Degradation of various polymeric materials in clean and salt fog conditions: measurements of AC flashover voltage and assessment of surface damages

This paper is aimed at the assessment of the resistance to tracking of insulators made of several polymers, widely used in electrical industry (medium voltage cable accessories such as terminations and insulators and anchoring clamps and mechanical screw fuses), under polluted environments. This new method performed on one insulator model is based on the electro-geometrical characteristics (AC flashover voltage versus leakage distance). The tested materials cover thermoplastics, (namely polyamide 6 (PA6/50), fireproofed polyamide 66 (PA66/50), polycarbonate (PC/40) and polyarylamide (PARA/50)) thermosetting (namely two cycloaliphatic epoxy resins (EP1 and EP2)) and elastomers (namely two EPDM materials noted EPDM and EPDM V0 (fireproofed)). Polluted environments such as clean (light) and salt (heavy) fogs have been created to assess the resistance of polymers to partial discharges (erosion and tracking). Results regarding the flashover voltage (FOV) show a significant reduction in the presence of clean fog equal to 50% of the value measured in dry conditions for all polymers. This decrease is more pronounced in salt fog (-80% reduction of FOV). Surface degradations suggest that epoxy resins and EPDM elastomers are subjected to fewer damages in salt fog when being compared to thermoplastics. It is established that epoxy resins behave better than EPDM elastomers against discharges. In addition, polycarbonate (PC/40) exhibits the worst properties because of large tracking paths that form on its surface.