Hi
To correct power factor and consequently reduce the amunt of current the source has to provide for the active power (true work we want) and the reactive power. The way is to add impedances to the circuit to the load impedances. The added ones are again of the reactive type. Formulas demonstrate this. But why , apart from formulas demonstration, adding, example, a condensator, in the proper way obviously, in a circuit that contains an inductance (example a motor) the goal is reached? I mean what happen to the current, to the electrons, how do they move in the new circuit causing a decreased need of electrons themselves generated by the source?

 

JeffersonAirplane...
Attached is an example of power factor correction that may help

 

Power factor correction

JeffersonAirplane...
Hi To correct power factor and consequently reduce the amunt of current the source has to provide for the active power (true work we want) and the reactive power. The way is to add impedances to the circuit to the load impedances. The added ones are again of the reactive type. Formulas demonstrate this. But why , apart from formulas demonstration, adding, example, a condensator, in the proper way obviously, in a circuit that contains an inductance (example a motor) the goal is reached? I mean what happen to the current, to the electrons, how do they move in the new circuit causing a decreased need of electrons themselves generated by the source?

Power Factor, Unmasked, Philip P. Corso Date: 07-Sep-2016
I’m sure at some time or another in your career you were informed about Power-Factor via one of the following popular analogies: "The Glass of Beer and Foam!"; or, perhaps it was the "Horse Pulling the Carriage!”; or another Goodie, but oldie, “Pulling a Railroad Car!” In another forum, someone uses a “Torque-to-Amps” relationship!

Recently, I uncovered the best Analogy I’ve ever encountered, and I’ve been in this business more than 63 years (60 as an EE, last 6 as Professor of Alternative and Renewable Energy Management, better known as AREM, at Everglades University, Boca Raton, Florida, USA.

It’s called, “Two Riders on a Tandem-Bike!” The front-rider, or “Peddler” is, of course, peddling, while the rear-rider, the “Free-Loader”, is not! Thus, the Peddler is providing all the work… his goal being to move the bike forward.
Suppose the Free-Loader unbalances the system by leaning to one-side. In addition, now the Peddler has to work harder to compensate for the Free-Loader’s action. But, none of the extra-effort by the Peddler is being used to move the bike forward! Thus, efficiency is reduced!

The Power world is similar. "Real-Power" is needed to heat, cook, wash, lift, move, cool, elevate, dig, compress, pump, etc. It's what would be found if power was Direct Current, or DC! But, in Alternating Current, or AC, a second-type of power must be provided. It's called "Reactive-Power" (a term I abhor, as some of you may already know)! it's needed to provide the means to energize the magnetic-structure found in electrical apparatus like motors, generators, transformers, lamp-ballasts, etc. Combined vectorially, they are called “Apparent-Power!”

My students were always confused because it isn't "Power” as defined by physics. So, I taught them The three sides of the “Power Triangle” were:
o The hypotenuse, the product magnitude, V x A, units are Volt-Ampere or S.
o The horizontal-axis, referred to as the real component, P = S x Cos(q), units are Watts.
o The vertical-axis, referred to as the reactive component, VAr = S x Sin(q), units are VA reactive, or VAr.

The angle between the real axis and the hypotenuse is defined as q! And PF = P/S = Cosine(q)
Power Factor can also be described using a football-pass analogy! But that's another story!

Feedback please… Good, Bad, or Ugly accepted!
Regards and Stay-Well to all!
Phil Corso

 

yes ok, (I am supposed to have understood what is it the power factor) but real question is why if i add a further load (of the reactive type) and apparently adding a further burden to the source I obtain that, instead, some relief is given the source?
As you say I read in the past the example of the beer and the foam and before it was not difficult in my opinion to understand that source has to give an extra effort in the case of a load that can store energy inside and thus creating also some disturbances (such as a phase delay/advance - current and voltage). So why with that further load, opportunely connected, electrons redistribute themselves in the circuit in order to decrease (and now I say it badly, I know) "reactive" current?

 

JeffersonAirplane
…. I mean what happen to the current, to the electrons, how do they move in the new circuit causing a decreased need of electrons themselves generated by the source?
=========================================================
Its all about timing. The inductive load of the motor causes the current wave to lag behind the voltage wave with respect to time. This is because the inductive nature tends to impede the change of current. When a power factor correction capacitor is added in parallel to the motor, its current wave will lead the voltage wave. This is because the capacitor will tend to impede the build up of voltage across the capacitor. Since the same voltage is applied to both devices, it is their currents which are occurring at different times.
I think people tend to forget that the current through the motor is still the same as it was before. The current from the source is what has changed because it is now the vector sum of these two currents (As PhilCorso states). Since the currents aren’t occurring at the same time, their effects tend to cancel each other out.
If you are pulling a rope to the right and I am pulling it equally to the left, the rope doesn't move, but we both are applying force to it. It would not be correct to say there is no force on the rope. So you aren't really reducing the current, you are adding an additional current at a slightly different time. This gives you the effect of current reduction.

Hope this helps.

 

@ Jefferson & MWO
Electrons drift a bit, but they don't travel thru any thing. I suggest you read some physics books!
Regards, Phil Corso

 

Conventional current flow vs. electron flow vs. "skin effect" (or whatever it's called) isn't the question here.

MWO pretty much has it correct in that by putting a "counter" to the prevailing reactive current dynamic is ONE way to shift the power factor back closer to unity (1.0). ELI the ICE man comes to this mind. Yes; there's going to be some losses (primarily due to heat if I'm remembering things correctly).

In many parts of the world the overwhelming load is inductive (induction motors; transformers). Many developing countries countered the effect of these loads for many decades with fourescent lights (a capacitive load). In some of those countries things actually shifted and the overall system load became more capacitive than inductive, at least for brief periods of time.

ANOTHER way to "correct" power factor--at least at the generator terminals--is to use the excitation system. "Lagging VArs feed a lagging load," is the saying that comes to mind. The cost-benefit analysis here is that this can also reduce the amount of real power a generator can supply, but, if it comes at the expense of preventing brown-outs or blackouts then some sacrifices may have to be made. It's very "interesting" watching ERCOT and the residents of the Lone Star State deal with their electricity system during this prolonged heat wave. Everything's bigger in Texas--except the electricity grid it seems (or should I say the power generation portion of the electricity grid). Anyway, it's still going to be interesting to read the analyses that will inevitably come out of this situation.

How electrons behave in an AC power system is kind of settled precedent--be it right or wrong, it's how most people learn and understand the system. A professor I had once was fond of saying that electricity is still a mystery; is it a charge with a mass, or a mass with a charge? BUT, we do know how to use it--it has been harnessed, and it is described in commonly accepted terms, until (as with electron flow theory) something discovered changes the reality. They're not alternative facts; they're just how it's commonly understood and thought of and described and used to visualize these things we can't really see with our own eyes.

But, again, whether electrons flow or drift or flutter along the outer perimeter of a conductor isn't answering the original poster's question, PhilCorso. You can do it.

If you chose to.

 

Conventional current flow vs. electron flow vs. "skin effect" (or whatever it's called) isn't the question here.

MWO pretty much has it correct in that by putting a "counter" to the prevailing reactive current dynamic is ONE way to shift the power factor back closer to unity (1.0). ELI the ICE man comes to this mind. Yes; there's going to be some losses (primarily due to heat if I'm remembering things correctly).

In many parts of the world the overwhelming load is inductive (induction motors; transformers). Many developing countries countered the effect of these loads for many decades with fourescent lights (a capacitive load). In some of those countries things actually shifted and the overall system load became more capacitive than inductive, at least for brief periods of time.

ANOTHER way to "correct" power factor--at least at the generator terminals--is to use the excitation system. "Lagging VArs feed a lagging load," is the saying that comes to mind. The cost-benefit analysis here is that this can also reduce the amount of real power a generator can supply, but, if it comes at the expense of preventing brown-outs or blackouts then some sacrifices may have to be made. It's very "interesting" watching ERCOT and the residents of the Lone Star State deal with their electricity system during this prolonged heat wave. Everything's bigger in Texas--except the electricity grid it seems (or should I say the power generation portion of the electricity grid). Anyway, it's still going to be interesting to read the analyses that will inevitably come out of this situation.

How electrons behave in an AC power system is kind of settled precedent--be it right or wrong, it's how most people learn and understand the system. A professor I had once was fond of saying that electricity is still a mystery; is it a charge with a mass, or a mass with a charge? BUT, we do know how to use it--it has been harnessed, and it is described in commonly accepted terms, until (as with electron flow theory) something discovered changes the reality. They're not alternative facts; they're just how it's commonly understood and thought of and described and used to visualize these things we can't really see with our own eyes.

But, again, whether electrons flow or drift or flutter along the outer perimeter of a conductor isn't answering the original poster's question, PhilCorso. You can do it.

If you chose to.

You got the point. I used a not appropriate language but it is not the word (or the way people commonly understand complex concepts as you say) . So now I don't speak of electrons, I speak of how energy flows.
MWO helped me but I still have some doubts. I try to explain. I start from an assumption that can be wrong and so please in case correct me. Then please excuse me but english is not my language and so this may cause misunderstanding.
When the current to do the real job flows in the inductor, the inductor creates a current opposite in direction of a certain amount. So the algebric sum should give a current to do the job lower than necessary and so source is required to supply more (and this is as the example of the Two Riders on a Tandem-Bike ). At the end we will have the active power to do the job and the reactive power.
Now I add a capacitor. This too makes its request of energy.
And this remind me something. I have a voltage generator V with a resistor R in parallel than I have a current I = V/R . If I put in parallel to the resistor another same resistor R also this is now requesting a current the same I = V/R. So at the end the current in the circuit with two R in parallel doubles. Source is requested to increase the supplied energy.
The MWO example of the rope is telling me that the extra energy required by the inductor (reactive) is balanced or supplied by the capacitor that stores some energy and that in the alternating process it will give in one direction or in the other to supply the reactive current of the inductor. But in any case source has to supply something to the capacitor too.
Now, since after all, practice demonstrates (and the fact that pfc is imposed by power suppliers to save money) that adding a pfc like a capacitor or whatever it is, this will decrease the total power (active + reactive) and so the current, I ask again why/how the currents redistribute themselves in order to better the situation?

 

Without any graphics (which would be helpful, I know...), here's how I imagine it. Power is measured at an instant in time, so imagine a current sine wave and a voltage sine wave superimposed on top of each other. And then imagine a vertical line over the two. If the two sine waves are in phase with each other then the power of them is V*I. If the two sine waves ARE NOT in phase with each other under that vertical line (an instant in time) then the power is still equal to V*I--but even if the two sine waves have exactly the same shapes as in the first example because they are offset from each other the product of the two will be less than in the first example.

Because of the phase shift, the system is less efficient at transmitting energy than if there was no phase shift. Same amount of current and voltage--but they aren't in phase with each other (which they would be with a purely resistive load).

So, by using some kind of power factor correction method (capacitors; inductors; excitation) to bring the two sine waves more in phase with each other the system is more efficient at transmitting energy even if some of that energy is supplying a reacitve load.

In my mind's eye, power is measured at an instant in time--the vertical line--and is the product of V*I. If the two sine waves are in phase with each other, then the energy being transmitted is at the maximum. If they are out of phase--even if the two sine waves are exactly the same magnitude (voltage and current) the amount of power at that instant in time is less than if the two sine waves were in phase with each other.

Sorry; that's all I got. It works for me. It might not be mathematically or even physically correct--but it works for me. When the two sine waves are in phase the maximum amount of energy is being transmitted. When they are out of phase even if they are the same magnitue the amount of power being transmitted is less than if they were in phase. Using power factor correction methods to shift the two sine waves so they are more in phase with each other makes the system more efficient at transmitting energy (power).

Regardless of how we view electron flow.

And reactive "power."

Again, that's all I got. I'm hoping PhilCorso can overlook my sad description and provide a better explanation, without sending us to reference or text books. It can't be this difficult.

And, again, man knows how to use electricity and how to control it. But he really doesn't know what it is; just that it's useful and there are methods to make it more efficient. Why do you think large industrial plants with lots of induction motors have a VAr hour meter in addition to the Watt hour meter? Because it takes energy to supply the VArs and that detracts from the other billable energy. Otherwise, why would they charge for VArs? (In reality, we all pay for VArs--it's just factored into our tarrif/fees.)

Adeus.

 

Ok you correct the phase and then mathematically V*I is at its topmost. This is the method and it works. I know (ar at least I am convinced of this) what is the phase shift and from the physics why this happens with devices like capacitors and inductors. That is not my problem. My problem is why a capacitor betters the PF. PF is the measure of the goodness not the reason.
Instead imagine that this method doesn't exists.
You are fighting with your source that always has to supply more power than what is really necessary and after a time you see your fuel decreasing more than you expected.
Would you have started directly from PF saying "if I correct the PF I have resolved the problem"?
If you could do this for sure something else, more deep, should have come to your mind.
Somebody, somewhere in sometime imagined that the "electrons" (now I am joking a little) could have a different way of recombining themselves in order to do an improvement in efficiency misurable with the PF.
Now I tried some guess. I think that with a capacitor the source anyhow is supplying a further reactive current and this will be greater at the transitory, the start of the process. Then capacitor can supply current to the inductor for its reactive part. After transition, probably, anyway source is providing some power to capacitor but this is smaller than that current it should generate without capacitor and this is the improvement of the PF. If it was in this way, it is not sufficient anyhiw for me because it is lacking of formulas showing the real amount of currents

 

Formulae?

That's the purview of Professor PhilCorso.

For me, I'm a practical person. Knowing the formulae/mathematics of the situation isn't enough. I need to understand what's really happening, and then the formulae/mathematics becomes easier. And when I was commissioning power plants trying to explain what's happening and how and why using formulae (even F=(PN)120, which is one of the most important concepts of AC power generation and transmission to fully understand (think Droop Speed Control and Isochronous Speed Control--both topics which have been covered in great detail on Control.com) just made people's eyes roll back in their heads.

But, I understand--it's different for everyone (what it takes to understand a nebulous concept). As an instructor that was my challenge: Finding out what makes the lights go on for different students, sometimes in the same class. I so loathe the "VArs are like foam on beer--they don't go anywhere or do anything." Foam on beer says the beer is not flat--meaning it has some "effervescence" and sparkle. (There are places in the world where it's illegal to serve beer without a "head" of foam--because centuries ago unscrupulous publicans/barkeeps served flat beer. So, the government had to step in and write (and ultimately enforce) that beer be served with foam, as that was the best way to demonstrate the beer was not flat. (And, in some parts of the world, serving flat beer might have resulted in the shooting death of the person serving flat beer--so the government had another interest in trying to ensure the beer being served wasn't flat....)

And, foam on the beer IS like VArs in one sense. The more foam on the top of the beer in the glass/stein the less beer that can be in the same glass/stein. In the same way that "excess" VArs has an effect on the efficiency of energy transmission, keeping VArs (represented by the power factor!) to a minimum means more energy can be transmitted for the same "effort." So, saying VArs are like foam on beer just isn't a good analogy--in fact, it's a very poor analogy. Just like VArs are the result of inducing magnetic fields in most motors, foam on beer is the result of proving that beer isn't flat--there's just about no other way to do that (prove beer isn't flat).

I'm sure there are YouTube videos about power factor correction and the effect that VArs have on transmission efficiency. (Just be careful--there are a lot of wanna-be video producers/directors out there that don't really have a proper grasp on the fundamentals but make some very good simulations that aren't very well explained. And some will be flat-out wrong, others will be missing some key concepts and explanations which would help most viewers more easily grasp the concepts and fundamentals.

There are also probably some very good websites and blogs about power factor correction and the effects of VArs on AC power generation, transmission and distribution. (The same caveats apply as with YouTube videos.) Here's the first search result using my web browser for "power factor correction".

How to Calculate Power Factor Correction: 8 Steps (with Pictures) (wikihow.com)

You can try your preferred Seach engine/web browser for more results. Remember, very often reading multiple Search results can be time very well spent as often new terms and analogies and different methods of explanations can help to reinforce or understand some concepts and fundamentals. (When I was a young teenager I spent HOURS and DAYS (literally) in the local public library going through the card catalog looking for books on topics I wanted to learn about and understand. I read a lot of fluff, but as I've gotten older I have come to realize it was time well spent and I made some very good friends (other people who were curious, as well as librarians who took my under their tutelage and taught me many things about how to search a library (including periodicals, films and microfiche--which was just being introduced then--no videos). It opened a lot of doors to better understanding and a knowledge that information and learning was there for the taking, if one wanted to explore and devote time to exploring.)

Hope this helps!

 

Ok in fact I was searching for a very intuitive explanation before formulas as you remember. Sometimes I have seen very nice gif around that in my opinion are very helpful. One I remember I lked very much is that of the thermic engine with valves, pistons, ... moving like in the reality. Sometimes I have seen some showing the flow of current in a circuit. I tried a guess in my previous post. I do not know if it can be taken as an explanation. I was only saying that just in case of that is correct, then formulas, differential equations, other should come to confirm that vision or to confirm a correct one. If process is very well understood, intuitively, there is no diffuculty, for one who can manage mathematic/physic (also at a normal level that I hope could be that of me) to find comfort in the formula that try to describe the process.
But after this what is it the "intuitive" explanation?. Was may guess to be discardes?
Then, I found around a reference to the Boucherot theorem that I am supposed to know but after many years of job in other fields I completely forgot. The total reactive power of a circuit is the algebric sum of all reactive powers, but positive for inductors and negative for capacitors.
This gives the answer in my opinion.
But since you said in one previous post that ...... electricity is still a mystery ...( that I subscribe), did Boucherot see in his mind the movement of the currents confirmed and quantified by the relevant equations or did he just try many tests and finally simply take the result from experience?
And I am not here to be critic upon this, just would like to know how the story was.

 

This is kind of getting into the surreal realm for me, a practical person. And, I don't like guessing; theorizing is good as is following the scientific method.

I apologize for the previous link--it's one of those misleading links that seems to think that power factor correction and power factor calculation are synonymous.... Again, one needs to be wary of everything one reads and exercise their critical thinking skills.

Here's a new search result I found when looking up Boucherot:

Paul Boucherot - Wikipedia

There's a section on 'Real and Apparent Power' that is a VERY brief description of what I've not been very good at saying/describing. The formulae and mathematics are for others to try to help you with.

Anyway, what I meant by "countering" is described in that section as "canceling" using positive and negative terms. (Inductive loads can be "canceled" (countered) by capacitive loads.)

You're on your own, here, JeffersonAirplane. (Think of what the world would be like if Janice Joplin had not died.... )

 

Not only she, Jim Morrison, Jimi Hendrix and all the other of that kind

 

I don't know why I didn't think to recommend this before:

Power factor - Wikipedia

LOTS of really good information there. Sorry about the previous link; what a disaster.

[Just don't go to Wikipedia looking for good info about Droop Speed Control.... 'Cause there ain't any there.]