Stupid question of the day....

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


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.
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(Don

--------------------- 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
--

Don Kelly @shawcross.ca
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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....
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On Wed, 3 Aug 2005 22:37:11 -0500, "DBLEXPOSURE"

--
Geez, you don't know when to quit, do you, Mr Passive-Aggressive?

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wrote:

--

Passive-Aggressive

Hmmmm......
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On Thu, 04 Aug 2005 13:09:19 -0500, John Fields

Your lame ass also accuses people of "self aggrandizement". I have yet to see one post from you where you don't do the same. Funny, since you're no more than a fat tub of lard.
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On Fri, 05 Aug 2005 04:36:15 GMT, TokaMundo

--
LOL, if I were to write the single line: "Tokamundo is a good guy."
and post it, you'd critcise it in your boring, predictable way.
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Or they need to be in Alameda. After all, Keptin, dis is vere dey keep da nuclear Bessels, no?
:-)
Bob M.
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On Thu, 04 Aug 2005 19:05:30 GMT, "Bob Myers"

That would be "wessels". It's a wessel function.
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On Tue, 02 Aug 2005 10:54:26 -0700, John Larkin

No shit.
For one thing, they are primarily designed for high tensile strength as they have to stay mounted through all weather and environmental conditions.
After that, their resistance is an issue as the primary material has to be steel for the tensile forces involved. They usually get clad in Aluminum as copper is too costly for such long runs, and the losses in using aluminum are little in comparison. This is also the reason that high voltages are used in long haul transmission lines. The loss over 2000 feet of line with 120 volts on it is significantly different than the loss over 2000 feet of line with 20,000 volts on it.
Corona will become a problem as that line voltage is raised. At that time line spacing becomes an issue.
Tower spacing is a function of the terrain being traversed. Line spacing ON a given tower design is a function only of the voltage that is proposed to be carried, and the total number of conductors.
Skin effect, in these high tension line realms is only an issue if the idiots that made the wire didn't know how deep to make the cladding. If the wire is clad to thinly, there will be more loss as the steel is more resistive, and the wire will heat more as well. If it is clad too thickly, an unnecessary cost is introduced.
This is specifically because the skin depth is so deep at this frequency, NOT due to it being a thin depth! So in power line cases, the effect is an issue of how deep the cladding is, not how thin.
In RF transmission lines, which are typically nickel or silver plated, it becomes a cost issue, and claddings are made as thin as possible for a given application frequency. These cases are where one will see hollow conductors, or plated tube or solids. This is where a Litz configuration or plated conductor will assist one in design of a circuit.
At 60Hz, a high voltage step up transformer will have some transfer efficiency number. At switching frequencies, the same transformer design (wire turn count wise) will operate better if the primary, and or secondary have litz wire used in them as the effective resistance of the winding will be reduced at the higher frequencies.
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Gave us:

-------- 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. -------------

------- 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. -------------
--

Don Kelly @shawcross.ca
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On Tue, 02 Aug 2005 10:54:26 -0700, John Larkin

0.85 cm is pretty thick. 8.5 mm in fact. Double that to get 17mm.
Unless the wire is larger than 17mm at 60Hz, the entire wire will carry current. VERY simple math.
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wrote:

Current begins to fall off monotonically from the very surface for any wire size at any AC frequency. There's no hard "skin boundary", and the 1/e density is just a handy if arbitrary measurement point.
I don't see why this needs arguing over. In a given situation, you just calculate the effects and decide how they affect things. Sometimes a 200% increase in resistance doesn't matter, and sometimes a 1% increase does. But skin effect does often matter in real situations at 60 Hz, and shouldn't be always/automatically discounted.
John
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Some people say that there is no such thing as a stupid question. Obviously there seems to be no shortage of stupid answers.
Bill
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On Wed, 03 Aug 2005 01:24:11 GMT, Repeating Rifle

There are no stupid questions, only stupid people.
John
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John Larkin wrote:

There are stupid questions, those that could be easily found on one's own.
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On 2 Aug 2005 22:09:22 -0700, "Autymn D. C."

--
Example???

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On Tue, 02 Aug 2005 19:50:04 -0700, John Larkin

Sometimes I find it hard to believe that we actually call ourselves sentient beings with the way some of you act.
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On Wed, 03 Aug 2005 07:19:12 GMT, TokaMundo

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I don't think anyone has ever called you sentient, much to their
credit.
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John Fields wrote:

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.
--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.
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