Air Blast Circuit Breaker (ABCB): Definition and Working Principle
Air blast circuit breakers (ABCBs) are electrical devices designed to interrupt electrical flow in a circuit by using compressed air as the interrupting medium. They were developed to overcome the shortcomings associated with oil circuit breakers, providing improved protection, reduced maintenance requirements and increased operating efficiency.
Working principle of Air Blast Circuit Breaker:
1. Interference medium:
ABCBs employ compressed air as the interrupting medium. When a fault occurs in the electrical system, the tripping mechanism initiates the release of compressed air into the arc extinction chamber.
2. Arc Interruption Process:
• The compressed air flows at high speed, pushing the moving contacts apart and creating a gap between them.
• Additionally, the air blast carries away the ionized gases produced by the electric arc, allowing rapid extinction of the arc.
3. Arc Extinction:
• The moving contacts separate, and an arc is initiated.
• The high-speed airflow along the arc removes heat, reducing the diameter of the arc.
• At the moment of current zero, the arc is interrupted, and the contact space is filled with fresh air.
4. Dielectric Strength and Pressure:
• The blockage procedure fills the blockage with high-pressure air, preventing re-attack.
• The dielectric strength of air increases with pressure, allowing fresh high-pressure air in the contact space to withstand the transient recovery voltage.
5. Types of ABCB:
• ABCBs come in a variety of types depending on the flow of compressed air around the contacts, including axial, radial, and cross-blast designs.
• Axial Blast Air Circuit Breaker:
• Air flows longitudinally along the arch, providing high-speed clearance with a small contact gap.
• Suitable for high voltage.
• Cross Blast Air Circuit Breaker:
• The air is directed at right angles to the arc, providing complete isolation without the need for a series isolator.
• Switch small currents efficiently without the need for switching resistance.
Advantages of Air blast circuit breakers :
1. High-Speed Operation: Rapid response time ensures quick interruption at various current values.
2. Suitability for frequent operations: Absence of oil allows frequent switching with minimum wear and tear.
3. High-speed reclosure: Enables rapid restoration of normal system operation after the fault is cleared.
4. Negligible Maintenance: Requires minimal maintenance as compared to oil circuit breakers.
5. Elimination of fire hazard: The absence of oil reduces fire hazard.
Drawbacks of Air blast circuit breakers:
1. Dependence on compressed air: Requires a constant supply of clean and dry compressed air, which can be challenging in smaller installations.
2. Fixed Air Pressure Challenges: Fixed air pressure can cause overvoltage in small streams.
3. Sensitivity to circuit severity: Some designs may experience high restricting voltages, requiring resistor switching.
4. Obsolete Technology: Gradually becoming obsolete with the advent of modern alternatives like SF6 and vacuum circuit breakers.
In short, ABCBs, through their innovative use of compressed air, provide a reliable and efficient means of interrupting electrical currents while addressing the shortcomings associated with conventional oil circuit breakers. However, advances in circuit breaker technology have led to new options being preferred in contemporary electrical systems.
• Air blast circuit breakers (ABCB) interrupt electrical flow using compressed air, overcoming the shortcomings of oil circuit breakers for better protection and efficiency.
• working principle:
• Compressed air released into the arc extinction chamber during a fault.
• The high-speed air separates the contacts, extinguishing the arc by removing ionized gases.
• Separating the contacts starts the arc, and the air flow reduces the diameter of the arc.
• Obstruction with high pressure air prevents re-ignition, preventing transient recovery voltage.
Types of ABCB:
• Axial blast: Longitudinal air flow suitable for high voltage.
Cross Blast: Air directed at right angles for complete separation, efficient for small streams.
• High speed operation, suitability for repeated operations, high speed recovery, negligible maintenance, elimination of fire hazard.
• Dependence on compressed air supply.
• Static air pressure can cause overvoltage.
• Sensitivity to circuit severity may require resistor switching.
• Has become obsolete with the rise of alternatives like SF6 and vacuum circuit breakes.