Kinetic Study of a Decaying SF₆ Arc Plasma in The Presence of Impurities

Abstract

A kinetics model has been developed to study the chemical composition of a decaying SF6 arc plasma in the presence of impurities such as copper, carbon and water, proceeding from electrode and nozzle erosion or desorption in real SF6 circuit-breakers. The model is based on the following main assumptions: the plasma is in thermal equilibrium (only one temperature for all the species); the plasma is homogeneous; the pressure remains constant during the decay; the transient temperature evolution is previously imposed. Experimental gas analysis by chromatography, after arcing in a circuit-breaker has confirmed the main results of the calculation: proportion of SOF2 is much more important than that of SO2F2 and very low formation of S2F10 molecules.

- circuit-breaker arc modelling around current zero: I. Free-recovery simulation using a collisional-radiative plasma model

“…All the necessary reaction rate coefficients, temperature dependences and collision cross sections have been compiled from numerous literature references as well as parametric studies. Differently from the initiatory paper by Brand and Kopainsky [3] and works of Gleizes et al [4] and Adamec and Coufal [5], the temperature calculation and the inclusion of electronimpact processes are the new points presented here. In addition to the chemical kinetics, we have also modelled a time-dependent diffusion rather than linking the chemical kinetics to the ideal gas law.…”

Composition and thermodynamic properties of reacting mixtures

“…for a 1 ≤ 1 and T ≤ 6 kK have been published by Coufal and Zajacová in [9]. Gleizes et al [18] were concerned with kinetics in the gaseous system S 1 with emphasis on the appearance of S 2 F 10 at temperatures T ≤ 1 kK.…”

“…The composition and thermodynamic properties of a system of products of the reaction SF 6 + a 4 Cu −→ S 4 have recently been published by Sakuta and Takashima [23], Chervy et al [13], Gleizes et al [18], Paul et al [17], Fleurier et al [25] and by the present author in [1,2,16,24]. In [16,24] the methods of calculating the composition and thermodynamic properties of a gaseous system are described.…”

“…In [18] the kinetics of chemical reactions in the gaseous system S 4 is discussed, with emphasis on the formation of S 2 F 10 at low temperatures. In a figure in [23] Sakuta and Takashima give the electron concentration in the composition of system S 4 (0.111) in terms of its dependence on a 4 for several temperatures in the range 4-14 kK at a pressure of 0.8 MPa.…”

- circuit-breaker arc modelling around current zero: II. Arc-circuit-interaction simulation using Boltzmann analysis

“…The model is completely self-consistent in that both the gas temperature and the electron temperature are calculated during the recovery time interval. Differently from the initiatory paper [4] and works of Gleizes et al [5] and Adamec and Coufal [6], the temperature calculation, the inclusion of electron-impact processes and the interaction between the arc and the connected circuit by means of a Boltzmann analysis, are all new points presented here. This study also differs from that of Yan et al [7], whose study included a Boltzmann analysis but skipped arc-circuit interaction in order to obtain and focus on the dielectric breakdown of a residual SF 6 plasma.…”