Question

The efficiency of a 20 KVA, 2000/200 V, single phase transformer at unity pf is 98%. The total losses at this condition is?

(a) 408W

(b) 4.08kW

(c) 204W

(d) 2.04kW

I had been asked this question during an interview for a job.

The origin of the question is Transformer Losses and Efficiency topic in chapter Transformers of Electrical Machines

Answer 1

Correct option is (a) 408W

For explanation: Efficiency = 1-(losses/input) = 1-(losses/output+losses)

              0.98 = 1-(Losses/20000+losses)

     Losses = 408 W.