Fluoronitrile/CO₂ mixture as an eco-friendly alternative to SF₆ for medium voltage switchgears

Recent studies suggest that fluoronitriles compound Novec 4710 possesses a dielectric strength two times higher than that of SF₆, while with a low global warming potential of only 2400. Mixed with CO₂ buffer gas, the Novec 4710 mixtures offer excellent dielectric properties and the possibility to be used as an eco-friendly alternative to SF₆ for medium voltage switchgears. This paper focuses on the comparative study of the breakdown strength and partial discharge (PD) characteristics between the fluoronitrile/CO₂ mixtures and SF₆ under AC voltages. Breakdown tests are conducted under different electrode configurations, i.e., planeplane, sphere-plane, rod-plane, and needle-plane, at different pressures and electrode gaps. In the uniform field, equivalent dielectric strength to SF₆ at 100 kPa can be reached by a mixture containing 15% fluoronitrile at identical total pressure; while in non-uniform and highly non-uniform fields, SF₆ exhibits higher dielectric strength than 20% mixture. The PD analysis suggests that SF₆ has much more PDs with lower magnitude and the 20% fluoronitrile/CO₂ mixture has less PDs but with higher magnitude. Due to the different PD characteristics, the corona stabilization effect may be responsible for the higher breakdown strength of SF₆ under highly non-uniform field.