OT: UPS for FreeBSD

[Ian Smith]

Re: freebsd-questions Digest, Vol 547, Issue 7, Message: 6
On Sat, 29 Nov 2014 16:04:03 -0500 "Matt Emmerton" <matt at gsicomp.on.ca> wrote:
 > > On 11/29/2014 12:56 PM, Darren Pilgrim wrote:
 > > > On 11/28/2014 8:12 PM, Erich Dollansky wrote:
 > > >> Real high voltage transmission
 > > >> lines using DC make sense.
 > > >
 > > > Someone already tried that.  It doesn't work.  The conductors have to 
 > > > be impractically large to get a useful amount of current, and the 
 > > > distance loss is so high you can't build even a metro grid with it, 
 > > > let alone a regional grid or the long-distance transmission systems we 
 > > > use now.
 > > >
 > > > 
 > > That is correct Darren - Long distance transmission, even for a scan few
 > > miles is impractical with DC.
 > 
 > You might be interested to learn that many electrical utilities across the
 > world use DC transmission systems over hundreds or thousands of kilometers.
 > 
 > http://en.wikipedia.org/wiki/List_of_HVDC_projects

Indeed, there's a lot of it about.  A broader treatment of HVDC is at:

http://en.wikipedia.org/wiki/High-voltage_direct_current

Particularly useful for undersea links, I'm familiar here with BassLink:

http://en.wikipedia.org/wiki/Basslink

which at 400kV / 500MW / 200km it's just a baby compared to the big 
ones, such as "The longest HVDC link in the world is currently the 
Xiangjiaba - Shanghai 2,071 km (1,287 mi), ±800 kV, 6400 MW link 
connecting the Xiangjiaba Dam to Shanghai, in the People's Republic of 
China" and "Early in 2013, the longest HVDC link will be the Rio Madeira 
link in Brazil, which consists of two bipoles of ±600 kV, 3150 MW each, 
connecting Porto Velho in the state of Rondônia to the São Paulo area, 
where the length of the DC line is 2,375 km (1,476 mi)."

On the smaller end of the scale, there's lots of microgrids being built, 
mostly in the developing world, many of which are partly or largely DC.

cheers, Ian