Protective devices and methods for preventing adhesion of main contacts in AC contactors

Abstract

This invention discloses a protection device and method for AC contactor main contact adhesion, including a first three-phase voltage detection unit for the incoming power supply and a second three-phase voltage detection unit for the lower end of the contactor. The first and second three-phase voltage detection units are connected to a remote cabinet communication board via an RS485 interface and a Modbus RTU communication bus. Additionally, a trip control circuit and a PLC control program are included. This invention provides a protection device and method for AC contactor main contact adhesion. When adhesion of the contactor main contacts is detected, the shunt trip coil of the main circuit breaker is energized and tripped, preventing the coil from engaging under adhesion conditions. The three-phase voltage at the lower end of the contactor is detected; if it exceeds a set value, the program issues a shunt trip command to the circuit breaker, effectively preventing abnormal energization and equipment malfunction caused by any phase adhesion of the main contacts after the AC contactor coil is de-energized. The trip control circuit has a self-test function.

Description

Technical Field

[0001] This invention relates to the field of protective devices for contact adhesion, and more specifically, to a protective device and method for the adhesion of main contacts of an AC contactor. Background Technology

[0002] Contactors are divided into AC contactors (voltage AC) and DC contactors (voltage DC), and they are used in power, power distribution, and power consumption applications. In a broader sense, a contactor is an electrical device in industrial electricity that uses the magnetic field generated by current flowing through a coil to close contacts, thereby controlling the load.

[0003] In industrial enterprises, there are a large number of AC contactor control devices. For some frequently operating equipment, the main contacts of the AC contactor, the moving and stationary contacts, work under heavy load and high current for a long time. The contact material is severely consumed or even completely consumed, the contact overtravel is reduced, the contact pressure is reduced or even fails to connect, resulting in increased contact resistance. At the same time, the mechanism may jam, which may also lead to poor contact between the moving and stationary contacts. All of these can cause arcing between the moving and stationary contacts of the contactor, which may cause serious consequences such as contact adhesion, and can cause fatal injuries to equipment and personnel.

[0004] Existing technologies for preventing AC contactor sticking often employ methods such as connecting AC contactors in series or using a relay at the lower end of the contactor for detection. Using contactors requires significant space, especially since contactors with high switching currents are often quite large. Using relays carries the risk of the relay itself failing to detect contact sticking in a timely manner if it malfunctions. Summary of the Invention

[0005] In view of the problems in related technologies, the present invention proposes a protective device and method for the adhesion of main contacts of AC contactors, so as to overcome the above-mentioned technical problems existing in the existing related technologies.

[0006] The technical solution of this invention is implemented as follows:

[0007] A control method for a protective device to prevent the main contacts of an AC contactor from sticking together, characterized in that: the device includes a first three-phase phase voltage detection unit (1), a second three-phase phase voltage detection unit (2) and a trip control circuit, the first three-phase phase voltage detection unit (1) is connected to the three-phase lines L1, L2, L3 and the neutral line N of the incoming power supply, the second three-phase phase voltage detection unit (2) is connected to the lower end of the contactor, the first three-phase phase voltage detection unit (1) and the second three-phase phase voltage detection unit (2) are connected to the CP341 communication board (3) in the PLC remote cabinet through the RS485 interface and the Modbus RTU communication bus;

[0008] The three-phase lines L1, L2, and L3 are connected to the main circuit circuit breaker QF1, which is connected to the forward and reverse AC contactors KM1 and KM2 respectively via wires.

[0009] The lower end of the reverse AC contactor KM2 is equipped with overheat protection FR1, and the output of overheat protection FR1 is connected to the three-phase AC motor M.

[0010] The control circuit is AC 220V. The trip control circuit includes the normally open contact QF1-1 of the main circuit circuit breaker set in series, the normally open contact K3-1 of the shunt trip protection 24V DC relay K3 controlled by PLC, and the shunt trip coil QS.

[0011] When the main circuit breaker QF1 is closed, the normally open contact QF1-1 of the main circuit breaker closes. After the shunt trip coil QS is energized, the main circuit breaker QF1 trips. The normally open contact QF1-1 of the main circuit breaker disconnects the trip coil circuit to prevent the trip coil from being damaged by long-term energization.

[0012] The normally closed contact K1-2 of the 24V DC relay K1 for forward rotation of the voltage machine, the normally closed contact K2-2 of the 24V DC relay K2 for reverse rotation of the motor, and the normally open contact OUT2-1 of the overvoltage protection alarm of the second and third phase voltage detection unit (2) at the lower end of the contactor are connected in series and then in parallel to the two ends of the normally open output point K3-1.

[0013] The series circuit connects one end of the trip coil, and the other end of the trip coil is connected to the other end of the 220V power supply (53); the normally open test button SB1 for the trip circuit is also connected in parallel with K3-1;

[0014] The first three-phase phase voltage detection unit (1) and the second three-phase phase voltage detection unit (2) are powered by AC 220V. The first three-phase phase voltage detection unit (1) and the second three-phase phase voltage detection unit (2) provide undervoltage OUT1 and overvoltage OUT2 protection alarm outputs. By setting the overvoltage value of the second three-phase phase voltage detection unit (2) at the lower end of the contactor, the corresponding overvoltage protection alarm normally open contact OUT2-1 is associated.

[0015] One end of the AC 220V working power supply is connected to the miniature circuit breaker QF2; the normally closed contact FR1-1 of the overheat protection in the main circuit is connected in series with the normally closed contact K3-2 of the DC 24V shunt trip relay, and then connected in series with the normally open contact of the emergency stop button associated with the operation site. When the emergency stop button is not pressed, the emergency stop relay is energized and the normally open contact is closed.

[0016] The normally open contact K1-1 of the forward 24V DC relay is connected in series with the normally closed contact KM2-1 of the reverse contactor and the coil (60) of the forward AC contactor KM1 to form a series circuit one. The normally open contact K2-1 of the reverse 24V DC relay is connected in series with the normally closed contact KM1-1 of the forward contactor and the coil (62) of the reverse AC contactor KM2 to form a series circuit two. Series circuit one and series circuit two are connected in parallel. One end of the parallel circuit is connected to the normally open contact of the emergency stop, and the other end is connected to the other end (53) of the 220V power supply.

[0017] The method includes the following steps:

[0018] S1: The system is powered on, the PLC is running, the first three-phase phase voltage detection unit (1) and the second three-phase phase voltage detection unit (2) are initialized and set, and the main circuit circuit breaker QF1 and the control circuit miniature circuit breaker QF2 are closed.

[0019] S2: When the PLC program does not issue a contactor operation command, and the main power supply, circuit breaker, and control power supply are closed, the coils of the main circuit contactor and the control circuit relay are all de-energized. At this time, the three-phase voltage detection device at the lower end of the main circuit contactor detects that any one phase voltage is greater than the overvoltage setting value set on the three-phase voltage detection device. The associated overvoltage alarm normally open contact closes, the shunt trip coil of the main circuit circuit breaker is energized, and the circuit breaker shunt trips.

[0020] S3: The PLC collects and analyzes the phase voltage values ​​of the three-phase phase voltage detection device on the incoming power cabinet and the voltage values ​​at the lower end of the contactor. When the system program issues a stop command, the running relay and AC contactor coil are de-energized. The program avoids the possible asynchronous disconnection of the contactor main contacts and delays for a set time. If the phase voltage at any phase at the lower end of the contactor is detected to be greater than the set value, a circuit breaker shunt trip action command is issued. The shunt trip DC 24V relay is energized, the auxiliary contacts close the shunt trip coil circuit, the circuit breaker shunt trips and gives an alarm signal.

[0021] S4: After receiving the circuit breaker trip feedback signal, the PLC will no longer allow the operation command to be issued. The contactor will only be allowed to run again after the fault is cleared, the circuit breaker is reset, and the alarm is cleared.

[0022] The above technical solution has the following advantages or beneficial effects:

[0023] 1. This invention provides a protective device and method for the adhesion of the main contacts of an AC contactor. When the adhesion of the main contacts of the contactor is detected, the shunt trip coil of the main circuit breaker is energized and tripped, thus preventing the coil from engaging when the main contacts of the contactor are stuck.

[0024] 2. This invention provides a protection device and method for the adhesion of main contacts of an AC contactor. The phase voltage value is simultaneously sent to the CP341 communication board 3 of the PLC controller via communication. The PLC analyzes and compares the phase voltage parameters. After the program issues a stop command, it detects the three-phase voltage at the lower end of the contactor. If the voltage exceeds the set value, the program issues a shunt trip command for the circuit breaker. This can effectively prevent any phase of the main contacts from sticking together after the AC contactor coil is de-energized, which could cause abnormal energization at the lower end of the contactor and equipment malfunction.

[0025] 3. This invention provides a protection device and method for the adhesion of main contacts of AC contactors. It effectively avoids the uncontrolled situation where the PLC issues a stop command but the contactor fails to respond due to contact adhesion of the 24V DC relays in the forward and reverse rotation of the control circuit. Simultaneously with issuing the shunt trip command of the main circuit breaker, the system promptly provides a fault alarm signal to remind maintenance personnel.

[0026] 4. This invention provides a protection device and method for the adhesion of the main contacts of an AC contactor. For the shunt trip circuit, a test button SB1 is provided. When the main circuit and control circuit are powered normally and the circuit breaker is closed, the trip coil and trip circuit can be tested to see if they are normal. It also has a diagnostic function for the abnormal adhesion of the normally open contacts of the 24V shunt trip DC relay. When the normally open contacts are abnormally adhered, the main circuit circuit breaker trips. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is an overall schematic diagram of a protection device for the adhesion of main contacts of an AC contactor according to an embodiment of the present invention.

[0029] Figure 2 According to an embodiment of the present invention, the main circuit breaker and contactor status feedback signal of the protection device for the main contact adhesion of the AC contactor are sent to the PLC;

[0030] Figure 3 This is a PLC signal diagram of a protection device for the adhesion of main contacts of an AC contactor according to an embodiment of the present invention.

[0031] Figure 4 This is a flowchart illustrating the operation of a protective device for the adhesion of main contacts of an AC contactor according to an embodiment of the present invention.

[0032] In the diagram: 1. First three-phase phase voltage detection unit; 2. Second three-phase phase voltage detection unit; 3. CP341 communication board. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0034] See appendix Figure 1-4 The following describes a control method for a protective device to prevent the main contacts of an AC contactor from sticking together. The device includes a first three-phase voltage detection unit 1, a second three-phase voltage detection unit 2, and a tripping control circuit. The first three-phase voltage detection unit 1 is connected to the three-phase power lines L1, L2, L3 and the neutral line N. The second three-phase voltage detection unit 2 is connected to the lower end of the contactor. The first three-phase voltage detection unit 1 and the second three-phase voltage detection unit 2 are connected to the CP341 communication board 3 in the PLC remote cabinet via an RS485 interface and a Modbus RTU communication bus.

[0035] After connecting to the 220V AC power supply, the three-phase voltage values ​​on the power supply side and the load side at the lower end of the contactor can be collected in real time. The voltage detection unit provides undervoltage OUT1 and overvoltage OUT2 protection alarm outputs. The overvoltage protection value of the second three-phase voltage detection unit 2 is set to 15V AC.

[0036] The three-phase lines L1, L2, and L3 are connected to the main circuit circuit breaker QF1, which is connected to the forward and reverse AC contactors KM1 and KM2 respectively via wires.

[0037] The lower end of the reverse AC contactor KM2 is equipped with overheat protection FR1, and the output of overheat protection FR1 is connected to the three-phase AC motor M.

[0038] The control circuit is AC 220V. The trip control circuit includes the normally open contact QF1-1 of the main circuit circuit breaker set in series, the normally open contact K3-1 of the shunt trip protection 24V DC relay K3 controlled by PLC, and the shunt trip coil QS.

[0039] When the main circuit breaker QF1 is closed, the normally open contact QF1-1 of the main circuit breaker closes. After the shunt trip coil QS is energized, the main circuit breaker QF1 trips. The normally open contact QF1-1 of the main circuit breaker disconnects the trip coil circuit to prevent the trip coil from being damaged by long-term energization.

[0040] The normally closed contact K1-2 of the 24V DC relay K1 for forward rotation of the voltage machine, the normally closed contact K2-2 of the 24V DC relay K2 for reverse rotation of the motor, and the normally open contact OUT2-1 of the overvoltage protection alarm of the second and third phase voltage detection unit 2 at the lower end of the contactor are connected in series and then in parallel to the two ends of the normally open output point K3-1.

[0041] The series circuit connects one end of the trip coil, and the other end of the trip coil is connected to the other end 53 of the 220V power supply; in parallel with K3-1 is the normally open test button SB1 for the trip circuit;

[0042] The first three-phase phase voltage detection unit 1 and the second three-phase phase voltage detection unit 2 operate on AC 220V. The first three-phase phase voltage detection unit 1 and the second three-phase phase voltage detection unit 2 provide undervoltage OUT1 and overvoltage OUT2 protection alarm outputs. By setting the overvoltage value of the second three-phase phase voltage detection unit 2 at the lower end of the contactor, the corresponding overvoltage protection alarm normally open contact OUT2-1 is associated.

[0043] One end of the AC 220V working power supply is connected to the miniature circuit breaker QF2; the normally closed contact FR1-1 of the overheat protection in the main circuit is connected in series with the normally closed contact K3-2 of the DC 24V shunt trip relay, and then connected in series with the normally open contact of the emergency stop button associated with the operation site. When the emergency stop button is not pressed, the emergency stop relay is energized and the normally open contact is closed.

[0044] The normally open contact K1-1 of the forward 24V DC relay is connected in series with the normally closed contact KM2-1 of the reverse contactor and the coil 60 of the forward AC contactor KM1 to form a series circuit one. The normally open contact K2-1 of the reverse 24V DC relay is connected in series with the normally closed contact KM1-1 of the forward contactor and the coil 62 of the reverse AC contactor KM2 to form a series circuit two. Series circuit one and series circuit two are connected in parallel. One end of the parallel circuit is connected to the normally open contact of the emergency stop, and the other end is connected to the other end 53 of the 220V power supply.

[0045] When the main circuit circuit breaker QF1 and the control circuit miniature circuit breaker QF2 are closed, and the PLC has not issued a contactor operation command, the coils of the main circuit AC contactors KM1 and KM2 and the control circuit 24V DC relays K1 and K2 are all de-energized, and the corresponding normally closed contacts K1-2 and K2-2 are closed. At this time, the second and third phase voltage detection unit 2 at the lower end of the contactor detects that any one phase voltage is greater than the overvoltage setting value of 15V set on the second and third phase voltage detection unit 2. The overvoltage alarm normally open output point OUT2-1 closes, the shunt trip coil QS of circuit breaker QF1 is energized, and circuit breaker QF1 trips. To prevent maloperation caused by asynchrony when the main circuit contactors are disconnected, the delay time of the alarm output OUT2-1 on device 2 can be set to about 80ms. Normally, it waits for the PLC to issue a contactor operation command.

[0046] The phase voltage values ​​of the first three-phase phase voltage detection unit 1 and the phase voltage values ​​of the second three-phase phase voltage detection unit 2 at the lower end of the contactor are connected to the CP341 communication board 3 in the PLC field ET200 cabinet via Modbus RTU communication. During normal operation, when a stop command is issued in the program, the coils of the running relays K1 or K2 and the main circuit contactors KM1 or KM2 are de-energized. The program avoids the possibility of asynchronous disconnection of the main contacts of the main circuit AC contactor. After a delay of 80ms, if any phase voltage at the lower end of contactor KM1 or KM2 is detected to be greater than the set value of AC 15V, a shunt trip command for the main circuit circuit breaker QF1 is issued. The shunt trip DC 24V relay K3 is energized, the auxiliary normally open contact K3-1 closes the shunt trip coil circuit, the shunt trip coil QS is energized, the circuit breaker QF1 shunt trips, and an alarm signal is issued. After receiving a circuit breaker trip feedback signal, the PLC will no longer authorize the issuance of operation commands. The contactor will only be allowed to operate again after the fault is cleared, the circuit breaker is reset, and the alarm is deactivated. This effectively prevents abnormal line energization or equipment malfunction caused by contactor KM1 or KM2 contactor contacts sticking together, as well as equipment malfunction caused by the PLC issuing a stop command but contactor KM1 or KM2 failing to respond due to the normally open contacts of the forward rotation K1 and reverse rotation K2 24V DC relays sticking together. K3 is a shunt trip 24V DC relay. Because it does not operate frequently, it is not easily damaged, and if the normally open contact sticks together, the shunt trip coil QS will be energized, and the main circuit QF1 switch will trip.

[0047] The method includes the following steps:

[0048] S1: The system is powered on, the PLC is running, the first three-phase voltage detection unit 1 and the second three-phase voltage detection unit 2 are initialized and set, and the main circuit circuit breaker QF1 and the control circuit miniature circuit breaker QF2 are closed.

[0049] S2: When the PLC program does not issue a contactor operation command, and the main power supply, circuit breaker, and control power supply are closed, the coils of the main circuit contactor and the control circuit relay are all de-energized. At this time, the three-phase voltage detection device at the lower end of the main circuit contactor detects that any one phase voltage is greater than the overvoltage setting value set on the three-phase voltage detection device. The associated overvoltage alarm normally open contact closes, the shunt trip coil of the main circuit circuit breaker is energized, and the circuit breaker shunt trips.

[0050] S3: The PLC collects and analyzes the phase voltage values ​​of the three-phase phase voltage detection device on the incoming power cabinet and the voltage values ​​at the lower end of the contactor. When the system program issues a stop command, the running relay and AC contactor coil are de-energized. The program avoids the possible asynchronous disconnection of the contactor main contacts and delays for a set time. If the phase voltage at any phase at the lower end of the contactor is detected to be greater than the set value, a circuit breaker shunt trip action command is issued. The shunt trip DC 24V relay is energized, the auxiliary contacts close the shunt trip coil circuit, the circuit breaker shunt trips and gives an alarm signal.

[0051] S4: After receiving a circuit breaker trip feedback signal, the PLC will no longer permit the issuance of run commands. The contactor will only be allowed to run again after the fault is cleared, the circuit breaker is reset, and the alarm is cleared. This effectively prevents abnormal line energization or equipment malfunction caused by contact sticking of any phase of the forward or reverse AC contactor, as well as equipment malfunction caused by the PLC program issuing a stop command but the main circuit AC contactor failing to respond due to contact sticking of the normally open contacts of the forward or reverse 24V DC relay. The shunt trip 24V DC relay is not prone to damage due to its infrequent operation, and if the normally open contact sticks, the shunt trip coil will be energized, causing the main circuit switch to trip.

[0052] In summary, the protection device and method for AC contactor main contact adhesion, upon detecting adhesion, energizes the shunt trip coil of the main circuit breaker and trips, preventing the coil from engaging under these conditions. Simultaneously, the phase voltage values ​​are transmitted to the CP341 communication board of the PLC controller. The PLC analyzes and compares the phase voltage parameters. After issuing a stop command, it detects the three-phase voltage at the lower end of the contactor. If the voltage exceeds the set value, the program issues a shunt trip command for the circuit breaker. This effectively prevents abnormal energization and equipment malfunction caused by any phase adhesion of the main contacts after the AC contactor coil is de-energized. It also effectively avoids situations where the PLC issues a stop command but the contactor fails to respond due to contact adhesion of the 24V DC relays in the forward and reverse rotation of the control circuit. Simultaneously with issuing the shunt trip command for the main circuit breaker, the system promptly provides a fault alarm signal to remind maintenance personnel. In addition, the system tripping circuit also has a self-testing function. When the main circuit and control circuit are powered normally and the circuit breaker is closed, pressing the test button SB1 can test whether the tripping coil and circuit are normal. It also has a diagnostic function for abnormal adhesion of the normally open contact of the 24V shunt tripping DC relay. When its normally open contact is abnormally adhered, the main circuit circuit breaker trips.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A control method for a protective device to prevent the main contacts of an AC contactor from sticking together, characterized in that: The device includes a first three-phase phase voltage detection unit (1), a second three-phase phase voltage detection unit (2), and a trip control circuit. The first three-phase phase voltage detection unit (1) is connected to the three-phase lines L1, L2, L3 and the neutral line N of the incoming power supply. The second three-phase phase voltage detection unit (2) is connected to the lower end of the contactor. The first three-phase phase voltage detection unit (1) and the second three-phase phase voltage detection unit (2) are connected to the CP341 communication board (3) in the PLC remote cabinet through the RS485 interface and the Modbus RTU communication bus. The three-phase lines L1, L2, and L3 are connected to the main circuit circuit breaker QF1, which is connected to the forward and reverse AC contactors KM1 and KM2 respectively via wires. The lower end of the reverse AC contactor KM2 is equipped with overheat protection FR1, and the output of overheat protection FR1 is connected to the three-phase AC motor M. The control circuit is AC 220V. The trip control circuit includes the normally open contact QF1-1 of the main circuit circuit breaker connected in series, the normally open contact K3-1 of the shunt trip protection 24V DC relay K3 controlled by PLC, and the shunt trip coil QS. When the main circuit breaker QF1 is closed, the normally open contact QF1-1 of the main circuit breaker closes. After the shunt trip coil QS is energized, the main circuit breaker QF1 trips. The normally open contact QF1-1 of the main circuit breaker disconnects the trip coil circuit to prevent the trip coil from being damaged by long-term energization. The normally closed contact K1-2 of the 24V DC relay K1 for forward rotation of the voltage machine, the normally closed contact K2-2 of the 24V DC relay K2 for reverse rotation of the motor, and the normally open contact OUT2-1 of the overvoltage protection alarm of the second and third phase voltage detection unit (2) at the lower end of the contactor are connected in series and then in parallel to the two ends of the normally open contact K3-1. This series circuit is connected to one end of the trip coil, and the other end of the trip coil is connected to the other end of the 220V power supply (53). In parallel with the normally open contact K3-1 of the 24V DC relay K3, there is also the normally open button SB1 for trip circuit testing. The first three-phase phase voltage detection unit (1) and the second three-phase phase voltage detection unit (2) are powered by AC 220V. The first three-phase phase voltage detection unit (1) and the second three-phase phase voltage detection unit (2) provide undervoltage OUT1 and overvoltage OUT2 protection alarm outputs. By setting the overvoltage value of the second three-phase phase voltage detection unit (2) at the lower end of the contactor, the corresponding overvoltage protection alarm normally open contact OUT2-1 is associated. One end of the 220V AC working power supply is connected to the normally closed contact FR1-1 of the overheat protection in the main circuit through the miniature circuit breaker QF2. The normally closed contact FR1-1 of the overheat protection is connected in series with the normally closed contact K3-2 of the 24V DC relay, and then connected in series with the normally open contact of the emergency stop button associated with the operation site. When the emergency stop button is not pressed, the emergency stop relay is energized and the normally open contact is closed. The normally open contact K1-1 of the forward 24V DC relay is connected in series with the normally closed contact KM2-1 of the reverse AC contactor and the coil (60) of the forward AC contactor KM1 to form a series circuit one. The normally open contact K2-1 of the reverse 24V DC relay is connected in series with the normally closed contact KM1-1 of the forward AC contactor and the coil (62) of the reverse AC contactor KM2 to form a series circuit two. Series circuit one and series circuit two are connected in parallel. One end of the parallel circuit is connected to the normally open contact of the emergency stop, and the other end is connected to the other end (53) of the 220V power supply. The method includes the following steps: S1: The system is powered on, the PLC is running, the first three-phase phase voltage detection unit (1) and the second three-phase phase voltage detection unit (2) are initialized and set, and the main circuit circuit breaker QF1 and the control circuit miniature circuit breaker QF2 are closed. S2: When the PLC program does not issue a contactor operation command, and the main power supply, circuit breaker, and control power supply are closed, the coils of the main circuit contactor and the control circuit relay are all de-energized. At this time, the three-phase voltage detection device at the lower end of the main circuit contactor detects that any one phase voltage is greater than the overvoltage setting value set on the three-phase voltage detection device. The associated overvoltage alarm normally open contact closes, the shunt trip coil of the main circuit circuit breaker is energized, and the circuit breaker shunt trips. S3: The PLC collects and analyzes the phase voltage values ​​of the three-phase phase voltage detection device on the incoming power cabinet and the voltage values ​​at the lower end of the contactor. When the system program issues a stop command, the running relay and AC contactor coil are de-energized. The program avoids the possible asynchronous disconnection of the contactor main contacts and delays for a set time. If the phase voltage at any phase at the lower end of the contactor is detected to be greater than the set value, a circuit breaker shunt trip action command is issued. The shunt trip DC 24V relay is energized, the auxiliary contacts close the shunt trip coil circuit, the circuit breaker shunt trips and gives an alarm signal. S4: After receiving the circuit breaker trip feedback signal, the PLC will no longer allow the operation command to be issued. The contactor will only be allowed to run again after the fault is cleared, the circuit breaker is reset, and the alarm is cleared.

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