Question

A single-phase two winding transformer is designed to operate at 400/200 V, 50 Hz. If the h.v. side is now energized from a 400 V, 40 Hz source, the no-load l.v. side voltage would be
1. 300 V
2. 250 V
3. 200 V
4. 150 V

Answer 1

Correct Answer - Option 3 : 200 V

For the transformer when excited from different frequencies, the ratio of voltage to frequency always remains constant.

\(\frac{{{V_1}}}{{{f_1}}} = \frac{{{V_2}}}{{{f_2}}}\)

So, applying this concept for the HV side:

\(\frac{{400}}{{50}} = \frac{{{V_2}}}{{40}}\)

Therefore, the voltage on the HV side is,

V₂ = 320 V

And Voltage on LV side using transformer by using turns ratio,

Turn ratio, \(a = \frac{{{V_{HV}}}}{{{V_{LV}}}}\)

Therefore, V_LV = 320 / 2 = 160 V

But we are asked the voltage at the LV side at no-load.

A no-load test is performed at the Rated Voltage and Rated Frequency condition.

Therefore, V_LV = 200 V, remains the same.