Surface conduction at 60 Hz

says...


<snip>
Enough. already. Google is your friend! ;-) http://en.wikipedia.org/wiki/Skin_effect
At 60Hz the skin depth in copper is about 8.5mm; not a big cable to power companies.
--
Keith

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Keith Williams wrote:

Exactly. The cable core already has to be large (relatively) diameter for strength. One does not need to make it larger to ensure that the copper cladding is not wasted expense. Skin effect has no bearing on the cable dimension. Whatever amount of copper is added as cladding will not be wasted. The reason copper is clad onto the steel is not because skin effect exists. Copper is clad onto the steel because it (copper) is a better conductor.
I suspect that this dispute was caused by my initial post that sounded too absolute. I get the sense that people think, based on that post, that I am claiming skin effect does not exist at 60 Hz. The bone of contention here is not the existence of skin effect. It is the rationale in the power line example used to support the idea that skin effect must often be considered at 60 Hz. The rationale does not stand up to examination, and even if it did, a single example does not provide evidence of "often". It gets discouraging when an example in Mhz or higher is offered.
Ed
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us:

I know! At 1 Mhz we can truly call it "skin effect". At 60 Hz, we should call it "clad effect". It even sounds thicker. Thickerer.
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"Roy L. Fuchs" wrote:

How about 'current density depth gradient'? That'll keep most of the know-it-alls tongue-tied.
;-)
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On Thu, 02 Mar 2006 18:31:32 -0800, "Paul Hovnanian P.E."

Hahahaha... at least I am not out of my depth, despite what some have stated.
If I am so slow, why then is my skin so thin? :-]
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----------------------------
wrote:

How many power lines now use copper? I recall some relatively low voltage distribution lines using steel with a copper cladding but any "real" transmission line over the order of 30Kv uses ACSR (Aluminum Cable, steel reinforced. With such cables, the 60Hz skin effect is much smaller than with an all aluminum or all copper cable because the current will flow in the outer Aluminum layer even at DC (serendipity?). However, any table of parameters for such cable shows that AC resistance is higher than for DC- In essence the effect of skin effect, however slight, is accounted for in the stated resistance- so you don't even have to think about it.
For example "Joree" has an AC/DC ratio of 1.05+ at 25C Mind you, the change in resistance in going from 25C to 75C is 15%.
This is a very large conductor and is rarely, if ever, used now- but I have seen larger conductors in the supply from a hydro plant to a nearby aluminum smelter (at 13.8KV).
--

Don Kelly @shawcross.ca
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On 3/2/06 7:31 PM, in article AMONf.89555$B94.21027@pd7tw3no, "Don Kelly"

The skin depth in aluminum is somewhat greater than it is in copper because Al has higher resistivity than Cu does. I don't know how economics factors in, but the price of Cu has greatly increased the last few years. What probably clinches the deal for Al is that its lower density allows for larger diameter conductors. In turn, that allows higher conductance for the conductors while also allowing increased separation between support towers.
Bill
-- Ferme le Bush
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----------------------------
wrote:

Actually, ACSR (Aluminum outer layers steel core) started to replace copper in the 1940's and at present, the use of copper, except for distribution (even there ACSR is common), ended long ago. You are right in that the economic/engineering constraints dictate the choice but that balance between copper and ACSR was won by ACSR a long time ago.
--

Don Kelly @shawcross.ca
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wrote:

He didn't explicitly mention steel clad copper.
But he may be referring to bus-work used in substations. For short runs between circuit-breakers, lightning arrestors, disconnects and other components, you will often see hollow tubing used for the conductors. If the same cross-sectional area of material were in the form of a solid bar, it would have higher resistance owing to the skin effect. By simply reshaping the material into a tube with a larger OD, more material is in the region near the 'skin', providing lower resistance.
(the tube also has more structural strength than a solid bar of the same material cross-section).
daestrom
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wrote:

Previous point proven.
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daestrom wrote:

I thought large diameter tubing conductors in HV substations was mostly for corona reduction.
bud--
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----------------------------
wrote:

Even in 1930+ when the lines from the then Boulder Dam to LA were built, the advantages of a larger diameter conductor were apparent as was the extra weight of a solid conductor considering skin effect. Rudenberg was one who did an in-depth analysis of this. The conductors used there were about 2.5cm diameter and were made of twisted "barrel staves" about 3 to 4 mm deep (working from memory of a sample). ACSR simply gave us the advantage of the larger diameter with the strength of a steel core (not intended for current carrying). Bundled conductors were a further improvement in terms of surface fields and reduced inductance as well as mechanical and construction advantages.
--

Don Kelly @shawcross.ca
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Salmon Egg schrieb:

Hello,
the steel core is used to carry the mechanical tension.
Bye
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"Proctologically Violated" wrote:

Its not so much the nickel plating as the maximum operating temperature of the conductor and insulation. The nickel plating only serves to protect the copper conductor from reactions with oxygen at higher temperatures.
The NEC ratings are based on conservative calculations of the ability of a conductor to radiate or conduct the thermal energy away that is produced by I^2R losses and still remain within the temperature limits of the surrounding insulation. The are affected by insulation thermal resistance and ambient temperature, among other factors.
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Meaningless questions like this from extremely uninformed people come up all the time.
It doesn't stop well informed, well intentioned people trying to read minds and rushing in with replies. Stop here.
Arthur Holland
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snipped-for-privacy@cogeco.ca wrote:

You're right. We shouldn't be answering questions for people unless they already know the answer.
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