Moulded Case Circuit Breakers (MCCBs) are used to distribute electrical energy and protect overloaded, short-circuited and under-voltage lines and supply equipment from damage. Their basic and important function is the correct operation and rapid troubleshooting of grid faults. Operational faults in MCCBs usually take the form of both dragging and malfunctioning. If a circuit breaker is dragged or malfunctioned, it poses a serious threat to the grid, amplifying the effects of an incident and potentially leading to a plant-wide blackout.

Causes of operational failure.

1. Defects in the operating mechanism

The operating mechanism mentioned includes electromagnetic mechanism, spring mechanism and hydraulic mechanism. For electromagnetic and spring mechanisms, the main cause of mechanical failure of the mechanism is the inflexible jamming of the mechanism. Another cause is improper adjustment of the pins. For the hydraulic mechanism, the mechanical failure is mainly due to poor sealing, so it is particularly important to ensure the reliability of the sealing of the high oil pressure components.

2. Mechanical defects of the body of the plastic case circuit breaker

Defects affecting the operation of the circuit breaker body, which mainly include damage to the porcelain bottle, connecting different parts of the loose, damaged parts products and foreign objects stuck, etc..

3. Operating (control) power failure

Insufficient working voltage is a common defect of the operating power supply. The main reason for this is that the power supply after silicon rectification uses AC power supply. When a fault occurs in the system, the voltage of the power supply is greatly reduced, or although a battery pack is available, the voltage drop of the operating power supply to the circuit breaker connection is too great, making the actual operating voltage lower than the lower limit. An example is a substation where a circuit breaker explodes on reclosing due to a fault in the distribution line.

Corresponding preventive measures.

1. Regular maintenance of the electromagnetic and spring mechanisms to prevent jamming and damage to parts.

2. Tighten the screws at the latches to prevent faults such as whether the screws are loose or dislocated.

3. Ensure the sealing performance of high oil pressure parts

4. Check whether the auxiliary switch, micro switch is intact to prevent the auxiliary switch from not switching or poor contact causing the operating coil to burn and refuse to start.

5. Timely overhaul and replacement of different parts of the link

6. New substations are recommended to use battery and storage type as a kind of operating system power supply.