Electrode processes and arc form in miniature circuit breakers

The electric arc in current limiting circuit breakers is often depicted as a well defined region of current flow. During a short circuit fault the current through the arc in a current limiting miniature circuit breaker can range from 100 to 10000 Amps. This range of current, along with varying electrode conditions, will lead to variation in both the form of the arc and the processes occurring at the electrodes. These electrode processes, in particular the emission mechanism at the cathode root, dominate the mobility characteristics of the arc. Previously proposed electrode processes are reviewed and the interaction of the mechanisms discussed. Using data recorded on a high speed Arc Imaging System observations about the arc behaviour at different intervals of the arc event are related to possible electrode processes. The variation of arc form in miniature circuit breakers is also discussed.