The working principle of vacuum circuit breaker is: when the moving and static contacts are switched off under the action of operating mechanism, an arc is generated between the contacts, and steam is emitted from the contact surface at high temperature. Because the contacts are designed in special shapes, a magnetic field is generated when current passes through, and the arc moves rapidly along the tangent direction of the contact surface under the action of this magnetic field, and some metal steam is condensed on the metal cylinder (shielding cover), and the arc goes out when it naturally crosses zero. Where vacuum circuit breakers are used, microcomputer protection devices are bound to be used. Microcomputer protection devices are relay protection composed of microcomputers, which are the development direction of power system relay protection. They have high reliability, high selectivity and high sensitivity. The hardware of microcomputer protection devices includes microprocessor (single chip microcomputer) as the core, with input and output channels, man-machine interface and communication interface. The system is widely used in electric power, petrochemical, mining and smelting, railways and civil buildings.