Question

Under commutation results ________

(a) sparking at the  trailing edge of brush

(b) sparking at the  leading edge of brush

(c) sparking at the  middle of brush

(d) any of the mentioned

I have been asked this question in examination.

The origin of the question is Action of Commutator in chapter Electrical Machine Applications/Armature Reaction and Commutation of Electrical Machines

Answer 1

Correct option is (a) sparking at the  trailing edge of brush

Explanation: Under commutation takes place when the commutation speed is slow and it takes more time than critical defined time for commutation. Because of this the trailing edge of the brush still remains under the commutation.