🔌 Circuit Breaker: Definition, Types, Working Principle, Circuit Diagram, Advantages & Uses

Circuit Breaker

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overcurrent, overload, or short circuits. Its basic function is to interrupt current flow after a fault is detected. Unlike fuses, which operate once and must be replaced, circuit breakers can be reset manually or automatically to resume normal operation.

🧠 Working Principle of a Circuit Breaker

A circuit breaker consists of fixed and moving contacts which touch each other and carry the current when the circuit breaker is closed. We can open and close it manually for switching and maintenance. But whenever a fault occurs on any part of the power system, the trip coil of the circuit breaker gets energized and moving contacts are separated by some mechanism.

⚡ Circuit Breaker with Relay – Explained (Diagram Interpretation)

🔍 Components in the Diagram:

1. Bus-bar
   • Supplies power to the system.
2. Circuit Breaker (CB)
   • A switching device that can interrupt the current in case of a fault.
3. C.T. (Current Transformer)
   • Measures current and sends a scaled signal to the relay coil.
4. Relay Coil
   • Gets energized when abnormal current flows (fault condition).
5. NO Contact of Relay (Normally Open)
   • Closes only when the relay is energized, completing the trip circuit.
6. Trip Circuit
   • Activates the Trip Coil when energized, triggering the breaker to open.
7. Trip Coil of C.B.
   • Mechanically opens the circuit breaker to interrupt current flow.

⚙️ Working Principle:

1. Under normal conditions, current flows from the bus-bar through the breaker and CT to the load. The relay coil remains unenergized, and the breaker remains closed.
2. During a fault (e.g., overload or short circuit):
   • The CT senses high current and energizes the relay coil.
   • The relay’s normally open (NO) contact closes.
   • This completes the trip circuit, energizing the trip coil of the CB.
   • The trip coil activates, causing the circuit breaker to open and isolate the faulty section.

🔧 Types of Circuit Breakers

1. Air Circuit Breaker (ACB)

• Arc Quenching Medium: Air.
• Application: Used for low-voltage applications.
• Advantage: Simple design and easy maintenance.
• Disadvantage: Limited to low-voltage applications.

2. Oil Circuit Breaker

• Arc Quenching Medium: Oil.
• Application: Used in high-voltage applications.
• Advantage: Effective arc quenching.
• Disadvantage: Requires regular maintenance and oil replacement.

3. Vacuum Circuit Breaker

• Arc Quenching Medium: Vacuum.
• Application: Suitable for medium-voltage applications.
• Advantage: Minimal maintenance and long service life.
• Disadvantage: Higher initial cost.

4. SF₆ Circuit Breaker

• Arc Quenching Medium: Sulfur Hexafluoride (SF₆) gas.
• Application: Used in high-voltage applications.
• Advantage: Excellent arc quenching properties.
• Disadvantage: SF₆ is a potent greenhouse gas; proper handling is essential.

 ​ 5. Molded-Case Circuit Breakers (MCCB):

Molded-Case Circuit Breakers are used primarily in low voltage circuits. In this model, all the parts that carry the current, mechanisms and switching devices, are embedded inside a molded box or circuit breaker box made of insulating material.

ADVANTAGES OF A CIRCUIT BREAKER OVER FUSE

1. The Circuit breaker operates at high voltages compared to a fuse.
2. Circuit breaker can be operated remotely by energizing the close or trip coil, which cannot be done in case of a fuse.
3. Circuit breaker functioning (Tripping or closing) can be tested easily.
4. No need to replace the circuit breaker after fault.

✅ Advantages of Circuit Breakers

• Reusable: Unlike fuses, they can be reset after tripping.
• Quick Operation: Rapidly interrupts fault currents.
• Selective Protection: Can be designed to trip specific circuits without affecting others.
• Remote Control: Some breakers can be operated remotely.
• Safety: Provides enhanced protection against electrical fires and equipment damage.

❌ Disadvantages of Circuit Breakers

• Cost: Generally more expensive than fuses.
• Complexity: More complex design requires careful installation and maintenance.
• Maintenance: Some types require regular maintenance to ensure reliability.

🛠️ Applications of Circuit Breakers

• Residential: Protecting household wiring and appliances.
• Commercial: Safeguarding office buildings and commercial establishments.
• Industrial: Protecting machinery and equipment in factories.
• Power Systems: Used in substations and power distribution networks.
• Transportation: Employed in railway systems and electric vehicles.

📚 Conclusion

Circuit breakers are essential components in modern electrical systems, offering reliable protection against faults and ensuring the safety of equipment and individuals. Understanding their types, working principles, and applications helps in selecting the appropriate breaker for specific needs.