Talk:High-voltage direct current
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Reversal of power flow is easy, whereas an AC system requires a duplicate set of conductors.
- Not clear. - Patrick 01:24 Jan 13, 2003 (UTC)
- I suspect that this article is not technically precise. In my experience, HVDC links are used in very specific situations. The advantages come from the high voltages used and lower insulation requirements compared to the equivalent AC voltage. While reversal of power flow may be practical using thyristors, it was not practical when mercury arc rectifiers were used. I also fail to appreciate why duplicate conductors are necessary for reverse power flow in an AC power transmission line. I understood that they could operate in a bidirectional manner, though this function had to be designed into protection switchgear rather than being a limiting factor of the power transmission line itself.
- I agree, I've removed this in my changes to this page. Feel free to reinstate it; it's always dubious when deleting something through lack of evidence, but there's been no recent contradiction. - Kaet 12:20, 14 Sep 2003 (UTC)
- The positive and negative coronas sentence in the monopolar and bipolar transmission section is ambiguous, as it is a stub. I don't understand coronas very well yet, I'm reading up on them right now. - Kaet 12:20, 14 Sep 2003 (UTC)
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- Coronas now done and sentence changed. See separate page. Fascinating subject, Gromit. - Kaet 22:49, 14 Sep 2003 (UTC)
- There are some editing discontinuities in this page right now, as I am in the middle of rearranging it over this weekend. - Kaet 12:20, 14 Sep 2003 (UTC)
There's a hyperlink that's attempting to link to the non-existing "cathrod" (which apparently means "cathode rod" or some such). If someone knows that this jargon is correct, could you create the "cathrod" article? And if someone knows the jargon is wrong, could you adjust it to a better hyperlink?
No such animal as "cathrod" in the (English-language) sources I've seen. The "earth return electrode" is referred to as such every place I've looked or heard of. I've removed the "cathrod". --Wtshymanski 20:01, 12 Dec 2004 (UTC)
The "health" effects section doesn't seem to recognize that the alleged effects of low-frequency EM fields have nothing to do with selection of a HVDC transmission scheme. Does this section belong here? I would also like to see the organization and language cleared up a little bit - I've made a start, though I had to undo and redo some editing just now. --Wtshymanski 00:11, 7 Dec 2004 (UTC)
I've whittled down the health effects section - there doesn't seem to be an article on EM fields and cancer, which is where all that detail would have belonged. I've also added the Thury system. No question ASEA is and was a big force in HVDC development but they don't claim to have invented it. More polishing, maybe some day this will be a feature article (but not this month!) --Wtshymanski 20:01, 12 Dec 2004 (UTC)
The section on "polarity" is confusing to me, at least - I'm going to try a rewrite over the next little while. The picture of the tube oscillator schematic is cute but somewhat mystifying to someone who doesn't read schematic diagrams -blow it away? Typically descriptions of HVDC schemes have some diagrams - which I want to do over the Christmas break. This will also clear up the "monopole" and "bipole" descriptions. We have articles on static inverter plant and valve halls which someone has included from the German version and which I've started polishing up, too - this main HVDC article should refer back to those for details, which would leave the main article for more of the system-level implications of HVDC. I've posted a picture of an HVDC valve at Nelson River Bipole. --Wtshymanski 16:01, 19 Dec 2004 (UTC)
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[edit] Practical Or Not?
I found this edit made:
Revision as of 09:41, 27 Jan 2005
The grid controlled mercury arc valve became practical' for power transmission during the period 1920-1940[9]
Current Revision
The grid controlled mercury arc valve became impractical for power transmission during the period 1920-1940[9]
Knowing nothing about the topic, I simply wish to bring this to the attention of those who do. I have not made any edits.
Cabhan 06:15, 6 Feb 2005 (UTC)
[edit] VfD!
Incredible. Imaginary kings invented as throw-away details in some overlong sword and socery epic are "encyclopedia-worthy", but billion-dollar projects sending gigawatts to millions of consumers AREN'T? I thought Wikipedia was supposed to be a serious encyclopedia, not just the home of "fancruft". If you're interested in this subject matter, please help with the HVDC related articles. We need to get the mechanical translations in the linked articles turned into good English, wikified, and with more links and references (and PICTURES! and diagrams!)
There was at least one HVDC project article listed as a VfD in January!
How do you do a "taxobox"? - It would be very useful to have a standardized form for HVDC project articles, which I submit are at least as individually socially significant as those damn Pokemon characters. --Wtshymanski 00:29, 8 Feb 2005 (UTC)
- Did I miss a memo? Where has an HVDC page been listed for deletion?
- Atlant 01:44, 8 Feb 2005 (UTC)
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- Check out the discussion here Wikipedia:Votes for deletion/GK Wien-Southeast. Now, I can see that we don't need an article on every 2 MVA substation out there, but any HVDC project is more significant than that. --Wtshymanski 20:18, 8 Feb 2005 (UTC)
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- Thanks for the pointer!
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- Atlant 20:38, 8 Feb 2005 (UTC)
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[edit] Realized HVDC systems
Expand the list of realized HVDC systems and expand the articles of realized HVDC systems
[edit] Photograph of Mercury Arc Rectifier for HVDC transmission
Add a picture of a Mercury Arc Rectifier fopr HVDC transmission. Especially good would be a picture of the Mercury Arc Rectifiers of Nelson River Bipole 1
- I've added a photo. See Nelson River Bipole 1. UMwoodr0 04:52, 25 August 2005 (UTC)
[edit] Back from DC to AC
Right now, I think it doesn't get clear enough how the HVDC is put back to AC. An explanation would be great, especially see Static inverter plant - i think that would be a good reference. Thanks, --Abdull 09:22, 22 July 2005 (UTC)
[edit] Corona discharge
Corona dicharge does not depend on an electromagnetic field neccessarily ( unless you are talking about RF corona when of course it does) So, to keep thing simple and improve accuracy, I ve changed electromagnetic to electric. Any comments. Please reply here initially. I watch this page. Light current 16:41, 5 August 2005 (UTC)
[edit] Advantages of HVDC over AC Transmission
Unfortunately there is no clear description of the advantages or comparison between the two principles given
[edit] Removed tripole
I removed the following text, which reads like an inventor pitching his new idea. Please feel free to edit and replace some, if it's worthwhile. kmccoy (talk) 04:55, 26 February 2006 (UTC)
[edit] Tripole - Current Modulating Control
A newly patented scheme (US Patent 6714427) is particularly applicable to conversion of existing AC transmission lines to HVDC. Two of the three circuit conductors are operated as a bipole. The third conductor is used as a parallel monopole, equipped with reversing valves (or parallel valves connected in reverse polarity). The parallel monopole periodically relieves current from one pole or the other, switching polarity over a span of several minutes. The bipole conductors would be loaded to either 1.37 or 0.37 of their thermal limit, with the parallel monopole always carrying +/- 1 times its thermal limit current. The combined RMS heating effect is as if each of the conductors was always carrying 1.0 of its rated current. This allows heavier currents to be carried by the bipole conductors, and full use of the installed third conductor for energy transmission. The higher current compared to AC operation may also help prevent ice build-up during winter storms. The system can be arranged to circulate high currents through the line conductors even if load demand is low.
Combined with the higher average power possible with a DC transmission line for the same line to ground voltage, a tripole conversion of an existing AC line could allow up to 80% more power to be transferred using the same transmission right-of-way, towers, and conductors. Some AC lines cannot be loaded to their thermal limit due to system stability, reliability, and reactive power concerns, which would not exist with an HVDC link.
The system operates without earth-return current. Since a single failure of a pole converter or a conductor results in only a small loss of capacity and no earth-return current, reliability of this scheme would be high. No time would be lost in switching if a conductor broke. The valves would inherently have an emergency overload rating in bipole mode. This would possibly allow great increase in power transmission with significant effect in congested transmission systems, where consequences of a single line failure limit the allowed loading of other parallel transmission lines. While capital costs are higher than for a bipole conversion operating at the same voltage class, the extra power capability reduces incremental cost per megawatt. Depending on transmission line physical configuration, replacement of insulators may be required to achieve the highest power rating, to insure proper line-to-line clearance distances.
As of 2005 no tri-pole conversions are in operation, although a transmission line in India has been converted to bipole HVDC.
See Presentation on Current-Modulated Control
[edit] Advantages of HVDC
I don't really understand one of the advantages of HVDC: Reducing I²R losses and line cost since HVDC transmission requires less copper conductor (i.e 2 conductors one is +ve another is -ve). Less copper means more resistance, not less, so at a given I, the losses should increase! -- CyrilB 13:24, 18 April 2006 (UTC)
Hmm... I didn't exactly understand this either. Perhaps what the other user meant to imply was that, by using bipolar DC transmission, the effective transmission voltage would be twice the transmission voltage (versus ground), and by using DC you'd also reduce line reactive, skin effect, and corona losses. The combination should allow smaller conductors to be used versus a HVAC transmission system of similar power handling capability?? Bert 14:26, 18 April 2006 (UTC)
[edit] Copper Losses
The aditional copper in AC lines is used do transmit the reactive power due to inductances. Since DC lines are not subject to reactive power, you can use less copper.
Alvaro Augusto alvaro@daelt.sh06.com
[edit] Itaipu converters
I don't want do edit this page, but I'm afraid the second Itaipu converter is located at Sao Paulo, not at Brasilia. Take a look at http://www.transmission.bpa.gov/cigresc14/Compendium/Itaipu%20Pictures.pdf. Brasilia is not shown, but it is at the heart of the country, while Sao Paulo is much closer to Foz do Iguacu, where Itaipu is located.
Alvaro Augusto alvaro@daelt.sh06.com
[edit] Split off the lists
Would anyone object to splitting off the lists into List of HVDC Projects? The lists are getting rather long - sure we have space (after all, every numbered asteroid has an entry in a list, even though there is nothing interesting to say about dirtball no. 3,141,593), but their educational value in the main article is not apparent to me. --Wtshymanski 22:48, 19 April 2006 (UTC)
