Question

What is the formula of window space factor, when the transformer rating is 20 kVA?

(a) 10 / (30+kV)

(b) 12 / (30+kV)

(c) 8 / (30+kV)

(d) 19 / (30+kV)

This question was addressed to me in a job interview.

The question is from Window Space Factor in chapter Design of Transformers of Design of Electrical Machines

Answer 1

Correct answer is (c) 8 / (30+kV)

To explain I would say: 10 / (30+kV) denotes the empirical value of window space factor for rating between 50-200 kilo-volt-amp. 12 / (30+kV) is the window space factor for transformers having rating around 1000 kVA.