Question

A 10KVA 400/200V single phase transformer with a resistance of 3% and a reactance of 6% is supplying a current of 50A to a resistive load. What will be the voltage across load​

Answer 1

Since you gave no line data, I will assume and ideal line with 0 impedance.

V-base = 220 volts, I base = 10 kVA / 220 V = 45.45 amps.

Since it is a standard to give the value of impedance for a transformer on the bases of the transformer voltage and VA capacity, I assume the %R + j%X to be as stated, 3 + j6 % = 0.03 +j 0.06 per unit.

V-load = (V-source) - (V-drop in the transformer) = V-source - (V-source - I-pu*Z-pu)

I - load = 50 amps at 0°, I-per unit then is 50/45.45 = 1.1 at 0°

V-Load = (1 at 0°) - (1@0° - [(1.0@0°) - (1.0@0° - (1.1@0° * [email protected]°)

V-Load = 1.0@0° - ([email protected]°) = [email protected]° Per unit = 213.2 Volts at -3.91°

Whoops, I used 220 volts and not 200 volts for the base voltage. My mistake. The method would be the same with V-base becoming 200 volts and I-base becoming 50 amps.