MAXIMUM OUTPUT TESTS 35 



The load at which a synchronous motor breaks 

 from synchronism when operating at its normal rated 

 voltage and frequency is often necessary. All maximum 

 output tests on synchronous motors, unless stated to 

 the contrary, should be made with a field excitation 

 giving minimum input armature current for a given 

 load. Readings must therefore be taken of volts arma- 

 ture, amperes armature, amperes field and volts field, 

 with various loads from no load to that load which 

 will cause the motor to break from synchronism, the 

 field strength being adjusted for each reading to give 

 minimum input. The speed of a synchronous motor 

 will be constant until the point of breakdown is reached, 

 whereas that of an induction motor will decrease from 

 no load to the breakdown point. 



In case sufficient power is not available to make a 

 maximum output test upon a synchronous motor at its 

 normal rated voltage, its voltage may be reduced below 

 normal, as described for induction motors. If the 

 minimum input obtains when the readings are taken, 

 the output of the motor at normal voltage may be 

 determined in the manner described for induction 

 motors. 



The wiring for this test must be arranged so that the 

 armature circuit of the motor can be opened imme- 

 diately when the motor breaks from synchronism. 



