Power factor and VA vs Watts

[Cold Fusion]

.... Yes it is rare that one uses concepts on instantaneous power in power engineering.

Infact there is only one case I can recall - and I am not real familiar with it. It has to do with setting generation protective relaying.

One deals with instantaneous power during loss of excitiation events to trip the generator main CB and gen driver before the shaft breaks. Anybody wants to correct me here I won't feel bad at all.

cf

 

[rattus]

Doubting CF:

Doubting CF:

I don't know what you are asking for. I didn't say anything about or refer to "lead or lag".


This is an example of the reptative, insistent postings. Saying this louder and more often does not make it any closer to truth or usefulness. As already discussed and answered, this reference you quote is a 1950's out-of-print, unavailable text. I believe I have no clue as to the context.

cf

If you don't understand lead and lag, then you can't understand these equations.

Furthermore, the literature is replete with examples of instantaneous sinusoidal functions. In general, these functions carry a phase angle even they are zero. To dismiss a reference because it was printed decades ago is reckless and unprofessional. If it was valid then, it is valid now. The basics haven't changed since 1951. Neither have the contributions made ages ago by Ohm, Faraday, Volta, Ampere, Henry, etc.

You should realize that these functions of time provide the basis for the steady-state solutions which are commonly used. Power Factor--for example--assumes a phase angle between v and i. That is the phi or theta in i(t).

 

[Cold Fusion]

If you don't understand lead and lag, then you can't understand these equations. ...

Ouch - what a deep cutting zinger. I don't agree with you , therefore I don't understand. Okay, I can deal with you thinking that.

Just a guess on my part: You design circuit boards and have never set a protective relay?

... To dismiss a reference because it was printed decades ago is reckless and unprofessional. If it was valid then, it is valid now. ...

And another zinger. Oh my goodness, you are sure putting me in my place.

In my reckless, unprofessional manner, I just have a problem with relying on your version of the context. You know, the reference uses an example to show the validity of some particular model and you (yes you personally) generalize to all models.

In any case, I'm not particular against you saying that an instantaneous point has a phase angle. If it helps you to understand power engineering concepts, it's okay with me. I am mostly just against the premise that this is a useful concept nor do I know of any models where this concept is used.

The basics haven't changed since 1951. Neither have the contributions made ages ago by Ohm, Faraday, Volta, Ampere, Henry, etc. ...

Smart isn't going to like that. These are the same ones I was refering to when he said I should put all of that book learning aside and think for my self

.... You should realize that these functions of time provide the basis for the steady-state solutions which are commonly used. Power Factor--for example--assumes a phase angle between v and i. That is the phi or theta in i(t).

Yes I should - except for the commonly used part.

Most of the stuff I deal with is of the f(t) = Ae^(iwt). You know that phasor thing you have discussed - from Euler. You missed him in your list of wizzards. Which is odd, since he is the one that ties these trig formulas to the phasors.

But those are all steady state concepts and wouldn't apply to this un-professional, reckless, un-knowledgable concept I have of instantaneous power ... well, occuring in an instant.

enough of this twaddle - and that is what this is

cf

 

[Smart $]

Quote from smart:
Taking a measure of v and i at time t is pointless in power engineering,
Generally, Yes -cf

for p does not exist where Δt=0.
That's the part that is just not true. p is a rate. And by definition a rate is an instantaneous measure - unless you want to use RMS values (for V and I) and get an average power over one period.-cf

Yes, you can call it the vi product. And you can assign the unit measure volt-ampere to it. However, by implicit definition, you cannot call it power (p).
I'm not going to use Noetic Science definitions. I'm going to stick with IEEE 100 concepts. Yes, it is power - cf

What I'm saying is there is no power rate if no energy is converted or work performed. The electrical definition of power is the rate at which work is performed or energy is converted. Neither work nor conversion can occur in an instant for they are time dependent. If you insist p exists for an instant, it is because the measured event occurs over time, and we have confined the data to a single point during that time span.

Using RMS values does not change the event, nor the instantaneous values or rates. It only changes our perception of the event.

Anyway, I have no idea who even brought up the idea of limiting ourselves to instantaneous measures of a single point in time, but that is simply not the case.
As I recall, that was you - remember back to your insistent discussions of impedance varying from zero to infinity depending on what part of the V-I waveform the cycle was in. - cf

At best I may have caused it to surface, but that's all I'll admit to. I know what my understanding of "instantaneous" is, and it certainly is not restricted to one instant only.

I've never even run across anyone (other than here) that would confine their defintion of instantaneous to a single point in time when discussing power engineering.
This one completely baffles me. Yes it is rare that one uses concepts on instantaneous power in power engineering. However there is no definition of "instantaneous" other than being confined to a single point in time. As Bes has said over and over, (paraphrased), "that's what instantaneous means - at a single point in time." -cf

"Instantaneous" can also mean (and I quote from Merriam-Webster's Collegiate Dictionary), "occurring or present at a particular instant". It is an adjective. When I and several others mention instantaneous voltage, for example, we mean continuous instantaneous measures of voltage, usually for some period of time.

Additionally, we basically use the term "instantaneous" to distinguish between DC-equivalent, single-value measures from measures that continually varying through expiration of time. Summarily, doing so is within the bounds of conventional concepts and calculations.
Huh? -cf

Graphic depiction...

 

[Besoeker]

When I and several others mention instantaneous voltage, for example, we mean continuous instantaneous

An excellent example of an oxymoron.

 

[rattus]

An excellent example of an oxymoron.

I believe Smart is saying that instantaneous values are based on continuous functions such as,

i(t) = Im(sin(wt + phi))

We are not talking about measurements with a Simpson or Triplett multimeter. We are talking about sampling instruments. A sampling oscilloscope would take a number of samples to recreate the waveform described above.

And, FWIW, we can calculate the values of these functions at any instant.

In short, we are talking of the value of a continuous function at a given instant. That is all.

 

[Smart $]

An excellent example of an oxymoron.

When we plot a waveform, we either use sampled data or calculate a multitude of instantaneous measurements. Each point along the path of the waveform is an instantaneous measurement, whether it be a real or calculated sample.

Because we plot each measurement side-by-side, should we call these measurements something other than instantaneous measurements?

Perhaps you would prefer one graph/chart for each measurement. Good luck with that... :roll::roll::roll:

"Continuous instantaneous measurements" is not an oxymoron. It is a refined and accurate description of a concept that you apparently refuse to accept.

 

[rattus]

Maybe:

Maybe:

Maybe some learned person could cite an authoritative reference that dictates that the Watt is the only appropriate unit for the vi product instead of merely repeating the claim.

 

[mivey]

Ouch - what a deep cutting zinger. I don't agree with you , therefore I don't understand. Okay, I can deal with you thinking that.
...
And another zinger. Oh my goodness, you are sure putting me in my place.

:grin: Nice to see you can see the lighter side of discourse as well as Smart$ and Rattus and some of the others that have posted in this long thread. A prima-donna would take things too personal too quick and I'm glad y'all are not like that. I have enjoyed reading through the thread and while I think their have been some pointed arguments, I don't think any of the posters mean any ill will to the others. I'm glad y'all can have a passionate debate without folks getting their knickers in a twist.

It is tough to convey everything you mean with just a few typed words so we sometimes over-emphasize to focus attention on certain key areas of communication or points we hope the other will expand upon. If we were face-to-face we would use facial expressions and voice tones but we don't have that luxury here. Anyway, I commend the players for not being over-sensitive and continuing to debate the points they are supporting.

Maybe some learned person could cite an authoritative reference that dictates that the Watt is the only appropriate unit for the vi product instead of merely repeating the claim.

You would need two authoritative references because there are two things being debated: "instantaneous" vs. "any one instant".

Bes is right that the power at any one instant is watts. The power is rate at which the energy is being absorbed (or delivered). It may be stored in an eletric field, magnetic field or dissipated but it is the rate at which energy is being absorbed by the load at that instant.

Smart$ is also right in that over time, we can see what energy is absorbed over time and what energy is delivered over time by the load. Over time, we can distinguish the watts that show the rate at which energy is being dissipated by the load and the watts showing the rate at which energy gets absorbed/returned. We can then label the "returned watts" using the energy exchange rate of vars. Same fundamental units for both, but we label them differently based on what happens to the energy over time.

Even if we have a steady-state value for vars, if we isolate the load at the right instant, some of the energy that was previously being returned every 1/2 cycle would be dissipated by the load. Then, what we previously thought was reactive power would actually be real power. In other words, the energy we stored in the electric or magnetic field would ultimately be consumed by the load.

Even so, the curves we plot are, as Smart$ stated, plots of the instantaneous values and we can calculate the instantaneous value at any point by using the equations. We can separate these into the instantaneous real power and instantaneous reactive power.

I have references covering both sides of the discussion but it should not take a list of reference to see both sides. I see no point in squaring off and saying the other side does not exist.

I will say that very little we deal with reacts in an "instant" so we are usually concerned with the energy over some discrete interval of time. That does not mean we can't discuss the instantaneous power, regardless to how we have classified it or if we have separated it into some component parts. That is no different than separating the current into its component parts (in-phase and leading/lagging component).

 

[mivey]

Looking back through some earlier posts, there was some mixing of power terms and units/values. These may have been cleared up, but in general:

S = Complex power = E?I* = P + jQ , with units of VA
|S| = Apparent power = |E?I*| = |E|?|I| , with units of VA
P = average, real or active power = Re{S}, with units of W
Q = Reactive power = Im{S} , with units of var
p(t) = e(t)?i(t) ≠ Apparent power ≠ Complex power ≠ P ≠ Q
p(t) can be broken into the component Real{p(t)} & Reactive{p(t)} parts if we can evaluate the changes in instantaneous power over a sufficient amount of time.

Also, V & A have been used as value place holders but in these cases, V?A does not mean apparent power because the result is an instantaneous power value. Apparent power may be called VA sometimes, but that is different from the derived VA unit.

 

[Cold Fusion]

... Anyway, I commend the players for not being over-sensitive and continuing to debate the points they are supporting. ...

I'm just curious: What thread are you reading?

cf

 

[rattus]

Looking back through some earlier posts, there was some mixing of power terms and units/values. These may have been cleared up, but in general:

S = Complex power = E?I* = P + jQ , with units of VA
|S| = Apparent power = |E?I*| = |E|?|I| , with units of VA
P = average, real or active power = Re{S}, with units of W
Q = Reactive power = Im{S} , with units of var
p(t) = e(t)?i(t) ≠ Apparent power ≠ Complex power ≠ P ≠ Q
p(t) can be broken into the component Real{p(t)} & Reactive{p(t)} parts if we can evaluate the changes in instantaneous power over a sufficient amount of time.

Also, V & A have been used as value place holders but in these cases, V?A does not mean apparent power because the result is an instantaneous power value. Apparent power may be called VA sometimes, but that is different from the derived VA unit.

That's all well and good Mivey, but the use of the modifier "instantaneous" means we are dealing with a different situation, and anyone proficient in the trade should know the difference.

Let me ask again, "If 'ivars' are acceptable, why not 'ivas'"?

 

[mivey]

That's all well and good Mivey, but the use of the modifier "instantaneous" means we are dealing with a different situation, and anyone proficient in the trade should know the difference.

Let me ask again, "If 'ivars' are acceptable, why not 'ivas'"?

I don't know any "in the trade" using "iws" or "ivars" or "ivas". Does the use of the "instantaneous" modifier mean we can use units like we want? Then I propose we use "instantaneous kilogram meters squared per second cubed" and derivatives thereof.

 

[mivey]

Let me ask again, "If 'ivars' are acceptable, why not 'ivas'"?

I was trying to think of an analogy but we already have an expression for "ivas" and it is called "instantaneous power".

Maybe we could use this, given that we have little boys & girls going to a movie:
little boys = W
little girls = var
children = little boys + little girls = power

If we are discussing the tickets, we would say we need "X children's tickets", not "X little boys & girls tickets". We don't need a new phrase for the children's tickets as we already have one. We might need to check with someone in the movie trade, but if you want to say "I need tickets for X little boys and girls" you would certainly be within your rights and not violating any laws of physics.

 

[rattus]

I don't know any "in the trade" using "iws" or "ivars" or "ivas". Does the use of the "instantaneous" modifier mean we can use units like we want? Then I propose we use "instantaneous kilogram meters squared per second cubed" and derivatives thereof.

Sure, you don't see these units because you seldom are concerned with instantaneous values, but that is not the point; This is a theoretical discussion, not necessarily related to one's daily work.

Now, the use of "ivars" has been referenced, so it is not much of a stretch to use ivas. If the situation demanded it, I would do so--with proper explanation.

 

[mivey]

I'm just curious: What thread are you reading?

cf

You could have easily taken offense and started blasting away. I found your response clever and humorous and you did not resort to pettiness. If that was you being bad, you must be a really, really nice guy.

Maybe I'm just too laid back, but I really don't think anyone here wishes anyone else ill intent. I think most are here to help others and to learn. People who have it in for others tend to drip vile comments with almost everything they post.

I think any discussion can get heated at times but it doesn't mean you have it in for somebody personally, even though you might have it in for their ideas.

I really don't think we all need to agree on everything. But agree or not, I would like for us all to understand what each is saying.

 

[charlie b]

OK, so I wasted (or should I have said “invested”) a few hours of my life this morning reading through this thread. My intent was not so much to form an opinion of who has been right and who wrong, or to find statements with which I could not agree, or to check anyone’s use of math or physics, and certainly not to join the fray. Rather, I wanted to discover whether this thread has been of value (it has), whether it answered the originator’s original question (it has), and whether it is time to close it out. But I think it would be wrong of me to simply lock the door. I would like to ascertain what the participants feel about putting this one to pasture.

I offer the following suggestion. This process was used once before, with (I believe) good results. I suggest taking the following steps:
1. I would temporarily close the thread.
2. I would open it after a delay of three days.
3. I would close it again, this time permanently, two days later.
4. Anyone who wishes to post a summary, a new statement, or a rebuttal of someone else’s earlier comments would have the three days to compose your post.
5. During the two days that the thread will be reopened, anyone can post one, and only one additional time. If you post a second time, the second post will be deleted.
6. I will post the final comment, stating that the thread is closed, and adding some statistical information just for the sake of interest.

I have opened a new thread, with a poll. It is located here: http://forums.mikeholt.com/showthread.php?t=125658

Please go to that thread, and vote on whether this discussion should be closed in the manner I have described.

 

[mivey]

Sure, you don't see these units because you seldom are concerned with instantaneous values, but that is not the point; This is a theoretical discussion, not necessarily related to one's daily work.

I don't really know anyone proficient in the theoretical discussion trade unless we could include some of my professors.

Now, the use of "ivars" has been referenced, so it is not much of a stretch to use ivas.

If the cobbler-product fits the situation, then by all means you have the permission of the Milky-Way Engineering Society. There is some dissent among the members in the Canis Major Dwarf group, but they will soon be assimilated.

If the situation demanded it, I would do so--with proper explanation.

And I don't think you would lose your engineer's membership over it.

PS:
Charlie: I did not see your post as I had not re-freshed before posting.

 

[charlie b]

Charlie: I did not see your post as I had not re-freshed before posting.

Not to worry. For the moment, at least, this thread is open for business as usual.

 

[Cold Fusion]

...If that was you being bad, you must be a really, really nice guy. ...

Well, yes, that would be an example of me being bad-to-the-bone:roll:

And yes, in addition to me having and excellent understanding of all things mechanical and electricial, I am a nice guy.

And none of this is conceit, just truth.

cf