Loop for preventing differential protection maloperation caused by disconnection of secondary loop of current transformer

Abstract

The invention provides a loop for preventing differential protection misoperation caused by disconnection of a secondary loop of a current transformer (CT), and the loop is used for preventing the differential protection misoperation caused by disconnection of the secondary loop of the CT by adding a disconnection monitoring module and a false differential identification mechanism. The detection module is used for detecting the disconnection state of the CT secondary circuit; the current detection module is used for distinguishing differential signals caused by secondary circuit disconnection and actual faults; the logic judgment module is used for integrating the disconnection signal and the differential signal and judging whether differential protection is locked or not; the protection locking and alarm module is used for sending out an alarm signal while locking the differential protection function pressing plate; according to the invention, the integrity of the CT secondary circuit can be monitored in real time, the disconnection state is accurately judged, differential protection is locked in time, and safe and stable operation of a power system is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection and control in power systems, and particularly to a circuit for preventing differential protection from malfunctioning due to the disconnection of the secondary circuit of a current transformer. Background Art

[0002] Differential protection is an important protection method for generators, transformers, and transmission lines. It determines faults by comparing whether the secondary currents of current transformers on each side within the protected area satisfy Kirchhoff's current law. However, in actual operation, if the secondary circuit of the CT is disconnected, it will cause false differential current, leading to misoperation of the protection, and thus may trigger unnecessary power outage accidents.

[0003] Most of the existing protection means rely on mechanical inspection of the secondary circuit connection or on-line monitoring devices. However, these methods often cannot identify and block the operation of differential protection in real time, and there are certain blind spots. Therefore, it is very necessary to design a protection circuit that can detect the disconnection of the CT secondary circuit in real time and effectively prevent differential misoperation. Summary of the Invention

[0004] The present invention proposes a circuit for preventing differential protection from malfunctioning due to the disconnection of the secondary circuit of a current transformer, which can monitor the integrity of the CT secondary circuit in real time, accurately judge the disconnection state, and timely block the differential protection to ensure the safe and stable operation of the power system.

[0005] The present invention adopts the following technical solutions.

[0006] A circuit for preventing differential protection from malfunctioning due to the disconnection of the secondary circuit of a current transformer. The circuit prevents differential protection from malfunctioning caused by the disconnection of the secondary circuit of the current transformer CT by adding a disconnection monitoring module and a false differential identification mechanism. The circuit includes the following modules: A secondary circuit disconnection monitoring module for detecting the disconnection state of the CT secondary circuit; A current detection module for distinguishing between differential signals caused by secondary circuit disconnection and actual faults; A logic judgment module for comprehensively judging whether to block the differential protection based on the disconnection signal and the differential signal; A protection blocking and alarm module for sending an alarm signal while blocking the differential protection function pressure plate.

[0007] The circuit is used for differential protection of transformers and transmission lines.

[0008] The secondary circuit disconnection monitoring module detects the CT disconnection situation by monitoring the voltage increase phenomenon caused by the increase of the equivalent impedance of the circuit and in the way of paralleling and monitoring overvoltage relays. The disconnection monitoring mechanism of the secondary circuit disconnection monitoring module is as follows: the three-phase voltage setting values ​​are UAs, UBs, and UCs respectively, and the three-phase current setting values ​​are IAs, IBs, and ICs respectively. An overvoltage relay is connected in parallel at both ends of the secondary winding of each phase CT. When the CT secondary circuit is disconnected, the secondary circuit disconnection monitoring module monitors the overvoltage. If the voltage is greater than the set value Us, the overvoltage relay node is turned on. At the same time, if the undercurrent relay connected in series with it detects that the phase current is lower than the set value Is, the undercurrent relay is energized and the normally open node is turned on. The two nodes are connected in series to start the CT disconnection relay CTDX. The CTDX normally closed node CTDX2 cuts off the differential protection function and opens the circuit. The differential protection function is locked, the normally open node CTDX1 is closed, an abnormal signal is reported, and a disconnection alarm signal is sent.

[0009] The current detection module performs a false differential identification mechanism with a phase current independent identification mechanism; the current detection module uses an undercurrent relay for detection, and when the current is less than a set threshold, the relay is activated to determine whether the circuit is open.

[0010] The phase current independent identification mechanism is specifically as follows: the overvoltage relay node UA is connected in series with the undercurrent relay node IA, the overvoltage relay node UB is connected in series with the undercurrent relay node IB, the overvoltage relay node UC is connected in series with the undercurrent relay node IC, and then the above three-phase series nodes A, B, and C are connected to the circuit in parallel. When a phase series node is closed, the line break monitoring mechanism is started, the CTDX normally closed node CTDX2 cuts off the differential protection function and opens the circuit, locking the differential protection, the normally open node CTDX1 is closed, and an abnormal signal is reported; The closure of a phase series node refers to the closure of the UA node and the IA node in the A phase at the same time, or the UB node and the IB node in the B phase at the same time, or the UC node and the IC node in the C phase at the same time.

[0011] The logic judgment module is used to execute the locking logic, which combines the normally closed nodes of the overvoltage relay and the undercurrent relay to form an "AND" logic relationship, and generates a differential protection function pressure plate locking instruction by causing the two relays to operate simultaneously.

[0012] The locking logic is specifically as follows: assume that the currents of the three-phase CTs of A, B, and C in the differential protection zone are collected in real time on the secondary side, respectively, as IA, IB, and IC, and the three-phase voltages of A, B, and C are collected as UA, UB, and UC, and the voltage and current at this moment are recorded as UA2, UB2, UC2, IA2, IB2, and IC2, respectively, and the voltage and current at the previous moment are recorded as UA1, UB1, UC1, IA1, IB1, and IC1, respectively; When it is found that for any phase, the voltage at the current moment is greater than that at the previous moment and the current at the current moment is less than that at the previous moment compared with the previous moment, and the voltage at this moment is greater than the set value of the phase voltage and the current is less than the set value of the phase current, that is: If this phase is phase A, then the voltage at this moment is greater than the set value of UA, and the current is less than the set value of IA, that is, when UA2 > UAs > UA1 and IA2 < IAs < IA1, If this phase is phase B, then the voltage at this moment is greater than the set value of UB, and the current is less than the set value of IB, that is, when UB2 > UBs > UB1 and IB2 < IBs < IB1, If this phase is phase C, then the voltage at this moment is greater than the set value of UC, and the current is less than the set value of IC, that is, when UC2 > UCs > UC1 and IC2 < ICs < IC1, The logic judgment module cuts off the differential protection function input circuit through the normally closed node CTDX2 of CTDX, locks the output of the differential protection, and prevents misoperation.

[0013] The protection locking and alarm module has a self-checking function, which is used to regularly check the working status of the secondary circuit open-circuit monitoring module and the logic judgment module; When the secondary circuit open-circuit monitoring module executes the locking of the differential protection, it sends a CT secondary open-circuit alarm signal to the backend management mechanism; at the same time as the differential protection action is locked, an alarm signal is issued to guide the operator to check the connection status of the secondary circuit; When the current detection module reports an abnormal signal, it sends a disconnection alarm signal to the backend management mechanism.

[0014] The control system of the circuit triggers the self-checking function automatically every preset time period to verify the signal acquisition ability of the secondary circuit open-circuit monitoring module and the correctness of the logic judgment module; when an abnormality is found, an equipment failure alarm is issued to guide the maintenance personnel to repair it in time.

[0015] The present invention effectively solves the problem of misoperation of the differential protection caused by the open circuit of the CT secondary circuit by adding an open-circuit monitoring module and a false differential identification mechanism, and is applicable to differential protection scenarios such as transformers and transmission lines, and has the advantages of high reliability and ease of use.

[0016] The beneficial effects of the present invention are as follows: 1. Strong real-time performance: It can quickly detect the open-circuit state of the CT secondary circuit and take protection measures; 2. Precise prevention of misoperation: Combining open-circuit monitoring and false differential identification, effectively avoiding misoperation of the differential protection; 3. High reliability: Ensuring the long-term stability of the open-circuit monitoring and logic judgment modules through the self-checking mechanism; 4. Strong engineering adaptability: There is no need to carry out large-scale transformation of the existing differential protection device, and it is easy to be popularized in engineering. Brief Description of the Drawings

[0017] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments: Attached Figure 1 is a schematic diagram of the line CT disconnection scenario; Attached Figure 2 is a schematic diagram of the installation of overvoltage relay and undercurrent relay; Attached Figure 3 is a schematic diagram of the CT disconnection relay starting; Attached Figure 4 is a schematic diagram of the real-time acquisition system of the locking logic; Attached Figure 5 is a schematic diagram of the protection locking and alarm module. Specific Embodiments

[0018] As shown in the figure, a circuit for preventing differential protection from malfunctioning due to the disconnection of the secondary circuit of a current transformer, that is, a circuit for preventing differential protection from malfunctioning due to the disconnection of the secondary circuit of a current transformer (CT). The circuit prevents differential protection from malfunctioning caused by the disconnection of the secondary circuit of the current transformer CT by adding a disconnection monitoring module and a false differential identification mechanism. The circuit includes the following modules: A secondary circuit disconnection monitoring module for detecting the disconnection state of the CT secondary circuit; A current detection module for distinguishing the differential signal caused by the disconnection of the secondary circuit from the actual fault; A logic judgment module for comprehensively judging whether to lock the differential protection based on the disconnection signal and the differential signal; A protection locking and alarm module for sending an alarm signal while locking the differential protection function pressure plate.

[0019] The circuit is used for the differential protection of transformers and transmission lines.

[0020] The secondary circuit disconnection monitoring module detects the CT disconnection situation by monitoring the voltage increase phenomenon caused by the increase of the equivalent impedance of the circuit and by monitoring the overvoltage relay in parallel The disconnection monitoring mechanism of the secondary circuit disconnection monitoring module is specifically as follows: Assume that the three-phase voltage set values are UAs, UBs, and UCs respectively, and the three-phase current set values are IAs, IBs, and ICs respectively. A overvoltage relay is connected in parallel at both ends of the secondary winding of each phase CT. When the CT secondary circuit is disconnected, the secondary circuit disconnection monitoring module monitors the overvoltage. If the voltage is greater than the set value Us, the node of the overvoltage relay conducts. At the same time, if the undercurrent relay connected in series with it detects that the current of this phase is lower than the set value Is, the normally open node of the undercurrent relay is energized and conducts. The nodes of both are connected in series to start the CT disconnection relay CTDX. The normally closed node CTDX2 of CTDX cuts off the differential protection function input circuit, and the differential protection function is blocked. The normally open node CTDX1 closes, reports an abnormal signal and sends a disconnection alarm signal.

[0021] The current detection module executes the false differential identification mechanism with a phase current independent identification mechanism; the current detection module uses an undercurrent relay for detection. When the current is less than the set threshold, the relay operates to determine whether the circuit is open.

[0022] The specific phase current independent identification mechanism is as follows: The node UA of the overvoltage relay is connected in series with the node IA of the undercurrent relay, the node UB of the overvoltage relay is connected in series with the node IB of the undercurrent relay, and the node UC of the overvoltage relay is connected in series with the node IC of the undercurrent relay. Then, the above series nodes of the three phases A, B, and C are connected to the circuit in parallel. When a series node of a certain phase is closed, the disconnection monitoring mechanism is started. The normally closed node CTDX2 of CTDX cuts off the differential protection function input circuit and blocks the differential protection. The normally open node CTDX1 closes and reports an abnormal signal; The closing of a certain phase series node means that the node UA and the node IA in phase A are closed at the same time, or the node UB and the node IB in phase B are closed at the same time, or the node UC and the node IC in phase C are closed at the same time.

[0023] The logic judgment module is used to execute the blocking logic. It combines the normally closed nodes of the actions of the overvoltage relay and the undercurrent relay to form an "AND" logic relationship, and generates a differential protection function pressure plate blocking instruction by making both relays act simultaneously.

[0024] The specific blocking logic is as follows: Assume that the currents of the CTs of the three phases A, B, and C in the differential protection area are collected in real time on the secondary side as IA, IB, and IC respectively, and the voltages of the three phases A, B, and C, UA, UB, and UC are collected. The voltage and current at this moment are respectively recorded as UA2, UB2, UC2, IA2, IB2, and IC2, and the voltage and current at the previous moment are respectively recorded as UA1, UB1, UC1, IA1, IB1, and IC1; When it is found that for any phase, the voltage at the current moment is greater than that at the previous moment and the current at the current moment is less than that at the previous moment compared with the previous moment, and the voltage at this moment is greater than the set value of the phase voltage and the current is less than the set value of the phase current, that is: If this phase is phase A, then the voltage at this moment is greater than the set value of UA, and the current is less than the set value of IA, that is, when UA2 > UAs > UA1 and IA2 < IAs < IA1, If this phase is phase B, then the voltage at this moment is greater than the set value of UB, and the current is less than the set value of IB, that is, when UB2 > UBs > UB1 and IB2 < IBs < IB1, If this phase is phase C, then the voltage at this moment is greater than the set value of UC, and the current is less than the set value of IC, that is, when UC2 > UCs > UC1 and IC2 < ICs < IC1, The logic judgment module cuts off the differential protection function input circuit through the normally closed node CTDX2 of CTDX, locks the output of the differential protection, and prevents misoperation.

[0025] The protection locking and alarm module has a self-checking function, which is used to regularly check the working status of the secondary circuit open-circuit monitoring module and the logic judgment module; When the secondary circuit open-circuit monitoring module executes the locking of the differential protection, it sends a CT secondary open-circuit alarm signal to the backend management mechanism; at the same time as the differential protection action is locked, an alarm signal is sent to guide the operating personnel to check the connection status of the secondary circuit; When the current detection module reports an abnormal signal, it sends a disconnection alarm signal to the backend management mechanism.

[0026] The control system of the circuit triggers the self-checking function automatically every preset time period to verify the signal acquisition ability of the secondary circuit open-circuit monitoring module and the correctness of the logic judgment module; when an abnormality is found, an equipment failure alarm is issued to guide the maintenance personnel to perform timely repairs.

[0027] In this example, a circuit is provided to prevent the differential protection from misoperating due to the disconnection of the secondary circuit of the current transformer, which can monitor the integrity of the CT secondary circuit in real time, accurately judge the disconnection state, and lock the differential protection in time to ensure the safe and stable operation of the power system; the circuit based on the CT secondary circuit open-circuit monitoring and protection locking logic mainly includes the following modules: Secondary circuit open-circuit monitoring module: A monitoring resistor is added to the CT secondary circuit or an overvoltage relay is connected in parallel, and the open-circuit state of the secondary circuit is jointly judged by monitoring the change of its current value.

[0028] Protection locking and alarm module: When it is confirmed that the CT secondary circuit is disconnected, it automatically locks the output of the differential protection action and issues an alarm signal to prompt the operating personnel.

[0029] Self-check module: Regularly self-check the operating status of the secondary circuit monitoring module and the logic judgment module to ensure the long-term reliable operation of the circuit.

[0030] The circuit operates based on the following mechanism principle: 1. Disconnection monitoring mechanism • Connect an overvoltage relay in parallel at both ends of the secondary winding of each phase CT. When the CT secondary circuit is disconnected, overvoltage is monitored. When the voltage is greater than the set value Us (the three-phase voltage set values are UAs, UBs, and UCs respectively), the node of the overvoltage relay conducts. At the same time, the series-connected undercurrent relay detects that the current of this phase is lower than the set value Is (the three-phase current set values are IAs, IBs, and ICs respectively), and the normally open node of the undercurrent relay that is energized conducts. The nodes of both are connected in series to start the CT disconnection relay CTDX. The normally closed node CTDX2 of CTDX cuts off the differential protection function input circuit, and the differential protection function is blocked. The normally open node CTDX1 closes, reports an abnormal signal and sends a "disconnection alarm" signal.

[0031] 2. Phase current independent recognition mechanism • Connect the node UA of the overvoltage relay in series with the node IA of the undercurrent relay, the node UB of the overvoltage relay in series with the node IB of the undercurrent relay, and the node UC of the overvoltage relay in series with the node IC of the undercurrent relay. Then connect the above series nodes of the three phases A, B, and C in parallel to the circuit. When a series node of a certain phase is closed (taking phase A as an example, when the UA node and the IA node are closed at the same time), start the disconnection monitoring mechanism. The normally closed node CTDX2 of CTDX cuts off the differential protection function input circuit, blocks the differential protection, and the normally open node CTDX1 closes, reports an abnormal signal and sends a "disconnection alarm" signal.

[0032] 3. Blocking logic • Real-time collect the currents IA, IB, and IC of the CTs of the three phases A, B, and C in the differential protection area on the secondary side, and collect the voltages UA, UB, and UC of the three phases A, B, and C. Record the voltage and current at this moment as UA2, UB2, UC2, IA2, IB2, IC2 respectively, and record the voltage and current at the previous moment as UA1, UB1, UC1, IA1, IB1, IC1 respectively. When it is found that for any phase, compared with the previous moment, the voltage at the current moment is greater than the previous moment and the current at the current moment is less than the previous moment, and the voltage at this moment is greater than the UA set value and the current is less than the IA set value (taking phase A as an example, UA2>UAs>UA1 and IA2<IAs<IA1), the logic judgment module cuts off the differential protection function input circuit through the normally closed node CTDX2 of CTDX, blocks the differential protection output, and prevents misoperation.

[0033] 4. Alarm and prompt • While the differential protection action is blocked, the system issues an alarm signal to guide the operator to check the connection status of the secondary circuit.

[0034] Embodiment 1: Real-time detection and blocking of CT secondary circuit disconnection: In this example, during the operation of a certain line, UA is the overvoltage relay for phase A, and IA is the undercurrent relay for phase A. Due to the disconnection of phase A in the CT secondary circuit, the differential current suddenly increases. The disconnection monitoring module detects in real time that the interphase voltage is greater than the threshold (UA operates), and the current is lower than the threshold (IA operates). Through logical judgment, the normally open nodes of UA and IA are closed, starting the CT disconnection relay CTDX to operate. The protection device module blocks the differential protection action and simultaneously sends an alarm of "CT secondary disconnection" to the background.

[0035] Embodiment 2: Quick identification of blocking logic: In this example, a transient impact current occurs in a certain transmission line. The differential protection device detects a significant increase in the differential current, but the symmetry of the CT secondary currents on each side is not damaged, and there is no alarm signal from the disconnection monitoring module. The logic judgment module determines that it is a normal operation phenomenon not caused by disconnection, and the differential protection continues to operate without misoperation.

[0036] Embodiment 3: Realization of self-check function: In this example, the system automatically triggers the self-check function once every 24 hours to verify the signal acquisition ability of the disconnection monitoring module and the correctness of the logic judgment module. When an abnormality is found, an equipment failure alarm is issued to guide the maintenance personnel to perform timely maintenance.

Claims

1. A circuit for preventing the differential protection from malfunctioning due to the disconnection of the secondary circuit of the current transformer, characterized in that: The circuit prevents the differential protection from malfunctioning due to a disconnection in the secondary circuit of the current transformer CT by adding a disconnection monitoring module and a false differential identification mechanism. The circuit includes the following modules: Secondary circuit disconnection monitoring module, used to detect the disconnection status of the CT secondary circuit; Current detection module, used to distinguish the differential signal caused by secondary circuit disconnection and actual fault; The logic judgment module is used to combine the disconnection signal and the differential signal to determine whether to lock the differential protection; The protection interlocking and alarm module is used to send out an alarm signal while interlocking the differential protection function pressure plate.

2. The circuit for preventing malfunction of differential protection caused by disconnection of the secondary circuit of the current transformer according to claim 1 is characterized in that: The circuit is used for differential protection of transformers and transmission lines.

3. The circuit for preventing malfunction of differential protection caused by disconnection of the secondary circuit of the current transformer according to claim 1 is characterized in that: The secondary circuit disconnection monitoring module detects the CT disconnection by monitoring the voltage increase caused by the increase in the equivalent impedance of the monitoring circuit, and by monitoring the overvoltage relay in parallel.

4. The circuit for preventing malfunction of differential protection caused by disconnection of the secondary circuit of the current transformer according to claim 3 is characterized in that: The disconnection monitoring mechanism of the secondary circuit disconnection monitoring module is as follows: the three-phase voltage setting values ​​are UAs, UBs, and UCs respectively, and the three-phase current setting values ​​are IAs, IBs, and ICs respectively. An overvoltage relay is connected in parallel at both ends of the secondary winding of each phase CT. When the CT secondary circuit is disconnected, the secondary circuit disconnection monitoring module monitors the overvoltage. If the voltage is greater than the set value Us, the overvoltage relay node is turned on. At the same time, if the undercurrent relay connected in series with it detects that the phase current is lower than the set value Is, the undercurrent relay is energized and the normally open node is turned on. The two nodes are connected in series to start the CT disconnection relay CTDX. The CTDX normally closed node CTDX2 cuts off the differential protection function and opens the circuit. The differential protection function is locked, the normally open node CTDX1 is closed, an abnormal signal is reported, and a disconnection alarm signal is sent.

5. The circuit for preventing malfunction of differential protection caused by disconnection of the secondary circuit of the current transformer according to claim 1 is characterized in that: The current detection module performs a false differential identification mechanism with a phase current independent identification mechanism; the current detection module uses an undercurrent relay for detection, and when the current is less than a set threshold, the relay is activated to determine whether the circuit is open.

6. The circuit for preventing malfunction of differential protection caused by disconnection of the secondary circuit of the current transformer according to claim 5 is characterized in that: The phase current independent identification mechanism is specifically as follows: the overvoltage relay node UA is connected in series with the undercurrent relay node IA, the overvoltage relay node UB is connected in series with the undercurrent relay node IB, the overvoltage relay node UC is connected in series with the undercurrent relay node IC, and then the above three-phase series nodes A, B, and C are connected to the circuit in parallel. When a phase series node is closed, the line break monitoring mechanism is started, the CTDX normally closed node CTDX2 cuts off the differential protection function and opens the circuit, locking the differential protection, the normally open node CTDX1 is closed, and an abnormal signal is reported; The closure of a phase series node refers to the closure of the UA node and the IA node in the A phase at the same time, or the UB node and the IB node in the B phase at the same time, or the UC node and the IC node in the C phase at the same time.

7. The circuit for preventing malfunction of differential protection caused by disconnection of the secondary circuit of the current transformer according to claim 1 is characterized in that: The logic judgment module is used to execute the locking logic, which combines the normally closed nodes of the overvoltage relay and the undercurrent relay to form an "and" logic relationship, and generates a differential protection function pressure plate locking instruction by causing the two relays to operate simultaneously.

8. The circuit for preventing malfunction of differential protection caused by disconnection of the secondary circuit of the current transformer according to claim 7 is characterized in that: The locking logic is specifically as follows: assume that the currents of the three-phase CTs of A, B, and C in the differential protection zone are collected in real time on the secondary side, respectively, as IA, IB, and IC, and the three-phase voltages of A, B, and C are collected as UA, UB, and UC, and the voltage and current at this moment are recorded as UA2, UB2, UC2, IA2, IB2, and IC2, respectively, and the voltage and current at the previous moment are recorded as UA1, UB1, UC1, IA1, IB1, and IC1, respectively; When it is found that the voltage at the current moment is greater than the previous moment and the current moment is less than the previous moment, and the voltage at this moment is greater than the set value of the phase voltage, and the current is less than the set value of the phase current, that is: If this phase is phase A, then at this moment the voltage is greater than the UA setting value and the current is less than the IA setting value, that is, UA2>UAs>UA1 and IA2<IAs<IA1, If this phase is phase B, then at this moment the voltage is greater than the UB setting value and the current is less than the IB setting value, that is, UB2>UBs>UB1 and IB2<IBs<IB1, If this phase is phase C, then at this moment the voltage is greater than the UC setting value and the current is less than the IC setting value, that is, UC2>UCs>UC1 and IC2<ICs<IC1, The logic judgment module cuts off the differential protection function opening loop through the CTDX normally closed node CTDX2, blocks the differential protection output and prevents false operation.

9. The circuit for preventing malfunction of differential protection caused by disconnection of the secondary circuit of the current transformer according to claim 1, characterized in that: The protection interlock and alarm module has a self-checking function, which is used to regularly check the working status of the secondary circuit disconnection monitoring module and the logic judgment module; When the secondary circuit disconnection monitoring module executes the locking differential protection, it sends the CT secondary disconnection alarm signal to the back-end management agency; while the differential protection action is locked, it sends an alarm signal to guide the operator to check the secondary circuit connection status; When the current detection module reports an abnormal signal, a disconnection alarm signal is sent to the back-end management agency.

10. The circuit for preventing malfunction of differential protection caused by disconnection of the secondary circuit of the current transformer according to claim 9, characterized in that: The control system of the loop automatically triggers a self-check function at a preset interval to verify the signal acquisition capability of the secondary loop disconnection monitoring module and the correctness of the logic judgment module; when an abnormality is found, an equipment fault alarm is issued to guide maintenance personnel to repair it in time.

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