Question

In the Hopkinson’s test on two DC machines. Machine A has field current of 1.4A and B has field current of 1.3A. Which machine acts as generator?

(a) B

(b) A

(c) A,B

(d) None of the mentioned

This question was addressed to me during an online interview.

Enquiry is from Efficiency and Testing of DC Machines topic in division DC Machines of Electrical Machines

Answer 1

The correct choice is (b) A

To elaborate: Ea/Eb = 1.4/1.3

             Ea = 1.077 Eb > Eb

             So, the machine will act as generator.