Question

If the per unit leakage impedance for the primary of a transformer is ‘x’ on the given rated base value. If the voltage and volt-amperes are halved, then the changed per unit impedance will be ___________

(a) 0.5x

(b) 2x

(c) 4x

(d) x

This question was addressed to me during a job interview.

The query is from Voltage Regulation of Transformer topic in chapter Transformers of Electrical Machines

Answer 1

Correct choice is (b) 2x

The explanation is: pu(new base) = (x)*(MVA(new)/MVA(old))*(kV(old)/kV(new))^2

                         = x*0.5*(4/)

    = 2x.