The vacuum interrupter is a crucial component in vacuum switches, responsible for making and breaking electrical circuits under vacuum conditions. It operates through an external mechanism that opens or closes a pair of opposing contacts inside the vacuum interrupter. The structure of a typical vacuum interrupter is illustrated in the diagram above.
The outer casing is typically made of inorganic insulating materials like ceramic or glass, forming a sealed cylindrical container. At both ends, metal covers are used to maintain the vacuum environment. Inside, there are two main contacts: one fixed on the static conductive rod and the other attached to the moving conductive rod. A bellows is positioned between the moving rod and the metal cover, allowing axial movement of the moving contact while maintaining the vacuum seal.
To ensure even electric field distribution, a shield is placed around the contacts and the bellows. The interior of the vacuum interrupter is maintained at a high vacuum level (≤1×10â»Â³ Pa). When the operating mechanism closes the contacts, the circuit is completed, allowing current to flow through the load. When the mechanism opens the contacts, a vacuum arc is formed due to the evaporation of metal vapor from the contact surfaces.
Unlike traditional arcs that rely on ionized gas molecules, the vacuum arc is sustained by the ionization of this metal vapor. As the contacts separate, the contact area rapidly decreases, forming one or a few small metal bridges. These bridges experience extremely high current density, leading to increased temperature and eventual melting and evaporation of the metal. This process generates a cloud of hot metal vapor, which then undergoes field emission and ionization, forming the vacuum arc.
Due to the special design of the contacts, the arc is evenly distributed across the contact surface, reducing arc energy and minimizing contact wear. After the arc is extinguished, the dielectric strength of the vacuum interrupter recovers quickly. Additionally, the metal vapor produced during the arc is condensed by the shield and partially absorbed by the getter material inside the chamber, helping to maintain the high vacuum required for reliable operation.
This advanced design ensures long service life, high reliability, and efficient performance in various electrical applications, making the vacuum interrupter an essential part of modern power systems.
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