A 100-MVA 230/115-kV D-Y three-phase power transformer has a per-unit resistance of 0.015 pu and a per-unit reactance of 0.06 pu. The excitation branch elements are
(a) If this transformer supplies a load of 80 MVA at 0.8 PF lagging, draw the phasor diagram of one phase of the transformer.
(b) What is the voltage regulation of the transformer bank under these conditions?
(c) Sketch the equivalent circuit referred to the low-voltage side of one phase of this transformer. Calculate all the transformer impedances referred to the low-voltage side.
(d) Determine the losses in the transformer and the efficiency of the transformer under the conditions of part (b)