high-speed imaging

Anode activity in high current vacuum arcs leads to the formation of various high current modes and transitions between them. Intense material evaporation during the anode spot mode and formation of a neutral vapour cloud during the anode plume mode modify the arc plasma properties and, hence, can have a crucial impact in applications, like e.g. reduction of interruption performance of switching devices.

Low direct current arcs generated between Cu electrodes in atmospheric pressure air are investigated in relation to low-voltage switching. Electrical and optical measurements and high-speed imaging give insight into the dynamics of the arc. Side-on spectroscopy with a grating spectrometer and suitable optical imaging delivers spatially resolved spectral emission coefficients of three emission lines of the Cu atom. The experimental findings are compared with results from modelling.

A pre-study of free burning arcs between carbon electrodes for potential use in gasification processes is presented. Free-burning arcs offer the potential to be used without additional gas feed or significant changes to gas flows in established gasification systems as well as with minimal cooling requirements for improved energy efficiency. Direct current (DC) arcs with currents up to 200 A and power levels up to 40 kW have been operated in molecular gas mixtures of H2, CO and CO2.

The data correspond to the results of modelling studies of DC electric arcs at a current of 2 A in air with admixture of copper metal vapour. Experimental findings are used to adjust input parametrs of the model in order to achieve a good match. The simulations are performed strating with a discharge burning with a minimum gap length of 30 µm for a physical time of 11 ms. Then, the separation of the electrodes is followed for further 51 ms and the discharge gap is increased up to 3 mm. The comparision of experimental and modelling data is based on the measured arc voltage.

Recent research of gas metal arc welding (GMAW) has proven that the sheath voltage dominates the total voltage fall in the current circuit and delivers most of the energy, which is finally transferred to the wire and the weld pool. This data set provides the results for droplet temperatures and the energy delivered to the wire anode in comparison with the sheath voltages. These quantities have been studied experimentally for a typical pulsed GMAW process in the one drop per pulse mode for mild steel under Ar with 2.5% CO2 with different peak currents from 350 to 650 A.

The relation between the voltage and the arc length in gas metal arc welding (GMAW) is an important characteristic. It depends on a complex distribution of the electric conductivity along the current path and does not depend on the arc length only. Based on electric measurements and the arc length determination from high-speed arc images, a simplified electrical model is introduced for a pulsed GMAW process. It shows the relation of voltage, current, arc length and free wire length and considers also their temporal evolution during the process in particular during the high-current phase.