Eddy Current Loss Minimization in Conducting Sleeves of High Speed Machine Rotors by Optimal Axial Segmentation and Copper Cladding

When a non-magnetic, high-strength metallic retaining sleeve offers advantages over a non-metallic (e.g. carbon fiber) one, it is possible to consider the application of a high conductivity shield "coating" on this sleeve to reduce the surface eddy current losses due to non-synchronous fields. One can start by using a Maxwell\´s equations based analytical model to "screen" for the optimal shield thickness and then employs a "2.5D" FE method that accounts for periodic fields and finite rotor length including axial segmentation and/or copper cladding. These are quantified to help design a low loss rotor sleeve for a high speed SPM machine with fractional-slot concentrated armature winding. With this type of windings the sleeve losses can be significant due to its rich asynchronous harmonic armature reaction mmf content.