Power Factor
Power factor is the ratio of real power (kW), which performs useful work, to the apparent power (kVA) drawn by an AC load. For purely sinusoidal waveforms it equals the cosine of the phase angle between voltage and current. Inductive loads such as induction motors and transformers draw reactive power (kvar) to magnetize their cores, lowering power factor, while non-linear loads introduce harmonic distortion that reduces it further. A low power factor increases the current needed for the same real power, raising cable and transformer losses and voltage drop and, under many tariffs, utility charges. Correction is achieved with fixed or automatic capacitor banks, detuned filter banks, synchronous condensers or active filters. When sizing generators, UPS systems, transformers and cables, both the kW and kVA ratings must be checked against the expected load power factor.
Examples
- Automatic power factor correction panel at a factory incomer
- Capacitor bank compensating a large induction motor
- Active harmonic filter on a VFD-heavy distribution board