Partial discharge inception of interface voids versus mechanical surface pressure

Interfaces between insulating solids are generally weak regions particularly if the electrical stress is applied parallel to the interface. This paper presents the results from theoretical and experimental examinations on the partial discharge inception 50 Hz stress of the interface from XLPE samples between two Rogowski profile electrodes. Based upon the measurement of surface roughness, a model was developed to predict the average size of air enclosed surface voids using the elastic contact theory. The effect of surface roughness and mechanical interfacial pressure on partial discharge inception stress was investigated. The estimated results were found to be in good agreement with the experimental observations for interface with rough surfaces. However, in case of smooth surface, the estimated values were about 50% higher than measured values, indicates probability of a few voids with larger size than the average estimated dimension.The surface roughness has a limited effect on the inception stress of interface, whereas increase of applied mechanical pressure from 3 bar to 8 bar raises the inception stress around 15%.