Surface Discharge Behaviour of Coated Electrodes in Gas-Insulated Systems Under DC Voltage Stress

Due to the increasing usage of renewable energy sources, it is necessary to transmit electrical energy over long distances. Apart from traditional AC interconnection, High-Voltage direct current (HVDC) links provide an economic option to transport bulk energy. Especially on offshore platforms it is beneficial to use gas-insulated substations (GIS) due to the saline atmosphere and the limited space available. Considering technical and economic aspects, it is advantageous to use DC-GIS on those platforms. The constant electrical field in DC-GIS may lead to charge accumulation on gas-solid interfaces - e. g. on the interface between the low-conductive electrode coatings and SF6• Previous investigations revealed that this charge carrier accumulation can lead to surface discharges on coated electrodes which may reduce the dielectric strength of the whole insulation system. In order to understand these phenomena comparative experiments with low and high conductive electrode coatings were performed.