Question

For 6252 AT/Poles, if brush shift is of 2.50 mech. Degrees, what will be the demagnetizing ampere-turns per pole for a 6-pole DC machine?

(a) 521

(b) 5731

(c) 5231

(d) 571

This question was posed to me during an interview.

This question is from Armature Reaction in section Armature Reaction of DC Machines

Answer 1

Right choice is (a) 521

The best I can explain: From given mech. Degrees shift we need to find electrical degrees shift. Electrical shift= mechanical shift*(P/2). Thus, electrical shift is equal to 7.50. Demagnetizing ampere-turns is given by 6250*(2*7.5/180) = 521 AT/Pole.