Spatial distribution of charged particle emission in a copper-chromium high-current vacuum arc

Summary form only given. Vacuum circuit breakers are widely used in high-power systems, because they are compact, reliable and provide excellent switching capabilities even at high currents up to tens of kA. The main tendency of vacuum circuit breaker development is nowadays to extend their ability to operate even at higher voltages and higher currents. Despite numerous studies of the vacuum arc properties there is still a lack of spectroscopic investigations of high-current vacuum arcs for advanced switching applications. Nevertheless fundamental investigations are required for a deeper understanding of the plasma properties and the physical processes taking place during current interruption.This contribution presents results obtained by optical emission spectroscopy applied to a high-current vacuum arc model experiment. The experimental setup allows to reproduce the arc behavior observed in real circuit breakers at 50 Hz sinusoidal currents with peak values of 2.3 kA. Copper Chromium (Cu-Cr) electrodes with 20 mm diameter are used, which are separated at a controlled velocity of 1.1 m/s to ignite the discharge. Overview spectra as well as highresolution spectra are shown (spectral resolution down to 30 pm). The optical emission spectroscopy is accompanied by high-speed video imaging to observe the arc behavior in general. By imaging of axial and radial sections of the arc onto the entrance slit of a spectrograph, spatial distributions of neutral and charged particle emission can be determined. In case of electrodes made of Cu-Cr alloys it is possible to detect emissions from Cu I, Cu II, Cu III as well as Cr I, Cr II and Cr III. Due to the multitude of partly overlapping spectral lines line identification is an important issue before conclusions can be drawn. Along the arc axis different zones can be discriminated where different ionization stages achieve maximum emission. To give an example, neutral atoms radiate strongly in the vicinity of the electrodes, which- is an expected behavior due to the eroded electrode material and the correspondingly high particle density. The results can reveal new information about charge distribution in the gap and describe elementary processes which are taking place in switching plasmas during current interruption giving options to increase the interruption behavior in future.