Power System Operation and Control

8.3 REACTIVE POWER

In a purely resistive AC circuit, voltage and current waveforms are in phase and reverse their polarity at the same instant in each cycle (illustrated in Fig. 8.3). When reactive loads are present (such as capacitors or inductors), energy is stored in the form of electric or magnetic fields respectively in the loads during part of the AC cycle and results in a time difference between the current and voltage waveforms (for a capacitor, current leads voltage; for an inductor, current lags voltage). This stored energy returns to the source during the rest of the cycle and is not available to do work at the load. This energy, continuously flowing back and forth (to and fro), is known as reactive power while the active power flows ...