PROBLEMS. 393 



equal to 100 amperes. What is the current in the common re- 

 turn wire? Ans. 141.4 amperes. 



68. The electromotive force of each phase, problem 67, is 500 

 volts. What is the electromotive force between the outside 

 wires ? Ans. 707 volts. 



69. A three-phase alternator is provided with 4 collecting rings 

 and 4 mains as shown in Fig. 94. Three similar receiving cir- 

 cuits are connected as follows : One from main I to main 4, one 

 from main 2 to main 4, and one from main 3 to main 4. Each 

 receiving circuit takes 1 50 amperes. When the armature wind- 

 ings are properly connected to the collector rings the current in 

 main 4 is zero. What is the current in main 4 when one arma- 

 ture winding has its connections reversed? Draw a diagram 

 showing the phase relations between the currents in mains I, 2, 

 3, and 4 when the armature winding A, Fig. 94, is reversed. 

 In constructing this diagram consider directions outwards from 

 machine as the positive direction in each main. Ans. 300 

 amperes. 



70. Three similar receiving circuits are A-connected to 3-phase 

 mains, the electromotive force between each pair of mains being 

 HO volts. The power delivered to the three circuits is 150 

 kilowatts and the power factor of each circuit is 0.90. What is 

 the current in each circuit and in each main ? Ans. 505 amperes, 

 875 amperes. 



71. Three similar receiving circuits are Y-connected to the 3- 

 phase mains, problem 71 ; the total power delivered is 150 kilo- 

 watts and the power factor of each circuit is .90. What is the 

 current in each circuit and in each main, and what is the electro- 

 motive force between the terminals of each circuit? Ans. 875 

 amperes, 875 amperes, 63.5 volts. 



72. A given 3-phase alternator is provided with six collector 

 rings so that it may be connected, A or Y, for experimental pur- 

 poses. The electromotive force developed by each winding is 

 100 volts. Find (a) the current in each receiving circuit, (^) the 

 current in each main, (c) the voltage between mains and (d) the 



