Power Factor Correction Calculator
Capacitor bank sizing from real power, existing and target power factor. Rounds up to a standard kvar rating and shows the resulting PF, current and loss reduction, and capacitance per phase — with a live power triangle.
Resulting PF 0.952 lagging
BasisQc = P (tan φ₁ − tan φ₂), rounded up to a standard bank · C from Q = V²ωC (delta) · current at constant kW
Frequently asked questions
How do you calculate the capacitor kvar needed for power factor correction?
Required reactive power is Qc = P × (tan φ1 − tan φ2), where P is real power in kW, φ1 = arccos(existing PF) and φ2 = arccos(target PF). For example, raising a 250 kW load from 0.78 to 0.95 PF needs 250 × (0.802 − 0.329) ≈ 118 kvar. The calculator rounds up to the next standard bank rating and reports the PF you actually get with that bank.
What target power factor should I use?
Most utilities apply a penalty or demand adjustment below 0.90 or 0.95 lagging, so 0.95 is a common target. Going beyond about 0.98 gives little extra benefit, increases bank size, and risks a leading power factor at light load — which can cause overvoltage and interact with generator voltage regulators.
How is capacitance per phase calculated?
From Q = V² ω C with ω = 2πf. For a single-phase capacitor C = Q / (ω V²). For a three-phase delta bank each capacitor sees the line-to-line voltage and carries one third of the kvar, so C = Q / (3 ω V_LL²). For a wye bank each capacitor sees V_LL / √3, giving C = Q / (ω V_LL²) per phase — three times the delta value.
How much does power factor correction reduce current and losses?
At constant real power, line current is proportional to apparent power (kVA), so it falls by the ratio PF_existing / PF_new. Resistive (I²R) losses in upstream cables and transformers fall with the square of the current. Correcting from 0.78 to 0.95 cuts current by about 18 % and conductor losses by about 33 %.
Are there risks with capacitor banks?
Yes. Capacitors combined with system inductance form a resonant circuit; with VFDs, rectifiers or other non-linear loads, harmonic resonance can overload capacitors and distort voltage. Where harmonic loads exceed roughly 15–20 % of transformer rating, use detuned (reactor-tuned) banks or active filters, and consider automatic stepped banks so correction follows the load. NEC Article 460 covers capacitor installation, discharge and overcurrent protection.