An investigation into late breakdown phenomena during capacitor switching performances in relation with vacuum interrupter design and field emission current

Various prototypes designs of 36 kV vacuum interrupters have been tested in high-power test station during capacitive switching operations. Back-to-back tests were performed for inrush current of 20 kA peak level and 4250 Hz frequency. Experiment was performed with a number of prototype vacuum interrupters of different geometry and contact material. Vacuum gap behavior under pre-arcing and inrush current conditions (pre-arc energy, duration and interruption of inrush current) will be highlighted. Field electron emission measurement has been used to monitor field electron emission current that flows in vacuum gaps after current interruption. Statistics will be presented in relation to the late breakdown events, field electron emission current measurement, vacuum interrupters design and contact material. It was observed that only the mechanism of electron field emission alone could not explain the breakdown in vacuum at the origin of late breakdown phenomena. Contact material, vacuum interrupter design as well as circuit breaker characteristics are determining the dielectric withstand during capacitor bank switching operations.