In polyphase working, it is evident that by the use of four equal independent windings on the armature, connected to eight terminals or slip rings, a two phase alternator can be built to supply currents of equal voltage to four independent circuits. Likewise, by the use of three equal independent windings, connected to six terminals or slip rings, a three phase alternator can be made to supply three independent circuits.
This is not the usual method employed in either case, however, as the star grouping or mesh grouping methods of connection not only gives the same results, but also, in star grouping, a greater plurality of voltages for the same machine, and a higher voltage between its main terminals.
Radial diagrams of the arrangement and connections of Y grouping of lap windings and wave windings for three phase alternators are shown by figs. 1,551 and 1,552.
Fig. 1,551.—Radial diagram of three phase lap winding with star connection.
Ques. In three phase star grouping, what is the point where the phases join, called?
Ans. The star point.
Ques. In a three phase star connected alternator what is the voltage between any two collector rings?
Ans. It is equal to the voltage generated per phase multiplied by √3 or 1.732.