List three functions which a transformer may perform in an electrical circuit. $[6$ marks$]($B$)$ A $100$kVA, $50$ Hz distribution transformer has $400$ turns in the primary and $80$ turns in the secondary$.$ The primary and secondary resistances are r$1=0\mathrm{.}3$ and r$2=0\mathrm{.}01$ respectively, and the corresponding leakage reactances are Xl$1=1\mathrm{.}1,$ and Xl$2=0\mathrm{.}035$ respectively. The supply voltage is $2200$V$.$ Calculate i$.$ The equivalent impedance, resistance and reactance, referring all quantities to the high voltage $($primary$)$ side; $[4$ marks$]$ ii$.$ The secondary terminal voltage for full load having a power factor of $0\mathrm{.}8$ lagging; $[6$ marks$]$ iii. The regulation in $($ii$)$