bennypass.com - Air Blast Circuit Breakers

Air Blast Circuit Breakers - Working Principle

blast circuit

Air blast circuit breakers (ABCB) use a high-pressure air blast (typically 20-30 kg/cm²) to extinguish electrical arcs formed during contact separation, acting within ~40 ms. When a fault occurs, compressed air from a reservoir is released through nozzles, cooling and sweeping away ionized gases, forcing the arc to extinguish at current zero.

Key Working Principles

Arc Initiation: When the circuit breaker operates under fault conditions, the moving contacts separate, creating an arc between the contacts due to air ionization.
Air Blast Activation: Simultaneously, a blast valve opens, allowing compressed air to flow at high velocity directly into the arcing zone.
Arc Extinction: The high-velocity air blast increases the arc's resistance by cooling it and replacing the ionized air with fresh air, forcing the arc to quench at the next current zero.
Types of Airflow:
- Axial Blast: Air flows parallel to the arc path.
- Radial Blast: Air flows radially across the arc.
- Cross Blast: Air flows perpendicular to the arc path.

Advantages:

Fast Operation: Ideal for high-speed fault clearing.
Reduced Risk: No fire hazards compared to oil circuit breakers.
Low Maintenance: Less carbonization due to air as the medium.

Disadvantages:

Noise: Significant noise pollution during operation.
Complexity: Requires a, constant supply of high-pressure air and compressors.
Current Chopping: Potential issues with premature current interruption.

Air blast circuit breakers are generally replaced by SF6 circuit breakers in modern, high-voltage applications.

The working principle of an Air Blast Circuit Breaker (ABCB) centers on using a high-velocity jet of compressed air to rapidly extinguish the electric arc formed when contacts separate during a fault.

Core Working Principle

Fault Detection: When a fault (such as a short circuit) occurs, the protection system sends a tripping signal to the breaker.
Blast Valve Opening: This signal triggers a pneumatic operating mechanism that opens a blast valve, releasing air stored in a high-pressure reservoir (typically 20–30 bar).
Contact Separation: The high-pressure air enters the arc extinction chamber and exerts force on the moving contact, pushing it away from the fixed contact.
Arc Quenching: As the contacts separate, an electric arc forms. The high-velocity air blast then:
- Cools the arc by rapidly absorbing and carrying away heat.
- Sweeps away ionized particles that sustain the current flow, replacing them with fresh, non-conductive air.
- Increases dielectric strength of the gap so rapidly that the arc cannot restrike after the first current zero.

Main Types by Blast Direction

Axial Blast: The air flows longitudinally along the arc path. It is the most common type for high-voltage applications.
Cross Blast: The air is directed at a right angle (90°) to the arc, forcing it into arc splitters and chutes to lengthen and cool it.
Radial Blast: The air is admitted radially into the gap and then flows axially, often used in double-blast configurations for extra-high voltage.

Key Components

Air Reservoir: Stores the compressed air needed for operation.
Hollow Insulator: Provides a path for high-pressure air while isolating live parts from the ground.
Arc Extinction Chamber: The housing where contact separation and arc quenching actually occur.
Series Isolator: Often included in axial types to provide additional clearance after the small contact gap has successfully interrupted the current.

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