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And Now MVaR in words of one sylable or less
5

And Now MVaR in words of one sylable or less

And Now MVaR in words of one sylable or less

(OP)
Here's one for all of you clever electrical chappies out there.
Imagine trying to explain MVaRs to a new starter, ie. in the simplest way possible.
All analogies welcome (except maybe the horse and barge one).
Points may be awarded for creativity but deducted for over technicality.
This has always been one of those questions that,(along with what is entropy?)has been a source of consternation in power stations since Michael Faraday was a lad.
Go On, you know you want to............

JJ

RE: And Now MVaR in words of one sylable or less

Beer and Froth. The bestest. cheers

Muthu
www.edison.co.in

RE: And Now MVaR in words of one sylable or less

My Fortran formatting is probably way off but;
10 Search this site for the Beer and froth analogy of power factor.
20 do: Take your student to the pub and order a beer for each of you.
30 Use the beer to explain the power factor analogy.
40 Drink the beer.
50 does the student understand power factor?: exit
60 loop to 20

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: And Now MVaR in words of one sylable or less

LOL, loop to 20...

55(?) Unable to stay upright on bar stool?: exit


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: And Now MVaR in words of one sylable or less

Well the M stands for Million or 106.

What do I get?  

Keith Cress
kcress - http://www.flaminsystems.com

RE: And Now MVaR in words of one sylable or less

and V is for Volt!!!

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: And Now MVaR in words of one sylable or less

2
I got this while surfing the web:
"MVARs are like managers, they take a lot of room, increase losses, doesn't do useful work, but are still required to obtain the "REAL" work at the end of the line."
Please wait 'til someone else tells you a far better answer!

RE: And Now MVaR in words of one sylable or less

Burned and Smoked

You two win the prize!

BTW. It is var nowadays. Not VAr or anything like that.

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: And Now MVaR in words of one sylable or less

vars are like railroad tracks.  They HAVE to be there to move the freight but aren't used up or directly paid for by the people receiving the freight.

Some companies will assess specifically for using the rails(vars) others won't.

Keith Cress
kcress - http://www.flaminsystems.com

RE: And Now MVaR in words of one sylable or less

JJayG;
We have many times in the past, tried to explain this concept. To para-phrase Lili von Stupt in Blazing Saddles:
"We're Tired!"
For a more serious treatment of the VARs concept, search this site. (I'm sorry Gunnar, I tried vars but I couldn't do it.)
Is this a European Union harmonization thing?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: And Now MVaR in words of one sylable or less


JJayG:
This thread got the responses it deserved. Sorry.

burnt2x:
Excellent description, I must remember this.

Gunnar:
V and A I've learned and I'm used to write in capital letters as they are derived from Mssrs. Volta and Ampere. The r stands for reactive and is always written as a small letter in Europe. In the U.S. they have a different opinion, however. Would be nice to know whether there is a new standard regulating this.

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM
 

RE: And Now MVaR in words of one sylable or less

Wolf and Bill,

Yes, as always, the BIPM has set the rule. Reactive VA is a unit (has been so for something like 20 years) and shall be written "var". If we are at all going to have a unified and standardized technical language, we need to adhere to rules laid down by the top standard institute.

I know, it hurts, but instead of using VAr or VAR or VaR or, perhaps vAr or... I think it is meeaningful to use what the BIPM says. Privatized writing like the ones used above only confuse. And so do "simplified" explanations. But I liked the manager explanation.

We had a similar discussion a few weeks ago where the unit for temperature change was discussed. Same thing there. K is the unit to use while C or F are units for temperature. Most people seem to think that C and K are identical. They are not. BIPM agan.

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: And Now MVaR in words of one sylable or less

While Gunnar is technically right, in this case the standard (IEC and SI) is not consistent or at least it feels that way.

The issue is that the common expressions, such as kVAR or KVAR have been in use longer than the so called adoption of 'standards'. And hence the use of var in common writing will not be any more accepted than it has been in the last 20 yrs.  Arbitrary and retrospective standards will always find the acceptance harder. Just like K vs. C or F.

I also start out writing var (since I learned of this not too long ago) in many cases and then usually decide to change it to kVAR to match with kVA in the reports.

It is no different than use of KVA for kVA. or KW for kW. All have been very common in writing and equipment data sheets/name plates with no real confusion or opposition.  

 

Rafiq Bulsara
http://www.srengineersct.com

RE: And Now MVaR in words of one sylable or less

Difficult to argue with the IEV even if the IEV flies in the face of common sense when the generic volt-ampere is denoted VA. Idiots.

The BIPM is run by the French isn't it? That explains everything... wink

http://www.electropedia.org/iev/iev.nsf/ff6940a6c7b56a02c12574360034c5e1/da8ebfc0351ec848c1257275005d79dc?OpenDocument
  

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If we learn from our mistakes I'm getting a great education!
 

RE: And Now MVaR in words of one sylable or less

It is not about being an idiot or not. The VA is V times A just like Nm is N times m. The var is different. It is not V times A times R. Hence the unit var.  

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: And Now MVaR in words of one sylable or less

For those who are graphically inclined: VARs, power factor, and phase angle can be illustrated by drawing two sine waves (preferably on a piece of graph paper) and their product. By changing the phase relationship, the unidirectional and reversing flows of real and reactive power components can be seen.

If the subject doesn't 'get' this, I usually fall back to the beer/suds explanation.  

RE: And Now MVaR in words of one sylable or less

Well, the V and A are both capitalised because they are the initials of the men they were named after. The 'V' and 'A' in 'var' represent the same Volt and Ampere that they do in VA, so they should be capitalised. Even the IEV acknowledge that it is a "special name of the voltampere in the case of non-active and reactive power". The 'r' would be a subscript if we were following the rules of logic and grammar. But we aren't. smile
  

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If we learn from our mistakes I'm getting a great education!
 

RE: And Now MVaR in words of one sylable or less

I am at least thankful that engineering standards have not reached the low of botanical or biological sciences where 'Turdus migratorius' can be insisted up on as the correct scientific name for a bird where just a American robin would do. tongue

Although, if the engineering standards keep up with nerdy ways, they will end up there.

Rafiq Bulsara
http://www.srengineersct.com

RE: And Now MVaR in words of one sylable or less

What does all this mean? Have we confused anyone yet?

We are off subject.

RE: And Now MVaR in words of one sylable or less

I am confused, I understood that the A was capitalized to show respect for André-Marie Ampère. Now I am told that is only the case if the A?amperes are in phase with The Volts, even though an instrument designed to measure Amperes only has no idea whatsoever as to the Amperes relationship to the Volts that cause the Amps to flow. Is this a reflection of some historical antagonism between Ampere and Voltaire?
But what plays in Vegas stays in Vegas and what the french do to their own should stay in france.
No that's not a typo, de-capitalizing Ampere seems a little reactionary and the new rules say that reactionary entities lose their capitalization.
On a little more serious note; (emphasis on little)
Many years ago I learned a little bit of English grammar. One subject I dimly remember is abbreviation. I seem to remember that abbreviations shall be capitalized.
AVR: automatic voltage regulator, PMG: permanent magnet generator, CT: current transformer, PT: potential transformer, VAR: Volt Amps reactive, oops.
Although some may prefer to use the more recent name,I prefer the full descriptive name, Volt Amps reactive, and following the rules of English grammar abbreviate this to VAR.
Should a German, an Italian, or a Russian challenge my use of the rules of the English grammar I would be offended. Should a Francophone challenge my or demand that I change my habits, Oh well, that's just the French. Look at the reactionary treatment of the memory poor André-Marie Ampère!
You may say var. When I say VAR I am abbreviating Volt Amps reactive. grin Now let's head for the pub and work on the beer analogy. VAR - Very Agreeable Refreshment.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: And Now MVaR in words of one sylable or less

OK. I give up - again. Beer wins. Hands down.

(You didn't get the unit multiplication thing. Think about it. It makes sense. But now for the beers!)

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: And Now MVaR in words of one sylable or less

I might as well put in my two cents worth.  The reactive power unit var is more like the real power unit watt.  It is not an acronym like VA or an abbreviation of a unit like V so it is not capitalized.  I've got to admit that the argument would be stronger if there were a Ferdinand Var out there somewhere who invented the electromagnet.

I also vote for beer.
 

RE: And Now MVaR in words of one sylable or less

That would make the argument even weaker, if it is indeed named after Ferdinand Var, then it should be called (named) Var and nor var. IEC/SI even says that var is the Name and the unit of reactive power. As far as I know, the name is still reactive power.

..keep going with beer! I will be designated driver.

Rafiq Bulsara
http://www.srengineersct.com

RE: And Now MVaR in words of one sylable or less

If this keeps going I'm quitting the beer and hitting the whisky! smile
  

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If we learn from our mistakes I'm getting a great education!
 

RE: And Now MVaR in words of one sylable or less

All this war over VAR ???

You guys must be really drunk.

BTW, I'm all for VAR, not some pansy var.

Muthu
www.edison.co.in

RE: And Now MVaR in words of one sylable or less

Muthu,

It's 0225hrs here. My litle girl has a cold and can't sleep, so I'm not allowed to sleep either. That whisky is looking more tempting by the minute! smile
  

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If we learn from our mistakes I'm getting a great education!
 

RE: And Now MVaR in words of one sylable or less

Hi Scotty

Hope your little girl gets better soon. Sick children take a lot out of you. Been there, done that. My kids are all grown up and I just exchanged one set of problems for another. Now the older problem doesn't look not so intimidating anymore.

PS: In your frustration, don't give the whiskey to the daughter. bigcheeks

Muthu
www.edison.co.in

RE: And Now MVaR in words of one sylable or less

My little guy will be 4 next month. We talk on the phone a lot. When he is sick, I can just worry and get telephone updates from his mother. Sympathy and a prayer for your daughter.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: And Now MVaR in words of one sylable or less

Edison;
I like your description, pansy var. The governor of California would probably call them "Girlie vars."

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: And Now MVaR in words of one sylable or less

I must add, from an antipodean point of view, vars just sounds so, errr...I'm sorry, I feel a bit queasy.

 

RE: And Now MVaR in words of one sylable or less

Quote:

All this war over VAR ???
var wars?

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RE: And Now MVaR in words of one sylable or less

We're still working on the beer and froth analogy. Another round please.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: And Now MVaR in words of one sylable or less

Bill:

Since you asked for it, here is some information from a more authentic source, the IEC website.

Which clarifies the following:
The name var is not related to a person's name. It in fact  stands for volt ampere reactive power and the unit is also var.  (not that it is widely accepted or all have to agree to it).

Also there is an official conversion factor: 1 var= 1 V.A

(How original and useful! Conversion factor for an arbitrarily invented unit!)

So what is wrong with writing a name in Upper case? and units can still be VA , using the conversion factor!)

Then there is a Statement by J.H. Dellinger (U.S. Bureau of Standards) in 1916, which is even true today.

"In conclusion, this study has shown that the international system, based upon representing the electromagnetic system, is a convenient and satisfactory system of units for the purposes of electric and magnetic measurements. Proposed changes in some or all of the units do not appear to offer advantages such as to justify the confusion and inconvenience of changing the units as ordinarily used."


The links are:
http://www.iec.ch/zone/si/si_statements.htm

http://www.iec.ch/zone/si/si_elecmag.htm


By the way, IEC has also created a storm or a debate in IT world as well by creating some arbitrary units like 1KB=1000 bytes where as the conventional wisdom and fact is 1024.  (or something like that).
 

Rafiq Bulsara
http://www.srengineersct.com

RE: And Now MVaR in words of one sylable or less

The reason for this is not obvious for those that do not use SI units.

The beauty with SI units is that they can be used to check validity of equations, among other things. But, if you use an arbitrary addition to the "pure" SI units, then validity check will not work. And since W and VA are reserved for active and apparent power, there is a problem with reactive power. Using VAR or VAr will not work, simply because the "R" or "r" doesn't fit when doing "unit algebra". That is why the unit var was defined. The dimension of var is still VA.

I think that you should accept that scientific work needs more than arbitray conventions. But use VAr or vaR or VaR or whatever you feel like. But be prepared to meet one or two elevated eyebrow now and then.

 

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: And Now MVaR in words of one sylable or less

Hi Gunnar,

I am trying to follow your logic - I promise, I really am - but I am so far failing. Keep trying!
  

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If we learn from our mistakes I'm getting a great education!
 

RE: And Now MVaR in words of one sylable or less

No Scotty, I will not. I just explained why the var unit was created and why it is used in natural sciences. I am not trying to force you or anyone else to use it. No way.

(Is it the "unit algebra" AKA "dimension analysis" that you don't understand? I shall google to find a few URLs for you, if that is the case).

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: And Now MVaR in words of one sylable or less

I can see the logic which does not admit separate units for VA and VAR.  However the same logic also should not admit different units for power (watts) and apparent power (va).  This also follows from dimensional analysis of:
S = P * P.F.
If P.F. is unitless, then S must have the same dimension as P.

 

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RE: And Now MVaR in words of one sylable or less

For what it's worth, I like Gunnar's explanation.
 

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: And Now MVaR in words of one sylable or less

Make that
P = S*P.F.  
Same conclusion.
 

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: And Now MVaR in words of one sylable or less

Power factor has no units, so that works.

 

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: And Now MVaR in words of one sylable or less

OK, I still like the beer / foan analogy better, bt this one is at least different. I heard this (or read it) once, I cannot find any other decent reference to it, but when I came across it the first time it made perfect sense. Now all I can do is regurgitate it as best as my failing memory can recall, here goes...

VARs and Slinky Analogy:

With two people on a long table, Holder A and Holder B, stretch a Slinky toy between them. Holder A (HA) is the utility generator, Holder B (HB) is the End User, representing the work being done. At one end, HA wiggles the slinky back and forth, making a series of sine waves. The energy exerted by HA is the Apparent Power (kVA) being exerted into the system. The relative motion of the wave peaks represents the AC current flow. The energy HB feels as the Slinky tries to move his hand is the work being performed (kW), the Real Power being delivered. But if you watch the slinky, the spring is being compressed and expanded by the action of delivering this "power"; that compression / expansion is the Reactive Power, the VARs, and is initially created by HA but then reflected back and forth between the two. It's just something that comes with the territory.

This is not as eloquent as I originally heard it, I know. If anyone has knowledge of the source of this, I'd love to see it again.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: And Now MVaR in words of one sylable or less

Thanks for your agreement (?).  My point was if we don't allow VAR as a unit distinct from VA, then we also shouldn't allow VA as a unit distinct from watts.   Of course V*A is a valid product of units, but that product has the name watts.

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RE: And Now MVaR in words of one sylable or less

Is the slinky submerged in beer?

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RE: And Now MVaR in words of one sylable or less

Gunnar - yes, although I've spent a bit of time looking myself and maybe understand what you were saying. Or maybe not!

I like the observation in ePete's second-from-last post too.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: And Now MVaR in words of one sylable or less

Some people seem to have no greater use than a slinky, but they can still bring a smile to your face when you see them falling down the stairs.
Publican, another round if you please, and by all means have one yourself.
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: And Now MVaR in words of one sylable or less

OP's reaction - hairpull

Muthu
www.edison.co.in

RE: And Now MVaR in words of one sylable or less

To summarize my opinion. There are two logical approaches:

1 - S, P, Q all have the same unit.
OR
2 - S, P, Q carry units with different names (VA, WATTS, VAR) which are all dimensionally equivalent:1watt=1va=1var.  The different names are simply a convenience to help match traditional notation.

Either approach is logical to me.  But picking on VAR without picking on VA not logical to me.   And if you say VA is not a unit but a product, you should be equally happy to label Q in watts.

At any rate, life goes on and we all get the right answers, even the heathens like me who don't use the SI system exclusively.

Now it is time for a beer while I think about that slinky.

=====================================
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RE: And Now MVaR in words of one sylable or less

electripete - I understand your point and I think I agree. Based on tradition, I would go with your option 2. In this case the confusion is created by mixing vector and scalar quantities. I think we could refer to Q as watts. In school I was taught that we call it VA because they didn't want to call it imaginary watts. VA seemed to work, but is perhaps not the most descriptive choice that could have been made.

Now I need a "real" tall beer (without suds please).
 

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: And Now MVaR in words of one sylable or less

Muthu,
I forget. Was there a point to all this? OP no doubt gave up on us.

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: And Now MVaR in words of one sylable or less

Alan

I agree. I don't think OP is ever coming back. We engineers have the uncanny knack of turning off people. sad

Muthu
www.edison.co.in

RE: And Now MVaR in words of one sylable or less

My head hurts.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: And Now MVaR in words of one sylable or less

What about torque (Nm) and work (Nm)? Same units, but torque is so obvious (force perpendicular to distance) and work is also obvious (force in same direction as distance) so the confusion never starts.

W and var reflect the same situation. W in same direction (angle 0 degrees) and var perpendicular (angle 90 degrees). But, as the OP implies, there is a lot of confusion about reactive power (I really do not see why) and thus the var was introduced as a separate unit so that the R (in VAR or vaR or whatever the preference is at the moment) shouldn't enter dimensional analysis.

The confusion about reactive power is probably mostly because of all the unnecessary simplified explanations. The produce nothing but confusion. The correct math is not hard to follow. And the results are easy to illustrate using an oscilloscope (or a simulation, or even pen and paper). So I would prefer not to see any simplified explanations at all. We are engineers - aren't we? Why, then, should we use electrician's thinking?

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: And Now MVaR in words of one sylable or less

Yes, I agree with you Gunnar, that if it's ok to say torque in N-m vs Joules, then it should be ok to say apparent power in VA vs watts. That supports your original post and undermines my objections.

I agree with you, for purposes of electrical engineers there is no benefit to give any analogy for power factor.   The benefit comes for folks that aren't electrical engineers.  I have to say I do benefit from analogies that convert mechanical problems (static springs or dynamic mass /  spring /damper) into electrical problems (R / L / C) simply because it transforms the problem into something I am more familiar with.  But transforming electrical into mechanical doesn't buy anything for me... maybe it would for a mechanical guy.  Go ask the question in the mechanical engineering other topics forum and you might get "better" answers (answers more useful for people that haven't studied the power triangle to the point that it is intuitive.
 

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RE: And Now MVaR in words of one sylable or less


Gunnar:

Your post 5 Oct 09 12:45 made it clear, but the BIPM rule definitely hurts me. And the reaction of the audience shows that very few people are aware of this BIPM regulation.

I myself don't wish to return to horsepowers or lbf ft/s, but I'd like to stick to Volts x Amperes = Watts for active power. For expressing apparent power I'll use VA and for reactive power its VAr (r for reactive). I'm used to it and its easy to understand. I must admit, however, that P for active power, S for apparent power and Q for reactive power would be an attractive alternative.

I can gladly report that I'm used to C and K.

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM



 

RE: And Now MVaR in words of one sylable or less

I'm a little late in chiming in.  I think my designer authored the comparison of vars as managers.  We measure the company's "power factor" by the ratio of engineers and designers to total employees on the phone list.

A good analogy is vars are electrical transmission fluid needed to transfer energy across the air gap in generators, motors and transformers. Before the energy (watts can flow) we have to send amps to fill up the transmission fluid.

A great teaching tool  is on this website(free)

http://www.powerstandards.com/PQTeachingToyIndex.htm

RE: And Now MVaR in words of one sylable or less

By the way, have you ever seen the expression "MX" used instead of "Mvar"?  

 

RE: And Now MVaR in words of one sylable or less

Not a familiar term in my part of the world. I'm UK-based but I've done a fair bit of work with European and US OEMs and haven't heard it in dealings with them either.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: And Now MVaR in words of one sylable or less

I've only heard it from a single person (a Canadian guy), and I thought maybe it's a common term in some parts of the world...

  

RE: And Now MVaR in words of one sylable or less

Hi Gunnar;
To quote myself;

Quote:

Should a German, an Italian, or a Russian challenge my use of the rules of the English grammar I would be offended. Should a Francophone challenge my or demand that I change my habits, Oh well, that's just the French.
I almost added, if a Swede challenges my use of the English language, tread cautiously, he may well be correct.
You are correct sir, as usual.
However, may I suggest an alternate point of view?

In a town lived a man and a Countess. The man despised the Countess and would only refer to her as a pig. (Please be patient, there is a point.)
Eventually the Countess had the man hauled into court. The judge explained to the man that he could not call the Countess a pig and he would be in serious trouble if he continued.
The man asked;
"If I am not allowed to call a Countess a pig, may I call a pig a Countess?"
"Yes you may." replied the judge.
The man then turned and said;
Good afternoon, Countess!"
That said,
I accept that I must call Volt Amps reactive vars.
But, may I call vars "Volt Amps reactive"?
If I am allowed to call vars "Volt Amps reactive" then by the accepted rules of English Grammar, the acronym VARs is acceptable.
I agree and accept that var is the proper name to use in a formula, and accept the responsibility for any  loss or confusion that may result should I inadvertently capitalize any part of var.
However, may I use the grammatically correct acronym to replace the term Volt Amp reactive when writing conversationally?
Example:
You may speak about VARs all you wish, but if you are using the term in a mathematical formula the correct term is var.
I hope this suggestion is acceptable to most if not all of the parties to this discussion.

Yuma, I spent most of my life in Canada and have not heard the term.
Scotty, I hope your daughter has recovered from her cold.

On a lighter note;
Voltaire? What on earth has he to do with electricity, the Volt is named after Volta.
Voltaire had a knack for antagonizing those in authority, (possibly mostly those who were abusing their authority).
Despite his unpopularity banishments and exiles, he lived to a good old age and probably died of mostly natural causes. (Overexertion? An arduous journey  of several days duration was the probable direct cause.)
Although Voltaire died when Ampere was a young boy and ten years before the French revolution,  Voltaire's ideas and attacks on the French system of government of the time was/is seen by some as part of reason for the French revolution, despite the ten years or so that elapsed between his death and the start of the revolution.
Ampere's father died in that revolution. Was there any family animosity, probably not, but it is possible.
Forgive me for a poor attempt at humor based on such a tenuous connection. It's the probably the result of a brain damaged by too many years of exposure to too many electro static and electro magnetic fields.
var has been around since about 1965? Yikes, I missed that one. Probably because I didn't stop drinking until the late 60's.
Despite no longer drinking myself, I'll be glad to buy you one of your choice, Gunnar and have a coffee with you.
When oh when will I learn never to doubt the master?

 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: And Now MVaR in words of one sylable or less

A question that I hope is related to this topic, by way of connection to the BIPM;
When I started to learn about electricity, from my father and uncles, to do with flashlights and bicycle generators and light switches, popular knowledge was that electricity flowed from positive to negative. Popular knowledge always lags behind scientific wisdom, witness the present discussion re: var, VARs.
As I grew older I learned about electrons and had to change my ideas. Electricity now travelled from negative to positive.
This was an advantage to dislectics everywhere. They could now use the right hand rule with their left hands.
Sometime later, word filtered down that electricity had been redefined from the movement of electrons to the movement of holes, or if you will, the movement of the absence of  electrons, or the movement of nothing. Much ado about nothing?
I remember a question from one of my fellow instructors in the staff room back in the early 70's.
"Should we be teaching electron flow or conventional flow?"
There were a couple of non committal sentences and the subject was changed.
Question:
Was the BIPM the body responsible for disregarding electrons and redefining the flow of electricity as positive to negative?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: And Now MVaR in words of one sylable or less

Bill,

Thanks for the kind thoughts for our little 'un. I fear she is going to spend her first birthday quite ill, which is a shame. Fingers crossed that she perks up a little in the next couple of days.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: And Now MVaR in words of one sylable or less

(OP)
There would appear to be quite a few trainee politicians in our midst. What was the original question again?
All I know is that it wasn't supposed to be an excuse for an argument on CaPitAl bLEediNg LetTers, how very very sad.
Why didn't you just tell me (as I suspected)that there isn't a simple answer and left it at that instead of going off on one?
Thanks to those who did take it in the spirit that it was written, and to those who merely used it as a vehicle to demonstrate their perceived intelectual superiority..........words fail me (But you don't quite spell it lIkE tHAt.
So, just to recap then:-

If I get two managers and tie them up in a vat of beer with a slinky on a railroad track...............

Never realised that my finger inadvertantly hitting/missing the shift key would cause such a fuss.

RE: And Now MVaR in words of one sylable or less

Hi JJayG;
Sorry for that. No reflection on you whatsoever, we do this to each other.
How to explain power factor to a starter?
An analogy works by transferring knowledge from one field to another. Water pumping analogies for electrical effects only work if the learner is familiar with water pumping.
An analogy about analogies.
We were playing with a small motor bike once. We encouraged my sister-in-law to try it. I can't ride that she kept saying.
We kept assuring her that it was "Just like riding a bicycle."
Lynn finally tried it. Off she went, full throttle. Didn't make the first turn and plowed full throttle into a stand of saplings. She kept the throttle pinned and we could hear her screaming, the engine put-put-putting and the saplings breaking. Finally she stopped, in the center of the stand of saplings. When we finally got her back out in the clear, she was not happy with us.
"But, it's just the same as riding a bicycle."
"BUT I CAN"T RIDE A BICYCLE!!!"
Well, using an analogy from an area that the learner doesn't understand may be just as futile if less exciting.
Analogies work best one on one, or at least with a group that is familiar with the field referenced by the analogy.
An analogy based on the wheat fields of Kansas may be lost on a learner from the Everglades as will an analogy based on the Everglades may be lost on a learner who has never left Kansas.
Power factor and Volt amps reactive;
For the purists let's stick with displacement power factor.
When an alternating current is applied to a circuit, it will cause a current to flow. The current will be alternating. But, some circuit elements affect the flow of the current. Inductors inhibit the flow of current so that the current in an inductor, while still a sine wave, is phase shifted and reaches its peak value later than the voltage reaches its peak value. The peak current through a capacitor reaches it's peak before the voltage reaches its peak.
This effect may be described by a right triangle, The actual power consumed by the circuit is represented by the base, the Volts times Amps or VA is represented by the hypotenuse, and the altitude of the triangle is represented by an imaginary quantity called Volt-Amps-reactive. The angle will be the angle of the phase shift, or the degrees of phase shift described as one degree equals 1/360 of a complete cycle.
The right triangle and Pythagoras' theorem.
Your mission JJayG, should you choose to accept it, is to find out what fields your learner is familiar with where there is an effect that may be described by the right triangle and Pythagoras' theorem and make an analogy to transfer that knowledge to the electrical field.
One analogy that will certainly give your learner a lot of practice with the mathematics of power factor is the railway analogy.
An engine on one track is pulling a car on a parallel track. It takes a force of X units to move the car. The tracks are Y units apart. A rope Z units long is used to pull the car. What is the tension in the rope?  
Solve for varying values of X, Y, and Z
Then have a beer and speculate on the ratio of beer to foam in relation to the volume of the mug.
Hope this helps.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: And Now MVaR in words of one sylable or less

Quote:

An analogy works by transferring knowledge from one field to another. Water pumping analogies for electrical effects only work if the learner is familiar with water pumping.
But we can safely assume that everyone knows about beer.

Beer is the Rosetta Stone of engineering.

RE: And Now MVaR in words of one sylable or less

Beer is still the best analogy.
The part people are missing is that Beer Mugs are very expensive and the price is proportional to volume.
So if your beer comes out of the tap with a healthy head of foam you have a bigger more expensive mug thna the people drinking out the tap that puts no foam on the beer.
To get the same beer you get they can buy a cheaper mug.

RE: And Now MVaR in words of one sylable or less

I will refer to an analogy between mechancial m / k / c  systems and electrical R / L / C systems which I have previously posted:

Quote:

You need only 6 simple rules in order to solve any sinusoidal steady state lumped linear m/k/c mechanical vibration problem using electrical circuit impedance (R/L/C) analysis techniques:

1 - mechanical force f plays the role of electrical current I

2 - mechanical velocity difference v plays the role of electr voltage difference V

3 - mechanical mobility  v/f plays the role of electrical impedance Z = V/I
(use the symbol Z throughout.   We use the term impedance to represent either electrical impedance or mechanical mobility .. avoid the term mechanical impedance which is the reciprocal of mobility).

4 - A spring (k) acts like an electrical inductor of inductance L=1/k  
The impedance is Zk = j*w/*k

5 - A damper (c) acts like an electrical resistor of resistance R = 1/c  
The impedance is Zc = 1/c

6 - A mass (m) acts like an electrical capacitor of capacitance C =m  **
The impedance is Zm = 1/(j*w*m)
** one terminal of this mass/capacitance is connected to ground.

Derivation of the impedances and their electrical equivalencies is as follows:
Spring:
f = k x
f = k (v/jw)
Zk = v/f = j*w / k
By comparison to ZL = j*w*L,  we find L = 1/k

Damping
f = c v
Zc = v/f = 1/C
By comparison to ZR = R,  we find R = 1/c

Mass
f = m a   (where a is referenced to ground)
f = m* (jw * v)   (where v is referenced to ground)
Zm = v/f = 1/ (jw*m)
By comparison to ZC = 1/(j*w*C),  we find C = m
(where C is connected between the location of the mass and ground).

The above derivations are based on phasor analysis. A note about phasors:
V, I, v, f above represent phasors (magnitude and phase at assumed frequency w)
Differentiation of the associated time signal corresponds to multiplying the phasor by j*w
Integration corresponds to multiplication by j*w

This analogy also preserves the definition of instantaneous power.
Pmech(t) =  V(t)*F(t)    vs   Pelec(t) =  v(t) i(t)

Also if you look carefully at the max stored energy W in the spring and mass elements, you will find they are exactly what is predicted by electrical calc of Winductor = 0.5*L*i^2 and Wcapacitor = 0.5*C*v^2.

So let's use this analogy to try to develop analogy for power system in the m / k / c world.  

I will start with a very simple mechanical system called 1m

System 1m:
Ground === vs(t) ===rigid bar===c_load ==== Ground
vs(t) = velocity source.  Note if we apply a source displacement d(t)=d0* cos(w*t), this is equivalent to a velocity source v(t) = d./dt (d(t)) = w*d0*sin(w*t) = v0 * sin(w*t) where v0=d0*w is peak velocity.

c_load is a visous damper which removes energy from the system.  Similar to a dashpot with viscuos fluid.  It obeys c = f / v.  f and v are the same as f and v of the source.  A

There is no energy storage, so any energy input by the source vs is instantly converted to heat in the load c_load.    f is in phase with v.

The average rate of energy transfer from source (vs) to the load (c_load) is:
Pm1 = 0.5 * v0 * f0 = 0.5 * v0^2*c
note vs as above, and fs is source force (which happens to be same as load force in this simple system.


and analogous electrical system will be called system 1e
System 1e:
Ground === Vs(t) ===ideal wire ===R_load ==== Ground
where Vs(t) = V0*sin(w(t),  Is=I0*sin(w(t) and the ideal wire had neither resistance nor inductance.

Again there is no energy stored in the system, so any energy input by the source Vs is instantly converted to heat in the load R_load.   I is in phase with V.

The average rate of energy transfer from source (Vs) to the load (R_load) is:
P1e = 0.5 * V0 * I0    = 0.5 * V0^2 / R

Now let us examine a second system Pm2
System 2m:
Ground === vs(t) ===k===c_load ==== Ground
where we have added spring k instead of bar.

The spring is an energy storage device and we now can have energy storage in the sytem within the spring.   The energy that comes out of the source does not instantly appear at the load.  The load can also pull energy out of the spring at times when the source isn't adding energy.   The force is no longer in phase with the voltage.

The average rate of energy transfer from source (vs) to the load (c_load) can be shown to be:
Pm2 = 0.5 * v0 * f0 * cos(theta)  where theta is the angle by which fs lags vs.
* I'm not going to dwell on the proof of this, but will come back later to disuss why it's important. *

We can also see that due to the presence of the new cos(theta) term resulting from energy storage within the system, we now need a higher magnitude f0 to transfer the same average power from the same source.

The electrical analogy to System 2m is System 2e
System 2e:
Ground === Vs(t) ===L ===R_load ==== Ground
Where we have replaced the "ideal" wire with one that has some inductance L.

We now have energy storage in the system (within the magnetic fields of L).  The power leaving the source no longer instantaneously enters the load.   The source current is no longer in phase with the source voltage.

The average rate of energy transfer from source (Vs) to the load (R_load) is:
P1e = 0.5 * V0 * I0 * cos(theta) where cos(theta) is power factor.

***  Most EE's are probably saying by now – this is worthless.... you haven't made the system easier you've made it harder.     And I agree 100%.  But turn it around and assume you were given the above mechanical system 2m and asked to analyse it!   It would take a little bit of work I imagine and results would not be intuitive.   But transfer it to electrical system 2e and it's a piece of cake.

Presumably, the situation is reversed for an ME.  He looks at system P2e and sees a tricky system, but he looks at system P2m and sees something recognizeable.   I think that is the same point waross was making.

By the way, turning this sytem from a mechanical system to a fluid system is fairly easy.    Velocity is replaced with volume flow rate.  Force remains force.  Ideal wires connecting components are replaced with rigid pipe filled with incompressible fluid.  Spring is replaced with elastic pipe or vessel containing incompressible fluid.  Damper can still be a dashpot since that is sort of a fluid device.
 

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RE: And Now MVaR in words of one sylable or less

Correction in bold:
"P1e = 0.5 * V0 * I0 * cos(theta) where cos(theta) is power factor."
should have been
"P2e = 0.5 * V0 * I0 * cos(theta) where cos(theta) is power factor."

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RE: And Now MVaR in words of one sylable or less

electricpete,

If I understand your analogy correctly, beer is damp and foam is springy.  I think I'll need another one to fully comprehend the situation.
 cheers

RE: And Now MVaR in words of one sylable or less

Hi folks,

Just to keep the "fire" on!

Gunnar is correct. The unit of reactive power is "var", not "VAR" nor "VAr". by SI convention. This was decided a long time ago. So, if we want to use correctly the SI units, we may use "var" for reactive power.
 
Also, we should write "ampère" not "Ampère" for current unit (the symbol is A). The same for the voltage: "volt" not "Volt" (the symbol is "V"). Also, "kV" (not "KV") and "kvar" (not "Kvar" nor "KVAR"). This is all by convention (according to SI).

I think that all this confusion is because we, as engineers, have the tendency to simplify the model of everything and. sometimes, we forget to go back to the basics.
 
Also, we always keep trying to visualize a mathematical entity as being physical entity. Most of the time, this is not possible.

In reality, there exist fundamentally the electric and the magnetic filed, which are associated to voltage (V) and current (A), respectively.  The electrical engineering "quantities" S, P and Q are derived mathematically from these two physical entities (electric and the magnetic field, so V and A) and they have different units, VA, W and var, respectively. So we can not just add P and Q to get S. Mathematically, S is the square root of the sum of P squared plus Q squared.
All these quantities (S, P and Q) were defined based on linear system and sinusoidal waves. If the voltage and/or current waveform are distorted, another electrical quantity D (distorted power) has been defined (I do not remember its unit). So, S will be now (?) the square root of the sum of P squared plus Q squared plus D squared. This quantities is only maths, not physical.

To finalize, I would like to stress and remind you all that the apparent (VA), real (watt), reactive (var) and (now) distorted (?) power are only mathematical models created to simplify (?) power system analysis. So, S, P, Q and D are defined as being components of the instantaneous power wave,  These components do not exist as separate entities but they might be conveniently considered for purpose of engineering analysis.

Herivelto Bronzeado
 

RE: And Now MVaR in words of one sylable or less

We are now very far from the OP's "One syllable explanation". But we have had a useful and sometimes refreshing discussion on topics that are usually considered less important.

Now, Herivelto, that D for distortion "power" is also something that needs discussion. Especially the way it is added perpendicular to P and Q. The D^2 in your expression for S.

That has been done for decades and I think that it is something one shouldn't do. It may very well be one of the "engineering simplifications" that you mention in your post.

The reason why I think it is wrong to do so is that "D" does not lend itself to a geometrical construction with fixed angles (because the frequencies involved are different). But, on the other hand, signal components with different frequencies have always been added as root mean square - or RMS. So, there may be a good reason for doing so. But, on still another hand, the RMS addition is used for components in noise where there is no relation between the different components and their frequencies.

Can anyone show that the geometrical addition of P, Q and D is correct? I am, of course, thinking of you, Pete.  

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: And Now MVaR in words of one sylable or less

How are milliwatts, millivolts, milliamps, milliohms etc. represented in SI ?

Muthu
www.edison.co.in

RE: And Now MVaR in words of one sylable or less

mW, mV, mA etcetera. Capital M is mega (million) and "m" is milli (1/1000). Also, there is no "K" - only "k" for 1000.

OK, there is one "K" - used for 1024 in KB as opposed to "k" as in kB (1000 bytes).

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: And Now MVaR in words of one sylable or less

So, mega gets a M and kilo gets only a puny k ?

Muthu
www.edison.co.in

RE: And Now MVaR in words of one sylable or less

Yes. Right!

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: And Now MVaR in words of one sylable or less

Gunnar, you succeeded in getting me to take an hour away from my family on a Sunday pc3 (I'm sure that was not your intent).

At any rate, I took the bait and here is my analysis of the relationships S, P, Q, D

First of all, D is sometimes defined as D is defined as sqrt(Strue^2 – P^2 – Q^2).  


In that case, the conclusion that Strue = SRSS (P, Q, D) is trivial.  
(SRSS = square root of sum of squares)

So I will instead use an alternate definition of D (more below)

Start with definition of apparent power:
Strue = Vrms * Irms  [equation 1 – definition]

With harmonics present (and the waveforms periodic in w0)
I(t) = Sum Im(t)  for m = 1 to m_max
where Im(t) = sqrt(2)*Im_rms_ * sin(m*w0*t + theta_m)

V(t) = Sum In(t)  for n = 1to n_max
where Vn(t) = sqrt(2)*Vn_rms * sin(m*w0*t + theta_n)

Strue = Irms * Vrms = SRSS(Im_rms) * SRSS (Vn_rms)  [equation 2]

If we multiply the terms of equation 1, we get a square root of  products of the form Im_rms^2 * Vn_rms^2.  But this represents SRSS combinations of the terms Im_rms and V_n_rms.  

So we can write:
Strue = SRSS (In_rms*Vm*rms) where all n and m combinations are included [eq 3]

Now we define the "SRSS combination property"
SRSS Combination Property:  SRSS(A,SRSS(B,C)) = SRSS(A, B, C).  
This can be verified by simple algebra and is an important property which will be used again and again.

Now let us look at the pile of terms Im*Vn within equation 3 and sort them into buckets D, P, Q:

If m < > N, then the term goes into the D bucket and combined using SRSS:
D = SRSS (Imrms Vnrms) for m < > n
(By the way, directly above is promised alternate definition of D)

If m = n,  then we need to break down Im further into two parts:  Imrms_p=Im_rms*cos(theta_mm) and Im_rms_q = Im_rms*sin(theta_mm) where theta_mm angle between voltage and current for this harmonic.  Then we use these two parts to fill the buckets P or Q accordingly
P = SRSS (Im_rms_p^2*Vnrms^2) where we include all m = n
Q = SRSS (Im_rms_q^2*Vnrms^2) where again we include all m = n

Define S1 =Sapparent power of fundamental components
S1 = SRSS(P,Q)  should be obvious since each we have broken Im_rms into two pieces (Im_rms_p and Im_rms_q)  whose SRSS combination is Im_rms based on sin^1+cos^2=1

Now at the end of all this, every term has ended up in one and only one bucket.
The terms where m=n have ended up in the P and Q bucket where S1 = SRSS(P,Q).
The terms were m<>n have ended up in the D bucket.

By the combination property of SRSS
S = SRSS(everything in the bucket) [equation 3]
S = SRSS(D, S1)
again by the combination property we can split S1 into P and Q
S = SRSS(D, P, Q)   [equation 4]

Sounds very complicated, but simple with the combination property.  Each term gets added directly into S in eqation 3.   We SRSS combine individual clumps of terms in equation 4.  By the SRSS combination property we expect the same results either way.
 

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RE: And Now MVaR in words of one sylable or less

A few corrections:

First of all, D is sometimes defined as D is defined as sqrt(Strue^2 – P^2 – Q^2).  

In that case, the conclusion that Strue = SRSS (P, Q, D) is trivial.  
(SRSS = square root of sum of squares)

So I will instead use an alternate definition of D (more below)

Start with definition of apparent power:
Strue = Vrms * Irms  [equation 1 – definition]

With harmonics present (and the waveforms periodic in w0)
I(t) = Sum Im(t)  for m = 1 to m_max
where Im(t) = sqrt(2)*Im_rms_ * sin(m*w0*t + theta_m)

V(t) = Sum In(t)  for n = 1to n_max
where Vn(t) = sqrt(2)*Vn_rms * sin(m*w0*t + theta_n)

Strue = Irms * Vrms = SRSS(Im_rms) * SRSS (Vn_rms)  [equation 2]

If we multiply the terms of equation 1, we get a square root of  products of the form Im_rms^2 * Vn_rms^2.  But this represents SRSS combinations of the terms Im_rms and V_n_rms.  

So we can write:
Strue = SRSS (In_rms*Vm*rms) where all n and m combinations are included [eq 3]

Now we define the "SRSS combination property"
SRSS Combination Property:  SRSS(A,SRSS(B,C)) = SRSS(A, B, C).  
This can be verified by simple algebra and is an important property which will be used again and again.

Now let us look at the pile of terms Im*Vn within equation 3 and sort them into buckets D, P, Q:

If m < > N, then the term goes into the D bucket and combined using SRSS:
D = SRSS (Imrms Vnrms) for m < > n
(By the way, directly above is promised alternate definition of D)

If m = n,  then we need to break down Im further into two parts:  Imrms_p=Im_rms*cos(theta_mm) and Im_rms_q = Im_rms*sin(theta_mm) where theta_mm angle between voltage and current for this harmonic.  Then we use these two parts to fill the buckets P or Q accordingly
P = SRSS (Im_rms_p*Vnrms) where we include all m = n
Q = SRSS (Im_rms_q*Vnrms) where again we include all m = n

Define S1 =Sapparent power of fundamental components
S1 = SRSS(P,Q)  should be obvious since each we have broken Im_rms into two pieces (Im_rms_p and Im_rms_q)  whose SRSS combination is Im_rms based on sin^1+cos^2=1

Now at the end of all this, every term has ended up in one and only one bucket.
The terms where m=n have ended up in the P and Q bucket where S1 = SRSS(P,Q).
The terms were m<>n have ended up in the D bucket.

By the combination property of SRSS
Strue = SRSS(everything in the bucket) [equation 3]

by the combination property (inverted), we can break that into terms where m<>n (show up in D and terms where m=1 (show up in S1):

Strue = SRSS(D, S1)
again by the inverse combination property we can split S1 into P and Q
Strue = SRSS(D, P, Q)   [equation 4]

Sounds very complicated, but simple with the combination property.  Each term gets added directly into S in eqation 3.   We SRSS combine individual clumps of terms in equation 4.  By the SRSS combination property we expect the same results either way.
 

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RE: And Now MVaR in words of one sylable or less

Q = SRSS (Im_rms_q*Vnrms) where again we include all m = n
was not correct.

Should have been:
Q = SRSS (Im_rms_q*Vnrms) where m=n=1

The remaining terms (Im_rms_q*Vnrms where m=n <>1) should be thrown into the D bucket.  We still have everything accounted for once and only once.  Btw voltage THD typically low so these terms generally not very big anyway.

JJayG - sorry for the tangent.

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RE: And Now MVaR in words of one sylable or less

Electricpete,

As you correctly note, voltage THD is typically low so the distortion power is small.  It brings into question how to account for the reactive component of each of the harmonics.  For each harmonic frequency, you could say:

Sh = Vh·Ih·[cos(ah) - j·sin(ah)]

where ah is the angle between Vh and Ih.

Because the system impedance is usually highly reactive (even more so at higher frequencies), a is usually close to 90° and the real component of the distortion power is low.
 

RE: And Now MVaR in words of one sylable or less

Good point.  I was a little off-track.  For m=n, the term needs to be split into in-phase/quadrature components and put into P and Q buckets.  D contains onl m<>n terms.

To summarize the partioning of Im_rms * Vn_rms into buckets:
For m<>n, the term goes into D
For m=n terms, we need to split the current into in-phase and quadrature components which results in two terms:   Vn_rms *In_rms_p  (goes into the P bucket) and Vn_rms *In_rms_q (goes into the Q bucket)

An interesting question, why bother splitting Q from D.... after all neither one contributes average real power and both add in the same way (SRSS) toward Strue.  

The answer is apparently that D is not "convserved" like P and Q are.  This is based on the excerpt below from "Electrical Power Systems Quality" by McGraw Hill (which also gives the definition of D as product of ImVn where m <> n).

Quote (ElectricalPowerSystemsQuality):

The reactive power when distortion is present has another interesting peculiarity. In fact, it may not be appropriate to call it reactive power. The concept of var flow in the power system is deeply ingrained in the minds of most power engineers. What many do not realize is that this concept is valid only in the sinusoidal steady state. When dis tortion is present, the component of S that remains after P is taken out is not conserved—that is, it does not sum to zero at a node. Power quantities are presumed to flow around the system in a conservative manner.

This does not imply that P is not conserved or that current is not conserved because the conservation of energy and Kirchoff's current laws are still applicable for any waveform. The reactive components actually sum in quadrature (square root of the sum of the squares).
This has prompted some analysts to propose that Q be used to denote the reactive components that are conserved and introduce a new quantity for the components that are not. Many call this quantity D, for distortion power or, simply, distortion voltamperes. It has units of voltamperes, but it may not be strictly appropriate to refer to this quantity as power, because it does not flow through the system as power is assumed to do. In this concept, Q consists of the sum of the
traditional reactive power values at each frequency. D represents all cross products of voltage and current at different frequencies, which yield no average power.

P, Q, D, and S are related as follows, using the definitions for S and P previously given in Eqs. (5.1 for S) and (5.5 for P) as a starting point:

S = SRSS(P,Q,D)
Q = Sum Vk Ik sin(thetak)
Therefore D can be determined after P and Q by
D = sqrt(S^2 – P^2 –Q^2

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RE: And Now MVaR in words of one sylable or less

I don't like McGraw Hill's "conserved' vs "not conserved" terminology as it applies to harmonic currents and voltages.

If one analyzes current harmonics in much the same way one separates fundamental components into positive, negative and zero sequence, you will find that these currents do result in real power being dissipated somewhere in the system. Typically in I^2R conductor losses. And this real power at higher frequencies does come from somewhere. Usually, the non-linear loads that produce the current harmonics also produce the power at those frequencies and feed it back into the system. But there are cases in which generators contribute to harmonic power flows. And this will result in torque harmonics, or vibration.

So just hand waving and saying that these components are not conserved could lead some to ignore their effects on other parts of the power system.  

RE: And Now MVaR in words of one sylable or less

The distinction between Q and D is related to tracing flow of "power", not power dissipation.  Q and D are very similar with respect to power dissipation, i.e. neither Q nor D directly represents power dissipation and both Q and D contribute to S and current losses in other parts of the system.

Now let's look at the "power flow" aspect.

Let's say I have two frequencies:  f1 and f50 = 50*F1  (never mind that even harmonics are uncommon... it's just an example)

There are 2 P terms:  I1p * V1 and  I50p*V50
There are 2 Q terms:  I1q * V1 and  I50q*V50
There are 2 D terms: I1*V50  and I50 * V1

Consider the above to be at the input to a shunt impedance  Zs = R + j*w*L.

Now I want to calculate the output quantities.... So I need to subtract the P, Q, and (?) D consumed  in Zs.

I can calculate the real power losses in Zs and the reactive (Q) power consumed in Zs.   The output S will be reduced by the amount of real and reactive power consumed.

But how am I going to calculate the D "consumed" in Zs so I can determine the output?  For example the term I1*V50 ... which frequency to use in computing D consumed in this shunt element?  

The answer is it is nonsensical to talk about D consumed.  D is an artificial quantity whose primary purpose is to enable us to predict D in presence of harmonic content.

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RE: And Now MVaR in words of one sylable or less

Correction:
D is an artificial quantity whose primary purpose is to enable us to predict S in presence of harmonic content.

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RE: And Now MVaR in words of one sylable or less

Quote:

There are 2 P terms:  I1p * V1 and  I50p*V50
There are 2 Q terms:  I1q * V1 and  I50q*V50
There are 2 D terms: I1*V50  and I50 * V1
I don't understand the purpose of multiplying the current of one frequency times the voltage of another frequency.  The reason for breaking a distorted waveform down into separate frequency components is to be able to analyze each harmonic separately.  
 

RE: And Now MVaR in words of one sylable or less

The only reason to do it is to compute S.

S = Irms * Vrms
where
Irms = SRSS(I1p, I1q,  I50p, I50q)
where p and q are components in-phase and in quadrature with respective  voltage harmonic
Vrms = SRSS(V1,  V50, V50)

Now plug the expression for Irms and Vrms into the expression for S:
S = sqrt<(V1*I1p)^2+(V1*I1q)^2+(V50*I50p)^2+(V1*I50q)^2 + (V1*I50p)^2+(V1*I50q)^2+(V50*I1p)^2+(V1*I50q)^2)

Now separate those terms into buckets:
S = SRSS(P, Q, D)
where
P = SRSS(V1*I1p, V50*I50p)
Q = SRSS(V1*I1q, V50*I50q)
D = SRSS(V1*I50p,V1*I50q,V50*I1,V1*I50q)
recombine the p and q components within D
D = SRSS(V1*I50,V1*I50)

So, the only purpose of D is to faciliate computing S.  I agree there is no other useful purpose of combining voltage and current of different frequencies.  That was the point of McGraw Hill's quote above - D is not real in any sense other than the leftover terms in S which are not captured in P and Q.

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RE: And Now MVaR in words of one sylable or less

Correction

Quote:

D = SRSS(V1*I50p,V1*I50q,V50*I1,V1*I50q)
recombine the p and q components within D
D = SRSS(V1*I50,V1*I50)

should have been

Quote:

D = SRSS(V1*I50p,V1*I50q,V50*I1,V50*I1q)
recombine the p and q components within D
D = SRSS(V1*I50,V50*I1)

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RE: And Now MVaR in words of one sylable or less

(OP)
Many thanks gentlemen, you can now stop arguing amongst yourselves (yeah, like THAT is going to happen). I think we can safely say beyond reasonable doubt that the question will remain contentious for some time. Lets face it if you lot can't explain it, what chance do us mere mortals stand?
Thanks especially to Waross (Bill) for his patient explanation as well as his Fortran program ( who'd have thought a 50 year old Formula Translator language would still be up and running, yeah OK limping a bit, today?
Thanks also to Burnt2x who has definitely won the prize for the answer to give on an interview.............

RE: And Now MVaR in words of one sylable or less

We can explain it, but you don't need to go to an EE for what you're asking for.  I had suggested the ME forum.

What was wrong with the analogy I posted  10 Oct 09 17:19?   In fact the analogy is mathematically exact as I have shown.  But to explain it to your non-technical buddy, you don't need the math, just the mechanical analogy which is something within the experience of most people.

First you just need an example of a viscous damper.  That could be moving a potato masher up and down in a bowl of molasses.  Or perhaps the hydraulic piston on a screen door (particularly in the closing direction, may have a check valved bypasss to allow rapid opening, but ignore that).  Or could just be moving

Now in scenario 1m, you push the piston using a rigid extension bar.  The damper is simply a mechanical heater – converting mechanical energy into heat.  The rigid extension bar has no effect on your efforts – your push/pull force/distance is the same as if the bar were absent.  (the extension bar is the lossless, inductanceless line).

Finally in scenario 2m, you add a spring in series.   Immediately you should realize you are going to have to push a little farther to accomplish the same heating since you have to compress and decompress the spring.   The product of force and velocity (apparent power) is higher in scenario 2m than scenario 1m to achieve the same heating.  As a result the pusher will probably need to drink more beer.
 

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