On Wed, 7 Jul 1999 12:34:29 +1000 "O'Regan, Emlyn"
>It's just come to mind that I remember mention of an idea some time
>ago, to extend the national electricity grids into a huge world-wide
>grid, which might sort out fluctuations in supply around the world, make
>solar power more feasible (the sun's shining somewhere), and create a
>global electricity market where the countries best placed to produce
>would be able to do it. I think it was also supposed to create a magical
>fairyland where cats and dogs lived together in peace.
>Anyone know anything about this? Come to think of it, if anyone does
>want to know more, and no-one can do any better, I can probably scratch
>electrical engineer or six from this end and get the low down.
>Zaps Taps and Craps company man
A world wide power grid is an interesting idea, but with present technology it is not practical to transmit electrical power more than about 1,000 miles. Hydro Quebec sells power to utilities in New York, which entails hundreds of miles transmission length, but that works because the hydro power is so cheap to generate that large losses in transmission can be tolerated. Regional power grids are typically 100 to 300 miles wide. The regional grids are themselves often connected to adjacent grids, but that is just for increased flexiblilty. The purpose of the gridding is not to increase the average distance over which power is transmitted, but rather to increase reliability. Normally power should be generated within 50 miles or so of the load to keep losses at a minimum. Even then, total transmission losses are between 10 and 20 percent. For example, Baltimore is normally supplied by the Baltimore Gas and Electric Company's Calvert Cliffs Nuclear Power Station, about 75 miles south of the city, on the Cheaspeake Bay. There may theoretically be a connection between the Grand Coulee Dam and Florida, but no meaningful amount of power can be transmitted over that distance without immense loss. If high temperature superconductors capable of carrying large currents were to be developed, the picture would change. Today's high temp superconductors cannot carry large currents. Transmission losses can be reduced by increasing the voltage, but in the US it has not been practical to use voltages greater than about 750 KV. The Russians have some 1 million volt lines.
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