Experimental and numerical study on surface streamer evolution in SF₆/N₂ gas mixtures

Abstract

The SF6/N2 gas mixture is a promising alternative to reduce SF6 usage in the power industry, with surface streamers being the dominant discharge form. This study develops an electrical-optical system based on the Pockels effect to measure the spatiotemporal morphology of surface streamers in pure N2 and SF6/N2 gas mixtures. In pure N2, surface streamers are filamentary with bifurcations. In contrast, in SF6/N2 gas mixtures, the morphology of surface streamers initially appears filamentary and transforms into clusters under alternating current (AC) applied voltage. The formation of clustered channels may be explained in terms of the lateral drift and diffusion of the net space charge. Two fluid models analyze the experimental results. The fluid simulation reveals a sheath between the surface streamer and the dielectric surface. The propagating surface streamer floats above the dielectric, with a net space charge layer lying at its bottom, sustaining its propagation through the net-charge-induced field. Due to the presence of the sheath, the surface streamer's morphology and properties are similar to those of volume streamers. This study enhances the understanding of surface streamer properties in insulating gases.