Stupid question of the day....

I thought large diameter conductors in switchyards were for corona reduction.

--------- Not directly related, an engineering handbook lists the skin effect for a 500MCM conductor as increasing the resistance by 2% - which I would say is significant.

----------- Since TokaMundo is infallable, consider the possibiltiy that he is actually the pope. He has also been identified as a troll.

Bud--

"TokaMundo" schreef in bericht news: snipped-for-privacy@4ax.com...

What is a high frequency? If this is not defined in the source, then most of the time a high frequency will be any frequency on what the voltage on the line cannot be taken equal at every place of the line because of linelength and wavelength. By this 60Hz can be a very high frequency if you have a cable of several kilometers.

On Wed, 03 Aug 2005 05:01:54 -0500, John Fields Gave us:

You wouldn't know what eloquence was if it bit you in the ass, you top posting Usenet retard.

On Wed, 03 Aug 2005 05:35:52 -0500, John Fields Gave us:

Yet another retarded post by Johnny boy.

Gee, someone must've received a bad grade last year in their freshman circuit analysis class...

Bob M.

On Wed, 03 Aug 2005 06:13:41 -0500, John Fields Gave us:

Yes, and it has a surface area function, retard boy.

Your IQ is ten.

Just as I stated, when the wire turns cherry red from current, it is uniformly heated.

The entire wire has the same temp and the same heat. The only exception is the connection points to the current source.

I never said it did. I said the current generates the heat, and then corrected to say that the resistance to said flow is the condition which causes the generated. I didn't say a damned thing about the current generating the resistance. That is a function of the media the current is passing through.

Your remark is retarded.

No shit. That's what "resistance to said flow" refers to, dipshit.

No shit.

What you have to say about it is certainly immaterial.

The phenomenon of the entire wire being at the same temperature.

You have no point. You and your stupidity has been exiled to the pointless forest.

Got something that proves otherwise? Otherwise your rebuttal is nothing more than bullshit opinion.

On Wed, 3 Aug 2005 18:29:47 +0200, "Alexander" Gave us:

The voltage on the line is different along its length for plenty of reasons, the least of which is skin effect.

A mile run at DC, and one at 60Hz won't yield significantly different losses. If the voltage is high enough the drop will be even less significant.

I think "Sediment" would be a better description for TokaMundo, John. At least that's the sound he made when he was tossed in my troll bucket weeks ago.

--------------------- In Engineering Electromagnetics, Hayt points out that in a power station a bus bar for alternating current at 60 Hz much more than 1/3rd of an inch (8 mm) thick is wasteful of copper, and in practice bus bars for heavy AC current are rarely more than 1/2 inch (12 mm) thick except for mechanical reasons. This seems to imply that the bulk of the current is in the outermost 4mm.

This does not mean that conductors, at 60 Hz, which are less than 8mm in diameter do not show skin effect. 60 Hz AC resistance/DC resistance for commonly used conductors (say 12 to 6 gauge) may be 1.1 to 1.25 in practice- this includes skin and proximity effects . However, anyone wanting to do the math from scratch better be familiar with Bessel functions. Are you?

Skin effect, per se, is not a concern with ACSR power cables as there are a number of other factors which are more important.

Possibly the approximations for high frequencies are not valid at 60Hz but this does not mean that skin effect is negligable- except for conductors 000 or higher - provided they are straight. . The point is that there is no hard and fast "rule" covering all situations

Thanks Don!

I have been watching this thread for days. I like your answer. It's allways give and take, no hard and fast rules that fit every situation. And even better yet, You made your point without slamming anybody..

Well Done, Hats off....

-------- Gee - I thought I^2R loss depended on the current, not the voltage. For a given power you are right but you didn't state this.

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------- Right -and I have seen ACSR cable with an aluminum depth that exceeds 2cm. This is unusual and now smaller conductors in bundles (spaced 30-45cm between conductors ) because of lower inductive reactance and surface fields that result-notghing to do with skin effect.

Not a big deal. The usual skin depth rules go out the window because of the magnetic core material and the fact that you have strands of aluminum in close proximity.

---------

-------- Note that the equivalent of Litz wire has been used and is used in 60 Hz generator windings. Wonder why? The individual strands are too small to have an appreciable skin effect but there is also the proximity effect which can be more of a problem.

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Skin effect has nothing to do with voltage. Nor is the 15KV level a "boundary" . It has long been recognised that larger diameter conductors will reduce surface fields and corona as well as reducing inductance. However, large diameter conductors are heavy. Initially a copper "barrel stave" conductor was used but then the idea of a steel core for strength and aluminum for conductivity replaced this original idea. Skin effect was reduced and was considered in ther design but basically strength without loss of conductivity was the basis for practical large diameter conductors. The bundling of conductors (say 2 to 4 conductors spaced 30-45cm apart) is an extension of this - effective very large diameter and lower surface fields and series inductance at a reasonable price and weight savings. This has nothing to do with skin effect.

On Wed, 03 Aug 2005 15:54:26 -0500, John Fields Gave us:

If it were modeled after the earth, with the heat source in the center, I would agree. I feel, however, that it is more closely modeled after Io, which is heated by the magnetic forces of Jupiter, and more closely approximates an evenly heated body.

In the wire, since the heat is generated throughout the medium via current flow, even from low currents on up to my cherry red scenario would show the wire at the same temp from center to outer surface.

The "thermal skin" of the wire that would be slightly cooler due to surface convection is very thin and beneath it the medium has even temperature, not a gradient to the center. The reason is that the surface that you claim to be giving up so much of its heat by convection isn't that large compared to the whole mass of the wire, and the source of the heat is throughout the wire's medium.

That's for bare wire and for sheathed or coated wire the containment is even better.

The word for today is emissivity.

Even though the number is high for bare, matte finished copper, it still doesn't give up its heat fast enough to have a full gradient throughout the wire. It would appear as a "skin" when graphed. A very thin skin.

On 30 Jul 2005 18:26:41 -0700, "Autymn D. C." Gave us:

Nice.

The condensed form (in a manner of speaking) :-]