Mingzhe Rong

Thermodynamic and transport properties of two-temperature SF6 plasmas

This paper deals with thermodynamic and transport properties of SF6 plasmas in a two-temperature model for both thermal equilibrium and non-equilibrium conditions. The species composition and thermodynamic properties are numerically determined using the two-temperature Saha equation and Guldberg-Waage equation according to deviation of van de Sanden et al. Transport properties including diffusion coefficient, viscosity, thermal conductivity, and electrical conductivity are calculated with most recent collision interaction potentials by adopting Devoto’s electron and heavy particle decoupling approach but expanded to the third-order approximation (second-order for viscosity) in the frame of Chapman–Enskog method. The results are computed for various values of pressures from 0.1u2009atm to 10u2009atm and ratios of the electron temperature to the heavy particle temperature from 1 to 20 with electron temperature range from 300 to 40 000u2009K. In the local thermodynamic equilibrium regime, results are compared with avail...

Dielectric breakdown properties of hot SF6/He mixtures predicted from basic data

Sulfur hexafluoride (SF6) gas has a quite high global warming potential and hence it is required that applying any substitute for SF6 gas. Much interest in the use of a mixture of helium and SF6 as arc quenching medium was investigated indicating a higher recovery performance of arc interruption than that of pure SF6. It is known that the electrical breakdown in a circuit breaker after arc interruption occurs in a hot gas environment, with a complicated species composition because of the occurrence of dissociation and other reactions. The likelihood of breakdown relies on the electron interactions with all these species. The critical reduced electric field strength (the field at which breakdown can occur, relative to the number density) of hot SF6/He mixtures related to the dielectric recovery phase of a high voltage circuit breaker is calculated in the temperature range from 300u2009K to 3500u2009K. The critically reduced electric field strength of these mixtures was obtained by balancing electron generation and...

Calculated rate constants of the chemical reactions involving the main byproducts SO2F, SOF2, SO2F2 of SF6 decomposition in power equipment

SF6 is widely used in electrical equipment as an insulating gas. In the presence of an electric arc, partial discharge (PD) or spark, SF6 dissociation products (such as SF2, SF3 and SF4) react with the unavoidable gas impurities (such as water vapor and oxygen), electrodes and surrounding solid insulation materials, forming several toxic and corrosive byproducts. The main stable decomposition products are SO2F, SO2F2 and SOF2, which have been confirmed experimentally to have a direct relationship with discharge faults, and are thus expected to be useful in the fault diagnosis of power equipment. Various studies have been performed of the main SF6 decomposition species and their concentrations under different types of faults. However, most of the experiments focused on the qualitative analysis of the relationship between the stable products and discharge faults. Although some theoretical research on the formation of main SF6 derivatives have been carried out using chemical kinetics models, the basic data (chemical reactions and their rate constants) adopted in the model are inaccurate and incomplete. The complex chemical reactions of SF6 with the impurities are ignored in most cases. The rate constants of some reactions obtained at ambient temperature or in a narrow temperature range are adopted in the models over a far greater range, for example up to 12 000 K, due to the difficulty in the experimental measurement and theoretical estimation of rate coefficients, particularly at high temperatures. Therefore, improved theoretical models require not only the consideration of additional SF6 decomposition reactions in the presence of impurities but also on improved values of rate constants. This paper is devoted to determining the rate constants of the chemical reactions relating to the main byproducts of SF6 decomposition in SF6 gas-insulated power equipment: SO2F, SOF2 and SO2F2. Quantum chemistry calculations with density functional theory, conventional transition state theory and Wigner’s tunneling effect correction are employed to estimate the rate constants of four important chemical reactions: F + SO2F → SO2F2, F2 + SO2 → SO2F2, SO2F + SF5 → SF6 + SO2 and SOF3 + SF3 → SF4 + SOF2. The results are derived for a large temperature range, from 300 to 12 000 K, and finally fitted by a three-parameter Arrhenius equation. This work lays a basis for the further study of the SF6 decomposition mechanism by means of chemical kinetics modelling. Journal of Physics D: Applied Physics Calculated rate constants of the chemical reactions involving the main byproducts SO2F, SOF2, SO2F2 of SF6 decomposition in power equipment

Simulation of Arc Splitting Process Considering Splitter-Plate Erosion

A 3-D simulation model of air arc plasma in a low-voltage circuit breaker, considering the production of iron vapor from splitter-plate erosion, is developed. The distributions of temperature and mass fraction of iron vapor are calculated. The simulation results indicate that the arc splitting process is strongly influenced by the presence of iron vapor from the splitter plate. Images of arc simulation results are presented.

Investigation on the Arc Phenomenon of Air DC Circuit Breaker

Comparison analysis on the arc phenomenon of an air dc circuit breaker both in the resistive and inductive circuit was conducted in this paper. It is an interesting phenomenon that severe restrikes occurred in the resistive circuit. According to the results, the reason is that the arc current falls sharply witbreak the rise of arc voltage in the resistive circuit so that the lack of the Lorentz force and the pressure difference before and behind the arc made the hot gas move back toward the entrance of the arc chamber.

Numerical Investigation on Arc Behavior in Low-Voltage Arc Chamber Considering Turbulence Effect

This paper is devoted to the modeling of air arc plasma in a simplified low-voltage arc chamber considering the turbulence effect. The numerical model is built based on the magnetohydrodynamics, and the turbulent flow field is described by the standard k-ε model. The calculated arc behavior is presented by the temperature distribution sequence and shows good agreement with the experimental results. Compared with the simulation results under laminar assumption, the simulated arc characteristics taking turbulence effect into consideration are closer to the real situation.

Investigation of DC hybrid circuit breaker based on high-speed switch and arc generator

A new design of DC hybrid circuit breaker based on high-speed switch (HSS) and arc generator (AG), which can drastically profit from low heat loss in normal state and fast current breaking under fault state, is presented and analyzed in this paper. AG is designed according to the magnetic pinch effect of liquid metal. By utilizing the arc voltage generated across AG, the fault current is rapidly commutated from HSS into parallel connected branch. As a consequence, the arcless open of HSS is achieved. The post-arc conducting resume time (Δ tc) of AG and the commutation original voltage (Uc), two key factors in the commutation process, are investigated experimentally. Particularly, influences of the liquid metal channel diameter (Φ) of AG, fault current rate of rise (di/dt) and Uc on Δ tc are focused on. Furthermore, a suitable Uc is determined during the current commutation process, aiming at the reliable arcless open of HSS and short breaking time. Finally, the fault current breaking test is carried out for the current peak value of 11.8 kA, and the validity of the design is confirmed by the experimental results.