POLYPHASE CIRCUITS 



115 



The core loss at the rated voltage is 3330 watts and may be 

 assumed constant. 



(a) When the power delivered to the transmission is 1280 kw. 

 at a power factor of 0.83 and a line voltage of 22,300 volts, what 

 is the combined efficiency of the generator and transformers? 

 Calculate the generator field current by the magnetomotive-force 

 method. 



(b) If this load is removed from the line and 'the field excita- 

 tion of the generator is unchanged, what is the high-tension line 

 voltage? 



56. A 1640-kw., 13,500-volt, 3-phase generator delivers 

 p<> \\t-r to a transmission line through three single-phase trans- 

 formers which are connected in Y on both the high- and low- 

 tension sides. The following data are given on this generator 

 and transformers: 



GENERATOR 



The core loss at the rated voltage is 21.3 kw., and the friction 

 and windage is 8.8 kw. Both of the losses may be assumed con- 

 stant. The effective resistance of the armature is 1.52 ohms per 

 phase. The resistance of the field circuit is 0.392 ohms. The 

 armature windings are connected in Y. 



THANSFOKV! l:> 



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The core loss at the rated voltage is 2960 watts, and may be 

 assumed constant. 



(a) When the output of the generator is linn kw., at 0.92 

 power factor and a terminal voltage of 13,600 volts what is the 

 combined efficiency of the generator and transformers? Cal- 

 culate field current of the generator by the magnetomotive-force 

 method. 



1 Cull-load cur 



