TRANSFORMERS 



191 



The following method is used by the General Electric 

 Company : 

 Let IT? = Total resistance drop due to load current 



expressed in per cent of rated voltage . 

 Let IX = Total reactance drop due to load current ex- 



pressed in per cent of rated voltage. 



IX = V(per cent impedance drop) 2 ( IR) 2 

 Let p = Power-factor (Cos 0) 

 Let w = Wattless factor (Sin 0) 



Per cent regulation = (IR)p + (IX)w+ 



This formula is approximate, but is satisfactory in 

 all practical cases. 



1100 



1000 

 900 

 GOO 

 700 

 600 



ddvCurren 



vt 40O 

 $300 



200 

 IOC 



55<5%Hyst<2 



G 10 12 14 16 /a 2O 22 24 26 23 30 Z2 34 36 J3 4O 

 Cyc/es per second 



Fig. 63 

 Separation Curve 



Special Engineering Tests 



The separation of the core loss from copper loss may 

 be considered as a special test on constant potential 

 transformers. The core loss of a transformer consists 

 of hysteresis and eddy current losses. The hysteresis 

 loss is that due to cyclic reversals of the magnetism of 

 the core, its value depending on the quality of the iron, 

 and in a given transformer varies directly as the frequency 



