Power distribution network cable fault relay protection system and method based on longitudinal differential protection

Abstract

According to the power distribution network cable fault relay protection system and method based on longitudinal differential protection provided by the invention, the second current transformers are additionally arranged on the two sides of each middle head of each cable; the second current transformers on the two sides of each intermediate head are in communication connection with the corresponding station building power distribution automation terminal through the longitudinal differential protection device, so that real-time current information at the two ends of the intermediate head can be compared in real time based on the longitudinal differential protection principle. The real-time current difference values are uploaded to the automation master station through the corresponding station building power distribution automation terminals, the automation master station receives the real-time current difference values uploaded by the station building power distribution automation terminals, then the fault position can be judged according to the real-time current difference values, comprehensive comparison of data of each group of current transformers is not needed, and the fault diagnosis accuracy is improved. Compared with the prior art, the method has higher reliability, selectivity and rapidness, the time required for fault judgment is greatly shortened, and then faults are rapidly isolated and user power supply is recovered.

Description

Technical Field

[0001] The present application relates to the technical field of relay protection, and in particular to a distribution network cable fault relay protection system and method based on longitudinal differential protection. Background Art

[0002] At present, the cable fault relay protection of the distribution network is mainly based on the current transformers at both ends of the cable to collect fault current information. The station house distribution automation terminal (DTU) uploads the fault information to the automation master station. The master station performs network topology analysis based on the grid structure of the distribution network and the real-time information of equipment operation, combined with the distribution automation terminal fault signal, switch status and other information, to locate the fault, isolate it and restore power supply to the non-fault area.

[0003] Indicatively, Figure 1 As shown, Figure 1 A schematic diagram of the structure of a current distribution network cable fault relay protection circuit provided by the prior art; Figure 1 In the case of a single-phase grounding fault in the cable between A1 and A2, the current transformer A1 has a zero-sequence current, and A2 to A8 have no fault current. The automation master station determines that the fault area is in the cable between A1 and A2 based on the fault current information of A1 to A8 uploaded by the DTU, and then remotely disconnects the switch K1 and closes the switch K6 to isolate the fault and restore power supply to the non-fault area.

[0004] It can be seen that the current method for determining the fault area of ​​distribution network cables only locks the fault to a certain cable, but cannot determine the specific cable segment or intermediate joint, which has certain limitations; moreover, the fault judgment requires that all DTUs on the feeder upload the fault current information of each current transformer and then make a comprehensive comparison to determine the fault area, which is time-consuming and seriously threatens the reliability of power supply of the power grid. Summary of the invention

[0005] The purpose of this application is to solve at least one of the above-mentioned technical defects, especially the technical defects that the distribution network cable fault relay protection method in the prior art has certain limitations and the fault judgment process is time-consuming, which seriously threatens the reliability of power supply of the power grid.

[0006] The present application provides a distribution network cable fault relay protection system based on longitudinal differential protection, the system comprising an automation master station and a plurality of station house distribution automation terminals, each station house distribution automation terminal is connected to a plurality of cables, a first current transformer is installed at both ends of each cable, each first current transformer is respectively connected to a corresponding station house distribution automation terminal in communication, each station house distribution automation terminal is connected to the automation master station in communication, the system further comprises:

[0007] A second current transformer is installed on both sides of each intermediate head of each cable, and the second current transformers on both sides of each intermediate head are communicatively connected with the corresponding station house power distribution automation terminal through a longitudinal differential protection device.

[0008] Optionally, each second current transformer has its own longitude and latitude information, and the longitude and latitude information of each second current transformer is uploaded to the power grid geographic information system.

[0009] Optionally, the system further comprises:

[0010] A switch is arranged between each cable and the corresponding station house power distribution automation terminal, and each switch is communicatively connected with the automation master station.

[0011] The present application also provides a distribution network cable fault relay protection method based on longitudinal differential protection, which is applied to an automation master station in a distribution network cable fault relay protection system based on the longitudinal differential protection principle described in any one of the above embodiments, and the method includes:

[0012] Receive the real-time current difference between the second current transformers on both sides of each middle head of each cable, which is uploaded by the distribution automation terminal of each station house and sent by each longitudinal differential protection device;

[0013] Whether each cable segment or intermediate joint of each cable is faulty is determined based on each real-time current difference.

[0014] Optionally, judging whether each cable segment or intermediate joint of each cable is faulty according to each real-time current difference value includes:

[0015] For each real-time current difference, comparing the real-time current difference with a preset difference threshold;

[0016] If the real-time current difference does not exceed the preset difference threshold, it is determined that the cable segment or the intermediate joint corresponding to the real-time current difference has no fault;

[0017] If the real-time current difference exceeds the preset difference threshold, it is determined that a cable segment or an intermediate joint corresponding to the real-time current difference is faulty.

[0018] Optionally, the method further comprises:

[0019] When a fault is detected in any cable segment or any intermediate joint, the longitude and latitude information of the faulty cable segment or intermediate joint is sent to the repair personnel based on the power grid geographic information system, so that the repair personnel can locate the fault and repair the fault based on the longitude and latitude information.

[0020] Optionally, the method further comprises:

[0021] When a fault is detected in any cable segment or any intermediate joint, the switch between the faulty cable and the corresponding station power distribution automation terminal is remotely disconnected, and the switch associated with the faulty cable is remotely closed to isolate the fault and restore normal power supply to the non-fault area.

[0022] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0023] The present application provides a distribution network cable fault relay protection system and method based on longitudinal differential protection. The system is equipped with a second current transformer on both sides of each middle head of each cable. The second current transformers on both sides of each middle head are connected to the corresponding station house distribution automation terminal through a longitudinal differential protection device. Therefore, the real-time current information at both ends of the middle head can be compared in real time based on the principle of longitudinal differential protection, and the real-time current difference can be uploaded to the automation master station through the corresponding station house distribution automation terminal. After receiving the real-time current difference uploaded by each station house distribution automation terminal, the automation master station can determine the fault location according to each real-time current difference, without the need to comprehensively compare each group of current transformer data. Compared with the existing technology, it has higher reliability, selectivity and speed, greatly shortens the time required for fault judgment, and then quickly isolates the fault and restores power supply to users. Moreover, compared with the existing distribution network fault area determination method, the present application can lock the fault point to a certain cable segment or a specific middle joint of a certain cable, thereby effectively improving the accuracy of cable fault location. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 A schematic diagram of the structure of a current distribution network cable fault relay protection circuit provided by the prior art;

[0026] Figure 2 A schematic diagram of the structure of a distribution network cable fault relay protection system based on longitudinal differential protection provided in an embodiment of the present application;

[0027] Figure 3 A schematic flow chart of a method for relay protection of cable faults in a distribution network based on longitudinal differential protection is provided in an embodiment of the present application. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0029] In one embodiment, Figure 2 As shown, Figure 2 A schematic diagram of a distribution network cable fault relay protection system based on longitudinal differential protection provided in an embodiment of the present application; the present application provides a distribution network cable fault relay protection system based on longitudinal differential protection, the system comprising an automation master station and a plurality of station house distribution automation terminals, each station house distribution automation terminal is connected to a plurality of cables, a first current transformer is installed at both ends of each cable, each first current transformer is respectively connected to a corresponding station house distribution automation terminal in communication, each station house distribution automation terminal is connected to the automation master station in communication, the system further comprises:

[0030] A second current transformer is installed on both sides of each intermediate head of each cable, and the second current transformers on both sides of each intermediate head are communicatively connected with the corresponding station house power distribution automation terminal through a longitudinal differential protection device.

[0031] In this embodiment, the prior art mainly collects the current information of the first current transformers at both ends of each cable through the distribution automation terminals of each station house when performing relay protection for distribution network cable faults, and uploads it to the automation master station. After receiving the current information of each first current transformer, the automation master station needs to comprehensively compare the current data of each group of first current transformers in order to make a fault determination. This process can neither accurately locate the specific cable segment or specific intermediate joint of the faulty cable, nor quickly make a fault determination, which leads to the existing fault determination method seriously threatening the reliability of power supply of the power grid.

[0032] Based on this, the present application, on the basis of the existing relay protection system, has added a second current transformer on both sides of each intermediate head of each cable. The second current transformers on both sides of each intermediate head are communicated with the corresponding station house distribution automation terminal through a longitudinal differential protection device. In this way, the current information received by the automation master station is the real-time current difference after comparison of each longitudinal differential protection device. According to the real-time current difference uploaded by each station house distribution automation terminal, it is possible to determine which cable segment or intermediate joint of which cable is currently faulty, thereby quickly and accurately locating the faulty cable.

[0033] It is understandable that under normal operation, the currents at both ends of the protected equipment or line are equal in magnitude and opposite in direction. For example, for a transmission line with power supply at both ends, the current flowing in from one end is equal to the current flowing out from the other end. The longitudinal differential protection device measures the current at both ends and compares them. Since the difference between the currents at both ends is zero or close to zero during normal operation, the protection device does not operate at this time. When a fault occurs inside the protected equipment or line, such as a short circuit, grounding, etc., the current at the fault point will change. At this time, the currents flowing in and out of the two ends are no longer equal, and a large current difference will be generated. When the longitudinal differential protection device detects that this current difference exceeds the set threshold, it will immediately operate and issue a trip command to cut off the faulty equipment or line from the system to prevent the fault from expanding, thereby protecting the safe and stable operation of the system.

[0034] For example, if Figure 2 As shown, assuming Figure 2 A single-phase grounding fault occurs in the cable A1A2, which has three cable middle heads. The fault occurs inside the second middle head. Then the current transformers C1 and C2 on both sides of the first middle head have zero-sequence current flowing through them, and their current difference is I1=IC1-IC2=0. The second middle head transformer C3 has zero-sequence current and C4 has no fault current. The current difference is I2=IC3-IC4=Id. The third middle head transformers C5 and C6 have no zero-sequence current flowing through them, and the current difference is I3=IC5-IC6=0. Similarly, the middle head transformers C7 and C8 of the non-faulty cable A4A5 have no zero-sequence current flowing through them, and the current difference is I4=IC7-IC8=0. After receiving the fault current I2, the automation master station immediately determines that the fault point is at the second middle joint between cables A1A2, thereby quickly locating the faulty cable.

[0035] In the above embodiment, the system is equipped with a second current transformer on both sides of each intermediate head of each cable, and the second current transformers on both sides of each intermediate head are connected to the corresponding station house distribution automation terminal through a longitudinal differential protection device, so that the real-time current information at both ends of the intermediate head can be compared in real time based on the principle of longitudinal differential protection, and the real-time current difference can be uploaded to the automation master station through the corresponding station house distribution automation terminal. After receiving the real-time current difference uploaded by each station house distribution automation terminal, the automation master station can determine the fault location according to each real-time current difference, without the need to comprehensively compare each group of current transformer data. Compared with the existing technology, it has higher reliability, selectivity and speed, greatly shortens the time required for fault judgment, and then quickly isolates the fault and restores power supply to users. In addition, compared with the existing distribution network fault area determination method, the present application can lock the fault point to a certain cable segment or a specific intermediate joint of a certain cable, thereby effectively improving the accuracy of cable fault location.

[0036] In one embodiment, each second current transformer has its own longitude and latitude information, and the longitude and latitude information of each second current transformer is uploaded to the power grid geographic information system.

[0037] In this embodiment, each second current transformer can not only realize its own related functions, but also carry its own longitude and latitude information, and upload its longitude and latitude information to the power grid geographic information system, which is a comprehensive management system that combines geographic information with power grid data. When a power grid fails, the system can quickly determine the fault location and display the surrounding equipment and environment conditions in combination with geographic information. This helps to quickly formulate emergency repair plans, shorten power outage time, and improve power supply reliability.

[0038] Therefore, the present application can connect the automation master station with the system. When the automation master station determines that a certain section of a cable or an intermediate joint has a fault, the fault information can be sent to the power grid geographic information system so that the power grid geographic information system can quickly determine the fault location and send it to the emergency repair personnel for emergency repair.

[0039] In one embodiment, the system may further include: a switch disposed between each cable and the corresponding power distribution automation terminal in the station building, each switch being communicatively connected to the automation master station.

[0040] In this embodiment, Figure 2 As shown, Figure 2 In the system, each station house power distribution automation terminal can be connected to the corresponding cable through a switch, and the switch can be communicated with the automation master station so that when the automation master station determines that the cable is faulty, it can directly remotely control the corresponding switch to open or close it, thereby effectively improving the fault handling efficiency and reducing power outage losses.

[0041] In one embodiment, Figure 3 As shown, Figure 3 A flow chart of a distribution network cable fault relay protection method based on longitudinal differential protection provided in an embodiment of the present application; the present application also provides a distribution network cable fault relay protection method based on longitudinal differential protection, which is applied to an automation master station in a distribution network cable fault relay protection system based on the longitudinal differential protection principle described in any one of the above embodiments, and the method may include:

[0042] S110: receiving the real-time current difference between the second current transformers on both sides of each middle head of each cable, which is uploaded by the distribution automation terminal of each station building and sent by each longitudinal differential protection device.

[0043] S120: Determine whether each cable segment or middle joint of each cable has a fault according to each real-time current difference value.

[0044] In this embodiment, the automation master station is communicatively connected to each station house power distribution automation terminal, and each station house power distribution automation terminal is connected to each longitudinal differential protection device. Therefore, when each longitudinal differential protection device receives the real-time current value of the second current transformer on both sides of the corresponding intermediate head and calculates the corresponding real-time current difference, it can be sent to the automation master station through the corresponding station house power distribution automation terminal. After the automation master station receives the real-time current difference sent by each station house power distribution automation terminal, it can determine whether each cable segment or intermediate joint of each cable is faulty according to each real-time current difference, thereby effectively improving the efficiency and accuracy of fault location.

[0045] For example, if Figure 2 As shown, assuming Figure 2 A single-phase grounding fault occurs in the cable A1A2, which has three cable middle heads. The fault occurs inside the second middle head. Then the current transformers C1 and C2 on both sides of the first middle head have zero-sequence current flowing through them, and their current difference is I1=IC1-IC2=0. The second middle head transformer C3 has zero-sequence current and C4 has no fault current. The current difference is I2=IC3-IC4=Id. The third middle head transformers C5 and C6 have no zero-sequence current flowing through them, and the current difference is I3=IC5-IC6=0. Similarly, the middle head transformers C7 and C8 of the non-faulty cable A4A5 have no zero-sequence current flowing through them, and the current difference is I4=IC7-IC8=0. After receiving the fault current I2, the automation master station immediately determines that the fault point is at the second middle joint between cables A1A2, thereby quickly locating the faulty cable.

[0046] In the above embodiment, since the system is equipped with a second current transformer on both sides of each intermediate head of each cable, the second current transformers on both sides of each intermediate head are connected to the corresponding station house distribution automation terminal through the longitudinal differential protection device, and then the real-time current information at both ends of the intermediate head can be compared in real time based on the principle of longitudinal differential protection, and the real-time current difference can be uploaded to the automation master station through the corresponding station house distribution automation terminal. After receiving the real-time current difference uploaded by each station house distribution automation terminal, the automation master station can determine the fault location according to each real-time current difference, without the need to comprehensively compare the data of each group of current transformers. Compared with the existing technology, it has higher reliability, selectivity and speed, greatly shortens the time required for fault judgment, and then quickly isolates the fault and restores power supply to users. Moreover, compared with the existing distribution network fault area determination method, the present application can lock the fault point to a certain cable segment or a specific intermediate joint of a certain cable, thereby effectively improving the accuracy of cable fault location.

[0047] In one embodiment, judging whether each cable segment or intermediate joint of each cable is faulty according to each real-time current difference in S120 may include:

[0048] S121: For each real-time current difference, compare the real-time current difference with a preset difference threshold.

[0049] S122: If the real-time current difference does not exceed the preset difference threshold, it is determined that the cable segment or the intermediate joint corresponding to the real-time current difference has no fault.

[0050] S123: If the real-time current difference exceeds the preset difference threshold, it is determined that a cable segment or an intermediate joint corresponding to the real-time current difference is faulty.

[0051] In this embodiment, when the distribution network operates normally, the difference in current at both ends of the cable is zero or close to zero. When a fault occurs in the protected equipment or line, such as a short circuit, grounding, etc., the current at the fault point will change. At this time, the current flowing into and out of the two ends of the cable will no longer be equal, resulting in a larger current difference.

[0052] Based on this, the present application can pre-set a difference threshold according to historical experience, and after receiving the real-time current difference between the second current transformers on both sides of each intermediate head of each cable uploaded by the distribution automation terminal of each station building and sent by each longitudinal differential protection device, each real-time current difference is compared with the preset difference threshold. If all real-time current differences do not exceed the preset difference threshold, it means that there is no fault in the current cables. If one or more real-time current differences exceed the preset difference threshold, it means that a cable segment or an intermediate joint of a certain cable is faulty, thereby quickly determining the location of the faulty cable.

[0053] In one embodiment, the method may further include:

[0054] S130: When a fault is detected in any cable segment or any intermediate joint, the longitude and latitude information of the faulty cable segment or intermediate joint is sent to the emergency repair personnel based on the power grid geographic information system, so that the emergency repair personnel can locate the fault and repair the fault based on the longitude and latitude information.

[0055] In this embodiment, since each second current transformer of the present application has its own longitude and latitude information, and the longitude and latitude information is uploaded to the power grid geographic information system. Therefore, when a fault is detected in any cable segment or any intermediate joint, the automation master station can send the detected fault information to the power grid geographic information system, so as to locate the specific fault location through the power grid geographic information system, and send the fault location to the emergency repair personnel. For example, the present application can send the longitude and latitude information of the faulty cable segment or intermediate joint and the surrounding equipment and environmental conditions to the emergency repair personnel, so that the emergency repair personnel can locate the fault and repair the fault based on the longitude and latitude information and the environmental conditions of the surrounding equipment.

[0056] In one embodiment, the method may further include:

[0057] S140: When a fault is detected in any cable segment or any intermediate joint, the switch between the faulty cable and the corresponding station house power distribution automation terminal is remotely disconnected, and the switch associated with the faulty cable is remotely closed to isolate the fault and restore normal power supply to the non-fault area.

[0058] In this embodiment, Figure 2 As shown, in the present application, each station house power distribution automation terminal can be connected to the corresponding cable through a switch, and the switch can be communicated with the automation master station so that when the automation master station determines that the cable is faulty, it can directly remotely control the corresponding switch to open or close it, thereby effectively improving the fault handling efficiency and reducing power outage losses.

[0059] Based on this, when the automation master station detects a fault in any cable segment or any intermediate joint, it can remotely disconnect the switch between the faulty cable and the corresponding station house power distribution automation terminal, and remotely close the switch associated with the faulty cable to isolate the fault and restore normal power supply to the non-fault area.

[0060] For example, if Figure 2 As shown, when the automation master station receives the fault current I2, it immediately determines that the fault point is at the second middle joint between cables A1A2. At this time, the automation master station can immediately remotely disconnect switch K1 and close switch K6 to isolate the fault and restore normal power supply to the non-fault area.

[0061] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0062] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can refer to each other.

[0063] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A distribution network cable fault relay protection system based on longitudinal differential protection, the system comprising an automated master station and a plurality of station house distribution automation terminals, each station house distribution automation terminal is connected to a plurality of cables, a first current transformer is installed at both ends of each cable, each first current transformer is respectively connected to a corresponding station house distribution automation terminal in communication, each station house distribution automation terminal is connected to the automated master station in communication, It is characterized in that The system further comprises: A second current transformer is installed on both sides of each intermediate head of each cable, and the second current transformers on both sides of each intermediate head are communicatively connected with the corresponding station house power distribution automation terminal through a longitudinal differential protection device.

2. According to claim 1, the distribution network cable fault relay protection system based on longitudinal differential protection, It is characterized in that Each second current transformer has its own longitude and latitude information, and the longitude and latitude information of each second current transformer is uploaded to the power grid geographic information system.

3. The distribution network cable fault relay protection system based on longitudinal differential protection according to claim 1 or 2, It is characterized in that The system further comprises: A switch is arranged between each cable and the corresponding station house power distribution automation terminal, and each switch is communicatively connected with the automation master station.

4. A distribution network cable fault relay protection method based on longitudinal differential protection, applied to the automation master station in the distribution network cable fault relay protection system based on the longitudinal differential protection principle as described in any one of claims 1 to 3 above, It is characterized in that The method comprises: Receive the real-time current difference between the second current transformers on both sides of each middle head of each cable, which is uploaded by the distribution automation terminal of each station house and sent by each longitudinal differential protection device; Whether each cable segment or intermediate joint of each cable is faulty is determined based on each real-time current difference.

5. The distribution network cable fault relay protection method based on longitudinal differential protection according to claim 4, It is characterized in that The method of judging whether each cable segment or intermediate joint of each cable is faulty according to each real-time current difference value comprises: For each real-time current difference, comparing the real-time current difference with a preset difference threshold; If the real-time current difference does not exceed the preset difference threshold, it is determined that the cable segment or the intermediate joint corresponding to the real-time current difference has no fault; If the real-time current difference exceeds the preset difference threshold, it is determined that a cable segment or an intermediate joint corresponding to the real-time current difference is faulty.

6. The distribution network cable fault relay protection method based on longitudinal differential protection according to claim 4 or 5, It is characterized in that The method further comprises: When a fault is detected in any cable segment or any intermediate joint, the longitude and latitude information of the faulty cable segment or intermediate joint is sent to the repair personnel based on the power grid geographic information system, so that the repair personnel can locate the fault and repair the fault based on the longitude and latitude information.

7. The distribution network cable fault relay protection method based on longitudinal differential protection according to claim 4 or 5, It is characterized in that The method further comprises: When a fault is detected in any cable segment or any intermediate joint, the switch between the faulty cable and the corresponding station power distribution automation terminal is remotely disconnected, and the switch associated with the faulty cable is remotely closed to isolate the fault and restore normal power supply to the non-fault area.

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