What is the Construction of Vacuum Circuit Breakers?

The technology of Vacuum Circuit breakers is still developing and dates back to the year 1960 when it was introduced. In the market, you may find various VCB manufacturers, and it is important to find the best hv circuit breaker manufacturers


A circuit breaker is a device that acts as a switch that interrupts an electrical circuit in case of faults. This is done to protect from the overload of electrical supply. It disrupts the flow of the current after detecting a fault. 


Circuit breakers are used in a variety of fields and places such as hotels, commercial complexes, industries, buildings, etc. 


VCB circuit Breaker is a type of circuit breaker where vacuum is the prime arc quenching medium. 

In this article, we will discuss vacuum interrupter, vcb mechanism, and working comprehensively. This will help you find the ideal circuit breaker service for you.

What is VCB?


VCB or Vacuum Circuit breaker is a circuit breaker where vacuum is used as a quenching medium in circuits. The technology is mainly created for medium voltage circuit breakers and high voltage breakers, it has been developed but not commercially feasible. It is a circuit breaker that is adequate for most standard voltage implementations. 


All the operations of turning on and off if the contacts carry current and correlated arc occur inside the vacuum chamber. The operations carry current and connect interruption of arc inside a vacuum chamber which is called vacuum interrupter. 

Why is Vacuum used?

The vacuum acts as an excellent arc-quenching medium. Its properties increase due to its high insulating properties. 

Construction of Vacuum Circuit Breakers

Vacuum Circuit breaker construction

As compared to other types of circuit breakers, you can consider that the construction of vacuum circuit breakers is fairly simple.
The VCB construction is divided into 3 main components. These components work together as a unit to help trip the electricity in case of an overload.

Here is the construction of a vacuum circuit breaker.

1. External Layer
2. Arc shield that is placed within the arc interrupting chamber
3. Fixed and moving contacts
4. Vacuum interrupter

1. External Layer

Some external layer of the vacuum circuit breaker is made up of glass. This setup ensures clear visibility of the entire VCB unit from outside. So, if the glass turns hazy and milky, it is a clear indication that the breaker is releasing a vacuum. Thus, the external shiny glass is important to monitor the function of the breaker after the operation. Some external layer is made of metal, which could resist external corrosion and dust.

2. Arc Shield

The arc shields are covered by insulating housing. These cover the shields and prevent any condensing on the enclosure. The arc shields block the metallic vapors from falling inside the surface of the outer insulating cover.

The arc shield holds the fixed and moving contacts.

Alloys like Copper- Chrome, and Copper-Bismuth are considered ideal materials to create VCB contacts. The materials of the contact play a major role in the performance of the high current circuit breaker.

The steel arc chamber is symmetrically mounted inside the ceramic insulators.

3. Fixed and moving contacts

The moving contact is connected with the help of stainless steel bellows. it is connected to the control mechanism.

While sealing off these contacts in the arc shield, the temperature is usually maintained at around 10 -6 torr. The operating voltage determines the motion of the moving contacts. Usually, the moving contacts are moved at a distance of about 5 to 10 mm.

4. Vacuum Interrupters

Vacuum circuit breaker

Vacuum Interrupters are sealed-off devices within the vacuum that are consolidated inside VCB. They cause an interruption in any fault currents. They include an arc chamber of steel placed inside symmetrical ceramic insulators. The vacuum pressure inside the vacuum interrupter can be maintained at 10-6 bar. It is assembled in a clean environment. 


The performance of the vacuum circuit breaker depends on the material of contacts carrying currents like Copper and Chromium. 

This explains the hv vacuum circuit breaker construction. 


This construction ensures to protect the electric strength of the circuit for a long time and ensures that it is safe from any internal damage from the vcb parts. To ensure that there is no possibility of a leak in the VCB circuit, the vacuum chamber is permanently sealed. For the outer body, a ceramic or a glass vessel is used as insulation. The insulation acts as a protective covering for the circuit.

Vacuum Circuit Working Principle

Vacuum Circuit breaker working

Vacuum circuit breakers are engaged at outdoor settings within the range of 22kV to 66kV. They are applicable for the majority of rural area applications. 


When the circuit breaks due to any reason, the moving contacts move away from the fixed contact and this produces an arc between the contacts. 


The arc is produced by the ionization of the metal ions and the reaction depends on the material of the contacts. 


When the contacts separate, they release metallic vapor that fills in the space. The vapors have positive ions from the contacts’ materials. The vapors help in the elimination of the arc. The rate of vapor release depends upon the rate of current. When the current starts to decrease, the level of vapors also decreases. Gradually the current decreases to zero, and so does the rate of vapors. This leads to the medium regaining its dielectric strength. 

When the current voltage is high, the arc is condensed in a small region. This leads to swift vaporization of the surface. When the arc is in a diffused stage, the interruption is possible. Otherwise, the arc will strike again. After the arc is interrupted finally, the dielectric strength builds up rapidly which is uncanny of the vacuum breaker. 


High voltage vacuum circuit breakers are ideal for capacitor switching and perform free from re-strikes.


The whole process of arc extinction is highly influenced by the shape and material of the contacts: Fixed contact and Moving contact. It also depends on how the metal vapor condenses.  


This is all about vacuum circuit breaker construction and working.

VCB Applications


VCB is considered one of the most reliable current interruption technologies for medium-voltage current switchgear. 


A vacuum circuit breaker has many advantages such as high-cost life, high efficiency, safety, long operation life, and high interruption capacity. Due to its high performance and low performance compared to the other technologies, new promising products are on their way. 


For the past years, vacuum circuit breaker technology is on the rise, even though its applications are not feasible at high commercial levels, it is highly suitable for medium-voltage applications. 


The technology of vcb is mainly applied in medium voltage circuit breaker applications. A vacuum circuit breaker is considered ideal for interruption of a DC circuit as it can handle high di/dt-dv/dt conditions and can handle the current very well. 


It does not produce any harmful gases like in the case of SF6 circuit breakers. Hence, they are ideal for the environment and humans. The scope of the vacuum circuit breaker is likely to increase in the future because of the high accessibility and simple circuit mechanism.

Table of Contents


Thus, this is all you need to know about the construction and working of the voltage circuit breaker. 

We have seen how the vacuum circuit breaker is efficient in its work, the mechanism of the industrial circuit breaker, and more. 

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