In electric power transmission and distribution, volt-ampere reactive (var) is a unit of measurement of reactive power. Reactive power exists in an AC circuit when the current and voltage are not in phase. The term var was proposed by the Romanian electrical engineer Constantin Budeanu and introduced in 1930 by the IEC in Stockholm, which has adopted it as the unit for reactive power.
Special instruments called varmeters are available to measure the reactive power in a circuit.
The unit "var" is allowed by the International System of Units (SI) even though the unit var is representative of a form of power SI allows one to specify units to indicate common sense physical considerations. Per EU directive 80/181/EEC (the "metric directive"), the correct symbol is lower-case "var", although the spellings "Var" and "VAr" are commonly seen, and "VAR" is widely used throughout the power industry.
Notes and references
- Wildi, Theodore (2002). Electrical Machines, Drives and Power Systems. Pearson. p. 137. ISBN 978-0-13-093083-5.
- SI Brochure, 8th ed.
- Council Directive on units of measurements 80/181/EEC Chapter 1.2.3., p. 6: "Special names for the unit of power: the name volt–ampere (symbol ‘VA’) when it is used to express the apparent power of alternating electric current, and var (symbol ‘var’) when it is used to express reactive electric power."