Question

For a single phase, 50 Hz transformer, if the open circuit test is conducted at 40 Hz. What is the variation in the no-load power factor of the transformer?

(a) Decreases

(b) Increases

(c) Remains constant

(d) None of the mentioned

I had been asked this question during an online exam.

I want to ask this question from Machine Ratings topic in chapter Rating and Loss Dissipation of Electrical Machines

Answer 1

Correct answer is (a) Decreases

Best explanation: If the frequency reduces then flux density increases, so the flux and then the magnetizing current. When magnetizing current increases power factor angle increases so the power factor decreases.