Question

In DC machines the residual magnetism is present. The order of residual magnetism is ___________

(a) 2 to 3 per cent

(b) 10 to 15 per cent

(c) 20 to 25 per cent

(d) 50 to 75 per cent

I had been asked this question in class test.

My question is taken from DC Motor Basics -1 in section DC Motors of DC Machines

Answer 1

Right answer is (a) 2 to 3 per cent

For explanation I would say: In a DC machine residual magnetism is present and it plays very important role in starting of any DC machine. It’s present because of the previous application on the same motor, it also provides some no-load voltage.