DetectingVacuum Degree Condition of Vacuum Interrupter by Partial Discharge Measurement

Reliability of vacuum circuit breaker (VCB) is dependent on the vacuum condition inside the interrupter. Partial Discharge (PD) measurement is a method used to determine the vacuum condition to detect early leakage from Vacuum Circuit Breaker (VCB). This paper presents the floating shield potential of an interrupter related to PD inception voltage (PDIV) as function of the internal pressure. PD phenomena were investigated regarding floating shield potential affected by variations in the shield to grounded plate distance. The discharge mechanism was also discussed in term of impact electron multiplication and ion drift in the vacuum. The result showed that lowering the shield to the grounded plate distance would shift the curve to a lower pressure region. At pressures less than 3 Pa, the discharge is found to obey Townsend-like mechanism, and change to streamer-like mechanism with increase in the pressure.