Breakdown modeling of SF6 and its environmentally friendlier alternatives in quasi uniform fields

A retrofill solution of non-switching high-voltage SF6 equipment using an environmentally friendlier alternative is an emerging solution different to a new-build approach where existing SF6 equipment is decommissioned and replaced with new equipment. This work develops a streamer criterion model to enable the screening of a large number of SF6 alternatives under representative parameters for retrofill application. Different operational parameters relevant to practical applications have been experimentally investigated under 50 Hz AC voltage waveform for absolute pressures of 1-6 bar, quasi uniform geometries with field utilization factors of 0.55-0.69 and average maximum surface roughness of 8–46.6 µm. The combined experimental and modeling validations inform that a 20% C3F7CN and 80% CO2 mixture has a comparable dielectric performance as SF6 over a wide-ranging conditions representative of gas-insulated line/busbar (GIL/GIB). Thus, this work demonstrates that a C3F7CN/CO2 mixture is suitable for retrofilling the existing SF6-designed equipment, which provides an economical and time saving approach that will expedite the transition to a more sustainable electricity grid through the complete phase-out of SF6.