Question

A transformer has an efficiency of 85% and works on 100V, 4 kVA. If the secondary voltage is 200 V then primary current is:
1. 10 A
2. 40 A
3. 20 A
4. 30 A

Answer 1

Correct Answer - Option 2 : 40 A

Concept:

In a transformer with a kVA rating of S,

The primary current \({I_1} = \frac{S}{{{V_1}}}\)

Secondary current \({I_2} = \frac{S}{{{V_2}}}\)

Where V₁ is the primary voltage

V₂ is the secondary voltage

Calculation:

Given that, kVA rating of transformer (S) = 4 kVA

Primary voltage (V₁) = 100 V

Secondary voltage (V₂) = 200 V

Primary current \({I_1} = \frac{{4 \times {{10}^3}}}{{100}} = 40\;A\)