Superconducting Power Grid Launches In New York

EmagGeek writes "IEEE is running a story about a new superconducting power grid that was energized in April in New York State. The lines operate at 138kV and are cooled to 65-75K to maintain superconductivity. These lines are run underground and can carry 150 times more electricity than copper lines of the same cross section. The project is funded with taxpayer dollars through the Department of Energy." A related story at MarketWatch indicates that this is part of a large-scale effort to upgrade aging infrastructure.

Comments

Re:reliability ?

[RustinHWright]

One of the characteristic sights on New York City streets is big tanks of liquid nitrogen standing on the sidewalk, steaming away, with lines running from them down a manhole. Why? Because, iirc, many of the telephone company switching systems already run supercooled and when a repair needs to be done they need supplementary chilling.
You might be surprised how little different it would be to have power lines running superconducting in parts of NYC. With the vastly complex infrastructure already in place, doing these lines might not be all that big a deal in some ways.

Re:Possible new 'Terrorism' target?

[lgw]

Underground power cables are struck by lightning amazingly often - I think more often than high-tension lines. Lighting strikes originate quite deep - given they cross 8 km of air gap, several meters of damp earth should come as no surprise.

Superconductors = almost no heat

[DrYak]

how much energy does it cost to keep them so cool?

Not as much as you may think.

The whole point of using super conductors is that their resistance is incredibly low, almost 0 ohm. They are thus highly efficient and don't lose much energy into heat through Joule effect, compared to classical conductors used in regular power lines. They will naturally stay cool.

So it costs some significant amount of power to cool them down to their working temperature, but once there, the super conductors keep their temperature almost for free, you only have to make up for what is lost because of the insulation.

Similar superconductors are used in the high-field super-magnet inside medial MRI machines. And those machine doesn't need a whole nuclear plant's worth of energy to keep them cool.

Re:Superconductors = almost no heat

[stevedcc]

The whole point of using super conductors is that their resistance is incredibly low, almost 0 ohm.

No, the whole point of using super conductors is that the resistance is EXACTLY 0 ohm, not incredibly near. There is no resistance, at all.

Re:Superconductors = almost no heat

[Antique Geekmeister]

But they do have impedance (which often confuses people). They also have radiative losses: some electro-magnetic enegy can, and will, couple into nearby objects and be dissipated there.

Re:Superconductors = almost no heat

[hardburn]

Superconductors break down if you put AC through them, so yes. AC might have been the right choice when Tesla was around, but not anymore.

Re:Superconductors = almost no heat

[tzanger]

You don't have inductive losses; you have losses due to skin effect -- basically alternating current in a conductor tends to travel along the outer surface of the conductor, rather than through it. The higher the frequency, the less of the conductor is used to actually carry current. All major transmission lines run DC for this very reason (and also to facilitate synchronization of different generation "zones").

Re:Superconductors = almost no heat

[OldMiner]

You use the right words for an electircal engineer, but your conclusions are inaccurate.

Skin effect doesn't reduce inductive losses. It just means you generally increase resistive losses bceause your effective cross section is reduced. High voltage AC transmission lines are famously inductive, such that transmission line workers where metal mesh in their suits so they don't get the weird feeling of the oscilating magnetic field through their bodies.

And, no, long distance transmission lines are most decidedly NOT DC in the U.S. Now, in Brasil and China, yes, long haul DC transmission lines exist. But they have to pay a huge cost in terms of equipment for this. It's balanced out due to the decreased construction cost and resistive losses. Long haul DC lines are only economical when you have a massive distance between your power generation and utilization, or you're trying to balance load over a rather massive area.

In the area of my ignorance, though, I don't know if inductive losses would ever be significant for a superconductor. One of the defining characteristics of superconductivity is that external magnetic fields only penetrate a tiny distance (~100 nanometers) into the superconductor. I don't know if there might be a similar oddity which prevents them from generating a magnetic field outside of the conductor and coupling with other conductors.

Re:Superconductors = almost no heat

[bcrowell]

In the area of my ignorance, though, I don't know if inductive losses would ever be significant for a superconductor. One of the defining characteristics of superconductivity is that external magnetic fields only penetrate a tiny distance (~100 nanometers) into the superconductor. I don't know if there might be a similar oddity which prevents them from generating a magnetic field outside of the conductor and coupling with other conductors.
No, there's nothing that keeps superconductors from making external fields. In fact, one of the most common applications of superconductors is as electromagnets.

The GP post is just completely incorrect about all transmission lines being DC. You are right, they're normally AC. However, the reasons they're AC might not apply to superconductors. The reason AC became the standard way to transmit electric power was that AC can be put through a transformer, and with a transformer you can step up the voltage for long-distance transmission, then step it back down again at the end. The higher voltage gives smaller ohmic power losses. With a superconductor, you don't have to worry about ohmic power losses, and that might make it more practical to transmit power using DC. The advantage would be that you'd have no inductive losses. The disadvantage would be that you'd need an inverter at the end in order to convert to AC, since the user's building is full of AC devices. Inverters are not perfectly efficient, and they're also not cheap, so maybe that's worse than just accepting the inductive losses.

Trying to imagine an application where you'd really want to use superconducting power transmission with DC, one that occurs to me is if you have a big photovoltaic farm in Arizona, and you want to send all that energy to Los Angeles. The photovoltaics produce DC, so somewhere, somehow you've got to have an inverter. Maybe you'd put the inverter at the LA end, and avoid inductive losses. But it would be a huge engineering project to lay a trench from Arizona to LA and fill it with liquid nitrogen.

Re:Possible new 'Terrorism' target?

[lgw]

Of course, a terrorist could blow up any sort of power line with a big enough bomb, but so what - there are far higher-value targets.

Aside from bombs, a coolant leak would be easily stopped in the short term by a water jacket. Do you know how you insulate liquid helium pipes in a lab? You pump liquid helium through them, and a 4 inch thick layer of ice forms in a few minutes, insulating the pipes just fine. At higher temperatures you'd want to provide the water, but I'd bet liquid nitrogen escaping through a layer of water would self-seal very quickly.

Lightning strikes are a problem for all buried power cables, but it's a well-solved engineering problem.

Re:reliability ?

[ptbarnett]

One of the characteristic sights on New York City streets is big tanks of liquid nitrogen standing on the sidewalk, steaming away, with lines running from them down a manhole. Why? Because, iirc, many of the telephone company switching systems already run supercooled and when a repair needs to be done they need supplementary chilling.

Those nitrogen tanks are used by Verizon to pressurize underground telephone cables and keep moisture out:

http://gothamist.com/2008/01/31/nitrogen_tanks.php

Re:Saving Energy

[maxume]

This is a pretty good write up of what is involved in an underground cable:

http://jwz.livejournal.com/94645.html

Wild stuff.