No, it was the acronyms that got me..
I've no recollection of that..refresh my memory.
It's important to have a physical understanding, you need to do that first.
Having the lectrons move as a consequence of magnetic field induced eddies is not quite as simple to understand, it doesn't appear very intuitive to many.
jn
Equivalent - in what sense? An unbiased capsule surely emits no AC voltage signal at all?scott wurcer said:
It includes the sentence: "Skin depth is only a function of frequency and conductor properties." Precisely what I have been saying all along. The article describes how to calculate conductor losses by doing a Fourier analysis of pulses and summing power loss for each, as each has a different spatial distribution due to frequency.marce said:
jn admits that most papers omit the effect he describes. He believes this is because they use averaging over the cycle. In fact it is because the effect does not exist, so there is nothing to average. Hence they don't do an average.
If we are getting beyond home wiring and sizes of currents and into high current affects ---> Most of the high current distribution is done as flat, parallel plate conductors (busbar); As in, a 480vac, 3KA, 3-phase power distribution buss. Very close spaced with thin insulator between the three plates. There's a reason round conductors are not used. Anyone care to get to that reason as it is more relevant to what consumer designers might apply?
THx-RNMarsh
THx-RNMarsh
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My googling didn't even find that one..I suspect we all get different results, and it may be due to our own personal history as stored by google.
That was an excellent link, thanks. Also, Dowell and Carsten are good, and well known, they are in the bib.
The best part of their paper is the depictions of proximity based current crowding. Those pics clearly show how the resistance climbs as current shifts.
But they don't delve into the actual voltage per unit length of the wire as a function of current and magfield simultaneously. That is where everybody is getting flummoxed.
But nicewriteup..
jn
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sigh...
The forces move the membranes at double the excitation frequency.
That was actually quite a good analogy Scott.
And if that is what we were talking about....
Do you really not understand proximity effect? Or are you just bustin chops?
No, they use approximation factors. Not the same thing.
jn
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I replaced my tubey television a while back with a flatscreen. That way my experiments in the basement don't change the colors..(mad scientist laugh)
jn
Sorry jn filled in the blank, I did mean you excite it with AC voltage and no DC (same with an unbiased electrostatic speaker).
One more thought experiment. One of my favorite test signals is a tri-wave, so let's let the magnetic field have a constant alternating rate of change. Now the resistance modulation is either DC or a square wave (the slope) and you have three choices, nothing, a square wave, the "linear" result (but that would mean an alternating increase and decrease of resistance and to me non-physical), or a DC offset (decrease) in the resistance due to the absolute value of the slope (I think jn's option).
EDIT - I should point out the third option produces 2nd harmonic when the excitation is a sine wave (if that was not obvious).
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They are all very good reasons.
For me, 3kA 3 phase means 18 pieces of 535kcmil conductor, and by NEC, that requires an 18 inch cable tray. (area fill).
jn
Sorry, when you said condenser mike I assumed you would be using it as a mike. OK, I see why you say this is an electrostatic analogue.scott wurcer said:
Well, you obviously think I (and the textbook authors?) don't. Proximity effect is the mutual version; skin effect is the 'self' version. Or am I wrong - are you saying that these are quite different phenomena?jneutron said:
The one paper you pointed me to did not use approximations. It did not do a cycle average, as you claimed. It simply did the calculations (IIRC).
Fourth option: Fourier analysis, with separate geometrical current distribution and hence separate constant resistance for each harmonic. This corresponds to what EM theory says. I don't think it corresponds to any of your three options.scott wurcer said:
Proximity effect is the mutual version; skin effect is the 'self' version. Or am I wrong - are you saying that these are quite different phenomena?[/quote]
Well we are starting to get somewhere, slowly.
Proximity modulates the current density profile at 2f when the external source is at the same frequency as the current. Which is why scotts analogy was so good.
Again, your going to have to be more specific. Clearly, we're both losing it..
jn
The problem has a unique solution so the analysis technique can not change the result. Constant rate of change of the field creates a constant restriction of the current path, the sign does not matter.
My gut feeling, just as with opposite charges always attracting regardless of their spacial orientation, is that any other result would violate symmetry or some other first principle related to there not being a prefered direction in space.
Tomorrow is a bench day. I will use a "high" value resistor and "DC" to feed a toroidal transformer and watch the voltage across the coil. I can do this with both polarities (phases actual since I am not immortal, alas.) The I can remove and reapply the same direction current and see the difference in time from starting with matching or opposing remnance.
I don't think so. Everything I read confirms my view, that skin and proximity effect are essentially the same thing. You have yet to present a single peer-reviewed paper or standard textbook which supports your view.jneutron said:
Agreed. The correct technique will give the correct answer. The correct technique is to use Fourier, as I said.scott wurcer said:
That is an assertion which I believe is not supported by EM theory, which shows that the spatial current pattern is set by geometry, frequency and material properties only.
If proximity effect gives rise to this alleged non-linearity then skin effect would do so to. It does not. I can understand why gut feelings might suggest an amplitude dependence; the maths says no.
The simplest way to see this, as I have said many times before, is to recognise that Maxwell's equations both in free space and in linear media are linear equations. Therefore they cannot give rise to non-linearity. Provided the geometry is fixed (i.e. the wires don't move) there is no effect.
Anyway, I am repeating myself. I said I was not going to go through the argument again so I will stop here. This should not be regarded as an admission of defeat, except in the sense that I have been unable to convince you. The burden of proof rests on those who claim that the accepted EM theory taught in textbooks is wrong.
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