AC corona resistance performance of silicone rubber composites with micro/nano silica fillers

Silicone rubber (SR) insulating surfaces are often subjected to corona partial discharges (PD) during outdoor operation which can change the surface chemistry significantly and result in considerable surface deterioration, hydrophobicity loss, and enhancement of PD activity. In this work, the effect of micro and nano-fillers addition on surface degradation of SR under AC corona discharge is examined by analyzing the PD characteristics, hydrophobicity and surface morphology. Nano precipitated silica and ground silica with particle size of ~20 nm and ~5 μm are adopted and incorporated in RTV silicone rubber by two different mixing techniques. Mechanical stirring followed by ultrasonic water bath are applied to achieve uniform dispersion of fillers in RTV SR matrix. The four different types of the composite, i.e. pristine SR, 30-wt% micro-silica/SR, 27.5-wt% micro with 2.5-wt% nano-silica/SR and 5-wt% nanosilica/SR composites are tested under AC corona discharge. It is found that, at the end of ageing, the nano-silica composite showed the best suppression against PD activity and higher resistance against surface damage as compared to other test samples. It is also found that resistance to hydrophobicity loss is offered by composites during the initial 48 h of corona treatment but it is completely lost at the end of 96 h of ageing.