Investigation of surface discharges in insulation gases through synchronisation of improved electrical and fast enhanced-imaging techniques

This thesis investigates the generation of discharge activity in the regions where gaseous and solid dielectrics meet with energised conductors, frequently referred to as triple points/junctions. Such conditions are frequently met in practical complex assemblies of equipment and apparatus used in medium- and high-voltage applications, and the common discharge phenomena to appear are known as surface discharges. An optimised test configuration which replicates strongly non-uniform field conditions on the surface of solid dielectric samples was developed. As gaseous insulation, atmospheric gases are considered namely, technical air (21/79 % O2 /N2), nitrogen (N2) and carbon dioxide (CO2 ), and the eco-friendly mixture of trifluoroiodomethane (CF3 I)with carbon dioxide (30/70 % CF3 I/CO2). The examined solid dielectric materials include polytetrafluoroethylene (PTFE), epoxy resin and silicone rubber, all of which are frequently found in electric power industry applications of different types. The experimental investigation included the electrical detection of surface discharge activity in various gaseous compound/solid dielectric type combinations with the use of optimally developed current sensing circuits. Furthermore, a new enhanced performance high-speed camera system was developed synchronised with the electrical detection system for the study of the propagation patterns and morphology of the discharges. From both electrical and optical detection methods, it could be concluded that the 30/70 % CF3 I/CO2 mixture performed the best with N2 being the least effective. Technical air was found to withstand flashover better compared to CO2 however, the latter showed better performance in suppressing the inception of partial discharge activity and the extension of surface streamers. A list of more detailed conclusions and discussion points are presented at the end of each chapter and which are further developed in the last chapter of this thesis. Suggestions that can potentially be implemented in future works, experimental and theoretical, are also listed