Comparative Performance of ATH and SiO2 Doped Silicone Rubber Microcomposites Exposed to Mineral Oil

Alumina-tri-hydrate (ATH) and Silica (SiO2) microfillers are widely used to enhance the pollution performance of room temperature vulcanized (RTV) silicone rubber (SR) coatings which are now increasingly being used in porcelain-based bushings of oil-immersed transformers to enhance their operational safety. However, exposure of SR to transformer oil is detrimental and is underexplored. Therefore, the current work involves experimental investigations on relative electrical, thermal, and mechanical performances of undoped and 50% by weight of ATH and SiO2 doped SR microcomposites thermally aged in transformer mineral oil at 80 °C for 200 h. Test specimens incurred significant physical changes such as swelling and weight gain post aging. The presence of black patches, voids, and dents on the specimen indicating morphological deterioration, along with an increase in surface roughness and decrease in hardness was noted through scanning electron microscopy (SEM), 3-D microscopy, and shore hardness investigations. Tracking and erosion resistance of the test specimens evaluated as per IEC 60587 inclined plane tracking and erosion test (IPT-E) demonstrated that neither of the micro fillers could prevent tracking and erosion in aged specimens. IPT-E results were supported by surface potential decay measurements, confirming that ATH-doped SR microcomposites exhibited the maximum tracking and erosion resistance. Thermal properties of the test specimens, investigated via thermogravimetric and differential thermal analysis (DTA), revealed higher thermal stability of ATH-doped specimens compared to mSiO2-doped and unfilled specimens. In conclusion, post-aging in mineral oil, micro-ATH-doped RTV SR outperformed the SiO2-doped and undoped specimens, making it more suitable for transformer bushing applications.