Insulating Materials for HVDC Cable Accessories: Effects on the Electric Field in Nonstationary Situations

Abstract

With the move to DC technologies for power transmission, the computation of the field distribution in insulations has become a tricky task as the materials response is less well mastered as under ac stress. This is true for HVDC cables where essentially the conductivity law must be identified for the used insulating material. Cables represent a relatively simple case study. Accessories as cable joints and terminations are certainly more delicate to address. First, more than one material has to be handled; second the translational symmetry is broken, and tangential fields have to be computed in a situation of inhomogeneous temperature conditions. Finally, non-stationary situations have to be managed and modelled for accounting for on-line operations as well as surges seen by cables. Our purpose in this work is to give an overview on how far these transient phenomena are handled in the literature and to demonstrate how far the electrical as well as thermal properties of materials actually determine the field distributions.