The impact of switching capacitor banks with very high inrush current on vacuum switchgear

Capacitor bank switching can cause significant inrush current to flow during the closing phase of circuit breakers. From test-statistics, it is derived that switching capacitor banks at higher voltage under the IEC ´back-to-back´ inrush current condition, is a significant challenge for SF6 and vacuum circuit breakers. In the case of vacuum circuit breakers, field electron emission (FEE) current during the opening phase under full recovery voltage conditions are measured. It was concluded that in spite of the wide variety of measured FEE current magnitude (from tens of μA up to several rnA) there is no direct relationship between magnitude of FEE current and probability of breakdown. Longer arc duration of the normal load current reduces the FEE current level after load current interruption.