What is “Power Factor”?
The definition of “Power Factor” relies on the definitions of “active power” and “apparent power”.
In an electrical circuit, the active power P is the real power transmitted to loads such as motors, lamps, heaters, computers … The electrical active power is transformed into mechanical power, heat or light.
The physical unit for the active power is one watt (W), with one kilowatt (kW) often used for commodity.
In a circuit where the applied r.m.s. voltage is Vrms and the circulating r.m.s. current is Irms, the apparent power S is the product Vrms x Irms.
The apparent power is then the basis for electrical equipment rating. One piece of electrical equipment (transformer, cable, switch …) must be designed in relation to the r.m.s. values of voltage and current.
The physical unit for the apparent power is one volt-ampere (VA), with one kilovolt-ampere (kVA) often used for commodity.
The Power Factor is the ratio of the active power P (kW) to the apparent power S (kVA) for a given circuit.
For the special case of sinusoidal voltage and current with a phase angle “phi”, the Power Factor is equal to cos(phi) , called Displacement Power Factor (DPF).