S YNCHRONO US GENERA TORS 43 



0.398 ohm per phase. The synchronous reactance is 15.4 ohms 

 per phase. With the armature short-circuited the armature 

 current is 108 amperes when the field current is 50 amperes. 

 The resistance of the field circuit is 0.82 ohm. The friction and 

 windage is 7.6 kw. The core loss due to rotation is 20.2 kw. 

 at 5200 volts and may be assumed to be constant. The open- 

 circuit characteristic is given by the following data: 



Field current Open-circuit terminal voltage 



125 

 150 

 175 



6060 



What is the efficiency of this generator when delivering 10 per 

 cent, overload current at 0.80' power factor (inductive)? 



Calculate the field current (1) by the synchronous impedance 

 method, and (2) by the magentomotive force method. 



73. Concerning the alternator described in problem 54 the 

 following additional data are given. The resistance of the field 

 circuit is 0.37 ohm. The friction and windage is 19 kw. The 

 core loss is given by: 



Terminal voltage on open circuit | Core loss 



1360 

 2000 



24X0 



18.0 kw. 

 36.5 kw. 

 60.0 kw. 



What is the efficiency of this generator for the load described 

 in problem 54? Calculate the field current (1) by the general 

 method, (2) by the synchronous impedance method, and (3) by 

 the magnetomotive-force method. 



74. Concerning the alternator described in problem 58 the 

 following additional data are given. The resistance of the tirl.l 

 circuit is 0.541 ohm. The friction and windage loss is 9.2 kw. 

 Tin- core loss is given by: 



Terminal voltaic on open circuit Con- loss 



x.soo 

 13,000 

 [0,600 



7.5 kw. 

 16.6 kw. 



j:, i ku 



I7.'j:>u B kw, 



What i> the efficiency of this generator for the load described 

 in problem 58? 



