SF6 Circuit Breaker (Sulphur Hexa Fluoride Circuit Breaker) - Electrical C & V

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20 March 2020

SF6 Circuit Breaker (Sulphur Hexa Fluoride Circuit Breaker)

SF6 Circuit Breaker ( Sulphur Hexa Fluoride Circuit Breaker )

SF6 circuit breaker uses SF6 gas to extinguish the arc. SF6 is an electro-negative gas with unmatched power to absorb free electrons.


SF6 Circuit Breaker ( Sulphur Hexa Fluoride Circuit Breaker )

                           

The contacts of the circuit breaker open inside the high pressure SF6 gas. The arc is produced as soon as the two contacts are separated from each other. The free electron present in the arc is rapidly absorbed by SF6 gas. The high resistance is generated as the free electron is absorbed, which extinguishes the arc.
SF6 circuit breakers are used at high voltage locations.


Structure of SF6 circuit breaker

The structure of the SF circuit breaker is shown below. It has movable and fixed contacts in a chamber called Interruption Chamber. This chamber is filled with SF6 gas. This chamber attaches to the Reservoir of SF6 gas. When the contacts are separated from each other, the SF6 gas exits the Gas Reservoir at High Pressure and strikes the Arc.


                            SF6 Circuit Breaker ( Sulphur Hexa Fluoride Circuit Breaker )


 The tip (tip) of movable contacts, fixed contacts and arching horns are coated with a metal of copper-tungsten which is the arc registers material. Since SF6 gas is very expensive, after each operation, it is purified by an external subsystem and reused.


Working of  SF6 Circuit Breaker 

 The gas pressure at the closed state of the circuit breaker is 2.8 kg / cm2. When the movable contact of the circuit breaker is different from the static contact, an arc (flame) is generated between the two contacts. The valve opens when the movable contact is in motion. As soon as the valve is opened, the SF6 gas enters the arc interruption chamber from the gas reservoir at high pressure - 14 kg / cm2. At high pressure SF6 gas absorbs free electrons very rapidly, which increases the di-electric strength between the contacts and extinguishes the arc. After operation the valve itself closes with a spring.


Benefits of SF6 Circuit Breaker  

(i) Due to the good quality of extinguishing the arc, the arching time of these circuit breakers is very short.

 (ii) The di-electric strength of SF6 gas is 2 to 3 times higher than Air, due to which these circuit breakers can also force high currents.

(iii) The operation of SF6 circuit breaker is peaceful.

(iv) Due to its operation in a closed chamber, the possibility of moisture in it is very less.

(v) There is no risk of fire in this circuit breaker as SF6 gas is flammable.


Disadvantages of SF6 Circuit Breaker 

1. SF6 circuit breakers are very expensive due to the high SF6 gas value.

2. After each operation, an additional device is required for purification of SF6 gas.


Application of SF6 Circuit Breaker

SF6 circuit breakers are used for high current 60 kA and high voltage 50–80 kV. SF6 circuit breaker is manufactured from 113 kV to 230 kV voltages whose power rating is from 10 MVA to 20 MVA. The arching time of these circuit breakers is less than 3 cycles.







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