What is a Vacuum Circuit breaker(VCB)?

Vacuum Circuit breaker (construction , Mechanism , Advantages & Disadvantages) - Electronicsinfos

A vacuum circuit breaker is a type of circuit breaker in which a vacuum is used as an insulating medium. The vacuum circuit breaker is used up to 28 kV for ideal circuits.

There are two contacts in the vacuum circuit breaker one is fixed contact and another one is variable contact which exists in the insulating envelope.

The main part of the Vacuum circuit breaker is the vacuum interrupter. The air pressure in the interrupter is 10-⁷ mm of Hg which is the highest vacuum.

We also used multi-unit VCB for up to 72kv. Multi-interrupter circuits are widely used in America, Japan and other countries.

There are many properties of vacuum circuit breakers including

Properties of Vacuum Circuit Breaker(VCB)

High insulating Strength
fast operation
Recovery of dielectric strength
suitable for repeated work
simple operating mechanism
flexible design
low weight
low distance between contacts
long life
less maintenance required

Construction of Vacuum Circuit Breaker(VCB)

VCB consist of steam-connected contact pieces that are held with the ceramics insulators. Fixed contacts are connected with the housing. The moving contact piece is connected with the vacuum-tight metal below.

The arching chamber acts like a vapour shield. When contacts are open the metal vapour arc is produced in the contact piece.

The Parts of VCB including

Parts Of the Vacuum Circuit Breaker(VCB)

Upper Support and heatsink
Terminal of pole
Insulator support rod
Fixed contact Piece
Moving contact piece
insulator
Metallic bellows
Lower terminal
Lower heat sink
Mechanism Linkage
Glass fibre rod
opening spring

The parts of a vacuum interrupter including

Parts Of Vacuum Interrupter

electrodes (Fixed and moving)
Metallic bellows
Vapour condensing Shield
Seals
Insulating envelope
End shields
Fixed contact stem
Moving contact stem
Shield support flange
Vacuum

Metallic Bellows

The metallic bellows are made of the material Stainless steel. One part of the bellows is connected with a metal flange and another one is connected with moving contact.

Vapour condensing Shields

The metal shields are used to avoid the arching effect in insulating enclosures. These shields are surrounded by the contact region.

Seals

Seals are used to maintain the vacuum in the circuit breaker for a long time. these seals are made with metal glass or metal-ceramic cells.

Insulating Envelope

The insulating envelope is used to tolerate the mechanical pressure. The glass material is used as an insulating Envelope.

End Shields

The End shields are non-magnetic materials that support the End flange, enclosure, fixed contact, vapour condensing shields, bellows etc.

Contact Stem

The back part of Contact faces is called the contact stem. This is made with a high-conducting material. the melting point of contact is high.

Properties of Electrodes

There are some properties of Electrodes including

The Electrodes must have good electrical conductivity.
The Electrodes must have good thermal conductivity to discharge the heat.
It must have a high cold and hot hardness to avoid wear and tear.
The electrodes must have a high-density
Electrodes must have a high thermionic function.
High boiling and melting point.
The contact resistance must be low.
The process of manufacturing is easy and economical.

There are many materials used for the manufacturing of electrodes including copper bismuth alloy, copper chromium alloy, copper-beryllium alloy etc

Types Of Vacuum Interrupters

There are two types of vacuum interrupters including

Single Unit Per pole Interrupter
Multi unit per pole interrupter

Mechanism of VCB

when current-carrying Contacts are separate in the VCB The arc is produced. In this circuit breaker, the Extinguish mechanism is different compared to other circuit breakers. In this circuit breaker, the vacuum is used as a dielectric medium.

when contacts are separated, the gas is ionized and some contact materials provide the charged particles due to the field's emission. As a result, the arc plasma state is created depending on the arc current.

when the current wave is low the discharge value of vapours is also low. when the current is zero the medium retains the actual value and provides better dielectric strength.

The most important thing in the VCB is the fast Recovery of dielectric strength. In the VCB The Arc distinction depends on the following things

The Vacuum degree in the interrupter
The Effectiveness of Operating Mechanism
The peak value of Arc's current
The changing ratio of Arc's current
The emission of energy
Arc plasma
The peak value of TRV (Transient Recovery voltage)

Advantages of vacuum circuit breaker (VCB)

fast recovery of dielectric Strength
The low weight of Moving parts
The efficiency is higher
free from pollution because of no gas decomposition.
No need for oil and gas.
No chance of Explosion in the VCB.
The lifetime is high
Fast operation
Need less maintenance
The contact resistance is not changed during the working of VCB.

Disadvantages of vacuum circuit breaker(VCB)

The Vacuum interrupter is Expensive compared to other interrupters.
The single interrupter is limited to up to 20KV. if we connect in series to obtain high value the cost is high.
High technology is needed to manufacture the Vacuum interrupter.
if the breaker fails the vacuum is also lost so no repair model.

Conclusions

In conclusion, VCB breakers utilize a high vacuum as the medium for extinguishing the arc formed when the contacts are separated during an interruption.VCBs have many benefits, including high breaking capacity, quick operation, and low maintenance requirements.VCBs are predominantly used for medium voltage ranges, typically from 11 KV to 33 KV.

Frequently Asked Questions – FAQs

What is a Vacuum Circuit Breaker (VCB)?

A VCB is a type of circuit breaker where the arc quenching takes place in vacuum conditions.

How does a VCB work?

It extinguishes the arc by creating a high dielectric strength in the vacuum, which is achieved at the first current zero after the contacts are opened.