Just wondering, even though they are rare, there are a few high voltage DC power transmission systems out there used by a few power companies.
How exactly does it get converted back to AC? Is it simply with a huge semiconductor based inverter? Or is it a mechanical DC motor / AC generator setup?
Besides the Wikipedia article Damon posted a link to, you might try searching for articles at the Bonneville Power Administration website. I remember finding some very interesting stuff there about the Pacific Intertie, between Sylmar, CA, just N. of Los Angeles, and the Bonneville dam on the Columbia river. At the time, probably ten years ago, I recall they were still using thyratron-type tubes ("mercury arc rectifiers??"), and an article I found was talking about the very high cost of retrofitting the inverter station to solid state. I believe the Sylmar station was pretty seriously damaged by a large earthquake in 1972. More stuff on the Pacific Intertie here:
This thing uses solid state thyristors to invert the DC back to AC.
The system has been upgraded over the years. It started with mercury arc switches (thyratrons) for inversion and has been upgraded several times. The most recent upgrade uses light activated thyristors (SCR's) from Siemens in the inverter.
The line carries plus and minus 500kVolts at up to 3100 megaWatts.
They're pretty hard to beat at high voltages. I've used them at 36KV at 100's of Amperes.
...Jim Thompson
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An ignitron has a pool of mercury to serve as its cathode. The Wikipedia article on them appears to agree with how I remember them being described in old books.
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
Hell, they're routinely used at as much voltage and a thousand times more amperes. Think quarter shrinker. :-) Great rise time, cheap to build (air is a quite suitable arc medium), great capacity.
Tim
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The Science Museum in London used to have a working one on display. IIRC the power for the museum flowed through it. Lots of blue flashes etc.
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Dirk
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Yeah, I remember about 35 years ago coming across the transmission line a bit north of its Sylmar terminus when my brother and I were out for a drive in the hills and seeing if a compass was affected by the field under the lines. Not that we could detect, but we also had no way of knowing what current was being carried at that moment anyway. It might be interesting to calculate how much the catenaries between towers move because of interaction of their magnetic fields when the line is carrying full power. Assuming the lines are reasonably high conductivity (copper or aluminum), the resistance must be on the order of 25 milliohms/mile-conductor, or 50 milliohms per round-trip mile. The whole line then is probably a little under 50 ohms, assuming it's not a really hot day. At 6000 amps, that's a lot of power and a voltage drop of close to 30kV. Wow. I wonder how efficient the AC--
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