Fundamental-frequency eddy-current loss due to rotating magnetic field. Part 1: Eddy-current loss in solid rotors

Abstract

The flux penetration in solid ferromagnetic cores is analysed without using the simplifying assumption that the B/H curve is a straight line, or a limiting step function. The nonlinear variation of the fundamental B1/H curve is included in its entirety by substituting the equation B1 = KH1–2/n, which fits the magnetisation curve very well, especially beyond the knee portion. The theory is applied to induction motors with solid-iron secondaries, and solutions are obtained for flux and current densities, rotor power factor and eddy-current loss. Simplified expressions are given for easy numerical calculation. Substitution of n = 2 in the equations leads to results which have already been obtained in previous literature using the limiting B/H curve. Results of experimental work carried out on a solid-rotor induction motor are also presented. Curves are given to obtain the eddy-current loss per unit surface of any given solid rotor, operating at any given slip, and with any surface magnetising force. This virtually eliminates numerical calculations when the theory is applied to a new solid-rotor machine.