RTV-SiR based composites aged in a multi-stressed environment under AC and bipolar DC voltages

Silicone rubber-based polymers are gradually replacing traditional insulators in outdoor applications due to their numerous advantages, in particular high hydrophobicity that is important for suppressing leakage current and hence surface flashover. However, the main problem with polymeric composites is their aging when exposed to environmental stresses causing loss of their desired properties and expected lifetime. In this work, aging behavior of three types of room temperature vulcanized silicon rubber (RTV-SiR) loaded with nano-silica and micro-ATH is studied. Samples of the materials with different specifications were fabricated and exposed to various environmental stresses in two specially designed weather chambers under both AC and bipolar DC voltages for a time period of 9000 hours. Thereafter, diagnosis was performed for identifying the degree of deterioration using several techniques. These include hydrophobicity classification, measurements of leakage current and mechanical properties, Fourier transform infrared spectroscopy, and Thermogravimetric analysis. Results of the conducted experiments indicated stronger degradation of the desired properties under positive DC stress as compared to the AC and negative DC voltages. Moreover, silicone rubber doped with nano-sized particles of silica filler demonstrated better anti-aging performance as compared to its micro-ATH filled counterpart.