Like the illusion of Wall Street, with its vast and powerful investment banks, now shuttered, China too is an illusion perpetuated by the Globalists that gave us the 15,000 mile Caesar salad, poisoned cat food and lead based paint on babies' pacifiers. Like the illusion that money would come from thin air to always push housing prices higher, China has spent a generation pursuing its illusion. Pursuing an unattainable dream to be like the West, while 6000 years of its carefully shepherded top soil blows into the sea.
Posted: Sun Jun 01, 2008 2:17 am Post subject: Re: Pick holes in this --> HVDC
small_steps wrote:
The 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).
So far, so clear. Thanks for the explanation.
Quote:
However, this can be compensated for by inserting a series capacitor (or capacitors) in the HVAC line. What this does is to add negative reactance (-j X_C) to the overall line impedance so that the overall line impedance takes a form of R + j X_L - j X_C. However, the ABB graphic neglects the addition of the series capacitor in the line, and then shows the cheap AC line vs the expensive DC line. Apples to oranges if you will.
Also 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.")
Quote:
This applies to overhead lines, underground lines are dominated by capacitive reactance, so compensation of the line is nearly impossible. This is where I see HVDC being the better choice, and you can see that in the installations (shown in your figure) of the undersea lines in northern Europe. HVDC lines are also used to connect areas which have different frequencies (50 / 60Hz) etc, which also accounts for a number of other installations in the figure.
This may be an unimportant technical detail, but I'm curious - why do undersea cables have a higher capacitance?
Posted: Tue Jun 03, 2008 9:48 pm Post subject: Re: Pick holes in this --> HVDC
ekaggata wrote:
Also 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.")
While one can compensate for the series inductance, there is also a shunt (parallel) reactance that is created by the charging and discharging of the capacitance (to ground - and other phases) of the line. (Ever hear of loading coils in telephone lines? - same effect - trying to compensate for the capacitance of the line - more below). But for high current lines, we are already trying to compensate for inductance, and inductors of these current ratings, would be by any measure, impractical.
I would say that the only practical method to transmit electrical power over significant distance is HVDC, because of these issues we have been discussing, not efficiency.
For AC systems, the ability to transmit power between two places is largely the relative phase angle between the locations, not the amplitude of the voltages, as well as the reactance between the locations. However, for DC systems, itis simply the relative voltage between the locations, as well as the resistance of the line.
Another manner to think about transmission lines is as a shaft between the generator and load. If the shaft is long, there is less likelyhood of both ends of the shaft to be nearly at the same angle.
ekaggata wrote:
This may be an unimportant technical detail, but I'm curious - why do undersea cables have a higher capacitance?
Capacitance is proportional to area, and inversely proportional to distance between potential. C~ A/d. Now undersea cables have only a fairly thin insulating layer between the current carrying conductor (at high voltage), while the overhead lines have significant distance between the conductor and ground (and much less capacitance).
Hope this helps clarify the issues.... _________________ "Sometimes one pays most for the things one gets for nothing."
Albert Einstein
Joined: Nov 15, 2007 Posts: 346 Location: US East Coast
Posted: Thu Jun 05, 2008 5:48 am Post subject: Re: Pick holes in this --> HVDC
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? _________________ When going through hell, keep going! Churchill
Nothing is ever lost by courtesy. It is the the cheapest of pleasures, costs nothing, and conveys much. E Wiman
I know there’s no solution, so I just enjoy what’s here and I enjoy the journey G Carlin
Posted: Fri Jun 06, 2008 8:17 am Post subject: Re: Pick holes in this --> HVDC
Newfie wrote:
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?
I don't have the numbers at my easy disposal, but much of the cost of transmission lines is due to litigation. The cost of the lines, the purchase of the right of way, and the man hours and equipment tends to be something on the order of 15% of the overall cost. Would be interesting if the litigation cost could be mitigated and the more capable more expensive HVDC lines were installed. What would the overall cost become?
Likely to be an effect of relative unfamiliarity of HVDC equipment and capabilities on NERC's part. Not sure however. Could be that the corridors are relatively short, and cost benefit does not favor HVDC, but I would have imagined that they would have commented on that if that were the case. _________________ "Sometimes one pays most for the things one gets for nothing."
Albert Einstein
Posted: Sun Jun 15, 2008 6:27 am Post subject: Re: Pick holes in this --> HVDC
Thanks again to small_steps from me I hope you're not too tired of all the questions!
Newfie wrote:
Sounds like ABB might be a decent investment choice?
It does indeed look like a superb company, doesn't it? And, glancing over its numbers, even with its recent run-up in price, I don't think it would be considered expensive by normal standards (e.g. P/E). When it comes to investment, I am a neophyte, but this one is tempting!
Here's someone probably talking their book, but all the same...
Joined: Nov 15, 2007 Posts: 346 Location: US East Coast
Posted: Sun Jun 15, 2008 9:38 am Post subject: Re: Pick holes in this --> HVDC
Hummmmmm..............
I bought some stock last week, maybe will buy some more. _________________ When going through hell, keep going! Churchill
Nothing is ever lost by courtesy. It is the the cheapest of pleasures, costs nothing, and conveys much. E Wiman
I know there’s no solution, so I just enjoy what’s here and I enjoy the journey G Carlin
Joined: Feb 20, 2005 Posts: 2888 Location: Uppsala, Sweden
Posted: Wed Jun 18, 2008 10:40 am Post subject: Re: Pick holes in this --> HVDC
Niagara wrote:
Starvid, something I've been meaning to ask for some time now.
Starvid wrote:
Peak oil is not an energy crisis. It is a liquid fuel crisis.
What kind of bullshit is that? Our nearly 7 billion inhabitants on the earth are a result of a drawdown of petroleum; millions of years of solar energy stored under the ground. Once that energy store is gone, it's 'dieoff' season.
Not an energy crisis? So if we don't have an energy problem, why can't we simply make liquid fuel to replace oil?
We could electrolyze seawater to make all the hydrogen we need to power out vehicles, heat our homes, make fertilizer from atmospheric nitrogen etc...
So there's no problem, right? I mean if there's no energy crisis, what stops the party from continuing on for centuries?
You come out with some good posts, but lose the sig line. You lose credibility.
Sorry for not answering you, but I haven't been in this forum section for a while.
And Dezakin pretty much nailed it. It's pretty much a question of building infrastructure, and having a pretty sucky life while we do it. At least for people who put great value in materialistic things.
Understanding this is absolutely fundamental, and most people around here still don't get it. Maybe they don't want to get it?
Anyway, that's why I have this sig line. I believe it is my most valuable contribution to this board.
I think it might even be a direct quote from Dr. Hirsch. _________________ Peak oil is not an energy crisis. It is a liquid fuel crisis.
Joined: Feb 20, 2005 Posts: 2888 Location: Uppsala, Sweden
Posted: Wed Jun 18, 2008 10:42 am Post subject: Re: Pick holes in this --> HVDC
ABB is a great company. But Siemens do pretty much the same things and is cheaper.
Disclosure: I don't own shares in ABB or Siemens, but I do have shares in the investment company Investor of which ABB shares is the biggest holding, and I'm waiting for Siemens to go down a bit more before I buy shares in said company. _________________ Peak oil is not an energy crisis. It is a liquid fuel crisis.
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I hope you're not too tired of all the questions!
