Popular Science Monthly/Volume 56/March 1900/What Makes the Trolley Car Go III
|WHAT MAKES THE TROLLEY CAR GO.|
ALTHOUGH the electric railway has been introduced throughout the civilized world with the most remarkable rapidity, replacing cable as well as horse roads, there has always been a strong opposition to the use of the overhead trolley, and in some places, as, for instance, the city of Kew York, this opposition has been so strong as to prevent the introduction of the system until some other means of conveying the current to the moving cars was devised. Many attempts have been made to solve this problem, and the patents taken out on such devices can be numbered by the hundred and possibly by the thousand. Inventors in this field, however, have not met with all the encouragement they could desire, owing to the fact that, notwithstanding opposition, the overhead trolley has been permitted in all but about three or four of the larger cities of this country, and the greater portion of those of other countries. The principal well-founded objection that can be raised against the trolley is that it is unsightly and destroys the appearance of the street, but those who are opposed to it also claim that it is dangerous, and that underground or surface systems would not be. As a matter of fact it is not dangerous, and there is nothing on record to show that it is. Many persons have been run over by trolley cars, but this is no fault of the overhead trolley; it is due to the fact that street railroads are permitted to run cars through crowded streets at a speed that is too great for safety. Underground conduit cars running at the same speed would run over just as many people. In accusing the trolley of being dangerous it is sought to prove that the current flowing in the wire can do harm; but the history of the numerous roads in existence shows that, so far as human beings are concerned, the trolley current is not fatal, although it can give a decidedly unpleasant shock, such as one would not care to experience the second time. There is
just as great, if not greater, liability of obtaining shocks from underground systems as from the trolley, therefore the only real gain that can be made by their use is in the artistic sense. From a financial point of view no underground system so far devised can compare with the overhead trolley; but if any one should devise anything hereafter that can be constructed at the same expense and will not cost more for maintenance it will undoubtedly find an extensive application. Until such a perfect solution of the problem makes its appearance the field for these devices will be confined to cities like New York and Washington, where the overhead trolley is not permitted.
Every system of conductors that dispenses with the overhead wire is called by the layman an underground trolley, but, properly speaking, these systems may be divided into surface and subsurface conductors. Both of these may again be divided into exposed and inclosed conductors, and also into continuous and sectional conductors. Finally, we may designate the various modifications as mechanical, electrical, and magnetic, the mechanical being those that accomplish the result by purely mechanical means, the electrical being those that employ electrical devices, and the magnetic those that depend for their action upon the attraction of magnets. The principal difficulties that the inventors in this field have to contend with are the cost of construction and the effective insulation of conductors. With the overhead trolley the current flows out from the power house to the cars through wires carried on poles, and the poles are themselves good insulators; but to make the work doubly sure the conductors are secured to glass insulators, which are practically perfect. The current returns to the power house through the ground and the track rails. As it is easier for the current to circulate in a short path than in a long one, there is a continual tendency for it to jump from the overhead wire through the insulation to the ground, but this is effectually prevented by the very perfect character of the insulation. When the outgoing and incoming wires are both placed upon or underground the strain upon the insulation is very much increased, for then instead of the two lines being separated by fifteen or twenty feet of pole, which is a very fair insulator, they are separated by only a few inches of earth or perhaps metal, the first of which is a fairly good conductor, while the last is a nearly perfect one. It is evident, therefore, that the insulation proper in an underground or surface system must be of the highest order. If the conduits in which the wires are located could be kept perfectly dry, there would be no difficulty in obtaining insulation that would withstand the strain it is subjected to; but rain in summer and snow in winter will at times cover the tracks and fill the conduits, hence the securing of perfect insulation presents great difficulties. The manner in which inventors have sought to surmount the obstacles can be made clear by the aid of a few illustrations of typical designs.
Fig. 25 shows one of the forms of a class of underground conduits belonging to the inclosed conductor type. The track rails are supported upon the outer ends of large castings, F F, commonly called yokes. These are made of such size that the portion below the opening which incloses the conduit may be of sufficient depth to afford the requisite strength to properly support the track. The conductor that carries the current is located at f and is insulated from the casing j, which forms the lower half of the conduit, by the stands g. From the car a bar, P, which is called a plow, projects downward through the slot between the rails, k k, and on its end is spread out into a fork, d, which carries a pulley, e. When this pulley is in contact with the conductor f the current passes through the plow P to the motors upon the car, and thence to the track rails and back to the power house.
As the yokes F F and the conduit casing j are made of iron and are in metallic connection with the track rails, it is evident that if the conduits should fill with water to the depth of the wire f the current would pass directly to the rails, and thus would avoid the longer path through the motors. To prevent this occurrence, the sides of the conduit are inclosed with the sheet-iron covers c c, which nominally are in the position shown by the dotted lines i i. The plow is also provided with the arms b b, upon the ends of which are mounted small wheels a a, and these run upon tracks attached to the covers c c. As is shown in the figure, the wheels a a, running upon the tracks attached to the covers c c, cause the latter to spread out to the position in which they are shown. This spreading, as can be readily understood, only takes place for a short distance ahead and behind the plow, but at all other parts of the conduit the sides assume the position i i, and thus close the conduit and exclude the water.
It can be easily seen that some difficulty would be encountered in making a tight joint at h h, and also that the opening and closing of the sides might not operate as perfectly in practice as upon paper, but it does not follow from these facts that the design is not practical; it simply illustrates that there are many minor difficulties to be overcome in order that complete success may be attained. Many designs operating upon this principle have been patented, and in some of them a great amount of ingenuity is displayed.
Fig. 26 illustrates another type of inclosed conductor which at a first glance appears to be far superior to that just described, but upon closer investigation it is found to be not wholly free from objections that are difficult to overcome. The yoke F F, as in the
design just described, is made wide enough to support upon its outer ends the track rails R R, and is cut away in the middle to an outline conforming with the shape of the conduit. The conductor that carries the current is located at d, being supported by the stands e. An elastic tube f is provided, which is water-tight and thus excludes moisture from its interior, within which the conductor d is located. On the top of tube f a flexible rail b is secured, and this connects with studs c, which are within the tube, as clearly shown in the drawing, and so situated that they may be forced down into contact with d. Normally these studs are separated from d, but when the car comes along, the wheel a, mounted upon the end of plow P, flattens the tube f and thus forces one or more of the studs c into contact with d. The distance between the studs c is such that at least two will always be in contact with d, thus insuring a continuous electrical connection with the motors so long as the plow is depressed.
The first impression upon looking at this design would be that it is entirely free from objections; for if we assume that the tube f is made of rubber, we can see it in our mind's eye springing up after the plow passes by and thus separating the contacts c from d, and at the same time yielding freely to the pressure of the wheel a. All of this is true, but rubber is not very durable when under such exposed conditions, and to maintain a length of several miles of it in a perfect state for even two or three years could not reasonably be expected; and if it became necessary to renew the tube oftener than this the cost of maintenance would be entirely too great. There is another objection, however, which is more serious, and that is that the conduit will gradually fill up with dirt, and this pressing against the rubber tube would force it out of shape, and thus cause the contacts c to bear permanently upon d, or else to become so far displaced that they would not touch it when depressed by the plow.
As the rubber tube can not be depended upon, inventors have sought to improve the construction by using sheet steel and making the tube flatter and much wider, so that a section of it would present an outline much resembling an elliptic carriage spring. Such a construction will meet the requirements as to strength and the retention of the contacts c in their proper position; but steel expands when warm and contracts when cooled, therefore a long tube would be stretched so much in winter that it might pull apart, while in summer it would be compressed and tend to buckle up and thus be forced out of place. These difficulties can be overcome by providing expansion joints at suitable intervals, so that they are not necessarily proof of the impracticability of devices based upon the principles involved in this design; they simply serve to forcibly bring to mind the fact that the path of the inventor of underground systems is not strewn with roses, no matter in what direction he may turn to find a solution of the problem.
The object in the designs Figs. 25 and 26 is to shield the conductor so that it will remain dry should the conduit be filled or partially filled with water. If water could be excluded from the conduit, the casing; c c, in the first figure, and the tube f, in the second one, would not be required, for there is no difficulty in providing an insulating support that will hold the conductor firmly in place and at the same time prevent the escape of the current; but as soon as moisture collects upon the surfaces of the insulating supports it acts as a conductor, and thus renders the insulation of little value.
If water runs into the conduit in such quantities as to come in contact with the conductor, then the effect of the insulation is entirely destroyed; the aim of the inventors, therefore, is to provide means for preventing the accumulation of water or moisture around the conducting wire. It can be readily seen that the shorter the conductor the easier it is to protect it, and this fact has given rise to the development of a great number of designs classified as sectional conductors. In these, two conductors are used, one of which is continuous and so situated and insulated that it can not under any conditions be reached by either moisture or water. The other conductor is made in lengths that vary all the way from fifteen to two or three hundred feet. Normally, these short sections are not
connected with the circuit—they are dead, as it is called—but when the car comes along, the plow, by acting upon suitable mechanism, establishes a connection between the continuous conductor and the portion of the sectional conductor that is directly under it, and in this way the current passes to the car. As soon as the car passes beyond a section of the sectional conductor, the connection between it and the continuous wire is broken automatically. Some of these arrangements depend upon mechanical devices, such as levers that are struck by the plow and thereby move a switch that closes a connection between the section and the continuous conductor, but in most instances the switch is operated by a magnet, which may be carried by the car or may be arranged so as to be energized as the car approaches it. Designs of this last type come under the head of electrically operated sectional conductor systems. There are other arrangements in which a magnet carried by the car attracts iron levers suitably disposed along the conduit, and these levers close switches that connect the section of conductor under the car with the continuous one. As the levers are actuated by the magnet, they only hold the switch closed while the latter passes over them; thus the electrical connection is made and broken as the car moves along.
Most of the designs in which sectional conductors are used can be placed much nearer to the surface of the street than the types illustrated in Figs. 25 and 26, and this is a decided advantage, as it greatly reduces the cost of construction. Any system that requires an underground conduit, with the yokes F F to support the track, can only be used by roads upon which the traffic is very great, for the cost of construction would be such as to prohibit its use under any other conditions, no matter how successful its operation might be. For small roads with moderate traffic the question of first cost is of paramount importance, and the only system that can offer a satisfactory solution of the problem for these is one that does not require an underground conduit.
Although many patents have been taken out for systems similar to those described in the foregoing, nothing has been done practically with any of them except in an experimental way. Some are in operation on small roads in out-of-the-way places, being intended principally to illustrate the practicability of the system and thus assist in promoting its introduction elsewhere, but the system that has been adopted in a commercial way is one in which no attempt is made to shield the conductor from moisture and water, and for its successful operation dependence is placed entirely upon, the proper drainage of the conduit. This system is well illustrated in Fig. 27. The plow P carries upon its end two brushes, b b, which are insulated from each other. These brushes rub against the conductors
a a, which are made of bars of channel iron and are well insulated from the yokes F F and the conduit casing to which they are attached by means of the supports c c. In the construction shown in the figure the current comes from the generator through one of the a bars and returns through the other, but both bars can be used to conduct the current from the generator, in which case the return can be effected through the track rails, just as in the designs already considered. If both the bars a a are used to convey the current from the power house the insulation between the brushes b b is not required. To avoid the accumulation of water in the conduit the drain G is provided with outlets d, located at suitable points.
Although this system is the simplest that can be devised for use in streets or public highways its construction is very costly, so much so that it can only be used in cities where the traffic is so great as to require the running of cars on short headway; and, furthermore, it can not be operated with any degree of success except in municipalities where there is a good sewage system. During the summer months it is liable to be more or less impaired by heavy showers, but the trouble in such cases is only temporary. In winter time snowstorms are liable to affect it in the same way, especially if, after a heavy fall, a warm wave comes along and produces a rapid thaw.
From the fact that no attempt whatever is made to protect the conductors, one would naturally suppose that every time there is a rain the road would be compelled to shut down; for, as the slot through which the plow travels is open, water can enter the conduit with the greatest freedom, and, in trickling down the sides, would be caught to some extent upon the brackets c c, and thus make its way over to the channel bars a a, and thereby destroy the insulation. Practice, however, shows that this action does not take place, at least not so often as to produce any serious trouble. The roads that are operated by electricity in New York, and also the lines of the Capital Traction Company, of Washington, D. C, employ this system, and they have been in operation a sufficient length of time to fully demonstrate that the difficulties actually developed by the action of the elements are not of a formidable character. On one occasion the Sixth Avenue road, in New York, was compelled to stop its cars for a short time just after a severe snowstorm, but the failure was not due to impairment of the insulation, according to the statements of the officials of the company, but to the fact that the melted snow froze upon the track and caused the wheels to slip around without sending the car ahead. The fact that other roads in New York, belonging to the same company, are being equipped with the system, is proof that, upon the whole, its practical operation is regarded as satisfactory; but it is very evident that it is not the final solution of the problem. A system to be a decided success must cost very little more than the ordinary overhead trolley, and its construction must be such that it will not easily get out of order. If it is not inexpensive it will not come into use except in places where the authorities will not permit the overhead wires. A surface or underground system ought to be more durable than the overhead, as the wires are not liable to be injured by high winds or the accumulation of ice and snow; and, furthermore, as the conductors are below the ground the danger of burning out motors and generators by lightning would be eliminated, and this is a serious matter with all trolley roads, especially in cities. Country roads do not suffer so much from lightning, because when there is a heavy thunderstorm the generators are stopped and the trolley poles are pulled away from the wire, the cars remaining stalled on the track until the storm passes over. This course can not be pursued by city roads, for the passengers feel that, lightning or no lightning, they must reach their destination, therefore the cars must continue to run and take their chances.
Lightning, however, does not strike trolley lines as often in cities as in the open country, owing to the fact that there are so many iron buildings and roofs to attract it in other directions.
Fig. 28 shows the appearance of the street surface when an underground system such as is illustrated in Fig. 27 is used. This figure is a photograph of the Capital Traction Company's lines in Washington. After looking at this picture one can not deny that the appearance of the streets of a city is greatly improved when the overhead wires are removed, but underground systems which require a plow to run in a groove are not without objection, for the groove forms a dangerous trap into which the narrow-tired wheels of light wagons can readily drop, and the toes and heels of horseshoes can be caught. Thus, unless the slot can be dispensed with the greater beauty overhead is obtained at the expense of increased danger on the street surface. There are quite a number of underground conductor systems in which the slot is not used, the current being conveyed to the car by contact made with plates set at suitable intervals between or along the sides of the tracks, and on a level with the street surface. Many of these arrangements appear to be quite practical, but none of them can attract the attention of railroad managers unless it can be constructed at a reasonable cost.
About two years ago the New York, New Haven, and Hartford Railroad published a report of the performance of a branch line that was equipped with electric motors, the current being conveyed to them by means of a third rail. Some of the sensational dailies at once took the matter up and heralded the third rail to the public as something entirely new and sure to supersede the trolley. Now, as a matter of fact, the third rail is one of the oldest arrangements that have been used, and was in daily operation in Baltimore in 1886. It is a very cheap system Fig. 31.—Cross-section of Railway Track, showing a Modification of the Third-rail System. and well adapted to roads owning the right of way or running upon elevated tracks, but could not be used on public highways or streets. The third-rail system in its simplest form is shown m Fig. 29, which represents a section through the roadbed. The log A represents a tie or sleeper, and c c are the track rails, while b is the third rail through which the current passes to the motors. Between the rail b and the tie A is placed a piece of insulating material, a, of such dimensions as may be necessary. If the track is high above the surrounding ground, so as to not be submerged when there is a heavy fall of rain, a may be thin, but otherwise it must be of sufficient thickness to raise the rail above the high-water mark. The car is provided with a wheel or brush to bear upon the rail b.
This is the construction used upon the New York, New Haven, and Hartford Railroad, as can be seen from Fig. 30, which is a photograph of a section of the road. The third rail, it will be seen, is raised but slightly from the ties, just about as shown in Fig. 29. One objection to this construction is that persons and animals can receive shocks by touching the center rail and one of the side ones at the same time, as, for example, by standing with one foot on each. Such shocks would not prove fatal to men, as the currents used for railway work are not of a sufficiently high
electro-motive force to produce death, but the shock is nevertheless very severe. Horses and cattle would be killed outright, as these animals are not able to withstand as strong a shock as human beings. To render the third-rail system safer, and also to improve the insulation of the conducting rail, the construction illustrated in Fig. 31 has been devised. The only difference between it and Fig. 29 is that the rail b, instead of resting upon the ties between the tracks, is carried upon a side support c c and is housed in with boards a a. To take the current from it a wheel is mounted upon a shaft projecting from the side of the car truck.
From the foregoing brief description of the essential features of the several systems devised for conveying current to the moving car by means of conductors placed underground or upon the surface, it can be seen that while the result can be accomplished in many ways, and is actually accomplished in a number of instances, nothing has been brought forward so far that is as free from objection as the simple trolley, if we disregard the unsightliness of the latter. It is this unsightliness that has created a demand for something else, but the substitutes, while capable of doing the work, are far more costly and can not be said to be as reliable under all conditions of weather.
The sphere of action of the electric-railway motor is not confined to street railways or suburban transit, but extends to the legitimate domain of the steam locomotive. In many places electric locomotives are used to move freight trains made up of cars of the largest capacity, this same work having been done formerly by steam locomotives. In the city of Baltimore, the Baltimore and Ohio Railroad uses electric locomotives, of greater capacity than any steam locomotives so far made, to draw trains through the tunnel that passes under the city. The general appearance of an electric locomotive can be judged from Fig. 32, which shows an engine of average size at the head of a long freight train.
Note.—Figs. 28 and 32 are reproductions of photographs kindly furnished by the General Electric Company, while for the view of car, Fig. 30, we are indebted to Colonel N. H. Heft, chief electrical engineer of the New York, New Haven, and Hartford Railroad.