Determination and Handling of Circuit Breaker Failures

1. Determination and Handling of “Refusal to Close” Failures

A “refusal to close” failure in a circuit breaker typically occurs during closing operations or recloser activation, posing significant risks. For instance, in emergency situations requiring the immediate activation of a backup power supply, a breaker refusing to close can escalate the incident. The process for diagnosing and addressing this issue generally involves three steps:

1. Check for Previous Operational Errors: Investigate whether the previous failure to close was due to operational errors, such as releasing the control switch too quickly. Attempt to close the breaker again using the control switch.
2. Examine Electrical Circuitry: If the breaker still fails to close, inspect various components of the electrical circuit to determine if there is a fault. Check if the closing control power supply is normal, the closing control circuit and closing circuit fuses are intact, the contacts of the closing contactor are in good condition, and whether the closing solenoid operates correctly when the control switch is set to the “close” position.
3. Assess Mechanical Issues: If the electrical circuitry is functioning properly but the breaker still does not close, mechanical faults may be the cause. The breaker should be taken out of service, and the issue reported to dispatch for repair.

After preliminary checks, one can ascertain whether the fault is electrical or mechanical. Common electrical and mechanical faults include:

1. Electrical Faults:
   • Both red and green indicator lights are off before closing, suggesting a lack of control power or a broken control circuit. Inspect the control power and all elements in the control circuit, such as operating voltage, fuses, anti-trip relays, and auxiliary contacts.
   • If the green light flashes after the closing operation, the red light is off, instruments show no readings, and the breaker remains in the open position, the problem could be misalignment between the operating handle and the breaker position. This may be caused by issues such as blown or poor connections in the closing circuit fuses, failure of the closing contactor, or problems with the closing coil.
   • If the green light turns off, the red light momentarily lights up then turns off, the green light flashes again, and an alarm sounds after attempting to close, the breaker may have auto-tripped due to a fault in the circuit. This could be due to either a fault in the protected circuit or mechanical issues preventing the breaker from remaining closed.
   • If the green light flashes or turns off, the red light is off, but the instruments show readings and the breaker is in the closed position, it indicates the breaker is closed. The potential issues include poor contact in the auxiliary contacts (e.g., normally closed contacts not opening or normally open contacts not closing), causing the green light to flash and the red light to remain off, or a broken wire in the closing circuit or a burnt-out red light.
   • Operational handle returning too early or operating voltage being too low (below 80% of the rated voltage).
2. Mechanical Faults:
   • Loose or detached linkage in the transmission mechanism.
   • Sticking of the closing solenoid.
   • Breaker mechanism not resetting to the pre-close position after opening.
   • Trip mechanism disengagement.
   • Excessive closing solenoid operating voltage, preventing the hook from latching.
   • Failure of the trip linkage to reset.
   • Mechanism jammed, with detached pivot pins causing the mechanism to fail to engage.
   • Repeated automatic opening and closing due to premature opening of the switch’s auxiliary normally closed contact.

2. Determination and Handling of “Refusal to Open” Failures

A “refusal to open” failure poses a significant threat to system safety. If a breaker refuses to open during a fault, it can lead to damage to electrical equipment or an upstream breaker tripping, causing a loss of power and a wide-scale blackout. Handling such failures involves the following steps:

1. Identify a “Refusal to Open” Incident: If symptoms include large-scale meter swings, significant voltage drops, and illuminated fault indicators with protection action signals, the breaker may have refused to open.
2. Manually Operate the Breaker: If the fault breaker is identified, attempt to manually trip the breaker. If the main transformer’s primary breaker shows a high current and intense noise without a clear fault, first trip the main supply breaker to prevent transformer damage. If a backup protection system has caused a power outage, identify the fault breaker and open it manually. If no specific fault is found, inspect all equipment within the outage area. Open all branch breakers and gradually reclose each one after restoring the main power breaker, identifying any breaker that causes the main breaker to trip again as the faulty one.
3. Examine and Repair the Breaker: If the issue is identified as an electrical fault, such as low control voltage or a faulty fuse, resolve these issues promptly. For more complex electrical or mechanical faults, contact dispatch for further action.

The following are common causes of refusal to open:

1. Electrical Causes:
   • Blown fuses or poor contact in the control circuit.
   • Faulty components in the tripping circuit, such as control switch contacts, breaker auxiliary contacts, anti-trip relays, or protective relay circuits.
   • Wiring faults or burnt-out trip coils.
   • Incorrect relay settings or low DC voltage (below 80% of rated voltage).
2. Mechanical Causes:
   • Insufficient trip coil impact force due to sticking or disengaged trip coil.
   • Welded or jammed contacts, and faults in the transmission mechanism, such as detached pins.

3. Determination and Handling of “Unintended Trip” Failures

An “unintended trip” occurs when a breaker opens without relay action and no short circuit or abnormal condition is present. Handling this typically involves three steps:

1. Identify an “Unintended Trip” Incident: If the breaker trips with normal meter and signal indications before the event, and after the trip, the green light flashes continuously, the red light is off, and all circuit indicators show zero, it can be identified as an unintended trip.
2. Check for Human Error: Assess if the trip was caused by accidental contact or mechanical vibrations. If so, rectify the issue and restore power immediately.
3. Examine Electrical and Mechanical Faults: If an immediate restoration is not possible due to electrical or mechanical issues, contact dispatch to arrange for the breaker to be taken out of service and repaired.

Common causes of unintended trips include:

1. Electrical Faults:
   • Misoperation or incorrect settings in protection systems, or faults in current or voltage transformer circuits.
   • Poor insulation in secondary circuits, or two-point grounding in the DC system causing false relay operations and signals, leading to a trip.
2. Mechanical Faults:
   • Failure to maintain the trip latch mechanism.
   • Improper adjustment of positioning screws causing the trip arm to be too high.
   • Deformed trip spring, insufficient tension, or damaged roller.
   • Large or improper slope on the trip arm or minimal contact area with the roller on the trip arm.

4. Determination and Handling of “Unintended Closing” Failures

“Unintended closing” occurs when a breaker closes without an operation command. Handling this generally involves:

1. Confirming Unintended Closing: If the operating handle is in the “off” position but the breaker is found closed with the red light flashing continuously, identify it as an unintended closing and open the breaker.
2. Further Investigation and Repairs: If the breaker recloses after being opened, remove the closing fuse and investigate electrical and mechanical causes. Contact dispatch for service and repair. Possible causes include:
   • Ground faults in the DC circuit causing the closing control circuit to complete.
   • Faults in the automatic reclosing relay components leading to unintended closing.
   • Low resistance in the closing contactor coil, and low starting voltage causing unintended closing due to DC system surges.

This detailed and technical approach ensures that faults are accurately identified and resolved to maintain the safety and reliability of the electrical system.