Sulphur Hexaflouride (SF6) Circuit Breaker Construction, working mechanism of SF6 breaker

    SF6 is an electro-negative gas and has a strong tendency to absorb free electron to build up high dielectric strength which is the most effective way to remove the arc.

Table of Contents:

1. Construction of SF6 Circuit Breaker.

2. Working of SF6 Circuit Breaker.

Construction of SF6 circuit breaker:

    The components of a standard SF6 circuit breaker are shown in the above diagram. It consists of moving and fixed contacts that are encased in an SF6 gas chamber. This chamber is also called arc interruption chamber connected to SF6 gas reservoir. 

    The valve mechanism enables a high pressure SF6 gas to flow toward the arc interruption chamber when the contacts of the circuit breaker are opened. The fixed contact is a hollow cylindrical current carrying contact fitted with an arc horn. 

    The moving contact is also hollow cylindrical with rectangular holes in the sides to permits the SF6 gas to let out through these holes after flowing along and across the arc.

    Copper-tungsten arc resistant material is applied to the tips of the fixed contact, moving contact, and arcing horn. Since, SF6 gas is costly, it is reconditioned and reclaimed by suitable auxiliary system after each operation of the breaker.

Related Post: Construction of Vacuum Circuit Breaker(VCB).

SF6 circuit breaker working:(SF6 breaker Operation)

    When the breaker is in the closed position, SF6 gas remains surrounded the contacts at a pressure of roughly 2.8 kg/cm2. The moving contact is pulled apart when the breaker operates and hence create an arc between the contacts.

    The valve that allows SF6 gas at a pressure of 14 kg/cm2 to flow from the reservoir to the arc interruption chamber opens in time with the movement of the moving contact. The free electrons in the arc path are quickly absorbed by the high pressure flow of SF6 gas, creating stationary negative ions that are useless as charge carriers.

    As a result, the arc is extinguished by a rapid buildup of high dielectric strength in the medium between the contacts. A set of springs acts to shut the valve after the breaker operationt each time.

Read more:

1. What is circuit breaker? Working principle of it.

2. What is fuse? Working principle of it. 

3. What are the differences between circuit breaker and fuse? 

4. What are the different ratings of a Circuit breaker?

5. What are the arc Extinction Methods.