Critical Electric Fields in Hot SF6, C2F4, and Cu Mixtures: Calculations With Experimental Validations for Gas Circuit Breaker Applications

We measured breakdown voltage
${V}_{\text {b}}$
, gas temperature
${T}_{{\text {g}}}$
, and gas density
${N}$
with the corresponding critical electric field
${E}_{{\textit {cr}}}/{N}$
in hot dissociated mixtures initially involving SF6, C2F4, and Cu highly diluted in argon. These gas mixtures are heated by a microwave source generating a plasma flame that ablates Cu atoms from a thin copper filament placed inside the cell of the hot gas conditioning. Densities of Ar, SF6, and C2F4 are controlled by flowmeters, while the density of ablated Cu is estimated from optical emission spectroscopy, which is also used for
${T}_{{\text {g}}}$
and
${N}$
estimation. The measured
${E}_{{\textit {cr}}}/{N}$
data in the considered experimental cases of gas temperatures and mixture compositions are needed to analyze the sets of the collision cross sections of species involved in hot dissociated SF6 (11 species), C2F4 (19 species), crossed species (two species), and copper byproducts (five species). The sets of collision cross sections of SF6/C2F4 byproducts were taken from a previous work and those of copper byproducts are fit and validated in the present work. Then, the sets of collision cross sections of all species are considered without argon in some hot specific SF6/C2F4/Cu mixtures to analyze the effect of more particularly copper on
${E}_{{\textit {cr}}}/{N}$
for large ranges of
${T}_{{\text {g}}}$
(up to 4000 K) at a given gas pressure using a rigorous multiterm solution of Boltzmann equation for electron energy distribution function (EEDF) while calculating based on thermodynamic equilibrium formalisms of hot gas composition for species proportions.