Vacuum circuit breaker current-zero phenomena

Post-arc current phenomena that occur when interrupting high currents with vacuum circuit breakers have been investigated. High resolution measuring equipment has been used to measure both the post-arc current and the arc voltage in the current-zero region. Three examples of frequently observed phenomena are described. The first describes the phenomenon that in the event of a current-chopping, the current is zero for a short period of time just before the natural alternating current zero, but continues to flow afterwards, in the form of a post-arc current. The second and third example deal with the post-arc phenomena after currents that are much higher than the test breaker´s rated short-circuit current. These examples show a low-voltage period after current-zero. Apparently, during this post-arc period, the residual plasma between the breaker´s contacts conduct well. In addition to the voltage-zero period, the voltage trace in the third example also shows evidence of current-chopping. This means that the plasma conducts poorly just before current-zero, but conducts well immediately afterwards. The post-arc current model of Andrews and Varey is verified with measurements.