Circuit breakers are mechanical devices that are meant to close or open an electrical circuit under normal and abnormal conditions.
What exactly is VCB?
VCB stands for vacuum circuit breaker and is a type of switchgear used for voltages greater than 1 or 3.3 KV. In vacuum circuit breakers, the vacuum used as the arc quenching medium. The vacuum has the greatest insulating strength.
High interruption capability, longer operation life, safety, and high cost-performance are all properties of VCB.
When the contacts of a breaker are opened in a vacuum, for example, the interruption happens at initial current zero, with dielectric strength between the contacts increasing at a pace thousands of times faster than with other types of circuit breakers.
Working Principle
According to the vacuum circuit breaker operating theory, when the contacts of the circuit breaker are opened in a vacuum, an arc can be produced between the contacts due to the ionization of metal vapors in the contacts. However, the arc is swiftly extinguished because the metallic vapors, electrons, and ions that are produced throughout the arc quickly condense over the outsides of the CB contacts, allowing the dielectric strength to be quickly restored.
The
most crucial characteristic of a vacuum is that, once an arc has been created
there, it may be swiftly put out due to the vacuum's fast increase in dielectric
strength.
A
steel arc chamber is part of the center-symmetrically organized ceramic insulators'
vacuum circuit breaker a steel arc chamber is part of the center-symmetrically
organized ceramic insulators' vacuum circuit breaker.
The
vacuum circuit breaker performance is significantly influenced by the material
selected for the current-carrying contacts. Copper-bismuth or copper-chrome
alloys are the best materials to use when creating VCB connections.
A
moving contact, a fixed contact, and a vacuum interrupter make up the vacuum
circuit breaker. A stainless steel bellow connects the moving contact to the
control mechanism. The insulating housing supports the arc shields in such a
way that they cover the shields and prevent condensation on the enclosure from
occurring.
Below
image, you can see all the important parts of the VCB.
Vacuum Interrupter
The
interruption of arc in a Vacuum Circuit Breaker is carried out by the vacuum
interrupters.
A vacuum interrupter, in theory, contains ceramic
insulators stacked symmetrically and a steel arc chamber in the middle.
Which demonstrate the basic components of a standard
vacuum interrupter. The arcing contacts of modern versions of this interrupter
are encircled by a metal shield.
The arc chamber and insulator diameters are matched
with the diameters of the contacts and their stems. The use of metallic bellows
allows the moving contacts to move.
A hermetically sealed interrupter is created by
joining the arc chamber to the housing flange, which is then brazed to metalized
ceramic insulators. Typically, the vacuum pressure is 10-6 bar.
Clearing and Closing time of a Circuit breaker - Below diagram shows the clearing and closing time of the circuit breaker.
Applications of VCB
Vacuum circuit breaker has the following applications:
- Circuits
with high voltage
- Electrical
substations and generators use it.
- Double
earth faults and out of phase currents are interrupted.
- We use VCB
for applications that require fast switching sequences.
- This
circuit breaker is used in railway applications for traction current and
electric supply switching.
- To turn on
and off motor drives.
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