The winding in which the e.m.f. is induced in a three-phase source consists essentially of three separate windings so disposed that there is a phase difference of 120° between each pair. Diagrammatically the arrangement is that of figure 15.1. Each separate winding is called a phase. In the diagram of induced e.m.f.s the arrows indicate the positive direction of the e.m.f. for each particular phase. If all three phases were kept separate a six-conductor line between source and load would be necessary. By interconnecting the phases the number can be reduced to three; in one special case four. There are two methods.
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© H. Cotton 1973