Analyses of RTV Composite Coating under DC Stress for High Voltage Outdoor Insulation

High Voltage Direct Current (HVDC) transmission poses stern threats to insulators due to unidirectional high voltages. Room temperature vulcanized (RTV) silicone rubber (SiR) coatings are highly preferred to cope with flashovers. In this work, RTV-SiR coating co-filled with silica
$({\text{Si}{\mathrm{O}_2}})$
and alumina trihydrate (ATH) fillers underwent prolonged accelerated weathering under bipolar direct current (DC) for an extended aging period of 10,000 hours. The results revealed that samples containing nano
$\text{Si}{\mathrm{O}_2}$
, and micron-ATH displayed enhanced hydrophobic recovery, leading to improved suppression of leakage current, whereas ATH-filled composites demonstrated better performance in surface resistivity with improved antiaging. In terms of the polarity impact of DC voltage, samples powered by negative voltage showed relatively less decrease in volume and surface resistivity. Moreover, scanning electron microscopy (SEM) images of samples filled with nano
$\text{Si}{\mathrm{O}_2}$
exhibited a lower degree of deterioration.