Partial Discharge Characteristics in a Vacuum Interrupter under Different Shield Potentials

Beyond the expected lifetime, vacuum interrupters (VIs) commonly lose the vacuum with a higher leakage rate due to several factors such as material degradation, mechanical wear and tear or manufacturing defects [1]. When the vacuum is lost, the VI is no longer able to isolate the arc between the contacts and the discharge voltage decreases. This can lead to the VI failing to interrupt the circuit during a fault or overload, which can result in damage to the equipment and potential safety hazards. Therefore, it is important to develop an earlier detection technique of vacuum leakage not only for the operating vacuum circuit breakers (VCBs) in medium voltage but also for the development of higher voltage VCBs [2]. The present study aims to detect the vacuum leakage inside the VI by measuring the partial discharges (PDs) characteristics inside the VI. The paper presents the PD characteristics at the different internal pressures under different shield potentials from the measured discharge waveforms, discharge occurrence frequency, PD location charged potential and $\Phi -\mathrm{q}$ pattern. The shield potentials are varied with the aim to verify that the shield potential control has the possibility for earlier detecting technique of vacuum leakage.