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Volt-amperes reactive
 
 
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In alternating-current power transmission
Power transmission

Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful Mechanical work....
 and distribution, volt-ampere reactive power (VAr) is a unit used to measure reactive power in an AC electric power system. 1 VAr = 1 V·A.

Electric power
Electric power

Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt .When electric current flows in a circuit, it can transfer energy to do mechanical work or work ....
 (watts) is transmitted by the simultaneous product of electric voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 and current
Current

Current may refer to:* Current affairs* Electric current* Current ** Ocean current* Current , geometrical current in differential topology...
 in a wire. If large amounts of current are present when there is less voltage, the wires, transformers and other power equipment are heated, but less power is transmitted by the equipment.






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In alternating-current power transmission
Power transmission

Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful Mechanical work....
 and distribution, volt-ampere reactive power (VAr) is a unit used to measure reactive power in an AC electric power system. 1 VAr = 1 V·A.

Electric power
Electric power

Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt .When electric current flows in a circuit, it can transfer energy to do mechanical work or work ....
 (watts) is transmitted by the simultaneous product of electric voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 and current
Current

Current may refer to:* Current affairs* Electric current* Current ** Ocean current* Current , geometrical current in differential topology...
 in a wire. If large amounts of current are present when there is less voltage, the wires, transformers and other power equipment are heated, but less power is transmitted by the equipment. Since equipment is designed to remain cool up to a certain amount of current, VArs waste some of the power unnecessarily as excess heat

Since AC power has a varying voltage, efficient power systems must therefore vary the current in synchrony with the voltage. VArs measure unsynchronized "leading" or "lagging" currents. These currents are usually caused by the side effects of powering equipment that behaves like coils
Inductor

An inductor is a Passive component Electronic component that can store energy in a magnetic field created by the electric current passing through it....
 (e.g. motors) or capacitor
Capacitor

A capacitor or condenser is a Passive component electronic component consisting of a pair of electrical conductor separated by a dielectric....
s (e.g. arc welders).

Technically, VArs are the product of the rms
Root mean square

In mathematics, the root mean square , also known as the quadratic mean, is a statistics measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids....
 voltage and current, or the apparent power
AC power

This article deals with power in AC systems. See Mains electricity for information on utility-supplied AC power.Power is defined as the rate of flow of energy past a given point....
, multiplied by the sine of the phase angle
Phase angle

In the context of vectors and Phasor , the term phase angle refers to the angular component of the polar coordinate representation. The notation   for a vector with magnitude A and phase angle ?, is called angle notation....
 between the voltage and the current. Or in mathematical terms, the reactive power , (measured in units of volt-amperes reactive or VAr), is given by

, where is the phase angle between the voltage and current.

The term VAR was introduced in 1930 by the IEC
International Electrotechnical Commission

The International Electrotechnical Commission is a Non-profit organization, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies ? collectively known as "electrotechnology"....
 in Stockholm
Stockholm

is the capital and largest city of Sweden. It is the site of the national Swedish Government of Sweden, the Parliament of Sweden, and the official residence of the Swedish Monarchy of Sweden....
, which has adopted it as the unit for reactive power (name: var, symbol: var [and not VAr], conversion factor: 1 var = 1 V·A)

Note 1: The unit VAr represents the power consumed by a reactive load
External electric load

If an electrical network has a well-defined output terminal, the circuit connected to this terminal is the load. Load affects the performance of circuits that output volts or Current s, such as sensors, voltage sources, and amplifiers....
, i.e. when there is a phase
Phase (waves)

The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0....
 difference between the applied voltage and the current.

Note 2: Only effective power
AC power

This article deals with power in AC systems. See Mains electricity for information on utility-supplied AC power.Power is defined as the rate of flow of energy past a given point....
, i.e. the actual power delivered to or consumed by the load, is expressed in watts. Imaginary power is properly expressed in volt-amperes reactive.

Note 3: To maximize transmission efficiency, VArs must be minimized by balancing capacitive and inductive loads, or by the addition of an appropriate (off-setting) capacitive or inductive reactance to the load.

Source: from Federal Standard 1037C
Federal Standard 1037C

Federal Standard 1037C, entitled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended....


Note 4: Apparent power, or the product of the rms voltage and current, measured in volt-amperes (VA), graphically presented as the hypotenuse of the power triangle, is typically the power rating
Power rating

In electrical engineering, the power rating of a device is a guideline set by the manufacturer as a maximum Electric power to be used with that device....
 measure of transmission or distribution equipment. Except in purely resistive circuits, apparent power is always larger than effective power (watts), hence the use of VA as the power rating measure in alternating circuits.