A method for identifying single-phase grounding fault interval in distribution network with low resistance grounding at neutral point

Abstract

The present invention proposes a method for identifying single-phase grounding fault intervals in a neutral point low-resistance grounding distribution network, the method comprising: 1. Determine whether to perform fault location according to the fault location start criterion; 2. Extract the zero-sequence current amplitude of each measuring point and calculate the zero-sequence current amplitude difference; 3. Select the zero-sequence current amplitude difference of two adjacent measuring points as the input of the density space clustering algorithm; 4. Set the DBSCAN radius parameter based on the maximum transition resistance that occurs when a single-phase grounding fault occurs in the line and the shortest fault interval in the system; 5. Use DBSCAN to identify and classify healthy intervals and fault intervals. Advantages of the present invention: 1) The present invention can realize fault location in a low-resistance grounding system; 2) The present invention has high positioning accuracy, is not affected by factors such as the initial phase angle of the fault, noise, etc., and has high reliability.

Description

Technical Field

[0001] The invention relates to a method for identifying a single-phase grounding fault interval of a neutral point low-resistance grounding distribution network, and belongs to the technical field of power grid fault location. Background Art

[0002] With the continuous improvement of the cableization rate of distribution networks, the capacitive current of distribution networks has increased from tens of amperes to hundreds of amperes. It is difficult to compensate for the capacitive current in the event of a single-phase grounding fault, and the arc extinguishing effect is not obvious. The neutral point grounding method of the distribution network has gradually been transformed into a low-resistance grounding method. After a low-resistance grounding system fails, whether it is metallic grounding or high-resistance grounding, it is required to quickly locate the fault, facilitate fault detection, isolation and processing, quickly restore power supply, and improve power supply reliability.

[0003] There is no specific analysis and discussion on the fault location method in the low-resistance grounding system in the existing section location method. Whether the existing method can still perform accurate positioning in the low-resistance grounding system remains to be verified. In addition, how to combine it with distribution network automation, reduce the installation of measuring equipment, improve the utilization of information, and reduce the impact of synchronization and communication issues on fault location in the low-resistance grounding system is an urgent problem to be solved.

[0004] In view of this, in low-resistance grounded distribution networks, accurate distribution network fault location technology is of great significance for speeding up fault handling and power supply restoration, providing strategic support for protection tripping, reducing power outage losses caused by faults, and ensuring the stability of the power system and the safety of electrical equipment. Summary of the invention

[0005] The present invention proposes a method for identifying a single-phase grounding fault interval in a neutral point low-resistance grounding distribution network, which aims to solve the problem that the prior art cannot realize fault location in a low-resistance grounding system.

[0006] The technical solution of the present invention is a method for identifying single-phase grounding fault intervals in a neutral point low-resistance grounding distribution network, the method comprising:

[0007] 1. Determine whether to perform fault location according to the fault location start criteria;

[0008] 2. Extract the zero-sequence current amplitude of each measuring point and calculate the zero-sequence current amplitude difference;

[0009] 3. The zero-sequence current amplitude difference between two adjacent measurement points is selected as the input of the density space clustering algorithm (DBSCAN);

[0010] 4. Use the maximum transition resistance that occurs when a single-phase ground fault occurs in the line and the shortest fault interval in the system as a benchmark to set the DBSCAN radius parameter;

[0011] 5. Use DBSCAN to identify healthy intervals and faulty intervals.

[0012] Furthermore, the specific process of determining whether to perform fault location according to the fault location start criterion includes the following:

[0013] (a) The measuring equipment at the head end of each outgoing line measures the three-phase current and three-phase voltage in real time, and calculates the zero-sequence current and zero-sequence voltage;

[0014] (b) Take five sampling points as a data window and determine whether there are three consecutive sampling points in a data window where the zero-sequence current and zero-sequence voltage satisfy the condition shown in formula (1):

[0015] (1);

[0016] In formula (1), , For the moment The instantaneous value of zero-sequence current and zero-sequence voltage, 、 For the moment The instantaneous value of zero-sequence current and zero-sequence voltage corresponding to the previous cycle, with 0.02 seconds as one cycle, , They are all judgment constants;

[0017] (c) From the time At the beginning, if there are three consecutive data windows that satisfy formula (1), then it can be judged The time is the fault time and fault location is started; if it is not satisfied, it can be judged that no fault occurs during this period of time and fault location is not performed.

[0018] Furthermore, the extraction of the zero-sequence current amplitude of each measuring point and the calculation of the zero-sequence current amplitude difference include calculating the zero-sequence current amplitude difference of the fault interval and calculating the zero-sequence current amplitude difference of the healthy interval; the calculation of the zero-sequence current amplitude difference of the healthy interval includes calculating the zero-sequence current amplitude difference of the upstream interval of the fault point. L 1n-1(n+1) The zero-sequence current phase difference and the downstream interval of the fault point are calculated L 3n-3(n+1) The zero-sequence current phase difference of the fault interval is calculated, and the zero-sequence current amplitude difference of the fault interval is calculated specifically including: L 3(n-1)-3n The zero-sequence current phase difference between the head and the end; the typical distribution network topology is as follows Figure 2 As shown, the distributed measuring devices are numbered mn according to their positions, where m represents the branch number of the current distributed measuring device in the system, and n represents the sequence number along the branch. LA single-phase grounding fault occurs on line 3, and the fault point is f .

[0019] Furthermore, the calculation of the upstream interval of the fault point L 1n-1(n+1) The zero-sequence current phase difference is as follows:

[0020] (2);

[0021] In the above formula, The upstream section of the fault point L 1n-1(n+1) The zero-sequence current phase difference, , 1 respectively n 、1( n +1) The distance between the node and the fault point.

[0022] Furthermore, the calculation of the downstream interval of the fault point L 3n-3(n+1) The zero-sequence current phase difference is as follows:

[0023] (3);

[0024] In the above formula, is the downstream section of the fault point L 3n-3(n+1) The zero-sequence current phase difference, , 3 respectively n 、3( n +1) The distance between the node and the fault point.

[0025] Furthermore, for the fault interval L 3(n-1)-3n In terms of the fault interval L 3(n-1)-3n The zero-sequence current phase difference between the first and the last terminals is the interval L 3(n-1)- f Partial zero sequence current and interval L f-3n The sum of the zero-sequence currents of the parts is as follows:

[0026] (4);

[0027] In the above formula Is the fault interval L 3(n-1)-3n The zero-sequence current phasor difference between the first and the last terminals, , They are 3( n -1),3 nThe distance between the node and the fault point, and They are the zero-sequence current flowing through the small grounding resistance and line n respectively.

[0028] In the above formulas, is the zero-sequence voltage at the beginning of the line, is the zero-sequence impedance of the fault line.

[0029] Furthermore, the criterion for identifying the fault interval is: selecting the zero-sequence current amplitude difference between two adjacent measuring points as the criterion for fault interval identification, and defining The fault interval location function is as follows:

[0030] (5);

[0031] in, , They represent the zero-sequence currents of the distributed measuring devices mn and m(n+1) respectively, then It represents the zero-sequence current amplitude difference between two adjacent measuring points. For a faulty line, the zero-sequence current amplitude difference will surge in the fault interval, while the zero-sequence current amplitude differences in the other intervals are extremely small. The specific judgment method is: if the zero-sequence current amplitude difference is greater than the constant K, it is a fault interval, otherwise it is a healthy interval; the value of the constant K is determined in advance through simulation according to the topological structure of the actual line.

[0032] Furthermore, the density space clustering algorithm (DBSCAN) requires the radius parameter to be pre-set and the minimum number MinPts The radius parameter is set based on the minimum value of the zero-sequence current amplitude difference of the healthy line. , minimum number MinPts Set to 3, that is, The neighborhood with 3 data points is a healthy interval, and the one without is a faulty interval.

[0033] Furthermore, the use of DBSCAN to identify and classify healthy intervals and faulty intervals specifically includes:

[0034] (a) The zero-sequence current amplitude of each measurement point is extracted using fast Fourier transform and stored in the matrix In the formula (6):

[0035] (6);

[0036] (b) Calculation The zero-sequence current amplitude difference between two adjacent elements in , and store it in the matrix Specifically, as shown in formula (7):

[0037] (7);

[0038] (c) Elimination Contains data calculated at the end-of-line measurement point, forming a matrix D 2m ;

[0039] (d) Use the maximum transition resistance that may occur when a single-phase ground fault occurs in the line and the shortest fault section in the system to set the radius parameter in DBSCAN ;

[0040] (e) Using DBSCAN to analyze the matrix D 2m The data is classified. If a section in the classification result is marked as a fault section, it is output as the positioning result; otherwise, it is judged that the fault occurs at the busbar or line end, and the fault is located at the busbar or line end. The data that was eliminated was classified again by DBSCAN;

[0041] (f) If there is a section marked as a faulty section in the secondary classification, it is judged that the fault occurs at the end of the line, and the faulty section is determined based on the line topology; if there is still no section marked as a faulty section in the secondary classification, it is judged that the fault occurs at the busbar, and the faulty section location is completed.

[0042] Furthermore, when determining whether to perform fault location based on the fault location starting criterion, the area between two distributed measuring devices in each branch of the distribution network can be defined as an interval, and each interval can be determined based on the fault location starting criterion to determine whether to perform fault location; compared with defining the area between the beginning and the end of the line as a section, the length of the section is shortened, the accuracy of section positioning is improved, and it is beneficial to reduce the fault range and accurately find the fault location.

[0043] Advantages of the present invention:

[0044] 1) The present invention can realize fault location in a low-resistance grounding system;

[0045] 2) The present invention has high positioning accuracy, is not affected by factors such as the initial phase angle of the fault and noise, and has high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Attached Figure 1 The present invention is a flowchart of a method for identifying a single-phase grounding fault interval in a neutral point low-resistance grounded distribution network.

[0047] Attached Figure 2 This is a schematic diagram of a typical distribution network topology. DETAILED DESCRIPTION

[0048] A method for identifying single-phase grounding fault intervals in a neutral point low-resistance grounding distribution network, the method comprising:

[0049] 1. Determine whether to perform fault location according to the fault location start criteria;

[0050] 2. Extract the zero-sequence current amplitude of each measuring point and calculate the zero-sequence current amplitude difference;

[0051] 3. The zero-sequence current amplitude difference between two adjacent measurement points is selected as the input of the density space clustering algorithm (DBSCAN);

[0052] 4. The radius parameter of the density space clustering algorithm (DBSCAN) is set based on the maximum transition resistance that may occur when a single-phase grounding fault occurs in the line and the shortest fault interval in the system;

[0053] 5. Use the density space clustering algorithm (DBSCAN) to identify and classify healthy intervals and faulty intervals.

[0054] When determining whether to perform fault location according to the fault location start criterion, the area between two distributed measuring devices in each branch of the distribution network can be defined as an interval, and each interval can be determined according to the fault location start criterion to determine whether to perform fault location; compared with defining the area between the beginning and the end of the line as a section, the length of the section is shortened, the accuracy of section positioning is improved, and it is beneficial to reduce the fault range and accurately find the fault location.

[0055] The specific process of determining whether to perform fault location according to the fault location start criterion is as follows:

[0056] (a) The measuring equipment at the head end of each outgoing line measures the three-phase current and three-phase voltage in real time, and calculates the zero-sequence current and zero-sequence voltage;

[0057] (b) Take five sampling points as a data window and determine whether there are three consecutive sampling points in a data window where the zero-sequence current and zero-sequence voltage satisfy the condition shown in formula (1):

[0058] (1);

[0059] In formula (1), , For the moment The instantaneous value of zero-sequence current and zero-sequence voltage, 、 For the moment The instantaneous value of zero-sequence current and zero-sequence voltage corresponding to the previous cycle, with 0.02 seconds as one cycle, , They are all judgment constants;

[0060] (c) From the time At the beginning, if there are three consecutive data windows that satisfy formula (1), then it can be judged The time is the fault time and fault location is started; if it is not satisfied, it can be judged that no fault occurs during this period of time and fault location is not performed.

[0061] Said , The value of is mainly related to the transition resistance at the time of the fault. In actual engineering applications, simulation is carried out in advance. In the distribution network model built, single-phase grounding fault experiments under different transition resistances are carried out. Since the zero-sequence current and voltage show a monotonically increasing trend after the fault occurs, it is only necessary to use the data of the first data window after the fault to determine the value of the judgment constant; calculate the change in the instantaneous value of the zero-sequence current and voltage in the first data window after the fault occurs, and use this to determine , In the later stage, if no action occurs, the value of , Adjust the value.

[0062] The method of extracting the zero-sequence current amplitude of each measuring point and calculating the zero-sequence current amplitude difference includes calculating the zero-sequence current amplitude difference of the fault interval and calculating the zero-sequence current amplitude difference of the healthy interval. The typical distribution network topology is shown in the attached figure. Figure 2 As shown, the distributed measuring devices are numbered mn according to their positions, where m represents the branch number of the current distributed measuring device in the system, and n represents the sequence number along the branch. L A single-phase grounding fault occurs on line 3, and the fault point is f ; The calculation of the zero-sequence current amplitude difference in the healthy interval includes calculating the upstream interval of the fault point L 1n-1(n+1) The zero-sequence current phase difference and the downstream interval of the fault point are calculated L 3n-3(n+1) The zero-sequence current phase difference of the fault interval specifically includes calculating the fault interval L 3(n-1)-3n The zero-sequence current phasor difference between the first and the last terminals.

[0063] The upstream interval of the fault point is calculated L 1n-1(n+1) The zero-sequence current phase difference is as follows:

[0064] (2);

[0065] In the above formula, The upstream section of the fault point L1n-1(n+1) The zero-sequence current phase difference, , 1 respectively n 、1( n +1) The distance between the node and the fault point, is the zero-sequence voltage at the beginning of the line, is the zero-sequence impedance of the fault line.

[0066] The downstream interval of the fault point is calculated L 3n-3(n+1) The zero-sequence current phase difference is as follows:

[0067] (3);

[0068] In the above formula, is the downstream section of the fault point L 3n-3(n+1) The zero-sequence current phase difference, , 3 respectively n 、3( n +1) The distance between the node and the fault point.

[0069] For the fault interval L 3(n-1)-3n For the zero-sequence current amplitude difference, L 3(n-1)- f Partial zero sequence current and interval L f-3n The sum of the partial zero-sequence currents:

[0070] (4);

[0071] In the above formula Is the fault interval L 3(n-1)-3n The zero-sequence current phasor difference between the first and the last terminals, , They are 3( n -1),3 n The distance between the node and the fault point, and They are the zero-sequence current flowing through the small grounding resistance and line n respectively.

[0072] In the above formulas, is the zero-sequence voltage at the beginning of the line, is the zero-sequence impedance of the fault line.

[0073] The criterion for identifying the fault interval is that the zero-sequence current amplitude difference of the fault interval is much greater than the zero-sequence current amplitude difference of the healthy interval, that is, ; The zero-sequence current amplitude difference between two adjacent measuring points is selected as the criterion for fault interval identification, and the definition is The fault interval location function is as follows:

[0074] (5);

[0075] in, , They represent the zero-sequence currents of the distributed measuring devices mn and m(n+1) respectively, then It represents the zero-sequence current amplitude difference between two adjacent measuring points. For a faulty line, the zero-sequence current amplitude difference will surge in the fault interval, and the zero-sequence current amplitude differences in the remaining intervals are extremely small and can be approximately regarded as zero. The zero-sequence current amplitude difference in the fault interval is much larger than that in the healthy interval. The specific judgment method is: if the zero-sequence current amplitude difference is greater than the constant K, it is a fault interval, otherwise it is a healthy interval; the value of the constant K needs to be determined in advance through simulation according to the topological structure of the actual line; for the topological structure of commonly used actual lines, the value of the constant K can also be directly taken between 0-0.1, for example: the value of the constant K can be directly preferably selected as 0.05 or 0.1.

[0076] The method uses the maximum transition resistance that may occur when a single-phase grounding fault occurs in the line and the shortest fault interval in the system as a benchmark to set the radius parameter of the density-based spatial clustering algorithm (DBSCAN), specifically including the radius parameter that needs to be set in advance for the density-based spatial clustering algorithm (DBSCAN) and the minimum number MinPts The radius parameter is set based on the minimum value of the zero-sequence current amplitude difference of the healthy line. , that is, the maximum transition resistance that may occur in the line when a single-phase grounding fault occurs and the shortest fault interval in the system are used as the basis for setting, and the minimum number MinPts Set to 3, that is, The neighborhood with 3 data points is a healthy interval, and the one without is a faulty interval.

[0077] The density space clustering algorithm (DBSCAN) is used to identify and classify healthy intervals and faulty intervals. The specific process is as follows:

[0078] (a) The zero-sequence current amplitude of each measurement point is extracted using fast Fourier transform and stored in the matrix In the formula (6):

[0079] (6);

[0080] (b) Calculation The zero-sequence current amplitude difference between two adjacent elements in , and store it in the matrix Specifically, as shown in formula (7):

[0081] (7);

[0082] (c) Elimination Contains data calculated at the end-of-line measurement point, forming a matrix D 2m ;

[0083] (d) Use the maximum transition resistance that may occur when a single-phase ground fault occurs in the line and the shortest fault section in the system to set the radius parameter in DBSCAN ;

[0084] (e) Using DBSCAN to analyze the matrix D 2m The data is classified. If a section in the classification result is marked as a fault section, it is output as the positioning result; otherwise, it is judged that the fault occurs at the busbar or line end, and the fault is located at the busbar or line end. The data that was eliminated was classified again by DBSCAN;

[0085] (f) If there is a section marked as a faulty section in the secondary classification, it is judged that the fault occurs at the end of the line, and the faulty section is determined based on the line topology; if there is still no section marked as a faulty section in the secondary classification, it is judged that the fault occurs at the busbar, and the faulty section location is completed.

[0086] The matrix The zero-sequence current amplitude difference of all adjacent measuring points is included in the matrix, and the data of the measuring point at the end of the line is removed to form a matrix D 2m , forming a matrix D 2m It is the zero-sequence current amplitude difference matrix of other adjacent measurement points except the measurement point at the end of the line. In this way, when clustering, the matrix is ​​first D 2m If a section in the classification result is marked as a fault section, it will be output as the positioning result; otherwise, it is judged that the fault occurs at the end of the bus or line, and then the sections marked by the matrix are The data clustering of the eliminated line ends, if there is a section marked as a fault section in the secondary classification, it is judged that the fault occurs at the line end, and the specific fault interval is determined according to the line topology; if there is still no section marked as a fault section in the secondary classification, it is judged that the fault occurs on the bus.

[0087] Simulation Verification

[0088] In order to verify the reliability and effectiveness of the present invention, an IEEE34-node system was built in PSCAD / EMTDC for simulation analysis. The system used a 110kV / 10kV transformer with Y-△ connection on the bus side, and the neutral point was set to 10 Resistance grounding is used, and 34 nodes and 33 lines are set up. In the setting of line parameters, the cable part adopts a three-core cable buried 1m underground, using YJV22-8.7 / 10kV-3×70 model cable, and the overhead line part adopts the Bergeron model.

[0089] In order to verify the accuracy of the interval positioning method proposed in the present invention, single-phase grounding faults are set on the bus, 814-850, 832-858, and 846-848 intervals respectively to verify the accuracy of the fault interval positioning method proposed in the present invention under different transition resistance conditions when the fault occurs in the overhead line or cable line, the line end and the bus; the fault occurs at 0.1s, the sampling frequency is 10kHz, and the specific fault settings are shown in Table 1.

[0090] Table 1 Interval positioning method simulation settings

[0091]

[0092] The fault interval location results of cases 1 to 6 are shown in Table 2. It can be seen from Table 2 that the fault interval location method proposed in the present invention can accurately locate the fault at different locations.

[0093] Table 2 Fault interval location results for cases 1 to 6

[0094]

[0095] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for identifying single-phase grounding fault interval in a neutral point low resistance grounding distribution network, characterized in that include: 1) Determine whether to perform fault location according to the fault location start criterion; 2) Extract the zero-sequence current amplitude of each measuring point and calculate the zero-sequence current amplitude difference; 3) The zero-sequence current amplitude difference between two adjacent measurement points is selected as the input of the density space clustering algorithm; 4) Set the DBSCAN radius parameter based on the maximum transition resistance that occurs when a single-phase ground fault occurs in the line and the shortest fault interval in the system; 5) Use DBSCAN to identify and classify healthy intervals and faulty intervals; The criterion for identifying the fault interval is: the zero-sequence current amplitude difference between two adjacent measuring points is selected as the criterion for fault interval identification, and η is defined mn The fault interval location function is as follows: η mn =|I mn -I m(n+1) | (5); Among them, I mn ,I m(n+1) Respectively represent the zero-sequence current of the distributed measurement devices mn and m(n+1), then η mn Indicates the zero-sequence current amplitude difference between two adjacent measuring points. For a faulty line, the zero-sequence current amplitude difference will surge in the faulty interval, and the zero-sequence current amplitude difference in the remaining intervals is extremely small. The specific judgment method is: if the zero-sequence current amplitude difference is greater than the constant K, it is a faulty interval, otherwise it is a healthy interval; the value of the constant K needs to be determined in advance through simulation according to the topological structure of the actual line; The density space clustering algorithm requires the presetting of the radius parameter ε and the minimum number MinPts. The radius parameter ε is set based on the minimum value of the zero-sequence current amplitude difference of the healthy line. The minimum number MinPts is set to 3, that is, if there are 3 data points in the ε neighborhood, it is a healthy interval, and if it does not meet the requirements, it is a fault interval. The use of DBSCAN to identify and classify healthy intervals and faulty intervals specifically includes: (a) The zero-sequence current amplitude of each measurement point is extracted using fast Fourier transform and stored in the matrix I m In the formula (6): I m =[I m1 I m2 … I mn ] (6); (b) Calculation I m The zero-sequence current amplitude difference η between two adjacent elements in mn , and store it in the matrix D 1m In the formula (7): D 1m =[the m1 or m2 … the m(n-1) ] (7); (c) Eliminate D 1m Contains the data calculated at the end of the line measurement point, forming a matrix D 2m ; (d) The radius parameter ε in DBSCAN is set using the maximum transition resistance that may occur when a single-phase grounding fault occurs in the line and the shortest fault section in the system; (e) Use DBSCAN to analyze the matrix D 2m The data is classified. If a section in the classification result is marked as a fault section, it is output as the positioning result; otherwise, it is judged that the fault occurs at the busbar or line end, and D 1m The data that was eliminated was classified again by DBSCAN; (f) If there is a section marked as a faulty section in the secondary classification, it is determined that the fault occurs at the end of the line, and the faulty section is determined based on the line topology; if there is still no section marked as a faulty section in the secondary classification, it is determined that the fault occurs at the busbar, and the faulty section location is completed; The method of extracting the zero-sequence current amplitude of each measuring point and calculating the zero-sequence current amplitude difference includes calculating the zero-sequence current amplitude difference of the fault interval and calculating the zero-sequence current amplitude difference of the healthy interval; the method of calculating the zero-sequence current amplitude difference of the healthy interval includes calculating the zero-sequence current amplitude difference of the upstream interval L of the fault point 1n-1(n+1) The zero-sequence current phase difference and the calculation of the downstream interval L of the fault point 3n-3(n+1) The zero-sequence current phase difference of the fault interval is calculated, and the zero-sequence current amplitude difference of the fault interval is calculated. 3(n-1)-3n Zero-sequence current phasor difference between the first and the last terminals; The fault interval L 3(n-1)-3n The zero-sequence current phase difference between the first and the last terminals is the interval L 3(n-1)-f Partial zero sequence current and interval L f-3n The sum of the zero-sequence currents of the parts is as follows: In the above formula is the fault interval L 3(n-1)-3n Zero-sequence current phasor difference between the first and the last terminals, x 3(n-1) 、x 3n The distances from 3(n-1) and 3n nodes to the fault point are respectively, and are the zero-sequence currents flowing through the small grounding resistance and line n respectively, is the zero-sequence voltage at the beginning of the line, Z 0f is the zero-sequence impedance of the fault line.

2. The method for identifying single-phase grounding fault interval in a neutral point low resistance grounding distribution network according to claim 1 is characterized by: The determining whether to perform fault location according to the fault location start criterion specifically includes the following: (a) The measuring equipment at the head end of each outgoing line measures the three-phase current and three-phase voltage in real time, and calculates the zero-sequence current and zero-sequence voltage; (b) Take five sampling points as a data window and determine whether there are three consecutive sampling points in a data window where the zero-sequence current and zero-sequence voltage satisfy the condition shown in formula (1): In formula (1), i0(t) and u0(t) are the instantaneous values ​​of zero-sequence current and zero-sequence voltage at time t, i0(t-0.02) and u0(t-0.02) are the instantaneous values ​​of zero-sequence current and zero-sequence voltage corresponding to time t in the previous cycle, with 0.02 seconds as one cycle, and k1 and k2 are both judgment constants; (c) Starting from time t, if there are three consecutive data windows that satisfy formula (1), time t is judged to be the fault time and fault location is started; if not, it is judged that no fault occurs during this period and fault location is not performed.

3. The method for identifying single-phase grounding fault interval in a neutral point low resistance grounding distribution network according to claim 1 is characterized by: The calculation of the upstream interval L of the fault point 1n-1(n+1) The zero-sequence current phase difference is as follows: In the above formula, The upstream interval L of the fault point 1n-1(n+1) The zero-sequence current phase difference, x 1n 、x 1(n+1) are the distances from 1n and 1(n+1) nodes to the fault point respectively. is the zero-sequence voltage at the beginning of the line, Z 0f is the zero-sequence impedance of the fault line.

4. The method for identifying single-phase grounding fault interval of a neutral point low-resistance grounding distribution network according to claim 1, characterized in that Calculate the downstream interval L of the fault point 3n-3(n+1) The zero-sequence current phase difference is as follows: In the above formula, is the downstream interval L of the fault point 3n-3(n+1) The zero-sequence current phase difference, x 3n 、x 3(n+1) are the distances from 3n and 3(n+1) nodes to the fault point respectively. is the zero-sequence voltage at the beginning of the line, Z 0f is the zero-sequence impedance of the fault line.

5. A method for identifying single-phase grounding fault intervals in a neutral point low-resistance grounded distribution network according to any one of claims 1 to 4, characterized in that When determining whether to perform fault location according to the fault location startup criterion, the area between two distributed measuring devices in each branch of the distribution network is defined as an interval, and each interval is determined according to the fault location startup criterion to determine whether to perform fault location.

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