GATE 2024 IN – Question 61
A 50 kVA transformer has efficiency 95% at full load and unity power factor. Core loss is negligible. Its efficiency at 75% of full load and power factor 0.8 is ______ % (one decimal place).
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Show answer and explanation
Correct answer: 95.2 to 95.4
Explanation
Full-load output at unity power factor is 50 kW. Copper loss is $50(1/0.95-1)=2.63158$ kW. At 75% load it is $0.75^2(2.63158)=1.48026$ kW. Output is $50(0.75)(0.8)=30$ kW. Efficiency is $100(30)/(30+1.48026)=\boxed{95.3}\%$.