High Voltage SF6 Circuit Breaker Working Principle

What is an SF6 circuit breaker?

The high voltage SF6 Circuit Breaker or Sulphur Hexafluoride is the circuit breaker that generates pressurized SF6 gas that can terminate the arc. The gas is also known as the dielectric gas which contains better insulation and there are arch-quenching elements that element is considered best than gas and oil. These elements are sometimes used for arc quenching with superior voltage circuit breakers which contains 400 KV which contain power stations, grids of electricity, and many more. The SF6 gas contains excessive electro-negativity. It has a high and strong propensity to captivate free electrons. However, the high voltage SF6 circuit breaker working principle lets us know how important it is to safe high-voltage crucial devices that are installed in the power station or electrical substation.

High voltage SF6 circuit breaker working principle

How SF6 Circuit Breaker Works? SF6 breaker is a gas-actuated breaker where SF6 gas is the main mechanism to reduce arc energy. It is noted that the high voltage SF6 circuit breaker working principle is the same as some other high voltage circuit breakers like air blast, vacuum, and oil circuit breakers. But their arc quenching mechanism is different. The SF6 Circuit Breaker is also known as the Sulfur hexafluoride circuit breaker which can be generated with the aid of a gas extinguishing medium.

The sulfur hexafluoride gas captivates free electrons. When the contacts of the circuit breaker remain open, the gas can easily flow through the chamber that strikes the arc. The free electrons are incorporated by the SF6 which works best in the immobile negative ions. The strength of the insulating medium can be and should be increased since the arc might get extinguished entirely.


Along with the gas and within the chamber of the arc the contacts are placed in a fixed and moving position. The contacts of the breaker remain closed during the moment of operating conditions. Whenever faults happen in the system, the contacts start to attract apart, and the arc gets stuck between the faults and contacts.

The replacement of the moving contacts becomes contemporized along with the valve that can enter the high-pressure SF6 gas inside the arc that interrupts the chamber at a pressure of 16kg/cm^2. The SF6 gas attracts the free electrons in the arc path and then it began to form ions that won’t act as the charge carrier. Those ions are responsible to improve the dielectric strengths of the gas and the arc then gets extinguished.

The procedure lessens the pressure of the SF6 gas up to 3kg/cm^2 and it is collected in the low-pressure reservoir. The low-pressure gas is attracted until it receives a high-pressure reservoir which can be utilized again and again. Presently, the piston pressures are utilized to generate the arc quenching pressure through the operation that has been opened by the mean of the piston which is associated with the moving contacts. 

What is the construction of SF6 circuit breaker?

The high voltage SF6 Circuit Breaker is involved with two elements, one is the interrupter unit and the second one is the gas system. The unit of interrupter involves fixed and moving contacts and deals with the set of currents which involves an arching probe and carrying parts. It is secured by the SF6 Gas Reservoir. The unit is associated with slide a vent which flows with the moving contacts that allow the high-pressure gas to enter into the main tank.

The secured circuit gas system is employed with the SF6 circuit breakers. The SF6 gas is very expensive for that reason it had to be recovered after every operation. This unit is surrounded by high and low-pressure chambers along with low-pressure alarms across the warning switches. When the pressure of the gas is low since the dialect strengths of gases decline and the capability of the arc quenching of the breakers is being jeopardized from that moment on the system starts to give warning alarms. 

What are the advantages and disadvantages of the SF6 circuit breaker?

SF6 circuit breaker are used in high-voltage applications like power plants, and grid substations. On the other hand, the SF6 gas circuit breaker is used at the high-power generator outlet like 30 MVA to 180 MVA. This type of high-voltage circuit breaker has a high current-carrying rating. SF6 breaker gas pressure values used in low factor ranges of breaker are 1.5 bar to 6.5 bar based on line voltage. It means if the transmission voltage becomes 220KV, 400KV, or more then the SF6 circuit breaker gas pressure maintains at 6.5 bar. However, there are some advantages and disadvantages these are given below.

The advantages of SF6 circuit breaker

  • The SF6 gas has outstanding insulating, and many different other elements and arc quenching are considered the biggest benefits of SF6 Circuit Breakers. 
  • The gas consists of non-combustible and chemically strong. Their dissolution products may not explode and this sign acts as the indicator that there may not be any risk associated with fire or outburst. 
  • Authorization of electricity is being lessened since the SF6 contains high dielectric strength. 
  • The performance of SF6 is not being affected since there are many variations consisting in the atmospheric condition. 
  • It aims to provide soundless operation and in there, no over-voltage issues have been found since the arc is extinguished with a current rate of zero. 
  • There is no demotion found for dielectric strength since during the moment of arcing, no carbon particles are formed. 
  • It requires an inexpensive constricted air system and less maintenance can be done to take care of the system. 
  • The SF6 attempts to perform several duties, for instance, clearing short-line faults, switching, the unloaded transmission lines get opened and the transformer reactor, and many other duties as well that usually don’t face many problems. 
  • The SF6 can operate several kinds of switching phenomena. 
  • Since the dielectric strength is high, it can punctuate well with a large current. 
  • The time of arching is very short.
  • Since the dielectric strength is high, secure the arc from striking if the required contact separation is small. 
  • The SF6 circuit breakers have a closed-circuit gas system that contains no leakage. By observing this advantage, many customers may buy the product since it can be installed anywhere and under any circumstances. 
  • The dielectric strength doesn’t get lessened, since no carbon particles can be formed with arcing. 
  • It may not require any costly and voluminous air compressing system that excludes the double pressure type that is outdated. 
  • If the high voltage circuit breaker goes bad then it may replace because we must ensure high safety for some other crucial devices in the station.

Disadvantages of the SF6 circuit breakers

  • The SF6 gas gets strangled at some moment. If any leakage happens then in the breaker tank then the SF6 gets heavier than the air and in the consequence of SF6 gets adjusted to the environment easily which leads to strangling the operating personnel. 
  • Accessibility of the moisture in the SF6 Breaker tank is very dangerous for the breaker and it may cause many disasters. 
  • The inner parts of the system should always be cleaned during the moment of occasional maintenance and then later they can be kept in dry and clean circumstances.  
  • A special facility is necessary for transportation and to conserve the quality of gas. 
  • Sometimes circuit breaker goes bad due to some failure

What is the application of the SF6 circuit breaker?

The SF6 Circuit Breaker is mainly used for medium-voltage applications. The SF6 circuit breaker is used for arc quenching since the capability of quenching the arc is effective. The applications of SF6 Circuit Breakers involve the following,

  • The circuit breakers are mainly used to secure very high and strong voltage-based circuits which consist of up to 800 kV.
  • It can break the powerful circuit which is based on a high voltage and it can easily de-energize to maintain and inspect.  
  • These circuit breakers secure power transmission and distribution. These are mainly used in power generation plants and power grids. 
  • It can control in a better way around and it has its power distribution.
  • They are mainly used in power circuits to protect the line.
  • Used for the capacitor circuits and inductor.
  • Used to secure the converter. 

Why is SF6 used in circuit breakers?

The SF6 gases are used in high-voltage circuit breakers and high voltage. The SF6 gases are not very inflammable to the circuit breakers, it contains properties of high electrical insulation, non-toxic properties, and competitive rate and it does not require much time for maintenance. The chemical and dielectric properties function well to keep the SF6 circuit breakers safe. The Chemical properties of SF6 include: 

  • The SF6 gas is very secure and it can maintain up to 500.
  • The SF6 gas is very dormant. The benefit of the chemical inertness of the gas relies upon the switchgear.
  • The life expectancy rate of metallic parts and contacts rises when they remain within the SF6 gas.
  • The important elements do not usually get deteriorated. Through this method, the cost and maintenance times are saved. 
  • The SF6 gas is the electronegative gas. 
  • Products of dissolution: 
  • At the procedure moment of arc extinction happens of the SF6 gas then it will be broken down into SF4 and SF2 extents.
  • The process of decomposition starts to mix when it starts to cool which will get turned into the original gas. 
  • One of the good dielectric materials is known as metallic fluorides which are secured for the electrical device. 

The Dielectric properties of the SF6 Gas:

  • The Dielectric strength of atmospheric pressure remains within 2.35 times; less than 30% dielectric oil is utilized for the circuit breakers. 
  • The dielectric strength of the gas rises at high pressure. The pressure of 3kg/ the dielectric strength of the SF6 gas is much higher than the dielectric oil. The property allows small clearances and small-scale equipment for the kV. 
  • The SF6 gas is also known as the electronegative gas.
  • The molecules of electronegative gases can captivate, influence free electrons, and then forms negative ions.
  • The negative ions are mobile and heavy so that’s why they cannot flow.
  • The dielectric strength of electronegative gases contains maximum air. 
  • The gas electro-negativity provides an inexpensive arc constant.
  • The time it takes to enhance the dielectric strength of the medium after the final current zero is known as the arc time constant. 

The arc extinction performs in the Circuit Breaker in the SF6 Gas.

  • In the period of arcing, the SF6 gas flows to the arc. The gas lessens the heat from the arc through axial convection and radial intemperance. 
  • 2, Due to low arc time constant and electro negativity, the SF6 gas recovers the dielectric strength after the final current hits zero, and the rate begins to raise dielectric strength rise. 
  • The primary requirement of arc extinction is the time when dielectric strength has recovered at a high rate.
  • The electrons get connected with the molecules to become ions in the SF6 gas. Through this procedure, the dielectric strength can recover as soon as possible. 

What are the properties of SF6 Gas?

Indeed the high voltage SF6 circuit breaker working principle is not complex. We must remove the arc energy whenever a fault occurs. In this case, the SF6 has a better arc quenching medium which entirely depends on the properties of chemical, physical, and electrical properties. 

Chemical Properties of SF6

  • The SF6 Gas is strong and inactive.
  • In the form of pure, it is not very toxic but the products might be toxic.
  • It contains excessive electro-negativity meaning it got a strong empathy for the free electrons.
  • The arc quenching gets connected very easily to have re-utilization. 
  • They are not very destructive.

Physical Properties of SF6

  • It is very incombustible.
  • The gas has no color and no odor.
  • It has better thermal conductivity.
  • It got a very high density and is usually much heavier than the air.
  • It precipitates within low temperatures and this can be considered as pressure dependent. 

Electrical properties of SF6

  • It contains worthier dielectric strength that remains directly proportional to the pressure. 
  • The capabilities of arc quenching are much better than the air.
  • The frequency of the voltage may not affect the dielectric strength.
  • In addition, the Sulphur Hexafluoride Circuit Breaker contains:
  • The processes of Sulphur Hexafluoride are best at insulating and it has better properties for arc quenching. Those qualities are:
  • It has no color, no odor, is not very toxic, and is incombustible gas.
  • The SF6 gas is more secure and unconcerned, and it got five times more density than the air. 
  • It has much better and more excessive thermal conductivity than the air and guides to cool the current carrying parts.
  • The SF6 has strong and better electronegative, simply it refers to free electrons that can be instantly removed from the discharge through the development of negative ions. 
  • It has an eccentric property which has the capability of quick recombination following the source that removes the dynamized part. It has been assumed that it is more constructive than the arc quenching medium. 
  • The strength of the dielectric is 2.5 times that of the air, and it contains less than 30% then dielectric oil. The dielectric strength of the gas might increase if there is an increase in high pressure.
  • Humidity is dangerous for the SF6 Circuit breaker. The hydrogen fluoride can be formed along with the combination of humidity and SF6 gas, (if the arc is terminated) which can charge the parts of the circuit breakers. 

Operating Mechanism of SF6 Circuit Breaker


The SF6 Circuit Breaker acquires a structure of self-energizing arc extinguishment which can be utilized with the high-pressure thermal expansion airflow within the cylinder pressure and obstructing effect of hitting the arc enhances the gas pressure of the high-pressure cylinder at the beginning of the circuit breaker. The operation mechanism of the SF6 breaker is divided into two types:

  • The first one is opening the operation
  • The second one is the closing operations.

The first one is the opening operation

The SF6 circuit breaker operating mechanism maintains the inner branch of support with the aid of an SF6 circuit breaker spring mechanism that attracts the insulating pull rod to make the beak downward and precipitate a specific arc between the separation of the principal contact, and invariable contact. These arcs will flow through the combustion that can generate high temperature and then it will generate high-pressure gas. Whenever the high-pressure gas circulates through the pressure cylinder, the pressure will expand in the pressure cylinder. The high-pressure gas of the pressure cylinder can get expelled from the neck of the flowing arc contact, whereby the extinguishing Arc, obtains the purpose of the contact. 

The second one is a closing operation

The Sulphur hexafluoride circuit breaker has a closing operation mechanism that manages the inner arm of the support with the aid of a spring operating mechanism to attract the insulating pull rod to move towards the nozzle in an upward way. Through this procedure, the closed state will be outreached and then the gas made of Sulphur hexafluoride invades the pressure cylinder. In the Centre, the SF6 circuit Breaker Operation will be working in the progress stage. The sulfur Hexafluoride circuit Breaker is controlled by six parts, which include, the potential element of sulfur hexafluoride, and the arc extinguishing part of the Sulphur hexafluoride circuit breaker.

The protected part of the Sulphur hexafluoride circuit breaker and another hexafluoride circuit breaker. The additional interconnecting device of the sulfur hexafluoride circuit breaker, the electrical guide, and the manipulating procedure of the sulfur hexafluoride circuit breaker. Following the framework and the formation of the sulfur hexafluoride circuit breaker, the sulfur hexafluoride circuit breaker can be divided into two types and two types of SF6 Circuit breakers have unique characteristics and different operation methods.

  • The tank type High voltage Sulphur hexafluoride circuit breaker, 
  • Ceramic column-type Sulphur hexafluoride circuit breaker

The tank type High voltage Sulphur hexafluoride circuit breaker, 

The tank-type high voltage Sulphur hexafluoride circuit breaker can be connected with separate switches, circuit breakers, and many more. To establish an open combination of electrical appliances that can lessen the area of the land, which can lessen the time of the maintenance. Let’s see an example, SF6 circuit breakers are appropriate to use in Xinjiang. Since the tank type high voltage Sulphur hexafluoride circuit breaker is acceptable for the environment which means it is sustainable and with the natural environment which can be relatively harsh. The circuit breaker might be vulnerable to use to solve any present electrical problems but the tank-type high voltage hexafluoride circuit breaker might not fail.

Ceramic column-type Sulphur hexafluoride circuit breaker

Nonetheless, the porcelain column type sulfur hexafluoride circuit breaker is simply easy to use and it lessens the cost of the economy in certain aspects but it may not provide better performance than the tank type high voltage sulfur hexafluoride gas circuit breaker since it has a low center of gravity. This type of sulfur hexafluoride circuit breaker may not be utilized widely.  

Does SF6 circuit breaker uses as 400 KV circuit breaker?

The SF6 full form in electrical Sulpher Hexafluoride breaker. If we would like to explain SF6 circuit breaker then we have to say that the SF6 breaker has a high cooling system that is sufficient to quench the arc level. For this reason, the SF6 circuit breaker uses as 400 KV circuit breaker220 KV circuit breaker132KV circuit breaker33 KV circuit breaker, and other indoor and outdoor applications. It is noted that 220 KV SF6 circuit breaker132 KV SF6 circuit breaker33KV SF6 circuit breaker, and 11 KV SF6 circuit breaker is satisfactorily used in different station due to their greater advantages. For this reason, it is also called an EHV circuit breaker.

What is EHV circuit breaker?

EVH breaker means extra high voltage breaker. Those breakers are used for the 400KV, 220KV, and 132KV such breaker is called EHV circuit breaker. SF6 breaker is one of the most popular and reputed extra high voltage breakers. If the grid substation steps down the voltage from 400 KV to 132 KV, SF6 breaker is necessarily installed and it is also called a 132KV SF6 circuit breaker. It is because the breaker rating depends on the output power of the breaker. On the other hand, if you use a 110 KV SF6 circuit breaker and step down in 110 kV such a breaker is also called a 110 KV SF6 circuit breaker.

SF6 gas circuit breaker in substation

An electrical substation is an important part of the electrical power system. The substation is used to divide the voltage level. It means the voltage level becomes up and down by using a power transformer. For this reason, very high voltage and highly valuable devices are installed there and safety is a must before running a substation. To make sure sufficient safety from surge voltage SF6 gas breaker is used due to its privilege. On the other hand, the SF6 gas pressure in breaker is so high that is so much eligible to reduce the arc level. SF6 pressure in circuit breaker has made it efficient to use for extra high voltage and high voltage operation. 

What do you mean by outdoor SF6 circuit breaker?

Those SF6 breakers are used in outdoor substations which is called outdoor SF6 circuit breakers. Basically, the high voltage SF6 circuit breaker working principle is to quench the arc or remove the arc. However, a 132 KV SF6 circuit breaker is used for the high-voltage substation to offer sufficient high-voltage protection. On the other hand, a 33KV SF6 outdoor circuit breaker is also used at the secondary substation where the voltage level becomes stepped down from 132 KV to 33KV. It is also a high-voltage substation. Such a breaker can completely remove the arc energy within very small as possible time.

The final thought of the high voltage SF6 circuit breaker working principle

SF6 gas full form is Sulphur hexafluoride circuit breaker. SF6 breaker is used to secure the device from damage from lightning, overvoltage, overcurrent, and other surge voltage. They precipitously break the circuits and put out the arc securely. Generally, the circuit breaking part is considered as the disconnection of the contract but the arc produces in a more eventual way which guides to keep the circuit secured from breaking and may cause some fatal damages that need to be extinguished as soon as possible.

The strength of the arc depends on multiple variables which involve, gaps joining the contact, voltage, pressure, temperature, and many more. The arc can be extinguished with the help of advanced technologies, mediums, and procedures. The high voltage SF6 circuit breaker is one of the circuit breakers among many different circuit breakers that utilize the SF6 gas since the arc quenching medium. It might break the high voltage circuit. However, we have discussed the high voltage SF6 circuit breaker working principle, construction, working mechanism, and some other parts. We hope that will help you to know more about the SF6 breaker.

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