A 20 kVA, 220 V / 110 V, 50 Hz single-phase transformer has a full load copper loss of 200 W and a core loss of 112.5 W. At what kVA and load power factor should the transformer be operated for maximum efficiency?
Two identical 100 kVA transformers have an iron loss of 150 W and a copper loss of 150 W at rated output. Transformer-1 supplies a constant load of 80 kW at a power factor of 0.8 lagging throughout 24 hours, while transformer-2 supplies 80 kW at a unity power factor for 12 hours and 120 kW at a unity power factor for the remaining 12 hours of the day. The all-day efficiency: