Synergistic effect of SF6/N2 gas mixtures on surface partial discharge under DC voltage

With the development of high-voltage direct-current (HVDC) transmission, DC gas insulated lines (GIL) with SF6/N2 gas mixtures as insulating medium have been successfully adopted. Space is typically the weak link of equipment insulation where surface discharge is one of the common discharge forms in power equipment. Therefore, research on the surface discharge characteristics of SF6/N2 under DC voltage can contribute to insulation design of SF6/N2 insulated DC GIS, GIL and other power equipment. In this paper, a DC high-voltage experimental system is established to study partial discharge (PD) along insulation surfaces. The characteristics at the initial discharge and the discharge development stages are analyzed in detail. Additionally, the synergistic effect of mixed gas is investigated based on the discharge characteristics and the synergistic effect coefficient is introduced. The experimental results show that the synergistic effect of mixed gas partial discharge inception voltage (PDIV) under high pressure is more obvious compared to low pressure and the discharge quantities of mixed gas is smaller than that of pure SF6 at the discharge development stage. This study on the multiple influencing factors of synergistic effect is expected to provide important insight for exploring the SF6/N2 discharge mechanism and helps decreasing the usage SF6.