The Air Circuit Breaker (ACB) and Vacuum Circuit Breaker (VCB) are two widely used types of circuit breakers in electrical systems, especially for medium voltage and low voltage applications. These breakers are used to protect electrical circuits from overloads, short circuits, and faults. Below is an explanation of the study of ACB and VCB, along with identification of different parts of each.

1. Air Circuit Breaker (ACB)

An Air Circuit Breaker (ACB) is a type of circuit breaker in which air is used as the medium for arc quenching when the contacts open. It is typically used in low voltage systems and is effective for currents up to 6300 A.

Parts of an Air Circuit Breaker (ACB):

  1. Frame / Enclosure:

    • The frame is the outer casing that houses all the internal components of the circuit breaker.
    • It provides mechanical protection and ensures safety during operation.

  2. Operating Mechanism:

    • The operating mechanism is the component that opens and closes the breaker contacts.
    • It includes springs or an electromagnetic coil that provide the force required to open and close the contacts.
    • Types of operating mechanisms include manual, motorized, or pneumatic.

  3. Contacts:

    • Fixed Contacts: These are the stationary contacts that remain fixed in place.
    • Moving Contacts: These contacts are movable and make or break the electrical connection with the fixed contacts. They are the core part of the breaking operation.
    • The contacts are made of highly conductive materials like copper or silver, with an arc-resistant coating.

  4. Arc Chute:

    • The arc chute is an essential part of the ACB. When the contacts open, an electric arc is formed. The arc chute helps to cool and extinguish the arc by dividing it into smaller arcs, allowing for faster dissipation of energy and preventing the arc from causing damage.
    • It is made of metal plates or other materials that help absorb the energy and extinguish the arc.

  5. Operating Springs:

    • These springs store energy that is released during the operation of the breaker. When a fault occurs, the springs release energy to quickly open the contacts and interrupt the current flow.

  6. Trip Mechanism:

    • The trip mechanism is responsible for detecting abnormal conditions like overloads, short circuits, and faults. When such conditions are detected, the trip mechanism activates the spring-loaded mechanism to open the contacts.
    • It can be a thermal-magnetic or electronic type, depending on the specific breaker design.

  7. Shunt Trip Coil:

    • A shunt trip coil is used for remote tripping of the breaker, allowing it to be opened from a distant location.
    • It is typically used in combination with protective relays or remote control systems.

  8. Overload and Short-Circuit Release:

    • These are protection devices designed to detect overload or short-circuit conditions in the circuit.
    • The overload release protects against sustained overcurrent, while the short-circuit release provides rapid tripping in case of short circuits.

  9. Busbar and Terminals:

    • The busbars are conductors that link the ACB to the system, transmitting current to the breaker. The terminals are the points where electrical connections are made to the circuit breaker.

2. Vacuum Circuit Breaker (VCB)

A Vacuum Circuit Breaker (VCB) uses a vacuum as the arc-extinguishing medium. VCBs are typically used for medium voltage systems (up to 33kV) and are highly reliable for fault clearing. The vacuum provides excellent dielectric properties, which makes it effective at quenching arcs.

Parts of a Vacuum Circuit Breaker (VCB):

  1. Frame / Enclosure:

    • Similar to ACBs, the frame of the VCB houses all components and provides mechanical protection.
    • The enclosure is usually made of insulating materials, and it keeps the internal components safe from external factors like dust and moisture.

  2. Vacuum Chamber (Arc Extinguishing Chamber):

    • The vacuum chamber is the heart of a VCB. Inside the chamber, there is a vacuum (a space with very low pressure), which acts as the arc quenching medium when the contacts open.
    • The vacuum provides superior dielectric strength, allowing it to quickly extinguish the arc formed during circuit interruption.

  3. Contacts:

    • Fixed Contacts: These are the stationary parts within the vacuum chamber that are designed to remain fixed during operation.
    • Moving Contacts: These contacts are attached to the mechanism and move in and out of the vacuum chamber to open or close the circuit.
    • The moving contacts are made of materials that are resistant to wear and can withstand the high temperatures generated during the arc.

  4. Operating Mechanism:

    • The operating mechanism controls the movement of the contacts and is responsible for opening and closing the VCB. It can be manual, spring-driven, or motor-driven.
    • This mechanism ensures that the contacts are moved with the required speed and force to quickly interrupt the current.

  5. Vacuum Interrupter:

    • The vacuum interrupter is the sealed unit inside which the arc is generated and extinguished. It contains the vacuum and is designed to withstand the pressure and temperature produced during the interruption of high fault currents.

  6. Spring Mechanism:

    • Similar to the ACB, VCBs use a spring-loaded mechanism to provide the energy needed to open and close the contacts. The spring stores energy and is released when a fault occurs, causing the contacts to open quickly.

  7. Trip Coil:

    • The trip coil is activated when abnormal conditions, such as short circuits or overloads, are detected. It is part of the protection system and ensures that the breaker opens rapidly in case of fault conditions.

  8. Control and Indication Panel:

    • The control panel provides the interface for operating the circuit breaker. It may include various indicators like open/close status, fault indication, and trip signals.
    • Remote control options may be integrated with the panel for system automation.

  9. Terminal Connectors:

    • The terminals are the points where the VCB connects to the electrical system, usually through conductors or busbars.

  10. Shunt Release and Auxiliary Contacts:

  • The shunt release is used for remote tripping. It allows the breaker to be operated from a distance.
  • Auxiliary contacts can be used to send signals to other equipment or systems, such as protection relays or alarms.

Comparison Between ACB and VCB

Component Air Circuit Breaker (ACB) Vacuum Circuit Breaker (VCB)
Arc Quenching Medium Air Vacuum
Voltage Range Low Voltage (up to 1000V) Medium Voltage (up to 33kV)
Applications Mainly in low voltage circuits Primarily used in medium voltage circuits
Maintenance Requires regular maintenance due to air contamination Requires less maintenance due to vacuum’s self-cleaning nature
Current Interrupting Capacity Higher fault interrupting capacity Lower interrupting capacity compared to ACB, but sufficient for medium voltage
Size and Cost Larger and more expensive Compact and cost-effective for medium voltage
Environment Suitability Less suitable for high fault currents and high-voltage More suitable for high-voltage and fault conditions

Conclusion

Both Air Circuit Breakers (ACBs) and Vacuum Circuit Breakers (VCBs) play critical roles in protecting electrical systems from faults and overloads. The main difference lies in the medium used to quench the arc (air for ACBs and vacuum for VCBs), which influences their design, size, maintenance requirements, and cost. Understanding the components of each type of circuit breaker helps in selecting the right breaker for specific applications, ensuring safety, reliability, and efficient operation of electrical systems.