Talk:Volt-ampere reactive

message: The unit for Reactive power must be written with small characters "var" according the IEC 60027. Most publications use wrong spelling, like VAr, VAR or Var. Multiplication factors follow their own rules like kvar, Mvar, etc.
Robert.
62.92.243.245 11:39, 17 January 2007 (UTC)
thread_title:  Lower case 

message: Robert is correct. Var is an ordinary word for the unit of reactive power.  It is treated just like the units for other electrical quantities such as watt for active power and volt for voltage. Unlike volt, which has an abbreviation, V, there is no abbreviation for var. Another misconception is that VAR is an abbreviation for the unit voltampere reactive. I do not believe there is any such standard unit, although voltampere is a standard unit. Robert is also correct in indicating that the unit is misused in all sorts of technical publications including refereed journals. Since var is a unit not a quantity, it is technically incorrect to say something like "... capacitors produce vars ...".  One should say instead that " ... capacitors produce reactive power ...".  More information on this subject can be obtained by checking the entry under 'magner' in the IEEE Standard 100 (the standard dictionary). This also gives insight into where the sign on the direction of reactive power came from. Also, note that the IEEE dictionary defines watts as the unit for 'active' power, not 'effective' power. Thus, there is active, reactive, and apparent power in power system.Rcdugan 17:31, 23 June 2007 (UTC)
replies: text: I probably agree that it shouldn't be, but I suspect it is the WP:COMMONNAME by now.  Anything used enough gets its own jargon, and we learn to live with it. Gah4 (talk) 19:35, 6 April 2019 (UTC)

text: Actually, SI does specifically allowCouncil 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." both VA and var. It is in a footnote for power in the table. Note var and not VAR, though. Gah4 (talk) 19:45, 6 April 2019 (UTC)
thread_title:  VAR or var or Var 

message: I added a section on the physical significance of vars since the original was lacking in those aspects. Real, reactive and complex power are interconnected and very important. The real power is the peak value of the instantaneous power absorbed by resistive components of a circuit, while the reactive power is the magnitude of instantaneous power consumed/produced by reactive (inductive or capacitive) components. The complex power is the vector sum of the two, and it's magnitude is known as the Apparent power which is seen by a load at the receiving end. Reactive power may be in the imaginary domain, but it performs the function of voltage regulation. Without reactive power, magnetic elements (including transformers) would be unable to function. At the same time, an excess of reactive power leads to greater line losses (since line losses depend on the inductance which in turn is affected by Q) and a reduced power factor. The power factor shows the proportion of power that is consumed for actual purposes. A low power factor indicates excessive reactive power and reduced efficiency for the device.  — Preceding unsigned comment added by Manishraje (talk • contribs) 01:32, 25 November 2013 (UTC)
thread_title:  November 24 2013 Edit by manishraje

message: There is something profoundly wrong with this article.  The entire article is premised on the mistaken idea that there can be different "types" of power, whereas in reality there can only be one - namely the average rate of transfer of energy, the average being over one complete cycle.  In an AC circuit the instantaneous rate of transfer of energy (and therefore the instantaneous power) can be positive or negative at different moments in the cycle, and it is for this reason that the power is averaged over a cycle.  If RMS values of current (I) and voltage (V) are used, the product VI is the value of average power (P) only in those cases where V and I are mutually in phase.  In all other cases, where there is a phase angle phi, the average power is P = VIcos(phi).  Thus when phi = 90deg, average power is zero even though VI might be finite.  The product VI is thus not a measure of power, and it is for this reason that it is given a different name: volt-amperes or VA.  The units of VA are not Watts, but simply VA.  VA is a general term for the product VI in all cases.  In the special case where voltage and current are in phase quadrature, and average power is zero, the product is termed volt-amperes-reactive (VAR), and the unit is VAR - again not Watts.  The following statement is thus fundamentally wrong -
"The unit "var" does not follow the recommended practice of the International System of Units, because the quantity the unit var represents is power, and SI practice is not to include information about the type of power being measured in the unit name. [2]".  There are no "types" of power corresponding to P, VA, and VAR; power is a completely general concept defined as rate of transfer of energy.  Where there is no transfer of energy, power is zero.  The idea that in an AC circuit the product VI is power (or a 'type' of power) is simply a mistake.  This misunderstanding is likely to be made by a student who has learned that P = VI in a DC circuit, but has not progressed sufficiently to grasp that this is simply not true in AC circuits except in special cases.
Vectorially, the complex quantity VA can be resolved into real and imaginary components corresponding to power (P) and VAR in the same way that impedance can be resolved into resistance and reactance.  Note that in this latter case, the 3 quantities are also given particular names which distinguish them, and are not considered to be different "types" of resistance.  However, it is perfectly correct to say that power and VAR are both 'types' of VA, just as resistance and reactance are 'types' of impedance - real and imaginary types respectively. g4oep  — Preceding unsigned comment added by 82.37.54.83 (talk) 15:06, 20 May 2016 (UTC)
replies: text: See above, where SI specifically allows VA and var. Gah4 (talk) 19:47, 6 April 2019 (UTC)
thread_title:  Type of power ? 

message: I suggested a change in title of the page to Reactive power instead as I will that is what the article is really talking about as opposed to the unit of measurement VAR and there is no comprehensive article on reactive power besides a small section in AC power. I added a sentence at the start about measurement of VAR by a varmeter and I wanted to submit a picture from a textbook but I guess there may be copyright issues. A more major edit was on the physical significance of reactive power. Generally, I find the original paragraph very convoluted and difficult to understand. A more important mistake, I think, is that the author seems to convey that reactive power is supplied on purpose to drive inductive loads and the failure of doing this will lead to failure to blackouts. However, I think it is better explanation would be that by virtue of the fact that most loads (transformers, motors etc) have high reactance and hence will consume reactive power due to the lagging current. The challenge electric power providers face is to balance generators and loads in such a way that reactive power is kept at the minimum to reduce line losses as well as to ensure stability of the system (stable voltage and frequency). Hence, I changed the paragraph to what I believe is a more accurate, understandable and generic explanation.  — Preceding unsigned comment added by Ezrapeh (talk • contribs) 09:53, 4 December 2016 (UTC)
thread_title:  Edits to article mainly changing the section on Physical significance of reactive power 

message: OK, electric motors do -- but do they do so only when spinning freely, not under load? or only when the mechanical load is heavy?  So transformers do .. does that include the transformer in my back yard, that steps down from 20KV to 120V?  What about switching power supplies in my computer/TV? mercury vapor lamps? Are there any capacitative loads, anywhere, in a typical house? How about a factory?  67.198.37.16 (talk) 13:07, 20 October 2017 (UTC)
replies: text: An unloaded transformer is just an inductor, so usual inductor phase shift applies. Similarly, an unloaded motor running at full speed also looks pretty much like an inductor. Under load, a back EMF occurs, corresponding to the actual load.  I believe that the unloaded reactive component stays, but becomes a smaller part of the actual load, but I never tried to compute it. A lightly loaded transformer or motor will still have a significant inductive component. Gah4 (talk) 06:47, 4 November 2017 (UTC)
thread_title:  what electrical components cause reactive power to be consumed/generated?