How to use the power factor correction calculator
- Enter the real power in kilowatts that the load draws.
- Enter the present power factor and the target power factor you want. The target must be higher.
- Choose single or three phase and, if you want currents, enter the line voltage.
- Read the kvar to remove, the apparent power and current before and after, and the share of apparent power saved.
Formula
Reactive power = kW x tan(arccos(power factor))
Capacitor kvar = kW x (tan(arccos(present pf)) - tan(arccos(target pf)))
Apparent power (kVA) = kW / power factor
Current = kVA x 1,000 / voltage (single phase) or kVA x 1,000 / (square root of 3 x voltage) (three phase)
Real power does the work. Reactive power moves back and forth with no net work, and it adds to the current. Capacitors supply reactive power locally, so the supply carries less.
100 kW from 0.80 to 0.95
A 100 kW load at 0.80 has tan(arccos 0.80) = 0.75, so 75 kvar of reactive power. At 0.95 the tangent is 0.32868, so 32.868 kvar. The capacitor bank must supply the difference, 42.132 kvar. The apparent power falls from 125 kVA to 105.26 kVA, a saving of 15.79 percent.
A 250 kW load at 480 V three phase going from 0.70 to 0.90 needs 133.97 kvar and the current falls from 429.58 A to 334.11 A. A 50 kW single phase load at 240 V going from 0.75 to 0.98 needs 33.943 kvar and the current falls from 277.78 A to 212.59 A.
What the numbers mean
A low power factor makes cables and transformers carry more current than the work needs. Some electricity bills charge for it. A higher power factor lowers the current for the same real power, as the before and after values show.
For the conversion between kilowatts and amps with a power factor, see the kW to amps calculator. The generator wattage calculator helps with start-up loads, and the RLC impedance calculator works with reactive parts.
What the page does not do
The page finds the arithmetic for a steady load. Real systems have changing loads, harmonics and resonance with the supply, and over-correcting can raise the voltage or cause problems. Capacitor banks need protection and switching suited to the site, so have a qualified person select and install any equipment.
Assumptions and limits
- The load is steady and its real power does not change when the power factor is corrected.
- Power factor is a number above 0 and up to 1. The target must exceed the present value.
- Voltage is optional. For three phase it is the line to line voltage.
- Harmonics, switching steps and equipment ratings are not modeled.
Frequently asked questions
How do I calculate kvar for power factor correction?
Multiply the real power in kW by the difference of tan(arccos(pf)) for the present and target power factors. For 100 kW from 0.80 to 0.95 that is 42.13 kvar.
What does improving the power factor save?
It reduces the apparent power and the current for the same real power. Going from 0.80 to 0.95 cuts the apparent power by about 15.8 percent.
Can the target power factor be 1?
Yes, up to 1. Then the reactive power is fully removed in theory, but real systems rarely aim for exactly 1.
Is a capacitor bank the only way?
It is the usual way to supply reactive power locally. This page calculates the size needed and does not recommend a design.