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Surface conduction at 60 Hz
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| Proctologically Violated©® 2006-02-24, 8:21 pm |
| Awl--
I thought I had learned that conductors carried most of the electron flow on
their surface, but recently was informed that this would only be true at
high freq (skin effect). I disputed this via Coulombic forces, but then
realized that maybe Coulomb's law does not apply to flowing current in a
conductor--sumpn about hole current as well??
But indeed, a wire carrying current to a bulb is not charged the way a
capacitor is.
But THEN,
I just happened to be reading the 1996 edition of the NEC, and I noticed an
unusual entry: Nickel plated wire has 3-4 TIMES the current-carrying
capacity as regular copper wire.
At first brush, this seemed to support my initial assertion, that conductors
DO carry their charge on the surface.
But THEN, I realized that nickel (likely) has lower conductivity than
copper, so such an effect would appear odd even if current flow did tend
toward the surface.
Finally, I seem to remember the expression "current density" as a function
of cross-sectional area, which would suggest current is distributed
throughout the wire's cross section, not just on the surface.
So what's up w/ nickel plated wire???
In my 1920's house (Yonkers, NY), the service is solid #9 (!!! heavier than
10, but lighter than 8??), and it seems to be doing the job of #6 or #4
wire. In fact, I believe *all* the wiring in the house (cloth-covered #14)
is plated, and is also in very good shape--thank god. Splices are wire
nutted AND soldered, as well. 
But back to the original topic:
At DC, or 60 hz, is current density uniform throughout the wire's cross
section? If not, what type of distribution does it have?
Why does Coulomb's law moot in a current carrying conductor?
TIA.
--
Mr. P.V.'d
formerly Droll Troll
| |
| chuck 2006-02-24, 10:23 pm |
| Wire ampacity ratings are based on temperature. Nickel-plated copper can
withstand higher temperatures than tin-plated copper and so higher
ratings are possible. Keep in mind that nichrome wire is typically used
in heater elements, whereas copper would typically be unsuitable for
that application.
Skin effect, cross-sectional area, and conductivity get at resistance,
which is not the primary factor in establishing current carrying capacity.
Does that make sense?
Chuck
Proctologically Violated©® wrote:
> Awl--
>
> I thought I had learned that conductors carried most of the electron flow on
> their surface, but recently was informed that this would only be true at
> high freq (skin effect). I disputed this via Coulombic forces, but then
> realized that maybe Coulomb's law does not apply to flowing current in a
> conductor--sumpn about hole current as well??
> But indeed, a wire carrying current to a bulb is not charged the way a
> capacitor is.
>
> But THEN,
> I just happened to be reading the 1996 edition of the NEC, and I noticed an
> unusual entry: Nickel plated wire has 3-4 TIMES the current-carrying
> capacity as regular copper wire.
>
> At first brush, this seemed to support my initial assertion, that conductors
> DO carry their charge on the surface.
> But THEN, I realized that nickel (likely) has lower conductivity than
> copper, so such an effect would appear odd even if current flow did tend
> toward the surface.
>
> Finally, I seem to remember the expression "current density" as a function
> of cross-sectional area, which would suggest current is distributed
> throughout the wire's cross section, not just on the surface.
>
> So what's up w/ nickel plated wire???
>
> In my 1920's house (Yonkers, NY), the service is solid #9 (!!! heavier than
> 10, but lighter than 8??), and it seems to be doing the job of #6 or #4
> wire. In fact, I believe *all* the wiring in the house (cloth-covered #14)
> is plated, and is also in very good shape--thank god. Splices are wire
> nutted AND soldered, as well.
>
> But back to the original topic:
> At DC, or 60 hz, is current density uniform throughout the wire's cross
> section? If not, what type of distribution does it have?
> Why does Coulomb's law moot in a current carrying conductor?
>
> TIA.
> --
> Mr. P.V.'d
> formerly Droll Troll
>
>
| |
|
|
"Proctologically Violated©®" <physical@erols.com> wrote in
message news:_eWdnZrPoJBtCGLenZ2dnUVZ_tSdnZ2d@rcn.net...
> Awl--
>
> I thought I had learned that conductors carried most of the
> electron flow on
....
>
> But back to the original topic:
> At DC, or 60 hz, is current density uniform throughout the
> wire's cross section? If not, what type of distribution does
> it have?
> Why does Coulomb's law moot in a current carrying conductor?
>
> TIA.
> --
> Mr. P.V.'d
> formerly Droll Troll
>
Per cubic volume, or square if you prefer a 2-D visualization,
the current passing thru a material is the same. A square foot
cross sectional area of a material, regardless of its shape
allows electron/hole flow at a consistant rate throughout its
area.
Say you have a cross sectional area of 100 pieces of one square
foot. Each square foot of area is allowing the same number of
electron/hole flow as each of the others. Now, take those
hundred squares and arrange them so they make an approximate
circle (as in the cross sectional area of a wire). Each square
foot of area still passes the same amount of current.
Then, if you look at the very center, there is only one square
foot of area tha can occupy the exact center. But, around the
outside perimeter, it takes several square feet of area to make
it all the way around the perimeter.
Therefore, if you take an area on the outside of our gigantic
wire on the outermost surface, it has many, many square feet of
area, and thus a lot more current passing through it than the
single square foot that occupies the center-most area. But, if
you limited the area you're looking ato to jsut one foot in
width, not the whole perimeter, it would be carrying the exact
same current as the square foot in the center.
THAT is why people get confused and think it's skin-effect,
which it is not. But, obviously, around the entire full outside
of the circle, there is a lot more current moving than in the
tiny center because of the greater number of square feet it takes
to make it round.
Hope that might help visualize it a little better?
Skin-effect is an entirely different phenominon and has no
relationship to what this anecdote describes. With skin effect,
current per square area of material is NOT the same - so, it's a
lot different. And, it takes high frequencies to make tha t
happen, but it's too much to go into here.
HTH,
Pop
| |
|
| Proctologically Violated©® wrote:
> Awl--
>
> I thought I had learned that conductors carried most of the electron flow on
> their surface, but recently was informed that this would only be true at
> high freq (skin effect). I disputed this via Coulombic forces, but then
> realized that maybe Coulomb's law does not apply to flowing current in a
> conductor--sumpn about hole current as well??
> But indeed, a wire carrying current to a bulb is not charged the way a
> capacitor is.
>
> But THEN,
> I just happened to be reading the 1996 edition of the NEC, and I noticed an
> unusual entry: Nickel plated wire has 3-4 TIMES the current-carrying
> capacity as regular copper wire.
>
> At first brush, this seemed to support my initial assertion, that conductors
> DO carry their charge on the surface.
> But THEN, I realized that nickel (likely) has lower conductivity than
> copper, so such an effect would appear odd even if current flow did tend
> toward the surface.
>
> Finally, I seem to remember the expression "current density" as a function
> of cross-sectional area, which would suggest current is distributed
> throughout the wire's cross section, not just on the surface.
>
> So what's up w/ nickel plated wire???
>
> In my 1920's house (Yonkers, NY), the service is solid #9 (!!! heavier than
> 10, but lighter than 8??), and it seems to be doing the job of #6 or #4
> wire. In fact, I believe *all* the wiring in the house (cloth-covered #14)
> is plated, and is also in very good shape--thank god. Splices are wire
> nutted AND soldered, as well.
>
> But back to the original topic:
> At DC, or 60 hz, is current density uniform throughout the wire's cross
> section? If not, what type of distribution does it have?
> Why does Coulomb's law moot in a current carrying conductor?
>
> TIA.
> --
> Mr. P.V.'d
> formerly Droll Troll
>
>
Forget skin effect at 60 hZ. The effect at such a low
frequency is of no practical concern. Even at the high
end of audio frequencies ~20kHz the effect is negligible.
Here's one audio site that makes that point:
http://www.audioholics.com/techtips...fect_Cables.htm
Watch for line wrap in the above.
Ed
| |
| Salmon Egg 2006-02-25, 2:21 am |
| On 2/24/06 9:37 PM, in article i2SLf.698$UN1.118@trndny08, "ehsjr"
<ehsjr@bellatlantic.net> wrote:
> Proctologically Violated©® wrote:
>
> Forget skin effect at 60 hZ. The effect at such a low
> frequency is of no practical concern. Even at the high
> end of audio frequencies ~20kHz the effect is negligible.
> Here's one audio site that makes that point:
> http://www.audioholics.com/techtips...ts/SkinEffect_C
> ables.htm
>
> Watch for line wrap in the above.
> Ed
I will take up a number of issues in sequence.
Forget about electrons, holes, and the like. They have no practical
significance in almost all cases except when ELECTRONIC DEVICE operation is
to be considered.
I don't believe the statement that nickel coated wire can higher currents
than uncoated copper. In most cases, the limitation is going to be the
maximum allowable temperature of the insulation. Skin depth is going to be
greater for nickel than for annealed pure copper because nickel has a lower
electrical conductivity. Countering that is the higher magnetic permeability
of nickel which will reduce skin depth. The nickel plating will dissipate
more power and reach a higher temperature than plain copper. In any event, I
would like to se a reliable citation.
Skin depth at 60Hz in copper is about 6 mm. While that is large compared to
typical wire radii in house wiring, it often cannot be neglected. That is
why why power transmission lines often are fabricated with steel cores clad
with copper or aluminum. Aluminum is preferred much of the time because of
its low density and greater skin depth.
Bill
-- Ferme le Bush
| |
|
|
"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C0253491.1B0DF%salmonegg@sbcglobal.net...
> On 2/24/06 9:37 PM, in article i2SLf.698$UN1.118@trndny08,
> "ehsjr"
> <ehsjr@bellatlantic.net> wrote:
>
>
> I will take up a number of issues in sequence.
>
> Forget about electrons, holes, and the like. They have no
> practical
> significance in almost all cases except when ELECTRONIC DEVICE
> operation is
> to be considered.
>
> I don't believe the statement that nickel coated wire can
> higher currents
> than uncoated copper. In most cases, the limitation is going to
> be the
> maximum allowable temperature of the insulation. Skin depth is
> going to be
> greater for nickel than for annealed pure copper because nickel
> has a lower
> electrical conductivity. Countering that is the higher magnetic
> permeability
> of nickel which will reduce skin depth. The nickel plating will
> dissipate
> more power and reach a higher temperature than plain copper. In
> any event, I
> would like to se a reliable citation.
>
> Skin depth at 60Hz in copper is about 6 mm. While that is large
> compared to
> typical wire radii in house wiring, it often cannot be
> neglected. That is
> why why power transmission lines often are fabricated with
> steel cores clad
> with copper or aluminum. Aluminum is preferred much of the time
> because of
> its low density and greater skin depth.
>
> Bill
>
> -- Ferme le Bush
>
>
Jeez, you've made some really bad rationalizations there! Better
go back to class for awhile!
| |
|
| Short of vaporization, and ignoring insulation, which is most definitely
not the subject of the OP's question, what exactly determines the
ampacity of a metal wire?
If it is not temperature, then what else is there?
Skin depth relates to resistance or impedance. These may influence the
suitability of a wire for a particular purpose, but they are not the
basis for ampacity ratings. There is no direct relationship between
resistance and ampacity if temperature is not considered.
A quick web search will reveal that nickel-plated copper wires DO carry
a higher temperature rating than tin-plated copper wires. Or, put
differently, they can carry higher currents at a particular temperature.
Look here, for example:
http://www.jamesmonroewire.com/conductors.html
Copper Conductor Information - Wire and Cable
Chuck
Salmon Egg wrote:
SNIP
>
> I don't believe the statement that nickel coated wire can higher currents
> than uncoated copper.
| |
|
| Salmon Egg wrote:
> On 2/24/06 9:37 PM, in article i2SLf.698$UN1.118@trndny08, "ehsjr"
> <ehsjr@bellatlantic.net> wrote:
>
>
>
>
> I will take up a number of issues in sequence.
>
<snipped issues not relating to skin effect>
>
> Skin depth at 60Hz in copper is about 6 mm.
Incorrect. It's > 9 mm
> While that is large compared to
> typical wire radii in house wiring, it often cannot be neglected. That is
> why why power transmission lines often are fabricated with steel cores clad
> with copper or aluminum. Aluminum is preferred much of the time because of
> its low density and greater skin depth.
So you are saying that *the reason* 60 Hz power transmission
lines are fabricated with steel cores clad with copper or
aluminum is *because* skin effect cannot be neglected in that
situation. And your reference for that is ?
Putting it another way, you imply that the transmission
line could not be made out of the same amount of copper that
is used in the cladded line you are talking about because of
losses due to skin effect. Do you have numbers that support
that idea?
With the lines you are talking about, would the greater
ductability and lower strength of a purely copper cable
(if it was made that way) preclude its use? Do you think
this might be a more compelling reason for using steel
core?
Ed
>
> Bill
>
> -- Ferme le Bush
>
>
| |
| Roy L. Fuchs 2006-02-25, 7:21 pm |
| On Sat, 25 Feb 2006 21:09:06 GMT, ehsjr <ehsjr@bellatlantic.net> Gave
us:
>Salmon Egg wrote:
>
><snipped issues not relating to skin effect>
>
>
>Incorrect. It's > 9 mm
>
>
>So you are saying that *the reason* 60 Hz power transmission
>lines are fabricated with steel cores clad with copper or
>aluminum is *because* skin effect cannot be neglected in that
>situation. And your reference for that is ?
>
>Putting it another way, you imply that the transmission
>line could not be made out of the same amount of copper that
>is used in the cladded line you are talking about because of
>losses due to skin effect. Do you have numbers that support
>that idea?
>
>With the lines you are talking about, would the greater
>ductability and lower strength of a purely copper cable
>(if it was made that way) preclude its use? Do you think
>this might be a more compelling reason for using steel
>core?
>
High tension lines are just that. Very high tensile forces are on
the line. That is why it HAS to be steel cables. The point at which
at attaches to the towers has several thousand pounds of weight
hanging on it. Aluminum or copper either one would creep and cause
breaks in the line. 5mm of Aluminum cladding reduces the resistance of
a tower to tower traverse quite a bit at 60Hz. Way better than plain
steel.
The aluminum, or copper cladding IS for better conduction. Even
though losses at such high voltages are not that great, minimizing
them is STILL part of the job, and in the case of high tension lines
at 60Hz, cladding the cable in a better conductor such as aluminum or
copper does make a better transmission line. Remember also that the
lines are grouped in bundles of 3 or 4 cables, separated by a few
inches of air, between towers. So they maximize the tower's capacity
for weight, and they maximize the amount of aluminum or copper that is
actually carrying flow, getting the most out of the tensile capacity
the steel core wire has.
So three or four resistors (wires) in parallel from tower to tower
to tower gives us the least lossy solution for passing the juice from
point to point.
| |
| Salmon Egg 2006-02-26, 4:21 am |
| On 2/25/06 4:39 AM, in article RdYLf.1271$AZ1.786@trndny07, "Pop"
<nobody@devnull.spamcop.net> wrote:
> Jeez, you've made some really bad rationalizations there! Better
> go back to class for awhile!
Please be more speciofic.
Bill
-- Ferme le Bush
| |
| Salmon Egg 2006-02-26, 4:21 am |
| On 2/25/06 1:09 PM, in article SH3Mf.3535$UN1.2478@trndny08, "ehsjr"
<ehsjr@bellatlantic.net> wrote:
>
> So you are saying that *the reason* 60 Hz power transmission
> lines are fabricated with steel cores clad with copper or
> aluminum is *because* skin effect cannot be neglected in that
> situation. And your reference for that is ?
>
> Putting it another way, you imply that the transmission
> line could not be made out of the same amount of copper that
> is used in the cladded line you are talking about because of
> losses due to skin effect. Do you have numbers that support
> that idea?
>
> With the lines you are talking about, would the greater
> ductability and lower strength of a purely copper cable
> (if it was made that way) preclude its use? Do you think
> this might be a more compelling reason for using steel
> core?
The purpose of the steel core is to provide the tensile strength that allows
longer spans (fewer towers) and less thermal expansion. Because of skin
effect, copper in the center of a large conductor is wasted. Skin depth is
about 6 mm. How much steel core and haw much copper or aluminum is placed on
top of the core is an economic decision. Remember that the radii of
conductors could be in the neighborhood of 20mm.
If copper were very cheap and spans small, wasting a bit of conducting metal
would not be a big deal.
Bill
-- Ferme le Bush
| |
|
| chuck wrote:
> Short of vaporization, and ignoring insulation, which is most definitely
> not the subject of the OP's question, what exactly determines the
> ampacity of a metal wire?
>
> If it is not temperature, then what else is there?
>
> Skin depth relates to resistance or impedance. These may influence the
> suitability of a wire for a particular purpose, but they are not the
> basis for ampacity ratings. There is no direct relationship between
> resistance and ampacity if temperature is not considered.
>
> A quick web search will reveal that nickel-plated copper wires DO carry
> a higher temperature rating than tin-plated copper wires. Or, put
> differently, they can carry higher currents at a particular temperature.
> Look here, for example:
>
> http://www.jamesmonroewire.com/conductors.html
> Copper Conductor Information - Wire and Cable
>
> Chuck
>
Copper wire run at high temperature will oxidize badly and that is the
limiting factor. I believe nickle-plated wire can operate at higher
temperatures without oxidizing. Same is true with high temp crimp lugs.
High temp nickle-plated wire will of course have high temp insulation.
bud--
| |
| Paul Hovnanian P.E. 2006-02-26, 5:21 pm |
| "Proctologically Violated©®" wrote:
>
> Awl--
>
> I thought I had learned that conductors carried most of the electron flow on
> their surface, but recently was informed that this would only be true at
> high freq (skin effect). I disputed this via Coulombic forces, but then
> realized that maybe Coulomb's law does not apply to flowing current in a
> conductor--sumpn about hole current as well??
> But indeed, a wire carrying current to a bulb is not charged the way a
> capacitor is.
>
> But THEN,
> I just happened to be reading the 1996 edition of the NEC, and I noticed an
> unusual entry: Nickel plated wire has 3-4 TIMES the current-carrying
> capacity as regular copper wire.
>
> At first brush, this seemed to support my initial assertion, that conductors
> DO carry their charge on the surface.
> But THEN, I realized that nickel (likely) has lower conductivity than
> copper, so such an effect would appear odd even if current flow did tend
> toward the surface.
>
> Finally, I seem to remember the expression "current density" as a function
> of cross-sectional area, which would suggest current is distributed
> throughout the wire's cross section, not just on the surface.
>
> So what's up w/ nickel plated wire???
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.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Programmers don't die, they just GOSUB without RETURN.
| |
| Paul Hovnanian P.E. 2006-02-26, 6:21 pm |
| "Roy L. Fuchs" wrote:
>
> On Sat, 25 Feb 2006 21:09:06 GMT, ehsjr <ehsjr@bellatlantic.net> Gave
> us:
>
>
> High tension lines are just that. Very high tensile forces are on
> the line. That is why it HAS to be steel cables. The point at which
> at attaches to the towers has several thousand pounds of weight
> hanging on it. Aluminum or copper either one would creep and cause
> breaks in the line. 5mm of Aluminum cladding reduces the resistance of
> a tower to tower traverse quite a bit at 60Hz. Way better than plain
> steel.
>
> The aluminum, or copper cladding IS for better conduction. Even
> though losses at such high voltages are not that great, minimizing
> them is STILL part of the job, and in the case of high tension lines
> at 60Hz, cladding the cable in a better conductor such as aluminum or
> copper does make a better transmission line. Remember also that the
> lines are grouped in bundles of 3 or 4 cables, separated by a few
> inches of air, between towers. So they maximize the tower's capacity
> for weight, and they maximize the amount of aluminum or copper that is
> actually carrying flow, getting the most out of the tensile capacity
> the steel core wire has.
All correct, except that the reason for the multiple phase conductors
has to do with the system voltage, not skin effect. At high voltages,
the E field strength in the vicinity of a small radius conductor will
exceed the ionization potential of the surrounding air. This ionization
will result in power loss (it can be modeled by an equivalent resistance
from conductor to ground per mile). A conductor bundle simulates a
single conductor with a diameter equivalent to the bundle spacing. The
field strength around this larger radius 'surface' is reduced below the
ionization potential.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
It is not enough to succeed. Others must fail. -- Gore Vidal
| |
| Don Kelly 2006-02-26, 9:21 pm |
| "Paul Hovnanian P.E." <Paul@Hovnanian.com> wrote in message
news:44021CE5.DAD083C0@Hovnanian.com...
> "Roy L. Fuchs" wrote:
>
> All correct, except that the reason for the multiple phase conductors
> has to do with the system voltage, not skin effect. At high voltages,
> the E field strength in the vicinity of a small radius conductor will
> exceed the ionization potential of the surrounding air. This ionization
> will result in power loss (it can be modeled by an equivalent resistance
> from conductor to ground per mile). A conductor bundle simulates a
> single conductor with a diameter equivalent to the bundle spacing. The
> field strength around this larger radius 'surface' is reduced below the
> ionization potential.
In addition, the use of bundled conductors appreciably reduces the series
inductance of the line even though it does produce a small increase in
capacitance to ground and ground level fields. This is not a negligable
factor.
--
Don Kelly @shawcross.ca
remove the X to answer
----------------------------
>
>
> --
> Paul Hovnanian mailto:Paul@Hovnanian.com
> ------------------------------------------------------------------
> It is not enough to succeed. Others must fail. -- Gore Vidal
| |
| Don Kelly 2006-02-26, 9:21 pm |
| ----------------------------
"Pop" <nobody@devnull.spamcop.net> wrote in message
news:5HPLf.868$AZ1.431@trndny07...
>
> "Proctologically Violated©®" <physical@erols.com> wrote in message
> news:_eWdnZrPoJBtCGLenZ2dnUVZ_tSdnZ2d@rcn.net...
> ...
> Per cubic volume, or square if you prefer a 2-D visualization, the current
> passing thru a material is the same. A square foot cross sectional area
> of a material, regardless of its shape allows electron/hole flow at a
> consistant rate throughout its area.
>
> Say you have a cross sectional area of 100 pieces of one square foot.
> Each square foot of area is allowing the same number of electron/hole flow
> as each of the others. Now, take those hundred squares and arrange them
> so they make an approximate circle (as in the cross sectional area of a
> wire). Each square foot of area still passes the same amount of current.
> Then, if you look at the very center, there is only one square foot of
> area tha can occupy the exact center. But, around the outside perimeter,
> it takes several square feet of area to make it all the way around the
> perimeter.
> Therefore, if you take an area on the outside of our gigantic wire on
> the outermost surface, it has many, many square feet of area, and thus a
> lot more current passing through it than the single square foot that
> occupies the center-most area. But, if you limited the area you're
> looking ato to jsut one foot in width, not the whole perimeter, it would
> be carrying the exact same current as the square foot in the center.
> THAT is why people get confused and think it's skin-effect, which it is
> not. But, obviously, around the entire full outside of the circle, there
> is a lot more current moving than in the tiny center because of the
> greater number of square feet it takes to make it round.
>
> Hope that might help visualize it a little better?
>
> Skin-effect is an entirely different phenominon and has no relationship to
> what this anecdote describes. With skin effect, current per square area
> of material is NOT the same - so, it's a lot different. And, it takes
> high frequencies to make tha t happen, but it's too much to go into here.
>
> HTH,
>
> Pop
>
Unfortunately, except at DC, that is not true. For AC there are inductive
effects and one result of this is a non-uniform current density
distribution. For 60 Hz, except for large diameter conductors, this is
negligable as the "depth" is larger than the conductor. A related
phenomena is proximity effect where the current in one conductor modifies
the current distribution in another conductor.
--
Don Kelly @shawcross.ca
remove the X to answer
| |
| ehsjr 2006-02-27, 12:21 am |
| Salmon Egg wrote:
> On 2/25/06 1:09 PM, in article SH3Mf.3535$UN1.2478@trndny08, "ehsjr"
> <ehsjr@bellatlantic.net> wrote:
>
>
>
>
> The purpose of the steel core is to provide the tensile strength that allows
> longer spans (fewer towers) and less thermal expansion.
Exactly. The steel is required for strength, *not* to increase
the amount of copper at the surface. The copper at the surface
is required to reduce the electrical resistance of the cable,
as copper or aluminium is a much better conductor than steel.
> Because of skin
> effect, copper in the center of a large conductor is wasted.
Your are comparing steel clad copper versus copper clad steel,
by implication. Do you seriously believe that, for a given
core diameter and a given cladding thickness, a copper core,
steel clad cable would be as strong as a steel core, copper
clad cable for the transmission lines we're talking about?
Whether copper in the center would be wasted or not is
irrelevant. The need for a large steel core for strength
puts the copper or aluminum on the surface in the first
place, so there is no need to consider skin effect.
Ed
Skin depth is
> about 6 mm. How much steel core and haw much copper or aluminum is placed on
> top of the core is an economic decision. Remember that the radii of
> conductors could be in the neighborhood of 20mm.
>
> If copper were very cheap and spans small, wasting a bit of conducting metal
> would not be a big deal.
>
> Bill
> -- Ferme le Bush
>
>
| |
| Salmon Egg 2006-02-27, 1:21 am |
| On 2/26/06 4:26 PM, in article BGrMf.75842$H%4.60848@pd7tw2no, "Don Kelly"
<dhky@shaw.ca> wrote:
>
> In addition, the use of bundled conductors appreciably reduces the series
> inductance of the line even though it does produce a small increase in
> capacitance to ground and ground level fields. This is not a negligable
> factor.
It may be so, but it is not immediately obvious to me that parallel bundles
of spaced wires will lower the electric field at the cylindrical surfaces.
Locally, the cylindrical surface of the individual conductor is going to
have the same radius as the conductor. To convince me, I would have to go
through a Schwarz transformation to solve the two dimensional potential
problem. I am not moved to do that.
Except for the skin effect, the velocity of propagation in the TEM mode
along the line will be the speed of light. This means that the product of
inductance and capacitance of the line stays relatively constant.
Bill
-- Ferme le Bush
| |
| Salmon Egg 2006-02-27, 1:21 am |
| On 2/26/06 7:51 PM, in article fHuMf.1060$FY1.982@trndny06, "ehsjr"
<ehsjr@bellatlantic.net> wrote:
> Salmon Egg wrote:
>
> Exactly. The steel is required for strength, *not* to increase
> the amount of copper at the surface. The copper at the surface
> is required to reduce the electrical resistance of the cable,
> as copper or aluminium is a much better conductor than steel.
>
>
>
> Your are comparing steel clad copper versus copper clad steel,
> by implication. Do you seriously believe that, for a given
> core diameter and a given cladding thickness, a copper core,
> steel clad cable would be as strong as a steel core, copper
> clad cable for the transmission lines we're talking about?
I hope this statement is not attributed to me because I never considered
steel clad copper.
>
> Whether copper in the center would be wasted or not is
> irrelevant. The need for a large steel core for strength
> puts the copper or aluminum on the surface in the first
> place, so there is no need to consider skin effect.
Central copper in large conductors is wasted! Skin effect can be
significant. Thin copper cladding on steel is often used for antennas where
the skin effect would make thick cladding very wasteful indeed.
Skin effect also shows up in large ac electrical machines. To use the copper
effectively, it is broken up into smaller separate conductors that are
smaller than the skin depth. These conductors are insulated from each other
and transposed. It is, in a sense, the machine analog of litz wire.
Bill[color=darkred]
>
> Ed
>
>
> Skin depth is
| |
| Don Kelly 2006-02-27, 2:21 am |
| ----------------------------
"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C02699F1.1B12D%salmonegg@sbcglobal.net...
> On 2/25/06 1:09 PM, in article SH3Mf.3535$UN1.2478@trndny08, "ehsjr"
> <ehsjr@bellatlantic.net> wrote:
>
>
> The purpose of the steel core is to provide the tensile strength that
> allows
> longer spans (fewer towers) and less thermal expansion. Because of skin
> effect, copper in the center of a large conductor is wasted. Skin depth is
> about 6 mm. How much steel core and haw much copper or aluminum is placed
> on
> top of the core is an economic decision. Remember that the radii of
> conductors could be in the neighborhood of 20mm.
>
> If copper were very cheap and spans small, wasting a bit of conducting
> metal
> would not be a big deal.
>
> Bill
> -- Ferme le Bush
>
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
remove the X to answer
| |
| Don Kelly 2006-02-27, 3:21 am |
| ----------------------------
"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C027C1C3.1B7A0%salmonegg@sbcglobal.net...
> On 2/26/06 4:26 PM, in article BGrMf.75842$H%4.60848@pd7tw2no, "Don Kelly"
> <dhky@shaw.ca> wrote:
>
>
> It may be so, but it is not immediately obvious to me that parallel
> bundles
> of spaced wires will lower the electric field at the cylindrical surfaces.
> Locally, the cylindrical surface of the individual conductor is going to
> have the same radius as the conductor. To convince me, I would have to go
> through a Schwarz transformation to solve the two dimensional potential
> problem. I am not moved to do that.
>
> Except for the skin effect, the velocity of propagation in the TEM mode
> along the line will be the speed of light. This means that the product of
> inductance and capacitance of the line stays relatively constant.
>
> Bill
>
> -- Ferme le Bush
>
I have done it the easy way -through computer modelling. The model used is
valid, external to the conductors, for multiple conductors above a ground
plane. The assumption in the program is that the charge of a conductor is at
its center, which is excellent for the typical distances involved -the
distance between the line charge location within the conductor to make it
an equipotential surface, and the true center of the conductor is
negligable. Corrections can be made but except for special cases such as
cables where distances are short, there is no point in doing so.
Input information is dimensional data (radii, height above ground plane,
spacing, etc) and voltage (instantaneous or rms) of each conductor with
respect to ground. There will be a reduction in surface E field and in a
short distance from the conductor bundle,-say 2 or 3 bundle radii- the field
will be near that of a single conductor of much large radius . Here is a
simple case. Single conductor radius 2 cm at height 10m and voltage of 100kv
surface field under conductor is 724.+ kV/m and at side it is 723+ kV
Two conductors, same size and voltage, spaced 30cm apart
field below =453kV/m, inside =418 kV/m and outside 478 kV/m
I also see that the charge on each conductor is appreciably lower than that
on the single conductor at the same voltage although the total charge is
greater.
The effective radius of the bundle is about 7.75cm in this case.
The ground level field is increased slightly in the bundled case as the
field is a bit more uniform. The line capacitance is increased by bundling
and the inductance is decreased. The decrease in line inductance is of more
importance, in most cases, than the increase in C. Note that in general
capacitance is based on the conductor radius while, for inductance, the
concept of GMR is considered and this takes into account internal flux
linkages. For ACSR, the GMR is measured but it can be calculated different
geometries in the absence of magnetic materials.
--
Don Kelly @shawcross.ca
remove the X to answer
| |
|
| ....
>
> Unfortunately, except at DC, that is not true. For AC there are
> inductive effects and one result of this is a non-uniform
> current density distribution. For 60 Hz, except for large
> diameter conductors, this is negligable as the "depth" is
> larger than the conductor. A related phenomena is proximity
> effect where the current in one conductor modifies the current
> distribution in another conductor.
No. It is true to all but the most extreme purists of the world
who will waste much time and energy on things that are not
discernible in the real world. At 60 Hz and much, much higher
frequencies, it will take some very expensive equipment to even
theorize the still negligible effects of it. People who think
like this are of no practical use for such areas as this thread;
it's been pretty well pointed out.
You sound like the kind who will claim your weight also varies
because you go from the first to the second floor of a building;
true, but of no use to anyone but an extreme purist or anecdotal
collector of trivia, just as your weight "changes" when you walk
into a tunnel but don't change your relation to the center of the
earth. interesting but useless information to the real world.
Pop
| |
| aholland51@cogeco.ca 2006-02-27, 11:21 am |
| 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
| |
| daestrom 2006-02-27, 6:21 pm |
|
"Pop" <nobody@devnull.spamcop.net> wrote in message
news:rIDMf.1389$%a2.539@trndny05...
> ...
>
> No. It is true to all but the most extreme purists of the world who will
> waste much time and energy on things that are not discernible in the real
> world. At 60 Hz and much, much higher frequencies, it will take some very
> expensive equipment to even theorize the still negligible effects of it.
> People who think like this are of no practical use for such areas as this
> thread; it's been pretty well pointed out.
Yeah, right. "Standard Handbook for Electrical Engineers, Ninth Edition" (a
really old copy), Tables 13-8 and 13-9 so DC, 25Hz, 50Hz and 60Hz
resistances for large cables.
For example, ACRS 900,000 circular mils, 0.115, 0.116, 0.118 and 0.119 ohms
per mile per conductor. 3.5% difference may not be anything *you* care
about, but some of us work with cables larger than what you work with. The
larger cables most definitely do have a difference resistance thanks to
skin-effect.
Building transmission lines is considered a 'practical use' by most folks.
daestrom
| |
| daestrom 2006-02-27, 6:21 pm |
|
"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:fHuMf.1060$FY1.982@trndny06...
> Salmon Egg wrote:
>
> Exactly. The steel is required for strength, *not* to increase
> the amount of copper at the surface. The copper at the surface
> is required to reduce the electrical resistance of the cable,
> as copper or aluminium is a much better conductor than steel.
>
>
>
> Your are comparing steel clad copper versus copper clad steel,
> by implication. Do you seriously believe that, for a given
> core diameter and a given cladding thickness, a copper core,
> steel clad cable would be as strong as a steel core, copper
> clad cable for the transmission lines we're talking about?
>
> Whether copper in the center would be wasted or not is
> irrelevant. The need for a large steel core for strength
> puts the copper or aluminum on the surface in the first
> place, so there is no need to consider skin effect.
>
He didn't explicitly mention steel clad copper.
But he may be referring to bus-work used in substations. For short runs
between circuit-breakers, lightning arrestors, disconnects and other
components, you will often see hollow tubing used for the conductors. If
the same cross-sectional area of material were in the form of a solid bar,
it would have higher resistance owing to the skin effect. By simply
reshaping the material into a tube with a larger OD, more material is in the
region near the 'skin', providing lower resistance.
(the tube also has more structural strength than a solid bar of the same
material cross-section).
daestrom
| |
| Salmon Egg 2006-02-27, 7:21 pm |
| On 2/26/06 10:40 PM, in article M9xMf.76311$H%4.16564@pd7tw2no, "Don Kelly"
<dhky@shaw.ca> wrote:
>
> I have done it the easy way -through computer modelling. The model used is
> valid, external to the conductors, for multiple conductors above a ground
> plane. The assumption in the program is that the charge of a conductor is at
> its center, which is excellent for the typical distances involved -the
> distance between the line charge location within the conductor to make it
> an equipotential surface, and the true center of the conductor is
> negligable. Corrections can be made but except for special cases such as
> cables where distances are short, there is no point in doing so.
> Input information is dimensional data (radii, height above ground plane,
> spacing, etc) and voltage (instantaneous or rms) of each conductor with
> respect to ground. There will be a reduction in surface E field and in a
> short distance from the conductor bundle,-say 2 or 3 bundle radii- the field
> will be near that of a single conductor of much large radius . Here is a
> simple case. Single conductor radius 2 cm at height 10m and voltage of 100kv
> surface field under conductor is 724.+ kV/m and at side it is 723+ kV
> Two conductors, same size and voltage, spaced 30cm apart
> field below =453kV/m, inside =418 kV/m and outside 478 kV/m
> I also see that the charge on each conductor is appreciably lower than that
> on the single conductor at the same voltage although the total charge is
> greater.
> The effective radius of the bundle is about 7.75cm in this case.
> The ground level field is increased slightly in the bundled case as the
> field is a bit more uniform. The line capacitance is increased by bundling
> and the inductance is decreased. The decrease in line inductance is of more
> importance, in most cases, than the increase in C. Note that in general
> capacitance is based on the conductor radius while, for inductance, the
> concept of GMR is considered and this takes into account internal flux
> linkages. For ACSR, the GMR is measured but it can be calculated different
> geometries in the absence of magnetic materials.
I was thinking a bit more about this and have resolved the paradox in my
mind.
For a given power capacity of a line, the voltage required is going to be
proportional to V^2/Zo. By putting multiple conductors in parallel, (per
unit length) the inductance is decreased while the capacitance is increased.
This lowers the characteristic impedance of the line. Thus, the voltage
required to transmit the original power is dropped, and the likelihood of
corona is diminished.
Bill
-- Ferme le Bush
| |
|
| OK, I'll rephrase and say what I meant, politeness aside since
you're so thick: Idiots who depart substantially from the post
topic in order to attempt a shot at some sort of infamy whether
it be good or negative in nature, and which serves to do nothing
but confuse and create a sense of information based on
misinformation, and under the guise of being a know it all. If
you were a fraction of what you say you are, you'd have a lot
more things to do than puppet around these groups.
There's no future in discussing anything further here as I
consider you to be an intentional moron in this area. Too bad
you never went to a real school.
Pop
"daestrom"daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
news:boKMf.34905$j53.21103@twister.nyroc.rr.com...
>
> "Pop" <nobody@devnull.spamcop.net> wrote in message
> news:rIDMf.1389$%a2.539@trndny05...
>
> Yeah, right. "Standard Handbook for Electrical Engineers,
> Ninth Edition" (a really old copy), Tables 13-8 and 13-9 so DC,
> 25Hz, 50Hz and 60Hz resistances for large cables.
>
> For example, ACRS 900,000 circular mils, 0.115, 0.116, 0.118
> and 0.119 ohms per mile per conductor. 3.5% difference may not
> be anything *you* care about, but some of us work with cables
> larger than what you work with. The larger cables most
> definitely do have a difference resistance thanks to
> skin-effect.
>
> Building transmission lines is considered a 'practical use' by
> most folks.
>
> daestrom
>
| |
|
|
"daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
news:vvKMf.34906$j53.13408@twister.nyroc.rr.com...
>
> "ehsjr" <ehsjr@bellatlantic.net> wrote in message
> news:fHuMf.1060$FY1.982@trndny06...
>
> 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
>
Previous point proven.
| |
|
|
"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C028C112.1B7FA%salmonegg@sbcglobal.net...
> On 2/26/06 10:40 PM, in article M9xMf.76311$H%4.16564@pd7tw2no,
> "Don Kelly"
> <dhky@shaw.ca> wrote:
>
>
> I was thinking a bit more about this and have resolved the
> paradox in my
> mind.
>
> For a given power capacity of a line, the voltage required is
> going to be
> proportional to V^2/Zo. By putting multiple conductors in
> parallel, (per
> unit length) the inductance is decreased while the capacitance
> is increased.
> This lowers the characteristic impedance of the line. Thus, the
> voltage
> required to transmit the original power is dropped, and the
> likelihood of
> corona is diminished.
>
> Bill
> -- Ferme le Bush
>
Actually, that's not bad; good going!
Pop
| |
| Paul Hovnanian P.E. 2006-02-27, 11:21 pm |
| aholland51@cogeco.ca wrote:
>
> Meaningless questions like this from extremely uninformed people come
> up all the time.
>
> It doesn't stop well informed, well intentioned people trying to read
> minds and rushing in with replies. Stop here.
You're right. We shouldn't be answering questions for people unless they
already know the answer.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
On a clear desk, you can sleep forever.
| |
| Don Kelly 2006-02-28, 12:21 am |
| ----------------------------
"Pop" <nobody@devnull.spamcop.net> wrote in message
news:rIDMf.1389$%a2.539@trndny05...
> ...
>
> No. It is true to all but the most extreme purists of the world who will
> waste much time and energy on things that are not discernible in the real
> world. At 60 Hz and much, much higher frequencies, it will take some very
> expensive equipment to even theorize the still negligible effects of it.
> People who think like this are of no practical use for such areas as this
> thread; it's been pretty well pointed out.
> You sound like the kind who will claim your weight also varies because
> you go from the first to the second floor of a building; true, but of no
> use to anyone but an extreme purist or anecdotal collector of trivia, just
> as your weight "changes" when you walk into a tunnel but don't change your
> relation to the center of the earth. interesting but useless information
> to the real world.
>
> Pop
If you had cared to read what I said. you would have seen that I indicated
that for most conductors, the effect is negligable at 60Hz. That doesn't
mean that it isn't there, it simply means that it can be ignored.
By the way, how does it take expensive equipment to "theorise" this effect?
Rudenberg and others did it with pencil, paper and brains in the 20's and
30's.
--
Don Kelly @shawcross.ca
remove the X to answer
>
>
| |
| Don Kelly 2006-02-28, 1:21 am |
| ----------------------------
"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C028C112.1B7FA%salmonegg@sbcglobal.net...
> On 2/26/06 10:40 PM, in article M9xMf.76311$H%4.16564@pd7tw2no, "Don
> Kelly"
> <dhky@shaw.ca> wrote:
>
>
> I was thinking a bit more about this and have resolved the paradox in my
> mind.
>
> For a given power capacity of a line, the voltage required is going to be
> proportional to V^2/Zo. By putting multiple conductors in parallel, (per
> unit length) the inductance is decreased while the capacitance is
> increased.
> This lowers the characteristic impedance of the line. Thus, the voltage
> required to transmit the original power is dropped, and the likelihood of
> corona is diminished.
>
> Bill
> -- Ferme le Bush
That too- and it is a fact. Single conductor lines may have a Zo of the
order of 350-400 ohms while a 3 or 4 conductor bundle line will have Zo
nearer to 250-300 ohms.
Of course, spacing and height have an effect as well.
Reduction of corona does occur with bundling but not due to any reduction
of voltage at any power level. A voltage is chosen that is economical for
the power level and the line design follows from that. Corona is only one
concern involved.
A lot of concepts that are extremely useful in communications are of more
limited use in power transmission (well under 1/4 wavelength without
sectionalization and compensation). One such is impedance matching which is
simply not done. --
Don Kelly @shawcross.ca
remove the X to answer
>
| |
|
| daestrom wrote:
>
> "ehsjr" <ehsjr@bellatlantic.net> wrote in message
> news:fHuMf.1060$FY1.982@trndny06...
>
>
> 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
>
I thought large diameter tubing conductors in HV substations was mostly
for corona reduction.
bud--
| |
| Salmon Egg 2006-02-28, 6:21 pm |
| On 2/27/06 8:22 PM, in article weQMf.78742$H%4.46124@pd7tw2no, "Don Kelly"
<dhky@shaw.ca> wrote:
<sni>
> A lot of concepts that are extremely useful in communications are of more
> limited use in power transmission (well under 1/4 wavelength without
> sectionalization and compensation). One such is impedance matching which is
> simply not done. --
Although power lines ordinarily do not run with impedance matched loads, you
still have forward and backward traveling wave on the lines. Each of these
two waves individually does have voltage/current = the characteristic
impedance.
Bill
-- Ferme le Bush
| |
| daestrom 2006-02-28, 6:21 pm |
|
"Pop" <nobody@devnull.spamcop.net> wrote in message
news:qOLMf.676$v34.632@trndny02...
> OK, I'll rephrase and say what I meant, politeness aside since you're so
> thick: Idiots who depart substantially from the post topic in order to
> attempt a shot at some sort of infamy whether it be good or negative in
> nature, and which serves to do nothing but confuse and create a sense of
> information based on misinformation, and under the guise of being a know
> it all. If you were a fraction of what you say you are, you'd have a lot
> more things to do than puppet around these groups.
>
Nice try fool.
Topic is surface conduction at 60 hz.
It is an issue with transmission line sized conductors. It can change the
effective resistance of the conductors by several percent. It is often
mitigated by the use of hollow conductors.
ACRS has a steel strands for strength. Because skin effect makes the center
area less useful for conducting electricity anyway, ACRS is built with the
steel strands in the center.
Your point? You seem to be ranting about things and upset because several
others have told you you're wrong, and you just can't handle it.
> There's no future in discussing anything further here as I consider you to
> be an intentional moron in this area. Too bad you never went to a real
> school.
>
You'll never know how wrong you are....
daestrom
| |
|
| Salmon Egg wrote:
> On 2/26/06 7:51 PM, in article fHuMf.1060$FY1.982@trndny06, "ehsjr"
> <ehsjr@bellatlantic.net> wrote:
>
>
>
>
> I hope this statement is not attributed to me because I never considered
> steel clad copper.
It says, if you read it, *by implication*.
If you did not consider steel clad copper, then you realize
that the larger diameter is created for the strength that the
steel core offers. Therefore, since the diameter is already
increased for strength, the reason for increasing the diameter
*cannot* be skin effect. In other words, skin effect is negligible.
The resistance of the steel core, however, cannot be neglected.
That is why it is copper clad. Nothing to do with skin effect.
>
>
>
> Central copper in large conductors is wasted! Skin effect can be
> significant. Thin copper cladding on steel is often used for antennas where
> the skin effect would make thick cladding very wasteful indeed.
Of for goodness sake. We are talking about *60 Hz*. We are
*not* talking about antennas and hardline.
Enough, already. Post something real that demonstrates that
skin effect often cannot be neglected at 60 Hz.
>
> Skin effect also shows up in large ac electrical machines. To use the copper
> effectively, it is broken up into smaller separate conductors that are
> smaller than the skin depth. These conductors are insulated from each other
> and transposed. It is, in a sense, the machine analog of litz wire.
>
> Bill
>
>
>
| |
| Don Kelly 2006-03-01, 12:21 am |
| ----------------------------
"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C02A01E2.1B90A%salmonegg@sbcglobal.net...
> On 2/27/06 8:22 PM, in article weQMf.78742$H%4.46124@pd7tw2no, "Don Kelly"
> <dhky@shaw.ca> wrote:
>
> <sni>
>
>
> Although power lines ordinarily do not run with impedance matched loads,
> you
> still have forward and backward traveling wave on the lines. Each of these
> two waves individually does have voltage/current = the characteristic
> impedance.
>
> Bill
>
> -- Ferme le Bush
>
True but not really of use in analysis of a power line's performance. One
goes from distributed parameters ("telegrapher's equations") to a lumped
model for a given line. Consideration of a standing wave can be used for
estimation of mid-line voltages where needed but even this can be avoided
by simply using multiple pi sections. For switching and lightning surges,
the travelling wave model is used where necessary. Dr. Hermann Dommel did a
lot of work on this and the models have become quite sophisticated.
--
Don Kelly @shawcross.ca
remove the X to answer
| |
| Don Kelly 2006-03-01, 1:21 am |
| ----------------------------
"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:8l6Nf.2355$SJ2.422@trndny01...
> Salmon Egg wrote:
>
> It says, if you read it, *by implication*.
> If you did not consider steel clad copper, then you realize
> that the larger diameter is created for the strength that the
> steel core offers. Therefore, since the diameter is already
> increased for strength, the reason for increasing the diameter
> *cannot* be skin effect. In other words, skin effect is negligible.
> The resistance of the steel core, however, cannot be neglected.
> That is why it is copper clad. Nothing to do with skin effect.
>
>
>
> Of for goodness sake. We are talking about *60 Hz*. We are
> *not* talking about antennas and hardline.
>
> Enough, already. Post something real that demonstrates that
> skin effect often cannot be neglected at 60 Hz.
---------------
I just looked at a wire table:
There are or were AAC conductors and the AC/DC resistance for a 1 inch
diameter conductor(approx) is about 1.02. 2% isn't much. However, for a 2
inch diameter conductor the ratio is 1.31 and I don't think that 30% is
negligable.
For ACSR
Kiwi (44mm diameter) the AC/DC resistance ratio is 1.11
For Drake (28mm diameter) the ratio is 1.01
Compared to all- aluminum conductors- the AC/DC ratio is lower because, even
without any skin effect, the current flows mainly in the lower resistivity
aluminum.
Of course, none of these conductors are used for house wiring.
The point is that there are situations where 60Hz skin effect does have some
significance and there are lots more where it doesn't. It also happens
that design for strength or rigidity such as hollow tubes also mitigates
skin effect.
Bill's comment regarding coil construction in large machines is true- heavy
duty litz wire to try to get a more uniform current distribution in a coil.
--
Don Kelly @shawcross.ca
remove the X to answer
[color=darkred]
>
| |
| Salmon Egg 2006-03-01, 3:21 am |
| On 2/28/06 8:26 PM, in article 8o9Nf.82843$H%4.69488@pd7tw2no, "Don Kelly"
<dhky@shaw.ca> wrote:
> Bill's comment regarding coil construction in large machines is true- heavy
> duty litz wire to try to get a more uniform current distribution in a coil.
I should add, that the subdivision of conductors also reduces the proximity
effect. Sometimes that can be of greater import than the skin effect. In any
event, skin effect and proximity effect are both manifestations of eddy
currents.
Bill
-- Ferme le Bush
| |
| Roy L. Fuchs 2006-03-01, 9:21 am |
| On Mon, 27 Feb 2006 14:07:19 GMT, "Pop" <nobody@devnull.spamcop.net>
Gave us:
>You sound like the kind who will claim your weight also varies
>because you go from the first to the second floor of a building;
>true, but of no use to anyone but an extreme purist or anecdotal
>collector of trivia,
Whatever.
> just as your weight "changes" when you walk
>into a tunnel but don't change your relation to the center of the
>earth.
Wrong. If you did not change altitude from the outside of the tunnel
to the inside postilion, your weight does not change.
| |
| Roy L. Fuchs 2006-03-01, 10:21 am |
| On Mon, 27 Feb 2006 23:19:50 GMT, "Pop" <nobody@devnull.spamcop.net>
Gave us:
>OK, I'll rephrase and say what I meant, politeness aside since
>you're so thick: Idiots who depart substantially from the post
>topic in order to attempt a shot at some sort of infamy whether
>it be good or negative in nature, and which serves to do nothing
>but confuse and create a sense of information based on
>misinformation, and under the guise of being a know it all. If
>you were a fraction of what you say you are, you'd have a lot
>more things to do than puppet around these groups.
>
>There's no future in discussing anything further here as I
>consider you to be an intentional moron in this area. Too bad
>you never went to a real school.
>
>Pop
This guy is a real prize. Too bad he's dumber than dogshit.
| |
| Roy L. Fuchs 2006-03-01, 10:21 am |
| On Tue, 28 Feb 2006 03:55:36 GMT, "Don Kelly" <dhky@shaw.ca> Gave us:
>----------------------------
>"Pop" <nobody@devnull.spamcop.net> wrote in message
>news:rIDMf.1389$%a2.539@trndny05...
>
>
>If you had cared to read what I said. you would have seen that I indicated
>that for most conductors, the effect is negligable at 60Hz. That doesn't
>mean that it isn't there, it simply means that it can be ignored.
>By the way, how does it take expensive equipment to "theorise" this effect?
>Rudenberg and others did it with pencil, paper and brains in the 20's and
>30's.
Didn't you know? Pops considers himself to be "expensive equipment".
| |
| Roy L. Fuchs 2006-03-01, 10:21 am |
| On Tue, 28 Feb 2006 21:53:18 GMT, "daestrom"
<daestrom@NO_SPAM_HEREtwcny.rr.com> Gave us:
>
>"Pop" <nobody@devnull.spamcop.net> wrote in message
>news:qOLMf.676$v34.632@trndny02...
>
>Nice try fool.
>
>Topic is surface conduction at 60 hz.
>
>It is an issue with transmission line sized conductors. It can change the
>effective resistance of the conductors by several percent. It is often
>mitigated by the use of hollow conductors.
>
>ACRS has a steel strands for strength. Because skin effect makes the center
>area less useful for conducting electricity anyway, ACRS is built with the
>steel strands in the center.
>
>Your point? You seem to be ranting about things and upset because several
>others have told you you're wrong, and you just can't handle it.
>
>
>You'll never know how wrong you are....
>
True, because now that you are on the bandwagon of folks that have
told him he is wrong, he will filter you. He uses the typical
California way around truths. When in doubt, bail out.
I wish there weren't so many WUSSIES in the world!
Get in an argument with someone bigger than you, and they want to
resort to fisticuffs. Get in an argument with someone smaller than
you, and someone bigger butts in and claims you are picking on the
little guy. Get in an argument on Usenet, and the pussies run like
hell. The world needs a few more drill sergeants.
| |
| Roy L. Fuchs 2006-03-01, 10:21 am |
| On Wed, 01 Mar 2006 00:58:44 GMT, ehsjr <ehsjr@bellatlantic.net> Gave
us:
>
>It says, if you read it, *by implication*.
>If you did not consider steel clad copper, then you realize
>that the larger diameter is created for the strength that the
>steel core offers. Therefore, since the diameter is already
>increased for strength, the reason for increasing the diameter
>*cannot* be skin effect. In other words, skin effect is negligible.
>The resistance of the steel core, however, cannot be neglected.
>That is why it is copper clad. Nothing to do with skin effect.
NOT TRUE! First off, there are no steel clad copper cables. There
is no reason to place the poorer conductor on the outside of a cable,
and the CORE of a cable MUST have a higher tensile strength than the
jacket or the cable will fail to work as designed.
The thin steel CENTRAL "carrier strand" is just that... A CARRIER.
It bears the weight of the cable, NOT the current. It is the
mechanism for providing a strong tensile link between towers. It is
clad with copper not to make the cable bigger, but to make it conduct
better.
A steel cable WILL work fine at the voltages carried on those towers.
The benefit from having the copper cladding is that nearly ALL of the
current will be IN the copper, and SKIN EFFECT IS the reason the
current will be there, and IS the reason the industry clads steel
cables in copper for HV power transmission lines.
So, yes, the cable has a lower resistance, but much of that lower
resistance is due to skin effect, as it relates to the characteristic
impedance of a given segment of high tension cabling.
| |
| Roy L. Fuchs 2006-03-01, 10:21 am |
| On Wed, 01 Mar 2006 00:58:44 GMT, ehsjr <ehsjr@bellatlantic.net> Gave
us:
>Enough, already. Post something real that demonstrates that
>skin effect often cannot be neglected at 60 Hz.
It CAN be and IS negligible in low power applications or where the
conductor diameter is smaller than the skin depth times two.
When the cable size is great enough that the skin depth can be a
factor, it WILL be a factor, and IS a factor on large diameter high
voltage high tension power lines.
| |
| ehsjr 2006-03-01, 12:40 pm |
| Roy L. Fuchs wrote:
> On Wed, 01 Mar 2006 00:58:44 GMT, ehsjr <ehsjr@bellatlantic.net> Gave
> us:
>
>
>
>
> NOT TRUE! First off, there are no steel clad copper cables. There
> is no reason to place the poorer conductor on the outside of a cable,
> and the CORE of a cable MUST have a higher tensile strength than the
> jacket or the cable will fail to work as designed.
Exactly right. You seem to be the only one who understands
what is going on. Salmon egg seemed to imply that there might
be such a thing as steel clad copper cable.
>
> The thin steel CENTRAL "carrier strand" is just that... A CARRIER.
> It bears the weight of the cable, NOT the current. It is the
> mechanism for providing a strong tensile link between towers. It is
> clad with copper not to make the cable bigger, but to make it conduct
> better.
Exactly right.
>
> A steel cable WILL work fine at the voltages carried on those towers.
> The benefit from having the copper cladding is that nearly ALL of the
> current will be IN the copper, and SKIN EFFECT IS the reason the
> current will be there, and IS the reason the industry clads steel
> cables in copper for HV power transmission lines.
Here we may disagree, not in the facts, but in the rationale.
I think the disagreement is probably a nit, based on your
last paragraph, below. I'll address the apparent disagreement:
The steel cable already must be some specific diameter,
for strength. While steel would work, it doesn't work
well enough for the power utility economics. The steel
is too lossy. So they use copper clad to lower the resistance.
The reason it lowers the resistance is that copper is a better
conductor than steel.
>
> So, yes, the cable has a lower resistance, but much of that lower
> resistance is due to skin effect, as it relates to the characteristic
> impedance of a given segment of high tension cabling.
That's the key. You understand the issue. What would
be nice is some real world numbers. I assume that in
designing the cable, skin effect is taken into consideration
as one of the factors to determine how thick to make the
cladding. I suppose they could use a standard - make a steel
core big enough that could be clad with 9+ mm of copper -
but I doubt that's real world.
Ed
| |
| Keith Williams 2006-03-01, 1:21 pm |
| In article <8l6Nf.2355$SJ2.422@trndny01>, ehsjr@bellatlantic.net
says...
> Salmon Egg wrote:
<snip>
[color=darkred]
>
> Of for goodness sake. We are talking about *60 Hz*. We are
> *not* talking about antennas and hardline.
>
> Enough, already. Post something real that demonstrates that
> skin effect often cannot be neglected at 60 Hz.
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
| |
| Roy L. Fuchs 2006-03-02, 3:21 am |
| On Wed, 01 Mar 2006 15:43:55 GMT, ehsjr <ehsjr@bellatlantic.net> Gave
us:
>Roy L. Fuchs wrote:
>
>Exactly right. You seem to be the only one who understands
>what is going on. Salmon egg seemed to imply that there might
>be such a thing as steel clad copper cable.
>
>
>Exactly right.
>
>
>Here we may disagree, not in the facts, but in the rationale.
>I think the disagreement is probably a nit, based on your
>last paragraph, below. I'll address the apparent disagreement:
>The steel cable already must be some specific diameter,
>for strength. While steel would work, it doesn't work
>well enough for the power utility economics.
They used to be ALL steel. We used to cherish our copper a lot more
in the days of full metal jackets, and we went through 3 wars
conserving it monetarily and industrially as well. The losses are
very low when one considers the voltage. At 100,000 Volts a couple
hundred volts lost is a very low number. It DOES add up though, so
yes, using copper clad cables reduce those losses considerably.
The losses I can't stand is where in Ohio, I could walk past a high
tension line and NOT hear leakage, and that is a high humidity part of
the world. Here in California, I can walk past nearly ANY high
tension insulator and line, and hear it leaking badly. I'd say that
california loses 20% more juice to leakage than any other state I have
ever been in. They just don't service their lines.
WE PAY FOR THAT... so they don't care! That is the OTHER reason why
privately held utilities suck big time. The bastards are worse than
the worst NYC landlord that ever lived. Rent keeps going up... while
quality of service keeps going down. Major LAME.
The criminals of Enron and Sempra energy ought to be lined up at a
wall and stoned to death with very small stones... thrown very hard,
like from a paintball gun(s). Either way, I want have my payments
over the last seven years back. The bastards!
| |
|
| Keith XXXXXXXX wrote:
> In article <8l6Nf.2355$SJ2.422@trndny01>, ehsjr@bellatlantic.net
> 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.
>
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
| |
| daestrom 2006-03-02, 6:21 pm |
|
"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:%ijNf.7676$UN1.6231@trndny08...
> Roy L. Fuchs wrote:
>
> Exactly right. You seem to be the only one who understands
> what is going on. Salmon egg seemed to imply that there might
> be such a thing as steel clad copper cable.
>
>
> Exactly right.
>
>
> Here we may disagree, not in the facts, but in the rationale.
> I think the disagreement is probably a nit, based on your
> last paragraph, below. I'll address the apparent disagreement:
> The steel cable already must be some specific diameter,
> for strength. While steel would work, it doesn't work
> well enough for the power utility economics. The steel
> is too lossy. So they use copper clad to lower the resistance.
> The reason it lowers the resistance is that copper is a better
> conductor than steel.
>
>
>
> That's the key. You understand the issue. What would
> be nice is some real world numbers. I assume that in
> designing the cable, skin effect is taken into consideration
> as one of the factors to determine how thick to make the
> cladding. I suppose they could use a standard - make a steel
> core big enough that could be clad with 9+ mm of copper -
> but I doubt that's real world.
>
Skin effect is also a problem in the short runs of bus-work used in
substations. These do not have a steel core (no need for excessive tensile
strength), but the bus-work is *not* solid aluminum or copper rods. It is
aluminum tubing with a large ID. The tubing wall isn't more than about 1/2
inch thick (close to 9mm). For larger ampacities, larger diameter tubing is
used, not tubing with different wall thickness.
daestrom
| |
| Roy L. Fuchs 2006-03-02, 10:21 pm |
| On Thu, 02 Mar 2006 16:56:00 GMT, ehsjr <ehsjr@bellatlantic.net> Gave
us:
>Keith XXXXXXXX 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
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.
| |
| Paul Hovnanian P.E. 2006-03-02, 11:21 pm |
| "Roy L. Fuchs" wrote:
>
> On Thu, 02 Mar 2006 16:56:00 GMT, ehsjr <ehsjr@bellatlantic.net> Gave
> 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.
How about 'current density depth gradient'? That'll keep most of the
know-it-alls tongue-tied.
;-)
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Think honk if you're a telepath.
| |
| Roy L. Fuchs 2006-03-02, 11:21 pm |
| On Thu, 02 Mar 2006 18:31:32 -0800, "Paul Hovnanian P.E."
<Paul@Hovnanian.com> Gave us:
>"Roy L. Fuchs" wrote:
>
>How about 'current density depth gradient'? That'll keep most of the
>know-it-alls tongue-tied.
>
>;-)
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? :-]
| |
| Don Kelly 2006-03-03, 12:21 am |
| ----------------------------
"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:AsFNf.6248$dj2.5885@trndny04...
> Keith XXXXXXXX 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
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
remove the X to answer
| |
| Salmon Egg 2006-03-03, 2:21 am |
| On 3/2/06 7:31 PM, in article AMONf.89555$B94.21027@pd7tw3no, "Don Kelly"
<dhky@shaw.ca> wrote:
> How many power lines now use copper?
> I recall some relatively low voltage distribution lines using steel with a
> copper cladding but any "real" transmission line over the order of 30Kv uses
> ACSR (Aluminum Cable, steel reinforced. With such cables, the 60Hz skin
> effect is much smaller than with an all aluminum or all copper cable because
> the current will flow in the outer Aluminum layer even at DC (serendipity?).
> However, any table of parameters for such cable shows that AC resistance is
> higher than for DC- In essence the effect of skin effect, however slight, is
> accounted for in the stated resistance- so you don't even have to think
> about it.
>
> For example "Joree" has an AC/DC ratio of 1.05+ at 25C Mind you, the change
> in resistance in going from 25C to 75C is 15%.
>
> This is a very large conductor and is rarely, if ever, used now- but I have
> seen larger conductors in the supply from a hydro plant to a nearby
> aluminum smelter (at 13.8KV).
The skin depth in aluminum is somewhat greater than it is in copper because
Al has higher resistivity than Cu does. I don't know how economics factors
in, but the price of Cu has greatly increased the last few years. What
probably clinches the deal for Al is that its lower density allows for
larger diameter conductors. In turn, that allows higher conductance for the
conductors while also allowing increased separation between support towers.
Bill
-- Ferme le Bush
| |
| Don Kelly 2006-03-05, 1:21 am |
| ----------------------------
"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C02D171F.1BC88%salmonegg@sbcglobal.net...
> On 3/2/06 7:31 PM, in article AMONf.89555$B94.21027@pd7tw3no, "Don Kelly"
> <dhky@shaw.ca> wrote:
>
>
> 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
>
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
remove the X to answer
| |
| Uwe Hercksen 2006-03-14, 12:21 pm |
|
Salmon Egg schrieb:
>
> Skin depth at 60Hz in copper is about 6 mm. While that is large compared to
> typical wire radii in house wiring, it often cannot be neglected. That is
> why why power transmission lines often are fabricated with steel cores clad
> with copper or aluminum. Aluminum is preferred much of the time because of
> its low density and greater skin depth.
>
Hello,
the steel core is used to carry the mechanical tension.
Bye
|
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