Accelerated aging of silicone rubber cable terminations

In order to ensure that the silicone rubber used for cable terminations will not track or erode due to dry-band arcing, inorganic fillers, such as alumina trihydrate or silica, are usually added to the polymer. However, in order to satisfy the easy installation requirement, the filler concentration is usually lower than that used for outdoor polymer insulators. The reduced filler loadings have caused premature failures in certain laboratory tests, but the same terminations have been successfully used in the field for over 20 years. In order to determine the factors of this discrepancy, a systematic evaluation in a fog chamber was performed, where the experimental conditions were varied over a wide range. Changes occurring in the polymer were monitored periodically using electron spectroscopy for chemical analysis. It is demonstrated that the experimental conditions play a significant role in the accelerated aging of silicone rubber terminations. Good correlation with experience in the field is obtained when the test parameters allow the material to recover its hydrophobicity