Criteria and propagation processes of electrode-initiated and electrodeless-initiated discharge in SF6

Abstract

The differences between the gas gap discharge and surface flashover have not been clarified because of the complexity of the flashover inception process at the solid–gas interface. In this paper, epoxy resin insulators with an adjustable inserted electrode for electric field regulation were employed to investigate the inception and propagation of electrodeless-initiated discharge (ELID) under the standard lightning impulse in SF6, and the differences from the breakdown process of an equal-sized gas gap (electrode-surface-initiated discharge, ESID) are discussed. Both a photomultiplier tube and a high-speed framing camera were used to observe the luminous strength and configuration of the initiation and propagation processes of the discharge. The results show that various luminous pre-signals can be detected before breakdown, indicating different physical processes during discharge. In ESID, the discharge begins with several streamer bursts followed by a step-by-step stem leader propagation and then breaks through the whole gas gap, with a submicrosecond time delay, whereas, in ELID, the streamer bursts are much weaker than those in ESID, and they turn into a bidirectionally propagated leader that breaks through the residual insulation faster, with a much shorter breakdown time delay, which is ≤300 ns. The criterion of streamer inception is also analyzed via the Raether–Meek criterion (K value), which is found to be higher in ELID (545 ± 20) than that in ESID (375 ± 25), which implies a higher requirement of an electric field for streamer inception and discharge initiation from the dielectric surface than that from the electrode surface.