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800kV DC for power transmission? what?!?

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LAN_403

haxor5354

Sat Aug 06 2011, 10:53PM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

just saw this video form Siemens

apparently they're trying to transmit power over long distances with 800kV of DC.
can't imagine how they generate 800kV DC then invert them back to AC to feed the grid.
and whats wrong with power transmission using AC anyways?
seems like the "war of currents" is not over yet

Thomas W

Sat Aug 06 2011, 11:11PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

A challanger has appered!

2Btesla

Tesla uses wireless energy
It has little effect

in all seriousness i realy wonder where this may take us in the future?

Dr. ISOTOP

Sun Aug 07 2011, 12:16AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

HVDC is a very desirable way to transmit power; its just the cost prevents it from being prevalent (giant inverter stack -> NOT CHEAP :( )

Inducktion

Sun Aug 07 2011, 01:33AM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

I thought AC was better for long distances than DC for some reason.

haxor5354

Sun Aug 07 2011, 01:43AM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

Inducktion wrote ...

I thought AC was better for long distances than DC for some reason.

I think AC generates too much EMF causing more line lost

Adam Munich

Sun Aug 07 2011, 03:50AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

With DC you have no capacitive or inductive losses, so it is actually a better system for transmitting power. The problem with it is the fact that you can't easily change the voltage. Transformers do not work, and making an 800kV DC DC converter... well it ain't cheap.

klugesmith

Sun Aug 07 2011, 04:21AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

HVDC power transmission has been around for decades, even when the rectifiers and inverters used mercury arcs instead of giant thyristors (which are probably the core of Siemens technical advances being promoted). You can learn plenty about it by searching the Internet.

There are, IIRC, three types of installation where HVDC makes economic sense.

1. Long point-to-point links carrying plenty of power -- the capital cost and power losses in converter stations are outweighed by lower capital cost and losses per mile of line.
(among other things, you need only 2 conductors, and the peak voltage for insulation and corona mitigation is 1.0 instead of 1.41 x RMS voltage.) Examples are the Pacific Intertie in western USA, and a major line in Congo between IIRC a big hydro generation plant and a mining/smelting district.

2. Exchanging power between independently synchronized AC grids. For example, North America has four separate grids (not overlapping geographically!), and a number of AC-DC-AC converter facilities on their boundaries.

3. Where power must be transmitted in submarine cables, for example to populated islands, the HV lines have much more capacitance per unit length than overhead lines. With AC, the reactive line-charging current can cause large I2R losses.

Maybe Radiotech can point out my mistakes & omissions.

Mads Barnkob

Sun Aug 07 2011, 01:08PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

or just read here:

Dr. Slack

Sun Aug 07 2011, 08:01PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Inducktion wrote ...

I thought AC was better for long distances than DC for some reason.

That was from way back in Nineteen Hundred and frozen to death, when the only practical way of converting between LowVolts-HighAmps and HighVolts-LowAmps was a transformer, so the only practical way to get long distance transmission, which needed high voltage low current to make copper losses bearable, was to use AC and transformers.

It was sort-of possible back in those days to transform DC up and down, but that meant either a motor-generator set, which was hugely more expensive to both buy and run than a transformer, or very lossy, very fragile things like mercury arc rectifiers. So it was never done for bulk power transmission, tying power stations together for instance, just ona factory by factory basis where it was needed.

In other words, given a vast amount of power to shift, transformers and AC were cheaper, then.

Now the costs are that a DC line with masses of silicon each end is cheaper than a more heavily insulated AC line with transformers at each end. So guess which the world is moving to.

Patrick

Sun Aug 07 2011, 08:57PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Japan has a HVDC transmission system through mountain tunnels... 300kV if i remember right.

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