Corona discharge activity on a string of glass cap-and-pin insulators under conditions of light wetting, light non-uniform contamination

The corona-like discharges on the top surfaces of lightly contaminated glass cap-and-pin insulators in a "V" configuration have been observed on an operational 400 kV line. Although it is postulated that such discharges may contribute to an insulator flashover, this is not the focus of this research. The objective of research described here is to replicate in the laboratory the corona-like discharges seen in the field. As a means of investigating this, field studies comprising the measurement of leakage current, insulator contamination and environmental parameters were done over a two-year period. The findings of this study were then used as the basis for controlled laboratory tests. The results and methods of this study have allowed replication of the top surface corona discharges seen in the field. The paper also discusses the role played by different wetting mechanisms associated with the observed types of discharge modes on lightly contaminated discs.