Popular Science Monthly/Volume 24/April 1884/The Electric Railway
|THE ELECTRIC RAILWAY.|
WITH most men who have not had time to follow the progress made of late in applying electricity to the practical work of the world, this form of energy is chiefly associated with certain experiments at school, by which the tedium of book-studying was enlivened with exhibitions of sparks and shocks and other curious and interesting phenomena, though it may be also connected in their minds with electric hair-brushes, electric corsets, magnetic clothing, etc. They regard it also as convenient for sending dispatches by telegraph, and in general for doing work where delicacy but not much force is requisite; but the idea seldom occurs to them that this versatile power is capable of swiftly moving the mightiest masses, as well as of operating the tiniest apparatus; of turning the wheels of ponderous machinery, as well as of vibrating thousands of times per second the little diaphragm of the telephone; of conveying to far-distant points the waste power of cataracts, as well as the minute forces liberated by the telegraphic key, and of illuminating, with the purest artificial light known, the most extensive and thickly populated cities.
Doubtless, one great cause of the skepticism with which many regard any project for using electricity upon a large scale is the fact that exhaustive experiments in this direction were made in the early part of the century, and the conclusion reached was that, though power and light could both be distributed by electricity, yet the expense would be so enormous as to render impracticable any extended electrical system.
It should not be forgotten, however, that the only great trouble found was the expense, and also that the principal source of this expense has been removed. In those days, the only way of generating an electric current was by the use of the voltaic battery, in which the electrical energy of the current was procured from the heat of the chemical combination going on in the battery; but in 1831 Faraday discovered a much cheaper way of generating electricity, when he found that it could be produced by simply moving magnets in the vicinity of coils of wire, or coils of wire in the vicinity of magnets. The significance of his discovery was so apparent that inventors began at once to devise means for generating currents upon an extended scale, by moving large magnets in the vicinity of large coils of wire by means of machinery; and this mechanical system has now been brought to such perfection that the cost of producing a horse-power of electrical energy can be as easily and almost as accurately calculated as the cost of producing a horse-power in a steam-engine or any other familiar apparatus.
In order to arrive at a clear comprehension of the present state of the art, it will be necessary to remember that any work which we perform must be performed by the expenditure of a certain and absolute amount of energy, and that we can not create this energy, but can only obtain it by changing the form of some other kind of energy. In the voltaic battery, as we have said, the electrical energy is obtained by transforming the heat of the chemical action going on in the cell into electrical energy, so that the amount of the latter that can be got out of any voltaic battery is limited by the amount of energy of the chemical combination. Now, the metal ordinarily used for furnishing chemical energy in a voltaic battery is zinc, and the heat of combination of zinc with oxygen is only about one sixth of that of coal, while its cost is more than twenty times as great; so that, to get the same amount of energy from zinc as from coal, would cost about one hundred and twenty times as much. Now, in the mechanical method of generating electricity, the electrical energy is produced by the mechanical means of moving large magnets near coils of wire; but the mechanical energy necessary to do this is obtained by the combustion of coal (i.e., the chemical combination of coal with oxygen).
It would be incorrect, however, to say that we can in this way produce electricity one hundred and twenty times as cheaply as by a battery, because there is an enormous loss in converting the heat of combustion of the coal into electricity, whereas the voltaic battery produces the electricity directly. The losses in converting the energy of the combustion of coal into mechanical energy are so prodigious that even a theoretically perfect engine could not get hold of more than from twenty to twenty-five per cent of the total energy in the coal, on account of the loss of the heat; so that, if an engine (a good one) has an efficiency of eighty per cent, it can not actually convert into work as much as twenty per cent of the total energy in the coal. The loss now in converting this mechanical energy into the electrical energy in the circuit where it is desired may be taken as about fifteen per cent, so that only about from fifteen to seventeen per cent of the total energy of the burning coal may be looked for in the electrical circuit. But, as the original cost of the coal is only 120 of that of the zinc furnishing an equal amount of energy, we see that the mechanical method of producing electricity is, roughly speaking, about twenty times as cheap as that of generating it by batteries.
The present way of generating large quantities of electricity requires, then, an engine and boiler for converting the chemical energy of burning coal into mechanical energy, and a device whereby this mechanical energy is made to move magnets in the vicinity of coils of wire or coils of wire in the vicinity of magnets, so as to convert the mechanical energy into electrical energy. Such a device is called an electric machine, or, ordinarily, a dynamo-electric machine; and this term is usually abbreviated into "dynamo."
A dynamo of a type in considerable use, and one of the earliest and best forms, is shown in Fig. 1. In this dynamo, coils of wire are wrapped about the long "armature" shown in the center, which is revolved between the poles of the large magnet (A) by a belt coming from a steam-engine, and going around the armature-pulley seen at
the rear. The approach to and recession from the poles of the different coils of wire of the armature generate a succession of currents which are collected by "brushes," and sent out into the circuit as a constant current.
But a most beautiful example of the truth of the theory of the conservation of energy is afforded by the fact that a dynamo will not only generate an electric current if it be revolved by mechanical means, but that it will itself revolve, if an electric current be sent through it from an exterior source; so that it not only can transform mechanical energy into electrical energy, but can also transform electrical into mechanical energy. "When used for this purpose it is called an "electro-motor," and sometimes an "electric engine."
Not only, however, is it necessary for an engine to be capable of doing a certain kind of work; it is also necessary for it to be capable of doing it economically, and it is for this reason that such a great future is prophesied for electric engines. For, while an excellent and elaborately constructed stationary steam-engine can produce but a small fraction of the energy it absorbs, a good electric engine (or electro-motor) will return seventy-five per cent of the electric energy given it by the generating dynamo. For the reason, however, that no economical means of generating large currents are yet discovered, except the method described of first burning coal, the use of electric machinery is at present restricted to certain industries. Now, one of these industries is believed to be railroading.
The opinion is generally held that railroad companies desire to obtain as large a return as possible upon their investment, and therefore to run their trains as cheaply as possible. If this be true, the value of an electric railway will become obvious, when one remembers that, of necessity, the present locomotive is wasteful in the extreme, and that in an electric railway a large and economical stationary engine renders its mechanical energy to a large and economical dynamo which sends an electric current to an economical motor on an electric locomotive. This motor is connected with the driving-wheels by gearing, belting, or other suitable devices, so that its revolution produces a revolution of the driving-wheels and a consequent progressive motion of the electric locomotive, in the same way that the engine of a steam-locomotive produces a rotary motion of the driving-wheels, and a consequent progressive motion of the steam-locomotive. There is a certain loss of electricity in passing from the dynamo to the motor on the locomotive, both from leakage and from overcoming the resistance of the conductors; but, for distances not too great, this loss, added to the losses in converting the mechanical energy of the stationary engine into electrical energy, and in reconverting this electrical energy back into mechanical energy by the motor, is not equal to the loss inseparable from even the best steam-locomotives.
It will be, of course, noticed that it is necessary constantly to maintain an electrical connection between the electro-motor on the locomotive and the stationary dynamo, in all positions of the locomotive. To accomplish this effectively, a number of systems have been invented. By one system the rails themselves act as conductors, the current going to the locomotive by one rail and returning by the other; while, in other systems, a third or auxiliary conductor is used. To collect the current and pass it through the motor, two strips of copper or brass in the circuit of the motor extend from the locomotive and press upon the conductors; so that, as the car advances, these keep up a scraping contact. Two wheels in circuit with the motor are also sometimes used as collectors.
The distinction of being the first to conceive and suggest the idea of an electric railway seems to belong to Dr. Werner Siemens, of the celebrated firm of Siemens & Halske, which has been more identified with the practical development of electrical science than any other firm in the world. In pursuance of his idea, Dr. Siemens constructed the first electrical railway at Berlin in 1879.
In this railway, whose length was about three hundred and fifty yards, and whose gauge was about three feet and three inches, a third or auxiliary conductor was used to convey the current from the dynamo to the motor. This conductor lay between and parallel to the other two rails, and the current was taken from it by a metal brush connected with the motor, which extended from the car and pressed upon the conductor. After going through the motor, the current went to both rails and by them back to the dynamo, the rails acting as the "return." The motor was placed upon a car, attached to which were three other cars, the first thus acting as the locomotive. Such was the interest excited by this novel system of transportation, and such its success, that it continued in operation for several months, and carried thousands of people, the money received for fares being contributed, it is said, to charitable institutions in the city.
The success of this experimental railway led the Messrs. Siemens to plan another upon a more extended scale; and they applied to the authorities for permission to build an elevated road in Berlin, six miles long, on which single cars, each fitted with an electro-motor, were to be run by means of electricity. Permission to do this was refused, on account of the inconvenience to the inhabitants which would result from the structure; but, ultimately, leave was given the same firm to build a surface electric railway from Lichterfelde, one of the suburbs, to the military academy. This railway is still running, and its operation has throughout, for more than two years, been of the most satisfactory character. No auxiliary conductor is used, the current going from the dynamo along one rail, through one of the wheels, through the motor, through a wheel on the opposite side of the car, and thence to the other rail, which acts as the "return." No trains are made up, but each car is fitted with an electro-motor, which lies beneath the flooring. As the authorities declare these cars to fall under the same heading as tram-cars, the speed at which they may be run is limited by law to twelve miles per hour. This speed is realized with ease, but a much greater rate could be attained, if it were allowed.
It can hardly be hoped, however, that such a simple system as this could be adopted for running cars in the streets of a city, for other difficulties would be introduced. The fact that the rails in the streets must, of necessity, be close to the surface of the ground, and that they are to be stepped upon by men and horses, shows at once the necessity of having the conductor out of the way, and the danger of having the current traverse the rails. At the Electrical Exposition held at Paris in 1881, Messrs. Siemens & Halske had an electric rail-way in operation, in which a third or auxiliary conductor was used; but this ran along on posts like a telegraph-wire, the current being conveyed from this conductor to the motor by means of a flexible conductor, which was connected at one end with the motor on the car, and at the other with a contact-carriage, or trolly, which was drawn along the conductor by the car as it advanced.
In mines, in tunnels, and in all places where the smoke of burning coal is objectionable, it would seem that the electric railway possesses unrivaled advantages. As the motor gives off no smoke, makes little noise, occupies but a small space, and does not have to carry its own
in the mines at Zankerode, where a Siemens electric railway is now running, a steam-locomotive would be not only undesirable but impossible.
In the Zankerode-mine railway, the current is sent from the dynamo along the roof of the tunnel through one of the inverted T-rails shown in Fig. 2, which thus acts as a conductor, and upon which slides a contact-carriage connected with the motor on the car by one of the flexible conductors, also shown. The return current coming from the motor goes to the other inverted T-iron by the other flexible conductor, and thence back to the dynamo.
The most extensive electric railway now in use is that constructed by Messrs. Siemens in Ireland, which runs from Portrush to Bushmills, a distance of about six miles. As at present operated, a dynamo revolved by a stationary steam-engine supplies the necessary current; but it is intended to utilize the waste power of a waterfall situated about three quarters of a mile from the end of the line, as soon as the necessary works can be constructed. The cost of running the electric locomotives is found to be less than that of running steam-locomotives over the same track, and it will be much reduced as soon as the utilization of the power of the waterfall (twenty-four feet) is made possible.
By another system of electric propulsion, it has been attempted to carry batteries of electric accumulators in the car, instead of conveying the current to the car by conductors. By this system, as yet undeveloped, a large stationary engine is to be used to turn a dynamo which will generate a current that will charge the accumulators or "storage-batteries," as they are sometimes called; these accumulators to lie under the seats or in some other convenient place, and render the current to the motor direct.
As accumulators may play an important part in electric railroading, and as much that is incorrect has appeared in print concerning them, a few words of description may not be out of place.
Probably the most prevalent conception of an accumulator is a box or other receptacle in which electricity is put and from which it can be drawn when desired; and for practical purposes this idea is sufficiently correct. From a scientific point of view, however, it is more satisfactory to regard an accumulator as a battery in which the electrical energy of the current which it renders arises from a chemical action due primarily to another current which was sent through it. To speak more in detail, the ordinary accumulator (Fig. 3) consists of two lead plates standing in acidulated water and capable of behaving like an ordinary voltaic battery, after they have been acted upon by a strong current. This current, called the charging current, when it goes through the liquid, decomposes it, the oxygen, separated, going to one lead plate and the hydrogen to the other lead plate. The oxygen attacks the lead plate to which it goes, thus forming peroxide of lead, and the hydrogen reduces any oxide that may be on the other lead Fig. 3.plate, thus producing pure lead, some of the surplus hydrogen forming as a film upon the surface. The charging current is then reversed, so that the latter plate is now attacked, and is then reversed again; the effect of these operations being to render the surfaces of both lead plates porous so that they present a large surface, and can therefore hold a great deal of peroxide of lead. When the charging current is broken, the oxygen, which has been forcibly separated from the liquid, seeks to recombine in the same way that a stone which has been forcibly separated from the earth seeks the earth when liberated. If now the two lead plates be joined with a wire, the effect of the oxygen in the peroxide of lead trying to recombine is to generate an electrical current in the opposite direction to the original one; and this is the current which is utilized. The value of accumulators would be much increased if this return current could be made greater, and if the weight and cost of the accumulators themselves could be made less. At present, however, their use is restricted by reason of their great cost and weight, and by the small ratio (about fifty per cent in practice) of the electrical energy returned to that expended in charging them. Nevertheless, the fact that the accumulator system of electric railroading obviates the necessity for any conductors, which sometimes are inconvenient and expensive, and which themselves occasion great loss of electrical energy, leads many to believe that for short routes, as upon street-car lines of cities, accumulators will be very efficient.
At the Chicago Exposition of Railway Appliances, which has just closed, the system of Messrs. T. A. Edison and S. D. Field, of New York, was tried, and with undeniable success. By this system a third conductor is used; but it is not placed upon poles, as in the Siemens system (for this would not be practicable in the streets of a city), but lies in a long sunken trough which runs between and parallel to the rails. The trough is covered, and a long and very narrow slit runs the whole length of the cover. Through this slit extends a strong metallic rod which is connected mechanically with a contact-carriage lying upon the conductor, and which is mechanically and electrically connected with the car.
It is claimed that by means of a scraper, carried by the contact-carriage, there will be no trouble occasioned by any accumulation on the conductor of ice, snow, or mud, but that the car can be satisfactorily run in all kinds of weather.Fig. 4 represents the generator and track as arranged at the
Chicago Exposition. It will be noticed that one pole of the generator (dynamo) is connected with the auxiliary middle rail, and the other with one of the two side-rails which are metallically connected together, as shown. The current goes to the motor on the car by the middle conductor, and is returned to the generator by the side-rails.
The advantages of the electric railway, should it be made practicable in all respects, are obvious, and there is good reason for believing that in time it will be made available and economical even for lines of considerable length.
In the streets of a city, electric cars would be advantageous upon the surface roads for the reason that they could be run more quietly and swiftly than horse-cars, and, as an electric car can be stopped in less than its own length, just as safely; in crowded parts of the city, they could thread their way more rapidly through the crowds of carts and other vehicles, because they can be stopped and started more quickly and require less room. But it would be upon elevated roads that their advantages would be pronounced, for we should then escape much of the noise and all of the smoke and smell that now attend the passing of elevated trains.
By reason of our ability to make every electrical car its own locomotive, it is clear that we can secure greater safety in traveling, and greater frequency in the times of arrival and departure, so that to reach the depot half a minute too late would not be so serious a thing as it now is. As each car is very light, it can be stopped in a much shorter distance than is now possible with a heavy train; and, even if a collision should occur, it would not be such a horrible thing as a collision between two ponderous trains, not only because of the lightness of the electric cars, but also because they do not carry steam and fire as locomotives do. Another advantage of the lightness of the cars lies in the fact that they will exert less "wear and tear" upon the tracks, and therefore occasion less outlay for repairs.
When the present mode of traveling in Pullman cars is compared with the mode in use not very long ago, by which people were cramped for hours and even days in a coach without springs worth calling by that name, and were jolted and tossed about over uneven roads, we conclude that traveling at the present time is a very luxurious thing. But what will it be when we can sit at an open window, and glide along at the rate of sixty miles an hour, without the fear of smoke or cinders; when electric bells are at hand leading to the inaccessible retreats where porters now secrete themselves safe from discovery; when we can start from our homes to take a car for Boston, as we now start to take an elevated train, knowing that, if we miss one car, another will be soon at hand; when electric incandescent lamps, which can not, in case of accident, scatter burning oil in all directions, shall fill the car with a mild and steady light; when dispatches can be received on board a train in motion as well as at an office; when the cars shall be heated and meals prepared by electric stoves which can not, in case of accident, set fire to the car—all the electricity needed for these and numberless other purposes being derived from the same convenient source—the conductor carrying the current which furnishes the propelling power?
That any such ideas as to what electricity can accomplish are visionary and impracticable may seem to be the case to some; that they are so in reality is not believed by many who have given the subject impartial study. Some of these believe that, in the very near future electric cars will supplant horse-cars; and upon short lines like elevated roads, steam-locomotives; but that it will not be practicable for many years to run electrical cars upon long lines. Such may be the case. But it should be remembered that, in most instances in the history of industrial progress, the practical developments of meritorious systems have surpassed in rapidity and extent the expectations of even impartial men. A very high scientific authority in England once spoke very favorably of the idea of using steam-vessels for accomplishing short distances, and for river navigation, but laughed heartily over the suggestion of their ever going to sea, and offered publicly to eat the boilers and engines of the first one that should cross the Atlantic. Probably there are not many men who, in the light of what has recently been accomplished, would promise to eat the motor of the first electric car that should run from New York to Chicago.