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Alumina ceramics are widely used as insulating envelopes in vacuum interrupters, and their vacuum surface flashover voltage directly affects the insulation level. Conventional improvement by increasing ceramic length enlarges the equipment and raises manufacturing costs. In this study, periodic triangular microgrooves were fabricated on cylindrical alumina surfaces to improve the flashover voltage per unit insulation length. DC vacuum flashover tests were conducted, and the results show that the microgrooves significantly increase the flashover voltage, with the enhancement becoming more pronounced as groove spacing decreases. At a spacing of 40 μm, the 50% flashover voltage was 52% higher than that of the ungrooved sample. Particle simulations were performed to clarify the mechanism. The grooves altered electron trajectories, impact angles, and energy distributions, while partially trapping electrons and promoting energy loss through repeated collisions. Consequently, the effective electron population, anode current, and secondary-electron multiplication along the surface were reduced. The microgroove design was further applied to the inner surface of a sealed alumina ceramic envelope for vacuum interrupters. Compared with the ungrooved envelope, the power-frequency AC and negative lightning-impulse flashover voltages increased by 27.4% and 52.5%, respectively. These results demonstrate that triangular microgrooves can increase vacuum surface flashover voltage and support compact insulation design for high-voltage vacuum interrupters.
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