Superconducting Levitation Styles for Superconducting Energy Storage Flywheel

Abstract

The flywheel comprising of magnetic and superconducting bearings, which will provide a stable levitation of rotor, is fit for energy storage. According to the HTS cooling mode, there are ZFC bearings and FC bearings. ZFC bearings produce a large levitation force, but they ensure only one direction suspension. FC bearings produce less level of levitation force, but they provide passive stability in all directions. In practice, the superconducting bearings are formed by field-cooled superconductors and PMs generally. With respect to the forces between a permanent magnet and a superconductor, there are axial (thrust) bearings and radial (journal) bearings. The axial gap type of superconducting bearings is suitable to bear axial load, while the radial gap type of superconducting bearings is suitable to hold a shaft on the center of a bearing. Accordingly, there are two main types of high-temperature superconducting energy storage flywheels, and if a system comprising both the thrust bearing and the radial bearing will have the characteristics of both types of bearings. To describe the levitation characteristics, there are three main parameters: magnetic force, magnetic stiffness and damping. Factors affecting on the magnetic levitation force of these superconducting bearings such as arrangement and shape of superconductors, thickness of superconductor, superconducting flux creep and critical current density of the superconductor are researched. All these results presented in this paper will give a reference to the research of the superconducting energy storage flywheel.