A systematic study of arc faulting between two cables in aeronautic conditions is performed and a power balance of the arc is realized. Electrical characteristics and radiative heat flux are recorded. The effect of the current mode (AC/DC), cable material and pressure is highlighted with the assessment of the power balance, which includes the mean power of the arc, power transferred to the cables that can cause melting and vaporization, and the power lost by radiation, conduction and convection in the arc column. The evaporated mass of the cables can be estimated in this way. Optical emission spectroscopy measurements of the induced plasma are performed rendering the overall temperature of the arc using a Boltzmann plot method. The overall temperature is higher for copper-contaminated plasma than for aluminium-contaminated plasma. Despite the erratic behaviour of the plasma, the trend shows that the DC as well as the use of lighter aluminium-based cables lead to higher power.

In this paper, we report experimental results based on the direct observation of the electric arc behaviour during vacuum arc remelting of a Ti alloy. These results were obtained in a specifically instrumented industrial furnace using high speed framing camera and optical emission spectroscopy, for a current density level of the order of 10 A/cm2 and a gap length of a few centimetres. It was observed that the arc exhibits a similar operating regime to that described in the literature for the case of Inconel 718 and Zr alloy electrodes. The arc structure corresponds essentially to that of a diffuse metal vapor arc with separate and rapidly moving cathode spots. Several critical parameters of the cathode spots, including their current, size and velocity, and of the interelectrode plasma were evaluated. Also, the interactions between the arc operation and the transfer of metal drops in the interelectrode gap were investigated. Three modes of transfer of the liquid metal drops in the interelectrode gap have been identified depending on the gap length: drop falling, drip short and drop erosion induced by the cathode spots.

High-speed camera imaging and optical emission spectroscopy have been used for investigating the structure of the electric arc and the transfer mechanisms of the liquid metal during vacuum arc remelting (VAR) of Ti alloys. The arc exhibited a similar operating regime to that described in the previous literature for the case of Inconel 718 and zirconium alloy electrodes. The arc behaved in a diffuse mode with many separate and rapidly moving cathode spots. Several parameters of the cathode spots, including their current, size and apparent velocity were evaluated. The application of an external axial magnetic field tended to encourage the cathode spots to locate themselves on the base of the electrode. A large density ratio of Ti+ ions and Ti atoms in the interelectrode plasma was evaluated, suggesting that the plasma was strongly ionized. The calculated excitation temperature of Ti+ ions (1–1.2eV) was about 1.5–2 times greater than that obtained for Ti atoms. The transfer mechanisms of the drops of liquid metal might be classified into three main modes depending on the gap length: drop falling, drip short and drop erosion induced by the cathode spots. The importance of the influence of the arc on the metal transfer mechanisms was inversely related to the gap length.

This paper describes measurements of the voltage and temperature profiles in a vacuum arc remelting (VAR) crucible during a series of melts of a 40CrMoV13-9 steel alloy electrode, which were used to obtain information about the current flows in the furnace. The results derived included the current leaving the crucible above the ingot crown, the current flowing between the crucible and the crown, the current transferred between the crucible and the ingot lateral surface and the current flowing through the ingot bottom. It was established that the crown (observed to be 5–10cm high) played a predominant role in the current distribution, as the crown carried more than 50% of the furnace current. A small but non negligible fraction of the furnace current (about 10%), which represents the lower limit of the side-arcing current, was found to leave the crucible above the crown. The effect of the arc gap length on the current distribution was examined, but no general trend was clearly identified. Finally, a summary of the results reported in this study and those previously obtained in the literature is presented. Significant differences regarding the estimated amount of the side arcing current were noted that did not seem to be directly related to the changes in the remelted materials or melting conditions. It was pointed out that a detailed understanding of the current partition in the furnace requires additional experimental and theoretical study to clarify the path of the current flowing through the ingot crown.

Low-current (similar to 250 mA), high-voltage (similar to 700 V), dc discharges are observed to operate in air at atmospheric pressure when a closed loop is included for current regulation on the power supply. A dynamic process might control the discharge steadiness more efficiently than the conventional stability criterion that compares the slope of the static volt-ampere characteristic to the value of the external ballast resistor. To check the validity of the inferred stabilization process, a typical 4.7 cm long plasma filament operates in ambient air. Optical and electrical diagnostics are performed to investigate the discharge properties. Measurements then reveal most typical features of an actual arc discharge in air. Consequently, a numerical simulation based on a time-dependent Elenbaas - Heller equation allows calculation of the time-evolution of the plasma in the discharge. Finally, electron density measurements using a specific microwave absorption device confirm the high rate of ionization of the plasma: almost two orders of magnitude higher than for a typical glow discharge in free air.

2-heptanone is representative of a class of odorous molecules. Recent studies have shown that by adding a catalyst to a dielectric barrier discharge (DBD) plasma, the elimination of 90% of this molecule can be achieved with low consumption of electric energy, at room temperature, for concentrations below 1000 ppm. In the presented work, the removal of the ketone by DBD, both in dry air and within a slice of a honeycomb monolith of cordierite without a catalyst, was studied. In both experiments, the discharge was operated in a plane-to-plane geometry with a discharge volume of 10 cm(3). A high voltage, bipolar pulse generator (40 kV max, 1-140 Hz frequency range) was used. In dry air, it was found that 2-heptanone is almost totally removed (> 95%) for a specific deposited energy of about 500 J (.) 1(-1), but this elimination is less effective in the porous cordierite reactor (80%) for the same energy. This effect is explained by the very different spatial distribution of the plasma within the discharge volume, as seen using a CCD camera. Moreover, the adsorption-desorption equilibrium of the molecule at the surface of the material is greatly influenced by the discharge.

Low current ( 250 mA), high voltage ( 700 V), DC arc discharges are observed to operate in air at atmospheric pressure when a close loop is included for current regulation of the power supply. A model of the low-current arc column is developed. Calculation results of the current and temperature on the axis of the discharge with and without the current regulation model taken into account show that the discharge steadiness is attributed to a dynamic process of the close loop.