THE MAGNETIC CIRCUIT 



[ART. 34 



the flux is approaching its maximum, the current is increasing 

 faster than the flux, on account of saturation. The amplitude 

 factor of the current wave, or the ratio of the amplitude to the 

 effective value is no more equal to V'2, but is larger. Let this 

 ratio be denotedby / a . Then eq. (41) becomes 



(43) 



whore to is as before the effective value of the reactive component 

 of the exciting current. The value of % a is obtained by actually 



2.5 



.2.0 



1.0 



0.5 



0.0 



ot- 



10 



15 

 Flux density in Kl. per Sq. Cm. 



FIG. 22. Ratio of the amplitude to the effective value of the magnetizing 



current. 



plotting the curve of the magnetizing current from point to point 

 and calculating its effective value. Since the procedure is rather 

 long, it is convenient to calculate the values of % a once for all for 

 the working range of values B m . This has been done for the mate- 

 rials represented in Fig. 3, and the results are plotted in Fig. 22. 



Strictly speaking, the exciting current is unsymmetrical, due 

 to the effect of hysteresis, and the values of y a ought to be cal- 

 culated, using the hysteresis loops of the steel. However, it is very 

 nearly correct to calculate / a from the magnetization curve, and to 



