Impact of Contact Pressure on Breakdown Strength of Solid-Solid Interfaces

Abstract

Solid-solid interfaces are considered as weak points ofthe insulation since combination of two solid dielectricsincreases the risk of cavities and moisture at the interfaceagainst the tangential component of the applied electricalstress. The main objective of this paper is to investigatethe impact of the applied contact pressure on shrinkageof the size of cavities on the interface that leads toenhancement in the breakdown strength. Experimentalmeasurements of AC 50 Hz breakdown voltage of solidsolidinterfaces assembled under standard laboratoryconditions were conducted using two differentspecimens, namely XLPE and silicon rubber. For thesame applied contact pressure, breakdown strength ofXLPE-XLPE and silicon rubber-silicon rubber interfaceswere also analyzed to yield the influence of elasticitymodulus (softness) of the solid material on theeffectiveness of the applied pressure. Two differentlevels of contact pressures were applied for each type ofinterface and higher interfacial pressure (8.02→11.59bar) led to improved breakdown strength about 50% forXLPE-XLPE interface whereas the enhancement for themuch softer interface (i.e. silicon rubber) was about 7%under increasing pressure (1.34→2.67 bar).Additionally, breakdown strength of silicon rubberinterface was found to be higher than that of XLPEinterface around 53% at the same applied pressure.