Positive synergy of SF₆ and HFO1234ze(E)

Abstract

We measured mixtures of SF6 and HFO1234ze(E) (C3H2F4) and determined the densityreduced critical electric field strength (E/N)crit in a pulsed Townsend experiment. HFO1234ze(E) is an environmentally friendly alternative to SF6 since contrary to SF6, its global warming potential is negligible. While SF6 is unsurpassed in its efficiency of attaching thermal electrons, HFO1234ze(E) appears to moderate electron energies very efficiently. Electron attachment to HFO1234ze(E), on the other hand, is much weaker. We find a positive synergism in SF6/HFO1234ze(E) mixtures in the sense that the mixture of both compounds has a higher electric field strength than each gas separately. A maximum (E/N)crit of 425 Td is reached for a mixture of 40% SF6 and 60% HFO1234ze(E). A mixture of 90% HFO1234ze(E) and 10% SF6 has a critical electric field strength of 360 Td, similar to pure SF6. We attribute this effect to the high efficiency of HFO1234ze(E) in moderating down the electron energies, which enhances electron attachment to SF6 and reduces electron impact ionization.

Discussion on the mechanism leading to positive synergism in SF6 mixtures with HFO1234ze(E)

“…The breakdown measurements are performed in the same experimental conditions as described in the previous section, in pure HFO1234ze(E) and SF 6 , and in 4.7%, 9.6%, 19.6%, 29.6%, 39.6%, 49.6% and 69.6% of SF 6 in the mixture. The measurement series in the PT experiment covers a larger set and in this section and in section 5.4, the data for the mixtures with 5%-55% SF 6 are taken from [7]. The total pressure is kept similar in all mixtures as well as in pure HFO1234ze(E), between 300 and 480 Pa in the swarm measurements and 100 kPa in the breakdown measurements, to remove one degree of freedom and facilitate the comparison between mixtures.…”

“…The research on synergy effect in binary mixtures has a long history not only for strictly scientific purposes but also, as seen in the frame of electrical insulation in GIS, for practical reasons. The aim of this work is to explain the mechanism at the basis of the observed positive synergy in the electric strength in HFO1234ze(E)/SF 6 mixtures and is thus a follow-up to [7]. The paper is structured as follows: section 2 summarizes the available literature on binary mixtures showing a positive synergy effect.…”

SF6-Free Gas-Insulated Switchgear: Current Status and Future Trends

“…The data of SF6/N2 mixtures is calculated with Bolsig+ [28] using cross section data from Magboltz [29]. The data for SF6/HFO1234ze mixtures has been measured in a swarm experiment [30].…”

“…An often-heard argument against this pathway is that gases for which the electric power industry is the only user cannot be manufactured cost-effectively. Regardless if this is correct or not, research combining existing compounds in a favorable way to create synergistic effects, in particular, the above-mentioned positive synergy of the electric strength [30], is an important research track that should be followed.…”

Environment-Friendly and Efficient Gaseous Insulator as a Potential Alternative to SF6

“…A notable thing here is the P/P ratios of the mixtures of gases because using the W/W ratio would render the calculations incorrect as the molar mass of molecules can change the pressure of the gas mixture heavily. The total amount of R152a and CO 2 needed is calculated using the ideal gas law as shown in Equation (1) [25].…”