Encapsulated HTS bearings: technical and cost considerations

Thermal encapsulation of HTS is one way to fabricate high-efficient HTS magnetic bearings for flywheels, motors and generators. We have been designed, manufactured and tested 200 mm axial and radial bearings for loads close to 300 kg. The maximum load to bearing weight is in the 10 to 1 ratio. At 77 K, a vacuum cryostat around the HTS reduces basic thermal losses to 6.4 W with very small rotational ac losses of 0.1 W/1000 rpm. The encapsulation reduces the cryogenic threshold in the application and allows a convenient adaptation of cryo-coolers. Basic elements are the melt textured YBCO single crystals, appropriately machined and glued in a copper ring in the center of the vacuum cryostat combined with an intrinsic cryo-sorption pump. Ten axially stacked 200 mm PM rings comprise the magnetic excitation system of the rotor. The coefficient of friction is about 10^-4 at ambient and 10 times lower at reduced pressure. For higher loads the manufacturing effort of HTS bearings, becomes comparable with mechanical bearings, increasing the chances of replacing mechanical bearings.