The working principles of Circuit Breaker

The working principle of a circuit breaker is to automatically interrupt the flow of electricity in an electrical circuit when it detects a fault condition such as overcurrent, short circuit, or overload, thereby protecting electrical systems and preventing damage or fire.

Key Components and Operation:

Sensing Mechanism (Trip Unit):

Detects abnormal current flow.

Uses either thermal, magnetic, or electronic methods:

Thermal Trip: A bimetallic strip bends with heat from overcurrent and triggers the trip.

Magnetic Trip: A solenoid creates a magnetic field strong enough (from a short circuit current) to move a lever that opens the circuit.

Electronic Trip: Uses sensors and microprocessors to detect and respond precisely to faults.

Mechanical Linkage:

Once the trip unit activates, it releases a spring-loaded mechanism that forces the contacts apart to open the circuit.

Contacts:

These are the conducting parts that open or close the circuit. When the breaker trips, the contacts are separated to interrupt current flow.

Arc Extinguishing System:

When contacts open, an electrical arc forms. The circuit breaker uses methods like arc chutes, air, oil, or vacuum to extinguish the arc quickly and safely.

Reset Mechanism:

After tripping, the breaker can be manually or automatically reset once the fault is cleared.

Types of Circuit Breakers (based on application and arc extinction method):

Miniature Circuit Breaker (MCB) – Used in low voltage applications.

Molded Case Circuit Breaker (MCCB) – For higher current ratings.

Air Circuit Breaker (ACB) – Uses air to extinguish the arc.

Vacuum Circuit Breaker (VCB) – Used in medium voltage systems.

SF₆ Circuit Breaker – Uses sulfur hexafluoride gas to quench the arc.

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