A $500$ KVA, $230/13\mathrm{.}8$ KV single$-$phase power transformer has a resistance

of $1\%$ per unit a reactance of $5\%$ per unit. The following data is the result of

the open circuit test which was performed on the low voltage side of the transformer.

$=13\mathrm{.}8=21\mathrm{.}1$A

$=90\mathrm{.}8$

a$)$ Find the equivalent circuit referred to the low voltage side of this

transformer.

b$)$ If the voltage on the secondary side is $13\mathrm{.}8$ kV and the power supplied is

$4000$ kW with a PF $=0\mathrm{.}8$ lagging, find the voltage regulation of the

transformer.