Four Common Faults and Handling Methods for Low-Voltage Circuit Breakers

(1) Fault Phenomenon: Circuit breaker fails to close.​​
Possible causes and handling methods are as follows:

The failure to close is mainly due to two reasons: electrical faults and mechanical issues.

​Electrical faults mainly include the following:​​

1. If both the red and green indicator lights are off before the closing operation, it indicates an open circuit in the control loop or a lack of control power. Check the control power supply and the components in the entire control loop for abnormalities.
2. If the red light remains off, the green light flashes, and the alarm sounds after the closing operation, it indicates a mismatch between the handle position and the circuit breaker position, meaning the circuit breaker has not closed. Possible causes:
• The fuse in the closing circuit is blown or has poor contact → Replace the fuse.
• The closing coil is faulty → Replace the coil.
3. If the green light goes off and the red light turns on after the closing operation, but the red light goes off instantly, the green light flashes, and the alarm sounds, it indicates that the circuit breaker closed but tripped automatically. This may be due to the circuit breaker closing on a faulty line, causing protective relay operation, or a mechanical fault preventing the circuit breaker from remaining closed.
4. If the green light goes off after the closing operation, but the red light remains off while the ammeter shows a reading, it indicates that the circuit breaker has closed. Possible causes:
• Poor contact of the circuit breaker auxiliary contacts or control switch contacts.
• An open trip coil disrupting the circuit.
• A blown control circuit fuse.
• A damaged indicator bulb.

​Mechanical faults mainly include the following:​​

1. Loose or detached transmission linkage.
2. Jamming of the closing iron core.
3. The mechanism not resetting after the circuit breaker trips.
4. Trip mechanism disengagement.
5. The closing spring in the spring-operated mechanism not storing energy.
6. The trip linkage not resetting.
7. The trip latch not engaging, or the trip four-bar linkage not adjusted beyond the dead center, preventing the circuit breaker from remaining closed.
8. In some cases, the circuit breaker repeatedly opens and closes multiple times during closing, indicating that the auxiliary normally closed contacts open too early.

​Handling methods:​​

1. Reattempt closing using the control switch to check if the previous failure was due to improper operation (e.g., releasing the control switch too quickly).
2. Inspect various parts of the electrical circuit to determine if there is an electrical fault. Specific steps:
• Check if the closing control power supply is normal.
• Inspect the closing control circuit and closing fuse for proper condition.
• Check the contacts of the closing contactor (e.g., for electromagnetic operating mechanisms).
• Move the control switch to the "closing" position and observe if the closing iron core operates (similar checks apply to hydraulic, pneumatic, and spring mechanisms). If the closing iron core operates normally, the electrical circuit is functioning properly.
3. If the electrical circuit is normal but the circuit breaker still fails to close, it indicates a mechanical fault. The circuit breaker should be taken out of service, and relevant personnel should be notified for maintenance. Based on the above preliminary checks, it can be determined whether the fault is electrical or mechanical.

​​(2) Fault Phenomenon: Circuit breaker fails to trip.​​
Possible causes and handling methods are as follows:

A circuit breaker's failure to trip poses a significant threat to system safety. If a circuit breaker fails to trip during a fault, it may cause the upstream circuit breaker to trip, resulting in "over-tripping."

1. If the main transformer power supply circuit breaker’s ammeter shows a full-scale reading and abnormal noises are loud, disconnect the circuit breaker power supply to prevent damage to the main transformer, before identifying the faulty circuit breaker.
2. If a backup protection operation causes a power outage:
• If branch protection operates but the circuit breaker fails to trip, disconnect the faulty circuit breaker and restore the upstream power supply breaker.
• If no branch protection operates (possibly due to protection failure), inspect the equipment within the outage range for faults. If no faults are found, disconnect all branch circuit breakers, restore the power supply breaker, and attempt to close each branch circuit breaker one by one. If the power supply breaker trips again when closing a specific branch, that circuit breaker is identified as the faulty one. Isolate it and restore power to other circuits.
3. When inspecting a circuit breaker that fails to trip, if the issue is not easily resolvable (e.g., low control power voltage, poor fuse contact, or blown fuse), contact the dispatcher to take the circuit breaker out of service for maintenance.

​​(3) Fault Phenomenon: Circuit breaker trips erroneously.​​
Possible causes and handling methods are as follows:

The main reasons for erroneous tripping are electrical faults and mechanical issues.

​Electrical faults mainly include:​​

1. Protection relay maloperation or incorrect settings, or faults in the current or voltage transformer circuits.
2. Poor insulation in the secondary circuit or a two-point ground fault in the DC system (occurring in the trip circuit).

​Mechanical faults mainly include:​​

1. Failure of the closing maintenance bracket and trip latch to hold, causing a trip.
2. Poor sealing or leakage in the hydraulic mechanism’s primary trip valve and check valve. Under normal conditions, the closing maintenance port supplies oil to the upper part of the secondary valve to keep the circuit breaker closed. If oil leakage exceeds the replenishment rate, a pressure difference forms between the upper and lower parts of the secondary valve. When the pressure above the secondary valve is lower than below, the secondary valve returns, releasing high-pressure oil from the closing chamber of the working cylinder, causing an "erroneous trip."

​Handling methods:​​

1. If the trip is caused by human error, accidental operation, or external vibration affecting the protection panel, eliminate the cause and restore power immediately.
2. For other electrical or mechanical faults that cannot be resolved immediately, contact the dispatcher and relevant personnel to take the circuit breaker out of service for maintenance.

​​(4) Fault Phenomenon: Circuit breaker closes erroneously.​​
Possible causes and handling methods are as follows:

​Causes of erroneous closing:​​

1. A two-point ground fault in the DC system, energizing the closing control circuit.
2. Misclosure of the automatic reclosing relay’s normally open contacts or other components energizing the control circuit, causing erroneous closing.
3. If the closing contactor coil resistance is too low and its operating voltage is insufficient, transient pulses in the DC system may cause "erroneous closing."
4. Unreliable latching of the energy storage spring in a spring-operated mechanism. Under vibration (e.g., during tripping), the latch may disengage automatically, causing the circuit breaker to close on its own.

​Handling methods:​​

1. If the handle is in the "trip" position but the red light flashes continuously, it indicates that the circuit breaker has closed erroneously.
2. Open the erroneously closed circuit breaker.
3. If the circuit breaker closes again after being opened, remove the closing power supply, inspect both electrical and mechanical aspects, and contact the dispatcher and relevant personnel to take the circuit breaker out of service for maintenance.