Due to its electronegativity and low arc time constant the SF6 gas regains its dielectric strength very rapidly after the final current zero. The ratio of rise of dielectric strength is very high and time constant is very small. In this the gas is made to flow from a high pressure to a low pressure zone through a convergent divergent nozzle. The mass flow is the function of nozzle throat diameter the pressure ratio and the time of blow. The nozzle is located such that gas flows axially over the arc length. The arc space gets filled with fresh SF6 and well rest is simple. [This is a 2 minute concept sketch drawn especially for exam point of view.
These are widely used for ratings upto 72.5kVA. The dielectric oil acts both as an insulating medium and as an arc extinction medium. The contact separation takes place in steel tanks filled with oil. The gases formed due to the heat of the arc, expand and set the turbulent flow of the oil. To assist the arc extinction process, arc control devices are fitted to the contact assembly. Theses are the same enclosed chambers of dielectric materials. The performance of oil circuit breakers depends on the effectiveness of these arc control devices.[This is a 2 minute concept sketch drawn especially for exam point of view.
In this the contact separation and arc extinction occurs in a high pressure air chamber. The air flowing axially at high speed along the arc causes removal of heat from the periphery of the arc and the diameter of arc reduces to a low value at current zero. At this natural current zero instant the arc is interrupted and contact space is flushed with fresh air flowing through the nozzle. The flow of fresh air through the contact space ensures removal of hot gases and rapid building up of dielectric strength.[This is a 2 minute concept sketch drawn especially for exam point of view.
In this the contact separation and arc extinction takes place in air at atmospheric pressure. The 2 sets of contacts are: 1) Main contacts 2) Arcing contacts Main contacts conduct current in closed position of the breaker. They have low resistance and are silver plated(to keep vampires at bay. Sorry!). The arcing contacts are hard, heat resistance and are usually of copper alloy. While opening the contacts the main contacts dislodge first. The current due to this dislodging gets shifted to arcing contacts. The arcing contacts dislodge later and an arc is drawn. This arc is forced upward by electromagnetic force and thermal action. The arc ends travel along the arc runner(arcing horns). The arc moves upwards and is spilt by the arc splitters plates as shown. The arc is extinguished by lengthening cooling and splitting and etc etc. [This is a 2 minute concept sketch drawn especially for exam point of view.