How Arc Extinction SF6 CB

Hello Friends!! today one of our subscriber ask me to know How SF6 circuit breaker work?

ANS:-  at first clear that the arc extinction process for SF6 circuit breaker is different from others.

Working: SF6 CB

when Arc produce SF6 gas is blown axially along the Arc. The heat is removed from the arc by axial convection. The arc diameter reduces during the decreasing mode of the current wave. The diameter becomes small during current zero. Turbulent flow is introduce around current zero the extinguish the arc.

As we know SF6 gas in high electronegative  and has low arc time constant. its regain dielectric strength rapidly after the final zero, the rate of rise of dielectric strength is very high and the time constant is very small.

SF6 is remarkable medium for arc extinction.

The arc extinction properties are improved by moderate rate of force of flow gas through arc space. 

The basic requirement of arc extinction is not primarily the dielectric strength , its rate of recovery of dielectric strength. In SF6 gas the dielectric strength is quickly regained.

In SF6 Circuit Breaker the gas is made flow from a high pressure zone to a low pressure zone through a convergent divergent nozzle. the nozzle is located such as the gas flow axially over the arc length . The flow gas attains almost super sonic speed in the divergent portion. Therefore the gas takes away the heat from the arc periphery and arc diameter is reduced. Finally the arc diameter become almost zero at current zero. And the arc is extinguished. After that the contact space is filled with fresh SF6 gas and its dielectric strength is rapidly gained because of electro-negativity and turbulent flow of fresh gas in the contact space. and ready to work again.