An approach to diagnose pressure hazard of vacuum bulbs

Vacuum bulbs may encounter the pressure rise hazard that results in failure in interrupting over currents in power systems. The pressure may unexpectedly increase due to a slow leak through cracks after a long period of operation in the power system. Several methods for monitoring the pressure onsite have been proposed so far, but most of them are poor in the ability to checkup the hazardous pressure level of 1 Pa or less. The present paper reports the results of a primitive attempt conducted for diagnostic purposes. In the study, by monitoring the electrification on the insulator surface of a real vacuum bulb, we successfully provide a method to detect the pressure rise around 10^-1 Pa.