Power:
Power may be defined basically as the rate of doing work. In an AC circuit, the electrical power may be of three categories:
Active Power:
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.
Reactive:
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)
Apparent Power:
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.