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

Self Cite

We have calculated the multi-temperature SF6 plasma composition by two different methods. One method is based on the mass action law whereas the other method uses a kinetic chemical reaction scheme. The first approach is furthermore split up in two different calculations. One is based on the multi-temperature Saha equation and the other is based on the excitation temperature of the involved species. With respect to the electron density we conclude that the multi-temperature Saha equation results in appreciable higher number densities compared to both the kinetic scheme and the excitation-temperature-based calculations. The difference increases with decreasing gas temperature and increasing electron temperature (i.e. with increasing degree of kinetic non-equilibrium). The kinetic scheme and the excitation-temperature-based calculation yield comparable results for higher gas temperatures. In this region the excitation-temperature-based method is preferable over the kinetic method. However, for the dielectric case (i.e. lower gas temperature) we find different results at higher electron temperatures. The excitation-temperature-based calculation method requires additional modelling at this point.

Section: Kinetic Steady Statementioning

confidence: 99%

On the determination of the multi-temperature SF₆plasma composition

Cliteur

Suzuki

Tanaka

et al. 1999

Self Cite

“…Such a method has not been used in SF 6 plasma until now, because of the complexity of chemical processes in this gas. Cliteur [11] recently published a collisional radiative model of composition, but in thermal equilibrium conditions. With our experience of SF 6 kinetics [25], we developed a kinetic model to compute the two-temperature composition.…”

Section: Equationsmentioning

confidence: 99%

“…There is in the literature a lot of study on SF 6 plasma composition (see e.g. [9][10][11]), but two-temperature calculations have appeared recently [12][13][14] to point out the impact of non-equilibrium phenomena on plasma properties, such as electrical conductivity [15]. Another aim of this paper concerns the kinetic mechanisms: we study how thermal departures from equilibrium can act on the composition of the plasma.…”

Section: Introductionmentioning

confidence: 99%

A two-temperature kinetic model of SF₆plasma

Girard

Belhaouari

Gonzalez

et al. 1999

Studying the influence of thermal departures from equilibrium in SF 6 circuit-breakers, we develop a two-temperature kinetic model to calculate the composition. Such a kinetic approach has not been adopted until now for SF 6 plasma because of the complexity of chemical processes. Our model takes into account the collisional mechanisms responsible for the creation and disappearance of atoms and molecules through 19 species linked by 66 chemical reactions. To solve the conservation equations, the model uses the direct rates of reactions, that mainly proceed from the literature, and reverse rates, that are computed by two-temperature micro-reversibility laws. Thus, we point out the importance of the choice of the expression of Saha law, comparing Potapov and van de Sanden formulations of this law. We then discuss the impact of thermal departures from equilibrium on plasma composition, on 'mean path' of molecules before dissociation in the plasma, and on the reactions that govern the disappearance of electrons.Disappearance frequency of species A through reaction 'p' (s −1 ) ν ATotal disappearance frequency of species A (s −1 ) θ Ratio between electrons temperature and heavy particles one (θ = T e /T h ) hPlanck constant (J s) k B Boltzmann constant (J K −1

“…In calculations starting from kinetic reactions, in most cases only 18 or 19 species, instead of the 28 used in equilibrium calculations, are taken into account as shown in table 1. Some kinetic calculations also take into account the vibrational states [39]. Of course, when calculating non-equilibrium effects by using multi-temperature methods such as those of Potapov [29], van de Sanden et al [30] and Cliteur et al, more species can be used [35,39].…”

Section: Number Of Species Considered In Non-equilibrium Calculationmentioning

confidence: 99%

“…Some kinetic calculations also take into account the vibrational states [39]. Of course, when calculating non-equilibrium effects by using multi-temperature methods such as those of Potapov [29], van de Sanden et al [30] and Cliteur et al, more species can be used [35,39].…”

Section: Number Of Species Considered In Non-equilibrium Calculationmentioning

confidence: 99%

A modified pseudo-equilibrium model competing with kinetic models to determine the composition of a two-temperature SF₆atmosphere plasma

Rat¹,

André²,

Aubreton³

et al. 2001

This paper is devoted to calculation of the non-equilibrium composition in a SF6 thermal plasma at atmospheric pressure. Non-equilibrium thermal plasmas are characterized by heavy species temperatures T h below 9000 K with electron temperatures at the maximum three times higher than T h when the latter is below 4000 K. Different theories have been used based on either multi-temperature plasmas, Saha-Potapov modified by André et al, van de Sanden et al, Cliteur et al, or kinetic calculations or the pseudo-equilibrium model, recently developed. This model gives results similar to those of kinetic calculations for N2 and H2 plasmas but with calculation times two orders magnitude faster. Pseudo-equilibrium calculation takes into account the reactions with low activation energies instead of ionization reactions, while keeping all the species present in the kinetic calculation. First, the theories are compared in a case already studied in the literature by Cliteur: a heavy species temperature T h at 6000 K, with the electron temperature T e varying between 6000 and 15 000 K. Comparison of the results shows that the multi-temperature calculations, except those of Cliteur, are far from kinetic especially for n e and n F - . In addition, the pseudo-equilibrium model fits rather well with the kinetic calculations as long as molecular species are present in the plasma. Second, to calculate the composition of non-equilibrium thermal plasmas the ratio T e /T h is assumed to vary as the logarithm of the electron densities ratio n e /n c max , n e max being the electron density over which equilibrium prevails, i.e. 1023 m-3. For kinetic reactions where electrons are involved (in the direct reaction while heavy species intervene in the reverse reaction), a temperature T* between T e and T h is defined. T* is calculated as a function of the electron flux to that of heavy species. The variation of T* with T h is smoother than that of T e . In such conditions again, there is an excellent agreement between kinetic and pseudo-equilibrium calculations performed at T*, which is not the case for multi-temperature calculations. These results demonstrate that the pseudo-equilibrium calculation developed for thermal plasma simple forming gases such as N2 and H2 can also be applied to more complex gases such as SF6.