380 



ELEMENTS OF ELECTRICAL ENGINEERING. 



extended over the whole cycle ; but the value of x- dy extended 

 over the whole cycle is the area enclosed by the cB and 3{ curve. 



Therefore, the total energy, in 

 ergs, lost in V cubic centimeters 

 of iron per magnetic cycle is equal 

 to abVI^-jr x area of $ and 3fC 

 curve. This energy loss is called 

 the hvsteresis loss and it is all con- 

 verted into heat. 



The hysteresis loss per cycle 

 increases with the range of flux 

 density during the cycle. This 

 energy loss per cycle may be ex- 

 pressed with sufficient accuracy 

 for most practical purposes (from 

 cB = 2,000 to cB = 12,000) 

 by the empirical equation 



Fig. 17. 



(16) 



which is due to Steinmetz. In this equation W is the loss of 

 energy in ergs per cycle, V is the volume of the iron in cubic 

 centimeters, dt cB is the range of flux density during the cycle, 

 and T; is a constant coefficient, the value of which depends upon 

 the chemical and physical qualities of the iron. The following 

 table gives the values of 77 for different kinds of iron and steel. 



TABLE. 



Values of hysteretic. coefficient rj. 



Best quality of sheet iron for transformer cores, annealed 0.0015 



Sheet iron for armature cores, annealed 0.003 



Ordinary sheet iron, annealed 0.004 



Soft annealed cast iron 0.008 



Soft machine steel.. 0.0095 



Cast steel 0.12 



Cast iron o. 16 



Hardened steel 0.25 



