Question

What will happen at poles due to armature reaction in DC generator?

(a) Demagnetisation of leading pole tip and magnetisation of trailing pole tip

(b) Demagnetisation of trailing pole tip and magnetisation of leading pole tip

(c) Demagnetising at the centre of all poles

(d) Magnetising at the centre of all poles

I got this question during an online interview.

Query is from Armature Reaction -1 topic in chapter Armature Reaction of DC Machines

Answer 1

Right answer is (a) Demagnetisation of leading pole tip and magnetisation of trailing pole tip

The best explanation: Leading pole tip (LPT) and trailing pole tip (TPT) are the two edges of the pole, they depend upon the direction of motion of the armature (in case of DC). While performing a motion the armature first saws an edge of the pole, that edge is called leading pole tip. Thus, at leading pole tip there will be demagnetization.