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Real World High-Temperature Superconductor Engine
wes33 writes "An amazing technological achievement deploying
high-temperature superconductors is reported
in Space Daily. American Superconductor
Corporation (nice scifi-ish name) has built
a 5MW electric ship motor using high-temp.
superconductor technology. The Queen Elizabeth's
44 MW engines weigh 400 tons each (and she has two);
a single comparable HST motor (36.5 MW) will weigh 75 tons!"
...says virtually nothing about the actual HTS technology, which seems to be the only really novel aspect of this equipment.
Or are there other limiting factors in the amount of power that is useable in such circumstances?
For a boat? Sure, cavitation. Propeller blades can only spin so fast (that is, push a certain amount of fluid) before they begin to create destructive turbulence in the fluid that cripples their pushing power. The same basic problem exists in aviation, which is why propeller-engine planes can only go so fast regardless of how big and numerous the engines and blades are. Jet engines, rockets, or some other form of propulsion are needed to go any faster.
Random and weird software I've written.
It's all about efficiency, and therefore running cost. Optimum cruising speed is set by considerations of wave drag for a given hull - there's a sharp curve, whereby faster cruises become *incredibly* inefficient. Big marine diesels providing this motive effort are far and away the most efficient prime movers on the planet, because economies of scale and the singular nature of the task lends itself very well to such optimisation - which the owners take advantage of.
The bottom line is that every single %age point gained represents a huge saving to the owners in fuel cost. If it can be done with a lighter/more efficient propulsion package, so much the better - that's extra cargo that's free to carry, but the prime incentive is fuel cost - you may not realise we're talking *thousands* of tons for oil bunkers on big ships...
I'm not at all surprised that marine propulsion is the first major application of high-temp superconductors in this regard.
After reading the arcticle, the reason why these motors can achieve higher density is because the thermal dissapation issues are reduced when you don't have DC losses in your coil windings.
You are right as far as lower freqencies needing more core material. But, I can't see how superconductors would change that equation at all. Even if the superconductor carries more current, the magnetic material has the same basic flux energy storage capacity. Ships tend to use higher frequencies anyway, such as 400Hz, so frequency probably isn't the problem. In a propulsion system, the design engineers are probably allowed to choose any frequency they want. Also, superconductors don't eliminate all loses. Core losses are still going to be an issue unless the motor design is significantly different than anything seen before, or uses superconducting mu-metal.
You can always make a slower, higher torque high-frequency direct-drive sync motor by adding more poles. But you can't make a low-freq motor faster. i.e. top speed for a 2-pole 60Hz sync motor is 3600 RPM.
Also, from what I remember, superconductors tend to lose superconductivity in strong magnetic fields. Hopefully, they have worked around that problem.