The Time-Resolved Characterization of Erosion Products from High-Current, Copper Vacuum Arcs

A vacuum arc at high enough current can produce gross melting on electrode surfaces as a consequence of anode spot formation and other high-current electrode phenomena. Erosion from the electrodes under this condition is much more rapid than at low-current (where material loss occurs principally from the cathode) and is a process that is presently poorly understood. The present work is aimed at characterizing the erosion products from cathode and anode surfaces during high-current arcs on copper electrodes for single half cycles (60 Hz) arcs having peak currents of 30 kA. Fully open gap lengths were approximately 18 mm. Among the findings were the following. a) Erosion rate determined by electrode weight loss was approximately 8 mg/C of arcing. b) Droplets ejected from the electrodes had masses varying from a few tenths to a few tens of micrograms and velocities typically up to 40 m/s, although higher velocities are seen. c) The greatest number of droplets are produced at, or just after the current peak, and higher droplet velocities are seen in this same time interval. d) Erosion in vapor form detected in the plane of the cathode surface and moving radially is a maximum just after the peak of current and is relatively abundant. Such vapor is essentially absent in the anode plane.