About Vacuum Circuit breaker or VCB – Construction, Working | New Topic [2024]

In this note, we are going to learn About Vacuum Circuit Breaker or VCB, also about its Construction, Working Principle, Advantages, and Disadvantages as well. Welcome to Poly Notes Hub, a leading destination for Polytechnic Notes for Diploma Engineering Students.

Author Name: Arun Paul.

What is Vacuum Circuit Breaker?

A Vacuum Circuit Breaker (VCB) is an electrical switching mechanism used to interrupt or break electrical circuits during normal conditions or fault situations. It works by creating a vacuum between its contacts, which extinguishes the arc that occurs when the circuit is interrupted. VCBs are widely employed in medium to high-voltage applications because of their ability to provide dependable and efficient circuit protection. They provide advantages such as quick operation, low maintenance requirements, and good insulating qualities, making them appropriate for a wide range of industrial and commercial applications.

Construction of Vacuum Circuit Breaker

Below is the Vacuum Circuit Breaker Diagram –

• Fixed Contact: The fixed contact is a stationary component of the circuit breaker that remains in place throughout operation. It provides a sturdy place for electrical connection and makes it easier to interrupt the circuit if necessary.
• Moving Contact: The moving contact is intended to establish or break electrical contact with the fixed contact. It is frequently linked to a mechanism that allows it to move quickly, opening or closing the circuit as needed.
• Bellows Shield: The bellows shield is a flexible, enclosed metal casing that protects the moving contact assembly. It shields the moving parts from environmental pollutants and aids in the maintenance of the vacuum within the circuit breaker.
• Sputter Shield: A metallic shield called a sputter shield is placed around the contacts to stop metal vapors produced during arcing from escaping. By lowering the possibility of contamination, it aids in preserving the integrity of the vacuum.
• End Cap: The circuit breaker assembly’s end caps are protective covers that are positioned at either end. It aids in sealing the enclosure and preventing the entry of moisture or extraneous objects that can impair the VCB’s functionality.
• Insulating Envelope: The VCB’s contacts and other internal parts are encased in an insulating envelope. To offer electrical insulation and support within the circuit breaker assembly, it is usually constructed of materials like ceramic or epoxy resin.

Working Principle of VCB

The Vacuum Circuit Breaker (VCB) uses a vacuum chamber to halt electrical current flow. When the circuit is closed, the fixed and movable contacts are in touch, allowing current to flow. However, when the circuit must be terminated, such as during a fault, the moving contact is quickly dragged away from the fixed contact, resulting in an arc between them due to the gap’s electrical resistance.

As the arc forms, the high temperature causes the surrounding metal to evaporate, ionizing the gas particles in the vacuum chamber. This ionization produces a conductive route for the electricity to flow temporarily. However, because the vacuum chamber contains no air or gas molecules, the arc dissipates fast, usually within milliseconds.

Once the arc is tempered, the moving contact separates from the fixed contact, ensuring that the circuit is safely interrupted. After the problem has been fixed, the circuit breaker can be closed again, allowing normal current flow. As a result, the absence of gas within the vacuum chamber precludes long-term arc development, allowing for efficient electrical circuit interruption.

Advantages of Vacuum Circuit Breaker

Below we listed some merits of Vacuum Circuit Breakers –

1. These circuit breakers has quick response time.
2. Also has high insulation properties.
3. VCBs feature fewer moving parts and don’t require frequent maintenance.
4. This circuit breaker is a Environmentally Friendly.
5. Because of their simple and robust construction, VCBs are highly reliable and have a long service life.

Disadvantages of Vacuum Circuit Breaker

Below we listed some demerits of Vacuum Circuit Breakers –

1. It has limiting breaking capacity.
2. Temperature and altitude restrictions may limit the operation of VCBs.
3. In some situations, there is a possibility of arc re-ignition in VCBs following interruption, particularly during high-current interruption or under certain fault conditions.