Cable Conduits with Non-linear Permeabilities

This paper discusses an electrical model for estimating the effects of magnetic field saturation in a ferromagnetic conduit, or shield. Starting with Maxwell's equations, a diffusion equation describing the magnetic field within the conduit material is developed. While this diffusion equation cannot be solved analytically for the general nonlinear case, it may be solved numerically using a finite difference time domain (FDTD) method. The steps in performing this analysis are described and several sample results are illustrated. The representation of the nonlinear behavior of the magnetic permeability of the conduit material is important in conducting such an analysis. A relatively simple functional form for the material magnetization curve is suggested and used in the sample analysis.