Magnetron-based on-site measurement of the internal pressure in vacuum interrupters

In the coming years an increasing quantity of vacuum interrupters (VI) is expected to reach the end of its service life. Leading manufacturers can provide a service life of up to 30 years due to high quality standards and sophisticated production processes. However, their operating performance observed so far indicates the possibility to extend this service life, in case of non-intrusive diagnosis methods being available for the assessment of the remaining service life and the simultaneous estimation of the technical risks. Amongst other factors especially the internal pressure is decisive for the condition of the VI. However, currently available test devices only provide qualitative information, which is insufficient to provide a basis for the assessment of the condition of vacuum switchgear and for a decision concerning potential extension of the service life. This contribution addresses a mobile test device based on the magnetron method for the quantitative assessment of the internal pressure in VIs. It identifies the magnetic flux density and its homogeneity as critical influencing factors in the design of a mobile magnetron-based test device. Based on the results, a simplified, exemplary prototype for on-site application is designed. The application of this device on industrially manufactured VIs verifies its functionality and generally demonstrates the proof of concept.