Surface Charging and Its Effects on DC Flashover Strength of Insulating Materials

Surface charging is a common occurrence during service for all HV insulators as well as live-line tools during live-line maintenance work. The main sources of non-uniform charging are corona discharges from nearby and/or direct contact with energized objects and cloth wiping by tribo-charging effect. This paper focuses on studying the DC charging characteristics of three different insulating materials and the flashover performance of such pre-charged insulating materials. The samples used are cylinders of 130 mm length with different diameters. Surface charging by cloth wiping is found to be much more than that of corona discharges from energized objects. Surface charges take more than four hours to decay by 80%. Moreover, surface charges can increase the positive and negative flashover voltages of pre-charged samples by up to 13%. Mitigation methods to improve the flashover performance of insulating materials are identified. The research on surface charging forms hypotheses and recommendations which may improve the live-line maintenance procedures in ways that protect live-line workers from accidents.