[ekaggata]

There are earlier topics but little or nothing in depth I could find.

High Voltage DC (HVDC) offers the ability to transfer electrical energy over thousands of kilometers with realistically lower power loss.

This, of course is NOT a direct solution for a liquid fuel crisis such as we currently have. It may not even be an indirect one.

But, to me, it is another very clear part of the overall solution we have for shifting to a renewable (maybe plus nuclear, but not necessarily) electricity generation, with all the advantages that confers re: climate, pollution and fossil fuel depletion.

I was reminded of this by The Watt Podcast 78. Certainly an interesting discussion from someone who's working directly in this field.

He speaks of the currently-being-installed Xiangjiaba-Shanghai UHVDC transmission project which is apparently about 2000km in length at a 6GW rating to take hydropower from Western China to the Eastern seaboard.
He talks more about the DESERTEC project, which has been mentioned on this website before, and there is a pdf available on the Watt Podcast notes to the show.

I think the point about the technology that impresses me the most is that it is already in use, even heavily in use, although the massive usage of Saharan sunlight is still merely an idea. He claims that a very large part of recent grid installation is HVDC, certainly in any case he quotes both Europe and China in this regard.

There are perhaps two distance scales on which this technology might be important:

First is that it can certainly allow large scale wind and solar arrays sited very far from population centres to be viable. This is a plausible short term scenario, but it can only partly offset the problem of intermittency which these sources suffer from.

Second, and this was not really discussed on the podcast, is the very largest scale possible implementation, not just North-Africa to Europe but across timezones. In theory this might take away the "availability" issue of solar (i.e. night time). I must admit that's a bit of a stretch, but to solve the extraordinary problems we have right now, you have to think big!


(PS To put my cards on the table, I am a strong fission advocate, so this to me is not the only game in town when it comes to the grid...)

[small_steps]

While the line losses for an HVDC line are smaller than traditional AC lines, HVDC is not a game changer in that respect. so we go from 92% to 95% efficiency for transmission from point A to point B (with conversion). Not a big deal in that respect. What is done, and is important, and mostly missed in the podcast for instance, is that there is no more reactive voltage drop in the cables (mostly capacitive for underground, and mostly inductive for overhead lines.) This effect (reactance) is what largely limits the power flow between ends of a line (at least for overhead lines). What appears to be happening is that they (ABB) are becoming more confident in the ability to series and parallel these switches.

+/-400kV line, how many series switches are needed in the converter if switches are rated at 4.5kV each?

That is what makes HVDC work, the podcast moderator had some odd fascination with the cables however.

We'll still have utilization issues (intermittent of source), which is the real deal breaker of RE. So you make the investment of resources and capital in RE, and the investment in the transmission, but you might be using 1/3 of the time. How does the economics work? How do the economics work relative to xxx?
Global Grid?

HVDC may be more efficient than conventional AC lines, but over distances that are meaningful, the efficiencies -> 0. Unless we somehow come to using superconducting lines of some sort, but that is adding a whole layer of wishes upon wishes.

[ekaggata]

Interesting post small_steps - I appreciate it. I'm off to bed now, I'll take a closer look tomorrow.

[TheDude]

Stu Staniford wrote a piece on a global solar grid tied together with HVDC: Powering Civilization to 2050. May be of interest.

[Newfie]

While I'm more than a little rusty on my power transmission theory there are some practical issues.

First, a couple of months ago Scientific American did a cover piece on how to save America by doing big, BIG, solar in the American SW. Then transmit it to the NE via HVDC, then store the energy underground in Natural Gas chambers, let it out at night.

By contrast read the North American Energy Reliability Corporation (NERC) 2008 reliability report. They have identified several major corridors where we need to reinvest in our transmission line infrastructure. Can't do it because of NIMBY. And these are relatively short lines of existing technology. You should read this report in any case. Scary stuff if you can parse out the technocratic BS.

Second I actually worked on a 3-phase to DC to 1-phase power system about 25 years ago. These are NOT simple transformation processes. Quite a bit more infrastructure is required to make it work, lots more than a simple transformer.

So I am skeptical. Still I need to read up on the technology more.

[tsakach]

There are non-technical issues at the heart of problem in the US power grid that need to be addressed before tinkering around with the technology.
$this->bbcode_second_pass_quote('', 'I')n the view of Casazza and many other experts, the key error in the new rules was to view electricity as a commodity rather than as an essential service. Commodities can be shipped from point A through line B to point C, but power shifts affect the entire single machine system. As a result, increased long distance trading of electric power would create dangerous levels of congestion on transmission lines where controllers did not expect them and could not deal with them.
The system was never designed to handle long-distance wheeling,” notes Loren Toole, a transmission-system analyst at Los Alamos National Laboratory.

[Starvid]

Soooo what?

HVDC has been around in one form or another for 50 years. Transmitting power has never been the problem we are facing now, nor has generating the power been.

We can for all practical means generate as much power as we could ever need, transmit it where ever we need it and do this for as long as we feel like.

That doesn't answer how people are going to be driving their cars in 10 or 20 or 30 years.

[small_steps]

$this->bbcode_second_pass_quote('Starvid', 'T')hat doesn't answer how people are going to be driving their cars in 10 or 20 or 30 years.

[pedalling_faster]

in order to handle HVDC you need very specialized power supply components, e.g. diodes with Peak Inverse Voltage of 1000 volts.

but, it creates jobs for high voltage power design engineers, which keeps us off the street. some of the most fun design projects i've had were HVDC supplies for travelling wave tubes, radar, etc.

i don't think there's anything to pick holes in. the technology works. i don't have a comprehensive overview; i just had the opportunity to work on some of the equipment for a few years.

[Newfie]

$this->bbcode_second_pass_quote('pedalling_faster', 'i')n order to handle HVDC you need very specialized power supply components, e.g. diodes with Peak Inverse Voltage of 1000 volts.
But, it creates jobs for high voltage power design engineers, which keeps us off the street. Some of the most fun design projects i've had were HVDC supplies for travelling wave tubes, radar, etc. I don't think there's anything to pick holes in. The technology works. i don't have a comprehensive overview; i just had the opportunity to work on some of the equipment for a few years.

[Niagara]

Starvid, something I've been meaning to ask for some time now.

$this->bbcode_second_pass_quote('Starvid', 'P')eak oil is not an energy crisis. It is a liquid fuel crisis.

[Dezakin]

$this->bbcode_second_pass_quote('Niagara', 'S')tarvid, something I've been meaning to ask for some time now.
$this->bbcode_second_pass_quote('Starvid', 'P')eak oil is not an energy crisis. It is a liquid fuel crisis.

[ekaggata]

Sorry I haven't found time to keep up with this thread...
Here are two pictures I took from Asplund's presentation at the DESERTEC conference. You can find his presentation along with lots of others at the site. This presentation was given on the afternoon of the 23rd April.


What I like about the first picture is that it illustrates in a very concrete fashion how much in use this technology already is. Lots more detail is of course fleshed out in the rest of the presentation, I recommend downloading it and all the rest. Most of the material is about Solar Thermal technology as far as I can tell. There are some very beautiful pictures, kind of renewables porn

[ekaggata]

$this->bbcode_second_pass_quote('small_steps', 'W')hile the line losses for an HVDC line are smaller than traditional AC lines, HVDC is not a game changer in that respect. so we go from 92% to 95% efficiency for transmission from point A to point B (with conversion). Not a big deal in that respect.

[small_steps]

$this->bbcode_second_pass_quote('ekaggata', 'O')ver 1000km distance scales it seems to make feasible what is totally infeasible with AC. This seems to line up with the real life installations he's talking about. Have I misread the information? How is it "not a game changer"?

[ekaggata]

$this->bbcode_second_pass_quote('small_steps', 'T')he graph shows the ability to transmit power vs distance. For DC lines, the only limiting factor is the IR (Current Resistance) drop. So as a line increases in length, the voltage that one sees on one end vs the other slowly varies in amplitude (given constant current through the line). For the AC line, there is an additional voltage drop, and that is due to the creation of the magnetic field(s) along the line from the current(s) in the line. Therefore, the impedance takes a form of R + j X, where R is again the resistance, and X represents the voltage drop accounting for the magnetic field (think Faraday's Law). So the voltage drop from one end to the other takes the form of I (R + j X_L). Now in HVAC lines, the "X_L" is much greater than "R", so the current (and power flow) is limited by the reactance (the j X_L portion of the impedance).

[small_steps]

$this->bbcode_second_pass_quote('ekaggata', 'A')lso very clear - in and of itself. What I don't understand, though, is why in that case we don't talk about HVAC over long distances. Is there some technical difficulty with having these capacitors, or is it only a matter of expense? In which case apples to apples ought to be easy to construct, no?
The impression I got was that HVDC is the only realistic option for 1000km+ installations. Would HVAC over 1000km be possible? Has it been done?
Are there stability issues? (From Wikipedia HDVC page: "A generator connected to a long AC transmission line may become unstable and fall out of synchronization with a distant AC power system.")

[Newfie]

Small steps,

Thanks for going over that, good refresher.

I have ignored HVDC for a long time and came across it once again in a recent Scientific American article which did nothing to explain the advantages.

The downside of HVDC is the expense of the converter station at each end. No? Higher voltage means less loss so, transformers were a cheap way to step up AC voltage. Back then the conversion methodology was mechanical. So that explains why we use AC.

Now solid state conversion makes HVDC more affordable. What I found interesting is the supposed increase in power density. By the articles I read we can move much more power on a given power line profile. That is a big issue due to the NIMBY factor.

The NERC (North American Electric Reliability Corporation) has identified several corridors that need to be strengthened and note the NIMBY factor. However I did not see where they identified HVDC as a potential solution. Or am I missing something?

Sounds like ABB might be a decent investment choice?

[small_steps]

$this->bbcode_second_pass_quote('Newfie', 'T')he downside of HVDC is the expense of the converter station at each end. No? Higher voltage means less loss so, transformers were a cheap way to step up AC voltage. Back then the conversion methodology was mechanical. So that explains why we use AC.

Now solid state conversion makes HVDC more affordable. What I found interesting is the supposed increase in power density. By the articles I read we can move much more power on a given power line profile. That is a big issue due to the NIMBY factor.

The NERC (North American Electric Reliability Corporation) has identified several corridors that need to be strengthened and note the NIMBY factor. However I did not see where they identified HVDC as a potential solution. Or am I missing something?

Sounds like ABB might be a decent investment choice?

[ekaggata]

Thanks again to small_steps from me I hope you're not too tired of all the questions!

$this->bbcode_second_pass_quote('Newfie', '
')
Sounds like ABB might be a decent investment choice?