A method and system for online detection of typical defects in high-voltage transmission cable grounding systems

Abstract

The present invention discloses a method and system for online detection of typical defects in the grounding system of a high-voltage transmission cable. The method of the present invention sets four grounding loop current measurement CTs at the direct grounding box and protective grounding box of each section of the high-voltage transmission cable, and sets three main core current measurement CTs on the cable main core. The type of each section of the high-voltage transmission cable is divided according to the sheath connection method. The three-phase grounding loop current at the beginning and end of each section and the total grounding loop current at the beginning and end are collected to determine whether each section has an abnormality. The current information of the abnormal section is then calculated to further uniquely identify and locate seven major types of typical grounding system defects in the abnormal section. By online monitoring of the main core current and sheath loop current at the direct grounding point and protective grounding point, and further analyzing the loop current data on the basis of improving the efficiency of the monitoring data, the unique identification and online precise location of the seven major types of typical grounding system defects are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage transmission cable fault detection, and in particular to an online detection method for typical defects in a high-voltage transmission cable grounding system. Background Art

[0002] With the development of social economy and urban construction, the volume of 110 kV and above transmission cables is increasing. Ensuring the safe operation of transmission cables is crucial. Ground loop current is a key indicator of the operating status of transmission cables. In recent years, online monitoring of ground loop current in transmission cables has become increasingly popular in various cities, but it has remained at the data collection stage and lacks further analysis and application of the monitoring data.

[0003] Typical defects in high-voltage transmission cable grounding systems include water ingress into the grounding box, breakdown of epoxy preforms within cable joints, loose joints and terminals leading to sheath open circuits, poor contact at sheath welds, and cross-connection misalignment. Existing technologies are unable to accurately classify, identify, and locate typical sheath grounding system faults.

[0004] Existing technologies, such as online partial discharge detection and dielectric loss monitoring, are primarily used for online monitoring of transmission cables. Partial discharge detection can only identify local insulation defects and cannot diagnose all fault types. Dielectric loss monitoring, on the other hand, reflects the overall aging of cable insulation. In transmission cables, leakage is associated with dielectric loss. In practical applications, it is difficult to distinguish leakage from induced current in sheath current, limiting the application of dielectric loss monitoring.

[0005] Transmission cables over 1 km in length often use cross-connections to reduce sheath induced voltage. Existing online monitoring technology for circulating current typically monitors ground current at each grounding box. The current monitored at the cross-connected grounding box is the composite current of the two sheath loops, making further analysis of circulating current data difficult. Furthermore, the number of online monitoring devices required increases the actual cost of implementation.

[0006] In view of this, this application is hereby filed. Summary of the Invention

[0007] The purpose of the present invention is to address the deficiencies in the existing technology and provide an online detection method and system for typical defects in a high-voltage transmission cable grounding system, thereby realizing the identification and location of six major types of defects in the transmission cable grounding system.

[0008] In a first aspect, the present application provides a method for online detection of typical defects in a high-voltage transmission cable grounding system, comprising the following steps:

[0009] S1: Setting up ground loop current measurement CTs and main core current measurement CTs; 4 ground loop current measurement CTs are installed at the direct grounding box and protective grounding box of each section of the high-voltage transmission cable, and 3 main core current measurement CTs are installed on the main cable core adjacent to the direct grounding box and protective grounding box. The positive direction of the ground loop current measurement CT is toward the earth, and the positive direction of the main core current measurement CT is toward the power receiving side. The types of high-voltage transmission cable sections are divided into single-terminal section, double-terminal section, and cross-connected section according to the sheath grounding method.

[0010] S2: Collect the three-phase ground loop current at the beginning and end of each section, and the total ground loop current at the beginning and end. The three-phase ground loop current at the beginning and end, as well as the total ground loop current at the beginning and end, are obtained using a ground loop current measurement CT. The beginning is located on the incoming power side, and the end is located on the receiving power side.

[0011] The three-phase grounding loop current at the first end is The three-phase grounding loop current at the end is The total ground loop current at the beginning and end is in, i represents the i-th segment, 1 represents the beginning of the segment, and 2 represents the end of the segment;

[0012] S3: Determine whether each section has any abnormalities. Analyze the three-phase grounding circulation current at the head end, the three-phase grounding circulation current at the end end, the total grounding circulation current at the head end, or the total grounding circulation current at the end end, based on the type of each section. Determine whether each section has any abnormalities. These abnormalities include abnormal protection tube current, excessively large or insufficient sheath circulation current, imbalanced sheath circulation current phases, or large phase variations in circulation current.

[0013] If there is an exception, the exception section and the exception are output;

[0014] If there is no abnormality, return to step S2;

[0015] S4: Acquisition of current information of the abnormal section; Calculation of current information of the abnormal section based on whether the beginning and the end of the abnormal section are common grounding terminals. The current information includes three-phase load current, actual three-phase grounding loop current at the beginning and the end, and actual total grounding loop current at the beginning and the end;

[0016] S5: Identification and location of defect types in abnormal sections; Identify and locate the defect types in abnormal sections based on current information and the type of abnormal section. Defect types include: protector abnormality, single-phase grounding fault of the protective layer, abnormal grounding resistance of the direct grounding point, abnormal single-circuit contact resistance, phase-to-phase short circuit fault, continuous reverse fault, and grounding loop current that does not meet regulatory requirements.

[0017] Furthermore, in S3, the type of the section is a single-terminal section, and it is determined whether there is an abnormal current in the protection tube;

[0018] If the first end of the section is the protective earthing side, It is judged that there is abnormal current in the protection tube;

[0019] If the end of the section is the protective earth side, It is judged that there is abnormal current in the protection tube;

[0020] in, k 1 is the normal current setting value of the protector, is the effective value of the three-phase grounding loop current at the beginning and end, It is the effective value of the total ground loop current at the beginning and end.

[0021] Furthermore, in S3, the type of the section is a double-terminal section or a cross-connected section, and it is determined whether the sheath circulation current is too large or too small or the sheath circulation current is unbalanced or the circulation phase changes greatly in the section.

[0022] Furthermore, the basis for judging whether there is excessive sheath circulation in the section is as follows:

[0023] It is judged that the protective layer circulation is too large;

[0024] The basis for judging whether there is a small protective layer circulation in the section is:

[0025] It is judged that the protective layer circulation is too small;

[0026] The basis for judging whether there is phase imbalance of sheath circulation in a section is:

[0027]

[0028]

[0029] It is judged that there is an imbalance between the phases of the sheath circulation;

[0030] The basis for judging whether there is a large change in the circulation phase in the section is:

[0031] It is judged that there is a large change in the circulation phase;

[0032] in, is the effective value of the three-phase grounding loop current at the beginning and end;

[0033] is the effective value of the total ground loop current at the beginning and end;

[0034] k 2 is the set circulation exceeding threshold;

[0035] k 3 is the set sheath circulation zero threshold;

[0036] k 4 is the threshold for alarming when the ratio of the maximum to minimum values of the three-phase grounding circulating current exceeds the limit;

[0037] k 5 is the setting coefficient for starting the sudden change of the sheath circulation phase;

[0038] is the absolute value of the phase change of the three-phase grounding loop current at the beginning and end, is the phase change of the three-phase grounding circulating current at the beginning and the end, which is obtained by calculating the three-phase grounding circulating current at the beginning and the end.

[0039] Furthermore, in S4, a direct grounding box is installed at the common grounding terminal, and the three-phase grounding loop current of the common grounding terminal is collected by the grounding loop current measuring CT at the direct grounding box at the common grounding terminal, and the three-phase main core current of the common grounding terminal is collected by the main core current measuring CT on the receiving side of the cable main core adjacent to the direct grounding box at the common grounding terminal;

[0040] When the head end of the abnormal section is a common grounding terminal, obtain the three-phase grounding loop current and three-phase main core current of the common grounding terminal for 4 cycles, and obtain the three-phase grounding loop current, the total grounding loop current, and the three-phase main core current at the end of the abnormal section for 4 cycles;

[0041] The three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the end of the abnormal section;

[0042] The actual three-phase grounding circulation current at the head end and the actual total grounding circulation current at the head end are the three-phase grounding circulation current at the receiving side of the common grounding terminal and the total grounding circulation current at the receiving side respectively;

[0043] The actual three-phase grounding loop current at the terminal and the actual total grounding loop current at the terminal are the three-phase grounding loop current at the terminal and the total grounding loop current at the terminal in the abnormal section respectively;

[0044] When the end of the abnormal section is a common grounding terminal, obtain the three-phase grounding loop current, the total grounding loop current, and the three-phase main core current of the abnormal section at the head end for 4 cycles, and obtain the three-phase grounding loop current and the three-phase main core current of the common grounding terminal for 4 cycles;

[0045] The three-phase load current is calculated based on the three-phase grounding loop current and the three-phase main core current at the head end of the abnormal section;

[0046] The actual three-phase grounding circulation current at the head end and the actual total grounding circulation current at the head end are the three-phase grounding circulation current at the head end and the total grounding circulation current at the head end of the abnormal section respectively;

[0047] The actual three-phase grounding circulation current at the terminal and the actual total grounding circulation current at the terminal are the three-phase grounding circulation current at the incoming power side and the total grounding circulation current at the incoming power side of the common grounding terminal respectively;

[0048] When the head and the end of the abnormal section are shared grounding terminals, obtain the three-phase grounding loop current and the three-phase main core current of the first section of the high-voltage transmission cable on the incoming power side; obtain the three-phase grounding loop current and the three-phase main core current of the shared grounding terminal of the head and the end for 4 cycles;

[0049] The three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the first end of the first section;

[0050] The actual three-phase grounding circulation current at the head end and the actual total grounding circulation current at the head end are respectively the three-phase grounding circulation current at the receiving side of the common grounding terminal of the head end and the total grounding circulation current at the receiving side;

[0051] The actual three-phase grounding circulation current at the terminal and the actual total grounding circulation current at the terminal are respectively the three-phase grounding circulation current at the incoming power side and the total grounding circulation current at the incoming power side of the common grounding terminal of the terminal;

[0052] When the beginning and the end of the abnormal section are not common ground terminals, obtain the three-phase ground loop current at the beginning and the end of the abnormal section for 4 cycles, the total ground loop current at the beginning and the end, and the three-phase main core current at the beginning and the end;

[0053] The three-phase load current is calculated based on the three-phase grounding loop current and the three-phase main core current at the first end of the abnormal section or the three-phase grounding loop current and the three-phase main core current at the last end of the abnormal section;

[0054] The actual three-phase grounding circulation current at the beginning and end is the three-phase grounding circulation current at the beginning and end of the abnormal section;

[0055] The actual total ground loop current at the beginning and end is the total ground loop current at the beginning and end of the abnormal section.

[0056] Furthermore, when the three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the head end of the abnormal section or the three-phase ground loop current and the three-phase main core current at the head end of the first section, the three-phase load current calculation formula is:

[0057] When the three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the end of the abnormal section, the three-phase load current calculation formula is:

[0058] Where, is the three-phase load current, They are the three-phase grounding loop current and the three-phase main core current at the first end of the abnormal section or the three-phase grounding loop current and the three-phase main core current at the first end of the first section;

[0059] They are the three-phase ground loop current and the three-phase main core current at the head end of the abnormal section respectively.

[0060] Furthermore, the calculation formulas for the three-phase ground loop current on the receiving side and the total ground loop current on the receiving side are:

[0061]

[0062] The calculation formulas for the three-phase ground loop current on the incoming power side and the total ground loop current on the incoming power side are:

[0063]

[0064] Where: is the three-phase load current, It is the three-phase grounding loop current on the receiving side; is the total ground loop current on the receiving side; It is the three-phase ground loop current on the incoming power side; is the total ground loop current on the incoming power side; It is the three-phase grounding loop current with a common ground terminal; It is the three-phase main core current of the common ground terminal.

[0065] Furthermore, in S5, the abnormal section is a single-terminal section, and the steps of identifying and locating the defect type of the abnormal section include:

[0066] S501: Calculation of judgment information;

[0067] Calculate the effective value of the three-phase grounding loop current on the protective grounding side of the abnormal section based on the current information;

[0068] When the protective earthing side is the head end of the abnormal section, the effective value of the three-phase grounding circulating current on the protective earthing side of the abnormal section is the effective value of the actual three-phase grounding circulating current at the head end of the abnormal section;

[0069] When the protective earthing side is at the end of the abnormal section, the effective value of the three-phase grounding circulating current on the protective earthing side of the abnormal section is the effective value of the actual three-phase grounding circulating current at the end of the abnormal section;

[0070] S502: Determine whether there is a protector abnormality;

[0071] Judgment criterion I is that the effective value of the three-phase grounding loop current on the protective grounding side of the abnormal section is greater than k The value of 1, where k 1 is the normal current setting value of the protector;

[0072] If the judgment criterion I is met, then according to the k The X phase corresponding to the value of 1 has an X phase protector abnormality in the output abnormal section, and the X phase is A phase, B phase, or C phase;

[0073] If the judgment basis I is not met, the judgment is terminated.

[0074] Furthermore, in S5, the abnormal section is a double-terminal section or a cross-connection section, and the steps of identifying and locating the defect type of the abnormal section include:

[0075] S501: Calculation of judgment information;

[0076] Based on the current information, calculate the effective value of the actual three-phase grounding loop current at the beginning and end of the abnormal section, the absolute value of the amplitude change of the actual three-phase grounding loop current at the beginning and end, the absolute value of the phase change of the actual three-phase grounding loop current at the beginning and end, the vector difference between the actual grounding loop current at the beginning and the actual grounding loop current at the end of phase A, phase B and phase C, the amplitude mutation of the actual three-phase grounding loop current vector at the beginning, the amplitude change of the actual total grounding loop current vector at the beginning, the amplitude mutation of the actual grounding loop current vector at the beginning and end of each loop, the vector difference of the actual grounding loop current at the beginning and end, and the difference between the amplitude mutation of the actual grounding loop vector at the beginning and end;

[0077] S502: Determine whether there is a sheath single-phase grounding fault;

[0078] Judgment basis II is that there is a loop K in the abnormal section and the actual ground loop current vector amplitude mutation is greater than k 7 E 0 is greater than 1.2 times the actual grounding loop current vector amplitude mutation at the head end of the other two loops and the actual grounding loop current vector difference between the head end and the end end of loop K is greater than k 8. The actual grounding current vector difference between the first and the last two loops is less than k 8;

[0079] Or there is a loop K at the end of the abnormal section, and the actual grounding loop current vector amplitude mutation is greater than k 7 E 0 is greater than 1.2 times the actual grounding loop current vector amplitude mutation at the end of the other two loops and the actual grounding loop current vector difference between the beginning and end of loop K is greater than k 8. The actual grounding current vector difference between the first and the last two loops is less than k 8;

[0080] in, E 0 is the amplitude reference value, k 7 is the setting coefficient for the sudden change of sheath current amplitude, k8 is the threshold of the normal current amplitude difference;

[0081] If judgment criterion II is met, calculate the fault distance of the circulating current loop K, and output the existence of a sheath single-phase grounding fault and the fault distance of the circulating current loop K in the abnormal section;

[0082] If judgment criterion II is not met, proceed to the next step;

[0083] S503: Determine whether there is abnormal grounding resistance at the direct grounding point;

[0084] Judgment basis III is that the actual three-phase grounding circulating current vector amplitude mutation at the head end of the abnormal section is greater than k 7 E 0 and the effective value of the actual three-phase grounding loop current at the head end is less than or equal to E 0;

[0085] If judgment criterion III is met, there is abnormal grounding resistance at the direct grounding point in the output abnormal section;

[0086] If judgment criterion III is not met, proceed to the next step;

[0087] S504: Determine whether there is a single-circuit contact resistance abnormality;

[0088] Judgment basis IV is that there is a loop K in the abnormal section and the actual ground loop current vector amplitude mutation is greater than k 7 E 0 is greater than 1.2 times the actual grounding circulation vector amplitude mutation at the head end of the other two circulation loops, and the difference between the actual grounding circulation vector amplitude mutation at the head end and the end end of the circulation loop K is less than k 8;

[0089] If judgment criterion IV is met, the circulating current loop K in the output abnormal section has a single-loop contact resistance abnormality;

[0090] If judgment criterion IV is not met, proceed to the next step;

[0091] S505: Determine whether a phase-to-phase short circuit fault occurs;

[0092] The judgment basis is that the absolute value of the actual ground loop current amplitude change at the X phase and the absolute value of the actual ground loop current phase change at the head end of the abnormal section V is greater than 2 times the absolute value of the actual ground loop amplitude change at the head end of the third phase and the absolute value of the actual ground loop phase change at the head end, and the amplitude of the actual total ground loop current vector change at the head end is less than k 8; X phase and Y phase are any two phases among A phase, B phase and C phase;

[0093] If the judgment criterion V is met, a phase-to-phase short circuit fault occurs between the X and Y phases at the head end of the output abnormal section;

[0094] If the judgment criterion V is not met, proceed to the next step;

[0095] S506: Determine whether there is a continuous reverse fault;

[0096] The judgment basis VI is that the effective value of the actual three-phase grounding loop current at the beginning or end of the abnormal section is greater than k 9 / 3 and the vector difference between the actual ground loop current at the beginning and the actual ground loop current at the end of phase A, phase B and phase C in the abnormal section is less than k 8, among which k 9 is the over-limit alarm threshold of the sheath circulation;

[0097] If the judgment criterion VI is met, there is a continuous reverse fault in the output abnormal section;

[0098] If judgment criterion VI is not met, proceed to the next step;

[0099] S507: Determine whether there is a ground loop current that does not meet regulatory requirements;

[0100] Judgment criterion VII is that the effective values of the actual three-phase grounding loop current at the beginning and end of the abnormal section are greater than 20% of the effective values of the corresponding three-phase load current;

[0101] Judgment criterion VIII is that the ratio of the maximum effective value of the actual three-phase grounding circulation current at the head end to the minimum effective value of the actual three-phase grounding circulation current at the head end of the abnormal section is greater than 3, or the ratio of the maximum effective value of the actual three-phase grounding circulation current at the end end to the minimum effective value of the actual three-phase grounding circulation current at the end end is greater than 3;

[0102] Judgment criterion VIIII is that the effective value of the actual three-phase ground loop current at the beginning or end of the abnormal section is greater than 100A;

[0103] If judgment criteria VII, VIII, or VIIII are met, then there is a ground loop in the output abnormal section that does not meet the requirements of the regulations;

[0104] If the criteria VII, VIII, and VIIII are not met, the judgment is terminated.

[0105] In a second aspect, the present application provides an online detection system for typical defects in a high-voltage transmission cable grounding system, comprising a front-end anomaly analysis system and a back-end defect identification and positioning system;

[0106] The front-end abnormality analysis system includes: section management module, section information collection module, abnormal section judgment and alarm module;

[0107] The background defect identification and positioning system includes: section current information collection and calculation module, abnormal section defect type identification and positioning module;

[0108] The section management module is used to manage section information of high-voltage transmission cables. Four ground loop current measurement CTs are installed at the direct grounding box and protective grounding box in the section, and three main core current measurement CTs are installed on the cable main core adjacent to the direct grounding box and protective grounding box. The positive direction of the ground loop current measurement CT is the grounding direction, and the positive direction of the main core current measurement CT is the receiving side direction. The section type is divided into single-terminal section, double-terminal section, and cross-connected section according to the sheath grounding method;

[0109] The section information collection module is used to collect the three-phase ground loop current at the beginning and end of each section, and the total ground loop current at the beginning and end. The beginning is located on the incoming power side of the loop, and the end is located on the receiving power side of the loop.

[0110] The abnormal section judgment and alarm module is used to judge whether there is any abnormality in each section. According to the type of each section, the module analyzes the three-phase grounding circulation current at the head end, the three-phase grounding circulation current at the end end, the total grounding circulation current at the head end, or the total grounding circulation current at the end end. It judges whether there is any abnormality in each section. The abnormality is abnormal protection tube current, excessive sheath circulation current, insufficient sheath circulation current, imbalance between sheath circulation phases, or excessive phase change of circulation current.

[0111] If there is an exception, the abnormal section and the exception are output; if there is no exception, the section information collection module is returned;

[0112] Section current information collection and calculation module: used to obtain the information collected by the section information collection module and calculate the current information of the abnormal section. The current information includes: three-phase load current, actual three-phase ground loop current at the beginning and end, and actual total ground loop current at the beginning and end;

[0113] The abnormal section defect type identification and positioning module is used to identify and locate the defect type of the abnormal section based on the current information and the type of the abnormal section. The defect types include: protector abnormality, single-phase grounding fault of the protective layer, abnormal grounding resistance of the direct grounding point, abnormal single-loop contact resistance, phase-to-phase short circuit fault, continuous reverse fault, and grounding loop current that does not meet the requirements of the regulations. The beneficial effects of the present invention are:

[0114] (1) The present invention proposes an online detection method for typical defects in the grounding system of a high-voltage transmission cable. By performing online monitoring of the main core current and sheath circulating current at the direct grounding point and protective grounding point, the circulating current data is further analyzed on the basis of improving the efficiency of the monitoring data, thereby realizing the identification and location of typical grounding system defects. The circulating current monitoring method is to divide the sections based on the direct grounding point and the protective grounding point, and the current monitoring equipment is arranged at the direct grounding and protective grounding positions. A set of monitoring devices includes 7 CTs, which respectively monitor the three-phase main core current, the three-phase sheath circulating current, and the total sheath grounding current.

[0115] (2) This application classifies the faults in the defective section into seven types: protector abnormality, sheath single-phase grounding fault, direct grounding point grounding resistance abnormality, single-circuit contact resistance abnormality, phase-to-phase short circuit fault, continuous reverse fault, and grounding loop current that does not meet the requirements of the regulations. It realizes the unique identification and online precise positioning of the seven types of typical grounding system defects. The loop current monitoring method is convenient and covers a full range of fault types. It can help high-voltage transmission cable operation and maintenance personnel to detect faults in the first time and improve cable operation safety and transmission capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0116] Figure 1 Schematic diagram of an online detection method for typical defects in high-voltage transmission cable grounding systems.

[0117] Figure 2 This is a current monitoring method for S1 in a typical online defect detection method for a high-voltage transmission cable grounding system.

[0118] Figure 3 Schematic diagram of S3 anomaly judgment in an online detection method for typical defects in a high-voltage transmission cable grounding system.

[0119] Figure 4 This is a schematic diagram of two groups of cross-connected unit lines.

[0120] Figure 5 FIG. 2 is a schematic diagram of the judgment flow for the single-terminal section S5. FIG.

[0121] Figure 6 It is a schematic diagram of the judgment process for the double-terminal area section and the cross-connection section S5.

[0122] Figure 7 The following is a block diagram of the composition of a typical online defect detection system for a high-voltage transmission cable grounding system.

[0123] Among them: 1 is the direct grounding box; 2 is the cross-connected grounding box; 3 is the protective grounding box; 4 is the ground loop current measurement CT; 5 is the main core current measurement CT. DETAILED DESCRIPTION

[0124] It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The method of the present invention is further described in detail below with reference to the accompanying drawings.

[0125] This embodiment discloses Figure 1 A method for online detection of typical defects in a high-voltage transmission cable grounding system is shown, which specifically includes the following steps:

[0126] S1: Setting up ground loop current measurement CTs and main core current measurement CTs; 4 ground loop current measurement CTs are installed at the direct grounding box and protective grounding box of each section of the high-voltage transmission cable, and 3 main core current measurement CTs are installed on the main cable core adjacent to the direct grounding box and protective grounding box. The positive direction of the ground loop current measurement CT is toward the earth, and the positive direction of the main core current measurement CT is toward the power receiving side. The types of high-voltage transmission cable sections are divided into single-terminal section, double-terminal section, and cross-connected section according to the sheath grounding method.

[0127] S2: Collect the three-phase ground loop current at the beginning and end of each section, and the total ground loop current at the beginning and end. The three-phase ground loop current at the beginning and end, as well as the total ground loop current at the beginning and end, are obtained using a ground loop current measurement CT. The beginning is located on the incoming power side, and the end is located on the receiving power side.

[0128] The three-phase grounding loop current at the first end is The three-phase grounding loop current at the end is The total ground loop current at the beginning and end is in, i represents the i-th segment, 1 represents the beginning of the segment, and 2 represents the end of the segment;

[0129] S3: Determine whether each section has any abnormalities. Analyze the three-phase grounding circulation current at the head end, the three-phase grounding circulation current at the end end, the total grounding circulation current at the head end, or the total grounding circulation current at the end end, based on the type of each section. Determine whether each section has any abnormalities. These abnormalities include abnormal protection tube current, excessively large or insufficient sheath circulation current, imbalanced sheath circulation current phases, or large phase variations in circulation current.

[0130] If there is an exception, the exception section and the exception are output;

[0131] If there is no abnormality, return to step S2;

[0132] S4: Acquisition of current information of abnormal section;

[0133] According to whether the beginning and the end of the abnormal section are common ground terminals, the current information of the abnormal section is calculated. The current information includes three-phase load current, actual three-phase grounding loop current at the beginning and the end, and actual total grounding loop current at the beginning and the end;

[0134] S5: Identification and location of defect types in abnormal sections; based on the current information and the type of abnormal section, the defect type of the abnormal section is identified and judged. The defect types include: protector abnormality, single-phase grounding fault of the protective layer, abnormal grounding resistance of the direct grounding point, abnormal single-circuit contact resistance, phase-to-phase short circuit fault, continuous reverse fault, and grounding loop current that does not meet the requirements of the regulations.

[0135] Specifically, step S1 realizes the collection of grounding loop current and main core current information of each phase in each section of the high-voltage transmission cable. The current monitoring method in this embodiment is as follows: Figure 2 As shown, 1#~4# connectors are all insulated connectors. Terminal 1# is specified as the incoming power side and terminal 2# is specified as the receiving power side. The types of sections are divided into single-terminal section, double-terminal section, and cross-connected section according to the sheath grounding method. Figure 2 It includes three cable sheath grounding methods: double-end grounding, cross-connected grounding and single-end grounding. In the figure, the 1# terminal to the 1# connector is directly grounded at both ends, which is the first section of the cable line (double-terminal section); the 1# connector to the 4# connector is a complete cross-connected unit, which is the second section of the cable line (cross-connected section); the 4# connector to the 2# terminal is single-end grounded, which is the third section of the line (single-terminal section).

[0136] In this embodiment, the current monitoring device is used to monitor the three-phase circulating current, grounding circulating current, total grounding circulating current and three-phase main core current at the beginning and end of the section. The grounding circulating current measurement CT is set at the direct grounding point and the protective grounding point. The main core current measurement CT is set on the cable main core adjacent to the direct grounding point and the protective grounding point. No monitoring device is arranged at the cross-interconnected grounding point.

[0137] This embodiment places ground loop current measurement CTs in both the direct grounding box and the protective grounding box, and three main core current measurement CTs in the cable core. These CTs provide online monitoring of the three-phase ground loop current, total ground loop current, and main core current. The positive direction of the ground loop current measurement CTs is toward the earth, while the positive direction of the main core current measurement CTs is toward the receiving side. This effectively simplifies the circulating current monitoring method, monitoring current only at the direct grounding point and the protective grounding point, obtaining valid data and saving equipment costs.

[0138] In step S2, the three-phase ground loop currents at the beginning and end of each section and the total ground loop currents at the beginning and end are obtained through the ground loop current measurement CT.

[0139] Step S3 analyzes the three-phase grounding loop current at the head end or the three-phase grounding loop current at the end end or the total grounding loop current at the head end or the total grounding loop current at the end end of each section according to the type of each section, and determines whether there is any abnormality in each section. Possible abnormalities include: abnormal protection tube current, large sheath loop current, small sheath loop current, imbalance between phases of sheath loop current, and large change in loop phase.

[0140] Different sheath connection methods are used for different section types. The sheath connection methods include single-end grounding, double-end grounding, and cross-connected grounding. Different sheath connection methods may cause different abnormalities. In order to accurately judge the abnormality of the section, it is first necessary to determine the type of section and select different abnormality judgment standards, such as Figure 3 As shown, different abnormal situations are judged for different sheath connection methods.

[0141] If the section type is single-end grounding, determine whether there is abnormal current in the protective tube based on the effective value of the three-phase grounding loop current at the first end, the three-phase grounding loop current at the last end, the total grounding loop current at the first end, or the total grounding loop current at the last end.

[0142] If the first end of the section is the protective earthing side, It is judged that there is abnormal current in the protection tube;

[0143] If the end of the section is the protective earth side, It is judged that there is abnormal current in the protection tube;

[0144] in, k 1 is the normal current setting value of the protector, is the effective value of the three-phase grounding loop current at the beginning and end, It is the effective value of the total ground loop current at the beginning and end.

[0145] Figure 2 The section from the 4# connector to the 2# terminal is the third section of the cable line. This section is a single-terminal section. For this section, it is only necessary to determine whether there is an abnormal current in the protection tube. In this embodiment, the 2# terminal is the protective grounding side, that is, the end of this section is the protective grounding side. When the effective value of the three-phase grounding loop current at the end of this section is greater than k 1 or the effective value of the total ground loop current at the end is greater than 1.5 times k The value of 1, k 1 The default value is 1-2A, which means there is abnormal current in the protection tube, and the output abnormal section is the 3rd section.

[0146] For sections with double-terminal connection or cross-connection connection, determine whether there is excessively large or insufficient sheath circulation, imbalanced sheath circulation, or excessively large phase changes in circulation.

[0147] The basis for judging whether there is excessive sheath circulation in a section is:

[0148] It is judged that the protective layer circulation is too large. k 2 is the set circulation exceeding threshold;

[0149] The basis for judging whether there is a small protective layer circulation in the section is:

[0150] It is judged that there is a small protective layer circulation, among which k 3 is the set sheath circulation zero threshold;

[0151] The basis for judging whether there is phase imbalance of sheath circulation in a section is:

[0152]

[0153]

[0154] It is judged that there is an imbalance between the phases of the sheath circulation. k 4 is the threshold for alarming when the ratio of the maximum to minimum values of the three-phase grounding circulating current exceeds the limit;

[0155] The basis for judging whether there is a large change in the circulation phase in the section is:

[0156] It is judged that there is a large change in the circulation phase. k 5 is the setting coefficient for starting the sudden change of the sheath circulation phase;

[0157] in, is the effective value of the three-phase grounding loop current at the beginning and end;

[0158] is the effective value of the total ground loop current at the beginning and end;

[0159] is the absolute value of the phase change of the three-phase grounding loop current at the beginning and end, is the phase change of the three-phase grounding circulating current at the beginning and the end, which is obtained by calculating the three-phase grounding circulating current at the beginning and the end.

[0160] In this embodiment, Figure 2 The section from terminal 1# to connector 1# is the direct connection section at both ends, which is the first section of the cable line. Figure 2 The 1# connector to the 4# connector is a complete cross-connection unit, which is the second section of the cable line. The section is a cross-connection connection area. It is judged whether the sheath circulating current is too large or too small or the sheath circulating current is unbalanced or the circulating current phase changes are too large in the section.

[0161] (1) The judgment basis for whether there is a large circulating current in the section is: when the effective value of the three-phase grounding circulating current at the beginning and end is greater than k 2 or the effective value of the total ground loop current at the beginning and end is greater than 1.5 timesk If the value is 2, it is judged that there is a large circulation. k 2 is the set circulating current exceeding threshold, the default value is 50-100A.

[0162] There is a large circulation; There is a relatively large circulation.

[0163] (2) The judgment basis for judging whether there is a small circulating current in the section is: when the effective value of the three-phase grounding circulating current at the beginning and end is less than k If the value is 3, it is judged that there is a small circulation, where k 3 is the set sheath circulating current zero threshold, the default value is 0.1-5A.

[0164] There is a small circulation.

[0165] (3) The judgment basis for whether there is phase imbalance of the sheath circulation in the section is: when the ratio of the maximum effective value of the three-phase grounding circulation at the head end to the minimum effective value of the three-phase grounding circulation at the head end is greater than k 4 and the minimum effective value of the three-phase ground loop current at the head end is greater than 5A, or the ratio of the maximum effective value of the three-phase ground loop current at the end end to the minimum effective value of the three-phase ground loop current at the end end is greater than k 4 and the minimum effective value of the three-phase grounding circulating current at the end is greater than 5A, it is judged that there is an imbalance between the phases of the sheath circulating current. k 4 is the threshold for the alarm when the ratio of the maximum value to the minimum value of the three-phase ground loop current exceeds the limit. The default value is 3-5A.

[0166] There is an imbalance between the phases of the sheath circulation;

[0167] There is an imbalance between the phases of the sheath circulation.

[0168] (4) The judgment basis for whether there is a large output circulating current phase change in the section is: when the absolute value of the phase change of the three-phase grounding circulating current at the head and the end is greater than k If the value is 5, it is judged that the output circulating current phase change is too large. k 5 is the setting coefficient for starting the sheath circulation phase mutation, and the default value is 10°-20°.

[0169] There is a large change in the output circulating current phase.

[0170] The existence of the abnormal section is determined through steps S1-S3. After completing the above steps, step S4 will further obtain the data of the abnormal section. For the abnormal section, it is first necessary to determine whether there is a common grounding terminal. In actual engineering applications, the beginning or end of the cross-connected grounding section is the common grounding terminal. The current collected by the ground loop current measurement CT and the main core current measurement CT at the common grounding terminal is the measured current, which is the sum of the sheath currents of the two sections. Therefore, when making an abnormal judgment, it is necessary to separate the values of the two sections in the measurement data before making a judgment, that is, to obtain the actual sheath currents at the end of the previous section and the beginning of the next section respectively.

[0171] S4: Acquisition of current information of the abnormal section; the current information of the abnormal section includes: three-phase load current, actual three-phase ground loop current at the beginning and the end, and actual total ground loop current at the beginning and the end.

[0172] To obtain current information, it is first necessary to determine whether the beginning or end of the abnormal section is a common grounding terminal. A direct grounding box is installed at the common grounding terminal. The three-phase grounding loop current at the common grounding terminal is collected using a grounding loop current measurement CT at the direct grounding box at the common grounding terminal. The three-phase main core current at the common grounding terminal is collected using a main core current measurement CT located on the receiving side of the cable main core adjacent to the direct grounding box at the common grounding terminal.

[0173] When the head end of the abnormal section is a common grounding terminal, obtain the three-phase grounding loop current and three-phase main core current of the common grounding terminal for 4 cycles, and obtain the three-phase grounding loop current, the total grounding loop current, and the three-phase main core current at the end of the abnormal section for 4 cycles;

[0174] The three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the end of the abnormal section;

[0175] The actual three-phase grounding circulation current at the head end and the actual total grounding circulation current at the head end are the three-phase grounding circulation current at the receiving side of the common grounding terminal and the total grounding circulation current at the receiving side respectively;

[0176] The actual three-phase ground loop current at the terminal and the actual total ground loop current at the terminal are the three-phase ground loop current at the terminal and the total ground loop current at the terminal in the abnormal section respectively.

[0177] When the end of the abnormal section is a common grounding terminal, obtain the three-phase grounding loop current, the total grounding loop current, and the three-phase main core current of the abnormal section at the head end for 4 cycles, and obtain the three-phase grounding loop current and the three-phase main core current of the common grounding terminal for 4 cycles;

[0178] The three-phase load current is calculated based on the three-phase grounding loop current and the three-phase main core current at the head end of the abnormal section;

[0179] The actual three-phase grounding circulation current at the head end and the actual total grounding circulation current at the head end are the three-phase grounding circulation current at the head end and the total grounding circulation current at the head end of the abnormal section respectively;

[0180] The actual three-phase grounding loop current at the terminal and the actual total grounding loop current at the terminal are the three-phase grounding loop current at the incoming power side and the total grounding loop current at the incoming power side of the common grounding terminal, respectively.

[0181] When the head and end of the abnormal section are common grounding terminals, the three-phase grounding loop current and the three-phase main core current at the head end of the first section on the incoming side of the high-voltage transmission cable are obtained; the three-phase grounding loop current and the three-phase main core current of the common grounding terminal at the head and end of the abnormal section of 4 cycles are obtained.

[0182] The three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the first end of the first section;

[0183] The actual three-phase grounding loop current and the actual total grounding loop current at the head end of the abnormal section are respectively the three-phase grounding loop current and the total grounding loop current at the receiving side of the common grounding terminal at the head end of the abnormal section;

[0184] The actual three-phase grounding loop current at the end of the abnormal section and the actual total grounding loop current at the end are respectively the three-phase grounding loop current at the incoming power side and the total grounding loop current at the incoming power side of the common grounding terminal at the end of the abnormal section.

[0185] When the beginning and the end of the abnormal section are not common ground terminals, obtain the three-phase ground loop current at the beginning and the end of the abnormal section for 4 cycles, the total ground loop current at the beginning and the end, and the three-phase main core current at the beginning and the end;

[0186] The three-phase load current is calculated based on the three-phase grounding loop current and the three-phase main core current at the first end of the abnormal section or the three-phase grounding loop current and the three-phase main core current at the last end of the abnormal section;

[0187] The actual three-phase grounding loop current at the beginning and end of the abnormal section is the three-phase grounding loop current at the beginning and end of the abnormal section;

[0188] The actual total ground loop current at the beginning and end of the abnormal section is the total ground loop current at the beginning and end of the abnormal section.

[0189] When the three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the first end of the abnormal section or the three-phase ground loop current and the three-phase main core current at the first end of the first section, the three-phase load current calculation formula is:

[0190]

[0191] When the three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the end of the abnormal section, the three-phase load current calculation formula is:

[0192]

[0193] in, is the three-phase load current, They are the three-phase grounding loop current and the three-phase main core current at the first end of the abnormal section or the three-phase grounding loop current and the three-phase main core current at the first end of the first section;

[0194] They are the three-phase ground loop current at the end of the abnormal section and the three-phase main core current at the end.

[0195] Figure 4 This is a schematic diagram of the wiring of two sets of cross-connection units. Terminal 1# is for incoming power measurement, and terminal 2# is for the receiving side. Connectors 1#, 2#, 4#, and 5# are insulated connectors; connector 3# is a straight-through connector. Section 1, with cross-connection arrangement ABC, is from terminal 1# to connector 3#; section 2, with cross-connection arrangement ACB. Online monitoring equipment is installed only at terminals 1#, 2#, and connector 3#. Connector 3# is directly grounded, serving as the common ground terminal for the cross-connection units on both sides. The ground line current is the vector sum current of the units on both sides. A three-phase main core measurement CT is uniformly placed on the receiving side at the common ground terminal.

[0196] The calculation formulas for the three-phase grounding circulation current on the receiving side of the common grounding terminal and the total grounding circulation current on the receiving side are:

[0197]

[0198] The calculation formulas for the three-phase ground loop current on the incoming power side and the total ground loop current on the incoming power side of the common ground terminal are:

[0199]

[0200] Where: is the three-phase load current, It is the three-phase grounding loop current on the receiving side; is the total ground loop current on the receiving side; It is the three-phase ground loop current on the incoming power side; is the total ground loop current on the incoming power side; It is the three-phase grounding loop current with a common ground terminal; It is the three-phase main core current of the common ground terminal.

[0201] by Figure 4 For example, the calculation formulas for the three-phase grounding circulating current and the total circulating current at the end of the first section, i.e., the incoming power side of the common grounding terminal, are:

[0202]

[0203] The calculation formulas for the three-phase grounding circulating current and the total circulating current at the first end of the second section, i.e., the receiving side of the common grounding terminal, are:

[0204]

[0205] In order to ensure the accuracy of defect judgment, a secondary judgment can be made on the abnormal section. In this embodiment, after step S4 and before step S5, a secondary judgment on the abnormality of the abnormal section is also included. Based on the information collected in step 4, a secondary judgment is made on whether there is an abnormality in the abnormal area.

[0206] If the result of the second judgment is consistent with the result of step 3, proceed to step 5;

[0207] If the result of the second judgment is inconsistent with the result of step 3, then the output is no exception.

[0208] After step 3, it is determined that the output circulation phase in the output abnormal section i is significantly changed.

[0209] Step 4: collect the three-phase ground loop current at the beginning and end of the abnormal section i, the total ground loop current at the beginning and end, and the three-phase main core current at the beginning and end;

[0210] The secondary judgment is to judge whether there is a large output circulating current phase change in the abnormal section i based on the information collected in step 4.

[0211] Step S5 obtains the current information of the abnormal section according to step S4, and identifies and locates the defect type of the abnormal section according to the obtained current information and the type of the abnormal section. The defect types include: protector abnormality, single-phase grounding fault of the protective layer, abnormal grounding resistance of the direct grounding point, abnormal single-loop contact resistance, phase-to-phase short circuit fault, continuous reverse fault, and grounding loop current that does not meet the requirements of the regulations.

[0212] Different judgment rules are adopted for different section types. In step S5, the type of the abnormal section is a single-terminal section. The steps of identifying and locating the defect type of the abnormal section include:

[0213] S501: Calculation of judgment information;

[0214] Calculate the effective value of the three-phase grounding loop current on the protective grounding side of the abnormal section based on the current information;

[0215] When the protective earthing side is the head end of the abnormal section, the effective value of the three-phase grounding circulating current on the protective earthing side of the abnormal section is the effective value of the actual three-phase grounding circulating current at the head end of the abnormal section;

[0216] When the protective earthing side is at the end of the abnormal section, the effective value of the three-phase grounding circulating current on the protective earthing side of the abnormal section is the effective value of the actual three-phase grounding circulating current at the end of the abnormal section;

[0217] S502: Determine whether there is a protector abnormality;

[0218] Judgment criterion I is that the effective value of the three-phase grounding loop current on the protective grounding side of the abnormal section is greater than k The value of 1, where k 1 is the normal current setting value of the protector;

[0219] If the judgment criterion I is met, then according to the k The X phase corresponding to the value of 1 has an X phase protector abnormality in the output abnormal section, and the X phase is A phase, B phase, or C phase;

[0220] If the judgment basis I is not met, the judgment is terminated.

[0221] If the abnormal section is a single-terminal section, it is only necessary to determine whether there is a protector abnormality in the abnormal section.

[0222] For abnormal sections whose types are double-terminal sections or cross-connected sections, it is necessary to judge in turn whether there is a single-phase grounding fault in the protective layer, abnormal grounding resistance at the direct grounding point, abnormal single-circuit contact resistance, phase-to-phase short circuit fault, continuous reverse fault, or grounding loop current that does not meet the requirements of the regulations.

[0223] In step S5, for the double-terminal section or the cross-connection section, the steps of identifying and locating the defect type of the abnormal section include:

[0224] S501: Calculation of judgment information;

[0225] Based on the current information, calculate the effective value of the actual three-phase grounding loop current at the beginning and end of the abnormal section, the absolute value of the amplitude change of the actual three-phase grounding loop current at the beginning and end, the absolute value of the phase change of the actual three-phase grounding loop current at the beginning and end, the vector difference between the actual grounding loop current at the beginning and the actual grounding loop current at the end of phase A, phase B and phase C, the amplitude mutation of the actual three-phase grounding loop current vector at the beginning, the amplitude change of the actual total grounding loop current vector at the beginning, the amplitude mutation of the actual grounding loop current vector at the beginning and end of each loop, the vector difference of the actual grounding loop current at the beginning and end, and the difference between the amplitude mutation of the actual grounding loop vector at the beginning and end;

[0226] S502: Determine whether there is a sheath single-phase grounding fault;

[0227] Judgment basis II is that there is a loop K in the abnormal section and the actual ground loop current vector amplitude mutation is greater than k 7 E 0 is greater than 1.2 times the actual grounding loop current vector amplitude mutation at the head end of the other two loops and the actual grounding loop current vector difference between the head end and the end end of loop K is greater than k8. The actual grounding current vector difference between the first and the last two loops is less than k 8;

[0228] Or there is a loop K at the end of the abnormal section, and the actual grounding loop current vector amplitude mutation is greater than k 7 E 0 is greater than 1.2 times the actual grounding loop current vector amplitude mutation at the end of the other two loops and the actual grounding loop current vector difference between the beginning and end of loop K is greater than k 8. The actual grounding current vector difference between the first and the last two loops is less than k 8;

[0229] in, E 0 is the amplitude reference value, k 7 is the setting coefficient for the sudden change of sheath current amplitude, k 8 is the threshold of the normal current amplitude difference;

[0230] If judgment criterion II is met, calculate the fault distance of the circulating current loop K, and output the existence of a sheath single-phase grounding fault and the fault distance of the circulating current loop K in the abnormal section;

[0231] If judgment criterion II is not met, proceed to the next step.

[0232] The cross-connection area segment connection mode is ABC or ACB, the former is referred to as mode 1 and the latter is referred to as mode 2 in the following text.

[0233] In this embodiment, a single-phase grounding fault occurs in the ABC circulation circuit as an example:

[0234] If the above judgment criteria are met, the grounding loop data at the beginning and end of the loop K are substituted into the corresponding positioning formula to calculate the fault distance, and the presence of a sheath single-phase grounding fault and the fault distance of the loop ABC in the abnormal section i are output.

[0235] S503: Determine whether there is abnormal grounding resistance at the direct grounding point;

[0236] Judgment basis III is that the actual three-phase grounding circulating current vector amplitude mutation at the head end of the abnormal section is greater than k 7 E 0 and the effective value of the actual three-phase grounding loop current at the head end is less than or equal to E 0;

[0237] If judgment criterion III is met, there is abnormal grounding resistance at the direct grounding point in the output abnormal section.

[0238] Specifically, There is abnormal grounding resistance at the direct grounding point in the output abnormal section i.

[0239] If judgment criterion III is not met, proceed to the next step;

[0240] S504: Determine whether there is a single-circuit contact resistance abnormality;

[0241] Judgment basis IV is that there is a loop K in the abnormal section and the actual ground loop current vector amplitude mutation is greater than k 7 E 0 is greater than 1.2 times the actual grounding circulation vector amplitude mutation at the head end of the other two circulation loops, and the difference between the actual grounding circulation vector amplitude mutation at the head end and the end end of the circulation loop K is less than k 8;

[0242] If judgment criterion IV is met, the circulating current loop K in the output abnormal section has a single-loop contact resistance abnormality;

[0243] If judgment criterion IV is not met, proceed to the next step.

[0244] In this embodiment, the ABC circuit takes the single-phase contact resistance abnormality as an example, and the judgment basis is

[0245] If the judgment criteria are met, the circulating current loop ABC in the abnormal section i has a single-loop contact resistance anomaly; if the judgment criteria are not met, go to the next step.

[0246] S505: Determine whether a phase-to-phase short circuit fault occurs;

[0247] The judgment basis is that the absolute value of the actual ground loop current amplitude change at the X phase and the absolute value of the actual ground loop current phase change at the head end of the abnormal section V is greater than 2 times the absolute value of the actual ground loop amplitude change at the head end of the third phase and the absolute value of the actual ground loop phase change at the head end, and the amplitude of the actual total ground loop current vector change at the head end is less than k 8; X phase and Y phase are any two phases among A phase, B phase and C phase;

[0248] If the judgment criterion V is met, a phase-to-phase short circuit fault occurs between the X and Y phases at the head end of the output abnormal section;

[0249] If the judgment criterion V is not met, proceed to the next step.

[0250] This embodiment takes the case where a short circuit occurs between phases A and B in the first cross-connection section of the first embodiment as an example. If the judgment criteria are met, the output is that a phase-to-phase short circuit fault occurs between phases A and B at the head end of the abnormal section i; if the judgment criteria are not met, go to the next step.

[0251] S506: Determine whether there is a continuous reverse fault;

[0252] The judgment basis VI is that the effective value of the actual three-phase grounding loop current at the beginning or end of the abnormal section is greater than k 9 / 3 and the vector difference between the actual ground loop current at the beginning and the actual ground loop current at the end of phase A, phase B and phase C in the abnormal section is less than k 8, among which k 9 is the over-limit alarm threshold of the sheath circulation;

[0253] If the judgment criterion VI is met, there is a continuous reverse fault in the output abnormal section;

[0254] If judgment criterion VI is not met, proceed to the next step;

[0255] In this embodiment, when

[0256] It is the vector difference between the actual ground loop current at the beginning and the end of phases A, B, and C in the abnormal section (section i). If the criterion is met, it is output that there is a continuous reverse fault in the abnormal section.

[0257] S507: Determine whether there is a ground loop current that does not meet regulatory requirements;

[0258] Judgment basis VII is

[0259] The effective values of the actual three-phase ground loop current at the beginning and end of the abnormal section are greater than 20% of the effective values of the corresponding three-phase load current;

[0260] Judgment basis VIII is

[0261] The ratio of the maximum effective value of the actual three-phase grounding circulation current at the head end of the abnormal section to the minimum effective value of the actual three-phase grounding circulation current at the head end is greater than 3, or the ratio of the maximum effective value of the actual three-phase grounding circulation current at the end end to the minimum effective value of the actual three-phase grounding circulation current at the end end is greater than 3;

[0262] Judgment basis VIIII is

[0263] The effective value of the actual three-phase ground loop current at the beginning or end of the abnormal section is greater than 100A;

[0264] If judgment criteria VII, VIII, or VIIII are met, then there is a ground loop in the output abnormal section that does not meet the requirements of the regulations;

[0265] If the criteria VII, VIII, and VIIII are not met, the judgment is terminated.

[0266] In the judgment of S507, as long as any one of judgment basis VII, judgment basis VIII, and judgment basis VIIII is met, the ground loop current exists in the output abnormal section and does not meet the requirements of the regulations.

[0267] This embodiment performs online monitoring of the main core current and sheath circulating current at direct and protective grounding points. This improves the efficiency of monitoring data and further analyzes the circulating current data to identify and locate typical grounding system defects. The circulating current monitoring method divides the system into sections based on direct and protective grounding points, with current monitoring equipment deployed at the direct and protective grounding locations. A monitoring system includes seven CTs, each monitoring three-phase main core current, three-phase sheath circulating current, and total sheath grounding current.

[0268] This embodiment classifies typical defects into seven types: protector abnormality, sheath single-phase grounding fault, direct grounding point grounding resistance abnormality, single-circuit contact resistance abnormality, phase-to-phase short circuit fault, continuous reverse fault, and grounding circulation current that does not meet regulatory requirements. It achieves unique identification and online precise positioning of the seven types of typical grounding system defects. The circulation current monitoring method is convenient and covers a full range of fault types. It can help high-voltage transmission cable operation and maintenance personnel to troubleshoot faults in the first time and improve cable operation safety and transmission capacity.

[0269] On the other hand, the present application provides an online detection system for typical defects in a high-voltage transmission cable grounding system, comprising a front-end anomaly analysis system and a back-end defect identification and positioning system;

[0270] The front-end abnormality analysis system includes: section management module, section information collection module, abnormal section judgment and alarm module;

[0271] The background defect identification and positioning system includes: section current information collection and calculation module, abnormal section defect type identification and positioning module;

[0272] The section management module is used to manage section information of high-voltage transmission cables. Four ground loop current measurement CTs are installed at the direct grounding box and protective grounding box in the section, and three main core current measurement CTs are installed on the cable main core adjacent to the direct grounding box and protective grounding box. The positive direction of the ground loop current measurement CT is the grounding direction, and the positive direction of the main core current measurement CT is the receiving side direction. The section type is divided into single-terminal section, double-terminal section, and cross-connected section according to the sheath grounding method;

[0273] The section information collection module is used to collect the three-phase ground loop current at the beginning and end of each section, and the total ground loop current at the beginning and end. The beginning is located on the incoming power side of the loop, and the end is located on the receiving power side of the loop.

[0274] The abnormal section judgment and alarm module is used to judge whether there is any abnormality in each section. According to the type of each section, the module analyzes the three-phase grounding circulation current at the head end, the three-phase grounding circulation current at the end end, the total grounding circulation current at the head end, or the total grounding circulation current at the end end. It judges whether there is any abnormality in each section. The abnormality is abnormal protection tube current, excessive sheath circulation current, insufficient sheath circulation current, imbalance between sheath circulation phases, or excessive phase change of circulation current.

[0275] If there is an exception, the abnormal section and the exception are output; if there is no exception, the section information collection module is returned;

[0276] The front-end anomaly analysis system communicates with the back-end defect identification and location system. If the front-end anomaly analysis system determines an abnormal section exists, it uploads data information, including the upload time, alarm information, four-cycle current data for seven CTs, and a flag indicating whether the upload was successful. The upload success flag is set as follows: If the data upload time, alarm information, and four-cycle current data for seven CTs are uploaded to the back-end, the back-end receipt determines that the data upload was successful and sets the success flag. If the front-end device does not receive a receipt or receives an upload failure receipt, it will upload the data again after 1 minute and 5 minutes. If it still does not receive a receipt or receives an upload failure receipt, the upload success flag is set to failure.

[0277] Section current information collection and calculation module: used to obtain the information collected by the section information collection module and calculate the current information of the abnormal section. The current information includes: three-phase load current, actual three-phase ground loop current at the beginning and end, and actual total ground loop current at the beginning and end;

[0278] The abnormal section defect type identification and positioning module is used to identify and judge the defect type of the abnormal section based on the current information and the type of the abnormal section. The defect types include: protector abnormality, single-phase grounding fault of the protective layer, abnormal grounding resistance of the direct grounding point, abnormal single-circuit contact resistance, phase-to-phase short circuit fault, continuous reverse fault, and grounding loop current that does not meet the requirements of the regulations.

[0279] An online detection system for typical defects in a high-voltage transmission cable grounding system in this embodiment realizes automated identification and is low-cost, simple and convenient, and has obvious effects. It has the advantages of reducing the workload of staff and improving work efficiency.

[0280] In order to improve the recognition accuracy of the system, the system also includes a secondary judgment module for abnormal sections. The secondary judgment module belongs to the background defect recognition and positioning system and is used for secondary judgment of abnormal information in abnormal sections.

[0281] The front-end abnormality analysis system reports that there is an abnormal current in the protection tube in the i-th section. The back-end defect identification and positioning system will verify the information after receiving it, and make a secondary judgment on whether there is an abnormal current in the protection tube in the i-th section through the abnormal section secondary judgment module. If the secondary judgment result is consistent with the judgment conclusion of the abnormal section judgment and alarm module, the abnormal section defect type will be further identified and located. If the judgment results are inconsistent, the output is that there is no abnormality.

[0282] The above are merely preferred embodiments of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art may modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the invention shall be included within the scope of protection of the invention.

Claims

1. A method for online detection of typical defects in a high-voltage transmission cable grounding system, characterized in that: The following steps are involved: S1: Setting of ground loop current measurement CT and main core current measurement CT; Four ground loop current measurement CTs are installed at the direct grounding box and protective grounding box of each section of the high-voltage transmission cable. Three main core current measurement CTs are installed on the main core of the cable adjacent to the direct grounding box and protective grounding box. The positive direction of the ground loop current measurement CT is the direction into the earth, and the positive direction of the main core current measurement CT is the direction of the power receiving side. The type of each section of the high-voltage transmission cable is divided into single-terminal section, double-terminal section, and cross-connected section according to the sheath grounding method; S2: Collect the three-phase ground loop current at the beginning and end of each section, and the total ground loop current at the beginning and end. The three-phase ground loop current at the beginning and end, as well as the total ground loop current at the beginning and end, are obtained using a ground loop current measurement CT. The beginning is located on the incoming power side, and the end is located on the receiving power side. The three-phase grounding loop current at the first end is 、 、 ; The terminal three-phase grounding loop current is 、 、 ; The total ground loop current at the beginning and end is 、 ; Where i represents the i-th segment, 1 represents the beginning of the segment, and 2 represents the end of the segment; S3: Determine whether each section has any abnormalities. Analyze the three-phase grounding circulation current at the head end, the three-phase grounding circulation current at the end end, the total grounding circulation current at the head end, or the total grounding circulation current at the end end, based on the type of each section. Determine whether each section has any abnormalities. These abnormalities include abnormal protection tube current, excessively large or insufficient sheath circulation current, imbalanced sheath circulation current phases, or large phase variations in circulation current. If there is an exception, the exception section and the exception are output; If there is no abnormality, return to step S2; S4: Acquisition of current information of the abnormal section; Calculation of current information of the abnormal section based on whether the beginning and the end of the abnormal section are common grounding terminals. The current information includes three-phase load current, actual three-phase grounding loop current at the beginning and the end, and actual total grounding loop current at the beginning and the end; S5: Identify and locate the defect type in the abnormal section. Based on the current information and the type of the abnormal section, the defect type in the abnormal section is identified and located. Defect types include: protector abnormality, sheath single-phase grounding fault, abnormal grounding resistance at the direct grounding point, abnormal single-circuit contact resistance, phase-to-phase short circuit fault, continuous reverse fault, and grounding loop current that does not meet regulatory requirements. In S5, the abnormal section is a double-terminal section or a cross-connection section. The steps of identifying and locating the defect type of the abnormal section include: S501: Calculation of judgment information; Based on the current information, calculate the effective value of the actual three-phase grounding loop current at the beginning and end of the abnormal section, the absolute value of the amplitude change of the actual three-phase grounding loop current at the beginning and end, the absolute value of the phase change of the actual three-phase grounding loop current at the beginning and end, the vector difference between the actual grounding loop current at the beginning and the actual grounding loop current at the end of phase A, phase B and phase C, the amplitude mutation of the actual three-phase grounding loop current vector at the beginning, the amplitude change of the actual total grounding loop current vector at the beginning, the amplitude mutation of the actual grounding loop current vector at the beginning and end of each loop, the vector difference of the actual grounding loop current at the beginning and end, and the difference between the amplitude mutation of the actual grounding loop vector at the beginning and end; S502: Determine whether there is a sheath single-phase grounding fault; Judgment criterion II is that in the abnormal section, there is a loop K whose actual grounding loop vector amplitude mutation at the head end is greater than k7E0 and is greater than 1.2 times of the actual grounding loop vector amplitude mutation at the head end of the other two loops, and the difference between the actual grounding loop vectors at the head and end of loop K is greater than k8, while the difference between the actual grounding loop vectors at the head and end of the other two loops is less than k8; Or in the abnormal section, there is a loop K whose end actual grounding loop vector amplitude mutation is greater than k7E0 and is greater than 1.2 times of the end actual grounding loop vector amplitude mutation of the other two loops, and the difference between the beginning and end actual grounding loop vectors of loop K is greater than k8, while the difference between the beginning and end actual grounding loop vectors of the other two loops is less than k8; Among them, E0 is the amplitude reference value, k7 is the setting coefficient for starting the sheath current amplitude mutation, and k8 is the threshold of the normal current amplitude difference; If judgment criterion II is met, calculate the fault distance of the circulating current loop K, and output the existence of a sheath single-phase grounding fault and the fault distance of the circulating current loop K in the abnormal section; If judgment criterion II is not met, proceed to the next step; S503: Determine whether there is abnormal grounding resistance at the direct grounding point; Judgment criterion III is that the actual three-phase grounding circulation current vector amplitude mutation at the head end of the abnormal section is greater than k7E0 and the effective value of the actual three-phase grounding circulation current at the head end is less than or equal to E0; If judgment criterion III is met, there is abnormal grounding resistance at the direct grounding point in the output abnormal section; If judgment criterion III is not met, proceed to the next step; S504: Determine whether there is a single-circuit contact resistance abnormality; Judgment criterion IV is that in the abnormal section, there is a loop K whose actual grounding loop vector amplitude mutation at the head end is greater than k7E0 and is greater than 1.2 times of the actual grounding loop vector amplitude mutation at the head end of the other two loops, and the difference between the actual grounding loop vector amplitude mutation at the head and end of loop K is less than k8; If judgment criterion IV is met, the circulating current loop K in the output abnormal section has a single-loop contact resistance abnormality; If judgment criterion IV is not met, proceed to the next step; S505: Determine whether a phase-to-phase short circuit fault occurs; The judgment basis V is that the absolute value of the actual ground loop current amplitude change and the absolute value of the actual ground loop current phase change at the head end of the X phase and Y phase of the abnormal section are respectively greater than twice the absolute value of the actual ground loop amplitude change and the absolute value of the actual ground loop phase change at the head end of the third phase, and the amplitude of the actual total ground loop current vector change at the head end is less than k8; X phase and Y phase are any two phases among A phase, B phase and C phase; If the judgment criterion V is met, a phase-to-phase short circuit fault occurs between the X and Y phases at the head end of the output abnormal section; If the judgment criterion V is not met, proceed to the next step; S506: Determine whether there is a continuous reverse fault; The judgment criterion VI is that the effective value of the actual three-phase ground loop current at the beginning or end of the abnormal section is greater than k9 / 3, and the vector difference between the actual ground loop current at the beginning and the end of phases A, B, and C in the abnormal section is less than k8, where k9 is the over-limit alarm threshold for the sheath loop current. If the judgment criterion VI is met, there is a continuous reverse fault in the output abnormal section; If judgment criterion VI is not met, proceed to the next step; S507: Determine whether there is a ground loop current that does not meet regulatory requirements; Judgment criterion VII is that the effective values of the actual three-phase grounding loop current at the beginning and end of the abnormal section are greater than 20% of the effective values of the corresponding three-phase load current; Judgment criterion VIII is that the ratio of the maximum effective value of the actual three-phase grounding circulation current at the head end to the minimum effective value of the actual three-phase grounding circulation current at the head end of the abnormal section is greater than 3, or the ratio of the maximum effective value of the actual three-phase grounding circulation current at the end end to the minimum effective value of the actual three-phase grounding circulation current at the end end is greater than 3; Judgment criterion VIIII is that the effective value of the actual three-phase ground loop current at the beginning or end of the abnormal section is greater than 100A; If judgment criteria VII, VIII, or VIIII are met, then there is a ground loop in the output abnormal section that does not meet the requirements of the regulations; If the criteria VII, VIII, and VIIII are not met, the judgment is terminated.

2. The method for online detection of typical defects in a high-voltage transmission cable grounding system according to claim 1 is characterized in that: In S3, the segment type is a single-terminal segment, and it is determined whether there is abnormal current in the protection tube; If the first end of the section is the protective grounding side, , it is judged that there is an abnormal current in the protection tube; If the end of the section is the protective earth side, , it is judged that there is an abnormal current in the protection tube; Among them, k1 is the normal current setting value of the protector, is the effective value of the three-phase grounding loop current at the beginning and end, It is the effective value of the total ground loop current at the beginning and end.

3. The method for online detection of typical defects in a high-voltage transmission cable grounding system according to claim 1, characterized in that: In S3, the type of the section is a double-terminal section or a cross-connected section, and the section is judged whether there is a large sheath circulation current, a small sheath circulation current, an imbalance in the sheath circulation current phase, or a large change in the circulation phase.

4. The method for online detection of typical defects in a high-voltage transmission cable grounding system according to claim 3 is characterized in that: The basis for judging whether there is excessive sheath circulation in a section is: when or , it is judged that the protective layer circulation is too large; The basis for judging whether there is a small protective layer circulation in the section is: when , it is judged that the protective layer circulation is too small; The basis for judging whether there is phase imbalance of sheath circulation in a section is: when and , or when and , It is judged that there is an imbalance between the phases of the sheath circulation; The basis for judging whether there is a large change in the circulation phase in the section is: when , it is judged that there is a large change in the circulation phase; in, is the effective value of the three-phase grounding loop current at the beginning and end; is the effective value of the total ground loop current at the beginning and end; k2 is the set circulation exceeding threshold; k3 is the set sheath circulation zero threshold; K4 is the threshold for the alarm when the ratio of the maximum value to the minimum value of the three-phase grounding circulating current exceeds the limit; k5 is the setting coefficient for starting the sudden change of the sheath circulation phase; is the absolute value of the phase change of the three-phase ground loop current at the beginning and end, ∆P ai-1 ,∆P bi-1 ,∆P ci-1 ,∆P ai-2 ,∆P bi-2 ,∆P ci-2 is the phase change of the three-phase grounding circulating current at the beginning and the end, which is obtained by calculating the three-phase grounding circulating current at the beginning and the end.

5. The method for online detection of typical defects in a high-voltage transmission cable grounding system according to claim 1 is characterized in that: In S4, a direct grounding box is installed at the common grounding terminal. The three-phase grounding loop current at the common grounding terminal is collected by the grounding loop current measuring CT at the direct grounding box at the common grounding terminal. The three-phase main core current at the common grounding terminal is collected by the main core current measuring CT on the receiving side of the cable main core adjacent to the direct grounding box at the common grounding terminal. When the head end of the abnormal section is a common grounding terminal, obtain the three-phase grounding loop current and three-phase main core current of the common grounding terminal for 4 cycles, and obtain the three-phase grounding loop current, the total grounding loop current, and the three-phase main core current at the end of the abnormal section for 4 cycles; The three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the end of the abnormal section; The actual three-phase grounding circulation current at the head end and the actual total grounding circulation current at the head end are the three-phase grounding circulation current at the receiving side of the common grounding terminal and the total grounding circulation current at the receiving side respectively; The actual three-phase grounding loop current at the terminal and the actual total grounding loop current at the terminal are the three-phase grounding loop current at the terminal and the total grounding loop current at the terminal in the abnormal section respectively; When the end of the abnormal section is a common grounding terminal, obtain the three-phase grounding loop current, the total grounding loop current, and the three-phase main core current of the abnormal section at the head end for 4 cycles, and obtain the three-phase grounding loop current and the three-phase main core current of the common grounding terminal for 4 cycles; The three-phase load current is calculated based on the three-phase grounding loop current and the three-phase main core current at the head end of the abnormal section; The actual three-phase grounding circulation current at the head end and the actual total grounding circulation current at the head end are the three-phase grounding circulation current at the head end and the total grounding circulation current at the head end of the abnormal section respectively; The actual three-phase grounding circulation current at the terminal and the actual total grounding circulation current at the terminal are the three-phase grounding circulation current at the incoming power side and the total grounding circulation current at the incoming power side of the common grounding terminal respectively; When the head and the end of the abnormal section are shared grounding terminals, obtain the three-phase grounding loop current and the three-phase main core current of the first section of the high-voltage transmission cable on the incoming power side; obtain the three-phase grounding loop current and the three-phase main core current of the shared grounding terminal of the head and the end for 4 cycles; The three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the first end of the first section; The actual three-phase grounding circulation current at the head end and the actual total grounding circulation current at the head end are respectively the three-phase grounding circulation current at the receiving side of the common grounding terminal of the head end and the total grounding circulation current at the receiving side; The actual three-phase grounding circulation current at the terminal and the actual total grounding circulation current at the terminal are respectively the three-phase grounding circulation current at the incoming power side and the total grounding circulation current at the incoming power side of the common grounding terminal of the terminal; When the beginning and the end of the abnormal section are not common ground terminals, obtain the three-phase ground loop current at the beginning and the end of the abnormal section for 4 cycles, the total ground loop current at the beginning and the end, and the three-phase main core current at the beginning and the end; The three-phase load current is calculated based on the three-phase grounding loop current and the three-phase main core current at the first end of the abnormal section or the three-phase grounding loop current and the three-phase main core current at the last end of the abnormal section; The actual three-phase grounding circulation current at the beginning and end is the three-phase grounding circulation current at the beginning and end of the abnormal section; The actual total ground loop current at the beginning and end is the total ground loop current at the beginning and end of the abnormal section.

6. The method for online detection of typical defects in a high-voltage transmission cable grounding system according to claim 5, characterized in that: When the three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the first end of the abnormal section or the three-phase ground loop current and the three-phase main core current at the first end of the first section, the three-phase load current calculation formula is: When the three-phase load current is calculated based on the three-phase ground loop current and the three-phase main core current at the end of the abnormal section, the three-phase load current calculation formula is: Where, is the three-phase load current, and , are respectively the three-phase grounding loop current and the three-phase main core current at the head end of the abnormal section or the three-phase grounding loop current and the three-phase main core current at the head end of the first section; and , which are the three-phase ground loop current and the three-phase main core current at the end of the abnormal section respectively.

7. The method for online detection of typical defects in a high-voltage transmission cable grounding system according to claim 5, characterized in that: The calculation formulas for the three-phase ground loop current on the receiving side and the total ground loop current on the receiving side are: The calculation formulas for the three-phase ground loop current on the incoming power side and the total ground loop current on the incoming power side are: Where: is the three-phase load current, It is the three-phase grounding loop current on the receiving side; is the total ground loop current on the receiving side; It is the three-phase ground loop current on the incoming power side; is the total ground loop current on the incoming power side; It is the three-phase grounding loop current with a common ground terminal; It is the three-phase main core current of the common ground terminal.

8. The method for online detection of typical defects in a high-voltage transmission cable grounding system according to claim 1, characterized in that: In S5, the abnormal section is a single-terminal section. The steps for identifying and locating the defect type in the abnormal section include: S501: Calculation of judgment information; Calculate the effective value of the three-phase grounding loop current on the protective grounding side of the abnormal section based on the current information; When the protective earthing side is the head end of the abnormal section, the effective value of the three-phase grounding circulating current on the protective earthing side of the abnormal section is the effective value of the actual three-phase grounding circulating current at the head end of the abnormal section; When the protective earthing side is at the end of the abnormal section, the effective value of the three-phase grounding circulating current on the protective earthing side of the abnormal section is the effective value of the actual three-phase grounding circulating current at the end of the abnormal section; S502: Determine whether there is a protector abnormality; The judgment basis I is that the effective value of the three-phase grounding circulating current on the protective grounding side of the abnormal section has a value greater than k1, where k1 is the normal current setting value of the protector; If the judgment criterion I is met, then according to the X phase corresponding to the value greater than k1, there is an X phase protector abnormality in the output abnormal section, and the X phase is phase A, phase B, or phase C; If the judgment basis I is not met, the judgment is terminated.

9. An online detection system for typical defects in a high-voltage transmission cable grounding system, used to implement the detection method according to any one of claims 1 to 8, characterized in that: Including the front-end abnormality analysis system and the back-end defect identification and positioning system; The front-end abnormality analysis system includes: section management module, section information collection module, abnormal section judgment and alarm module; The background defect identification and positioning system includes: section current information collection and calculation module, abnormal section defect type identification and positioning module; The section management module is used to manage section information of high-voltage transmission cables. Four ground loop current measurement CTs are installed at the direct grounding box and protective grounding box in the section, and three main core current measurement CTs are installed on the cable main core adjacent to the direct grounding box and protective grounding box. The positive direction of the ground loop current measurement CT is the grounding direction, and the positive direction of the main core current measurement CT is the receiving side direction. The section type is divided into single-terminal section, double-terminal section, and cross-connected section according to the sheath grounding method; The section information collection module is used to collect the three-phase ground loop current at the beginning and end of each section, and the total ground loop current at the beginning and end. The beginning is located on the incoming power side of the loop, and the end is located on the receiving power side of the loop. The abnormal section judgment and alarm module is used to judge whether there is any abnormality in each section. According to the type of each section, the module analyzes the three-phase grounding circulation current at the head end, the three-phase grounding circulation current at the end end, the total grounding circulation current at the head end, or the total grounding circulation current at the end end. It judges whether there is any abnormality in each section. The abnormality is abnormal protection tube current, excessive sheath circulation current, insufficient sheath circulation current, imbalance between sheath circulation phases, or excessive phase change of circulation current. If there is an exception, the abnormal section and the exception are output; if there is no exception, the section information collection module is returned; Section current information collection and calculation module: used to obtain the information collected by the section information collection module and calculate the current information of the abnormal section. The current information includes: three-phase load current, actual three-phase ground loop current at the beginning and end, and actual total ground loop current at the beginning and end; The abnormal section defect type identification and positioning module is used to identify and locate the defect type of the abnormal section based on the current information and the type of the abnormal section. The defect types include: protector abnormality, single-phase grounding fault of the protective layer, abnormal grounding resistance of the direct grounding point, abnormal single-loop contact resistance, phase-to-phase short circuit fault, continuous reverse fault, and grounding loop current that does not meet the requirements of the regulations.

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