Question

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

(a) 521

(b) 5731

(c) 5231

(d) 571

The question was asked during a job interview.

I'd like to ask this question from Armature Reaction topic in portion Armature Reaction of DC Machines

Answer 1

Right option is (b) 5731

For explanation: For calculations, 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. Cross-magnetizing ampere-turns is given by 6250*(1-2*7.5/180) = 5731 AT/Pole.