Vacuum interrupters: pressure vs. age A Study of Vacuum Levels in 314 Service Age Vacuum Breakers

摘要

All vacuum interrupters (VIs) increase in internal pressure over time. [Authors' note: In this paper the modern term vacuum interrupter will be used in lieu of the now obsolete vacuum bottle.] The pressure increase may be due to small, long-path leaks from outside to inside, diffusion through the container materials and/or virtual leaks from materials within the internal volume. Ⅵ manufacturers design and test their vacuum interrupters for a minimum lifetime of twenty to thirty years. VIs may successfully operate beyond this period but it is beyond their design life. Since the first large influx of vacuum interruption in the early 1970s, the technology has become the most widely applied power interruption technique in the medium voltage range (2.4kV - 38kV). Vacuum technology now dominates the interrupter market throughout the world. This means that there are hundreds of thousands of VI breakers and contactors in field that were manufactured twenty or more years ago. Inevitably, in-service Ⅵ failures caused by vacuum loss have greatly increased over the last ten years. Until recently there was no technology that allowed field testing vacuum levels in VIs. Using a field portable magnetron, test technicians can now test vacuum level and thereby evaluate the Ⅵ condition based on that parameter. The vacuum level test is called the Magnetron Atmospheric Condition (MAC) test. To further knowledge in this area, the authors have performed vacuum level tests on 314 circuit breakers (809 VIs). The VIs being tested were installed in breakers that had manufacturing dates ranging from 1978 through 2014. It is assumed that the VIs were manufactured at the same time as the breakers. The results of these tests have been evaluated. This paper describes the data gathering methodology, shows the analysis that was done, and presents the results of that analysis.