Skin Effect

[Miguel Villarroel]

Who can explain clearly why skin effect exist? Does it exist less at dc current or none exist? Why there is more skin effect at ac current?

If there was no electricity there would be no internet. Good point, don´t you?

 

[ScottyUK]

A reasonable starting point:

http://www.copperinfo.co.uk/busbars/pub22-copper-for-busbars/sec4.htm

Did you try google?


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If we learn from our mistakes I'm getting a great education!

 

[electricpete]

A simplified description for skin effect is that the effective inductance is lower at outside edge of conductor than it is at the inside. This is because the center filament links flux from all current (for cylindrical geometry... which will have flux pattern function of distance from center, but not of angle) and so sees highest inductance. The outer filament links some but not all of the flux from current that is further in (it only links that portion of flux from that further-in current that is further out, including completely outside the conductor).

We can see it does not apply to dc because inductance does not affect dc circuits.

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(2B)+(2B)' ?

 

[electricpete]

I forgot to say of course that the effect of higher inductance in center and lower on outside is that current tends to crowd the outside, resulting in higher effective resistance and lower effective inductance.

This effect increases with frequency, increases with conductivity of the material, and increases with magnetic permeability of the material.

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(2B)+(2B)' ?

 

[electricpete]

....and increases with size of the conductor.

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(2B)+(2B)' ?

 

[Miguel Villarroel]

Yes but skin effect keep linear relation with frecuency and relative permeability in accordance with some bessel or kelvin functions too, then do you mean that temperature doesn´t affect skin effect? or yes?, or if i put one cable as a whole kilo of rags tangled it changes skin effect? or it is only valid at overhead lines?

If there was no electricity there would be no internet. Good point, don´t you?

 

[electricpete]

do you mean that temperature doesn´t affect skin effect?

Temperature would only come into the picture to the extend that it will probably affect conductivity, and possibly (?) permeability.

If i put one cable as a whole kilo of rags tangled it changes skin effect?

Skin effect generally accounts for the change in current distribution in a given conductor due to the flux field set up by that conductor (not other conductors). Conductors can influence the current distribution in adjacent conductors.... that is a similar phenomenon, but goes by another name: "proximity effect"



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(2B)+(2B)' ?

 

[VTer]

Please see attached for a very brief explanation. This is how I explained it to myself. Hope it helps.

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[Miguel Villarroel]

OK very good explanation but I think that temperature has an important role too in all this. Do you think temperature is the same inside at the center than outside on the surface? resistivity changes with temperature, don´t you?

If there was no electricity there would be no internet. Good point, don´t you?

 

[ScottyUK]

Well, copper is a pretty good thermal conductor and the electrical insulating layer is not likely not a very good thermal conductor, so, unless there is something unusual about the winding design such as forced liquid cooling, yes I'd expect the temperature gradient across the conductor diameter to be small.

Why do you think temperature has such a big effect?


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If we learn from our mistakes I'm getting a great education!

 

[Miguel Villarroel]

Ok, cuz surface has more chance to interchange heat than center?, don't you?

If there was no electricity there would be no internet. Good point, don´t you?

 

[dpc]

Skin effect is due to the magnetic field and non-uniformity of the inductive reactance across the cross-section of a conductor. If there is any influence of temperature on the current density across a conductor it will be much less significant and more importantly, it will not be called "skin effect".





David Castor

http://www.cvoes.com

 

[Miguel Villarroel]

then if you use a copper tube to send ac energy disappears skin effect? or otherwise current is divided between two surfaces?

If there was no electricity there would be no internet. Good point, don´t you?

 

[electricpete]

then if you use a copper tube to send ac energy disappears skin effect? or otherwise current is divided between two surfaces?

If you use a hollow copper tube thicker than the skin depth, the current will crowd toward the OD. It will not crowd toward the ID. Again you can see that by considering flux linkage as discussed above.


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(2B)+(2B)' ?

 

[Miguel Villarroel]

What would happen to a tube of a superconductor, does the skin effect occur? someone has heard something about that

If there was no electricity there would be no internet. Good point, don´t you?

 

[electricpete]

The better the conductor, the more pronounced the skin effect. For a given frequency, the concentration of current toward the outside should be much more pronounced for superconductor than for copper conductor of comparable size.

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(2B)+(2B)' ?

 

[Miguel Villarroel]

then, at superconductors occurs the same phenomena

If there was no electricity there would be no internet. Good point, don´t you?

 

[waross]

Many years ago copper pipe was used as bus bars for large currents.
These days aluminum pipe is often used for substation conductors for heavy currents. The pipe is frequently made to Iron Pipe Sizes (aluminum IPS or copper IPS).


Bill
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"Why not the best?"
Jimmy Carter

 

[ScottI2R]

Hi all,
I am not trying to go O/T here, but does this lend any credibility to high end audio speaker cable manufacturers that sell flat speaker "wire"? Personally, I have never been able to tell a difference audibly and I think my friend wasted his $$$.

Scott

I really am a good egg, I'm just a little scrambled!

 

[waross]

I'm not sure Scott, and I am really skeptical about the audiophile use of fine strand wire to combat skin effect in speaker leads (not Litz wire). Gee, if it mitigates skin effect at audio frequencies why won't it mitigate skin effect at power frequencies? I have suggested to a couple of audiophiles that they would be better served by using PVC clad copper tubing for speaker leads. They were horrified.

Bill
--------------------
"Why not the best?"
Jimmy Carter