SYNCHRONOUS GENERATORS 29 



slots with 5 inductors in series per slot. The coil pitch is one. 

 The field structure has 96 poles. What is the generated armature 

 voltage when the resultant air-gap flux is 6.3 megalines per pole 

 and the speed is 74 rev. per min.? 



31. The armature of a 3-phase, 50-cycle, 12-pole alternating 

 current generator has 54 slots with 2 inductors per slot. The 

 inductors are arranged symmetrically in the following order, which 

 repeats itself for every pair of poles, i.e., for every 9 slots. In the 

 first, third, fourth, sixth, seventh and ninth slots both inductors 

 are in phases 1, 3, 2, 1, 3 and 2 respectively. In the second, 

 fifth and eighth slots the top inductors are in phases 3, 1, and 2 

 respectively, and the bottom inductors are in phases 1, 2 and 

 3 respectively. The inductors in each phase are connected in 

 series and the phases are connected in Y. 



(a) If the resultant no-load air-gap flux is sinusoidally distrib- 

 uted and has a value of 8 X 10 5 lines per pole what is the terminal 

 voltage? 



(b) What are the reduction factors for the fifth and seventh 

 harmonics in the phase voltage? 



(c) For what harmonics are the reduction factors zero? 



32. The armature core of a 3-phase alternating-current gener- 

 ator has 12 slots per pole. Each slot contains 2 coil sides, so that 

 while there are 8 inductors per slot each coil has 4 turns. The 

 coil pitch is 10 slots. 



What are the total reduction factors for the fundamental and 

 th<- third, fifth and seventh harmonics in the phase voltage? 



33. A 3-phase, Y-connected, 25-cycle, alternating-current 

 gem -rator is rated to deliver 7500 kv.-a at a terminal potential 

 difference of 12,000 volts. The field structure has 12 poles and 

 the armature has 180 slots. There are 4 inductors in series per 

 slot. What is the no-load terminal voltage when the air-gap 

 flux is 52 megalines per pole and the generator is driven at IN 

 rated speed'.' 



34. (a) In problem 27. what i* tin- armature reaction in 

 ampere terms per pole when the alternator is delivering it- rated 

 load at unit power factor? 



(b) What is the leakage reactance voltage at this load? The 

 armature inductors are 41 in. long. Assume that the leak M in- 

 flux is 7 liin- pa ampriv pr inch of inductor. 



(c) If the armature winding had been equally distributed in 

 5 adjacent slots instead of in 10 what would have been the leakage 



