Question

A step-down transformer converts transmission line voltage from $11000V$ to $220V$ The primary of the transformer has $6000$ turns and the efficiency of the transformer is $60$ %. If the output power is $9kW,$ then the input power will be

• A. $11kW$
• B. $12kW$
• C. $14kW$
• D. $15kW$

Answer 1

The correct option is D $15kW$

Here, $V_p=11000V,V_s=220V$
$N_p=6000,\eta =60$

Efficiency, $\eta =\frac{output}{Inputpower}=\frac{P_0}{P_i}$

$\therefore p_i=\frac{P_0}{\eta }=\frac{9\times {10}^3}{60/100}=1.5\times {10}^4=15kW$