Optical and Electrical Investigation of High-Current Arcing Modes and Correlation with Contact Microstructure after Single Current Interruption

This research work evaluates the appearance and transition of the arcing modes under the conditions of a model vacuum switch for various current amplitudes. The modes that can be observed during the current interruption are determined with the help of high-speed video recording and correlated with the characteristic arcing voltages. The current amplitudes have been chosen to represent the variety of different arcing modes. After the arcing load the melted region of the contacts is metallographically analyzed to gather additional information about the conditions during current interruption. With increasing current amplitude, the observed anode phenomena are as follows: “footpoint”, “anode spot type II” and “jet mode”, with unstable and stable contact jets. In comparison to the limits of current interruption, the threshold currents for the active anode and the higher mode transitions occur at relatively low currents. The occurrence of the arcing modes, the behavior of arcing voltage and the resulting microstructure can be correlated with very high consistency. A current leading to the formation of the “jet mode” surprisingly results in a reduction of the melted depth on the anode side but in an increase in the same on the cathode side. Apparently, this mode influences the microstructure of both electrodes in the same way.