. A textbook on electric lighting and railways. International correspondence schools, Scranton, Pa. v. 1-3, 5 . same time using a higher line voltageis to operate the cars on the three-wire system, as shown inFig. II. ./ and /) are the two tracks of a double-trackroad and r, d the two trolley wires. (7, G are two 500-voltgenerators connected in series and running the railway onthe three-wire system. The track constitutes the neutralconductor, and it is evident that if the load on the two tracksis balanced, no current flows through the rails. The trackreturn is called on to carry only the diffe
. A textbook on electric lighting and railways. International correspondence schools, Scranton, Pa. v. 1-3, 5 . same time using a higher line voltageis to operate the cars on the three-wire system, as shown inFig. II. ./ and /) are the two tracks of a double-trackroad and r, d the two trolley wires. (7, G are two 500-voltgenerators connected in series and running the railway onthe three-wire system. The track constitutes the neutralconductor, and it is evident that if the load on the two tracksis balanced, no current flows through the rails. The trackreturn is called on to carry only the difference in the load,and as there are four rails to serve as a conductor, there is 30 ELECTRIC RAILWAYS. §23 little tendency for the current to come back through pipes orother conductors. The use of this three-wire arrangementallows the power to be transmitted at 1,000 volts insteadof 500, and therefore effects a saving in copper. The highpressure is, however, objectionable, especially in thicklypopulated districts, but it seems as if the system would bewell adapted for cross-country and suburban lines. The. saving in copper is not as great as that effected in changinga two-wire lighting system to a three-wire system, becausein the simple 500-volt trolley system the track is alreadyutilized, whereas in the three-wire method of operation it isused very little. The saving in copper will, however, be from20 to 40 per cent., depending on the quality of the trackreturn. Fig. 12 shows the three-wire system used on a single-trackroad. The trolley wire is here cut into sections, the length ofwhich depends on the traffic. These sections are connected 11 / ■^ ^Feeder Tro//ey Wire ~^/?(7// — ^Feeder alternately to the two sides of the system and the trackforms the neutral conductor. By choosing the length ofthe sections properly, the load on the two sides of the systemmay be balanced closely enough for all practical purposes. §23 ELECTRIC RATEWAYS. 31 T^ITS^E TESTS. 31. AVith the ordin
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