Exam Question

(a) Draw the complete phasor diagram of the transformer under no-load conditions. (6)

(b) The following results were obtained on a 50 kVA transformer: open-circuit test - primary voltage, 3300 V; secondary voltage, 415 V; primary power, 430 W. Short circuit test - primary voltage, 124 V; primary current, 15.3; primary power, 525 W; secondary current, full-load value.

Calculate: (10)

(a) the efficiencies at full load and at half load for 0.7 power factor.

(b) the voltage regulations for power factor 0.7, (i) lagging,

(ii) leading;

(c) the secondary terminal voltages corresponding to (i) and (ii)