Question

What will happen if field current of generator in Hopkinson’s test is increased?

(a) Current through motor armature will increase

(b) Current through motor armature will decrease

(c) Current through motor armature will remain constant

(d) Motor armature current cannot be determined

I have been asked this question during an interview.

Question is from Hopkinson’s Test in section Efficiency and Testing of DC Machines

Answer 1

Right option is (a) Current through motor armature will increase

The best explanation: If field current through generator is increased, back emf of generator will increase thus it’ll become greater than back emf of a motor, so to compensate this effect armature current in generator will increase thus, motor armature current will also increase.