The armature slots produce flux density pulsations in the pole face and hence eddy current losses, the calculation of which has not been fully satisfactory to date. One consideration ignored is that, since the ac field in the pole face oscillates in the presence of a strong dc field, eddy currents are induced by a field whose mean value is at a point on the B/H curve dictated by the dc flux density so that the incremental permeability becomes important. In order to study this effect we require knowledge of both relative (?r) and incremental (pri) permeabilities. Some measurements have been made of ?ri as a function of Hdc in a ring sample and form the basis on which an analytical model of the phenomenon has been developed and some finite‐element studies have been performed.
Stoll, R.L. and Sytulski, J.K. (1992), "MODELLING TOOTH RIPPLE LOSSES IN THE SOLID POLE FACES OF SYNCHRONOUS MACHINES", COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, Vol. 11 No. 1, pp. 105-108. https://doi.org/10.1108/eb051763
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