LONG DISTANCE TRANSMISSION OF t ENERGY BY ELECTRICITY. By W. M. Venable. A PAPER READ BEFORE THE ENGINEERS CLUB OF CINCINNATI, MAY 16, 1895. Electrical energy is usually transmitted over long distances for one of two purposes, namely : 1. To distribute light and power from a central station to scattered consumers ; and 2. To utilize natural power, otherwise unavailable, by send- ing its energy to some distant point where power or light is re- quired. Frequently both transmission and distribution are accom- plished by the same plant. In any particular case where transmission is to be undertaken the cost of equipping the generating station and the expenses of operating the plant are fixed, and are largely independent of the system of transmission used and of the distance over which the power is to be transmitted. On the other hand, the price which can be obtained for the power delivered to the consumer is fixed by competition with steam engines, water motors, gas engines, and other sources of power, while the price of light is also fixed by competition, or by the requirements of law. Thus between a l fixed cost of energy delivered to the line and a fixed price for it taken from the line, whether or not a transmission plant will pay becomes a question of the cost of the line and the losses on it. The cost of the line depends entirely on the electrical system used. An electric current flowing in a wire is often compared to a current of water flowing in a pipe ; with a pipe of fixed size, and a fixed amount of flow of water, the energy which is trans- mitted through the pipe is proportional to the pressure. The same is true of electrical currents. If a certain size of copper wire is used, and a certain fixed current is allowed to pass, the power transmitted is directly proportional to the pressure of elec- tricity. This is true without any assumption as to the real nature of electricity. Now, if we desire to transmit a greater amount of energy per second, we can do so by increasing either the current or the pressure. If we increase the current we will have to use a larger wire in order to carry the increased amount, but if we can increase the pressure with safety, a small wire Avill be sufficient. As cop- per is quite expensive, we wish to use as little of it as possible ; therefore it is of the greatest importance to determine the best working pressure for a transmission plant. But there are conditions which limit the pressure of elec- tricity, or voltage, at which we can operate electrical machinery, and it is entirely impracticable to deliver power to consumers at the high voltages desired for transmission, for the following reasons : 1 . Incandescent lamps do not operate successfully on voltages much above 125, and much lower voltages are prefer- able. 2. Wires brought within reach of the public must not be charged with more than 250 volts, for shocks received from currents at higher voltages than this might have serious consequences. 3. For power only, where machines are in charge of com- petent persons, 500 volts may be used successfully and safely. To successfully operate the various kinds of electrical appar- atus in general use, it is not only necessary to have a low voltage, but also a constant one. If there is 10 per cent, loss in power on a transmission line, the voltage at the receiving point will be 10 per cent, less than that at the generating station. At no load there is no loss, while at full load the loss may be large, the actual amount of it depending on the size and material of the conducting wires. If the pressure at the lamps when only one light is burn- ing is just what it should be, when many lamps are turned on, it will be too low to give the proper amount of light unless the loss is very small, or some method of compensating for it is employed. Trouble with incandescent lamps which do not furnish the proper amount of light is very common. It is usually caused by cheap wiring, and the line alone is to blame. A steady pressure is also very desirable in operating motors and most electrical apparatus. The expense of line construction at low voltages is so great that it is not profitable to transmit power over long distances at the voltage which is needed for distribution to the public. Where power only, and not light, is required, continuous cur- rent at 500 volts or more can be economically transmitted ; as in our street railway systems. Much more loss may be permitted on the line than in supplying lights. All of us have noticed how dimly the incandescent lamps in a street car near the heart of town burn at about six o’clock in the evening, while the cars still perform good service. The limit of economy is soon reached, however, and only the necessities of street car service make it profitable to use such long lines at such voltage. That the cost of copper for such lines may be appreciated, I give a few figures showing the cost of copper only, without insu- lation, poles, construction work, etc., to convey various amounts of power various distances at 500 volts pressure delivered to the motor, and 10 per cent, loss on the line, copper being worth 12 cents per pound. Cost of Copper. To transmit 10 h. p, 1 mile at 500 volts at motor $ 115 “ “ 10 “ 2 “ “ “ “ “ “ 460 10 “ 5 “ “ “ “ “ “ 2,875 “ “ 20 “ 1 “ “ “ “ “ “ 230 “ “ 20 “ 2 “ “ “ “ “ “ 920 “ “ 20 “ 5 " ■“ “ “ “ “ 5,750 With a loss greater than 10 per cent, the cost would be less ; to transmit 10 h. p. 5 miles with 5 h. p. loss on the line would take $217 worth of copper. Continuous current machines of much higher voltages are operated with success in special installations, where the proper care is taken of the commutators and the conditions of distribu- tion are such as to admit of their use. Several plants for trans- mitting power for use in mines have been installed in this coun- try, but the growing practice here has been to prefer alternating current machines. • In Europe, however, several plants operating at from 1,000 to 7,000 volts are in use and giving good satisfac- tion. Most prominent among the successful plants may be men- tioned one installed in Switzerland by M. Thury, of Geneva. The generating station is located at Frinvilliers, and transmits 400 horse-power to the paper mills at Biberst, a distance of 20 miles. It operates at about 6,600 volts on the line. There are two gen- erators and two motors connected in series, so that each machine has about 3,300 volts at its terminals. It must be said in regard to such plants, that while for special purposes they may be very serviceable, still they do not afford a ready means of distributing the energ}^ to a number of points, without the expense of rotating transformers, which require constant attention, and add a very great expense to the cost of the plant. A rotating transformer for continuous current machinery is practically a combination of a motor and a dynamo, connected together on the same shaft. The motor operates with the high pressure current, and turns the dynamo which supplies a current at low voltage for distribution. High tension continuous current machines are used also in arc lighting. The lines supplying current for arc lights often extend for many miles, embracing in one circuit from 50 to 125 arc lamps. At 50 volts per lamp this would make a voltage of 2,500 to 6,250 at the terminals of the dynamos. These circuits are in use in every town which is supplied with electric arc lights. The machines are adapted for arc lighting only, and are not used for general distribution of power. The wires pass through the most densely populated portions of the cities, and are the most dangerous of all circuits. It is worthy of remark also that the highest voltages are used in central stations situated near the hearts of towns, because the expense of real estate there makes it necessary to install as few machines as possible, in order to econo- mize space. There has in the past been much discussion on the relative advantages of alternating and continuous current machinery ; but it is now recognized that there are separate and wide fields for both. The advantages of continuous currents are these : 1. For a fixed maximum voltage or average voltage they require less copper for transmission than alternating currents. 2. They are readily applied to motors, belts, incandescent or arc lamps, and all other electrical devices. 3. Continuous current machines are cheaper and usually run at slower speed than alternating current machines. Their chief disadvantages are : 1. The use of a commutator, which is troublesome at large loads and at high voltages. 2. There is no simple and cheap way of efficiently altering the voltage ; therefore, the chief places where continuous — 6 — currents are used are in small lighting and power plants transmitting over very short distances at one voltage. Alternating currents possess these advantages : 1 . They are readily converted from one voltage to another. 2. They have no commutators, often no sliding contacts and no moving wires. On the other hand : 1. There is always a loss in the transformers, even when no power is being used. This loss amounts to about five per cent, of full load. 2. Machines are more expensive than those for continuous current. 3. Problems in self-induction and capacity, which affect both transmission and regulation very greatly, require the employment of first-class men to design and install the plant. Alternating currents are therefore used very generally in distributing light from central stations and in long-distance trans- mission of power. As already pointed out, it is necessary to use high voltages in transmission and low voltages in distribution. We can do this by means of alternating currents and stationary transformers. This is the system in most extensive use in electric lighting in cities and towns. Its chief disadvantage, as usually installed, is that motors can not conveniently be operated from the same mains as the lights. Within the last three years this disadvan- tage has been overcome in various ways, and it is now the best practice to install alternating current machinery for supplying both light, and power on the same system of distributing mains. An alternating current is one which flows first in one direc- tion and then in the other, in the same wire. In practice, alter- nating currents reverse their direction from 60 to 250 times in each second. The average voltage at the dynamo terminals is 1 - 7 — from 1,100 to 2,200. The current is carefully insulated, and con- veyed on moderate sized conductors to a point near the center of the district where the lights are required. Here it enters a sta- tionary transformer, which converts it into a large current at a voltage suitable for use in incandescent lamps. A stationary transformer consists of two coils of wire, one of many turns and one of few, wound around a laminated iron core and insulated from it and from each other. The high pressure current passes through the coil of many turns, while the low pressure current is taken from the coil of few turns. As there are no moving parts to these transformers, they require almost no attention after being once put in place, and on account of their simplicity they are not expensive. Being thus able to transmit at high pressure and to distribute from the transformer at any pressure which we may select, we are at liberty to use on the line as high a voltage as is consistent with safety and reliability. The difference in cost of copper for transmission at high and low voltages is easily shown. To trans- mit 20 h. p. 5 miles at 2,000 volts continuous current with 10 per cent loss, would take $350 worth of copper ; with the same mean voltage with alternating current would require $470 worth, while as stated before to transmit this power at 500 volts would require $5,750 worth. If 100 volts, such as is used in distribution, were used, the cost of copper would reach the enormous sum of $144,000. The chief difficulty in the use of alternating currents until within the last three years was in securing self-starting motors to , operate* on them. It used to be necessary to have the motor run- ning so as to synchronize with the alternations before it would work at all. One of the fundamental facts of electricity and magnetism is that a current flowing through a coil of wire which surrounds an iron core will magnetize that core. If the current is reversed in direction, the magnetism in the core will also be reversed in direc- tion ; but reversing the magnetism reacts on the current so as to force it to take an appreciable time to reverse. If the reversals are very rapid, very little current will be able to flow, and very little magnetism will be produced. This is practically what we have in the armature of an alternator when the current is turned on, and the motor is not running. If the armature is made to turn so rapidly that the alternations each occupy just the amount of time that it takes a coil of the armature to pass from one pole- piece of the field to another, the magnetism of the pole-pieces will overcome the weakening effect on the current due to the re- versals, and the motor will run. It is then said to be in phase. But if by any means we can produce a rotating magnetic pole, we will be able to construct a machine which will start itself. The principle upon which this is done is claimed by patents granted to Nicola Tesla, and owned by the Westinghouse Com- pany, although priority of invention is claimed by many others. If we have a coil of wire with a continuous current flowing in it, one face of the coil will be positively and the other negatively magnetized. Now, if we place a second coil at right angles to the first, and gradually start a current in the second coil, diminishing the current in tne first at the same time, the magnetism will ro- tate around the common axis of the coils until it becomes normal to the face of the second coil as the current in the first becomes zero. Let the current in the first be reversed, and that in the second diminished, and the magnetism will continue its rotation. Thus, by combining the magnetic effects of two alternating cur- rents of the same periodicity, but differing in phase, we obtain a rotating magnetic field. Surround this field by a ring of iron, and the iron will tend to rotate at the same speed as the mag- netism. There are now on the market at least three successful sys- tems of transmission, ahd three classes of generators which will accomplish all that may be required, and there -are efficient rotary field motors to operate on these systems. All three of them re- quire at least one more wire for power distribution than is neces- sary for light only, although they do not all require an additional actual weight of copper. The 2 -phase system is offered by the Westinghouse Electric and Manufacturing Company and by the Stanley Electric Manufacturing Company, and the 3-pMse and Monocyclic systems are the property of the General Electric Co. The 3-phase system is the most economical of all alternating current systems. It is especially adapted for very long distance transmission work, where motors of various sizes 'utilize the trans- mitted power. The monocyclic system is designed to meet those cases where it is desired to furnish power from a central station, which is already supplying light. Among 2-phase transmission plants may be cited one being installed by the Stanley Electric Co. at Quebec. The source of power is at Montmorency Falls, which have a head of over 300 feet. Three 675 h. p. 2-phase dynamos are to generate current at 5,500 volts. The current will be carried by four wires from each machine to a sub-station in Quebec, with 6 per cent, loss on the line. At Quebec it will be transformed to current at 2,000 volts for distribution on the lines already installed for supplying the city with light. The current will also be used for general power distribution and for street railway work. The largest power transmission plant ever projected is that at Niagara Falls, where the generators are to be of 5,000 h. p, each, and are to deliver current at 2,900 volts. Among 3-phase transmission plants may be mentioned one at Taftville, Conn., the power being transmitted 4 ^ miles from Baltic to. Taftville. There are two generators of about 330 h. p. each, delivering current at 2,500 volts to a line of bare copper wire mounted on oil insulators which are supported on wooden poles. The power is used in operating a street railway and a — 10 — large cotton mill. The efficiency at full load from the dynamo pulley to the motor pulley is said to be 80 per cent. At Sewall’s Falls, on the Merrimac River, there are six 330-h. p. generators supplying current to the city of Concord, about three miles dis- tant. The voltage is the same as at Taftville. Twelve miles from the city of Portland, Oregon, on the Wil- lamette River, are a series of broken falls, around which the State Government designed a canal for vessels. The Portland General Electric Co., having obtained control of this canal is installing a transmission plant with the proposed ultimate capacity of 12,000 h. p. Each dynamo has an output of 600 h. p., and is directly connected to a 60-inch and a 42-inch cylinder gate Victor turbine. Many instances of transmission plants operating over from 5 to 15 miles, and using natural water power, might be mentioned, but the cases cited will give a fair idea of what is being done in this direction. The great advantages possessed by stations which produce large amounts of electrical energy over those where only small amounts are produced will, doubtless, increase the distances over which power is sent from one generating station even where steam is used to generate electricity, for whatever is gained in economy of production may be lost in transmission without effect- ing the market price of the power. Large stations save in several ways, such as : 1 . Reduction in cost of plant per horse power (a) by using a few large machines instead of many small ones, and ( b ) by using the same poles, conduits, etc. for many 'wires. 2. Reduction in operating expenses (a) by greater economy in the use of coal, water, oil, waste, etc. ; (b) by saving in labor, superintendence, etc.; (c) by reducing the amount of repairing and depreciation on machinery. 3. Reduction in rent by economizing floor space occupied by plant. ♦ ft — 11 - In the transmission of power it is probable that within a few years distances of twenty or thirty miles will not present any formidable obstacles to the engineer, and that the whole question of power transmission will have become one simply of convenience and cost. With the increase of population greater care will be taken to use natural water-power and inaccessible fields of impure coal, which can be converted into electrical energy and sent to distant markets for consumption. The growth of rapid transit electric railroads througliQUt the country, joining town to town, will probably open up a vast field for long distance work. In extending the distances of electrical transmission the chief diffi- culty is in preserving proper insulation. Next to this in import- ance is overcoming the action of alternating currents on them- selves and on the line, causing peculiar losses of power which do not become serious in shorter distance work, or at lower voltages. Numerous perplexing problems have arisen in the development of long distance transmission, which have been satisfactorily solved as they arose, and there is scarcely any obstacle which can not now be overcome, provided the amount of power is large enough and the demand for it sufficient. Many conditions come into the consideration of each case ; and each problem should be solved on its own merits only, for the conditions governing one installation may not apply to another. Dr. Louis Bell, Avho has probably investigated more schemes for long distance power transmission than any other man in this country, in an interview in the Street Railway Journal for March, states that where cheap water-power of from ioo to 1,000 h. p. is available, it is practicable to transmit it over io to 15 miles at from 5,000 to 15,000 volts with almost a certainty of commercial success. In special climatic conditions, such as exist in some parts of Mexico, 30,000 to 50,000 volts might be .used, and in a few cases it would pay to transmit 30 to 50 miles. — 12 - 3 0112 072903690 Besides the usual text books on electricity very little has been published in collected form on long distance transmission. It is only within the last few years that long distance work has been carried out to commercial success. Prominent engineers have published in the electrical journals from time to time such information as they could without injury to the companies which employ them, while descriptions of plants in successful operation have formed a prominent feature of several publications. I feel myself indebted to the Electrical World for much information, both practical and theoretical, which has appeared in its columns during the past two years. Dr. Bell is now publishing in that journal a comprehensive series of articles which, when completed, will doubtless be the best book on Electrical Power Transmission yet given to the public, presenting the matter in a practical and scientific and yet not too technical a manner.