Generator KVAR?
- Thread starter tepres
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fc
Senior Member
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- New Jersey
Re: Generator KVAR?
Term kilo Volts Amps Reactive--Definition : Unit of Reactive Power
Term kilo Volts Amps Reactive--Definition : Unit of Reactive Power
fc
Senior Member
- Location
- New Jersey
Re: Generator KVAR?
Here is a good web site that also may help.
http://www.powerstudies.com/content/resources/Diane%20Power%20Factor.pdf
Here is a good web site that also may help.
http://www.powerstudies.com/content/resources/Diane%20Power%20Factor.pdf
Re: Generator KVAR?
You are basically correct. The power triangle has real power (Watts) at a right angle to reactive power (Volt-Amps-Reactive), and their vector sum is the the apparent power (volt-amps).
Real power is usually drawn on the real horizontal axis, and the VAR's are usually drawn on the imaginary vertical axis. So yes, VAR's are the vertical component. And multiplying the KVA by the sine of the angle between the real power and the VA gives the VAR's.
You are basically correct. The power triangle has real power (Watts) at a right angle to reactive power (Volt-Amps-Reactive), and their vector sum is the the apparent power (volt-amps).
Real power is usually drawn on the real horizontal axis, and the VAR's are usually drawn on the imaginary vertical axis. So yes, VAR's are the vertical component. And multiplying the KVA by the sine of the angle between the real power and the VA gives the VAR's.
Ed MacLaren
Senior Member
Re: Generator KVAR?
I got a kick out of the beer-foam analogy they used at that site.
Here is another analogy that I have used to explain power factor with my apprentice students.
It can be described in terms of the old method of door-to-door milk delivery in the days when they used reusable glass milk bottles.
The delivery function required the delivery person to transport, from the dairy to the consumer?s house, a total load consisting of milk and glass.
Of this total, only the milk component was paid for and consumed by the customer. The glass, although essential to the operation, was stored at the customer?s home, washed and returned to the dairy on the next delivery day.
The function of an AC electrical circuit is to deliver energy from a source, through the circuit conductors to a load, in this example, a motor.
The energy consumed (actually converted by the motor into output horsepower and heat losses) is called true power. It is the product of the "in-phase" current times the voltage, and is measured in watts. This is paid for by the consumer, and is analogous to the milk in the comparison.
The energy required to create the motor?s magnetic flux is not converted (consumed), it is stored in the magnetic field and returned to the source during the next cycle. It is called reactive power, it is the product of the "out-of-phase" current times the voltage, and measured in vars. (volt-amps reactive) It would be analogous to the glass in the comparison.
The total energy input to the motor, the product of the total current times the voltage is called the apparent power. It is measured in va (volt-amps), and would be analogous to the total load carried into the home by the delivery person, milk and glass, in the comparison.
Ed
I got a kick out of the beer-foam analogy they used at that site.
Here is another analogy that I have used to explain power factor with my apprentice students.
It can be described in terms of the old method of door-to-door milk delivery in the days when they used reusable glass milk bottles.
The delivery function required the delivery person to transport, from the dairy to the consumer?s house, a total load consisting of milk and glass.
Of this total, only the milk component was paid for and consumed by the customer. The glass, although essential to the operation, was stored at the customer?s home, washed and returned to the dairy on the next delivery day.
The function of an AC electrical circuit is to deliver energy from a source, through the circuit conductors to a load, in this example, a motor.
The energy consumed (actually converted by the motor into output horsepower and heat losses) is called true power. It is the product of the "in-phase" current times the voltage, and is measured in watts. This is paid for by the consumer, and is analogous to the milk in the comparison.
The energy required to create the motor?s magnetic flux is not converted (consumed), it is stored in the magnetic field and returned to the source during the next cycle. It is called reactive power, it is the product of the "out-of-phase" current times the voltage, and measured in vars. (volt-amps reactive) It would be analogous to the glass in the comparison.
The total energy input to the motor, the product of the total current times the voltage is called the apparent power. It is measured in va (volt-amps), and would be analogous to the total load carried into the home by the delivery person, milk and glass, in the comparison.
Ed
- Location
- Lockport, IL
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- Retired Electrical Engineer
Re: Generator KVAR?
Not a bad analogy, Ed. One difference is worth noting: The customer pays for the KVA (ie., including the KVAR), not just for the KW. It's kind of like paying for the milk bottle at every delivery cycle, and not getting a refund when you give the empty bottle back. Sort of a bad deal, huh?
Not a bad analogy, Ed. One difference is worth noting: The customer pays for the KVA (ie., including the KVAR), not just for the KW. It's kind of like paying for the milk bottle at every delivery cycle, and not getting a refund when you give the empty bottle back. Sort of a bad deal, huh?
peter d
Senior Member
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- New England
Re: Generator KVAR?
Here is an example. Let's say I buy one of those cheap "barn lights" with a 175 watt mercury vapor lamp. Due to poor power factor, this thing has a current rating of 4.0 amps at 120 volts. So true power, factoring ballast losses, is about 200 watts, give or take 10 watts.
Apparent power is 4.0 amps X 120 volts = 480 watts.
So I am paying for 480 watts of apparent power but only using 200 watts of true power? Now I'm really
If I attach my home's electric meter to this fixture only, won't it only measure the 200 watts it is consuming to produce light?
I thought that we only paid for true power?
Here is an example. Let's say I buy one of those cheap "barn lights" with a 175 watt mercury vapor lamp. Due to poor power factor, this thing has a current rating of 4.0 amps at 120 volts. So true power, factoring ballast losses, is about 200 watts, give or take 10 watts.
Apparent power is 4.0 amps X 120 volts = 480 watts.
So I am paying for 480 watts of apparent power but only using 200 watts of true power? Now I'm really
If I attach my home's electric meter to this fixture only, won't it only measure the 200 watts it is consuming to produce light?
Ed MacLaren
Senior Member
Re: Generator KVAR?
Ed
We don't here. Our POCO uses kilowatt-hour meters. They have a surcharge for industrial users that have low power factors.
Ed
Re: Generator KVAR?
tepres, let me point out that apparent power can be represented as a complex number, but it is not a vector as are voltage and current. The waveform is not sinusoidal, and the period is half that of the voltage and current waves.
[ March 29, 2005, 12:21 PM: Message edited by: rattus ]
Charlie B., you know better than that. The customer pays for real power and may pay a power factor penalty, but watt-hour meters do just that; they meter watt-hours, not volt-ampere hours.Originally posted by charlie b:
Not a bad analogy, Ed. One difference is worth noting: The customer pays for the KVA (ie., including the KVAR), not just for the KW. It's kind of like paying for the milk bottle at every delivery cycle, and not getting a refund when you give the empty bottle back. Sort of a bad deal, huh?
tepres, let me point out that apparent power can be represented as a complex number, but it is not a vector as are voltage and current. The waveform is not sinusoidal, and the period is half that of the voltage and current waves.
[ March 29, 2005, 12:21 PM: Message edited by: rattus ]
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Generator KVAR?
The power factor penalty was what I was talking about. I should have restricted my comment to the larger industrial facilities that I usually deal with. Mea culpa.
The power factor penalty was what I was talking about. I should have restricted my comment to the larger industrial facilities that I usually deal with. Mea culpa.
Re: Generator KVAR?
Power waveforms are not sinusoidal. This is a requirement for phasors.
The frequency of the power waveform is twice that of the AC voltage and current. Phase has no meaning for signals of different frequencies.
Power has no phase angle which is a requirement for a phasor.
Power is added algebraically, never vectorially.
Power is the product of scalar quantities, therefore it cannot be a phasor.
I posted a reference about this subject a few weeks back, but now I cannot find it. If you have a reference which indicates otherwise, I would like to see it.
Steve, you have it backwards. Vectors can be represented as complex numbers, but a complex number is not necessarily a vector (phasor). Your statement is obviously a response to my claim that power is not a vector. I make this claim for several reasons:Originally posted by steve66:
Any complex number can be represented by a vector.
Power waveforms are not sinusoidal. This is a requirement for phasors.
The frequency of the power waveform is twice that of the AC voltage and current. Phase has no meaning for signals of different frequencies.
Power has no phase angle which is a requirement for a phasor.
Power is added algebraically, never vectorially.
Power is the product of scalar quantities, therefore it cannot be a phasor.
I posted a reference about this subject a few weeks back, but now I cannot find it. If you have a reference which indicates otherwise, I would like to see it.
Re: Generator KVAR?
Rattus, you said:
[ April 04, 2005, 09:36 AM: Message edited by: steve66 ]
Rattus, you said:
We were talking about "vectors", not phasors. No sine waves are required for vectors.
Once again, that has nothing to do with vectors.
Again, vectors, not phasors. But vectors do also require a phase angle. The phase angles that we have are the angles between "VA", "VAR", and "Watts". It's called the "power triangle".
Wrong. See the item above. "VA", "VAR", and "Watts" are added vectorially.
I don't know why you would refer to two sine waves (and all the information we can deduce from them - like their relative phases) as "scalars". That's just ignoring half the information you are given. Would you also say that "20 feet Northwest" is just "20"? And again, vecotrs, not phasors.
[ April 04, 2005, 09:36 AM: Message edited by: steve66 ]
Re: Generator KVAR?
Quote from Steve66:
?We were talking about "vectors", not phasors. No sine waves are required for vectors.?
Reply: Steve, vectors must have a direction; power has no direction. The phase angles of AC voltages, currents, and impedances indicate phase, not direction; therefore the term phasor.
Apparent power is simply VxI?the product of RMS magnitudes which are scalars.
Real power is simply VxIxPF?still another scalar.
AC voltages and currents are called phasors because they are not true vectors. The phase angle denotes a time delay. Power is not even a phasor.
An electric field has direction; electric current in bulk material has direction; velocity has direction, acceleration has direction, power can be only positive or negative.
Yes, you can treat apparent power as a complex number, but that does not make it a vector for the reasons stated above. The power triangle is just that, a triangle. Using vector algebra on apparent power does not make it a vector.
There are no vectors in AC analysis, only phasors, and they must be sinusoidal, or fixed as an impedance.
Unless you can provide a solid reference which defines power to be a vector, you have not proved your point. My statement was that power is not a vector.
Quote from Steve66:
?We were talking about "vectors", not phasors. No sine waves are required for vectors.?
Reply: Steve, vectors must have a direction; power has no direction. The phase angles of AC voltages, currents, and impedances indicate phase, not direction; therefore the term phasor.
Apparent power is simply VxI?the product of RMS magnitudes which are scalars.
Real power is simply VxIxPF?still another scalar.
AC voltages and currents are called phasors because they are not true vectors. The phase angle denotes a time delay. Power is not even a phasor.
An electric field has direction; electric current in bulk material has direction; velocity has direction, acceleration has direction, power can be only positive or negative.
Yes, you can treat apparent power as a complex number, but that does not make it a vector for the reasons stated above. The power triangle is just that, a triangle. Using vector algebra on apparent power does not make it a vector.
There are no vectors in AC analysis, only phasors, and they must be sinusoidal, or fixed as an impedance.
Unless you can provide a solid reference which defines power to be a vector, you have not proved your point. My statement was that power is not a vector.
Re: Generator KVAR?
Rattus, Steve is right. Any complex number can be represented by a (2-dimensional) vector. Real and imaginary parts are rectangular form, and can be converted to polar form (magnitude and angle/direction). When you treat phasors this way, complex power is voltage time the complex conjugate of the current. So power can be a complex number. In rectangular form, the real part is real power and the imaginary part is reactive power. In polar form the magnitude is apparent power and the cosine of the angle is the power factor. And like someone pointed out in another thread, you cannot add apparent power number like scalars, just like it is meaningless to add complex numbers by adding their magnitudes.
Rattus, Steve is right. Any complex number can be represented by a (2-dimensional) vector. Real and imaginary parts are rectangular form, and can be converted to polar form (magnitude and angle/direction). When you treat phasors this way, complex power is voltage time the complex conjugate of the current. So power can be a complex number. In rectangular form, the real part is real power and the imaginary part is reactive power. In polar form the magnitude is apparent power and the cosine of the angle is the power factor. And like someone pointed out in another thread, you cannot add apparent power number like scalars, just like it is meaningless to add complex numbers by adding their magnitudes.
Re: Generator KVAR?
Paul and Steve too,
No one is arguing about real and reactive power--only that power is not a vector. To call power a vector on the basis of the power triangle is a misapplication of the word "vector".
Go back and read my previous post, then come back and rebut each of the points I have made, and to ice the cake, you can provide the solid reference that defines power to be a vector.
Until you do that, you are simply confusing vectors with hypotenuses and making unsupported claims.
Rattus
Paul and Steve too,
No one is arguing about real and reactive power--only that power is not a vector. To call power a vector on the basis of the power triangle is a misapplication of the word "vector".
Go back and read my previous post, then come back and rebut each of the points I have made, and to ice the cake, you can provide the solid reference that defines power to be a vector.
Until you do that, you are simply confusing vectors with hypotenuses and making unsupported claims.
Rattus
Re: Generator KVAR?
Rattus -
Power transmission calculations are done with Complex Power, usually denoted as S = P + jQ
This is a bit out of my area, since the only places I have seen it is in power transmission classes. I deal a lot with generation, but it doesn't come up a lot - well, never has yet.
Complex power looks like a vector to me.
My inclination is that if one multiplies two vectors together, the result is a vector. One can really get messy and multiply two complex numbers together, or one can change to polar coordinates and multiply the magnatudes, and the phase angle is the sum of the original vector phase angles. Voltage is a vector, current is a vector. Their product is a vector.
carl
Rattus -
Power transmission calculations are done with Complex Power, usually denoted as S = P + jQ
This is a bit out of my area, since the only places I have seen it is in power transmission classes. I deal a lot with generation, but it doesn't come up a lot - well, never has yet.
Complex power looks like a vector to me.
Sure they are. Multiply two sine functions together, and you get (drum roll) a sine function - Frequency is twice and the phase angle is changed, but it is a sine.
My inclination is that if one multiplies two vectors together, the result is a vector. One can really get messy and multiply two complex numbers together, or one can change to polar coordinates and multiply the magnatudes, and the phase angle is the sum of the original vector phase angles. Voltage is a vector, current is a vector. Their product is a vector.
That's true, but why sould one want to compare the voltage phase angle with the power angle. One application I've seen for power angle is comparing two generating sources that one is planning on connecting. I can't say it has come up very often in my business - okay maybe never.
carl
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Re: Generator KVAR?
Again, I will come out of hiding and support rattus on this one - power is not a vector
From IEEE Std 100-1996, The IEEE Standard Dictionary of Electrical and Electronics Terms:
The problem is, for practical purposes, the "math" appears to be the same, so we attribute "vectorness" to power. But in "real life" there is no "relative change in position" for power as there is with current and voltage. (And don't try to make the argument of generation / consumption - it won't fly - you know the "vector" diagram isn't showing that)
"Real Power" is the scalar product of the instantaneous current and voltage vectors. Apparent Power" and "Reactive Power" are pseudo-vectors created to make the math work.
That is indeed the problem - it looks like one.
Again, I will come out of hiding and support rattus on this one - power is not a vector
From IEEE Std 100-1996, The IEEE Standard Dictionary of Electrical and Electronics Terms:
I chose this site to explain the parallelogram law of addition because it emphasises the concept that "A vector can be seen as relative changes in position."
The problem is, for practical purposes, the "math" appears to be the same, so we attribute "vectorness" to power. But in "real life" there is no "relative change in position" for power as there is with current and voltage. (And don't try to make the argument of generation / consumption - it won't fly - you know the "vector" diagram isn't showing that)
"Real Power" is the scalar product of the instantaneous current and voltage vectors. Apparent Power" and "Reactive Power" are pseudo-vectors created to make the math work.
Re: Generator KVAR?
One more time:
You do not multiply vectors to obtain power. You drop the phase angle from the voltage and current phasors and you are left with the RMS magnitudes. Multiply these scalars together for apparent power. Throw in PF, another scalar, for real power.. I have never seen power expressed with an angle.
The product of two sinusoids is not another sinusoid. The power wave for a resistive load is sin squared and looks something like full wave rectified DC. It is all positive and is certainly not sinusoidal.
You can add real and reactive power as you would add two vectors, but that does not make the sum a vector. The angle of the power triangle is arccos(PF); it is not the sum of the voltage and current angles.
The power triangle is just that, a triangle. There are an infinite number of triangles in the universe; not all describe vectors. The power triangle is one of them.
Thank you, rbalex, for your solid reference which proves my point beyond a doubt.
One more time:
You do not multiply vectors to obtain power. You drop the phase angle from the voltage and current phasors and you are left with the RMS magnitudes. Multiply these scalars together for apparent power. Throw in PF, another scalar, for real power.. I have never seen power expressed with an angle.
The product of two sinusoids is not another sinusoid. The power wave for a resistive load is sin squared and looks something like full wave rectified DC. It is all positive and is certainly not sinusoidal.
You can add real and reactive power as you would add two vectors, but that does not make the sum a vector. The angle of the power triangle is arccos(PF); it is not the sum of the voltage and current angles.
The power triangle is just that, a triangle. There are an infinite number of triangles in the universe; not all describe vectors. The power triangle is one of them.
Thank you, rbalex, for your solid reference which proves my point beyond a doubt.
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