Eddy currents in a passive magnetic axial thrust bearing for a flywheel energy storage system

Abstract

Two types of passive magnetic lift bearings were evaluated in terms of thrust force and eddy current losses. The first type of bearings were based on two sets of segmented Halbach arrays mounted in repulsive mode, and the second type was based on ring-magnets. The eddy-currents studied arose in the bearing due to manufacturing variations of magnetic remanence, and due to non-radial magnetization. Both a 3D time-dependent and a quasi-stationary Finite-Element Method (FEM) formulation were used, and the simulated results were compared with lift-force measurements from experiment. The losses were found (by FEM) to be in the order of 25 W at a rotational speed of 30000 rpm while lifting a 45 kg rotor with a stiffness of 359 N/mm.