High Voltage Oil Circuit Breaker Working Principle

What is an oil circuit breaker?

The oil circuit breaker (OCB) is an oil filled circuit breaker where oil is the main mechanism to extinguish the arc energy. Whenever excessive current flows through it the breaker moving contact and fixed contact become separated due to ionizing the particle. In this case, the arc is induced between the contacts. In this case, oil is used to remove this contact between the two parts. Basically, oil is mineral oil or insulating oil that can completely remove the arc energy within a very short time. However, we will let you know the high voltage oil circuit breaker working principle or how OCB works. It is noted that we can compare OCB with the SF6 circuit breaker working principle but the arc quenching mechanism is different (oil and SF6 gas).

High voltage oil circuit breaker working principle

Oil Circuit Breaker (OCB) is a circuit breaker that utilizes oil in connection with a dielectric or the insulating medium that considers arc extinction. Within the oil circuit breaker, the contacts of the breaker have been created to remain independent within the insulating oil.

Whenever the fault happens within the system, the contracts of the breaker begin to move and the arc affects the contracts. For this arc, a wide range of heat has been freed and the excessive temperature has been extended that verifies the surrounding oil within the gas.

The gas had been freed which was surrounded by the arc and its extreme growth has replaced the oil. When the distance gets connected within the moving and fixed contracts achieve the critical value, the arc gets extinguished which can be determined by the recovery voltage and arc current. It is less expensive and authentic during operation. The most special attribute is that it requires no devices are needed to handle the arc. 

oil circuit breaker working process

The Oil Circuit Breakers (OCB) cooperate with those currents that carry the contacts which include weather repellent earth metal tank and a tank full of transformer oil. The oil is mainly used to generate the insulator and arc extinguishing medium that connects the earth and the occupied part. 

On top of the oil, the tank filled with air performs as the cushion to rein the replaced oil of the arc and to captivate the automatic shock of the rising development of oil. The breaker tank has been perfectly bolted which conducts the vibration that happened when the interrupting high current took place. The OCB incorporates the gas outlet that suits the cover of the tank to reduce the number of gases. 

To protect the OCB it is important to check and change the oil along with the contacts. Due to arching, the contacts might get ruined. The dielectric oil might get burned inside the regions of contacts and this process can lessen the dielectric strength and lessens the breaking capacity. 

It is always better to make sure to:

  • Check the arching contacts and intrinsic parts. The contacts should reduce the risk of short circuits.
  • Detect the strength of the coil’s dielectric.
  • The surface of the breaker should remain cleansed and it reduces the carbon layers which are mostly gathered from the dried fabric. 
  • The closing mechanism and tripping should also be checked. 

The advantages of oil circuit breaker:

  • It applies a small amount of oil.
  • The oil dielectric strength is strong
  • When it starts to degrade, the oil of the breaker captivates the energy of the arc.
  • Lessens the hazard of fire.
  • Few spaces.
  • Less maintenance cost.

Application of oil circuit breaker 

Indeed the oil circuit breaker application is known to every electrical and electronics engineer. The OCB is applied in high voltage applications for instance in substations, power lines, power grids, transmission, and distribution systems up until 220kV. It means where high voltage is available OCB can be installed there. (So, let’s see how to install a new circuit breaker). It is good to say that air blast circuit breakers and OCB both are used for high voltage applications.

The function of an oil circuit breaker 

The OCB can be recognized as the eldest type of circuit breaker. It incorporates some separate contacts that perform an objective to separate the insulating oil. It has some better quality insulating elements that are compared with air. The contracts of the breaker might get opened below the oil whenever the fault takes place. 

  • During the operating time, the circuit breakers’ contacts remain closed which can transfer the current. 
  • Whenever a fault occurs within the system, the contacts start to get divided and contain an arch within the contacts. 
  • The arch begins to get heated extremely when it generates excessive temperature, then the heat transforms the oil into gas. 
  • Through this procedure, the gas circumscribes the arch, saves the device from explosive growth, and replaces the oil.
  • The distance that connects the operative and still contacts reach a certain value, then the arch might get tyrannized that depends on the recovery voltage and current. 

Operation of oil circuit breaker 

Whenever the fault happens, the currents that carry the contacts are divided within the insulating oil. When the high voltage differs within the contacts the medium that surrounds it and the arc is being affected. The arc’s extensive heat verifies the oil which is already surrounded by the contacts. The oil begins to degrade into hydrogen gas which involves, ethylene, acetylene, and along with a small level of methane.

The hydrogen gas is divided into forms of atoms that release extreme heat that advances the arc’s temperature. Therefore, it improves oil vaporization. The volume of the gas which has been created is 1000 times greater than the dissolved oil. The size of the gas bubble gradually starts to improve for the temperature which is in the highest condition. The surrounding oil creates a lot more pressure over the gas bubble which remains within the enclosed container. 

Bulk oil circuit breaker diagram

The circuit breaker utilizes a bulk amount of oil for the benefits of insulation and arc extinction. This circuit breaker is also known as the dead tank type circuit breaker since the tanks are earthed from the foundation perspective. These types of circuit breakers can be recognized as plain break Circuit Breakers. How much oil can be used entirely depends on the input ratings of the circuit breakers. For output ratings of 110 KV, the circuit breaker might require 8000 to 10000 kg of oil. If the output ratings hit 200Kv then the circuit breaker might need 50,000 kg of oil. 


The Bulk OCB is widely used for two purposes:

  • For arc extinction. 
  • To insulate those currents that carry the elements of the circuit breaker from the ground.

The arc extinction uses one-tenth of the oil and the rest of the oil is used for insulating reasons. 

The framework of bulk oil circuit breaker

Within the insulating oil, the moving and fixed contacts of the circuit breakers had been absorbed which had been stored in the metal tank or metal vessel which is being maintained within the ground potential. Throughout normal operating circumstances, the moving and fixed contacts stay within closed positions. When the faults happen within the system, through the help of the secured mechanism of the circuit breaker the moving contacts get divided from the fixed contacts and the arc begins to develop within the moving and fixed contacts.

A wide range of heat energy dissolves from the arc within the oil that gets deteriorates and verifies the oil. A large number of gaseous pressures have been made within the oil that has replaced the insulating oil from the surrounding the moving and fixed contacts. The internal walls of the circuit breaker resist excessive pressure. The strong metal tank can tolerate the excessive pressure of oil.

The top covers of the circuit breaker are perfectly sealed and have been bolted with the structure and tank that are properly placed along with the solid substructure or else the breaker might jump in the intervention moments when the excessive fault current took place. The gas vent has been appropriately placed as the top cover which eliminates the oil gases but the oil tank does not always remain filled with oil but it needs some extra space to expand. 

Working on the bulk oil circuit breaker

With the help of an insulating mechanism, whenever the moving and fixed contacts have been eliminated from one another throughout the fault and the arc develops within the moving and fixed contacts. This arc improves the hydrogen gas bubbles. The length of the arc starts to increase the moving contacts get eliminated from the fixed contacts which improves the resistance of the arc.

The improved arc resistance lessens the development of gases that are surrounded by the arc among the contacts and lessens the temperature. Whenever the arc moves within the zero-crossing, the arc quenching begins to take place, and later on, this arc will be extinguished and the fault current begins to delay. The hydrogen gas cools the arc which assists the arc quenching to operate the oil circuit breaker or (oil CKT breaker). 

What are the types of oil circuit breaker? 

There are four main types of oil circuit breakers

  1. Plain break oil circuit breaker or plain oil circuit breaker.
  2. Arc control oil circuit breaker and
  3. Low oil circuit breaker or minimum oil circuit breaker or MOCB circuit breaker
  4. Bulk oil circuit breaker. 

Plain break oil circuit breaker or plain oil circuit breaker

The Plain Break Oil Circuit Breaker proceeds well with a very straightforward method that divides the contracts of the tank which is full of oil. This circuit breaker is also known as the advanced type through which many circuit breakers have been improved. It incorporates the moving and fixed contracts which have been surrounded by the secured weatherproof earth tank that contains some oil and it contains the air cushion that remains above the oil.

This circuit Breaker is associated with these currents that carry the strong contracts which can tackle the enormous pressures which were advanced due to dissipation with better energies), earthed metal tank, weather tight and immersed in oil which can be referred to as the transformer oil. The oil handles the extinguishing medium and insulator amidst the earth and live parts. 

Arc control oil circuit breaker  

The arc extinction should take place whenever the gap of the contract is small. To fulfill the objective, many arc controls will be provided and the breakers which are arranged with the arc control are known as the arc control circuit breakers. 

There are two types of arc breakers

1. Self-Blast Oil Circuit Breaker through which the arc control has been prepared by the interior means. For instance, the arcs are used for their extermination effectively. 

2. Superficially generated pressure or impulse oil circuit breakers through which arc control has been prepared for the automatic means outside of the circuit breakers. 

The Self Blast Oil Circuit Breaker has many different pots which include:

 To operate this type of breaker, the air-pressured arc has been invented to try its best to quicken the movement of oil within the space of the contract instantly until it comes to zero. The high-pressured arc generates the instant displacement of oil within the space that connects the contracts until it hits zero. This consequence can take place when it surrounds the contracts through the pot and pressure chamber. 

This has led to many different types of pots:

  • Plain Explosion Pot is the cylinder for the insulating element that surrounds the fixed and moving contracts, although it might be easy to open it has a secured top, which can be recognized as the throat within the bottom. The moving contract is also known as the cylindrical rod that passes through the throat.
  • Cross-Jet Explosion Pot: This sort of pot can be referred to as the reduction of plain explosion pot. It has been invented as an insulating material and it contains a channel on one side that performs as the arc splitter. The arc splitters guide to enhancing the arc length that assists in arc extinction. 
  • Self-Compensated Explosion Pot: This type of pot is known as the union of the cross jet pot and plain explosion. For this reason, it can get terminated in a slow procedure since the strong short circuit currents are within the affordable validity.
  • Oil Blast Explosion Pot: This pot is incorporated with three important compartments the intermediate contract, low hollow moving contract, and upper fixed contract and this contact is considered under pressure. 

Low oil circuit breaker (LOCB) or minimum oil circuit breaker (MOCB)

The circuit breaker utilizes a small amount of oil to achieve the arc quenching medium which is known as the low oil circuit breaker. Since it takes a very short space to store the oil for this reason, transportation has become complex and it has lessened the size of the circuit breaker but it has lessened the maintenance costs which operate all activities of voltage ratings.

Since the circuit breakers perform better with a small amount of oil, there is a rise in the degree of carbonization which can be more inappropriate to operate for other activities very effectively. These circuit breakers are mainly used to operate the applications of high voltage till 132Kv. Sometimes it gets complex to eliminate the gases through the contact space. 

This circuit breaker has some unique features that are connected with the features of the Bulk Oil Circuit Breaker is utilizes several amounts of oil. The oil fulfills two benefits. In the moment of opening the contracts, it eventually extinguishes the arc and then it insulates the present conducting parts from each other and across and away from the earthed tank. This circuit breaker can operate within the lowest voltage of 380kV. With the advancement of system voltage, the bulk OCB might require excessive oil. 

Low immersed circuit breaker

The Low Immersed Circuit Breaker contributes to the perfect protection for the distribution transformers from the short circuit, over current, overload, and excessive heat lessening the levels of erosion and assisting to lessen the costs of maintenance. These circuit breakers have originated with the help of top-notch technology and along with some authentic raw materials that aim to provide better performance and greater operational life.

These circuit breakers have been made within the transformer which exceeds the vital coil assembly and is directly associated with the connecting rod and extrinsic operating handle. Along with the secondary winding or low voltage, the inputs of the breaker are connected and along with the transformers’ Low Voltage Bushing Terminal, the output leads are connected.

It is also known as the principal element of the CSP (the completely Self Protected) Distribution Transformer security framework. Here, the thermal settlement took place between the breaker and the transformer’s windings, in this situation it might only trip whenever it needs to protect the transformer windings from extrinsic faults and extreme overloads. This circuit breaker improves the load proficiency of the transformer and constantly through the transformer lets it supply the load since it can protect the insulating system.

The CSP technology has created a better path for better quality distribution system management and excellent performance distribution transformer. Although overloading can be an inevitable element of the Power Sector, utilizing this sort of circuit breaker helps to improve the lifespan of electrical distribution transformers.

Some of the benefits of the Oil Immersed Circuit Breaker are:

  • Associated leads have been invented from the Standard Cross-Sectional Area along with copper braids with better lengths that may not need any joint to attach the terminals of the transformer. 
  • The tripping mechanisms are joint-free. 
  • The best automatic strength makes sure the ruggedness is present until the transformer is in a work in progress. 
  • Best insulating contacts make sure that the transformer oil has a better lifespan to operate in a better way and highest levels of insulation are available. 
  • To create better joint-free loops the signal light Wire Length will be distributed.
  • The terminals of Contact points are within the bigger size which improves the area of the contact that lessens the resistance. 

Can I use an 11KV oil circuit breaker?

Whether or not you can use an 11KV oil circuit breaker depends on the specific requirements of your electrical system. The 11KV OCB is typically used in high-voltage applications. But the specific voltage and current requirements will depend on the specific application and the technical specifications of the equipment being used. The vacuum circuit breaker is used for low-voltage and medium-voltage applications.

Final thought

A high voltage oil circuit breaker is a type of circuit breaker used to protect electrical power systems from damage caused by overloads and faults. It operates by using a high-pressure insulating oil to extinguish the arc that is generated when the circuit occurs. The high voltage oil circuit breaker working principle is simple. Whenever the circuit breaker is closed, the oil is forced into the arc chamber, where it cools and extinguishes the arc. The oil also acts as an insulator to prevent any further arc event. When the circuit breaker is opened, the oil is released back into the reservoir, and the contacts are separated. The high voltage oil circuit breakers are typically used in high voltage power systems of 115 kV and above.

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