Factors influencing the tangential AC breakdown strength of solid-solid interfaces

The combination of two solid dielectrics (interface) increases the risk of formation of microscopic cavities reducing the breakdown strength (BDS) of the interface considerably, particularly when the electric field has a tangential component. The main purpose of this paper is to investigate the impact of the applied contact pressure and composite elastic modulus on the tangential ac BDS of the solid-solid interfaces experimentally. In the experiments, three different contact pressures were applied using different mechanical loads with two different materials having different elastic moduli, i.e. cross-linked polyethylene (XLPE) and silicon rubber (SiR). Two rectangular prism shaped samples were placed between two vertical Rogowski shaped electrodes either in air or oil. The type of the interface (air/oil) is highlighted duly upon showing the results. Increase in contact pressure caused relatively higher increase in the tangential BDS of dry SiR-SiR (assembled in air) than that of XLPE-XLPE, revealing that elastic modulus facilitated significantly to reduce the mean void size in SiR that in turn improved the tangential BDS. Likewise, the tangential BDS of hybrid interfaces formed by XLPE-SiR specimens increased by 43% compared to that of XLPE-XLPE interface at the same pressure. Additionally, the same set of experiments assembled in oil reveals that the presence of oil enhanced the tangential BDSs around 2-3 times for all three-interface cases. Moreover, with the increase of applied pressure the tangential BDS of air-filled and oil-filled cavities tended to get significantly higher.