SF6-N2 Gas Mixtures Research Articles

Porous carbon nanotube networks and pillared graphene materials exhibiting high SF6 adsorption uptake and separation selectivity of SF6/N2 fluid mixtures: A comparative molecular simulation study

Abstract SF6 and SF6–N2 gas mixtures are well known insulators used in industry applications, but SF6 has to be recovered due to its high global warming potential. In this study, the adsorption of the pure SF6 and N2 fluids and the separation of their mixture with SF6:N2 = 1:9 composition, using three-dimensional porous carbon nanotube networks and pillared graphene materials has been studied by employing Monte Carlo and Molecular Dynamics simulations at ambient temperature and pressure up to 20 bar. The results obtained reveal a significant SF6 uptake and high adsorption selectivity for SF6 over N2, compared to the best performing materials in the literature. The selectivity for SF6 decreases in the case of pillared graphene and strongly depends on the nanotube pillar and graphene layer distances. The saturation capacity of the investigated materials is also achieved at very different pressure ranges, as it has been reflected on the calculated adsorption isotherms. Due to this fact, the translational diffusion coefficients of the adsorbed SF6 and N2 molecules in each material are significantly different at ambient conditions. The results obtained might be used as a springboard towards the rational design of carbon-based materials for the capture of the very potent greenhouse gas SF6.

Inception corona discharge voltages in SF6-N2 gas mixtures at high gas pressure

The use of sulphur hexafluoride (SF6) has led to increased concentration of this gas in the atmosphere. The purpose of this work is to investigate the behaviour of SF6-N2 mixtures that can be considered as a potential substitute of pure SF6. The onset corona discharge voltages have been determined from the measurements of the currentvoltage characteristics under high pressures and with highly inhomogeneous fields. The results show that the onset voltages increase with the increase of the gas pressure and are relatively higher for positive polarity. It can also be seen that for low concentrations of SF6 in the mixture the increase of the onset voltages is substantial, followed by a slow increase for elevated concentration of SF6 in the mixture, which, can be an advantage for the substitution of SF6.

SF6 concentration sensor for gas-insulated electrical switchgear

The use of SF6-N2 gas mixtures in gas insulated electrical switchgear (GIS) is becoming more wide-spread. This is motivated by the reduction of environmental impact associated with SF6 emission and the increasing number of GIS located in low temperature environments where pure SF6 cannot be employed. We present a cost-efficient sensor system that tracks gas composition based on a measurement of pressure, density and temperature. To reach the necessary measurement accuracy, a reliable calibration routine was developed. The robustness and high-end performance of the sensor system is demonstrated on a lab setup in which the thermal and convective conditions that develop in a GIS under operation can be reproduced.

Multichannel Discharge Characteristics of Gas Switch Gap in SF6-N2 or SF6-Ar Gas Mixtures Under Nanosecond Triggering Pulses

Experiments were carried out to ascertain multichannel discharge characteristics in a self-designed coaxial field-distortion gas switch filled with SF6-N2 or SF6-Ar gas mixtures of different mixing ratios. In these experiments, the pressure varied from 0.1 MPa to 0.2 MPa, the voltage pulse peak applied to the switch was in the range from 40 kV to 78 kV, and the pulse rise time was 11 ns. The static breakdown strength of the gas switch gap in the switch was also measured. The results show that in general the average number of discharge channels for SF6-Ar or SF6-N2 gas mixture which contains less SF6 is larger than that for gas mixture which contains more SF6, however, the average number of channels almost keeps constant as the gas mixing ratio varies when the pulse rise rate is high enough. The static breakdown strength of the gas switch gap decreases slightly as the content of argon or nitrogen increases.

急峻方形波高電圧を用いた SF<sub>6</sub>-N<sub>2</sub>混合 ガス中<i>V-t</i>特性の測定

A square pulse voltage is useful for studying electrical discharge physics and/or very fast transient overvoltage issues. This paper describes sparkover voltages and time lag (V-t) characteristics of SF6-N2 gas mixtures in a very short time range below a microsecond, which are measured by using a steep-front square voltage with a rise time of 16 nanoseconds and a peak value of 200 kilovolts. SF6-N2 gas mixture, which contains nitrogen gas at a ratio of 60 % or less, has equivalent dielectric strength to pure SF6 gas even in the short time range around 10 nanoseconds. Sparkover voltage and time lag characteristics are evaluated by using the equal area criterion even in the short time range below a microsecond.

Nanosecond Electrical Discharge Development in SF6-N2 Gas Mixtures

Both an experimental observation and a numerical modeling of streamer development in SF6-N2 gas mixtures are performed and the results are compared with each other. By using a steep-front square high voltage in the measurements, it is possible to keep the constant condition of the electric field during the streamer development. Minimum sparkover voltage and streamer velocities obtained from the numerical modeling show good agreement with those from the experimental observation, and the change in the streamer velocity against the gas mixture ratio shows a similar tendency.

On the effect of the addition of SF<inf>6</inf>to a N<inf>2</inf>electrical discharge laser

The electron distribution function has been calculated for simulated conditions of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> -N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixtures under conditions typical of a N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> electrical discharge laser. The results indicate that the electron distribution function, transport quantities, and electronic excitation rates change only a few percent in the presence of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> provided E/N is unchanged. The enhancement in laser power output with the addition of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> is attributed to an increased operating value of E/N in the electrical discharge.