Investigation on space charge behavior in water tree aged crosslinked polyethylene (XLPE) cable by experiment and simulation

This paper presents the space charge behavior in water tree aged crosslinked polyethylene (XLPE) cable samples, measured by the full-scale pulsed electro-acoustic (PEA) method. A modified bipolar charge transport model, taking into account the cylindrical geometry, is introduced to explain the procedure of charge formation in the water tree aged cable insulation. In this paper, the finite difference method is employed to solve the electric field in the presence of space charge, and the finite volume method is employed to solve the charge continuity equation. And the dielectric parameters in this paper are not instantaneous near the interface but are functions of radius. In order to overcome the Courant-Friedrichs-Lewy (CFL) condition, Crank-Nicolson method is introduced to separate the governing equations in time domain. The experimental results show that the homocharges are injected under high electric field. And during the depolarization process, the shallow trap charges gradually disappear while homocharges still reside forming a positive peak signal. It is also found in the simulation that the homocharges accumulate in the surface of insulation due to the dielectric characteristics had been changed during water tree aged process. The model is proved having the capabilities to describe the behavior of space charge in the insulation of cylindrical geometry, and there are also some improvements need to be performed in the future.