An analysis of tooth-ripple phenomena in smooth laminated pole-shoes

Classical linear electromagnetic theory is used to investigate the mode of penetration of tooth-ripple flux into smooth laminated poleshoes, without making any assumption as to the thickness of the laminations employed. It is shown that, apart from the mode corresponding to the classical ‘depth of penetration’ concept, there also exists a completely different mode which penetrates to a much larger radial depth but has a non-uniform distribution across the thickness of the laminations, the maximum values occurring at the interfaces. With thicknesses usually employed in practice, at least 60% of toothripple eddy-current loss is found to arise from this latter mode of penetration, so that only a fraction of the total loss could properly be called a ‘pole-face’ loss.