FE calculation of transient eddy currents in thin conductive sheets using dynamic boundary conditions

This paper presents an FE modelling approach for the calculation of transie nt eddy currents in thin conductive layers, where the complexity of the geo metry prohibits both a detailed FE modelling and the use of analytical tool s. The method allows an estimation of the maximum values of eddy currents a t a highly reduced modelling effort and the use of a commercial FE software package. A prerequisite is a slowly varying magnetic field that can be ass umed to be unaffected by the eddy currents. It is shown that neither the so urce of the magnetic held nor the insulating environment has to be modelled . The model is built up exclusively from 2D elements and is excited via the magnetic vector potential. The spatial distribution of the latter is calcu lated separately in a magnetostatic calculation based on Biot-Savart's law. It is then applied in time-varying form as a dynamic boundary condition at every node of the model. The method was applied to a simple problem for wh ich the results of a detailed FE calculation were available, to document it s validity. Further numerical results are presented for the plasma vessel a nd the heat radiation shield of the Wendelstein 7-X fusion experiment in th e case of an emergency discharge. (C) 1998 John Wiley & Sons, Ltd.