Polymer housing material for transmission line insulators offers superior pollution performance compared to glass and ceramic. However, in coastal and high pollution environments polymer insulators are susceptible to accelerated aging caused by electrical tracking and erosion. In the last couple of decades, field and laboratory studies on polymeric insulators have shown that tracking and erosion are more severe for outdoor insulation under DC voltage stress compared to AC stress at similar voltage magnitudes. Therefore, with the increased development in DC mode of power delivery, design of erosion resistant materials to improve the reliability of DC insulation systems has become an important task. This task relies on a thorough understanding of the mechanisms that lead to material erosion.

This thesis investigates partial discharge (PD) characteristics of discharges that lead to erosion of silicone rubber (SR) polymer under AC stress and DC stress of both polarities. The experiments are performed on high temperature vulcanized SR material samples. The inclined plane test apparatus, constructed in accordance with IEC 60587 requirements, is employed to produce the surface partial discharges and the resulting accelerated aging of the specimens. Two commercial instruments are used to obtain PD data. A concurrent analysis of visual observations of discharge and partial discharge data is performed to classify discharges based on the severity of material degradation that each type causes.

PD characteristics were identified for three types of discharges, using phase resolved PD patterns, PD histograms, and a signal processing technique called Time Frequency mapping. Individual pulse waveshapes of each type of discharge were also analyzed. Amplitude, energy, pulse width, and frequency spectrum were evaluated and compared for the eroding discharge pulses at the three voltage types. It was concluded that greater pulse width and the presence of dominant DC component in the spectrum are attributable to discharges that cause greater severity of SR erosion under DC stress relative to AC.