Question

A 300 kVA transformer has a core loss of 1.5 kW and a full load copper loss of 4.5 kW, the maximum efficiency of the transformer is _____________%

• A. 98.29

Answer 1

The correct option is A 98.29
Maximum efficiency occurs at unity power factor and when copper loss is equal to the iron loss.

$\text{kVA rating at maximum efficiency}$
$S_m=S_{fl}\sqrt{\frac{P_i}{P_{cu}}}=300\times \sqrt{\frac{1.5}{4.5}}=173.205kVA$

$\therefore \text{Maximum efficiency}=\frac{\text{Power output}}{\text{Power output + losses}}$

${\eta }_{max}=\frac{173.205}{173.205+1.5+1.5}\times 100\%=98.29\%$