Question

What is the relation between maximum power and the number of poles?

(a) maximum power factor is directly proportional to the number of poles

(b) maximum power factor is directly proportional to the square of the number of poles

(c) maximum power factor is indirectly proportional to the number of poles

(d) maximum power factor is indirectly proportional to the square of the number of poles

The question was asked during a job interview.

Asked question is from Dispersion Coefficient topic in portion Three Phase Induction Motor of Design of Electrical Machines

Answer 1

The correct choice is (c) maximum power factor is indirectly proportional to the number of poles

Explanation: Short circuit current is indirectly proportional to the number of poles. The short circuit current increases the dispersion coefficient. As the dispersion coefficient increases, the maximum power factor decreases.