SATURATION TESTS 



15 



made. In this case the machine is operated as a free 

 running motor. The driving power must be furnished 

 from a variable voltage circuit. A certain voltage is 

 impressed upon the armature, and the motor field 

 weakened or increased in the case of direct current 

 machines until normal speed is obtained, when a record 

 is made of the volts armature, amperes armature, 

 amperes field, volts field, and speed. The starting 

 voltage should be at least 50 per cent lower than the 



TABLE I SATURATION 



normal voltage of the apparatus. The applied voltage 

 at the armature should be increased by steps to 25 per 

 cent above normal value, and the field increased corres- 

 pondingly to keep the speed constant ; the same readings 

 being recorded at the various steps as before. Readings 

 should also be taken at three or four points as the 

 impressed voltage and field current are lowered to 

 approximately the value at the beginning of the test. 



When testing direct current apparatus in the above 

 manner care should be taken to see that excessive speeds 

 do not result from unstable electrical conditions, and 



