A 300-kVA transformer has a core loss of 1.5 kW and a full-load copper loss of 4.5 kW.
(a) Calculate its efficiency corresponding to 25, 50, 75, 100, and 125% loads at unity power factor.
(b) Repeat the efficiency calculations for the 25% load at power factors of 0.8 and 0.6.
(c) Determine the fraction of load for which the efficiency is a maximum, and calculate the corresponding efficiencies for the power factors of unity, 0.8, and 0.6.