122 COMMERCIAL ELECTRICAL TESTING 



next higher taps on the compensator, and so on until 

 the motor starts. Readings should be taken on each of 

 the taps of the compensator in the starting position, 

 with the machine at rest, to determine the voltage ratio 

 of the taps of the compensator. All these tests should 

 be made with the field circuit of the motor open, and 

 enough time allowed between trials to permit the com- 

 pensator to cool, since it is designed for intermittent 

 service only. See Table XIV. 



Input-output efficiency test is made by the input- 

 output method. 



Standard efficiency tests are made by the method of 

 losses. In calculating efficiency, the same nomenclature 

 is used as that employed for alternating current gener- 

 ators. C\ is either taken from the phase characteristics 

 or is calculated in the same manner as for alternating 

 current generators. 



Watts input W a =V L CL+C l 2 R 2 . 

 Watts output = W b = W a -2W. 



- . W b 



bmciency = =r=^- 



W a 



W = open circuit core loss corresponding to VL ~ CR on 

 the core loss curve. 



Wh 

 Horse power output = - 



See Table XV and Fig. 37. 



The non-inductive load heat run is made as follows: 

 Run the machine under load at unity power-factor until 

 it has reached constant temperature and record temper- 

 atures. Take readings of regulation at normal and no 

 load and full load phase characteristics. 



The non-inductive overload heat run consists in bring- 

 ing the machine to normal load temperature, applying 

 the overload for the specified time, recording temper- 

 atures and taking readings of regulation at unity power- 

 factor. 



Normal load power-factor heat run is similar to the 

 normal load non-inductive run, except that the machine 

 is operated at a specified power-factor. Wattmeters 



