"John Fields" schreef in bericht news: snipped-for-privacy@4ax.com...
If you connect Au to Cu and put a Current through it, for best results AC, the Cu starts corroding at the transistion from Cu to Au. This is always the case when putting to metals together, the greater the difference between the metals the faster the corroding will be.
"Alexander" schreef in bericht news:dcmtj7$a9d$ snipped-for-privacy@news4.zwoll.ov.home.nl...
This is also the reason why silver and gold contacts should never be soldered with normal Sn63Pb37 solderwire
-- Tzortzakakis Dimitrios major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr Ï "daestrom" Ýãñáøå óôï ìÞíõìá news:XmzHe.1962$ snipped-for-privacy@twister.nyroc.rr.com...
Yes, but also in voltages >=15 kV there's a signifigant skin effect, that's why all transmission conductors are constructed with a steel *core* and an
*aluminium* outer sheath, because the current tends to flow on the skin of the conductor.I mentioned corona discharge, to bring into evidence the very strong electric field around the conductor in very high voltages.Op [GMT+1=CET], hakte John Fields op ons in met:
You're right it needs also an electrlyt which is most of the times present.
Not nil. Do the math.
John
Firstly, Aluminium is Al not Au. Au is gold. You are speaking of aluminium and coper?
Galvanic Corrosion Is possible when Al and Cu are in contact with one and other. If I recal correctly a dialectric such as water needs to be present. Cathodic protection, (electric current) can be used to slow or stop this proccess. I Imagine reversing the polarity may speed it up. Aluminium is the "Less Nobel" of the two metals so I would imagine that it would be the one to corrode.
Op [GMT+1=CET], hakte DBLEXPOSURE op ons in met:
Correct I also added the remark of the diëlectricum to the discussion. And your remark about Aluminium is correct, however as stated in some applications I have seen an Copper core and an Gold (aurum) shell. And since the combination gold-copper is worse then the well known combination aluminium-copper.
But at least ThanX for confirming my statement and not saying its not true without giving a reason as someone else did.
On Mon, 01 Aug 2005 20:21:31 -0700, John Larkin Gave us:
Did you even look at that number? That is 8.5 mm!
No? OK. So for all practical purposes that do not have 20 cm wire involved (ie any normal residential application) there is NO skin effect! Where in everyday life does a person use wire that has a diameter greater than 8.5 mm that would present anything other than
100% current density in the conductor? The wave is just too slow for anything other than full propagation. Hell, even a 25kW transformer won't see any difference.In ohms per foot DC or AC at 60Hz the value is the same for all wire diameters that have a gauge number.
Before any difference could even be noted, the wired diameter would have to be over 16 mm.
What part of the word negligible, or not of any effect do you not understand?
On Mon, 01 Aug 2005 21:28:10 -0700, Don Bowey Gave us:
Your logic varies.
Tell us, guru don, where does 100kHz get used as an AC power line frequency?
On Tue, 02 Aug 2005 04:41:38 -0500, John Fields Gave us:
It's called galvanic reaction.
The Navy seems to think it's real. Does that make you an idiot?
On Tue, 2 Aug 2005 15:33:21 +0300, "Dimitrios Tzortzakakis" Gave us:
Wrong! Skin effect is a function of frequency, not voltage. The reason YOU think there is a significant skin effect is likely due to the method at which your "15kV" source was generated.
That being likely a high frequency switcher or oscillator.
No, it isn't. FREQUENCY is the reason. The other reason steel cores are used is due to the fact that transmission lines are typically hung from between two points separated by some great distance such that the wire itself needs to be able to support the weight of itself. The steel cores are there to increase the tensile strength of the overall transmission line. This is a reference to high frequency RF transmission lines. For power lines, steel is used for the same, tensile increasing reason. The cladding is used to reduce the ohms per foot of the strand. At 60Hz, however, the skin effect hovers near NIL.
That is 100% dependent upon frequency.
Corona is a function of voltage and the capacity for air to ionize. How much corona is on a wire in oil that carries a high voltage AC or DC? Same wire in air?
Electric fields increase with current in a wire. Look at a quarter shrinker. Low voltage, high current, huge field.
On Tue, 02 Aug 2005 08:06:25 -0700, John Larkin Gave us:
Very much so as close to nil as it gets. Review the math.
Wow, and I thought it was a Mexican beer that tastes so bad you have to add lime to it before consumption.
Not only did I look at it, but I calculated it, and typed it.
I just bought a building that has 3-phase, 800-amp service, and skin effect certainly has affected the sizing of the main feeder wires. And I work with people who build gigawatt 60 Hz power plants and jumbo-jet
400 Hz power systems. That's my "everyday life."In big AC transmission lines, there's a complex optimization involving wire weight, tensile strength, ohmic losses, skin effect, corona losses, wire cost, and tower spacing/cost.
Not so. At 0.85 cm depth, current density is down to 1/e (ie, only
0.37 of) the surface density. That's pretty significant.
I'm an engineer, so I consider something to be "negligable" if I can demonstrate, quantitatively, that it doesn't matter enough to affect a system. 37% is therefore worth a second look.
To speak in your style, what part of "doing the math" do you not understand?
John
On Tue, 02 Aug 2005 17:43:16 GMT, Owamanga Gave us:
And they have the nerve to call it a "specialty beer" here in So Cal.
Just so the idiots can charge more for less!
Talk about misnomers!
Give me a Sam Adams or Chimay Gold ANYDAY!
Bass Ale... anything!
Sheesh Coors' "Killian's Red" is better than that Mexican crap!
On Tue, 02 Aug 2005 10:54:26 -0700, John Larkin Gave us:
0.85cm is 8.5 mm. That means that the wire has to be bigger than that number as a radius before the current flow anywhere else besides the entire wire.So, again, if the wire is less than 17mm in diameter, there will be no skin effect involved. You may note some other effects, but skin effect won't be one of them.
On Tue, 02 Aug 2005 10:54:26 -0700, John Larkin Gave us:
No shit.
Your application of your "math" is what needs a second look.
What part of "you did the math wrong" do you not understand?
Before it would make a difference, the wire will have to be pretty big (over 17mm diameter) , and before it will make a 37% difference, it would have to be bigger still! Real simple math, there.
Your welcome, I thought you deserved a respectful reply...
On Tue, 02 Aug 2005 10:54:26 -0700, John Larkin Gave us:
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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