Experimental Investigation of Anode Activities in High-Current Vacuum Arcs

It is well known that the melting of electrodes (mainly anode melting) in vacuum arc can increase the metal vapor density around current zero and even lead to interruption failure. In order to clarify the anode activities and their influence on arc appearance and interruption capacity, series experiments of cup-shaped axial magnetic field copper electrodes were conducted. Obvious anode melting was detected; the liquid copper flowed on the contact plate of anode and formed a clockwise swirl flow. The appearance of anode melting is likely to correlate to the transition of arc mode from high-current diffuse mode to high-current diffuse column mode. The melting of anode was severer than cathode and was influenced by the distribution of cathode spots. Various kinds of copper particles at macroscopic level can be seen in arc column. Even at the interruption limit, the majority of melted copper of anode sputtered out of gap in form of liquid droplets or was pressed into the cup of anode, the copper vapor evaporated into arc column only accounted for a few portion and no obvious anode jets was found due to large plasma pressure in arc column.

I. Introduction

IT IS WELL known that inside the vacuum interrupters, the vacuum arc is in diffuse state and the arc plasma mainly comes from cathode spots when arc current is not very high and a moderate axial magnetic field (AMF) is applied. At the diffuse state, homogeneous heat flux to anode could avoid overheating at single locations, only cathode erosion can be found and the anode is still in passive state [1]–[6]. However, when arc current exceeds a critical value, anode becomes active due to large and inhomogeneous heat flux from arc column to anode, it becomes to be a new source of metal vapor and arc plasma [7]–[9]. The anode evaporation can influence the high-current vacuum arc (HCVA) characteristics [10], [11], such as arc appearance and current distribution in arc column. Meanwhile, anode activities have great influence on the interruption performance of vacuum interrupters as excessive metal vapor at current zero may lead to failure of interruption [12]–[14].