Question

What is a commutator in DC machines?

(a) electrical device which reverses the current direction between the rotor and external circuit

(b) mechanical device which reverses the current direction between the rotor and external circuit

(c) electrical device which allows the current flow between the rotor and external circuit

(d) mechanical device which allows the current flow between the rotor and external circuit

I have been asked this question in a job interview.

Question is taken from Design of Commutator and Brushes topic in chapter Thermal Design Aspects of Electrical Machines & D.C of Design of Electrical Machines

Answer 1

Correct choice is (a) electrical device which reverses the current direction between the rotor and external circuit

To explain: Commutator is an electrical device found only in DC machines. It is used to reverse the current direction between rotor and external circuit. It also changes dc voltage to alternating voltage.