Performance Evaluation of Transformer Mineral Oil Aged Silicone Rubber/BN Nanocomposites

Due to its exceptional thermal conductivity and enhanced insulating properties, boron nitride (BN) is increasingly employed as a filler in room temperature vulcanized (RTV) silicone rubber (SR) coatings, serving as external insulation for oil-immersed ceramic-based porcelain transformer bushings. However, the effectiveness of these RTV SR coatings may significantly degrade when exposed to transformer mineral oil. Hence, this study examines the impact of mineral oil on SR doped with BN nanoparticles. SR nanocomposites with varying concentrations of wt.% 1, 3, 5, and 7 nano-BN are synthesized and thermal aged in mineral oil at 80°C for 200 hrs. Experimental results reveal a substantial degradation of the SR matrix post-aging, attributed to the infiltration of mineral oil. Fourier transform infrared (FTIR) spectroscopy, mass analysis and 3-D microscopy results reveal the breaking of the side methyl groups and the main chain of silicone rubber (Si-O-Si), along with the detachment of filler particles, resulting in increased surface roughness. Tracking and erosion of the test specimens evaluated through inclined plane tracking and erosion tests (IPT) as per IEC 60587, shows a reduction in tracking and erosion resistance for all test specimens after aging. Further, the surface temperature distribution measured through infrared thermography during IPT demonstrates that all doped specimens experienced a lower surface temperature than the unfilled specimen. The thermal stability further investigated through thermogravimetric analysis reveals that 5wt.% composite exhibits higher thermal stability post aging. The experimental results reveal that the nanocomposite with 5wt.% BN exhibits superior resistance to degradation caused by mineral oil.