MEASUREMENT OF EMISSION CURRENTS IMMEDIATELY AFTER ARC POLISHING OF CONTACTS - METHOD FOR INTERNAL-PRESSURE DIAGNOSTICS OF VACUUM INTERRUPTERS

The inherent high reliability of vacuum interrupters is determined by the maintenance of a high degree of vacuum in the vacuum tube for a long time. Rise of internal pressure exceeding a certain threshold value causes loss of the current switching capability and at a pressure, which is about one or two orders higher, the loss of the electric insulating properties. Pressure measurements after manufacturing and re-examining the internal pressure of vacuum interrupters after several years of service require different procedures, measuring methods and diagnostic techniques. In this paper the fundamentals of a new method based on the measuring of emission currents immediately after arc polishing of the contacts have been presented. This method is appropriate to estimate the internal pressure of the vacuum interrupters after long-time service and to give information about the remaining safety margin.