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Interesting! Thanks, John. Sorry that was so basic. FWIW, I defer to people who really know when power distro comes up - it's not my field at all. I keep thinking it's mainly impedance mismatch, when it's not really...

No, no, no! Think back about the definition of Power (which is the the integral of V(t)*I(t) averaged over the period of interest. Then think of apparent power as Irms*Vres (taken over the same period of interest). Power factor is Power/(Irms*Vrms). These definitions can be used anywhere at any time under any circumstances and are always correct. Knowing phase is a special case of using the above on sine waves to make it easier to calculate under those circumstances.

PF is signed. Power/(Irms*Vrms) isn't.

Why isn't Power/(Irms*Vrms) signed? What happens if the current is flowing in the opposite direction to the voltage? The RMS value will be negative and the above equation will be negative. That is the meaning of a negative power factor, no?

Rick

No. Wikipedia defines PF as a dimensionless value from 0 to 1, but hangs "leading" and "lagging" off to the side.

If voltage and current are in phase, PF is 1 and the sign is indeterminate. If current phase leads voltage (capacitive load), by even one degree, PF is called "leading" and if current waveform peaks later, it's called "lagging." Capacitive (leading) loads are usually assigned a negative PF if the word "leading" isn't used instead. Whichever terminology is used, something often needs to be said about whether the current leads or lags the voltage, and the simple Power/(Irms*Vrms) equation loses that.

For nonlinear and time-variant loads (like burst-mode temperature controllers) the exact meaning of PF is debatable.

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Just think of it as PF=W/VA It doesn't matter whether the reason is phase offset of two sine waves or harmonic distortion.

Wikipedia seems to think PF is only 0 to 1...

This is getting into the twilight zone territory. Near the top of this post you are quoted saying, "PF is signed". Now you are saying it is NOT signed, no?

The point is that power factor is a result of reactance in the load, or non-linearities. When reactive, the current will be out of phase with the voltage. Blah, blah... The power factor with a reactive load tells you how much of the current is reactive and how much is dissipative. But what if the load is actually shoving power back into the line?

BTW, Wikipedia is not a primary source. In other words, I don't rely on it for significant facts unless the references are consulted. Wikipedia often gets facts *wrong*. Who was the reference they cited for the power factor info?

Rick

It has a phase. Some people call it "leading" and "lagging". Some prople use - and + to express the same thing. That's just conventions.

If utilities want to switch in PF correction devices, they need to know which direction they are trying to correct. It matters. They are usually trying to correct for lag, so they usually switch in real or simulated (rotating) capacitors.

That's a different issue, but the same ideas apply.

I took two semisters of Electrical Machinery in college, and I've designed a dozen or so electronic AC power meters, many of which have been tested by utilities, universities, and test labs. I wouldn't cite Wiki if I thought they were wrong.

There's debate about what PF really means in non-constant/unbalanced/non-sinusoidal situations.

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Some one finally hits the nail.....!

Jamie

Please read this. I won't bother to explain it myself because everyone thinks I am an idiot, they maybe correct in that insertion, I am an idiot in trying to lead people in the correct direction.

True power (Resistive), Reactive Power(Xl,XC etc..) and Apparent, the difference between the two = PF...

Jamie

You miss the point about Wikipedia. If I cited my cousin on this problem what would you say about that? He isn't wrong just because he isn't a primary reference. But he still *isn't* a primary reference, so I don't cite him. Wikipedia is full of errors whether this one is right or wrong.

The point is that citing Wikipedia without citing the real source of the info is just like citing my cousin. It lends nothing to your case.

Rick

You miss the point about Wikipedia. If I cited my cousin on this problem what would you say about that? He isn't wrong just because he isn't a primary reference. But he still *isn't* a primary reference, so I don't cite him. Wikipedia is full of errors whether this one is right or wrong.

The point is that citing Wikipedia without citing the real source of the info is just like citing my cousin. It lends nothing to your case.

Rick

Thank you.

Rick

Case? I'm telling you how people define and measure PF in the real world. If you disagree on anything substantive, say so.

The ratio, actually. PF = real_power/apparent_power

where real power is in watts and apparent power is in volt-amps.

You don't get what I'm saying at all, do you?

Rick

Actually, no. Something about your cousin?