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Rotational loss analysis of thrust bearing using a superconducting coil for flywheel energy storage

A 50 kWh/1 MW class flywheel energy storage system has been developed. The system has a steel flywheel, a thrust bearing using a superconducting coil and iron cores, and active magnetic bearings for stabilization in the radial direction. FEM analysis of electromagnetic characteristics of the thrust bearing was performed for studying rotational losses caused by eddy currents induced in the rotor core. The results indicate that under the force balance condition between vertical magnetic force and rotor weight the eddy current loss is slightly dependent on the superconducting coil current, and therefore the rotor weight almost determines the eddy current loss for a given lateral displacement.