CHAPTER II 



SATURATION TESTS, GENERATOR, 

 MOTOR, BALLISTIC 



In order to ascertain the characteristics of the magnetic 

 circuit, a test known as "saturation" is made. The 

 characteristic curve may be obtained by any of the 

 following methods: "generator saturation/' "motor 

 saturation," and "ballistic saturation." 



The test usually made is "generator saturation." 

 To obtain a saturation curve by this method, the machine 

 is driven as a generator, preferably at constant speed. 

 If, however, a set of readings is known for one speed, 

 they can be obtained for any other by direct proportion. 

 Hence a saturation curve taken at any constant speed 

 at once gives the saturation curve at any other speed. 

 On direct current machines the brushes should always 

 be set on the neutral point when taking a no-load sat- 

 uration. 



In taking a saturation curve on polyphase alternating 

 current generators, a reading of the voltage across each 

 phase must be taken at normal field current, to ascertain 

 if the phases are properly balanced. If they do not 

 balance, an error in the armature is indicated, which 

 must be corrected. On rotary converters careful read- 

 ings should be taken of the direct current voltage, as 

 well as the alternating current voltage between all 

 phases, with the field excitation giving normal voltage. 

 The phase voltages must be also closely balanced. 

 Generator Saturation 



The usual method of taking a generator saturation 

 curve is to hold the speed constant and increase the 

 field current step by step until at least 125 per cent of 

 the normal voltage of the machine is reached, taking 

 simultaneous readings at each step of volts armature, 



[13] 



