| This thesis addresses the topic of corona-induced degradation of nonceramic insulator (NCI) housing materials as it relates to NCI long-term performance. Three commonly used NCI housing materials, namely silicone rubber (SIR), ethylene propylene diene monomer (EPDM) and a blend of SIR and EPDM were studied. Through comprehensive experimental and analytical investigations, the mechanisms responsible for corona-induced degradation of NCI housings and the main factors involved therein have been identified. Conditions favoring or restricting NCI corona-promoted degradation and the influence of the varying character of corona-related processes on NCI field performance have been evaluated. Data gathered from electrical and physicochemical analyses show that NCI housing corona-induced degradation possesses a strong chemical nature. Factors such as ambient humidity, material formulation, and corona polarity and intensity play a determining role on the amount and character of degradation. Computation of the energy magnitudes required to provoke severe material surface damage has allowed a correlation with expected field operating conditions to be performed. Results obtained from such analysis seemingly indicate that NCI housing corona-induced degradation similar to that observed in this study is fairly unlikely to occur for service times amounting to many years. These estimates of degradation-free time expectancy of NCI housing materials have been found to strongly agree with observations made on actual NCIs in service for approximately 20 years. |
