Investigation of replacement gas ina bushing filled with SF6

Electrical bushings are important components in high voltage systems, enabling currents to pass through grounded barriers while preventing electrical breakdown. Gas insulated bushings typically use SF6 to its excellent insulating properties, but environmental concerns have led to restrictions on its use. The aim of this project is to find alternative options for gases to be used in a gas insulated wall bushing. This project explores alternative insulating gases for gas insulated wall bushings through simulations in COMSOL Multiphysics. Various gases were evaluated through simulations to analyze both the electric field distribution and the thermal behavior as well as the fluid flow inside the bushing. The electric field simulations indicated that the maximum electric field strength decreased with lower relative permittivity and lower electrical conductivity. The field strength was compared to the dielectric strength for all gases and to avoid dielectric breakdown it was deemed relevant to have the gases at higher pressure. The CFD simulations showed that helium at 100 kPa was the most promising gas but as its dielectric strength was to low to be deemed an alternative it was not a viable alternative. Air, nitrogen and carbon dioxide all behaved similar both in fluid flow behavior and temperature. They marked higher maximum values than SF6 and helium but their dielectric strength makes them viable alternatives to SF6. Overall, air, nitrogen, and carbon dioxide, when used at elevated pressures, all seem to be possible replacements. However, further research regarding the material properties is required before any definitive conclusions can be drawn.