Breakdown strength of solid|solid interface

Interfaces between solids are generally considered weak regions in electrical insulation systems. This is particularly so if the electrical stress is applied parallel to the interface. Important parameters, affecting the breakdown strength, are interface pressure, humidity, presence of liquid dielectric and the surface roughness of the solid in contact. The main aim of the work presented here is to examine, theoretically and experimentally, the effect of interfacial pressure and roughness on the tangential breakdown strength. The size and gas pressure of enclosed surface voids were estimated using mechanical contact theory. The dielectric 50 Hz AC tangential strength of XLPE|XLPE interface was investigated for various values of pressure and roughness. The increase in breakdown strength due to increased pressure was largest in case of surfaces with the high degree of roughness. As expected the highest breakdown strength was observed in case of the smoothest surfaces. The estimated results of void size and gas pressure were found to be in good agreement with the experimental observations.