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(1) Interruption overvoltage. When a vacuum switch opens a low-current circuit, due to characteristics of the arc extinguishing chamber itself, the arc goes out before the current drops to its natural zero level, resulting in an abrupt interruption of the current. This phenomenon is what is commonly referred to as switching overvoltage. Due to the sudden interruption of the current, the electromagnetic energy remaining in the inductive load generates an overvoltage. (2) Multiple reignition overvoltages. When vacuum switches are used to connect or disconnect power capacitor banks or to interrupt large inductive currents (such as motor starting currents), even if suppressing the switching overvoltage is not a problem, an overvoltage hazard often occurs, which can cause the capacitor bank or the inter-turn insulation of the motor to be damaged. Studies have shown that this is caused by overvoltage resulting from multiple reignitions of the vacuum switch. (3) Three-phase simultaneous switching overvoltage. In a three-phase AC circuit, when the contactor for one phase opens that phase’s circuit, the contacts for the other two phases generally take a quarter cycle before being opened as well. If arcing reoccurs in the primary phase, the high-frequency current flowing through the gap will also be added to the line-frequency currents of the other two phases. As the voltage level of the primary phase increases, the high-frequency current flowing into the second and third phases also increases, causing the currents in these phases to force a zero crossing; an equivalent current interruption occurs in all three phases of the circuit, leading to multiple arcing events and thus very high overvoltages. (4) Interrupt overvoltage on capacitive loads. (5) Connect the voltage. When a vacuum switch connects a circuit, the distance between the contacts gradually decreases. Before the mechanical contact is made, pre-breakdown occurs, and high-frequency overcurrent flows between the contacts. Then, it is turned off at the zero crossing of the high-frequency current, and similar to the switching condition, overvoltage is also generated.