--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "John Fields" ?????? ??? ??????
...
On Sat, 30 Jul 2005 10:50:24 -0700, John Larkin
wrote:

On Sat, 30 Jul 2005 09:39:58 -0700, John Larkin
wrote:


At higher frequency AC, current in a wire tends to avoid the center
and crowd near the surface, "skin effect."


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?

---
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.
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).