Power Factor Correction Calculator

Industrial capacitor banks for power-factor correction emerged in the 1910s as factories scaled up induction motor installations. Early banks used oil-filled paper capacitors rated at line voltage — bulky, expensive, and flammable if they failed. Mass adoption followed the 1920s-era spread of kVA-based utility tariffs, which financially punished factories for drawing reactive current they weren't paying for in kWh.

The mid-1960s brought a major shift with self-healing metallized polypropylene film capacitors, replacing oil-paper types. A small dielectric puncture vaporizes the metallized electrode locally, isolating the fault — so a single internal short no longer takes the unit out of service. Modern LV PFC banks at 480 V use these, typically arranged in switched steps of 25/50/100 kVAR controlled by a regulator that samples line current and adds steps as load PF drops.

Over-correction is a real hazard: leading power factor causes voltage rise on lightly-loaded feeders and — more dangerously — can resonate with transformer inductance at harmonic frequencies (5th, 7th, 11th) from nonlinear loads. This is why modern installations use detuned capacitor banks (with small series reactors) or active harmonic filters instead of raw capacitor banks on feeders with significant VFD/UPS loads.

Enter the load's real power (kW), current PF, target PF, line-to-line voltage, and line frequency. The tool computes the required capacitor reactive power Qc = P·(tan φ₁ − tan φ₂), then the capacitance in both delta and wye configurations at line frequency. Delta needs one-third the capacitance of wye for the same kVAR because each capacitor sees full L-L voltage instead of L-N.

Practical notes: size to a target PF of 0.95–0.98, not unity — over-correction risks leading PF and resonance. Real installations use switched steps controlled by a PF regulator, detuning reactors in harmonic-rich environments, and discharge resistors on each step. This tool gives the ideal per-step rating; derate by 10–15% for harmonic current headroom. Everything runs client-side; no values leave your browser.