34 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



(b) The synchronous reactance voltage is 24 per cent, of the 

 open-circuit phase voltage when the armature winding is con- 

 nected in Y. With the same field current what per cent, of the 

 open-circuit armature voltage will the synchronous reactance 

 voltage be when the windings are connected to form a single- 

 phase, open-circuit armature winding? 



48. In problem 47 what is the synchronous reactance voltage 

 with an armature current of 60 amperes i.e., 30 amperes per 

 inductor when the 6 windings are connected to form a single- 

 phase, 2-circuit armature winding? 



(b) With the same field current as in 47 (b) what per cent, of 

 the open-circuit armature voltage will the synchronous react- 

 ance voltage be when the windings are connected to form a 

 single-phase, 2-circuit armature winding? 



49. In problem 47 what is the synchronous reactance voltage 

 with an armature current of 30 amperes when the 6 windings 

 are connected to form a 2-phase armature winding? 



(b) With the same field current as in 47 (b) what per cent, of 

 the open-circuit armature voltage will the synchronous reactance 

 voltage be when the windings are connected to form a 2-phase 

 armature winding? 



60. Two three-phase, 60-cycle alternating-current generators 

 have the same current and voltage rating. The first has 12 

 slots per pole and the second has 9 slots per pole. Each alter- 

 nator has the same number of turns per phase. The first has 

 4 poles and the second 6 but the dimensions of the magnetic 

 circuit are such that the same number of ampere turns on the 

 field produces the same flux per pole in each. The shape of the 

 armature slots is such that the leakage flux per ampere per 

 inductor is also the same for each. 



The armature leakage reactance and the synchronous react- 

 ance of the first alternator are respectively 0.54 ohms and 2.13 

 ohms. What are the corresponding constants of the second 

 alternator? 



51. A 3-phase, delta-connected alternating-current generator 

 is rated to deliver 15 kv.-a. at 230 volts when running at a speed 

 of 1200 rev. per min. There are 6 field poles each of which is 

 wound with 398 turns. The armature has 72 slots with 8-induc- 

 tors in series per slot. Each inductor is 5 in. long. The hot 

 resistance of the armature measured between any two terminals 

 is 0.126 ohm. The effective resistance is 1.6 times the ohmic 



