Impulse Surface Flashover Development with Transient Charging on Solid Insulators in Vacuum through Streak Image Observation

Summary

As one of the most important technical issues for the advanced vacuum circuit breakers and vacuum interrupters, the suppression of surface flashover on solid insulator in vacuum is needed. To clarify the mechanism of the vacuum surface discharge, charge activities during the development of surface flashover on solid dielectrics have been investigated. In addition to fast-framing photography and real-time measurement with electrostatic probes on the grounded electrode behind the alumina dielectrics, we newly introduced a streak camera and measured the ultra-high speed streak image of the surface flashover development. Experimental results of streak images revealed that light emissions concentrated around the cathode at the start of the flashover development due to explosive electron emission (EEE). Then, the light emissions spread with secondary electron emission avalanche (SEEA), expanding transient charging distribution on the alumina dielectrics due to EEE. At this time, a dark area, where light emissions are less intense than these of SEEA region, was observed in the charged area around the cathode, where the electric field by the transient charging on the alumina dielectrics becomes dominant than that by the cathode. The streak image also revealed that the development time to surface flashover was determined by the formation of the transient charging and the subsequent SEEA development toward the anode with constant speed along the insulator surface with the distortion of the electric field on the alumina dielectrics.

Additional informations

Authors

Hao Xiwei, Wimmer Rene, Wei Bin, Psotta Torsten