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DC power transmission

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 21 January, 2009 » DC power transmission « Previous Next »

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ant
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Username: ant

Post Number: 391
Registered: 05-2006

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Posted on Thursday, 15 January, 2009 - 09:41 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello all,

I read recently that some countries have undersea interconnectors to exchange power at very high DC voltages. How is this translated back to AC, I wonder?

Regards Ant
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alexr
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Post Number: 37
Registered: 02-2008

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Posted on Thursday, 15 January, 2009 - 10:36 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Laser controlled thyristors.
Lots and lots of very big laser controlled thyristors!
See this link for details.
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zeitghost
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Username: zeitghost

Post Number: 1246
Registered: 01-2006

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Posted on Thursday, 15 January, 2009 - 04:24 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

A.K.A. Static Inverters.
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ant
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Username: ant

Post Number: 392
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Posted on Thursday, 15 January, 2009 - 11:04 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello both,

Thankyou - I bet the salesman who clinched that deal got a good bonus!

How long before Linux come up with a free control system, I wonder?

Interesting that DC is more power-efficient than AC but I shall take their word for it, my background is almost certainly inadequate.

Regards Ant
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atferrari
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Username: atferrari

Post Number: 657
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Posted on Saturday, 17 January, 2009 - 08:04 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Interesting that DC is more power-efficient than AC

I am surprised to see they did that way. I always seen explained that power transmission using AC was better because it had smaller losses than with DC. How they actually managed to get the opposite, it is not explained there.

Interesting and intriguing.
Agustín Tomás - Buenos Aires - Argentina
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ant
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Username: ant

Post Number: 393
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Posted on Saturday, 17 January, 2009 - 10:32 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello Agustin et al,

There's a similar thread starting on the BVWS forum and it seems that there's capacitative loss because the cable is surrounded by water.

Regards Ant
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eagre
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Post Number: 320
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Posted on Sunday, 18 January, 2009 - 01:18 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Agustin -

The advantage of AC power transmission is that voltages can be stepped up to efficient (kV) transmission levels and back down to domestic (safer) levels quite simply with with transformers.

Ed
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atferrari
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Posted on Sunday, 18 January, 2009 - 12:07 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The advantage of AC power transmission is that voltages can be stepped up to efficient (kV) transmission levels...

Bringing voltage high, current goes down and ohmic losses go down as well, right?
Agustín Tomás - Buenos Aires - Argentina
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johnboy
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Post Number: 2
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Posted on Sunday, 18 January, 2009 - 02:31 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

An interconnector between England and France of 2000Mwatts was installed in 1986 between Sellindge in Kent and Les Mandarins in France. It goes under the Channel between Folkstone and Calais. It was decided to use DC as it is more efficient with less power loss and so allowed smaller cable sizes to be used, has no problems with synchronisation and does not interfere with shipping equipment. The conversion is by thyristor banks which were built by GEC for the Sellindge control centre not sure if they built the ones used at Les Mandarins.
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stylers
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Username: stylers

Post Number: 154
Registered: 04-2005

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Posted on Sunday, 18 January, 2009 - 03:40 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

There will be big transmission losses with AC and underground cables because long power lines are effectively transmission lines with inductive and capacitive components (think coax cable) and there is capacitance to the ground along the length of the cable, even more so when the cables are buried in close proximity to the earth. So even at the relatively low frequency involved, losses become substantial. Using DC reduces this problem.
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steerpike
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Username: steerpike

Post Number: 428
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Posted on Tuesday, 20 January, 2009 - 10:12 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The Cabora Bassa transmission line from Mocambique to South Africa is DC because of its length. It's a multiple of the 50Hz wavelength, and with all transmission lines, at a particular length, an open circuit at the destination-end is reflected back as a short circuit at the generator-end, making AC impossible to use.

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