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Superconducting Cables To Carry Power In Detroit 161

bewert writes: "Check out [this Knight-Ridder wire story.] This could change electricity distribution economics as we know it. A project is under way to replace 9 major copper power distribution cables with 3 smaller ones made from a high-temperature superconducting material called BSCCO (pronounced bisco). Pretty interesting technology, and one that could have huge implications for reduction of transmission power losses and the need for more generation." Not to mention that it means a 25-fold reduction in the weight of the cables used to carry electricity for a large chunk of Detroit.
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Superconducting Cables To Carry Power In Detroit

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  • by Anonymous Coward
    Cable is light... But liquid nitrogen cooled? How would that react under (summer heat, nuclear war, y2k, world war 3)
  • by Anonymous Coward
    What you talking about foo?
    y2k=year 2048..
    Every self-respecting dork should know that...
  • The line losses are mostly from resistance. Power disapated is equal to I*I*R. In fact, line losses are commonly called "i-squared r" losses. That's why we use high voltage lines for long distance transmission- higher voltage means the current required for the same power is less. Power = V*I, so raising voltage means less current. Less current means less resitive losses. Net-net, less resistance is a good thing.

    Part of the reason we use AC is that it's easy to change it's voltage, which comes in handy when you step it up at the generator to put on the grid, and step it down several times before it's actually used. Another reason though is it's *much* easier to generate. DC generation requires commutators & brushes, which have to be replaced, etc. Also, most household electric loads do fine with AC. Lights, anything with a motor or a resitive heater (>90% of household loads) do just as well if not better with AC.

  • by Anonymous Coward on Tuesday February 13, 2001 @05:19AM (#435821)
    Yikes, let's clean this engineering up.

    1. One of the main reasons for using the HTS cables is space. Detroit Edison needs to increase the current carrying capability at the station, and using the HTS means they get more capacity with the same underground conduit, so they don't have to excavate to improve the circuit. big savings. Plus, the smaller diameter and weight make it easier to pull the cable through the conduit, and eliminates the need for splices in the cable due to maximum pull weights. Bad splices are a common cause of failure in underground cables. Of course, if you are ComEd in Chicago, you just ignore that until the city goes dark...

    2. Cables have higher capacitance than overhead transmission lines, because the conductor is closer to the ground potential. It also has lower inductance for the same reason. There is no external electric field. The sheath is at ground potential, so the field is between the conductor and the sheath.

    3. Long distance cables are typically DC because in high voltage AC cables the voltage increases at the sending end due to the high capacitance of the line. That's why underground AC networks have shunt reactors, to keep the voltage down.
    Although inductance does reduce the maximum power transfer in a circuit, it's due to its affect on voltage.

    4. Although the lossless characteristics of HTS are important, that doesn't by itself make the economics attractive. Avoiding construction costs and pushing more power through the same rights of way due to higher current density is the niche that HTS is currently filling.

    Elvis, the power engineer-nerd.
  • I'm trying to figure out who the major players in the comercial superconductor game are, and i'm curious if any /.ers have come across who they're buying the cables from and who's going to be maintaining them... slinted (ofthehillpeople)
  • The first bird that perches on these power lines and puts a talon through the insulation is going to get a nasty surprise.

    I wonder what the cooling system looks like for these new lines? It seems quite challenging to cool all that cable and prevent any LN2 leakage. More importantly, if a leak happens, and the cable rises above its transition temperature while carrying a large current, there must be some kind of backup system to shunt off the current and prevent the heat generated by the sudden resistance from damaging the cable. Perhaps that's why the ceramic ribbon is wrapped in silver.

    I don't do hardware -- would some actual power engineers care to comment on the cable design?
  • nature already delivers free power to each and every home in the USA. It's called sunlight.

    But I guess if we learned to take advantage of that, then there would be no use for bloated inefficient electricity utilities.
  • Just do away with the power company altogether. No reliance on the power grid or power lines when you generate your own electricity more efficiently using a fuel cell. See www.plugpower.com
  • You've applied this equation incorrectly. Yes, P=V^2/R, but V is the voltage difference between the potential at one end of the wire and the potential at the other. If the power plant is producing 500KV, and the potential on the wire when it reaches the transformer is 499 KV, then you're only loosing 1KV^2/1Ohm, not 500KV^2/1Ohm, which would be the total power used including line loss plus the power used by the consumer which is not inefficiency.
  • A cool use for high-Tc superconductors :)
  • I have to love the obscure reference to
    Ringworld. :)
  • No offense, but unless I missed an important lecture in thermodynamics, how can they hope to make money from this? It takes more power (which equals money in the eyes of the power companies) to pump water uphill then they can get from it going downhill...

    You didn't miss a thermo lecture, just a economics one. A given commody market value can vary over time. Storing it and paying rent on the storage and selling it later can be quite profitable. It can also lead to quite a loss if the price never goes up enough (or you can't wait that long).

    That's what makes the stock market work. And the power market. And the futures market. And...

  • by stripes ( 3681 ) on Tuesday February 13, 2001 @04:28AM (#435830) Homepage Journal
    Trading a thick heavy but otherwise low-maintenance copper cable for a thin light but very high-maintenance superconducting one?

    According to the article the existing copper cables are cooled with oil. I expect that means they are only replacing existing high mantinance (high capicity?) cables with these things.

    I don't know enough about power distribution systems to know where these cables live, but I'm betting they are not the overhead phone pole kind. Maybe they are only found much closer to the genneration systems.

  • <rant>no, because YOU CAN'T DIVIDE BY ZERO!

    a number divided by zero is NOT infinity, it is undefined.
  • DETROIT, Michigan (Reuters) - 2 members of a work crew were simultaneously fried to a crisp and frozen solid today after their backhoe hit the new superconducting power line that was recently installed by Detroit Edison.

    The new superconducting line carries power for half the city of Detroit, and that half of the city immediately blacked out after the superconducting line was cut. Officials have given no estimate of when power will be restored, but say they are "working on it" and additionally commented that "this superconducting line is a bitch to work with".

    The shift supervisor was on site at the time of the accident. When asked about the accident, he commented "I'm just glad I was here, because they'd have a really hard time identifying the bodies otherwise". When asked how the accident happened, he said "we hit all sorts of lines with our backhoe all the time, but most of them are phone and data lines, so it's rare that there is a safety issue". Officials at Detroit Edison confirmed this, saying "most of the lines we hit belong to UUnet. We're proud to be helping to give those bastards a bad reputation".

    Family members of the deceased could not be reached for comment.

  • Space may be cold but it is a wonderful insulator. The only way to lose heat in space is to radiate it off. Keeping a superconductor cold enough would be a challenge.
  • Liquid nitrogen is a lot of fun. You can stick your finger into it without being harmed. You only get hurt by it if you drink it or if you touch water that has been in contact with it. (Water ice cooled by liquid nitrogen is fairly nasty. It sticks.)
  • Going AC->DC->AC is getting fairly cheap these days with power electronics. Of course it would be much nicer if we just got rid of AC.
  • Better check nearby space for Kemplerer Rosettes, so we can be sure we won't get mysterious bouts of superconductor plagues...


  • (By the way: one of the cool things about BSCCO -- I wonder when they made up this "Bisco" business, that's a new one on me -- but all the components are relatively non-toxic. At least they're not using something really evil like Thallium.)
    Yeah, especially Thallium Oxide , that's really a bad one!


  • If I'm not mistaken, the phase shift that inductance causes can be a big source of loss too. If your voltage and amperage waves are completely out of phase with eachother, you lose most of your power. So, I suspect in that way you can use capacitors to keep that from happening.

  • I used to live in Detroit and every year would see a lot of downed power lines.

    They don't explicitly explain (at least in this article) what effect the new cables will have on the prevalence of downed lines. However, they do mention that they're more brittle so unless they're much stronger, it seems as though this problem will get worse.

    Am I correct?
  • by Space ( 13455 )
    Would you call any computations concerning Bisco, Bisco-Math? IIRC, wasn't Bisco-Math the primary means of computation in one of Douglas Adams' ships in the Hitchhikers Guide Trilogy?
  • Found a link [naxs.com] to the bistromathematic drive
  • As usual, newspaper technical articles are pretty sketchy on the interesting bits.

    For instance, temperature is just one parameter to look at when you're looking at superconducting cables. Increasing the current density and/or the magnetic field will also tend push you out of the superconducting state. Tc is the temperature when current and field is zero, and the trouble with the high Tc superconductors is that you don't have a lot of clearence between the temperature of liquid N2 (77K) and Tc. When you try and load the cable with current, what you might call the "effective" critical temperature is going to be lower. The easy form of BSSCO is only something like 90K -- can't believe I don't remember more precisely than that, I used to work on this stuff -- anyway, I refuse to believe that they've managed to reliably come up with the 125K form of BSSCO, that's one holy grail that was looking pretty elusive, at least as of ten years ago.

    A minute with google turns up what looks like a pretty good technical article about the processing of BSCCO/Ag tape: Is Low Cost BSCCO Tape Just Around the Corner? [teameurus.com]. (ObGripe: sure would be nice if the slashdot crew would do a teeny bit of background research on these stories, instead of just pointing us at junk news sources). Looks like I might be wrong about the 125K form of the stuff: they talk about working with both the 2223 and 2212 compositions (the numbers there are the main stoichiometries of the compound, e.g. Bi2 Ba2 Ca2 Cu3 Ox... as I remember it they don't usually specify the amount of Oxygen in the mix, because it's a bitch to measure it, and it tends to vary anyway). But then, they wouldn't be talking about both forms if they had the 125K form working really well.

    Looks like they've got some decent numbers from direct measurements of current/area, which makes sense, or they wouldn't be announcing projects like this.

    (By the way: one of the cool things about BSCCO -- I wonder when they made up this "Bisco" business, that's a new one on me -- but all the components are relatively non-toxic. At least they're not using something really evil like Thallium.)

  • All superconductors have a characteristic
    called critical current. Go above it and
    superconductivity is destroyed. The lower the
    temperature, the higher the critical current.
  • Nice reference. As for oxygen content,
    you can estimate it from T_c. In fact,
    oxygen content changes with time, so
    I wonder if commercial tapes have a
    limited life-span. Keeping the tapes
    at LN2 will help, but even so oxygen
    diffusion will happen.
    BSCCO indeed is nice and safe and non-toxic
    but from engineering perspective hard to
    work with. It cleaves easily and is brittle.
    YBCO is better in that sense.
    Lastly, do you know the procedure (hasmat) for
    working with TBCO? Any nasty things from
    handling it?
  • <i>Not to mention that it means a 25-fold reduction in the weight of the cables used to carry electricity for a large chunk of Detroit.</i>

    Thank God. And just when it looked like Detroit was going to sink into the ocean under its own weight.
  • The article states that the old copper-cables where cooled by oil. Thus the argument that you're using energy to circulate the nitrogen is likely irrelevant, since circulating oil takes a lot *more* energy, especially since the old copper cables produce heat.

    Underground cables typically need to be cooled in some fashion if they're high-capacity, otherwise the heat would keep building up and cause damage at some point. (not to mention that resistance increases with temperature in copper, so you want them cold for reducing transmission-loss.)

  • Fissure erupts, turns citizen into pillar of salt! Story at 11.

    (so what's ksu's analogue to ku's kulua?)
  • Things that can make logic gates:

    Vacuum tubes
    Streams of water
    Ropes and pulleys
    Brain cells

    If you can create an intelligent out of semicondutors, then you can do it with a sufficiently complex plumbing system.
  • Excellent! Now I can finally replace my gold metal speaker wires with liquid nitrogen cooled, silver encased, bisco ribbon cables! Then I'll finally be able to sleep at night. Well, as long as I have the cryo, can I replace my tubes with Josephson junction? Thermal noise begone!
  • It's not that the single electrons 'don't collide': coupled pairs of electrons are bosons, since spin 1/2 cross spin 1/2 yields either spin 1 or spin 0: both of which are bosonic.

    You're probably familiar with the Pauli exclusion principle for electrons - this says that no two electrons (fermions) can occupy the same quantum state. This is because electrons, having spin 1/2, are fermions, and obey Fermi-Dirac statistics (interchanging fermions changes the sign of the wavefunction).

    Bosons don't have a Pauli exclusion principle - interchanging bosons doesn't change the sign of the wavefunction at all, and so the number of particles which can occupy a state is unlimited.

    Thus, imagine a pair of electrons in a material- nothing is stopping them from radiating their energy away and settling into the ground state- it doesn't matter that there are other pairs of electrons there, since a pair of electrons is a boson. They then settle into the ground state - the lowest energy state.

    Now, you've got a curious situation. The electron pair is propagating through the material since there's a potential well - there are particles which they COULD scatter off of and lose energy - but they're in the ground state - they CAN'T lose energy, so they CAN'T scatter. It's not that the electrons don't collide 'as much': ideally, they don't collide at ALL - resistance zero.

    As for the 'electron-pair' waves: the idea of waves and particles being separate things is a classical idea: Nature doesn't quite agree with that. Particles are waves, waves are particles, it's all the same bloody thing. Calling them 'electron-pair' waves is fine: calling them 'electron-pair' particles is also fine. de Broglie matter waves are also a semi-classical idea: halfway between QM and classical mechanics - it would be a good thing to abandon that idea, and just accept that fundamentally, all matter has a wavelike nature.

    For a good start in QM, read D. Griffiths "Introduction to Quantum Mechanics": Griffiths's texts are usually quite amazingly good at allowing students to actually understand the physics of the situation. Getting rid of classical intuition like "physical location of a particle" and "momentum of a particle" and "particle" in general is a good thing to learn as soon as possible if you are interested in higher physics.

    There are other processes in superconductors which do cause resistance-like effects, but fundamentally, the superconductor itself has zero resistance - you might have things like thermal resistance, or 'magnetic resistance', or impurity resistance, but the superconductor literally has zero resistance, almost (note almost) by definition.
  • No, actually, impedance is a 'resistance' to current flow due to a changing magnetic field, which induces an opposite EMF in the circuit. Physically, the best analogy would be if you imagine resistance to be traffic slowing you down in a car: impedance would be similar to something like bad gas in a car reducing the amount of power available, or going up a hill (going up a hill is a weak analogy, but it has a strong parallel in the whole EMF/potential well thing).
  • Argh, argh, argh. Somehow hit 'submit' before I was finished typing. How aggravating.

    It's true - there is no resistance in a true superconductor, isolated from all else, with an isolated current inside of it. However, place that superconductor in a circuit, and many various issues will arise, again, especially in T2 superconductors which will admit magnetic fields through their volume.

    Still, the best way to describe it is to say that the superconductor has zero resistance, and that effectively you have additional objects introducing mitigating effects.

    The first superconductor wasn't lead - distinctly not! - it was mercury. 1911, Heike Kammerlingh-Onnes, using liquid helium to cool mercury below 4K.
  • by barawn ( 25691 ) on Tuesday February 13, 2001 @08:04AM (#435853) Homepage
    Actually, no... its resistance does drop to zero, literally. However, the behavior becomes 'curious' when you actually try to drive current through it - especially since this is a T2 superconductor,which means that it forms magnetic whorls at any non-zero magnetic field. As you know, a current creates a magnetic field, and so you get a sort of 'balance' between the amount of current you can drive and the maximum field that the superconductor can support. If you try to drive more current than that, then you will begin to drive the substance out of a superconducting state.

    Is it a resistance? Well, no, distinctly not - it's not linear in voltage, for one. It could be thought of as an 'effective' resistance, but it's not resistance.

    Incidentally, it's very dangerous to simply show "Look, it's infinity!" and use that as a disproof - several things in nature are extremely curious and are literally infinity: take for instance a superfluid, which has, literally, zero viscosity, or an electron, which has (as far as we know...!) zero volume. Dividing by either of those things would tend towards infinity - the fact that it does not actually get to infinity simply means that another process begins to dominate and damp the previous one.
  • "High temperatures", like 22 degrees C? I don't think so. Not that high yet.
  • This system has a much higher energy density than copper cables. If something happens to a copper cable you get an arc which may cause a fire but hopefully the cutoff will stop the current before that happens.

    If you're carrying more electricity, then the cutoff has to be higher, and if you take the explosive effect of converting liquid nitrogen back to a gas by applying heat which in itself will cause the superconductor to stop superconducting I believe you'd get quite a big bang.

    I've seen the effect of too high a safety cutoff, in a (experimental) home storage heater that was designed to be high-ampage but it had a break in its insulation and leaked 5000watts straight back to earth. It melted the bricks round the cable but still didn't trip the fuse.

    So to summarise, don't put the wires anywhere where the cooling can be lost, such as in earthquake zones. That'll have to wait for room temperature superconductors.
  • I've always understood that this type of higher temperature superconductivity breaks down in the presence of strong magnetic fields, such as produced by strong currents in the material itself.

    Any ideas how this has been solved ?
  • (ObGripe: sure would be nice if the slashdot crew would do a teeny bit of background research on these stories, instead of just pointing us at junk news sources).

    Who would you trust to do research on this stuff, you (someone who apparently has _some_ knowledge regarding this stuff) or Rob and Hemos? This is what /. is about and why it's cool. BTW: thanks for looking it up :)

  • Oops, that's Y Ba_2 Cu_3 O_6 superconductors, and I may also get to play with NbSe_2 superconductors, too. The cyclotron is pretty cool, too.
  • Good point. Maybe they should switch to DC for these lines. Then there would be effectively no inductance losses, either.
  • by tbo ( 35008 ) on Tuesday February 13, 2001 @12:15AM (#435860) Journal
    The energy savings is in power loss. I suspect space/weight savings are secondary. Superconductivity means no resistive power loss, whereas normal transmission means usually lose you 10% or so.

    As for the cost of cooling the nitrogen, that's trivial. LN2 is as cheap as soda pop.

    This summer, I'll be working at the local particle accelerator doing beta-NMR and muon spin rotation experiments on high-temperature superconductors... Should be lots of fun! We aren't studying that particular kind, though (I think just the Yt-Ba-CuO ones).
  • Ohm's Law only applies to what are called Ohmic resistors. Some metals are generally Ohmic; others are generally Ohmic but only at particular temperatures. Some substances are not Ohmic at all, such as the YBCO superconductors I worked with as a research aide at the Texas Center for Superconductivity.

    For comparison: Ohm's Law generally applies to copper, no matter what the temperature is. Ohm's Law stops applying to aluminum once you cool it to about 4K.

    Remember: Ohm's Law is a macro-scale observation, and superconductivity is a quantum-scale event. At the quantum level, all sorts of strange things happen that are totally contrary to our macro-scale observations. The Einstein-Bose Condensate is a great example, as is superfluidity in liquid helium. (Anyone who is not utterly shocked and amazed by superfluidity apparently hasn't seen superfluids before.)
  • This is now my sig.

    The abbreviated Laws of Thermodynamics:
    1)You can't win.
    2)You can't break even.
  • But the looks of it the system is an experiment, everyone has mentioned problems, like super conductivity break down, cooling problems and the like. I feel, they are building it to find out how to solve these problems, as its built it might as well work for a living, but that is not WHY it was built.

  • > The majority of the loss is due to inductance

    Although inductance is an impedance, i.e. it will limit the current that is transmitted at a specific voltage, it does so without loss.
    The only loss through inductance is indirect. Power delivered is V*I*cos(phi), and thus diminishes when voltage and current are out of phase. Power lost is I*I*R, and thus independent of cos(phi). For the same power delivered, lowering cos(phi) will diminish efficiency, _as_long_as_there_is_R_! Without resistance, the cos(phi) will not matter!
  • Besides, "High Temperature" for a superconductor means "above 79 Kelvins". Considering that the Holy Grail of superconductor research is "room temperature", meaning "above 280 Kelvins", the high temperature stuff isn't that hot.
  • Someone please moderate this up. There's been all kinds of speculation as to what the benefit is here of using superconductors, and this is the only post I've seen that makes any sense.

    Thanks, Elvis ;)
  • I mean seriously, they need to implement this right away if possible. They say we're going to have a power crisis for the next 2 years until they start building new power plants or come up with a better idea. Think how much power they would save if they used superconducting cables that could be put towards the larger power pool.
  • No, no, no!

    1) You can't win.

    2) You can only break even on a cold day.

    3) It never gets that cold.

  • wow.. maybe I should move to the US, where you can't only run your computer on illegally tapped power, but also tap the liquid N2 for that perfect overclocking cooling system!

  • And when you run on a spot market, power on 30 seconds notice can be sold for quite a tidy profit. (Even power on 10 minutes notice, the way these plants normaly work, can be sold for quite a tidy profit).

    These plants make their money becouse off-peak power is cheap but on-peak power can be very expencive.
  • The cables they are replacing are already oil cooled so there is not a great increase in maintenance.
    They are replacing 9 wires with 3. I am guessing these are parallel lines running underground. The 3 will take up much less room, which is a big deal. In central cities power lines are run through underground conduits/pipes. These conduits are very crowded due increasing power requirements in central cities. Replacing copper lines with superconducting lines allows the power companies to meet rising power requirements without tearing up the streets to lay new conduits.
  • Of course we have to remember that refrigerating nitrogen takes a fair bit of energy.

    It will be interesting to see how much they have to spend on cooling & maintaining the cladding on the cables.

    A loss of cooling would be interesting as well - the transition from superconductor to insulator as these materials warm up is quite abrupt.

    I don't think that a section of power grid would have a high enough energy density to cause much damage if it lost superconductivity (unlike some magnets & storage rings), but you might get a bit of boiling nitrogen coming out of the ground.

  • Lack of resistance (up to a point), and greater over-all power capacity.. The article says 150 times, meaning if we had 50 or so separatly maxed out copper cables running at a constant voltage, we could combine them into 1 (with the same voltage or current (or combination of the two)). Traditionally if you wanted greater power capacity, you'd do what you needed to the wire to allow higher and higher voltages to minimize the current. Higher voltage usually requires greater separation between lines (since there is significantly enhanced potential for shorts). So by not _having_ to up the voltage, you can keep lines closer together.

    So the benifits are power efficiency, and that you need less total physical stuff to get the power downtown.

  • by iceT ( 68610 ) on Tuesday February 13, 2001 @06:10AM (#435874)
    ...to replace 9 major copper power distribution cables with 3 smaller ones...

    So, we'll only need to have 3 cables break before Detroit will lose power...

    There's something to be said for redundancy and multiple paths...
  • Sorry, but who said microporcessors have to be made out of smi-conductors? Thet's NOT the only technology that allows the creation of logical circuits. There is an ATM switch, for example, made by Hitachi, that uses superconducting circuitry. [hitachi.co.jp] The superconducting devices I know of, use the Josephson junction to operate as logical gates. Derivatives are Single Flux Quantum Logic and Quantum Magneto Flux Logic. And Josephson junctions are not new technology, actually. We studied them in Uni 7 years ago, from a book that was already 4 years old.

    I am sure this only shows what is the difference between a self-proclaimed geek mentality, and a scientist: a true scientist is open-minded, while the others can't see over their nose. That's why most of ./ readers will claim Linux to be superior to anything, even if they don't know about the laternatives. Same thing here: there is a whole world of different solid-state technologies that are not based on silicon, you just have to open your mind to, arrgh, sciences like phisics and chemistry.

  • Why don't we use them then?
    Just follow the fucking link.

  • Hmm... Imagine the possibilities of a superconducting network cable. Loop-length restrictions could become a thing of the past, repeaters would be almost totally unnecessary, and the geek factor is nearly off the scale. Grated, this would only work for systems using copper wiring (though a fiber that was truly 100% transparent would also be nifty).

  • I didn't glean from the article if Detroit Edison is sponsoring the technology, Detroit Public Lighting, or Detroit Edison, the two major players. I assume it's Detroit Edison, as DPL usually operates with a deficit. This would be a boon for the stability of the grid, as the Detroit Public Lighting grid has had repeated, major problems in the last few years, mainly with their central distribution lines which feed the smaller lines running out to communities and schools. I hope the city of Detroit gets the hint and starts dissolving the antique public service.
  • How would a superconducting cable stand against fiber?
  • At 500kV, you have an incredible amount of loss! Assuming a relatively low resistance, say only an ohm, you're losing thousands of watts of power to heat over a lenghthy run. (P=V^2/R) As far as inductance and capicitance goes, this doesn't effect the overall power, ie, it is not parasitic. They change the phase of the current waveform, which IS a problem still, because the line load needs to match the waveform to get the maximum power transfer and the smallest reflection coefficient.
  • Even with only 100A of current, there still is a huge amount of loss in the line. I very recently graduated with my EE in power systems as well. A tour of Detroit Edison not long ago confirmed this.

  • I hope they have considered the risk of nitrogen leaks in the confined spaces of the tunnels. Even a relatively small leak could quickly push out the oxygen and result in the death of anyone who happens to be nearby.
  • I suspect it is also justified as a test case. These cable could be much more useful for long distance, large-scale power transfers. For example, in Calif. at the moment, they are going to have to import power from other states, but this is wasteful because of the transmission distance.

    Things will be easier if we don't have to produce power close to where it is consumed. This isn't just a case of moving pollution to someone else's back yard - the "power loss" due to having to transport fuel counts for a lot too.

    I know here in Australia they have at least 2 long distance DC links due to the lower losses. Superconductiong cables would be wothwhile in this case due to huge power savings. As for maintenance, the main problem with ordinary cables is overheating when they are heavily loaded, the problems of SC cable will be totally different, and I think it's a bit premature to speculate on them. Obviously the SC cable will cost more in general but we're talking about a lot of power savings (and with the price increasing).

  • It will only work for as long as the heat/energy contained in your finger is high enough to maintain boiling the liquid before it begins to cover your finger. After that point, your finger will quickly become like the raquet balls, pens, and other items that get shattered for demonstrations.

    Your finger has an advantage in that hot blood gets circulated to it, so it generally can boil the N2(liq) for longer than similar sized inanimate objects.
  • Trading a thick heavy but otherwise low-maintenance copper cable for a thin light but very high-maintenance superconducting one?

    I'm trying to picture this setup in my mind. As best I can figure, there is an underground conduit that has a single cable running through it, that they then pump full of liquid nitrogen.

    They say it can carry electricity with virtually no resistance, but consider the electricity to cycle the liquid nitrogen and cool it down when it evaporates?

    Since it's all underground, I don't see the space saving aspects of reducing nine wires to three.

    Can anyone explain the key advantage to this new system? Is copper becoming that scarce/rare that they can't just throw down three more copper cables to increase capacity?

    - JoeShmoe
  • in the UK Maplin magazine recently about this. They have no web site, but baically the cables will run underground (no fried birds).

    The cables are (I think) manufacured by Pirelli and consist of a central LN2 tube surrounded by the conductor, then several layers of insulation. This is (apparently) the most efficient way of doing things
  • True, but the generators generate AC which would have to be converted to DC which would constitute a loss. Just think why your PC's power supply has all those fans and cooling vents.

    And the reason why generators generate AC and not DC is the way they work. The energy comes from spinning a loop (area A) in a magnetic field (magnetic induction B); the voltage is related to the angle between the loop and the magnetic flux density. Thus, a sinewave.

  • Hm? This is most interesting then.

    You know, this R != 0 is not my invention, I heard it somewhere. It was offered with an explanation that the reason that the resistance drops dramatically is that under some circumstances, electrons form up pairs, which don't collide as much with the material as single electrons would. This sounds quite reasonable to me, but then again, it boils down to quantum mechanics I'd suppose where common sense just aint enough.

    A quick search on google gave me this page [wspc.com.sg], which uses the term "electron-pair" waves. This particular term sounds like quantum mechanic atomic model. Would this mean that electrons in a superconductor should be considered de Broglie matter waves rather than actual particles?

    This is very interesting. I tried to look up further with google but no luck so far. Pointers would be appreciated.

    And the notion about R = U/I.. as someone mentioned, it applies only to ohmic resistors which superconductors definately are not. Shoot me in the head if I make that mistake again. I blame the lack of caffeine on that one :-)

  • Resistance R: p = 1.678E-8 Ohms/m for copper
    l = 10000m for instance
    A = 1.0 cm2 = 1E-4 m2
    R = p l/A = 1.7 Ohms

    Inductive reactance XL:
    f = 50 Hz
    û = 50kV
    î = 100A
    h = 10 m (height above ground)
    r = 0.0056 m (wire radius)
    u0 = 1.25664E-6 N/A^2
    ur = 0.99990 (copper)
    L = l * (u0*ur)/(2 pi) * cosh^-1 h/r = 0.016 H
    XL = 2*pi*f*L = 5.0 Ohms

    Comparing R = 1.7 Ohms and XL = 5.0 Ohms proves your point.

  • you think that stuff's bad -- check out sulfate of thanatol.
  • I don't think such a system is practical yet.

    The most practical energy storage system in use right now is pumped storage hydroelectric.

    This is used with a hydroelectric generator plant. When demand is low, it will use excess power to pump water uphill into a reservoir; then, during peak demand times, it uses water from the reservoir to generate electricity. Here's a link [grda.com] to one in Oklahoma.


  • by steveha ( 103154 ) on Tuesday February 13, 2001 @12:23AM (#435892) Homepage
    Can anyone explain the key advantage to this new system?

    I really want to read more details about this. But I'm pretty sure that the key advantage is the lack of resistance.

    Superconducting wires don't just have less resistance to current flow, they have no resistance at all. A superconducting cable will not have any losses due to resistance. (This means that when you run current through the superconducting cable, the cable won't heat up, so the cable won't be boiling off your liquid nitrogen.) I guess the reduced losses make up for the power needed to keep the cables as cool as liquid nitrogen.

    My main worry is whether depending on liquid nitrogen for cooling will make this system more prone to failure. I'm sure they are not replacing all the copper, at least right away!

    They wouldn't take risks with this if they were just breaking even. I'm sure that the new cables can carry more electricity than the ones they replace, not just the same amount; and the reduced losses might mean the same power plants can provide more useable power than previously.


  • I doubt there is any substantial weight savings in the superconducting cabling system. While the superconductor is substantially lighter than the copper, the cooling jacket (we're probably talking a vacuum insulated LN2 jacket) is probably quite heavy.

    There are also some technology/safety issues related to the operation of superconductors. A superconducting line carrying a large amount of current can do some pretty catastrophic things if the temperature rises above the critical superconducting temperature. The transition from no resistance to substantive resistance can turn the wire into a nice big heater element inside an LN2 cooled system. Explosive vaporization of the superconducting element has happened in laboratories before. The other problem to be alert for is critical current. Superconductors are only superconducting up to a critical current level. Attempts to pump more than the critical current through the wire will result in it transitioning from superconducting to normal conductivity with the same results as above.

    I'm sure the engineers who have designed the system have taken this into account. But the deployment of a crygogenically cooled power distribution system is far from a trivial exercise.

    BTW, I've been told that power distribution systems consume almost half of the power generated just in getting the power from the plant to our homes/offices. Also while the superconducting lines can save a lot of energy, it takes a lot of energy to make LN2.
  • Cable is light... But liquid nitrogen cooled? How would that react under (summer heat, nuclear war, y2k, world war 3)

    Oh jesus....I'm sure it would be fine in the summer heat. If there was a nuclear war, getting power to detroit probably doesn't rank really high on priorities. No one'll need lights since they'll glow anyways! :)

    And dude, Y2K ended last year.

  • Nah, that's not how LN2 is normally dealt with.

    Even inside a good vacuum insulator, the stuff IS going to boil off. Trying to maintain a sealed system will just create a bomb.

    Undoubtedly, the stuff will vent to the air around it, and an appropriate amount of circulation will be ensured. I suspect there are fans down there already, so they probably don't need to change anything significantly.

  • Having read a good few responses to this article, I have come to the conclusion that I often do when reading slashdot.

    A little ignorance goes a long way.

    Come on people, don't post just for the sake of it.

  • Here [google.com] is Google search that turns up lots of useful info. Every article on the first page of results is worth looking at. Here are the first three matches.

    The first link [bnl.gov] is slide from a Brookhaven talk. Not much useful info here, and the picture doesn't match what the other links describe. The entire slide show is fairly interesting, though.

    The second link [amsuper.com] is PDF whitepaper discussing the commercial production of such cable. A great read, if you have the time to wade through it.

    The third link [sciencenews.org] is an article from the Nov. 18, 2000, issue of "Science News" on the same subject as the Knight-Ridder article. Much more technical details.

  • No a Super conductor has zero resistance, the complete circuit however does not have zero resistance, the resistance at the load end of the circuit, and at the battery/generator end limit the current.

    If the current in a superconducting wire reaches a high enough level its magnetic field will destroy the superconductive properties of the wire, so there is an maximum current possible in the wire.

    For A/C currents while the Superconducting wire has zero resistance, it does have some impedance which also limits the maximum current but in a way that doesn't dissapate energy as heat.

  • Looking though some EE books I have, the actual power loww of a 10km wire (1/4 inch diamete) is going to be around 4.7% or so. This is actually using methods in Physics more than in circuit analysis, but should still work.

    Also, the frequency is a major contributing factor in such line, being the higher the frequency (8khz as compared to 4khz) you get from around 500 watts power loss to 2000 watts depending how much your line amperage is (RMS).

    Lastly, though inductors can cause more power loss than the line resistance themselves, you have a assume you have a high variance of power output from a power station. The less the variance, the less that has to do with induction. But, in the cases of power spikes and such, I think I'd take power loss over my house being pumped with 500 amps (when ~200 is what's running my computers, TVs, toasters, etc).

  • They say it can carry electricity with virtually no resistance, but consider the electricity to cycle the liquid nitrogen and cool it down when it evaporates?
    Since electrical resistance is minimal, the only cooling required once the sysem is up and running is to compensate for pressure in the Nitrogen circulation system, and for heat that leaks in. Quality of insulation is important.

    Economics thus look best where electrical demand is constant. Use copper as a supplement for peak loads

    IANAPBIPOOS (I Am Not A Physicist But I Play One On Slashdot)

  • Keep in mind that you can also use the same linquid nitrogen to overclock your PC to kingdom come! ;)
  • One of the great secrets of why companies move away from copper wires is that the sale market for it will help cover costs of the replacement. The telecom industry actually MADE money in the replacement of copper with fiber optic cable. While high temp superconducters may be a bit more pricey the cost will be offset by the resale of the old copper wire...

  • Shouldn't they be trying this out in California ?
  • Seeing as microprocessors are based on semi-conductors, which are always going to be resistant, it's just not going to happen.
  • Basically the use of stored hydro is to accomodate changing loads. Most power generation systems (especially nuclear) tend to work better if they work at a constant rate. Stored hydro allows you to use excess power to pump water up the hill, which is then used to generate power in times of increased load. That means that the rate of power generation can be kept at the mean power useage (over a given period) while demand can fluctuate.

    Ok so some energy is lost, but then energy is lost in all parts of the power generation and distribution system. It is cheaper and easier to run power generators at a constant rate all the time, especially nuclear.
  • by otter42 ( 190544 ) on Tuesday February 13, 2001 @05:50AM (#435920) Homepage Journal
    Working in cryobiology, a cryogenic field, I am familiar with some of the problems of liquid nitrogen.

    Really, there aren't any. The stuff is insanely cheap. Like so cheap, you want to start using it as car fuel and stop drinking milk. I purchase 210L for $35.67, which works out to something around 55 cents a gallon!

    Nitrogen is cheap, inert, catastrophic leaks have no effect on the world(unless it's in a closed room and someone can't get out before they suffocate), readily availalble (comprises 79% of air), and would only get cheaper to produce as power plants used more of it.

    Keeping cables cool is also very easy since LN2 can be easily run through a pressurized system. There is no need to circulate the LN2 since the addition of heat will make some LN2 boil away. Simply allow the vapor to dissapate and replace any lost fluid.

    The biggest problem with this project is what happens if the LN2 system fails for some reason. Fortunately, though, they will have an extremely long heads up on a failure and will be able to shut a cable down with plenty of time to spare.

    On a side note, the cables use silver because it allows for proper grain growth and flexibility. Otherwise you couldn't make a cable out of the material. A big squarish chunk of it, sure, but not something long, thin, and reasonably flexible like a cable. Science News did an article on it a couple months ago.

  • Erm, but pure inductance (or a combination of inductance and capacitance, which any transmission line has) is lossless, isn't it?

    I think that the main problem with the inductance of long lines is the I and V getting out of phase, which results in less true power being delivered to the load. In addition, heavy industrial machinery is largely inductive by nature, adding to the problem. The power company monitor changes in phase when connecting stuff up, and add power-factor correction capacitors where neccessary.

    The problem with saltwater may be true, in that the AC flowing in the line induces eddy currents in the partially conductive saltwater, which then will heat up, ie contributes a loss. I would think that the higher the power and line length the worse the problem.
  • Would it hurt the bird's talon if it punctured the cable?

    I suppose this would teach the bird to stay off superconducting cables and go back to being a penis bird instead.
  • This works great on paper but no so in the real world. In reality, you have a rather large magnetic field changing direction at 60Hz. Now some of the energy from this magnetic field is absorbed into the surrounding enviroment - hence, is lost. Much of this depends on the enviroment but it's safe to say that anything metal will have induced currents. The end result - on HV systems most of the power loss is not due to resistance, but due to the inductance (indirectly, but still due to the inductance.)


  • by willy_me ( 212994 ) on Tuesday February 13, 2001 @12:25AM (#435937)
    When you have power distribution lines running at 500kV, there isn't that much loss due to resistance. The majority of the loss is due to inductance. In order to really benefit from the superconductor they will have to convert AC to DC, transmit in DC, then convert back to AC before being delivered to customers.

    Going from AC to DC then back to AC isn't the most efficient way of doing things. It is however still done. For example, power is distributed from the mainland to Vancouver island via underwater DC power lines. I believe DC is used here because of the increased effect of inductance with the lines going under salt water.

    Using superconducters is great, really, it is... But just because there is basically zero resistance in those superconducters it doesn't mean that all of our problems will be solved. Line losses due to resistance aren't the main loss when it comes to distributing power. There are also losses with the generators, transformers, AC/DC/AC converters and most importandly - inductance. It's a start, not a solution...


  • by willy_me ( 212994 ) on Tuesday February 13, 2001 @01:00AM (#435938)
    Sorry, but you don't lose 10% of power due to resistive losses - not even close.

    First of all, most of the losses are due to inductance, not resistance (this assumes you're using HV lines - 500kV is typical.) And at 500kV there isn't that much current flowing. 50MWatts just requires 100Amps - very reasonable.

    I wish I still had my college books, I could tell you exactly what the losses would be. (I graduated in power systems electronics - this is what we did.) Unfortunately I don't - but I assure you that resistive losses are not the main source of loss from a high voltage power distribution system.


  • Ah, a Darwin Award Applicant! Somehow I don't think these things will be 120 volts. A warm spot in the cable could be interesting when the resistance goes up and it isn't superconducting anymore. Third strike is Liquid Nitrogen does not contain Oxygen. I wonder which is first, the Arc, the Explosion, or the Asphyxiation :-)
  • Umm, Have you priced the "high Power" stuff lately. Silicone has it's limits. Anythig over about 100 KW gets pricey fast. It's also harder to protect from the overcurrent/overvoltage effects of lightning. BPA has been doing this stuff for years on a long line. (DC 1,200,000 volts) The North end of the line is at The Dalles Oregon on the Columbia River and the South end of the line is 60 Miles North of Los Angeles California. This line has no substations in between due to the high cost of the DC/AC converters. The line is a long running experiment. The converters are two kinds. One is all solid state, the other is Mecury Thyritron. I don't know if BPA has any public website with details on the DC line. I know about it because my father was a Substation Operator for BPA before he retired. I have had a full tour. The line was built in the '60's if I remember right. The California substation yard is fully enclosed in a farady cage for RFI with chokes on the lines to the yard, while The Dalles one does not. The reason for the experiment was to find a cheap way to transport power over long distance without the usual transmission losses. (inductive, capacitive, & coupling to parallel lines like ranchers fences) They were testing the ability to protect it from lightning and see the advantages of DC over AC for the long haul and see if it made good business sense. Anybody in the LA area may want to look up the Sylmar Converter East Station. It was dammaged in an earthquake 1994, and they had a fire in 1993. This has not been a low cost maitenance project.
  • Well, it all depends on where in space you are. An object that both absorbs and emits perfectly, put at a distance from the Sun equal to that of Earth, will stabilize at a temperature of about 280 K or 7 C. If it's shielded from the Sun but exposed to inter-planetary and inter-stellar radiation, it reaches about 5 K or -268 C. If it were far from all stars and galaxies, it would come into equilibrium with the microwave background at about 2.7 K. Now, the last is not feasible at this time.

    Depending on how it is constructed, you'd have to use a lot less energy to keep it cool then a similar system on the ground, but there you go...

  • And I can say, with great precision, that the cables will be stolen and sold at a pawnshop.
  • One of the bigest advanatages of HTS Transmission is a not only less resistance but lower power operating temperatures. This is not a direct affect of the Nitrogen cooling. When the Material is operating at superconducting temperatures the lack of resistance creates absoluty no heat in transmission. Once the temperature is reached it is easy to maintain. The transmission of power through the cable has no affect on core temperature. Very little energy is needed to keep it in a supercontuctive state once it is reached. burying the cable will assist in prviding a natural and cost effective way of assisting in ambient temperature degridation. Here is a company that was the first to have an operational prototype. picture included. Intermagnetics
  • They can make money from that if they have a power plant that can provide the same output with minimal variable cost 24 hours a day. At night they will likely not use their full capacity. By using the surplus power produced during the night to pump water into a reservoir, heat up a well, or do anything which will allow them to produce more power at daytime, they may be able to improve throughput during the times of day when the power drain is highest.

    It's not about increasing power production, but about efficient short term storage.

As of next Tuesday, C will be flushed in favor of COBOL. Please update your programs.