Question

A 4-pole Dc wound machine is lap wound with 400 conductors. The pole shore is 20 cm long and average flux density over one-pole pitch is 0.4 T, the armature diameter being 30 cm. What is the value of flux/pole?

(a) 0.188 Wb

(b) 18.88 Wb

(c) 0.0188 Wb

(d) 1.888 Wb

This question was addressed to me during an interview.

I want to ask this question from EMF and Torque Production topic in portion Circuit Model, Emf and Torque of DC Machines

Answer 1

Right option is (c) 0.0188 Wb

To explain I would say: Flux is defined as flux density for a given surface area. Here, Surface area can be calculated and multiplied with B to give the value of flux. Flux= 2πr*l*B. now, for calculating flux per pole, divide it by P=4. So, Flux per pole after substituting all values is equal to 0.0188 Wb.