Stupid question of the day....

[DBLEXPOSURE]

<snip>

It is not a stupid question--it is just irrelevant. Current flows in
various
ways, and in almost all cases, the details of the flow is unimportant. The
"wires" can be made from metals, semimetals, hot glass, semiconductors,
ionic solutions, etc. Each has a different kind of conduction mechanism.

I have taken the probably impossible task upon myself to discourage
thinking
of conduction as a flow of electrons.

Bill

Not so impossible. I think many think of the electron as some little
microscopic BB with a negative charge. It may be more accurate to think of
the buggers as a microscopic region of space/time with properties that give
it a negative charge among other properties. It takes an enormous amount of
mass to move space/time. It is the properties that are passed along the
way. A bit of an illusion perhaps.



So yes, I agree, not a flow of electrons but a flow of energy...



Whatever that is.....



It is all speculation of course. I have never seen an electron, Have you?


I don't think we should judge the OP on the relevancy of his question, as we
have no idea why he asked it...

 

[JoeSixPack]

wrong:
http://groups.google.com/group/sci....1738a7b007dc8c?lnk=st&rnum=1#f31738a7b007dc8c

We are indeed gifted to have so many brainiacs in here.

 

[Jasen Betts]

wrong:
http://groups.google.com/group/sci....1738a7b007dc8c?lnk=st&rnum=1#f31738a7b007dc8c

I looked at it, and you're right, the posting at that URL is wrong.
here's another time wasting URL http://www.geocities.com/jasen_betts/Autymn.txt

 

[Autymn D. C.]

---
Wrong.

Since an electron has a rest mass, m0, and since:


m0
mr = -------------------- ,
sqrt (1 - (v²/c²))


its relativistic mass, mr, will tend toward infinity as its
velocity, v, approaches that of light, c.

Read my proof or shut up. You do not even know what "tend" intends.

-Aut

 

[Dimitrios Tzortzakakis]

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

Most of the times this just aplies to AC (high frequency) circuits

Or of line-to-line voltage equal or above 220 kV.Therefore transmission
lines of 400 kV are always designed with a double conductor, thus to reduce
the corona discharge due to skin effect.

 

[Dimitrios Tzortzakakis]

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

Hmmm...

Copper does have a weak Hall effect. And the current through a round
wire does make a circular/transverse magnetic field. So, at very high
DC currents, is the current density a bit non-uniform?

Very high AC currents are much more common.The output of a moderate 300 MW
alternator is 10 kA at 21 kV.A nuclear power station alternator with a
voltage of 27 kV almost reaches 20kA, with a nominal power output of 1500
MVA.Always talking about balanced three-phase systems.The output of the 300
MW power-station at 400 kV transmission voltage is just 400 A.Conductors in
all LV circuits are made of electroletically purified solid copper, 99,99 %
Cu.In MV, HV and EHV distribution and transimission voltages respectively,
they use ACSR conductors (Aluminium Conductor Steel Reinforced)that have a
steel core, but an aluminium outer sheath.

 

[Dimitrios Tzortzakakis]

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
That can happen in high impulse short circuit currents.An unfused 220 V
circuit shortcircuited between live and earth, can have an impulse current
of 20 kA.Properly fused with a circuit breaker, up to 50 A.In normal
operating conditions, a transmission line of 150 kV operating at 200 A with
an ambient teperature of 20 deg.C (65deg.F)should not exceed 50
deg.C(105deg.F)however as it operates continually at these conditions the
temperature is uniform across the conductor (ACSR).

 

[John Fields]

Read my proof or shut up. You do not even know what "tend" intends.

---
I see. Instead of reason, you prefer insult.

I will neither read your "proof" nor will I shut up, and if you
don't like it, you miserable son of a bitch, you can go ****
yourself.

 

[John Fields]

John Fields wrote:

I would think that simple thermal effects would cause charge to flow
closer to the surface just because that part of the conductor would
be cooler, ergo lower resistance than the hotter interior.


To which Tzortzakakis Dimitrios replied:

That can happen in high impulse short circuit currents.An unfused
220 V
circuit shortcircuited between live and earth, can have an impulse
current
of 20 kA.Properly fused with a circuit breaker, up to 50 A.In normal
operating conditions, a transmission line of 150 kV operating at 200
A with
an ambient teperature of 20 deg.C (65deg.F)should not exceed 50
deg.C(105deg.F)however as it operates continually at these
conditions the
temperature is uniform across the conductor (ACSR).

---
I think you misunderstood my point, which was that the copper at the
surface of the conductor would, by virtue of radiation and
convection, be cooler than the copper at the center of the
conductor. Such being the case, the resistance of the cooler copper
at the surface would be less than the resistance of the copper in
the core, leading to a non-uniform radial current gradient in the
conductor.

 

[Alexander]

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

Or of line-to-line voltage equal or above 220 kV.Therefore transmission
lines of 400 kV are always designed with a double conductor, thus to
reduce
the corona discharge due to skin effect.

A tranismission line always has an AC element according to fourier Analysis.
Some times it is superimposed on an DC element but nearly always you want to
avoid this.

 

[Alexander]

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

Very high AC currents are much more common.The output of a moderate 300 MW
alternator is 10 kA at 21 kV.A nuclear power station alternator with a
voltage of 27 kV almost reaches 20kA, with a nominal power output of 1500
MVA.Always talking about balanced three-phase systems.The output of the
300
MW power-station at 400 kV transmission voltage is just 400 A.Conductors
in
all LV circuits are made of electroletically purified solid copper, 99,99
%
Cu.In MV, HV and EHV distribution and transimission voltages respectively,
they use ACSR conductors (Aluminium Conductor Steel Reinforced)that have a
steel core, but an aluminium outer sheath.

Sometimes you have something like Aluminium inside (for the weight) and
Cupper on the outside for conductivity. Due to the Skin Effect this is where
the most (AC) current will flow.
On some application I have even seen Cu on the inside and Au on the outside,
my guess there is at least one other material between the two for obvious
reasons.

Alexander (ACE, Applied Communications Engineer)

 

[John Fields]

Sometimes you have something like Aluminium inside (for the weight) and
Cupper on the outside for conductivity. Due to the Skin Effect this is where
the most (AC) current will flow.
On some application I have even seen Cu on the inside and Au on the outside,
my guess there is at least one other material between the two for obvious
reasons.

Really? The reasoning for that layering doesn't seem obvious to me,
so would you mind explaining it in greater detail?

 

[daestrom]

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

Or of line-to-line voltage equal or above 220 kV.Therefore transmission
lines of 400 kV are always designed with a double conductor, thus to
reduce
the corona discharge due to skin effect.

Oh boy, you have a 'couple of crossed wires' there.

"Skin effect" is the phenomenon where electric current flow is forced out
from the center of a conductor due to the self-inductance in the conductor
when carrying AC current. The higher the frequency, the more pronounced the
current shift to the exterior. It's mostly a problem with high current
situations, even if the voltages are so low that corona discharge is not a
problem.

"Corona discharge" is *NOT* caused by AC or skin effect. Corona discharge
is caused by a high voltage gradient in the space around a conductor. This
is a combination of the voltage applied to the conductor and the effective
radius of the conductor. A high voltage, or very small effective radius can
increase the gradient to the point where the air is ionized. Simple proof
is that corona discharge is a problem with high DC voltage systems as well
as AC.

Sometimes hollow tubes are used for high frequency power conductors. This
reduces the weight and cost by eliminating the central part of the
conductor, where 'skin effect' has rendered the impedence high anyway. So
little admittance is lost for a great savings in material/weight.

And for high voltage systems, multiple parallel conductors are used to give
a larger 'effective radius', thereby reducing the corona losses.

But the two phenomenon are not related, and the two techniques used are not
really related.

daestrom

 

[daestrom]

An interesting point. *IF* the current density is uniform across the
conductor, then the heat generated would be uniform in each unit
cross-section. And a uniform heat generation in a cylindrical rod leads to
a parabolic temperature profile, the highest exactly at the centerline,
dropping of as you move outward along any radial line.

Of course, in an AC line, the current density isn't uniform, so neither is
the heat generation. So when it comes to skin effect, it tends to lower the
peak, centerline temperature.

Now, given that both copper and aluminum are excellent heat conductors, it
might be interesting to calculate how big a temperature profile could be
expected, and from this calculate the variation in resistivity.

I suspect the work has been done before, and that the difference is rather
modest for all but the largest cylindrical conductors.

daestrom

 

[daestrom]

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

Very high AC currents are much more common.The output of a moderate 300 MW
alternator is 10 kA at 21 kV.A nuclear power station alternator with a
voltage of 27 kV almost reaches 20kA, with a nominal power output of 1500
MVA.

Yes, but most of the phase conductors that I've seen from large alternators
(500MW to 1200MW) to the step-up transformers are not simple round
conductors. In fact, rectangular tubing is used for the conductors (at
least those used in many nuclear stations). The tube is encased within an
outer 'pipe' and H2 is forced down the center of the tube to the end, where
it exits the tube and returns outside the tube within the outer pipe. Such
'isophase busses' are specifically designed to carry this large amount of
current just far enough to reach the main step-up transformer where it rises
from the nominal 25kv to 345kv or higher. The secondary is connected with
'normal' ACRS conductor to the remaining switch yard equipment.

daestrom

 

[TokaMundo]

An interesting point. *IF* the current density is uniform across the
conductor, then the heat generated would be uniform in each unit
cross-section. And a uniform heat generation in a cylindrical rod leads to
a parabolic temperature profile, the highest exactly at the centerline,
dropping of as you move outward along any radial line.

Of course, in an AC line, the current density isn't uniform, so neither is
the heat generation. So when it comes to skin effect, it tends to lower the
peak, centerline temperature.

Now, given that both copper and aluminum are excellent heat conductors, it
might be interesting to calculate how big a temperature profile could be
expected, and from this calculate the variation in resistivity.

I suspect the work has been done before, and that the difference is rather
modest for all but the largest cylindrical conductors.

For AC at this frequency there is nil skin effect.

Current in a wire will heat the wire evenly if it is of one
material. a cladded conductor will disperse heat according to the
thermal and electrical conductivities of the mediums that make up the
wire.

A copper cladded aluminum wire (never seen it) will heat more
inside as aluminum has poorer electrical conductivity and nearly
identical thermal conductivities. The result will *still* be even
heating for the most part.

An Aluminum cladded Copper conductor will heat evenly as the
differences are so slight as to make no difference.

 

[TokaMundo]

Oh boy, you have a 'couple of crossed wires' there.

"Skin effect" is the phenomenon where electric current flow is forced out
from the center of a conductor due to the self-inductance in the conductor
when carrying AC current. The higher the frequency, the more pronounced the
current shift to the exterior. It's mostly a problem with high current
situations, even if the voltages are so low that corona discharge is not a
problem.

It becomes more prevalent as frequency goes up, not current.

"Corona discharge" is *NOT* caused by AC or skin effect. Corona discharge
is caused by a high voltage gradient in the space around a conductor. This
is a combination of the voltage applied to the conductor and the effective
radius of the conductor. A high voltage, or very small effective radius can
increase the gradient to the point where the air is ionized. Simple proof
is that corona discharge is a problem with high DC voltage systems as well
as AC.

Sometimes hollow tubes are used for high frequency power conductors. This
reduces the weight and cost by eliminating the central part of the
conductor, where 'skin effect' has rendered the impedence high anyway. So
little admittance is lost for a great savings in material/weight.

VERY high frequency. NOT AC line frequencies.

 

[John Larkin]

VERY high frequency. NOT AC line frequencies.

Not so. At 60 Hz, copper skin depth is about 0.85 cm.

John

 

[DBLEXPOSURE]

---
I see. Instead of reason, you prefer insult.

I will neither read your "proof" nor will I shut up, and if you
don't like it, you miserable son of a bitch, you can go ****
yourself.

Any math that results in infinity might be fundamentally flawed. Infinity
is a mathematical impossibility. No mathematical functions can be performed
on infinity. It cannot be divided, multiplied, added to or subtracted from.
It is a non-quantity. Therefore, can it be a solution to an equation?



Just as Newton's equations where once considered mathematical law, until
professor Einstein proved otherwise, Einstein's theories may also someday be
shown to be incomplete.



It is possible that when an electron or photon reaches Einstein's cosmic
speed limit something entirely different happens than what the currently
accepted math would tell us is happening.



It may very well be that electrons can and do travel at speeds faster than C
but we cannot observe nor comprehend what happens at this point.



So for practical reasons, I must agree with Fields. But for philosophical
reasons, I must agree Auytm. However, none of you have the answer so it is
silly to stake out some absolute ground.. Is better to dream about it.



Exuse me for now I must return to my game, rolling dice with God. It seems
every time I get up on him he changes the rules.........



Herr Fields, wünsche ich, daß Sie das Verwenden solcher Geflügelsprache im
allgemeinen Forum nehmen würden.



Fale não com o tounge do diabo

 

[Don Bowey]

It becomes more prevalent as frequency goes up, not current.


VERY high frequency. NOT AC line frequencies.

Define "VERY." Is that higher than Very and very?

Skin effect is measurable in cables at as low as 100 kHz.

Don