ELECTRICITY IN LOCOMOTION - BOOK

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ELECTRIC TRACTION ON MAIN LINE RAILWAYS

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On tramways, automobiles, and 'third-rail' lines, the electric current used belongs to the type described as 'continuous' or 'direct,' because the flow is always in the same direction. The other type of current is known as 'alternating,' as it flows backwards and forwards many times per second. There are several kinds of alternating current—single-phase, two-phase, three-phase, and polyphase—each produced from generators designed in a particular way. It is not possible to give any adequate account of these different kinds of alternating current without going rather deeply into the theory of electricity. The ultimate practical point is that in transmitting alternating currents the circuits increase in number with the phases. Thus, three-phase current requires three wires, two-phase current three or four wires, and single-phase current a single circuit like that of continuous current . Fig. 12. Photograph of a train on the electrif...
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ACCUMULATOR ELECTRIC TRACTION. THE ELECTRIC AUTOMOBILE

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The use of the accumulator or storage battery in electric traction affords a very good example of how a means of propulsion may fail in one set of circumstances and contrive to succeed in another. Its history serves to remind us that the problem of cheap transport is really a group of problems, each one of which demands a particular solution. The accumulator is a device for storing electrical energy in the form of chemical energy. Its action depends upon the effect of currents of electricity on lead plates in a bath of sulphuric acid. The passage of the current through the battery produces chemical changes which enable the battery to give out current when required. As the battery may remain 'charged' for several days, and may be discharged slowly or quickly, it provides a means of 'storing' electrical energy. In practice, and under favourable conditions, the efficiency of the storage battery is about 80 per cent. That is to say, there is a loss of about 20...
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