Alternators: Better Conductors than Copper? Carbon Nanotubes, Superconductors

[eli_lied]

is there a better conductor than copper to be used in the windings? Could carbon nanotubes be used instead? what if a superconducting material is made into a tube and a coolant is run through it...would that affect the material's tendency to stop conducting as a strong magnetic force permeates it?

 

[Vanadium 50]

I'm pretty sure that driving around with a cryogenic refrigerator will negate any power savings from the windings.

 

[russ_watters]

The efficiency of alternators is already pretty high. I don't think there is much value in exotic upgrades. It isn't worth the cost.

[edit] ...Ranger Mike said in the related thread that alternators are only about 40% efficient. It would surprise me if they were really that low.

[edit2] ...According to the wiki, car alternators are 50-60% efficient. Still pretty surprising to me.

 

[Bob S]

Here is a list of the electrical condutivity of metals at room temperature:
http://en.wikipedia.org/wiki/Electrical_conductivity
Silver is about 10% better than copper. Silver was used in the Calutron coils during WW II, not because silver has a better conductivity, but because copper was needed to make brass shell casings. Aluminum is best per unit mass density.
Research has been done on superconducting generators and alternators. The biggest problem is getting adequate cooling to the rotating armature. Google superconducting generator OR alternator.
Bob S

 

[Bob S]

what if a superconducting material is made into a tube and a coolant is run through it...would that affect the material's tendency to stop conducting as a strong magnetic force permeates it?

Liquid helium permeates the windings of magnets using superconducting wire to keep it cool.

Superconductors have a "critical field" limit, the magnetic field beyond which the superconductor "quenches" or becomes normal (non-superconducting).

Superconductors exhibit the Meissner effect, which leads to the superconductor excluding the magnetic field. There are type I and type II Meissner effect superconductors. This causes magnets to lose inductance as the conductor becomes superconducting. See thumbnail in post #3 in
https://www.physicsforums.com/showthread.php?t=317523
The upper curve is at 10 kelvin, above the critical temperature (the critical temperature for niobuim-3 tin is about 9 kelvin). The lower curve is at 4.2 kelvin.
Bob S

 

[f95toli]

I'm pretty sure that driving around with a cryogenic refrigerator will negate any power savings from the windings.

You can use a "bolt on" cryocooler. As long as you only need to go down to 50-60K a very simple single-stage cooler is enough and they don't use much power as long as the system is well insulated.
There have been plenty of demonstratations of working superconducting generators, etc based on high-temperature superconductors although as far as i know there are yet no commercial products available. Last I heard American Superconductor were developing equipment for wind energy and I am sure they are not the only ones.

Cooling a normal metal wouldn't make sense. If you are going to cool it down you might as well use superconducting wires.

 

[seerongo]

You can use a "bolt on" cryocooler. As long as you only need to go down to 50-60K a very simple single-stage cooler is enough and they don't use much power as long as the system is well insulated.
There have been plenty of demonstratations of working superconducting generators, etc based on high-temperature superconductors although as far as i know there are yet no commercial products available. Last I heard American Superconductor were developing equipment for wind energy and I am sure they are not the only ones.

Cooling a normal metal wouldn't make sense. If you are going to cool it down you might as well use superconducting wires.

Which leads back to the Big Problem in developing practical high temp superconductors: So far, all high temp superconducting materials have been non-malleable ceramics which cannot be made into practical wires for conventional windings, at least the last time I looked.

Can anyone bring us up to date on this problem? I haven't looked into it for a while.

 

[f95toli]

Which leads back to the Big Problem in developing practical high temp superconductors: So far, all high temp superconducting materials have been non-malleable ceramics which cannot be made into practical wires for conventional windings, at least the last time I looked.

Well, the latest generation of wires (well, tapes) are quite malleable. The reason being that the superconductor is deposited on a thin metallic tape and is granular, meaning the tape is easy to bend. The performance of tape now exceeds most of the design goals that people set up 10-15 years ago.

Currently,the main problem with HTS cables is the insulation (specifically the conduits for the coolant) which tend to break if you bend it too many times. There are also issues when it comes to aging (the main issue being that there aren't any old cables around, and companies aren't willing to invest money in a technology until it has been shown to be reliable).
However, this is not an issue for generators etc where the whole assembly is cooled.

The US Navy succesfully tested a HTS ship propulsion motor a couple of years ago. As far as I remember it was built by American Superconductor.
A few Japanese companies have also demonstrated motors for ships (I saw one at a conference a couple of years ago).

Somewhat OT: One of the main reasons why I don't go to conferences on applied superconductivity anymore is that they are now completely dominated by power applications. At the last one I went to it seemed like a half the participants were actually power engineers and not physicists; there were whole poster sessions on bending cables, generators, flywheels, fault current limiters etc.
How many of these potential applications that will actually reach the market is hard to say; but the physics relevant for power applications (flux pinning etc) seems to be done; it is up the engineers to design products.

 

[seerongo]

f95toli: Very interesting information. Thank you. Does all this imply that materials people are giving up on developing inherently malleable materials? That is, are we stuck with ceramics? I've always hoped that some niobium alloy-like material could somehow be found. Or perhaps the viability and economy of the tapes is good enough? I see that the tapes can be made quite thin, measuring in microns.

In particular, I'm interested the application of these HTS technologies to high field magnets, >1Tesla or so. From what I can determine, superconducting magnets for MRI's and such are still using older technology cooled by LHe. I wonder what the problems are for adapting these tapes to this particular application? I have a background in MRI systems (but not for a while) and the magnets are a terrible problem in maintenance and cryogen expense. Not only is LHe expensive, but the cryostats have to be buffered by L nitrogen or expensive refrigeration systems (cold-heads). I can only imagine the magnitude of the problem at the LHC! High temp current-carriers have always been the holy grail for large magnets.

Do you know the status of HTS application to these kinds of magnets?