Tracking behaviour in the presence of conductive interfacial defects

The study presented in this paper aim at extending the knowledge on how interfacial defects in composite insulation systems may affect surface tracking under contaminated conditions. Model samples mimicking an inter-facial conducting defect were made of high temperature vulcanised silicone rubber moulded on epoxy substrate with a circular metallic foil inserted at the interface. They were tested for the tracking resistance by means of the inclined plane test procedure. The samples with defects exhibited shorter time to track compared to reference samples without defects. In addition the tracking was more severe on the defected samples. Electric field simulation performed in parallel revealed that presence of surface contamination increases the distortion of electric field around the defect and thus explain both the effects of more severe damage of material surface and lower time to tracking experienced in this study.