INDUCTION MOTORS 



129 



induction motors depends entirely on test results, and 

 great care must therefore be taken to obtain accurate 

 measurements . 



The motor should be located so that all the conditions 

 affecting its operation during test remain unchanged 

 throughout the run. A solid foundation is necessary to 

 prevent vibration at full speed, and the table must not 

 be near any source of stray field. The driving alternator 

 should be at least J4 the kw. capacity of the motor. 



M L 



/? C 5 



Fig. 38. Wattmeter Connections for Excitation' 



The transformers and other apparatus must be con- 

 nected so that the alternator will work under normal 

 conditions, since satisfactory wattmeter readings cannot 

 be obtained if the alternator is run too low on the 

 saturation curve. Transformers, when used, must be 

 well balanced and not forced beyond their voltage 

 range, otherwise unsatisfactory results may be obtained. 

 The table must be adapted for wattmeters by provid- 

 ing a special wattmeter switch connected on two of the 

 three phases as shown in Fig. 38. A and B are the ter- 

 minals for the current leads to the wattmeters, X and Z 

 being the short circuiting switches. Calling the phases 



