Question

A single phase, 10 kVA, 2400/240 V, 60 Hz, distribution transformer has the following characteristics:
Core loss at rated voltage = 100 W
Copper loss at half load = 60 W
If the transformer delivers full load at 0.8 p.f. lagging then the efficiency is ______%.

• A. 95.92

Answer 1

The correct option is A 95.92
$P_{\text{core loss}}=100W$

$\text{Copper loss at half load = 60 W}$
$\therefore \text{Copper loss at full load}=\frac{60}{(0.5{)}^2}=240W$
$\therefore \%{\eta }_{fl}=\frac{(10\times {10}^3\times 0.8)}{(10\times {10}^3\times 0.8)+P_{core}+P_{copper}}\times 100\%$
$=\frac{(10\times {10}^3\times 0.8)}{(10\times {10}^3\times 0.8)+100+240}\times 100\%$

$\%{\eta }_{fl}=95.92\%$