Composite materials for low loss rotor construction

The use of concentrated windings in electrical machines leads to significant rotor losses due to severe space harmonics in the airgap. Metallic retaining sleeves and sintered magnets used in high speed rotor construction have low electrical resistivities, leading to larger associated eddy currents loss. Composite materials like carbon fiber and plastic bonded magnets are investigated, due to their relative low conductivity. Analysing eddy current loss in composites can be cumbersome as they are frequently anisotropic. By observing eddy currents induced in a sample material, the material resistivity may be derived for a given direction by reverse finite element modelling. Resistivity values may be further used to calculate rotor eddy current loss.