Power may be defined basically as the rate of doing work. In an AC circuit, the electrical power may be of three categories:
Actually, the power consumed by an AC circuit is called Active or True power. It is the product of the apparent power and the power factor of the AC circuit.
The power taken by pure inductance or the capacitance of an AC circuit is known as the reactive power.
Now, reactive power = VRMS x IRMS x sinΦ
= Apparent power x sinΦ
The unit of reactive power is volt-ampere reactive (VAR)
It is the product of the RMS value of the applied voltage and the RMS value of the circuit current.
Apparent Power = V x I
In the case of DC, the unit is watt, but in the case of AC, the unit is volt-ampere.