Question

A step down transformer converts transmission line voltage from 11000 V to 220 V. The primary of the

transformer has 6000 turns and efficiency of the transformer is 60%. If the output power is 9kW, then the input

power will be

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

Answer 1

Answer: (D)

15 kW

Answer 2

: Here, $V_{P} = 11000V,V_{s} = 220V$

$N_{P} = 6000,\eta = 60\%$

$P_{o} = 9kW = 9 \times 10^{3}W$

Efficiency, $\eta = \frac{Outputpower}{Inputpower} = \frac{P_{o}}{P_{i}}$

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