Numerical simulation of coupled problem of electromagnetic field and heat conduction in superconducting magnetic bearing

Abstract

Abstract The superconducting magnetic bearing (SMB) system consists of the HTSC stator and the PM rotor, and is a no-contact bearing system using the levitation force between them. The SMB was expected to be applied to the electric power storage flywheel system because no friction causes the rotation speed degradation and decreases the energy storage capability. However, it was found that the electromagnetic friction of the SMB was not zero, due to electromagnetic forces; (1) the magnetic force interaction between the inhomogeneous magnetic field of the PM rotor and the eddy current it induces in the cryostat, (2) the magnetic force between the inhomogeneous magnetic field of the PM rotor and the shielding current it induces in the superconductor, (3) the magnetic force between the magnetic field of superconductors yielding the levitation force and the eddy current induced in the PM rotor. The magnetic field of superconductor is inhomogeneous too, because the superconductors consist of several HTSC bulks. We improved the PM rotor and succeed in suppressing the rotation speed degradation by inhomogeneous magnetic field of HTSC bulks by preventing the eddy current with many insulator thin films in the PM rotor [Trans. Supercond. (in press)]. On the other hand, the rotation speed degradation by inhomogeneous magnetic field of the PM rotor have not been able to be removed. The induced eddy currents generate temperature rise with Joule heat in HTSC bulks. Therefore we are able to estimate the rotation speed degradation by evaluating the temperature rise. Furthermore temperature rise can cause inhomogeneous magnetic field because physical properties is varied by it. The purpose of this research is to develop the electromagnetic field analysis method coupled with thermal analysis.