# GATE Papers >> EEE >> 2018 >> Question No 11

Question No. 11

A single-phase 100 kVA, 1000 V / 100 V, 50 Hz transformer has a voltage drop of 5% across its series impedance at full load. Of this, 3% is due to resistance. The percentage regulation of the transformer at full load with 0.8 lagging power factor is

Solution of Question No 11 of GATE 2018 EEE Paper

Impedance = 5% = 0.05 pu

Resistance = 3% = 0.03 pu

Reactance = $\sqrt{\left(0.05\right)^2-\left(0.03\right)^2}$ = 0.04 pu

VR (0.8 pf log) = R cos$\mathrm\phi$ + X sin$\mathrm\phi$ = 0.03 $\times$ 0.8 + 0.04 $\times$ 0.6 = 0.048 pu = 4.8%