Electric Railway

Electric Railway is such that trains thereon are supplied with electric current as motive power. Since 1879, when Werner Siemens opened an exhibition line at Berlin, on which a train of three carriages carrying twenty people was driven by a stationary dynamo at a speed of seven miles an hour, the subject has received much attention at the hands of electrical engineers, and various plans have been devised and tested practically. The train carries some form of electric motor, which will produce mechanical motion if a proper electric current at a suitable potential be supplied. [Dynamo.] There are two ways of so supplying the current; the one from a fixed dynamo or generator to the train by means of conductors, the other by means of charged accumulators carried on the train, which supply electricity for a definite length of time till their charge is exhausted. In the conductor system there must be some arrangement by which two terminals of the motor are kept at a constant D.P. The plan of supplying the rails on which the train runs with electricity at different potentials is not entirely practicable, because of the difficulty of insulating them from the ground. A single raised conductor has been employed successfully, kept at the required potential and supplying this to the moving motor by means of a sliding or rolling contact; the other terminal of the motor is kept at zero potential by contact with the rails. The parallel system is adopted when several cars are to run on the railway at the same time. It means the working of the motor by means of two conductors at different potentials, which are joined across by the motor wherever it may be placed. One of the conductors may be at zero potential. The series system is to use only one conductor, which is divided up into short segments insulated from each other. The terminals of the motor are connected by sliding or rolling contact with points on the conductor sufficiently far apart to stretch from one segment to another. The different segments being kept at different potentials, a D.P. must exist between the terminals of the motor, which may therefore be driven if the D.P. is sufficient. The advantage of this plan is, that while the motor is on one section it may be made to cut off the supply from the one behind, and so prevent too close an approach of another train. A special application of this series system is that of telpherage (q.v.), introduced by Fleeming Jenkin. In the Glynde telpher-line the conductor is supported in the air, and from it the train hangs. The carriages are small buckets, and are employed for carrying clay. The storage system has many advantages over the other. Much less difficulty presents itself in planning the installation; there is no laying down of conductors along the route, and each train is complete in itself. On the other hand, efficient accumulators are large and heavy, they are subject to damage by jerking, etc., their dead weight has always to be carried, and there is the trouble of periodically charging them; but the system is adopted in many long-line cases with advantage, though in short lines the conductor system has the preference.