I put few quick figures on a wind turbine alternator with chilled Al coils
and I didn't get a complete proof-of-concept
, for lack of technical documentation and time.
I started from the Vensys 136
turbine: 3.5MW @0.178Hz rotation, magnetic gap estimated 1.0T D≈5.4m L≈1.4m. Possibly 288 slots, where 65% Cu lose ≈4% (not accurate).
The currents induce only 0.2T=2kOe in the slots. This multiplies the resistivity of 20K pure Al by only (1.0+2.2) while Cu isn't usable lss.fnal.gov
At 33% of Carnot's limit, and without iron losses, the cryocooler would dissipate 0.4%
of the 3.5MW. Gained 3.6% of mean 3.5MW/3 would pay a turbine half a year earlier.
I didn't check the eddy current losses in cold Al at low induction and frequency. Solutions exist qualitatively.
Heat insulation demands vacuum
. The magnets too must be cold unless we insulate the magnetic gap. Small shaft diameters ease seal rings, a significant change for wind turbines with slow alternators. Then, multilayer insulation leaks very little heat
Transmitting the huge torque leaks very little heat
if done near the gap diameter with trusses of tubes. Titanium, stainless steel or glass fibers suffice.Extracting the current does leak heat
. Figures are bearable if 3kV reduce the section of the 3 conductors of pure Al. 500V seem little. A resonant power supply might transmit magnetic power over the temperature drop, but I dislike that.
The magnetic materials I checked dissipate too much
. Hysteresis losses need improvement because this loss would be extracted from cold. Fe-Si worsens at cold, Fe-Co is too expensive, Fe-Ni carry less flux. Existing amorphous Fe-Si-B
provide no big dimensions.
Maybe an adequate magnetic material exists - somewhere. Or small Fe-Si-B parts can make a big magnetic path
if overlapping as in the past or if pressed together. Coil insertion would get easier too.
Then the design should be reoptimized, rather at 40K, with more poles, possibly less induction and sleeker deeper slots. I stopped before.
Marc Schaefer, aka Enthalpy