2,000 KV DC Line Going Up In China

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MSimon
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2,000 KV DC Line Going Up In China

Post by MSimon »

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http://tdworld.com/projects_in_progress ... hina-0109/

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ABB has successfully tested a new type of transformer that is a key component of power superhighways, or power links that can deliver vast amounts of electricity over very long distances.

ABB developed the 800-kV transformer within one year of winning a major order to equip the ultrahigh-voltage direct current (UHVDC) transmission corridor from the Xiangjiaba hydropower plant in western China to Shanghai, 2,000 kV to the east. It is the world’s highest-voltage power link and will have a record capacity of 6,400 MW, capable of supplying about 31 million people.
The transformer is the first of several ordered by the State Grid Corporation of China (SGCC), and is a critical element of the systems that ABB is supplying to convert AC current to DC and back, and to alter the voltage at each end. Among other challenges, raising the voltage to as much as 800 kV increases the technical requirements on a transformer’s insulation and on the design of critical parts such as bushings.

“The cooperation between ABB and SGCC has played a key role in this success, which is further evidence of ABB’s commitment to technology and innovation,” said Bernhard Jucker, head of ABB’s Power Products division. “UHVDC technology enables more efficient use of renewable energy sources, reducing dependence on fossil fuels and cutting carbon dioxide emissions.”

Power transmission at ultrahigh voltage has considerable advantages for the environment, as it reduces the power losses and requires a smaller transmission corridor than conventional technologies. UHVDC technology is particularly suitable for large countries such as China, where the centers of power consumption are often far from the power sources. UHVDC is a technological development of HVDC, pioneered by ABB more than 50 years ago, and is the biggest leap in capacity and efficiency of transmission in more than two decades.
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KitemanSA
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Post by KitemanSA »

Unhh... that should read 800 kV running 2000 km to the east. An 800 kV line running a distance of 2000 km. Their report had a typo.

Sorry.

MSimon
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Post by MSimon »

Thanks.

It is a step in the right direction. For a Polywell a buck converter might be used to convert the DC output to a standard DC line voltage.
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easyBob
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Post by easyBob »

But isn't it easier to use AC over long distances? How much does this cost compared to using all AC stuff?

I guess what I'm saying is, what's the point? Is it economical to do this? Ease of long distance travel over smaller lines is why AC won over DC, right?

I understand converting DC to AC for long distance, from the POV of a polywell, but not the other way around, know what I'm saying?

-Chris

Tom Ligon
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Post by Tom Ligon »

Some long-distance portions of the US power grid are DC.

The original idea of AC was to allow transformation to high voltage, so wire resistance would be less a killer. If you drop current by a factor of ten, voltage drop goes down with it, and if you up voltage by a factor of ten, the voltage drop is ten times less significant. The result is a 100:1 benefit.

But the downside of AC is it induces current in the ground beneath the lines, and any nearby metal structures. Farmers stealing power using fence lines has been a known issue almost from the start.

DC transmission has the benefit of transforming to high voltage without the downside of inducing losses. The technology was beyond the capabilities of Tesla at the time AC went into use for power transmission.

EPRI (probably actually Dr. Hirsch) has indicated they think DC power from Polywells will be a straightforward engineering issue.

MSimon
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Post by MSimon »

easyBob wrote:But isn't it easier to use AC over long distances? How much does this cost compared to using all AC stuff?

I guess what I'm saying is, what's the point? Is it economical to do this? Ease of long distance travel over smaller lines is why AC won over DC, right?

I understand converting DC to AC for long distance, from the POV of a polywell, but not the other way around, know what I'm saying?

-Chris
But isn't it easier to use AC over long distances? How much does this cost compared to using all AC stuff?
No. DC is easier. No synchronizing problems or phase current problems with round about interties. Also DC is a two wire system with lower losses both from an induced ground current perspective and from a I-squared-R perspective. In addition AC requires 3 wires which can be used to about 80% of capacity. DC is a two wire system that can be used to 100% of max wire capacity. So the AC system has about 20 to 25% more conductor for a given maximum power.

AC won over DC because it is easier to convert AC to a high voltage: a transformer will do the trick. With semiconductors now making DC to AC conversion and DC step up/step down easy the reliance on AC is strictly an economics problem.

So far DC looks good for long distance transmission while AC makes sense for local distribution.
Engineering is the art of making what you want from what you can get at a profit.

Helius
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Post by Helius »

MSimon wrote: So far DC looks good for long distance transmission while AC makes sense for local distribution.
What are the respective energy losses per unit distance? I heard High Voltage AC looses about 7% per 100 miles. Is this accurate? What is the loss for DC? Is there a table / formula somewhere?

Another question: What legislation was it that separated Power generation from distribution? It seems to me, that if the Distribution company doesn't buy or sell electricity, but just gets paid for delivery, they they won't care how much simply "blows off the truck". It seems to me there will be no differential charged for power relative to the source of generation. Alcoa built an aluminum plant in the Saint Lawrence River Valley because of the close proximity of the Saint Lawrence power Project. Under the Current scheme, they'd be encouraged to build their plant in the Hudson Valley, more central to political power. What was that ugly legislation?

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