High speed alternator/motor

Eddy current loss is a significant problem in high speed permanent magnet alternator/motors. Leakage flux from the rotor magnets 32, which flows through any stationary electrically conductive material such as a bearing housing 12 will result in eddy current loss. The invention uses a magnetic flux barrier means 29,36 to prevent magnetic flux leakage from the magnets 32 to the stationary electrically conductive material 12. The flux barrier means may comprise a diverter disk 29 made from a magnetically permeable material which is located on the shaft 18 next to the rotor 26 and rotates integrally with the rotor. Alternatively it may comprise a barrier ring 36 made from an electrically conductive material which is stationary on the end of the stator 27 and extends across the air gap 38 between the rotor 26 and the stator 27.