A semi-permeable containment sleeve for highspeed PM machines

This paper presents an alternative permanent magnet rotor containment technology. The use of a semi-permeable material is shown to result in a step improvement in magnetic loading compared to the use of magnetically inert materials such as carbon fibre or high strength metallic alloys. The choice of sleeve material requires the use of a laminated structure which has the added benefit of minimising eddy current losses in the containment layer. An analytical model is presented that enables the optimal sleeve permeability to be calculated for a given rotor magnetisation. This is validated against finite element analysis. The fabrication of a prototype machine is detailed and results presented that demonstrate good agreement with the analysis.