Late Dielectric Breakdown Phenomenon Caused by Microparticles Released after Current Interruption

High speed laser Shadowgraph photography demonstrated that the microparticle induced by arc interruption phenomenon caused the Non-Sustained Disruptive Discharge (NSDD) during the recovery voltage application. The NSDD was caused by two types of microparticles originating from AgWC electrodes. One type of microparticles had particle sizes of ~20 to 40μm and moving speed of ~15 m/s, while the sizes and speed of the other type of particles were ~ 100μm and ~3m/s, respectively. The big slow microparticles caused the NSDD several times during the up-and-down motion between the electrodes. All particle-induced NSDD occurred at timing of the particle collision to the cathode defined by the polarity of the recovery voltage. On the other hand, even when the cathode collision occurred, some particles were just reflected on the cathode surface without causing the NSDD. Our experimental results suggested that the particle-induced NSDD could not be explained by the present theoretical models.