Quantifying eddy current effects on a magnetic thrust bearing used in a high speed electrical machine

Abstract

Magnetic bearings are now consistently used in high speed motors owing to their many advantages over traditional bearings. However, the bandwidth of magnetic bearings may be severely limited due to the occurrence of eddy currents which cause power loss and instability in nominal operation. This problem is generally overcome in radial magnetic bearings by laminating the core. This solution is difficult to implement in a thrust magnetic bearing mainly due to high cost associated with complexity of machining and assembly. As a result, the solid thrust stator is fragmented into several pieces, which are mounted onto a common plate. In several applications, it is not possible to add this common plate due to size limitations. To improve the controller response, it is thought that a single slit can be introduced. To quantify this improvement, a Finite element model study was conducted. By extension, the minimum number of slits that need to be introduced to keep eddy currents at a minimum was also studied. This paper studies and compares the eddy current effects in different thrust bearing configurations which include a single slit, double slit, four slit and eight slit thrust magnetic bearing. Finite element analysis techniques are used to model and simulate these different configurations. Based on these results several configurations are being built to validate and test the models.