Reactive power

Article By:

McGillis, D. Department of Electrical and Computer Engineering, McGill University, Montreal, Québec, Canada

El-Arroudi, K. Department of Electrical and Computer Engineering, McGill University, Montreal, Québec, Canada

Galiana, Francisco D. Department of Electrical and Computer Engineering, McGill University, Montreal, Québec, Canada.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.802370

The concept of reactive power arises in electrical circuits operated from alternating-current sources. Electric fields (associated with capacitive effects) and magnetic fields (associated with inductive effects) are alternately charged and discharged according to the transfer of energy that takes place in each cycle. Reactive power is related to the peak of power entering either capacitance or inductance in the circuit. The term “real or active power” is used to describe the average (or mean) value of the power waveform. All power system equipment generates or receives reactive power, including synchronous generators, synchronous condensers, static var compensators, capacitive and inductive compensators, overhead lines and underground cables, transformers, and consumer loads. Real power controls the frequency of the system, while reactive power controls the voltage. Both are required for proper functioning of the electric power system, and a balance must be maintained between the real and reactive power everywhere in the network. To violate the real power balance is to invite a condition known as transient instability, while violating the reactive power balance may lead to voltage instability or eventually voltage collapse. See also: Static var compensator; Synchronous motor; Transformer; Transmission lines

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