Gas insulated switchgear (GIS) are essential parts of a safe, robust, and flexible energy system. Circuit breakers in GIS disconnect the power when faults such as lightning strike occur. Additionally, they are used to redirect power to reduce the energy system losses. The most common gas used as an insulation medium in GIS today is sulfur hexafluoride, SF6. However, SF6 is the most potent greenhouse gas in existence with a global-warming potential 23 000 times higher than CO2. Replacing this gas would reduce the national and global use of SF6, making GIS-technology more sustainable. The project will obtain fundamental knowledge on discharge behaviour of the alternative gases and gas mixtures through experimental and computational research.
A PhD candidate started at NTNU in the fall of 2021 and is working on experimental characterization and computational modelling of electrical discharges in SF6-alternatives. A setup consisting of a 400 L, 1.5 bar pressure vessel with custom made electrodes has been established and connected to a lightning impulse generator. Advanced high-speed cameras capture the discharge development in the tank with up to 1 billion frames per second. A photo-multiplier tube detects the discharge light emission, and a high-frequency measurement system records the discharge current. The initial tests have been made in both air and C5-FK gas mixture, and a conference paper on these initial tests has been submitted for Nordic Insulation Symposium 2022. There is also ongoing work on planning future experiments for further studies of the discharges, as well as preparing for computer simulations of the electrical discharges in order to use the lab-results to verify the simulation model.