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Power Factor Correction (kVAr) Calculator
Calculate the capacitor reactive power (kVAr) needed to correct the power factor of an electric motor or installation from cos φ₁ to a target cos φ₂.
Required capacitor: — kVAr
Qc = P · (tan φ₁ − tan φ₂)
About power factor correction
Asynchronous electric motors draw reactive power, lowering the power factor and increasing current and losses. Adding capacitors (kVAr) raises cos φ, reduces demand charges and frees up transformer/cable capacity. Always coordinate capacitor sizing with your electrical engineer and avoid over-compensation on lightly loaded motors.
Related tools: Electric Motor Calculator · Energy Savings · Pump & Fan Power.
Typical motor power factor by load
| Load | cos φ |
|---|---|
| Full load | ~0.85 |
| 3/4 load | ~0.80 |
| 1/2 load | ~0.70 |
| No load | ~0.20 |
Lightly loaded motors have a poor power factor — a key reason to right-size the motor (see our energy savings tool).
Frequently asked questions
What is power factor correction?
It is adding capacitors to supply the reactive power that motors draw, raising cos φ closer to 1. This lowers current, losses and reactive-energy charges.
How many kVAr do I need?
Qc = P · (tan φ₁ − tan φ₂). Enter the active power and the current/target power factor in the calculator above.
What target power factor should I aim for?
Typically 0.95–0.99. Many utilities penalise below ~0.95. Avoid going to exactly 1.0 to prevent over-compensation.
Is over-compensation harmful?
Yes. Too much capacitance leads to a leading power factor, possible overvoltage and resonance. Size carefully, especially for lightly loaded motors, and prefer automatic banks for varying loads.
Fixed or automatic compensation?
Fixed capacitors suit a single steady motor; automatic (switched) banks suit installations with varying load.