Soon after the Sprague Company entered the railway field, the Thomson-Houston and West inghouse companies took up electric railway work, and greatly aided its development by adding their inunense resources to the resources of the Sprague Company. From this time the development of street railway apparatus was rapid. The first motors of all the companies used double reduction gearing, and one of the first improvements, after the introduction of the carbon brush, was the design of a comparatively slow-speed motor which allowed a single reduc tion gearing to be used. The first motor of this kind was made by the Wenstrom C,ompany, and within a short time other manufacturers were tnalcing slow-speed motors — some going so far as to attempt gearless motors; the latter, how ever, were not successful owing to their great weight and lacic of efficiency at reasonable speed. Most of the slow-speed motors that were made at this time were not thoroughly en closed, their efficiency being such that a better ventilation than could be obtained by a totally enclosed machine was necessary. The machines were, as a rule, of the four-pole type, with parallel armature windings, requiring four brushes and causing, under certain conditions, unbalancing in the carcuits that greatly increased the armature losses and decreased the efficiency. The next step in motor development was made by the Westinghouse Company in what they called their No. 3 motors, a machine much like those at present in use. It had four poles, each of them provided with a field coil, while the ar mature was provided with what is called a series winding, necessitating only two brushes and doing away with the unbalanced armature circuits of the earlier machines. This type, with the modifications suggested by experience, is the one used in this country at the present time, and almost universally used abroad.
Controllers.— The first method used for regulating railway motors was by inserting re sistance in the circuit of the machine; this was modified and developed until, in the Richmond motors of the Sprague Company, the series parallel system was used, combined with a vari able resistance obtained by making different combinations of the coils into which the field windings of the machine were divided. On starting and for slow speeds the two motors were used in series, while for the higher speeds they were placed in parallel. This system was abandoned, and for some years a parallel sys tem for operating two motors on a street car was used. One difficulty found in the early series-parallel control was the liability of the motors to slip when in series position. The slipping on one pair of wheels would allow the motor connected to these wheels to revolve at such a high speed that its counter-electromotive force would cut off the power from the other, and the car would not start. This difficulty, which always exists, but which is not of im portance on ordinary roads, was further com plicated by the electrical difficulties in the con troller — the method of control not being as efficient as that used at present. In the Sprague system, there was no resistance outside of the motors, but the motor fields were divided into a number of coils, and the relations of these coils were varied, giving first a high resistance and a very strong field for a given current, and afterward a comparatively low resistance and a comparatively weak field. The difficulty of this system lay in the fact that all the heating inci dental to the low efficiency of the motors on starting was liberated in the field; and, further, the inductance of the fields was greatest at the breaking of the circuit, when all the coils were in series. The Thomson-Houston Company modified this by placing a variable resistance di rectly in the motor circuit, the resistance being regulated by a movable contact arm, con trolled by the motorman. This gave better re
sults than the Sprague system, but it also lacked efficiency. In 1891 the General Electric Com pany brought out a series-parallel controller, similar in some respects to the early Sprague control, but differing from it in the fact that the regulating resistances were not obtained by vari ations of the different motor field windings, but by resistances outside of the motor. This sys tem, with variations due to different conditions of operation, is still used and gives excellent re sults. Perhaps the most important develop ment in controller work was due to the intro duction of the magnetic blow-out devised by Prof. Elihu Thomson. This apparatus is so placed as to control the breaking of the cir cuits, and almost entirely eliminates the destruc tive effects of sparking, due to the breaking. The method of operation is as follows: At first the two motors are placed in series, the re sistance being also in series with them; then the resistance is gradually cut out, until finally the motors are in series across the with line wi no outside resistance in their circuits. Then the resistance is again cut in and one of the motors is short-circuited; the next operation cuts out the short-circuited motor, the next places it in parallel with the other motor, a large part of the resistance still being in series with them; the rest of the operations consist in cutting out the resistances until finally the mo tors are in parallel across the line. The shifting of the circuits, due to the various operations necessary for regulation and cross circuiting, is carefully guarded against by enclosing the dif ferent sections in compartments.
System of In ur ban train service, where a number of cars are i operated in one train, with frequent stops, the question of acceleration is of the utmost import ance. In order to accelerate quickly, it is nec essary to have a large margin of tractive effort on the train — that is, it is necessary to have a large proportion of the total weight of the train on the driving wheels. When the question of displacing steam locomotives for elevated rail way service first came up, and was attacked on the basis of using electric locomotives, the ad vantages of the latter were not apparent. There was, of course, some advantage in the-matter of expense, but not enough to justify the expendi ture necessary to change from steam to electric service. Mr. Sprague devised a system by which a number of cars on a train could be equipped with electric motors and controlled from any one of the cars; this system he called the ((mul tiple-unit" system. At first it was opposed by most of the manufacturing companies and by many electrical engineers. With his customary energy, however, Mr. Sprague worked his sys tem out to a practical demonstration, and to-day all. trains operated by electricity employ his fundamental methods. The advantages of this system are these: It gives a large proportion of the total weight of the train on the driving wheels, and at the same time distributes this weight over the whole length of the train. In the first place, this allows rapid acceleration without slipping of the wheels, and it in the sec ond place, t does not impose an undue strain on any elevated structure. It is also possible, of course, to change the number of units on a train without changing the relative weights of the driving mechanism of the car. It further more utilizes all the train space for the trans portation of the passengers. Its disadvan tages, compared with a single locomotive, lie in the fact that it necessitates a greater num ber of motors, thus adding to the cost of in stallation and repairs, and it greatly compli cates the system of control.