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Smart $

Esteemed Member
Location
Ohio
...

Anyway, I did not ask about the average absolute value. I asked you have at specific instant of time the following data

Here at time equal to 0.020828 you have got the following data. please tell me each one unit

vX(t)*i(t) ( Reactive Power ) = 0.99670 unit?
vR(t)*i(t) ( Real Power ) = 1.11807 unit?
v(t)*i(t) ( Apparent power which is called by you) = 2.11478 unit?
The units are the same for all three. I'm saying this for Besoeker's sake. In essence he is correct that 1 volt and 1 ampere at any one instant in time is 1 watt. However, that 1 watt (W) can also be 1 volt-ampere (VA), or 1 volt-ampere reactive (VAr) under a more-refined condition. They are all technically the same unit; we just assign the different terms to distinguish what type of power is under scrutiny. In the order you have listed, I use volt-amperes reactive, watts, and volt-amperes.

s(t), p(t), and q(t) are really new for me and I had not seen such a these thinks. I need others confirmation and explaination about this because I dont know about this
Yeah, you likely will not see such anywhere but from me and a few others. It is a result of the technical community generally being a conformist's society ;)


As long as what mivey has posted and hinting, I am completely agree with him. There is no error in his graph and calculation. See the formula and calculation does not match your graph and calculation. That's why there is a difference.
As noted in my post with graphs, the parameters I used in the QUCS circuit simulator do not match the example scenario which mivey's graphs depict. Additionally, the QUCS simulator provided the data via its virtual probes (one current probe and three voltage probes).

Upon importing the 'raw' data into Excel, all I did was multiply the current value by each correlated voltage value then calculated the power averages from those results. The original data used for those calculations is highlighted yellow. If you check the formula used in the 'product' cells, it will verify all I did was multiply values furnished by QUCS. (btw, QUCS is a free downloadable program)
 

Smart $

Esteemed Member
Location
Ohio
Guys, this may be due to a browser setting. I believe there is a setting for whether your computer always refreshed web images you've seen, or whether it uses the last version of that image you saw, for faster browsing.

I think you can manually refresh an image when you're viewing it, as well as change a browser setting so the newest version of the image is always downloaded when you re-visit the site and re-view the image. I think.
That is what I thought... but I can't find the setting you refer to in IE8, and a manual refresh of the page does not update the image.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
The units are the same for all three. I'm saying this for Besoeker's sake. In essence he is correct that 1 volt and 1 ampere at any one instant in time is 1 watt. However, that 1 watt (W) can also be 1 volt-ampere (VA), or 1 volt-ampere reactive (VAr) under a more-refined condition. They are all technically the same unit; we just assign the different terms to distinguish what type of power is under scrutiny. In the order you have listed, I use volt-amperes reactive, watts, and volt-amperes.

I completely agree. The units are all the same. VA's, VAR's, and Watts are all "joules per second". So "watts" is just a shorthand notation for "joules per second".

Bes is right in that textbooks usually use a "Watt" to refer to a 1 volt * 1 amp. But I think this is only because textbooks usually only discuss power as a function of time before introducing the power triangle, and before they introduce VA's and VAR's.

Personally, I'm with Smart$. I'd rather call a 1 volt*1 amp a "VA", at least until we know how much power is real and how much is reactive.

And I would rather save the term "Watt" for power that leaves the circuit (in the form or heat or something else) and never comes back.

But that's just my personal opinion.

Steve
 

rattus

Senior Member
At the same instant in time there is no lag or lead.
Just instantaneous values.

I think Bes is belaboring a very fine point. Perhaps he is saying that instantaneous values do not carry phase angles as do steady state values of voltage and current. They are just numbers even if the equations do include phase angles. Is that it Bes?
 

Besoeker

Senior Member
Location
UK
Seems I have heard this unsupported claim before. In general, the lead or lag is present whatever you do even if you do nothing.
Lag (or lead) is both a phase difference and a time difference.
For instantaneous values of current and voltage at the same instant there is NO time difference.
This not a debatable point.
It's just simple physics.
 
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rattus

Senior Member
Lag (or lead) is both a phase difference and a time difference.
For instantaneous values of current and voltage at the same instant there is NO time difference.
This not a debatable point.
It's just simple physics.

I think Bes just said that t1- t1 = 0. I'll buy that.

I think he also said that although the equations for v(t) and i(t) carry phase angles, the values of v(t) and i(t) do not. I'll buy that too and pay in cash.
 

Smart $

Esteemed Member
Location
Ohio
I think Bes just said that t1- t1 = 0. I'll buy that.

I think he also said that although the equations for v(t) and i(t) carry phase angles, the values of v(t) and i(t) do not. I'll buy that too and pay in cash.
I have no problem with that either, but I do not foresee any exchange of cash, or plastic, on my part ;):D

Yet I never really considered the preceding aspect of the discussion as the real argument. Rather the argument in my mind is of treating the term 'instantaneous' as meaning a single measure at one instant versus measures taken continuously in equal increments of time duration required for one complete voltage cycle to occur or multiples thereof.
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
There have been three different threads that are diverging into the same argument. The odd thing is that this topic is covered quite thoroughly in power engineering classes and text books; as either fundamentals or basic concepts. I know I learned them in junior level courses in college.

Making an argument for or against, IMO is rather absurd. These formulas and concepts were developed by guys that had much more advanced understanding and knowledge of these things; and are the cornerstone of power engineering.

Not to say it isn't good to question concepts and principles, but trying to rewrite what has been tested time and again by academia is non-productive.
 

mivey

Senior Member
Well I can tell you that your average, S, will be in error if you do it that way. Let's work a backward example...
I'm not sure the average has any meaning anyway. In fact, I'm not sure all of these terms are defined in the way we have been playing with them.

But you do have the issue that power factor is also real power divided by apparent power and that pf is always a positive number.

At the very least, some of the classic definitions would have to be modified.
 

Smart $

Esteemed Member
Location
Ohio
I'm not sure the average has any meaning anyway. In fact, I'm not sure all of these terms are defined in the way we have been playing with them.
The averages S, P, and Q are not defined by their scale average. The scale offset is adjusted such that the minimum amplitude value is 0, then averaged.

But you do have the issue that power factor is also real power divided by apparent power and that pf is always a positive number.

At the very least, some of the classic definitions would have to be modified.
I prefer to say correlated rather than modified.
 
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