Insulators are widely used in various power equipment and many modern vacuum devices, and are also used in large-scale sophisticated devices. For example: X-ray tubes, high-power microwave tubes, high-power klystrons, neutron beam diodes, pulsed power switches, particle accelerators, and the like. The use of insulators in vacuum has a special phenomenon: when an insulator is supported in a vacuum gap, the insulator system will be broken down at a lower voltage, that is, the surface of the insulator breaks down.

When a destructive discharge occurs in a solid dielectric, it is called breakdown.Upon breakdown, marks remain in the solid dielectric, permanently disabling the insulating properties of the solid dielectric. If the insulation board breaks down, it leaves a hole in the board.