Articles techniques et présentations

Used for welding, cutting, deposition by projection, for the treatement of waste, or in analysis for ICP torches, for the synthesis of high purity silica or for the manufacture of nanometric powders or nanoparticules, thermal plasmas are fundamental in processing of materials and in energy industry, especially through plasma torches. However, this type of plasma is not always desired: a short circuit can cause an electric arc which generally manifests itself in the form of a high current discharge. When this problem occurs between two cables of an electrical network, there is a risk that the arc will remain for a few tens to a few hundred milliseconds and will propagate along the cables. This phenomenon, called "arc tracking", is accompanied by the ablation of the cables, by the melting and the partial vaporization of the metal and the complete degradation of the insulation, but also by the damage of the immediate environment by the projection of molten metal droplets and incandescent residues. Thus, the consequences are not only the interruption of the current and the information that passed through the circuit, but also the damage that the arc is likely to cause, which can be very significant, especially for the aeronautical field. The establishment of a model to simulate the creation and maintenance of a thermal plasma at atmospheric preasure is an important issue, particularly in this field where the setting up of experiments proves to be very complex due to the large temperature values (several tens of thousands of Kelvin), but also the large voltage or current values necessary in order to achieve the breakdown of the arc. To model this thermal plasma, we used the Plasma Module of COMSOL®, firstly starting with the case of a free burning arc, then with a non-tranferred plasma torch. We used the Equilibrium Discharges interface, studying different meshes and solvers. Once these models validated and influences of parameters understood (current density, velocity of the particules at the inlet, cathode tip geometry, gas nature) we studied the case of two cables facing each other (10A, see figures for the simplifyed geometry), looking into the influence of radiative tranfer and the arc-electrode interactions. Some results of the validated steps and first results about arc-tracking modelling will be presented with issues to discuss on.