Criteria for successful short circuit current interruption on a real 245 kV 40/50 kA SF6 circuit breaker

Abstract

Special attention needs to be given to the processes that occur in alternating current arcs at the instant when the current naturally passes through a zero. The short interval of time around current zero, named the interaction period [1], is of crucial importance for arc-quenching, when it is decided whether the interruption will be definite or whether arc reignition will occur. As a matter of fact, regardless of the SF6 circuit breaker working principle, its rated voltage and history of the short circuit current interruption process, there is a critical value of arc extinction voltage peak which must be reached to make a successful interruption possible [2]. The arc extinction voltage peak can be increased by elongating the arc (in other words by increasing the distance between arcing contacts) and/or by increasing the pressure of SF6 gas inside the thermal chamber around current zero instant. This means that it is possible to find a critical value of distance between arcing contacts and a critical value of SF6 gas pressure inside the thermal chamber at current zero instant as criteria for successful short circuit current interruption. Based on the results of type tests in high power laboratory (including current zero measurement — CZM) and the calculation results of the software HV CB Simulation, these criteria for short circuit current interruption are successfully established for a real SF6 circuit breaker 245 kV 40/50 kA.