Effect of AC corona discharge on aging of silicone rubber nanocomposites at high altitude

During service, corona discharge could arise on outdoor composite insulators under wet conditions and its intensity can be accelerated at high altitude due to low air pressure. This phenomenon reduces the surface hydrophobic characteristics. In this paper, AC corona aging studies are carried out on silicone rubber (SR) nanocomposites at low pressure of 60kPa. Nano-silica with size of ~20nm is used as filler. SR nanocomposites with different loading by weight are prepared by using mechanical stirrer and ultrasonic water bath techniques. For the creation of AC corona discharge, a point to plane electrode configuration is used in a glass chamber and its internal ambient pressure is decreased to 60kPa using vacuum pump to simulate high altitude condition. The specimens are sandwiched between the electrodes, in direct contact with the plane electrode (ground) but separate from the point electrode by a fixed air gap. The specimen surfaces are exposed to continuous corona discharge from the point electrode for extended periods. Results of accelerated corona aging test at 60kPa indicate that corona resistance of SR is remarkably improved by dispersing nano-silica in base matrix at 5wt% loading. After 48 hours of continuous corona exposure, loss in hydrophobicity is reduced by 18° and the formation of cracks on surface is significantly suppressed in the 5wt% sample. It is also perceived that absorption peak heights of Si-O-Si and Si-CH₃ in 5wt% aged sample are less decreased by 4% and 12.5%, respectively as compared to unfilled aged SR sample.