Ans. Since the current in the common return wire is 41.4 per cent. higher than that in either of the other wires it must be of correspondingly larger cross section, to keep the loss equal.
Figs. 2,156 and 2,157.—Conventional diagrams illustrating star and delta connected three phase alternator armatures.
Ques. What is the effect of an inductive load on the two phase three wire system and why?
Ans. It causes an unbalancing of both sides of the system even though the energy load be equally divided. The self-induction pressure in one side of the system is in phase with the virtual pressure in the other side, thus distorting the current distribution in both circuits.
Ques. Describe the two phase five wire system.
Ans. A two phase circuit may be changed from four to five wires by arranging the transformer connections as in fig. 2,158.
As shown, the secondaries of the transformers are joined in series and leads brought out from the middle point of each secondary winding and at the connection of the two windings, giving five wires.
With 1,000 volts in the primary windings and a step down ratio of 10:1, the pressure between A and C and C and E will be 100 volts and between the points and the connections B or D at the middle of the secondary coils, 50 volts.