"Steve Asher" wrote to "All" (23 Dec 02  01:50:17)
 --- on the topic of "HVDC Transmission Lines"

 SA> My understanding was that DC had lost out to AC a century ago (Thomas
 SA> Edison) for power distribution due to resistance losses &
 SA> inefficiencies.
 SA> Does anyone know of any compelling reasons for adopting DC for high
 SA> voltage transmission?

Indeed there are a couple of reasons. One is financial and the other is
compatibility between networks. For the first reason, as you know
Alternating Current exhibits a skin effect so that a flowing current in
a wire cable doesn't go much deeper than about 1 skin depth of the
surface. DC on the other hand will go right to the core so the cable can
be thinner (less copper).

For 60 Hz AC the skin depth is about 1/3 of an inch. The greater part of
the current flows in this outer area but the total current flows out to
about 5 skin depths, less and less as it goes deeper. Below this 5 skin
depth no current flows and the wire may as well be hollow or made out of
steel, which is exactly what is used to make the cables strong.

The other reason is distant networks won't need to be synchronized with
each other if they are using a DC link between them to exchange power
back and forth.

 Mike
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