[Electric engineering.] . w alarger load to be car-ried without increas-ing the size of theline wires. In suchcases it has beencommon practice toconnect old 1,000-volt transformers upin pairs, as shownin Fig. 27. In thiscase, the primariesof the two trans-formers A, B are connected in series across the 2,000 voltmains and the secondaries are connected in parallel. fig. 27. 64 ELECTRIC TRANSMISSION. 14 78. Transformers on the Three-Wire System.—The general tendency is to use a few large transformers forsupplying a given district rather than a number of smallones. Small transformers are wasteful
[Electric engineering.] . w alarger load to be car-ried without increas-ing the size of theline wires. In suchcases it has beencommon practice toconnect old 1,000-volt transformers upin pairs, as shownin Fig. 27. In thiscase, the primariesof the two trans-formers A, B are connected in series across the 2,000 voltmains and the secondaries are connected in parallel. fig. 27. 64 ELECTRIC TRANSMISSION. 14 78. Transformers on the Three-Wire System.—The general tendency is to use a few large transformers forsupplying a given district rather than a number of smallones. Small transformers are wasteful of power, andthough each in itself may not represent a very large amountof waste, yet when a large number are connected up, thetotal amount of energy that might be saved during a yearby using a few large transformers may be surprisingly course, in most cases where the customers are scattered,it is impossible - to avoid using a number of small trans-formers, but in business districts it is generally easy to use. Three Wire Secondary f Mains 6 O O O o [ Fig. 28. a few large transformers of high efficiency. These are fre-quently connected in pairs so as to feed into three-wiresecondary mains m, m, ;//, as shown in Fig. 28. Theprimaries are connected directly across the line in parallel,and the secondaries are connected in series with the neutralwire connected between them at the point o, just as in thecase where two dynamos are operated on the three-wire sys-tem. Care must be taken in connecting the secondariesto see that the terminals a and b are of opposite sign. Ifthey are correctly connected, a pair of lamps /, / connectedin series across the outside lines should burn up to full § 14 ELECTRIC TRANSMISSION. 65 brightness. If they are wrongly connected, the lamps willnot light at all, showing that terminals a and b are of thesame polarity and that c and d are also the same, the second-aries being connected so that the two outside mains are ofthe same polarity with a
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