"Dimitrios Tzortzakakis" wrote in message
...


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

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