ALTERNATORS. 



229 



In fact the greater the angle of lag or lead the less is the 

 proportionate effect of decrease in the power-factor. This is 

 owing to the fact which has been stated already, that 

 the demagnetising action of the armature current is propor- 

 tional to sin 0. The rate of increase of sin <f> is most rapid 

 when <f> is small and decreases as sin approaches its 

 maximum value of 1. Thus, a given increase in the value 

 of <t> produces a much greater effect when the actual angle of 

 lag is small. Further, the angle whose cosine is -9, is 26 

 and the angle whose cosine is -8 is 37, so that by taking 

 successive equal increments or decrements of power-factor 

 or cos 0, we are taking successively decreasing values of <j>. 

 There is thus a double reason for the apparently rapidly 

 diminishing effect of decrease in power-factor upon the slope 



i-o 



70 



80 



90 



Volts 



100 



110 



120 



FIG. 106. VARIATION OF VOLTAGE WITH POWER FACTOR. LEADING CURHK.NTS. 



