Question

A compensating winding with ampere-turns greater than peak ampere turns is required in order to neutralize the effect of armature reaction because _____________

(a) Pole arc = Pole pitch

(b) Pole arc > Pole pitch

(c) Pole arc < Pole pitch

(d) Can’t be determined using pole arc, pole pitch

I had been asked this question in examination.

The origin of the question is Ways to Reduce Effects of Armature Reaction topic in portion Armature Reaction of DC Machines

Answer 1

Right choice is (b) Pole arc > Pole pitch

Easy explanation: The number of ampere-turns required for compensating winding in a DC machine is ATcw /pole = ATa (peak) *(pole arc/pole pitch) = [IaZ/(AP2)] * (pole arc/pole pitch). Thus, if compensating winding ampere turns are more then, pole arc is definitely greater than pole pitch.