An AC system’s power factor (PF) is the ratio of the load’s real power to its apparent power. PF is frequently expressed as a percentage (i.e., 0.8 PF = 80% PF).
Reactive loads—ones that contain capacitors and/or inductors, such as electric motors—store part of the energy supplied to them, and then return it to the power source. This energy is in addition to the energy used to operate the load, and it results in additional current flowing back and forth between the power source and the load.
Real power is the circuit’s capacity for performing work over a particular duration. Apparent power is the product of a circuit’s voltage and current (volt–amps; VA).
A washing machine can have a fairly low PF (about 50%). Contrast this with a PF-corrected battery charger, which can have a PF of about 98%.
In an electrical system, a load with a low PF draws more current than a load with a high PF, for the same amount of useful power transferred. The higher currents increase the energy lost in the distribution system, and require larger wires, among other things. And, since generators are current-limited power sources, and the low PF loads draw relatively high current, less current is available to power other loads, thereby effectively reducing the generator’s functional capacity.