VA vs. Watts

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Besoeker

Senior Member
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UK
That is not the definition of either item.


Definitions of watt on the Web:

a unit of power equal to 1 joule per second;
The watt (symbol: W) is the SI derived unit of power, equal to one joule of energy per second. It measures a rate of energy conversion.
joule

Definition
Metric (SI) unit of work and energy. (1) As a unit or work, it is defined as the work done by a force of one newton acting on an object to move it through a distance of one meter in the direction the force is applied. One joule per second equals 1 watt

In passing, it is one of the merits of SI that conversion factors are not required for many basic units.
One Watt is one Volt times one Amp.
One Watt is one Newton though one metre in one second.
One Joule is one Watt for one second.
That covers some of the fundamental units of power and energy.

I'm old enough to be able to do calculations in both Imperial and SI.
And I'm pragmatic enough to embrace the merits of the latter.
 

drbond24

Senior Member
All you did was repeat what charlie b has already agreed with; a watt and a joule per second are equal. Nowhere in the quotes you posted does it say "A watt is defined as one joule per second." Or vice versa. It says a watt is equal to one joule per second. That is entirely different.

Even in your definition of the joule, it says a joule is defined using newtons and meters, but then it says that a joule per second is equal to a watt. It never associates a watt or a J/s as being the definition of the other. They are just equal.




I daresay this discussion isn't going any further without getting some new blood involved. We are just repeating ourselves and it obviously isn't changing anyone's mind. ;):grin:
 

Cold Fusion

Senior Member
Location
way north
rattus said:
---Energy is scalar; it may carry a sign, but you cannot describe energy with a complex number, therefore it cannot be quantified with a vector. ---

---Regarding item 4, if I were to choose to give the answer in that unit of measure, it would be incumbent upon me, for the sake of avoiding future confusion, to mention that this number of Joules per second is being exchanged at a phase angle of 90 degrees from the number Joules per second that is being supplied to resistive loads. It would certainly be simpler if I gave the answer in units of VAR. That way, I would have less explaining to do. --- emphasis is mine - cf
Are we in agreement that the watts and VARS are vectors? I hope so.

As for the energy, take a look at the attachment.

Integrate the power and one gets the energy. The power is a vector. The integral of the power is a vector.

If you don't want the Joules to be a vector - okay, but it certainly appears the integral of Joules/second is a vector. What am I missing?

cf
 
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charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Are we in agreement that the watts and VARS are vectors? I hope so.
I agree that real and reactive power can be modeled with vectors.

Integrate the power and one gets the energy. The power is a vector. The integral of the power is a vector.
I am not conceding that point. I know that integration distributes over addition. But I don?t think it works that way with vectors. That is, I do not know that the integral of the sum of two vectors is equal to the sum of the integrals of the two vectors. My college textbook from my complex calculus course is at home, so I can?t look it up just now. My belief, however, is that if you integrate ?apparent power, as a function of time,? you are going to get a scalar function.
 

ptrip

Senior Member
I can see your attachment CF ...

I'm not in a position to comment on it as it's this kind of stuff I'm shaky on ... but it looks familiar!
 
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Cold Fusion

Senior Member
Location
way north
I can see the attachment on the post. The pdf opens on my desk top, but when I try to open it from the post it says, 'File can not be found"

So I did a save from the post to desktop and it opens :-?:-?:-?

I guess it is okay and I have it redudently, redundently posted. aarrrgggggg

cf
 

Cold Fusion

Senior Member
Location
way north
--- My belief, however, is that if you integrate ?apparent power, as a function of time,? you are going to get a scalar function. (emphasis is mine - cf)

It may not matter at all, but it's 'complex power', not "apparent power" Yes, I knew you knew that. The only reason I pointed it out is to keep the discussion vector centered. Apparent power is directionless (pointless:roll:) Complex power has a dircetion.

cf
 

Cold Fusion

Senior Member
Location
way north
---That is, I do not know that the integral of the sum of two vectors is equal to the sum of the integrals of the two vectors. My college textbook from my complex calculus course is at home, so I can?t look it up just now. ---
I can't help with this - my references say it is. However, I agree you need to do this one yourself - I had to look it up after rattus mentioned it.

Or maybe this reference:
http://www.libraryofmath.com/vector-integration.html

(fourth one on google - "vector integration by parts")

cf
 

Cold Fusion

Senior Member
Location
way north
I can see your attachment CF ...

I'm not in a position to comment on it as it's this kind of stuff I'm shaky on ... but it looks familiar!

Thanks.

I would not discount your position. From the way the rest of us are dithering around in an area we don't normally work with, you opinion may well be just fine:)

My math skills and understanding are pretty good, but complex vector integration is really getting out there. I do feel a need to understand the concepts. However, other than understanding the concepts, can't say I ever have - or ever needed to - or ever will need to - and I'm okay with that.:cool:

cf
 

ptrip

Senior Member
Thanks.

I would not discount your position. From the way the rest of us are dithering around in an area we don't normally work with, you opinion may well be just fine:)

My math skills and understanding are pretty good, but complex vector integration is really getting out there. I do feel a need to understand the concepts. However, other than understanding the concepts, can't say I ever have - or ever needed to - or ever will need to - and I'm okay with that.:cool:

cf

Kind of similar to ... I don't need to know exactly how and why the engine in my car works ... I just need to know how to use it.

But then, it's always good to know some of the theory in case something goes wrong!

I appreciate this thread, I know more today than I did last Thursday about the subject!

Can we go back to beer foam now? :grin:
 

cadpoint

Senior Member
Location
Durham, NC
After what Charlie said, what was said, in #54 that really got me thinking.

Here's a nice web site for all of you reading along, enjoying the headaches and the watered eyes and deep thoughts of well what ever your reflecting on.

This web sight will handle in layman's terms most every high-end term used here in this thread...

http://www.absoluteastronomy.com

I was looking up foot-pound , and vectors, and a few of the other terms used in the thread... Again, what a Great Thread ...

Enjoy.
 

Cold Fusion

Senior Member
Location
way north
---Can we go back to beer foam now? :grin:
I hope not. It's cute, but ...:roll:

Real power turns the motor shaft with torque. Actual work goes out the end of the shaft.

Reactive power charges (delivers energy to) the motor magnetic field on part of the AC cycle. On another part of the AC cycle, the motor magnetic field collapses sending the energy all the way back to the generator.

The motor has to have reactive power (a magnetic field that charges and uncharges) or it won't work.

While the reactive power is shuttling back and forth from motor to generator, it is heating the utility company's distribution lines and transformers. That is power going away in waste heat that they don't get paid for - and they don't like not getting paid.

Capacitors located close to the motors can store the magnetic field energy when the motor is dumping it and then give it back when the motor is taking it. Saves a lot of money from not heating the wires and transformers for a 100 miles back to the generator.

Electricians/Engineers/Designers need a way to account for the reactive/real power. So they use power factor. That's the ratio of (real power)/(apparent power).

Once one gets past this, it's gets real math intensive. The voltages, currents, power flows, energy transfers, are all interrelated. And the math is the model that predicts how a system will behave.

We have a lot of members that like to say, "Well it's like that in theory, but in the real world ...." To which I would reply, "Within the limits of the math model, it accurately predicts the 'real world' - that's why the EEDs use the model."

None of this is new - I really want to acknowledge all this has been pretty well been said - a lot of times, and likely better.

cf
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Energy is scalar; it may carry a sign, but you cannot describe energy with a complex number, therefore it cannot be quantified with a vector. Energy cannot be quantified as a phasor either. Only RMS voltages, currents, and impedances can be described as phsors.

Here is my take on the scalar/phasor issue.

Power is also a scalar (that's from my enigneering handbook). It can only flow in two directions. For example, it can only flow to a load, or away from a load. Or it can flow to a source, or away from a source.

However, the power that flows can either be lost or stored. The stuff that gets stored winds up coming back on the next half cycle (for sinusoidal AC circuits.)

That's a total of 4 directions power can flow on. All the power that flows must stay exactly on one of these directions. There is no power that flows 18 degrees clockwise from the real axis. It cant happen. With a true vector, you can walk 18 degrees north of east.

So some mathmatical genuis decided to make life easy for all of us by plotting the real power on the real axis, and by plotting the stored energy on the imaginary (vertical) axis. Even though there isn't really any difference in direction between the two. (At least, there really isn't a direction between the two unless you want to talk about linear algebra, independent components, and orthagonal components -which I can't even remember how to spell. Anyhow, that really all the theory that says all the bookkeeping works by using phasors even though we really have scalars.)

All the math works so well that we tend to forget that power isn't really a vector or a phasor.

Personally, I'm also ready to get back to the beer foam:grin:

Steve
 
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rattus

Senior Member
Are we in agreement that the watts and VARS are vectors? I hope so.

As for the energy, take a look at the attachment.

Integrate the power and one gets the energy. The power is a vector. The integral of the power is a vector.

If you don't want the Joules to be a vector - okay, but it certainly appears the integral of Joules/second is a vector. What am I missing?

cf

You are missing the point that a true vector--not a phasor--is a complex number expressing magnitude and direction, e.g., an electric field or magnetic field. Power has no directional angle, therefore it cannot be a vector.

A phasor is a complex number expressing the magnitude and phase angle of a sinusoidal voltage or current, or the magnitude and phase angle of an impedance. Power is not sinusoidal and does not carry a phase angle, therefore it cannot be a phasor either.

As Charlie has implied already, you can treat real and reactive power as pseudovectors, the sum of which is apparent power, but power is still scalar.
 

markstg

Senior Member
Location
Big Easy
You are missing the point that a true vector--not a phasor--is a complex number expressing magnitude and direction, e.g., an electric field or magnetic field. Power has no directional angle, therefore it cannot be a vector..

A true vector is not a complex number....take velocity, a true vector, 25 mph north and 25 mph east vectorially adds up to 35.36 mph NorthEast, no j operator for complex arithmetic there.

A phasor is a complex number expressing the magnitude and phase angle of a sinusoidal voltage or current, or the magnitude and phase angle of an impedance. Power is not sinusoidal and does not carry a phase angle, therefore it cannot be a phasor either..

Power is indeed Sinusoidal as it is the product of 2 Sinusoids. The phase angle it carries is the phase difference between the Voltage and Current.

As Charlie has implied already, you can treat real and reactive power as pseudovectors, the sum of which is apparent power, but power is still scalar.

The sum you refer to is not the arithmetic sum, but the Magnitude of the complex power components, Real and Reactive.

But none of this changes your point. A phasor is technically not a vector.
 

Cold Fusion

Senior Member
Location
way north
--- Power is not sinusoidal and does not carry a phase angle, therefore it cannot be a phasor either. ---
rattus -
Your math skills are pretty good. But as mark says, you may want to try this one again.

--- As Charlie has implied already, you can treat real and reactive power as pseudovectors, the sum of which is apparent power, but power is still scalar.
Again, crediting mark: Hummm, ... the sum of which is complex power, not apparent power. Better try this one again as well.

If you like the term phasor instead of vector, I'm fine with that - the math is the same.

And you are correct, pseudovector is a better term. There is no physical direction one can point for the power, real or unreal. Math still works the same.

cf
 

rattus

Senior Member
A true vector is not a complex number....take velocity, a true vector, 25 mph north and 25 mph east vectorially adds up to 35.36 mph NorthEast, no j operator for complex arithmetic there.

Power is indeed Sinusoidal as it is the product of 2 Sinusoids. The phase angle it carries is the phase difference between the Voltage and Current.

The sum you refer to is not the arithmetic sum, but the Magnitude of the complex power components, Real and Reactive.

But none of this changes your point. A phasor is technically not a vector.

Velocity is often represented in polar form which has its rectangular coordinate equivalent. Whether you use the "i" operator in this case or not is merely your personal choice. Suffice it to say that any vector may be quantified with a complex number in two or three dimensions.

The sum of two sinusoids is another sinusoid; the product of two sinusoids is a sine squared function comprising a number of harmonics, the lowest of which is 2f plus a DC component. Since it is not a pure sinusoid, it cannot be a phasor and cannot carry a phase angle.

The sum of the pseudovectors is of course the vectorial sum which is equal to the apparent power, but these are neither vectors nor phasors.
 

markstg

Senior Member
Location
Big Easy
Velocity is often represented in polar form which has its rectangular coordinate equivalent. Whether you use the "i" operator in this case or not is merely your personal choice. Suffice it to say that any vector may be quantified with a complex number in two or three dimensions.

The sum of two sinusoids is another sinusoid; the product of two sinusoids is a sine squared function comprising a number of harmonics, the lowest of which is 2f plus a DC component. Since it is not a pure sinusoid, it cannot be a phasor and cannot carry a phase angle.

The sum of the pseudovectors is of course the vectorial sum which is equal to the apparent power, but these are neither vectors nor phasors.

Please give an example of a Complex number in 3 dimensions.

The product of 2 sinusoids with the same frequency is a pure sinusoid of frequency 2f with a bias. It as you say is not a phaser, but in power ElectricLand the angle resulting is the phase difference between the Voltage and Current.
 
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