This topic has been aired in some recent posts, so there may have been an answer, but I stopped following the threads when the invectives started.
Could someone please explain clearly what the definition of power factor is in the case of a nonlinear load? Preferably something official, such as maybe from the IEC standards.
I keep seeing references to the power factor of things like CFLs being 'low', I'm not sure on what basis that's being stated. For a true voltage source, if the current spikes are right on the voltage peaks, then there is a good argument that the PF should be 1.
Thanks for the clear definition, Phil. I hope people will bear with me while I take this a bit further.
I thought this formula would calculate a PF of 1.0 for a nonlinear load typical of an SMR waveform, with sharp current spikes around the voltage peaks, but fortunately decided to shut up and try a few simulations before making any more comment. To my surprise, when I applied Phils formula to such a current waveform, I came up with a 'result' (whether it's 'power factor' or not is a very moot point) that is well under 1.0.
Why is this so? The reason a PF in the sinusoidal (linear, reactive load) situation is low is that the voltage and current are out of phase, so that there are portions of the cycle where the voltage and current are opposite, and the reactive load behaves like a generator, returning energy back to the source. So on average, the energy dissipated in the load is less than the total volts * amps. But with the SMR waveform, the voltage and current are always of the same sign at any one instant, so there is no time when energy is being passed back from the load ot the source. Shouldn't the PF be 1.0?
I can't come up with a clear explanation for the result yet, it might be just a mathematical artefact, with no clear physical significance.
Is this important? IMO, yes. Because we're talking of two completely different loss mechanisms, that may require quite different approaches for mitigation. In the case of true, low PF, the losses are due to that excess current, that heats the transmission system up but doesn't show on your meter and doesn't do anything useful (ignoring reactive power system stability issues). In the case of the nonlinear load, the problem is the nonlinear effects, of which 'harmonics' might be only part of it (because superposition doesn't apply, if you want the technical reason for that). Conventional PF correction is unlikely to help here, in fact providing nice big fat caps to help the high frequencies to circulate could well make things worse. I don't know what you do for a power network driving millions of switchmode devices, all the way from tiny phone chargers up to big VVVF drives.
All this might be related to whether it's smart policy to chuck out trannies and light bulbs too...
Which covers some of the points you made, and references this document:
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Which specifically addresses the impact of harmonic distortion on the power system, and mentions the negative side-effects of power factor correction caps when confronted with harmonic distortion.
Incidentally, today I was talking to a pump supplier about a new unit for a site, and they suggested a variable-speed drive unit to drive a 3-phase pump - these units commonly quote a power factor of 1, but on a 6 KW pump I imagine the harmonics would be a significant issue that seems to be ignored. Then again, while I think a 6KW pump is kind of a big motor, it seems every Dick and Harry is installing 6KW split-system heat pumps in their homes, many of which are "inverter" style, variable speed units...
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