Outdoor ageing of silicone rubber based polymeric materials

Two silicone rubber based polymeric materials for outdoor insulation were studied under field conditions for about nine years. Then they were evaluated in the laboratory. The field test was conducted in an environment of light coastal pollution where the materials were non-energized as well as energized with both HVAC and HVDC. The long-term study focused on the hydrophobicity and the material changes of the insulator surfaces combined with the leakage current performance of the insulators. In general, the results presented in this paper show that the surface ageing of the two types of silicone rubbers was relatively moderate and that both the non-energized and energized materials remained highly water repellent. Moreover, no substantial differences in the hydrophobicity between the two material types were observed after almost nine-years in the field. However, the leakage currents of the insulators differed. This indicates that the hydrophobicity, as it is usually measured, is not a good indicator of the surface resistance of the insulator material.