AC Corona Resistance of Micro-ATH/Nano-Al2O3 filled Silicone Rubber Composites

Alumina tri-hydrate (ATH) filled silicone rubber composite insulators are widely used for outdoor insulation purposes. They are often affected by corona discharges. A high reduction in hydrophobicity, surface mangling and roughness variation are ramifications of corona discharges. In this paper, resistance against corona damage of pure, ATH and ATH+nano Al2O3 filled silicone rubber is compared through SEM, surface roughness and hydrophobicity recovery performance. Micron ATH (similar to 5 mu m) and nano Al2O3 (similar to 40 nm) are selected for composite fabrications. The three different samples, i.e. pure silicone rubber (USiR), 40wt%-ATH/silicone rubber (MSiR) and 39wt%-ATH+1wt%-nano Al2O3 (MNSiR) are fabricated and tested under AC corona discharge for 168 h. A pin-plane electrode geometry enclosed in a glass chamber is employed for corona discharge exposure. Test results show that severe defects in the form of surface rupture appeared in USiR. Such defects are not found in MSiR and MNSiR but in the form of voids and craters in MSiR. A smooth surface with minor cracks and low peak roughness is observed in MNSiR. Comparatively, higher increment in average and peak roughness is seen in USiR. Furthermore, it is found that the pace of hydrophobicity recovery is marginally lower in MSiR and MNSiR. Besides, hydrophobicity recovery in the region below the electrode tip is substantially higher in USiR followed by MSiR and MNSiR.