| Summary: | Polymers used as electrical insulators in high voltage (RV) plant are subjected to inherent design and fault level stresses during service. As a result of these stresses the materials degrade and deteriorate, reducing equipment life and lowering reliability of power systems. Defects in polymeric insulators will result in partial discharge (PD) activity, potentially leading to plant failure. PD is both a symptom of a fault in insulation and the source of various stress mechanisms, that cause further material degradation. It is important to understand correlations between PD signal parameters, discharge induced degradation and defect type. In this thesis PD activity and subsequent material degradation for void defects in different polymeric insulators are studied. The ability to relate identifiable specific signal characteristics at a fault would aid asset managers with assessment of the insulation degradation. This project measures and identifies differences in characteristics of PD and PD induced material degradation in different types of void defects to quantify the material physical conditions. The results of this research correlate changes in the PD patterns for single void and multiple void arrangements with induced chemical and physical changes on the surface of the void. This work also shows that PD activity in air voids in polymeric insulators is dependent on the void shape, size and sample construction. This thesis investigates the relationship between the PD characteristics and the induced material degradation in four different polymer materials, to aid development of mechanisms to enable prediction of the level of degradation of a known polymeric insulator by measuring its PD characteristics and vice-versa. The results show that there are identified differences in PD activity and subsequent chemical and morphological changes for the four different polymers due to difference in polymer structure, chemistry, morphology and ability to extract initiating electrons from the material surface. Most of the experiments conducted in past research work on PD in voids have been perfol1ned using self-contained internal voids. This work compares PD characteristics and material degradation in unvented and vented voids. This investigation enables analysis of the influence of vents on PD processes in voids. The results show that that there is a sharp increase in the PD activity and subsequent void surface changes over time for the unvented voids, whereas the PD activity for vented voids increase very slowly over time.
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