Inside the Vacuum Interrupter
The vacuum interrupter is the heart of every vacuum circuit breaker. Understanding its key components helps engineers evaluate breaker quality, predict service life, and make informed purchasing decisions. This guide examines the three most critical components: the arc shield, the contacts, and the bellows system.
Arc Shield (屏蔽罩)
The arc shield is a metal sleeve or cylinder that surrounds the contact assembly inside the vacuum interrupter. During a breaking operation, the electrical arc between separating contacts produces metal vapor, molten droplets, and ionized particles. The arc shield serves three vital functions:
First, it captures and absorbs the metal vapor and liquid particles generated during arcing, preventing them from depositing on the inner surface of the ceramic or glass insulating envelope. Without the shield, these conductive deposits would gradually reduce the dielectric strength of the interrupter, eventually causing it to fail.
Second, the shield prevents re-ignition by ensuring that metal particles cannot bridge back across the contact gap after arc extinction. Third, it protects the insulating envelope from direct thermal radiation damage caused by the arc.
Contact System
Vacuum circuit breaker contacts typically use a butt-contact (对接式) configuration where two flat or cup-shaped contacts meet face-to-face. The contact material is usually a copper-chromium (CuCr) alloy, chosen for its combination of high electrical conductivity, good arc erosion resistance, and low tendency for contact welding.
One design challenge with butt contacts is contact bounce — when the contacts close, they can rebound briefly before settling. Contact bounce creates momentary arcing that erodes the contact surface and can cause pre-strike damage. High-quality breakers like NAIJI's VN and CE series address this through optimized closing spring force (initial contact pressure) and precision-machined contact surfaces that minimize bounce duration.
Bellows System
The bellows is a flexible metal component that allows the moving contact to travel in and out of the sealed vacuum chamber while maintaining the vacuum seal. It must withstand tens of thousands of compression and extension cycles without developing leaks — a demanding requirement that places strict demands on material quality and manufacturing precision.
Modern vacuum interrupters use stainless steel bellows manufactured through hydroforming or mechanical forming processes. The bellows design must balance flexibility (to allow full contact travel) with durability (to maintain vacuum integrity over the rated mechanical life). A bellows failure means vacuum loss, which renders the interrupter unable to extinguish arcs — a critical safety concern.