An $11$ kV $/250$ V$,50$ kVA single$-$phase transformer is

supplied from a constant $11$ kV source. The primary and

secondary windings have resistances of $20$ W and $0\mathrm{.}015$ W

respectively. The leakage reactance of the transformer

referred to the primary side is $120$ W$.$

Calculate the full$-$load regulation at $($i$)$ unity power factor,

$($ii$)0\mathrm{.}8$ pf lagging and $($iii$)0\mathrm{.}8$ pf leading.