frequency converter is essentially an induction motor, and operates on the principle of the variation, with slip, of the frequency of its rotor E.M.F. The usual method for raising the frequency of supply is to couple a synchronous motor to the shaft of an induction CONVERTERS 307 308 LONG-DISTANCE ELECTRIC POWER TRANSMISSION motor, and cause the driving motor to turn the rotor of the induction motor in an opposite direction to the direction of rotation of the driven motor's field. The primary windings of the induction motor and also the terminals of the driving motor are connected to the low-frequency source of supply. The higher-frequency current is taken from the secondary Fig. 136. A Large-Frequency Converter Unit i of the induction motor by means of slip rings mounted on the shaft. The voltage of the delivered current and its frequency are governed by the speed of the rotor. For definite values, they are the algebraic sum of the current variations in both machines. When the rotor is revolved at its rated speed in a direction opposite to its normal direction of rota- CONVERTERS 309 tion, the frequency of the delivered current is double that of the received current. Likewise, if the rotor is revolved at half speed in its normal direction, the frequency of the output is one half that of the supply. The output of the synchronous motor which drives the frequency converter must be of the same proportion of the total output as the increase in frequency is to the higher frequency. Use of Frequency Converters in High-Tension Practice. In addition to transforming low-frequency current into frequencies suitable for the operation of lights and other apparatus which require high frequencies for satisfactory operation, or vice versa, frequency converters find a valuable field of service in cases where several transmission lines operated at different frequencies supply a center of distri- bution. In such cases, the frequency converter is an alter- nating-current generator driven by an induction or syn- chronous motor. A notable instance of this kind is that of the electrical supply of Montreal, Canada. Energy is supplied by three transmission companies, all operating at different frequen- cies. The three frequencies, 66, 60, and 30 cycles respec- tively, are transformed by five frequency converter units into 63 cycle current which is supplied to all customers in the city. Fig. 1 36 shows a type of large-frequency con- verter unit. 310 LONG-DISTANCE ELECTRIC POWER TRANSMISSION BIBLIOGRAPHY Elements of Electrical Engineering. Steinmetz. McGraw Publishing Co. N. Y. 1902. Alternating Currents and Alternating Current Machinery. Jackson & Jackson. Macmillan Co. N. Y. 1901. The Rotary Converter. Berg. Transactions American Institute of Electrical Engineers, Vol. 18, p. 607. The Design and Action of the Rotary Converter. Rushmore. (Serial.) Engineering Magazine, N. Y., Vol. 22 (1901). PP- 4*4-422, Energy Transformations in the Synchronous Converter. Franklin. Transactions American Institute Electrical Engineers, Vol. 20, p. 876. Operation of Converters. American Electrician, N. Y., Sept., 1903. Voltage Regulation of Rotary Converters. Lincoln. Electric Club Journal, Pittsburg, March, 1904, p. 55. CHAPTER X PRACTICAL PLANTS Architectural Designs of Buildings for Hydro-Electric Central Stations. The majority of power houses gener- ating current for long-distance transmission are similar in architectural features, differing chiefly in dimensions, minor details, and materials of construction. The type of building which has now become almost the standard de- sign as a containing structure for hydro-electric machinery is a square or rectangular building with its greatest dimension longitudinally. Foundations for power houses are usually concrete and granite masonry. In a few instances wooden piles have been used where the character of the soil did not permit the use of a masonry foundation. The foundation of the Sault Ste. Marie structure, which is the largest building thus far erected for housing hydro-electric machinery, has a wooden pile support. Various materials of construction are employed for power-house structures, among which may be included nearly all of the common building materials, such as wood, brick, concrete, granite masonry, sandstone, corrugated iron, and structural steel. Except for power houses of small output, wood is now rarely used entirely as a build- ing material. The three materials most employed for this purpose are concrete, brick, and granite masonry, with or without 312 LONG-DISTANCE ELECTRIC POWER TRANSMISSION structural steel frames. Some buildings on the Pacific coast are constructed of corrugated iron over a wooden frame, while in a few instances (notably the Sault Ste. Marie Plant) power houses have been constructed of the sandstone which was excavated from the canal. Floors for hydro-electric stations are made of concrete, cement, brick, tile over concrete, and, in a few instances, wood. When the structure is provided with a gallery, it is constructed either of wood (rarely) or of steel and con- crete ; not infrequently it is constructed of a combination of the three materials. Roof trusses are usually of the arched type and are generally made of structural steel in a variety of designs. Roof coverings consist of corrugated iron, a combina- tion of concrete tar and gravel, or asbestos covered by one of the numerous patented roof coverings. The general practice with most transmission companies is to erect as substantial and fire proof structures as pos- sible, since the ultimate economy and safety are far greater. Arrangement of Machinery and Apparatus in High- Tension Central Stations. In the arrangement and location of hydraulic and electrical machinery and auxiliary apparatus in high-tension plants the controlling factors are considerations of safety, space economy, and accessibility, and in many instances the necessity of conforming strictly with the peculiar circumstances of the case. In most Western practice, where the water supply is conducted through the power plant latitudinally, the hydraulic machines are installed with their shafts parallel to the walls of the structure, or lengthwise in the building and close to the wall. In cases where the water is con- ducted through the structure longitudinally the hydraulic PRACTICAL PLANTS 313 machines are usually set with shafts parallel to the width of the building. When vertical turbines are used the hydraulic units are usually installed in a straight line a few feet from the lengthwise wall of the building. In some hydro-electric power houses, notably those in the East, the building is divided into compartments by partitions, the turbines being installed in a separate wheel room, and the generators in so-called generator chambers. The wheel chambers generally have arched concrete roofs with concrete floors ana sides, while the head wall. that separates each chamber from the generator room is 5 or 6 feet thick, and is fitted with a large bulkhead of cast iron, which carries a water-tight bearing for the wheel shaft. In the location of transformers practice varies widely. They are either installed in the power plant proper on the main floor near the walls, or in line with the space back of the low-tension switchboard on one side and the exciters on the other, or are placed in a compartment partitioned off from the rest of the structure, or are located on the upper or gallery floor. In some plants they are placed in a separate transformer house. In plants where air-blast transformers are used they are placed on the main floor with air cham- bers underneath or in a basement. Switchboards in hydro-electric plants are installed either on the same floor as the generators, on the side of the power house or at the end, or are mounted on a platform or ros- trum of masonry a few feet above the floor level, or they are installed in a gallery above the main floor. The atter practice is more general in cases of plants of large output at very high potentials. As in the case of transformers, no uniformity of practice 314 LONG-DISTANCE ELECTRIC POWER TRANSMISSION obtains in the location of switchboards. In many instances, the matter of convenience, accessibility, and economy de- mands that the switchboard be installed on the same floor as the generators, so that the men attending wheels and generators can also perform the switching operations. In some high-tension plants on the Pacific coast, the high-potential board is installed separately from the gener- ator switchboards, being usually mounted in a gallery over and slightly to the rear of the generator board, and is placed half way between the inner rail of the crane and the wall of the building, and facing the tailrace. The lightning arresters for high-tension stations are in- stalled either in a separate building, termed the lightning ar- rester house, or are located in the main building. Arresters for protecting transformers are mounted on the faces of vertical marble panels located near the transformers. Parallel Operation of Plants. Many Western long- distance transmission plants miles apart are successfully operated in parallel, the problem of parallel running being regarded as no more serious than the parallel operation of direct-current plants. A notable instance is the system of the Edison Electric Company of California, which con- sists of seven plants separated by wide distances, all of which are operated in parallel with the greatest of ease. Regulation of Plants. In long-distance power plants one of the highest essentials of successful operation is good regulation. The requirements of close regulation are in the main a recapitulation of the principles outlined in pre- vious chapters. They are: (i) A considerable voltage vari- ation in the generators, and generators and transformers designed for close inductive load regulation ; (2) a trans- mission line so designed that the capacity current will be PRACTICAL PLANTS 315 a minimum ; (3) avoidance of attempts to balance the capacity of the circuits against the power lag ; (4) constant capacity of the line balanced with reactance; (5) the variable inductance of circuits and the induction motor load to be balanced by variable capacity in the form of synchronous motors. Sub-Stations: Materials of Construction and Arrange- ment of Apparatus. Architecturally the majority of high- tension sub-stations are closely similar to the main power structures. The type of building generally used is of square or rectangular shape, one or two stories in height, depending on the capacity in translating apparatus which is needed at the particular point of distribution. In West- ern practice sub-stations are sometimes designed so that a second story may be added to provide for increased de- mands for power. Considerations of safety and reliability of operation de- mand that sub-stations be of the most substantial and fire- proof character. Formerly it was the practice to place the translating apparatus in a hastily put up structure, often- times of a character which barely protected the machinery from the elements. In the best modern practice as much attention is given to the sub-stations as to the central station, and their construction is of a very rugged character. Brick is mostly employed for constructing sub-stations, although stations of granite masonry, concrete masonry, and sandstone are frequently met with in Western practice. The incoming high-tension wires are passed into sub- stations through long porcelain sleeves or through marble and glass bushings ; and the current is usually conducted through a set of single-throw fused switches, one switch per leg. Thence the high-tension current is passed through 316 LONG-DISTANCE ELECTRIC POWER TRANSMISSION non-arcing lightning arresters fitted sometimes with static interrupters, finally being conducted to the step-down trans- formers. Step-down transformers in sub-stations are usually arranged in pairs or groups and installed near the length- wise wall of the building ; or, in case they are the only translating apparatus in the station, are placed near the center of the structure. Switchboards in sub-stations are generally installed near the lengthwise wall of the structure. In most cases they contain a separate panel for each transformer and are equipped with the necessary measuring and indicating instruments and the protective devices which have been mentioned before (Chapter IV). The switchboard in most sub-stations is equipped with a high-tension plug board which permits of any desirable combination of the incoming and outgoing circuits. Thus in some cases all of the load may be put on either, trans- mission line, or it may be divided so that the steady load is on one circuit and the fluctuating load on the other ; or both circuits may be connected in multiple. Cost of Electrical Power Transmission. To justify an electrical transmission project, the value of the energy at the point of distribution should at least equal the value of the generating plant plus the cost of transmission. The cost of energy at the generating end being known and its value at the receiving end, the difference between the two represents the maximum cost at which the transmis- sion will pay. The factors which enter into the cost of a power trans- mission scheme are : (-C&st- of water rights, the land flooded by back-water or for a reservoir site ; (2) cost of PRACTICAL PLANTS 3 I/ dam and its auxiliaries which may be conveniently termed the "hydraulic end"; (3) cost of powerhouse and aux- iliary structures ; (4) cost of station machinery and auxiliary apparatus; (5) cost of transmission lines and translating apparatus ; (6) cost of operation ; (7) cost of repairs, maintenance, and depreciation. In most instances there is the additional cost of the water-conveying system, a pipe, flume, or canal line. The cost of hydraulic pipe differs widely. The table on page 60 may be taken as a good average of the cost per foot of riveted sheet steel pipe. The cost of buildings will include the cost of the main power plant and auxiliary houses, such as lightning arrester and transformer buildings (if such apparatus is not installed in the central station). Also the cost of various sub-stations for distributing the power. Many considerations govern the cost of the generating station, as, for instance, the diffi- culties of preparing a suitable foundation, the prevalence or absence nearby of the particular building material desired, the cost of transporting the materials of construction to the site, and the cost of labor in the section. The cost of buildings involves too many variable factors to attempt here to give any hard and fast rules. The cost of machinery includes the cost of turbines or water wheels and auxiliary apparatus pertaining thereto, such as governors, valves, and gate-controlling devices, the cost of generators and station apparatus. The cost of water wheels varies from $2.50 to $7.50 per horse-power out- put, depending upon their capacity. In general, the cost per kilowatt of generated power varies from $100 to $250 p ' -"Hill" 1 - The Sault Ste. Marie plant complete cost $4,000,000, or 318 LONG-DISTANCE ELECTRIC POWER TRANSMISSION $135 per kilowatt. This is but a moderate cost per unit of power compared with some water-power plants. The cost per unit of power has many variables, such as the outpu* of the plant, the conditions of operation, the cost of building material in the neighborhood, the cost of labor, and the kind of machinery used. The cost of transformers varies directly with the highest rate of transmission, and is approximately independent of voltage, the distance of transmission, and the line loss. The cost of transformers varies from $6 to $10 per horse- power. For large capacities a good average figure is $7.50. The cost of the transmission line proper, which consists of the pole line and the conductors, varies according to the conditions of each case. In the total cost of delivered power the highest and the average rates of power trans- mitted, the maximum pressure of transmission, the per- centage of line loss, and the distance of transmission, fix the ratio of line cost. The pole line varies in first cost with the distance of transmission, but is almost unaffected by the factors above stated. Since reliability of operation is the foremost con- sideration in long-distance power transmission, a pole line of the stoutest and most substantial construction is re- quired. In regions where timber is procurable at a mod- erate cost, the cost of pole lines, exclusive of the right of way, will range from $450 to $600 per mile; a good aver- age is $525. In many instances the right of way will cost nothing. For a fixed and maximum percentage of line loss, the cost of conductors varies directly with the square of the distance of transmission, and with the rate of transmitted power. The first cost of conductors, however, decreases PRACTICAL PLANTS 319 with increase of pressure, as the square of the voltage of transmission ; and also decreases with increase of line loss. Hence, the transmission voltage and the permissible line loss at maximum load will fix the weight and cost of line conductors. With a given amount of power to be transmitted, the length of transmission and the voltage, the weight of con- ductors required varies inversely as the percentage of en- ergy lost as heat in the wires. A fair average for line conductors is from 18.5 to 20.5 cents per pound for copper conductors, and about 28.5 to 31 cents per pound for aluminum conductors. The cost of operation, which includes management, labor, and incidental expenses, repairs, maintenance, interest, and depreciation, will vary widely with the circumstances in each case. No fixed and definite figures obtain, since in each transmission plant the cost of operation is governed by different factors. In general, the cost of management, labor, and incidentals ranges from three to eight per cent yearly on the total first cost, depending on the size of the power development and the length of the transmission system ; and hence the number of employees required to operate it. The cost of repairs, maintenance, interest, and deprecia- tion will also vary with the size and length of the transmis- sion system, the character of the machinery employed, and the line construction. The annual allowance necessary for repairs, maintenance, and depreciation will vary from five to twenty per cent of the total first cost of the transmission. Interest charges will range from three to six per cent per annum on the total investment. Mr. Alton D. Adams says : " If a given amount of 320 LONG-DISTANCE ELECTRIC POWER TRANSMISSION power is to be transmitted at a certain percentage of loss in the line, and at a fixed voltage over distances of 50, 100, and 200 miles, respectively, the following conclusions obtain : The capacity of the transformers being fixed by the rate of transmission will be the same for either distance, and their cost is therefore constant. Transformer losses, interest, depreciation, and repairs are also constant. The cost of pole lines, depending on their length, will be twice as great at 100 miles, and four times as great at 200 as at 50 miles. Interest, depreciation, and repairs will also go up with the length of the pole lines. " Line conductors will cost four times as much for the 100 mile as the 50 mile transmission, because their weight will be four times as great, and the annual interest and depreci- ation will go up at the same rate. For the transmission of 200 miles the cost of line conductors and their weight will be sixteen times as great as the cost at 50 miles. "It follows that interest, depreciation, and maintenance will be increased sixteen times with the 200 mile transmis- sion over what they were at 50 miles if voltage and line loss are constant." The cost of an electric horse-power hour at the switch- board in a hydro-electric station will differ in each particular case, on account of the different outlays required in hydraulic installations per unit of developed power. Where only moderate amounts of power are developed the cost per electric horse-power hour at the switchboard may range from 8 down to I cent. Where large outputs of power are developed the cost may range from 3 to 6 cents per electric horse-power hour. To obtain the total cost of transmission per electric horse-power, the percentage found by dividing the cost of operation by the number of horse-power hours PRACTICAL PLANTS $21 per annum of output, must be added to the product obtained by multiplying the cost of a unit of power at the switch- board into the cost of a percentage of a horse-power hour which is lost in transmission. The sum obtained by adding the cost of a unit of power at the switchboard, the cost of energy transmitted, and the cost of the percentage of a horse-power hour lost in trans- mission, gives the total cost of transmission per electric horse-power. The Limitations of Electric Power Transmission. Theo- retically, it is possible to transmit electric power around the globe, provided the available voltage is unlimited. Such a statement follows from the law that a certain amount of power may be conducted to any distance with a steady efficiency and a predetermined weight of conductors, pro- vided the pressure of transmission is increased in direct proportion to the distance. In practical working, however, the maximum voltage at which it is safe and economical to transmit power is the limiting factor in the present stage of long-distance power transmission. The limits to the pressure which can be em- ployed in practice may be divided into several factors which enter into the transmission part of the system, per se: (i) Definite limits to the pressure of transmission beyond which temporary arcing between the wires on a pole will occur, and the less significant but constant exchange of energy from one conductor to another ; (2) leakage losses through the air from wire to wire of the line (see Chapter VI) ; (3) the necessity of stringing each wire of a transmission line on a separate pole line, or at wider distances apart, thereby greatly increasing the cost of line construction when press- ures much higher than those used in present practice are 322 LONG-DISTANCE ELECTRIC POWER TRANSMISSION employed ; (4) the difficulty of obtaining an insulator which is capable of withstanding very high pressure. The first limitation to high-tension power transmission- arcing, is caused by one of several causes. A broken or defective insulator may give rise to a current flow along a wet cross-arm from one conductor to another, so that in time the wood is carbonized, and finally a vicious arc burns up the cross-arm and not infrequently the pole itself. Lines running in close proximity to the sea coast some- times have a heavy deposit of salt formed on the insulators and cross-arms which sets up an arc between the conductors, frequently resulting in the destruction of the cross-arm. The same trouble may occur in cases where the line crosses an alkali desert or runs near a dried-up salt lake or basin. Arcing troubles, however, are less frequent in localities where the lines are not exposed to sea fogs or salt dust. (2) Leakage losses through the air from wire to wire of a line directly through the air is the most serious limitation to the voltages which can be employed with existing line construction. The most notable experimental work which has been thus far done to ascertain the rates at which en- ergy is lost by passing through the air from wire to wire of the same circuit is that of Messrs. Scott and Mershon at Telluride, Colorado. Lately Professor Ryan, of Leland Stanford University (see Chapter VI), has made a note- worthy contribution on the same subject. Measurements made by Scott show that the leakage through the air varies directly with the length of the line, as might be presumed. With fiinrkilovolts line pressure and with wires 15 inches apart, the loss between wires wasA approximately 1 50 watts per mile. With the same pressured PRACTICAL PLANTS 323 and with conductors 52 inches apart, the loss was only 84 watts per mile. When the voltage was increased to 44,000 and the wires separated by 1 5 inches, the leakage loss was increased to nearly 413 watts per mile. At 44,000 volts and a distance of 52 inches between conductors, the loss was only 94 watts per mile. The maximum pressure employed for the conductors 15 inches apart was 47,300 volts, at which the leakage between the two wires became nearly 1,215 watts per mile. At five kilovoltsand a distance of 52 inches between wires the loss was 140 watts per mile. As the pressures increased the losses went up at a very rapid rate, becoming at the high- est voltage measured (59,300 volts) nearly 1,368 watts per mile. It is manifest, if the leakage losses increase at a corre- sponding rate above yP kilovolts, which is to be expected, that at above- oightTfnd a half kilovolts, the loss will become (with wires 52 inches apart) more than 7,000 watts per mile. If such is the case, it is clear that a long line at this pressure would be impossible. But to overcome this limitation requires only that the electrical resistance of the air be increased by stringing the wires of the circuit at greater distances apart. At the present time the greatest distance apart of the conductors of a transmission line is 78 inches, the three wires of a single circuit being strung on one pole line. There is no reason why this distance cannot be considerably increased if the conditions demand. (3) Increased difficulties and expense of line construc- tion when pressures above seven kilovolts are employed. From what has been said concerning line leakage it is clear that if pressures above seven or eigM kilovolts are employed, the present general practice of stringing wires will have to 324 LONG-DISTANCE ELECTRIC POWER TRANSMISSION be radically modified. In present practice, the two or three conductors of a transmission line are carried on a single pole line, or in a number of instances, several circuits are carried on the same pole line. Although the method of stringing each wire on a single pole line could be carried up to a limit of perhaps eleven feet between any single wire of a circuit, the cost of the large poles demanded would increase the expense of line construction enormously. Moreover, at pressures of about letfLp or ii kilovolts this mode of line construction would not reduce the leakage losses to a permissible value. It is not improbable that when line pressures a few tens of kilovolts higher than present practice come into use, each conductor of a circuit will be carried on a separate pole line. Since the distance between wires with such radical line construction could be made of any desirable value the losses by leakage through the air would be negligible regardless of the voltage of transmission. It would seem that the use of steel towers for carrying the conductors offers the best solution to this limitation. (4) The difficulties of obtaining an insulator which will not break down under the severe stresses of high potentials impose another limitation upon the pressure permissible in power transmission. Although at the present time insu- lators have been developed which ^/ill safely and satisfactorily withstand pressures of over 'fifteen kilovolts in laboratory tests, it remains to be seen what will be their behavior when called upon to insulate a transmission line under the trying conditions of actual practice. The principal shortcoming of high-potential insulators is their relatively low surface resistance as compared with the body of the insulator, which results in insidious break- PRACTICAL PLANTS 325 downs due to arcs between the insulator pin and the cross- arm. As the voltage of transmissions has gone up, the length of insulator pins has been gradually increased, so that in some transmissions of the present day a distance of nine or ten inches between the lower wet edge of the insulator and cross-arm has been attained. It is feasible by using still longer pins and umbrella-type insulators of a larger size to increase this striking distance to at least two feet, at which distance breakdowns from this cause would be nearly unknown. Some experimental work has been done to discover a dielectric which will fulfill the exacting requirements of line insulation to a higher degree than porcelain, although at the present time it seems unlikely that the desideratum will be found. At the least, the insulator problem is a less serious limitation to high-pressure transmission than leak- age losses from bare conductors. BIBLIOGRAPHY Evolution in High Voltage Transmission. Scott. Electrical Review, N. Y., Jan. 10, 1903. Costs of and Losses in Electric Power Transmission. Adams. Mines and Mining, N. Y., Feb., 1903. Does Transmission Pay ? Journal of Electricity, Power, and Gas, San Francisco, Feb., 1903, p. 136. Depreciation of Plants. Electrical World and Engineer, N. Y., Nov. 17, 1900. Organization of the Operative Forces of a Transmission Plant. Hancock. Journal of Electricity, Power, and Gas, San Francisco, August, 1903, p. 277. Regulation of a Transmission System for any Load and Power Factor. Baum. Electrical World and Engineer, May 18, 1901, p. 822. CHAPTER XI DISTINCTIVE FEATURES OF PROMINENT LONG- DISTANCE ELECTRIC POWER TRANSMISSIONS. THE SNOQUALMIE FALLS PLANT THIS is a 20,000 horse-power transmission from the falls of the Snoqualmie River to Seattle, Washington, about 25 miles distant, and Tacoma, 44 miles distant. The falls have a vertical drop of 270 feet, which is greater by over 100 feet than the falls of Niagara. The water-shed sup- plying the river is over 500 square miles in area, and con- tains numerous mountain lakes and natural basins, which it is possible to utilize when the present power development is increased to meet future demands. The river does not Ireeze during the winter months, and hence the plant is free from the serious difficulties encountered in many other plants, from anchor or floating ice. The most distinctive feature of the power development is the location of the plant in a subterranean chamber. The reason for this lies in the fact that the great volume of spray at the base of the falls would have kept the build- ing and apparatus damp during the summer season, while in winter the coating of ice on the building would have been a serious disadvantage. The water is conducted directly into an intake constructed of steel and concrete, and extending about 60 feet along the river bed. To prevent floating timber and driftwood from entering the intake the front is guarded by a grating 326 PROMINENT POWER TRANSMISSONS 327 of 12 inch by 12 inch timbers placed horizontally with 1 2 inch spaces between them ; the whole is supported by an iron girder frame made into the masonry. The subterranean power house is located about 300 feet above the falls, at which point a shaft 10 feet by 27 feet was sunk in the bed of the river to the water level below the falls. From the face of the ledge below the falls to the bottom of the shaft, a tunnel 650 feet long and 12 feet by 24 feet in cross-section was excavated. This tunnel extends under the bottom of the subterranean chamber and forms the tailrace. The power house is a chamber dug into the rock formation and is 350 feet long, 40 feet wide, and 30 feet high. Ventilation of the chamber is accomplished by the natural draft through the tailrace. The mean temperature of the chamber is 55 F. which is very favorable to high generator efficiency. The main wheel units in the plant are probably the largest and most powerful of the tangential type which have ever been operated under the same head. The origi- nal installation consisted of four 2,000 horse-power units. The wheels are of the type (Doble tangential) described in Chapter III. The water-distributing receiver is 48 inches inside dia- meter and 20 feet 8 inches in length, and is constructed of marine steel plates \ inch thick with dished heads. The shell is constructed of two plates 10 feet wide and suffi- ciently long to make a cylinder with only one longitudinal seam, which is double riveted. All flanges are of semi-steel. The distributing receiver stands directly over the foun- dation and is held in position by six regulating nozzles, which are mounted in a vertical plane upon the foundation. Thus the water is delivered from the receiver into the 328 LONG-DISTANCE ELECTRIC POWER TRANSMISSION nozzles without undergoing any change in direction. The nozzles are curved so as to direct the water upward against the wheels. Each nozzle is fitted with two tips, the diameter of the jet discharged from each being 3^ inches. The auxiliary wheels for driving the exciters are also of the tangential ellipsoidal type. They are mounted in steel housings and are supplied with water through a regulating nozzle which gives a jet of 3 inches diameter. The regu- lating nozzles are so constructed that by merely opening the nozzle to the maximum diameter any trash or foreign matter which may have lodged in the nozzle is immediately washed out, and the nozzle can be adjusted to the proper jet diameter. There are seven generators in the plant, four of which generate three-phase current at 1,000 volts and 60 cycles. The other three machines are each of 3,000 kilowatts out- put and generate three-phase current at 1,100 volts and 60 cycles. The E.M.F. is raised to 30,000 volts by oil-insulated, water-cooled transformers, delta connected on both the primary and secondary sides. Nine of these transformers are of 1,000 kilowatts capacity and weigh 11,000 pounds each ; and each requires 500 gallons of oil. The switchboard consists of fourteen panels of white marble with separate generating and multiplying panels. The poles for the transmission line are of cedar, stripped of the bark, and either tarred or burnt at the butts. Their average length is 36 feet, but this varies with the contour of the country; the maximum length being 154 feet. Where the lines cross the channel in the harbor, the poles are 1 54 feet long, 47 inches in diameter at the PROMINENT POWER TRANSMISSIONS 329 butt, and 23 inches at the top, and weigh 2,500 pounds each. The line is in duplicate and is carried through a right of way averaging 50 feet in width. In some sections of tim- ber land the company has a right of way extending 300 feet on each side of the line, through which sections trees of over 300 feet in height had sometimes to be felled in order to insure immunity from injury to the line. Two circuits are strung on each pole line, one on each side, with a triangular spacing of 30 inches between con- ductors. Cross-arms are 4^ inches by 6 inches and 8 and 10 feet long. On all turns and crossings double cross- arms are used. Four conductors are strung on the lower cross-arm, the inner two of which are 75 inches from the center of the pole and the outer two 25 inches from these. The upper cross-arm is 25.5 inches above the lower arm, and on it are strung two wires, each 40 inches from the pole center. The conductors are of stranded aluminum, and about 125 tons of metal were required for constructing one of the lines. Triple-petticoat porcelain insulators are used throughout. Each insulator is 4.5 inches in height and 6.5 inches in diameter and weighs four pounds. The insu- lator pins are of locust wood boiled in paraffine. The distance from the lower edge of the insulator to the cross- arm is four inches. The length of span on the circuit to Seattle ranges from 90 to 150 feet, the. average being no feet. The sag between spans is about 15 inches, which is much greater than is permissible with copper conductors. Transpositions divide the line into six equal sections ; the spans in which the transpositions are made are hung 330 LONG-DISTANCE ELECTRIC POWER TRANSMISSION between two poles 6 feet apart. Where transpositions are made the circuits are given a third of a turn always in the same direction. A telephone line of No. 10 B. & S. gauge aluminum wire is carried on the same pole line with one of the power cir- cuits, at a distance of about 5 feet below the power wires. At every fifth pole the telephone circuit is transposed. In common with most Western long-distance power transmission systems the lines are patrolled, each patrol- man having a ten-mile stretch to inspect and report its condition to the sub-stations from booths located every three miles. The power is utilized in coal-mining operations along the route of the transmission line, and in lighting several small towns. The greater part of the energy is supplied to the cities of Seattle and Tacoma, where it is consumed by manufacturing and street railway properties, etc. The Missouri River Power Company. This transmission plant enjoys the distinction of being the first to employ a potential of 50,000 volts and at the present time is trans- mitting power at 57,000 volts. Current is also generated at 1 2,000 volts for supplying a small distribution area. The power plant is located on the Missouri River near Canyon Ferry (Mont.) and is 17 miles from Helena and 65 miles from Butte. A dam 900 feet long was constructed across the river at a point where the walls of a canyon rise to a considerable height. The main dam is built up of earth with a core wall of masonry, located on the east side of the river. The auxiliary dam is a rock-filled, timber crib structure with masonry abutments. The east abutment is about 325 feet from the east bank; and between the abutment is a free spillway 472.75 feet in length. From PROMINENT POWER TRANSMISSIONS 331 the west abutment, a masonry bulkhead extends 90 feet to an almost vertical cliff. The dam forms a reservoir of about 7 miles length and over 6 square miles area. The main power house is 228 feet in length and 50 feet in width, and is constructed of granite masonry with steel roof trusses and corrugated iron. It contains a gallery 18 feet wide which extends throughout the building on the west side, and has floors of steel and concrete construction. The masonry used throughout the work was obtained from the region and cut near the site. Tt contains a gallery 18 feet wide, which extends through- out the building on the west side, and has floors of steel and concrete construction. Water for operating the turbines is conducted to the power house through a canal 275 feet long and 54 feet wide. The canal wall is constructed of thick granite masonry and is lined throughout with Portland cement. The head gates are electrically operated by a very in- genious mechanism, consisting of a car moving over rails laid over the east wall of the canal, and equipped with the controlling mechanism ; the clutches are lever operated and the car is equipped with a ten horse-power direct-current motor, receiving current from an overhead wire through the medium of a trolley wheel. The car rails are so de- signed that they support the car only when it is traveling between gates, or when it is throwing pinions into or out of mesh with the racks on the gate-lifting bars. The hydraulic equipment of the plant consists of ten pairs of McCormick turbines, two single turbines, and one pair of small units for driving the exciters. Each shaft of the main turbines has two water bearings, one of which is 332 LONG-DISTANCE ELECTRIC POWER TRANSMISSION at the outside of the turbine on the canal side, and the other inside the draft chest. Another thrust bearing of the ring-oiling type is placed outside of the wheel case, close to the generator coupling, and has two solid project- ing rings, fitting into grooves in the surface of the bearing. All of the turbines are controlled by Lombard governors. The machines discharge their water into central cast-iron draft chests, and thence through elliptical draft tubes into the tail race. The generator equipment consists of ten revolving arma- ture, 750 kilowatt, three-phase, 550 volt, 60 cycle machines, each direct connected to a pair of turbines by means of flexible couplings. Exciting current is supplied by four 150 volt direct-current generators, one of which is coupled to an induction motor, and the other three directly con- nected to 24 inch turbines. The switchboards and the raising transformers for the 12,000 volt service are installed on the gallery floor. There is a separate panel for each generator, and each machine is wired directly to its panel on the board. For the 57,000 volt service there aresix raising transform- ers, each of 950 kilowatts capacity and of the oil-insulated, water-cooled type, cooled by water from the canal. They are installed in a transformer room between the wall of the power house and the east wall of the canal, and are arranged in two groups with delta connection. The protective apparatus for the 57,000 volt transformers con- sists of lightning arresters combined with static interrupt- ers. Each lightning arrester consists of 114 units with six small gaps, and a large adjustable gap close to the line. High-tension switches between the two 57,000 volt circuits are designed so that both groups of transformers PROMINENT POWER TRANSMISSIONS 333 may be put into joint operation on one or both lines ; or one group of transformers may be used to operate both circuits. The 57,000 volt main conductors in the station are 800,000 circular mill cable with rubber insulation and ex- ternal lead sheath. The line conductors for the 57,000 volt circuit are bare copper cables, each composed of seven strands. The circuit is strung in the form of an equilateral triangle with conductors 78 inches apart, two wires being carried on the cross-arm and the third at the top of the pole. The insulator pins are of white oak, kiln dried and boiled in paraffine. For insulation of the circuits depend- ence is placed entirely upon the insulators, sleeves, and pins. Transpositions on each of the main circuits are made at average distances of thirteen miles, making five transposi- tions to Butte, and giving two complete turns between the power plant and the Butte sub-station. A telephone line is carried on pony glass insulators, 5^ feet below the power circuit cross-arm, and is transposed every fifteen poles. The main circuits are carried over a right of way 200 feet wide for the greater portion of the distance, and all trees and brush for a distance of 50 feet on either side of the line are cleared away. The 1 2,000 volt transmission carrying 4,000 horse-power is mainly utilized by smelting works at Helena seventeen miles distant. The remainder of the medium tension transmission supplies the incandescent and arc lighting, street railway and manufacturing properties of Helena. The 57,000 volt transmission to Butte, aggregating about 8,000 horse-power, is consumed principally by the large 334 LONG-DISTANCE ELECTRIC POWER TRANSMISSION Anaconda mine. Power is also supplied to various manu- facturing interests. The Bay Counties Power Company of California. This transmission system is the longest in existence and was first put in operation on April 27, 1901. The company sup- plies power from three plants operated in parallel. Power is transmitted at 40,000 volts to Oakland, a distance of 142 miles from the main generating station ; and power is sup- plied to the Standard Electric Company, for transmission to various points along San Francisco Bay, the farthest of which is Stockton, 218 miles distant from the main power plant. The main power plant of the system is located at Colgate, on the north Yuba River. At a point about eight miles above the power house a dam was constructed across the river. Thence the water is conducted through a flume to a point about 700 feet above the power-house structure. The flume system is laid on a gradient of 1 3 feet to the mile and has a nominal capacity of 20,000 miner's inches. The flume is about 7 feet wide and 5f feet deep and is supported on trestles averaging 8f feet in height. At the pony- v, here the flume system ends, five pipe lines conduct the water down the mountain side to the distributing re- ceiver in the power house. The five p ; pe lines are each 30 inches in diameter, made of cast iron at the bottom and steel at the top, and anchored in massive concrete blocks. At the foot of the pipe lines is a massive penstock or water receiver, which distributes the water to the water wheels under a head of 702 feet. The power-house structure is located at the base of the mountain and is 275 feet long and 40 feet wide. It is con- PROMINENT POWER TRANSMISSIONS 335 structed of ' ttive rock with steel roof trusses and corru- gated iron covering. There are at the present writing seven hydraulic units installed, consisting of three 3,000 horse-power Risdon wheels, and four 1,500 horse-power wheels, all of the tan- gential type. In addition to the main water wheels there are two 50 horse-power wheels for driving the exciters. All units are direct connected, and the shafts of the larger units (and the larger generators) have a flange at each end for leather link driving. This arrangement permits any generator to be driven by either of two water-wheels, with the exception of the outer generator and water wheel units. The smaller units are independent of one another, and each is coupled to its respective wheel through flexible couplings. The generating equipment of the power house consists of three 2,200 kilowatt, three-phase, 60 cycle Stanley in- ductor alternators, each direct connected to a 3,000 horse- power wheel; and four 1,125 kilowatt generators, each driven by a 1,500 horse-power wheel. The raising transformers are of the oil-insulated, water- cooled type, and are installed in the main power house. The transmission line for the 142 mile circuit is in dupli- cate and is carried on cedar poles with fir cross-arms. The average length of span is 132 feet. The insulator pins are mainly of eucalyptus wood, although on some parts of the system locust is used. The insulators are of porcelain and the special design of Mr. R. H. Sterling, superin- tendent of the Bay division. The upper part is of porcelain with a very wide lip, and cemented on to a glass insulator with a long petticoat by means of a sulphur cement. One of the transmission circuits is composed of three No. oo hard-drawn copper wires, strung in the form of an 336 LONG-DISTANCE ELECTRIC POWER TRANSMISSION equilateral triangle with 36 inches space between wires. Line joints on the copper circuits are of the regular West- ern Union type with nine wraps on each side and soldered the entire length. The other circuit, which is strung par- allel to the copper line, is composed of three No. oooo, seven-strand aluminum cables with joints of the thimble form. Both circuits are transposed every mile by making one third of a turn. The Hudson River Water Power Company. The power house is 392 feet long and 71 feet wide with a space 28 feet by 34 feet omitted at one corner. Extending across the entire width of the structure and 40 feet in the direction of its length is a compartment, in which are installed the transformers and the high and low-tension switch- boards. The remainder of the structure is divided into two sections in the lengthwise direction by a water-tight brick wall which gives the wheel chamber a width of 34 feet and the generator chamber a width of 35 feet. Ten steel penstocks each 12 feet in diameter enter from the canal along the outside wall of the canal. The water supply from eight of these penstocks drives a pair of hori- zontal turbine wheels that discharge through a single draft tube, and are coupled direct to a 2,500 kilowatt generator. The other two penstocks supply each one pair of wheels direct connected to a 2,000 kilowatt generator and also a wheel coupled to a 200 kilowatt exciter dynamo. The power house has a basement in that part in which are installed the transformers and switchboards, with the dam as one of its side walls. The basement contains a central air chamber wherein are installed blowers which maintain a pressure of five eighths ounce per square inch for cooling the transformers on the floor above. PROMINENT POWER TRANSMISSIONS 337 The low and high-tension switchboards are installed at opposite sides of this air chamber. The switching on the high-tension board is performed by motor-operated oil switches, the legs of which are contained in separate brick compartments. The 30,000 volt connections are fastened on the stone and concrete masonry by means of porcelain insulators. For this purpose each insulator is fastened to an iron pjn and has a cast-iron top or cap. The point be- tween the pin and the insulator and also the point between the insulator and the iron cap are made with a thin mortar of Portland cement. The step-up transformer equipment is entirely of the air- blast type, and each unit is designed to operate at 2,000 volts primary and either 1 5,000 or 30,000 volts secondary. The transformers are connected in groups of three to a generator unit. Lightning arresters for protecting the transformers are installed in stone and brick cells, each unit in a separate cell. Each conductor of the transmission circuit is con- nected to an arrester plate through a knife switch. The transmission line is carried on chestnut poles of a standard length of 3 5 feet and regularly spaced I oo feet apart. On curves and turns the pole tops are pulled over 6 to 12 inches by guy wires made of seven-strand No. 12 B.W.G. galvanized steel wire having a maximum tensile strength of 80,000 pounds. On some angles pole braces not under 22 inches in circumference at their tops are employed. The standard cross-arms used are i oj feet long, 4 inches thick, and 6 inches deep. Each arm is given two coats of metallic paint. Each cross-arm is fastened to the pole by a single through bolt J inches in diameter and galvanized. 338 LONG-DISTANCE ELECTRIC POWER TRANSMISSION The bolt has a thread cut over 4 inches of its length and is used with its nut next to the cross-arm with galvanized washers under both head and nut. Each cross-arm is braced with a single piece of galvanized iron bent into bow form. The insulator pins are of iron. Two types are employed, one for the straight runs and the other for curves and corners. The pin for straight lengths of line is constructed of a malleable iron casting with f inch wrought iron or steel stud screwed into its base. The stud goes through the cross-arm, and the casting is mounted on the arm and carries the insulator. On curves and turns a bolt is passed entirely through the cast-iron part of the pin and is thence passed down through the arm with a nut and washer under- neath. The length of the f inch through bolt for this strain pin is about 16^ inches; the length of the cast-iron section mounted above the cross-arm is 8f inches ; the flange of the casting that rests on the arm is 3| inches by 5 inches ; the top of this casting is if inches in diameter with inch threads for the insulator. Two types of porcelain insulators with brown glaze are used. The form most largely used is molded in a single piece with double petticoats. The newer type of insulator is made in three parts and then cemented together. The insulators are fastened to the pins by Portland cement poured into the pin hole of the insulator while the free pin top is held in a central position. The line wires are tied to the sides of the insulators, but the insulators are designed for either top or side tying. The line conductors are made up of solid, hard-drawn bare copper of 98.5 per cent conductivity. One of the three-phase circuits from the Spier Falls plant contains PROMINENT POWER TRANSMISSIONS 339 three four-pin cross-arms per pole with wires spaced 36 inches apart. Two conductors of a circuit are mounted on the two insulators which are on that half of a top cross-arm on one side of its support. The remaining conductor of this line is carried on the insulator at the end of the next lower arm and immediately below the outer of the two wires of that line on the top arm. This method of string- ing leaves the inner insulator on the same end of the middle arm and the two insulators on the corresponding end of the third or bottom cross-arm for another three-phase line. The six conductors on the opposite side of the pole are arranged in a like way. The conductors are transposed one third of a turn for each section of 130 poles. Thus each wire passes through a complete circle every 7.5 miles, there being 52 poles per mile of straight line. In crossing several railway tracks special constructions are employed. The poles of the double line are 9 feet apart. The top cross-arm is 16 feet in length, the middle arm 10.5 feet, and the lowest arm 14 feet long. The towers are constructed of Georgia pine and chestnut. Each is 66. 5 feet high from the base to the upper side of the top cross-arm and is set 10.5 feet in the earth. The wood in the towers is treated with carbolineum, while all plates and bolts on the subterranean parts are coated with coal tar. Guard wires are not used for lightning protection on any of the transmission lines, and arresters are employed only at the central stations, sub-stations, and switch houses. Where the conductors enter or leave a generating or sub-station a weather shield is provided. The shield is constructed of boards on the side of the structure which 34-O LONG-DISTANCE ELECTRIC POWER TRANSMISSION the high-voltage lines* enter, and is provided with an inclined roof and gutter, so that water falling on the roof is conducted off the sides and falls clear of the wires. At central stations, sub-stations, and switch houses throughout the transmission system the arrangement of the circuits and -switches is such that the attendants can connect any particular generator or step-up transformer to any circuit, any transmission circuit to any step-down transformer, and any distribution line to the bus-bars supplied from any generator. The 40,000 (nominal) horse-power developed by the two plants is transmitted to Troy, Albany, Schenectady, Cohoes, Lansingburg, Ballston Spa, Saratoga, Fort Edward, Sandy Hill, and Glens Falls, with an aggregate population of 300,000. The power is mainly utilized by manufacturing and electric railway properties. The General Electric Company alone has contracted for 10,000 horse-power. INDEX Admittance, definition, 171. equivalent of several admittances in parallel, 171. Aluminum, advantages and disad- vantages as conductor, 180. Area, cross section of jet, 6. method of determining stream, 27. Arresters, type of lightning, 148- 152. use of choke coils with, 221. Bibliography (Chapter II), 64. (Chapter III), 108. (Chapter IV), 158. (Chapter V), 177. (Chapter VI), 237. (Chapter VII), 265. (Chapter VIII), 290. (Chapter IX), 310. (Chapter X), 325. Bodies, laws of falling, 2. Breakers, circuit, 144-147. Buildings, designs of for power plants, 311. foundations for, 311. materials of construction, 311. Calculation of 75 Mile Three-Phase Line, 231. Canals and conduits, mean velocity of flow in, 45. definition of, 62. Missouri River Power Company, 33 i^- Capacity or condenscance, definition of, 167. effect of in circuits, 168. methods of overcoming, 168. Coefficient of contraction, 10. of discharge, n. of velocity, 10. Conductance, definition of, 171. Conductors, kinds of, 178. devices for fastening to insulators, 212. Constants, electrical, of lines Stan- dard Electric Co. of California, 174; electrical, of Bay Counties Power Company's transmission lines, 176. Contraction, influence of suppres- sion, ii. Converters, definition of synchro- nous, 291. advantages of over motor-genera- tors, 302, 304. definition of inverted, 291. determination of E. M. F. of, 292. frequency, use of, 309. General Electric, 301. hunting of, 298. racing of armature, 300. ratios of conversion and capacity, 294. starting of, 295. troubles of high frequency, 300. Westinghouse, 302. Copper, advantages of as conductor, 179. amount for given loss on maxi- mum difference of potential, 1 86. amount for given loss on mini- mum potential, 186. Coronal discharges on high-tension circuits, 225. Ryan's equation for, 228. Cost per kilowatt of hydro-electric power, 317. Alton D. Adams on cost, 319. of conductors, 319. of pole lines, 318. 341 342 INDEX Cost, continued. of transformers, 318. of water wheels, 317. Sault Ste. Marie plant, 317. Cross-arms, methods of attaching, 192. arrangement of on curves and dead ending, 195. arrangement of on straight lines, 195- treatment of before attaching, 192. Current, charging of Bay Counties Power Company's line, 176. Cycle, definition of, 161. Dams, types of, 29. "arch," 30. earthern, 31. "gravity," 30. hydraulic fill, 30. Missouri River Power Co., 330. pressure on, causes of failure, 32, 33- requirements of masonry, 29, rock-fill, 30. Detectors, ground, 152. connections of, 153. Farad, value of, 167. micro, value of, 167. Floats, kinds of, 25. method of determining velocity, by, 26. Flumes, construction, 46. Francis formula of, for velocity, 26. of Bay Counties Power Co., 334- stave and binder, 48. support of, 47. waste, 49. Forebays, purpose of, 61. Frequency, definition of, 161. Fuses, 134-137- Gates, head of Missouri River Power Co., 331. Gauging, method of determining dis- charge by, 27. Generators, kind used in long-dis- tance transmissions, 109. efficiency of, 114. inductor, HI. Generators, continued. parallel operation of, 114, regulation of, 112. revolving armature, 109. revolving field, no. types of American, 117-119. Governors, requisites of good, 79. electric speed controller of, 82. induction motor, 81. kinds of, 80. Lyndon "rapid," 92. switchboard control of, 81. types of American, 83-92. "Grizzles," definition of, 62. Grounding, of high-potential lines, 228. Head of water, definition, 2. Hydraulic radius, definition of, 23. machines, efficiencies of, 68. necessity for high efficiency, 70. power of waterfall utilized by, 76. requirements for high efficiency, 69. Impedance, definition of, 170. equivalent of several impedances in series and parallel, 171. resultant of several impedances in series, 170. Impulse, definition of, 7. Inductance, definition of, 162. definition of coefficient of, 163. effect in A. C. circuits, 162. methods of decreasing self circuits, 1 66. methods of expressing, 164. methods of mutual of circuits, 166. mutual of circuits, 164. Instruments, hydraulic measuring, 18. current meter, 20. differential mercury gauge, 20. differential pressure gauge, 19. hook-gauge, 18. piezometer, 18. water meter, 21. Insulators, kinds of, 205. advantages of glass, 208. advantages of porcelain, 206. clamp for standard, 213. INDEX 343 Insulators, continued. clamp, interlocking, 212. clamp, under-locking, 213. combination, 208. Locke high-tension, 210-211. "Muncie" type, 212. "Provo " type, 211. testing of, 209. Jet, energy of, 5. area of, 6. impulse and dynamic reaction of, 6. Kutter's formula, 46. Lightning, effects of, on circuits, 220. methods of safeguarding against, 222. Limitations of electric power trans- mission, 321. Lines, construction of pole, 189. factors which govern design and construction of transmission, 178. stresses on pole, 191. Losses, leakage and electrostatic, in lines, 224. Motor generators, ad vantage pf over- converters, 304. efficiencies of, 305. Motor repulsion, 287. Motors, behavior of synchronous, on starting, 267. curves of, 289. definition of slip, 275. efficiencies of induction, 281. faults of, 282. features of squirrel-cage induction, 27. features of variable-resistance in- duction, 275. General Electric, 288. induction, description" of, 274. limit of output of synchronous, 267. methods of starting synchronous, 267. power factor, 282. relations between torque and slip, 277- Motors, continued. relations between torque, speed, power, factor, etc., 278. speed regulation of induction, 278. synchronous, definition of, 266. theory of operation of induction, 277. troubles of synchronous, 272. use of synchronous, as voltage regulators, 270. Westinghouse, 285. Nozzles for water wheels, 75. deflecting, 78. needle regulating, 105. plug, 780 Orifices, flow from, 4. discharge from small, 4. flow from circular, 13. flow from rectangular and square vertical, 13. measurement of water by, 14. Pins, kinds of insulator, 203. advantage of metallic, 205. faults of wooden, 204. insulator, of Hudson River Power Co., 338. treatment of wooden, 203. Pipe lines, loss of head in, 37. cast iron, advantages, 54 circumferential pressure in, 51. construction of, 52. determination of diameter to dis- charge given quantity of water, 42. determination of discharge from, _42. friction, factor of, 37. influence of contraction of cross section, 38. kind of joints used on solid metal, 54- kinds of joints used on, 56. long pipes, 43. loss of head in, 39. maximum energy transmitted by, 44. mean velocity of flow in, 40. riveted pipe, 55. 344 INDEX Pipe lines, continued. stove pipe, advantages and disad- vantages of, 53. method of anchoring on steep grades, 59. auxiliaries of, 61. curve factors, 40. loss of head by curves, 39. safety devices for, 59. table of riveted, 60. Pipes, long, 43. expression for velocity in, 43. stresses in riveted steel, 51. Pole lines, patrolling of, 230. Poles for transmission lines, 187. sizes of and setting, 188. Power factor, definition of, 160. Power house of Missouri River Power Co., 331. of Bay Counties Company of Cali- fornia, 334. of Hudson River Company, 33.6- Power in an alternating current cir- cuit, 159. Power plants, arrangement of ma- chinery in, 312. description of Missouri River Power Co., 330. description of Snoqualmie Falls, 326. parallel operation of, 314. regulation of, 314. transmission, factors which govern cost, 317. Power transmission, electrical fac- tors of, 161. Pressure of water, i. distinction between pressure and head, 2. pressure head, 9. Protective devices, automatic station, 134- Protection of transmission lines from lightning, 220. Reactance, inductive, 165. capacity, 168. effect of, in circuits, 165. Receiver, water distributing, 327. Relay, overload, 137. Relay, continued. circuit connections of reverse cur- rent, 143- construction of time limit, 140- 142. function of overload time, 138. overload time limit, 138. reverse current, 142. reverse current time element, 143. Reservoirs, storage, 34. Resistance, definition of in a. c. cir- cuits, 169. Resonance, definition of, 172. effect of in series and parallel, 173- Right of way of Snoqualmie Falls Power Co., 327. of Missouri River Power Co., 333. Sand boxes, types of, 62. Scott, Charles F., investigation of losses on high-tension lines, 225. method of hysteresis measure- ment, 246. Spans, factors which govern length, 218. length for aluminum circuits, 220. length for copper circuits, 220. length of on Snoqualmie Falls line, 3 2 9- Speed of impulse and reaction tur- bines, 67. Star and delta methods of transfor- mer connections, 253. Static, strains in transformers, 251. interrupters for protecting, 252. Steel-supporting structures for trans mission lines, 197. advantages over pole lines, 199. comparison of cost, 200. types of, 200-203. Steinmetz, Charles P., investigation of losses on high-tension lines, 225. Storage reservoirs, factors which de- termine size of, 35. Streams, flow in, 23. definition of slope of water surface, 24. determination of energy of, 24. equations for discharge, 17-28. hydraulic radius of, 23. INDEX 345 Streams, continued. method of making weir measure- ments of, 17. willed perimeter of cross section, 2 3- Substations, design of, 315. methods of conducting current in, 3*5> 339- Surges in transmission lines, 220. causes of, 223224. Susceptance, definition of, 171. Switchboards for high-tension cur- rent, 119. instrument equipment, 120. location in power plants, 313. Switches for high voltages, 122. oil-break, 122-129. air-break with fuse, 129. "rams' horn" air-break, 132. Switching, when necessary, 133. Synchronizing, devices for, 153. Lincoln synchroscope, 155. principles of operation of, 154. synchronism indicator, 157. Table of loss of head in pipes, 41. riveted hydraulic pipe, 60. Transformers, capacity of, 243. comparison between Y and A methods of connection, 253. definition of, 239. efficiencies of, 244. equation for hysteresis loss in, 241 . Foucault current loss in, 242. grounding, secondaries of, 255. heating, test of, 249. insulation, test of, 250. kinds used in high-tension prac- tice, 257. location in power plants, 313. losses in, 240. methods of installation, 256. methods of making efficiency tests of, 250. Stanley water-cooled, 264. static interrupters for, 252. static strains in, 251. testing of, 245. various connections of, 253. Westinghouse air blast, 262. Westinghouse water-cooled, 264. Transpositions, on lines of Snoqual- mie Falls Power Co., 329. Turbine, definition of, 65. conditions to which impulse and reaction are adapted, 67. downward flow, 66. "impulse" and "reaction," 65. inward flow, 66. outward flow, 66. Turbines, types of American, 71. accessories of, 105. faults of, 99. installation of, 312. McCormick, 75. regulation of water supply to, 73. regulation of speed, 77. Samson, 71-72. testing of, 98. Victor, 72-73. Valves, gate, 105. safety relief, 106. Velocity, equations for, 3. head, 9. Water wheels, definition of, 65. accessories of, 105. bucket construction of, 75. Doble, 104. faults of, 99. impulse, effective headon, 77. Pelton, 100. principles of operation, 74. Risdon, 102. speed regulation of, 77. testing of, 98. things upon which speed and power depend, 76. types of American, 100-105. Weight of copper for various circuits, 182. WtirSj definition of, 14. equations for discharge of, 36. forms of, 36. kinds of, 15. waste, 35. Wood, methods of preserving, 195. Wires, methods of stringing, 214. factors which govern number of transpositions, 216. transposition of, 216. 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. 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