102 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



slot. The field structure has 8 poles witu 1501 turns in the shunt 

 winding and 2 turns in the series winding per pole. A current of 

 5.6 amperes in the shunt field winding alone is the normal excita- 

 tion and produces a voltage of 600 volts on the direct-current 

 side at no load when running as a generator. 



When this rotary delivers 1500 amperes at 600 volts what should 

 be the shunt field current in order that the current on the alter- 

 nating-current side shall be leading and not exceed its full- load 

 value and the power factor have its least value? What is this 

 power factor? Neglect any change in the efficiency. 



54. l At full load and when operating at unit power factor a 

 6-phase, 60-cycle rotary converter receives a line current of 840 

 amperes at a voltage of 424 volts between diametrical points of 

 the armature and delivers on the direct-current side a current of 

 1667 amperes at 600 volts. The armature has 15 slots per pole 

 with 6 inductors in series per slot. On each field pole there are 

 864 turns in the shunt winding and 2 turns in the series winding. 

 A current of 9.3 amperes in the shunt field winding alone is the 

 normal excitation and produces a voltage of 600 volts on the 

 direct-current side at no load when running as a generator. 

 When this rotary delivers 1460 amperes at 600 volts what are 

 the limits of the shunt field current in order that the current 

 on the alternating-current side shall not exceed its full-load 

 value and the power factor have its least value? What are 

 these limiting power factors? Neglect any change in the 

 efficiency. 



55. l At full load and when operating at unit power factor a 

 6-phase, 25-cycle rotary converter takes a line current of 840 

 amperes at a voltage of 424 between diametrical pointe and 

 delivers 1667 amperes at 600 volts. The armature has 21 slots 

 per pole with 6 inductors in series per slot. Each field pole is 

 wound with 1501 turns. The resistance of the field circuit with 

 the regulating rheostat cut out is 76.6 ohms. A current of 5.6 

 amperes in the field winding is the normal excitation: i.e., for 

 full load and unit power factor. With an output of 850 kw. at 

 600 volts what is the least power factor at which this rotary can 

 be operated when overexcited? What per cent, is the current 



1 In calculating the armature reaction do not neglect the distribution of 

 the winding, and assume that the constant usually given as 0.707 is 0.60. 

 This makes an approximate correction for the effect of the ratio of pole arc 

 to pole pitch. 



