mivey
Senior Member
Maybe they do things differently across the big pond.I think you have encapsulated the basic misconception at a stroke.
Maybe they do things differently across the big pond.I think you have encapsulated the basic misconception at a stroke.
They...we...whatever.:wink:Maybe they do things differently across the big pond.
No, this statement is wrong. Yes, I do understand what you are trying to say, but nevertheless, it is wrong.Repeat after me:
Watts + Vars = Complex power.
No. VA is a unit of measure. Apparent Power has the units of VA, but it is incorrect to say that VA is Apparent Power. In a sense, you are putting the cart before the horse.VA is apparent power.
Indeed they do:Maybe they do things differently across the big pond.
Is that another way of you trying to say that no energy is flowing to the capacitor or inductor? I think you will find that is does flow. Internationally.But fundamental electrical units are fundamental units.
Internationally.
By the way, how about explaining your reasoning why vars are a special case and watts are not.---You think vars are a special case because they are reactive. Well, watts are a special case because they are real. VA is pointless (that would be a pun)---
You are taking a logical discussion of a topic pretty personally. No one has chastised you, but you have chosen to take it that way. I wasn't correcting your statements simply to be mean, but because it went to the core of the discussion we are engaged in.- after chastising me twice.
I already did explain this, but actually, Larry's suggested analogy does a better job.By the way, how about explaining your reasoning why vars are a special case and watts are not.
Mikey also explained it quite well too. The differences are merely convention, but you are treating them as absolute. The convention is that the units on the right side of the equation are dictated by the function on the left side of the equation. You have reversed this and are stating that the function on the left side of the equation is dictated by the units on the right side of the equation. That might sound trivial at first glance, but it is very significant.What if you used feet up for real power, and feet left and right for reactive power? Would that make for a better analogy?
And is also the units for complex powerVA is the units for apparent power.
You will find some reference texts that do exactly that, even if it does not strictly adhere to what I would call standard conventions (and is the convention used in most of the texts I have).I promise to not use the term "Apparent Power" when describing a complex quanity.
Yes. In and out. Mean value is zero. Mean work is zero. Mean power is zero.Is that another way of you trying to say that no energy is flowing to the capacitor or inductor? I think you will find that is does flow. Internationally.
I agree the real power (or mean power) is zero at steady-state as shown in your graphic. I also agree that using the VA term will help show the energy flowing in & out of the load in equal quantity, creating a net zero flow of energy over the interval.Yes. In and out. Mean value is zero. Mean work is zero. Mean power is zero.
That's why you need the term VA to describe it.
ammended from Cold Fusion;1068330
Note: Definition of the idomatic phrase, "have/has a direction": The function/unit shown has vector properties, It can be described in a variety of ways (A +jB), (i,j), magnitude/phase angle.
Watts have a direction
Vars have a direction
Real power + reactive power = Complex power (not apparent power)
Complex power has a direction
VA is the units for apparent power.
Apparent power = magnitude [complex power]
Apparent power does not have direction
Repeat after me:
P = EI* = Complex power. Complex power is a vector. Unless we are sizing wire, (which includes generators, transformers, switchgear) apparent power is pointless (not a vector) I promise to not use the term "Apparent Power" when describing a complex quanity.
cf
If it works for voltage, current, & impedances, why not for complex power as well since it is the product of two phasors?Impedances and sinusoidal voltages and currents are properly described with phasors, the angles denote time, not direction--not so with complex power.
If it works for voltage, current, & impedances, why not for complex power as well since it is the product of two phasors?
The voltage phasor:
|E|e^jα
The current phasor:
|I|e^jβ
The conjugate of the current phasor:
|I|e^-jβ
Complex power is also called phasor power and is given by:
EI* = |E||I|e^j(α-β) = |E||I|e^j(Θ) = |E||I|(CosΘ+jSinΘ)
and the complex value is given by P+jQ
---So called "complex power" is nothing more than the power triangle expressed with complex numbers. We can do that to any right triangle. It is only a means of representation and does not make the scalar quantities into vectors--phasors either. The angle involved is the power factor angle. The so called "directions" are always zero, ninety degrees, and the PF angle.
Electromagnetic fields are properly described with vectors because the angles denote a direction in space--not so with complex power.
Impedances and sinusoidal voltages and currents are properly described with phasors, the angles denote time, not direction--not so with complex power.
Originally Posted by Cold Fusion http://forums.mikeholt.com/showthread.php?p=1068391#post1068391
By the way, how about explaining your reasoning why vars are a special case and watts are not.
I already did explain this, but actually, Larry's suggested analogy does a better job.
Lets see - Watts are left to right; VARS are up and down, complex power goes tail of watts to head of vars.Mikey also explained it quite well too. The differences are merely convention, but you are treating them as absolute.
The convention is that the units on the right side of the equation are dictated by the function on the left side of the equation. You have reversed this and are stating that the function on the left side of the equation is dictated by the units on the right side of the equation. That might sound trivial at first glance, but it is very significant.
You are taking a logical discussion of a topic pretty personally. No one has chastised you, but you have chosen to take it that way. I wasn't correcting your statements simply to be mean, but because it went to the core of the discussion we are engaged in.