I think it's unecessary and even inaccurate to say that power factor ranges between -1 and 1. You have actually 4 quadrants - +/- real power, +/- reactive power. A single sign doesn't accurately convey all four possiblities (is it even meaningful to say that leading reactive power flowing to the load is the negative of lagging power flowing from the load?) Power factor meters I've seen tend to be marked "lead" and "lag" instead of +/-.
I don't even understand what a power factor of -1 means -what is happening in the circuit at -1 power factor that is different from a +1 power factor?
All the definitions of power factor in IEEE Std. 100 say something along the line of the ratio of real power to total power, with no qualifications as to direction.
With respect, citing credentials on Wikipedia is unproductive - we've had some quite amazing credentials claimed that turned out to be inaccurate. -- Wtshymanski ( talk) 17:23, 14 December 2008 (UTC)
Thanks for the response. (And I truly appreciate your comment about citing credentials; I offered mine to you only to assure you that I'm not a flake, and certainly not as an argument that I'm correct. Heaven knows, even with my credentials I'm wrong often enough!)
You are absolutely correct: there are 4 quadrants for sinusoidal single-phase situations, and you are correct that they are +/- real power, and +/- reactive power. And we all seem to agree that true power factor is defined as the ratio of real power to apparent power; and we all agree that the definition of apparent power is RMS volts multiplied by RMS amps. Because of the "square" term in root-mean-square, RMS values can only be positive.
So I'm not sure which of the following statements you disagree with: (1) power factor is the ratio of watts to volt-amps; (2) watts can be either positive or negative; (3) volt-amps can only be positive; (4) watts is always less than or equal to volt-amps. In my opinion, those four statements imply that power factor can take any value between -1 and 1. That was my intention the last time I worked on the IEEE 100 definition of power factor, many many years ago, but perhaps we didn't get it clear enough. (Now, if you really want to get confused, join us on IEEE 1459 where we're writing the power definitions for balanced and unbalanced, sinusoidal and non-sinusoidal, three-phase systems - just try to get consensus on the meaning of "VAR" on an unbalanced, non-sinusoidal corner-grounded delta system!)
You ask an interesting and useful question: what is happening in the circuit at -1 power factor that is different from +1 power factor? So let's assume that we're asking this question standing in front of a revenue meter (American terminology - my apologies - but I mean the meter where the electric power company connects to your house). If you have a power factor of +1, then your house is acting like a nice, pure resistive load, and the losses in the grid conductors (as a percentage of the power delivered) are minimized. If you have a power factor of -1, then somewhere inside your house you've got a photovoltaic inverter, or a natural gas generator, or a hybrid vehicle functioning as a generator, and you're pushing power back onto the electric company's grid, and, again, the losses are minimized. A power factor of +0.5 means essentially that your house is drawing twice as much current as would be optimal for the amount of power your house is using. A power factor of -0.5 means that your house's generator, whatever it is, is supplying twice as much current to the grid as would be optimal for the amount of power your house is delivering to the grid. In other words, the distance from "1" in the power factor tells you how much extra current is flowing, and the sign of the power factor tells you the direction the power is flowing.
Of course, the direction is arbitrary; a "-1" just means the power is flowing the opposite direction from what's expected: from the nominal source to the nominal load. If we're looking at a meter on a building that houses a big rotating generator, we usually thing of the nominal source as the building, and the nominal load as the grid. If we're looking at a house, we usually think of the nominal source as the grid, and the nominal load as the building. In either case, it's possible for the power to flow in the opposite-from-expected direction: we can use the generator as a motor, for example, or we can install a micro-grid generator inside the house.
Going back to my historic discussion on your talk page, where I mentioned that in displacement power factor (not true power factor), we sometimes used the sign to indicate leading or lagging, even though that was mathematically incorrect. In that (incorrect) case, there was no difference between a power factor of -1 and a power factor of +1. But nobody does that any more, except maybe some of us old power engineers when we're in a reminiscing mood, and thinking longingly of the days when currents were sinusoidal. As you correctly observe, more modern meters tend to say "lead" and "lag", which -- assuming they are measuring displacement power factor and not true power factor -- is a more accurate description. Of course, true power factor doesn't have a lead or a lag; it's just the ratio of watts to volt-amps, and there's no angle associated with it at all.
The reason I'm putting so much effort into this is that one of my young engineers, a very bright young man named Chao Yang who has joined us from U.C. Berkeley, made an error in the firmware for a new power meter we're designing. He incorrectly took the absolute value of the true power factor before putting it on the meter's display. When I asked him why, he showed me the Wikipedia article that says "true power factor is in the range of 0 to 1." Young engineers take Wikipedia articles seriously, and sometimes even base part of their designs on what they read here. So I want to help correct the errors, if they are errors...
Again, it's quite possible that I'm wrong, and I would be glad (and rather excited) to learn that I'm wrong. Could you review these comments and see if you are persuaded? if you are not, could you educate me? Thanks! Alex McEachern AMcEachern ( talk) 03:11, 15 December 2008 (UTC)
I think it's unecessary and even inaccurate to say that power factor ranges between -1 and 1. You have actually 4 quadrants - +/- real power, +/- reactive power. A single sign doesn't accurately convey all four possiblities (is it even meaningful to say that leading reactive power flowing to the load is the negative of lagging power flowing from the load?) Power factor meters I've seen tend to be marked "lead" and "lag" instead of +/-.
I don't even understand what a power factor of -1 means -what is happening in the circuit at -1 power factor that is different from a +1 power factor?
All the definitions of power factor in IEEE Std. 100 say something along the line of the ratio of real power to total power, with no qualifications as to direction.
With respect, citing credentials on Wikipedia is unproductive - we've had some quite amazing credentials claimed that turned out to be inaccurate. -- Wtshymanski ( talk) 17:23, 14 December 2008 (UTC)
Thanks for the response. (And I truly appreciate your comment about citing credentials; I offered mine to you only to assure you that I'm not a flake, and certainly not as an argument that I'm correct. Heaven knows, even with my credentials I'm wrong often enough!)
You are absolutely correct: there are 4 quadrants for sinusoidal single-phase situations, and you are correct that they are +/- real power, and +/- reactive power. And we all seem to agree that true power factor is defined as the ratio of real power to apparent power; and we all agree that the definition of apparent power is RMS volts multiplied by RMS amps. Because of the "square" term in root-mean-square, RMS values can only be positive.
So I'm not sure which of the following statements you disagree with: (1) power factor is the ratio of watts to volt-amps; (2) watts can be either positive or negative; (3) volt-amps can only be positive; (4) watts is always less than or equal to volt-amps. In my opinion, those four statements imply that power factor can take any value between -1 and 1. That was my intention the last time I worked on the IEEE 100 definition of power factor, many many years ago, but perhaps we didn't get it clear enough. (Now, if you really want to get confused, join us on IEEE 1459 where we're writing the power definitions for balanced and unbalanced, sinusoidal and non-sinusoidal, three-phase systems - just try to get consensus on the meaning of "VAR" on an unbalanced, non-sinusoidal corner-grounded delta system!)
You ask an interesting and useful question: what is happening in the circuit at -1 power factor that is different from +1 power factor? So let's assume that we're asking this question standing in front of a revenue meter (American terminology - my apologies - but I mean the meter where the electric power company connects to your house). If you have a power factor of +1, then your house is acting like a nice, pure resistive load, and the losses in the grid conductors (as a percentage of the power delivered) are minimized. If you have a power factor of -1, then somewhere inside your house you've got a photovoltaic inverter, or a natural gas generator, or a hybrid vehicle functioning as a generator, and you're pushing power back onto the electric company's grid, and, again, the losses are minimized. A power factor of +0.5 means essentially that your house is drawing twice as much current as would be optimal for the amount of power your house is using. A power factor of -0.5 means that your house's generator, whatever it is, is supplying twice as much current to the grid as would be optimal for the amount of power your house is delivering to the grid. In other words, the distance from "1" in the power factor tells you how much extra current is flowing, and the sign of the power factor tells you the direction the power is flowing.
Of course, the direction is arbitrary; a "-1" just means the power is flowing the opposite direction from what's expected: from the nominal source to the nominal load. If we're looking at a meter on a building that houses a big rotating generator, we usually thing of the nominal source as the building, and the nominal load as the grid. If we're looking at a house, we usually think of the nominal source as the grid, and the nominal load as the building. In either case, it's possible for the power to flow in the opposite-from-expected direction: we can use the generator as a motor, for example, or we can install a micro-grid generator inside the house.
Going back to my historic discussion on your talk page, where I mentioned that in displacement power factor (not true power factor), we sometimes used the sign to indicate leading or lagging, even though that was mathematically incorrect. In that (incorrect) case, there was no difference between a power factor of -1 and a power factor of +1. But nobody does that any more, except maybe some of us old power engineers when we're in a reminiscing mood, and thinking longingly of the days when currents were sinusoidal. As you correctly observe, more modern meters tend to say "lead" and "lag", which -- assuming they are measuring displacement power factor and not true power factor -- is a more accurate description. Of course, true power factor doesn't have a lead or a lag; it's just the ratio of watts to volt-amps, and there's no angle associated with it at all.
The reason I'm putting so much effort into this is that one of my young engineers, a very bright young man named Chao Yang who has joined us from U.C. Berkeley, made an error in the firmware for a new power meter we're designing. He incorrectly took the absolute value of the true power factor before putting it on the meter's display. When I asked him why, he showed me the Wikipedia article that says "true power factor is in the range of 0 to 1." Young engineers take Wikipedia articles seriously, and sometimes even base part of their designs on what they read here. So I want to help correct the errors, if they are errors...
Again, it's quite possible that I'm wrong, and I would be glad (and rather excited) to learn that I'm wrong. Could you review these comments and see if you are persuaded? if you are not, could you educate me? Thanks! Alex McEachern AMcEachern ( talk) 03:11, 15 December 2008 (UTC)