Re: Sahar solar farm project to power Europe?

On Thu, 24 Jul 2008 02:03:24 +0100, Robert Sneddon
<fred@xxxxxxxxxxxxxxxxxx> wrote:

In message <o6hf849dm9m2uarje8phefgid67faqe2q8@xxxxxxx>, mike weber
<fairportfan@xxxxxxxxx> writes

But then they started talking about a new transcontinental power grid
to deliver the juice northward ... and they said it would be DC,
because AC transmission involves too much loss.

Huh?

I thought line losses was one of the primary reasons to use AC rather
than Dc...

It used to be true that DC had more problems than AC long distance.
It's easy to shift AC voltages up and down with transformers.
Transmitting power long distances is best done at high voltages (the
UK's supergrid runs at 400kV 50Hz) to combat resistive losses. I squared
R, lower voltage = higher current = greater losses. In the past the only
way to voltage-shift DC was to use motor-generator sets which were
expensive, less efficient than transformers and they had moving parts.

This i know, it was what i was thinking of. I've been so far away
from anything involving Really High Voltages long enough that the
stuff in your next paragraph didn't occur to me.

Nowadays with modern electronics DC can be easily shifted up and down
although it's still more expensive than AC transformers. However
inductive losses from AC transmission lines can make UHV DC systems more
economic, especially for very long tie-lines connecting remote
generators to consumer grids.

Okay; i had forgotten is is possible to shift DC voltages like that
these days.

Never mind.

(Meanwhile, there's something of a shift from DC to AC power in diesel
electric locomotives, i think.)
.

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