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International Fusion Reactor Project Moves Forward
mjgp2 writes to mention a BBC article about an agreement which will begin construction on the second most expensive scientific collaboration, after the ISS : the world's first large-scale fusion reactor. From the article: "The seven-party consortium, which includes the European Union, the US, Japan, China, Russia and others, agreed last year to build Iter in Cadarache, in the southern French region of Provence ... He said that the participants would aim to ratify their agreement before the end of the year so construction on the facility could start in 2007. Officials said the experimental reactor would take about eight years to build. The EU is to foot about 50% of the cost to build the experimental reactor. If all goes well with the experimental reactor, officials hope to set up a demonstration power plant at Cadarache by 2040. "
Physics tells us that the energy lost from transmitting electricity (as heat) is RI^2, and power is IV (I = Current, V = Voltage, R = Resistance). So to send lots of power without much heating, you use high voltages and low current. This is whats done currently, to the point where the wires can't really take much more voltage (well, not cheaply anyway).
There's only one proposed solution I'm aware of, which is using high temperature superconductors as wires. These have very low resistance (in some cases theoretically 0) so reduce the energy lost by ohmic heating (the RI^2 thing). Plus they can conduct around 10* the voltage of current wires. The only problem is there still very difficult to make at all, let alone into wires, having only been discovered in 1986. The link below has some more info,
http://ec.europa.eu/energy/electricity/publicatioSuperconducting wires would elminate resistive losses but I think you'd still have inductive and capacitive effects so there's no way to get a perfect lossless line.
I think you could take care of inductive and capacitive losses by going to DC. If you really could use superconductors for the entire distribution network, then in theory, you'd eliminate the need for high-voltage AC transmission to avoid I^2*R losses, followed by step-down transformers to provide safer low-voltage levels in customers' homes. Funny -- as I recall, didn't Thomas Edison propose DC in the first place?
If it weren't for deadlines, nothing would be late.
in some cases theoretically 0)
It's not theoretically 0, it's really actually 0. It's a macroscopic manifestation of a quantum-level effect. In high-temperature superconductors, there is a finite resistance, but in 'classical' superconductors, it's really zero: current flows with no applied voltage.
The problem with superconductors as a transmission line isn't so much the temperature (although that is a problem). It's not even the materials properties (high-temperature superconductors are basically ceramics. They're brittle and not very strong, which means they aren't very useful as wires). It's the fact that, in addition to a critical temperature Tc above which they don't superconduct, superconductors also have a critical magnetic field and a critical current density. Exceed any of those, and they stop being superconductors, which can lead to some quite catastrophic failures. High-temperature superconductors have much higher critical field strengths than low-temperature ones, and higher critical current densities, but you can't just run all the current you want through them and expect them to not blow up/melt/spontaneously disassemble.
Actually, inductive and capacative losses don't really play into the equation with superconductors. They expell any external magnetic or electric fields, so there's nothing to induce a current with.
Fields inside the conductor are not the issue. The inductive and capacitive effects occur when two conductors, super or not, are near each other, as they would be if they were part of an AC transmission-line network.
If it weren't for deadlines, nothing would be late.
Actually... even in residential areas (US and Canada), the line voltage on overhead transmission wires is typically 13800 volts, and long distance power transmission is done at 45000 volts and higher, up to 500 kV for really high power, long distance lines. These voltages are high enough that you need to use 3, 4, or six-wire bundles (spaced about 8 inches or so apart) to keep the electric field gradient low enough so you don't get corona discharge around the wires.
Less is more.
Only for DC current. AC current always has a finite resistive component to it.
Regarding critical current, one could effectively run up a huge potential (eg millions of volts) and send a trickling DC supercurrent to the receiving station. Of course this brings with it all sorts of high voltage problems beyond the typical substations have dealing with high-tension wires. One being the much larger potentials, the other being efficiently converting DC to DC (as opposed to transforming the AC, as traditional power stations do).
The other thing mentioned is very true, regarding catastrophic failure of the lines. I work with superconducting magnets, where to pack a huge magnetic field, you need tiny wires to get enough wrappings in a small space. So we're basically putting 70+ amps through a 22 gauge wire. That's all fine and dandy when the magnet is immersed in liquid helium at 4K, but if you do something dumb, like change the magnet current too quickly or go past the critical current, you can cause part of the magnet to go normal (as opposed to superconducting), in which case that 70A is going to dissipate LOTS of heat, causing more parts of the magnet to go normal, and ultimately cause the whole magnet to go normal, dissipating the induction energy stored in the magnet as heat, which can boil the liquid helium vigourously, build up pressures, damage the magnet and electronics, etc. Very dangerous. Now imagine a similar scenario but in some transission wires at a potential of millions of volts running through a forest or a neighborhood.