LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class Published by the McGraw-Hill Book. Company Ne~w York. to the BookDepartments of the McGraw Publishing Company Hill Publishing" Company FViblishers of Books for Electrical World The Engineering and Mining Journal The Engineering Record Power and The Engineer Electric Railway Journal American Machinist ffffmTlTBfflTfflTlMTffffl ELECTRIC TRANSMISSION OF WATER POWER By ALTON D. ADAMS, A.M. MEMBER AMERICAN INSTITUTE OF ELECTRICAL ENGINEERS NEW YORK Me GRAW-HILL BOOK Co. 1906 Copyrighted, 1906, by the McGRAW PUBLISHING COMPANY NEW YORK TABLE OF CONTENTS CHAPTER PAGE I. WATER-POWER IN ELECTRICAL SUPPLY i II. UTILITY OF WATER-POWER IN ELECTRICAL SUPPLY 10 III. COST OF CONDUCTORS FOR ELECTRIC-POWER TRANSMISSION . . 19 IV. ADVANTAGES OF THE CONTINUOUS AND ALTERNATING CURRENT . 31 V. THE PHYSICAL LIMITS OF ELECTRIC-POWER TRANSMISSION . . 44 VI. DEVELOPMENT OF WATER-POWER FOR ELECTRIC STATIONS ... 51 VII. THE LOCATION OF ELECTRIC WATER-POWER STATIONS .... 64 VIII. DESIGN OF ELECTRIC WATER-POWER STATIONS 83 IX. ALTERNATORS FOR ELECTRICAL TRANSMISSION 103 X. TRANSFORMERS IN TRANSMISSION SYSTEMS 122 XI. SWITCHES, FUSES, AND CIRCUIT -BREAKERS 135 XII. REGULATION OF TRANSMITTED POWER 155 XIII. GUARD WIRES AND LIGHTNING ARRESTERS 168 XIV. ELECTRICAL TRANSMISSION UNDER LAND AND WATER .... 187 XV. MATERIALS FOR LINE CONDUCTORS 200 XVI. VOLTAGE AND LOSSES ON TRANSMISSION LINES 215 XVII'. SELECTION OF TRANSMISSION CIRCUITS 233 XVIII. POLE LINES FOR POWER TRANSMISSION 246 XIX. ENTRIES FOR ELECTRIC TRANSMISSION LINES 261 XX. INSULATOR PINS . . .* . 270 XXI. INSULATORS FOR TRANSMISSION LINES 287 XXII. DESIGN OF INSULATOR PINS FOR TRANSMISSION LINES .... 298 XXIII. STEEL TOWERS 306 215144 ELECTRIC TRANSMISSION OF WATER- POWER. CHAPTER I. WATER-POWER IN ELECTRICAL SUPPLY. ELECTRICAL supply from transmitted water-power is now distributed in more than fifty cities of North America. These include Mexico City, with a population of 402,000; Buffalo and San Francisco, with 352,387 and 342,782 respectively; Montreal, with 266,^26, and Los Angeles, St. Paul, and Minneapolis, with populations that range between 100,000 and 200,000 each. North and south these cities extend from Quebec to An- derson, and from Seattle to Mexico City. East and west the chain of cities includes Portland, Springfield, Albany, Buffalo, Hamilton, To- ronto, St. Paul, Butte, Salt Lake City, and San Francisco. To reach these cities the water-power is electrically transmitted, in many cases dozens, in a number of cases scores, and in one case more than two hundred miles. In the East, Canada is the site of the longest transmis- sion, that from Shawinigan Falls to Montreal, a distance of eighty-five miles. From Spier Falls to Albany the electric line is forty miles in length. Hamilton is thirty-seven miles from that point on the Niagara escarp- ment, where its electric power is developed. Between St. Paul and its electric water-power station, on Apple River, the transmission line is twenty-five miles long. The falls of the Missouri River at Canon Ferry are the source of the electrical energy distributed in Butte, sixty-five miles away. Los Angeles draws electrical energy from a plant eighty-three miles distant on the Santa Ana River. From Colgate power-house, on the Yuba, to San Francisco, by way of Mission San Jose, the transmission line has a length of 220 miles. Between Electra generating station in the Sierra Nevada Mountains and San Francisco is 154 miles by the electric line. These transmissions involve large powers as well as long distances. The new plant on the Androscoggin is designed to deliver 10,000 horse- ELECTRIC TRANSMISSION OF WATER-POWER. Fort Ann Ashley Falls Power Statio Greenwich Waterford Lansingburgh on Met Station ELECTRIC RAILWAYS TRANSMISSION LINES Scale of Miles 10 Remission Lines. WATER-POWER IN ELECTRICAL SUPPLY. 3 power for electrical supply in Lewiston, Me. At Spier Falls, on the Huason, whence energy goes to Albany and other cities, the electric gen- erators will have a capacity of 32,000 horse-power. From the two water power stations at Niagara Falls, with their twenty-one electric generators of 5, ooo. horse-power each, a total of 105,000, more than 30,000 horse- power is regularly transmitted to Buffalo alone; the greater part of the capacity being devoted to local, industries. Electrical supply in St. Paul is drawn from a water-power plant of 4,000 and in Minneapolis from a like plant of 7,400 horse-power capacity. The Canon Ferry sta- tion, on the Missouri, that supplies electrical energy in both Helena and Butte, has a capacity of 10,000 horse-power. Both Seattle and Tacoma draw electrical supply from the 8,000 horse-power plant at Snoqual- mie Falls. The Colgate power-house, which develops energy for San Francisco and a number of smaller places, has electric generators of 15,000 horse-power aggregate capacity. At the Electra generating sta- tion, where energy is also transmitted to San Francisco and other cities on the way, the capacity is 13,330 horse-power. Electrical supply in Los Angeles is drawn from the generating station of 4,000 horse-power, on the Santa Ana River, and from two stations, on Mill Creek, with an aggregate of 4,600, making a total capacity of not less than 8,600 horse- power. Five water-power stations, scattered within a radius of ten miles and with 4,200 horse-power total capacity, are the source of electrical supply in Mexico City. The foregoing are simply a part of the more striking illustrations of that development by which falling water is generating hundreds of thou- sands of horse-power for electrical supply to millions of population. This application of great water powers to the industrial wants of distant cities is hardly more than a decade old. Ten years ago Shawinigan Falls was an almost unheard-of point in the wilds of Canada. Spier Falls was merely a place of scenic interest; the Missouri at Canon Ferry was not lighting a lamp or displacing a pound of coal ; that falling water in the Sierra Nevada Mountains should light the streets and operate electric cars in San Francisco seemed impossible, and that diversion of Niagara, which seems destined to develop more than a million horse-power and leave dry the precipices over which the waters now plunge, had not yet begun. In some few instances where water-power was located in towns or cities, it has been applied to electrical supply since the early days of the indus- try. In the main, however, the supply of electrical energy from water- power has been made possible only by long-distance transmission. The extending radius of electrical transmission for water-powers has formed 4 ELECTRIC TRANSMISSION OF WATER-POWER. FIG. 2. Snoqualmie Falls Transmission Lines. WATER-POWER IN ELECTRICAL SUPPLY. 5 the greatest incentive to their development. This development in turn has reacted on the conditions that limit electrical supply and has mate- rially extended the field of its application. Transmitted water-power has reduced the rates for electric service. It may not be easy to prove this reduction by quoting figures for net rates, because these are not generally published, but there are other means of reaching the conclusion. In the field of illumination electricity competes directly with gas, and in the field of motive power with coal. During the past decade it is well known that the price of gas has materially declined and the price of coal, barring the recent strike period, has certainly not increased. In spite of these reductions electrical supply from water-power has displaced both gas and coal in many instances. Moreover, the expansion of electric water-power systems has been decidedly greater, as a rule, than that of electrical supply from steam- driven stations. An example of the fact last stated may be seen in Port- land, Me. In the spring of 1899, a company was formed to transmit and distribute electrical energy in that city from a water-power about thirteen miles distant. For some years, prior to and since the date just named, an extensive electric system with steam-power equipment has existed in Portland. In spite of this, the system using water-power, on January i st, 1903, had a connected load of 352 enclosed arcs and 20,000 incandescent lamps, besides 835 horse-power in motors. Comparing the expansion of electric water-power systems with those operated by steam, when located in different cities, Hartford and Spring- field may be taken on the one hand and Fall River and New Bedford on the other. The use of water-power in electrical supply at Hartford be- gan in November, 1891, and has since continued to an increasing extent. Throughout the same period electrical supply in Fall River has been derived exclusively from steam. In 1890 the population of Hartford was 53,230, and in 1900 it stood at 79,850, an increase of 50 per cent. At the beginning of the decade Fall River had a population of 74,398, and at its close the figures were 104, 863, a rise of 40.9 per cent. In 1892 the connected load of the electric supply system at Fall River included 451 arc and 7,800 incandescent lamps, and motors aggregating 140 horse- power. By 1901 this load had increased to 1,111 arcs, 24,254 incandes- cent lamps, and 600 horse-power in motors. The electric supply system at Hartford in 1892 was serving 800 arcs, 2,000 incandescent lamps, and no motors. After the use of transmitted water-power during nine years the connected load of the Hartford system had come to include 1,679 arcs, 68,725 incandescent lamps, and 3,476 horse-power of motor capac- 6 ELECTRIC TRANSMISSION OF WATER-POWER. ity in 1901. At the beginning of the decade Hartford was far behind Fall River in both incandescent lamps and motors, but at the end Hart- ford had nearly three times as many incandescent lamps and nearly six times as great a capacity in connected motors. As Fall River had a pop- ulation in 1900 that was greater by thirty-one per cent, than the popula- tion of Hartford, and the percentage of increase during the decade was only 9.1 lower in the former city, water-power seems to have been the most potent factor in the rise of electric loads in the latter. Electric gains at Hartford could not have been due to the absence of competition by gas, for the price of gas there in 1901 was $i per 1,000 cubic feet, while the price in Fall River was $1.10 for an equal amount. Water-power began to be used in electrical supply at Springfield dur- ing the latter half of 1897. ^ n that year the connected load of the Spring- field electric system included 1,006 arcs, 24,778 incandescent lamps, and motors with a capacity of 647 horse-power. Five years later, in 1902, this connected load had risen to 1,399 arc lamps, 45,735 incandescent lamps, and a capacity of 1,025 horse-power in electric motors. At New Bedford, in 1897, the electric system was supplying 406 arc and 22,122 incandescent lamps besides motors rated at 298 horse-power. This load, in 1902, had changed to 488 arcs, 18,055 incandescent lamps, and 432 horse-power in capacity of electric motors. From the foregoing figures it appears that while 82 arc lamps were added in New Bedford, 393 such lamps were added in Springfield. While the electric load at New Bedford was increased by 134 horse-power of motors, the like in- crease at Springfield was 378 horse-power, and while the former city lost 4,067 from its load of incandescent lamps, the latter gained 20,957 ^ these lamps. During all these changes electrical supply in Springfield has come mostly from water-power, and that in New Bedford has been the product of steam. Population at Springfield numbered 44,179 in 1890 and 62,059 in 1900, an increase of 40.5 per cent. In the earlier of these years New Bedford had a population of 40,733, and in the later 62,442, an increase of 53.3 per cent. In 1902 the average price obtained for gas at Springfield was #1.04 and at New Bedford #1.18 per 1,000 cubic feet. Springfield contains a prosperous gas system, and the gross income there from the sale of gas was thirty-one, per cent greater in 1902 than in 1897. During this same period of five years the gross income from sales of electrical energy, developed in large part by water-power, in- creased forty-seven per cent. For the five years of general depression, ending in 1897 tne gross annual income of gas sales in Springfield rose WATER-POWER IN ELECTRICAL SUPPLY. 7 only five per cent, and the like electric income nine per cent. In the five years last named the electrical supply system was operated with coal. The application of transmitted water-power in electrical supply has displaced steam as a motive power in many large industrial plants that never would have been operated from steam-driven electric stations. An example of this sort exists at Portland, where one of the motors operated by the electric water-power system, in an industrial plant, has a capacity of 300 horse-power. Every pound of coal burned in Concord, N. H., is hauled by the single steam railway system entering that city, which rail- way operates large car and repair shops there. Some years ago the rail- way installed a complete plant of engines, dynamos, and motors for elec- tric-driving throughout these shops. These engines and dynamos now stand idle and the motor equipment, with an aggregate capacity of 590 horse-power, is operated with energy purchased from the local electrical supply system and drawn from water-power. Another striking example of the ability of electric water-power systems to make power rates that are attractive to large manufacturers may be seen at Manchester, N. H. One of the largest manufacturing plants in that city purchases energy for the operation of the equivalent of more than 7,000 incandescent lamps, and of motors rated at 976 horse-power, from the electrical supply system there, whose generating stations are driven mainly by water-power. The Manchester electrical supply system also furnishes energy, through a sub-station of 8oo-horse-power capacity, to operate an electric railway connecting Manchester and Concord. This electric line is owned and operated in common with the only steam rail- way system of New Hampshire, so that the only inducement to purchase energy from the water-power system seems to be one of price. In Buffalo the electric transmission system from Niagara Falls supplies large motors of about 20,000 horse-power capacity in manu- facturing and industrial works, and 7,000 horse-power to the street rail- way system, besides another 4,000 horse-power for general service in lighting and small motors. Few large cities in the United States have cheaper coal than Buffalo, and in Portland, Concord, and Manchester coal prices are moderate. In the Rocky Mountain region, where coal is more expensive, the greater part of the loads of some electric water-power systems is made up of large industrial works. In Salt Lake City the elec- trical supply system, which draws its energy almost exclusively from water-powers, had a connected load of motors aggregating 2,600 horse- power as far back as 1901, and also furnished energy to operate the local electric railway, and several smelters six miles south of the city, besides 8 ELECTRIC TRANSMISSION OF WATER-POWER. all the local lighting service. As good lump coal sells in Salt Lake for #4.50 per ton, slack at less than one-half this figure, and the population there by the late census was only 53,531 , the figures for the load of motors are especially notable. At Helena energy from the 10,000 horse-power station at Canon Ferry operates the local lighting and power systems, two smelting and a mining plant. In Butte, energy from the station just named operates the works of five smelting and mining companies, driving motors that range from i to CITIES WITH ELECTRICAL SUPPLY FROM WATER-POWER. City. Miles from Water- Power to City. Horse-Power of Water- Driven Stations. Population. Mexico City I O to I ^ 4 200 402 ooo Buffalo 2 3 #2Q OOO 2IT2 387 Montreal . 8? 266,826 San Francisco 147 I 3 3 30 742,782 Minneapolis 2O2 7l8 St Paul . 2? 4 ooo 163 o6"\ Los Angeles. 8* 8 600 IO2 47O Albany. . . o 4.O 32 ooo O4 I ^1 Portland, Ore. . oo 426 Hartford I j 3600 70 8<;o Springfield, Mass 6 3 780 62 o^o Manchester N H T 2 CQ 08? Salt Lake City 1 6'5 26 c >6/ while the line from Colgate to Oakland with 31.5 times the length of the former operates at an average of only 422 volts per mile. Of the fifteen transmissions considered, six are over distances of less than 15 miles, and for four of the six the voltage is more than 900 per mile. Eight transmissions range from 23 to 83 miles in length, with voltages that average between 1,000 volts per mile at 25 miles and only 397 per mile on the 83 -mile line. The volts per mile are 6 times as great in the Ludlow as in the Oakland transmission. These wide variations in the volts per mile on transmission lines and COST OF CONDUCTORS FOR TRANSMISSION. 27 in length of lines lead to different weights of conductors per kilowatt of generator capacity. All other factors remaining constant, the weight of conductors per kilowatt of generator capacity would be the same what- CAPACITY OF GENERATING STATIONS AND WEIGHT OF CONDUCTORS. Location of Transmission. Kilowatt Capacity at Generators. Total Weight of Conductors. Pounds of Conductors per Kilowatt Capacity. Wilbraham to Ludlow 4,600 17 820 , 7* Se wall's Falls to railroad shops 4?o 6,0 1 4 I r Into Victor Colo. . . . 600 i ^ 060 To Dales, Ore. ooo 7-2 Q7Q Apple River to St. Paul ,000 I 555 28 ELECTRIC TRANSMISSION OF WATER-POWER. volts per mile have the equivalent of 7.4 to 15 pounds of copper each, pet kilowatt of generator capacity. Of the seven transmissions using between 36 and 79 pounds of cop^ per for each kilowatt of generator capacity, four have voltages ranging from 827 to 1,000 per mile, and on only one is the pressure as low as 643 volts per mile. Five transmission lines vary between 115 and 295 pounds of copper, or its equivalent, per kilowatt of generator capacity, and their voltages per mile are as high as 769 in one case and down to 281 in another. Allowing for some variations in the percentages of loss in transmission lines at full load, the fifteen plants plainly illustrate the ad- . vantage of a high voltage per mile, as to the weight of conductors. This advantage is especially clear if the differences due to the lengths of the transmissions are eliminated by dividing the weight of conductors per kilowatt of generator capacity in each case by the length of the transmis- sion in miles. This division gives the weight of conductors per kilowatt of generators for each mile of the line, which may be called the weight WEIGHT AND COST OF CONDUCTORS. Pounds per Kilowatt Mile. Dollars per Generator Kilowatt. o 86* ill Se wall's Falls to railroad shops 2 7 2 2< Into Victor, Colo O I ^O To Dales, Ore. 5IO Apple River to St. Paul 2 I AV -* 7 O< Farmington River to Hartford 32 /vo 10 80 Canon Citv to Cripple Creek . . i 6 z 8< Yadkin River to Salem 2 6 * 8s Montmorency Falls to Quebec ..... 112 j-'-'j ii.Sq Canon Ferry to Butte 1.7 17. 2S San Gabriel Canon to Los Angeles 2 6 o 8s Welland Canal to Hamilton . I 7 4S Madrid to BlaoJ, N. M. 66 31 80 Ogden to Salt Lake City 3e 10 "?S Santa Ana Riverto Los Angeles ... 3.C 44. 2S Colgate to Oakland . . \ -S6 24. i; 1 .27* *Aluminum. per kilowatt mile. For the Ludlow transmission this weight is only 0.86 pound of aluminum, the equivalent of 1.72 pounds of copper, while the like weight for the line into Quebec is 11.2 pounds of copper, or 6.5 times COST OF CONDUCTORS FOR TRANSMISSION. 29 that for the former line. But the voltage per mile on the Ludlow is 3.2 times as great as the like voltage on the Quebec line. The weight of conductor per kilowatt mile in the Victor line is only 0.9 pound, and the like weight for the line between Madrid and Bland is 6.6 pounds, or 7.3 times as great. On the Victor line the voltage per mile is 2.5 times as great as the voltage for each mile of the Bland line. Comparing systems with nearly equal voltages per mile, it appears in most cases that only such difference exists in their pounds of conduc- tors per kilowatt mile as may readily be accounted for by designs for vari- ous percentages of loss at full load. Though the transmission line into Butte is nearly twice as long as the one entering Hamilton, the weight of conductors for each is i .7 pounds per kilowatt mile. The line from Santa Ana River is more than twice as long as the one entering Salt Lake City, but its voltage per mile is only nine per cent less, and there are 3.5 pounds of copper in each line per kilowatt mile. The final, practical questions as to conductors in electrical transmis- sion relate to their cost per kilowatt of maximum working capacity, and per kilowatt hour of delivered energy. If the cost of conductors per kilo- watt of generator capacity is greater than that of all the remaining equip- ment, it is doubtful whether the transmission will pay. If fixed charges on the conductors more than offset the difference in the cost of energy per kilowatt hour at the points of development and delivery, it is certain that the generating plant should be located where the power is wanted. The great cost of conductors is often put forward as a most serious impediment to long-distance transmission, and the examples here cited will indicate the weight of this argument. In order to find the approximate cost of con- ductors per kilowatt of generator capacity for each of the transmission lines here considered, the price of bare copper wire is taken at 1 5 cents l and the price of bare aluminum wire at 30 cents per pound . In each case the weight of copper or aluminum conductor per kilowatt of generator capacity is used to determine their costs per kilowatt of this capacity at the prices just named. This process when carried out for the 15 transmis- sion lines shows that their cost of conductors per kilowatt of generator capacity varies between #i .1 1 for the 4.5 mile line into Ludlow and #44.25 for the line of 83 miles from the Santa Ana River. It should be noted that the former of these lines operates at 2,555 an< ^ the latter at 397 volts per mile. The line into Madrid shows an investment in conductors of #3 1 .80 per kilowatt of generator capacity with 625 volts per mile. That a long transmission does not necessarily require a large investment in conduc- tors per kilowatt of generator capacity is shown by the line 65 miles long 30 ELECTRIC TRANSMISSION OF WATER-POWER. into Butte, for which the cost is $17.25 per kilowatt, with 769 volts per mile. For the transmission to St. Paul, a distance of 25 miles, at 1,000 volts per mile, the cost of conductors is $7.95 per kilowatt of generator capacity. The seven-mile line into Quebec shows an investment of $i i .85 per kilowatt of generator capacity. CHAPTER IV. ADVANTAGES OF THE CONTINUOUS AND ALTERNATING CURRENT. ELECTRICAL transmission over long distances in America have been mainly carried out with alternating current. In Europe, on the other hand, continuous current is widely used on long transmissions at high voltages. So radical a difference in practice seems to indicate that neither system is lacking in points of superiority. A fundamental feature of long transmissions is the high voltage neces- sary for economy in conductors, and this voltage is attained by entirely different methods with continuous and alternating currents. In dyna- mos of several hundred or more kilowatts capacity the pressure of con- tinuous current has not thus far been pushed above 4,000 volts, because of the danger of sparking and flashing at the commutator. Where 10,000 or more volts are required on a transmission line with continuous current a number of dynamos are connected in series so that the voltage of each is added to that of the others. In this way the voltage of each dynamo may be as low as is thought desirable without limiting the total line volt- age. There is no apparent limit to the number of continuous-current dynamos that may be operated in series or to the voltage that may be thus obtained. In the recently completed transmission from St. Maurice to Lausanne, Switzerland, with continuous current, ten dynamos are con- nected in series to secure the line voltage of 23,000. When occasion re- quires twenty or thirty or more dynamos to be operated in series, giving 50,00001' 75,000 volts on the line, machines exactly like those in the trans- mission just named, may be used. No matter how many of these dyna- mos are operated in series the electric strain on the insulation of the windings of each dynamo remains practically constant, because the iron frame of each dynamo is insulated in a most substantial manner from the ground. The electric strain on the insulation of the windings of each dynamo in the series is thus limited to the voltage generated by that dynamo. There is no practical limit to the thickness or strength of the insulation that may be interposed between the frame of each dynamo and the ground, and hence no limit to line voltage as far as dynamo in- sulation is concerned. 32 ELECTRIC TRANSMISSION OF WATER-POWER. It is impracticable to operate alternating dynamos in series so as to add their voltages, and the pressure available in transmission with alter- nating current must be that of a single dynamo or must be obtained by the use of transformers. The voltage of an alternating may be carried much higher than that of a continuous-current dynamo of very large capacity, and in many cases pressures of 13,200 volts are now sup- plied to transmission lines by alternating dynamos. Just how high the voltage of single alternating dynamos will be carried no one can say, but it seems probable that the practical limit will prove to be much less than the voltages now employed in some transmissions. As the voltage of alternating dynamos is carried higher the thickness of insulation on their armature coils and consequently the size or number of slots in their armature cores and the size of these cores increase rapidly. The dimensions and weight of an alternating dynamo per unit of its capacity thus go up with the voltage, and at some undetermined point the cost of the high-voltage dynamo is greater than that of a low- voltage dynamo of equal capacity with raising transformers. To the voltage that may be supplied by transformers there is no practical limit now in sight. Lines have been in regular operation from one to several years on which transformers supply 40,000 to 50,000 volts; some large transformers have been built for commercial use at 60,000 volts, and other transformers for experimental and testing purposes have been employed in a number of cases for pressures of 100,000 volts and more. Available voltages for continuous- and alternating-current transmis- sions are thus on a practically equal footing as to their upper limit. The amount of power that may be generated and delivered with either the alternating- or continuous-current system of transmission is practically unlimited. Single alternating dynamos may be had of 5,000 or even 8,000 kilowatts capacity if desired, but it is seldom that these very large units are employed, because the capacity of a generating station should be divided up among a number of machines. It is perhaps impractica- ble to build single continuous-current dynamos with capacities equal to those of the largest alternators, but as any number of the continuous- current machines may be operated either in series or multiple, the power that may be applied to a transmission circuit is unlimited. At the plant or plants where the power transmitted by continuous current is received, a number of motors must be connected in series to operate at the high-line voltage. These motors may all be located in a single room, may be connected to machinery in different parts of a build- ing, or may be in use at points miles apart. The vital requirement is that CONTINUOUS AND ALTERNATING CURRENT. 33 the motors must be in series with each other so that the line voltage divides between them. If simply mechanical power is wanted at the places where the motors are located, they complete the transmission system and no further electrical apparatus is required. Where, however, as at Lausanne, the transmitted power is to be used in a system of gen- eral electrical supply, the motors that receive the current at the line volt- age must drive dynamos that will deliver energy of the required sorts. In the station at Lausanne four of the motors to which the transmission line is connected each drives a 3,000- volt three-phase alternator for the distribution of light and power. The fifth motor at this station drives a 6oo-volt dynamo which delivers continuous current to a street railway. A sixth motor in the same series drives a cement factory some distance from the station. Neglecting minor changes in capacity due to losses in the line and motors, this continuous-current system must thus include three kilowatts in motors and dynamos for each kilowatt delivered for general electrical distribution at the receiving station. In a case in which only mechanical power is wanted at the receiving station, the dynamos and motors concerned in the transmission must have a combined capac- ity of two horse-power for each horse-power delivered at the motor shaft. In contrast with these figures, the electrical equipment in a trans- mission with alternating current for mechanical power alone includes two kilowatts capacity in generators and motors, besides two kilowatts ca- pacity in transformers for each corresponding unit of power delivered at the motor shaft unless generators and motors operate at the full line voltage. If a general electrical supply is to be operated by the alter- nating system of transmission, either motors and dynamos or rotary converters must be added to transformers where continuous current is required. An alternating transmission may thus include as little as one kilowatt in dynamos and one in transformers, or as much as two kilowatts capacity in dynamos, two in transformers, and one in mo- tors for each kilowatt delivered to distribution lines at the receiving station. Line construction from the continuous-current transmission is of the most simple character apart from the necessity of high insulation. Only two wires are necessary and they may be of any desired cross-section, strung on a single pole line and need not be transposed. On these wires the maximum voltage for which insulation must be provided is the nom- inal voltage of the system. It is possible under these conditions to build a single transmission line with two conductors of such size and strength and at such a distance apart that a high degree of reliability is attained 3 34 ELECTRIC TRANSMISSION OF WATER-POWER. against breaks in the wires or arcing between them. In a transmis- sion of power by two- or three-phase alternating current at least three wires are necessary and six or more are often employed. If six or more wires carrying current at the high voltages required by long trans- missions are mounted on a single line of poles, it is not practicable to obtain such distances between the wires as are desirable. The repair of one set of wires while the other set is in operation is a dangerous task, and an arc originating between one set of the wires is apt to be com- municated to another set. For these reasons two pole lines are frequently provided for a transmission with alternating current, and three or more wires are then erected on each line. Compared with a continuous-cur- rent transmission, one with alternating current often requires more poles and is quite certain to require more cross-arms, pins, insulators, and labor of erection. For a given effective voltage of transmission it is harder to insulate an alternating- than a continuous-current line. In the first place the maximum voltage of the alternating line with even a true sine curve of pressure is 1.4 times the nominal effective voltage, but the insulation must withstand the maximum pressure. Then comes the matter of resonance, which may carry the maximum voltage of an alter- nating circuit up to several times its normal amount, if the period of electrical vibration for that particular circuit should correspond to the frequency of the dynamos that operate it. Even where the vibration period of a transmission circuit and the frequency of its dynamos do not correspond, and good construction should always be planned for this lack of agreement, resonance may and often does increase the normal voltage of an alternating transmission by a large percentage. The alter- nating system of transmission must work at practically constant voltage whatever the state of its load, so that the normal stress on the insulation is always at its maximum. In a transmission with continuous current on the other hand, if the prevailing practice of a constant current and varying pressure on the line is followed, the insulation is subject to the highest voltage only at times of maximum load on the system. Lightning is a very real and pressing danger to machinery connected to long trans- mission lines, and this danger is much harder to guard against in an alternating system than in a system with continuous constant current. The large degree of exemption from damage by lightning enjoyed by series arc dynamos is well known, the magnet windings of such machines acting as an inductance that tends to keep lightning out of them. More- over, with any continuous-current machines lightning arresters having large self-induction may be connected in circuit and form a most effective CONTINUOUS AND ALTERNATING CURRENT. 35 safeguard against lightning, but this plan is not practicable on alternat- ing lines. In the matter of switches, controlling apparatus, and switchboards, an alternating transmission requires much more equipment than a sys- tem using continuous, constant current. The ten dynamos in the gen- erating station at St. Maurice, with a capacity of 3,450 kilowatts at 23,000 volts, are each connected and disconnected with the transmission by a switch in a small circular column of cast-iron that stands hardly breast high. An amperemetre and voltmetre are mounted on each dynamo. The alternating generators in a station of equal capacity and voltage would require a large switchboard fitted with bus-bars, oil switches, and automatic circuit-breakers. Relative efficiencies for the continuous- current and the alternating-transmission systems vary with the kind of service required at receiving stations and with the extent to which trans- formers are used in the alternating system, other factors being constant. For purposes of comparison the efficiency at full load of both alternating- and continuous-current dynamos and motors, also of rotary converters, may be fairly taken at 92 per cent, and the efficiency of transformers at 96 per cent. For the line an efficiency of 94 per cent may be assumed at full load, this being the actual figure in one of the Swiss transmissions of 2,160 kilowatts at 14,400 volts to a distance of 32 miles. Where the continuous current system must simply deliver mechanical power at the receiving stations, its efficiency under full load amounts to92X-94X-9 2 = 79.65 per cent from dynamo shaft to motor shaft. An alternating sys- tem delivering mechanical power will have an efficiency of 92 x -94 X .96 x -9 2 = 76.46 per cent between dynamo shaft and motor shaft, if the line voltage is generated in the armature coils of the dynamo and the line loss is 6 per cent. If step-up transformers are employed to secure the line voltage the efficiency of the alternating transmission de- livering mechanical power drops to the figure of 92 x -96 X -94 X -96 X .92 = 73.40 per cent. It thus appears that for the simple delivery of mechanical power the continuous current transmission has an advan- tage over the alternating of three to six per cent in efficiency, depending on whether step-up transformers are employed. When the receiving station must deliver a supply of either continuous or alternating current for general distribution, the efficiency of the con- tinuous-current transmission amounts to 92 x -94 X -9 2 X -9 2 = 73- 2 7 per cent. The alternating-transmission system in a case in which no step- up transformers are employed will deliver alternating current of the same 36 ELECTRIC TRANSMISSION OF WATER-POWER. frequency as that on the transmission line at any desired pressure for general distribution at an efficiency of 92 x -94 X -96 = 83.02 per cent, if step-down transformers are used, brut the efficiency drops to 83.02 x .96 = 79.70 per cent, when step-up transformers are introduced. If the alternating transmission uses no step-up transformers and delivers either alternating or continuous current by means of motor generators, its efficiency at full load is 83 .02 x -9 2 X -9 2 = 70.26 per cent, but with step-up transformers added the efficiency drops to 70.26 x -96 = 67.43 per cent. In a transmission where electrical energy must be delivered for general distribution, the full-load efficiency of an alternating system ranges either higher or lower than that of a continuous-current system depending on whether the current from the transmission line must be converted or not. Line loss is the same whatever the load in a constant-current trans- mission, so that line efficiency falls rather rapidly with the load. On the other hand, at constant pressure the percentage of energy loss on the line varies directly with the load, but the actual rate of energy loss with the square of the load. On partial loads the line efficiency is thus much higher with alternating than with continuous constant current. Efficiency of electrical machinery is generally low at partial loads, so that in cases in which the number or capacity of alternating dynamos, transformers, motors, or rotary converters for a transmission would be greater per unit of delivered power than the corresponding number or capacity of machines for a transmission by continuous current, the latter would probably have the advantage in the combined efficiency of ma- chinery at partial loads. In this way the lower-line efficiency of one sys- tem might offset the lower efficiency of machinery in the other. Energy is usually very cheap at the generating station of a transmission system. For this reason small differences in the efficiencies of different systems should be given only moderate weight in comparison with the items of first cost, reliability, and expense of operation. In the matter of first cost at least the continuous-current system seems to have a distinct advantage over the alternating. Without going into a detailed estimate, it is instructive to consider the figures given by a body of five engineers selected to report on the cost of continuous- and alternat- ing-current equipments for the St. Maurice and Lausanne transmission. According to the report of these engineers, a three-phase transmission sys- tem would have cost $140,000 more than the continuous-current system actually installed, all other factors remaining constant. It should be noted that the conditions of this transmission are favorable to three-phase work- CONTINUOUS AND ALTERNATING CURRENT. 37 ing and unfavorable to continuous-current equipment, because all of the energy except that going to the 400 horse-power motor at the cement mill must be delivered at the receiving station for general distribution. More- over, four out of the five motors at Lausanne drive three-phase generators, and only one drives a continuous-current dynamo for the electric railway, so that a three-phase transmission would have required only one rotary converter. Had the transmission been concerned merely with the de- livery of mechanical power, as at the cement mill, the advantage of the continuous- over the alternating-current system in the matter of first cost would have been much greater than it was. Long-distance transmission with three-phase current began at Frank- fort, in 1891, when 58 kilowatts were received over a 2 5,000- volt line from Lauffen, 109 miles away. Shortly after this historic experiment, three-phase transmission in the United States began on a commercial scale, and plants of this sort have multiplied rapidly here. Meantime very little has been done in America with continuous currents in long transmissions. In Europe, the birthplace of the three-phase system, it has failed to displace continuous current for transmission work. About a score of these continuous-current transmissions are already at work there. If the opinion of European engineers as to the lower cost of the continuous-current system, all other factors being equal, is confirmed by experience, this current will yet find important applications to long trans- missions in the United States. Systems of transmission with continuous-current may operate at con- stant voltage and variable current, at constant current and variable volt- age, or with variations of both volts and amperes to correspond with changes of load. Dynamos of several thousand kilowatts capacity each can readily be had at voltages of 500 to 600, but the attempt to con- struct dynamos to deliver more than two or three hundred kilowatts each at several thousand volts has encountered serious sparking at the commutator. Thus far, dynamos that yield between 300 and 400 kilo- watts each have been made to give satisfactory results at pressures as high as 2,500 volts. Another one of the Swiss transmissions takes place over a distance of thirty- two miles at 14,400 volts, the capacity being 2,160 kilowatts. To give this voltage and capacity, eight dynamos are connected in series at the generating station, each dynamo having an output of 150 amperes at i, 800 volts, or 216 kilowatts. Continuous-current motors are, of course, subject to the same limita- tions as dynamos in the matter of capacity at high voltage, so that a series 38 ELECTRIC TRANSMISSION OF WATER-POWER. of motors must be employed to receive the high-pressure energy from the line. The number of these motors may just equal, or may be less or greater than the number of dynamos, but the total working voltage of all the motors in operation at one time must equal the total voltage of the dynamos in operation at that time minus the volts of drop in the line. Each constant-current motor may have any desired capacity up to the practicable maximum, but it must be designed for the current of the system. The voltage at the terminals of each motor varies with its load, being greatest when the motor is doing the most work. Constant speed is usually attained at each motor by means of a variable resistance con- nected across the terminals of the magnet coils. The amount of this re- sistance is regulated by a centrifugal governor, driven by the motor shaft. This governor also shifts the position of the brushes on the commutator to prevent sparking as the current flowing through the magnet coils is changed. For a constant-current transmission the magnet and armature wind- ings of both dynamos and motors are usually connected in series with each other and the line so that the same current passes through every element of the circuit, except that each motor may have some current shunted out of its magnet coil for the purpose of speed regulation. In some cases, however, the magnet coils of the dynamos are con- nected in multiple with each other and receive their current from a sep- arate dynamo designed for the purpose. With this separate excitation of the magnet coils, the dynamo armatures are still connected in series with each other and the line. The total voltage at the generating station and on the line af a con- stant-current system varies with the rate at which energy is delivered, and has its maximum value only at times of full load. To obtain this varia- tion of voltage, it is the general practice to change the speed of the dyna- mos by means of an automatic regulator which is actuated by the line current. Any increase of the line current actuates the regulator and re- duces the speed of the dynamos, while a decrease of the line current raises the dynamo speed. With a good regulator the variations of the line current are only slight. Under this method of regulation the dyna- mos in operation have a substantially constant current in both armature and magnet coils at all times, so that there is no reason to shift the posi- tion of the brushes on the commutator. Generating stations of constant current transmission systems are generally driven by water-power and the speed regulator operates to change the amount of water admitted to each wheel. Each turbine CONTINUOUS AND ALTERNATING CURRENT. 39 wheel usually drives a pair of dynamos, but one or any number of dyna- mos might be driven by a single wheel. The two dynamos driven by a single wheel are generally connected in series at all times, and are cut in or out of the main circuit together. When the load on a constant- current generating station is such that the voltage can be developed by less than all the dynamos, one or more dynamos may be stopped and taken out of the circuit. To do this the dynamo or pair of dynamos to be put out of service may be stopped, their magnet coils having first been short-circuited, and then a switch across the connections of their armatures to the lines closed, after which the connections of the armatures to the line are opened. By a reverse process, any dynamo or pair of dynamos may be cut into the operating circuit. At the terminals of each dynamo in the series, while in operation, the voltage is simply that developed in' its armature, so that the insulation between the several windings is subject to only a corresponding stress. The entire voltage of the line, however, tends to force a current from the coils of the dynamo at one end of the series into its frame, thence to any substance on which that frame rests, and so on to the frame and coils of the dynamo at the other end of the series. To protect the insulation of the dynamo coils from the line voltage, thick blocks of porcelain are placed beneath the dynamo frames, and the armature shafts are con- nected to those of the turbines by insulating couplings. Besides the switches, already mentioned, a voltmeter and ammeter should be provided for each dynamo and also for the entire series of machines. This completes the switchboard equipment, which is, there- fore, very simple. As the line loss of a constant-current system is the same whatever the load that is being operated, this loss may be a large percentage of the total output when the load is light. If, for illustration, five per cent of the maximum voltage of the station is required to force the constant current through the line, the percentage of line loss will rise to ten when the station voltage is one-half the maximum, and to twenty when the station is delivering only one-quarter of its full capacity. In view of this property of constant-current working, the line loss should be made quite small in its ratio to the maximum load, as most stations must work on partial loads much of the time. Five per cent of maximum station voltage is a fair general figure for the line loss in a con- stant-current transmission, but the circumstances of a particular case may dictate a higher or a lower percentage. 40 ELECTRIC TRANSMISSION OF WATER-POWER. On the 32-mile transmission, above named, the loss in the line is six per cent of the station output at full load. If a transmission with continuous current is to be carried out at con- stant pressure the limitation as to the capacity and voltage of each dy- namo is about the same as with constant current. Probably more energy is now transmitted by continuous current at constant pressure than by any other method, the greater part being devoted to electric railway work at 500 to 600 volts. Dynamos for about these voltages can readily be had in capacities up to several thousand kilowatts each, but the length of transmission that can be economically carried out at this pressure is comparatively small. For each kilowatt delivered to a line at 500 volts and to be transmitted to a distance of five miles at a ten per cent loss in the line, the weight of copper conductors must be 372 pounds, costing #56.80 at 15 cents per pound. This sum is twice to four times the cost of good continuous-current dynamos per kilowatt of capacity. If the distance of transmission is ten miles and the voltage and line loss re- main as before, the weight of copper conductor must be increased to 1,488 pounds per kilowatt delivered to the line, costing #227.20. Experience has shown that in sizes of not more than 400 kilowatts, continuous-current dynamos may safely have a voltage of 2,000 each, and any number of such dynamos may be operated in multiple, giving whatever capacity is desired. At 2,000 volts and a loss of 10 per cent in the line the weight of copper conductors per kilowatt would be 93 pounds, costing #13.95, f r eacn kilowatt delivered to the line on a 10- mile transmission. With 2,000 volts on a 2o-mile transmission the weight of conductors per kilowatt would be the same as their weight on a 5-mile transmission at 500 volts, the percentage of loss being equal in the two cases. Large continuous-current motors of, say, 50 kilowatts or more can be had for a pressure of 2,000 volts, so that any number of such motors might be operated from a 2,000- volt, constant-pressure line entirely independent of each other. From these figures it is evident that a transmission of 10 miles may be carried out with continuous-current at constant pressure from a single dynamo with good efficiency and a mod- erate investment in conductors. When the distance is such that much more than 2,000 volts are re- quired for the constant-pressure transmission, with continuous current, resort must be had to the connection of dynamos and motors in series. Any number of dynamos may be so connected as in the case of constant- current work. The combined voltages of the series of motors connected to the constant-pressure transmission line must equal the voltage of that CONTINUOUS AND ALTERNATING CURRENT. 41 line, so that the number of motors in any one series must be constant. If the voltage of transmission is so high that more than two or three motors must be connected in each series, there comes the objection that motors must be operated at light loads during much of the time. Moreover, each series of motors must be mechanically connected to the same work, as that of driving a single dynamo or other machine, because if the loads on the motors of a series vary differently, these motors will not operate at constant speed. Continuous-current transmission at constant pres- sure with motors in series thus lacks the flexibility of transmission at constant current where any motor may be started and stopped without regard to the others in the series, the line voltage being automatically regulated at the generating station according to the number of motors in use at any time and to the work they are doing. In the efficiency of its dynamos, motors and line, a constant-pressure system of transmission is substantially equal to one with constant cur- rent at full load. At partial loads the constant-pressure line has the ad- vantage because the loss of energy in it varies with the square of the load. Thus at constant pressure the line loss in energy per hour at half -load is only one-fourth as great as the loss at full load. On the other hand, the energy loss in the constant-current line is the same at all stages of load. Because of these facts it is good practice to allow, say, a ten-per-cent loss in a constant-pressure line and only five per cent in a constant-current line at full load. In a generating station at 2,000 volts or more constant pressure, it is desirable to have the magnet coils of the main dynamos connected in multiple and separately excited by a small dynamo at constant pressure. This plan is especially desirable when the armatures of several dynamos are connected in series to obtain the line voltage. Separately excited magnet coils make it easier to control the operation of the several dy- namos, coils of low- voltage are cheaper to make than coils of high voltage, and the low voltage windings are less liable to burn out. If a series of constant-pressure motors is in use at one point, it may be cheaper and safer to excite its magnet coils from a special dynamo than from the line. In a transmission carried out with series- wound dynamos and motors, the speed of the motors may be constant at all loads without any special :egulating mechanism. To attain this result it is necessary that all the motors be coupled so as to form a single unit mechanically and that the dynamos be driven at constant speed. A transmission system of this sort may include a single dynamo and a single motor, or two or more dy- namos, and two or more motors may be used in series. 42 ELECTRIC TRANSMISSION OF WATER-POWER. When the dynamos of such a system are driven at constant speed and a variable load is applied to the single motor, or to the mechanically con- nected motors, both the voltage of the system and the amperes flowing in all its parts change together so that practically constant speed is main- tained at the motors, provided that the design of both the dynamos and motors is suitable for the purpose. With the maximum load on the motors the volts and amperes of the system have their greatest values, and these values both decline with smaller loads. The chief disadvantage of this system lies in the fact that where more than one motor is employed all the motors must be mechanically joined together so as to work on the same load. Compared with the constant-current system, this combination of series dynamos with mechanically connected series motors has the dis- tinct advantage that neither the dynamos nor motors require any sort of regulators in order to maintain constant motor speed. It is only neces- sary that the dynamos be driven at constant speed and that both the dy- namos and motors be designed for the transmission. In comparison with a constant-pressure system, the one under consideration has the advan- tage that neither its dynamos nor motors require magnet coils with a high voltage at their terminals and composed of fine wire or separate excita- tion by a special dynamo. These features of the system with series dy- namos and motors, the latter being joined as a mechanical unit, make it cheaper to install and easier to operate than either of the other two. This system is especially adapted for the delivery of mechanical power in rather large units. The voltage available may be anything desired, but is subject to the practical limitations that all the motors must deliver their power as a mechanical unit, so that unless the power is quite large the number of motors in the series and, therefore, the voltage is limited. An interesting illustration of the system of transmission just described exists between a point on the River Suze, near Bienne, Switzerland, and the Biberest paper mills. At the river a 400 horse-power turbine water- wheel drives a pair of series- wound dynamos, each rated at 130 kilowatts and 3,300 volts. These dynamos are connected in series, giving a total capacity of 260 kilowatts and a pressure of 6,600 volts. At the Biberest mills are located two series-wound motors, mechanically coupled and connected in series with each other and with the two-wire transmission line, which extends from the two dynamos at the River Suze. Each of these motors has a capacity and voltage equal to that of either of the dy- namos previously mentioned. The coupled motors operate at the con- stant speed of 200 revolutions per minute at all loads and deliver over CONTINUOUS AND ALTERNATING CURRENT. 43 300 horse-power when doing maximum work. Between the generating plant at the river and the Biberest mills the distance is about 19 miles, and the two line wires are each of copper, 275 mils, or a little more than one-fourth inch in diameter. The dynamos and motors of this system are mounted on thick porcelain blocks in order to protect the insulation of their windings from the strain of the full-line voltage. Either of the three systems of transmission by continuous-current that have been considered requires a smaller total capacity of electrical appar- atus for a given rate of mechanical power delivery than any system using alternating current except that where both the dynamos and motors operate at line voltage. CHAPTER V. THE PHYSICAL LIMITS OF ELECTRIC-POWER TRANSMISSION. ELECTRICAL energy may be transmitted around the world if the line voltage is unlimited. This follows from the law that a given power may be transmitted to any distance with constant efficiency and a fixed weight of conductors, provided the voltage is increased directly with the dis- tance. The physical limits of electric-power transmission are thus fixed by the practicable voltage that may be employed. The effects of the voltage of transmission must be jnet in the apparatus at generating and receiving stations on the one hand, and along the line on the other. In both situa- tions experience is the main guide, and theory has little that is reliable to offer as to the limit beyond which the voltage will prove unworkable. Electric generators are the points in a transmission system where the limit of practical voltage is first reached. In almost all high-voltage transmissions of the present day in the United States alternating gene- rators are employed. Very few if any continuous-current dynamos with capacities in the hundreds of kilowatts and voltages above 4,000 have been built in Europe, and probably none in the .United States. Where a transmission at high voltage is to be accomplished with continuous cur- rent, two or more dynamos are usually joined in series at the generating station, and a similar arrangement with motors is made at the receiving station, so that the desired voltage is available at the line though not present at any one machine. Alternating dynamos that deliver current at about 6,000 volts have been in regular use for some years, in capacities of hundreds of kilo- watts each, and may readily be had of several thousand kilowatts capacity. But even 6,000 volts is not an economical pressure for trans- missions over fifteen to fifty miles, such as are now quite common ; conse- quently in such transmissions it has been the rule to employ alternators that operate at less than 3,000 volts, and to raise this voltage to the de- sired line pressure by step-up transformers at the generating station. More recently, however, the voltage of alternating generators has been pushed as high as 13,000 in the revolving-magnet type where all the arma- 44 PHYSICAL LIMITS OF TRANSMISSION. 45 ture windings are stationary. This voltage makes it practicable to dis- pense with the use of step-up transformers for transmissions up to or even beyond 30 miles in some cases. This voltage of 13,000 in the arma- ture coils is attained only by constructions involving some difficulty be- cause of the relatively large amount of room necessary for the insulating materials on coils that develop this pressure. The tendency of this con- struction is to give alternators unusually large dimensions per given ca- pacity. It seems probable, moreover, that the pressures developed in the armature coils of alternating generators must reach their higher limits at a point much below the 50,000 and 60,000 volts in actual use on present transmission lines. In the longest transmissions with alternating current there is, therefore, little prospect that step-up transformers at the gen- erating stations and step-down transformers at receiving stations can be dispensed with. The highest voltage that may be received or delivered at these stations is simply the highest that it is practicable to develop by transformers and to transmit by the line. A very high degree of insulation is much more easy to attain in trans- formers than in generator armatures, because the space that can be readily made available for insulating materials is far greater in the trans- formers, and further because their construction permits the complete immersion of their coils in petroleum. This oil offers a much greater resistance than air to the passage of electric sparks, which tend to set up arcs between coils at very high voltages and thus destroy the insulation. Danger to insulation from the effect known as creeping between coils at widely different pressures is largely avoided by immersion of the coils in oil. For several years groups of transformers have been worked regu- larly at 40,000 to 60,000 volts, and in no instance is there any indica- tion that the upper limit of practicable voltage has been reached. On the contrary, transformers have repeatedly been worked experimentally up to and above 100,000 volts. From all these facts, and others of similar import, it is fair to con- clude that the physical limit to the voltages that it is practicable to obtain with transformers is much above the 50,000 or 6o,coo volts now in prac- tical use on transmission systems. So far as present practice is con- cerned, the limit to the use of high voltages must be sought beyond the transformers and outside of generating and receiving stations. As now constructed, the line is that part of the transmission system where a physical limit to the use of higher voltages will first be reached. The factors that tend most directly to this limit are two: temporary arcing between the several wires on a pole, and the less imposing but constant 46 ELECTRIC TRANSMISSION OF WATER-POWER. passage of energy from one wire to another. On lines of very high volt- age arcing is occasionally set up by one of several causes. At a point where one or more of the insulators on which the wires are mounted become broken or defective, the current is apt to flow from one wire to another along a wet cross-arm, until the wood grows carbonized and an arc *is formed that ends by burning up the cross-arm or even the pole. Where lines are exposed to heavy sea fog, the salt is in some cases de- posited on the insulators and cross-arms to an extent that starts an arc between the wires, and ends often in the destruction of the cross-arm. In some instances the glass and porcelain insulators supporting wires used with high voltages are punctured by sparks that pass right through the material of the insulator to the pin on which it is mounted, thus burn- ing the pin and ultimately the cross-arm. This trouble is easily met, however, by the adoption of a better grade of porcelain or of an insulator with a greater thickness of glass or porcelain between the wires and the supporting pin. Arcs between lines at high voltages usually start by sparks that jump from the lower edges of insulators, when they are wet or covered with salt deposit, to the cross-arm. As the lower edges of insulators are only a few inches from their cross-arms, the sparks find a path of comparatively low resistance by passing from insulator to cross- arm and thence to the other insulator and wire. The wood of a wet cross-arm is a far better conductor than the air. Where wires are several feet or more apart, sparks probably never jump directly through the air from one to the other. Large birds flying close to such wires, however, have in some instances started momentary arcs between them. The treatment of cross-arms with oil or parafnne reduces the number of arcs that occur on a line of high voltage, but does not do away with them. As the voltages of long transmissions have gone up, the distance through the air between wires and the distances between the lower wet edges of insulators and the cross-arms have been much increased. Most of the earlier transmission lines for high voltages were erected on insula- tors spaced from one to two feet apart. In contrast with this practice, the three wires of the transmission line in operation at 50,000 volts be- tween Canon Ferry and Butte are arranged at the corners of a triangle seventy-eight inches apart, one wire at the top of each pole and the other two at opposite ends of the cross-arm. A voltage that would just start an arc along a wet cross-arm between wires eighteen inches apart would be quite powerless to do so over seventy-eight inches of cross-arm, the lower wet edges of insulators being equidistant from cross-arms in the two cases. To reach the cross-arm, the electric current passes down over PHYSICAL LIMITS OF TRANSMISSION. 47 the wet or dirty outside surface of the insulator to its lower edge. In the older types of insulators the lower wet edge often came within two inches of the cross-arm. For the 5o,ooo-volt line just mentioned the insulators (see illus.) are mounted with their lower wet edges about eight inches above the cross-arms. At its lower edge each insulator has a diameter of nine inches, and a small glass sleeve extends several inches below this edge and close to the wooden pin, to prevent sparking from the lower wet edge of the insulator to the pin. These increased distances between wires in a direct line through the air, and also the greater distances be- tween the lower wet edges of insulators and their pins and cross-arms, are proving fairly effective to prevent serious arcing under good climatic con- ditions, for the maximum pressures of 50,000 to 60,000 volts now in use. If these voltages are to be greatly exceeded it is practically certain that the distance between wires, and from the lower wet edges of insulators to the wood of poles or cross-arms, must be still further increased to avoid destructive arcing. The nearest approach to an absolute physical limit of voltage with present line construction is met in the constant current of energy through the air from wire to wire of a circuit. A paper in vol. XV., Transac- tions American Institute Electrical Engineers, gives the tests made at Telluride, Col., to determine the rates at which energy is lost by passing through the air from one wire to another of the same circuit. The tests at Telluride were made with two-wire circuits strung on a pole line 11,720 feet in length, at first with iron wires of 0.165 inch diameter and then with copper wires of 0.162 inch diameter. Measurements were made of the energy escaping from wire to wire at different voltages on the line, and also with the two wires at various distances apart. It was found that the loss of energy over the surfaces of insulators was very slight, and that the loss incident to the passage of energy directly through the air is the main one to be considered. This leakage through the air varies with the length of the line, as might be expected. Tests were made with pairs of wires running the entire length of the pole line and at distances of 15, 22, 35, and 52 inches apart respectively. Losses with wires 22 or 35 inches apart were intermediate to the losses when wires were 15 and 52 inches apart respectively. Results given in the original paper for the pair of wires that were 1 5 inches apart and for the pair that were 52 inches apart are here reduced to approximate watts per mile of two- wire line. At 40,000 volts the loss between the two wires that were 1 5 inches apart was about 1 50 watts per mile, and between the two wires that were 52 inches apart the loss was 84 watts per mile. The two 48 ELECTRIC TRANSMISSION OF WATER-POWER. wires 15 inches apart showed a leakage of approximately 413 watts per mile when the voltage was up to 44,000, but the wires 52 inches apart were subject to a leakage of only 94 watts per mile at the same volt- age. At 47,300 volts, the highest pressure recorded for the two wires 15 inches apart, the leakage between them was about 1,215 watts per mile, while an equal voltage on the two wires 52 inches apart caused a leakage of only 122 watts per mile, or one-tenth of that between the wires that were 1 5 inches apart. When about 50,000 volts were reached on the two wires 52 inches apart, the leakage between them amounted to 140 watts per mile; but beyond this voltage the loss went up rapidly, and was 225 watts per mile at about 54,600 volts. For higher pressures the loss between these two wires still more rapidly increased, and amounted to 1,368 watts per mile with about 59,300 volts, the highest pressure re- corded. With a loss of about 1,215 watts per mile between the two wires 52 inches apart, the voltage on them was 58,800, in contrast with the 47,300 volts producing the same leakage on the two wires 15 inches apart. Evidently, however, at even 52 inches between line wires the limit of high voltage is not far away. When the voltage on the 5 2 -inch line was raised from 54,600 to 59,300, the leakage loss between the two wires in- creased about 1,143 watts per mile. If the leakage increases at least in like proportion, as seems probable, for still higher pressures, the loss between the two wires would amount to 6,321 watts per mile with 80,000 volts on the line. On a line 200 miles long this loss by leakage between the two wires would amount to i ,264,200 watts. Any such leakage as this obviously sets an absolute, physical limit to the voltage, and consequently the length of transmission. Fortunately for the future delivery of energy at great distances from its source, the means to avoid the limit just discussed are not difficult. Other experiments have shown that with a given voltage and distance between conductors the loss of energy from wire to wire decreases rapidly as their diameters increase. The electrical resistance of air, like that of any other substance, increases with the length of the circuit through it. The leakage described is a flow of electrical energy through the air from one wire to another of the same circuit. To reduce this leakage it is sim- ply necessary to give the path from wire to wire through the air greater electrical resistance by increasing its length, that is, by placing the wires at greater distances apart. The fact demonstrated at Telluride, that with 47,300 volts on each line the leakage per mile between the two wires 15 inches apart was ten times as great as the leakage between the two wires PHYSICAL LIMITS OF TRANSMISSION. 49 52 inches apart, is full of meaning. Evidently, leakage through the air may be reduced to any desired extent by suitable increase of distance be- tween the wires of the same circuit. But to carry this increase of distance between wires very far involves radical changes in line construction. Thus far it has been the uniform practice to carry the two or three wires of a transmission circuit on a single line of poles, and in many cases sev- eral such circuits are mounted on the same pole line. For the 65 mile transmission into Butte, Mont., only the three wires of a single circuit are mounted on one pole line, and this represents the best present practice. The cross-arms on this line are each 8 feet long, and one is attached to each pole. The poles are not less than 35 feet long and have 8-inch tops. One wire is mounted at the top of each pole, and the other two wires near the ends of the cross-arm, so that the three wires are equidistant and 78 inches apart. By the use of still heavier poles the length of cross-arms may be increased to 12 or 14 feet, for which their section should be not less than 4 by 6 inches. Placing one wire at the pole top, the 1 2-foot cross-arm would permit the three wires of a circuit to be spaced about 10.5 feet apart. The cost of extra large poles goes up rapidly and there are alternative constructions that seem better suited to the case. More- over, a few tens of thousands of volts above present practice would' bring us again to a point where even 10.5 feet between wires would not prevent a prohibitive leakage. Two poles might be set 20 feet apart, with a cross-piece between them, extending out 5 feet beyond each pole and having a total length of 30 feet. This would permit three wires to be mounted along the cross-piece at points about 14 feet apart. If the present transmission pressures of 50,000 to 60,000 volts are to be greatly exceeded, the line structure may involve the use of a sepa- rate pole for each wire of a circuit, each wire to be mounted at the top of its pole. This construction calls for three lines of poles to carry the three wires of a three-phase transmission. Each of these poles may be of only moderate dimensions, say 30 feet long with 6- or y-inch top. The cost of three of these poles will exceed by only a moderate percentage that of a 35- or 40-foot pole with an 8- to lo-inch top, such as would be necessary with 1 2-foot cross-arms. The distance between these poles at right angles to the line may be anything desired, so that leakage from wire to wire through the air will be reduced to a trifling matter at any voltage. Extra long pins and insulators at the pole tops will easily give a distance of two feet or more between the lower wet edge of each insulator and the wood of pin or pole. Such line construction would probably safely carry two or three times the maximum voltage of present practice, and 50 ELECTRIC TRANSMISSION OF WATER-POWER. might force the physical limit of electrical transmission back to the highest pressure at which transformers could be operated. With not more than 60,000 volts on the line the size of conductors is great enough in many cases to keep the loss of energy between them within moderate limits when they are six feet apart, but with a large increase of voltage the size of conductors must go up or the distances between them must increase, CHAPTER VI. DEVELOPMENT OF WATER-POWER FOR ELECTRIC STATIONS. ELECTRICAL transmission has reduced the cost of water-power de- velopment. Without transmission the power must be developed at a number of different points in order that there may be room enough for the buildings in which it is to be utilized. This condition necessitates relatively long canals to conduct the water to the several points where power is to be developed, and also a relatively large area of land with canal and river frontage. With electrical transmission the power, however great, may well be developed at a single spot and on a very limited area of land. The canal in this case may be merely a short passageway from one end of a dam to a near-by power-house, or may disappear entirely when the power-house itself forms the dam, as is sometimes the case. These differences between the distribution of water for power pur- poses and the development by water of electrical energy for transmission may be illustrated by many examples. A typical case of the distribution of water to the points where power is wanted may be seen in the hydraulic development of the Amcskeag Manufacturing Company at Manchester, N. H. This development includes a dam across the Merrimac River, and two parallel canals that follow one of its banks for about 3,400 feet down stream. By means of a stone dam and a natural fall a little beyond its toe a water head of about forty-eight feet is obtained at the upper end of the high-level canal. Below this point there is little drop in the bed of the river through that part of its course that is paralleled by the two canals. All of the power might be thus developed within a few rods of one end of the dam, if means were provided for its distribution to the points where it must be used. Years ago, when this water-power was developed, the electrical trans- mission or distribution of energy was unheard of, and distribution of the water itself had therefore to be adopted. For this purpose the two canals already mentioned were constructed along the high bank of the river at two different levels. ELECTRIC TRANSMISSION OF WATER-POWER. The high-level canal, so called, was designed to take water di- rectly from the basin or forebay a little below one end of the dam, so that between this canal and the river there is a full water head of about forty-eight feet. Over nearly its entire course the nearer side of this high-level canal runs between 450 and 7 50 feet from the edge of the river wall, and thus includes between it and the river a large area on which factories to be driven by water-wheels may be lo- cated. It was thought, however, that this strip of land between the high-level canal and the river was too wide for a single row of mill sites, and the lower level canal was therefore constructed parallel with that on the higher level, but with about twenty-one feet less elevation. Between these two canals a strip of land about 250 feet wide was left for the location of mills. By this arrangement of canals it is possible to supply wheels located between the high and the low levels with water under a head of about twen- ty-one feet, and to supply w r heels between the lower canal and the river with water undei a head of about twenty-nine feet. The en- tire area of land between the high canal and the river is thus made readily available for factory build- ings. Water for the lower canal is drawn mainly from the high canal WATER-POWER FOR ELECTRIC STATIONS. 53 through the wheels in buildings that are located between the two canals. It is desirable in a case of this sort to have as much water flow through the wheels between the high and low canal as flows through the wheels between the low canal and the river, but this is not always possible. A gate is therefore provided at the f orebay where the two canals start, by which water may pass from the forebay directly into the low canal when necessary, but the head of twenty-one feet between the forebay and the low canal is lost as to this water. Between the high and low canal, and between the low canal and the river twenty-three turbine wheels or pairs of wheels have been connected, and these wheels have a combined rating of 9,500 horse-power. To carry out this hydraulic development it thus appears that about 1.3 miles of canal have been constructed; one-half this length of river- front has been required, and about one-sixth square mile of territory has been occupied. Contrast with this result what might have been done if electrical transmission of power had been available at the time when this water-power was developed. All but a few rods in length of the existing 1.3 miles of canal might have been omitted, and an electric generating station with wheels to take the entire flow of the river might have been located not far from one end of the dam. Factories utilizing the electric power thus developed might have been located at any convenient points along the river-front or elsewhere, and no space would have been made unavailable because of the necessity of head- and tail-water connections to scattered sets of wheels. Compare with the foregoing hydraulic development that at Canon Ferry on the Missouri River, in Montana, where 10,000 horse-power is developed under a water-head of 32 feet. At Canon Ferry the power- house is 225 feet by 50 feet at the floor level inside, contains turbine wheels direct-connected to ten main generators of 7,500 kilowatts, or 10,000 horse-power combined capacity, and is built on the river bank close to one end of the 5oo-foot dam. The canal which runs along the land side of the power-house, and takes water at the up-stream side of the abutment, is about twice the length of the power-house itself. The saving in the cost of canal construction alone, to say nothing of the saving as to the required area of land, is evidently a large item in favor of the electrical development and transmission. In its small area and short canal the Canon Ferry plant is not an exception, but is rather typical of a large class of electric water-power plants that operate under moderate heads. A like case may be seen in the plant at Red Bridge, on the Chicopee 54 ELECTRIC TRANSMISSION OF WATER-POWER. River, in Massachusetts, where a canal 340 feet long, together with pen- stocks 100 feet long, convey water from one end of the dam and deliver it to wheels in the electric station with a head of 49 feet. This station contains electric generators with a combined capacity of 4,800 kilowatts or 6,400 horse-power, and its floor area is 141 by 57 feet. So, again, at Great Falls, on the Presumpscot River, in North Gor- ham, Me. (see cut), the electric station sets about 40 feet in front of FIG. 5. Canal at Red Bridge on Chicopee River. the forebay wall, which adjoins one abutment of the dam, and there is no canal whatever, as short penstocks bring water to the wheels with a head of 35 feet. In ground area this station is 67.5 by 55 feet, and its capacity in main generators is 2,000 kilowatts or 2,700 horse-power. A striking illustration of the extent to which electrical transmission reduces the cost of water-power development may be seen at Gregg's Falls on the Piscataquog River, in New Hampshire, where an electric station of 1,200 kilowatts capacity has been built close to one end of the dam, and receives water for its wheels under a head of 51 feet through a short penstock, 10 feet in diameter, that pierces one of the abutments. Perhaps the greatest electric water-power station anywhere that rests close to the dam that provides the head for its wheels is that at Spier WATER-POWER FOR ELECTRIC STATIONS. 55 56 ELECTRIC TRANSMISSION OF WATER-POWER. Falls (see cut), on the upper Hudson. One end of this station is formed by the high wall section of the dam, and from this wall the length of the station down-stream is 392 feet, while its width is 70 feet 10 inches, both dimensions being taken inside. The canal or forebay in this case, like that at Canon Ferry, lies on the bank side of the power-station, and is about equal to it in length. From this canal ten short penstocks, each 1 2 feet in diameter, will convey water under a head of 80 feet to as many sets of turbine wheels in the station. These wheels will drive ten gen- erators with an aggregate capacity of 24,000 kilowatts or 32,000 horse- power. Sometimes the slope in the bed of a river is so gradual or so divided up between the number of small falls, or the volume of water is so small, that no very large power can be developed at any one point without the construction of a long canal. In a case of this sort electrical transmission is again available to reduce the expense of construction that will make it possible to concentrate all the power from a long stretch of the river at a single point. This is done by locating electric generating stations at as many points as may be thought desirable along the river whose energy is to be utilized, and then transmitting power from all of these stations to the single point where it is wanted. A case in point is that of Garvins Falls and Hooksett Falls on the Merrimac River and four miles apart. At the former of these two falls the head of water is twenty-eight feet, and at the latter it is sixteen feet. To unite the power of both these falls in a single water-driven station would obviously require a canal four miles long whose expense might well be prohibitive. Energy from both these falls is made available at a single sub-station in Manchester, N. H., by a generating plant at both points and transmission lines thence to that city. At Hooksett the present capacity of the electric station is 1,000 horse- power, and at Garvins Falls the capacity is 1,700 horse-power. The river is capable of developing larger powers at both of these falls, how- ever, and construction is now under way at Garvins that will raise its station capacity to 5,000 horse-power. A similar result in the combination of water-powers without the aid of a long canal is reached in the case of Gregg's Falls and Kelley's Falls, which are three miles apart on the Piscataquog River. At the former of these two falls the electric generating capacity is 1,600 horse-power, as previously noted, and at the latter fall the capacity is 1,000 horse-power. In each case the station is close to its dam, and no canal is required. Electrical transmission unites these two powers in the same sub-station WATER-POWER FOR ELECTRIC STATIONS. 57 at Manchester that receives the energy from the two stations above named on the Merrimac River. Instead of transmitting power from two or more waterfalls to some point distant from each of them, the power developed at one or more falls may be transmitted to the site of another and there used. This is, in fact, done at the extensive Ludlow twine mills on the'Chicopee River, in Massachusetts. These mills are located at a point on the river where its fall makes about 2,500 horse-power available, and this fall has been developed to its full capacity. After a capacity of 2,400 horse-power in steam-engines had been added, more water-power was sought, and a new dam was located on the same river at a point about 4.5 miles up-stream from the mills. The entire flow of the river was available at this new dam, and a canal 4.5 miles long might have been employed to carry the water down to wheels at the mills in Ludlow. Such a canal would have meant a large investment, not only for land and construction, but also, possibly, for damages to estates bordering on the river, if all of its water was diverted. Instead of such a canal, an electric generating station was located close to the new dam with a capac- ity of 6,400 horse-power, and this power is transmitted to motors in the mills at Ludlow. Even where the power is to be utilized at some point distant from each of several waterfalls, it may be convenient to combine the power of all at one of them before transmitting it to the place of use. This is actually done in the case of two electric stations located respectively at Indian Orchard and Birchem Bend on the Chicopee River, whose energy is de- livered to the sub-station of the electrical supply system in Springfield, Mass. At the Indian Orchard station the head of water is 36 feet, and at Birchem Bend it is 14 feet, while the two stations are about 2 miles apart. A canal of this length might have been built to give a head of 50 feet at the site of the Birchem Bend dam, but instead of this an elec- tric station was located near each fall, and a transmission line was built between the two stations. Each generating station was also connected with the sub-station in Springfield by an independent line, and power is now transmitted from one generating plant to the other, as desired, and the power of both may go to the sub-station over either line. In the In- dian Orchard station the dynamo capacity is about 2,000 kilowatts, and at Birchem Bend it is 800 kilowatts. Another case showing the union of two water-powers by electrical transmission, where the construction of an expensive canal was avoided, is that of the electrical supply system of Hartford, Conn. This sys- 5 8 ELECTRIC TRANSMISSION OF WATER-POWER. tern draws a large part of its energy from two electric plants on the Farmington River, at points that are about 3 miles apart in the towns of Windsor and East Granby, respectively. At one of these plants the head of water is 32 feet, and at the other it is 23 feet, so that head of 55 feet might have been obtained by building a canal 3 miles long. Each of these stations is located near its dam, and the generator capacity at one station is 1,200 and at the other 1,500 kilowatts. Transmission lines deliver power from both of these plants to the same sub-station in Hart- ford. Sometimes two or more water-powers on the same river that are to be united are so far apart that any attempt to construct a canal between them would be impracticable. This is illustrated by the Spier and Me- chanicsville Falls on the Hudson River, which are 25 miles apart in a direct line and at a greater distance by the course of the stream. At Spier Falls the head is 80 feet, and at Mechanicsville it is 1 8 feet. Union of the power of these two falls is thus out of the question for physical reasons alone. Electrical transmission, however, brings energy from both of these water-powers to the same sub-stations in Schenectady, Albany, and Troy. In another class of cases electrical transmission does what could not be done by any system of canals, however expensive; that is, unites the water-powers of distinct and distant rivers at any desired point. Thus power from both the Merrimac and the Piscataquog rivers is distributed over the same wires in Manchester; the Yuba and the Mokelumne con- tribute to electrical supply along the streets of San Francisco; and the Monte Alto and Tlalnepantla yield energy in the City of Mexico. It does not follow from the foregoing that it is always more economical to develop two or more smaller water-powers at different points along a river for transmission to some common centre than it is to concentrate the water at a single larger station by more elaborate hydraulic construc- tion, and then deliver all of the energy over a single transmission line. The single larger hydraulic and electric plant will usually have a first cost larger than that of the several smaller ones, because of the re- quired canals or pipe lines. A partial offset to this larger hydraulic in- vestment is the difference in cost between one and several transmission lines, or at least the cost of the lines that would be necessary between the several smaller stations in order to combine their energy output before its transmission over a single line to the point of use. Against the total excess of cost for the single larger hydraulic and electrical plant there should be set the greater expense of operation at WATER-POWER FOR ELECTRIC STATIONS. 59 several smaller and separate plants. Even a small water-driven electric station that can be operated by a single attendant at any one time must have two attendants if it is to deliver energy during the greater part or all of every twenty-four hours. But a single attendant can care for a water- power plant of 2, ocx) horse-power or more capacity, so that two plants of 750 horse-power each will require double the operating force of one plant of 1,500 horse-power. If two such plants are constructed instead of one that has their combined capacity, the monthly wages of the two addi- tional operators will amount to at least one hundred dollars. If money is worth six per cent yearly, it follows that an additional investment of #1,200 -:- 0.06 =1 $20,000 might be made in hydraulic work to concen- trate the power at one point before the annual interest charge would equal the increase of wages made necessary by two plants. Reliability of operation is one of the most important requirements in an electric water-power plant, and its construction should be carried out with this in view. Anchor ice is a serious menace to the regular opera- tion of water-wheels in cold climates, because it clogs up the openings in the racks and in the wheel passages. Anchor ice is formed in small particles in the water of shallow and fast-flowing streams, and tends to form into masses on solid substances with which the water comes in con- tact. At the entrance to penstocks or wheel chambers, steel racks with long, narrow openings, say one and one-quarter inches wide, are regularly placed to keep all floating objects away from the wheels. When water bearing fine anchor or frazil ice comes in contact with these racks, it rap- idly clogs up the narrow openings between the bars, unless men are kept at work raking off the ice as it forms. At the Niagara Falls electric station, in some instances, when the racks become clogged, they have been lifted, and the anchor ice allowed to pass down through the wheels. This is said to have proved an effective remedy, but it would obviously be of no avail in a case where the ice clogged the passages of the wheels themselves. The best safeguard against anchor ice is a large, deep forebay next to the racks, where the water, being comparatively quiet, will soon freeze over after cold weather commences. The anchor ice coming down to this forebay and losing most of its forward motion, soon rises to the sur- face or to the under side of the top coating of solid ice, and the warmer water sinks to the bottom. Good construction puts the entrance ends of penstocks well below the surface of water in the forebay, so that they may receive the warmer water that contains little or no anchor ice. 60 ELECTRIC TRANSMISSION OF WATER-POWER. Illustrations of practice along these lines, as to size, depth of forebay, and location of penstocks may be seen in many well-designed plants. One instance is that at Garvins Falls, on the Merrimac River, where the new hydraulic development for 5,000 horse-power is now under way. Water from the river in this case comes down to the power-station through El. 9i.OOF.ooJ Water FIG. 7. Cross Section of Dike on Chicopee River at Red Bridge. a canal 500 feet long, and of 68 feet average width midway between the bottom and the normal flow line. In depth up to his flow line the canal is 12 feet at its upper and 13 feet at its lower end, just before it widens into the forebay. In this forebay the depth increases to 1 7 feet, and the width at the rack is double that of the canal. The steel penstocks, each 1 2 feet in diameter, terminate in the forebay wall at an average distance of 7 feet behind the rack, and each penstock has its centre 10.6 feet below the water level in the forebay. As there is a large pond created by the dam in this case, and as the flow of water in the canal is deep rather than swift, enough opportunity is probably afforded for any anchor ice to rise to the surface before it reaches the forebay in this case. Penstocks for the electric station at Great Falls, on the Presumpscot River, whence energy is drawn for lighting and power in Portland, Me., are each 8 feet in diameter, and pierce the forebay wall behind the rack with their centres 15 feet below the normal water level in the forebay. In front of the forebay wall the water stands 27 feet deep, and the pond formed by the dam, of which the forebay wall forms one section, is 1,000 feet wide and very quiet. Though the Maine climate is very cold in winter and the Presumpscot is a turbulent stream above the dam and pond, there has never been any trouble with anchor ice at the Great Falls plant. An excellent illustration is thus presented of the fact that deep, still water in the forebay is a remedy for troubles with ice of this sort. Maximum loads on electrical supply systems are usually from twice to four times as great as the average loads during each twenty-four hours. WATER-POWER FOR ELECTRIC STATIONS. 61 A pure lighting service tends toward the larger ratio between the average and maximum load, while a larger motor capacity along with the lamps, tends to reduce the ratio. Furthermore, by far the greater part of the energy output of an electrical supply system during each twenty-four hours must be delivered between noon and midnight. For these reasons there must be enough water stored, that can flow to the station as wanted, to carry a large share of the load during each day, unless storage bat- teries are employed to absorb energy at times of light load, if the entire normal flow of the river is to be utilized. It is usually much cheaper to store water than electrical energy for the daily fluctuations of load, and the only practicable place for this stor- age is most commonly behind the dam that maintains the head for the power-station. This storage space should be so large that the drain upon FIG. 8. -Valley Flooded above Spier Falls on the Hudson River. it during the hours of heavy load will lower the head of water on the wheels but little, else it may be hard to maintain the standard speed of revolution for the wheels and generators, and consequently the trans- mission voltage. At the Great Falls plant, water storage to provide for the fluctuations of load in different parts of the day takes place back of the dam, and for 62 ELECTRIC TRANSMISSION OF WATER-POWER. about one mile up-stream. This dam is 450 feet long in its main part, and a retaining wall increases the total length to about i ,000 feet. For half a mile up-stream from this dike and dam the average width of the pond is 1,000 feet, and its greatest depth is not less than 27 feet. As the station capacity is 2,700 horse-power in main generators, with a head of 35 feet at the wheels the storage capacity is more than ample for all changes of load at different times of day. The dam at Spier Falls, on the Hudson River, it 1,820 feet long be- tween banks, 155 feet high above bedrock in its deepest section, and raises the river 50 feet above its former level. Behind the dam a lake is formed one-third of a mile wide and 5 miles long. Water from this storage reser- voir passes down through the turbines with a head of 80 feet, and is to develop 32,000 horse-power. As a little calculation will show, this lake is ample to maintain the head under any fluctuation in the daily load. At Canon Ferry, where electrical energy for Butte and Helena, Mont., is developed, the dam, which is 480 feet long, crosses the river in a narrow canyon that extends up-stream for about half a mile. Above this canyon the river valley widens out, and the dam, which maintains a head of 30 feet at the power-station, sets back the water in this valley, and thus forms a lake between two and three miles wide and about seven miles long. At the station the generator equipment has a total rating of 10,000 horse- power. From these figures it may be seen that the storage lake would be able to maintain nearly the normal head of water for some hours, when the station was operating under full load, however small the flow of the river above. WATER-POWER FOR ELECTRIC STATIONS. CHAPTER VII. THE LOCATION OF ELECTRIC WATER-POWER STATIONS. COST of water-power development depends, in large measure, on the location of the electric station that is to be operated. The form of such a station, its cost, and the type of generating apparatus to be employed are also much influenced by the site selected for it. This site may be exactly at, or far removed from, the point where water that is to pass through the wheels is diverted from its natural course. A unique example of a location of the former kind is to be found near Burlington, Vt, where the electric station is itself a dam, being built entirely across the natural bed of one arm of the Winooski River at a point where an island near its centre divides the stream into two parts. The river at this point has cut its way down through solid rock, leaving perpendicular walls on either side. Up from the ledge that forms the bed of the stream, and into the rocky walls, the power-station, about no feet long, is built. The up-stream wall of this station is built after the fashion of a dam, and is reenforced by the down-stream wall, and the water flows directly through the power-station by way of the wheels. A construction of this sort is all that could well be attained in the way of economy, there being neither canal nor long penstocks, and only one wall of a power-house apart from the dam. On the other hand, the location of a station directly across the bed of a river in this way makes it impossible to protect the machinery if the up-stream wall, which acts as the dam, should ever give way. The peculiar natural conditions favorable to the construction just considered are seldom found. One of the most common locations for an electric water-power station is at one side of a river, directly in front of one end of the dam and close to the foot of the falls. A location of this kind was adopted for the station at Gregg's Falls, one of the water-powers included in the electric system of Manchester, N. H., where the spray of the fall rises over the roof of the station. Two short steel penstocks, each ten feet in diameter, convey the water from the forebay section of the dam to wheels in the station with a head of fifty-one feet. A similar location was selected for the station at Great Falls, on the 64 LOCATION OF WATER-POWER STATIONS. 66 ELECTRIC TRANSMISSION OF WATER-POWER. I LOCATION OF WATER-POWER STATIONS. 67 Presumpscot River (see cuts), whence electrical energy is delivered in Portland, Me. Four steel penstocks, a few feet long and each eight feet in diameter, bring the water in this case from the forebay section of the dam to the wheel cases in the power-house. Where the power-station is located at the foot of the dam, as just described, that part which serves as a forebay wall usually carries a head gate for each penstock. The overfall section of a dam may give way in F FIG. 12. Power-house on Hudson River at Mechanicsville. cases like the two just noted without necessarily destroying the power- station, but in times of freshet or very high water the station may be flooded and its operation stopped. The risk of any such flooding will vary greatly on different rivers, and in particular cases may be' very slight. Location of the generating station close to the foot of the dam at one end obviously avoids all expense for a canal and cuts the cost of penstocks down to a very low figure. Such locations for stations are not limited to falls of any particular height, and the short penstocks usually enter the dam nearer its base than its top and pass to the station at only a slight inclination from the horizon- tal. At Great Falls, above mentioned, the head of water is thirty-seven feet. A short canal is constructed in some cases from one end of a dam to a little distance down-stream, terminating at a favorable site for the elec- tric station. Construction of this sort was adopted at the Birchem Bend Falls of the Chicopee River, whence energy is supplied to Springfield, Mass. These falls furnish a head of fourteen feet, and the water-wheels are located on the floor of the open canal at its end. The power-station is on the shore side of this canal, and the shafts of the water-wheels extend through bushings in the canal wall, which forms the lower part of one side of the station, to connect with the electric generators inside. 68 ELECTRIC TRANSMISSION OF WATER-POWER. This rather unusual location of water-wheels has at least the obvious advantage that they require no room inside of the station. Furthermore, as the canal is between the station and the river, any break in the canal is not apt to flood the station. An illustration of the use of a very short canal to convey water from one end of a dam to a power-station exists in the 10,000 horse-power plant at Canon Ferry, Mont., where the head of water is thirty feet. In this case the masonry canal is but little longer than the power-house, and this latter sits squarely between the canal and the river, virtually at the - FIG. 13. York Haven Power-house, on Susquehanna River, Pennsylvania. foot of the falls. Other examples of the location of generating stations between short canals and the river may be seen at Concord, N. H., where the head of water is sixteen feet; at Lewiston, Me., where the head is thirty-two feet; and at Spier Falls, on the Hudson River, New York, where there is a head of eighty feet. There is some gain in security in many cases by locating the power- station several hundred feet from the dam and a little to one side of the main river channel. For such cases a canal may be cheaper than steel penstocks when the items of depreciation and repairs are taken into ac- count. Aside from the question of greater security for the station in the event of a break in the dam, it is necessary in many cases to convey the water a large fraction of a mile, or even a number of miles, from the point where it leaves its natural course to that where the power-station should be located. An example in point exists at Springfield, Mass., where one of the electric water-power stations is located about 1,400 feet down- stream from a fall of thirty-six feet in the Chicopee River, because land close to the falls was all occupied at the time the electric station was built. LOCATION OF WATER-POWER STATIONS. 69 70 ELECTRIC TRANSMISSION OF WATER-POWER. LOCATION OF WATER-POWER STATIONS. 71 The Shawinigan Falls of the St. Maurice River in Canada occur at two points a short distance apart, the fall at one point being about 50 and at the other 100 feet high. A canal 1,000 feet long takes water from the river above the upper of these falls and delivers it near to the electric power-house on the river bank below the lower falls. In this way a head of 125 feet is obtained at the power-house. The canal in this case ends on high ground 130 feet from the power-house, and the water passes down to the wheels through steel penstocks 9 feet in diameter. Another interesting example of conditions that require a power-house to be located some distance from the point where water is diverted from its natural course may be seen at the falls on the Apple River, whence FIG 16. Power-house on White River, Oregon. energy is transmitted to St. Paul, Minn. By means of a natural fall of 30 feet, a dam 47 feet high some distance up-stream, and some rapids in the river, it was there possible to obtain a total fall of 82 feet. To utilize this entire fall a timber flume, 1,550 feet in length, was built from the dam to a point near the power-house on the river bank and below the falls and rapids. The flume was connected with the wheels, 82 feet below, by a steel penstock 313 feet long and 12 feet in diameter. As the St. Mary's River leaves Lake Superior it passes over a series of rapids about half a mile in length, falling twenty feet in that distance. To make the power of this great volume of water available, a canal 13,000 feet long was excavated from the lake to a point on the river bank below the rapids. Between the end of the canal and the river sits the power- station, acting as a dam, and the water passes down through it and the wheels under a head of twenty feet. 72 ELECTRIC TRANSMISSION OF WATER-POWER. LOCATION OF WATER-POWER STATIONS. 73 By means of a canal 16,200 feet long from the St. Lawrence River a head of water amounting to fifty feet has been made available at a point on the bank of Grass River near Massena, N. Y. There again the power-station acts as a dam, and the canal water passes down through it to reach the river. From these illustrations it may be seen that in many cases, in com- paratively level country, a water-power can be fully developed only by FIG. iS. Canal and Station on Payette River, Idaho. means of canals or pipe lines, and the generating stations cannot be lo- cated at the points where the water is diverted. Thus far the cases considered have been only those with moderate heads and rather large volumes of water. In mountainous country, where rivers are comparatively small and their courses are marked by numerous falls and rapids, it is generally necessary to utilize the fall of a stream through some miles of its length in order t& effect a satisfactory development of power. To reach this result, rather long canals, flumes, or pipe lines must be utilized to convey the water to power-stations and deliver it at high pressures. In cases of this kind the cost of the canal or pipe line may be the larg- est item in the power development, and it may be an important question whether this cost should be reduced or avoided by the erection of several 74 ELECTRIC TRANSMISSION OF WATER-POWER. small generating plants instead of one large one. California offers nu- merous examples of electric-power development with water that has been carried several miles through artificial channels. An illustration of this class of work exists at the Electra power-house on the bank of the Mo- kelumne River, in the Sierra Nevada Mountains. Water is supplied to the wheels in this station under a head of 1,450 feet through pipes 3,600 feet long leading to the top of a near-by hill. To reach this hill the water, after its diversion from the Mokelumne River at the dam, flows twenty miles through a canal or ditch and then through 3,000 feet of wooden stave pipe. Another example of the same sort may be seen in the power-house at Colgate, on the North Yuba River, in the chain of mountains above named. Water taken from this river passes through a wooden flume nearly eight miles long to the side of a hill 700 feet above the power- house, and thence down to the wheels through steel and cast-iron pipes, five in number and thirty inches each in diameter. Even with long flumes, canals, and pipe lines, it may be necessary to locate a number of generating stations along a single river of the class now under consideration in order to utilize its entire power. Thus on the Kern River, which rises in the Sierra Nevada Mountains 'and empties into Tulare Lake, two electric power-stations are under construction, and surveys are being made for three more. Of these stations, the one at the lowest level will operate under an 872-foot head of water, and this water, after its diversion from the river, will pass through twenty-one tunnels, with an aggregate length of about ten miles, and through six flumes mounted on trestles and having a total length of 1,703 feet. Next up-stream is a station near the point where water is diverted for the plant just named. This second station will work under a head of 317 feet, and water for it will come from a point farther up-stream by canals, tunnels, and flumes, with an aggregate length of eleven and one- half miles. At three points still higher up on this river it is the intention to locate three other power-stations by conducting the water in artificial channels, about twelve and one-half, fifteen, and twenty miles in length respectively. Farther south in California, on the Santa Ana River and Mill Creek, extensive power developments on the lines just indicated have been car- ried out. On Mill Creek, about six miles from the city of Redlands, is an electric station operating under a head of 530 feet, with water in part diverted from the stream a little less than two miles above and brought LOCATION OF WATER-POWER STATIONS. 75 FIG. 19. Canal and Power-station on Neversink River, New York. 76 ELECTRIC TRANSMISSION OF WATER-POWER. down through a steel pipe 10,250 feet long and thirty inches in diame- ter. This pipe line also takes water from the tail race of another gener- ating plant at its upper end. With some additions and modifications, the station just described is the famous Redlands plant, built in 1893, and believed to be the first for three-phase transmission in the United States. At the upper end of the pipe line just named the second station oper- ates, in part, with water drawn from Mill Creek through a combination of tunnels, flumes, and cement and steel pipes, with a combined length of about three miles, and delivered to some of the wheels with a head of 627 feet. The other wheels at this plant receive water drawn from the same creek by a pipe line about six miles long. A large part of this line is composed of 31 -inch cement pipe, laid in trenches and tunnels. The water in the 8,000 feet of pipe next to the power-house has a fall of 1,960 feet, and this pipe is of steel and 24 and 26 inches in diameter. The head of 1,960 feet, minus friction losses in the steel pipes, is delivered at the wheels. From the foregoing it appears that in a space of eight miles along Mill Creek there is a fall of more than 2,490 feet. To utilize this fall, water is diverted from the creek at three points within a distance of six miles and delivered in two power-stations under three different heads. As the stream gathers in volume between the upper and the lower in- takes, an equal amount of power could have been developed in a single station only by taking the three separate conduits or pipe lines to it and delivering their water there at three heads. Whether the expense of extending conduits and pipe lines to a single generating station will more than offset the advantages to be gained thereby is a question that should be decided on a number of factors vary- ing with each case. In general, it may be said that the smaller the volume of water to be handled and the greater its head, the more ad- vantageous is it to concentrate the generating machinery in the smallest practicable number of stations. On the Santa Ana River, into which Mill Creek flows, the Santa Ana plant, whence energy is transmitted to Los Angeles, is located. Water reaches this plant through a conduit of tunnels, flumes, and pipes, with a total length of about three miles from the point where the flow of the river is diverted. The 2,210 feet of this conduit nearest the power- plant are composed of 30-inch steel pipe, with a fall of 728 feet. Within fifteen miles of Mexico City are five water-power stations that supply energy for its electrical system. Two of these stations are on the LOCATION OF WATER-POWER STATIONS. 77 Monte Alto and three are on the Tlaluepantla River, the two former stations being about three miles, and the more distant of the three latter stations five miles, apart. At a distance of several miles above the highest station on each river the water is diverted by a canal, and the water of each of these canals, after passing through the wheels of the highest station, goes on to the remaining station, or stations, on the same river by a continuation of the canal. By placing the stations so short a distance apart the head of water at each station is reduced. On one stream these heads are 492 and 594 FIG. 20. Wood Pipe Line to Pike's Peak Power-house. feet respectively, and at two of the stations on the other stream they are 547 and 295 feet respectively. This division of the total head of water afforded by each river results in a rather small capacity for each station, the total at the five plants being only 4,225 kilowatts. In contrast with this figure the already mentioned Electra plant has generators of 10,000, the Santa Ana plant generators of 3,000, and the larger of the two Mill Creek plants generators of 3,500 kilowatts capac- ity. It should be noted that the cost of operation, as well as that of original construction, will vary materially between one large and several smaller stations of equal total capacity, the advantage as to operative cost being obviously with the one large plant. 78 ELECTRIC TRANSMISSION OF WATER-POWER. O O CQ Crib Dam, Rock Filled LOCATION OF WATER-POWER STATIONS. 79 All of the power-stations here considered have been equipped with water-wheels and generators operating on horizontal shafts, and this is the general practice. This arrangement brings the generators and the floor of the power-station within a few feet of the level of the tail-water. By the general use of draught tubes with turbine wheels the floors of sta- tions are often kept twenty feet or more above the tail-water level. Where the total available head of water is quite small, as is often the case with rivers where the volume of water is great, it is generally neces- sary to bring the level of the station floor down to within a few feet of the tail-water. The Birchem Bend station of the Springfield, Mass., electric system affords a good example of this sort, the floor of this station being only 2.6 feet above the ordinary level of the tail- water. At this station the difference of level between the head- and tail-water is only fourteen feet, and even with the low floor level named the top sides of the horizontal turbine wheels are covered only by 4.5 feet of water. At the Garvin's Falls station of the Manchester, N. H., electric sys- tem the level of the floor of the generator room is thirteen feet above the ordinary level of the Merrimac River, on the bank of which this sta- tion is located ; but in this case the total head of water is about twenty- eight feet. The high water of the Merrimac in 1896, before the Garvin's Falls station was built, reached a point 5.24 feet above its present floor level, and 18.24 feet above the ordinary level of the river at the point where the station is located. Under the Red Bridge electric station of the Ludlow Manufacturing Company, on the Chicopee River, in Massachusetts, the tail-water is twenty feet below the level of the floor and twenty- four feet below the cen- tres of the water-wheel and generator shafts. The difference between wheel-shaft and tail- water levels at this station is near the maximum that can be attained with horizontal pressure turbines, because a draught tube much longer than twenty-five feet does not give good results. In a pressure turbine the guides and wheel must be completely filled with water, as must also the draught tube, for efficient operation. If draught tubes are much more than twenty-five feet long, it is hard to keep a solid column of water from turbine to tail-water in each, and if this is not done a part of the head of water becomes ineffective. As pressure tur- bines are employed almost exclusively at electric stations with low heads of water, it is frequently impossible to locate such stations above tlie pos- sible level of tail-water in times of flood if horizontal wheels direct-con- nected to generators are employed. If turbines with vertical shafts are to be used, a power-station may be 8o ELECTRIC TRANSMISSION OF WATER-POWER. LOCATION OF WATER-POWER STATIONS. 81 so located or constructed that all the electrical equipment will be above the highest known water-mark. With vertical shafts, connecting wheels, and generators, the main floor of an electric station may be located above the crest of the falls where the power is developed instead of at or near their base. By far the most important examples of electric stations laid out on this plan are those at Niagara Falls, where there are four such plants. Two FIG. 23. Power-house No. 2 at Niagara Falls. of these generating plants, with an aggregate capacity of 105,000 horse- power, stand a mile above the falls, and are supplied with water through a short canal from Niagara River. Beneath each of these two stations a long, narrow wheel pit has been excavated through rock to a depth of 172 feet below the level of water in the canal. Both wheel pits terminate in a tunnel 7,000 feet long that opens into the river below the falls. In this wheel pit the tail-water level is 161 feet below that of the water in the canal, and 166 feet below the floor of the power-station. Water passes from the canal down the wheel pits to the wheels near the bottom through steel penstocks, each seven feet in diameter, and a vertical shaft extends from each wheel case to a generator in the station above. Locations like that at Niagara give great security against high water and washouts, but are seldom adopted because of the large first cost of plant construction. With heads of water from several hundred to 2,000 feet the loss of a few feet of head reduces the available power 'to only a 82 ELECTRIC TRANSMISSION OF WATER-POWER. very slight extent, and impulse wheels are usually employed. Draught tubes are not available to increase the heads at such wheels, and any fall of the water after it leaves the wheels does no useful work. Electric stations driven by impulse wheels under great heads, like those at Colgate, Electra, Kern River, Santa Ana River, and Mill Creek, may be located far enough above the beds of their water-courses to avoid dangers from freshets, without serious loss of available power. CHAPTER VIII. DESIGN OF ELECTRIC WATER-POWER STATIONS. WATER- WHEELS must be located at some elevation between that of head- and tail-water. With horizontal shafts and direct-connected wheels and generators the main floor of the station is brought below the level of the wheel centres. This is much the most general type of construction, and was followed in the Massena, Sault Ste. Marie, Canon Ferry, Col- FlG. 25. Cross Section of Columbus, Ga., Power-station. gate, Electra, Santa Ana, and many other well-known water-power sta- tions. If horizontal shafts are employed for wheels and generators with belt or rope connections between them the floor of the generator room may be elevated a number of feet above the wheels. This difference of elevation is usually provided for either by upper and lower parts of the same room, or by separate rooms one above the other and a floor between them. A two-story construction of this latter sort was frequently adopted 83 84 ELECTRIC TRANSMISSION OF WATER-POWER. in the older water-power stations, and good examples of it may be seen in connection with the electrical supply system at Burlington, Vt., and the Indian Orchard station in the Springfield, Mass., system. Vertical wheel shafts make the elevation of the main or generator floor of a station independent of that of the wheels, and thus give the highest degree of security against high water. After the vertical wheel shaft reaches the generator room, it may be geared to a horizontal shaft that has one or more dynamos directly mounted on it, or drives dynamos through belts or ropes. Belt-driving in this way, from horizontal shafts connected by bevel gears with vertical wheel shafts, is not uncommon in the older class of water-power stations. Generators mounted singly or in pairs on hori- FiG. 26. Cross Section of Combined Steam- and Water-power Station at Richmond, Va. zontal shafts that are driven by gearing on vertical wheel shafts have been adopted at the Lachine Rapids and South Bend plants, and it seems to offer a desirable method of connection in cases where vertical wheels are necessary and the cost of generators must be kept at a low figure. With this method of driving the generators can be designed for any economical speed and step bearings avoided. The most desirable method of driving generators with vertical wheels, where the expense, is not too great, is the direct mounting of each gen- DESIGN OF WATER-POWER STATIONS. 85 erator on the upper end of a wheel shaft (see cut). This method of con- nection not only requires a special type of generator, but may put serious limits on its speed. In general, the peripheral speed of a pressure turbine should be about 75 per cent of the theoretical velocity of water issuing under a head equal to that at which the wheel operates, in order to give the best efficiency. The rotative speeds of turbines, operating under any given head, should thus increase as their capacities and diameters de- crease. Because of these principles it is the common practice, with hori- zontal wheels, to mount two or more on each shaft to which a generator FIG. 27. Cross Section of Wheel House at Buchanan, Mich. is direct-connected in order to obtain a greater speed of rotation than could be obtained with a single wheel of their combined power. Thus, at Sault Ste. Marie the horizontal shaft on which each 4oo-kilowatt gen- erator is mounted is driven at 180 revolutions per minute by four turbines under a head of about 20 feet. At Massena the head of water is 50 feet, and each 5,000 horse-power generator is driven at 150 revolutions per min- ute by six turbines on a horizontal shaft. Vertical turbines are sometimes mounted singly on their shafts, as was done in the hydroelectric plant at Oregon City on the Willamette River, and this practice gives speeds that 86 ELECTRIC TRANSMISSION OF WATER-POWER. are too low for direct-connected dynamos of moderate cost, unless the head of water is unusually great. At the Oregon City plant the head of water is only 40 feet, and yet a single 42-inch turbine was mounted on the vertical shaft that drives each generator. The most notable examples of direct-connected generators and ver- tical turbines is that at Niagara Falls, where twenty-one generators of 5,000 horse-power each are mounted at the tops of as many vertical wheel shafts in two of the four stations. Each vertical shaft in the Niagara stations is driven at 250 revolutions per minute by a pair of Generator Room FIG. 28. Longitudinal Section of Buchanan, Mich., Power-house. turbines, one above the other. The maximum head between the water in the Niagara canal and that in the tunnel which forms the tail-race is 161 feet. On ten shafts the centres of the wheel cases are 136 feet below the level of water in the canal, and no draft tubes are used. The eleven pairs of wheels at the second Niagara power-house have their centre line 128.25 feet below the canal level and a draft tube for each pair of wheels extends to a point below the 'tail-water level. It is entirely practicable to use more than a single pair of turbines on the same vertical shaft, as is shown at the Hagneck station on the Jura, in DESIGN OF WATER-POWER STATIONS. FIG. 29. Section of Power-house No. 2 at Niatrara Falls 88 ELECTRIC TRANSMISSION OF WATER-POWER. DESIGN OF WATER-POWER STATIONS. . 89 Switzerland, where the head of water is about twenty-one feet and four turbines are mounted on each vertical shaft. The combined capacity of these four wheels on each shaft is 1,500 horse-power and its speed is 100 revolutions per minute. At the top of each shaft an 8,000- volt generator, with external, revolving magnet frame, is mounted. The use of four wheels per vertical shaft presents no great difficulty and should be resorted to more frequently in the future. For horizontal, direct-connected turbine wheels and generators the nearly uniform practice is to locate the generators in a single row from one end of a station to the other, and this brings the turbines into a paral- lel row. On this plan the shaft of each connected generator and its group of turbines sets at right angles to the longer sides of a station and approximately parallel with the direction in which water flows to the wheels. The typical water-power station with direct-connected units is thus a rather long, narrow building into which water enters on one side through penstocks and leaves on the other through tail-races. Such sta- tions usually set with one of the longer sides parallel to the river into which the tail-water passes and between this river and the canal or pipe line. At Massena the electric station occupies the position of a dam be- tween the end of the power canal and the Grass River, being about 150 feet wide and 550 feet long. Canal water entering this station passes through its wheels to the river under a head of about 50 feet. A similar construction was followed at Sault Ste. Marie, where the power-station separates the end of the canal from the St. Mary's River. This station is 100 feet wide, 1,368 feet long, and is to contain 80 sets of horizontal wheels, each set being connected to its own generator, and through these wheels the canal water passes under a head of approximately 20 feet. Ten generators are placed in line at the Canon Ferry station which is 225 by 50 feet inside, and each generator is driven by a pair of horizontal wheels under a head of 30 feet. This station sets between a short canal and the Missouri River, near one end of the dam. Passing from water-heads of less than 50 to those of several hundred or even more than i ,000 feet, the general type of station building remains about the same, but there is an important change in the arrangement of direct-connected wheels and generators. With these high heads of water, wheels of the impulse type, to which the water is supplied in the form of jets from nozzles, are em- ployed. These jets pass to the wheels in planes at right angles to their shafts, instead of flowing in lines parallel to these shafts like water to pres- sure turbines. The shafts of impulse wheels and their direct-connected generators are consequently arranged parallel with the longer instead of 9 o ELECTRIC TRANSMISSION OF WATER-POWER. the shorter sides of their stations. This plan results in long, narrow sta- tions with water entering at one and leaving at the other of the longer sides, just as in the case of direct-connected turbines under moderate heads. Stations with direct-connected impulse wheels are even longer -45 ft 30'x80' FIG. 31. Plan of Generating Station near Cedar Lake for City of Seattle, Wash. for a given number and capacity of units than are stations with pres- sure turbines. Colgate power-house, on the North Yuba River, contains seven generators, each direct-connected to an impulse wheel and shafts all parallel to its longer sides. This station is 275 feet long by 40 feet wide, and the water which enters one side by five iron pipes, 30 inches DESIGN OF WATER-POWER STATIONS. 92 ELECTRIC TRANSMISSION OF WATER-POWER. each in diameter, under a head of about 700 feet, is discharged from the other side into the river. At Electra station on the Mokelumne River five pairs of impulse wheels are direct-connected to five generators, each unit having its shaft k- Flu. 33. Plan of Power-station at Great Falls. diagonal with the walls of the building, and pipes deliver water to the wheels under a head of 1,450 feet. The ground plan of the generator room at this plant is 40 by 208 feet. The power-station on Santa Ana River, whence energy is transmitted 83 miles to Los Angeles, measures 127 feet long and 36 feet wide inside, and contains four generating units DESIGN OF WATER-POWER STATIONS. 93 in line, each of which consists of a direct-connected dynamo and impulse wheel, with shafts parallel to the longer sides of the station. Jets driving the wheels in this station are delivered under a head of 728 feet minus the loss by friction in a penstock 2,210 feet long. Both of the first Niagara plants, with vertical wheels far below the sta- tions in the pits, are long and narrow and have their generators in a single row. The later of these two stations has a ground area of approximately 72 by 496 feet outside, and contains eleven generators all in line. From these examples it may be seen that the prevailing type of electric water- power station, whether designed for horizontal or vertical wheels of either the pressure or impulse type, is wide enough for only a single row of gen- r FIG, 34. Power-house at Red Bridge on Chicopee River. erators and wheels, and has sufficient length to accommodate the required number of units. A few modern stations that depart from this general plan will be found, as that at Great Falls, on the Presumpscot River, whence elec- trical supply for Portland, Me., is drawn. This station sets about forty feet in front of the forebay end of the dam, and two penstocks enter the rear wall, while the other two enter one each through two of the remaining opposite sides. Of the four generators, with their direct-connected 94 ELECTRIC TRANSMISSION OF WATER-POWER. wheels, two are arranged with parallel shafts, while the other two have their shafts in line and at right angles to the lines of the former two. The station containing these generating sets has a floor area of 55 by 67.5 feet. Modern electric stations driven by water-po\ver are usually but one story in height and are clear inside from floor to roof, save for cranes and roof trusses. This construction may be seen in the Niagara, Spier Falls, lilHijjijg 5tms [-T:KI J!||| !j T*2-!2^ tl-2**^ ^^rs i ^^i^took : FIG. 35. Plan and Elevation of Red Bridge Station on the Chicopee River. Canon Ferry, Colgate, Electra, Santa Ana River and many other notable plants. In spite of this one-story style of construction, the electric sta- tions reach fair elevations because of the necessity for head room to oper- ate cranes in placing and removing generators. At Garvin's Falls, on the Merrimac River, the electric station contains generators of 650 kilo- watts each and the distance from floor to the lower cords of roof trusses is 27 feet. In the station at Red Bridge, on the Chicopee River, where generators are of i ,000 kilowatts capacity each, the distance between floor DESIGN OF WATER-POWER STATIONS. 95 and the under side of roof beams is 30.66 feet. Between the floor and roof trusses at the Birchem Bend station, on the river last named, the dis- tance is 26.25 feet, but each generator is rated at only 400 kilowatts. In the Canon Ferry plant, with its generators of 750 kilowatts each, the dis- tance from floor to roof trusses is 28 feet. At the plant on Santa Ana River, the 750-kilowatt generators, being connected to impulse- wheels, operate at 300 revolutions per minute, have relatively small diameters and are mounted over pits in the floor so that their shaft centres are only about two feet above it. By these means the distance from floor to roof trusses was reduced to 18.25 feet. All these examples of elevations be- tween floors and roof supports are for stations with direct-connected gen- erators and horizontal wheels. In the new Niagara station, where gen- erators of 3,750 kilowatts each are mounted oh' vertical wheel shafts that rise from the floor, the distance between the floor and roof trusses is 39.5 feet. Electric stations driven by water-power are now constructed almost entirely of materials that will not burn that is, stone, brick, tile, concrete, cement, iron, and steel. Stone masonry laid with cement mortar cr con- crete masonry is very generally employed for all those parts of the foun- dations that come in contact with the tail-water. For sub-foundations bedrock is very desirable, but where this cannot be reached piles are driven closely and their tops covered with several feet of cement concrete as a bedding for the stone foundation. Where stone is plenty or bricks hard to obtain, the entire walls of a water-power station are frequently laid en- tirely with stone in concrete mortar. If bricks can readily be had they are more commonly used than stone for station walls above the foundations. Concrete formed into a monolithic mass is a favorite type of construction for the foundations, walls and floors of water-power plants in Southern California. Cement and concrete are much used for station floors in all parts of the country, and these floors are supported by masonry arches in cases where the tail-water flows underneath the station after leaving the wheels. Station roofs are usually supported by steel trusses or I- beams, and slate and iron are favorite roof materials. With iron roof- plates an interior lining of wood, asbestos, or some other poor conductor of heat is much used to prevent the condensation of water on the under side of the roof in cold weather. Walls of water-power stations are usually given sufficient thickness of masonry to support all loads that come upon them without the aid of steel columns. In some cases where cranes do not extend entirely across their stations, one end of each crane is supported by one of the station walls and the other end 96 ELECTRIC TRANSMISSION OF WATER-POWER. by a row of iron or steel columns rising from the floor. Where the generator-room of a station has its floor level below high-water mark especial care should be taken to make the walls water-proof to an ele- vation above this mark. As the travelling-crane and the loads which it carries in erecting wheels and generators form a large part of the weight on the station walls, these walls are often reduced as much as one-half in thickness at the level of the crane, thus forming benches on which the ends of the cranes rest. The Garvin's Falls station, on the Merrimac River, rests on arches of stone masonry through which the tail-water passes, and the brick walls FIG. 36. Steel Penstocks at Chamblay Power-house. are water-proofed to an elevation eight feet above the floor. At twenty feet above the floor the twenty-four-inch brick walls on the two longer sides are reduced to eight inches in thickness, thus forming benches each sixteen inches wide on which the crane travels. Arches of stone masonry support the twenty-four-inch brick walls of the station at Red Bridge, on the Chicopee River, and these walls on the two longer sides decrease in thickness to twelve inches at an elevation of twenty-one feet above the floor, thus forming benches twelve inches wide for the ends of the crane. One concrete wall of the Santa Ana station is 2.5 feet thick to a dis- DESIGN OF WATER-POWER STATIONS. 97 tance of 13.5 feet above the floor, and th 77.3 ^=-86.25 K- 89.4 = 91.0 < = 91.6 4- 91.8 Volts, 450"E.: both Machin I i fficienc ^ from EtlieSei cy froi -20 -10 1 1 Output- 800 K.W..2300 Volts, 450 R P Jtt 1 100%-power Factor on both Machines Outp 10 loa it-lOi trpow (5K.-W sr Fac J .M. OB r ] i < i i c fi 1 , ,L 1 j ( > d~] K 1 * FIG. 51. Efficiency Curves for Motor Generators at Montreal Sub-station of the Shawinigan Transmission Line. adopted as the standard in many cases. This number of periods in comparison with a smaller one tends to increase the cost of rotary con- verters but decreases the cost of transformers, and is suitable for both incandescent and arc lighting. Few, if any, transmission systems have recently been installed for frequencies above sixty cycles, and the older plants that worked at higher figures have in most cases been remodelled. During the past decade the voltages of alternators have been greatly n8 ELECTRIC TRANSMISSION OF WATER-POWER. increased, but have not caught up with the demand for high pressures on long-transmission lines. Ten years ago when the first long transmis- sions were going into operation 2,000 volts was considered high for an alternator. As this voltage is too low for economy of conductors longer than three or four miles, the important early transmissions were all car- ried out with the aid of step-up transformers at generating stations. The ALTERNATORS IN TRANSMISSION SYSTEMS. Location of System. Number at Plant. Kilowatts Each. Alternator Voltage. * i PH J I pj Q, fcjO "o Method of Connections. Niagara Falls * Niagara Falls * . 16 5" 3>75 37CO 2,300 2 7OO 2 2 25 2C. 250 External revolving Internal Direct Colgate to Oakland. . Colgate to Oakland. . Electra to S.Francisco Portsmouth to Pelh'm Portsmouth to Pelh'm Virginia City 3 4 5 i 2 2 2,250 1,125 2,000 2,000 1,000 7C.O 2,400 2,400 13,200 13,200 coo 3 3 3 3 3 60 60 60 25 25 60 285 400 240 83-3 94 4OO Inductor Internal External Ogden & Salt Lake . . Chaudiere Falls Yadkin River Falls . . Lewiston, Me. . 5 2 2 750 750 750 7^0 2,300 10,500 12,000 10,000 3 3 3 ? 60 66.6 66 60 300 400 1 66 180 Internal Farmington River ) to Hartford, Conn ) Canon Ferry to Butte Apple Riv. to St. Paul Edison Co., L.Angeles Madrid to Bland Canon City to Cripple Creek 2 2 IO 4 4 2 750 600 750 75 700 600 500 500 500 800 75 605 coo 3 2 3 3 3 3 2 60 60 60 60 60 157 300 90 :: Sault Ste. Marie St. Hyacinthe, Que. . . Great Falls to Port- land, Me. . . 80 3 400 1 80 coo 2,400 2,500 10,000, 3 3 2 3 60 60 1 80 600 M * Niagara Falls Power Company. practice then was, and to a large extent still is, to design the alternators for a transmission with a voltage well suited to their economical construc- tion, and then give the step-up transformers any ratio necessary to attain the required line voltage. Thus in the two water-power plants connected with the electrical supply system of Hartford, Conn., the alternators operate at 500 volts with transformers that put the line voltage up to 10,000. In the station ALTERNATORS FOR TRANSMISSION. 119 on Apple River that supplies the lighting system of St. Paul, Minn., the al- ternators operate at 800 volts, and this is raised to 25,000 volts for the line. At Canon Ferry the alternator voltage of 500 is multiplied by 100 in the transformers giving 50,000 on the line. Electric Roads High Tension Lines-. Rotary Stations F.G. 52. Transmission Line of New Hampshire Traction Company. Where the generating station of a transmission system is located close to a part of its load the alternators are given a voltage suitable for distribution, say about 2,400, and any desired pressure on the line is then obtained by means of step-up transformers. Two of the Niagara 120 ELECTRIC TRANSMISSION OF WATER-POWER. Falls plants are an illustration of this practice, the voltage of all the alternators there being 2,200, which is raised to 22,000 for the transmis- sion of a part of the energy to Buffalo. A similar practice is followed in the water-power plant at Ogden, where the generators furnish current at. 2, 300 volts for local distribution, and transformers raise the pressure to 26,000 volts for the transmission to Salt Lake City. In the 32,000- kilowatt plant at Sault Ste. Marie, Mich., the alternators operate at 2,400 volts and a large part of their load is local, but this voltage will no doubt be raised by transformers when transmission lines are operated. For generating stations that carry little or no local loads the cost of transformers can be saved if the generators develop the voltage required on the transmission lines. This possible saving has led to the develop- ment of alternators that generate voltages as high as 15,000 in their armature coils. Such alternators have stationary armatures in all cases and are of either the revolving magnet or inductor type. At the present time many transmission systems in the United States operating at 10,000 or more volts develop these pressures in the arma- ture coils of their alternators, and the number of such systems is rapidly increasing. It is now the rule rather than the exception to dispense with step-up transformers on new work where the line voltage is any- thing under 15,000. Perhaps the longest transmission line now in regular operation with current from the armature coils of an -alternator is that at 13,200 volts between the generating station at Portsmouth and one of the sub-stations of the New Hampshire Traction system at Pel- ham, a distance of forty-two miles. In at least one transmission system now under construction, that of the Washington, Baltimore & Annapolis Electric Railway, the voltage of generators to supply the line without the intervention of step-up trans- formers will be 15,000. The company making these alternators is said to be ready to supply others that generate 20,000 volts in the armature coils whenever the demand for them is made. In quite a number of cases alternators of about 13,000 volts have been installed for transmissions along electric railway lines. Systems Using High-voltage Alternators. Electrical Development Co. of Ontario, Niagara Falls ................. 12,000 Lighting and Street Railway, Manchester, N. H ...................... 10,000 Lighting and Street Railway, Manchester, N. H ...................... 12,500 Lighting and Power, Portland, Me ............................... 10,000 Lighting and Power, North Gorham, Me ............................. 10,000 Mallison Power Co., Westbrook, Me ................................ 10,000 Lighting and Power, Lewiston, Me ...... .......................... 10,000 ALTERNATORS FOR TRANSMISSION. 121 Systems Using High-voltage Alternators. Voltages. 1 " Electric Railway, Portsmouth, N. H 13,200 Electric Railway, Pittsfield, Mass 12,500 Ludlow Mill?, Ludlow, Mass 13,200 Electric Railway, Boston to Worcester, Mass 13,200 Electric Railway, Albany & Hudson, N. Y 12,000 Empire State Power Co., Amsterdam, N. Y 12,000 Lehigh Power Co., Easton, Pa 12,000 Hudson River Power Co., Mechanicsville, N. Y 12,000 Light and Power, Anderson, S. C 11,000 Fries Mfg. Co., Salem, N. C 12,000 Light and Power, Ouray, Col 12,000 Washington & Baltimore Electric Railway 15,000 Canadian Niagara Power Co., Niagara Falls 12,000 Ontario Power Co., Niagara Falls 12,000 This list of high-voltage alternators is not intended to be exhaustive, but serves to indicate their wide application. If such alternators can be purchased at a lower price per unit of capacity than alternators of low voltage plus step-up transformers, there is an apparent advantage for transmission systems in the high-voltage machines. This advantage may rest in part on a higher efficiency in the alternators that yield the line voltage than in the combination of low-voltage alternators plus step-up transformers. It is not certain, however, that depreciation and repairs on the generators of high voltage will not be materially greater than the like charges on generators of low voltage, and some advantage in price should be required to cover this contingency. Just how far up the voltage of alternators can be pushed for practi- cal purposes is uncertain, but it seems that the limit must be much below that for transformers where there is ample room for solid insu- lation and the coils can be immersed in oil. The use of generators at 10,000 volts and above tends to lower the volts per mile on transmission lines, because it seems better in some cases to increase the weight of line conductors rather than to add step-up transformers, as in the 4 2 -mile transmission from Portsmouth to Pelham. CHAPTER X. TRANSFORMERS IN TRANSMISSION SYSTEMS. TRANSFORMERS are almost always necessary in long electric systems of transmission, because the line voltage is greater than that of genera- tors, or at least that of distribution. As transformers at either generat- ing or receiving stations represent an increase of investment without cor- responding increase of working capacity, and also an additional loss in operation, it is desirable to avoid their use as far as is practicable. In short transmissions over distances of less than fifteen miles it is generally better to avoid the use of transformers at generating stations, and in some of these cases, where the transmission is only two or three miles, it is even more economical to omit transformers at the sub-stations. Thus, where energy is to be transmitted two miles and then applied to large motors in a factory, or distributed at 2,500 volts, the cost of bare copper conductors for the three-phase transmission line will be only about #6 per kilowatt of line capacity at 2,500 volts, with copper at 15 cents per pound, and a loss of 5 per cent at full load. The average loss in such a line will probably be as small as that in one set of transformers and a line of higher voltage. Furthermore, the first cost of the 2,5oo-volt generators and line without transformers will be less than that of gener- ators and line of higher voltage with step-down transformers at the sub- station. As generators up to 13,500 volts are now regularly manufactured, it is quite common to omit step-up transformers at the main stations of rather short transmission systems. This practice was followed in the 1 3, 500- volt transmission to Manchester, N. H., the 10,000- volt transmis- sion to Lewiston, Me., and the 12,000- volt transmission to Salem, N. C. In most transmission over distances of twenty-five miles or more, step-up transformers at generating stations as well as step-down trans- formers at sub-stations are employed. As yet the highest voltages that have been put into practical use on transmission lines (that is, 50,000 to 60,000) are much below the pressures that have been yielded by trans- formers in experimental work. These latter voltages have in a number of instances gone above 100,000. The numbers and capacities of trans- 122 TRANSFORMERS IN TRANSMISSION SYSTEMS. 123 i2 4 ELECTRIC TRANSMISSION OF WATER-POWER. formers used at main stations vary much in their relation to the numbers and individual capacities of generators there. In some cases there are three times as many transformers as three-phase generators, and the capacity of each transformer is either equal to or somewhat greater than one-third of the capacity of each generator. Thus in the station at Spier Falls on the Hudson, whence power is transmitted to Albany and other cities, the number of step-up trans- formers will be thirty and their aggregate capacity will be 24,014 kilo- watts, while the total number of three-phase generators will be ten, with a combined capacity of 24,000 kilowatts. Another practice is to give each transformer a capacity greater than one-third of that of the three- phase generator with which it is to be connected, and make the total num- ber of transformers less than three times as great as the number of gen- erators. An example of this sort exists in the station on Apple River, whence power is transmitted to St. Paul. This station contains four three-phase generators of 750 kilowatts each, and six transformers of 500 kilowatts each, these latter being connected in two sets of three each. The use of three transformers for each three-phase generator instead of three transformers for each two or three generators, tends to keep trans- formers fully loaded when in use, and therefore to increase their effi- ciency. On the other hand, efficiency increases a little with the size of transformers, and the first cost per unit capacity is apt to be less the greater the size of each. Another solution of the problem is to provide one transformer for each three-phase generator, each transformer being wound with three sets of coils, so that the entire output of a generator can be sent into it. This practice is followed at the Hochfelden water-power station, whence power is transmitted to Oerlikon, Switzerland, also in the water-power station at Grenoble, France, whence energy at 26,000 volts is transmitted to a number of factories. With three-phase transformers each generator and its transformer may form an independent unit that can be connected with the line at pleasure, thus tending to keep transformers at full load. Though three-phase transformers are much used in Europe, they have thus far had little application in the United States. Single-phase transformers may, of course, be limited in number to that of the three- phase generators with which they are used, but such transformers must regularly be connected to the generators and line in groups of two or three. Such an equipment was provided in part at the 7,5oo-kilowatt station on the Missouri River at Canon Ferry, which contains ten three-phase gen- erators of 750 kilowatts each. The transformers at this station include TRANSFORMERS IN TRANSMISSION SYSTEMS. 125 twelve of 325 kilowatts each, connected in four groups of three each, also six transformers of 950 kilowatts each which are also connected in groups of three. Three of these larger transformers have a capacity of 2,850 kilowatts, or nearly equal to that of four generators. With two-phase generators single-phase transformers must be con- nected in pairs, and it is common to provide two transformers for each generator. Thus, in the Rainbow station on the Farmington River, whence energy is transmitted to Hartford, there are tw r o generators of the two-phase type and rated at 600 kilowatts each, also four transformers rated at 300 kilowatts each. As the regulation of transformers on overloads is not as good as that of generators, it seems good practice to give each group of transformers a somewhat greater capacity than that of the generator or generators whose energy is to pass through it. This plan was apparently followed at the Canon Ferry station, where the total generator capacity is 7,500 kilowatts and the total capacity of step-up transformers is 9,600 kilowatts. Each group of the 325-kilowatt transformers there has a capacity of 975 kilowatts, while each generator is only of 750 kilowatts. Usually the number of groups of transformers at a two-phase or three-phase generat- ing station is made greater than the number of transmission circuits sup- plied by the station, for some of the reasons just considered. When this is not trie case it is commonly desirable in any event to have as many groups of step-up transformers as there are transmission circuits, so that each circuit may be operated with transformers that are independent of the other circuits. At sub-stations it is desirable to have a group of transformers for each transmission circuit, and it may be necessary to subdivide the trans- former capacity still further in order to keep transformers in operation at nearly full load, or to provide a group of transformers for each sort of service or for each distribution circuit. All of the transformers at a sub- station should have a total capacity at least equal to that of the generators whose energy they are to receive, minus the losses in step-up transformers and the line. Transformers at sub-stations do not necessarily corre- spond in number or individual capacity with those at generating stations, and the number of sub-station transformers bears no necessary relation to the number of generators by which they are fed. Two transmission circuits extend from Canon Ferry to a sub-station at Butte, and in that sub-station there are six transformers divided into two groups for three-phase operation, each transformer being rated at 950 kilowatts. This sub-station equipment thus corresponds to only the 126 ELECTRIC TRANSMISSION OF WATER-POWER. six 95o-kilowatt transformers in the generating station, because the four groups of smaller transformers there are used to supply the transmission line to Helena. In the sub-station at St. Paul that receives the entire output of the plant on Apple River, where the six transformers of 500 kilowatts each are located, ten transformers receive energy from two three-phase trans- mission circuits. Six of these transformers are rated at 300 kilowatts each. The 3oo-kilowatt transformers are connected in two groups of three each, and the 2oo-kilowatt in two groups of two each, transforming current from three-phase to two-phase. The aggregate capacity of the sub-station transformers is thus 2,600 kilowatts, while that of transform- ers at the generating station is 3,000 kilowatts. With four generators at the water-power plant there are ten transformers at the sub-station, where all the energy, minus losses, is delivered. At Watervliet, where one of the several sub-stations of the system with its larger generating plant at Spier Falls is located, the capacity of each transformer is 1,000 kilowatts, though each transformer at Spier Falls has a rating below this figure. In the sub-station at Manchester, N. H., that receives nearly all of the energy from four water-power plants, containing eight generators with an aggregate capacity of 4,030 kilowatts, there are located twenty- one step-down transformers that have a total rating of 4,200 kilowatts. These twenty-one transformers are fed by six circuits, of which five are three-phase and one is two-phase. A part of the transformers supply current to motor-generators, developing 5oo-volt current for a street rail- way, and the remaining transformers feed circuits that distribute alter- nating current. From these examples it may be seen that in practice either one or more groups of transformers are employed in sub-stations for each trans- mission circuit, that the total number of these transformers may be just equal to or several times that of the generators from which they receive energy, and that the individual capacities of the transformers range from less than one-third to more than that of a single generator. Groups of transformers at a main station must correspond in voltage with that of the generators in the primary and that of the transmission line in the secondary windings. Sub-station transformers receive current at the line voltage and deliver it at any of the pressures desired for local distribu- tion. Where step-up transformers are employed the generator pressure in nearly all cases is at some point between 500 and 2,500 volts. At the Canon Ferry station the voltage of transformers is 550 in TRANSFORMERS IN TRANSMISSION SYSTEMS. 127 in the primary and 50,000 in the secondary windings. In the Colgate power-house, whence energy is transmitted to Oakland, the generator pressure of 2,400 volts is raised to 40,000 volts by transformers. Gen- erator voltage in the power-house on Apple River is 800 and transform- ers put the pressure up to 25,000 for the line to St. Paul. Transformers at the Niagara Falls station raise the voltage from 2,200 to 22,000 for the transmission to Buffalo. As transformers can be wound for any desired ratio of voltages in their primary and secondary coils, a generator pressure that will allow the most economical construction can be selected where step-up trans- formers are employed. In general it may be said that the greater the capacity of each generator, the higher should be its voltage and that of the primary coils of step-up transformers, for economical construction. At sub-stations the requirements of distribution must obviously fix the secondary voltages c-f transformers. Weight and cost of transformers depend in part on the frequency of the alternating current employed, transformers being lighter and cheaper the higher the number of cycles completed per second by their current, other factors remaining constant. In spite of this fact the tendency dur- ing some years has been toward lower frequencies, because the lower frequencies present marked advantages as to inductive effects in trans- mission systems, the distribution of power through induction motors, the construction and operation of rotary converters, and the construction of generators. Instead of the 133 cycles per second that were common in alternating systems when long transmissions first became important, sixty cycles per second is now the most general rate of current changes in such transmission systems. But practice is constantly extending to still lower frequencies. The first Niagara Falls plant with its twenty-five cycles per second reached the lower limit for general distribution, because incandescent lighting is barely satisfactory and arc lighting decidedly undesirable at this figure. In contrast with the great transmissions from Canon Ferry to Butte, Colgate to Oakland, and Electra to San Francisco, which operate at sixty cycles, the system between Canon City and Cripple Creek, in Colorado, as well as the great plant at Sault Ste. Marie, employs thirty-cycle current, and the lines from Spier Falls to Schenectady, Albany, and Troy are intended for current at forty cycles per second. From these examples it may be seen that the bulk and cost of transformers is not the controlling factor in the selection of current frequency in a trans- mission system. 128 ELECTRIC TRANSMISSION OF WATER-POWER. S3 1 l~ "S" u J J Air Compressor D ooo Work Room Cell Room FIG. 54. First Floor of Saratoga Sub-station. TRANSFORMERS IN TRANSMISSION SYSTEMS. 129 Transformers used at either generating or sub-stations are cooled by special means in many cases. The advantages of so-called artificial cooling are smaller weight and first cost in transformers, and perhaps longer life for the insulation of windings. For these advantages a small increase in the cost of opera- tion must be paid. Station transformers are usually cooled either by forcing air through their cases under pressure, or else by passing water through pipes in the oil with which the transformer cases are filled. If cooling with air-blast is adopted, a blower, with electric motor or some other source of power to operate it, must be provided. Where trans- formers are oil-insulated and cooled with water there must be some pres- sure to maintain the circulation. If free water under a suitable head can be had for the cooling of transformers, as in most water-power plants, the cost is very slight. Where water must be purchased and pumped through the transformers its cost will usually be greater than that of cool- ing with air-blast. One manufacturer gives the following as approximate figures for the rate at which water at the temperature of 15 centigrade must be forced through his transformers to prevent a rise of more than 35 centigrade in their temperature, probably when operating under full loads. Transformers Kilowatts. Gallons per minute. 150 0-5 400 .75 400 i.oo 1,000 1.5 75 -37 An air-blast to cool transformers at main or sub-stations may be pro- vided in either of two ways. One plan is to construct an air-tight com- partment, locate the transformers over openings in its top, and maintain a pressure in the compartment by means of blower-fans that draw cool air from outside. Such an arrangement has been carried out at the sub- station in Manchester, N. H. The basement underneath this sub-sta- tion is air-tight, and in the concrete floor over it there are twenty-seven rectangular openings, each twenty-five by thirty inches, and intended for the location of a 2oo-kilowatt transformer. Aggregate transformer capac- ity over these openings will thus be 5,400 kilowatts. Pressure in this basement is maintained by drawing outside air through a metal duct that terminates in a hood on the outside of the sub-station about nine feet above the ground. In the roof of this sub-station there are ample sky- light openings to permit the exit of hot air that has been forced through the transformers. In the air-tight basement are two electric motors of 9 i3o ELECTRIC TRANSMISSION OF WATER-POWER. ten horse-power each, connected to the blower that maintains the pressure. It may be noted that in this case there is less than one-horse power of motor capacity for each 200 kilowatts capacity in transformers. Where there are not more than six or nine transformers to be cooled, it is common practice to provide a separate motor and blower for each group of three transformers, and lead the air directly from each blower to its group of transformers by a metal duct, thus avoiding the necessity for an air-chamber. In such cases a blower giving a three-eighth-ounce air pressure per square inch and a motor of one horse-power capacity are generally provided for each group of three transformers rated at 100 to 150 kilowatts each. Where cooling with air-blast is adopted, oil-insula- tion cannot be carried out because the air must come into intimate con- tact with the transformer coils and core. Both oil-insulation with water cooling and dry insulation with cooling by air-blast have been widely used in transmission systems of large capacity and high voltage. In the Colgate plant, where the line pressure is 40,000 volts, the 700- kilowatt transformers are oil-insulated and water-cooled, and this is also true of the 95o-kilowatt transformers in the 5o,ooo-volt transmission be- tween Canon Ferry and Butte. On the other hand, the transmission system between Spier Falls, Schenectady, and Albany, carried out at 26,500 volts, includes transformers that range from several hundred to 1,000 kilowatts each in capacity and are all air-cooled. Either a water- cooled transformer or one cooled by air-blast may be safely overloaded to some extent, if the circulation of air or water is so increased that the overload does not cause heating beyond the allowable temperature. The circulation of air or water through a transformer should never be forced to an extent that cools the transformer below the temperature of the air in the room where it is located, as this will cause the condensa- tion of water on its parts. In some cases it is desirable that means for the regulation of trans- former voltages through a range of ten per cent or more each way from the normal be provided. This result is reached by the connection of a number of sections at one end of the transformer winding to a terminal board, where they may be cut in or out of action at will. Regulation is usually desired, if at all, in a secondary winding of comparatively low voltage, and the regulating sections generally form a part of such wind- ing, but these sections may be located in the primary winding. In order to keep the number of transformers smaller and the capacity of each larger than it would otherwise be, it is practicable to divide the low-voltage secondary winding of each transformer into two or more TRANSFORMERS IN TRANSMISSION SYSTEMS. 131 parts that have no electrical connection with each other. These different parts of the winding may then be connected to distinct distribution lines or other services. An example of this sort exists in the Hooksett sub- station of the Manchester, N. H., transmission system. Three-phase current at about 11,000 volts enters the primary windings of three trans- formers at this sub-station. Each of these transformers has a single primary, but two distinct secondary windings. Three of these second- aries, one on each transformer, are connected together and feed a rotary converter at about 380 volts, three-phase. The other three secondary windings are connected in like manner to a second rotary converter. Each of these transformers is rated at 250 kilowatts, and each rotary is rated at 300 kilowatts, so that the transformer capacity amounts to 750 kilowatts and that of the converters to 600 kilowatts, giving a desirable margin of transformer capacity for railway service. With the ordinary method of connection and windings, six transformers of 125 kilowatts each would have been required in this sub-station. High voltage for transmission lines may be obtained by the combina- tion of two or more transformers with their secondary coils in series. This method was followed in some of the early transmissions, as in that at 10,000 volts to San Bernardino and Pomona, begun in 1891, where twenty transformers, giving 500 volts each, were used with their high- voltage coils in series. Some disadvantages of such an arrangement are its high cost per unit of transformer capacity and its low efficiency. In a single-phase system the maximum line pressure must be de- veloped or received in the coils of each transformer, unless two or more are connected in series. This is also true as to either phase of a two- phase system with independent circuits. In three-phase circuits the coils of a transformer connected between either two wires obviously operate at the full line pressure. The same result is reached when the three transformers of a group are joined to the line in mesh or A -fashion. If the three transformers of a group are joined in star or Y-fashion, the coils of each transformer are subject to fifty-eight per cent of the voltage be- tween any two wires of the three-phase line on which the group is connected. It is no longer the practice to connect two or more transformers in series either between two wires of a two-phase or between two wires of a three- phase circuit, because it is cheaper and more efficient to use a single trans- former in each of these positions. Where very high voltage must be de- veloped or received with a three-phase system, the star or Y-connection of each group of three transformers has the advantage of a lower strain on the insulation of each transformer than that with the mesh or A - 132 ELECTRIC TRANSMISSION OF WATER-POWER. grouping. Thus if the A -grouping is used, the line pressure equals that of each transformer coil, but if the Y-grouping is used the line voltage is 1.73 times that of each transformer coil. At the Colgate power-house, the yoo-kilowatt transformers are de- signed for a maximum pressure of 60,000 volts on the three-phase line when Y-connected, so that the corresponding voltage is 34,675 in their secondary coils. The primary coils of these same transformers are con- nected in mesh or A -form and each coil operates at 2,300 volts, the generator pressure. Transformers are in some cases provided with several sets of connec- tions to their coils so that they may be operated at widely different press- ures. Thus, in the Colgate plant, each transformer has taps brought out from its secondary coils so that it can be operated at either 23,175, 28,925, or 34,675, with 2,300 volts at its primary coil. Corresponding to the three voltages named in each secondary coil are voltages of 40,000, 50,000, and 60,000 on a three-phase line connected with three of these transformers in Y-fashion. The mesh or A -connection is used between the coils of transformers on some transmission lines of very high voltage. The 950 kilowatt transformers in the system between Canon Ferry and Butte illustrate this practice, being connected A -fashion to the 50,000- volt line. When transformers that will operate at the desired line voltage on A -connection can be obtained at slight advance over the cost of trans- formers requiring Y-connections, it is often better practice to select the former, because this will enable an increase of seventy-three per cent in the voltage of transmission to be made at any future time by simply changing to Y-connections. Such an increase of voltage may become desirable because of growing loads or extension of transmission lines. An example of this sort came up some time ago in connection with the transmission between Ogden and Salt Lake City, which was operat- ing at 16,000 volts, three-phase, with the high-pressure coils of transform- ers connected in A -form. By changing to Y-connections the line voltage was raised seventy-three per cent without increasing the strain on trans- former insulation. In some cases it is desirable to change alternating current from two- phase to three-phase, or vice versa, for purposes of transmission or distri- bution, and this can readily be done by means of static transformers. One method often employed to effect this result includes the use of two transformers connected to opposite phases of the two-phase circuit. The three-phase coil of one of these transformers should be designed for the TRANSFORMERS IN TRANSMISSION SYSTEMS. 133 desired three-phase voltage, and should have a tap brought out from its central point. The three-phase coil of the other transformer should be designed for 87 per cent of the desired three-phase voltage. One end of the coil designed for 87 per cent of the three-phase voltage should be con- nected to the centre tap of the three-phase coil in the other transformer. The other end of the 87 per cent coil goes to one wire of the three-phase circuit. The other two wires of this circuit should be connected, respect- ively, to the outside end of the coil that has the central tap. As a matter of illustration it may be required to transform 500- volt, two-phase current from 'generators, to 20,000- volt, three-phase current for transmission. Two transformers designed for 500 volts in their primary coils are neces- sary for this work. One of these transformers should have a secondary coil designed for 20,000 volts, so that the ratio of transformation is 20,000 -^ 500 or 40 to i , and a tap should be brought out from the centre of this coil. The other transformer should have a secondary voltage of 0.87 x 20,000 = 17,400, so that its ratio of transformation is 34.8 to i. These two transformers, with the connections above indicated, will change the 5oo-volt, two-phase current to 20,000 volts, three-phase. At one of the water-power stations supplying energy for use in Hart- ford, four transformers of 300 kilowatts each change 5oo-volt, two- phase current from the generators to 10,000- volt, three-phase, for the transmission line. In the Niagara water-power station the generators deliver two-phase current at 2,200 volts, and 975-kilowatt transformers are connected in pairs to change the pressure to 22,000 volts, three-phase, for transmission to Buffalo. A transformer is used in some cases to raise the voltage and compen- sate for the loss in a transmission line. For this purpose the secondary of a transformer giving the number of volts by which the line pressure is to be increased is connected in series with the line. The primary wind- ing of this transformer may be supplied from the line boosted or from another source. Transformers ranging in capacity from 100 to 1,000 kilowatts each, such as are commonly used for transmission work, have efficiencies of 96 to 98 per cent at full loads, when of first-class construction. Efficiency increases slowly with transformer capacity within the limits named, and 98 per cent can be fairly expected in only the larger sizes. In any given transformer the efficiency may be expected to fall a little, say one or two per cent, between full load and half load, and another one per cent be- tween half load and quarter load. These figures for efficiencies at par- i 3 4 ELECTRIC TRANSMISSION OF WATER-POWER. tial loads vary somewhat with the design and make of transformers. In general, it may be said that step-up or step-down transformers will cost approximately #7.50 per kilowatt capacity, or about one-half of the like cost of low-voltage dynamos. If dynamos of voltage sufficiently high for the transmission line can be had at a figure below the combined cost of low- volt dynamos and raising transformers, it will usually pay to avoid the latter and develop the line voltage in the armature coils. This plan avoids the loss in one set of transformers. TRANSFORMERS IN TRANSMISSION SYSTEMS. Transformers Transformers Generators at at Power- at Power- Transmission System. stations. Sub-stations. stations. No. Kw. Each. No. Kw. Each. No. Kw. Each. Canon Ferry to Butte 12 * * Apple River to St. Paul 6 95 6 6 95 10 75 6 500 4 200 4 75 White River to Dales 400 77C 2 COO Farmington River to Hartford 4 300 ... 2 500 600 Ogden to Salt Lake t9 250 .5 750 Colgate to Oakland 7 3 1125 ' U 2250 Presumpscot River to Portland. . . ... ... fj 2OO 4 500 f' 180 1 3 300 Four water-powers to Manchester. ... ... 21 2OO 45 4 650 LI 1200 * Other transformers at Helena sub-stations. t Part of energy distributed directly from generators. CHAPTER XI. SWITCHES, FUSES, AND CIRCUIT-BREAKERS. ELECTRICAL transmission has worked a revolution in the art of switch- ing. As long as the distances to be covered by distribution lines required pressures of only a few hundred volts, the switch contacts for generators and feeders could well be exposed in a row on the surface of vertical marble slabs and separated from each other by distances of only a few inches. These switches were capable of manual operation even at times of heavy overload without danger of personal injury to the operator or of destructive arcing between the parts of a single switch or from one switch to another near-by. On the back of these marble slabs one or more sets of bare bus-bars could be located without much probability that an accidental contact between them would start an arc capable of destroying the entire switchboard structure and shutting down the sta- tion. The rise of electric pressures to thousands and tens of thousands of volts in distribution and transmission systems has vastly increased the difficulty of safe and effective control with open-air switches. The higher the voltage of the circuit to be operated under load the greater must be the distance between the contact parts of each switch and also between adjacent switches. Such switches must also be farther removed from the operators as the voltages of their circuits go up, as a person cannot safely stand very close to an electric arc of several feet or even yards in length. In the West, where long transmissions are most common, long break-stick switches have been much used with high voltages. These switches depend on the length of the break to open the circuit and on the length of the stick that moves the switch-jaw or plug to insure the safety of the operator. Where switches of this sort are used it is highly impor- tant to have ample distances between the contact points of each switch and also between the several switches. On circuits of not more than 10,000 volts an arc as much as a yard long will in some cases follow the opening switch blade and hold on for several seconds. On the 33,000- volt transmission line at Los Angeles a peculiar form of switch is used 136 ELECTRIC TRANSMISSION OF WATER-POWER. which makes a break between a pair of curved wire horns that are ten inches apart at their nearest points. When the contact between these horns is broken the arc travels up between portions of the horns that curve apart and is thus finally ruptured. Besides the very large space required for open switches on circuits of 5,000 to 10,000 volts or more, there is a further objection that the arcs developed by opening such switches under heavy loads rapidly destroy the contact parts and produce large quantities of metallic vapor that is objectionable in a central sta- tion. In some experiments performed at Kalamazoo (A. I. E. E., vol. xviii., p. 407) with open-air switches the voltages ranged from 25,000 to 40,000. The loads on circuits broken by the switches were highly in- ductive and mounted from 1,200 to 1,300 kilovolt-amperes. At 25,000 volts the arc produced by the open-air switch held on for several seconds. At 40,000 volts the arc following the opening of this switch was over thirty feet long, and being out of doors near the pole line the arc struck the line wires and short-circuited the system. It has been shown that the oscillations of voltage occurring when a circuit under heavy load is opened by an open-air switch may be very dangerous to insulation (A. I. E. E., vol. xviii., p. 383). In the Kalamazoo test the oscillations of this sort were reported to have reached two or three times the normal voltage of the system when the open-air switch was used. Facts of the nature just outlined have led to the development of oil switches. The general characteristic of oil switches is that the contact parts are immersed in, and the break between these contacts takes place under, oil. Two types of the oil switch are made, one having all of its contact parts in the same bath of oil and the other having a separate oil-bath for each contact. Compared with those of the open-air type, oil switches effect a great saving of space, develop no exposed arcs or metallic vapors, cause little if any oscillation or rise of voltage in an alter- nating circuit, and can be depended on to open circuits of any voltage and capacity now in use. In the tests above mentioned at Kalamazoo, a three-phase oil switch making two breaks in each phase and with all the six contacts in a single oil-bath was used to open circuits of 25,000 volts and 1,200 to 1,300 kilovolt-arcs with satisfactory results. At 40,000 volts, however, this type of switch spat fire and emitted smoke, indicating that it was working near its ultimate capacity. A three-phase switch with each of its six contacts in a separate cylindrical oil-chamber was used to open the 40,000- volt i ,300 kilovolt-arc circuit at Kalamazoo with perfect success even under conditions of short-circuit and without the appearance of fire or smoke at the switch. The three-phase switch used SWITCHES, FUSES, AND CIRCUIT-BREAKERS. 137 in the tests at Kalamazoo and having each of its contacts in a separate oil-chamber was similar in construction to the switches used in the Metro- politan and Manhattan railway stations in New York City. In each of these switches the two leads of each phase terminate in two upright brass cylinders. These cylinders have fibre linings to prevent side-jumping of the arcs when the switch is opened, and each cylinder is filled with oil. Into the two brass cylinders of each phase dips a H -shaped contact piece through insulating bushings, and the ends of this contact piece fit into terminals at the bottom of the oil pots. A wooden rod joins the centre or upper part of the fl -contact piece, and the three rods of a three-phase switch pass up through the switch compartment to the operating mechan- ism outside. The six brass cylinders and their three -contact pieces are usually mounted on a switch cell built entirely of brickwork and stone slabs. For a three-phase switch the brick and stone cell has three Feeders Feeders > POWER HOUSE } No2 . , I Bus,. Bars, 1 |*| nBu.|*UJ ^ ' ... 'tr I'ti fy Hr l*Yt ' v " .' *YT f l Xi I 1 *] l [ }\ f l Xr " N i j' I i Bus jl Bars | I J >{ Bus J Bars t j j i i 6 o o 6 6 6 6 o oiM Gensrators Gene/ators t>| i? Ml j j Generators Generators g! I !l Q Q (5 G) Q 9 9 G> ' 9 9 f! i I - . b t . I Bu ? . I Ba . f S I >- ,1 . ,1 Bus! Bars I ,1 f "l ! - r *r.l M. '* T . i^. J/'MV"" **i I 1 *! UM. l l *i I 1 *' J M Bus U Bars Lr W IvfBus POWERHOUSE Feeders Feeders IrfBt^f I FIG. 55. Connections between Power-houses i and 2 at Niagara Falls. entirely separate compartments, and each compartment contains the two brass cylinders that form the terminals of a single phase. On top of and outside the cell the mechanism for moving the wooden switch rods is mounted. In the Metropolitan station, where the voltage is 6,000, the vertical movement of the fl -shaped contact piece with its rod is twelve inches. At the Manhattan station, where the operating voltage is 1 2,000, the vertical movement of the f| -con tacts in opening a switch is seventeen inches. The total break in each phase in a switch at the Metropolitan station is thus twenty-four inches, or four inches per i ,000 volts, and the 138 ELECTRIC TRANSMISSION OF WATER-POWER. total break per phase in switches at the Manhattan station is thirty-four inches, or 2.66 inches per 1,000 volts total pressure. Oil switches are now very generally employed on alternating circuits that operate at 2,000 volts or more for purposes of general distribu- tion. On circuits of moderate voltage like that just named, and even higher, it is common practice to use oil switches that have only a single reservoir of oil each, the entire six contacts in the case of a three-phase switch being immersed in this single reservoir. Such switches are usu- ally operated directly by hand and are located on the backs of or close to the slate or marble boards on which the handles that actuate the switch mechanism are located. A good example of this sort of work may be seeC at the sub-station in Manchester, N. H., where energy from four water-power stations is delivered over seven transmission lines and then distributed by an even larger number of local circuits at 2,000 volts three- phase. At the Garvin's Falls station, one of the water-power plants that delivers energy to the sub-station in Manchester, the generators operate at 1 2,000 volts three-phase, and these generators connect directly with the bus-bars through hand-operated oil switches on the back of the marble switchboard. These last-named switches, like those at the Manchester sub-station, have all the contacts of each in a single res- ervoir of oil. With very high voltages, where only a few hundred kilowatts are con- cerned, and also with powers running into thousands of kilowatts at as low a pressure as 2,000 volts, it is very desirable to remove even oil switches from the switchboard and the vicinity of the bus-bars. Great powers as well as very high voltages not only increase the element of personal danger to an attendant who must stand close to a switch while operating it, but also render the damage to other apparatus that may result from any failure of or short-circuit in a switch much more serious. As soon as the switches are removed to a distance from the operating board the necessity for some method of power control becomes evident, since the operator at the switchboard should be able to make or break connections of any part of the apparatus quickly. The necessity for the removal of switches for very large powers to a distance from the operating boards and for the application of mechanical power to make and break connections was met before the development of oil switches. Thus at the first Niagara (A. I. E. E., vol. xviii., p. 489) power-house, in 1893, the switches for the 3,750-kilowatt, 2,2oo-volt generators, though of the open-air type, were located in a special switch compartment erected in SWITCHES, FUSES, AND CIRCUIT -BREAKERS. 139 FIG. 56 Wire-room Back of Switchboard in Power-station on French Broad River, North Carolina. 140 ELECTRIC TRANSMISSION OF WATER-POWER. the generator room and over a cable subway at some distance from the operating board. These switches were actuated through compressed-air cylinders into which air was admitted by the movement of levers near the switchboard. Evidently a switch of this capacity i ,000 amperes per pole and 2,200 volts, two-phase could not well be operated by hand- power wherever located, because of the large effort required. In the second generating station at Niagara Falls oil switches similar to those FIG. 57. Section through Cable Subway under Oil Switches in Niagara Power-house No. 2. used at the Manhattan Elevated Railway plant in New York, but two- phase, were employed. Each of these oil switches at Niagara Falls has a capacity of 5,000 horse-power, like the previous open-air switches, and is electrically actuated. In these electrically operated oil switches a small motor is located on top of the brick cell that contains the contact parts, and this motor re- leases and compresses springs that open and close the switch. While it is not desirable to employ open-air switches to open circuits of several thousand or even hundreds of kilowatts at voltages of 2,000 or more, it SWITCHES, FUSES, AND CIRCUIT-BREAKERS. 141 is nevertheless possible to do so. This is shown by the experience of the first Niagara Falls station, where the 2, 200- volt two-phase switches are reported to have opened repeatedly currents of more than 600 amperes per phase without injurious sparking. The great rise of voltage that was shown by the experiments at Kalamazoo to follow the opening of a simple open-air switch was avoided at the first Niagara switches by a simple expedient. In these 5,000 horse-power open-air switches a shunt of high resistance was so connected between each pair of contacts that the blades FIG. 58. Schenectady Switch-house on Spier Falls Line. and jaws that carried the main body of the current never completely opened the circuit. When the main jaws of one of these switches were opened the shunt resistance continued in circuit until subsequently broken at auxiliary terminals. That no excessive rise of voltage took place when one of these switches was open was shown by connecting two sharp terminals in parallel with the switch and by adjusting these termi- nals to a certain distance apart. Had the voltage risen on opening the switch above the predetermined amount there would have been an arc formed by a spark jumping the distance between the pointed terminals. 142 ELECTRIC TRANSMISSION OF WATER-POWER. Safety and reliability of operation at high voltages, say of 5,000 or more, require that each element of the equipment be so isolated as well as insulated from every other element that the failure or even destruction of one element will not seriously endanger the others. With this end in view the cables from each generator to its switch should be laid in a con- duit of brick or concrete that contains no other cables. The brick or FIG. 59. Second-floor Plan of Saratoga Switch-house on Spier Falls Line. stone compartment for each phase of each switch should be so substantial that the contacts of that phase may arc to destruction without injury to the contacts of another phase. Bus-bars, like switches, should be re- moved from the operating switchboard, because an arc between them might destroy other apparatus thereon, and even the board itself. It is not enough to remove bus-bars from the switchboard where very high voltages are to be controlled, but each bar should be located in a separate brick compartment so that an arc cannot be started by accidental contact SWITCHES, FUSES, AND CIRCUIT-BREAKERS. 143 between two or more of the bars. It is convenient to have the brick and stone compartments for bus-bars built horizontally one above the other. The top and bottom of each compartment may conveniently be formed of stone slabs with brick piers on one side and a continuous brick wall on the other to hold the stone slabs in position. Connections to the bus-bars should pass through the continuous brick wall that forms what may be termed the back of the compartments. To close the open- FlG. 60. Ground Floor of Saratoga Switch-house. ings between the brick piers at the front of the compartments movable slabs of stone may be used. Feeders passing away from the bus-bars, like dynamo cables running to these bars, should not be grouped close together in a single compartment, but each cable or circuit should be laid in a separate fireproof conduit to the point where it passes out of the station. The folly of grouping a large number of feeders that transmit great powers together in a single combustible compartment was well illus- trated by the accident that destroyed the cables that connected the first Niagara power-station with the transformer-house on January 29th, 144 ELECTRIC TRANSMISSION OF WATER-POWER. 1903. On the evening of that day lightning short-circuited one of the cables in the short bridge that connects No. i station with the trans- former-house, and all the cables in this bridge, supplying local consumers as well as railways and lighting in Buffalo, were destroyed. This bridge contained probably more than thirty-six cables, as that number of new cables was put in position within twenty-four hours after the accident, and these cables, covered with inflammable insulation, were close together. The result was not only the loss of the cables, but also the damage to power users. If these cables had been located in separate fire-proof conduits, it is highly probable that only the one directly affected by lightning would have been destroyed. The brick and stone compartments for bus-bars may be located in the basement underneath the switchboard, as at the Portsmouth station of the New Hampshire Traction Company, or at any other place in a station where they are sufficiently removed from the other apparatus. In power-house No. 2 at Niagara Falls a cable subway beneath the floor level runs the entire length, parallel with the row of generators (A. I. E. E., vol. xix., p. 537). In this subway, which is thirteen feet nine and three-quarter inches wide and ten feet six inches high, the two structures for bus-bar compartments are located. Each of these structures meas- ures about 6.6 feet high and 1.8 feet wide, and contains four bus-bar compartments. In each compartment is a single bar, and the four bars form two sets for two-phase working. Above the bus-bar compartments and rising from the floor level are the oil switches. A space over the cable subway midway of its length and between the two groups of oil switches is occupied by the switchboard gallery which is raised to some elevation above the floor and carries eleven generator, twenty-two feeder, two interconnecting, and one exciter panels. In power-house No. i the bus-bars are located in a common space above the 5,000 horse-power open-air switches already mentioned, and each bar has an insulation of vulcanized rubber covered with braid and outside of this a wrapping of twine. Of course; an insulation of this sort would amount to nothing if by any accident an arc were started between the bars. Where each bus- bar is located in a separate fireproof compartment, as at Niagara power- house No. 2, the application of insulation directly to each bar is neither necessary nor desirable. Consequently the general practice where each bar has its own fireproof compartment is to construct the bars of bare copper rods. With main switches for generators and feeders removed from the operating board and actuated by electric motors or magnets, the small SWITCHES, FUSES, AND CIRCUIT-BREAKERS. 145 switches at the board with which the operator is directly concerned must of course control these magnets or motors. The small switches at the operating board are called relay switches, and the current in the cir- cuits opened and closed by these switches and used to operate the mag- nets or motors of the oil switches may be conveniently obtained from a storage battery or from one of the exciting dynamos. Probably the best arrangement of the relay switches is in connection with dummy bus-bars on the face of the switchboard, so that the connec- tions on the face of the board constitute at all times a diagram of the actual connections of the generator and feeder circuits. It is also desira- ble for quick and correct changes in the connections of the main appa- ratus that all the relay switches and instruments necessary for the control of any one generator or any one feeder be brought together on a single panel of the switchboard. If this plan is followed, the operator at any time will have before him on a single panel all of the switches and instru- ments involved in the connections then to be made, and the chance for mistakes is thus reduced to a minimum. The plan just outlined was that, adopted at the Niagara power plant No. 2, where a separate panel is provided for each of eleven generators and each of twenty-two feeders. On each of the eleven generator panels there are two selector relay switches, one generator relay switch, and one relay generator field switch. On each of the twenty-two feeder panels there are two relay selector switches. The relay switches on the two interconnecting panels serve to make connections between the two groups of five and six generators respectively in power-house No. 2 and the ten generators of power-house No. i . On each panel there are relay indicators to show whether the oil switches that carry the main current respond to the movements of their relay switches. Where the electric generators operate at the maximum voltage of the system, as at Garvin's Falls and in the power-house of the Manhattan Elevated Railway, there may be said to be only one general plan of con- nections possible. That is, the generators must connect directly with the main bus-bars at the voltage of the system, and the feeders or trans- mission lines must also connect to these same bars. Of course there may be several sets of bus-bars for different circuits or classes of work, but this does not change the general plan of through connections from generators to lines. So, too, the arrangement of switches is subject to variations, as by placing two switches in series with each other in each dynamo or feeder cable, or by connecting a group of feeders through their several switches to a particular set of bus-bars and then 10 146 ELECTRIC TRANSMISSION OF WATER-POWER. supplying this set of bars from the generator bus-bars through a single switch. Where the voltage of transmission is obtained by the use of step-up transformers, the connections of these transformers may be such as to Transformer"^ n n n LO^ *+ ^,1 k/ ly U^ FIG. 61. Switchboard Wiring, Glens Falls Sub-station on Spier Falls Line. require nearly all switching to be done on either the high- or low-tension circuits. The more general practice was formerly to do all switching in the generator circuits and on the low-tension side of transformers, except in the connection and disconnection of transformers and transmission lines SWITCHES, FUSES, AND CIRCUIT-BREAKERS. 147 with the high-tension bus-bars, when not in operation. Where generators operate at the maximum voltage of the system only two main groups of switches are necessary, one group connecting generators to bus-bars, and the other group connecting bus-bars to the transmission lines. As soon as step-up transformers are introduced the number of switch groups must be increased to four if the usual method of connection is followed, and there must be both a high voltage and a low voltage set of bus-bars. That is, one set of switches must connect generators with low-tension bus-bars, another group must connect low-tension bars with the primary coils of transformers, a third group joins the secondary coils of transform- ers with the high-tension bars, and the fourth group of switches joins the transmission lines to the high-tension bus-bars. Switches connecting the secondary coils of step-up transformers to the high-tension bus- bars, and also the transmission lines to these same bars, have often been of the simple open-air type with short knife-blade construction. These switches have been used to disconnect the secondary coils of transformers and also the transmission lines from the high-tension bus- bars when no current was flowing, and switches of the simple knife- blade construction with short breaks could of course be used for no other purpose. With switches of this sort on the high-tension side of apparatus the practice is to do all switching of line circuits on the low- tension side. It is possible to avoid some of this multiplication of switches if each generator with its transformers is treated for switching purposes as a unit and the switching for this unit is done on the secondary or high-voltage side of the step-up transformers. The adoption of this plan, of course, implies the use of switches that are competent to break the secondary circuit of any group of transformers under overload conditions and at the maximum voltage of the system, but oil switches as now made are competent to meet this requirement. When all switching of live circuits is confined to those of high voltage there is also the incidental advantage that heavy contact parts carrying very large currents are avoided in the operating switches. Where each gen- erator is connected directly to its own group of transformers the secon- dary coils of these transformers will pass through oil switches to high- tension bus-bars, and the use of low-tension bus-bars may be avoided. From these high-tension bus-bars the transmission lines will pass through oil switches, so that on this plan there are only two sets of oil switches, namely, those connecting the secondary coils of transformers to the high- tension bus-bars, and those connecting the transmission lines to the same i 4 8 ELECTRIC TRANSMISSION OF WATER-POWER. bars. Each group of two or three transformers, according as two or three are used with each generator, should be connected to its generator through short-break, open-air knife switches for convenienec in discon- necting and changing transformers that are not in operation, but these switches are not intended or required to open the circuit of the generators and primary coils when in operation. A plan similar to that just outlined was followed at the station of the Independent Electric Light and Power Company, San Francisco, where SWITCHES, FUSES, AND CIRCUIT-BREAKERS. 149 each of the 5 50- volt generators is ordinarily connected directly to the primary coils of two transformers that change the current from two-phase to three-phase and then deliver it through oil switches to the high-tension bus-bars at 11,000 volts. To these bus-bars the n,ooo-volt feeders for five sub-stations are connected through switches. At this station there is a set of 5 50- volt bus-bars to which any of the generators may be con- nected, but to which no generator is connected in ordinary operation. The generators alone have switches connecting with these bars. When it is desirable to operate any particular generator on some pair of trans- FlG. 63. Switchboard at Chambly Power-station. formers other than its own, that generator is disconnected from its own transformers and connected to the 5 50- volt bus-bars. The generator whose transformers are to be operated by the generator before mentioned next has its switch connected to the 5 50- volt bus-bars, while the brushes of the contact rings of the former generator are raised. As the leads from each generator to its two switches are permanently joined, the switching operations just named connect the transformers of one generator with the other generator that has its switch closed on the 5 50- volt bars. Where it is desired that a single reserve transformer may be readily substituted for any one of a number of transformers in regular use, the connections to each of these latter transformers may be provided with 150 ELECTRIC TRANSMISSION OF WATER-POWER. double-pole double-throw knife switches on both the primary and sec- ondary sides, so that when these switches are thrown one way at any transformer in regular use the reserve transformer will be connected in its place. Fuses and automatic circuit-breakers alike are intended to break con- nections without the intervention of human agency under certain prede- termined conditions. In the fuse the heat generated by a certain cur- rent is sufficient to melt or vaporize a short length of special conductor. In the circuit-breaker a certain current gives a magnet or motor sufficient strength to overcome the pressure of a spring, and contact pieces through which the current is passing are pulled apart. The primary object of both the fuse and the circuit-breaker is thus to open connections and stop the flow of energy when more than a certain current passes. When any current passes through a circuit in the reverse of its regular direction the circuit-breaker can be arranged to break the connections, though the fuse cannot. A fuse must carry the current at which it is designed to melt during some seconds before enough heat is developed to destroy it, and the exact number of seconds for any particular case is made a little uncertain by the possibility of loose connections at the fuse tips which develop additional heat and also by the heat-conducting power of its con- necting terminals. A circuit-breaker may be set so as to open its connec- tions in one or more seconds after a certain current begins to flow. When connections are broken by a fuse the molten or vaporized metal forms a path that an arc may easily follow. A circuit-breaker with its contacts under oil offers a much smaller opportunity than a fuse for the maintenance of an arc. These qualities of fuses and circuit-breakers form the basis of their general availability and comparative advantages in transmission circuits. Much variation exists in practice as to the use of fuses and circuit- breakers on transmission circuits. One view often followed is that fuses and circuit-breakers should be entirely omitted from the generator and transmission lines. The argument in favor of this practice is that tem- porary short circuits due to birds that fly against the lines or to sticks and loose wires that are thrown onto them will interrupt all or a large part of the transmission service if fuses or circuit-breakers that operate instantly are employed. On the other hand, it may be said that if fuses and cir- cuit-breakers are omitted from the generator and transmission circuits a lasting short circuit will make it necessary to shut down an entire plant in some cases until it can be removed. Electric transmission at high voltages became important before magnetic circuit-breakers competent SWITCHES, FUSES, AND CIRCUIT-BREAKERS. 151 to open overloaded circuits at such voltages were developed. Conse- quently the early question was whether a transmission line and the gen- erators that fed it should be provided with fuses or be solidly connected from generators to the distribution circuits of sub-stations. The original tendency was strong to use fuses in accord with the practice at low volt- ages. The great importance of continuous service from transmission systems and the many interruptions caused by temporary short circuits where fuses were used led to their abandonment in some cases. An example of this sort may be seen at the first Niagara station. In 1893, when this station was equipped, no magnetic circuit-breaker was availa- ble for circuits of either 11,000 or 2,200 volts, carrying currents of several thousand horse-power, and fuses were employed in lines at both these pressures (A. I. E. E., vol. xviii., pp. 495, 497). The fuses adopted in this case were the same for both the 2,200 and the n,ooo-volt lines and were of the explosive type. Each complete fuse consisted of two lignum- vitae blocks that were hinged together at one end and were secured when closed at the other. In these blocks three parallel grooves for fuses were cut and in each 'groove a strip of aluminum was laid and connected to suitable terminals at each end. Vents were provided for the grooves in which the aluminum strips were placed so that the expanding gas when a fuse was blown would escape. When these fuse blocks were new and the blocks of lignum vitae made tight joints the metallic vapor produced when a fuse was blown was forced out at the vents and the connections of the line were thus broken. After a time, however, when the joints between the blocks were no longer tight because of shrinkage, the expanding gas of the fuse would reach the terminals and an arc would continue after the fuse had blown. These aluminum fuses, which were adopted about 1 893 , were abandoned at the Niagara plant in 1 898. Since this later date the 2, 200- volt feeders from the No. i power-house to the local consumers have had no fuses at the power-house, nor have circuit-breakers been installed there in the place of the fuses that were removed. At tKe large manufacturing plants supplied through these local Niagara feeders, the feeders formerly terminated in fuses, but these have since been displaced by circuit-breakers. In the second Niagara power-station, completed in 1902, the local 2, 200- volt feeders are provided with circuit-breakers, but no fuses. Between the generators and bus-bars of the first Niagara plant the circuits were provided with neither fuses nor automatic circuit-break- ers, and this practice continues there to the present time. Besides the aluminum fuses in the n,ooo-volt transmission line at the first Niagara station, there were lead fuses in the 2, 200- volt primary 152 ELECTRIC TRANSMISSION OF WATER-POWER. circuits of the step-up transformers that supplied these lines. At the other end of these lines, in the Buffalo sub-station, another set of alumi- num fuses was inserted before connection was made with the step-down transformers. Between the secondary coils of these transformers and the 5 50- volt converters there were no fuses, but these converters were con- nected to the railway bus-bars through direct current circuit-breakers. These lead fuses, which contained much more metal than those of alu- minum, when blown set up arcs that lasted until power was cut off by opening a switch, and usually destroyed their terminals. An effort was made to so adjust the sizes of the fuses in this transmission system that in case of a short circuit in distribution lines at Buffalo only the fuses in the sub-station would be blown, leaving those at Niagara entire. This plan did not prove effective, however, and a severe overload on the distri- bution lines in Buffalo would blow out fuses clear back to the generator bus-bars at the Niagara station. In order to accomplish the opening of overloaded circuits with greater certainty, to delay such opening where the overload might be of only a momentary nature, and to confine the open circuit to the lines where the overload existed, automatic circuit-breakers were substituted for the fuses named in the Niagara and Buffalo transmission system. This system was also changed from 11,000 to 22,000 volts on the transmission lines, thus rendering the requirements as to circuit-opening devices more se- vere. These circuit-breakers were fitted with time-limit attachments so that any breaker could be set to open at the end of any number of seconds after the current flowing through it reached a certain amount. A circuit- breaker with such a time-limit attachment will not open until the time for which it is set, after the amperes flowing through it reach a certain figure, has elapsed, no matter how great the current may be. Moreover, if the overload is removed from a line before the number of seconds for which its time-limit circuit-breaker is set have elapsed, the circuit-breaker resets itself automatically and does not open the connections. If a cir- cuit-breaker is set to open a line after an interval of say three seconds from the time when its current reaches the limit, the line will not be opened by a mere momentary overload such as would blow out a fuse. By setting the time-limit relays of circuit-breakers in transmission lines to actuate the opening mechanism after three seconds from the time that an overload comes on, and then leaving the breakers on distribution lines to operate without a time-limit, it seems that the opening of breakers on the distribution lines should free the system from an overload there before the breakers on the transmission lines have time to act. Such a result SWITCHES, FUSES, AND CIRCUIT-BREAKERS. 153 is very desirable in order that the entire service of a transmission system may not be interrupted every time there is a fault or short circuit on one of its distribution lines. This plan was followed in the Niagara and Buffalo system. In the 2 2,000- volt lines at the Niagara station the time relays were set to actuate the breakers after three seconds, at the terminal house in Buffalo, where the transformers step down from 22,000 to 1 1 ,000 volts, the circuit-breakers in the 1 1 ,000 volt lines to sub-stations had their relays set to open in one second. Finally the circuit-breakers in the distribution lines from the several sub-stations were left to operate without any time limit. By these means it was expected that a short circuit in one of the distribution circuits from a sub-station would not cause the connections of the underground cable between that sub-station and the terminal house to be broken, because of the instant action of the circuit-breaker at the sub-station. Furthermore, it was expected that a short circuit in one of the underground cables between the terminal house and a sub-station would be disconnected from the transmission line at that house and would not cause the circuit-breakers at the Niagara sta- tion to operate. It is reported that the foregoing arrangement of circuit- breakers with time relays failed of its object because the breakers did not clear their circuits quick enough and that the time-limit attachments on the 22,000 and 11,000 volt lines are no longer in use (A. I. E. E., vol. xviii., p. 500). As the circuits under consideration convey thousands of horse-power at 11,000 and 22,000 volts it may be that time-limit de- vices with circuit-breakers would give good results under less exacting conditions. Time-limit relays are perhaps an important aid toward relia- ble operation of transmission systems, but they are subject to the objec- tion that no matter how great the overload they will not open the circuit until the time for which they are set has run. In the case of a short circuit the time-limit relay may lead to a prolonged drop in voltage throughout the system, which is very undesirable for the lighting service and also allows all synchronous apparatus to fall out of step. With a mere momen- tary drop in voltage the inertia of the rotating parts of synchronous ap- paratus will keep them in step. For these reasons it is desirable to have circuit-breakers that will act immediately to open a line on which there is a short circuit or very great overload, but will open the line only after an interval of one or more seconds when the overload is not of a very extreme nature. This action on the part of circuit-breakers at the second Niagara power-station was obtained by the attachment of a dash-pot to the trip- ping plunger of each circuit-breaker (A. I. E. E., vol. xviii., p. 543). With moderate overloads of a very temporary nature this dash-pot so retards 154 ELECTRIC TRANSMISSION OF WATER-POWER. the action of a tripping plunger that the circuit-breaker does not open. When a short circuit or great overload comes onto a line the pull on the tripping plunger or the circuit-breaker on that line is so great that the resistance of the dash-pot to the movement is overcome at once and the line is disconnected from the remainder of the system. The fact that a circuit-breaker may be designed to open the line which it connects, whenever the direction from which the flow of energy takes place is reversed, is taken advantage of at some sub-stations to guard against a flow of energy from a sub-station back toward the generating station. By this means a flow of energy from a sub-station to a short circuit in one of the lines or cables connecting it with the generating plant is prevented. CHAPTER XII. REGULATION OF TRANSMITTED POWER. REGULATION of voltage at incandescent lamps is a serious problem in the distribution of electrically transmitted energy. Good regulation should not allow the pressure at incandescent lamps rated at no to 1 20 volts to vary more than one volt above or below the normal. Electric motor service is much less exacting as to constancy of voltage, and the pressure at motor terminals may sometimes be varied as much as ten per cent without material objection on the part of users. A mixed service to these three classes of apparatus must often be provided where transmitted energy is used, and the limitations as to variations at incandescent lamps are thus the ones that must control the regulation of pressure. Transmission systems may be broadly divided into those that have no sub-stations and must therefore do all regulation at the generating plant, and those that do have one or more sub-stations so that regulation of voltage may be carried out at both ends of the transmission line. As a rule, a sub-station with an operator in attendance is highly desirable between transmission and distribution lines, and this is the plan generally followed at important centres of electrical supply, even though the transmission is a short one. One example of this sort may be noted at Springfield, Mass., where energy for electrical supply is transmitted from two water-power plants on the Chicopee River only about four and a half and six miles, respectively, from the sub-station in the business centre of the city. The voltage of transmission for two- phase current in this case is 6,000, and is reduced to about 2,400 volts at the sub-station for the general distribution of light and power. A similar instance may be seen at Concord, N. H., where electrical energy at both 2,500 and 10,000 volts is delivered to a sub-station in the business section from a water-power plant at Sewall's Falls, on the Merrimac River, four and one-half miles distant. From this sub-station the current is dis- tributed at about 2,500 volts for the supply of lamps and motors. A sub- 156 ELECTRIC TRANSMISSION OF WATER-POWER. REGULATION OF TRANSMITTED POWER. I S7 station was found desirable at Concord for purposes of regulation before the voltage of transmission was raised above that of distribution. Sub- sequently, when the load increased, the voltage of 10,000 was adopted on a part of the transmission circuit in order to avoid an increase in the size of their conductors. In some instances, however, transmission and distribution lines are FIG. 65. -Area of Electrical Distribution at Montreal. joined without the intervention of a sub-station, where regulation of voltage can be accomplished, though this practice has little to recom- mend it aside from the savings in first cost of installation and subsequent cost of operation. These savings are more apparent than real if fairly constant pressure is to be maintained at the lamps, because what is gained by the omission of sub-stations will be offset, in part at least, by additional outlays on the lines if good regulation is to be maintained. This fact may be illustrated by reference to Figs. 66, 67, and 68, in each 158 ELECTRIC TRANSMISSION OF WATER-POWER. of which D represents a generating station and A, B, and C towns or cities where energy from the station is to be distributed. In the case of each figure it is assumed that the distance between the generating station and each of the cities or towns is such that distributing lines with a loss of, say, not more than two per cent in voltage at full load cannot be provided between the generating station and each city or town because of the cost of conductors. This being so, one or more TRANSMITTED Powi FIG. 66. T RAN8MITTED POWER. FIG. 67. FIG. 68. centres of distribution must be located in each town, and the trans- mission lines must join the distribution lines at these centres either on poles or in sub-stations. If several of these towns are in the same gen- eral direction from the generating plant so as to be reached by the same transmission line, as A , B, and C in Fig. 66, this one line will be all that is necessary with a sub-station in each town. Where sub-stations are not employed a separate transmission circuit must be provided between the generating plant and each town for reasons that will appear presently. The percentage of voltage variation in a transmission line under changing loads will be frequently from five to ten, and is thus far beyond the allowable variations at incandescent lamps. To give good lighting ser- REGULATION OF TRANSMITTED POWER. 159 vice the centre of distribution, where the transmission line joins the dis- tribution circuits, must be maintained at very nearly constant voltage if no sub-station is located there. Regulation at a generating station will compensate for the changing loss of pressure in a line under varying loads so as to maintain a nearly constant voltage at any one point thereon. No plan of station regulation, however, can maintain constant voltages at several points on the same transmission line when there is a varying load at each. The result is that even though the several towns served are in the same general direction from the generating station, as in Fig. 67, yet each town should have its separate transmission line where no sub-sta- tions in the towns are provided. In the case illustrated by Fig. 68, where the towns served are in very different directions from the generating station, there should be a separate transmission line to each, regard- less of whether there is a sub-station or only a centre of distribution there. Even in the case illustrated by Fig. 68, as in each of the others, there is a large saving effected in the cost of distribution lines by the employ- ment of a sub-station at the point where these lines join the trans- mission circuit, provided that the variation of pressure at lamp terminals is to be kept within one volt either way from the standard. With the variations of loads the loss of pressure in the distribution lines will range from zero to its maximum amount and the connected lamps will be sub- jected to the change of voltage represented by this total loss, unless the distribution start from a sub-station where the loss in distribution lines can be compensated for by regulation. To give good service the dis- tribution lines should be limited to a loss of one per cent at full load if there is no sub-station where they join transmission lines. With oppor- tunity for regulation at a sub-station the maximum loss in distribution lines may easily be doubled, thus reducing their weight by one-half in comparison with that required where there is no sub-station. Another advantage of connecting transmission and distribution lines in a sub-station, where regulation of voltage can be had, lies in the fact that it is practically impossible to maintain an absolutely constant press- ure miles from a generating plant at the end of a transmission line that is carrying a mixed and varying load. A result is that without the in- tervention of regulation at a sub-station it is almost impossible to give good lighting service over a long transmission line. Furthermore, the labor of regulation at a generating station is much increased where there are no sub-stations, because it must be much more frequent and accu- rate. The absence of sub-stations from a transmission system thus im- 160 ELECTRIC TRANSMISSION OF WATER-POWER. plies more transmission circuits, heavier distribution circuits, more labor at the generating plant, and a poor quality of lighting service. Where stationary motors form the great bulk of the load on a trans- mission system, and good lighting service is of small importance, it may be well to omit sub-stations at some centres of distribution. This is a condition that sometimes exists in the Rocky Mountain region where the main consumers of power along a transmission line may be mines or works for the reduction of ores. An example of this sort exists in the system of the Telluride Power Transmission Company, in Utah, which extends from Provo Canon, on the river of the same name, entirely around Utah Lake by way of Mercur, Eureka, and Provo, and back to the power-house in Provo Canon, a continuous circuit of 105 miles. The transmission voltage on this line is 40,000, and at intervals where there are distributing points the voltage is reduced to about 5,000 by transformers on poles, and without the aid of regulation at sub-stations in some cases. The power thus transmitted is largely used in mines and smelters for the operation of motors, but also for some commercial light- ing. Regulation at generating stations of the voltage on transmission lines may be accomplished by the same methods whether there are sub-sta- tions at centres of distribution or not. In any such regulation the aim is to maintain a certain voltage at some particular point on the transmis- sion line, usually its end, where the distribution circuits are connected. If more than one point of distribution exists on the same transmission line, the regulation at the generating plant must be designed to maintain the desired pressure at only one of these points, leaving regulation at the others to be accomplished by local means. One method of regulation consists in the overcompounding of each generator so that the voltage at its terminals will rise at a certain rate as its load increases. If a gen- erator and transmission line are so designed that the rise of voltage at the generator terminals just corresponds with the loss of voltage on the line when the output of that generator alone passes over it to some par- ticular point, then the pressure at that point may be held nearly con- stant for all loads if no energy is drawn from the line elsewhere. These several conditions necessary to make regulation by the compounding of generators effective can seldom be met in practice. If a varying num- ber of generators must work on the same transmission line, or if varying loads must be supplied at different points along the line, no compound winding of generators will suffice to maintain a constant voltage at any point on the line that is distant from the power-station. For these reasons REGULATION OF TRANSMITTED POWER. 161 the compound winding of generators is of minor importance so far as the regulation of voltage on transmission lines is concerned, and on large alternators is not generally attempted. An example may be noted on the 3,750-kilowatt generators at Niagara Falls, where the single magnet winding receives current from the exciters only. A much more effective and generally adopted method of regulation of voltage at the generating plants of transmission systems is based on the action of an attendant who varies the current in the magnet coils of each generator so as to raise or lower its voltage as desired. The regula- tion must be for some one point on the transmission line, and the attend- ant at the generating plant may know the voltage at that point either by means of a pair of pressure wires run back from that point to a voltmeter at the generating plant, by a meter that indicates the voltage at the point in question according to the current on the line, or by telephone connec- tion with a sub-station at the point where the constant voltage is to be maintained. Pressure wires are a reliable means of indicating in the generating station the voltage at a point of distribution on the line, but the erection of these wires is quite an expense in a long transmission, and in such cases they are only occasionally used. Owing to inductive effects and to variable power-factors the amperes indicated on a line carrying alternating current are far from a certain guide as to the drop in voltage between the generating station and the distant point. In long transmis- sions, telephone communication between the generating plant and the sub-stations is the most general way in which necessary changes to maintain constant voltage at sub-stations are brought to the attention of the attendant in the generating plant. Few, if any, extensive trans- mission systems now operate without telephone connection between a generating plant and all of its sub-stations, or between a single sub-sta- tion and the several generating plants that may feed into it. Thus, the generating plant at Spier Falls, on the Hudson River, will be connected by telephone with sub-stations at Schenectady, Albany, Troy, and some half-dozen smaller places. On the other hand, the single sub-station in Manchester, N. H., that receives the energy from four water-power plants has a direct telephone line to each. Where two or more transmission lines from the same power-station are operated from the same set of bus-bars the voltage at a distant point on each line cannot be held constant by changes of pressure on these bus-bars. One generator only may be connected to each transmission line and be regulated for the loss on that line, but this loses the ad- vantages of multiple operation. Another plan is to connect a regula- 1 1 162 ELECTRIC TRANSMISSION OF WATER-POWER. tor in each transmission line before it goes from the generating plant, One type of regulator for this purpose consists of a transformer with its secondary coil divided into a number of sections and the ends of these sections brought out to a series of contact segments. The pri- mary coil of this transformer may be supplied with current from the bus-bars and the secondary coil is then connected in series with the line to be regulated, so that the secondary voltage is added to or sub- tracted from that of the main circuit. A movable contact arm on the segments to which the sections of the secondary coil are connected makes it possible to vary the secondary voltage by changing the number of these sections in circuit. In another transformer used for regulating purposes the primary coil is connected to the bus-bars as before and the movable secondary coil is put in series with the line to be regulated. The regula- tion is accomplished in this case by changing the position of the secondary relative to that of the primary coil and thus raising or lowering the sec- ondary voltage. Both of these regulators require hand adjustment, and the attendant may employ the telephone, pressure wires, or the compen- sating voltmeter above mentioned, to determine the voltage at the centre of distribution. The voltage indicated by this so-called "compensator" is that at the generating station minus a certain amount which varies with the current flowing in the line to be regulated. The voltmeter coil of the compensator is connected in series with the secondary coils of two transformers, which coils work against each other. One transformer has its secondary coil arranged to indicate the full station voltage, and the other secondary coil is actuated by a primary coil that carries the full current of the regulated line. By a series of contacts the effect of this last-named coil can be varied to correspond with the number of volts that are to be lost at full load between the generating station and the point on the transmission line at which the voltage is to be held constant. If there is no inductive drop on the transmission line, or if this drop is of known and constant amount, the compensator may give the actual volt- age at the point for which the regulation is designed. Automatic regulators are used in some generating stations to maintain a constant voltage either at the generating terminals or at some distant distributing point on a line operated by a single generator. These regu- lators may operate rheostats that are in series with the magnet windings of the generators to be regulated, and raise or lower the generator voltage by varying the exciting current in these windings. These regulators are much more effective to maintain constant voltage at generating stations than at the distributing end of long transmission lines with variable, REGULATION OF TRANSMITTED POWER. 163 power-factors. In spite of the compound winding of generators, of auto- matic regulators for the exciting currents in their magnet coils, and of regulating transformers in the transmission circuits, hand-adjustment of rheostats in series with the magnet coils of generators remains the most generally used at the generating stations of long transmission systems. Automatic regulators at the ends of transmission lines in sub-stations are now being introduced, and may prove very desirable. The more exacting and final work of regulation in transmission sys- tems is usually done at the sub-stations. After a nearly constant voltage FIG. 69. Motor-generators in Shawinigan Sub-station at Montreal. is delivered at the high-pressure coils of step-down transformers in a sub-station, there remains the varying losses in these transformers, in motor-generators or converters, in distribution lines and in service trans- formers, to be compensated for. In general, three or four sorts of loads must be provided for, namely, arc or incandescent lamps for street light- ing on series circuits, usually of 4,000 to 10,000 volts. Arc and incandes- cent lamps on constant-pressure circuits of 2,000 to 2,500 volts for com- mercial lighting, direct-current stationary motors on constant-pressure circuits of about 500 volts, and alternating motors which may be served at either 2,500 or 500 volts according to their sizes and locations. To these loads may be added that of street-car motors of 500 volts, direct current. Both the stationary and the street-car motors, but more es- 164 ELECTRIC TRANSMISSION OF WATER-POWER. pecially the latter, by their changes of load give rise to large and rapid fluctuations of voltage on the distri- bution lines to which they are con- nected. The problem of regulation with combined lamp and motor loads is not, therefore, so much to maintain a nearly constant voltage at the motors as to protect the lamps from the fluctua- tions of vol tage which th e moto rs set up . For street-car motors using direct current at about 500 volts, the sub- station equipment includes either step- down transformers and converters or motor-generators with or without transformers. It is the practice in some cases where both lighting and street-railway service are drawn from the same transmission system to keep these two kinds of service entirely separate, devoting independent gen- erators and transmission lines, as well as independent transformers and con- verters or motor-generators, to the street-car work. 'This is done in the transmission system centring at Manchester, N. H., in which each one of the four water-power plants, as well as the sub-station, has a double set of bus-bars on the switch- board; and from each water-power plant to the sub-station there are two transmission circuits. In operation, .one set of generators, bus-bars, trans- mission circuits, and transformers supply converters or motor-generators for the street-car motors; and another set of generators, bus-bars, trans- mission circuits, and transformers are devoted to lighting and stationary REGULATION OF TRANSMITTED POWER. 165 motors in this system. Where street-car motors draw their energy from the same generators and transmission lines that supply commercial in- candescent lamps, some means must be adopted to protect the lighting circuits from the fluctuations of voltage set up by the varying street-car loads. One way to accomplish this purpose is to operate the lighting circuits with generators driven by synchronous motors in the sub-stations. These generators may, 1 Number Wires. Size of Each Wire B. & S. Gauge. Metal in Wire. Length of Transmis- sion. Miles. Cafion Ferry to Butte. 50,000 6 o Copper 6q Colgate to Oakland 40,000 7 oo v ^ vy rr v ' i Copper w j 142 o 3 ooo A1 ^ Aluminum xi T* 142 Electra to San Francisco 40,000 3 471,034 C.M. 147 Santa Ana R. to Los Angeles. 33,000 6 i Copper 83 Apple River to St. Paul 25,000 6 2 2C Welland Canal to Hamilton . 22,500 3 I * J 35 3 OO 37 Canon City to Cripple Creek. 20,000 3 *3i Madrid to Bland 20,000 ^ 4 32 White River to Dales 22,000 7 6 O 27 Ogden to Salt Lake City 16,000 O 6 i / 36} San Gabriel Canon to Los Angeles 1 6,000 6 c 23 To Victor Col 12,600 3 3 A Niagara Falls to Buffalo .... 22,000 6 *T 350,000 C. M. 23 22,000 3 500,000 C. M. Aluminum 20 Yadkin River to Salem .... I2,OOO 7 i Copper 14.^ Farmington Riv'r to Hartford IO,000 o 3 336,420 C.M. Aluminum ifc r'0 II Wilbraham to Ludlow Mills. 11,500 6 135, 247 C.M. M 4-5 Niagara Falls to Toronto . . . 6o,OOO 6 190,000 C. M. Copper 75 and Oakland is carried out with three aluminum and three copper line wires. For the third transmission in point of length, that from Shawini- gan Falls to Montreal, a distance of 85 miles, three aluminum conductors are employed. The three transmissions just named have unusually large capacities as well as superlative lengths, the generators in the Electra plant being rated at 10,000, in the Colgate plant at 11,250, and in the Shawinigan plant at 7,500 kilowatts. Weight and cost of such lines are very large. For the three No. oooo aluminum conductors, 142 miles each in length, between Colgate and Oakland, the total weight must be about 440,067 pounds, costing $132,020 at 30 cents per pound. Between Electra and Mission San Jose, where the line branches, is ioo miles of the 14 7-mile transmission from Electra to San Francisco. On the Electra and Mis- MATERIALS FOR LINE CONDUCTORS. 209 sion San Jose section the aluminum conductors comprise three stranded cables of 471,034 circular mils each in sectional area and with a total weight of about 721,200 pounds. This section alone of the line in ques- tion would have cost $216,360 at 30 cents per pound. The 85-mile aluminum line from Shawinigan Falls to Montreal is made up of three- stranded conductors each with a sectional area of 183,708 circular mils. All three conductors have a combined weight of about 225,300 pounds, and at 30 cents per pound would have cost $67,590. Aluminum lines are not confined to new transmissions, but are also found in additions to those where copper conductors were at first used. Thus, the third transmission circuit between the power-house at Niagara Falls and the terminal house in Buffalo, a distance of 20 miles by the new pole line, was formed of three aluminum cables each with an area of 500,000 circular mils, though the six conductors of the two previous circuits were each 350,000 circular mils copper. From these examples it may be seen that copper has lost its former place as the only conductor to be seriously considered for transmission circuits. Aluminum has not only disputed this claim for copper, but has actually gained the most conspicuous place in long transmission lines. This victory of aluminum has been won in hard competition. The decisive factor has been that of cost for a circuit of given length and resistance. From the standpoint of cross-sectional area aluminum is inferior to copper as an electrical conductor. Comparing wires of equal sizes and lengths, the aluminum have only sixty per cent of the conductivity of the copper, so that an aluminum wire must have 1.66 times the sectional area of a copper wire of the same length in order to offer an equal electrical resistance. As round wires vary in sectional areas with the squares of their diameters, an aluminum wire must have a diameter 1.28 times that of a copper wire of equal length in order to offer the same con- ductivity The inferiority of aluminum as an electrical conductor in terms of sectional area is more than offset by its superiority over copper in terms of weight. One pound of aluminum drawn into a wire of any length will have a sectional area 3.33 times as great as one pound of copper in a wire of equal length. This follows from the fact that the weight of copper is 555 pounds while that of aluminum is only 167 pounds per cubic foot, so that for equal weights the bulk of the latter is 3.33 times that of the former metal. As the aluminum wire has equal length with and 3.33 times the sectional area of the copper wire of the same weight, 210 ELECTRIC TRANSMISSION OF WATER-POWER. the electrical conductivity of the former is 3.33 -- 1.66 = 2 times that of the latter. Hence, for equal resistances, the weight of an aluminum is only one-half as great as that of a copper wire of the same length. From this fact it is evident that when the price per pound of aluminum is anything less than twice the price of copper, the former is the cheaper metal for a transmission line of any required length and electrical re- sistance. The tensile strength of both soft copper and of aluminum wire is about 33,000 pounds per square inch of section. For wires of equal length and resistance the aluminum is therefore sixty-six per cent stronger because its area is sixty-six per cent greater than that of a soft copper wire. Medium hard-drawn copper wire such as is most com- monly used for transmission lines has a tensile strength of about 45,000 pounds per square inch, but even compared with this grade of copper the aluminum wire of equal length and resistance has the advantage in tensile strength. While the aluminum line is thus stronger than an equivalent one of copper, the weight of the former is only one-half that of the latter, so that the distance between poles may be increased, or the sizes of poles, cross-arms, and pins decreased with aluminum wires. In one respect the strain on poles that carry aluminum may be greater than that on poles with equivalent copper lines, namely, in that of wind press- ure. A wind that blows in a direction other than parallel with a transmission line tends to break the poles at the ground and prostrate the line in a direction at right angles to its course. The total wind pressure in any case is obviously proportional to the extent of the surface on which it acts, and this surface is measured by one-half of the external area of all the poles and wires in a given length of line. As the aluminum wire must have a diameter twenty-eight per cent greater than that of copper wire of equal length, one-half of the total wire surface will also be twenty-eight per cent greater for the former metal. This carries with it an increase of twenty-eight per cent in that portion of the wind pressure due to wire surface. In good practice the number of transmission wires per pole line is often only three, and seldom more than six, so that the sur- face areas of these wires may be no greater than that of the poles. It fol- lows that the increase of twenty-eight per cent in the surface of wires may correspond to a much smaller percentage of increase for the entire area exposed to wind pressure. Such small difference as exists between the total wind pressures on aluminum and copper lines of equal conductivity is of slight importance in view of the general practice by which some straight as well as the curved portions of transmission lines are 14 MATERIALS FOR LINE CONDUCTORS. 211 now secured by guys or struts at right angles to the direction of the wires. Vibration of transmission lines and the consequent tendency of cross- arms, pins, insulators, and of the wires to work loose is less with alu- minum than with copper conductors as ordinarily strung, because of the greater sag between poles given the former and also probably be- cause of their smaller weight. An illustration of this sort may be seen on the old and new transmission lines between Niagara Falls and Buf- falo. The two old copper circuits consist of six cables of 350,000 circular mils section each on one line of poles, and are strung with only a moderate sag. In a strong wind these copper conductors swing and vibrate in such a way that their poles, pins, and cross-arms are thrown into a vibra- tion that tend to work all attachments loose. The new circuit consists of three 500,000 circular mil aluminum conductors on a separate pole line strung with a large sag between poles, and these conductors take positions in planes at large angles with the vertical in a strong wind, but cause little or no vibration of their supports. One reason for the greater sag of the aluminum over that of the copper conductors in this case is the fact that the poles carrying the former are 140 feet apart while the distance between the poles for the latter is only seventy feet, on straight sections of the line. The necessity for greater sag in aluminum than in copper conductors, even where the span lengths are equal, arises from the greater coefficient of expansion possessed by the former metal. Between 32 and 212 Fahrenheit aluminum expands about 0.0022, and copper 0.0016 of its length, so that the change in length is 40 per cent greater in the former than in the latter metal. The conductors in any case must have enough sag between poles to provide for contraction in the coldest weather, and it follows that the necessary sag of aluminum wires will be greater than that of copper at ordinary temperature. In pure air aluminum is even more free from oxidation than copper, but where exposed to the fumes of chemical works, to chlorine com- pounds, or to fatty acids the metal is rapidly attacked. For this reason aluminum conductors should have a water-proof covering where exposed to any of these chemicals. The aluminum line between Niagara Falls and Buffalo is bare for most of its length, but in the vicinity of the large chemical works at the former place the wires are covered with a braid treated with asphaltum. Aluminum alloyed with sodium, its most com- mon impurity, is quickly corroded in moist air, and should be carefully avoided. All of the properties of aluminum here mentioned relate to the 212 ELECTRIC TRANSMISSION OF WATER-POWER. pure metal unless otherwise stated, and its alloys should not, as a rule, be considered for transmission lines. As aluminum is electropositive to most other metals the soldering of its joints is quite sure to result in elec- trolytic corrosion, unless the joints are thoroughly protected from mois- ture, a result that is hard to attain with bare wires. The regular practice is to avoid the use of solder and rely on mechanical joints. A good joint may be made by slipping the roughened ends of wires to be connected through an aluminum tube of oval section, so that one wire sticks out at each end, then twisting the tube and wires and giving each of the latter a turn about the other. Aluminum may be welded electrically and also by hammering at a certain temperature, but these processes are not con- venient for line construction. Especial care is necessary to avoid scar- ring or cutting into aluminurti wires, as may be done when they are tied to their insulators. Aluminum tie wires should be used exclusively. To avoid the greater danger of damage to solid wires and also to obtain greater strength and flexibility, aluminum conductors are most fre- quently used in the form of cables. The sizes of wires that go to make up these cables commonly range from No. 6 to 9 B. & S. gauge for widely different cable sections. Thus the 183,708 circular mil aluminum cable between Shawihigan Falls and Montreal is made up of seven No. 6 wires, and the 471,034 circular mil cable between Electra and Mission San Jose contains thirty-seven No. 9 wires. From the Farmington River to Hartford each 336,420 circular mils cable has exceptionally large strands of approximately No. 3 wire. It appears from the description of a 43-mile line in California (vol. xvii., A. I. E. E., p. 345) that a solid aluminum wire of 294 mils diameter, or No. i B. & S. gauge, can be used without trouble from breaks. This wire was tested and its properties reported as follows: Diameter, 293.9 mils. Pounds per mile, 419.4. Resistance per mil foot, 17.6 ohms at 25 C. Resistance per mile at 25 C., 1.00773 ohms. Conductivity as to copper of same size, 59.9 per cent. Number of twists in six inches for fracture, 17.9. Tensile strength per square inch, 32,898 pounds. This wire also stood the test of wrapping six times about its own diameter and then unwrapping and wrapping again. It was found in tests for tensile strength that the wire in question took a permanent set at very small loads, but that at points between 14,000 and 17,000 pounds per square inch the permanent set began to increase very rapidly. From this it appears that aluminum wires and cables should be given enough MATERIALS FOR LINE CONDUCTORS. 213 sag between poles so that in the coldest weather the strains on them shall not exceed about 15,000 pounds per square inch. This rather low safe working load is a disadvantage that aluminum shares with copper. From the figures just given it is evident that the strains on aluminum conductors during their erection should not exceed one-half of the ulti- mate strength in any case, lest their sectional areas be reduced. ALUMINUM CABLES IN TRANSMISSION SYSTEMS. "o 1 a s. . i| Locations. J! J 11 h Jl c/5 Si Sti u K < Niagara Falls to Buffalo 2 20 500,000 Shawinigan Falls to Montreal 3 85 183,708 7 6 Electra to Mission San Tosd IOO 471 O^4 77 Colgate to Oakland . } 144 211 ,OOO 7 Farmington River to Hartford 3 II 7 3 Lewiston, Me ? 2. cr 144,688 7 Q Ludlow Mass 6 4e TTC 247 7" 7" This table of transmission systems using aluminum conductors is far from exhaustive. Aluminum is also being used to distribute energy to the sub-stations of long electric railways, as on the Aurora and Chicago which connects cities about forty miles apart. The lower cost of alu- minum conductors is also leading to their adoption instead of copper in city distribution of light and power. Thus at Manchester, N. H., the local electric lines include about four miles each of 500,000 and 750,000 circular mil aluminum cable with weather-proof insulation. The larger of these cables contains thirty-seven strands of about No. 7 wire. As may be seen from the foregoing facts, the choice of copper or aluminum for a transmission line should turn mainly on the cost of con- ductors of the required length and resistance in each metal. So nearly balanced are the mechanical and electrical properties of the two metals that not more than a very small premium should be paid for the privilege of using copper. As already pointed out, the costs of aluminum and copper conductors of given length and resistance are equal when the price per pound of aluminum wire is twice that of copper. During most of the time for several years the price of aluminum has been well below double the copper figures, and the advantage has been with aluminum conduc- tors. With the two metals at the same price per pound aluminum would 2i 4 ELECTRIC TRANSMISSION OF WATER-POWER. cost only one-half as much as equivalent copper conductors. When the price of aluminum is fifty per cent greater per pound than that of copper, the use of the former metal effects a saving of twenty-five per cent. For the new Niagara and Buffalo line, completed early in 1901, aluminum was selected because it effected a saving of about twelve per cent over the cost of copper. All of the aluminum lines here mentioned, except the short one near Hartford, were completed during or since 1 900. Most of the facts here stated as to the line between Niagara Falls and Buffalo are drawn from vol. xviii., A. I. E. E., at pages 520 and 521. The greater diameter of aluminum over equivalent copper conduc- tors has advantages in transmission with alternating current at very high voltages. At high voltages, say of 40,000 or more, the constant silent loss of energy from one conductor to another of the same circuit through the air tends to become large and even prohibitive in amount. This loss is greater, other factors being constant, the smaller the diameter of the conductors in the line. It follows that this loss is more serious the smaller the power to be transmitted, because the smaller the diameter of the line wires. The silent passage of energy from wire to wire increases directly with the length of line and thus operates as a limit to long transmissions. CHAPTER XVI. VOLTAGE AND LOSSES ON TRANSMISSION LINES. THE voltage on a transmission line may be anything up to at least 60,000, and the weight of conductors varies inversely with the square of the figures selected, the power, length and loss being constant. What- ever the total line pressure, the weight of conductors varies inversely with the percentage of loss therein. The case of maximum- loss and minimum weight of conductors is that in which all of the transmitted energy is expended in heating the line wires. Such a case would never occur in practice, because the object of power transmission is to perform some useful work. Minimum loss is theoretically zero, and the corresponding weight of conductors is infinite, but these conditions obviously cannot be attained in practice. Between these extremes of minimum and of in- finite weights of conductors comes every practical transmission with a line loss greater than zero and less than 100 per cent. To determine the weight and allowable cost of conductors, the cost of the energy that will be annually lost in them enters as one of the fac- tors. At this point the distinction between the percentage of power lost at maximum load and the percentage of total energy lost should come into view. Line loss ordinarily refers to the percentage of total power consumed in the conductors at maximum load. This percentage would correspond with that of total energy lost if the line current and voltage were constant during all periods of operation, but this is far from the case. A system of transmission may operate with either constant volts or constant amperes on the line conductors, but in a practical case con- stancy of both these factors is seldom or never to be had. This is because the product of the line volts and amperes represents accurately in a con- tinuous-current system, and approximately in an alternating-current sys- tem, the amount of power transmitted. In an actual transmission sys- tem, the load that is, the demand for power is subject to more or less variation at different times of the day, and the line vots or amperes, or both, must vary with it. 215 2i 6 ELECTRIC TRANSMISSION OF WATER-POWER. If the transmission system is devoted to the operation of one or more factories the required power may not vary more than twenty-five per cent during the hours of daily use ; but if a system of general electrical supply is to be operated, the maximum load will usually be somewhere between twice and four times as great as the average load for each twenty-four hours. Such fluctuating loads imply corresponding changes in the volts or amperes of the transmission line. A number of rather long transmissions is carried out in Europe with continuous, constant current, and in such systems the line volt- age varies directly with the load. As the loss of power in an electrical conductor depends entirely on its ohms of resistance, which are constant at any given temperature, and on the amperes of current passing through it, the line loss in a constant-current system does not change during the period of operation, no matter how great may be its changes of load. For this reason the percentage of power loss in the line at maxi- mum load is usually smaller than the percentage of energy loss for an entire day. If, for example, the constant-current transmission line is designed to convert into heat 5 per cent of the maximum amount of energy that will be delivered to it per second that is, to lose 5 per cent of its power at maximum load then, when the power which the line receives drops to one-half of its maximum, the percentage of loss will rise to 10, because 0.05 -f- 0.5 = o.i. So again, when the power sent through the line falls to one-quarter of the full amount, the line loss will rise to 0.05 -^ 0.25 = 0.2, or 20 per cent. From these facts it is clear that a fair all-day efficiency for a constant- current transmission line can be obtained only in conjunction with a high efficiency at maximum load, if widely varying loads are to be oper- ated. It does not necessarily follow from these facts as to losses in con- stant-current lines that such losses should always be small at maximum loads, for if a large loss may be permitted at full load a still greater percentage of loss at partial loads may not imply bad engineering. In a large percentage of electric water-power plants some water goes over the dam during those hours of the day when loads are light, the stor- age capacity above the dam not being sufficient to hold all of the surplus water during most seasons of the year. If, therefore, the line loss in a constant-current transmission, where all of the daily flow of water cannot be used, is not great enough to reduce the maximum load that would otherwise be carried, then the fact that the percentage of line loss at small loads is still larger is not very important. VOLTAGE AND LOSSES ON TRANSMISSION. 217 Obviously, it makes little difference whether water goes over a dam or through wheels to make up for a loss in the line. In a case where all the water can be stored during small loads and used during heavy loads, it is clearly desirable to keep the loss in a constant-current line down to a rather low figure, say not more than five per cent, at maximum load. Much the greater number of electrical transmissions are carried out with nearly constant line voltage, mostly alternating, and the line cur- rent in such cases varies directly with the power transmitted, except as to certain results of inductance on alternating lines. As line resistance is constant, save for slight variations due to temperature, the rate of energy loss on a constant-pressure line varies with the square of the number of amperes flowing, and the percentage of loss with any load varies directly as the number of amperes. These relations between line losses and the amperes carried follow from the law that the power, or rate of work, is represented by the prod- uct of the number of volts by the number of amperes, and the law that the power actually lost in the line is represented by the product of the number of ohms of line resistance and the square of the number of am- peres flowing in it. In each of these cases the power delivered to the line is, of course, measured in watts, each of which is 1-746 of a horse- power. Applying these laws, it appears that if the loss of a certain constant- pressure transmission line is 10 per cent of the power delivered to it at full load, then, when the power, and consequently the amperes, on the line is reduced one-half, the watts lost in the line as heat will be (J) 2 = J of the watts lost at full load, because the number of amperes flowing has been divided by 2. But the amount of power delivered to the line at full load having been reduced by 50 per cent, while the power lost on the line dropped to one- fourth of 10 per cent, or to 2.5 per cent of the full line load, it follows that the power lost on the line at half-load is represented by 0.025 ^- 0.5 = 0.05, or 5 per cent of the power then delivered to it. This rise in the efficiency of a constant-pressure transmission line as the power delivered to it decreases, together with the fact that maximum loads on such lines continue during hardly more than one to two hours daily, tends to raise the allowable percentage of line loss at maximum loads. This is so because a loss of fifteen per cent at maximum load may easily drop to an average loss of somewhere between five and ten per cent for the entire amount of energy delivered to a line during each day under 2i8 ELECTRIC TRANSMISSION OF WATER-POWER. ordinary conditions in electrical supply. In the practical design of trans- mission lines, therefore, the sizes of conductors are influenced by the relation of the largest load to be operated to the greatest amount of power available for its operation, and by questions of regulation, as well as by considerations of all-day efficiency. If the maximum load that must be carried by a transmission system during a single hour per day requires nearly as much power as can be delivered to the line conductors, either because of lack of water storage or of water itself, even if it is stored, it may be desirable to design these conductors for a small loss at maximum load, rather than to install a steam plant. So again, as the fluctuation in voltage at the delivery end of a trans- mission line between no load and full load will amount to the entire drop of volts in the line at full load, if the pressure at the generating end is constant, the requirements of pressure regulation on distribution circuits limit the drop of pressure in the transmission conductors. For good lighting service with incandescent lamps at about no volts, the usual pressure, it is necessary that variations be held within one volt either way of the pressure of the lamps that is, between 109 and in volts. Every long-transmission system for general electrical supply neces- sarily includes one or more sub-stations where the distribution lines join the transmission circuits, and where the voltage for lighting service is regulated. As the limits of voltage variations on lighting circuits are so narrow, it is necessary to keep the changes of pressure on the transmis- sion lines themselves within moderate limits, or such as can be com- pensated for at sub-stations. This is particularly true in cases where energy transmitted over a single circuit is distributed for both incandescent lamps and large electric motors, because the starting and operation of such motors causes large fluctuations of amperes and terminal voltage on the transmission cir- cuits. To hold such fluctuations within limits which a sub-station can readily compensate for, it is necessary that the loss in the transmission line be moderate, say often within ten per cent of the total voltage de- livered to it at maximum load. Capacity and cost of equipment at generating stations go up with the percentage of line loss, and thus serve to limit its economical amount. For every horse-power delivered to a transmission line at a water-power station there must be somewhat more than one horse-power of capacity in water-wheels, at least one horse-power in generators, and frequently a further capacity of one horse-power in step-up transformers. Every VOLTAGE AND LOSSES ON TRANSMISSION. 219 additional horse-power lost in the line at maximum load, if the generating plant is to be worked up to its full capacity, implies ^n addition of some- what more than one horse-power capacity in water-wheels, one horse- power in generators, and one horse-power in transformers. Since the cost of a generating station is thus increased as the maxi- mum line loss is raised, a point may be reached where any further saving in the cost of the line is more than offset by the corresponding addition to the cost of the station and of its operation. Just where this point, as indicated by a percentage of line loss, is to be found depends on the factors of each case, important among which is the length of the trans- mission line. Much effort has been made to fix some exact relation for maximum economy between the first cost of conductors for a transmission line and the amount of energy annually lost as heat therein. The best-known statement applying to this case is that of Lord Kelvin, made in a paper read before the British Association in 1881. According to the rule there laid down, the most economical size for the conductors of a transmission line is that for which the annual interest on first cost equals the cost of the energy annually wasted in them. If transmission systems were designed for the sole purpose of wasting energy in their line conductors this rule would exactly apply, for it simply shows how the cost of energy wasted, plus the interest on the cost of the conductor in which it is wasted, may be brought to a minimum. As a matter of fact, transmission systems are primarily intended to de- liver energy rather than to waste it ; but of the proportions of the entire energy to be delivered and wasted (which is exactly what we want to know), the rule of Kelvin takes no account. According to his rule, the cheaper the cost of power where it is de- veloped, the less should be paid for conductors to bring it to market. The obvious truth is that the less the cost of power development at a particular point, the more may be invested in a line to bring it to market. If power cost nothing whatever at its source it would not be worth while to build any transmission line at all if this rule is correct. A modification of Lord Kelvin's rule has been proposed by which it is said that the interest on the cost of the conductors and the annual value of the energy lost in them should be equal, value here meaning what the energy can be sold for. This rule would make an investment in line conductors too large. The entire cost of production and transmission for the delivered energy should not be greater than the cost of a like amount of energy de- 2 2o ELECTRIC TRANSMISSION OF WATER-POWER. veloped at the point where the delivery is made. In this entire cost of production and transmission, interest on the investment in line conduc- tors is only one item. It is perhaps impossible to state any exact rule for the most eco- nomical relation between the cost of conductors and the loss of energy therein that will apply to every transmission. A maximum limit to the weight of conductors may, however, be set for most cases. This limit should not allow the annual interest and depreciation charges on the investment in line conductors, plus all other costs of development and transmission, to raise the total cost of the transmitted energy above the cost of development for an equal amount of energy at the point where the transmitted energy is delivered. While the maximum investment in transmission conductors may be properly limited in the way just stated, it by no means follows that this maximum limit should be reached in every case. In the varying require- ments of actual cases, the problem may be to deliver a fixed amount of power at the least possible cost, or to deliver the largest possible amount of power at a cost per unit under that of development at the point of use. Frequently a transmission system has a possible capacity in excess of present requirements, and a line that would not be too heavy for future business might put an unreasonable burden of interest charges on present earnings. The foregoing considerations apply to the design of conductors for a transmission line after the voltage at which it is to operate has been decided on. Quite a different set of facts should influence the selection of this voltage. A transmission that would be entirely impracticable with any percentage of line loss that might be selected, if carried out at some one voltage, might represent a paying business at some higher voltage and any one of several sizes of line conductors. The power that could be delivered by a line of practicable cost, operated at one voltage, might be too small for the purpose in hand, while the available power at a higher voltage might be ample. If any given power is to be transmitted with a given percentage of maximum loss in line conductors, the weight of these conductors will increase as the square of their length, and decrease as the square of the full voltage of operation in every case. Thus, if the length of this transmission is doubled, the weight of the conductors must be multiplied by four, the voltage remaining the same; but if the voltage is doubled and the line length remains unchanged, the weight of conductors must be divided by four. With the length of line VOLTAGE AND LOSSES ON TRANSMISSION. 221 and the voltage of transmission either lowered or raised together, the weight of the conductors remains fixed, for constant power and loss. An illustration of this last rule may be drawn from the case of lines designed to transmit any given power a distance of ten miles at 10,000 volts, and a distance of fifty miles at 50,000 volts, in which the total weight of conductors would be the same for each line if the percentage of loss was constant. This statement of the rule as to proportionate increase of voltage and distance presents the advantages of high voltages in their most favorable light. Though a uniform ratio between the voltage of operation and the length of line allows a constant weight of conductors to be employed for the transmission of a given power with unchanging efficiency of conductors, yet other considerations soon limit the advantage thus ob- tained. Important among these considerations may be mentioned the me- chanical strength of line conductors, difficulties of line insulation, losses between conductors through the air, limits of generator voltages, and the cost of transformers. If the ten-mile transmission at 10,000 volts, above mentioned, requires a circuit of two No. i/o copper wires, the total weight of these wires will be represented by (5,500 x 10 X 2 X 320) -=- 1,000 35,200 pounds, allowing 5,500 feet of wire per mile of single conductor to provide some- thing for sag between poles, and 320 pounds being the weight of bare No. i/o copper wire per 1,000 feet. When the length of line is raised to 50 miles, the two-wire circuit will contain 5,500 X 50 X 2 = 550,000 feet of single conductor, and since the voltage is raised to 50,000 at the same time, the total weight of conductors will be 35,200 pounds as before. The weight of single conductor per 1,000 feet is therefore only 64 pounds in the 5o-mile line. A No. 7 copper wire, B. & S. gauge, has a weight of 63 pounds per i ,000 feet, and is the nearest regular size to that required for the 5o-mile line as just found. It would be poor policy to string a wire of this size for a transmission line, because it is so weak mechanically that breaks would probably be frequent in stormy weather. The element of unre- liability introduced by the use of this small wire on a 5o-mile line would cost far more in the end than a larger conductor. As a rule, No. 46. & S. gauge wire is the smallest that should be used on a long transmission line in order to give fair mechanical strength, and this size has just twice the weight of a No. 7 wire of equal length. 222 ELECTRIC TRANSMISSION OF WATER-POWER. Here, then, is one of the practical limits to the advantages that may be gained by increasing the voltage with the length of line. As line voltage goes up, the strain on line insulation increases rapidly, and the insulators for a circuit operated at 50,000 volts must be larger and of a much more expensive character than those for a 10,000- volt cir- cuit. In this way a part of the saving in conductors effected by the use of very high voltages on long lines is offset by the increased cost of insulation. Another disadvantage that attends the operation of transmission lines at very high voltages is the continuous loss of energy by the silent pas- sage of current through the air between wires of a circuit. This loss in- creases at a rapid rate after a pressure between 40,000 and 50,000 volts is reached with ordinary distances between the wires of each circuit. To keep losses of this sort within moderate limits, and also to lessen the probability of arcs on a circuit at very high voltage, the distance of eigh- teen inches or two feet between conductors that carry current at 10,000 volts should be increased to six feet or more on circuits that operate at 50,000 volts. Such an increase in the distance between conductors makes the cost of poles and cross-arms greater, either by requiring them to be larger than would otherwise be necessary or by limiting the number of wires to two or three per pole and thus increasing the number of pole lines. These added expenses form another part of the penalty that must be paid for the use of very high voltages and the attendant saving in the cost of conductors. Apparatus grows more expensive as the voltage at which it is to oper- ate increases, because of the cost of insulating materials and the room which they take up, thereby adding to the size and weight of the iron parts. Generators for alternating current can be had that develop as much as 13,500 volts, but such generators cost more than others of equal power that operate at between 2,000 and 2,500 volts. These latter voltages are as high as it is usually thought desirable to operate distribution circuits and service transformers in cities and towns, so that if more than 2,500 volts are employed on the transmission line, step-down transformers are required at a sub-station. For a transmission of more than ten miles the saving in line conductors by operation at 10,000 to 12,000 volts will usually more than offset the additional cost of generators designed fcr th's pressure and of step-down transformers. If the voltage cf transmission is to exceed that of distribution, it will generally be VOLTAGE AND LOSSES ON TRANSMISSION. 22$ found desirable to carry the former voltage up to 10,000 or 12,000, at least. As the cost of generators designed for the voltage last named is less than that of lower voltage generators plus transformers, step-up trans- formers should usually be omitted in systems where these pressures are not exceeded. For alternating pressures above 13,000 to 15,000 volts, step-up transformers must generally be employed. In order that the saving in the weight of line conductors may more than offset the addi- tional cost of transformers when the voltage of transmission is carried above 15,000, this voltage should be pushed on up to as much as 25,000 in most cases. Power transmission with continuous current has the advantage that the cost of generators remains nearly the same whatever the line voltage, and that no transformers are required. Such transmissions are common in Europe, but have hardly a footing as yet in the United States. The reason for the uniform cost of continuous-current generators is found in the fact that they are connected in series to give the desired line voltage, and the voltage of each machine is kept under 3,000 or 4,000. As a par- tial offset to the low cost of the continuous-current generators and to the absence of transformers, there is the necessity for motor-generators in a sub-station when current for lighting as well as power is to be distributed. In spite of the various additions to the cost of transmission systems made necessary by the adoption of very high voltages, these additions are much more than offset by the saving in the cost of conductors on lines 30, 50, or 100 miles in length. In fact, it is only by means of voltages ranging from 25,000 to 50,000 that the greatest of these distances, and others up to more than 140 miles, have been successfully covered by transmission lines. Above 60,000 volts there has been but slight prac- tical experience in the operation of transmission lines. Calculations to determine the sizes of conductors for electric trans- mission lines are all based on the fundamental law discovered by Ohm, which is that the electric current flowing in a circuit at any instant equals the electric pressure that causes the current divided by the electric re- sistance of the circuit itself, or current = pressure -=- resistance. Substituting in this formula the units that have been selected because of their convenient sizes for practical use, it becomes, amperes = volts -i- ohms, in which the ohm is simply the electrical resistance, taken as unity, of a certain standard copper bar with fixed dimensions. The ampere is the unit flow of current that is maintained with the unit pressure of one volt between the terminals of a one-ohm conductor. 224 ELECTRIC TRANSMISSION OF WATER-POWER. When this formula is applied to the computation of transmission lines the volts represent the electrical pressure that is required to force the desired amperes of current through the ohms of resistance in any par- ticular line, and these volts have no necessary or fixed relation to the total voltage at which the line may operate. Thus, if the total voltage of a transmission system is 10,000, it may be desirable to use 500, 1,000, or even 2,000 volts to force current through the line, so that one of these numbers will represent the actual drop or loss of volts in the line con- ductors when the number of amperes that represent full load is flowing. As it is a law of every electric circuit that the rate of transformation of electric energy to heat or work in each of its several parts is di- rectly proportional to the drop of voltage therein, it follows that a drop of 500 or 1,000 or 2,000 volts in the conductors of a 10,000- volt trans- mission line at full load would correspond to a power loss of five to ten or twenty per cent respectively. Any other part of 10,000 volts might be selected in this case as the pressure to be lost in the line. Evidently no formula can give the number of volts that should be lost in line con- ductors at full load for a given power transmission, but this number must be decided on by consideration of the items of line efficiency, regula- tion, and the ratio of the available power to the required load. Having decided on the maximum loss of volts in the line conductors, and knowing the full voltage of operation, the power and consequently the number of amperes delivered to the line at maximum load, the resist- ance of the conductors may then be calculated by the formula, amperes = volts -f- ohms. Thus, if the proposition is to deliver 2,000,000 watts or 2,000 kilowatts to a two-wire transmission line with a voltage of 20,000, the amperes in each wire must be represented by 2,000,000 -4- 20,000 = 100. With a drop of ten per cent or 2,000 volts in the two line conductors, their combined resistance must be found from 100 = 2,000 -^ ohms, and the ohms are therefore twenty. If the combined length of the two conductors is 200,000 feet, corresponding to a trans- mission line of a little under twenty miles, the resistance of these conduc- tors must be 20 -f- 200 = o.i ohm per 1,000 feet. From a wire table it may be seen that a No. i/o wire of copper, B. & S. gauge, with a diameter of 0.3249 inch, has a resistance of o.iooi ohm per 1,000 feet at the tem- perature of 90 Fahrenheit, a little less at lower temperatures, and is thus the required size. Obviously, the resistance of twenty ohms is entirely independent of the length of the line, all the other factors being constant, and wires of various sizes will be required for other distances of trans- mission. VOLTAGE AND LOSSES ON TRANSMISSION. 225 It is often convenient to find the area of cross section for the desired transmission conductor instead of finding its resistance. This can be done by substituting in the formula, amperes = volts -=- ohms, the ex- pi ession for the number of ohms in any conductor, and then solving as before. Electrical resistance in every conductor varies directly with its length, Inversely with its area of cross section, and also has a constant factor that depends on the material of which the conductor is composed. This con- slant factor is always the same for any given material, as pure iron, < upper, or aluminum, and is usually taken as the resistance in ohms of a round wire one foot long and o.ooi inch in diameter, of the material to be used for conductors. Such a wire is said to have an area in cross section of one circular mil, because the square of its diameter taken as unity is still unity, that is, i x i i In like manner, for the conven- ient designation of wires by their areas of cross-section, each round wire of any size is said to have an area in circular mils equal to the square of its diameter measured in units of o.ooi inch each. Thus, a round wire of o.i inch diameter has an area of 100 x 100 = 10,000 circular mils, and a round wire one inch in diameter has an area of 1,000 x 1,000 = 1,000,000 circular mils. The circular mils of a wire do not express its area of cross section in terms of square inches, but this is not necessary since the resistance of a wire of one circular mil is taken as unity. Ob- viously, the areas of all round wires are to each other as are their circular mils. From the foregoing it may be seen that the resistance of any round conductor is represented by the formula, ohms = / x -i- circular mils, in which / represents the length of the conductor in feet, s is the resis- tance in ohms of a wire of the same material as the conductor but with an area of one circular mil and a length of one foot, and the circular mils are those of the required conductor. Substituting the quantity, / x 5 -j- circular mils, for ohms in the formula, amperes = volts -f- ohms, the equation, amperes = volts -j- (I X s -5- circular mils), is obtained, and this reduces to circular mils = amperes x I X 5 -f- volts. For any pro- posed transmission all of the quantities in this formula are known, except the desired circular mils of the line conductors. The constant quantity 5 is about 10.8 for copper, but is conveniently used as eleven in calcula- tion, and this allows a trifle for the effects of impurities that may exist in the line wire. The case above mentioned, where 2,000 kilowatts were to be delivered to a transmission line at 20,000 volts, and a loss of 2,000 volts at full load 15 226 ELECTRIC TRANSMISSION OF WATER-POWER. was allowed in the line conductors, may now be solved by the formula for circular mils. Taking the resistance of a round copper wire o.ooi inch in diameter and one foot long as eleven ohms, and substituting the 100 amperes, 2,000 volts, and 200,000 feet of the present case in the formula, gives circular mils = (100 x 200,000 x IJ ) -f- 2,000 = no,- ooo. The square root of this 110,000 will give the diameter of a copper wire that will exactly meet the conditions of the case, or the more prac- tical course of consulting a table of standard sizes of wire will show that a No. i-o B. & S. gauge, with a diameter of 0.3249 inch, has a cross section of 105,500 circular mils, or about five per cent less than the cal- culated number, and is the size nearest to that wanted. As this No. i-o wire will give a line loss at full load of about 10.5 per cent, or only one- half of one per cent more than the loss at first selected, it should be adopted for the line in this case. The formula just made use of is perfectly general in its application, and may be applied to the calculation of lines of aluminum or iron or any other metal just as well as to lines of copper. In order to use the formula for any desired metal, it is necessary that the resistance in ohms of a round wire of that metal one foot long and o.ooi inch in diameter be known and substituted for 5 in the formula. This resistance of a wire one foot long and o.ooi inch in diameter is called the specific resistance of the substance of which the wire is composed. For pure aluminum this specific resistance is about 17.7, for soft iron about sixty, and for hard steel about eighty ohms. The use of these values for s in the form- ula will therefore give the areas in circular mils for wires of these three substances, respectively, for any proposed transmission line. In the same way the specific resistance of any other metal or alloy, when known, may be applied in the formula. The foregoing calculations apply accurately to all two-wire circuits that carry continuous currents, whether these circuits operate with con- stant current, constant pressure, or with pressure and current both vari- able. Where circuits are to carry alternating currents, certain other factors may require consideration. Almost all transmissions with alter- nating currents are carried out with three-phase three-wire, or two-phase four-wire, or single-phase two-wire circuits. Of the entire number of such transmissions, those with the three-phase three-wire circuits are in the majority, next in point of number come the two-phase transmissions, and lastly a few transmissions are carried out with single-phase currents. The voltage of a continuous-current circuit, by which the power of the transmission is computed and on which the percentage of line loss is VOLTAGE AND LOSSES ON TRANSMISSION. 227 based, is the maximum voltage operating there ; but this is not true for circuits carrying alternating currents. Both the volts and amperes in an alternating circuit are constantly varying between maximum values in opposite directions along the wires. It follows from this fact that both the volts and amperes drop to zero as often as they rise to a maximum. It is fully demonstrated in books on the theory of alternating currents, that with certain ideal constructions in alternating generators, and cer- tain conditions in the circuits to which they are connected, the equivalent or, as they are called, the virtual values of the constantly changing volts and amperes in these circuits are 0.707 of their respective maximum values. Or, to state the reverse of this proposition, the maximum volts and amperes respectively in these circuits rise to 1.414 times their equiv- alent or virtual values. These relations between maximum and virtual volts and amperes are subject to some variations with actual circuits and generators, but the virtual values of these factors, as measured by suitable volt- and amperemeters, are important in the design of transmission cir- cuits, rather than their maximum values. When the volts or amperes of an alternating circuit are mentioned, the virtual values of these factors are usually meant unless some other value is specified. Thus, as com- monly stated, the voltage of a single-phase circuit is the number of virtual volts between its two conductors, the voltage of a two-phase circuit is the number of virtual volts between each pair of its four conductors, and the voltage of a three-phase circuit is the number of virtual volts between either two of its three conductors. Several factors not present with continuous currents tend to effect the losses in conductors where alternating currents are flowing, and the im- portance of such effects will be noted later. In spite of such effects, the formula above discussed should be applied to the calculation of trans- mission lines for alternating currents, and then the proper corrections of the results, if any are necessary, should be made. With this proviso as to corrections, the virtual volts and amperes of circuits carrying alternat- ing currents may be used in the formula in the same way as the actual volts and amperes of continuous current circuits. Thus, reverting to the above example, where 2,000 kilowatts was to be delivered at 20,000 volts to a transmission line in which the loss was to be 2,000 volts, the kilowatts should be taken as the actual rate of work represented by the alternating current, and the volts named as the virtual volts on the line. The virtual amperes will now be 100, as were the actual amperes of continuous cur- rent, and the size of line conductor for a single-phase alternating trans- mission will therefore be i-o, the same as for the continuous-current line. 228 ELECTRIC TRANSMISSION OF WATER-POWER. If the transmission is to be carried out on the two-phase four- wire system, the virtual amperes in each of these wires will be fifty instead of 100, as the power will be divided equally between the two pairs of conductors, and each of these four wires should have a cross-section in circular mils just one-half as great as that of the No. i-o wire. The required wire will thus be a No. 3 B. & S. gauge, of 52,630 circular mils, this being the nearest standard size. In weight the two No. i-o wires and the four No. 3 wires are almost equal, and they should be exactly equal to give the same loss in the single-phase and the two-phase lines. For a three- phase circuit to make the transmission above considered, each of the three conductors should have an area just one-half as great as that of each of the two conductors for a single phase circuit, the loss remaining as before, and the nearest standard size of wire is again No. 3, as it was for the two-phase line. This is not a self-evident proposition, but the proof can be found in books devoted to the theory of the subject. From the fore- going it is evident that while the single-phase and two-phase lines require equal weights of conductors, all other factors being the same, the weight of conductors in the three-phase line is only seventy-five per cent of that in either of the other two. Neglecting the special factors that tend to raise the size and weight of alternating-current circuits, the single-phase and two-phase lines require the same weight of conductors as does a continuous-current transmission of equal power, voltage, and line loss. It should be noted that in each of these cases the factor / in the formula for circular mils denotes the entire length of the pair of conductors for a continuous-current line, or double the distance of the transmission with either of the alternating-current lines. Having found the circular mils of any desired conductor, its weight per 1,000 feet can be found readily in a wire table. In some cases it is desirable to calculate the weight of the conductors for a transmission line without finding the circular mils of each, and this can be done by a modi- fication of the above formula. A copper wire of i ,000,000 circular mils weighs nearly 3.03 pounds per foot of its length, and the weight of any copper wire may therefore be found from the formula, pounds = (circular mils x 3-03 X -i- i, 000,000, in which pounds indicates the total weight of the conductor, /, its total length, and the circular mils are those of its cross-section. This formula reduces to the form, circular mils (i ,000,- ooo x pounds) -=- (3.03 x 0, and if this value for circular mils is sub- stituted in the formula above given for the cross-section of any wire, the result is (1,000,000 x pounds) -f- (3.03 x = (I X amperes x n) -j- volts. Transposition of the factors in this last equation brings it to the VOLTAGE AND LOSSES ON TRANSMISSION. 229 form, pounds = (3.03 x I* X amperes x ") -r- (1,000,000 x volts), which is the general formula for the total weight of copper conductors when /, the length of one pair, the total amperes flowing, and the volts lost in the conductors are known for either a continuous-current, a single- phase, or a two-phase four-wire line. If the value of /, 200,000, of amperes, 100, and of volts, 2,000, for the transmission above considered are substituted in the formula for total weight, just found, the result is pounds = (3.03 (200,000)" x 100 x n) -i- (1,000,000 x 2,000), which reduced to pounds . 66,660, the weight of copper wire necessary for the transmission with either continuous, single-phase or two-phase current. Witli three-phase current the weight of copper in the line for this transmission will be 75 per cent of the 66,660 pounds just found. One or more two-wire circuits may be employed for the continuous current or for the single-phase transmission, and if one such circuit is used the weight for each of the two wires is obviously 33,660 pounds. For a two-phase transmission two or more circuits of two wires each will be used, and in the case of two circuits, if all four of the wires are of equal cross section, as would usually be the case, the total weight of each is 16,830 pounds. If the transmission is made with one three-phase circuit, the weight of each of the three wires is 16,830 pounds, and their combined weight, 50,490 pounds of copper. In each of these transmission lines the length of a single conductor in one direc- tion is 100,000 feet, or one-half of the length of the wires in a single two- wire circuit. For the two-wire line the calculated weight of each con- ductor amounts to 66,660 -j- 200 = 333.3 pounds per 1,000 feet. For a two-phase four-wire line and also for a three-phase three-wire line, the weight of each conductor is 16,830 -j- 100 = 168.3 pounds per 1,000 feet. On inspection of a table of weights for bare copper wires it may be seen that a No. i-o B. & S. gauge wire has a weight of 320 pounds per 1,000 feet, and being much the nearest size to the calculated weight of 333 pounds should be selected for the two-wire circuit. It may also be seen that a No. 3 wire, with a weight of 159 pounds per 1,000 feet, is the size that comes nearest to the calculated weight of 168 pounds, and should therefore be employed in the three-wire and the four-wire circuits, for two- and three-phase transmissions. Either a continuous-current, single- phase, two-phase, or three-phase transmission line may of course be split up into as many circuits as desired, and these circuits may or may not be designed to carry equal portions of the entire power. In either case the combined weights of the several circuits should equal those above found, the conditions as to power, loss, and length of line remaining constant. 230 ELECTRIC TRANSMISSION OF WATER-POWER. It will be noted that the formulae for the calculation of the circular mils and for the weight of the conductors in the transmission line lead to the selection of the same sizes of wires, as they obviously should do. Several laws governing the relations of volts lost, length and weight of line conductors, may be readily deduced from the above formulae. Evidently the circular mils and weight of line conductors vary inversely with the number of volts lost in them when carrying a given current, so that doubling this number of volts reduces the circular mils and weight of conductors by one-half. If the length of the line changes, the circular mils of the required conductors change directly with it, but the weight of these conductors varies as the square of their length. Thus, if the length of the line conductors is doubled, the cross-section in circular mils of each conductor is also doubled, and each conductor is therefore four times as heavy as before for the same current and loss in volts. Should the length of the conductors and also the number of volts lost in them be varied at the same rate, the circular mils of each conductor re- main constant, and its weight increases directly with the distance of transmission. Thus, with the same size of line wire, both the number of volts lost and the total weight are twice as great for a 100- as for a fifty- mile transmission. If the total weight of conductors is to be held con- stant, then the number of volts lost therein must vary as the square of their length, and their circular mils must vary inversely as the length. So that if the length of a transmission line is doubled, the circular mils for conductors of constant weight are divided by two, and the volts lost are four times as great as before. Each of these rules assumes that the watts and percentage of loss in the line are constant. The above principles and formulae apply to the design of transmission lines for either continuous or alternating currents, but where the alterna- ting current is employed certain additional factors should be considered. One of these factors is inductance, by which is meant the counter-electro- motive force that is always present and opposed to the regular voltage in an alternating current circuit. One effect of inductance is to cut down the voltage at that end of the line where the power is delivered to a sub- station, just as is also done by the ohmic resistance of the line conductors. Between the loss of voltage due to line resistance and the loss due to in- ductance there is the very important difference that the former represents an actual conversion of electrical energy into heat, while the latter is simply the loss of pressure without any material decrease in the amount of energy. While the loss of energy in a transmission line depends directly on its resistance, the loss of pressure due to inductance depends VOLTAGE AND LOSSES ON TRANSMISSION. 231 on the diameter of conductors without regard to their resistance, on the length of the circuit, the distance between the conductors, and on the frequency or number of cycles per second through which the current passes. As a result of these facts, it is not desirable or even practicable to use inductance as a factor in the calculation of the resistance or weight of a transmission line. On transmission lines, as ordinarily constructed, the loss of voltage due to inductance generally ranges between 25 and 100 per cent of the number of volts lost at full load because of the resist- ance of the conductors. This loss through inductance may be lowered by reducing the diameter of individual wires, though the resistance of all the circuits concerned in the transmission remains the same, by bringing the wires nearer together and by adopting smaller frequencies. In prac- tice the volts lost through inductance are compensated for by operating generators or transformers in the power-plant at a voltage that insures the delivery of energy in the receiving-station at the required pressure. Thus, in a certain case, it may be desirable to transmit energy with a maximum loss of ten per cent in the line at full load, due to the resistance of the conductors, when the effective voltage at the generator end of the line is 10,000, so that the pressure at the receiving-station will be 9,000 volts. If it appears that the loss of pressure due to inductance on this line will be i ,000 volts, then the generators should be operated at 1 1 ,000 volts, which will provide for the loss of i ,000 volts by inductance, leave an effective voltage of 10,000 on the line, and allow the delivery of energy at the sub-station with a pressure of 9,000 volts, when there is a ten-per- cent loss of power due to the line resistance. Inductance not only sets up a counter-electromotive force in the line, which reduces the voltage delivered to it by generators or transformers, but also causes a larger current to flow in the line than is indicated by the division of the number of watts delivered to it by the virtual voltage of delivery. The amount of current increase depends on both the induct- ance of the line itself and also on the character of its connected apparatus. In a system with a mixed load of lamps and motors there is quite certain to be some inductance, but it is very hard to predetermine its exact amount. Experience with such systems shows, however, that the in- crease of line current due to inductance is often not above five and usually less than ten per cent of the current that would flow if there were no inductance. To provide for the flow of this additional current, due to inductance, without an increase of the loss in volts because of ohmic re- sistance, the cross section of the line conductors must be enlarged by a percentage equal to that of the additional current. This means that in 232 ELECTRIC TRANSMISSION OF WATER-POWER. an ordinary case of a transmission with either single, two, or three-phase alternating current, the circular mils of each line wire, as computed with the formulae above given, should be increased by five to ten per cent. Such increase in the cross section of wires of course carries with it a like rise in the total weight of the conductors for the transmission. If wire of the cross section computed with the formulae is employed for the alternat- ing current transmission, inductance in an ordinary case will raise the assumed line loss of power by five to ten per cent of what it would be if 'no inductance existed. Thus, with conductors calculated by the formulae for a power loss of ten per cent at full load, inductance in an ordinary case would raise this loss to somewhere between 10.5 and eleven per cent. As a rule it may therefore be said that inductance will seldom in- crease the weight of line conductors, or the loss of power therein, by more than ten per cent. When an alternating current flows along a conductor its density is not uniform in all parts of each cross section, but the current density is least at the centre of the conductor and increases toward the outside surface. This unequal distribution of the alternating current over each cross section of a conductor through which it is passing increases with the diameter or thickness of the conductor and with the frequency of the alternating current. By reason of this action the ohmic resistance of any conductor is somewhat greater for an alternating than for a con- tinuous current, because the full cross section of the conductor cannot be utilized with the former current. Fortunately, the practical importance of this unequal distribution of alternating current over each cross section of its conductor is usually slight, so far as the sizes of wires for transmis- sion lines are concerned, because the usual frequencies of current and diameters of conductors concerned are not great enough to give the effect mentioned a large numerical value. Thus, sixty cycles per second is the highest frequency commonly employed for the current on transmission lines. With a 4-0 wire, and the current frequency named, the increase in the ohmic resistance for alternating over that for continuous current does not reach one-half of one per cent. Having calculated the circular mils of weight of a transmission line by the foregoing formulae, it appears that the only material increase of this weight required by the use of alternating current is that due to inductance. This increase cannot be calculated exactly beforehand be- cause of the uncertain elements in future loads, but experience shows that it is seldom more than ten per cent of the calculated size or weight of conductors. CHAPTER XVII, SELECTION OF TRANSMISSION CIRCUITS. MAXIMUM power, voltage, loss, and weight of conductors having been fixed for a transmission line, the number of circuits that shall make up the line, and the relations of these circuits to each other, remain to be determined. In practice wide differences exist as to the number and relations of circuits on a single transmission line between two points. Cases illus- trating this fact are the 1 47-mile transmission from Electra power-house to San Francisco and the 65-mile transmission between Canon Ferry, on the Missouri River and Butte, Mont. At the Electra plant the gen- erator capacity is 10,000 kilowatts, and the transmission to San Francisco is carried out over a single pole line that carries one circuit composed of three aluminum conductors, each with an area in cross section of 471,000 circular mils. From the generators at Canon Ferry, which have an aggregate capacity of 7,500 kilowatts, a part of the energy goes to Helena over a separate line, and the transmission to Butte goes over two pole lines that are 40 feet apart. Each of these two pole lines carries a single circuit composed of three copper conductors, and each conductor has a cross section of 105,600 circular mils. The difference in practice illus- trated by these two plants is further brought out by the fact that their voltages are not far apart, as the Canon Ferry and Butte line operates at 50,000, and the Electra and San Francisco line at 60,000 volts. Economy in the construction of a transmission line points strongly to the use of a single circuit, because this means only one line of poles, usually but one cross-arm for the power wires per pole, the least possible number of pins and insulators, and the smallest amount of labor for the erection of the conductors. In favor of a single circuit there is also the argument of greatest mechanical strength in each conductor, since the single circuit is to have the same weight as that of all the circuits that may be adopted in its place. Where each conductor of the single circuit would have a cross section of less than 83,690 circular mils, if of copper, corresponding to a No. i B. & S. gauge wire, the argument as to me- chanical strength is of especial force, since two equal circuits instead of 233 234 ELECTRIC TRANSMISSION OF WATER-POWER. one, in the case where one circuit of No. i wires would have the required weight, reduce the size of each conductor to No. 4 wire, of 41,740 circular mils cross section, and this is the smallest wire that it is practicable to use on long lines for mechanical reasons. Opposed to these arguments for a single circuit are those based on the supposed greater reliability of two or more circuits, their greater ease of repair, their more effective means of regulation, and the influence on inductance of a reduction in the size of conductors. In spite of the consequent reduction in the size of each conductor, the use of two or more separate circuits for the same transmission is sometimes thought to increase its reliability, because in case of a break or short-circuit on one of the circuits the other will still be available. Breaks in transmission conductors are due either to mechanical strains alone, as wind pressure, the falling of trees, or the accumulation of ice, or else to an arc between the conductors that tends to melt them at some point. As a smaller conductor breaks or melts more readily than a large one, the use of two or more circuits instead of a single circuit tends to increase troubles of this sort. It thus seems that while two or more cir- cuits give a greater chance of continued operation after a break in a con- ductor actually occurs, the use of a single circuit with larger conductors makes any break less probable. When repairs must be made on a transmission line, as in replacing a broken insulator or setting a pole in the place of one that has burned, it is certainly convenient to have two or more circuits so that one may be out of use while the repairs on it are made. It is practicable, however, to make such repairs on any high-voltage circuit, even when it is in use, provided the conductors are spaced so far apart that there is no chance of making a contact or starting an arc between them. To get such dis- tance between conductors there should be only one circuit per pole, and even then more room should be provided for that circuit than is common in this type of construction. On each of the two pole lines between Canon Ferry and Butte there is a single circuit of three conductors arranged in triangular form, two at the opposite ends of a cross-arm and one at the top of the pole, and the distance from each conductor of a circuit to either of the other two is 6.5 feet. This distance between con- ductors is perhaps as great as that on any transmission circuit now in use, but it seems too small to make repairs on the circuit reasonably safe when it is in operation at a pressure of 50,000 volts. There seems to be no good reason why the distance between the conductors of a single circuit to which a pole line is devoted might not be increased to as much SELECTION OF TRANSMISSION CIRCUITS. 235 as ten feet, at the slightly greater expense of longer cross-arms. With as much as ten feet between conductors, and special tools with long wooden handles to grasp these conductors, there should be no serious danger about the repair of even 6o,ooo-volt lines when in operation. As the 6o,ooo-volt line between Electra and San Francisco consists of only one circuit, it seems that repairs on it must be contemplated during operation. Another example of a high-voltage transmission carried out with a single circuit is that between Shawinigan Falls and Montreal, a distance of eighty-five miles. In this case the circuit is made up of three alumi- num conductors, each of which has an area in cross section of 183,750 circular mils, and these conductors are located five feet apart, one at the top of each pole, and two at the ends of a cross-arm below. This single circuit is in regular operation at 50,000 volts for the supply of light and power in Montreal, and it is hard to see how repairs while there is current on the line are to be avoided. Inductance varies with the ratio between the diameter of the wires in any circuit and the distance between these wires, but as inductance simply raises the voltage that must be delivered by generators or trans- formers, and does not represent a loss of energy, it may generally be given but little weight in selecting the number of circuits, the distance be- tween conductors, and the size of each conductor. If two or more circuits with smaller conductors have a combined resistance in multiple equal to that of a single circuit with larger conductors, the loss of voltage due to in- ductance may be greater on the single circuit than the corresponding loss on the multiple circuits, but the advantages due to the single circuit may more than compensate for the higher pressure at generators or trans- formers. That such advantages have been thought to exist in actual construction may be seen from the fact that the 1 4 7 -mile line from Electra power-house to San Francisco, and the 83 -mile line from Sha- winigan Falls to Montreal, are composed of one circuit each. As induc- tance increases directly with the length of circuits, these very long lines are especially subject to its influence, yet it was thought that the advan- tages of a single circuit more than offset its disadvantages in each case. Where several sub-stations, widely separated, are to be supplied with energy by the same transmission line, another argument exists for the division of the line conductors into more than one circuit, so that there may be an independent circuit to each sub-station. As the pressure for local distribution lines must be regulated at each sub-station, it is quite an advantage to have a separate transmission circuit between each sub- 236 ELECTRIC TRANSMISSION OF WATER-POWER. station and the power plant, so that the voltage on each circuit at the power-house may be adjusted as nearly as possible to the requirements of its sub-station. An interesting illustration of this practice may be noted in the de'sign of transmission circuits for the line between Spier Falls on the Hudson River and the cities of Schenectady, Troy, and Albany, located between thirty and forty miles to the south, which passes through Saratoga and Ballston on the way. When this transmission line is completed, four three-phase circuits, one of No. o and three of No. ooo copper wire, will run to the Saratoga switch-house from the generating plant at the Falls, a distance of some eight miles. From this switch-house two circuits of No. o conductors go to the Saratoga sub-station, a little more than one mile away, two circuits of No. ooo wires run to the Watervliet sub-station, across the river from Troy and thirty-five miles from the generating station, and one circuit of No. o and one circuit of No. ooo wires are carried to Schenectady, thirty miles from Spier Falls, passing through and supplying the Ballston sub-station on the way. Other circuits connect the sub-station at Water- vliet with that at Schenectady and with the water-power station at Mechanicsville. From the Watervliet sub-station secondary lines run to sub-stations that control the local distribution of light and power in Albany and Troy. This network of transmission circuits was made desirable by the conditions of this case, which include the general supply of light and power in three large and several smaller cities, the operation of three large electric railway systems, and the delivery of thousands of horse-power for the motors in a great manufacturing plant. In not every transmission system with different and widely scattered loads it is thought desirable to provide more than one main circuit. Thus, the single circuit eighty-three miles long that transmits energy from Shawinigan Falls to Montreal is designed to supply power also in some smaller places on the way. So again, the 1 47-mile circuit from Electra power-house to San Fran- cisco passes through a dozen or more smaller places, including Stockton, and is tapped with side lines that run to Oakland and San Jose. In cases like this, where very long lines run through large numbers of cities and towns that sooner or later require service, it is obviously impracticable to provide a separate circuit for each centre of local distribution. It may well be in such a case that a single main transmission circuit connected to a long line of sub-stations will represent the best possible solution of the problem. At the power-house end of such a circuit the voltage will naturally be regulated to suit that sub-station where the load is the most SELECTION OF TRANSMISSION CIRCUITS. 237 important or exacting, and each of the other sub-stations will be left to do all of the regulating for its own load. The greater the total loss of voltage on a transmission line supplying sub-stations that are scattered along much of its length, the larger will be the fluctuations of voltage that must be compensated for at all of the sub-stations save one, under changing loads, if only one circuit is em- ployed between the power-plant and these sub-stations. Suppose, for example, that a transmission line 100 miles long is composed of a single circuit, and supplies two sub-stations, one located 50 miles and the other 1, 1. 1 : fl fl 1 [ f ' s [ ? . t t a ft o^cv. 1 1 1 1 r3 La qj 13 13 w q q m un 3 rl fl 11 II il rl a ii FIG. 76. Connections at Watervliet Sub-station on Spier Falls Line. ioo miles from the power-plant. Assume at first that there is no load whatever at the intermediate sub-station. If the single transmission cir- cuit operates with 50,000 volts at the power-plant, and 45,000 volts at the sub-station ioo miles away when there is a full load there, correspond- ing to a loss of ten per cent, then the pressure at the intermediate sub- station will be 47,500 volts. If, now, the load at the sub-station ioo miles from the power-house drops to a point where the entire line loss is only 1,000 volts, and the pressure at the generating plant is lowered to 46,000 volts so as to maintain 45,000 volts at the more distant sub- station, then the pressure at the intermediate sub-station will be 45,500 volts, or 2,000 volts less than it was before. If the loss on the entire line at full load were only five per cent, making the voltage at the sub-station ioo miles away 47^,500 when that at the generating station is 50,000, 238 ELECTRIC TRANSMISSION OF WATER-POWER. then the pressure at the intermediate sub-station will be 48,750 volts. Upon a reduction of the loss on the entire length of line to one-fifth of its maximum amount, or to 500 volts, the pressure at the generating sta- tion must be reduced to 48,000 volts, if that at the more distant sub- station is to be held constant at 47,500. At the intermediate sub-station the pressure will then be 47,750 volts, or 1,000 volts less than it was at full load. From these two examples it may be seen that the extent of pressure variation at the intermediate sub-station will depend directly FIG. 77. Sections of Switch-house on New Hampshire Traction System. on the maximum line loss, if the regulation at the generating station is such as to maintain a constant voltage at the sub-station 100 miles away. All the foregoing has assumed no load to be connected at the inter- mediate sub-station, and with a load there the fluctuations of pressure will of course depend on its amount as well as on the load at the more distant sub-station. One of the strongest reasons for the use of two or more circuits in the same transmission line arises from the rapid fluctuations of load where large stationary motors or an electric railway system is operated. When a transmission line must carry a load of stationary or railway motors, it is a common practice to divide the line into at least two cir- SELECTION OF TRANSMISSION CIRCUITS. 239 cuits, and to devote one circuit exclusively to railway or motor work and another to lighting, at any one time. In some cases this division of the transmission system into two parts, one devoted to the lighting and the other to the motor load, is carried out not only as to the sub- station apparatus and the line, but also as to the transformers, genera- tors, water-wheels, and even the penstocks at the power-plant. It is possible even to carry this division of the transmission system still fur- ther, and to separate either the motor or the lighting load, or both, into sections, and then to devote a distinct transmission circuit, group of transformers, generator, and water-wheel to the operation of each sec- tion. An example of the complete division of generating and transmit- ting apparatus into independent units may be noted in the case of the system that supplies light and power in Portland, Me., from a generating plant on the Presumpscot River, thirteen miles away. At this station four steel penstocks, each provided with a separate gate at the forebay wall, bring water to as many pairs of wheels, and each pair of wheels drives a direct-connected generator. Four three-phase circuits connect the generating plant with the sub-station at Portland, and each circuit between the generating plant and a transformer-house outside the busi- ness section of the city is made up of No. 2 solid soft-drawn copper wires. Each of these four sets of apparatus, from head-gate to sub-station, is usually operated independently of the others, and supplies either the motor load or a part of the electric lighting. In this way changes in the amount of one section of the load cause no fluctuation of the voltage on the other sections. At Manchester, N. H., the sub-station receives energy from four water-power plants, and is provided with two sets of low-tension, 2,3oo-volt, three-phase bus-bars, one set of these bus-bars being devoted to the operation of the local electric railway system, and the other set to the supply of lamps and stationary motors. Each set of these bus-bars is divided into a number of sections, and by means of these sections different transmission circuits are devoted to different portions of the lighting and motor loads. As three of the four water- power plants are connected to the sub-station by two circuits each, the division of loads in this case is often carried clear back to the generators, one generator in a power-house being operated, for instance, on railway work and another on a lighting load at the same time. This plan has the obvious advantage that much of the regulation for the several parts of the entire load may be done at the generators, thus reducing the amount of regulation necessary at the sub-station, and that fluctuat- 240 ELECTRIC TRANSMISSION OF WATER-POWER. ing motor loads do not affect the lamps. In this case the conductors of the several transmission circuits are all of moderate size, and the division of the lines was evidently adopted for purposes of regulation, rather than to reduce the amount of inductance. Thus the line between Gregg's Falls and the sub-station, a distance of six miles, is made up of one three-phase circuit of No. 4 and one circuit of No. 6 bare copper wires. The fourteen-mile line between the plant at Garvin's Falls and the sub-station, the longest of the four transmissions, is made up of two three-phase circuits, each composed of No. o bare copper wires. In the case of the Gregg's Falls plant the subdivision of the line has gone further than that of the generating equipment, for the station there contains only a single generator, the rating being 1,200 kilowatts, while two circuits run thence to the sub-station. Another instance showing extensive sub- division of a line into separate circuits may be noted in the seven-mile transmission from Montmorency Falls to Quebec, Canada, where six- teen conductors, each No. o copper wire, make up four two-phase cir- cuits that connect a plant of 2,400 kilowatts capacity with its sub-station. Such multiplication of transmission circuits has some advantages from the standpoint of regulation, but there are good reasons for limiting it to rather short lines, where it is, in fact, almost exclusively found. On very long lines the use of numerous circuits composed of rather small conductors would obviously increase the constant expense of inspection and repairs and add materially to uncertainty of the service. Very few, if any, transmission lines of as much as twenty-five miles in length are divided into more than two circuits, and in several instances lines of superlative length have only a single circuit each. The greatest single power transmission in the world, that between Niagara Falls and Buffalo, is carried out with two pole lines, one of which is about twenty and the other about twenty-three miles long. The longer pole line, which is also the older, carries two three-phase circuits, each of which is made up of three 350,000 circular mil copper conductors. The shorter pole line carries a single three-phase circuit composed of aluminum conductors, each of which has an area in cross section of 500,000 circular mils. In electrical conductivity the aluminum circuit is intended to be equal to each of the two that are composed of copper. According to the descrip- tion of the Niagara Falls and Buffalo transmission system in vol. xviii., A. I. E. E., pages 518 to 527, each of these three circuits is designed to transmit about 7,500 kilowatts, and the maximum power transmitted up to August, 1901, was 15,600 kilowatts, or about the calculated capacity of two of the circuits. According to the description just mentioned, the SELECTION OF TRANSMISSION CIRCUITS. 241 transmission circuits used to supply energy for use at Buffalo are regu- larly operated in parallel, and this is also true of the generators and the step-down transformers, though the uses to which this energy is applied include lighting, large stationary motors, and the electric railway system. Apparatus in the generating station at Niagara Falls and in the terminal- house near the city limits of Buffalo is so arranged, however, that two of the 3,750 kilowatt generators and eight step-up transformers at the power-house, together with one transmission circuit and three step-down transformers in the terminal-house at Buffalo, may be operated inde- pendently of all the other apparatus. As already pointed out, the use of separate circuits for each sub- station, and for lighting and power loads at each sub-station in very long transmission systems, is often impracticable. Even in comparatively short transmissions the multiplication of circuits and the use of rather small and mechanically weak conductors increased the first cost of installation and the subsequent expense of inspection and repairs. An objection to operation with a single circuit in a transmission line that supplies widely separated sub-stations with lighting, power, and railway loads is the consequent difficulty of pressure regulation on the distribution lines at each sub-station. Such a transmission line necessarily delivers energy at different and fluctuating voltages at the several sub-stati 3ns, and these fluctuations are of course reproduced on the secondary side of the step-down transformers. Fortunately, however, the use of syn- chronous motor generators, either in place of or in connection with static transformers, goes far to solve the problem of pressure regulation for dis- tribution circuits supplied with energy from transmission lines. This is due to the well-known fact that with constant frequency the speed of rota- tion for a synchronous motor is constant without regard to fluctuations in the applied voltage or changes in its load. With a constant speed at the motor and its connected generator it is of course easy to deliver current at constant voltage to the distribution lines. This constancy of speed makes the synchronous motor generator a favorite in large transmission systems with both power and lighting loads. The satisfactory lighting service in Buffalo, operated with energy transmitted from Niagara Falls, seems to be due in some measure to the use of synchronous motor gen- erators at the sub-station in Buffalo, whence lighting circuits are sup- plied. As above stated, the three circuits that make up the transmission line between Niagara Falls and Buffalo are operated in multiple, and in the latter place there is a large load of both railway and stationary motors. As the three circuits are operated in multiple, they of course amount to 16 242 ELECTRIC TRANSMISSION OF WATER-POWER. only a single circuit so far as fluctuations of voltage due to changes in these several sorts of loads are concerned. According to vol. xviii., A. I. E. E., pages 125 and following, the load on the transmission system at Buffalo in 1901 was made up of about 7,000 horse-power in railway motors, 4,000 horse-power in induction motors, and 4,000 horse-power divided up between series arc lamps, constant pressure incandescent lamps, and continuous current motors. The railway load is operated through step-down transformers and rotary converters. The induction motors are connected either to the 2,000- volt secondary circuits of the step-down transformers or to service transformers supplied by these circuits. On these railway and stationary motor loads there is of course no necessity for close pressure regulation. Series arc lamps are operated through step-down transformers and synchronous motors direct-con- nected to constant continuous current dynamos. Continuous current stationary motors draw power from the transmission lines through step- down transformers and rotary converters, like the railway load. For the 2,200 volt circuits that supply service transformers for commercial arc and incandescent lighting the transmitted energy passes through step-down transformers and synchronous motor-generators. These motor-genera- tors raise the frequency from twenty-five to sixty cycles per second. Finally the continuous current three-wire system for incandescent light- ing at about 250 volts between outside wires is operated through step- down transformers and synchronous motors direct-connected to continu- ous current generators. For this last-named service rotary converters were at first tried, but were found to be impracticable because voltage fluctuations on the transmission line (due largely to the railway and motor loads) were reproduced on the continuous-current circuits by the rotary converters. Since the adoption of motor-generators this fluctua- tion of the service voltage is no longer present. Another case in which synchronous motor-generators deliver power from a transmission line that carries both a lighting and a motor load is that of the Shawinigan sub-station in Montreal. At this sub-station the 85-mile transmission line from the generating plant at Shawinigan Falls terminates. As already pointed out, this line is composed of a single three-phase circuit of aluminum conductors, each of .which has a cross section of 183,750 circular mils. In the Montreal sub-station the thirty-cycle, three-phase current from Shawinigan Falls is delivered to transformers that lower the voltage to 2,300. The current then goes to five synchronous motor-generators of 1,200 horse-power capacity each, and is there converted to sixty-three cycles per second, two-phase, at the SELECTION OF TRANSMISSION CIRCUITS. 243 same voltage. This converted current passes onto the distribution lines of the local electrical supply system in Montreal, which also draws energy from two other water-power plants, and is devoted to lighting, stationary motors, or to the street railway work, as may be required. Though sep- arate local distribution circuits are devoted to these several loads, the fluctuations in the stationary and railway motor work necessarily react on the voltage of the transmission line and transformers at the sub-station. By the use of the synchronous motor-generators the lighting circuits are protected from these pressure variations. As the numbers of sub-stations at different points on long transmis- sion lines increase, and stationary motor and railway loads at each be- Power tine \Y\\\\\\\\\ FIG. 78. Transfer Switches at Saratoga Switch-house on Spier Falls Line. come more common, it is to be expected that the use of synchronous motor-generators for lighting service will be much more frequent than at present. With such use there will disappear one of the reasons for the multiplication of transmission circuits. Where several transmission circuits connect a generating plant with a single sub-station, or with several sub-stations in the same general direction, it is desirable to have switches so arranged that two or more circuits may be combined as one, or so that any circuit that ordinarily operates a certain load or sub-station may be devoted to another when occasion requires. For this purpose transfer switches on each circuit 244 ELECTRIC TRANSMISSION OF WATER-POWER. are necessary at generating plants, sub-stations, and often at switch- houses. These transfer switches will ordinarily be of the knife type, and intended for manual operation when the circuits to which they are connected are not in use. As such switches are exposed to the full voltage of transmission, the insulation of their conducting parts should be very high. In the extensive transmission system between the power- plants at Spier Falls and Mechanicsville and the sub-stations at Troy, Albany, and Schenectady, N. Y., a transfer switch of highly insulated construction has been much used. The two blades of this switch move independently of each other, but both are mounted between the same FIG. 79. Cross Section of Schenectady Switch-house on Spier Falls Line. metal clips. Each blade is of two by one-quarter inch drawn copper rod, and the clips supporting the two blades are mounted on top of a circular metal cap four and three-quarter inches in outside diameter and two inches high, that is cemented over the top of a large, double petti- coat, porcelain line insulator. Clips into which these copper blades are swung in closing the switch are also mounted in caps carried by insulators in the way just described. Each of these insulators is mounted on a large wooden pin, and these pins are secured in timbers at the points where the switches are wanted. This construction of switches gives ample insulation for the line voltage SELECTION OF TRANSMISSION CIRCUITS. 245 of 30,000 in this system. By means of the transfer switches just de- scribed, either of the transmission circuits leaving the Spier Falls power- plant may be connected to any one of the ten generators and ten groups of transformers there. At the Saratoga switch-house, any one of the twelve conductors, making up the four three-phase circuits from Spier Falls may be connected to any one of the eighteen conductors making up the six three-phase circuits that go south to Saratoga, Watervliet, and Schenectady sub-stations, in the way indicated by the drawing. So again at the Watervliet sub-station, where energy at 26,500 volts is re- ceived from Spier Falls and energy at 10,800 volts from Mechanicsville, any single conductor from either of these water-power plants may be connected, either directly or through a transformer, with either conductor running to the railway and lighting sub-stations about Albany and Troy. Where several transmission circuits are employed, this complete flexibility of connection evidently adds materially to the convenience and reliability of operation. CIRCUITS IN TRANSMISSION LINES. .2 5s jj| i-Sui It %** Location of Lines. |a J5 3 B| ly 111 111 J fc 6^^ UC Electra to San Francisco 147 I J *47l 0^4 60 Colgate to Oakland Cal J42 2 < 2 ' 60 *2 1 1 ,000 Santa Ana River to Los Angeles ^ 2 83,690 60 Shawinigan Falls to Montreal 85 I 3 Caiion Ferry to Butte fio Welland Canal to Hamilton ?r I 87 6OO 60 Welland Canal to Hamilton . 77 c \5> u y u 60 Spier Falls to Schenectadv . . . 2 3 167,800 Spier Falls to W r atervliet, N. Y. ... 35 2 167,800 40 Ogden to Salt Lake City 36 2 87 600 60 Apple River Falls to St. Paul 27 2 66 370 60 Niagara Falls to Buffalo 27, 2 7CO OOO 2 ? Niagara Falls to Buffalo . 2O Farmington River to Hartford II I 60 Niagara Falls to Toronto. . . 7$ 2 j + 2 5 * Aluminum "conductor. t Steel towers. CHAPTER XVIII. POLE LINES FOR POWER TRANSMISSION. LONG transmission lines should follow the most direct routes between generating and sub-stations as far as practicable. The number of poles, cross-arms, and insulators increases directly with the length of line, and the weight of conductors with the square of that length, other factors remaining equal. Every material deviation from a straight line must therefore be paid for at a rather high rate. Distribution lines necessarily follow the public streets in order to reach consumers, but the saving of the cost of a private right of way and ease of access are the main considerations which tend to keep transmis- sion lines on streets and highways. Except in very rough or swampy country, the difficulty of access to a pole line on a private right of way is not a serious matter and should be given but little weight. The cost of a private right of way may be more important, and should be compared with the additional cost of the pole line and conductors if erected on the public highway. In this additional cost should be included any items for paving about the poles, extra pins, insulators, and guys made necessary by frequent turns in the highway, and the sums that may be required to secure the necessary franchises. There is also the possible contingency of future legislation as to the voltage that may be maintained on wires located over public streets. These considerations taken together give a strong tendency to the location of long transmission lines on private rights of way, especially where the amount of power involved is great and the voltage very high. A transmission line 80.3 miles in length recently erected between Rochester and Pelham, N. H., by way of Portsmouth, where the gen- erating station is located, to feed an electric railway system, operates at 13,200 volts and is mainly located on private rights of way. Deeds conveying the easements for this right of way provide that all trees or branches within one rod on either side of the line may be cut away. The transmission line between Niagara Falls and Buffalo, about twenty- three miles long and operating at 22,000 volts, is largely on a private way thirty feet wide. 246 POLE LINES FOR POWER TRANSMISSION. 247 248 ELECTRIC TRANSMISSION OF WATER-POWER. For the transmission between Canon Ferry and Butte the line is mainly located on a private way. Between Colgate and Oakland the transmission line is mostly on private way, and this is also true of the greater part of some other high-pressure lines in California. These pri- vate rights of way range from fifty to several hundred feet wide, it being necessary in forests to cut down all trees that are tall enough to fall onto the wires. In some cases of transmission at very high voltage two independ- ent pole lines are erected and one or more circuits are then run on each set of poles. This construction has been followed on the transmission line between Niagara Falls and Buffalo, Canon Ferry and Butte, Welland Canal and Hamilton, and between Colgate and Oakland. Such double pole lines are more usually located on the same right of way, this being true of the Canon Ferry and Colgate systems, but this is not always the case. In the Hamilton system the two lines of poles, one thirty-five miles and the other thirty-seven miles in length, are located several miles apart. The two sets of poles on a part of the Buffalo line are less than thirty feet, on the Colgate line are twenty-five feet, and on the Canon Ferry line are forty feet apart. The main reasons for the use of two pole lines instead of one are the probability that an arc started on one circuit will be communicated to another on the same poles, and the greater ease and safety of repairs when each circuit is on a separate line of poles. On each pole line of the Canon Ferry transmission, and also on each pole line of the Colgate transmission, there is only one three- wire circuit. On the Canon Ferry line each wire of the two circuits has a cross-section of only 106,500 circular mils, and on the Colgate line one circuit is of 133,225 circular mils wire and the other circuit is of 21 1 ,600 circular mils cable. In contrast with these figures the line of the Standard Electric Company between Electra and Mission San Jose, a distance of ninety-nine miles, is made up of only three conductors, each being an aluminum cable of 471,034 circular mils section. Induct- ance increases with the frequency of the current in a conductor, and in each of the three systems just considered the frequency is sixty cycles per second. The use of one circuit of larger wire instead of two circuits of smaller wire has the obvious advantage of greater mechanical strength in each conductor, saves the cost of one pole line and of the erection of the second circuit. With voltages above 40,000 to 50,000 on long transmission lines there is a large loss of energy by leakage directly through the air from wire to wire. To keep this loss within desirable limits it may be necessary to POLE LINES FOR POWER TRANSMISSION. 249 give each wire of a circuit a greater distance from the others of the same circuit than can readily be had if all the wires of each circuit are mounted on one line of poles. If there is only one three- wire circuit to be provided for, three lines of poles or two lines with a long crosspiece between them may be set with any desired distance between the lines so that the leak- age through the air with one wire on each pole will be reduced to a small quantity. On a line built in this way it would be practically impossible for an arc to start between the wares by any of the usual means. Distances from pole to pole in the same line vary somewhat with the number, size, and material of the conductors to be carried. On ordinary FIG. 81. Chambly- Montreal Line Crossing the Chambly Canal. construction in a straight line poles are often spaced from 100 to no feet apart that is, about fifty poles per mile. On curves and near corners the spacing of poles should be shorter. Poles for the 80.3 miles, men- tioned in New Hampshire, are regularly located 100 feet apart. Of the two pole lines between Niagara Falls and Buffalo, the older was de- signed to carry twelve copper cables of 350,000 circular mils each, and its poles were spaced only 70 feet apart. The newer line is designed to carry six aluminum cables of 500,000 circular mils each and its poles are 140 feet apart. Poles in each of the lines between Canon Ferry and Butte are regularly spaced no feet apart and each pole carries three copper cables of 106,500 circular mils. 250 ELECTRIC TRANSMISSION OF WATER-POWER. The two 142-mile lines between Colgate and Oakland are each made up of poles 132 feet apart, and one line of poles carries the three copper conductors and the other line of poles the aluminum conductors already named. As aluminum wire has only one-half the weight of copper wire of equal conductivity, the length of span between poles carrying aluminum wire may be greater than that where copper is used. Only a part of the strain on poles is due to the weight of wires carried, how- ever. Where a body of water must be crossed, a very long span, with special supports for the wires at each side, may be necessary. A case FIG. 82. Special Wooden Structures on Line Between Spier Falls and Schenectady. of this sort was met where the Colgate and Oakland line crosses the Carquinez Straits at a point where the waterway is 3,200 feet wide. It was necessary to have the lowest part of the cables across these straits at least 200 feet above the surface of the water so that vessels with the tallest masts could pass underneath. To secure the necessary elevation for the cables a steel tower was built on each bank of the straits at such a point that the distance between the points for cable support on the two towers is 4,427 feet apart. As the banks rise rapidly from the water level, one steel tower was given a height of only 65 feet, while the height of the other was made 225 feet. Between these two towers four steel cables were suspended, each cable being made up of nineteen strands of galvanized POLE LINES FOR POWER TRANSMISSION. 251 steel wire, having an outside diameter of seven-eighths inch and weighing 7,080 pounds for the span. The breaking strain of each cable is 98,000 pounds, and it has the electrical conductivity of a No. 2 copper wire. The cables are simply supported on the towers by steel rollers, and the pull of each cable, amounting to twelve tons, is taken by an anchorage some distance behind each tower, where the cable terminates. Each anchorage consists of a large block of cement deeply embedded in the ground, and with anchor bolts running through it. Each cable is secured to its anchorage through a series of strain insulators, and the regular line Fio. 83. Special Structure on Line Between Spier Falls and Schenectady. cables of copper and aluminum are connected with the steel cables just outside of the shelter built over the strain insulators of each anchor. Steel cables were used for the long span across the straits because of the great tensile strength that could be had in that metal. This span is, no doubt, the longest and highest that has ever been erected for electrical transmission at high voltage. It has been suggested in one instance that steel towers ninety feet high and 1,000 feet apart be substituted for pole lines and the wires strung from tower to tower. Such construction would increase the difficulty of insulation and would cost more at the start than a line of wooden poles. The question is whether a lower maintenance and depreciation rate for the steel towers would offset their disadvantages 252 ELECTRIC TRANSMISSION OF WATER-POWER. compared with poles. Pole lines should be staked out with a transit, and the same instrument can be used to give a perpendicular position to each pole and bring it into line. Wooden poles are used in most cases of high-voltage transmission lines. Iron poles would make it unsafe to work on any circuit carried by them when it was transmitting current at high voltage. With iron poles a defective insulator might lead to FIG. 84. Crossing of Delaware and Hudson Railway Tracks by 30,ooo-volt Line at Saratoga, N. Y. the destruction of the conductors at that point through continuous arcing on to the iron. The kinds of wood used for poles vary in different sections of the country. In New England, chestnut poles are a favorite and were used on the 80.3 miles of transmission line mentioned in New Hampshire. Cedar poles are used to some extent in nearly all parts of the country, including Canada. Spruce and pine poles are employed to some extent, . especially in lengths of more than fifty feet. In the Rocky Mountain region and in California round cedar poles from the forests of Oregon, POLE LINES FOR POWER TRANSMISSION. 253 Washington, and Idaho are much used. Sawed redwood poles from the trunks of large trees were erected on the 14 7-mile line between Electra power-house and San Francisco. For the Colgate and Oakland line Oregon cedar poles were selected, and the transmission between Canon Ferry and Butte was carried out with cedar poles from Idaho. For transmission circuits it is far more important at most points to have poles FIG. 85. Pole Line from Spier Falls over Mount McGregor. very strong rather than very long. Where wires or obstructions must be crossed by the high-voltage circuits the poles should be long enough to carry these circuits well above everything else. In the open country, where no obstructions are to be avoided, it does not pay to use poles with a length greater than thirty-five feet. Short poles offer less surface to the wind, the length of the lever through which wind pressure acts to break the pole at the ground de- creases with the length of pole, and the shorter the poles the smaller is the strain on struts and guy wires. If poles are only thirty or thirty-five 254 ELECTRIC TRANSMISSION OF WATER-POWER. feet long, they may be large in diameter without excessive cost. As a rule, no pole should be used with a top less than seven inches in diame- ter, and a pole with thi stop should not be required to carry more than three wires. A pole with seven- or eight-inch top and thirty feet long should measure not less than twelve inches in diameter at the butt. For longer poles the diameters at the butt should increase up to at least eigh- teen inches for a round pole sixty feet long. In the New Hampshire transmission above named the standard length of poles is thirty-five feet. On the line between Canon Ferry and Butte the poles range from thirty-five to ninety feet in length. The round cedar poles used in the Colgate and Oakland line range from twenty-five to sixty feet in length, from eight to twelve inches diameter at the top, and from twelve to eighteen inches diameter at the butt. On the line between Electra and San Francisco the square-sawed redwood poles are reported to have the following dimensions, in a paper read at the annual convention of Edison Illuminating Companies in 1902. Height, Felt. Top, Inches. Butt, Inches. Depth in Ground. 35 7X 7 12 X 12 5-5 40 8X 8 13* X 13^ 6 45 9X 9 15 x 15 6-5 10 X 10 ii X ii 16 X 16 17 X 17 8 The relative dimensions of these poles are of interest because, being sawed from the trunks of large trees, they could have any desired meas- urements at the tops and butts. These poles, over the greater part of the line, carried the three aluminum cables of 471,034 circular mils each, previously mentioned. Depth to which poles are set in the ground ranges from about five feet for twenty-five- or thirty-foot poles to eight feet for poles sixty feet long. In locations where the soil is very soft or where poles must resist heavy strains the stability of each pole may be much increased by digging the hole two feet or more larger in diameter than the butt of the pole, and 'then filling in cement concrete one part, by measure, of Portland cement, three of sand and five of broken stone all around the butt of the pole after it is in the hole. The butts of poles up to a point one foot or more above the ground line are fre- quently treated with hot tar, pitch, asphalt, or carbolineum before the poles are erected, and in Salt Lake City salt is said to be used around pole butts after they are in the hole. POLE LINES FOR POWER TRANSMISSION. 255 In some cases the poles of transmission lines are painted over their entire length. Pole tops should always be pointed or wedge-shaped, to shed water, and paint or tar should be applied to these tops. In some cases poles are filled with crude petroleum or other preservative com- pound in iron retorts, where moisture is withdrawn from the pole by exhausting the air, and then, after treatment with dry steam, the poles have the compound forced into them by hydraulic pressure. In favorable soils cedar poles may remain fairly sound for twenty years, chestnut poles more than one-half of that time, and spruce and ,pine about five years. Poles up to forty feet in length may be readily FIG. 86. Chambly-Montreal Line the Richelieu River. set with pike poles, but when they are much longer than this a derrick will save time and labor. A derrick should have a little more than one- half the length of the poles to be set. Poles should be guyed or braced at all points where there are material changes in the direction of the line, and on long straight stretches about every fifth pole should be guyed or braced in both directions to prevent the poles setting back when the line wire is cut or broken at any point. Where there is room for wooden struts, as on a private right of way, they should be used instead of guys because of their more substantial character and the higher security of insulation thus obtained. Ordinary strain insulators cannot be relied on with lines that operate at very high voltages, and where guys must be used a timber four by six inches and 256 ELECTRIC TRANSMISSION OF WATER-POWER. ten to twenty feet long may have the guy twisted about each end of it and be used as a strain insulator. A guy or strut should come well up under the lower cross-arm on a pole to avoid breaking of the pole at the point of attachment. Where poles have heavy circuits and several cross-arms each it is sometimes desirable to attach a guy or strut beneath the lowest arm and also a guy close to the pole top. Galvanized iron or steel wire is the material best suited for guys, and the cable form has greater strength and is more flexible than solid wire. On the transmission line between Electra and San Francisco, which is intended to operate at 60,000 volts, the use of guys has been mostly avoided and struts employed instead. Where a guy had to be used, a POLE LINES FOR POWER TRANSMISSION. 257 strain insulator of wood six by six inches and twenty feet long was in- serted in it. The number and spacing of cross-arms on the poles of transmission lines are regulated by the number of circuits that each pole must carry and by the desired distance apart of the wires. Formerly it was com- mon to carry two or more circuits on a single line of poles, but now a frequent practice is to give each pole line only one circuit and each pole only one cross-arm, except that a small cross-arm for a telephone circuit is placed some feet below the power wires. With only one^ transmission circuit per pole line, one wire is usually placed at the top of the pole and the other two wires at opposite ends of the single cross-arm. The older pole line for the transmission between Niagara Falls and Buffalo carried two cross-arms per pole for the power wires, these cross-arms being two feet apart. Each cross-arm was of yellow pine, twelve feet long, four by six inches in section, and intended to carry four three-wire circuits, but only two circuits have been erected on these two cross-arms. On the later pole line for this same transmis- sion each pole carries two cross-arms, the upper intended for four and the lower cross-arm for two wires, so that one three-wire circuit may be strung on each side of the poles, two wires on the upper and one on the lower arm in the form of an equilateral triangle. The pole lines between Canon Ferry and Butte, Colgate and Oakland, and Electra and San Francisco all have only one cross-arm for power wires per pole, and the third wire of the circuit in each case is mounted at the top of the pole so that the three conductors are at the corners of an equilateral triangle. This relative position of the conductors makes it easy to transpose them as often as desired. On the line from Canon Ferry to Butte the cross-arms are each eight feet long with two holes for pins seventy-eight inches apart, and are attached to the pole five feet ten and one-half inches from the top. Gains for cross-arms should be cut from one to two inches deep in poles before they are raised, and one hole for three- quarters or seven-eighths-inch bolt should be bored through the centre of the cross-arm and of the pole at the gain. Each cross-arm should be attached to the pole by a single bolt passing entirely through the pole and cross-arm with a washer about three inches in diameter next to the cross-arm. One large through bolt weakens the pole and arm less than two smaller bolts or lag-screws, and the arm can be more easily replaced if there is only one bolt to remove. Alternate poles in a line should have their cross-arms bolted on opposite sides, and at corners double arms should be used. 258 ELECTRIC TRANSMISSION OF WATER-POWER. Yellow pine is a favorite wood for cross-arms, though other varieties are also used. The large, long pins necessary on high voltage lines tend to increase the sectional area of cross-arms, and a section less than five and one-half by four and one-half inches is seldom desirable. On the line between Electra and San Francisco, which carries the three alu- minum cables of 471,034 circular mils each, the cross-arms of Oregon pine have a section of six by six inches each. Standard dimensions of some smaller cross-arms are four and three-quarters by three and three-quarters inches, but it may be doubted whether these arms are FIG. 88. Tail Race and Pole Line at Chambly, Quebec Power-station, strong enough for long transmission work. Cross-arms should be surfaced all over and crowned one-quarter to one-half inch on top so as to shed water. After being kiln dried, cross-arms should be boiled in asphaltum or linseed oil to preserve the wood and give it higher insulating properties. Cross-arms longer than five feet should be secured by braces starting at the pole some distance below each arm and extending to points on the arm about half-way between the pole and each end of the arm. Each brace may be of flat bar iron about one and one-half by one- quarter inch in section, or the brace for both ends of an arm may be made POLE LINES FOR POWER TRANSMISSION. 259 of a single piece of angle-iron bent into the proper shape. For high- voltage lines it is undesirable to employ iron braces of any sort, since these braces form a path of low resistance that comes much too close to the pins on which the insulators and wires are mounted. Braces formed of hard wood are much better as to insulation, and such braces of maple are in use on the line between Butte and Canon Ferry where the voltage is 50,000. Each brace on that line is thirty-six inches long and three inches wide, with one end bolted to the centre of its pole and the other end to the cross-arm twenty-three inches from the pole centre. The line from Electra has hard-wood braces secured with wood pins. Wood is the most common material for pins on which to mount the insulators of high-voltage transmission circuits. Iron has been used for pins to some extent, and its use is on the increase. Oak and locust pins are generally used, the latter being stronger and more lasting. In Cali- fornia, pins of eucalyptus wood are much used and are said to be stronger than locust. All wooden pins should be boiled several hours in linseed oil after being well dried. This increases the insulating and lasting properties of the pins. High-voltage lines require long pins to hold the lower edges of in- sulators well above the cross-arms, and these pins must be much stronger than those used on ordinary lines, because of the increased leverage of each wire. A pin twelve inches long over all and having a diameter of one and one-half inches in the part that enters the cross-arm has been much used for transmission circuits, but is much too short and weak for high voltages. On the 5o,ooo-volt line between Canon Ferry and Butte the pins are seasoned oak boiled in paraffin. Each of these pins is seventeen and one-half inches long, two and one-half inches in diameter for a length of four and one-half inches in the middle part, two inches in diameter for a length of five and one-half inches that fits into the cross- arm or pole top, and one and one-half inches in diameter at the top of the thread inside of the insulator. These pins hold the outside edges of the insulators nine inches above the tops of cross-arms. Each of these pins is held in its socket by a three-eighths-inch bolt that passes entirely through the pin and the cross-arm or pole top. On the line between Electra and San Francisco the pins are each sixteen and seven-eighths inches long, two and three-quarters inches in diameter at the largest central part, and two and one-quarter inches in diameter in the lower part, five inches long, that fits into the cross-arm or pole top. One of these'pins broke at the shoulder with a pull of 2,200 2 6o ELECTRIC TRANSMISSION OF WATER-POWER. pounds at the threaded part. Carriage bolts one-half inch in diameter pass through the cross-arm and pin two inches from the top of the arm, and one bolt three inches from the pin on each side. Without these bolts the arms split on test with a pull of 1,200 pounds on the pin, but with the bolts the pin broke as above. CHAPTER XIX. ENTRIES FOR ELECTRIC TRANSMISSION LINES. THE entrance of transmission lines into generating plants and sub- stations presents special problems in construction and insulation. One of these problems has to do with the mechanical security of each conductor at the point where it passes through the side or roof of the station. Con- ductors are sometimes attached to the station so that the strain of the line is borne by the side wall where they enter and tends to pull it out of line. This practice has but little to commend it, aside from convenience, for unless the conductors are rather small, or the wall of the station is unusually heavy, the pull of the former is apt to bulge the latter in the course of time. For any heavy line the end strain is ultimately most suitably taken by an anchor securely fixed. As special insulators must be used where a conductor is secured directly to such an anchor, it is usually more convenient to set one or more heavy poles with double cross- arms at the end of a line, and then to make these poles secure by large struts, or by guys attached to anchors. Extra heavy cross-arms on these end poles should be provided with iron pins for the line insulators ; two or more of the insulators mounted in this way within a few feet of each other, for each wire, will stand up against the end strain on almost any line. Insulators that are to take the end strain of a line in this way should allow attachment of the wire at the side, so that the force exerted by each conductor tends to press the insulator against the side of its pin, rather than to pull off the top of the insulator. The end strain of the line hav- ing been taken on poles close to the station, the conductors may be at- tached to insulators on the wall, the latter thus being subjected to very little mechanical strain. Overhead lines usually enter a station through one of its side walls, but an entry may be made in the roof. It is desirable to have a side entry on the gable end of a building rather than on a side below the eaves where there will be much dripping of water. If an entry must be made below the eaves, a shelter should be provided above the entry, and the 261 262 ELECTRIC TRANSMISSION OF WATER-POWER. roof of this shelter should have a gutter that will carry water away from the wires. Entrance of each conductor into a station must be effected in such a way that ample insulation of the circuit will- be maintained, and in some cases so that rain, snow, and wind will be excluded. The line voltage and the climate where the station is located thus have an important bearing on the form of entry that is suitable in any particular case. The simplest form of entry for a high-voltage line is a clear opening, usually circular in form, through the wall of the station for each wire. Insulators for each wire should be provided both inside and outside of the wall to hold the wire at the centre of this opening. Such insulators are usually most conveniently supported by fixtures attached to both sides of the wall, and insulators on the outside should of course be kept in an upright position, unless completely protected from rain and snow. The diameter of the openings through the wall should be great enough to prevent any visible discharge of current between the wire and wall under the worst conditions of snow, rain, fog, or dust. Such an opening must, therefore, increase in diameter with the voltage of the line. The larger these openings for the line wires, the greater is the opportunity for rain, snow, dust, and cold air to enter the station through them. Openings may be so protected as to keep out snow and rain by means of shelters on the outside of the wall on which they are placed, but such shelters cannot keep out the cold air. If the openings for the entrance of wires are located in the wall of a room that contains air-blast trans- formers, the area of openings for circuits of very high voltage may be no greater than is necessary to allow the escape of heated air from the transformers. The milder the climate, other factors being the same, the higher the voltage of circuits which may enter a station through openings that are free for the movement of air. With circuits of only moderate voltage, say less than 15,000, it is quite practicable to admit wires to a station through perfectly free openings, in the coldest parts of the United States. With voltages of 20,000 to 60,000 it is often necessary, in the colder parts of the country, to close the opening in the wall through which each wire enters with a disc of insulating material. In order to keep the current leakage over these discs within proper limits, the diameters of the discs must increase with the voltage of the circuit. This increase of disc diameter obviously lengthens the path of leakage current over the disc surface. Where the openings in a wall for the entrance of high-voltage circuits are closed by insulating discs about ENTRIES FOR TRANSMISSION LINES. 263 the wires, these discs may make actual contact with bare wires, or the wire at each entry may have some special insulation. In the side wall of the sub-station at Manchester, N. H., the entrance of transmission lines from four water-power plants is provided for by circular openings in slate slabs that are built into the brickwork. The transmission circuits from three of the water-power plants operate at 10,000 to 12,000 volts, and the circuit from the fourth plant at about 6,000 volts. Circular openings in the slate slabs are each five inches in diameter, and they are spaced twelve to fifteen inches between centres. A single wire enters through each of these openings and is held at the centre by insulators both inside and outside of the wall. Each wire is bare where it passes through the slate slab, and the circular openings are not closed in any way. The largest wires passing through these five- inch circular openings in the slate slabs are of solid copper, No. o, of 0.3 2 5-inch diameter each. Before passing through the opening in the slate slabs the wires of these transmission circuits are tied to regular line insulators supported by cross-arms secured to the outside of the brick wall by iron brackets. The point of attachment of each wire to its insulator is about nine inches below the centre of the circular hole by which it enters the sub-station. This Manchester sub-station is equipped with air-blast transformers from which the hot air is discharged into the same room that the trans- mission lines enter. Along one side of the sub-station there are twenty- seven of these five-inch circular openings in the slate slabs for entrance of the high- voltage lines, and on another side of the sub-station there are a greater number of smaller openings for the distribution circuits. Were it not for the air-blast transformers, all of these openings would probably admit more air than would be desirable in a climate as cold as that at Manchester. Another example of openings in the walls of a station for the entrance of transmission circuits, where there is free movement of the air between the inside and outside of the building, is that of the 33,ooo-volt line be- tween Santa Ana River and Los Angeles, Cal. In this case a sewer pipe twelve inches in diameter is built into the wall of the station for each wire of the line, so that there is a free opening of this size from inside to outside. Each wire of the 33,000- volt circuit enters the station through the centre of one of these twelve-inch pipes, and is thus surrounded by six inches of air on every side. As the temperature near Los Angeles sel- dom or never goes down to zero, these large openings do not admit 264 ELECTRIC TRANSMISSION OF WATER-POWER. enough air to be objectionable. Besides this mild climate, air-blast transformers add to the favorable features in the stations having the twelve-inch openings. In another case, however, where the openings for the entrance of wires of very high voltage allow free movement of air between the inside and outside of the station, the climate is cold and the winter temperatures go down to 30 or more below zero. This condition exists on the 25,000- volt line between Apple River Falls and St. Paul, where six No. 2 wires enter the generating station through plain circular openings in the brick side wall of a small extension where the lightning arresters are located. Air-blast transformers are located in the end of the station next to this lightning-arrester house, but it is not certain that the hot air from them escapes through the openings for the wires. In another case where the climate is about as cold as that just named, a gallery is built along one side of the exterior of the station at some dis- tance above the ground, and two openings are provided for each wire of the high-tension line. One of these two openings is in the horizontal floor of the gallery and allows the entrance of the wire from the outside, and the other opening is in the side wall of the station against which the gallery is built. The two openings for each wire being thus at right angles to each other, and the opening to the outside air being protected from the wind by its horizontal position, no more than a permissible amount of cold air, it is said, finds its way into the station. In some cases with lines of moderate voltage, say 10,000 to 15,000, and in probably the majority of cases with lines of 25,000 volts or more, the entry for the high-tension wires is entirely closed. An example of this practice may be seen at the various sub-stations of the New Hamp- shire Traction Company, which are located along their 12,000- volt line between Portsmouth and Pelham, in that State. For the entry of each wire on these lines a sixteen-inch square open- ing is made in the brick wall of the sub-station. On the outside of this wall a box is built about a group of three or more of these openings located side by side. The top or roof of this box is formed by a slab of bluestone three inches thick, which is set into the wall and extends twenty-six inches from the face of the wall, with a slight slope from the horizontal. The ends, the bottom, and the outer side of this box are formed by slabs of slate one inch thick, so that the enclosed space has an area in vertical cross section at right angles to this building 15.5 inches high and twenty-two inches wide. ENTRIES FOR TRANSMISSION LINES. 265 FIG. 89 Cable Entering Building. 266 ELECTRIC TRANSMISSION OF WATER-POWER. In the bottom of this box there is a circular opening for each wire, and into this opening fits a heavy glass or porcelain bushing through which the wire passes. After reaching the inside of the box the wire turns at right angles and passes through the sixteen-inch square opening into the sub-station. Beneath the box a special insulator is secured by an iron bracket to the outside of the brick wall for each line wire, and this insulator takes the strain of the wire before it is carried up through the bushing in the bottom of the box. This form of entry is permissible where the desire is to exclude cold air from the station, and where the voltage is not high enough to cause serious leakage over the surface of the bushing and the slate forming the bottom of the box. In all of the cases above mentioned the wires used to enter the stations were the regu- lar line conductors and were bare. Another type of entry in sub-stations is that employed on the extensive transmission system between Spier Falls, Schenectady, and Albany, N. Y. The maximum voltage on this system is 30,000, and the lines usually enter each sub-station through the brick wall at one of its gable ends. Outside of and about the entry of each circuit or group of circuits a wooden shelter is built on the brick wall of the sub-station. Each shelter has a slanting roof that starts from the brick wall at some distance above the openings for the entrance of the line, and terminates in a gutter. The front of each shelter is carried dov/n three feet below the centre of the openings in the brick wall, and the ends go still lower. The front of each shelter is four feet in height, is four feet from the face of the brick wall, and has a circular opening of lo-inch diameter for each wire of the transmission line. In line with each circular opening in the wooden shield there is an opening of 1 5-inch diameter in the brick wall of the sub-station, and into this opening in the brickwork fits a ring of wood with 1 5-inch outside and 1 1 -inch inside diameter. To this wooden ring a 1 5-inch disc of hard fibre J-inch thick is secured, and a porcelain tube 24 inches long and of 2-inch inside diameter passes through a hole in the centre of this disc. Within the wooden shield and in line with each circular opening in it and with the corresponding porcelain tube through the fibre disc a line insulator is secured. Within the sub-station and in line with each tube there is also an insulator, and the two insulators near opposite ends of each tube hold the line wire that passes through it in position. Each wire of the transmission lines, of which the largest is No. ooo solid of o.4io-inch diameter, terminates at one of the insulators within the wooden shield, and is there connected to a special insulated wire that ENTRIES FOR TRANSMISSION LINES. 267 passes through one of the porcelain tubes into the sub-station. A copper trolley sleeve 1 2 inches long is used to make the soldered connection be- tween the bare line wire and the insulated conductor that passes through the porcelain tube. Each of these entry cables, whatever its size, is insulated first with a layer of rubber -sVmch thick, then with varnished cambric wound on to a thickness of sV-inch, and lastly with two layers of weather-proof braid outside of the cambric. This form of closed entry for the transmission lines obviously excludes snow, rain, cold air, and dust from the station. Whether the fibre discs and wooden rings, together with the insulation on the entry cables, are as desirable as a glass disc at the entry is another question. Another instance where the entry for a high-tension line is closed with the aid of combustible material is that of the 2 5, coo- volt transmission between the water-power plant at Chambly, on the Richelieu River, and the sub-station in Montreal. The four three-phase circuits of this line are made up of No. oo wires of o.365-inch diameter each, which enter the power-station at Chambly and the terminal-house in Montreal bare, as they are outside. At each end of the line the wires are secured to insulators on a horizon- tal arm with their centres twenty-two inches outside of an end wall of the station or terminal building. The insulators are mounted with their centres thirty inches apart, and a few inches above the tops of these insulators a corresponding row of wooden bushings pass through the wall with an outward slant. At the Chambly end of the line each of these bushings is of oak, boiled in stearin, four inches in diameter and twelve inches lon|;. At the Montreal end the wall bushings are of boxwood, and each is four inches square and twelve inches long. Each of the wooden bushings carries a glass tube, and is itself held in position by the concrete of the wall in which it is located. Entrance to the station by each of the bare No. oo wires is gained through one of these glass tubes, and cold air is ex- cluded. Quite a different type of closed entry for the wires of a transmission line is in use on that between Shawinigan Falls and Montreal, which operates at 50,000 volts. For the entry of each of the three aluminum cables that make up this line, each cable being composed of seven No. 6 B. & S. gauge wires, a tile pipe of twenty-four-inches diameter was set into the station wall. The end of each tile pipe is closed by a glass plate, with a small hole at its centre, through which the cable passes. As the cable is thus held twelve inches from the terra cotta pipe all 268 ELECTRIC TRANSMISSION OF WATER-POWER. the way around, any leakage of current must pass over this length of glass surface at each cable or through the air. A heavy coating of frost sometimes collects on these plates, and this increases the amount of current leakage over them. Surface leakage in a case of this sort, of course, varies with the size of the glass plate, and if a tile pipe is used the limit of size is soon reached. There seems to be no good reason, however, why a glass plate of any desired dimensions should not be set directly into the brick wall of a station for each line wire and the tile pipes entirely omitted. This plan is followed on the system of the Utah Light & Power Company, which extends to Salt Lake City, Ogden, Provo, and a number of other points in that State. On the 40,ooo-volt line of that system an entry for each wire is pro- vided by setting two plates of glass into the brick wall, one plate being flush with the inner surface and the other with the outer surface of the wall. In the centre of each plate there is a hole of about 2. 5 -inch diameter, into which a glass or porcelain tube fits. The line wire enters the station through this tube, and it does not appear that any shelter for the glass plates is located outside of the building. An entry of this type for the 40,ooo-volt line with glass plates in a brick wall at a gable end of the Murphy mill is said to have given satisfactory results during four years, though that wall faces the southwest, from which direction most of the storms come. At this entry each glass plate is not more than eighteen inches in diameter, and the wires are about four feet apart. On a 1 6,000- volf line of the same company, a glass plate twelve inches square with a three-quarter-inch hole at its centre, and the bare wire passing through without a tube, has given results that were entirely satisfactory. Two quite different types of entry to stations are used on the 50,000- volt line between Canon Ferry and Butte, Mont. One type, employed at the side wall of a corrugated iron building, consists of a thick bushing of paraffined wood carrying a glass tube two inches in diameter, four feet long, with a side wall of five-eighths to three-quarter-inch, through which the line conductor passes. On the roof of the power-station at Canon Ferry a vertical entry is made with the 5o,ooo-volt circuit. For this purpose each line wire is brought to a dead end on three insulators carried by a timber fixture on the roof. A vertical tap drops from each line wire and passes through the roof and into the station. This roof is of wood, covered with tin outside and lined with asbestos inside. Each tap is an insulated wire, ENTRIES FOR TRANSMISSION LINES. 269 and elaborate methods are adopted in the way of further insulation, and to prevent water from following the wire down through the roof. Over the point of entrance sits a large block of paraffined wood with a central hole, and down through this hole passes a long cylinder of paper that extends some distance above the block. Into the top end of this cylinder fits a wood bushing, and a length of the tap wire that has been served with a thick layer of rubber is tightly enclosed by this bushing. The rubber-covered portion of the tap wire also extends above the bush- ing, and has taped to it a paper cone that comes down over the top of the paper cylinder to keep out the water. On the outside of this paper cylinder, at a lower point, a still larger paper cone is attached to prevent water from following the cylinder down through the wooden block. At the lower end of the paper cylinder, within the station, there is another bushing of wood, and between this and the wooden bushing at the top of the cylinder and inside of the paper cylinder there is a long glass tube. Down through this tube and into the station the insulated tap wire passes. From the experience thus far gained with high-voltage lines, it seems that their entrance into stations should always be at a side wall, unless there is some imperative reason for coming down through the roof. If climatic conditions permit, no form of entry can be more reliable than a plain, ample opening through the wall with a large air-space about each wire. If the opening must be closed, it had better be done with one or more large plates of thick glass set directly into the brickwork of the wall. Some additional insulation is obtained by placing a long glass or porcelain tube over each wire where it passes through the central hole in the glass plates. Each conductor should be bare at the entry, as it is on the line. Some of the above examples of existing practice in entries for transmis- sion lines are taken from Vol. xxii., A. I. E. E. CHAPTER XX. INSULATOR PINS. WOODEN insulator pins are among the weakest elements in electric transmission systems. As line voltages have gone up it has been nec- essary to increase the distances between the outside petticoats of insu- lators and their cross-arms and to lengthen the insulators themselves in order to keep the leakage of current between the conductors within per- missible limits. To reduce the leakage, the wires on most lines are located at the tops instead of in the old position at the sides of their insulators. All this has tended to a large increase of the mechanical strains that operate to break insulator pins at the point where they enter the cross- arm, because the strain on each line wire acts with a longer leverage. Again, it is sometimes necessary that transmission lines make long spans across rivers or elsewhere, and a very unusual strain may be put on the insulator pins at these places. As long as each electric system was confined to a single city or town a broken insulator pin could be quickly replaced, and any material inter- ruption of service from such a cause was improbable. Where the light and power supply of a city, however, depends on a long transmission line, as is now the case in many instances, and where the line voltage is so great that contact between a wire and a cross-arm will result in the speedy destruction of the latter by burning, a broken pin may easily lead to a serious interruption of the service. Besides the increase of mechanical strains on insulator pins, there is the danger of destruction of wooden pins by charring, burning, and other forms of disintegration due to leakage of current over the insulators. This danger was entirely absent in the great majority of cases so long as lines were local and operated at only moderate voltages. These several factors combined are bringing about marked changes in design. On straight portions of a transmission line the insulator pins are sub- ject to strains of two principal kinds. One of these is due directly to the weight of the insulators and line wire, and acts vertically to crush the pins by forcing them down onto the cross-arm. The other is due to the hori- 270 INSULATOR PINS. 271 zontal pull of the line wire, which is often much increased by coatings of ice and by wind pressure, tending to break the pins by bending most frequently at the point where they enter the cross-arm. A strain of minor importance on pins is that encountered where a short pole has been set between two higher ones, and the line at the short pole tends to lift each insulator from its pin, and each pin from the cross-arm. Where the line changes its direction, as on curves and at corners, the side strain on pins is greatly increased, and such places give by far the largest amount of trouble through the breaking of pins. The latter sel- dom fail by crushing through the weight of the lines they support, be- cause the size of pin necessary to withstand the bending strain has a large factor of safety as to crushing strength. Insulators are sometimes lifted from wooden pins, and the threads of these pins stripped where a short pole is used, as already noted; but failure of this kind is not common. Iron pins are either screwed or cemented into their insulators, but the cemented joint is much more desirable, because where a screw joint is made the unequal expansion of the iron and the glass or porcelain is apt to result in breakage of the insulator. Where cement is used, both the pins and insulators should be threaded or provided with shoulders of some sort, so that, although the shoulders of threads do not come into contact with each other, they will, nevertheless, help to secure a better hold. Pure Portland cement, mixed with water to a thick liquid, has been used with success, the insulator being placed upside down and the pin held in a central position in the hole of the insulator while the cement is poured in. Another cement that has been used for the same purpose is a mixture of litharge and glycerin. Melted sulphur is also available. The same forces that tend to lift an insulator from its pin tend also to pull the pin from its socket in the cross-arm or pole top. With wooden pins the time-honored custom has been to drive a nail into the side of the cross-arm so that it enters the shank of the pin in its socket. This plan is good enough so far as immediate mechanical strength is concerned, but is not desirable, because it is hard to remove a nail when a pin is to be removed, and also because the rust of the nail rots the wood. A better plan is to have a small hole entirely through each cross-arm and in- sulator pin at right angles to the shank of that pin in its socket, and then to drive a small wooden pin entirely through from side to side. Some of the important factors affecting the strains on insulator pins vary much on different transmission lines, as may be seen from the following table of lines on which wooden pins are used. On the 272 ELECTRIC TRANSMISSION OF WATER-POWER. older line between Niagara Falls and Buffalo, the regular length of span is 70 feet, and each copper conductor of 350,000 circular mils is attached to its insulator 7.5 inches above the cross-arm. On the new TABLE I. DATA OF LINES ON WOODEN PINS. Location of the Lines. Circular Mils of Each Conductor. M JK tgcng [i/o .5 Inches from Wire to Shank of Pin. Colgate to Oakland "|"I7? IOO 1 3 Electra to San Francisco T C Canon Ferry to Bulte tine 600 M u Mi Shawinigan Falls to Montreal *l8l 7SO IOO lit Niagara Falls to Buffalo . . + 7CQ OOO 7O Niagara Falls to Buffalo *roO OOO ry I dO IO Chambly to Montreal j- j ? ? i QO QO si Colgate to Oakland *2II 6OO I ^ *Aluminum conductors. f Copper conductors. line the length of span is 140 feet, and each aluminum conductor of 500,000 circular mils is attached to its insulator 10 inches above the cross-arm. TABLE II. DIMENSIONS OF WOODEN PINS IN INCHES. Location of Lines. Length of Stem. Length of Shank. Diameter of Shank. Diameter of Shoulder. Diameter of Threaded End. Length of Threaded Part. Colgate to Oakland io| 5 2 i 2i i3 2 Electra to San Francisco . . . 12 41 2* 2! 1 1 2 Caiion Ferry to Butte I2i 5i 2 Z\ ii Shawinigan Falls to Montreal Niagara Falls to Buffalo* fl 1 2f 2 3 2^ I ii Niagara Falls to Buffalo "J" 71 6 2l 2 f ii 2* Chambly to IVlontrealt 7 c ii jl Canon Ferry to Butte Ml 7l 4 2* ij * Pins on old line, f Pins on new line. t Approximate dimensions. Pole top pins. To compensate for the greater strains introduced by doubling the length of span and using pins of longer stem, the diameter of the shank of the new pins was increased to two inches. One line between Colgate INSULATOR PINS. 273 and Oakland is of copper, and the other is of aluminum conductors, but the same pins appear to be used for each. On the line between Canon Ferry and Butte, Mont., the pin used in pole tops has a shank i\ inches longer and J-inch greater in diameter than the pin used in cross-arms. The weakest pin included in the table seems to be that in use on the line between Chambly and Montreal, which is of hickory wood, about ij inches in diameter at the shank, and carries its No. oo copper wire 8J inches above the cross-arm. The following dimensions for standard wooden insulator pins to be used on all transmission lines are proposed in vol. xxi., page 235, of the Transactions of the American Institute of Electrical Engineers. These pins are designed to resist a uniform pull at the smaller end and at right angles to the axis in each case. The length of each pin, in inches be- tween the shoulder and the threaded end, is represented by L, and the diameter of each pin at its shank by D. L. i D. o 87 L. D. I 82 2 10 IO i 88 26 J J 7Q I 3 I -95 r. . CQ TC 217 I....:::.:: . C.Q 17 2 25 7- - 67 10 **!) 2 3d *:: 75 21. . * -o^t . 2.42 The two strongest pins in Table II. appear to be those in use on the line between Shawinigan Falls and Montreal and on the line from Niag- ara Falls to Buffalo. The former have a diameter of 2} inches at the shank, and the wire is carried 16} inches above the shoulder of the pin. On the new Niagara line the shank diameter of each pin is only 2} inches, but the line wire is only 10 inches above the shoulder. It was found by tests that a strain of 2,100 pounds at the top of the insulator and at right angles to the axis of this Niagara pin was necessary to break it at the shank. This strain is about six times as great as the calculated maxi- mum strain that will occur in service on the line. Some of the pins here noted are much stronger than those proposed in the above specifications for standard pins. The pins on the old Niag- ara line have a shank diameter of 2 inches, with a stem only 5^ inches long, while the proposed pin of 2 inches diameter at the shank has a stem 1 1 inches long. On the Colgate and Oakland line a shank diameter of 2$ inches goes with a length of lof inches in the stem, but the pro- posed pin with this size of shank has a stem 13 inches long. For a shank 274 ELECTRIC TRANSMISSION OF WATER-POWER. ^ of 2j inches diameter the proposed pin has a stem 15 inches long, but the pins with this diameter of shank on the Electra line are only 12 inches long in the stem. The 2j-inch diameter of shank in the pins on the new Niagara line goes with a length of only 7! inches in the stem. The new Niagara pin is thus almost exactly twice as strong as the proposed pin, since the strength of a pin where the shank joins the stem varies inversely as the length of the stem, all other factors being the same. Pins on the Shawinigan Falls line have a shank 2} inches in diameter, with a length of 13 J inches in the stem; but the largest of the proposed pins, that with a stem 19 inches long, has a diameter of only 2^ inches in the shank. It is hardly too much to say in the interest of good engineering that the wooden pin of about 5 inches length of stem and ij inches diameter of shank, as well as all longer pins of no greater strength, should be dis- carded for long transmission lines of high voltage. These pins have done good service on telegraph and telephone lines, and on local lighting cir- cuits of No. 6 B. & S. gauge wire or smaller, and they may well be left for such work. To meet the conditions of transmission work a change in both the shape and size of pins is necessary. In the first place, the shoulder on pins where the shank and stem meet, that relic of telegraph practice, should be entirely discarded. This change will save considerable lumber on pins of a given diameter at the shank, and will increase the strength of the pin by avoiding the sharp corner at the junction of the shank and stem. Another change of design should leave an excess of strength in the stem of the pin, to provide for deterioration of the wood, and particularly for charring by current breakage. This increase of diameter and strength near the top of the pin will cost nothing in lumber, for the wood is necessarily there unless it is turned off. The shank of each pin should be proportionately shorter than in the older type, and the pin hole should be bored only part way through the cross-arm. A saving in lumber for pins and for cross-arms will thus be made, since the size of the cross-arm may be less for a given resistance to splitting. With these changes in general design the pin is a simple cylinder in the shank, with a gentle taper from the shank to form the stem. An example of this design, which might well serve as a basis for a line of standard pins, would be a pin 2 inches in diameter and 3 J inches long in the shank, and tapering for a length of 5 inches from the shank to form 18 INSULATOR PINS. 275 the stem, with a diameter of i^ inches at the top. The hole in a cross- arm for this pin should be 3^ inches deep, and this, in an arm 4} inches deep, would leave i J inches of wood below the pin. From the lower end of the pin hole, a hole J-inch in diameter should run to the bottom of the cross-arm to drain off water. A line of longer pins designed to resist the same line pull as this short one would be strong enough for small conductors, say up to No. i B. & S. gauge wire. For larger wires, long spans and sharp angles in a line, a pin 2j inches in diameter and 4^ inches long in the shank, tapering for 5 inches to a diameter of if inches at the top, or longer pins of equal strength, should be used. Where the pin holes do not extend through the cross-arm there is no need of a shoulder on the pin to sustain the weight of the line wire. In the cross-arm on the new Niagara Falls line each pin hole is bored to a depth of 5 inches, leaving i inch of wood below the hole. On the line from Electra to San Francisco the depth of each pin hole is again 5 inches, and the depth of the cross-arm 6 inches. The pins for use on the Electra line were kept for several hours in a vat of linseed oil at a temperature of 210 F. The pins for the Shawini- gan line were boiled in stearic acid. All wooden pins should be treated chemically, but the object of this treatment should be to prevent decay rather than to give them any particular insulating value. The lack of strength in wooden pins and their destruction in some cases by current leakage are leading to the use of iron and steel pins. Such a pin, in use on the lines of the Washington Power Company, of Spokane, Wash., is made up of a mild steel bar 17^ inches long and ij inches in diameter, cast into a shank at one end, so that the total length is 18 inches. The cast-iron shank has a diameter of 2^ inches, with a shoulder of 2^ inches diameter at its upper end. To prevent the pin from lifting out of its hole a small screw enters the top of the cross-arm and bears on the top end of the shank. Above the cast-iron shank the length of the steel rod is 1 2 inches, and starting J inch down from its top a portion of the rod J inch long is turned to a diameter of one inch. It is said that this pin begins to bend with a pull of 1,000 pounds at its top, but that it will support the insulator safely even when badly bent. Insulators may resist puncture and prevent surface arcing from wire to pin, but still allow a large though silent flow of energy over the pins and cross-arms between the conductors of a transmission circuit. The rate at which current flows from one wire of a transmission circuit to 276 ELECTRIC TRANSMISSION OF WATER-POWER. another in this way depends on the total resistance of each path over insulator surfaces and through air to the pins and cross-arm, and then over these parts. If the pins and cross-arm are entirely of iron, the total resistance of the path through them from wire to wire is practically that of the insulator surfaces. If the pins and cross-arm are of wood which is dry, they may offer an appreciable part of the total resistance of the path through them between the wires of a circuit ; but if the wood be wet, its resistance is very much reduced. The resistance of wooden pins and cross-arm may be so small com- pared with that of the air and insulator surfaces that complete the path through them from wire to wire of a circuit, that the effect of these wooden parts in checking the flow of current between conductors is relatively unimportant, and yet the resistances of these pins and the cross-arm may affect their lasting qualities. The current that flows over the pins and cross-arms from one wire to another of a high-tension circuit may be so small as not to injure these wooden parts when evenly distributed over them, and yet this same cur- rent may char or burn the wood if confined to a narrow path. Such a leakage current will naturally cease to be evenly distributed over pins and their cross-arms when certain portions of their surfaces are of much lower resistance than others, because an electric current divides and fol- lows several possible paths in the inverse ratio of their resistances. These narrow paths of relatively low resistance along wooden pins and cross-arms are heated and charred by the very current that they attract, so that the conductivity of the path and the heat developed therein react mutually to increase each other, and tend toward the de- struction of the wood. Among causes that tend to make some parts of pins and cross-arms better conductors than others, there may be mentioned cracks in the wood, where dirt and moisture collect, dust, with a mixture of salt de- posited on the wood by the winds at certain places, and sea fogs that are often blown only against one side of the pins and arms and deposit salt. To make matters worse, the same cause that creates a path of rela- tively good conductivity along wooden pins and cross-arms often materi- ally lowers the resistance offered to the leakage of current by the insulator surfaces. Thus an increase of the rate at which energy passes from wire to wire of a circuit, and the concentration of this energy in certain parts of the wooden path, are sometimes brought about at the same time. Where the line insulators employed are so designed that the re- INSULATOR PINS. 277 sistance of the dry wooden pins and cross-arms forms a material part of the total resistance between the wires of a circuit, a rain or heavy fog may cause a very large increase in the rate at which energy passes over these wooden parts between the conductors. As long as only moderate voltages were carried on line conductors, the charring and burning of their pins and cross-arms was a very unusual matter; but with the application of very high pressures on long circuits the destruction of these wooden parts by the heat of leakage currents has become a serious menace to transmission systems. Even with low volt- ages there may be charring and burning of pins and cross-arms if the line insulators are very poor or if the conditions as to weather and flying dust are sufficiently severe. In vol. xx. of the Transactions of the American Institute of Electrical Engineers, pages 435 to 442 and 471 to 479, an account of the charring and burning of pins on several transmission lines is given, from which some of the following examples are taken. In one case a line that ran near a certain chemical factory was said to be much troubled by the burning of its pins, though the voltage em- ployed was only 440, and the insulators were designed for circuits of 10,000 volts. In rainy weather, when insulators, pins, and cross-arms were washed clear of the chemical deposits, there was no pin burning. Similar trouble has been met with on sections of the 4o,ooo-volt Provo line, in Utah, where dust, mixed with salt, is deposited on the insulators, pins, and cross-arms. On page 708 a 2,000- volt line is mentioned on which fog, dust, and rain caused much burning of pins. . When circuits are operated at voltages of 40,000 to 60,000, no very severe climatic conditions are necessary to develop serious trouble in the wooden pins by leakage currents, even where the transmission lines are supported in insulators of the largest and best types yet developed. Striking examples along this line may be seen in the transmission systems between Colgate and Oakland, Cal., and between Electra and San Fran- cisco. Both of these systems were designed to transmit energy at 60,000 volts, but the actual pressure of operation seems to have been limited to about 40,000 volts during much of their period of service. Insulators of a single type and size are used on both of these transmis- sion lines, and are among the largest ever put into service on long cir- cuits. Each of these insulators is n inches in diameter, and nj inches high from the lower edge to the top, the line wire being carried in a central top groove. The wooden pins used on the two lines vary a little in size, so that on the Electra line each pin stands nj inches above its 278 ELECTRIC TRANSMISSION OF WATER-POWER. cross-arm, while on the Colgate line the corresponding distance is 12 inches. As the insulators are of the same size in each case, the length of the pin between the lower edge of each insulator and the top of the cross-arm is 4 inches on the Colgate line and 3 finches on the Electra line. On the latter line a porcelain sleeve, entirely separate from and mak- ing no contact with the insulator, covers each pin from the top of its cross-arm to a point above the lower edge of the insulator. On the Col- gate line each insulator makes contact with its pin for a length of 2^ inches down from the top of its thread, and on the Electra line the contact of each insulator with its pin runs down 3^ inches below the top of the thread. This leaves 9 inches in the length of the pin between the insula- tor contact and the top of each cross-arm on the Colgate line, and a cor- responding length of pin amounting to 8 J inches on the Electra line. Of this 8.i inches of pin surface, about 6 inches is covered by the porcelain insulating sleeve used on each pin of the Electra line, so that only about 2\ inches of the length of each pin on that line is exposed to the leakage of current from the insulator directly through the air. Both the sizes of pins just mentioned were made of eucalyptus wood, boiled in linseed oil. Each one of three pins taken from a pole, between North Tomer and Cordelia, on the Colgate line, was badly charred and burned on its side that faced the damp ocean winds. This charring extended all the way down each pin from the point where the insulator made con- tact with it, a little under the threads, to the top of the cross-arm nine inches below. Two of these pins were located at the opposite ends of a cross-arm, and the third was fixed in the top of the pole. This cross-arm was charred or burnt, as well as the pin, but no defects could be detected in the insulators that the pins supported. As to these three pins, the most reasonable explanation seems to be that enough current leaked over both the outside and inside surfaces of each insulator and through the air to char the pin and cross-arm. In flowing down each pin, the current was naturally concentrated on the side exposed to the damp winds of the ocean, because the deposit of moisture by these winds lowered the resistance on that side. When these winds were not blowing, and before a pin became charred on one side, its resistance was probably about the same all the way around, and the leakage current, being distributed over the pin, was not sufficient to char it. The damp wind would, of course, lower the surface resistance of each insulator, and this, with the deposit of moisture on the pins and cross-arm, many have made a very material reduction in the total resist- ance from wire to wire. INSULATOR PINS. 279 The insulators used on these pins each had two petticoats, an upper one, ii inches in diameter, and a lower one, 6J inches in diameter, the lower edge of the smaller petticoat being yi inches beneath the lower outside edge of the larger petticoat. As the inner surface of the larger petticoat was much nearer to a horizontal plane than the inner surface of the smaller petticoat, moisture would have been more readily retained on it, and the greater part of the surface resistance of the insulator during wet weather must therefore have been on the inside of the smaller petti- coat. At its lower edge the smaller petticoat was distant radially about if inches from the pin, and the distance between the pin and the inside surface of the smaller petticoat gradually decreased to actual contact at a point 5^ inches above this lower edge. The path of the current from the line wire to the pin in this case seems to have been first over the entire insulator surface to the lower edge of the smaller petticoat and then partly up over the inner surface of this petticoat and partly from that surface through the air. On each of these three pins the charring was quite as bad just below the thread as it was further down, so that a large part of the leakage current seems to have gone up over the interior surface of the smaller petticoat. The charred portion of these pins extended but little, if at all, into the threads near the tops or into the part of the pin fitting into the cross-arm. The pres- ervation of the part of each pin that entered the cross-arm seems to have been due to the increase of surface and decrease of resistance of the cross-arm in comparison with the pin. Preservation of the threaded part of each pin seems to have been due to its protection from moisture and its high resistance, so that little or no current passed over it. Another pin taken from the same line as the three just considered was badly burned at a point about 1.75 inches below the threads, but on sawing it completely across at two points below the charred spot the entire sec- tion was found to be perfectly sound and free from any sign of burning. The explanation of the condition of this pin is, perhaps, that the resist- ance of the burned part, owing to its additional protection and dryness, was high compared with that of the lower part of the pin, and thus de- veloped most of the heat on the passage of current. It is not clear, how- ever, why this pin should burn only just below the thread, while other pins of the same kind on the same line were charred all the way down from the thread to the cross-arm. Another curious result noticed in some pins on this same line is the softening of the threads so that they can be rubbed off with the fingers. 280 ELECTRIC TRANSMISSION OF WATER-POWER. RELATION OF PINS AND INSULATORS. Location of Line. Voltage of Line. Diameter of Insulator. 21 |9 O> tn Length of Pin Covered by Insulator. Electra to San Francisco . . . 60 ooo Inches. Inches. Inches. 12 Colgate to Oakland. 60 ooo 1 1 ill 8 Canon Ferry to Butte . . . ^o ooo 12 Shawinigan Falls to Montreal . . "50,000 10 I 3 lof Santa Ana River to Los Angeles Provo around Utah Lake 33,000 40 ooo 7 Spier Falls to Schenectady 10 ooo uj rl Niagara Falls to Buffalo. 22 OOO 7* 7" The softened wood of the threads is not charred, but is said to have a sour taste and to resemble digested wood pulp. While the threads of a wooden pin are destroyed in this way the remainder of the pin may still remain perfect and show no charring. RELATIONS OF PINS AND INSULATORS. Location of Line. Length of Pin Between Insulator and Cross-arm. Distance from Outer Pettitoat to Pin Through Air. Distance from Lowest Pet- ticoat to Pin Through Air. Electra to San Francisco Inches, o Inches. iol Inches. 3i Colgate to Oakland si IO i Canon Ferry to Butte i* o i Shawinigan Falls to Montreal 31 91 Santa Ana River to Los Angeles Provo around Utah Lake . . . 3i 1 2 J "2\ Spier Falls to Schenectady .... . 4 i Niagara Falls to Buffalo J A\ 2 In explanation of this disintegration of the threads of wooden pins it was stated that a number of these pins, the tops of which were reduced to a white powder, had been taken from the line between Niagara Falls and Buffalo, on which the voltage is 22,000, and that this powder proved on analysis to be a nitrate salt. This salt was thought to be the result of the action of nitric acid on the wood, it being supposed that the acid was formed by a static discharge acting on the oxygen and nitrogen of INSULATOR PINS. 281 the air between the threads of the insulator and pin. In support of this view it was stated that an experimental line of galvanized-iron wire at Niagara Falls, which was operated at 75,000 volts continuously during nearly four months, turned black over its entire length of about two miles. This surface disintegration was not due to the normal action of the air, for similar wire at the same place remained bright when not used as an electrical conductor. These facts seemed to indicate that the brush discharge from the wires carrying the 7 5,000- volt current developed nitric acid from the oxygen and nitrogen of the air, and that this acid attacked the wire. One of the above-mentioned pins used on the Electra line was much charred and burned away at a point a little below the threads. The charred path of the current could also be traced down the side of the pin to the cross-arm, but this path was not as badly burned as the spot near the top of the pin. A composite pin from a 3 3,000- volt line, probably a part of the trans- mission system between the Santa Ana River and Los Angeles, was burned through its wooden threads to the central iron bolt, along a nar- row strip at one side. Every pin burned on this line was said to show the effects of the current in the way just described, but no cross-arms were burned and very few insulators punctured. The composite pin was made up of a central iron bolt 19! inches long, J-inch in diameter, and with a thin head above the wooden threads, a sleeve of wood 2f inches long and i inch in diameter in its threaded portion, and a sleeve of porcelain 3^ inches long and i J inches in diam- eter at its upper and 2yi inches at its lower end. The sleeves of wood and porcelain were slipped over the central iron bolt so that the portions of the pin above the cross-arm measured 5! inches. In this case the path of the leakage current seems to have been over both the exterior and interior surface of the insulator and then through the wooden sleeve to the central bolt and the cross-arm. The facts just outlined certainly indicate a serious menace to the per- manence and reliability of long, high-voltage transmission lines sup- ported by insulators on wooden pins. If such results have been encoun- tered on the lines above named, where some of the largest and best designs of insulators are employed, it is only fair to assume that similar destructive effects of leakage currents are taking place on many other lines that operate at high voltages. It seems at least doubtful whether any enlargement or improvement of the insulators themselves will entirely avoid the destruction of their 282 ELECTRIC TRANSMISSION OF WATER-POWER. wooden pins in one of the ways mentioned. It is probable, but not cer- tain, that further extension of distances through air and over insulator surfaces, both exterior and interior, between line wires and wooden pins, will prevent charring and burning of the latter by leakage currents. Much has already been done in the way of covering most of the pin above its cross-arm with the insulator parts, but even those por- tions of the pin that are best protected in this way are not free from burning. Thus, on the Colgate line, eight inches of each pin is protected by the interior surface of its insulator, but these pins were charred quite as badly where best protected, up close to the thread, as they were down near the cross-arm. The same is true of the Electra line, where a porce- lain sleeve runs up about the pin from the cross-arm to a point above the inner petticoat of each insulator, so that the entire length of the pin above the cross-arm is protected. On the Canon Ferry line, a glass sleeve that virtually forms a part of each insulator, though mechanically separate from it, protects the pin from its threaded portion to within 1.5 inches of the cross-arm. Insulators on the line from Shawinigan Falls to Montreal are each 13 inches long and extend down over the pin to within 1.5 inches of the cross-arm. The burned portion of each pin from the Santa Ana line was that carrying the threads, and thus in actual contact with that part of the insulator which was separated by the greatest surface distance from the line wire. Aside from the burning of pins is the destruction of their threaded parts by some chemical agency that is developed inside of the tops of the insulators, as shown in the cases of the Colgate and Niagara lines. It does not appear that any improvement of insulators will necessarily prevent chemical action. Though it may not be practicable to so increase the surface resistance of each insulator that the burning of wooden pins by leakage current will be prevented, the substitution of a conducting for an insulating pin may remedy the trouble. As the insulators, pins, and cross-arm form a path for the leakage current from wire to wire, the wooden pins by their re- sistance, especially when dry, must develop heat. In pins of steel or iron this heat would be trifling and would do no damage. With pins of good conducting material, like iron, the amount of leakage from wire to wire, with a given design of insulator, would, no doubt, be somewhat greater than the leakage with wooden pins. It will be cheaper, however, to increase the resistance of new insulators INSULATOR PINS. 283 up to the combined resistance of present insulators and their wooden pins than it will be to replace these pins when they are burned. From all the evidence at hand, it seems that insulators which reduce the leakage of current over their surfaces to permissible limits as far as mere loss of energy is concerned, even with iron pins, will not prevent the charring and destruction of wooden pins. When any suitable insulator is dry and clean it offers all necessary FIG. 90. Glass Insulator and Sleeve on 5o,ooo-volt Line Between Caflon Ferry and Butte, Mont, resistance to the leakage of current over its surface, and any resistance in the pin that carries the insulator is of small importance. If the resist- ance of an insulator needs to be reinforced by that of its pin in any case, it is when the surface of the insulator is wet or dirty. Unfortunately, however, the same weather conditions that deposit dirt or moisture on an insulator make similar deposits on its pin, and the resistance of the pin is lowered much more than that of the insulator by such deposits. The increase of current leakage over the surface of an insulator during rains and fogs usually does no damage to the insulator itself, but such leakage over the wet pin soon develops a surface layer of carbon that continues to act as a good conductor after the moisture that temporarily 284 ELECTRIC TRANSMISSION OF WATER-POWER.. lowered the resistance has gone. Reasons like these have led some engi- neers to prefer iron pins with insulators that offer all of the resistance necessary for the voltage employed on the line. It may be suggested that the use of iron pins will transfer the charring and burning to the wooden cross-arms, but this does not seem to be a necessary result. The comparative freedom of cross-arms from charring and burning where wooden pins are used seems to be due to the larger surface and lower resistance of the cross-arms. With iron pins having a shank of small diameter, so that the area of contact surface between the pin and the wooden cross-arm is relatively small, there may be some charring of the wood at this contact surface. Should it be thought de- sirable to guard against any trouble of this sort, the surface of the iron pin in contact with the cross-arm may be made ample by the use of large washers, or by giving each pin a greater diameter at the shank than elsewhere. It may be noted that the pins with a central iron bolt only half an inch in diameter, that were used on the 3 3,000- volt Santa Ana line, were said to have caused no burning of their cross-arms in those cases in which the wooden threads about the top of the central bolt were burned through. Another possible trouble with iron pins is that they, by their greater rate of expansion than glass or porcelain, will break their insulators. Such results can readily be avoided by cementing each iron pin into its insulator, instead of screwing the insulator onto the pin. Iron pins will, no doubt, cost somewhat more than those of wood, but this cost will in any event be only a small percentage of the total investment in a transmission line. Considering the cost of the renewals of wooden pins, there seems little doubt that on a line where the voltage and other conditions are such as to result in frequent burning, iron pins would be cheaper in the end. Iron pins have already been adopted on a number of high-voltage lines. Not only iron pins, but even iron cross-arms and iron poles are in use on a number of transmission lines. On a long line now under construction in Mexico, iron towers, placed as much as 400 feet apart, are used instead of wooden poles, and both the pins and cross-arms are also of iron. The 75-mile line from Niagara Falls to Toranto is carried entirely on steel towers. The Vancouver Power Company, Vancouver, British Columbia, use a pin that consists of a steel bolt about 1 2 inches long fitted with a sleeve of cast iron 4^ inches long to enter the cross-arm, and a lead thread to screw into the insulator. On the 1 1 i-mile line of the Washington Power INSULATOR PINS. Company, of Spokane, which was designed to operate at 60,000 volts and runs to the Standard and Hecla mines, a pin consisting of a steel bar i J inches in diameter, with a cast-iron shank 2yV inches in diameter to enter the cross-arm, and with the lead threads for the insulator, is used. On the network of transmission lines between Spier Falls, Schenec- tady, Albany, and Troy, in the State of New York, the insulators are supported on iron pins of two types. One of these pins, used at corners and where the strain on the wire line is exceptionally heavy, is made up FIG. 92 Iron Pins on Spier Falls Line. of a wrought-iron bolt j-inch in diameter and i6j inches long over the head, and of a malleable iron casting 8} inches long. This casting has a flange of 5 by 3! inches at its lower end that rests on the top of the cross- arm, and the bolt passes from the top of the casting down through it and the cross-arm. Threads are cut on the lower end of the bolt, and a nut and washer secure it in the cross-arm. The total height of this pin above the cross-arm is gj inches. For straight work on this line a pin with stem entirely of malleable iron, and a bolt that comes up through the cross-arm and enters the base of the casting, is used. The cast top of this pin has four vertical webs, 286 ELECTRIC TRANSMISSION OF WATER-POWER. and its rectangular base, which rests on the top of the cross-arm, is 3 J by 4 inches. The bolt that comes up through the cross-arm and taps into the base of the casting is {-inch in diameter. The cast part of this pin has such a length that the top of its insulator is carried lof inches above the cross-arm. For the casting the length is gj inches. Both of the types of iron pins in use on the Spier Falls lines are se- cured to their insulators with Portland cement poured into the pin hole while liquid when the insulator is upside down and the pin is held cen- FIG. 93 Standard Pin, Toronto and Niagara Line. trally in its hole. The top of each casting is smaller in diameter than the hole in the insulator, and is grooved so as to hold the cement. On a long line designed for 60,000 volts, and recently completed in California, wooden pins are used with porcelain insulators, each 14 inches in diameter and 1 2^ inches high. Each of these pins is entirely covered with sheet zinc from the cross-arm to the threaded end, and it is expected that this metal covering will protect the wood of the pin from injury by the leakage current. CHAPTER XXI. INSULATORS FOR TRANSMISSION LINES. LINE insulators, pins, and cross-arms all go to make up paths of more or less conductivity between the wires of a transmission circuit. The amount of current flowing along these paths from one conductor to another in any case will depend on the combined resistance of the insulators, pins, and cross-arm at each pole. As a general rule, the wires of high-voltage transmission circuits are used bare because continuous coverings would add materially to the cost with only a trifling increase in effective insulation against high volt- ages. In some instances the wires of high-pressure transmission lines have individual coverings for short distances where they enter cities, but often this is not the case. At Manchester, N. H., bare conductors from water-power plants enter the sub-station, well within the city limits, at 12,000 volts. From the water-power at Chambly the bare 25,000- volt circuits, after crossing the St. Lawrence River over the great Victoria bridge, pass overhead to a terminal-house near the water-front in Mont- real. In order to reach the General Electric Works, the 30,ooo-volt circuits from Spier Falls enter the city limits of Schenectady, N. Y., with bare overhead conductors. Where transmission lines pass over a territory exposed to corrosive gases, it is sometimes desirable to give each wire a weather-proof cover- ing. An instance of this sort occurs near Niagara Falls where the aluminum conductors forming one of the circuits to Buffalo are covered with a braid that is saturated with asphaltum for some distance. Each path, formed by the surface of the insulators of a line and the pins and cross-arm by which they are supported, not only wastes the energy represented by the leakage current passing over it, but may lead to the charring and burning of the pins and cross-arm by this current. To prevent such burning, the main reliance is to be placed in the surface resistance of the insulators rather than that of pins and cross- arms. These insulators should be made of glass or porcelain, and should be used dry that is, without oil. In some of the early trans- mission lines, insulators were used on which the lower edges were 287 288 ELECTRIC TRANSMISSION OF WATER-POWER. turned inward and upward so that a circular trough was formed beneath the body of the insulator, and this trough was filled with heavy petroleum. It was found, however, that this trough of oil served to collect dirt and thus tended to lower the insulation between wire and cross-arm, so that the practice was soon abandoned. Glass and porcelain insulators are rivals for use on high-tension lines, and each has advantages of its own. Porcelain insulators are much stronger mechanically than are those of glass, and are not liable to crack because of unequal internal expansion, a result sometimes met with where glass insulators are exposed to a hot morning sun. In favor of glass insulators it may be said that their insulating properties are quite uniform, and that, unlike porcelain, their internal defects are often apparent on inspection. In order to avoid internal defects in large porcelain insula- tors, it has been found necessary to manufacture some designs in several parts and then cement the parts of each insulator together. Defective insulators may be divided into two classes those that the line voltage will puncture and break and those that permit an excessive amount of current to pass over their surfaces to the pins and cross-arms. Where an insulator is punctured and broken, the pin, cross-arm, ami pole to which it is attached are liable to be burned up. If the leakage of current over the surface of an insulator is large, not only may the loss of energy on the line where the insulator is used be serious, but this energy follows the pins and cross-arm in its path from wire to wire, and gradually chars the former, or both, so that they are ultimately set on fire or break through lack of mechanical strength. The discharge over the surface of an insulator may be so large in amount as to have a dis- ruptive character, and thus to be readily visible. More frequently this surface leakage of current over insulators is of the invisible and silent sort that nevertheless may be sufficient in amount to char, weaken, and even ultimately set fire to pins and cross-arms. All insulators, whether made of glass or porcelain, should be tested electrically to determine their ability to resist puncture, and to hold back the surface leakage of current, before they are put into practical use on high-tension lines. Experience has shown that inspection alone cannot be depended on to detect defective glass insulators. Electrical testing of insu- lators serves well to determine the voltage to which they may be subjected in practical service with little danger of puncture by the disruptive passage of current through their substance. It is also possible to determine the voltage that will cause a disruptive discharge of current over the surface of an insulator, when the outer part of this surface is either wet or dry. INSULATORS FOR TRANSMISSION LINES. 289 This is as far as electrical tests are usually carried, but it seems desirable that such tests should also determine the amount of silent, invisible leak- age over the surface of insulators both when they are wet and when they are dry, at the voltage which their circuits are intended to carry. Such a test of silent leakage is important because this sort of leakage chars and weakens insulator pins, and sets fire to them and cross-arms, be- sides representing a waste of energy. The voltage employed to test insulators should vary in amount according to the purpose for which any particular test is made. Glass and porcelain, like many other solid insulators, will withstand a voltage during a few minutes that will cause a puncture if continued indefinitely. In this respect these insulators are unlike air, which allows a disruptive discharge at once when the voltage to which it is exposed reaches an amount that the air cannot permanently withstand. Because of this property of glass and porcelain insulators, it is necessary in making a puncture test to employ a voltage much higher than that to which they are to be permanently exposed. In good practice it is thought desirable to test insulators for puncture with at least twice the voltage of the cir- cuits which they will be required to permanently support on transmis- sion lines. For the first transmission line from Niagara Falls to Buffalo, which was designed to operate at 11,000 volts, the porcelain insulators were tested for puncture with a voltage of 40,000, or nearly four times that of the circuits they were to support. Porcelain insulators for the second line between Niagara Falls and Buffalo, after the voltage of transmission had been raised to 22,000, were given a puncture test at 60,000 volts. Of these insulators tested at 60,000 volts only about three per cent proved to be defective. These puncture tests were carried out by placing each insulator upside down in an open pan containing salt water to a depth of two inches, partly filling the pin hole of the insulator with salt water, and then connecting one terminal of the testing circuit with a rod of metal in the pin hole, and the other terminal with the pan. Alternating current was employed in these tests, as is usually the case (Volume xviii., Transactions A. I. E. E., pp. 514 to 520). For the transmission lines between Spier Falls, Schenectady, Albany, and Troy, where the voltage is 30,000, the insu- lators were required to withstand a puncturing test with 75,000 volts for a period of five minutes after they had been soaked in water for twenty-four hours. There is some difference of opinion as to the proper duration of a 2 9 o ELECTRIC TRANSMISSION OF WATER-POWER. puncturing test, the practice in some cases being to continue the test for only one minute on each insulator, while in other cases the time runs up to five minutes or more. As a rule, the higher the testing voltage compared with that under which the insulators will be regularly used, the shorter should be the period of test. Instead of being tested in salt water as above described, an insulator may be screwed onto an iron pin of a size that fits its threads, and then one side of the testing circuit put in contact with the pin and the other side connected with the wire groove of the insulator. Care should be taken where an iron pin is used either in testing or for regular line work, that the pin is not screwed hard up against the top of the insulator, as this tends to crack off the top, espe- cially when the pin and insulator are raised in temperature. Iron ex- pands at a much higher rate than glass or porcelain, and it is desirable to cement iron pins into insulators rather than to screw them in. There seems to be some reason to think that an insulator will puncture more readily when it is exposed to severe mechanical stress by the expansion of the iron pin on which it is mounted. Tests of insulators are usually made with alternating current, and the form of the voltage curve is important, especially where the test is made to determine what voltage will arc over the surface of the insulator from the line wire to the pin. The square root of the mean square for two curves of alternating voltage or mean effective voltage, as read by a voltmeter, may be the same though the maximum voltages of the two curves differ widely. In tests for the puncture of insulators, the average alternating voltage applied is more important than the maximum volt- age shown by the highest points of the pressure curve, because of the influence of the time element with glass and porcelain. On the other hand, when the test is to determine the voltage at which current will arc over the insulator surface from the line wire to the pin, the maximum value of the pressure curve should be taken into consideration because air has no time element, but permits a disruptive discharge under a merely instantaneous voltage. Alternators used in transmission systems usually conform approx- imately to a sine curve in the instantaneous values of the pressures they develop, and it is therefore desirable that tests on line insulators be made with voltages whose values follow the sine curve. Either a single trans- former or several transformers in series may be employed to step up to the required voltage, but a single transformer will usually give better regulation and greater accuracy. An air-gap between needle points is not a very satisfactory means by which to determine the average voltage INSULATORS FOR TRANSMISSION LINES. 291 on a testing circuit, because, as already pointed out, the sparking dis- tance between the needle points depends mainly on the maximum instan- taneous values of the voltage, which may vary with the load on the generator, and the saturation of its magnets. For accurate results a step-down voltmeter transformer should be used on the testing circuit. An insulator that resists a puncture test may fail badly when sub- jected to a test as to the voltage that will arc over its surface from line wire to pin. This arc-over test should be made with the outer surface of the insulator both wet and dry. For the purpose of this test the insulator should be screwed onto an iron pin, or onto a wooden pin that has been covered with tinfoil. One wire of the testing circuit should then be secured in the groove of the insulator, and the other wire should be connected to the iron or tin foil of the pin. The voltage that will arc over the surface of an insulator from the line wire to the pin depends on the conditions of that surface and of the air. In light air, such as is found at great elevations, an arc will jump a greater distance than in dry air near the sea-level. A fog in- creases the distance that a given voltage will jump between a line wire and its insulator pip, and a heavy rain lengthens the distance still further. The heavier the downpour of rain the greater is the distance over the outside surface of an insulator that a given voltage will arc over. The angle at which the falling water strikes the insulator surface also has an influence on the voltage required to arc over that surface, a deviation from a downpour perpendicular to the plane of the lower edge of the petticoat of the insulator seeming to increase the arcing distance for a given voltage. An insulator should be given an arc-over test under conditions that are approximately the most severe to be met in practice. These condi- tions can perhaps be fairly represented by a downpour of water that amounts to a depth of one inch in five minutes for each square inch of the plane included by the edge of the largest petticoat of the insulator, when the direction of the falling water makes an angle of forty-five de- grees with that plane. A precipitation of one inch in depth on a horizontal plane during five minutes seems to be a little greater than any recorded by the United States Weather Bureau. Under the severe conditions just named, the voltage required to arc over the insulator surface from line wire to pin should be somewhat greater at least than the normal voltage of the circuit where the insulator is to be used. For the trans- mission line between Spier Falls and Schenectady, on which the maxi- mum voltage is 30,000, the insulators were required to stand a test of 292 ELECTRIC TRANSMISSION OF WATER-POWER. 42,000 volts when wet, without arcing over from line wire to pin. In these wet tests the water should be sprayed evenly onto the insulator surface like rain, and the quantity of water that strikes the insulator in a given time should be measured. When the outside of an insulator is wet with rain, it is evident that most of the resistance between the line wire and the insulator pin must be offered by the inside surface of the petticoat of the insulator. For this reason an insulator that is to withstand a very high voltage so that no arc will be formed over its wet outside surface must have a wide, dry surface under its petticoat. In some tests of line insulators reported in Volume xxi., Transactions A. I. E. E., p. 314, the results show that the voltage required to arc over from line wire to pin depends on the shortest dis- tance between them, rather than on the distance over the insulator sur- face. Three insulators, numbered 4, 5, and 7 in the trial, were in each case tested by a gradual increase of voltage until a discharge took place between the wire and pin. The pins were coated with tinfoil, and the testing voltage was applied to the tie wire on each insulator and to the tinfoil of its pin. Insulators 4, 5, and 7 permitted arcs from wire to pin when exposed to 73,800, 74,700, and 74,700 volts respectively, the sur- faces of all being dry and clean. The shortest distances between wires and pins over insulator surface and through air were 6f, 6J, and 7$ inches respectively for the three insulators, so that the arcing voltages amounted to 11,140, 11,952, and 9,479 per inch of these distances. Measured along their surfaces, the distances between wires and pins on these three insulators were 8, nj, and 15 J inches respectively, so that the three arcing voltages, which were nearly equal, amounted to 9,225, 6,640, and 4,819 per inch of these distances. These figures make it plain that the arcing voltage for each insulator depends on the shortest distance over its surface and through the air, from wire to pin. It might be expected that the voltage in any case would arc equal distances over clean, dry insulator surface or through the air, and the experiments just named indicate that this view is approximately correct. The spark- ing distance through air between needle points, which is greater than that between smooth surfaces, is 5.85 inches with 70,000 volts, and 7.1 inches with 80,000 volts according to the report in Volume xix., A. I. E. E., p. 721. Comparing these distances with the shortest distances between wires and pins in the tests of insulators numbered 4, 5, and 7, which broke down at 73, 800 to 74,700 volts when dry, it seems that a given voltage will arc somewhat further over clean, dry insulator surface than it will through air. This view finds support from the fact that only INSULATORS FOR TRANSMISSION LINES. 293 a part of each of the shortest distances between wire and pin was over insulator surface, the remainder being through air alone. The fact that the dry part of the surface of an insulator and the air between its lower wet edge and the pin or cross-arm offer most of the resistance between the line wire and the pin and cross-arm is plainly brought out by the results of the tests above mentioned, in the cases of insulators numbered 4 and 7. While 73,800 volts were required to arc from line-wire to pin when the entire insulator was dry and clean, the arc was formed at only 53,400 volts during a moderate rain-storm, in the case of No. 4 insulator. With insulator No. 7 the arcing voltage was 74,700 when the entire surface was clean and dry, but the arc from wire to pin was started at 52,800 volts during a moderate rain. No. 5 insulator seems to present an erratic result, for when dry and clean the arc jumped from wire to pin at 74,700 volts, and yet during a moderate rain no arc was formed until a voltage of 70,400 was reached. For each of the seven insulators on which tests are reported as above, the voltage required to arc from line wire to pin was nearly or quite as great during a dry snow-storm as when the insulator surface was clean and dry. When the insulators were covered with wet snow their surface insulation broke down at voltages that were within ten per cent above or below the arcing voltages during a moderate rain in five cases. With two insulators the arcing voltages, when they were covered with wet snow, were only about sixty per cent of the voltages necessary to break down the surface insulation between wire and pin during a moderate rain. When the outside surface of an insulator is wet, as during a moderate rain, it seems that the under surface of the insulator, and the distance through air from the lower wet edge of the insulator to the pin or cross- arm, make up most of the insulation that prevents arcing over from the wire to the pin or cross-arm. It further appears that it is useless to extend the distance across the dry under surface of the insulator indefi- nitely without a corresponding increase of the direct distance through air from the lower wet edge of the insulator to the wood of cross-arm or pin. Insulator No. 7 in the tests under consideration had a diameter at the lower edge of its outer petticoat of seven inches, and was mounted on a standard wooden pin. The diameter of this pin in the plane of the lower edge of the insulator was probably about ij inches, so that the radial distance through air from this edge to the pin must have been 2j inches approximately. During a moderate rain the surface insulation of this insulator broke down and an arc was formed from wire to pin with 52,800 volts. The sparking distance between needle points at 50,000 volts is 294 ELECTRIC TRANSMISSION OF WATER-POWER. 3.55 inches, according to Volume xix., A. I. E. E., p. 721, and must be shorter between smooth surfaces, such as the wire and pin in question, so that nearly all of the 52,800 volts in this case must have been required to jump the 2f inches of air, leaving very little to overcome the slight resistance of the wet outside surface of the insulator. On this insulator the surface distance from wire to pin was 15^ inches, while the shortest breaking distance was only yf inches, so that the distance across the dry under surface of the insulator must have been 15^ (yf 2f) = loj inches approximately. It is evidently futile to put a path ioj inches long across dry insulator surface in parallel with a path only 2f inches long in air, as an arc will certainly jump this shorter path long before one will be formed over the longer. The same line of reasoning applies to No. 3 insulator in this test, which had a diameter of 6} inches, a surface distance from wire to pin of 13 inches, and a minimum distance of yj inches, and whose surface insulation broke down at 48,600 volts during a moderate rain. The necessity of increasing the distance between the INSULATORS ON TRANSMISSION LINES. Location of Line. Voltage of Line. Material of Insulator. Inches Diameter of Insulator. Inches Height of Insulator. Electra to San Francisco 60,000 60,000 50,000 50,000 40,000 33,000 30,000 25,000 25,000 22,000 I3,OOO I2,OOO Porcelain Porcelain Glass Porcelain Glass Porcelain Porcelain Glass Porcelain Porcelain Porcelain Glass II II 9 10 I* 8j ij 51 5 i nl 12 i3j 5J 41 61 ii l\ 4^ 1 Colgate to Oakland Canon Ferry to Butte Shawinigan Falls to ^Montreal . . Provo around Utah Lake . Santa Ana River to Los Angeles. . . . Spier Falls to Schenectady Apple River Falls to St Paul Charnbly to Montreal Niagara Falls to Buffalo Portsmouth to Pelham, N. H Garvins Falls to Manchester, N. H. lower wet edges of insulators and the pins and cross-arm, as well as the distance across the dry under surfaces of insulators, led to the adoption of the so-called umbrella type for some high-voltage lines. In this type of insulator the main or outer petticoat is given a relatively great diam- eter, and instead of being bell-shaped is only moderately concave on its under side. With an insulator of this type mounted on a large, long pin, the lower edge of the umbrella-like petticoat may be far removed from the pin and cross-arm. Beneath the large petticoat of such insulators for high voltages there are usually one or more smaller petticoats or INSULATORS FOR TRANSMISSION LINES. 295 sleeves that run down the pin, and increase the distance between it and the lower edge of the largest petticoat. The inner petticoat or sleeve that runs down over the pin and some- times reaches nearly to the cross-arm, of course becomes wet on its outside surface and at its lower edge during a rain; but between this lower wet part of the inner petticoat, or sleeve, and the lower wet edge of the larger outside petticoat, there is a wide, dry strip of insulator sur- face. A result is that an arc over the surface of the outside petticoat can reach the wet edge of the sleeve only by crossing the strip of dry under surface or jumping through the air. The same type of insulator is used on the 6o,ooo-volt lines between Electra and San Francisco and between Colgate and Oakland, each insulator having an outer petticoat 1 1 inches in diameter and one inner petticoat or sleeve 6 J inches in diameter. This inner petticoat runs down the pin for a distance of 7^ inches below the outer petticoat. Slightly INSULATORS ON TRANSMISSION LINES. Location of Line. Inches from Top of In- sulator to Cross-arm. Inches from Outside Petticoat to Cross-arm. Inches from Lowest Petticoat to Cross-arm. c^o> 1 C 3 M-*- 1 ^J ^ O _O O -^ Electra to San Francisco He* Hdi-tiiiidaoKfci HM Tt 10 rO\O 00 O O 00 II Pj 7\ 7i 5i 1 si 4 1 4i 3 2 8i 3f 2 $ Colgate to Oakland . Canon Ferry to Butte . . Shawinigan Falls to Montreal . . Santa Ana River to Los Angeles. . . Spier Falls to Schenectady Niagara Falls to Buffalo Chambly to ^Montreal On each of the lines named in this table the wires are strung on the tops of their insulators. different pins are used for mounting the insulators on the two transmis- sion lines just named, so that on the former the distance through air from the lower edge of the outer petticoat to the cross-arm is 1 1 inches, and on the latter the corresponding distance is 1 1 \ inches. On the Elec- tra line the lower edge of the inner petticoat of each insulator is about 3i inches, and on the Colgate line about 4 inches above the cross-arm. The Canon Ferry line is carried on insulators each of which has three short petticoats and a long separate sleeve that runs down over the pin to within i inches of the cross-arm. This sleeve makes contact with its insulator near the pin hole. The outside petticoat of each insulator 296 ELECTRIC TRANSMISSION OF WATER-POWER. on this line is 7} inches above the cross-arm and 6J inches above the lower end of the sleeve. Both the main insulator and the sleeve, in this case, are of glass. White porcelain insulators are used to support the 5o,ooo-volt Sha- winigan line, and are of a recent design. Each of these insulators has three petticoats ranged about a central stem so that their lower edges are 4^ inches, 9 inches, and 13 inches respectively, below the top. The highest petticoat is 10 inches, the intermediate 9! inches, and the lowest 4j inches in diameter. The height of this insulator is 13 inches, com- pared with ii J inches for those used on the Electra and Colgate lines and 12 inches for the combined insulator and sleeve used on the Canon Ferry line. When mounted on its pin, this insulator on the Shawinigan line holds its wire i6j inches above the cross-arm, compared with a cor- responding distance of 14^ inches on the Electra, 15 inches on the Col- gate, and 13 J inches on the Canon Ferry line. The two upper petticoats on each of these insulators are much less concave than the lowest one, and the edges of all three stand respectively nj, 7}, and 3^ inches above the cross-arm. From the edge of the top to the edge of the bottom petticoat the direct distance is 8J inches. Of the three transmission lines above named that operate at 50,000 to 60,000 volts, that between Shawinigan Falls and Montreal leads as to distances between the line wire and insulator petticoats and the cross-arm. On the Santa Ana line, where the voltage is 33,000, the insulator is of a more ordinary type, being of porcelain, 6J inches in diameter, 4^ inches high, and having the lower edges of its three petti- coats in the same plane. Each of these insulators holds its wire 8f inches above the cross-arm, and has all of its petticoats 3^ inches above the cross-arm. Unlike the three insulators just described, which are mounted on wooden pins, this Santa Ana insulator has a pin with an iron core, wooden threads, and porcelain base. This base extends up from the cross-arm a distance of 3 \ inches, and the wooden -sleeve, in which the threads for the insulator are cut, runs down over the central bolt of the pin to the top of the porcelain base, which is f-inch below the petticoats. The 30,000- volt lines from Spier Falls are carried 10} inches above their cross-arms by triple petticoat porcelain insulators. Each of these insulators is 8J inches in diameter, 6f inches high, and is built up of three parts cemented together. A malleable-iron pin cemented into each insulator with pure Portland cement carries the outside petticoat 7^ inches and its lowest petticoat 4^ inches above the cross-arm. When INSULATORS FOR TRANSMISSION LINES. 297 the voltage on the Spier Falls lines was raised from about 13,000 to 30,000, the circuits being carried in part by one-piece porcelain in- sulators, a number of these insulators were punctured at the higher pressures, and some cross-arms and poles were burned as a result. No failures resulted on those parts of these lines where the three-part insula- tors were in use. The second pole line between Niagara Falls and FIG. 93A. The Old and New Insulators on the Niagara Falls-Buffalo Line, Buffalo was designed to carry circuits at 22,000 volts, or twice that for which the first line was built. Porcelain insulators were employed on both of these lines, but while the n,ooo-volt line was carried on three- petticoat insulators, each with a diameter of 7 inches and a height of 5^ inches, the 2 2,000- volt line was mounted on insulators each 7^ inches in diameter and 7 inches high, with only two petticoats. The older insula- tor has its petticoats 2 inches above the cross-arm, and the lower petti- coat of the new insulator is 3 inches above the arm. These two insulators illustrate the tendency to lengthen out along the insulator axis as the voltage of the circuits to be carried increases. For future work at still higher voltages, the advantage as to both first cost and insulating qualities seems to lie with insulators that are very long in an axial direction, and which have their petticoats arranged one below the other and all of about the same diameter, rather than with insulators of the umbrella type, like those on the Electra and Colgate lines. CHAPTER XXII. DESIGN OF INSULATOR PINS FOR TRANSMISSION LINES. BENDING strains due to the weights, degree of tension, and the direc- tions of line wires, plus those resulting from wind-pressure, are the chief causes that lead to the mechanical failure of insulator pins. Considering the unbalanced component of these forces at right angles to the axis of the pin, which alone produce bending, each pin may be considered as a beam of circular cross section secured at one end and loaded at the other. For this purpose the secured end of the beam is to be taken as the point where the pin enters its cross-arm, and the loaded end of the beam is the point where the line wire is attached to the insulator. The dis- tance between these two points is the length of the beam. The maxi- mum strain in the outside fibres of a pin measured in pounds per square inch of its cross section, represented by S, may be found from the for- mula, PX " .0982 D 3 where P is the pull of the wire in pounds, D is the diameter of the pin at any point, and X is the distance in inches of that point from the wire. Inspection of this formula shows that S, the maximum strain at any point in the fibres of a pin, when the pull of the line-wire, P, is constant, in- creases directly with the distance, X, from the wire to the point where the strain, S, takes place. This strain, S, with a constant pull of the line wire, decreases as the cube of the diameter, D, at the point on the pin where S occurs increases. That cross section of a pin just at the top of its hole in the cross-arm is thus subject to the greatest strain, if the pin is of uniform diameter, because this cross section is more distant from the line wire than any other that is exposed to the bending strain. For this reason it is not necessary to give a pin a uniform diametei above its cross-arm, and in practice it is always tapered toward its top. Notwithstanding this taper, the weakest point in pins as usually made is just at the top of the cross-arm, and it is at this cross section where pins usually break. This break comes just below the shoulder that is 2Q8 DESIGN OF INSULATOR PINS. 299 turned on each pin to prevent its slipping down through the hole in its cross-arm. If the shoulder on a pin made a tight fit all around down onto the cross-arm, the strength of the pin to resist bending would be thereby increased, but it is hard to be sure of making such fits, and they should not be relied on to increase the strength of pins. By giving a pin a suitable taper from its shoulder at the cross-arm to" its top, the strain per square inch, S, in the outside fibres of the pin may be made constant for every cross section throughout its length above the cross- arm, whatever that length may be. The formula above given may be used to determine the diameters of a pin at various cross sections that will make the maximum stress, S, at each of these cross sections con- stant. By transposition the formula becomes P D 3 = - z- X. .0982 S Where the pin is tapered so that S is constant for all cross sections, then p for any pull, P, of the line wire on the pin the quantity ( - - j m ust be constant at every diameter, D, distant any number of inches, X, ( P \ from the point where the wire is attached. If the constant, ( - } ^.0982 S/ is found for any one cross section of a pin, therefore, the diameter at each other cross section with the same maximum stress, S, may be readily found by substituting the value of this constant in the formula. The so-called "standard'' wooden pin that has been very generally used for ordinary distribution lines, and to some extent even on high-voltage transmission lines, has a diameter of nearly 1.5 inches just below the shoulder. The distance of the line wire above this shoulder varies be- tween about 4.5 and 6 inches, according to the type of insulator used, and to whether the wire is tied at the side or top of the insulator. If the line wire is tied to the insulator 5 inches above the shoulder of one of the standard pins, then X becomes 5, and D becomes 1.5 in the formula last given. From that formula by transposition and substitution P D 3 (i-5) 3 p Substituting 0.675 for tne quantity - - in the formula D 3 = 0.0982 S - X gives the formula D 3 = 0.675 X, from which the diame- 0.0982 b ters at all cross sections of a tapered pin above its shoulder, that will 300 ELECTRIC TRANSMISSION OF WATER-POWER. give it a strength just -equal to that of a section of 1.5 inches diameter and 5 inches from the line wire, may be found. To use the formula for this purpose it is only necessary to substitute any desired values of X therein and then solve in each case for the corresponding values of D. Let it be required, for instance, to determine what diameter a pin should have at a cross section one inch below the line wire in order that the maximum strain at that cross section may equal the corresponding strain at a cross section five inches below the line wire and of i .5 inch diameter. Substituting one as the value of X, the last-named formula becomes D 3 = 0.675, an d from this, D = 0.877, which shows that the diameter of the pin one inch below the line w r ire should be 0.87 7-inch. A similar calculation will show that if a pin is long enough so that a cross section above the cross-arm is 1 2 inches below the line wire, the diameter of this cross section should be equal to the cube root of 0.675 * 1 2 8 - I > which is 2.008, or practically two inches. It should be observed that the calcu- lations just made have nothing to do with the ability of a pin to resist any particular pull of its line wire. These calculations simply show what diame'ters a pin should have at different distances below its line wire in order that the maximum stress at each of its cross sections may equal that at a cross section 5 inches below the wire where the diameter is 1.5 inches. In Vol. xx., A. I. E. E., pp. 415 to 419, specifications are proposed for standard insulator pins based on calculations like those just made. As a result of such calculations, the following table for the corresponding values of X and D, as used in the above formula, are there presented, each expressed in inches. X D X D X D X D i 0.877 -INCH SLEET, 100 MILES WIND. Span, feet. Degrees and Minutes. 0.30 1.30 2.30 3-30 4-30 5.30 o.. 100.. 200.. 700.. 800.. 900.. 1,000.. o 256 512 768 1,024 1,280 1,536 1,792 2,048 35 291 i,o59 69 1,093 1,349 2,117 2.373 2,629 104 360 616 872 1,128 1,640 1,896 2,152 2,408 2,664 050 906 1,162 1,418 1,674 173 $ 94i i,i97 i,453 1,709 1,965 2,221 2,477 2,733 207 463 719 975 i,743 i,999 2,255 2,511 2,767 242 498 754 1,010 1,266 1,522 2^034 2.290 2,546 2,802 $ 1,044 1,812 2,068 2,324 2,580 2,836 3 11 823 1,079 A-7 2,103 2-359 2.615 2,871 345 601 857 1,113 i,369 1,625 i|88i 2,137 2,393 2,649 2,905 1,916 2,172 2,428 2 ;68 4 2,940 926 1,182 1,438 1,694 i,95o 2,206 2,462 2,718 2,974 The copper cables were so strung as to have a minimum distance from the ground of 25 feet at the lowest points of the spans. In order to do this the standard steel towers that hold the lower cables 40 feet above the ground level at the insulators are spaced at varying distances apart, according to the nature of the ground between them. At each tower the upper cable of each circuit is 5 feet 3 inches higher than the two lower cables, and this distance between the eleva- tions of the upper and the lower cables is maintained whatever the STEEL TOWERS. 325 amount of sag at the centre of each span. If there is a depression be- tween two standard towers on a straight portion of the line, the sag in the centre of a span 400 feet long may be as much as 18 feet. Where a rise and fall in the ground between towers make it necessary to limit the sag to 14 feet in order to keep the lowest cables 25 feet above the highest point of earth, the length of span is limited to 350 feet. If the rise and fall of ground level between towers allow a sag of only ii feet with the lowest cable 25 feet above the earth, the length of span with 40-foot towers is reduced to 300 feet ; and if for a like reason the sag is limited to 8 feet, the span may only be 250 feet. At each terminal tower, where the cables are secured before they pass into a terminal-station, the three insulators for each cable are in a FIG. 105. Take-up Arrangement on Terminal Tower. straight line with their centres, 30 inches apart. When a line cable reaches the first insulator of the three to which it is to be attached on one of ';hese towers, it is passed around the neck of this insulator and then secured on itself by means of two clamps that are tightened with bolts and nuts. See Fig. 105. The cable thus secured turns up and back over the tops of the three insulators and goes to the terminal-sta- tion. Around the neck of the insulator to which the line cable has been secured in the way just outlined a short detached length of the regular copper cable with the parts of a turnbuckle at each end is passed, and this same piece of cable also passes around the neck of the next insulator in the series of three. By joining the ends of the turnbuckle and tight- ening it, a part of the strain of the line cable in question is transferred from the first to the second insulator of the series. In the same way a part of the strain of this same line cable is transferred from the second insulator of the series to the third, or one nearest to the terminal-station. INDEX. AIR-BLAST cooled transformers, 129 Air-gap data, 183 Air gaps, number in series to stand given voltage, 183 Albany-Hudson Ry. Plant, 121 Alternating currents, 227 Alternator voltage, 118 Alternators, 103 data, 118 for high voltage, 120 inductor, 112 types of, in Aluminum as a conductor, 200, 209 cables in use, 213 conductor joints, 206 conductors, 27, 28 corrosion of, 211 properties of, 212 soldered joints, 206 vs. copper, 209 wire, cost of, 29 Amoskeag Mfg. Co. plant, 51, 52 Amsterdam (N. Y.) plant, 121 Anchor ice, 59 Anderson (S. C.) plant, 121 Apple River (Minn.) plant, i, 26, 27, 28, 71, 97, 98, 99, 102, 118, 119, 124, 126, 127, 134, 174, 187, 190, 192, 208, 245, 264, 294 Arc lighting, 167 Arcing, 46 Automatic regulators, 162 BARBED wire, 169, 175 Belt drive, 83, 107 Bienne plant (Switzerland), 42 Birchem Bend, 57, 67, 79, 95, 97, 98, 102 Blower capacity necessary to cool trans- formers, 130 Boosters, 133 Boston-Worcester Ry. plants, 121 Braces for cross-arms, 259 Bronze conductors, 200 Brush discharge, 281 Buchanan (Mich.) plant, 88 Building materials, 95 Bulls Bridge plant, 63 Burrard Inlet (B. C.) plant, in, 112 Bus-bars, 142, 147 dummy, 145 CABLE insulation, 195 sheaths, 194 ways, 140 Cables, aluminum, 212 aluminum, in use, 213 charging current, 197 cost of, 188, 196 for alternating current, 194 high-voltage, 191 paper insulated, 196 protection against electrolysis, 195 rubber-covered, 195 submarine, 192 temperature of, 198 voltage in, 190, 196 Canadian-Niagara Falls Power Co., 121 Canals, 51, 53 long, 68 Canon City plant, 26, 27, 28, 117, 118, 127, 208 Canon Ferry plant, i, 3, 26, 27, 28, 46, 49, 53, 62, 68, 69, 83, 89, 94, 95, 97, IO2, IO5, 112, 113, Il8, 119, 124, 125, 126, 127, 130, 132, 134, 174, 208, 233, 234, 245, 246, 249, 254, 257, 259, 268, 272, 280, 282, 294, 295, 302 Cedar Lake plant, 90 Chambly plant, 96, no, 149, 156, 172, 189, 249, 255, 256, 257, 267, 272, 287, 294, 295, 311, 312 Charging current for cable, 197 327 328 INDEX. Charring of pins, 276, 278 Chaudiere Falls plant, 118 Choke-coil used with lightning arresters, 180 Circuit breakers, 135, 150 breakers, time limit, 152 Circuits, selection of, 233 Coal, price of, in Salt Lake City, 8 Colgate plant, i, 3, 26, 27, 28, 74, 82, 83, 9> 94, 97, 9 8 > 99, IQ i> 102, 108, 112, 113, 118, 127, 130, 132, 134, 187, 190, 201, 206, 208, 213, 245, 246, 250, 254, 257, 272, 277, 280, 282, 294, 295, 304, 309 Columbus (Ga.) plant, 83, 115 Compounding, 160 Compressive strength of woods, 302 Conductivity of the conductor metals, 201 Conductors, 200 aluminum, 27, 28, 206 aluminum, properties of, 212 coefficients of expansion, 200 corrosion of, 211 cost of, 22, 29, 203, 204, 205 cost of aluminum, 29 cost of per k. w., 28 cost of copper, 29 data, 204 data from representative transmis- sion plants, 208 expansion of aluminum and copper, 211 melting points, 200 minimum size for transmission line, 202 properties of ideal, 200 relative conductivity, 201 relative cost of, 20 relative properties for equal lengths and resistances, 204 relative strengths for given area, 203 relative weight for given conductiv- ity, 202 relative weight of, 202 relative weights of three-phase, two- phase, and single-phase lines, 220 Conductors, resistance of, 225 skin effect, 206, 233 weight per k. w., 27 Conduits, 195 radiation loss in, 198 temperature rise in, 198 Constant current regulator, 167 transformer, 167 Control equipment for d. c. and a. c. plants, 35 Copper conductors, 200 cost of, 22 vs. aluminum, 209 wire, cost of, 29 Corrosion of conductors, 211 Cross-arm braces, 258 iron, 284 location of, 257 material, 258 Cross-arms, 49, 256 Crossings, 187 DALES plant (White River), 26, 27, 28, 71, 134, 208 Dams, 62 Delta connection, 131 Depreciation, u Design of power-plant, 83 Dike, 60 Direct connection, 84 Discharge, static, 170 Distribution system, 158 Draught tubes, 79 Dummy bus-bars, 145 EASTON (Pa.) plant, 121 Edison Co. (Los Angeles) plant, 118 Efficiency constant-current transmis- sion, 216 curves, motor-generator set, 117 of constant-voltage transmission, 217 of transformers, 133 relative, of a. c. and d. c. transmis- sion, 35 Electra plant, i, 3, 74, 82, 83, 92, 94, 97, 98, 101, 102, 108, 112, 113, 118, 127, 174, 206, 208, 212, 213, 233, 235, 236, INDEX. 329 245, 248, 253, 254, 256, 259, 272, 275, 277, 280, 281, 282, 294, 295 Electric power, market for, 7 Electrical Development Co., Niagara plant, 120 Electricity vs. gas, 6 Electrolysis, 195 Energy curves of hydro-electric stations, !3 electrical, cost of at switchboard, 23 Entrance end strain, 261, 325 insulating discs, 262 into buildings, 179 of lines, 179, 261, 265 through roof, 269 wall openings, 262 Entries for transmission lines, 261 Expansion, coefficient of, for copper and aluminum, 211 coefficients of, for various conduc- tor metals, 200 FARMINGTON RIVER (Conn.) plant, 26, 27, 28, 58, 118, 125, 134, 208, 212, 213, 245 Feeders, 143 Ferranti cables, 192 Fire-proofing, 95 Floor, distance from roof to, 95 location of, 79 space, 12, 101, 102 space per k. w. of generators, 12 Floors, 95 Fog, 46, 277 Fore-bay, 59, 60 Foundations, 95 Frequency, 113, 127 effect on transformer cost, 116 Fuel, price of, in Salt Lake City, 8 Fuses, 135, 150 GARVINS FALLS plant, 56, 60, 79, 80, 94, 96, 97, 102, 113, 145, 240, 294 Gas vs. electricity, 6 Gears, 84, 108 Generators (a. c.), 103 d. c. vs. a. c., 31 Generators, belt-driven, 107 capacity of, 32 compounding of, 160 cost of, 40 (a. c.) cost, 32 (a. c.) data, 118 direct-connnected to horizontal tur- bines, 89 to impulse wheels, 90 connection to vertical shafts, 84 (d. c.) field excitation of, 41 floor space, 101 per k. w., 12 gear-driven, 108 (a. c.) high -voltage, 120 (d. c.) in series, 31 (d. c.) installation of, 41 insulation of, 39, 45 lightning protection, 34 limiting voltage of, 44 (a. c.) limiting voltage of, 32 (d. c.) limiting voltage of, 31 overload capacity, 103 relation between voltage and capac- ity, 127 revolving armatures, 112 fields, 112 series-wound, 41 speed regulation, 38 Glass vs. porcelain insulators, 288 Great Falls plant, 54, 60, 61, 64, 67, 78, 92, 93, 102, 114, 118 Greggs Falls plant, 54, 56, 64, 240 Ground connections, 178 for guard wires, 171, 172 Grounded guard wires, 168 Guard wires, 168 installation of, 175 Guying of poles, 255 HAGNECK (Switzerland) plant, 86 Hooksett Falls plant, 56, 131 Hydro-electric plants, i built at the dam, 64-67 canals, long, 68-73 long and short, 58 short, 53-56 330 INDEX. Hydro-electric plants, capacity and weight of conductors per k. w. for various plants, 27 (800 k. w.) cost of, 10 (1500 k. w.) cost of, ii cost of labor, 12 cost of operation, 12, 77 design of, 83 floor, 79 space per k. w., 101 interest and depreciation, u linked together, 56-58 load factors, 14, 15 location of, 64 model design, 12 operation, 59 vs. steam plant, 5, 12 with pipe-lines, 73-77 with steam auxiliary, 84 ICE, 59 Impulse wheel speed, 108 wheels, 82, 90 location of, 99 Indian Orchard plant, 57, 84 Inductance, 206, 230 Induction, electro-magnetic, electro- static, 1 68 on lines, 206 regulator, 162 Inductor alternators, 112 Insulation, as affected by ozone, 197 cost of paper vs. rubber, 196 of a. c. and d. c. lines, 34 of apparatus, 142 of cables, 195 of electrical machines, 45 of generators, 39 protection against ozone, 198 Insulator arc -over test, 291 .-pins, 270 (see Pins) Insulators, 277, 282, 287, 322 and pins, data from various plants, 280 defective, 288 glass vs. porcelain, 288 in snow, 293 method of fastening to iron pins, 271 Insulators, novel clamp, 323 on various transmission Hnes, 294 petticoats, 294 testing of, 288 tests, 290 test voltage, 289 with oil, 287 Iron conductors, 200 KELLEY'S FALLS plant, 56 Kelvin's law, 219 LABOR, cost of, 12 in hydro-electric stations, 12 Leakage, 275, 287 line, 207, 214 Lewiston (Me.) plant, 118, 120, 122, 167, 213 Lighting, incandescent, minimum fre- quency, 116 series distribution, 167 Lightning arrester, effect of series re- sistance, 185 arresters, 168, 176 ground connection, 178 multiple air-gap, 176, 183 non-arcing metals in, 184 series connection of, 180 shunted air-gaps, 185 with choke coil, 180 protection, 34 Line calculations, 221-232 charging current, 197 conductors, 200 conductors, cost of, 22 weight of, 21 construction, 222 cost, 310 cross-arms, 49 spacing of wires, 46 (a. c.) transmission, 34 (d. c.) transmission, 33 end strain, 325 leakage, 47 loss, 39 losses due to grounded guard wires, 176 Lines, sag, 309 INDEX. Lines, transposition of, 314 Line voltages, 45 Load factors, 14, 15 lighting, 6 1 maximum, 60 motor, 1 60 railway, 164 Loss in conduits, 198 relation to weight of conductors, 215 Losses due to grounded guard wire, 176 on transmission lines, 215 Ludlow Mills plant, 26, 27, 28, 57, 79, 100, 121, 208^ 213 MADRID (N. M.) plant, 26, 27, 28, 118, 208 Manchester (N. H.) plants, 120 Market for electric power, 7 Materials, building, 95 for line-conductors, 200 Mechanicsville plant, 58, 67, 109, 121, 174 Melting points of conductor metals, 200 Montmorency Falls plant, 26, 27, 28, 240 Motor load, 160 Motor-generator set efficiency curve, 117 Motors, series- wound, 41 (d. c.) speed regulation, 38 synchronous, 241 Multiple air-gap arrester, 176 NEEDLE-POINT spark-gap for measuring pressure, 290 Neversink River plant, 75, 179 Niagara Falls Power Co., 3, 59, 81, 86, 8 7> 93> 94, 95> 97> IOI > I02 > IO 5> Io6 > 107, 108, 112, 113, 117, 118, 119, 127, J 33> *?>*l, MO, i43, !45> I 5 I > J 53> l6l > 165, 170, 181, 188, 194, 195, 208, 211, 240, 245, 246, 257, 272, 273, 275, 280, 287, 289, 294, 295, 297 Nitric acid from air, 281 Non-arcing metals, 184 North Gorham (Me.) plant, 120 Ogden (Utah) plant, 26, 27, 28, 118, 120, 132, 134, 208, 245 Ohm's law, 223 Oil switches, 136 Ontario Power Co., 121 Operating expenses, 59 Operation, cost of, 12, 77 Operations, reliability of, 311 Ouray (Col.) plant, 121 Overhead line connection to under- ground, 197 Overload capacity of generators, 103 Ozone, 197 PAINTING of poles, 255 Paper insulated cables, 196 vs. rubber insulation, 196 Payette River (Idaho) plant, 73, 101 Penstocks, 59, 98 Phase, 113 Pike's Peak plant, 77 Pilot wires, 161 Pins, 259, 270 and insulators, data from various plants, 280 burning of, 270, 276, 278 charring of, 276, 278 composite, 281 compressive strength of woods, 302 design of, 298 dimensions of, 301 formula for diameter of, 299 iron, 275, 285, 286 expansion of, 290 method of fastening insulators, 271 method of fastening to cross-arms, 271 metal, 271, 275, 282, 285, 286 of uniform strength, 300, 302 proportions, 301 relative cost of metal and wooden, 284 shank, 274 shoulder, 275, 299, 305 softening of threads, 280 steel, 275, 312 strain with $-inch sleet and 100- mile wind for different spans, 324 strains on, 270, 298 332 INDEX. Pins, strength of, 303 table of standard, 301 treatment of, 259, 275 weakest point, 298 wooden, data from various plants, 272 dimensions of, 272 dimensions of standard, 273 Pipe-lines, 73 Pittsfield (Mass.) plant, 121 Pole line, cost of, 21 lightning arresters, 179 relative cost of, 20 lines, 246 Poles, cost, 310 depth in ground, 254 diameter of, 254 dimensions of, 254 guying of, 255 iron, 284 length of, 253, 309 life of, 255 setting of, 252 spacing of, 249 steel, cost of, 307 treatment of, 255 woods for, 252 Porcelain vs. glass insulators, 288 Portland (Me.) plant, 120, 166, 239 Portsmouth, N. H. plant (steam), 102, 118, 119, 120, 121, 144, 194, 264, 294 Power plant, relative cost of a. c. and d. c., 36 transmitted, total cost of, 24 RADIATION loss in conduits, 198 Railway crossing, 187, 252 service, 164 Red Bridge plant, 53, 60, 79, 93, 94, 96, 97, 99, 101, 102 Regulation, 155, 239 as effected by synchronous motors, 165 at receiving end, 162 hand, 161 Regulator, automatic, 162 constant-current, 167 induction, 162 Relay-switches, 145 Resistance, 225 in series with lightning arrester, 185 Revolving armature alternators, 112 field alternator, 112 River crossings, 187, 190, 249 Roof, distance from floor, 95 Roofs, 95 Rope-drive, 83 Rotaries, cost of, 117 suitable frequency for, 115 Rubber-covered cables, 195 maximum temperature, 198 protection against ozone, 198 SAG in lines, 309 St. Hyacinthe (Que.) plant, 118 St. Joseph plant, 66 St. Maurice plant (Switzerland), 31 Salem (N. C.) plant, 121, 122 San Gabriel Canon plant, 26, 27, 28, 208 Santa Ana plant, i, 26, 27, 28, 74, 76, 82, 83, 92, 94, 95, 96, 97, 98, 99, 101, 102, 208, 245, 263, 280, 281, 294, 295, 296 Sault Ste. Marie plant, 72, 83, 85, 89, 97, 102, 104, 105, 112, 113, 117, 118, 120, 127 Scott system, 132 Series distribution, 167 machines, 41 Sewall's Falls plant, 26, 27, 28, 155 Shawinigan Falls plant, i, 70, 71, 107, 116, 117, 163, 164, 166, 209, 212, 213, 235, 236, 242, 245, 267, 272, 273, 280, 282, 294, 295, 296 Sheaths for cables, 194 Shunted air-gaps, 185 Skin effect, 206, 232 Snoqualmie Falls plant, 3, 4 map of transmission lines, 4 Snow, 293 Soldered joints, 206 Spacing of poles, 249 of wire, 234 Spans, long, 190, 250 strains for different lengths, 324 Sparking distances, 182 voltages, 182 INDEX. 333 Speed, peripheral, of impulse wheels, 108 peripheral of turbines, 85, 103 regulation, 38, 42 d. c. motors, 38 Spier Falls plant, i, 2, 3, 54, 58, 61, 62, 68, 91, 94, 98, 124, 126, 127, 130, 141, 142, 146, 161, 174, 236, 237, 243, 244, 245, 250, 253, 266, 280, 285, 287, 289, 291, 294, 295, 296, 312 Star connection, 131 Static discharges, 170 Steam and water-power station com- bined, 84 electric plant, cost of labor, 12 cost of operation, 12 floor area per k. w., 102 vs. water-power, 5 Steel towers, 306 Storage capacity, 15 Strains on insulation as affected by re- sistance in series with arrester, 185 Stray currents, protection against, 195 Submarine cables, 187, 192, 194 Sub-station, arrangement of apparatus, 128 Sub-stations, 157, 237 Surges, 136 Switchboard, 156 wiring, 146, 148, 149 Switches, 135, 244 arcing of, 135 electrically operated, 140 long break, 135 oil, 136 open-air, 136 pneumatically operated, 140 power operated, 138 relay, 145 Switch-houses, 141, 142, 2-38, 244 Switching, 146 high-tension, 147 Synchronous converters, 115 cost, 117 motors, 165, 241 TAIL-RACE, 96 Telephone, 161 Telluride plant, 47, 160, 169, 181 Temperature of cables, 198 rise in conduits, 198 Tensile strength of conductor metals, 201 Time-limit circuit-breaker, 152 Time relays, 152, 153 Towers, 250, 306 angle, 320 cost, 310 dimensions, 314 erection of, 316-319 heavy, 320 reliability of operation, 311 spans, 313 steel, cost, 307, 308 steel pins, 312 strain on, 324 Transformers, 122 air-blast vs. water-cooled, 129 artificially cooled, 129 at sub-stations, 125 blower capacity necessary to cool, 130 constant-current, 167 cooling, quantity of water neces- sary, 129 cost, 21, 116, 124, 134 cost of operation, 129 cost of, relative, 20 delta and star connections, 131 efficiency, 133 frequency, effect of, 116 insulation, 45 in transmission systems, 134 limiting voltage for, 32 location of, 97 polyphase, 124 regulation, 125 reserve, 149 secondary, in series, 131 single-phase, 124 two- to three-phase, 132 used to compensate drop, 133 used to regulate voltage, 162 voltages, 45 when to use, 122 Transmission, constant-current, 38, 216 constant-voltage, 40, 217 334 INDEX. Transmission, continuous-current, 31, 32 control equipment, 35 cost of, 19, 40, 222 (d. c.) cost of, 40 efficiency, 35, 41 first long line, 37 frequency, 113 generator end, 103 lightning protection, 34 limiting voltage, 44 lines, arcing, 46 calculation of, 221-232 charging current, 197 construction, 222 cost, 310 cross-arms, 49, 256 crossings, 187, 190 data from various plants, 245 effect of length on cost, 20 effect of length on cost of power, 24 efficiency, 22, 24 end strain at entries, 325 entrance to buildings, 179, 261 inductance, 206 induction, 168 insulation, 34 insulators (see Insulators), 287 insulator-pins (see Pins), 270 interest, maintenance and de- preciation, 22 leakage, 47, 207, 214 length of, capacity of, popula- tion supplied, 8 lightning arresters (see Light- ning Arresters), 179 lightning protection, 118 long spans, 190 loss, 22, 39 losses, 215 maximum investment in, 220 ; method of fastening conductors ... to insulators, 323 operation, 311 pole spacing, 249 regulation with synchronous motors, 241 Transmission lines, relative weights of three-phase, two-phase, and single-phase, 228 right-of-way, 246 sag in, 309 spacing of wire, 234 steel towers (see Towers), 306 switch-houses, 238 switches, fuses, and circuit- breakers, 135 take up, arrangement for, 3 2 5 total cost of, 22 total cost of operation, 23 transposition of wires, 206, 3i4 voltage, 21, 215 in cables, 190 regulation, 130 wind pressure, 210 long line, 221 minimum-sized wire, 202 physical limits of, 44 a. c. pole line construction, 34 d. c. pole line construction, 33 pole lines, 246 problems, 19 regulation, 155, 239 selection of circuits, 233 single vs. parallel circuits, 241 spacing of conductors, 46 submarine, 187 three-phase, 113 three-phase and two-phase, 228 ewo-phase, 113 underground, 187 ' without step-up transformers, 120 Transposition of wires, 206 Turbines, high-speed, 107 horizontal, 79, 83, 89, 97 impulse, 82, 90, 99 speed of, 108 low-head good speed, 105 peripheral, speed of, 85, 103 pressure, 79 several on same shaft, 85, 105 vertical, 79, 84, 85, 86, 97 INDEX. 335 UNDERGROUND cable connected to over- head line, 197 cables, 187 VICTOR (Colo.) plant, 26, 27, 28, 208 Virginia City plant, 118 Voltage drop compensation, 133 fluctuations, 218 high, alternators, 120 measurements, 290 in cables, 190, 196 limiting, 44 for a. c. machines, 32 for d. c. machines, 31 of transmission lines, 21, 215 regulation, 130, 155 sparking, 182 test for insulators, 289 Volts per mile, 26 WAGES paid attendants, 12 Walls, 95 Washington & Baltimore Ry., 121 Washouts, 8r Water-cooled transformers, 129 Water-power, development of, 51 high head, 74-77 low head, 51-74 per cent, of energy available, 16 pure hydraulic development, 51 stations (see Hydro-electric Sta- tions) storage capacity, 15, 6 1 utilization of, 10 vs. steam, 5 Water, storage of, 15, 61 Weight of the conductor metals, 202 Welland Canal plant, i, 26, 27, 28, 208, 245, 248 Westbrook (Me.) plant, 120 White River to Dales plant, 26, 27, 28, 7 J > 134 Wind, 324 pressure on lines, 210 Winooski River plant, 64 Wire room, 139 Wood, compressive strength of, 302 Woods for poles, 252 Yadkin River (N. C.) plant, 26, 27, 28, 118, 208 THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. , LD 21-100m-8,'34 YC