Question

For a 100 hp 250 V, compound dc motor with compensating winding has a field current of 5 A to produce a voltage of 250 V at 1200 rpm. What will be the shunt field current of this machine at no load?

(a) 5 A

(b) 5.6 A

(c) 4 A

(d) 0 A

I had been asked this question in an interview.

The above asked question is from Operating Characteristics of DC Motors in chapter DC Motors of Electrical Machines

Answer 1

The correct choice is (a) 5 A

Easiest explanation: At no load, armature current is zero, so the internal generated voltage is 250 V. So 5 A will be the shunt field current at no load.