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Dave ,

DC Converter stations are not experimental. You can find references to them back almost a hundred years. What they generally do is chop up the DC and add it to the local grid as high voltage AC in the 230kv range. The plant here is the Southern end of the Pacific DC Intertie and has an interesting history and after 1985 has a slight resemblance to a massive SS Tesla Coil driver. I've been through it top to bottom a number of times and it's always impressive.


Sylmar Converter Station (34°18′39″N 118°29′21″W) is the southern converter station of the electric power transmission line Pacific DC Intertie which transmits electricity from the Celilo Converter Station outside The Dalles, Oregon to Sylmar at the northern outskirts ofLos Angeles, California, USA.
The converter station converts the 500 kV direct current coming from the northern converter station Celilo to alternating current at 60 Hz and 230 kV synchronized with the Los Angeles power grid. The station capacity is 3,100 megawatts.
Originally only mercury arc rectifiers were used as static inverter valves. The valves were series connected in three six-pulse valve bridges for each pole. The blocking voltage of the valves was 133 kV with a maximum current of 1,800 amperes, for a transmission rate of 1,440 megawatts with a symmetrical voltage of 400 kV against earth.
In 1972, after the Sylmar earthquake, the static inverter station in Sylmar had to be reconstructed after damage to the largest part.
In 1982, the power rating of the mercury arc valve rectifiers was raised by various improvements to 1,600 megawatts.
In 1985 two six-pulse valve groups of thyristors were added in order to increase the voltage to 500 kV per pole for a total differential voltage of 1,000 kV In 1989 the station was extended on the field east of the highway (called Sylmar East Converter Station), where two new 1,100 ampere, 500 kV 12-pulse thyristor converters were added in parallel with the two existing converters, giving a total transmission power of 3,100 Megawatts (3,100 Amperes at +/-500 kV
In 2004, Sylmar East station was upgraded from 1,100 MW to 3,100 MW (rededicated as the Sylmar Converter Station in 2005). The controls and older converters, including the mercury arc valves, were completely replaced (in the same valve hall) by a single pair of 3,100 MW 12-pulse converters built by ABB. The upgrade was made to eliminate the environmental risks of mercury and to reduce the maintenance costs of the obsolete mercury arc valves.

On Jul 29, 2012, at 8:03 PM, David Speck <Dave@xxxxxxxxxxxxxxxx> wrote:

> Neon,
> Come to think of it, solid state pole pigs are not so entirely unbelievable.
> On the experimental HV Direct Current transmission lines, they use semiconductor devices to downconvert megavolt DC back to low voltage, high current AC.  That's sorta like a pole pig, and the opposite of a rectifier bridge.  Pretty impressive technology.
> Dave
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