To guarantee seamless operation, electric power systems require dependable, secure, and effective protective measures. The vacuum Circuit Breaker is one of the most reliable options for medium-voltage applications among the several kinds of circuit breakers that are currently on the market. The VCB is widely utilized in power distribution networks and industries because of its high dependability, low maintenance requirements, and effective fault current interruption capabilities. In 1960, the vacuum interrupter technology was first presented. However, the technology is still in its infancy. Due to many technological advancements in this area of engineering, the vacuum interrupter’s size has decreased over time from its initial size in the early 1960s. A circuit breaker is a device that cuts off an electric circuit to stop excessive current from flowing through a short circuit, which usually happens as a result of an overload. Its primary duty is to stop the flow of electricity when a fault is identified. An overview of the vacuum circuit breaker’s operation is covered in this article.
- What Does a Vacuum Breaker Do?
- Is a Vacuum Breaker Necessary?
- Construction of Vacuum Circuit Breaker
- Working of the Vacuum Circuit Breaker
- Vacuum circuit breaker types
- Where Vacuum Circuit Breaker is Used?
- How to test Vacuum Circuit Breaker?
- Property of contact material
- Why we use Vacuum Circuit Breaker?
- Disadvantages of Vacuum Circuit Breaker
- Conclusion
What Does a Vacuum Breaker Do?
A vacuum circuit breaker is a particular kind of breaker
that uses a vacuum as a means of putting out arcs. Both the fixed and movable contacts
of the circuit breaker are housed in the permanently sealed vacuum interrupter.
The extinction of the arc is guaranteed when contacts are separated in a high
vacuum. In any system, the device is utilized to stop an unexpected current
that results from a short circuit. Additionally, in certain applications, it
disrupts the voltage. Arc quenching essentially occurs in this vacuum medium. Compared
to a conventional circuit breaker, the arc extinction circuit has a higher
insulating medium.
Is a Vacuum Breaker Necessary?
There are two remarkable features of the vacuum circuit breaker:
High insulating strength: Vacuum is a better dielectric medium than many other insulating media used in circuit breakers. With the exception of air and SF6, which are used at high pressure, it is superior to all other media.
An interruption happens at the first current zero when an arc is created by separating the contacts in a vacuum. Compared to conventional breakers, their dielectric strength increases up to thousands of times with the arc interruption.
The two characteristics mentioned above increase the breakers' efficiency, reduce their bulk, and lower their cost. They also require virtually no maintenance and have a far longer service life than any other circuit breaker.
Construction of Vacuum Circuit Breaker
The vacuum circuit breaker is made out of ceramic insulators symmetrically distributed in the center of a steel arc chamber. The vacuum interrupter’s internal pressure is kept below 10^-4 Torr. The vacuum circuit breaker’s performance is significantly influenced by the material selected for the current-carrying contacts. The best alloys to use for VCB connections are copper-bismuth or copper-chrome alloys.
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| Construction of a Vacuum Circuit Breaker Source: www.elprocus.com |
The vacuum circuit breaker is made up of a vacuum
interrupter, a moving contact, and a fixed contact, as seen in above diagram.
The stainless steel bellow connects the moving contact to control mechanism. In
order to prevent condensation on the insulating enclosure, the arc shields are
mounted on the insulating housing such as that they cover the shields. By
permanently closing the vacuum chamber and using a glass or ceramic vessel as
the outside insulating body, the chance of a leak is removed.
Working of the Vacuum Circuit Breaker
The vacuum circuit breaker works on the principle of that
metal vapor ionization in the contacts of the circuit breaker can cause an arc to
form when the contacts are opened in a vacuum. However, due to the production
of electrons, ions, and metallic vapours throughout, the arc can be quickly quenched.
Thus, the dielectric strengths can be rapidly restored as the arc rapidly condenses
on the exterior of the CB contacts.
The diagram below depicts the sectional view of a vacuum circuit breaker. When contacts are separated owing to abnormal conditions, an arc is struck between them. This arc is caused by the ionization of metal ions and is highly dependent on the contact’s substance. Vacuum interrupters differ from one kind of circuit breaker in how they interrupt arcs. The vapor that fills the contact space is released as the contacts separate. Positive ions that have been released from the contact material make up this substance.
The arc’s current determines the vapor density. The rate of vapor release slows as the current drops, and if the vapor density is decreased aster current zero, the medium regains its dielectric strength. The arc has multiple parallel courses when the current to be halted is very modest in a vacuum. Numerous parallel arcs that repel one another and disperse across the contact surface make up the total current. This is known as a dispersed arc because it is easily interrupted.
The
arc becomes focused in a limited area at high current levels. The contact surface
vaporizes quickly as a result.. If the arc stays in a dispersed state, the arc
may be interrupted. The arc will re-strike if it is promptly removed from the
contact surface. The material and geometry of the contacts, as well as the
method used to account for metal vapor, have a significant impact on arc
extinction in the vacuum breakers. To prevent a high temperature at any one
location, the arc’s route is maintained in motion.
A characteristic of the vacuum breaker is the quick increase
in dielectric strength following the last arc interruption. Their
re-strick-free behavior makes them appropriate for capacitor switching.
Depending on the substance of contact, the level of chopping may result from
the little current being cut off before the natural current reaches zero.
Vacuum circuit breaker types
A basic explanation of the many kinds of vacuum circuit
breakers is provided below:
Indoor Vacuum Circuit Breaker: A vacuum circuit breaker is used indoors in areas that are shielded from the elements. Though it lacks a sturdy enclosure, the design is similar to the outdoor type.
Oil Vacuum Circuit Breaker: An insulating oil medium inside the tank is used in conjunction with vacuum interrupters by the oil vacuum circuit breaker. Older designs are uncommon these days because of oil-related environmental concerns.
Phase Segregated Vacuum Breaker: Each phase has an independent vacuum interrupter and contacts.
Where Vacuum Circuit Breaker is Used?
- Vacuum circuit breakers are particularly helpful as very high speed making switches in many industrial applications because of their narrow gap and excellent recovery.
- These breakers clearly outperform the others when the voltage is high and the current to be interrupted is low.
- These breakers are ideal for systems that need power between 11 and 33 kV since they require the least amount of maintenance.
- The most dependable current interruption method for medium voltage switchgear nowadays is the vacuum circuit breaker. Compared to other circuit breaker technology, it requires less maintenance.
- The technology is particularly suitable for mostly medium voltage applications. Although vacuum technology has been developed for higher voltages, it is not yet commercially viable. Both porcelain-housed circuit breakers and metal-clad switchgear use vacuum circuit breakers.
How to test Vacuum Circuit Breaker?
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| Contact Resistance Test Source: www.geeksforgeeks.org |
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| High Potential Testing Source: www.geeksforgeeks.org |
Property of contact material
- High electrical conductivity is necessary for the material to withstand typical load currents without overheating.
- High density and low resistance are desirable properties for the contact material.
- High thermal conductivity is necessary for the material to quickly dissipate the significant heat produced during arcing.
- The material should have a low level of current chopping and a strong arc resist ability.
Why we use Vacuum Circuit Breaker?
- There is no need to fill the vacuum circuit breaker with gas or oil. Periodically replenishing them is not required.
- After appropriate contact separation, there is a quick return of high dielectric strength on current interruptions with arcing that lasts only half a cycle or less.
- The breaker unit is small and independent. Any necessary orientation can be used for installation.
- The aforementioned factors, along with the financial benefit, contribute to the widespread use of vacuum circuit breakers.
Disadvantages of Vacuum Circuit Breaker
- High technology is needed to produce vacuum interrupters.
- To stop low magnetizing currents within a specific range, more surge suppressors are required.
- The entire interrupter becomes worthless if the vacuum is lost as a result of failure or damage during transit, and it cannot be fixed on location.
Conclusion
One of the biggest advancements in electrical protection systems is the vacuum circuit breaker. Compared to conventional breakers, VCBs offer unparalleled dependability, safety, and environmental friendliness by employing a vacuum to put out arcs. They are essential to contemporary power networks because they guarantee operator safety, equipment protection, and supply continuity. Anywhere dependable medium-voltage protection is needed, from industrial facilities to renewable energy sources, VCBs are used. They proved decades of dependable service when properly tested and maintained.
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