Performance and degradation analysis of HTV-SiR polymeric composites under the influence of bipolar DC voltages along with multiple stresses.

High temperature vulcanized silicon rubber (HTV-SiR) insulating materials are employed around the globe for the outdoor insulation of high voltage transmission lines. The biodegradable nature of these materials is the main hurdle to their reliable operation under severe outdoor conditions. For this reason fillers with different sizes, concentrations, shapes and dimensions are added to the base polymers to improve their performance. In this work, one pristine and three HTV-SiR composites were prepared having micro/nano fillers of silica and ATH. The samples were placed in a specially fabricated weathering chamber for a time period of 5000 h having different stresses along with bipolar DC voltage. The performance of prepared composite materials was analyzed using electrical, mechanical, thermal, surface and chemical analysis techniques. After aging, the highest value of leakage current recorded for sample S1 was 8.12 µA under positive DC voltage and the lowest value recorded was 5.82 µA for sample S4 under negative DC voltage. S1 became hydrophilic having HC4 and HC5 classes and S4 retained its hydrophobicity having HC3 and HC2 classes under bipolar DC voltage at the end of aging duration. TGA results showed residual % yield for S1, S2, S3 and S4 was 35.4%, 40.99%, 42.84% and 45.9% respectively under positive DC voltage. Moreover, fourier transform infrared spectroscopic analysis revealed that hybrid composite S4 showed the highest intactness in siloxane backbone (Si–O–Si) bonds with a decrease in its peak of 32.3% for positive DC and 17.2% for negative DC. Scanning electron microscopy showed voids, cracks, increased roughness and chemical structure damages on samples S1 and S2, whereas, co-filled composites S3 and S4 had better surface morphology. [ABSTRACT FROM AUTHOR]