Function

• SF6 circuit breakers work through arc interruption. When electrical current exceeds a certain level (called a rating), the breaker will trip and contacts within the circuit breaker will open to interrupt the circuit. When the current is interrupted, an electrical arc is created. An arc contains heat and voltage, so it must be contained and extinguished. The SF6 circuit breaker uses compressed sulfur hexafluoride (SF6) gas to cool the arc and absorb free conducting electrons. The electrons captured by the gas form mostly immobile negative ions, creating dielectric insulation and extinguishing the arc.
  
  

Advantages

• SF6 gas is extremely efficient at extinguishing or "quenching" electrical arcs. This ensures shorter arc times, allowing less damage to occur. The dielectric strength of sulfur hexafluoride gas is also much higher than air, so SF6 breakers can interrupt much larger currents than other types of breakers. Sulfur hexafluoride is inflammable, so there is no danger of fire. Additionally, SF6 circuit breakers are completely enclosed and sealed so they may be used in many environments.
  
  

Disadvantages

• SF6 circuit breakers are extremely costly due to the complicated nature of the enclosed system, and the high price of obtaining the SF6 gas. Additionally, faulted SF6 gas must be carefully removed and can be toxic. Solid arc products are also a toxic byproduct sometimes created, and must be removed with caution.
  
  

Maintenance

• Maintenance of an SF6 circuit breaker depends on its use, including the number of operations over time and the amount of total current interrupted. Most SF6 circuit breakers, used under normal conditions, never exceed their specified current limits. Therefore, the need for repair or replacement of any parts will be rare and they can almost be considered maintenance free. Typically, maintenance is restricted to routine cleaning of external surfaces and the checking and lubrication of the mechanism, including the trip contacts and auxiliary switches.