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Superconducting Power Cable in Detroit 144

mgarraha writes: "According to a Washington Post article, this summer Detroit Edison will lay 1200 feet of superconducting power cable near their Frisbie substation, which serves 14,000 customers in downtown Detroit. The cable, made by American Superconductor and Pirelli, consists of silver-clad HTS ceramic ribbons woven around a pipe for liquid nitrogen." We've mentioned this particular project before. It's not room-temperature, but still interesting to see superconductors coming into large-scale, common use.
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Superconducting Power Cable in Detroit

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  • by Anonymous Coward
    But you can't keep it pressurized. Like all refrigeration systems, it works by compressing the refrigerant into a liquid (where it will give off heat, like at the back of your fridge) then releasing it into a low pressure area (known as an evaporator) where it will evaportate. The process of evaporation requires heat, and it will take it from its surroundings, therefore leaving its surroundings cooler. That's how refrigeration works, so keeping it pressurized doesn't do anything until you allow it to depressurize and evaporate.
  • by Anonymous Coward
    The expensive part is the pipe and the buried tunnel. For superconductors to solve our most major electrical distribution problems, they'll have to run for thousands of miles.

    Unfortunately, you're not going to see these brittle ceramic superconductors dangling in the wind from cheap steel towers. That means huge expenses incurred creating an entirely new underground long-distance power infrastructure. The real question is, will that expense be recovered?

  • Superconducting Niobium alloys (of the traditional Liquid Helium temp variety so as to avoid quenching in high fields) have been in use for more than 20 years now. Do you know of a major North American metro area that does not have an MRI imaging facility? No? That means superconductors have been in widespread use in routine clinical NMR-MRI imaging for all sorts of medical conditions (heart patients, epileptics and brain imaging, etc.). None of the liquid nitro temp ceramic compounds has the magnetic quench resistance that the niobium alloys do. A typical MRI coil needs to maintain a uniform field of 1.5 Tesla across the body parts being imaged - including whole body NMR scanners.
  • by Anonymous Coward
    I think that in this case supercritical refers to a fluid that has been heated behond its boiling point, but has not undergone a phase transition. The liquid will undergo a phase change as soon as a nucleation site for bubble formation is introduced. Once bubbles start to form the liquid can boil explosively.

    This is one of the reasons why chemists wear goggles.

    You can do this one at home: Get a *clean* pan (glass is best), and fill it with water. Gently heat to boiling point.

    Allow it to cool slightly, then heating *very* gently. If there are no jaggy bits in the pan, bits of dirt in there etc you should be able to superheat the liquid. If you want to test this then stand back and throw in a pinch of salt, bit of sand, pet gerbil, whatever.

    Ice formation also needs to start somewhere - it is possible to supercool liquids. I believe that some arctic fish exist in a supercooled state during winter - stick a pin in them and they freeze solid in a couple of seconds.
  • by Tony Shepps ( 333 ) on Sunday May 20, 2001 @06:56PM (#209178) Homepage
    Once those Detroit sorts find out there's Nitro in the streets, they'll be tearing 'em up for the liquid nitro-burnin funny cars! SATURDAY! SATURDAY! SATURDAY!

    Koff-koff-koff OH man it's been a while.

  • Still, I wouldn't want to be too close then the 1200 foot long fuse blows...
  • "There is such a thing as a supercritical fluid, but that is way beyond the scope of this discussion."

    Hi, I'm not a ChemE, just a mathematician. But what little I know about supercritical fluids pertains to their use as solvents -- which sounds like a bad idea for underground cabling. However, I'm glad you mentioned them. This is the first time I've seen mention of supercritical fluids since the summer of 1991.

    There was a question above about the environmental impact of the nitrogen line breaking. Using supercritical fluids, for instance supercritical nitrogen, to replace nasty organic solvents has great environmental benefits. And just as funny as the worry about releasing nitrogen into the air, was that you could (jokingly) negate any greenhouse effects from supercritical carbon dioxide by putting a plant where this solvent was exhausted.

    -Paul Komarek

    environmentally-friendly aspects of replacing traditional organic solvents with supercritical carbon dioxide,
  • As noted numerous times what we breath is ~75% Nitrogen (unless you live in LA, Denver or Dallas then check today's stats.) It's pretty much inert in the conditions most of us are familier with and would be so in the environment around a cooled-cable break.

    Indeed if one had to dump something in the atmosphere this would be most folks #1 choice followed by pure water.

    The biggest danger would be freezing something important like a bodypart from extended immersion. However since liquid Nitrogen behaves like most liguids and doesn't do anything funny it's not hard to understand/predict & it does evaporate easily.

  • It is already extracted from the air, at roughly US$0.10/Liter which covers the cost of the equipment & handling plus some profit.

    Liquid Nitrogen is used in LOTS of processes and has a well established production infrasructure. Indeed if you were to call a local distributer you'd find they likely deliver to most of the research, manufacturing & medical facilities around you; those they don't likely have on-site production.

    If liquid-Nitrogen cooling cables takes off you'll likely see sales of modular production facilities increase but I doubt the overall economics will change: This is pretty basic & well established stuff.

  • I was just at the Beckman Institute at the University of Illinois at Urbana/Champaign and got to play with this unsealed tank of lN2 - you just tipped it (It was on this hinged mount) and liquid nitrogen poured out of it. Great fun.

    I poured it all over my hand, and hit it with a banana - my hand shattered into several pieces. Just had to hold them in place until they thawed and everything was as good as new!

    (I am so full of shit. You ever call anyone a 'this'? It means 'mixed up piece of shit' - same letters, just mixed up. *snork*)

  • Better yet, hold the base of the bulb in one hand, and piss into the toilet with the other!

    Hey, it's time to winnow out the Slashdot crowd. Evolution in action...

  • This wasn't about transmission losses.

    I'm pretty sure this is about not digging up the streets. Read the article.

    They're only running 1200 feet of cable. That's not enough for transmission to be a problem. But it is a helluva problem to expand the system: the old conduits were laid down a looooong time ago, and are at capacity.

    The new cabling allows them to triple the capacity without digging new trenches.

    I'm pretty sure that's what this is about: expanding inner-city capacity without the expense and trouble of laying new conduits.

  • Switching those wires to superconductors would take care of the loss due to resistance in the wires, but it would not prevent the inductive transfer of power to other conductors (like the "capture coil" and florescent light you mention).

  • So, it sounds like a good idea, but what is the environmental impact of a break in that pipe with that liquid nitrogen in it? Ain't it going to go liquid to gas awful damn fast?
  • Get off it, all you idiots who think I don't know that nitrogen ITSELF is harmless.

    But tell me, don't you think a rapid underground expansion of gas is going to have some "explosive" consequences?

  • These only look feasable for a few miles-
    i.e. putting those high tension wires underground
    in an urban area. Still need a power plant to
    generate electricity.
  • I expect the problems causing the power outages in California are due to management decisions, not lossy transmission. New transmission technology, coupled with the new lossless cables, will just result in the same brownouts. The management, in their race to make as much profit for the shareholders as possible, will just shutdown the 20% extra generation that they no longer need.

  • That's so funny because it could be true!

    And that would be Sunday! Sunday! Sunday! At the Pontiac Sil-verdome! dome! dome!

    -- A dyed-in-the-wool Detroiter
  • And perhaps read the article? The wire itself isn't made of poisonous material. And if the enclosing pipe breaks it'll release Nitrogen into the atmosphere. You know, the same atmosphere we breath...which is a bit over 75% Nitrogen.

    Watch that knee!
  • I hope all the engineers working on this project have thought of this! Quick, what's the number for their offices so I can warn them!

  • If the nitrogen is kept at the right pressure, then it doesn't even have to be kept cold

    Yes, but this would be useless for superconducting applications. The whole point is for it to be cold, or else the superconductor won't work.
  • Liquid nitrogen is cheap!!. If the nitrogen is kept at the right pressure, then it doesn't even have to be kept cold. Pressurized lines are already in use for gas and steam. I'm sure that liquid nitrogen isn't much different.
    Nitrogen, like hydrogen, helium, oxygen, methane, and lots of other gasses cannot exist as a liquid at room temperature under any pressure. I used to work in a lab where we used alot of lN2 and the number one rule was "never seal a container with lN2 in it". If a container ever did have to be closed, it was done so with some sort of stopper or cork that would easily pop off the moment the pressure rose. If you do seal in some of one of these liquids and let the temperature rise, the liquid will turn to gas and exert extreme pressure on the container. This is the reason why hydrogen and natural gas powered cars are not popular.

    Also, superconductors that conduct at lN2 temperatures do so not because they are surrounded by lN2, but because they are at or below the boiling temperature of lN2 under standard pressure. Even if you could keep the lN2 liquid at a higher temperature by pressurizing it, the superconductor would still cease to superconduct the moment it's threshold temperature is reached. The good news is the superconductors produce no heat so all that's needed to keep the lN2 around is good insulation.

    Finally, both gas and steam are gasses.

  • If anyone is interested, I just looked up the critical point for nitrogen at []. It's 126.2K [or -146.9 C (-232.4 F)]. Regardless of the pressure, it is not possible to liquify nitrogen (or keep it liquid) above this temperature.
  • I'm looking at my sigaret lighter now. It's one of those see through models. It seems as though there is some fluid in there. If I let some of that fluid escape, it's suddenly not a fluid! Huh? But it is at room temperature! Huh? And it is methane! What? I just read this is impossible.
    You know that person who told you there is methane in your lighter; don't listen to that person anymore. The critical temperature for methane is 190.56K (way below room temperature), see for yourself []. Also, definition of critical temperature [].
  • Yeah, but there's not _much_ value in that. You still have to wrap the wire around rigid pipes. and once the system is in place and operating at supercooled temperatures it's going to be relatively brittle anyway --- probably not earthquake proof in any event.
  • Yes, you would see a localized increase of nitrogen. Just as you see a localized decrease at the facility where the nitrogen is extracted from the atmosphere. It's not proof - but this has been going on for decades. It's not as if they're MAKING nitrogen - they're only moving it from one part of the world to another. That's just got to be harmless.

  • 1. Liquid Nitrogen is cheaper than beer.

    That's not much help. Cheaper than what beer? Chimay runs about $9.00US/liter around these parts.

    Of course, it's worth it!
  • There's still a good reason to use AC:

    Transformers are a heck of a lot cheaper than DC-DC or DC-AC converters, and can be made about as efficient as a solid state converter. When you're dealing with such high voltages, high currents, or both, you'll find the solid state converters are significantly more expensive.


    Honk if you've... Oh, nevermind. ***WHOOOSH***

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  • Actually, there are two ways energy is lost, only one of which is inductively. You can harness the magnetic field generated by the power line with a coil (inductive), but you can also harness the electrostatic force generated by the line. This is what happens when you bring a flourescent light close to a high tension line.

    Given that a high tension line is, say, 40ft in the air (for good reason), and is at 40kV, then there is 1000V per foot between the line and the ground. The air has a very high resistance, but a few pico or nano amps does flow from the wire to the ground. This is not enough to be felt by the human body, but will light a flourescent bulb (not full brightness, but close). As the lines get close to the ground (as when coming to a substation) they put fencing around it because the voltage can get as high as 10kV per foot, generating more current, more ozone, and a more hazardous place for the human body.

    At any rate, I mention this because the superconductor will have very little electrostatic energy (underground cables are insulated better than just with air), but will create a greater magnetic field. This inductive energy is only lost when there are ferrous materials (or conducting loops) within its field. If they engineer it well, they can even limit those losses significantly.


    Root. It does the body good.

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  • No, he is right. I don't know where you took your thermodynamics classes, but you were misled. All materials have a "critical point" above which there is no liquid state. To be more precise, there is no liquid-gas phase transition -- in fact what you get at high pressures is a mush that transforms smoothly from "mostly liquid like" to "mostly gas like", but there is never any 2 phase seperation.

    For N2, the critical point is below room temperature.

    I suspect that there was at the very least a pressure release valve somewhere on your ln2 tank.

    Finally, I suppose they could use N2 based vapor cooling along the length of this pipe, but they would have to be screwed in the head to want to. You would have to build the whole system to withstand several thousands of psi with controlled bleed valves the whole way. It is much, much simpler to pump low temperature lN2 the whole way where your equipment only has to handle a small pressure over 1 atm.
  • Well, like any electric line, the person who cut it is in a world of hurt. Presumably the lN2 system has some sort of safety shutoff the prevents it from pumping too much lN2 out of a rupture, but even so, there could be enough cold nitrogen gas in the area to suffocate someone nearby.

    It sounds from the article like this isn't likely to be a problem in their location: They are doing this because it is so hard to dig there.
  • The cool thing about MgB2 is that people are hoping they can "tweak" it to superconduct above the magic 77K (the cupric oxide semiconductors were also discovered with a Tc around 40K, and quickly improved), while still being easier to work with than ceramic superconductors and more importantly, it points to new areas of research that might improve our understanding of superconductors in general, possibly leading to mugh higher temperature supercondutors
  • by norton_I ( 64015 ) <> on Sunday May 20, 2001 @06:56PM (#209206)
    Actually, it should be substantially cheaper. High power underground lines, including these ones, are usually oil cooled. Oil cooling is pretty expensive, since you have to somewhere dissipage quite a bit of heat. Liquid nitrogen is cheaper than water, and the superconductor doesn't produce any heat.

    People are also looking at using this kind of wire in high power electric motors and transformers for the same reason -- not efficiency, but size and cost.
  • OK, maybe this is covered in other material, but it wasn't in the article. What happens if the cable breaks? I realize that once the liquid nitrogen gets out of the pipe, it will evaporate pretty quickly. But it's still a hazard, over and above the electrical current.


  • They do if they work for NASA :0
  • Also, since the power lines must run both ways, coming and going (at least, I believe that's how it works to close the circuit)

    Actually, this isn't right. The general scheme is to use an earth return to the power plant. Even if there is a conductor running as a return it shouldn't be carrying any current. You can demonstrate how this works pretty easily with a cheap 2 prong extension cord and a lightbulb.

    • Cut the extension cord so that you have a length of cord attached to the end that plugs into the wall. You may discard the end which you'd plug lamps into.
    • Cut the wider prong off of the plug end.
    • Remove the side of the cord associated with the removed prong.
    • Strip a small amount of the insulation from the end of the remaining wire.
    • solder this to the threaded part of a lightbulb.
    • Plug your modified plug into the wall and touch the base of the bulb to a faucet or other grounded metal object.
    • If the bulb doesn't light, turn the plug over and try again.
    This works because one line in your home sockets is always held at ground potential while the other one varies between -120 and +120 volts (If you live in the US or another place with a 120V household supply). This page [] does a little bit of explaining on how all of this works. You might also want to check out this article [] at the always informative [] site.

  • It's lossy enough that California can't easily buy power from other states or countries which have the power. Ontario is going to bring back Bruce B nuclear power plant (more than enough to power a few small cities). Not because we need it now, but we may in another decade or so. I'm sure British Energy is willing to sell the power being generated to the south. Good luck getting it there though.
  • Liquid N2 is very cheap (a gallon of LN2 is cheaper than a gallon of milk in most places). Also, if you keep it presurized, then you don't have to worry about keeping it cold since it can't expand.

    Mark Duell
  • -- A dyed-in-the-wool Detroiter

    I'm sorry..

    Really sorry.

    Really, really sorry.
  • The magnetic fields around an electrical conductor actually rotate around the core, rather then attract it...
    The magnetic fields around a linear conductor circle it, true; by the right-hand rule, if you point your thumb in the direction of current flow (positive to negative - just think of the carriers as holes instead of those pesky electrons) and curl your fingers, your fingers will go around in the direction that the field circles.

    However, you're wrong about the attraction. If you have a chunk of ferromagnetic material, it will feel a force pulling it toward the area of stronger B field. This happens to be toward the conductor. The gradient isn't as strong near a linear conductor (1/r) as it is near a solenoid (1/r), but it is an attractive force nevertheless.

    The superconducting cables are all but certainly set up as coax (DC) or twisted triplets (3-phase AC). The field from these will be mostly self-cancelling due to the balanced currents.

    Where are you from anyway? I'm assuming it's the US based on the sorry state of education there.
    That remark was just too ironic for this US-born and -educated geek to resist quoting.
  • Who gave this a 4?
    Thermodynamics 101:
    1. Pressure is released from room temperature Liquid nitrogen.
    BEEEEP! You lose, but thanks for playing. Room temperature is far above the critical temperature of nitrogen, above which it cannot exist as a liquid.

    Maybe you should stick to grammar.

  • Notice the words "carrying capacity" in what you just quoted? That means they can ramp up the amount of power carried by the lines which risking burning them UP!
  • Now, now, don't jump down his throat too soon. Current environmentalist dogma is that no new technology should be deployed until it is absolutely proven safe (the "precautionary principle"). Can any of you actually *prove* there are not adverse environmental effects of increased nitrogen levels? Saying, "any idiot can see that there aren't", while true, still isn't absolute *proof*.
  • We ran this story in February in Future Energies [] (which in turn we picked up on from Salt Lake Tribune), and we were also excited about the possible power savings. We know that in conventional grid it's around 20%. When carrying the AC current there will be losses by motion of magnetic flux though the superconductor. Can anyone tell us what the losses will be through the superconducting cable?

  • Ya, thats why its +60% of the air we breath is Nitrogen.
  • Actually, transmission lines already have very little loss due to the extremely high voltage they operate at. Superconducting cables could reduce loss in distribution systems considerably, but there is still the loss in transformers and low voltage wiring, which is considerable.

    The real killer here is the initial cost, although a 57MVA (I think) cable is very impressive, I'd bet it's still 10 times the cost of the aluminium-plastic cables currently used. Another thing against it is that smaller capacity cables are often good - if you have 5 normal cables and one has a fault, you're OK but if you're supplying a large area with one of these babies and it goes, it will take a long time and a lot of money to fix.

    And considering the current price of electricity (even in California), I suspect this is not going to be economically justifiable for a long time.

  • As others have pointed out, LN2 (liquid nitrogen) is very cheap, but that's not the issue. It merely has to be cheaper than doing it the conventional way.
  • If the nitrogen is kept at the right pressure, then it doesn't even have to be kept cold.

    Well, the whole point of having liquid nitrogen is to keep the supraconductor cold... There's no point in having liquid nitrogen at room temperature.
  • Uh... the atmosphere is 79% nitrogen already. I wouldn't be too worried about that.

    The thing I would worry about is the cable catching fire at the point it breaks, but that's a safety issue rather than an environmental one.

  • Where are you from anyway? I'm assuming it's the US based on the sorry state of education there.

    Hey, don't judge us all based on the comments of a few idiots..... oh wait, nevermind.

  • From the American Superconductor site link I wasn't able to determine any details of the actual manufacturing process. It does indicate that the there are "oxide compounds" involved - but..!

    I also couldn't find any indication of the life of this. How long until it begins to breakdown, and when it does what compounds will be released into the ground? And what does the manufacturing process put into the atmosphere in the way of by-product gases and other exhaust? If I understand correctly there is a stream of coolant (liquid nitrogen!) inside the pipe bundle - what happens if the pipe breaks? And of course - what are they going to do with all that cable that was ripped out..

    Sounds like a neat idea, but not enough info for me to decide if they really thought this through..
  • by jharper ( 98953 ) on Sunday May 20, 2001 @05:58PM (#209225)
    Using liquid nitrogen, while expensive, will certainly save money. Our current power grid can lose twenty percent or more power in transit. Keeping a constant flow of liquid nitrogen is pittances compared to the enormous savings of a 25% increase in power distribution. That's a LOT of power. Granted, we won't reap the benefits of this until after much of the United States has better power cabling, but this is just a start. |JH|
  • by cybercuzco ( 100904 ) on Sunday May 20, 2001 @05:29PM (#209226) Homepage Journal
    The article also talks about magnesium diboride, a newly discovered metallic superconductor, but they make it out to be more than it atcually is. They say it conducts at twice the temperature of similar conductors, which is true, but it still conducts at a lower temperature than what theyre using in detroit. Yes its metallic, yes it superconducts at liquid nitrogen temperatures, but i dont think itll revolutinize things any more than the current crop of ceramic conductors. Give me a room temp superconductor and the world will be a different place, until then the revolution moves slowly.

  • It sounds pretty expensive - will the extra efficiency be worth all the money spent on liquid nitrogen? Anybody have any stats about this?
  • Wouldnt really matter anyway because we took the nitrogen from the atmosphere so it's not like we're putting anything bad back into it.
  • Yes... But this time there's more details. Think of it as "followup", which is sorely lacking in virtually all other "news" media.


  • Of course, if you are a Chem E and you I am wrong, then please enlighten us!!

    uh? Are you the grammar nazi or not? Second post with a second gramatical error.

    Tsk tsk tsk
  • Heh, if you happen to have a steel plate in your head, better make sure you don't walk over that underground superconducting cable, else your head could get glued to the ground.

    That will be funny. Also, imagine all the lose coins that this thingy will collect...
  • Cable gets cold and becomes a superconductor. Nitrogen is still piped around at room temperature or, more accurately, underground temperature. The only cold nitrogen was the stuff that was allowed to escape to become a gas.

    Informative? Perhaps. Wrong? You bet!

    The gas that escapes is actually hotter than the rest of the liquid, and takes energy away from it. Thus the liquid becomes colder. You have to apply energy to remove the vapor, so overall you lose energy. (Otherwise you would have a perpetuum mobile.)

    How can a cable get cold from contact with liquid which is at room temperature? Think about it for a second.

  • Well, it's slightly more complicated than that. Once the nitrogen leaks out and the ceramic loses its superconductive properties, the megawatts (they said 14000 homes split over three cables) running through that cable will make it heat up faster than a light bulb filament, igniting the cable's insulation. It could possibly become hot enough to ignite aluminum and other light metals that may happen to be nearby.

    It's a safety issue, not an environmental issue. I hope they include an automatic temperature shutdown feature.

  • Yes. Stuff could still catch fire in the meantime though.
  • Inductive coupling is not a "loss". If you remove that coil you're not "losing" anything anymore. It's just a way of transferring energy via EM fields. Oh, you thought that the energy actually travel inside the wires? Not so. Go read up on your EM theory.
  • 1. Liquid Nitrogen is cheaper than beer.

    2. Because superconductors offer zero resistance, they also do not become hot. The only gain of heat (and need for more liquid nitrogen) come from losses to the air (conduction, radiation).

    If it wasn't cheaper, they wouldn't do it.

  • I'm sorry, I doubt this project will ever pay for itself. for 1500 ft. they would have been far better off using another low loss system, like UHV or something.

    Treatment, not tyranny. End the drug war and free our American POWs.
  • First, this really is a neat thing. However...
    Our current power grid can lose twenty percent or more power in transit.
    Keeping a constant flow of liquid nitrogen is pittances compared to the enormous savings of a 25% increase in power distribution.

    Where are you getting that number(25%)? In the studies I have done, modeling the transmission network down to the sub-transmission (roughly 34kV) I saw about 5% loss. I seriously doubt there's another 20% in the distribution network. Another 5%, maybe. After all, the distribution network is pretty much analogous to the "last mile" of data transmission. About 95% plus of the distance traveled along the electrical network is on the transmission(138kV and above, probably higher) system.
  • Just for reference, liquid nitrogen costs about the same as milk, and is not much more dangerous unless you stick and hold your hand in a vat of it.
    Unless you drink [] it.
  • Can you propose some mechanism where the nitrogen gas would "slurp up enough energy to cover it's (sic) latent heat of condensation" that didn't involve what we commonly think of as a temperature differential?

    I didn't pay nearly enough attention in my PChem class, but I did pay some attention in the diff. eq., and I don't remember many situations where a cold material would transfer heat to a warm material. Can you elaborate on this?
  • Grammar Nazi, you really must stop drinking on Sunday nights. Barring that, you must teach yourself to post as an anonymous coward when you are drunk. I don't believe you've managed to nail a single homonym all evening, and it's really grating on my nerves.
  • Ok... so what you're proposing is that they compress the nitrogen (which would heat it), then allow heat to escape (to bring the nitrogen back down to ambient temperature), and then decompress the nitrogen (which would make the decompressed nitrogen extremely cold).

    That's a pretty damned good idea. Maybe they could catch this cold nitrogen, and repeat the cycle many, many times, and make it even colder. In fact, perhaps they could cool and catch all the nitrogen this way, and avoid having to deal with highly pressurized nitrogen. Then, it would all be cold, but they would be able to keep it at a much lower temperature, and much less of it would escape as a gas and waste energy. Then only stuff above room temperature would be the stuff in the isolated compressor!

    Wow! I should get a patent on this "refridgeration" method! I'll make a billion dollars!
  • by tcc ( 140386 )
    " this summer Detroit Edison will lay 1200 feet of superconducting power cable near their Frisbie "

    Uhmmm, I dunno about you, but that's gonna be one hell of a frisbie to throw.
  • In my opinion, any one worrying about the environmental impact of releasing nitrogen gas should be shot in the head immediately.

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  • Yes, I'm sure the city of Detroit hasn't done any estimation or analysis, and has no idea how much this will actually cost, unlike some random slashdot poster who must clearly be some kind of electrical infrastructure idiot savant.

    Of course you must be right, what was I thinking. I mean, you have so much support to go a long with your opinion. Christ, how the hell did a fucking idiot like you get +2?

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  • The magnetic fields around an electrical conductor actually rotate around the core, rather then attract it; counterclockwise, if you were facing the current flow. A coil will produce a nice directed magnetic flow, though.

    Also, coins do not contain ferromagnetic elements.

    Where are you from anyway? I'm assuming it's the US based on the sorry state of education there.

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  • According to the second law of thermodynamics the amount of energy needed to cool all that wire cannot, according to the law, be less than the energy saved by the reduction in resistance, because that would decrease entropy, which is impossible.

    That isn't even remotely True. It wouldn't decrease entropy; it would just bring the rate of entropy creation down to zero (or near zero). Or are you saying everything has an equal amount of efficiency?

    God, why are so many people so stupid!

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  • how so?

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  • Nitrogen gas is not a hazard unless it can displace all of the oxygen in the aria.

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  • But it takes power to compress nitrogen; i.e., power roughly equal to the heat it gives off.

    But they recover this heat, and use it to power a steam turbine at the liquid nitrogen producing plant, which means that it is far more efficent than a regular air conditioner, where all the heat is pumped away into the air. I seem to remember a figure of 75% of the energy used in the compression is recoverd from the heat.

  • Wouldn't the act of the wire melting/burning cause the cable to self destruct and stop conducting?

  • If the pipe breaks then the nitrogen will boil and release gas back into the atmosphere, which is over 70% nitrogen anyway.
    It could easily be detected by loss of pressure in the section of broken pipe.

  • by Ig0r ( 154739 ) on Sunday May 20, 2001 @06:15PM (#209254)
    You'd better think a little more slowly next time.
    The pipes that carry the nitrogen and wire will be buried, and any escaping liquid would quickly evaporate.
    Also, nitrogen isn't flammable. It's the major componant of our atmosphere.

  • Of course, the homeless are going to be plenty pissed because they can't tap it for free juice, and they can't rip it out and sell it to the local scrap dealer.
  • Doesn't have to have a constant flow.

    Superconductors conduct heat as well as electricity near perfectly.

    so the temperature will be evenly distributed

  • how dumb are u?

    where do u think they get the Nitrogen from???

    It's ubiquitous and harmless in air

    Admittedly u'll asphyxiate if you're trapped over the stuff venting, but that close u'd be worried about the loose high-voltage cable.

  • I don't understand how they can have the constant flow of liquid nitrogen...won't this send the price of the whole operation up really high? does anyone have any information on how they plan on implementing the liquid nitrogen?

    I think it is pretty cool that superconducting is actually gonna be used for something bigger than laboratory tests. :)

  • according to the article, Liquid Nitrogen is about 10 cents a liter.

    this looks like the first run for power transmission over superconducting lines. So even if this is break even otherwise, there is a bonus in the practical experience you would gain just in maintaining the thing. Little stupid things like "apply rubber hammer here" stuff.

    so it is worth while just for that

    Check out the Vinny the Vampire [] comic strip

  • While supercooling my overclocked toaster?

    "It'll flash fry a buffalo in 30 seconds..."
    "Aww, but I want it now!"

  • I know that 2 summers ago, there were many problems with rolling brownouts and whatnot, do to a screwed up grid in the Detroit area. This cable will be a welcome relief!

    The grammar nazi happens to have a large amount of Stock in DTE Energy, hence anything that makes money for Edison, eventually lines the grammar nazi's pockets!!

  • Liquid nitrogen is cheap!!. If the nitrogen is kept at the right pressure, then it doesn't even have to be kept cold. Pressurized lines are already in use for gas and steam. I'm sure that liquid nitrogen isn't much different.

    Of course, if you are a Chem E and you I am wrong, then please enlighten us!!

  • With all due respect MrChips, I've had one undergraduate course and one graduate course in Thermodynamics, and I've never heard of this. In addition, I've done much electron microscopy using liquid nitrogen from a large tank, that was completely sealed and at room temperature.

    According to physics, the liquid will stay a liquid. It will exert a high pressure, but it will remain a liquid and it will remain at room temperature.

    I'm sorry if this surprises you.

    Keeping the superconductor below temperature has to do with vaporizing *some* of the Liquid N2, just enough to keep the cable cold. The room temperature liquid is kept separate from the superconductor until it is needed.

  • I stand corrected. Now I remember those diagrams with the pressure, temperature, and phase !!

    Sorry. I guess a was a little to forward with my comments. I'll make sure I only post what I completely understand from now one.

  • by grammar nazi ( 197303 ) on Sunday May 20, 2001 @06:41PM (#209277) Journal
    Yes, but this would be useless for superconducting applications. The whole point is for it to be cold, or else the superconductor won't work.
    Thermodynamics 101:

    1. Pressure is released from room temperature Liquid nitrogen.

    2. Liquid Nitrogen becomes gas.

    ... Wait, it can't become a gas unless it slurps up enough energy to cover it's latent heat of condensation. Enough energy get's absorbed to cause the surroundings to get cold (-195 Deg C. cold).

    5. Cable gets cold and becomes a superconductor. Nitrogen is still piped around at room temperature or, more accurately, underground temperature. The only cold nitrogen was the stuff that was allowed to escape to become a gas.

  • Liquid nitrogen is cheaper than water

    Municipal water costs what, a few cents per cubic foot?

    Liquid N2 costs what, a few cents per liter (in bulk purchase)?

    Well, there are 28.32 liters in one cubic foot, so I don't think LN2 is cheaper than H20.

  • by 3-State Bit ( 225583 ) on Sunday May 20, 2001 @07:27PM (#209289)
    Using liquid nitrogen, while expensive, will certainly save money. Our current power grid can lose twenty percent or more power in transit. Keeping a constant flow of liquid nitrogen is pittances compared to the enormous savings of a 25% increase in power distribution. That's a LOT of power. Granted, we won't reap the benefits of this until after much of the United States has better power cabling, but this is just a start. |JH|
    I wonder though. The article says 1200 would think the vast majority of your "twenty percent" (although it surprises me that it could really be so high) is either in the megawatt long-distance things (what you drive next to and oooh at), or else power loss in house wiring or in downstepping the current to it. Between the two, relatively little of the length of wire that's in our power grid is over distances of 1200 feet...and if you started doing ALL wiring with this system, it would get really expensive. The way to do the estimation right is to figure out:
    1. Over which "type" of wiring are we looking at the most significant power loss?
    2. How much of this is convertible to superconducting?
    3. What is the percent loss in power?
    4. What is the current cost of power?
    5. What is the current 'marginal' (ie. minus base overhead, looking at what "one more foot" would cost) cost/foot of carrying the power?
    6. What is the 'marginal' "superconducting" cost/foot of carrying the power?
    7. What is the base cost to setting up an area with superconducting?
    8. What is the running cost of superconducting? (In this case keeping a flow of liquid nitrogen).
    Give me these data and I'll tell you whether it's worth it -- or even remotely feasible. If it's something like "damn-near break even" then it's probably a good sign -- this is first-generation stuff. From what I know about silver-clad HTS ceramic ribbons, though (ha!), I would guess that this is unreasonable expensive technology.
  • by RavStar ( 252707 ) on Sunday May 20, 2001 @07:23PM (#209295) Homepage
    The power grid is so lossy, you can power a house by setting up a capture coil near a high tension line. Or, you can light up a florescent light by just holding it near one. We loose 20% of our generated power by the air and resistance loss from the power grid. If we replaced all high tension lines with this technology, we would have 15-20% more power without ever building a new power plant. Plus, we could efficiently move power where it is easy to make it (nuke, hydro, wind) to places it cant be made easy. With a super-conducting power rail from one coast to the other, we would have the ability to send power from one end of the nation to the other with less than 1% loss. This is only a dream with copper and Al cable.
  • by Topgun1 ( 261377 ) on Sunday May 20, 2001 @08:42PM (#209296)
    Alright. You asked for a chemical engineer, you got it. Whether liquid nitrogen is cheap really depends on the process you use to compress it for reuse. To answer your question about the cold, yes, in this case it does have to be kept cold. However, you can liquify nitrogen at temperatures much higher than that at 1 atmosphere. It's all about phase diagrams, which are functions of temperature AND pressure. So, if you put enough pressure on the gas, you can have a liquid at relatively "high" temperatures. There is such a thing as a supercritical fluid, but that is way beyond the scope of this discussion.

    The interesting part here, at least from a transport aspect, is going to be the heat transfer. That is, you have to REALLY insulate them lines, or else you will vaporize the liquid notrogen in the line and potentially lose the superconducting capability of the ceramic. This is especially true, since you have a difference in pressure accross the power line (this pressure drop is what allows the liquid to flow). Again, from phase diagrams, pressure and temperature dictate the phase. So unless Q (the heat flow in the system) inside the line is very low (close to adiabatic), this could be a very tough engineering problem. This is especially true when you consider that even a small change in the environment might cause an incredible amount of change in the process as a whole. My congratualtions to the team of engineers that pulled this one off.

  • When you compress nitrogen, it gives off heat.

    When you let it expand, it sucks in heat, giving off cold, at a certain equilibrium temperature if you mix the liquid and gas phases adequately.

    But it takes power to compress nitrogen; i.e., power roughly equal to the heat it gives off.

    The net effect is, you might as well build a big air-conditioner and use that to cool the pipes, because even if you put canisters and a ride in a truck in the middle, that's all you're getting.

    You're heating up Flint to cool down a tube in Detroit.

    The question is, how much power is needed to compress air, remove the oxygen (you don't want the cable blowing up if it sparks), and transport the product to the head end of this cable? Is it less than the power lost in an ordinary cable? You're kidding.

  • >But they recover this heat, and use it to power
    >a steam turbine at the liquid nitrogen producing
    >plant, which means that it is far more efficent
    >than a regular air conditioner, where all the
    >heat is pumped away into the air.


  • Its a test basicly, they aren't too concerned with cost. Why bother at all? No one wants new overhead wires in their neighborhood. Putting BIG transmission lines underground is VERY expensive. Using superconducting cable you can use an existing small tunnel and put a LOT more electricity through it. It will only be economical in urban areas for many years to come. As for safety, superconductiing or not, shorts etc... are detected and the power is shut off automatically. Its a normal part of the design of any transmission and distribution system. I'm sure they will be monitoring the pressure of the liquid nitrogen, and a drop in pressure will trigger safety shut offs. This sort of "protection and control" is completley routine.

    Just for reference, liquid nitrogen costs about the same as milk, and is not much more dangerous unless you stick and hold your hand in a vat of it.

  • Imagine yourself being electrocuted and frozen to death at the same time... also the power would probably go out...
    Not much different, I'd think, than standard high voltage wire.

In less than a century, computers will be making substantial progress on ... the overriding problem of war and peace. -- James Slagle