Study on Transient Overvoltage in SF ₆ / N ₂

To reduce atmospheric pollution caused by carbon emissions, SF ₆ /N ₂ mixed gas is now widely adopted in gas‐insulated substations. This paper investigates two core issues regarding the third‐generation gas‐insulated switchgear (GIS) insulated with SF ₆ /N ₂ mixed gas: whether very fast transient overvoltage (VFTO) will be generated during disconnector operation, and the energy characteristics required for such rapid discharge processes. First, an arc model in the mixed gas is proposed. A 220 kV third‐generation GIS model is built based on ATP‐EMTP, and the VFTO generated by both the SF ₆ /N ₂ mixed gas and the original pure SF ₆ gas is obtained through simulation calculations. From the perspective of energy, the relationship between each VFTO discharge event and its corresponding energy consumption is analyzed. Simulation results show that when the gas pressure of the mixed gas is increased to make its insulation strength equivalent to that of pure SF ₆ gas, the GIS equipment filled with the mixed gas will produce more severe VFTO. Both the energy consumed by VFTO and its amplitude tend to increase with the enlargement of the disconnector gap distance. © 2026 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.