Effective ionization coefficient of C5 perfluorinated ketone and its mixtures with air

C5 perfluorinated ketone (C5 PFK with UIPAC chemical name 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)-2-butanone and sold by 3M as Novec ™ 5110) has a high dielectric strength and a low global warming potential, which makes it interesting as an insulating gas in medium and high-voltage applications. The study was carried out to determine the effective Townsend ionization coefficient α eff as a function of electric field strength and gas density for C5 PFK and for its mixtures with air. The non-self-sustained Townsend discharge between parallel plate electrodes was initiated by illuminating the cathode by UV radiation. The discharge current, I , was measured as a function of inter-electrode distance, d , at different gas densities, N , and electric field strengths, E . The effective ionization coefficient α eff was determined from the semi-logarithmic plots of I / I 0 against d . For each tested gas mixture, the density normalized effective ionization coefficient α eff / N was found to be a unique function of reduced electric field strength E / N . The measurements were carried out in the absolute pressure range of 0.05–1.3 bar and E / N range of 150–1200 Td. The increasing fraction of C5 PFK in air resulted in the decrease of effective ionization coefficient. The limiting electric field strength ( E / N ) lim where the effective ionization coefficient α eff became zero was 770 Td (190 kV cm −1 at 1 bar) for pure C5 PFK and decreased to 225 Td (78 kV cm −1 at 1.4 bar) for 7.6% C5 PFK/air mixture. The latter value of ( E / N ) lim is still more than two times higher than the ( E / N ) lim value of synthetic air and about two-thirds of the value corresponding to pure SF 6 . The investigated gas mixtures have the potential to become an alternative to SF 6 in numerous high- and medium-voltage applications.