Ageing and degradation of silicone rubber insulators due to dry band arcing under contaminated conditions

Chemical changes along the surface of silicone rubber material due to partial arcs and dry band arcing were studied in this paper. Rectangular samples of silicone rubber were used for experiments and pollution was applied using the modified solid layer method based on IEC 60507. All tests were carried out in a climate chamber having temperature, humidity and fog rate control. Clean bands of 1 cm were inserted at the high voltage end, ground end and middle part of the sample. The heat generated due to partial arcs along clean and dry bands causes chemical changes decreasing hydrophobicity of silicone rubber insulators. These surface modifications were analysed using Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy. Ageing analysis was carried out after 24 hour of the high voltage application, to provide sufficient relaxation time for hydrophobicity recovery. After dry band arcing, hydroxyl group (OH) were formed on the insulator surface while the hydrophobic group (CH) content was reduced. The results of this study will further our knowledge regarding the performance of polymeric insulators in humid and contaminated conditions.