Question

In differential compound excited machine, what is the variation in air gap flux per pole with respect to armature current?

(a) Increases

(b) Decreases

(c) Remains constant

(d) Always varies

I had been asked this question in an interview for job.

This interesting question is from Methods of Excitation in chapter Commutation Process & Excitation Methods of DC Machines

Answer 1

The correct choice is (b) Decreases

To explain: If the two fields oppose each other, the excitation is called differential compound. The air gap flux/pole decreases with armature current. The series field is so designed that the increase or decrease in flux/pole is to a limited extent.