Question

A step up transformer operates on a $200 \,V$ line and supplies to a load of $2\, A$. The ratio of primary to secondary windings is $1 : 25$. Determine the primary current.

• A. 8.8 A
• B. 0.08 A
• C. 12.5 A
• D. 50 A

Answer 1

Answer: (D)

In a step-up transformer Power in secondary $=$ Power in primary
$V_{s} i_{s}=V_{p} i_{p} \ldots$(i)
Also, from transformation ratio
$\frac{V_{s}}{V_{p}}=\frac{N_{s}}{N_{p}}$
Given, $\frac{N_{p}}{N_{s}}=\frac{1}{25}$,
$V_{p}=200 V$
$\therefore V_{s}=200 \times 25=5000 V$
From Eq. (i),
$5000 \times 2=200 \times i_{p}$
$\Rightarrow i_{p}=50 A$