en>KylieTastic: Reverted 1 edit by 73.188.210.250 (talk): Revert vandal. (TW)

2014-12-10T22:52:15Z

Reverted 1 edit by 73.188.210.250 (talk): Revert vandal. (TW)

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174.29.72.96: /* Temperature */

2014-03-02T00:07:12Z

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en>ClueBot NG: Reverting possible vandalism by 74.135.97.61 to version by KConWiki. False positive? Report it. Thanks, ClueBot NG. (1682781) (Bot)

2014-02-03T20:06:28Z

Reverting possible vandalism by 74.135.97.61 to version by KConWiki. False positive? Report it. Thanks, ClueBot NG. (1682781) (Bot)

← Older revision		Revision as of 22:06, 3 February 2014
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	~~Commissioned Fire Officer Lorenzo Obryan from Moncton~~, ~~spends time~~ with ~~pursuits including karaoke~~, ~~10 hatha yoga positions~~ and ~~home brewing~~. ~~Recalls what~~ a ~~pleasant spot~~ it ~~ended up having made~~ a ~~vacation~~ in ~~Nord~~-~~Pas de Calais Mining Basin.~~		In electric power [[Electric power transmission\|transmission]] and [[Electric power distribution\|distribution]], '''volt-ampere reactive''' ('''var''') is a unit used to measure [[reactive power]] in an AC electric power system. Reactive power exists in an AC circuit when the current and voltage are not in phase. The correct symbol is var and not Var, VAr, or VAR,<ref>[http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:1980:039:0040:0050:EN:PDF Council Directive on units of measurements 80/181/EEC]: "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." Chapter 1.2.3., p. 6</ref> but all three terms are widely used. The term ''var'' was proposed by the Romanian electrical engineer [[Constantin Budeanu]] and introduced in 1930 by the [[International Electrotechnical Commission\|IEC]] in [[Stockholm]], which has adopted it as the unit for [[electrical reactance\|reactive]] power.

			Vars may be considered as either the [[imaginary part]] of [[apparent power]], or the power flowing into a reactive load, where voltage and current are specified in [[volt]]s and [[ampere]]s. The two definitions are equivalent.

			==Reactive power==
			[[File:Cmplxpower.svg\|thumb\|The apparent power S (measured in units of volt-amperes) is the [[vector sum]] of the reactive power Q (in volt-amperes reactive) and the real power P (in watts). ]]
			{{main\|AC power}}
			A [[Sine wave\|sinusoid]]ally alternating [[voltage]] applied to a purely [[electrical resistance\|resistive]] load results in an alternating [[Electric current\|current]] that is fully in phase with the voltage. However, in many applications it is common for there to be a reactive component to the system, that is, the system possesses [[capacitance]], [[inductance]], or both. These electrical properties cause the current to change phase with respect to the voltage: capacitance tending the current to lead the voltage in phase, and inductance to lag it.

			For sinusoid currents and voltages at the same frequency, reactive power in vars is the product of the [[Root mean square\|RMS]] voltage and current, or the [[AC power\|apparent power]], multiplied by the sine of the [[phase angle]] between the voltage and the current. The reactive power <math>Q</math>, (measured in units of volt-amperes reactive or var), is given by:

			:<math>Q = V_\mathrm{rms}I_\mathrm{rms}\sin \left(\phi \right)\,</math>

			where <math>\phi</math> is the phase angle between the voltage and current.
			Q refers to the maximum value of the instantaneous power absorbed by the reactive component of the load.

			Only [[AC power\|effective power]], the actual power delivered to or consumed by the load, is expressed in watts. Imaginary power is properly expressed in volt-amperes reactive.

			==Physical significance of Reactive power==

			Reactive power (measured in vars) is present in a system containing reactive (inductive or capacitive) components and can be either produced or consumed by different load/generation elements. Though "imaginary", the reactive power has great physical significance and is very essential to the operation of the electrical system as a whole. While the Real Power P is used to supply the energy required to perform actual work (such as running a motor), the reactive power regulates the voltage in the system. If the reactive power is too low, inductive loads such as transformers will be unable to maintain voltages necessary for the generation of electromagnetic fields, leading to a "Voltage collapses" that create [[Power Outage\|blackouts]] . [[Transmission line]] impedances also make it necessary to provide reactive power to maintain voltage levels necessary for active power to flow through. Therefore Reactive power is essential to move active power through transmission and distribution systems to the customer. However if reactive power in a system is too high, there is increased heat loss in transmission lines and loads as the current flowing through the system is much higher, creating a potentially hazardous breakdown situation. The power factor of a load tells us what fraction of the [[AC power\|apparent power]] is in the form of Real Power and performs actual work. A high [[power factor]] is desirable since it minimizes the amount of reactive power needed by the load, reducing heat losses and maximizing efficiency.

			==See also==
			*[[Power factor]]
			*[[Volt-ampere]]
			*[[Watt]]

			==Notes and references==
			{{reflist}}
			* {{FS1037C}}

			[[Category:Electricity]]
			[[Category:Units of power]]

en>RockMagnetist: Reverted 1 edit by 76.7.5.232 (talk) identified as vandalism to last revision by ClueBot NG. (TW)

2012-08-31T22:05:27Z

Reverted 1 edit by 76.7.5.232 (talk) identified as vandalism to last revision by ClueBot NG. (TW)

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Commissioned Fire Officer Lorenzo Obryan from Moncton, spends time with pursuits including karaoke, 10 hatha yoga positions and home brewing. Recalls what a pleasant spot it ended up having made a vacation in Nord-Pas de Calais Mining Basin.

Troposphere - Revision history

en>KylieTastic: Reverted 1 edit by 73.188.210.250 (talk): Revert vandal. (TW)

174.29.72.96: /* Temperature */

en>ClueBot NG: Reverting possible vandalism by 74.135.97.61 to version by KConWiki. False positive? Report it. Thanks, ClueBot NG. (1682781) (Bot)

en>RockMagnetist: Reverted 1 edit by 76.7.5.232 (talk) identified as vandalism to last revision by ClueBot NG. (TW)