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Old 29th January 2013, 08:18 PM   #33841
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UK is probably too small a distance to bother with DC. In the US there's a DC long line from the Dakotas' (Minnesota?) coal regions to California. I believe there're some in Russia too.

Thanks,
Chris
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Old 29th January 2013, 08:37 PM   #33842
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Just curious, how did they transform AC to DC motors and dynamos ? And back, Alternators ?
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Last edited by Esperado; 29th January 2013 at 08:55 PM.
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Old 29th January 2013, 08:48 PM   #33843
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Here's a pretty cool picture: File:Pole 2 Thyristor Valve.jpg - Wikipedia, the free encyclopedia

but I remember one from _National Geographic_ from about 15 or 20 years ago that was stunning.

Thanks for making me look!
Chris

ps: in the English language Wikipedia, it's under "HVDC".

Last edited by Chris Hornbeck; 29th January 2013 at 08:51 PM.
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Old 29th January 2013, 09:04 PM   #33844
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Amazing ! Thank Chris.
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Old 29th January 2013, 11:11 PM   #33845
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The Krell did it first! '-)
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Old 30th January 2013, 01:11 AM   #33846
fas42 is online now fas42  Australia
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Quote:
Originally Posted by john curl View Post
The Krell did it first! '-)
Love that movie ... so impressive with the special effects they managed to conjure up back then ...

Frank
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Old 30th January 2013, 01:40 AM   #33847
bcarso is offline bcarso  United States
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Quote:
Originally Posted by fas42 View Post
Love that movie ... so impressive with the special effects they managed to conjure up back then ...

Frank
Yes, a class act indeed. I love that scene as they are walking on the ramp into the generator area.

And in the "control" room:

Captain: What was the power source?

DR. MORBIUS: May I draw your attention to these gages all around here, gentlemen. Their calibrations seem to indicate that they are set in decimal series, each division recording exactly 10 times as many Amperes as the one preceding it. Ten times ten times ten times ten …. on and on and on, row after row, gauge after gauge. But, there is no direct wiring that I can discover. However, when I activate this machine it registers infinitesimally, you see down there in the lower left-hand corner. And, then, when I activate the educator here, it registers a little bit more.

Dr. ???: But this much is negligible, the total potential here must be nothing less than astronomical.

DR. MORBIUS: Nothing less, the number ten raised almost literally to the power of infinity.

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Old 30th January 2013, 08:38 AM   #33848
RNMarsh is online now RNMarsh  United States
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Default Multiple ground points outside the home -

Grounding in the home -- between video/cable/internet and audio systems:

Attached is a quick sketch of the problem when there are just two ground points - one at power entrance panel and one at catv entrance (not at same location). When the two systems are connected together via coax cable, ground potential differences will go thru the A-V equipment instead of grounds (lowest R path). This creates noise and also a path for lightning strikes/transients thru equipment. A ground isolation is needed on the cable - such as a video isolation transfomer or cap coupled rf HP filter to break the ground path. However high volt age transients will go thru. So a surge protection device across the cable is also needed (often a gas discharge tube or other suitable device). Thx-RNMarsh


Ground Current bypass.pdf

Ground-Loops.pdf
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Old 30th January 2013, 12:01 PM   #33849
DF96 is offline DF96  England
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Quote:
Originally Posted by wrinkle
I thought that the UK supergrid was still AC, it is only the Power share with Europe in undersea cables that is DC.
Yes, UK transmission and distribution is all AC. Interconnectors to other grids are DC for two reasons:
- no need to synchronise frequency
- no AC losses in underground/undersea cables

I suspect (not sure) that AC ground losses may exceed AC radiation losses for overhead lines. The main loss is just ohmic heating in the conductors.

If a long transmission line was forced underground (e.g. due to visual impact in a National Park) then there might be some advantage in using DC. It is a matter of balancing the AC losses in the ground vs. conversion losses in AC/DC converters at each end.
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Old 30th January 2013, 12:13 PM   #33850
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"The main loss is just ohmic heating in the conductors."

Not helped by the use of aluminium wire, for other reasons.
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