Complex Power and Reactive Power

Complex Power

The Complex Power S is the product of the complex effective voltage and the complex effective conjugate current. In our notation here, the conjugate is indicated by an asterisk (*).Complex power can also be computed using the peak values of the complex voltage and current, but then the result must be divided by 2. Note that complex power is applicable only to circuits with sinusoidal excitation because complex effective or peak values exist and are defined only for sinusoidal signals. The unit for complex power is VA.

Reactive Power

Reactive power Q is the imaginary part of the complex power. It is given in units of volt-amperes reactive (VAR). Reactive power is positive in an inductive circuit andnegative in a capacitive circuit. This power is defined only for sinusoidal excitation. The reactive power doesn't do any useful work or heat and it is the power returned to the source by the reactive components (inductors, capacitors) of the circuit.