Vacuum Degree Prediction Technology of Vacuum Interrupter through AC / DC Partial Discharge Measurement

If the vacuum degree of vacuum interrupter (VI) is decreased by arc heat, ceramic cracking, gas leakage, and manufacturing defects, partial discharge occurs between the contact and the floating shield. Accordingly, the reliability of the solid insulation high voltage apparatus is lowered, and an electrical accident is occurs. Therefore, time monitoring of the vacuum degree inside VI should be considered for a high reliability power transmission. However, R&D of related companies is quite insufficient, so there is a difficulty in commercialization. Therefore, in this paper, a study was conducted on the vacuum degree prediction technology through AC and DC partial discharge measurement for time monitoring of VI. Partial discharge pattern and apparent charge according to the decrease of vacuum degree were measured under AC and DC voltage. As a result, the partial discharge under AC voltage between the contact and the floating shield is generated from $1\sim 5 \times 10^{-3}$ torr. However, the partial discharge occurs at about $1\times 10^{-2}$ torr in DC voltage. Moreover, the time interval between partial discharge and flashover was different according to the polarity of the DC voltage.