A novel sight for understanding surface charging phenomena on downsized HVDC GIL spacers with non-uniform conductivity

Abstract Surface charging phenomena on DC GIL spacers is a complicated process affected by lots of factors, among which surface conductivity is an important dielectrics parameter. In this study, experimental and theoretical research are carried out to investigate the effects of non-uniform surface conductivity on surface charge accumulation behaviours of downsized HVDC GIL spacers. A SiC/epoxy layer is partially coated on alumina/epoxy spacers to form a non-uniform surface conductivity. The coating manners include sector-shaped coating and ring-shaped coating. The accumulated surface charges show a rising first and then decreasing trend with the increase of SiC contents in coated area. When surface conductivity is high enough, there is almost no charge accumulation. Bipolar charges, which are generally observed on raw alumina/epoxy spacers, are found to be preferable to accumulate at interface region between high and low surface conductivity. The orientation of bipolar charges is determined by the distribution of inhomogeneous surface conductivity. The formation mechanism of bipolar charges at the interface is revealed based on the experiment and simulation results. Besides, a uniform surface conductivity contributes to suppressing randomly distributed surface charges including bipolar charges, which can provide guidance for designing and optimizing highly reliable and stable HVDC GIL.