Question

A balanced three-phase inductive load is supplied in steady state by a balanced three-phase voltage source with a phase voltage of 120Vrms. The load draws a total of 10kW at a power factor of 0.9. Calculate the rms values of the phase currents and the magnitude of per-phase load impedance, assuming a wye-connected load. Draw a phasor diagram showing all three voltages and currents.

Answer 1

Answer: Voltage, V=120V; Power,P=10kW or 10,000W

P = V*I (where I is current)

∴ I = P/V =10000/120 = 83.3A

Resistance, R = V/I = 1.44 ohms

Power Factor(cosФ)= 0.9 = Resistance, R/Impedance, Z

∴ Z = 1.44/0.9 = 1.6 ohms

Explanation: The three-phase inductive load supply carries alternating current of the same frequency and voltage amplitude relative to a common reference but phase difference of one third of a cycle between each of three voltages and currents.