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Power factor
Intermediate
Cosine of the phase angle.
cosφ = R/Zcosφ = R/Z: the fraction of apparent power doing real work. Low power factor means large currents for the same power; industries add capacitors to correct it.
A motor at pf 0.7 draws 43% more current than at pf 1.
Utilities charge penalties.
In more detail
The power factor is the cosine of the phase angle, and it measures how much of the apparent power is real power. A power factor of one means voltage and current are in phase.
Real-world uses
- Industrial plants improve power factor to reduce charges and losses.
- Electric motors have low power factor, which utilities compensate for.
- Electricity companies penalise factories with a low power factor, because the extra current wastes energy in the cables.
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Frequently asked questions
What is a typical power factor?
Often between 0.8 and 0.95 for industrial loads.
Why does poor power factor matter?
It increases current for the same real power, causing higher losses in cables.
What is a good power factor?
Close to one, which means the current is nearly in phase with the voltage and little energy is wasted.
Related topics in AC Circuits & EM Waves
Series resonance · Quality factor in LCR · Bandwidth · Wattless current · LC oscillations · Parallel resonance