Discrimination of Discharge Pattern in Cut Model of Vacuum Interrupter

Electrical insulation of a vacuum interrupter (VI) is a composite system composed of vacuum, metal, and solid insulator. Detection of weak points in insulation is important for insulation design of VI. However, solid insulators of VI are mostly made of opaque ceramics, and it is very difficult to directly visually observe discharge sites and patterns inside VI. Previously, we have proposed a discrimination method of discharge patterns in VI by extracting features of applied voltage, discharge current, and shield potential change. In this study, we aim to verify that our proposing method can be applied to an actual structure of VI. We prepared a cut model of VI, whose shield electrode and alumina ceramic insulators have been partly cut for observing the discharge site. In this VI cut model, we simulated the weak points in insulation by additional needle electrodes. We applied a negative standard lightning impulse voltage between contact electrodes, and measured the applied voltage, the shield potential, and the anode current. In various settings, we almost succeeded to discriminate the initiation pattern of discharge, even in the case of complex discharge pattern with gap and/or surface discharge. In this verification, we found the new discharge pattern, in which the first gap discharge induced another gap discharge due to the diffusion of particles from the first discharge. However, by modifying the discrimination method based on the above physical mechanism of new discharge pattern, we got the prospects that the method can be applied to actual VI structure.