Fault Handling and Maintenance of Low-Voltage Intelligent Circuit Breakers

1. Common Fault Analysis and Handling of Low-Voltage Intelligent Circuit Breakers​

1. ​Failure of the Low-Voltage Circuit Breaker to Close​
   (1) ​Undervoltage Release Mechanism Failure Preventing Closing​
• Cause: Abnormal power supply voltage to the undervoltage release or a burnt-out undervoltage coil, resulting in the circuit breaker's inability to close.
• Analysis and Handling: The undervoltage release is the actuating component for undervoltage and loss-of-voltage protection. It operates when the coil is de-energized. Therefore, before closing, the undervoltage coil must be energized. If the undervoltage release is not connected to a power source or the supply voltage is below 85% of the standard value, it is considered abnormal, and the circuit breaker cannot close. A common fault is a burnt-out power module. A simple diagnostic method is to manually force the undervoltage release armature to engage while pressing the close button. If the circuit breaker closes and does not trip automatically, the issue is likely due to a faulty undervoltage release. If the undervoltage coil is burnt out, it must be replaced along with the power board or the entire undervoltage release.

(2) ​Energy Storage Mechanism Failure Preventing Closing​

• Cause: The energy storage motor fails to store energy, preventing the circuit breaker from closing automatically.
• Analysis and Handling: If the energy storage indicator light is off before closing, check the control power supply of the energy storage motor. Lack of voltage or excessively low voltage will prevent electric energy storage. Inspect the terminal block for proper contact. If the energy storage motor is burnt out, electric energy storage will also fail (normal resistance of the energy storage motor is approximately 86 ohms). If manual operation also fails to store energy, the fault lies within the energy storage mechanism itself. Check for issues at the connection points of the closing coil, shunt trip release, undervoltage release, and other accessories.

(3) ​Closing Solenoid Failure Preventing Closing​

• Cause: A burnt-out closing solenoid coil prevents the circuit breaker from closing.
• Analysis and Handling: Under normal conditions, after energy storage is complete, pressing the close button activates the closing solenoid, releasing the energy stored in the spring mechanism to close the circuit breaker. If the circuit breaker fails to close, inspect the closing solenoid coil for damage. If burnt out, replace it. Actual measurements of multiple circuit breakers show that the resistance of a normal closing coil ranges between 2.750 and 2.770 kΩ. The resistance values of the opening coil and undervoltage coil are similar.

(4) ​Reset Button of Smart Controller Not Timely Reset, Preventing Closing​

• Cause: The reset button of the smart controller pops out due to a fault and is not reset in time, preventing the circuit breaker from closing.
• Analysis and Handling: If the circuit breaker trips due to grid fluctuations or other reasons, the fault trip indicator/reset button of the smart controller pops out. Without pressing the reset button, the circuit breaker will mistakenly assume the fault persists and refuse to close, even after the fault is resolved. Check if the fault trip indicator/reset button is popped out. If so, press the reset button to restore normal closing. For smart controllers with fault memory功能, manually confirm that the fault is resolved, clear the fault memory, and press the reset button to close the circuit breaker normally.
1. ​Normal Closing but Frequent False Tripping​
• Symptom: The circuit breaker closes normally under no load but trips falsely under load, even with no faults, overload, or short circuit in the line. False tripping is more frequent and noticeable under light loads.
• Analysis and Handling: The circuit breaker closes normally under no load but fails to operate under load, primarily due to aging of the control unit causing false trips. The control unit of the smart controller is an electronic board with a semiconductor chip. The operational lifespan of semiconductors is 15–20 years, beyond which their performance becomes unstable. Additionally, the chip's power supply is provided by the circuit breaker's own current transformer. When the load is below 20%, the chip's power supply becomes unstable, increasing the likelihood of false trips.
2. ​Excessive Temperature Rise in Low-Voltage Circuit Breaker​
• Cause: Excessive reduction in contact pressure. Adjust the contact pressure or replace the spring. This issue may also arise from severe contact surface wear or poor contact, necessitating replacement of the circuit breaker. If the temperature rise is excessive due to loose connecting screws between conductive parts, tighten them securely.
3. ​Failure to Trip Normally​
• If the circuit breaker fails to trip when the current reaches the set value, check if the bimetallic strip of the thermal release is damaged. If damaged, replace it. Then, inspect the air gap between the armature and core of the electromagnetic release or check for coil damage. Adjust the armature-core distance or replace the circuit breaker. If the circuit breaker trips immediately when starting a motor, the instantaneous trip setting of the overcurrent release may be too low, or vibrations may have altered the setting. Adjust the instantaneous trip setting to the specified value. If components are damaged, replace the release.

​II. Current Status and Existing Issues​
As critical equipment in low-voltage distribution networks, low-voltage circuit breakers provide protection and energy distribution. They are categorized into thermal-magnetic and electronic types based on protection devices, and into current protection circuit breakers and leakage/current protection circuit breakers based on functionality. The current status and issues are as follows:

1. Thermal-magnetic circuit breakers offer only two-stage protection, with difficulty in accurately setting protection parameters. They are unsuitable for applications requiring differential protection, as false tripping can occur, expanding the scope of power outages.
2. After an overload fault, thermal-magnetic circuit breakers require a cooling period before reclosing. In high-temperature environments, power cannot be quickly restored.
3. Electronic circuit breakers currently fail to meet the requirements of low-voltage distribution network nodes. Their communication功能 is often limited by field conditions and remains largely unused.
4. Low-voltage circuit breakers lack sufficient measurement capabilities for precise monitoring of voltage, current, energy, and temperature. External current transformers and secondary devices are widely used in the field, increasing construction and maintenance costs.
5. Inconsistent communication interfaces and protocols for low-voltage circuit breakers result in lengthy wiring debugging cycles and unreliable communication.
6. Fierce market competition and low-cost promotions have led to uneven product quality and severe low-end trends in low-voltage circuit breakers.

​III. Operational Inspection and Maintenance of Low-Voltage Intelligent Circuit Breakers​

1. ​Operational Inspection​
   Routine inspections include:
• Verifying if the load current matches the rated current of the circuit breaker.
• Checking for damage or loosening of the arc chute and detecting discharge sounds caused by poor contact.
• Monitoring the undervoltage release coil for overheating or abnormal noises.
• Inspecting auxiliary contacts for signs of burning or erosion.
• Ensuring all component connection points are not overheating.
• Confirming that the indicator lights match the circuit's open/close status.
2. ​Operational Maintenance​
   Maintenance tasks include:
• Periodically lubricating moving parts.
• Regularly cleaning surface dust to maintain insulation levels.
• Inspecting the arc chute for severe burning, checking contact integrity, and verifying the arc wall for cracks after a short-circuit fault.
• Upon acquiring new circuit breakers, inspecting for damage, rust on exposed metal parts, or defects caused by improper transportation and storage. If any issues are found, contact the supplier immediately.

​Conclusion​
Low-voltage intelligent circuit breakers are compact, feature-rich, and provide precise protection against short circuits, overloads, and grounding faults. They ensure safe and reliable power supply and are widely used in systems below 3KV. As commonly used low-voltage main switches, intelligent circuit breakers require continuous learning and in-depth research to enhance fault analysis and resolution capabilities. This ensures timely and effective handling of various faults in practical work, guaranteeing normal and safe production operations.