Numerical evaluation of rotational speed degradation in the superconducting magnetic bearing for various superconducting bulk shapes

In constructing the 100 kWh flywheel energy storage systems, the performance of the Superconducting Magnet Bearing (SMB) needs to be calculated to get better technical and practical results. The SMB system mainly consists of the Superconducting (SC) stator and the Permanent Magnet (PM) rotor. The SMB has the advantage that the rotational dragging force between the PM rotor and the SC stator is greatly smaller compared with the usual bearing systems. However, the magnetic friction becomes large enough to cause significant rotational speed degradation. The rotational speed degradation, which cuts down the stored energy, occurring in the PM rotors is one of the most significant problems for the practical use of the SMBs. It is caused mainly by the Lorentz force due to the inhomogeneous magnetic field of the SC stator and the induced eddy current in the PM rotor. In this study, we tried up various shapes of the SC stator to smooth the magnetic field and decrease the energy loss and then evaluated the levitation force, the magnetic field of the SC stator and the energy loss.