High-resistance grounding fault protection method based on general small-resistance grounding system

Abstract

The invention provides a high-resistance grounding fault protection method based on a general small-resistance grounding system in the technical field of power distribution network relay protection. The high-resistance grounding fault protection method comprises the following steps: collecting a bus zero-sequence voltage after a fault and a zero-sequence current at an outgoing line of a power distribution network; when the bus zero-sequence voltage is greater than a zero-sequence voltage starting value or the difference between any two adjacent zero-sequence voltage sampling values is greater than a zero-sequence voltage break variable starting value, constructing an array according to the collected zero-sequence current, and calculating the similarity between the zero-sequence current at any two outgoing lines to obtain a similarity matrix; presetting the value range of the clustering number according to the access condition of the distributed power supply, and determining the optimal clustering number by adopting the principle of minimizing the sum of squares in the cluster; and based on the similarity matrix and an improved k-means algorithm, executing clustering analysis according to the optimal clustering number to obtain a clustering analysis result, judging a fault type and selecting a fault line. The problem that a setting value needs to be set manually in traditional high-resistance protection is solved.

Description

Technical Field

[0001] The invention relates to a high-resistance grounding fault protection method based on a universal low-resistance grounding system, belonging to the technical field of distribution network relay protection. Background Art

[0002] With the modernization of urban distribution network lines, the proportion of cable-overhead hybrid lines and pure cable lines has increased significantly, prompting the increasing application of low-resistance grounding systems in distribution networks. Low-resistance grounding systems can effectively limit the overvoltage level during single-phase grounding faults and ensure the safe and stable operation of the power grid. At present, the mainstream protection strategy for low-resistance grounding systems in distribution networks is zero-sequence current protection. This method detects and locates faults based on the zero-sequence current generated during a fault, and its effectiveness is particularly prominent when the grounding resistance is small and the fault zero-sequence current is large. In order to overcome the limitations of zero-sequence overcurrent protection in some cases, such as when the fault current is not obvious due to large grounding resistance, researchers have proposed a new protection method based on the zero-sequence electrical quantities of the fault line and the non-fault line, including the phase and amplitude differences. By analyzing the phase relationship of the steady-state electrical quantities, this method can avoid the transient process of the zero-sequence component during data acquisition, and set a reasonable protection setting value accordingly, thereby significantly improving the accuracy of single-phase grounding fault detection and the tolerance to transition resistance.

[0003] Although the new protection method based on the phase and amplitude relationship of zero-sequence electrical quantities of faulty and non-faulty lines has made significant progress in the detection of single-phase grounding faults in low-resistance grounding systems, this technology still has some limitations. First, this method mainly focuses on the characteristics of the traditional distribution network system and does not fully consider the new challenges brought by the access of a large number of renewable energy sources in the current distribution network. The access of renewable energy has changed the power flow distribution and fault characteristics of the distribution network, which may cause more complex changes in zero-sequence electrical quantities, thereby affecting the accuracy and reliability of protection. Secondly, although this method performs well under steady-state conditions, it still has certain difficulties in dealing with transient fault processes. The rapid change of zero-sequence components in transient processes may make it difficult to judge the relationship between phase and amplitude, thereby affecting the rapid response capability of protection. In addition, with the increasing complexity of the distribution network structure and the improvement of the intelligence level, the requirements for the adaptability and intelligence of protection methods are also getting higher and higher, and the existing methods need to be further improved and perfected in these aspects.

[0004] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgement or any form of suggestion that the information constitutes the prior art already known to ordinary technicians in this field. Summary of the invention

[0005] The technical problem to be solved by the present invention is: how to solve the problem that the setting value needs to be manually set in traditional high-resistance protection.

[0006] In order to solve the above technical problems, the present invention is implemented by adopting the following technical solutions.

[0007] This paper proposes a general high-resistance grounding fault protection method for low-resistance grounding systems based on an improved clustering algorithm and zero-sequence current similarity. It does not require manual setting of the protection setting value, and does not need to avoid the zero-sequence component transient process in the fault collection link. The data collection time window is short and it can be applied to distribution networks with multiple outgoing renewable energy access and those without renewable energy access.

[0008] The present invention provides a high-resistance grounding fault protection method based on a universal low-resistance grounding system, comprising:

[0009] Collect the bus zero-sequence voltage after the fault occurs and the zero-sequence current at each outgoing line of the distribution network;

[0010] When the bus zero-sequence voltage is greater than the zero-sequence voltage starting value or the difference between any two adjacent zero-sequence voltage sampling values ​​is greater than the zero-sequence voltage mutation starting value, the following steps are performed:

[0011] An array is constructed according to the collected zero-sequence current, and the similarity between the zero-sequence currents at any two outgoing lines is calculated to obtain a similarity matrix containing the characteristic information of the fault line and the characteristic information of the non-fault line;

[0012] The value range of the number of clusters is preset according to the access situation of distributed power sources, and the optimal number of clusters is determined by adopting the principle of minimizing the sum of squares within the cluster;

[0013] Based on the similarity matrix and the improved k-means algorithm, performing cluster analysis according to the optimal number of clusters to obtain a cluster analysis result;

[0014] The fault type is determined according to the cluster analysis result and the faulty line is selected.

[0015] Further, judging the fault type according to the cluster analysis result includes:

[0016] When a distributed power source is connected to a low-resistance grounded distribution network system with multiple outgoing lines:

[0017] When the number of clusters k=2, a bus single-phase grounding fault occurs;

[0018] When the number of clusters k = 3, a single-phase grounding fault occurs in the smallest cluster;

[0019] In a low-resistance grounded distribution network system without distributed power generation:

[0020] When the number of clusters k=1, a busbar single-phase grounding fault occurs;

[0021] When the number of clusters k=2, a single-phase grounding fault occurs in the smallest cluster.

[0022] Furthermore, the method for calculating the similarity between the zero-sequence currents at any two outgoing lines includes:

[0023] The cosine distance is used to measure the similarity between the zero-sequence currents at any two outgoing lines.

[0024] Furthermore, the cosine distance is calculated based on the cosine value of the angle between the zero-sequence current vectors at any two outgoing lines in the vector space, and the calculation expression of the cosine value of the angle is:

[0025] (1);

[0026] In the formula, is the cosine value of the angle between the zero-sequence current vectors at any two outgoing lines, Indicates the outlet Zero sequence current vector With the output line Zero sequence current vector The cosine calculation formula between Indicates the total number of outgoing lines in the distribution network. Indicates the outlet The zero-sequence current vector samples, Indicates the outlet The zero-sequence current vector samples.

[0027] Furthermore, the cosine distance is calculated based on the cosine value of the angle between the zero-sequence current vectors at any two outgoing lines in the vector space, wherein the closer the cosine value of the angle is to 1, the more similar the waveforms of the zero-sequence current at any two outgoing lines are; the closer the cosine value of the angle is to -1, the more opposite the waveforms of the zero-sequence current at any two outgoing lines are.

[0028] Furthermore, the mathematical expression of the similarity matrix containing the fault line characteristic information and the non-fault line characteristic information is:

[0029] r = [ r 11 r 12 ⋯ r 1 n r 21 r 22 ⋯ r 2 n ⋮ ⋮ ⋮ ⋮ r n 1 r n 2 ⋯ r nn ] (2);

[0030] Where r is the similarity matrix containing the characteristic information of the faulty line and the characteristic information of the non-faulty line, Indicates the cosine similarity of the zero-sequence current of line 1 itself, represents the cosine similarity between line 1 and line 2, represents the cosine similarity between line 1 and line n, = represents the cosine similarity between line 2 and line 1, Indicates the cosine similarity of the zero-sequence current of line 2 itself, represents the cosine similarity between line 2 and line n, = represents the cosine similarity between line n and line 1, = represents the cosine similarity between line n and line 2, It represents the cosine similarity of the zero-sequence current of line n itself, where: Indicates the total number of outgoing lines in the distribution network.

[0031] Furthermore, the range of values ​​of the number of clusters preset according to the access situation of distributed power sources includes: when there is no distributed power source connected to the distribution network outgoing line, the number of clusters k=1 or 2; when there is a distributed power source connected to the distribution network outgoing line, the number of clusters k=2 or 3.

[0032] Furthermore, the improved method of the k-means algorithm includes:

[0033] When the number of clusters k is equal to 1, a vector is randomly generated as the cluster center;

[0034] When the number of clusters k is equal to 2 or 3, perform the following steps to select cluster centers:

[0035] Randomly select a row vector in the similarity matrix as the initial cluster center, and the remaining vectors are candidate row vectors;

[0036] Repeat the following steps until k-1 cluster centers are selected;

[0037] Calculating in sequence the shortest distances between the unselected candidate row vectors in the similarity matrix and the selected cluster centers;

[0038] Based on the weighted probability distribution of the shortest distance, a candidate row vector is randomly selected from the currently unselected candidate vectors as a new cluster center.

[0039] Further, calculate the candidate row vector that is not currently selected R j = [ r j 1 r j 2 ⋯ r jn ] and the selected k-th cluster center R k = [ r k 1 r k 2 ⋯ r k ] The mathematical expression for the shortest distance between is:

[0040] (3);

[0041] In the formula, Represents the candidate row vector that is not currently selected With the selected cluster center The shortest distance between.

[0042] Further, based on the weighted probability distribution of the shortest distance, a candidate row vector is randomly selected from the currently unselected candidate row vectors as a new cluster center, wherein the probability of the currently unselected candidate row vector being selected as the new cluster center is:

[0043] (4);

[0044] In the formula, represents the probability that the candidate row vector that is not currently selected is selected as the new cluster center, Indicates that any unselected m Candidate row vectors The shortest distance between the selected k-th cluster center.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The present invention can realize fault identification and fault line selection for active distribution networks and traditional distribution networks by changing the value range of cluster centers;

[0047] (2) The present invention uses cosine distance to characterize the similarity of zero-sequence current at each outgoing line of the distribution network, and utilizes the characteristic that cosine distance is insensitive to the vector size, so that it can effectively identify faults when the zero-sequence current of high-resistance grounding is small;

[0048] (3) The improved k-means method adopted by the present invention can effectively mine the information in the similarity matrix representing the fault characteristics by improving the selection of cluster centers. Therefore, in the data collection link, there is no need to avoid the transient process of zero-sequence electrical quantities, and the data collection time window is short. In addition, the method provided by the present invention does not require setting a threshold, which solves the problem of how to set the setting value in traditional high-resistance protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a flow chart of a high-resistance grounding fault protection method based on a universal low-resistance grounding system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. The embodiments of the present invention and the technical features in the embodiments may be combined with each other unless there is a conflict.

[0051] The term "and / or" is only a description of the association relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " generally indicates that the related objects are in an "or" relationship.

[0052] Example 1

[0053] like Figure 1 As shown, this embodiment introduces a high-resistance grounding fault protection method based on a universal low-resistance grounding system, including:

[0054] Step 1: Collect the zero-sequence voltage of the busbar and the zero-sequence current of each outgoing line of the distribution network after the fault occurs.

[0055] The present invention acquires the electrical quantity information after the fault occurs by collecting the zero-sequence voltage of the busbar and the zero-sequence current at each outgoing line of the distribution network, and performs fault analysis and positioning.

[0056] Step 2: When the bus zero-sequence voltage is greater than the zero-sequence voltage starting value or the difference between any two adjacent zero-sequence voltage sampling values ​​is greater than the zero-sequence voltage mutation starting value, perform the following steps:

[0057] The present invention uses the bus zero-sequence voltage being greater than the zero-sequence voltage starting value or the difference between any two adjacent zero-sequence voltage sampling values ​​being greater than the zero-sequence voltage mutation starting value as a starting criterion for triggering a subsequent fault diagnosis process. By setting the zero-sequence voltage starting value and the zero-sequence voltage mutation starting value, it is ensured that the fault diagnosis process is started in time when a fault occurs, avoiding unnecessary calculation and analysis in a non-fault state, and improving the efficiency and accuracy of fault diagnosis.

[0058] Among them, when the power system is operating normally, due to the possible imbalance of the three-phase system, a certain unbalanced zero-sequence voltage will appear on the bus. However, this voltage is usually not greater than 15% of the bus phase voltage. When the bus zero-sequence voltage is greater than the preset zero-sequence voltage starting value, it is considered to be a ground fault, etc. In some special cases, such as when a ground fault occurs suddenly, the zero-sequence voltage may mutate. By detecting whether the difference between two adjacent zero-sequence voltage sampling values ​​is greater than the zero-sequence voltage mutation amount starting value, the initial moment of the fault can be accurately captured, which helps to locate the fault point more accurately.

[0059] Step 2.1: Build an array based on the collected zero-sequence current, and calculate the similarity between the zero-sequence currents at any two outgoing lines to obtain a similarity matrix containing the characteristic information of the fault line and the characteristic information of the non-fault line.

[0060] The present invention constructs a similarity matrix reflecting the electrical connection between each outgoing line by calculating the similarity between the zero-sequence currents at any two outgoing lines. The similarity matrix contains the characteristic information of the fault line and the non-fault line, so that the cluster analysis can more accurately reflect the electrical connection and fault characteristics between each outgoing line.

[0061] Step 2.2: Preset the range of the number of clusters according to the access situation of distributed generation, and determine the optimal number of clusters by adopting the principle of minimizing the sum of squares within the cluster.

[0062] The present invention presets the value range of the number of clusters by considering the access situation of distributed power sources, and uses the principle of minimizing the sum of squares within the cluster to determine the optimal number of clusters, so as to ensure that the data of the similarity matrix is ​​accurately and reliably divided into a reasonable number of categories in the cluster analysis, thereby avoiding analysis errors.

[0063] Step 2.3: Based on the similarity matrix and the improved k-means algorithm, cluster analysis is performed according to the optimal number of clusters to obtain cluster analysis results.

[0064] The present invention uses an improved k-means algorithm to perform cluster analysis on the similarity matrix to obtain cluster analysis results. The cluster analysis results divide each outgoing line into different classes, each class represents a specific electrical connection or fault feature, making fault diagnosis more accurate and efficient.

[0065] Step 2.4: Determine the fault type and select the faulty line based on the cluster analysis results.

[0066] The present invention determines the fault type and selects the faulty line according to the cluster analysis result. By comparing the characteristic information of different types, the type and location of the fault can be determined, and finally the fault type can be determined and the faulty line can be selected.

[0067] Example 2

[0068] Based on the same inventive concept as that of Example 1, this embodiment introduces a high-resistance grounding fault protection method based on a universal low-resistance grounding system, which specifically includes the following steps:

[0069] Step 1: Collect the bus zero-sequence voltage after the fault occurs and the zero-sequence current at each outgoing line of the distribution network;

[0070] Step 2: When the bus zero-sequence voltage Greater than zero-sequence voltage starting value Or the difference between any two adjacent zero-sequence voltage sampling values Greater than the zero-sequence voltage sudden change starting value , perform the following steps, where: Indicates time The zero-sequence voltage sampling value, Indicates time Zero-sequence voltage sampling value:

[0071] Step 2.1: Build an array based on the collected zero-sequence current, and calculate the similarity between the zero-sequence currents at any two outgoing lines to obtain a similarity matrix containing the characteristic information of the fault line and the characteristic information of the non-fault line.

[0072] The method for calculating the similarity between zero-sequence currents at any two outgoing lines includes:

[0073] The cosine distance is used to measure the similarity between the zero-sequence currents at any two outgoing lines.

[0074] The cosine distance is calculated based on the cosine value of the angle between the zero-sequence current vectors at any two outgoing lines in the vector space. The calculation expression of the cosine value of the angle is:

[0075] (1);

[0076] In the formula, is the cosine value of the angle between the zero-sequence current vectors at any two outgoing lines, Indicates the outlet Zero sequence current vector With the output line Zero sequence current vector The cosine calculation formula between Indicates the total number of outgoing lines in the distribution network. Indicates the outlet The zero-sequence current vector samples, Indicates the outlet The zero-sequence current vector samples.

[0077] Among them, the cosine value of the angle between the zero-sequence current vectors at any two outgoing lines is The value range of is [-1,1], and the cosine distance is calculated based on the cosine value of the angle between the zero-sequence current vectors at any two outgoing lines in the vector space, wherein, the closer the cosine value of the angle is to 1, the more similar the waveforms of the zero-sequence current at any two outgoing lines are; the closer the cosine value of the angle is to -1, the more opposite the waveforms of the zero-sequence current at any two outgoing lines are.

[0078] The mathematical expression of the similarity matrix containing the fault line characteristic information and the non-fault line characteristic information is:

[0079] r = [ r 11 r 12 ⋯ r 1 n r 21 r 22 ⋯ r 2 n ⋮ ⋮ ⋮ ⋮ r n 1 r n 2 ⋯ r nn ] (2);

[0080] Where r is the similarity matrix containing the characteristic information of the faulty line and the characteristic information of the non-faulty line, Indicates the cosine similarity of the zero-sequence current of line 1 itself, represents the cosine similarity between line 1 and line 2, represents the cosine similarity between line 1 and line n, = represents the cosine similarity between line 2 and line 1, Indicates the cosine similarity of the zero-sequence current of line 2 itself, represents the cosine similarity between line 2 and line n, = represents the cosine similarity between line n and line 1, = represents the cosine similarity between line n and line 2, It represents the cosine similarity of the zero-sequence current of line n itself, where: Indicates the total number of outgoing lines in the distribution network.

[0081] Since the cosine distance normalizes the lengths of two high-dimensional zero-sequence current vectors, the normalized calculation result only reflects the similarity in the vector direction and has nothing to do with the length of the vector itself. Therefore, when the fault current is weak due to a high-resistance grounding fault, the similarity algorithm can still maintain its effectiveness.

[0082] Step 2.2: Preset the range of the number of clusters according to the access situation of distributed generation, and determine the optimal number of clusters by adopting the principle of minimizing the sum of squares within the cluster.

[0083] This embodiment sets the value range of the number of clusters according to the access status of distributed power sources in the distribution network system. Specifically:

[0084] In traditional distribution networks, since there are only two situations: busbar single-phase grounding and outgoing line single-phase grounding, the number of clusters may be set to 1 or 2 to accommodate these two different fault modes.

[0085] When there are multiple outgoing lines connected to distributed power sources in the distribution network, the situation becomes more complicated. At this time, the non-faulty lines are further subdivided into two categories: with distributed power sources connected and without distributed power sources connected. Therefore, the number of clusters may be set to 2 or 3 to more accurately reflect the difference between faulty lines and non-faulty lines (including with / without distributed power sources connected).

[0086] Such a setting is intended to ensure that cluster analysis can accurately reflect the actual operating status of the distribution network, thereby improving the accuracy and reliability of fault identification.

[0087] In summary, the present invention sets up two scenarios: one with and without distributed power source access. Therefore, the value range of the number of clusters is preset according to the access situation of the distributed power source, including: when there is no distributed power source access in the distribution network outgoing line, the number of clusters k=1 or 2; when there is distributed power source access in the distribution network outgoing line, the number of clusters k=2 or 3.

[0088] Step 2.3: Based on the similarity matrix and the improved k-means algorithm, cluster analysis is performed according to the optimal number of clusters to obtain cluster analysis results.

[0089] Since the zero-sequence current of the fault line and the normal line with or without distributed generation access is significantly different, the cluster centers of each type of line should be as far as possible. Based on the above reasons, the original k-means algorithm is improved.

[0090] The improved method of the k-means algorithm includes:

[0091] When the number of clusters k is equal to 1, a vector is randomly generated as the cluster center;

[0092] When the number of clusters k is equal to 2 or 3, perform the following steps to select cluster centers:

[0093] Randomly select a row vector in the similarity matrix as the initial cluster center, and the remaining vectors are candidate row vectors;

[0094] Repeat the following steps until k-1 cluster centers are selected;

[0095] The shortest distances between the candidate row vectors that are not currently selected in the similarity matrix and the selected cluster centers are calculated in sequence.

[0096] The calculation of the candidate row vector that is not currently selected R j = [ r j 1 r j 2 ⋯ r jn ] and the selected k-th cluster center R k = [ r k 1 r k 2 ⋯ r k ] The mathematical expression for the shortest distance between is:

[0097] (3);

[0098] In the formula, Represents the candidate row vector that is not currently selected With the selected cluster center The shortest distance between.

[0099] Based on the weighted probability distribution of the shortest distance, a candidate row vector is randomly selected from the candidate row vectors that are not currently selected as a new cluster center; wherein the probability that the candidate row vector that is not currently selected is selected as the new cluster center is:

[0100] (4);

[0101] In the formula, represents the probability that the candidate row vector that is not currently selected is selected as the new cluster center, Indicates that any unselected m Candidate row vectors The shortest distance between the selected k-th cluster center.

[0102] Step 2.4: Determine the fault type and select the faulty line based on the cluster analysis results.

[0103] Wherein, judging the fault type according to the cluster analysis result includes:

[0104] When a distributed power source is connected to a low-resistance grounded distribution network system with multiple outgoing lines:

[0105] When the number of clusters k=2, a bus single-phase grounding fault occurs;

[0106] When the number of clusters k = 3, a single-phase grounding fault occurs in the smallest cluster;

[0107] In a low-resistance grounded distribution network system without distributed power generation:

[0108] When the number of clusters k=1, a busbar single-phase grounding fault occurs;

[0109] When the number of clusters k=2, a single-phase grounding fault occurs in the smallest cluster.

[0110] In the actual application of the present invention, corresponding alarms or removal instructions may be given based on the fault judgment results.

[0111] Step 3: Simulation verification.

[0112] This embodiment uses MATLAB / Simulink to simulate a single-phase grounding fault in a typical 10kV low-resistance grounding distribution network.

[0113] In this embodiment, five outgoing lines are set to be cable lines, with lengths of 6 km, 10 km, 12 km, 13 km and 20 km respectively. The neutral point grounding resistance Rn=10Ω. The fault trigger time is set to 0.1 second, the initial fault phase angle is set to 0°, and the sampling frequency is set to 6.4kHz. The fault type is a single-phase grounding fault, and the fault point is located on phase A of outgoing line 1, 3 km away from the busbar. The line parameters in the simulation model are shown in Table 1.

[0114]

[0115] In this embodiment, the grounding transition resistance is set to 100Ω, 1000Ω, 2000Ω and 2500Ω respectively, and the unfiltered half cycle after the fault occurs is used as the data acquisition window, wherein the data acquisition window length of the half cycle is 10ms. When the transition resistance is 100Ω, the similarity matrix between the outgoing lines and the clustering labels and fault line selection results under different transition resistances are shown in Table 2 and Table 3.

[0116]

[0117]

[0118] It can be seen from Table 2 and Table 3 that when the grounding resistance in the low-resistance grounding system is from 100 to 2500Ω, the method provided in this embodiment can achieve reliable line selection of the fault line.

[0119] When a distributed power source is connected, the amplitude and phase relationship of the zero-sequence current of each outgoing line will change significantly. When outgoing lines 2 and 4 are connected to the distributed power source, assuming that outgoing line 1 still fails and the transition resistance is 1000Ω, according to the method provided in this embodiment, the clustering label result is "1 2 3 2 3", indicating that the fault occurs in outgoing line 1, and the outgoing lines are divided into faulty outgoing lines, non-faulty outgoing lines connected to the distributed power source, and non-faulty outgoing lines not connected to the distributed power source.

[0120] Example 3

[0121] Based on the same inventive concept as other embodiments, this embodiment introduces a computer-readable storage medium on which computer instructions are stored, characterized in that when the computer instructions are executed by a processor, the steps of the method of the above-mentioned embodiment 1 or embodiment 2 are implemented.

[0122] In summary, the present invention has demonstrated a high degree of flexibility and adaptability in fault identification and fault line selection. By dynamically adjusting the value range of the cluster center, the present invention can not only be effectively applied to the fault diagnosis of traditional distribution networks, but also adapt to the complex environment of active distribution networks. This feature enables the present invention to achieve accurate fault identification and line selection when facing different types of distribution networks without additional configuration or adjustment. In addition, by constructing a similarity matrix containing characteristic information of fault lines and non-fault lines, and combining an optimized cluster analysis algorithm, the present invention can quickly and accurately lock the fault line from a large number of lines, thereby greatly improving the efficiency and accuracy of fault handling.

[0123] The present invention has achieved significant improvement in the effectiveness of fault identification. The cosine distance is used to characterize the similarity of zero-sequence current at any outgoing line of the distribution network. This method makes full use of the characteristic that the cosine distance is insensitive to the vector size. Even in the case of a high-resistance grounding fault with a small zero-sequence current, effective fault identification can be achieved. This innovation not only broadens the scope of application of fault identification, but also improves the accuracy of identification.

[0124] At the same time, the improved k-means method adopted by the present invention further optimizes the selection process of the cluster center, so that the fault feature information in the similarity matrix can be fully mined and utilized. Therefore, in the data collection link, the present invention can perform fault identification without waiting for the transient process of the zero-sequence electrical quantity to end, which greatly shortens the time window for collecting data. In addition, the method provided by the present invention does not need to set a complex threshold, solves the problem of difficult setting of the setting value in traditional high-resistance protection, and further improves the convenience and practicality of fault identification.

[0125] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0126] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0127] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0128] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0129] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which all fall within the protection of the present invention.

Claims

1. A high-resistance grounding fault protection method based on a universal low-resistance grounding system, characterized in that: include: Collect the bus zero-sequence voltage after the fault occurs and the zero-sequence current at each outgoing line of the distribution network; When the bus zero-sequence voltage is greater than the zero-sequence voltage starting value or the difference between any two adjacent zero-sequence voltage sampling values ​​is greater than the zero-sequence voltage mutation starting value, the following steps are performed: An array is constructed according to the collected zero-sequence current, and the similarity between the zero-sequence currents at any two outgoing lines is calculated to obtain a similarity matrix containing the characteristic information of the fault line and the characteristic information of the non-fault line; The value range of the number of clusters is preset according to the access situation of distributed power sources, and the optimal number of clusters is determined by adopting the principle of minimizing the sum of squares within the cluster; Based on the similarity matrix and the improved k-means algorithm, performing cluster analysis according to the optimal number of clusters to obtain a cluster analysis result; The fault type is determined according to the cluster analysis result and the faulty line is selected.

2. The high-resistance grounding fault protection method based on a universal low-resistance grounding system according to claim 1 is characterized in that: Determining the fault type according to the cluster analysis result includes: When a distributed power source is connected to a low-resistance grounded distribution network system with multiple outgoing lines: When the number of clusters k=2, a bus single-phase grounding fault occurs; When the number of clusters k = 3, a single-phase grounding fault occurs in the smallest cluster; In a low-resistance grounded distribution network system without distributed power generation: When the number of clusters k=1, a busbar single-phase grounding fault occurs; When the number of clusters k=2, a single-phase grounding fault occurs in the smallest cluster.

3. The high-resistance grounding fault protection method based on a universal low-resistance grounding system according to claim 1 is characterized in that: Methods for calculating the similarity between zero-sequence currents at any two outgoing lines include: The cosine distance is used to measure the similarity between the zero-sequence currents at any two outgoing lines.

4. The high-resistance grounding fault protection method based on a universal low-resistance grounding system according to claim 3 is characterized in that: The cosine distance is calculated based on the cosine value of the angle between the zero-sequence current vectors at any two outgoing lines in the vector space. The calculation expression of the cosine value of the angle is: （1）； In the formula, is the cosine value of the angle between the zero-sequence current vectors at any two outgoing lines, Indicates the outlet Zero sequence current vector With the output line Zero sequence current vector The cosine calculation formula between Indicates the total number of outgoing lines in the distribution network. Indicates the outlet The zero-sequence current vector samples, Indicates the outlet The zero-sequence current vector samples.

5. The high-resistance grounding fault protection method based on a universal low-resistance grounding system according to claim 4 is characterized in that: The cosine distance is calculated based on the cosine value of the angle between the zero-sequence current vectors at any two outgoing lines in the vector space, wherein the closer the cosine value of the angle is to 1, the more similar the waveforms of the zero-sequence currents at any two outgoing lines are; the closer the cosine value of the angle is to -1, the more opposite the waveforms of the zero-sequence currents at any two outgoing lines are.

6. The high-resistance grounding fault protection method based on a universal low-resistance grounding system according to claim 1 is characterized in that: The mathematical expression of the similarity matrix containing the fault line characteristic information and the non-fault line characteristic information is: （2）； Where r is the similarity matrix containing the characteristic information of the faulty line and the characteristic information of the non-faulty line, Indicates the cosine similarity of the zero-sequence current of line 1 itself, represents the cosine similarity between line 1 and line 2, represents the cosine similarity between line 1 and line n, = represents the cosine similarity between line 2 and line 1, Indicates the cosine similarity of the zero-sequence current of line 2 itself, represents the cosine similarity between line 2 and line n, = represents the cosine similarity between line n and line 1, = represents the cosine similarity between line n and line 2, It represents the cosine similarity of the zero-sequence current of line n itself, where: Indicates the total number of outgoing lines in the distribution network.

7. The high-resistance grounding fault protection method based on a universal low-resistance grounding system according to claim 1 is characterized in that: The value range of the number of clusters preset according to the access situation of the distributed power source includes: When there is no distributed generation connected to the outgoing line of the distribution network, the number of clusters k=1 or 2; when there is distributed generation connected to the outgoing line of the distribution network, the number of clusters k=2 or 3.

8. The high-resistance grounding fault protection method based on a universal low-resistance grounding system according to claim 7 is characterized in that: The improved method of the k-means algorithm includes: When the number of clusters k is equal to 1, a vector is randomly generated as the cluster center; When the number of clusters k is equal to 2 or 3, perform the following steps to select cluster centers: Randomly select a row vector in the similarity matrix as an initial cluster center, and the remaining vectors are candidate row vectors; Repeat the following steps until k-1 cluster centers are selected; Calculating in sequence the shortest distances between the unselected candidate row vectors in the similarity matrix and the selected cluster centers; Based on the weighted probability distribution of the shortest distance, a candidate vector is randomly selected from the currently unselected candidate row vectors as a new cluster center.

9. The high-resistance grounding fault protection method based on a universal low-resistance grounding system according to claim 8, characterized in that: Calculate the candidate row vector that is not currently selected and the selected k-th cluster center The mathematical expression for the shortest distance between is: （3）； In the formula, Represents the candidate row vector that is not currently selected With the selected cluster center The shortest distance between.

10. The high-resistance grounding fault protection method based on a universal low-resistance grounding system according to claim 8, characterized in that: Based on the weighted probability distribution of the shortest distance, a candidate vector is randomly selected from the candidate row vectors that are not currently selected as a new cluster center, wherein the probability of the candidate row vector that is not currently selected being selected as the new cluster center is: （4）； In the formula, represents the probability that the candidate row vector that is not currently selected is selected as the new cluster center, Indicates that any unselected m Candidate row vectors The shortest distance between the selected k-th cluster center.

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