THE PHYSICS OF... POWER

[dionysius]

VArs give you a measure for the reactive component hence the "r". VA gives you current rating so you can size current carrying capacity of components. Neither is a measure of power. I'm sorry if you find that scary.

No energy is dissipated in the 100% reactive components. Thus the only power dissipated is in the resistive part of the load. A resonant tank circuit (i.e. a pure capacitor and inductor in parallel) simply bounces back and forth the same energy packet stored as an electrical field in the capacitor with the inductive energy stored magnetically in the inductor. At resonance since Xc = Xl this energy packet has a periodic time of 1/2*Pi*sqrt(LC).

I could give you a fluid analogy but I do not want to be beaten up and demonized once again as I was a couple of months ago when I did so. I upset those who do not need to really understand the physics and have resorted to not going further that simply learning the math model by heart. Nikola Tesla truly despised those types of 'con by rote' characters.

 

[Ingenieur]

No energy is dissipated in the 100% reactive components. Thus the only power dissipated is in the resistive part of the load. A resonant tank circuit (i.e. a pure capacitor and inductor in parallel) simply bounces back and forth the same energy packet stored as an electrical field in the capacitor with the inductive energy stored magnetically in the inductor. At resonance since Xc = Xl this energy packet has a periodic time of 1/2*Pi*sqrt(LC).

I could give you a fluid analogy but I do not want to be beaten up and demonized once again as I was a couple of months ago when I did so. I upset those who do not need to really understand the physics and have resorted to not going further that simply learning the math model by heart. Nikola Tesla truly despised those types of 'con by rote' characters.

no one (except you) is 'upset'
no need for insults or backbiting just because your feelings were (apparently still are) hurt
we understand the physics, you appear not to, hopefully you learned a little
the hydraulic analogy for an AC ckt is not useful, hence not done, it makes it more complex and difficult to understand

Tesla developed some of the math models, as you call them, most would call them the math representation of the physical system


reactive power IS dissipated AND absorbed by reactive loads
it performs no net work though

 

[Carultch]

reactive power IS dissipated AND absorbed by reactive loads
it performs no net work though

As I understand it, reactive power is the time average rate at which energy is stored in reactive components such as capacitors and inductors. And real power is the time average rate at which energy is delivered from the source to the load.

Apparent power is simply what you get, when you do a raw multiplication of the voltage and amperes, neglecting the fact that they may be out of synchronization. And primarily has the application of transmission component sizing, because it helps you keep track of the volts you have to insulate and the current you have to account for to prevent overheating.

 

[Ingenieur]

As I understand it, reactive power is the time average rate at which energy is stored in reactive components such as capacitors and inductors. And real power is the time average rate at which energy is delivered from the source to the load.

Apparent power is simply what you get, when you do a raw multiplication of the voltage and amperes, neglecting the fact that they may be out of synchronization. And primarily has the application of transmission component sizing, because it helps you keep track of the volts you have to insulate and the current you have to account for to prevent overheating.

the way I visualize it
active AC power: the electrons (or holes) oscillate at 60 Hz and migrate so they have a net displacement, hence work is performed
reactive power: the electrons (or holes) oscillate at 60 Hz but do not migrate so they have no net displacement, hence no work is performed

this is a pretty good description

 

[GoldDigger]

the way I visualize it
active AC power: the electrons (or holes) oscillate at 60 Hz and migrate so they have a net displacement, hence work is performed
reactive power: the electrons (or holes) oscillate at 60 Hz but do not migrate so they have no net displacement, hence no work is performed

this is a pretty good description

Quite to the contrary, if they migrate to have a net displacement you have a DC component to the current. Nothing at all to do with work related versus reactive current.
I also have a problem with the statement in the PDF that reactive power is the maximum value of the rate of energy transfer into/out of a reactive component. It is actually a measure of the rate at which energy is moved whose value is the time average of the absolute value of the amount of energy stored. (Multiply the 1/4 cycle integral of current x voltage by four and divide by the period of the AC).

 

[Besoeker]

reactive power IS dissipated AND absorbed by reactive loads

It is not dissipated.

 

[Besoeker]

Quite to the contrary, if they migrate to have a net displacement you have a DC component to the current.

Quite right. With AC they oscillate back and forth - a very tiny distance.

 

[jtinge]

VArs give you a measure for the reactive component hence the "r". VA gives you current rating so you can size current carrying capacity of components. Neither is a measure of power. I'm sorry if you find that scary.

When I try to explain how low pf makes equipment sizes bigger with no increase in ability to do work I show them the beer mug analogy. pf is the ratio of foam to beer. Mug sized to handle both but a pf closer to unity maximizes your drinkable beer for the same mug size.

 

[GoldDigger]

When I try to explain how low pf makes equipment sizes bigger with no increase in ability to do work I show them the beer mug analogy. pf is the ratio of foam to beer. Mug sized to handle both but a pf closer to unity maximizes your drinkable beer for the same mug size.

A delicious analogy!

 

[Ingenieur]

Quite to the contrary, if they migrate to have a net displacement you have a DC component to the current. Nothing at all to do with work related versus reactive current.

I also have a problem with the statement in the PDF that reactive power is the maximum value of the rate of energy transfer into/out of a reactive component. It is actually a measure of the rate at which energy is moved whose value is the time average of the absolute value of the amount of energy stored. (Multiply the 1/4 cycle integral of current x voltage by four and divide by the period of the AC).

wrong
the migration can be oscillatory and out of phase with the reactive component, with a displacement greater in the direction of power/current flow


wrong, their definition is correct, yours' is wrong
take it up with the authors, lol, I'm sure they care


http://www.failureelectrical.com/resume.html

	Ph.D., Electrical Engineering, Massachusetts Institute of Technology, 1971 M.S., Electrical Engineering, Massachusetts Institute of Technology, 1968 B.S., Electrical Engineering, University of Massachusetts, 1966 lol post yours​

 

[GoldDigger]

wrong
the migration can be oscillatory and out of phase with the reactive component, with a displacement greater in the direction of power/current flow


wrong, their definition is correct, yours' is wrong
take it up with the authors, lol, I'm sure they care

1. You are sooo wrong on that. I find it hard to believe that you have thought seriously about what you are saying. Real versus reactive power is related to the phase of alternating current relative to load voltage.
Net movement of electrons over time past a plane defines whether or not there is a DC component to the current, totally independent of the phase of the applied voltage.

2. I will give you a conditional pass on that one, since for the specific case of purely reactive "power" the maximum product of instantaneous voltage and instantaneous power is in fact 1/sqrt(2) times the product of maximum voltage and maximum current. But we normally define the value of sinusoidal alternating voltage and current by the RMS and not the peak value.

 

[Besoeker]

wrong
the migration can be oscillatory and out of phase with the reactive component, with a displacement greater in the direction of power/current flow

Not so.
That would infer a DC component.

 

[Ingenieur]

1. You are sooo wrong on that. I find it hard to believe that you have thought seriously about what you are saying. Real versus reactive power is related to the phase of alternating current relative to load voltage.
Net movement of electrons over time past a plane defines whether or not there is a DC component to the current, totally independent of the phase of the applied voltage.

2. I will give you a conditional pass on that one, since for the specific case of purely reactive "power" the maximum product of instantaneous voltage and instantaneous power is in fact 1/sqrt(2) times the product of maximum voltage and maximum current. But we normally define the value of sinusoidal alternating voltage and current by the RMS and not the peak value.

1 you can't even begin to see the err of your ways, your lack of understanding confounds me, have you had any training in this material?

2 you give me nothing, the text definition is correct, you are wrong, no ifs, ands or buts...pure squirming 'unconditionally' lol

 

[Ingenieur]

Not so.
That would infer a DC component.

only if non-oscillatory

 

[Ingenieur]

.....

 

[wwhitney]

I'm with Golddigger, it's 3 to 1 against you.

Let me ask you this: in a pure AC waveform, what is the value of the integral of the current over any whole number of cycles?

The integral of current over time is the net total electron flow past the point at which current is measured.

Cheers, Wayne

 

[GoldDigger]

only if non-oscillatory

By most definitions an oscillatory motion cannot have a net component. So if there is a net movement, the electron movement is non-oscillatory. There would then be a DC component to the current. I get the feeling that somehow you are using different definitions of the words than Besoeker and I [are using].

1 you can't even begin to see the err of your ways, your lack of understanding confounds me, have you had any training in this material?

Other than a BA in math (Summa Cum Laude), an MS in physics, and eight years of pursuit of a PhD (that can happen in high energy physics :happyyes no I have no training.

 

[Ingenieur]

I'm with Golddigger, it's 3 to 1 against you.

Let me ask you this: in a pure AC waveform, what is the value of the integral of the current over any whole number of cycles?

The integral of current over time is the net total electron flow past the point at which current is measured.

Cheers, Wayne

unfortunately physics is not by vote, not a popularity contest
it is by fact

you tell me, I'm sure you have an answer contrived lol

 

[Ingenieur]

By most definitions an oscillatory motion cannot have a net component. So if there is a net movement, the electron movement is non-oscillatory. There would then be a DC component to the current. I get the feeling that somehow you are using different definitions of the words than Besoeker and I [are using}

Other than a BA in math (Summa Cum Laude), an MS in physics, and eight years of pursuit of a PhD (that can happen in high energy physics :happyyes no I have no training.

then no current flows
it's counted once for each pass thru the plane regardless of direction
the net is not 0, it is 2 times the 1/2 cycle

get your $$$ back lol
you should know the basics

 

[wwhitney]

it's counted once for each pass thru the plane regardless of direction

If you want to talk about net electron migration you can best count your current with sign. It's the integral of I, not |I|.

Cheers, Wayne