Transient 3D Simulation of Electric Field in Defects of Mass-Impregnated HVDC Insulation

In HVDC insulation formed by layered oil-impregnated paper gaps are often left to allow for mechanical flexibility between neighbouring layers. Such gaps which are usually filled with oil may develop gas-filled voids when the electric field is turned off and the temperature is consequently reduced. To assess the impact of such defects on the dielectric stress experienced by the cable during on/off transients, one dimensional simulations are not sufficient due to the inherently 3-D geometry and non-homogeneity of the materials. We present a numerical simulation of the transient electric field within a 3-D insulation material containing a butt-gap with a void region inside, and discuss its predictions in terms of peak electric field as a function of time. The simulation is based on a numerical modelling technique we have recently introduced, called Auxiliary Differential Equation-Finite Element Method.