Long-term vacuum integrity of vacuum interrupters

Vacuum interrupters (VI's) are the primary switching technology for medium voltage (1-52kV) electrical power systems. The extensive field service of VI's is now raising interest in determining the end of life for these devices, with the primary concern being the loss of vacuum. The manufacturing method of the VI's can affect the calculated long-term life. In particular, there are three main design groups to evaluate. The key differences between these three groups are the processing temperature and permeability of the housing to hydrogen and helium. Many potential failure modes occur independently of the field application or lack thereof, and can be evaluated based data from VI's in long-term storage or after operations, such as seen during development and certification testing. The field returns history from VI manufacturers also provided critical information on the VI lifetime. These various factors can be combined to identify risk factors that could alter the estimated life.