FIELD DISTRIBUTION IN CABLE TERMINATIONS FROM A QUASI-STATIC APPROXIMATION OF THE MAXWELL EQUATIONS

A new model for the evaluation of the electric field in a cable termin ation realized through a nonlinear stress control tube (SCT), is prese nted in this paper. It is based on the electro-quasistatic approximati on of the Maxwell equations: the Laplace equation describes the field in the nonconducting regions whereas a diffusion-like equation gives t he field dynamics in the stress control tube. A numerical model is dev ised by solving the Laplace equation by finite difference and diffusio n equations by the Galerkin method. It is shown that even the well-kno wn RC transmission line model can be derived from this general approac h. The underlying approximations leading to the circuital model are di scussed in detail. The proposed model, in contrast with the circuital one, allows us to take into account properly the nonlinear SCT charact eristics and the actual boundary conditions: in this way both spatial and temporal effects of the nonlinearity are considered. The numerical results obtained by considering the general field approach and by usi ng the transmission line model are compared.