Hacker News Reader

Comment by intrepidhero | Hacker News Reader

They spent $47 million[1] on 600m of cable that can do 574MVA. It's underground and cooled with liquid nitrogen. TIL. On the one hand, I'm impressed. I didn't think we were close to this sort of thing being feasible at all.

On the other, it sounds like a huge money pit. Ongoing maintenance of buried cryogenic cooling systems can not be cheap.

[1] https://www.energy.gov/oe/downloads/long-island-hts-power-ca...

View on HN

I imagine the maintenance is the same as with any cable. If it fails, you dig it up and fix the broken part.

With superconducters there's a phase transition if they rise above their operable temperatures. This can introduce sudden forces. In LHC for example loss of cooling has led to substantial physical damage to the magnets. I imagine a simple transmission line isn't quite so likely to be violent, but there's probably some bad things that can happen with this thing if it bonks.

Yes, there will be some mild violence underground if the cable fails. Probably more because of the liquid nitrogen than the electricity itself. Electricity stops almost instantly, as superconductors tend to be very bad conductors above their operational temperature.

If that happens, you pull the cable out, and fix the broken part (probably replacing some of the cable). You may need to patch some pavement too, if the cable is superficial.

How much current can it carry? I saw 138,000 volts.

V=IR, I=V/R, R = 0 , I = Well A Very Very Big Number if all goes well

And it should stay cool as Power = Volts x Amps

574MVA / 138kV = 4160A.

What is mva? Oh basically watts?

It's a higher number than the carried power, because AC electricity has those stages when the voltage is smaller than the nominal value. (Unless it's a DC line, then they are the same.)

Surely this would be a DC line, right? AC induces resistance in superconductors because it necessarily induces a changing magnetic field, iirc (or maybe that's only particular types of superconductors).

Edit: Found this, which isn't specific but refers to it as a three-phase transmission cable which implies it is indeed AC http://www.jicable.org/2007/Actes/Session_A3/JIC07_A34.pdf

http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/scbc2.html

AC doesn't directly induce resistance, no. But there's a shared budget of current and magnetic field, and if you blow the budget the wire becomes a normal conductor.

Reply on news.ycombinator.com