Question

The power factor of a synchronous motor __________

(a) Improves with an increase in excitation and may even become leading at high excitations

(b) Decreases with increase in excitation

(c) Is independent of its excitation

(d) Increase with loading for a given excitation

I had been asked this question during an online interview.

This key question is from Effect of Starting on Power Supply, Motor and Load in portion Starting of Electric Drives

Answer 1

Right option is (a) Improves with an increase in excitation and may even become leading at high excitations

Easiest explanation: From inverted V-curve we can see when the power factor is leading power factor decreases when the excitation increases and it is over-excited conditions and when power factor is lagging if the motor power factor is increasing if excitation increases.