Tracking and erosion requirements for high voltage silicone rubber insulators

One of the important disadvantages of the silicone rubber insulators is the ageing caused by its exposition to pollution and environmental factors such as UV, rain, and temperature. The degradation can be highly dependent on the quality of the compound used in the manufacturing of the insulators. Moreover, the quality of the silicone compound depends strongly of the cost, the brand, production country, etc. On the other hand, for tracking evaluation, the IEC 62039 standard recommends for high voltage insulators a minimum requirement of 3.5 kV and a satisfactory 2.5 kV for medium voltage applications. However, the IEC standard does not mention if this classification is valid for all the environments including the highly polluted, where tracking failures can be developed. Several failures occurred in two different 400 kV transmission lines, where polymeric insulators failed; the failure was due to pollution and because of the materials' quality and design. On the other side, inclined plane test were done on insulators' semicircular sheds and most of the specimens did not pass 4-4.75 kV; due to that, a tracking voltage should be established for silicone compounds exposed to polluted environments.