192 



COMMERCIAL ELECTRICAL TESTING 



and as the 1.6 power of the magnetic density. Eddy 

 current loss is due to electric currents flowing in the iron, 

 and varies with the conductivity of the iron, the thick- 

 ness of the laminations, and the square of the frequency. 

 The method for separating the losses is as follows: 

 Since the hysteresis loss varies directly as the frequency 

 and the eddy current loss as the square of the frequency, 

 by maintaining a given density in the core and varying 

 the frequency, data can be obtained from which a separa- 

 tion curve can be plotted. The voltage to be applied 



1000 

 900 



eoo 



7OO 

 600 



\aoo 



4OO 

 300 

 ZOO 

 .'00 



O 2 4 6 6 IO 12 14 16 IQ 2O 22 Z4 26 2Q 3O 32 34 36 3d 



Cyc/es per second 



Fig. 64 

 Separation Curve 



varies directly with the frequency at which it is applied; 

 thus 100 volts at 60 cycles becomes 200 volts at 120 

 cycles. Plotting watts per cycle as ordinates and cycles 

 per second as abscissas, curves similar to those shown in 

 Fig. 63 are obtained. At least four points should be taken 

 to determine the curve. By comparing the losses at 

 normal frequency and density, the quality of the iron and 

 the insulation between laminations can be deduced. 



The eddy current loss in the copper conductors of a 

 transformer may be separated from the ohmic loss in 

 the following manner : The ohmic loss is independent of 

 frequency, while the eddy current loss varies with the 

 square of the frequency. Hold the current constant and 



