🌀 Power Factor Correction Calculator
Find the capacitor bank kVAR needed to lift your power factor from one value to another, with the kVA and line-current reduction and the next standard bank size.
⚙️ Load
📊 Result
For plant and facility engineers reducing kVA demand and utility PF penalties.
How it is calculated
· Reactive power: Qc = P × (tan(acos PF1) − tan(acos PF2)).
· Apparent power: S = P ÷ PF (before and after correction).
· Selection: next standard bank from the 25–1000 kVAR series.
Referenced standards
| Standard | Scope |
|---|---|
| IEC 60831 | Shunt power capacitors for AC systems |
Worked example — 250 kW, 0.75 → 0.95 → 138 kVAR
1. 250 kW, PF1 = 0.75, PF2 = 0.95.
2. Qc = 250 × (tan(acos 0.75) − tan(acos 0.95)) = 250 × (0.882 − 0.329) = 138 kVAR.
3. Next standard bank = 150 kVAR; kVA demand falls from 333 to 263 kVA (−21%).
FAQ
How do I calculate the capacitor kVAR for power factor correction?
Required kVAR = kW x (tan(acos(pf1)) - tan(acos(pf2))). To correct 300 kW from 0.8 to 0.95: 300 x (0.75 - 0.33) = 126 kVAR, so select a 150 kVAR bank. The calculator computes the kVAR and picks the next standard bank size.
Why do utilities penalize low power factor?
Low Power Factor means higher current for the same real power, so the utility needs larger conductors and transformers and suffers higher losses. Most utilities require 0.9-0.95 and add a penalty or demand charge below ~0.9. Correcting to 0.95 typically cuts the reactive current 40-60%. The calculator shows the kVAR needed.
What is the difference between leading and lagging power factor?
Lagging power factor means the load is inductive (motors, transformers) and current lags voltage. Leading power factor means capacitive (over-compensation). Over-compensating past unity creates a leading pf that can cause overvoltage and resonance. Target 0.95 lagging, not unity; the calculator avoids over-correction.
Fixed or automatic capacitor bank — which do I need?
Fixed banks suit steady loads; automatic (switched) banks step capacitors in and out to follow varying load and avoid over-compensation at light load. For a plant whose load swings 30-100%, use an automatic bank. The calculator sizes the bank; larger variable loads recommend switched stages.
What power factor do I save on my electricity bill?
Correcting power factor reduces reactive current and often removes a penalty charge (typically 0.5-3% of the bill per 0.01 below 0.9). For a plant with a $120,000/yr bill at 0.78 pf, correction to 0.95 can save $2,000-6,000/yr. The calculator quantifies the kVAR and the bill impact.
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