Power factor is active power divided by apparent power, a number between 0 and 1 described as lagging for inductive loads or leading for capacitive ones. For pure sine waves it equals the cosine of the angle between voltage and current, but harmonic currents push true power factor below that displacement value. Utilities penalise industrial customers who fall below a threshold, commonly 0.9 or 0.95, because low power factor means more current, more losses and more voltage drop for the same kilowatts.
Plant power factor dropped to 0.78 after they added the new compressors, we pay a reactive penalty every month until the cap bank goes in.
A meter that shows only cos phi flatters a site full of drives and rectifiers; ask for true power factor when harmonics are present.
Also heard as
- PF
Do not mix it up with
- Doble test: Insulation power factor in a Doble test describes dielectric losses, not the power factor of a load.
Related terms
Active power
The part of electrical power that does real work, averaged over each cycle and measured in watts.
Apparent power
Product of RMS voltage and RMS current, the figure transformers, generators and UPS units are rated on.
Reactive power
Power that surges back and forth between the source and the fields of inductors and capacitors, doing no net work.
Harmonics
Voltage or current components at whole multiples of the supply frequency, produced mostly by nonlinear loads.