180 TREATISE ON ALTERNATING CURRENTS. 



3. The ratio of the watts lost in the armature of an w-phase rotary converter 

 with power factor unity to the watts lost in it when running as a direct-current 

 machine, is 



n* sin 2 - 

 n 



For what value of n is this a minimum ? 



&r 



oo, or n = 



where m is any positive integer. 



Answer. n = oo, or n = -r + m* 



