Power Factor Correction
Capacitor kvar to raise a load’s power factor from where it is to your target, the current and kVA it frees, and the µF per phase for a delta or wye bank.
The reactive power the capacitor bank must supply, the apparent power and current before and after, and the capacitance each phase needs at your voltage and frequency.
Example: A 100 kW load at PF 0.75 on 400 V needs 55.3 kvar of capacitors to reach 0.95: current drops from 192 A to 152 A, and a delta bank needs 367 µF per phase at 50 Hz.
Cancel the vars,
keep the watts.
The power triangle before and after, how the bank is sized in kvar and then in µF, and what capacitors do not fix.
Sizing the bank
A load drawing real power P at power factor PF₁ also draws reactive power Q₁ = P × tan θ₁ with θ₁ = arccos PF₁. To reach PF₂ it may only draw Q₂ = P × tan θ₂, so capacitors must supply the difference: Q_c = P (tan θ₁ − tan θ₂). Real power is unchanged; the apparent power falls from P ÷ PF₁ to P ÷ PF₂, and with it the current, I = S ÷ (√3 × V) for three-phase or S ÷ V for single-phase. The freed kVA is capacity the transformer and cables get back.
From kvar to µF
A capacitor C at voltage V and frequency f supplies Q = 2πf C V². For a three-phase bank each phase supplies Q_c ÷ 3: in delta each capacitor sees the line-to-line voltage, in wye the phase voltage V ÷ √3 — so a wye bank needs three times the capacitance for the same kvar. Bank ratings on nameplates are in kvar at a stated voltage; kvar scales with V², so a bank rated at a higher voltage delivers less at yours.
Choosing the target
The kvar needed grows quickly as the target approaches 1 while the current relief flattens, and a fixed bank sized for full load over-corrects at light load — a leading power factor the utility may also penalise. Targets around 0.95 and switched capacitor steps are common practice; the right target is set by your tariff and your load profile, not by this page.
What the number does not settle
Capacitors correct displacement power factor — the lag of a mostly inductive load. They do not correct distortion power factor from drives, rectifiers and switch-mode supplies, and a plain bank can resonate with those harmonics; a harmonic study and detuned reactors are separate work. Capacitor voltage rating, discharge resistors, switching and protection follow the manufacturer and the code that applies to you. Inputs stay in your browser; the same four anonymous usage counts as the rest of the site apply.