Use of numerical analysis of nonlinear eddy current problems by finite elements in the determination of parameters of electrical machines with solid iron rotors

This paper reports on the application of the concept of effective permeability using the finite element technique, to the solution of eddy current problems, and the determination of damping resistances as well as the characteristics of the solid iron rotors in rotating machinery during transients. The formulation is based on the concept of magnetic vector potential in phasor form, coupled with effective permeability which is related to the average magnetic energy throughout an a.c. cycle. The technique is applied to the solid iron rotors of turbogenerators for the determination of equivalent damping resistances, etc., during asynchronous operation. Sample eddy current loss results compare favorably with experimental test data. Instantaneous change in damping resistances during machine transients are obtained and reported on here based on this technique.