PROBLEMS. 403 



gives out power or receives power); (c) the current flowing in 

 coil AB and the power developed in coil AB (specify whether 

 this coil gives out power or receives power), and (d) the total 

 current delivered by the supply mains. 



116. Three similar 1,000 to roo-volt transformers have their 

 i,ooo-volt coils delta-connected to three-phase i,ooo-volt mains, 

 and the secondaries are Y-connected to service mains. Give a 

 diagram of the connections and find the electromotive force between 

 the pairs of service mains. Ans. 173 volts. 



117. The primaries of the transformers in problem 1 16 are Y- 

 connected to the 3 -phase supply mains and the secondaries are 

 delta-connected to the service mains. Find the electromotive 

 force between each pair of service mains. 



118. Two loo-kilowatt transformers are arranged as shown 

 in Fig. 187, Chapter X for the step-down transformation of a 

 3 -phase supply. Find the power which can be delivered to 

 balance receiving circuits of which the power factor is 0.85 

 without exceeding the voltage and current ratings of the two 

 transformers. 



119. Two transformers are connected as shown in Fig. 187, 

 Chapter X, and they deliver current to three similar receiving cir- 

 cuits of which the power factor is 0.80. The total power deliv- 

 ered is 50 kilowatts, find the power delivered by each trans- 

 former. Ans. 14.18 kilowatts, 35.82 kilowatts. 



120. Find the power delivered by each transformer specified in 

 problem 1 1 9 if the power factor of the similar receiving circuits 

 is 0.30. Ans. 70.9 kilowatts, 20.9 kilowatts. 



121. The primary coils of two transformers have each 560 

 turns of wire and they are connected to two-phase mains, the 

 electromotive force of each phase being 800 volts. Calculate the 

 turns of wire in each of two secondary coils (one on each trans- 

 former) so that these coils when connected in series may give an 

 electromotive force of 400 volts, 30 ahead of one of the two- 

 phase electromotive forces. Ans. 140 turns, 242.5 turns. 



122. A Scott transformer is to transform from 1,000 volts, 60 



