No, it isn't a different subject at all.

Yes, it is a different subject all together.

You presented a cosine(Θ) based definition of "power factor" and I just applied it is all.

But you failed to follow what the formula was meant to tell you.

You're completely stuck in an out-dated "power only goes one way" universe...

I did not say "power goes only one way". I fact, I have said the opposite. And since when was "power goes one way" dated? Power has been known to flow in different directions for about as long as power has been discussed in human history.

...and instead of just admitting you're wrong, you're now claiming that some "definition" prevents the voltage and current phase relationship from exceeding +/- Π/2 radians.

Given a generator instead of a load with a normal impedance, the voltage and current can indeed lag or lead each other more than 90 deg. But you fail to get what we have defined. We have defined the magnitude of the active component relative to the magnitude of the apparent component.

The phase angle of the voltage is one of the components that is used to calculate the power factor of a normal load. Instead of getting caught up in some new definition have you stopped to consider the goal of the calculation? You are missing the intent of using the angle between the voltage and current. We are really after the percentage of apparent (total) power that is composed of active (real) power. This factor shows the relationship between the real component of power that our equipment has to handle and the total power that our equipment has to handle.

In other words, the angle we are after is the angle between the current on the real axis and the total current. For normal loads, the active power is in phase with the voltage because it is a resistive component of the load. But for any load you want, call it positive or negative real or positive or negative reactive, we get two components: one on the real axis and one on the imaginary axis. These components add vectorially to give us the total component. Indeed, you will often find the definition of power factor as pf = |I_real|/|I_total|.

The angle between the active and apparent power (or current) will be between zero and 90. On planet Earth, that is the nature of a rectangular coordinate system. It should be no mystery why cosine was used to map the real component.

I will concede that using lag or lead is probably not the best choice when discussing the relationship between the active and apparent current.

Well, times change. Relative to a reference frame in which voltage and current are positive, it is now possible for voltage to be positive and current to be negative.

Time has nothing to do with it. In case you did not know, it has always been that way.

Do words and measurements =actually= mean anything? In particular, for a 120 VAC system, the voltage is a measurement of the root mean square voltage of the conductor. The only reason RMS voltages are always positive is because of what "root mean square" means and the convention that the positive root is the one that is used (square roots have two solutions -- one positive, the other negative ...).

Changing an AC voltage by =any= DC offset increases the RMS voltage by the magnitude of the DC voltage the AC voltage rides on). Which pretty much means it's impossible to ever have a negative RMS voltage, even if you try playing games with the AC, unless you through more than a hundred years of what "Volts, RMS" means out the window.

Give me any voltage you want and I will give you a reference frame in which that voltage is a negative. You do realize that we have RMS current don't you?

On which planet?

No, seriously -- on which planet is "power" an absolute value with no direction, because the =definition= of "power" is either "volts * amps", or it isn't.

On planet Earth, we have some machines that are generators and some machines that are motors. The traditional method sees a generator as having a positive power output, not a negative output. But you can view it either way with no real harm done. Knock yourself out.

For you to say

tallgirl said:

Nor can you say that when a PV system is 'exporting' power then the power is positive

is really quite silly. Not only are you wrong, you are arguing against your own self because you are now saying the direction must be fixed the other way.

You can't make "volts" arbitrarily negative without breaking everyone else and arbitrarily deciding which way volts is volts based on which way current is heading -- and the physics of "current" makes it very obvious that current has a direction (sign).

The choice of direction is completely arbitrary. I can base it on a reference voltage or a reference current. Also, in case you were not aware, voltage is bound by physics just like current is bound by physics because it is a physical phenomena, not just some mathematical construct.

Yes, you are.

The direction of current flow determines the nature of the magnetic field created by a conductor on which said current is flowing. A change in current creates a magnetic field that is directly related (in a counter-clockwise manner ...) to the direction of current flow. You want to have current be an absolute value measurement, in which case AC transformers no longer work. Since the Laws of Nature aren't subject to whim, I think they're going to ignore your request to cease working properly.

Complete twaddle.

I used your definition for "power factor" -- cosine(Θ), where Θ is the phase angle different between the same location on the voltage and current waves. Don't complain to me when it produces a negative value for Θ between Π/2 and 3Π/2 radians.

Then quit blindly applying a formula and try to figure out what the formula is supposed to do.

Your meter isn't the basis for Physics or Electromagnetics. Fortunately.

Fortunately, no meter is the basis for Physics or Electromagnetics. Fortunately for me, my meter does follow the laws of Physics and Electromagnetics.

Now you can define anything you want to in your world and no one will be able to argue since you are making the rules. But just because you make something up does not mean the rest of the world will follow your lead.

You are trying to take a negative sign that is a placeholder for the term delivered or received and turn it into something else. May I recommend you read the following:

__Understanding Power Flow and Naming Conventions__