A Vacuum Circuit Breaker (VCB) is a type of circuit breaker that uses a vacuum as the arc-extinguishing medium to interrupt fault or load current in medium-voltage (typically 3.3kV to 36kV) electrical systems. VCBs have become the dominant technology for MV switchgear worldwide, largely replacing older oil circuit breakers (OCBs) and air-blast circuit breakers.
How a VCB Works
Inside a VCB, the current-carrying contacts are housed in a sealed vacuum interrupter (VI) — a ceramic or glass envelope evacuated to a very high vacuum (around 10⁻⁶ to 10⁻⁸ torr). When the contacts separate to interrupt current, an arc briefly forms, but because there's no gas medium to sustain it, the arc extinguishes almost immediately as the current crosses zero — typically within one half-cycle. This gives VCBs extremely fast, reliable interruption with minimal contact erosion.
Why VCBs Replaced Oil and Air Breakers
- No flammable insulating oil — eliminating fire risk and the need for oil testing/replacement.
- Sealed for life — the vacuum interrupter needs no maintenance of the interrupting medium itself.
- Compact size — significantly smaller footprint than equivalent oil or air-blast breakers.
- Long mechanical and electrical life — typically rated for tens of thousands of mechanical operations.
- Fast reclosing capability — useful for auto-reclose schemes on overhead distribution feeders.
Typical Applications
VCBs are used wherever medium-voltage power needs to be switched or protected: utility substations, industrial MV switchgear (feeding large motors, transformers, and process loads), captive power plants, and renewable energy substations (solar/wind). They're available in both fixed and withdrawable (truck-mounted) configurations for use in metal-clad switchgear panels.
Key Ratings to Check
When specifying or replacing a VCB, the important nameplate ratings are: rated voltage, rated normal current, rated short-circuit breaking capacity (kA), rated short-time withstand current, and number of operating cycles. Always match these to your system's fault level and load requirements — see our VCB maintenance guide for ongoing care once installed.
TEKTOW supplies genuine VCBs and spares from ABB, Siemens, Schneider and other leading brands. Request a quote with your voltage and current requirements.