14 



COMMERCIAL ELECTRICAL TESTING 



volts field, and amperes field. After reaching the 

 maximum value of the field current, without opening 

 the field reduce the current gradually in four or five 

 steps, again taking readings to determine the value 

 of the residual magnetism at various points along the 

 curve. Special care should be taken to insure accurate 

 readings at and above normal voltage, since with alter- 

 nating current generators, this is the portion of the 



7OO 



600 



SOO 



400 



300 



ZOO 



/OO 



20 



40 60 SO XX) 

 Amperes Fie /a 



I2O 



Fig. 4. Saturation Curve on a 500 Kw., 600 Volt, 20-Pole, 360 R.P.M. 

 3-Phase, 60 Cycle, A-C. Generator 



curve used for calculating the regulation under load. 

 Whenever saturation curves are taken, a record of the 

 air gap from iron to iron should be made upon the record 

 sheet. The length and circumference of spools should 

 also be entered, together with the armature and field 

 specifications. 

 Motor Saturation 



When it is inconvenient or impossible to drive the 

 machine as a generator, a motor saturation may be 



