Question

A 400 kVA transformer has core loss of 700 W and a full load copper loss of 2800 W. The maximum efficiency of the transformer at unity power factor will be

• A. 95.70%
• B. 99.30%
• C. 98.10%
• D. 92.70%

Answer 1

The correct option is B 99.30%

For maximum efficiency at unity power factor using condition,
$(kVA{)}_m=(kVA{)}_{fl}\sqrt{\frac{P_i}{P_{cu}}}=400\sqrt{\frac{700}{2800}}$
$=400\sqrt{\frac{1}{4}}=200kVA$

$\text{At maximum efficiency,}$ $P_c=P_i$

$\%{\eta }_{max}=\frac{200}{200+\frac{700}{1000}+\frac{700}{1000}}=99.30\%$