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.