The tips of all circuit breaker contacts are coated with a copper-tungsten arc-resistant material. The main body of the interrupter which is filled with SF 6 gas contains a moving puffer cylinder that can axially slide upward and downward along the contacts. There is one stationary piston inside the cylinder which is fixed with other stationary parts of the SF 6 circuit breaker, in such a way that it cannot change its position during the movement of the cylinder.
A nozzle is located at the opening of the cylinder. The interrupter unit is vertically mounted on top of an insulating stack which is made up of a hollow insulator encapsulating the drive rod which connects the mechanical operating mechanism of the circuit breaker to the moving contacts housed within the interrupter. Depending on the voltage rating of the system, the insulating stack may be a single piece, or multiple segments mechanically coupled in series.
Just like any other insulator , it provides adequate line-to-ground dry arcing and creepage distance to prevent flashovers associated with transient overvoltages and ambient pollution. The complete circuit breaker unit is usually fixed on a steel structure which secures it to an embedded concrete foundation. The driving apparatus provides the kinetic energy required to open and close the circuit breaker contacts.
It consists of a set of opening and closing springs that are charged manually, or with the help of a small electric motor. The control cubicle communicates between the circuit breaker mechanical operating mechanism, system protection relays and supervisory devices. At extra high voltage usually kV and above , due to manufacturing economics and design requirements, the SF 6 circuit breaker may have notable differences in construction and may also feature additional components:.
In the normal condition, the circuit breaker contacts are closed and current flows from one contact carrier to the other via the main contacts and the sliding puffer cylinder.
When the circuit breaker control panel receives an opening command to clear a fault or disconnect part of a network , it sends a signal to the trip coil of the mechanical operating mechanism, which in turn releases the latch holding the charged opening spring. As the opening spring discharges, it pulls the drive rod connected to the interrupter in a linear direction, which causes the moving contacts and puffer cylinder to move downwards. Due to contact overlap , gas compression starts before any contacts open.
As the downward movement continues, the main contacts separate and the current commutates to the arcing contacts which are still in the closed position due to their physically longer construction. During the course of further opening, the arcing contacts start to separate and an arc is established between them. As the arc flows it blocks the flow of SF 6 gas through the nozzle to some extent. Due to the superior arc quenching properties of SF6 gas, the SF6 circuit breakers have many advantages over oil or air circuit breakers.
Some of them are listed below :. SF6 circuit breakers Applications: A typical SF6 circuit breaker consists of interrupter units each capable of dealing with currents up-to 60 kA and voltages in the range of 50—80 kVA number of units are connected in series according to the system voltage.
Tags Switchgear and Protection. You might like Show more. Post a Comment. There are vents inside the cylinder that are previously blocked by the upper fixed contact. The vents open up when the cylinder moves further down.
The compressed SF6 gas moves out at high speed through the vents. The flow of the SF6 gas quenches the arc. Such type of SF6 circuit breaker uses compressed SF6 gas in a cylinder to quench the arc.
Such CB are obsolete and not used anymore. Such SF6 circuit breaker has a fixed contact and moving contact. The moving contact is hollow from inside having a cylinder that stores compressed SF6 gas. The tip of the moving contact is designed in such a way to form a nozzle that increases the speed of the gas when it passes through it.
The fixed contact is designed in such a way when it is in the closed position, it blocks the flow of SF6 gas. When the contacts separate, the path for gas flow is opened which releases a blast of SF6 gas. It has the same working operation as an air blast circuit breaker except the gas is recombined, compressed and stored in the gas cylinder again. Which makes it very complex and quite expensive gas system is required for operation.
Under normal conditions, the contacts are connected blocking the SF6 gas inside. When a fault occurs, the moving contact separates from the fixed contact and an arc is produced.
Due to the movement of contacts, the highly pressurized SF6 gas is released. The pressure inside the cylinder is higher than the pressure outside, therefore, the gas flows out.
The nozzle helps increase the speed of the gas which quenches the arc as discussed earlier. The released SF6 gas is filtered, recombined, compressed and then stored in the cylinder for further reutilization.
The system required to maintain the gas is quite complicated and expensive. Therefore, these circuit breakers are obsolete and not used anymore. Furthermore, due to changes in pressure, the gas temperature falls down very quickly which may liquefy the gas. Therefore, a heater system is also used to prevent the gas from liquification. SF6 circuit breakers are used for high and ultrahigh voltages. Their maintenance is very important for smooth operation. They do not require such frequent maintenance because.
However, there is only one thing that must be maintained that is to check the leakage of SF6 gas. The leakage of SF6 can cause the following issues. The leakage can be monitored through the pressure gauge or by using the SF6 detector. SF6 circuit breakers are mainly used for the protection of very high voltage circuits up to kV from fault current.
Each interrupter unit is capable of handling 60 kA in the range of 80 kV. Nowadays, SF6 technology is even more important to bring bulk power at a high-voltage level closer to the consumers as for megacities. SF6 circuit breaker uses sulfur Hexafluoride SF6 gas is used to extinguish the arc. There are some benefits and drawbacks of using SF6 circuit breakers. Despite all the technical advantages of the SF6 technology, SF6 is a potent greenhouse gas that is covered by the Kyoto Protocol.
Therefore, SF6 must be managed within a closed cycle , avoiding any deliberate release to the atmosphere. During the last 20 years, as a consequence, significant effort has been undertaken to reduce SF6 emissions.
The focus for manufacturers and asset owners was on finding ways of increasing the tightness of equipment and reducing handling losses. SF6 breakers are enclosed and sealed from the atmosphere, they are particularly suitable where explosion hazard exists. There is no risk of fire as SF6 is non-inflammable.
The closed gas enclosure keeps the interior dry so that there is no moisture problem. Sulfur hexafluoride SF6 is a synthetic compound showing a unique combination of physical properties: High dielectric strength, high arc quenching capabilities, and high heat transfer performance, which is about twice of air. SF6 circuit breaker uses Sulphur hexafluoride gas in its construction.
The contacts of the breaker arc opened in a high-pressure flow of SF6 gas and the arc is struck between them. This gas has a great extinguishing property. Many manufacturers prefer sulfur hexafluoride gas over oil and air. Sulfur hexafluoride has a high electronegativity, perfect for insulation.
SF6 is an odorless, tasteless, colorless, non-toxic, non-flammable, very stable, and inert gas at room temperature. Due to spontaneous recombination, the molecule is extremely stable even at very high temperatures in the arc plasma during switching operation.
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