📘 Vacuum Circuit Breaker (VCB) – Construction, Working & Advantages
A Vacuum Circuit Breaker uses vacuum as arc quenching medium. It is widely used in medium voltage systems such as 11 kV and 33 kV distribution networks.
🔹 1️⃣ Why Vacuum?
- Extremely high dielectric strength
- No ionization medium present
- Very fast arc extinction
- No fire hazard
- Environment friendly
In vacuum, absence of gas particles prevents arc sustainment.
🔹 2️⃣ Construction
Main components of Vacuum Circuit Breaker:
- Fixed Contact
- Moving Contact
- Vacuum Interrupter Chamber
- Arc Shield
- Operating Mechanism
Vacuum level maintained: 10-7 to 10-5 torr.
🔹 3️⃣ Working Principle
- Under normal condition → Contacts closed
- Fault occurs → Relay sends trip signal
- Contacts separate
- Metal vapor arc forms between contacts
- Arc extinguishes at natural current zero
- Dielectric strength recovers very rapidly
Vacuum has very high dielectric recovery strength.
🔹 4️⃣ Advantages
- Long operational life
- Very low maintenance
- Compact size
- No gas refilling required
- No explosion risk
🔹 5️⃣ Disadvantages
- Not suitable for extra high voltage applications
- Initial manufacturing cost high
🔹 6️⃣ Application Voltage Range
- 11 kV
- 22 kV
- 33 kV
- Indoor Substations
🎯 GATE Important Points
- Arc extinction occurs at current zero
- Very high dielectric recovery
- Preferred for medium voltage systems
- Environment friendly compared to SF₆
Vacuum Circuit Breaker = Reliable & Low Maintenance Protection
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