Reactive Power:
Reactive power (Q) is the power consumed within an AC circuit since of the expansion and collapse of magnetic (inductive) and electrostatic (capacitive) fields. A Reactive power is expressed in volt-amperes-reactive (VAR). Given Equation (9-3) is a mathematical representation for reactive power.
Q= I2X = EI sinθ (9-3)
where
Q = reactive power (VAR)
I = RMS current (A)
X = net reactance ( ? )
E = RMS voltage (V)
θ = angle between the E and I sine waves
Unlike true power, reactive power is not useful power since it is stored in the circuit itself. This power is stored through inductors, since they expand and collapse their magnetic fields in an attempt to remain current constant and through capacitors, since they charge and discharge in an attempt to keep voltage constant. A Circuit inductance and capacitance consume and provide back reactive power. A Reactive power is a function of a system's amperage. In the magnetic field the power delivered to the inductance is stored whenever the field is expanding and returned to the source when the field collapses. Within the electrostatic field the power delivered to the capacitance is stored whenever the capacitor is charging and returned to the source whenever the capacitor discharges. No one of the power delivered to the circuit through the source is consumed. It is all returned to the source. The true power, that is the power consumed, is therefore zero. We know in which alternating current constantly changes; therefore, the cycle of expansion and collapse of the electrostatic and magnetic fields constantly occurs.