A single$-$phase transformer, $50$ Hz$,2400/240$ V$,50$ kVA:

OC test from the LV side: $240$ V$,4\mathrm{.}71$ A$,865$ W

SC test from the HV side: $96$ V$,20\mathrm{.}8$ A$,1420$ W

The transformer is supplied with a voltage of $2400$ V$.$

a$.$ Calculate the daily efficiency if the transformer is loaded at $80\%$ of full load with a power factor of $0\mathrm{.}9$ lagging from $07$:$30$ to $16$:$30.$

b$.$ Draw the equivalent circuit of the transformer under no$-$load conditions, as seen from the LV side.

c$.$ Do you agree that the transformer should operate at maximum efficiency? Why?