CHAPTER VIII 



PHASE CHARACTERISTIC-SYNCHRO- 

 NOUS AND STATIC IMPEDANCE- 

 WAVE FORM POTENTIAL 

 CURVE 



Phase Characteristic 



In taking phase characteristic curves to determine 

 the field current for minimum input at a given load 

 on either synchronous motors or rotary converters, 

 the machine must be operated as a motor from some 

 source of alternating current, of correct frequency 

 and nearly constant voltage. A reading of amperes 

 input on all phases should be taken with zero field on 

 the motor, when this is possible. Starting with a weak 

 field, volts and amperes armature and volts and amperes 

 field should be read, and the field increased by small 

 steps until the point of minimum input armature current 

 is found. Increasing the field current beyond this 

 point increases the amperes armature. On a no-load 

 phase characteristic curve, the watts input at the 

 lowest point should check very closely with the sum 

 of the core loss, friction and windage losses, since the 

 power-factor is unity on synchronous motors at 

 this point. With a weak field the current is lagging 

 and with a strong field it is leading. In taking a no- 

 load phase characteristic the current should rise to a 

 value of at least 50 per cent of full load current. 



A load phase characteristic should be taken, in a 

 manner similar to that employed in obtaining the no- 

 load characteristic. The input is held constant and the 

 amperes load recorded in addition to the readings 

 specified above. It is impossible to obtain a zero field 

 point on the full load characteristic, since the current 



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