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Molded case circuit breaker is used to distribute electric energy and protect lines and power supply equipment from overload, short circuit, undervoltage and other faults. Its basic and important function is to act correctly and quickly remove power grid faults. The operation failure of molded case circuit breaker is usually manifested in the following two forms: drag and misoperation. If the circuit breaker is dragged or misoperated, it will pose a serious threat to the power grid, expand the impact scope of the accident, and may also cause power failure of the whole plant.

Causes of operation failure:

1. Defect of operating mechanism.

The operating mechanism includes electromagnetic mechanism, spring mechanism and hydraulic mechanism. For electromagnetic and spring mechanisms, the main cause of mechanical failure is jamming and inflexibility. Another reason is improper adjustment of the latch. For the hydraulic mechanism, its mechanical failure is mainly caused by poor sealing, so it is particularly important to ensure the reliable sealing of high oil pressure parts.

2. Mechanical defects of molded case circuit breaker body

The defects that cause the failure of the circuit breaker include porcelain bottle damage, loose connection parts, parts damage, foreign matter jamming and so on.

3. Operation (control) power supply defect

In the defects of operating power supply, insufficient operating voltage is a common defect. Most of the reasons are that the power station uses AC power supply as the operating power supply after silicon rectification. In case of system failure, the power supply voltage is greatly reduced, or although there is a battery pack, the voltage drop of the connecting line from the operating power supply to the circuit breaker is too large, so that the actual operating voltage is lower than the specified lower limit. For example, a substation has a fault due to a distribution line, and the circuit breaker explodes when reclosing.

Corresponding preventive measures:

1. Regularly maintain the electromagnetic and spring mechanism to prevent jamming and parts damage.

2. Tighten the screw at the locking buckle to prevent screw loosening, displacement and other faults.

3. Ensure the tightness of high oil pressure parts

4. Check whether the auxiliary switch and microswitch are intact to prevent the operating coil from burning out and refusing to move due to non switching or poor contact of the auxiliary switch.

5. Timely repair and replace the parts at the link

6. It is recommended to use battery and energy storage type as operating power supply for the new substation.