Question

The armature reaction in a DC machine causes distortion in the main field flux. Effect of armature reaction can be reduced by_________

(a) Increasing the length of air gap

(b) Decreasing the length of air gap

(c) Increasing the number of poles

(d) Decreasing the number of poles

This question was addressed to me at a job interview.

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

Answer 1

The correct choice is (b) Decreasing the length of air gap

To elaborate: Decreasing the air gap is simple to say but hard to achieve, due to various other limitations. But it is one of the way to reduce dropping down of armature mmf flux density distribution, which further reduces the distortion of resultant flux density.