THE TRANSFORMER. 211 



The effect of eddy currents in the core is to cause a harmonic current in phase with 

 E ' to flow through the primary coil in addition to the current represented by the 

 curve m in Fig. 177. 



103. Loss of power in transformers. The power output of a 

 transformer is always less than its power intake because of the 

 loss of power in the transformer. This loss of power in a trans- 

 former consists of two parts, namely, (a) The iron or core loss 

 due to eddy currents and hysteresis ; and (b) The copper loss 

 due to the resistances of the primary and secondary coils. 



The iron losses are practically the same in amount at all loads, 

 and they depend upon the frequency, upon the range of the flux 

 density <$, upon the quality and volume of the iron, and upon 

 the thickness of the laminations. 



The hysteresis loss in watts is 



P h = aVf& (26) 



where / is the frequency in cycles per second, cB is the maxi- 

 mum flux density in lines per square centimeter, V is the volume 

 of the iron in cubic centimeters, and a is a constant depending 

 upon the magnetic quality of the iron. For annealed refined 

 wrought iron the value of a is about 3 x IO~ 10 . 

 The eddy current loss in watts is : 



P e = bVfW&? (27) 



where / is the thickness of the laminations in centimeters, and b 

 is a constant depending upon the specific electrical resistance of 

 the iron. For ordinary iron the value of b is about 1.6 x io~ u . 

 Insufficient insulation of laminations causes an excessive eddy cur- 

 rent loss. 



Equations (26) and (27) may be used for calculating the hys- 

 teresis and eddy current losses in any mass of laminated iron 

 subjected to periodic reversals of magnetization, such as alternator 

 armature cores and the rotor and stator iron in an induction 

 motor. 



The copper loss is : 



P c = R'I n + R"I"' i (28) 



