Development of model specimen for evaluating insulation properties and partial discharge phenomena of polymeric solid-solid internal interface

We have been developing a standard specimen to evaluate electrical insulation properties at polymeric solid-solid internal interface, especially modeling the interface in EHV extruded cable splices. The degradation at polymeric solid internal interface in cable splices is considered to be initiated by the partial discharge (PD) phenomena. This paper describes the partial discharge (PD) behavior of the developed specimen when a tungsten fine wire is introduced at the interface as a conductive foreign substance. Under the voltage application the maximum PD magnitude (Qmax) and PD number (n) decreased with time and PD tended to disappear. This phenomenon is not a swarming pulsive microdischarge one, since the PD inception voltage (Vi) increased with the voltage application time. When voltage application is stopped for a long time, Vi decreased to the initial value and the values of both Qmax and n recovered. The recovery of PD characteristic became faster when the pause of voltage application became shorter. The surface resistance between two tungsten wires installed at the interface decreased after suffering the PD and then recovered with the pause of voltage application with similar time variation of PD characteristic. These PD behaviors are to be related to the electric field relaxation at the tungsten wire tip.