Diagnosis of Discharge Pattern in Vacuum Interrupter by Shield Potential Measurement

In vacuum discharge, we found that the discharge developing time depends only upon the discharge path length in the case of gap discharge, whereas it is in inverse proportion to the square of the discharge inception voltage in the case of surface flashover. Based on the database for fundamental electrode configuration, we have proposed a diagnosing method of discharge pattern in vacuum interrupter (VI). In this paper, we applied the diagnosing method to an actual VI model and verified the effectiveness of the method. We measured the applied voltage and the shield potential with voltage dividers and the discharge current with high-frequency current transformer. We also captured the still image of discharge by a digital camera to verify the discharge path in the VI model with an observation aperture. By changing the electrode configuration in the VI model, we observed the various discharge patterns, e.g. the gap discharge between contacts, the surface flashover on the solid insulator through the shield, and the combination of them. Experimental results revealed that we succeeded in diagnosing the discharge pattern with the validity higher than 90%.