Find the capacitor bank you need to raise power factor. Enter the load in kW, the power factor you have now and the one you want. You get the kVAR, the nearest standard size and how much the current falls.
Sizes the capacitor bank for a steady load. For loads with harmonics (VFDs, UPS) get a detuned reactor bank and an engineer to check it.
Formulas and assumptions
- Capacitor kVAR: kW times (tan of the existing angle minus tan of the target angle), where the angle is the arc cosine of the power factor
- kVA: kW divided by power factor
- Current: kVA times 1000, divided by (1.732 times line voltage)
- Current reduction: 1 minus (existing power factor divided by target power factor)
Example
A 100 kW load at power factor 0.8 raised to 0.95 needs 42.1 kVAR, so a 50 kVAR bank. Apparent power falls from 125 kVA to 105.3 kVA, and the current at 400 V from 180.4 A to 151.9 A.
Frequently asked questions
Why correct the power factor?
A low power factor means more current for the same useful power. That raises cable and transformer loading and losses, and many utilities charge a penalty below about 0.9.
What power factor should I aim for?
Most utilities want 0.95 or higher. Going very close to 1 can cause overcorrection at light load, so 0.95 to 0.98 is usual.
Can I connect the capacitor at the motor?
Yes for a single large motor, but keep it small enough to avoid overvoltage when the motor is switched off. For many loads, use a central automatic bank at the panel.
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