skin depth, 60 Hz, tubular conductor
skin depth, 60 Hz, tubular conductor
(OP)
I'm trying to calculate the AC resistance at 60 Hz of a copper pipe with 3/4" I.D., 1/16" wall thickness, and 7/8" O.D., not near any other conductors.
Can anyone step me through this?
It must be several times the DC resistance but I'd like to know this AC value to at least two significant figures, if possible.
Thanks.
Can anyone step me through this?
It must be several times the DC resistance but I'd like to know this AC value to at least two significant figures, if possible.
Thanks.






RE: skin depth, 60 Hz, tubular conductor
You don't say if the pipe is in a coil configuration so I assume it's straight.
Roy
RE: skin depth, 60 Hz, tubular conductor
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RE: skin depth, 60 Hz, tubular conductor
Roydm, for large diameter conductors, the 60 Hz skin effect can be very significant. Thus the preference for hollow shapes for large bus conductors. At least one company also makes an almost hollow overhead conductor.
RE: skin depth, 60 Hz, tubular conductor
The ac resistance at 60 Hz will be somewhat higher than dc, but not anywhere near twice the dc resistance.
RE: skin depth, 60 Hz, tubular conductor
I suspect that errors in the figure used for the conductivity of the pipe will be greater than skin effect errors.
Bill
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"Why not the best?"
Jimmy Carter
RE: skin depth, 60 Hz, tubular conductor
The whole CDA document is an excellent reference.
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If we learn from our mistakes I'm getting a great education!
RE: skin depth, 60 Hz, tubular conductor
The measurements and graphs in this thread show otherwise.
Thanks, all.
RE: skin depth, 60 Hz, tubular conductor
RE: skin depth, 60 Hz, tubular conductor
RE: skin depth, 60 Hz, tubular conductor
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: skin depth, 60 Hz, tubular conductor
The current densities for the hollow part of the conductor are obviously eliminated, but what happens to the actual current? Does the current that would have flowed in the hollow part just flow in the rest of the conductor? Does the current not flow at all (therefore raising the resistence of the overall conductor)? Or is it a combination of the two?
Thanks!
Mark
RE: skin depth, 60 Hz, tubular conductor
This is true regardless of the shape of the conductor.
RE: skin depth, 60 Hz, tubular conductor
With the help of a spreadsheet I have found that the (Rac/Rdc)/(Rindreact/Rdc) ratio rises more rapidly with wall thickness than a straight line relationship.
This is opposite to what you'd expect with a skin effect. That is, the thicker the conductor wall, the less resistance due to skin effect there should be.
I have to sleep on this one.
RE: skin depth, 60 Hz, tubular conductor
RE: skin depth, 60 Hz, tubular conductor
You can solve skin effect resistance analytically using Bessel functions for simple solid conductors... I don't know of any closed form solutions for hollow conductors.
fwiw, here is a finite element solution using free F.E.M.M. software. Assuming copper conductivity of 58 MS/m, it predicts that the 60hz resistance of this geometry is 5.11282e-5 ohm/ft (slide 2) while the dc resistance is 5.11232e-5 ohm/ft (slide 3). I didn't go through the links, but I'd be interested if this agrees with what their tables show.
As you can see, there is not much difference but the 60hz is a tad higher. If it were a thicker wall, the crowding against the outer wall would be more noticeable and the difference in resistance would be more noticeable.
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RE: skin depth, 60 Hz, tubular conductor
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