The design of transmission systems requires electric field distribution estimation, which, in case of HVDC application is strongly sensitive to thermal and electrical configuration as well as to the nature of dielectric materials being used owing to the resistive field distribution. In this paper, the field distribution in a dielectric bi-layer of XLPE and rubber materials, as representative of cable junctions, is estimated based on experimental data on field and temperature dependencies of conductivity. Through space charge measurements on bi-layer dielectrics, it is shown that the space charge density and electric field distributions are to a first order estimation consistent with data issued from conductivity measurements. Most notably, the interface charge building up between the two dielectrics changes sign, depending on field and temperature. However, in the high field range (order of 20 kV/mm), charge build-up in the bulk of dielectric materials introduces further distortion to field distribution.

Abstract:The development of high voltage direct current (HVDC) technologies generates new paradigms in research. In particular and contrary to the AC case, investigation of electrical conduction is not only needed for understanding the dielectric breakdown but also to describe the field distribution inside the insulation. Here, we revisit the so-called Maxwell-Wagner effect in multi-layered dielectrics by considering on the one hand a non-linear field dependent model of conductivity and on the other hand by performing space charge measurements giving access to the interfacial charge accumulated between different dielectrics. We show that space charge measurements give access to the amount of interfacial charge built-up by the Maxwell-Wagner effect between two dielectrics of different natures. Measurements also demonstrate that the field distribution undergoes a transition from a capacitive distribution to a resistive one, under long lasting stress.