Research on grooving method to improve the surface insulation performance of stage insulators in multi-gap gas switch under repetitive microsecond pulsed voltage in SF6

Surface flashover damage across stage insulators persists as a primary bottleneck for improving insulation strength in compact Tesla-type pulse generators, even when conventional rectangular surface grooving is applied under repetitive microsecond pulses in SF6. To enhance the insulation performance of stage insulators in a multi-stage gas switch (MGS) operating at 1 MV (130 kV per stage), this study systematically investigates the influence of the surface grooving method and conducts the verification of the optimized design. Cylindrical, rectangle-grooved, and wave-grooved insulator samples were compared experimentally under simulated MGS conditions to evaluate the effectiveness of wave grooves in increasing flashover voltage (Uf). Electric field analysis and flashover path observations show that wave grooves suppress streamer development and improve surface insulation strength. Electric field distributions along the surface and within the gas-solid interaction region indicate that the wave-grooved structure promotes surface charge drift and exhibits a stronger normal electric field, which favors deviation of the flashover path from the insulator surface. Consequently, streamer propagation shifts from a surface-dominated to a gas-dominated mode. Observations confirm that wave grooves extend the effective creepage distance and increase the probability of a "gas" path-a dual modulation mechanism that explains their superior improvement in surface flashover characteristics. Based on these findings, the stage insulator in the MGS was redesigned with wave grooves, raising the Uf improvement from 0.89% to 7.70%, extending the operational lifetime by an order of magnitude, and mitigating abrupt insulation failures in SF6.