Re: power-grid physics

["James R. Frysinger" <frysingerj@COFC.EDU>]

On Friday 2003 August 22 17:24, you wrote:
....
> Regarding 1908, one major concern of engineers was the mass of copper
> required in the transmission lines. There were various schemes for
> arranging "mains" and "feeders" to minimize the cost of the copper, as well
> as the voltage drop from one end of the system to the other. Longer
> distances required thicker lines to keep the ohmic heating manageable, and
> copper wasn't cheap even then. With AC, one can use smaller wires because
> there's a thermal duty cycle.  I'll have to go back & look at the book,
> since AC vs. DC was a raging controversy at the time it was written.  Mass
> of copper in the transmission lines is *still* a major concern of
> engineers...it's a non-trivial economic matter.

        Right! Most high tension lines today use aluminum conductors, sometimes with
a copper cladding. The lines are often hollow since most of the current flows
on the outside of a wire due to the skin effect under these conditions.
Sometimes oil-filled lines are used; I haven't figured out the purpose for
the oil yet.

        My dad witnessed a vendor's experiment with an insulated, solid sodium
underground line. Superb conductivity specs but there were, understandly,
concerns about insulation failure. So the vendor had a backhoe operator
(perhaps not fully briefed....) purposely slice into the cable while it was
under load. There was a sizzle and the sodium formed some sort of oxidized
layer that turned out to be  a non-conductor! At the time (due to the Viet
Nam War) copper prices were so  high that the sodium line was a cheaper
option. Never caught on though...

Jim

--

James R. Frysinger
Lifetime Certified Advanced Metrication Specialist
Senior Member, IEEE

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