First slide

Electrical machines and devices

Question

A step-down transformer is used on a 1000 V line to deliver 20 A at 120 V at the secondary coil. If the efficiency of the transformer is 80% the current drawn from the line is .

Moderate

A

3 A
B

30 A
C

0.3 A
D

2.4 A

Solution

$\begin{array}{l} η = \frac{Output}{Input} \Rightarrow \frac{80}{100} = \frac{120 \times 20}{1000 \times i_{l}} \\ \Rightarrow i_{l} = \frac{20 \times 120 \times 100}{1000 \times 80} = 3 A . \end{array}$

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