I. cause analysis of open circuit coil burn of molded case circuit breaker

    1. Mechanical failure of open electromagnet. When the coil is loose, the iron core of the electromagnet moves when the breaker is disconnected, the iron core is stuck, and the coil is burnt; or because the active stroke of the iron core is short, when the power of the opening circuit is connected, the top of the iron core will not open the tripping mechanism, so that the coil is energized for a long time, causing combustion.

    2. When the control circuit of circuit breaker misoperation is normal, the linkage mechanism causes the failure of circuit breaker misoperation. Improper adjustment of dead point makes the mechanism unable to release in time, overload the coil and burn the opening coil.

    3. The stroke adjustment of the auxiliary switch in the open circuit state is improper. The auxiliary switch shall be adjusted within the stroke range of the opening state of the circuit breaker. However, when the parameters such as opening distance and override are adjusted, the initial state of opening will change. If no corresponding adjustment is made, the auxiliary switch will not be able to switch the opening circuit normally, resulting in the burnout of the opening coil.

    4. Improper use of auxiliary switch contacts in open circuit control circuit. However, when the closing time of the circuit breaker is very short, it is far less than the opening time of the circuit breaker. When the circuit breaker is not in time, the circuit breaker is in the closed position. At this time, the delay contact delay effect of the switch control circuit will be lost. On the contrary, due to the small insulation gap between the dynamic and static contacts of the auxiliary switch, arcing often occurs, which burns out the contacts of the auxiliary switch and causes the opening coil to burn out.

    5. The protection control device fails. The distributor command is issued by the protection control device. If the diverter relay in the device fails, or the auxiliary switch contact of the diverter control circuit moves greatly, which causes the diverter command not to exit in time, the diverter coil will be charged for a long time. And then it was burned

    6. The open circuit resistance is too high. The circuit insulation of the switch coil is reduced, or the circuit resistance is too small, which leads to the voltage attenuation of the switch circuit and the control voltage can not reach the switching voltage action value of the coil. The switch coil takes a long time to charge, and the coil is burnt out.

    Molded case circuit breaker to prevent winding coil from breaking

    1. Change the delay action closing contact of the open circuit circuit to a pair of common normally open contacts, frequently check the contact of the auxiliary switch and the crank arm screw of the auxiliary switch, and correctly adjust the position of the auxiliary switch. Make the opening and closing positions of auxiliary switch and circuit breaker correct and effective.

    2. Fix the switch coil and check whether the core of opening coil is stuck.

    Three. The closing command time sent by the protection control device can make the closing coil fully work, and can close the turn of the closing command within the specified time.

    4. In the annual maintenance work, the connecting rod mechanism of the circuit breaker shall be adjusted correctly, whether the free tripping of the circuit breaker is normal, and whether it can reliably trip between 30% and 65% of the rated voltage during the low-voltage operation test.

    3. The cause of the burning out of the closed coil of the plastic case circuit.

    1. When the switch control circuit of the circuit breaker is normal, the internal conducting pole of the circuit breaker body is not well blocked due to the mismatching of the working mechanism of the circuit breaker, the transmission connecting rod, etc. due to the improper operation of the protection locking interlock mechanism, the protection locking interlock mechanism cannot open the circuit breaker, so the closing coil is burnt due to the overload of the closing iron core.

    2. The travel position of auxiliary switch is improper. When the breaker is normally closed, the coil circuit of the breaker contactor is connected in series with the dynamic fracture delay contact of the auxiliary switch. After closing, the helper switch contacts automatically cut off the closing circuit, and the auxiliary contacts cannot be opened or arced. The closing contactor insists on itself through the reclosing circuit or the green light circuit, and the closing coil is charged for a long time and burned.

    3. Protection control failed. When the protection control device sends the opening command, if the switch relay in the device fails or the auxiliary switch contact of the sub gate control circuit has a large operating stroke, the opening command cannot be withdrawn in time, and the switch coil can be charged and burnt for a long time.

    4. Closing contactor fault. When the circuit breaker is closed, due to the large closing current, the control circuit can not directly control the closing coil, only indirectly connect the closing coil through the closing contactor. Therefore, when the closing contactor fails, it cannot be opened in time, so that the opening time of the closing coil is too long and the coil is burnt. In addition, if the coil resistance of the closing contactor becomes larger, it will make the closing contactor lack of suction force when it is normally energized, the main contact will produce arcing, and the contact resistance of the main contact of the closing contactor will increase, which will indirectly affect the excitation current of the closing coil of the circuit breaker, so that the excitation force of the closing coil is insufficient, the iron core cannot operate normally, and the closing coil is overloaded and burnt.

    5. The capacity of the closed power supply is reduced. In other words, the conductor resistance of the closed control circuit is large, so that the voltage at both ends of the closed coil is lower than 80% of the rated voltage at the moment of closing, and is burnt.

    IV. measures to prevent the closing coil of molded case circuit breaker from burning out

    1. Strengthen the inspection and maintenance of closing "contactor". The contact area and contact pressure of dynamic and static contact surfaces shall be checked for each minor repair and regular maintenance.

    2. Adjust the position of auxiliary switch correctly.

    3. The shutdown command time sent by the protection control device can not only work with the switch coil, but also exit the opening command in a short time.

    4. The operator on duty must remove the control circuit fuse and open the reclosing switch circuit before permission to work, so as to avoid burning the closing coil during inspection and test.