Passive Axial Thrust Bearing for a Flywheel Energy Storage System

Two types of passive magnetic lift bearings are evaluated in terms of lift force and eddy current losses. Two sources of eddy currents are analyzed with help of the finite element method, firstly losses due to non-radial magnetization of magnets, and secondly losses due to variations in remanence. Magnets placed are placed in a Halbach array on the rotor and ring-magnets are placed on the stator. Denoted semi-segmented bearings, these produce low losses in the rotor, thus limiting the need of heat transport during vacuum operation. Experimental results of lift force are presented, together with simulations results. The losses were found to be in the order of 9 W at a rotational speed of 30 000 rpm while producing 900 N of thrust. The FEM-problem is solved with time-dependent terms, and is compared with a stationary approximation.