Power factor
Introduction


In [electrical engineering](/wiki/Electrical_engineering "Electrical engineering"), the **power factor** of an [AC power](/wiki/AC_power "AC power") system is defined as the [ratio](/wiki/Ratio "Ratio") of the *[real power](/wiki/Real_power "Real power")* absorbed by the [load](/wiki/Electrical_load "Electrical load") to the *[apparent power](/wiki/Apparent_power "Apparent power")* flowing in the circuit. Real power is the average of the instantaneous product of voltage and current and represents the capacity of the electricity for performing work. Apparent power is the product of [root mean square](/wiki/Root_mean_square "Root mean square") (RMS) current and voltage. Due to energy stored in the load and returned to the source, or due to a non\-linear load that distorts the wave shape of the current drawn from the source, the apparent power may be greater than the real power, so more current flows in the circuit than would be required to transfer real power alone. A power factor magnitude of less than one indicates the voltage and current are not in phase, reducing the average [product](/wiki/Product_%28mathematics%29 "Product (mathematics)") of the two. A negative power factor occurs when the device (normally the load) generates real power, which then flows back towards the source.

In an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. The larger currents increase the energy lost in the distribution system and require larger wires and other equipment. Because of the costs of larger equipment and wasted energy, electrical utilities will usually charge a higher cost to industrial or commercial customers with a low power factor.

**Power\-factor correction** increases the power factor of a load, improving efficiency for the distribution system to which it is attached. Linear loads with a low power factor (such as [induction motors](/wiki/Induction_motor "Induction motor")) can be corrected with a passive network of [capacitors](/wiki/Capacitor "Capacitor") or [inductors](/wiki/Inductor "Inductor"). Non\-linear loads, such as [rectifiers](/wiki/Rectifier "Rectifier"), distort the current drawn from the system. In such cases, active or passive power factor correction may be used to counteract the distortion and raise the power factor. The devices for correction of the power factor may be at a central [substation](/wiki/Electrical_substation "Electrical substation"), spread out over a distribution system, or built into power\-consuming equipment.


How can active or passive power-factor correction counteract current distortion in non-linear loads?