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 lo ng time. Rise of internal pressure exceeding a certain threshold value causes loss of the current switching capability and at a pressure, wh ich is about one or two orders higher, the loss of the electric insula ting properties. Pressure measurements after manufacturing and re-exam ining the internal pressure of vacuum interrupters after several years of service require different procedures, measuring methods and diagno stic 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 est imate the internal pressure of the vacuum interrupters after long-time service and to give information about the remaining safety margin.