Resistance against AC corona discharge of micro-ATH/ nano-Al2O3 co-filled silicone rubber composites

Abstract

Exposure to corona discharge damages the polymeric structure of alumina trihydrate (ATH) filled silicone rubber composite insulators. In this work, an attempt has been made to enhance the resistance against sustained long term corona exposure of ATH filled silicone rubber by fabricating its co-filled composites through addition of a small amount of nano Al2O3. Fabricated specimens comprise a pristine sample of silicone rubber (SR), one micro {40wt% ATH (MSR)} composite and two co-filled {39wt% ATH+1wt% nano Al2O3 (MSR1%) and 38wt% ATH+2wt% nano Al2O3 (MSR2%)} composites with total particle loading of 40wt%. They are subjected to AC corona exposure produced from a needle electrode tip for seven days. Performance evaluation is achieved through SEM (Scanning electron microscopy), FTIR (Fourier transform infrared spectroscopy), hydrophobicity, and surface roughness. Test results show severe material ruptures occurred in SR but damage in the form of pits and voids in MSR and MSR1% in the area directly below the needle tip. Interestingly, MSR2% exhibits subdued damage and a compact lump structure. The hydrophobicity recovery rate is significantly higher below the needle tip than in the vicinity, and in the SR as compared to the other composites. Also noted is higher increment in average and peak surface roughness below needle tip, and strong resistance to roughness increment by MSR2%. FTIR results show higher concentration of hydroxylation and aluminum nitrites in MSR and the absorbance intensities of principal functional groups show fewer deviations in MSR1% and MSR2% relative to their virgin states. Based on experimental results, it is concluded that corona resistance of micro ATH filled silicone rubber can be enhanced through addition of small amount of Al2O3 by fabrication of co-filled composites.