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mike

hr(bob) wrote:
On Nov 18, 8:21 am, dpb wrote:
On 11/18/2011 6:36 AM, Han wrote:
...

Somewhere I read that the battle between DC and AC is being revived. DC
should be better at withstanding weather related interruptions, so fewer
(big) power outages at the transmission line and transformer(?) levels.
Don't ask me about the physics ...
I don't think that a branch falling down on an AC line and breaking it is
any different from a DC line, but apparently it would be easier and
cheaper to bury DC lines than AC lines.
Any weather-related issues are only a side-effect--the underlying reason
for DC over AC for transmission is cutting the AC losses.

It's now a possibility that wasn't practical before the advent of
solid-state electronics that could be made to handle the necessary
voltages/currents.

Manitoba Hydro has been an early implementor...

http://www.hydro.mb.ca/corporate/facilities/transmission_system.shtml
http://www.hydro.mb.ca/corporate/facilities/ts_nelson.shtml

Siemens has been building transmission lines in China and India, last I
knew there were plans on east coast in US w/ PEPCo altho I haven't
followed progress. Anything like offshore wind will rely on them to get
large amounts of power back to shore.

--

Also, the insulation required for a DC line is whatever the nominal
voltage is, while the insulation on an AC line must be 1.414 times the
nominal voltage. The line losses are similar,

Look up "skin effect". Even at 60 Hz., it's much shallower than you'd
expect.

but there has to be an
efficient way to transform from one voltage to another at the end
points, that is where semiconductors can now replace the transformer
and its losses.