Power Factor Correction Capacitor (kVAR) Calculator
Capacitor kVAR needed to raise a load’s power factor from its present value to a target, the reduction in apparent power and line current, released transformer capacity, capacitance in microfarads per phase, and the utility penalty saved.
How it works
kVAR = kW × (tan(acos PF₁) − tan(acos PF₂)); kVA = kW ÷ PF; I = kVA × 1,000 ÷ (√3 × V) three-phase; C per phase (delta) = Q_phase ÷ (2π f V²)
Induction motors, transformers and older lighting draw magnetising current that does no work but still flows through every conductor: it shows up as reactive power (kVAR) and a power factor below 1. Utilities bill for it directly or through kVA demand, and it consumes transformer and cable capacity. A capacitor supplies reactive power locally, so the kVAR needed is simply the difference between the reactive power at the present power factor and at the target — the tangent of the phase angle times the real power. Correcting to about 0.95 captures most of the benefit; going to unity risks a leading power factor and overvoltage when load drops. Banks are switched in steps or with individual motors, and where drives and rectifiers inject harmonics, detuning reactors keep the capacitors from resonating with the supply.
Worked example
A 300 kW load at 0.76 power factor draws 395 kVA and 475 A at 480 V three-phase. Raising it to 0.95 needs 158 kVAR (a 200 kVAR standard bank gets to 0.98), cutting apparent power to 316 kVA and current to 380 A — 79 kVA freed on a 500 kVA transformer and about $1,700 a year in reactive charges at 90¢ per kVAR-month.
Frequently asked questions
Where should the capacitors go?
At the motor terminals (switched with it) for large constant loads, or as an automatic bank at the main switchboard for varying plant loads; the closer to the load, the more cable loss you save.
Can capacitors fix a low power factor caused by VFDs?
No — drives have near-unity displacement PF but distort current with harmonics (low “true” PF). That needs line reactors, harmonic filters or active front ends, not plain capacitors.
Related calculators
Engineering estimate for planning; installations must be designed and verified by a qualified electrician or engineer to the local code (NEC, IEC, CEC) and manufacturer data.