Arc ignition through pre-arc from extra fine copper wire
Metal ignition wires are widely used in power arc tests on insulator sets and similar. Finer metal ignition wires are preferred from the point of view of influence on the apparatus tested. However, if the metal ignition wires are too fine, the arc cannot be sustained. To perform power arc tests successfully, therefore, they need to have some degree of thickness. With these requirements in mind, we proposed a new arc ignition method that allows the use of extra fine wires by leading to the pre-arc in a current of several dozens amperes, and examined it for practical use. In this paper, the sustainment characteristics of arcs ignited from extra fine copper wires using this new method were investigated with a gap between the rod electrodes. The results showed that kA-class arcs with a gap length of 1.5 m could be ignited through pre-arc from 0.03 mm diameter copper wire at a voltage of 12 kV. The influence of the ignition wire thickness on arc characteristics was also studied by comparing the arcs ignited by this new method with those ignited by the general method in which copper wires exceeding 0.3 mm in diameter was used.
Calculation of net emission coefficient of thermal plasmas in mixtures of gas with metallic vapour
The net emission coefficient of Ar-Cu, N2-Cu, SF6-Cu and Ar-Fe mixtures was calculated for homogeneous and isothermal plasmas at atmospheric pressure in the temperature range between 3000 and 25000 K. The increase in power radiated due to the presence of metal vapours depends on the vapour itself (the net emission is higher with iron than with copper) and on the type of gas. The influence of pressure was calculated for the SF6-Cu mixture. In the last part of the paper the values of the net emission coefficient were used to calculate the temperature profile in stationary arc in Ar-Cu and N2-Cu mixtures. The influence of copper on radiation is preponderant on the temperature field at higher currents whereas the effect on electrical conductivity is important at lower currents.
Continuum absorption coefficient in SF6 and SF6-N2 mixture plasmas
The computation of continuous absorption coefficient for SF6 plasmas has been carried out taking into account free-free radiation, using the scaled Thomas-Fermi potential for the determination of the terms resulting from the radiative recombination. The authors have computed the continuum absorption coefficient K' in SF6-N2 mixtures (for pressure values between 1 and 8 bar, in the temperature range 8000 to 24000 K) assuming that the plasma is in local thermodynamic equilibrium, by combining their results obtained in the case of SF6 with those concerning N2 from the literature. The evolution of K' with nu is explained in terms of electronic configuration of the species and of the variations of electron and ion densities with pressure, temperature and SF6 proportion.