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What are a trip coil and a close coil in a breaker ?

In the context of circuit breakers, trip coils and close coils are essential components that control the opening and closing mechanisms of the breaker. Circuit breakers are devices designed to interrupt the flow of electric current in the event of a fault or when the circuit needs to be manually disconnected. Let’s explore in detail the functions and characteristics of trip coils and close coils:

Trip Coil:

  1. Function:
    • The trip coil is a crucial component in a circuit breaker that is responsible for initiating the opening of the circuit breaker contacts. It is an electromechanical device that, when energized, produces a magnetic field that acts on the moving parts of the breaker, causing it to trip or open.
  2. Operation:
    • When a fault or abnormal condition occurs in the electrical system, the protective relay detects the fault and sends a trip signal to the trip coil. The trip coil then energizes, creating a magnetic field that interacts with the moving parts of the circuit breaker. This magnetic force overcomes the mechanical latch or spring holding the contacts in the closed position, causing the contacts to separate and interrupt the current flow.
  3. Types of Trip Coils:
    • Trip coils can be of various types, including thermal magnetic, electronic, or digital trip coils, depending on the design and application of the circuit breaker. Each type is optimized for specific conditions and fault characteristics.
  4. Protective Function:
    • The trip coil is a crucial element for the protective function of the circuit breaker. It ensures that the breaker responds promptly to faults, preventing potential damage to the electrical system and equipment.
  5. Resetting:
    • After a trip event, the trip coil needs to be reset to restore the circuit breaker to its normal closed position. This reset process often involves a manual operation, but in some cases, it may be automated.

Close Coil:

  1. Function:
    • The close coil is another electromechanical component in a circuit breaker that is responsible for initiating the closing or reclosing of the circuit breaker contacts. It is energized to close the contacts, restoring the electrical continuity after a trip event or when the breaker needs to be manually closed.
  2. Operation:
    • When it is necessary to close the circuit breaker, the close coil is energized. This energizes the coil, creating a magnetic field that acts on the closing mechanism of the breaker. The magnetic force overcomes any mechanical resistance, bringing the contacts back into a closed position.
  3. Reclosing Function:
    • The close coil is particularly important in circuit breakers with automatic reclosing capabilities. After a fault is cleared, the close coil is energized to close the contacts and restore the circuit. Automatic reclosing enhances the reliability of the power system by attempting to restore power without manual intervention.
  4. Manual and Remote Operation:
    • The close coil can be operated manually by an operator, often using a control switch on the breaker or through a remote control mechanism. Remote operation allows for control from a distance, improving safety and convenience.
  5. Interlocking:
    • In many circuit breaker designs, there are interlocking mechanisms between the trip coil and close coil to prevent simultaneous energization, ensuring that the breaker cannot be closed immediately after tripping without manual intervention.

Overall Interaction:

  1. Protective Scheme:
    • The combination of trip coils and close coils forms an integral part of the protective scheme in electrical systems. They provide the necessary control to isolate faulty circuits and restore normal operation.
  2. Coordination with Protective Relays:
    • The operation of trip coils and close coils is coordinated with protective relays, ensuring that the breaker responds appropriately to different fault conditions and follows the predefined protection and reclosing strategies.
  3. Maintenance and Testing:
    • Periodic maintenance and testing of trip coils and close coils are essential to ensure their proper functioning. This may involve verifying the insulation, checking electrical connections, and conducting functional tests to confirm their response to control signals.

In summary, trip coils and close coils are integral components in circuit breakers, playing a crucial role in the protective and operational functions of the electrical system. Their proper design, coordination, and maintenance are essential for ensuring the reliability and safety of power distribution systems.

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