[TowerTalk] DC very high voltage transmission lines

[Jim Lux]

At 07:28 PM 8/15/2006, Nick Pair wrote:
>The reason for DC over AC is lower transmission losses.


Losses are about the same inasmuch as they try to keep the reactive power 
flow in the line minimized, and for active power, IR loss is IR loss, 
whether it's DC or AC.  Skin effect is there, but probably compensated by 
just using larger conductors (or ACSR type cables) for AC. Corona losses 
might be different too (peak voltage is higher for a given RMS AC voltage 
than for the same DC voltage), but I suspect that's not a huge 
factor.  Converter losses for DC will certainly be higher (since there's no 
converters for AC).

  Controllability is really where it's at for DC links (that, and the 
ability to use reasonably long underground or underwater lines with high 
capacitance).  Imagine how simple it would be if all you had to feed from 
your transmitter to the antenna was DC... no hassles with VSWR, mismatch, 
etc. (all of which have equivalents in the power transmission business)

>  They have experimented with lines up to 1 million volts in the U.S. and 
> we do have some lines running DC now in the states.

The Pacific Intertie includes is a +/- 400 kV DC link that has been in 
operation since the 1960s
http://www.abb.com/cawp/gad02181/c3e8e6cc588aa8c3c1256d8800402284.aspx
This link (now running at +/- 500kV, since 1982) terminates at the Sylmar 
converter substation just north of Los Angeles and carries arount 3 GW.

http://www.transmission.bpa.gov/cigresc14/Compendium/PACIFIC.htm

Now there's a hard core DC power supply...

The 500 kV AC link that's part of the intertie terminates at Lugo, which 
many of you have probably seen in a web video of a huge (>50 ft) spark 
being drawn during a test



Rummaging around on the web, the Wikipedia has the following interesting entry:
http://en.wikipedia.org/wiki/HVDC
which lists dozens of HVDC power links.


>You can blaim Thomas Edison for all our AC troubles, Tesla had it right.
>

Oh.. I don't know about that.  Edison was a better marketeer than Tesla, 
particularly considered over their respective lifespans. Tesla was probably 
brighter, and certainly would have been a more entertaning dinner party guest.

Jim, W6RMK