Electrode phenomena before long delayed breakdowns in vacuum after switching capacitive currents

Due to breakdown of vacuum interrupters used for switching of capacitor banks, high overvoltages are produced, which could result in damages in capacitor banks. Besides breakdowns of the vacuum gap during voltage rise, some breakdowns with much larger delays have been observed. The mechanism of such breakdowns is studied in this paper experimentally by considering the light intensity emitted from the vacuum gap during voltage application. The emitted light intensity is recorded using a charge coupled device (CCD) camera. The recorded light intensities show that an emission center building at the anode surface precedes the breakdown of the vacuum gap.