Question

In order to neutralize armature mmf perfectly under the pole shoe, the ampere-conductors of compensating winding must be (pole arc/pole pitch=1) _______

(a) Not equal to the total armature ampere conductors under the pole shoe

(b) Equal to the total armature ampere conductors under the pole shoe

(c) Half of the total armature ampere conductors under the pole shoe

(d) Twice of the total armature ampere conductors under the pole shoe

I have been asked this question during a job interview.

My question comes from Ways to Reduce Effects of Armature Reaction topic in portion Armature Reaction of DC Machines

Answer 1

Correct answer is (b) Equal to the total armature ampere conductors under the pole shoe

To explain: The number of ampere-turns required for compensating winding is ATcw /pole = ATa (peak) *(pole arc/pole pitch) = [IaZ/(AP2)]*(pole arc/pole pitch). Here, pole arc= pole pitch, is given. Thus ampere-conductors required are equal to the total armature ampere conductors under the pole shoe.