📘 SF₆ Circuit Breaker – Construction, Working & Advantages
SF₆ Circuit Breaker uses Sulphur Hexafluoride gas as arc quenching medium. It is widely used in high voltage and extra high voltage systems.
🔹 1️⃣ Why SF₆ Gas?
- Very high dielectric strength (2.5 times air)
- Excellent arc quenching property
- Electronegative gas (absorbs free electrons)
- High thermal conductivity
- Non-flammable
SF₆ quickly removes electrons → Arc extinguishes rapidly.
🔹 2️⃣ Construction
Main Parts:- Fixed contact
- Moving contact
- Arc chamber
- SF₆ gas chamber
- Nozzle arrangement
- Operating mechanism
🔹 3️⃣ Working Principle
- Under normal condition → contacts closed
- Fault occurs → relay sends trip signal
- Contacts separate
- Arc forms between contacts
- High-pressure SF₆ gas blasts across arc
- Electrons absorbed → arc extinguished
Arc extinguishes at natural current zero.
🔹 4️⃣ Types of SF₆ Breakers
- Single Pressure Type
- Double Pressure Type
- Puffer Type (Most Common)
🔹 5️⃣ Advantages
- High breaking capacity
- Compact size
- Low maintenance
- No fire hazard
- Suitable for 400 kV and above
🔹 6️⃣ Disadvantages
- Costly
- SF₆ is greenhouse gas
- Gas leakage detection required
🔹 7️⃣ Application Voltage Range
Used in:
- 132 kV
- 220 kV
- 400 kV
- 765 kV systems
🎯 GATE Important Points
- SF₆ has high dielectric strength
- Electronegative gas
- Arc extinction at current zero
- Preferred for EHV systems
SF₆ CB = High Voltage, High Reliability Protection
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