Study on degradation of polymeric nanocomposite dielectric materials used for high voltage outdoor insulation

Abstract

Silicone rubber is a hydrophobic polymer which is widely employed for high voltage outdoor insulation under contaminated environments. Corona discharge can alter the basic chemical structure of polymer and degrade surface properties. Ultraviolet (UV) weathering is considered one of the major issues that influence the surface and dielectric properties of outdoor polymeric insulators. Moreover, pristine silicone rubber has low thermal properties and this may cause tracking and erosion failure due to severe dry band arcing on the insulating surface. This thesis investigates the effect of adding micro and/or nano fillers in silicone rubber composites to enhance the corona and UV weathering resistance. Furthermore, this thesis investigates the effect of material thermal characteristics on the tracking and erosion resistance of silicone rubber filled with micron, nano and hybrid set of particles. Experimental results proclaimed that addition of nano–sized silica can be an attractive solution to improve the corona resistance of micron–sized silica filled silicone rubber. Also, 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. UV weathering results indicate that the addition of nano silica to pure or micro silica filled silicone rubber can enhance its UV weathering resistance considerably. The nano fillers form an effective UV shielding layer which makes the silicone rubber less susceptible to UV. Furthermore, it is concluded that addition of BN-composites improves ability to impede the tracking and erosion process relative to AlN and ATH -composites, the reasons being better thermal stability and enhanced thermal conduction in the discharge region. On the other hand, infrared analysis revealed thermal accumulation is remarkably higher in AlN-composites which promotes dry band arcing and results in tracking and erosion failure. Micro-AlN/nano-SiO2 co-filled composites are found to be the most promising co-filled composites with high thermal stability, dielectric properties and erosion resistance. Moreover, silicone rubber filled with higher nano-SiO2 doping contents suppresses tracking growth and erosion. It could be due to collision-induced scattering of nano–SiO2 particles which reduces the secondary electron collapse and thus impedes the release of high energy and restricts thermal degradation.