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HV DC transmission design / theory 2

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neskowin

neskowin

Computer
Aug 22, 2006
2
I'm curious about the design of this apparently HV DC transmission circuit. What is the theory behind the third conductor suspended in the "V" ? It's insulated very differently than the 2 primary conductor bundles, so I'm pretty sure this is not multiphase AC. This circuit is located near Littleton, MA. Sorry the pic is not a bit clearer. Thanks !

25a0nqe.jpg
 
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3rd conductor? I only count 1.

>There are 6 HV lines suspended from the long insulators current-carrying

>There are 2 lightning protection lines that have no insulators, non-current carrying, since they are way thinner than all the others

>There is a single line suspended from short insulators, current-carrying.

TTFN



 
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There are several configurations.

The first HVDC lines used only one conductor and used ground for return. They were built to bridge waters (Gotland, Pas de Calais, Sicily etc). Environmentalists then made this arrangement more or less impossible. The wide DC current loop also disturbed magnetic compasses on ships. So later on one plus conductor and one minus conductor was used. The middle point (you could call it Neutral or Zero) was tied to ground. In this installation, it looks like the "neutral" has been brought all the way from source to sink - at least, that's how I interpret the thin low voltage (maybe 20 - 40 kV) insulated top conductor.

Gunnar Englund
 
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Bipolar HVDC lines are designed to be able to operate in monopolar mode during emergencies and maintenance. Maybe they are supplementing the monopolar operation earth return with the neutral conductor.
 
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About the same time DC transmission lines appeared so did insulated joints in pipelines. An insulated joint in a 2,000 PSI natural gas pipe line is an impressive thing.
I have read on artical where the "earth" terminals on HVDC line caused water to the break down of ground water into hydrogen and oxygen. Lots of interesting research and papers written on the subject. The geological formations where the "ground" is connected is significant.
 
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Thanks for all your replies ! Can anyone point me to a publication (online or otherwise) that would show the design of the circuit endpoint where the conversion back to AC is done ?

Thanks,

dave
 
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neskowin,

The transmitting and the receiving terminals are identical. They are both mains-commutated, which means that the 50 (or 60) Hz mains does the commutation. No islanding possible - there must be a rather stiff grid to connect to at both ends.

I shall try and dig out some diagrams that show this more clearly.

Gunnar Englund
 
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I have enjoyed reading the links that you have provided.
Thanks Gunnar
Respectfully
 
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Sorry I missed you cucky2000;
Thank you also for your graphic.
Respectfully
 
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HVDC transmission lines have advantages over HVAC transmission lines for a majority of environmental impact indices.
However, there are several undesirable side effects. One of these effects is stray current corrosion of underground metallic structures such as pipelines. Other environmental concern may be the chlorite generation in HVDC submarine cable.
 
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I have posted a question in the "Marine/Ocean engineering other topics" forum, (thread321-163751) as to whether mariners have experienced any effects on navigational equipment when crossing undersea cables.
I hope this is considered a related side issue rather than cross posting.
I hope for a wider response by posting a specific question rather than posting a link to this thread.
respectfully.
 
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The reason I ask is because a buddy who went to Stanfurd was working for a prof who was studying the "Weekend Effect". Strange fluctuations in the Earth's magnetic field had been detected and soon found to change subtly on Saturdays and Sundays. After about two and a half years it was found to be caused by BART (Bay Area Rapid Transit). Seems week days heater-ed up the shift in the Earth's field due to the large magnetic loops carrying more current. So what about some straight 500 mile DC link? Maybe the current is still too small?

Keith Cress
Flamin Systems, Inc.-
 
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This High Voltage Direct Current stuff is very interesting.
I had thought that Tesla & Westinghouse had shown that HV AC was better than Edison's DC for transmitting power.
Does this mean that newer equipment such as ABB's vindicate Edison in this respect???
 
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The Edison's arguments in favor of the DC was primarily based in safety reasons.

The HVDC system became advantageous over to the AC system in a large amount of power transmitted in long distance. During Edison and Westinhouse time only limited amount of power and relative short distances was required. Also the power electronic technology to support the HVDC, apperars meny years leter after Edison and Westinhouse.
 
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AC had the inherent advantage that it can be easily transformed in voltage allowing long distance transmission with low losses. DC converter stations were a little beyond the technology available to Tesla and Westinghouse at the dawn of the electrical industry!

The idea of DC being safer is curious: anyone who has seen a major fault on a DC system will know how tough it is on the switchgear. Once a powerful DC arc is established it is not a trivial task to interrupt it. I treat all electricity as dangerous, but I'm especially wary of big DC systems.

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image.php
Sometimes I only open my mouth to swap feet...
 
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Hi Scotty,

Perhaps you are thinking in current interruption of DC vs. AC. However, comparing the DC with AC at industrial power frequency of 60 or 50 Hz there are many evidence to conclude that T. Edison was right from the safety point of view.

I took the liberty to plot the physiological effect of electric current in human body based on the Charles Deziel experiment in human body that confirming that the AC current at power frequency of 60 Hz require of a fraction as low as 15% of the DC current to produce a painful electric shock with muscular control loss by 0.5%.

Another interesting data shows that AC current at high frequency such as 10,000 Hz is less dangerous than the DC counterpart.

For illustration of the physiological effect on human body, see the enclose link.


T. Edison said:
"Invention was 1 percent inspiration and 99 percent litigation"
Click to expand...
.
"Edison spent a great deal of time dealing with lawyer-suing other companies for stealing his patents, getting sued in turn for stealing theirs".
 
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