Question Three

A $3-,1200$kVA,$\frac{6\mathrm{.}6}{1\mathrm{.}1}kV$ transformer has Delta$/$Star connection. The per phase resistance is $2$ and $0\mathrm{.}03$ on primary and secondary respectively. Calculate the efficiency on full load at $0\mathrm{.}9$ p$.$f$.$ lagging, if iron losses are $20$ kW $.$ Question Four

A $5000$kVA,$3$ phase transformer $\frac{6\mathrm{.}6}{33}kV,\frac{}{Y}$ has a no$-$load loss of $15$ kW and full load of $50$ kW $.$ The impedance drop at full load is $7\%.$ Calculate the primary voltage when a load of $3200$ kW at $0\mathrm{.}8$ p$.$f$.$ is delivered at $33$ kV $.$

Question Four

A $500$ kVA, $3-$phase, $50$ Hz transformer has a voltage ratio $($line voltage$)$ of $\frac{33}{11}$ kV and is delta$/$star connected. The resistances per phase are:

high voltage $35,$ low voltage $0\mathrm{.}876$ and the iron loss is $3050$ W $.$ Calculate the value of efficiency at full load and one$-$half of full load with $0\mathrm{.}8$ lagging power factor.