Question

Exercises

1. A 25 kVA single-phase transformer has the primary and secondary number of turns of 200 and 400, respectively. The transformer is connected to a 220 V, 50 Hz source. Calculate the (i) turns ratio, and (ii) mutual flux in the core.

2. A 25 kVA, 2200/220 V, 50 Hz single-phase transformer’s low voltage side is short-circuited and the test data recorded from the high voltage side are P=150 W, I1 = 5A and V1 = 40 V. Determine the (i) equivalent resistance, reactance and impedance referred to primary, (ii) equivalent resistance, reactance and impedance referred to secondary.

3. A 30 kVA transformer has the iron loss and full load copper loss of 350 and 650 W, respectively. Determine the (i) full load efficiency, (ii) output kVA corresponding to maximum efficiency, and (iii) maximum efficiency. Consider that the power factor of the load is 0.6 lagging. (97.74%, 13.2 kW, 94.96%).

4. A 2.5 kVA, 200 V/40 V single-phase transformer has the primary resistance and reactance of 3 and 12 Ω, respectively. On the secondary side, these values are 0.3 and 0.1 Ω, respectively. Find the equivalent impedance referred to the primary and the secondary. (17.9ohms, 0.72ohms).

Answer 1