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 SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , while with a low global warming potential of only 2400. Mixed with CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer gas, the Novec <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sup> 4710 mixtures offer excellent dielectric properties and the possibility to be used as an eco-friendly alternative to SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> for medium voltage switchgears. This paper focuses on the comparative study of the breakdown strength and partial discharge (PD) characteristics between the fluoronitrile/CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixtures and SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> under AC voltages. Breakdown tests are conducted under different electrode configurations, i.e., plane-plane, sphere-plane, rod-plane, and needle-plane, at different pressures and electrode gaps. In the uniform field, equivalent dielectric strength to SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> 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, SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> exhibits higher dielectric strength than 20% mixture. The PD analysis suggests that SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> has much more PDs with lower magnitude and the 20% fluoronitrile/CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> under highly non-uniform field.