Comparison of Arc Motion in Different Lifetime Sealed Vacuum Interrupters With RMF Contacts

Vacuum circuit breakers are well established in the distribution levels of the electrical power grids. To maximize the short-circuit interruption performance, an radial magnetic field (RMF)-contact design forces the arc from a fault current to rotate. The performance of the RMF-contact designs is usually evaluated in a model vacuum chamber with viewing ports that allows observing arc rotation with the help of high-speed cameras. These setups differ significantly from lifetime sealed vacuum bottles in geometry (and thus volume) and due to the fact that the main metallic vapor shield cannot be present. This, in turn, can affect the arc rotation behavior. In order to overcome these shortcomings, a new diagnostic tool has been developed to analyze the arcing behavior in standard lifetime sealed vacuum interrupters. Optical methods are not possible here, since the view is blocked by the opaque ceramics and the metallic vapor shield. For this reason, a Hall-sensor-based measuring system is applied, in which the variation in the magnetic field from the arc position is observed by multiple sensors. This paper presents the comparison of arc motion in lifetime sealed vacuum interrupters with different bottle geometries. For this purpose, investigations with identical spiral-shaped RMF contacts inside different vacuum bottle designs with differing vacuum volumes are performed. Also, for comparison, an interrupter with contrate cup contacts was investigated. Similarities and differences between the corresponding arc motion behaviors are discussed.