Question

Four-point starter is used when ______________

(a) Motor field current is varied in narrow range

(b) Motor speed is varied in small range

(c) Motor field current is varied over wide range

(d) Can be used anywhere

I had been asked this question in an interview.

Query is from Starting of DC Motors in portion DC Motors of DC Machines

Answer 1

Correct option is (c) Motor field current is varied over wide range

The best I can explain: Three-point starter is employed where motor field current can be varied in a narrow range and so does the motor speed while four-point starter is used when motor field current can vary over a wide range and so does the motor speed.