Causes and Preventive Measures for Burnt Circuit Breaker Opening and Closing Coils

The circuit breaker is a type of load switch with short-circuit and overload protection functions. The short-circuit protection function is realized by an electromagnetic coil. Because of its complete protection functions, easy maintenance and use, it is widely used in power systems. This article introduces the causes and preventive measures of circuit breaker opening and closing coil burnout.

Reasons why the opening coil is burned out

1. Mechanical failure of the opening electromagnet. The loosening of the coil causes the electromagnet to shift when the circuit breaker is opened, causing the iron core to become stuck, causing the coil to burn out; or due to the short moving stroke of the iron core, when the power supply of the opening circuit is turned on, the iron core does not open the tripping mechanism, causing the coil to be energized for a long time. burn.

2. The circuit breaker refuses to break. When the control circuit is normal, faults in the circuit breaker that refuse to open are all problems with the linkage mechanism. For example, if the apex is improperly adjusted, the force of the ejector rod of the circuit breaker's opening core cannot cause the mechanism to trip in time; or the protective locking mechanism does not act, resulting in the failure of the circuit breaker. The coil is overloaded, causing the opening coil to burn out.

3. The stroke of the auxiliary switch in the open state is improperly adjusted. When the circuit breaker is in the open state, the auxiliary switch should be adjusted to be within the travel range of the open state. However, when adjusting parameters such as the opening distance and overtravel of the circuit breaker, the initial state of the circuit breaker opening is not adjusted accordingly, which will cause the auxiliary switch to be unable to switch the opening circuit normally, causing the opening coil to burn out.

4. Improper use of auxiliary switch contacts of the opening control circuit. When the closing time of the circuit breaker is extremely short, much less than the opening time of the circuit breaker, the circuit breaker will be closed before it has time to trip. At this time, the delay function of the delay contact will be meaningless. On the contrary, during the opening process of the delay contact, due to the small insulation gap between the dynamic and static contacts of the auxiliary switch, arcing often occurs, which will burn the contacts of the auxiliary switch, and then cause the opening coil to burn.

5. Protection control device failure. The opening command is issued by the protection control device. If the opening relay in the device fails, or the auxiliary switch contact action stroke of the opening control loop is large, causing the opening command to not be exited in time, the opening coil will become long. Time is electrified and burned.

6. The resistance of the opening circuit is too large. The insulation of the opening coil loop is reduced, or the control loop path is too small, causing the resistance to be too large, resulting in a large voltage drop in the opening control loop, causing the voltage to fail to reach the value of the coil opening action, causing the opening coil to be charged for a long time and burned out. .

Measures to prevent the opening coil from burning out

1. Change the delayed moving and closing contacts of the opening circuit to a pair of moving and closing contacts, frequently check the contacts of the auxiliary switch and the arm screws of the auxiliary switch, and correctly adjust the position of the auxiliary switch to ensure that the auxiliary switch is in contact with the open circuit. The opening and closing positions of the device must be coordinated correctly and effectively.

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

3. The opening command time issued by the protection control device must not only enable the opening coil to operate, but also be able to exit the opening command within a short period of time.

4. During the annual maintenance work, the connecting rod mechanism of the circuit breaker should be correctly adjusted, and the free tripping of the circuit breaker should be checked frequently to see if it is normal and whether it can be reliably maintained between 30% and 65% of the rated voltage during the low-voltage action test. Trip.

The reason why the closing coil is burned out

1. Circuit breaker mechanism failure. When the circuit breaker closing control circuit is normal, the internal conductive rods and transmission connecting rods of the circuit breaker body are stuck, or the circuit breaker operating mechanism has poor connection and coordination, or the protective locking interlocking mechanism has not acted, and the apex is adjusted skewed. High, causing the circuit breaker to refuse to close, overloading the closing core, and causing the closing coil to burn out.

2. The auxiliary switch stroke position is improper. During normal closing, the coil circuit of the closing contactor of the circuit breaker is connected in series with the dynamic breaking delay contact of the auxiliary switch. After closing, the auxiliary switch contact automatically cuts off the closing circuit. The auxiliary contact cannot open or arcs. The closing contactor is self-maintained through the reclosing circuit or the green light circuit. The closing coil is charged for a long time and is burned.

3. Protection control device failure. The closing command is issued by the protection control device. If the closing relay in the protection device fails, or the action stroke of the auxiliary switch contact of the closing control loop is long, causing the closing command not to be exited in time, the closing coil will be Burned out if charged for a long time.

4. Closing contactor failure. When the circuit breaker is closed, due to the relatively large closing current, the control loop cannot directly control the closing coil and can only indirectly connect the closing coil through the closing contactor. Therefore, when the closing contactor fails, it cannot be disconnected in time. , causing the closing coil to be energized for too long and burning the coil. In addition, the coil resistance of the closing contactor increases, which will cause the closing contactor to have insufficient suction force when it is normally energized, causing the main contact to arc, and the contact resistance of the main contact of the closing contactor to increase, indirectly affecting the circuit breaker. The excitation current of the closing coil makes the excitation strength of the closing coil insufficient, the iron core cannot operate normally, and the closing coil is overloaded and burned out.

5. The closing power supply capacity decreases or the wire resistance of the closing control circuit is too large, causing the voltage at both ends of the closing coil to be lower than 80% of the rated voltage at the closing moment and burnt out.

Measures to prevent closing coil from burning

1. Strengthen the inspection and maintenance of closing contactors. During every minor repair and periodic overhaul, the surface contact area and contact pressure of the moving and static contacts must be checked.

2. Adjust the position of the auxiliary switch.

3. The closing command time issued by the protection control device can be enough to make the closing coil work, and the closing command can be exited within the specified time.

4. The attendant is required to remove the control circuit fuse and open the reclosing switching circuit before allowing work to avoid burning the closing coil during maintenance and testing.

HZ-2009 Circuit Breaker Characteristic Tester