Design and characteristics of a superconductor bearing

A high-temperature superconductor (HTS) journal bearing was designed for a flywheel energy storage system. A rotor was supported at top and bottom by two HTS bearings. The rotor weight is 4 kg and the length and diameter of shaft were about 300 mm and 40 mm, respectively. Both the top and bottom bearings have two permanent magnet (PM) rings with an iron pole piece separating them. Static properties of the bearing were calculated by frozen image method and verified by experiments. The vertical stiffness of the bearing was 38.9 N/mm. The rotational drag and vibration were measured up to 8000 rpm. The loss coefficient was linear up to 8000 rpm and the final value was 7.5×E-6. The average of vibration was about 10 micrometer (zero_peak) except the resonance speed range. Rotation tests were conducted over the same speed range at several chamber pressures. Chamber pressure of 0.4 mtorr is sufficiently low to minimize windage loss.