Question

What is the reason behind short circuit in armature?

(a) Insulation failure between two commutator bars

(b) Insulation failure between two turns of a coil

(c) Two or more turns of the same coil getting grounded

(d) Insulation failure between two commutator bars, two turns of a coil or the same coil getting grounded

This question was posed to me in an interview for internship.

My doubt is from Armature Reaction -1 in division Armature Reaction of DC Machines

Answer 1

Correct choice is (d) Insulation failure between two commutator bars, two turns of a coil or the same coil getting grounded

Best explanation: Armature short circuit may occur due to contact of two commutator bars or due to contact in of two coil turns as commutators are connected to respective coil sides. If two or more turns of coil are grounded then they have common end which again leads to short circuit.