Electro-Thermal Stress of Dielectric Coated Electrodes in Gas-Insulated Systems under DC Voltage Stress

The use of high-voltage direct current (HVDC) links becomes economic for the transport of electrical energy over vast distances. Gas-insulated systems (GIS) provide advantages due to a compact design, high reliability and independence from environmental conditions. A combination of both technologies for converter stations on e.g. offshore platforms has various technological and economical advantages. In contrast to AC-GIS there is a lack of experience in the application of DC-GIS in transmission systems. In comparison to AC applications, changed electrical stresses under DC voltage require the development of new dimensioning guidelines. Charge carriers can accumulate on dielectric coated surfaces and can lead to surface discharges at the gas-solid interface. The experimental investigations show that the surface discharge behaviour is strongly temperature dependent, due to the temperature dependent electric conductivity of the used coating material. A safe and reliable operation of high-voltage devices can be ensured by partial discharge (PD) measurements. The most common used method for PD detection according to IEC 60270 is suitable for a reliable detection of surface discharges in gas-insulated DC systems.