>> I don't think any country uses DC for power transmission.
>
>Except for a couple 0.5MV systems, you're right.

DC is used for very long transmission lines. The wavelength at 50Hz is
6000km and if any line segment approaches (even by far) one quarter of
this (1500km) then a significant part of the energy will be radiated into
space. Also dielectric loss in air becomes very high over such distances.
So people who have really long overland line segments use very high DC
voltages. What I was intrigued by was, how does one convert 0.5MV DC
*down* (up is relatively easy) to something reasonable, like 110kV. Are
they using valves ? If they do, are they buried in lead ? (500kV + vacuum
electrons = hard x-rays).  What semiconductors would work at 500kV and
several amps ? (2A at 500kV is 1MW.  - wow). What happens to birds that
sit on the wire ? (corona at 500kV is fierce). What about lightning. The
wires must be really high up. 500kV would jump 0.5 meter gaps w/o corona
but much more with ? Uhh.

Peter

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