58 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



The friction and windage loss is 62.8 h.p. 



What is the efficiency of this motor when rt receives 450 

 amperes at unit power factor, and its rated voltage? 



15. The following test data are given on a 1340-h.p., 13,800- 

 volt, 3-phase synchronous motor. The armature windings, 

 which are connected in Y, have an effective resistance of 2.18 

 ohms per phase. The resistance of the field circuit is 0.541 ohm. 



The friction and windage loss is 11.2 h.p. 



What is the efficiency of this motor when it delivers 1200 h.p. 

 if the excitation is greater than normal and is adjusted so that 

 the motor takes an armature current of 47.6 amperes at a 

 terminal voltage of 13,500 volts? 



16. A synchronous motor, whose armature windings are 

 connected in Y, has an effective resistance of 0.94 ohm and a 

 synchronous reactance of 56 ohms per phase. This motor 

 receives a line current of 60 amperes at a terminal potential 

 difference of 11,000 volts and the excitation is adjusted so that 

 the power factor is 0.85. 



What power does the motor receive? What is the exci- 

 tation voltage (a) if the excitation is greater than normal, 

 (b) if the excitation is less than normal? 



17. A 2-phase synchronous motor has an effective armature re- 

 sistance of 0.64 ohm and a synchronous reactance of 23 . 7 ohms 

 per phase. The motor receives 3000 kw. at a line potential 

 difference of 10,000 volts and the excitation adjusted so that 

 the line current is 200 amperes. 



