Influence of copper vapors on thermal properties of SF6/Cu mixtures existing in High
Voltage Circuit Breakers.
L.D Hermette1,2, Y Cressault1, A Gleizes1, K. Bousoltane2
1
Université de Toulouse; UPS, INPT; LAPLACE (Laboratoire Plasma et Conversion
d’Energie), 118 route de Narbonne, F-31062 Toulouse cedex 9, France
2
SIEMENS T&D ET HP GS R&D DG R1, 1 rue de la Neva, BP 178 38004 Grenoble, France
e-mail: [email protected]
The establishment of an electrical arc inside a HVCB causes the erosion of nozzles,
walls and contacts. These organic/metallic vapors come to mix with the SF6 initial gas and
modify the thermal properties of the plasma. The knowledge of these properties and their
implementation in numerical models enable them to better quantify the effect of these vapors
on the arc behavior and its extinction.
This work presents the radiative properties, the transport (the viscosity , the electrical
conductivity σ and the thermal conductivity ) and the combined diffusion coefficients
(CDCs) for SF6/Cu plasmas in LTE, at 1bar, and temperatures between 300K and 30kK.
To perform this calculation the plasma was assumed in local thermodynamic
equilibrium (LTE). In high power arc, radiation represents a preponderant term in the energy
balance. The radiative properties are obtained according to the Net Emission Coefficient
(NEC) method [1] solving the radiation transfer equation supposing spherical isothermal and
homogeneous plasma. The transport coefficients are calculated according to the method of
Chapman-Enskog [2] based on the resolution of Boltzmann’s integro-differential equation.
The CDCs are deduced from the concept developed by Murphy which consists of a
combination of diffusion flux [3]. The advantage of this method lies in the fact that it’s
independent of the number of chemical species and only depends on the elementary
constituents present in the plasma. The diffusion is then taken into account through one
diffusion coefficient.
Figure 1 : Influence of copper on Net Emission Coefficient
The results are presented for different molar proportions of copper in SF6/Cu mixtures.
They highlight the influence of copper on the properties: the copper lines are strongly
emissive but also strongly absorbed in the first millimeters, a small percentage of copper
(<1%) strongly increases the NEC and σ up for temperatures below 15kK (fig.1); and are
modified for proportions higher than 20%, and the CDCs have the same shape showing a
maximum at around 10kK which depends on the concentration of copper.
Partial financing of this work by Siemens Company is acknowledged.
[1] B.Liani, M.Rahmouni, A.H.Belbachir, H.Riad, A.Gleizes, J.Phys D:Appl.Phys, 30, 2964
(1997)
[2] S.Chapman and T.G. Cowling, The Mathematical Theory of Non-Uniform Gases (NewYork) (1958)
[3] A.B.Murphy, J.Chem.Phys, 99, 2, 1340 (1993)