Power Factor Correction Capacitor

Formula

Description

Power factor correction (PFC) capacitors supply leading reactive power to compensate for the lagging reactive power drawn by inductive loads like motors, transformers, and fluorescent lighting. The required capacitance depends on the reactive power to be compensated (in VAR), the line frequency, and the voltage. By improving the power factor close to unity, PFC capacitors reduce current drawn from the utility, lower I²R losses in wiring, and avoid utility power factor penalties. In industrial settings, PFC capacitor banks are often switched in stages to match varying loads.

Variables

• C — Required capacitance (F)
• Qc — Reactive power to compensate (VAR)
• f — Line frequency (Hz)
• V — RMS line voltage (V)

Practical Notes

Qc = P × (tan(φ₁) − tan(φ₂)), where φ₁ is the initial power factor angle and φ₂ is the target. PFC capacitors must be rated for continuous AC operation and are typically self-healing metallized polypropylene film. Do not confuse with active PFC in switch-mode power supplies, which is a different technique using boost converter topology.