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Superconducting Power Cable in Detroit
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.
Koff-koff-koff OH man it's been a while.
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.
-Adam
Root. It does the body good.
This sig 80% recycled bits, 20% post user.
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.
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|
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.
--
Soma: because a gramme is better than a damn.
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.
Keeping
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.
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.
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.
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