Reactive power is a type of power that does not do any real work and is generally associated with reactive elements such as inductors and capacitors. It is measured in VAR or kVAR and is the power that flows back into the source from the inductors and capacitors. Reactive power can best be described as the quantity of "unused" power that is developed by reactive components in an AC circuit or system. In a circuit with reactive components, the voltage and current are out of phase, and power is being absorbed by the circuit at those times when the voltage and current are in the same direction (both positive or both negative). Power is returned to the source when the voltage and current are not in the same direction (one positive and one negative) .
The combination of reactive power and true power is called apparent power, and it is the product of a circuits voltage and current, without reference to phase angle. Apparent power is measured in the unit of Volt-Amps (VA) and is symbolized by the capital letter S. True power is a function of a circuits dissipative elements, usually resistances (R), while reactive power is a function of a circuits reactance (X) .
