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Superconductors as Electrical Grid Surge Suppressors
securitas writes "The New York Times published a story about Intermagnetics -- a company that plans to use 'superconductors as valves on the electric-utility power grid, letting their temperature rise to choke off the flow of power,' a day before the largest blackout in North American history. The timing couldn't have been better. On the day of the blackout, Intermagnetics announced a $6 million contract from the Department of Energy to develop and install superconductor 'valve' prototypes by 2006 in the Niagara Mohawk distribution system. Considering that one of the leading theories for the cause of the cascading blackout is a surge in the Niagara Mohawk power grid, this announcement seems incredibly timely."
Given the amount of power flowing through these lines, you cannot use a normal or even semi-normal fuse.
A fuse works by breaking the conductor path, stopping the current flow. At high currents and voltages, the breakpoint will heat up, ionize, and provide a LOW impedence path, which is difficult to break.
Some devices that are used to interrupt mains current are switches with contacts immersed in heavy oils, those that use an air blast to disperse the ionized air path, and other more exotic systems.
How is this a storage device? It's supposed to increase its resistance when a large, sudden change in current takes place. In other words, it sounds like it would dampen an oscillation. I don't see how it could "inject" current into the grid.
says the cause of the blackouts were 3 OHIO transmission lines.
for all of us who failed electronics/electrical engineering: blackouts for dummys
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Once upon a time, it was discovered that if you cool certain materials below a critical temperature, they lose all resistivity, i.e. superconducting magnets are only superconducting below a certain temperature. Once their temperature exceeds that critical temperature, "quenching" occurs. The resistance suddenly becomes "normal," i.e. dramtically increasing. This can be catastrophic, the temperature and resistance suddenly becoming directly related and both increasing at accelerated rates. All that energy in the magnetic field suddenly becomes heat.
When I was an undergraduate at Rice University, I got to use the NMR machine in the chemistry department. Essentially, it's a large superconducting magnet that is used to investigate the structure of chemical samples with radio waves.
The superconductor is contained in a large steel thermos. The inner layers are cooled by liquid helium (4 K), outer layers by liquid nitorgen (78 K). Superconductors are used because a large amount of current can be used, producing a larger magnetic flux, etc. The more powerful the magnet, the easier the determination of structure.
Every few days the liquid helium and liquid nitrogen would have to be added to maintain the temperature control.
I was warned that if the magnetic every quenched, it would sound like a freight train. Remaining liquid nitogen or helium would boil and the magnet itself would probably melt. One moment it's a multi-million dollar instrument, the next it's a steam whistle with a heart of worthless slag.
I was told that if this happened on my watch, I should run to my car, drive to Mexico, and hope the my professor's hitmen never found me.
Magnets are transported to the location of installation before being cooled and and superconducting is initiated. Once installed, they are precarious to relocate. Major concerns:
1) slight bumps can disrupt internal structures causing annoying variations in the magnetic field- don't be the chemist who brings a wrench in the room and gets it permanently attached to the side of the container
2) loss of temperature control - the quenching phenomenon.
3) a very high-powered magnetic field- you can exactly push down the hallway without causing damage to nearby objects or its own the magetic field
If this quenching was used to control current, it would have to be carefully controlled to avoid catastrophic damage to the superconductor itself. This seems a nontrivial engineering problem.
They were supposed to have protection systems to prevent a cascade failure like this. Making the protection systems fancier isn't going to help too much if they don't install/maintain them properly.
Actually, the primary purpose of the protection systems in place is to prevent grid trouble from physically destroying generators, transformers, transmission lines and other infrastructure hardware. And they worked, otherwise it would have taken weeks rather than hours to get the grid up again. IIRC, in the blackout of 1965>, major infrastructure damage resulted from a grid collapse and it was from this experince that many of the currently implemeted ideas were learned.
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