A single phase motor connected to 415 V, 50 Hz supply takes 30 A at a power factor of 0.7 lagging. Calculate the capacitance required in parallel with the motor to raise the power factor to 0.9 lagging.

• A. 66.32 µF
• B. 86.32 µF
• C. 76.32 µF
• D. 96.32 µF

Answer: (B)

P = VIcosφ = 8715 watt
Q = VAR required to improve PF = P(tanφ₁ - tanφ₂) = 4670 VAR
Capacitive Reactance, Xc = V²/Q = 36.8790 ohm.
C = (2πfXc)⁻¹ = 86.314 μF