Study of High-Current Anode Modes for Various Electrode Materials

Electrodes made from CuCr alloy with the same composition, but different thermal processing have been analysed in a vacuum interrupter model at AC currents up to 6.5 kA in a vacuum current breaker model. The appearance of various anode modes has been analysed by optical observation using high-speed imaging, as well as by arc voltage measurements. Existence ranges of anode modes leading to intense evaporation have been determined. Simultaneously to the optical observations, the anode surface temperature was determined by means of NIR spectroscopy. In addition, the density of neutral chromium vapour after current zero crossing was measured by means of broadband optical absorption spectroscopy. Three Cr I resonance lines in the region 425-429 nm are used for the analysis. The morphology of the anode surface after appearance of various anode modes have been analysed by microscopy. The results show a clear influence of material properties on the anode activity and electrode erosion.