A fault line selection method using zero sequence current phase characteristics

Abstract

The application discloses a fault line selection method using zero sequence current phase characteristics, comprising the following steps: setting a setting threshold, monitoring a bus side zero sequence voltage in real time, judging whether the bus side zero sequence voltage amplitude is less than the setting threshold, if yes, continuing to monitor the bus side zero sequence voltage, if no, putting in a parallel small resistance, collecting zero sequence currents before and after the parallel small resistance of each line is put in, and constructing a two-dimensional image of the zero sequence currents before and after the parallel small resistance of each line is put in; using a DTW distance algorithm to calculate phase longitudinal variation characteristics of adjacent stage zero sequence currents of each line; and performing fault line selection according to the phase longitudinal variation characteristics of the adjacent stage zero sequence currents of each line. The application has the beneficial effects that: single-phase high-resistance grounding fault line selection is realized without using adjacent line information and only using current information of the line itself, transient time-frequency bands at the time of fault are not needed to be acquired, the data acquisition accuracy of a mutual inductor is low, and the adaptation degree is wider.

Description

Technical Field

[0001] This application relates to the field of single-phase high-resistance grounding fault handling technology in flexible grounding distribution systems of power distribution networks, and in particular to a fault selection method utilizing the phase characteristics of zero-sequence current. Background Technology

[0002] Single-phase grounding faults are frequent in distribution networks. Timely identification of the faulty line is crucial for rapid fault isolation and restoration of power to non-faulty sections. Medium-voltage distribution networks often employ neutral-point grounding via an arc-suppression coil to effectively suppress fault current and improve the system's arc-extinguishing rate. However, this method results in high overvoltage levels after a fault, weak fault current characteristics, and difficulty in detecting single-phase faults. Currently, urban distribution networks with high cable penetration rates in China mostly use low-resistance grounding, which effectively reduces overvoltage levels but suffers from frequent tripping. Combining the advantages of these two grounding methods, a flexible grounding distribution system with a parallel low-resistance arc-suppression coil has been proposed and implemented in several regions.

[0003] Currently, flexible grounding distribution systems still rely on zero-sequence overcurrent protection for fault identification, but its transient resistance capability is only around 100 ohms, which cannot meet the requirements for high-resistance grounding faults. Existing protection methods mainly utilize the fault information itself and can be divided into transient quantity methods and steady-state quantity methods. Among them, the transient quantity method includes the first half-wave method, wavelet analysis method, and transient energy method. While fault transient information is abundant, in the case of high-resistance grounding faults, the fault characteristic quantities decay rapidly, making it difficult to determine the transient time-frequency band and extract fault information. Line selection based on fault steady-state information has become a current hot topic in flexible grounding distribution systems, including methods that utilize the abrupt change characteristics of zero-sequence impedance before and after the connection of parallel resistors, the change in the phase difference between zero-sequence current and voltage, and the change characteristics of zero-sequence admittance.

[0004] In related technologies, line selection methods all rely on horizontal feature comparison of fault information between lines. Factors such as different line models, lengths, or zero-sequence current transformer data acquisition accuracy may interfere with the similarity calculation value and affect the line selection result.

[0005] Chinese patent "Method and Device for Selecting Single-Phase Ground Fault Line in Low-Current Grounding System", publication number: CN108562820A, publication date: September 21, 2018, includes: S1, when a single-phase ground fault is detected in a low-current grounding system, collecting zero-sequence current data at the instant of the single-phase ground fault; S2, extracting a portion of the periodic waveform before the single-phase fault and a portion of the periodic waveform after the single-phase fault from the zero-sequence current data, and preprocessing the extracted waveforms; S3, calculating the morphological distance between pairs of waveforms in the preprocessed waveforms using an improved dynamic time bending algorithm; S4, determining the single-phase ground fault line based on the morphological distance between pairs of waveforms. This scheme calculates the morphological distance between pairs of waveforms in the preprocessed waveform using an improved dynamic time bending algorithm, and determines the single-phase grounding fault line based on the morphological distance. However, it requires extracting part of the periodic waveform before and after the single-phase fault from the zero-sequence current data. In the case of high-resistance grounding faults, the fault characteristic quantities decay rapidly, the transient time-frequency band is difficult to determine, and the fault information is not easy to extract. It requires extremely high-precision current transformers for data acquisition, which is costly and prone to data errors.

[0006] Chinese patent "A Dynamic Time Bending Distance Fault Segment Location Method Based on Time Series Compression", publication number: CN 108181547A, publication date: June 19, 2018, specifically discloses a method including: preprocessing fault waveform data collected from feeder terminal equipment, including extracting the initial value, extreme value, and changes in the waveform data to obtain a new time series of the waveform data; sending the time series to the master station, and using the master station to calculate the similarity of the zero-mode current of two adjacent feeder terminal equipment using a dynamic time bending distance algorithm, thereby determining the fault segment. This method requires waveform data of one power frequency cycle after the fault in the zero-sequence current waveform channel, and still needs to determine the fault time frequency, thus requiring a very high-precision current transformer for data acquisition, which is costly and prone to data errors. Summary of the Invention

[0007] This application addresses the problem in existing technologies that require determining the fault time-frequency, which places extremely high demands on the accuracy of instrument transformer data acquisition. It provides a fault location method utilizing the phase characteristics of zero-sequence current. By analyzing the longitudinal variation characteristics of the zero-sequence current in the healthy and faulty lines during two adjacent stages—before and after the parallel small resistor is connected—in a single-phase ground fault in a flexible grounding distribution system, the method uses the DTW distance algorithm to calculate the difference in the longitudinal phase variation of the zero-sequence current waveform in each line during these two adjacent stages. This allows for fault location based solely on the current information of the line itself, without requiring information from adjacent lines. Furthermore, it eliminates the need to acquire the transient time-frequency segment during the fault, reducing the accuracy requirements for instrument transformer data acquisition and thus broadening its applicability.

[0008] To achieve the above technical objectives, this application provides a technical solution: a fault location method utilizing the phase characteristics of zero-sequence current, comprising the following steps: Step 1: Setting a setting threshold U 0set Real-time monitoring of zero-sequence voltage on the bus side Calculate the zero-sequence voltage amplitude on the bus side Determine the amplitude of zero-sequence voltage on the bus side Is it less than the set threshold U? 0set If so, continue monitoring the zero-sequence voltage on the bus side. If not, proceed to step 2; Step 2: Connect the parallel small resistors and collect the zero-sequence current i0(nT) of each line before connecting the parallel small resistors. s ) and the zero-sequence current i0′(nT) after the parallel small resistor is connected. s Step 3: Based on the two-dimensional images of zero-sequence current before and after the parallel small resistors of each line are connected, use the DTW distance algorithm to calculate the phase longitudinal change characteristics of the zero-sequence current in adjacent stages of each line; Step 4: Based on the phase longitudinal change characteristics of the zero-sequence current in adjacent stages of each line, perform fault line selection.

[0009] Furthermore, step 2 includes: Step 21: Before connecting the parallel small resistors, perform fault verification to determine if a fault exists. If yes, proceed to step 22; otherwise, end the line selection process. Step 22: Connect the parallel small resistors and collect the zero-sequence current i0(nT) of each line before connecting the parallel small resistors. s ) and the zero-sequence current i0′(nT) after the parallel small resistor is connected. s Construct a two-dimensional image of the zero-sequence current before and after the small resistors in parallel are connected to each line.

[0010] Furthermore, the threshold U is set. 0set For: U 0set =kU N Among them, U N The value of k is the phase voltage amplitude of the system, and the value of k is 10% to 15%.

[0011] Furthermore, constructing a two-dimensional image of the zero-sequence current before and after the connection of the parallel small resistors in each line includes: normalizing the zero-sequence current. Among them, i 0_peak The zero-sequence current peak value is given by n, where n is the sampling sequence and T is the peak value. s The sampling period.

[0012] Furthermore, the phase longitudinal change characteristics of the zero-sequence current in adjacent stages of each line are calculated using the DTW distance algorithm as follows: Based on the discrete datasets of the zero-sequence current in the two stages before and after the parallel small resistor is connected, as two finite point sets I1 and I2, the DTW distance coefficient between the two point sets I1 and I2 is obtained using the DTW distance algorithm: Where d(i,j) represents the Euclidean distance between the corresponding index elements of the two point sets.

[0013] Furthermore, step 3 includes: based on the two-dimensional images of the zero-sequence current before and after the parallel small resistors of each line are connected, using the DTW distance algorithm to calculate the DTW distance coefficient D of the zero-sequence current in adjacent stages of each line. i .

[0014] Furthermore, step 4 includes: setting a difference threshold λ th Utilizing the zero-sequence current DTW distance coefficient D of each line in adjacent stages i Calculate the waveform difference λ between each line. i According to the difference threshold λ th and the waveform differences λ of each line i Perform fault location.

[0015] Furthermore, the waveform difference λ of line i i for: Among them, D min This is the minimum DTW distance coefficient.

[0016] Furthermore, step 4 also includes: constructing line selection criteria: If all lines λ i <λ th If all lines do not meet the line selection criteria, it indicates a busbar fault; if some lines i meet the criteria λ... i ≥λ th If so, then the busbar is not faulty.

[0017] Furthermore, step 4 includes: Step 41: Setting the difference threshold λ th Utilizing the zero-sequence current DTW distance coefficient D of each line in adjacent stages i Calculate the waveform difference λ between each line. i Determine whether there exists a line i that satisfies λ. i ≥λ th If yes, proceed to step 42; otherwise, determine that the bus is faulty. Step 42: Determine whether line i satisfies Num[λ]. i ≥λ th ] <N-Num[λ i ≥λ thIf yes, then line i is determined to be a faulty line; otherwise, line i is determined to be a healthy line; where N is the total number of lines, Num[λ] i ≥λ th [] indicates that among all routes, the one that meets the route selection criterion λ is [the route that meets the criterion λ]. i ≥λ th The number of lines under the conditions.

[0018] The beneficial effects of this application are: (1) The DTW distance coefficient used can further highlight the difference in the longitudinal phase change between the two adjacent stages before and after the parallel small resistor is put into operation during a single-phase fault, and the selection of the line for high-resistance grounding fault still has high sensitivity.

[0019] (2) It only needs to extract the zero-sequence current of the line itself, without relying on the fault information of adjacent lines for comparison and judgment, and has good performance under different transition resistance, fault location and other conditions, with a wider range of applicability. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating a fault location method utilizing the phase characteristics of zero-sequence current in one embodiment of this application.

[0021] Figure 2 A schematic diagram of a single-phase grounding fault structure in a flexible grounding power distribution system.

[0022] Figure 3 This application is as follows Figure 1 The diagram illustrates the single-phase grounding fault handling process of a flexible grounding power distribution system in the illustrated embodiment.

[0023] Figure 4 This application is as follows Figure 1 A schematic diagram of the Euclidean distance matrix between two point sets in the illustrated embodiment.

[0024] Figure 5 This is a system zero-sequence voltage waveform diagram under another embodiment of this application.

[0025] Figure 6 This is a zero-sequence current waveform diagram before and after a small resistor is applied to a faulty circuit in another embodiment of this application.

[0026] Figure 7 This is a waveform diagram of zero-sequence current before and after a small resistor is applied to a healthy circuit in another embodiment of this application.

[0027] Figure 8 This is a comparison diagram of the zero-sequence current waveforms of a healthy circuit and a faulty circuit in another embodiment of this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description of this application is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely one preferred embodiment of this application and are only used to explain this application. They do not limit the scope of protection of this application. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] like Figure 1 As shown in the first embodiment of this application, a fault location method utilizing the phase characteristics of zero-sequence current includes the following steps: Step 1: Set the tuning threshold U 0set Real-time monitoring of zero-sequence voltage on the bus side Calculate the zero-sequence voltage amplitude on the bus side Determine the amplitude of zero-sequence voltage on the bus side Is it less than the set threshold U? 0set If so, continue monitoring the zero-sequence voltage on the bus side. If not, proceed to step 2; Step 2: Connect the parallel small resistors and collect the zero-sequence current i0(nT) of each line before connecting the parallel small resistors. s ) and the zero-sequence current i0′(nT) after the parallel small resistor is connected. s Construct two-dimensional images of the zero-sequence current before and after the small resistors in parallel are connected in each line; Step 3: Based on the two-dimensional images of zero-sequence current before and after the parallel small resistors of each line are connected, use the DTW distance algorithm to calculate the phase longitudinal change characteristics of the zero-sequence current in adjacent stages of each line. Step 4: Select the fault line based on the phase longitudinal change characteristics of the zero-sequence current in adjacent stages of each line.

[0030] In this embodiment, by analyzing the longitudinal variation characteristics of the zero-sequence current of the healthy and faulty lines in two adjacent stages before and after the parallel small resistor is connected during a single-phase ground fault in a flexible grounding distribution system, the DTW distance algorithm is used to calculate the difference in the longitudinal phase change of the zero-sequence current waveform of each line in the two adjacent stages before and after the neutral point small resistor is connected, and fault line selection is performed. This achieves single-phase high-resistance ground fault line selection without the need for information on adjacent lines, only using the current information of the line itself. At the same time, it does not require the acquisition of the transient time-frequency band at the time of the fault, and the requirements for the accuracy of the current transformer data acquisition are low, thus making it more adaptable.

[0031] Specifically, in step 1, based on the zero-sequence voltage on the bus side... Calculate the zero-sequence voltage amplitude on the bus side Setting threshold U0set : U 0set =kU N ; Among them, U N The system phase voltage amplitude, k takes a value of 10% to 15%, when the zero-sequence voltage amplitude on the bus side is... Greater than the protection setting threshold U 0set At that time, it was considered a single-phase ground fault.

[0032] When the zero-sequence voltage amplitude on the bus side in step 1 After determining a single-phase ground fault, proceed to step 2: Step 21: Before connecting the parallel small resistor, perform fault verification to determine if a fault exists. If yes, proceed to step 22; otherwise, end the line selection process. Step 22: Connect the parallel small resistors and collect the zero-sequence current i0(nT) of each line before connecting the parallel small resistors. s ) and the zero-sequence current i′0(nT) after the parallel small resistor is connected. s Construct a two-dimensional image of the zero-sequence current before and after the small resistors in parallel are connected to each line.

[0033] like Figure 2 As shown, line L in the network n A phase-A ground fault occurs, L P R is the inductance of the arc suppression coil. b For parallel small resistors, K b For parallel small resistance switching, R f This is the transition resistance at the fault point. When the system is operating normally, K... b Disconnect, R b When not in operation, the system is directly grounded via the arc suppression coil. When a transient single-phase ground fault occurs on the line, the arc suppression coil generates an inductive current to deeply compensate for the ground capacitance current, extinguishing the fault arc. The system can still operate normally for 1-2 hours without requiring the R... b If a permanent fault occurs, close switch K. b Invest in R b The neutral grounding method is changed to an arc suppression coil with a small resistor in parallel, and the fault is identified according to the corresponding fault selection procedure. Therefore, before the small resistor in parallel is connected, fault verification is performed. If the fault has disappeared, the small resistor in parallel is not connected, and the zero-sequence voltage on the bus side continues to be monitored. Determine the amplitude of zero-sequence voltage on the bus side Is it less than the set threshold U? 0setIf the fault does not disappear within a short period of time, it is determined that a single-phase permanent ground fault has occurred. A parallel small resistor is then connected, and the fault selection procedure is executed. This ensures that the fault selection procedure is only executed when a single-phase permanent ground fault occurs, avoiding incorrect fault selection caused by transient faults and guaranteeing the accuracy of fault selection.

[0034] In step 22, the zero-sequence current i0(nT) of each line before the parallel small resistor is connected is collected over a period of time. s ) and the current i0′(nT) after the parallel small resistor is connected s ), where n is the sampling sequence, T s The sampling period is T. In this embodiment, the sampling period is T. s Take 10 -5 s, normalize the zero-sequence current: Among them, i 0_peak This represents the peak value of the zero-sequence current.

[0035] In some embodiments, if the zero-sequence current after connecting a small parallel resistor is... Then, based on the zero-sequence voltage, it is indirectly derived that... Otherwise, the result can be obtained directly from the current transformer.

[0036] like Figure 3 In the fault equivalence network shown, The zero-sequence equivalent voltage source at the fault point. For line L i Zero-sequence current at the beginning, 1 / jωC 0i For line L i Zero-sequence equivalent capacitive reactance to ground, j3ωL P This is the zero-sequence equivalent reactance of the arc suppression coil.

[0037] Zero-sequence current in any sound circuit This refers to the line's own capacitance current to ground. The zero-sequence voltage of the system: Therefore, it can be seen that the phase change of the zero-sequence current in a healthy circuit is longitudinal in the two adjacent stages before and after the parallel small resistor is connected. for: The longitudinal phase change of the zero-sequence current in a sound circuit before and after the parallel small resistor is connected consists of the phase change of the zero-sequence voltage in two stages. Consistent.

[0038] For a faulty line, the zero-sequence current of the faulty line after the parallel small resistor is connected Adding a resistive component. The zero-sequence current in the two adjacent stages before and after the parallel small resistor is connected is: Therefore, we can see the longitudinal phase change of the zero-sequence current in the faulty line before and after the parallel small resistor is connected. for: Therefore, it can be seen that the longitudinal phase change of the zero-sequence current before and after the small resistor in parallel is connected in the faulty line is due to the phase change of the zero-sequence voltage in two stages. and admittance phase change A joint decision.

[0039] The zero-sequence voltages in two adjacent stages before and after the parallel small resistor is connected are: in, Let C be the voltage of phase A of the system. ∑(0) ν is the sum of the zero-sequence capacitances to ground of all lines; ν is the compensation degree of the arc suppression coil. Under overcompensation, ν is taken as -10% to -5%.

[0040] Furthermore, the phase change δ of the zero-sequence voltage before and after the parallel small resistor is connected is analyzed. U0 for: It is approximately assumed that ωC ∑(0) ∈[1.15, 11.5]mS; Arc suppression coils often use overcompensation v=-10%, ωL P ≥26.35Ω. In practical engineering, a small resistor R is connected in parallel. b The typical resistance is 4Ω to 16Ω.

[0041] Phase change of system admittance Range of variation: It can be known That is, the phase change of the system admittance. Mainly affected by the parallel small resistor R b The impact, received

[0042] As can be seen from the above, the longitudinal phase change of the zero-sequence current in any sound circuit before and after the parallel small resistor is connected is as follows: The longitudinal change of the zero-sequence current phase in the faulty line is

[0043] like Figure 4As shown, for the two-dimensional images of zero-sequence current before and after the parallel small resistor is connected to each line, the DTW distance algorithm is adopted. This algorithm, based on the simple principle of the Euclidean distance algorithm, adjusts the distance between the two time series through dynamic programming, so it is still applicable to two time series with unequal lengths. The basic idea of ​​the DTW distance algorithm is to stretch the length of the time series and adjust the correspondence between the elements at different time points of the two series and align them, and finally search for an optimal curved path under the path where the DTW distance coefficient between the two point sets is minimized. Discrete datasets of zero-sequence current in any line before and after the parallel small resistor is connected are monitored and collected as two finite point sets I1 and I2. Assume that I1:{i0(1),i0(2),…,i0(j),…i0(b)}; I2:{i′0(1),i′0(2),…,i′0(i),…i′0(a)}, and calculate their Euclidean distance to form an Euclidean distance matrix. When searching for the optimal curved path in the distance matrix, the following constraints are satisfied: (1) Boundary constraints. The starting point of the search path is the lower left element d(1,1) of the Euclidean distance matrix, and the ending point is the upper right element d(a,b) of the matrix; (2) Continuity and monotonically non-decreasing constraint. In the process of seeking the optimal curved path, the size of the rows and columns is monotonically non-decreasing. Taking any element d(i,j) in the Euclidean distance matrix as an example, there are three possible directions to reach the point, namely d(i-1,j), d(i,j-1) and d(i-1,j-1).

[0044] The core step of the DTW distance algorithm is to find an optimal curved path L. * Minimize ∑d(i,j). Assume L * The elements traversed sequentially in the Euclidean distance matrix are {d1, d2, d3…d…} s}, where max(a,b)≤s≤a+b, s is called the length of the optimal path, and the final DTW distance coefficient between the two point sets I1 and I2 is: The DTW distance coefficient directly reflects the similarity between two point sets. The larger the distance value, the lower the similarity between the two point sets; conversely, the smaller the value, the higher the similarity.

[0045] As a second embodiment of this application, step 3 includes: based on the two-dimensional image of the zero-sequence current before and after the parallel small resistors of each line are connected, calculating the DTW distance coefficient D of the zero-sequence current in adjacent stages of each line using the DTW distance algorithm. i ; Step 4 includes: setting the difference threshold λ th Utilizing the zero-sequence current DTW distance coefficient D of each line in adjacent stages iCalculate the waveform difference λ between each line. i According to the difference threshold λ th and the waveform differences λ of each line i Perform fault location.

[0046] In this embodiment, the difference threshold λ th =2~3. Let there be two time series I1:{i0(1),i0(2),…,i0(j),…i0(b)} and I2:{i′0(1),i′0(2),…,i0′(i),…i′0(a)} of length b and a, respectively, forming a Euclidean distance matrix between the series, where d(i,j) represents the Euclidean distance between corresponding indices of the two series. Let L be a path with constraints. Find an optimal curved path L within L. * To minimize ∑d(i,j), assume L * The elements visited in sequence are {d1, d2, d3…d} s}, where max(a,b)≤s≤a+b, and s is the length of the optimal path. Calculate the DTW distance coefficient between the current sampling dataset [I1] before the small resistor is installed and the current sampling dataset [I2] after the small resistor is installed for each line: The DTW distance coefficient directly reflects the similarity between two sequences. If the DTW distance coefficient is 0 for two identical time series, it means that the smaller the DTW distance coefficient, the higher the similarity between the two sequences, and vice versa. It is also applicable to two time series of different lengths.

[0047] The DTW distance coefficient D between the zero-sequence current waveforms before and after the parallel small resistor is connected to line i is calculated. i At this time, the waveform difference λ of line i i for: Among them, D min To determine the minimum DTW distance coefficient, construct the route selection criterion: If all lines λ i <λ th If all lines do not meet the line selection criteria, it indicates a busbar fault; if some lines i meet the criteria λ... i ≥λ th If so, then the busbar is not faulty.

[0048] Furthermore, step 4 includes: Step 41: Set the difference threshold λ th Utilizing the zero-sequence current DTW distance coefficient D of each line in adjacent stagesi Calculate the waveform difference λ between each line. i Determine whether there exists a line i that satisfies λ. i ≥λ th If yes, proceed to step 42; otherwise, determine that there is a bus fault. Step 42: Determine whether line i satisfies Num[λ] i ≥λ th ] <N-Num[λ i ≥λ th If yes, then line i is determined to be a faulty line; otherwise, line i is determined to be a healthy line. Wherein, the difference threshold λ th =2, N is the total number of lines, Num[λ i ≥λ th [] indicates that among all routes, the one that meets the route selection criterion λ is [the route that meets the criterion λ]. i ≥λ th The number of lines under the given conditions.

[0049] As a third embodiment of this application, a specific embodiment is provided for illustration: constructing as follows... Figure 2 The 10kV flexible grounding distribution system model shown has an arc suppression coil with 10% overcompensation. A single-phase ground fault is assumed to occur on line L4 in 0.1 seconds, with an initial phase angle of 0 rad. The fault point is 18 km from the busbar, and the grounding resistance R... f =100Ω, the neutral point parallel resistor is connected at 1s and disconnected at 2s. Taking time 0 as the starting sampling point, the system zero-sequence voltage is as follows: Figure 5 As shown, the zero-sequence voltage of the system changes significantly before and after the neutral point small resistor is connected, and the zero-sequence voltage after connection shows a significant decrease compared to before connection.

[0050] Calculate the normalized DTW distance coefficients [D] for each line: [D1, D2, D3, D4] = [0.3226, 0.3219, 0.3208, 156.333]. Take the smallest DTW coefficient as D. min DTW difference coefficients for each line corresponding to the baseline: Among them, only line L4 has a DTW difference coefficient that is much greater than the threshold value of 2, indicating that there is a certain phase difference in the zero-sequence current waveform of the faulty line before and after the parallel small resistor is connected, and the waveform difference is large. The zero-sequence current before and after the small resistor is connected to the faulty line is as follows: Figure 6 As shown; the DTW difference coefficient of any sound circuit is stable at around 1, that is, the phase change of the zero-sequence current waveform in the two stages of the sound circuit is basically the same, and the waveform similarity is high. The zero-sequence current before and after the small resistor is connected to the sound circuit is as follows: Figure 7As shown, the zero-sequence current waveforms of a healthy circuit and a faulty circuit are compared. Figure 8 As shown. Line L4 satisfies the criterion λ4≥λ th Meanwhile, all routes meet the route selection criterion λ4≥λ. th The number of lines under the condition satisfies the criterion Num[λ4≥λ] th ] <N-Num[λ4≥λ th Therefore, line L4 is determined to be a faulty line, and conversely, line L4 is a healthy line.

[0051] This application utilizes the longitudinal phase change characteristics of the zero-sequence current of each line in two stages: before and after the parallel small resistor is connected. It employs the DTW distance coefficient to characterize the longitudinal phase change characteristics of the zero-sequence current in each line during these two stages and constructs a fault selection criterion based on the DTW distance coefficient. Therefore, it is largely unaffected by factors such as fault location and transition resistance, and utilizes only the current information of the line itself, without requiring current information from adjacent lines. It can accurately identify faulty lines even for high-resistance grounding faults with weak characteristics, has low requirements for the accuracy of current transformer data acquisition, and has a wide range of applications.

[0052] The above-described specific embodiments are preferred embodiments of a fault location method utilizing the phase characteristics of zero-sequence current in this application, and are not intended to limit the specific scope of this application. The scope of this application includes but is not limited to these specific embodiments. All equivalent changes made in accordance with the shape and structure of this application are within the protection scope of this application.

Claims

1. A fault location method utilizing the phase characteristics of zero-sequence current, characterized in that: Includes the following steps: Step 1: Set the tuning threshold Real-time monitoring of zero-sequence voltage on the bus side Calculate the zero-sequence voltage amplitude on the bus side. Determine the amplitude of the zero-sequence voltage on the bus side. Is it less than the set threshold? If so, continue monitoring the zero-sequence voltage on the bus side. If not, proceed to step 2; Step 2: Connect the parallel small resistors and collect the zero-sequence current of each line before connecting the parallel small resistors. and the zero-sequence current after the parallel small resistor is connected. Two-dimensional images of the zero-sequence current before and after the small resistors in parallel are connected in each line are constructed; among them, The sampling period; Step 3: Based on the two-dimensional images of zero-sequence current before and after the parallel small resistors of each line are connected, use the DTW distance algorithm to calculate the phase longitudinal change characteristics of the zero-sequence current in adjacent stages of each line. Step 4: Select fault lines based on the phase longitudinal change characteristics of the zero-sequence current in adjacent stages of each line. Step 3 includes: based on the two-dimensional images of the zero-sequence current before and after the parallel small resistors of each line are connected, calculating the DTW distance coefficient of the zero-sequence current in adjacent stages of each line using the DTW distance algorithm. ; Step 4 includes: setting a difference threshold. Utilizing the DTW distance coefficient of the zero-sequence current in adjacent stages of each line Calculate the waveform differences of each line According to the difference threshold and waveform differences between lines Perform fault location; line Waveform differences for: ； in, This is the minimum DTW distance coefficient.

2. The fault location method utilizing the phase characteristics of zero-sequence current as described in claim 1, characterized in that: Step 2 includes: Step 21: Before connecting the parallel small resistor, perform fault verification to determine if a fault exists. If yes, proceed to step 22; otherwise, end the line selection process. Step 22: Connect the parallel small resistors and collect the zero-sequence current of each line before connecting the parallel small resistors. and the zero-sequence current after the parallel small resistor is connected. Two-dimensional images of zero-sequence current before and after the small resistors in parallel are connected to each line are constructed.

3. The fault location method utilizing the phase characteristics of zero-sequence current as described in claim 1, characterized in that: The set threshold for: ； in, The system phase voltage amplitude is given by k, which ranges from 10% to 15%.

4. The fault location method utilizing the phase characteristics of zero-sequence current as described in claim 2, characterized in that: The construction of the two-dimensional image of zero-sequence current before and after the connection of the parallel small resistors in each line includes: Normalize the zero-sequence current: ； in, This is the peak value of the zero-sequence current. For sampling sequences, The sampling period.

5. The fault location method utilizing the phase characteristics of zero-sequence current as described in claim 1, characterized in that: The phase longitudinal change characteristics of the zero-sequence current in adjacent stages of each line, calculated using the DTW distance algorithm, are as follows: The discrete datasets of the zero-sequence current in the line during the two stages before and after the parallel small resistor is connected are used as two finite point sets. , The two point sets are obtained using the DTW distance algorithm. , The DTW distance coefficient between them is: ； in, This represents the Euclidean distance between corresponding index elements of two point sets. Represents the th bend on the optimal curved path The Euclidean distance values ​​corresponding to each element. This represents the length of the optimal curved path.

6. The fault location method utilizing the phase characteristics of zero-sequence current as described in claim 1, characterized in that: Step 4 also includes: constructing line selection criteria: ； If all lines If all lines fail to meet the line selection criteria, it indicates a busbar fault; if some lines... Satisfying the criteria If so, then the busbar is not faulty.

7. The fault location method utilizing the phase characteristics of zero-sequence current as described in claim 1, characterized in that: Step 4 includes: Step 41: Set the difference threshold Utilizing the zero-sequence current DTW distance coefficient of each line in adjacent stages Calculate the waveform differences of each line Determine if a line exists. satisfy If yes, proceed to step 42; otherwise, determine that there is a bus fault. Step 42: Determine the route Does it meet the requirements? If so, then determine the line. If it is a faulty line, then determine the line. To improve the route; in This represents the total number of lines. This indicates that the route selection criteria are met among all routes. The number of lines under the conditions.

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