Static properties of high temperature superconductor bearings for a 10 kW h class superconductor flywheel energy storage system

Abstract

A superconductor flywheel energy storage system (SEES) is mainly used as an electro-mechanical battery which transforms electrical energy into mechanical energy and vice versa. Many aspects of the dynamic behavior of flywheel rotors still need to be examined closely, and the rotors require a high capacity supporting system such as high temperature superconductor (HTS) bearings, which offer dynamic stability without the use of active control. Static properties of HIS bearings provide data to solve problems which may occur easily in a running system. Since stiffness in countering rotor vibration is the main parameter for designing an HTS bearing system, we investigated the static properties of the magnetic force between permanent magnets (PMs) and HIS bearings. We measured axial and radial stiffness, and discovered that bearing stiffness varied greatly depending on the direction of vibration of PM relative to the HIS bulk. Especially, when the rotor vibrated in the radial direction of the HTS bearing, HIS bulks of the bearing showed a large difference in stiffness depending on the orientation of the HTS bulk relative to the direction of vibration. As a result, we discussed the critical factors that affect the stiffness of HIS bearings and studied efficient ways to increase bearing stiffness. These results are used to determine the optimal design for a 10 kW h class SEES.