Structure and working principle of vacuum circuit breaker

Vacuum circuit breaker is a kind of electrical equipment which realizes circuit opening and breaking by using high vacuum environment, and its core components and principles are as follows:

1. Main structure

Vacuum interrupter

As the core component, it adopts a high vacuum environment (vacuum degree of 1.3×10-² to 1.3×10-⁴ Pa) to realize arc extinguishing and insulation. When the contacts are divided and closed in vacuum, only metal vapor arcs are generated, and the arc is extinguished by using the rapid diffusion of metal vapors and the cooling characteristics.

Operating Mechanism

This consists of an electromagnetic or spring-operated mechanism, which is responsible for actuating the contacts to open and close.1 The spring-operated mechanism, for example, achieves a rapid separation of the contacts by means of the energy storage and release of the breaking spring.

Supporting and insulating parts

Support : Holds the interrupter and supports other components.

Insulation linkage, switching spring, double-arm moving linkage : Transmits the operating force and ensures the accuracy of the switching action of the contacts.

Insulators: support the contacts during closing and provide insulation from ground.

Other parts

Busbar compartment : Holds contacts and conductive parts.

Cable compartment : Connects external circuits.

2. Principle of operation

Normal operation

When closing the vacuum circuit braker, the contacts make good contact and the circuit is conducted. The vacuum circuit breaker is insulated from ground by supporting insulators.

Fault opening

When a fault occurs on a line (e.g., a short circuit), a high voltage is generated between the contacts, resulting in the formation of a metal vapor arc. As the arc burns in a vacuum, the evaporated metal on the surface of the contacts forms a conductive channel.

Arc extinguishing mechanism

Physical quenching : When the arc current passes zero, the contact temperature decreases, evaporation is weakened, and the arc is extinguished when the energy is depleted.

Advantage of vacuum environment: gas molecules in a vacuum are thin, low probability of collision free, the arc is difficult to sustain. At the same time, the rapid diffusion of metal vapor and recombination process accelerates the arc cooling.

Insulation Recovery

After the arc is extinguished, the vacuum is rapidly restored, and the strength of the insulation between the contacts is re-established, allowing multiple switching without affecting performance.

3.Key Features

High insulation: The insulation strength of the vacuum gap is higher than that of ordinary gas, and the contact distance can be shortened to 2-3mm.

Fast arc extinguishing : Metal vapor diffusion and cooling mechanism ensures that the arc is extinguished in milliseconds.

High reliability : Can withstand multiple opening and closing operations, suitable for high voltage levels (e.g. 10kV and above).

Through the above structural design and principle optimization, vacuum circuit breakers have the advantages of strong breaking capacity, long service life and low maintenance cost in the power system.