Single-phase earth fault line selection method, system and device based on cosine similarity and medium

Abstract

The invention relates to the technical field of fault discrimination, and discloses a cosine similarity-based single-phase earth fault line selection method, system and device and a medium, and the method comprises the steps: obtaining real-time signals of zero-sequence current and voltage of a bus; comparing the rated voltage of the bus with the real-time voltage, and judging whether fault line selection is started or not; if so, sampling to obtain zero-sequence current and bus zero-sequence voltage of each line in the first period after the fault; calculating a cosine similarity coefficient of each line; constructing a main criterion, and distinguishing a faulty line and a non-faulty line; and if the cosine similarity coefficient does not conform to the main criterion, constructing an auxiliary criterion, and determining a fault line. The difference between the polarity of the zero-sequence current and the derivative of the zero-sequence voltage is measured through a cosine similarity comparison method, and an equivalent capacitance value does not need to be determined; according to the method, the comprehensive detection criterion based on the synergistic effect of the main criterion and the auxiliary criterion is constructed, the simplification error of the line model is considered, the reliability is high when the high-resistance grounding fault occurs, and the zero-sequence current does not need to be filtered.

Description

Technical Field

[0001] This invention relates to the field of fault identification technology, and in particular to a method, system, device and medium for selecting single-phase grounding faults based on cosine similarity. Background Technology

[0002] Fault location in medium-voltage distribution networks is a crucial step in ensuring power supply safety and power quality. When a single-phase ground fault occurs, the fault current is very small, especially in resonant grounding distribution networks. Due to the compensation of arc suppression coils, the transient fault process becomes particularly complex, and traditional overcurrent protection devices cannot distinguish between the fault current and normal load current, resulting in unsatisfactory detection performance in practical applications. Therefore, ensuring the stability of the power grid, preventing serious events, and accurately identifying the faulty line during a single-phase ground fault are of great significance. Currently, researchers both domestically and internationally have conducted extensive research on how to improve the accuracy of fault location during ground faults. Existing detection methods can be divided into signal processing-based methods and feature learning-based methods. Signal processing-based methods mainly apply modern signal processing algorithms to extract minute fault features from transient zero-sequence currents based on time-domain and frequency-domain analysis. For example, one method uses the Variable Mode Decomposition (VMD) algorithm to extract low-frequency features from the zero-sequence current and constructs a first-order differential extremum; another method uses a fundamental component shifting method to remove the fundamental frequency component in the transient ZSC and combines transient energy and polarity characteristics to detect the faulty line. In addition, wavelet transform, S-transform, and other methods are also widely used as feature extraction tools. Based on feature learning, deep learning algorithms are often used to adaptively extract fault features from the original fault signal and classify feeders based on feature fusion. For example, a lossless image is generated by sequentially superimposing the zero-sequence current waveforms of the feeders, and a convolutional neural network (CNN) with an attention strategy is built for image recognition. Alternatively, a zero-sequence voltage-zero-sequence current image is generated using the zero-sequence voltage on the bus and the zero-sequence current of a single feeder, and then a CNN is used for recognition, proposing a local detection method.

[0003] The aforementioned methods, considering their unique feature extraction capabilities, achieve high detection accuracy. However, they require further parameter optimization, such as selecting basis functions and decomposition layers in signal processing algorithms, and stacking efficient backbones and attention mechanisms in deep learning networks. The inherent limitations of these algorithms hinder their practical application to some extent. Signal processing algorithms use fixed basis functions to extract fault features, deep learning algorithms lack interpretability during detection, and while these methods employ complex tools to improve detection performance, they fail to demonstrate reliability under extreme fault conditions (high impedance faults and strong background noise) of single-phase grounding faults. Furthermore, they require large amounts of data for training, resulting in high costs. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, this invention provides a single-phase ground fault location method and system based on cosine similarity to solve the problem that current fault location methods using transient quantities are easily affected by complex fault conditions in distribution network fault location.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for selecting a single-phase ground fault based on cosine similarity, comprising: Acquire real-time signals of bus zero-sequence current and voltage; Compare the rated voltage of the busbar with the real-time voltage, and based on the comparison results, determine whether to initiate fault line selection; If started, the zero-sequence current of each line and the zero-sequence voltage of the bus will be sampled and acquired in the first cycle after the fault. Based on the acquired data, the cosine similarity coefficient of each line is calculated; Construct a primary criterion to distinguish faulty lines from non-faulty lines by comparing the signs of the cosine similarity coefficients; If the cosine similarity coefficient does not meet the primary criterion, then a secondary criterion is constructed to determine the faulty line.

[0007] As a preferred embodiment of the single-phase ground fault location method based on cosine similarity described in this invention, the method involves: calculating the cosine similarity coefficient of each line based on the acquired data, including: Calculate the derivatives of the measured zero-sequence current and the normalized zero-sequence current and zero-sequence voltage based on similarity comparison. Based on the derivatives of zero-sequence current and zero-sequence voltage, the cosine similarity coefficient of each line is calculated.

[0008] The beneficial effects of this preferred technical solution are: by using cosine similarity quantification, a similarity coefficient sequence for each line is generated, providing a unified and comparable similarity index for subsequent judgments, thus laying the foundation for line selection.

[0009] As a preferred embodiment of the single-phase ground fault line selection method based on cosine similarity described in this invention, the main criterion is constructed as follows: for fault line selection under a single-phase ground fault, if only one feeder exhibits a negative cosine similarity coefficient, then the corresponding feeder is identified as the faulty line, expressed as: By comparing the signs of the calculated cosine similarity coefficients, faulty lines and non-faulty lines can be distinguished.

[0010] As a preferred embodiment of the single-phase ground fault location method based on cosine similarity described in this invention, if the cosine similarity coefficient does not meet the primary criterion, a secondary criterion is constructed to determine the faulty line, including: Based on the cosine similarity coefficient of each line, the minimum cosine similarity value is identified; Calculate the average similarity coefficient of the remaining lines, excluding the line with the minimum similarity value; The waveform similarity distance is calculated based on the average similarity coefficient and the minimum cosine similarity value.

[0011] As a preferred embodiment of the single-phase ground fault location method based on cosine similarity described in this invention, if the cosine similarity coefficient does not meet the primary criterion, a secondary criterion is constructed to determine the faulty line, further comprising: Set a distance threshold; If the calculated waveform similarity distance is greater than the distance threshold, then the line with the minimum cosine similarity value is a faulty line. Otherwise, it indicates a busbar fault.

[0012] The beneficial effects of this preferred technical solution are: it strengthens the blind spot of the main criterion and can improve the robustness and reliability of line selection under different conditions.

[0013] As a preferred embodiment of the single-phase ground fault location method based on cosine similarity described in this invention, the method includes: comparing the rated bus voltage with the real-time voltage, and determining whether to initiate fault location based on the comparison result, including: Set startup threshold coefficient ; If the bus real-time voltage Greater than If the fault is detected, then the faulty line should be selected; where, This is the rated voltage.

[0014] As a preferred embodiment of the single-phase ground fault location method based on cosine similarity described in this invention, the derivatives of the calculated and measured zero-sequence current and the normalized zero-sequence current and zero-sequence voltage after similarity comparison are expressed as: in, and This indicates the normalized first phase after a single-phase ground fault. The derivatives of the zero-sequence current of the line and the zero-sequence voltage of the bus; Indicates the first The instantaneous value of the zero-sequence current of the line; Represents the absolute value function; This represents the measured value of the zero-sequence voltage at the busbar. Represented as at discrete time points The zero-sequence voltage value of the bus at the location; Represents a time variable; Indicates the time of occurrence of a single-phase ground fault; This indicates the period of the zero-sequence current.

[0015] Secondly, the present invention provides a single-phase ground fault location system based on cosine similarity, comprising: The first acquisition module is used to acquire the real-time signals of the zero-sequence current and voltage of the bus. The first judgment module is used to compare the rated voltage of the bus with the real-time voltage, and based on the comparison result, to determine whether to activate the fault line selection. The second acquisition module is used to sample and acquire the zero-sequence current of each line and the zero-sequence voltage of the bus in the first cycle after the fault if it is started. The first calculation module is used to calculate the cosine similarity coefficient of each line based on the acquired data; The second judgment module is used to construct the main criterion, which distinguishes faulty lines from non-faulty lines by comparing the signs of the cosine similarity coefficients. The second calculation module is used to construct a secondary criterion to determine the faulty line if the cosine similarity coefficient does not meet the primary criterion.

[0016] Thirdly, the present invention provides a computer device, comprising: Memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions, which, when executed by the processor, implement the steps of a single-phase ground fault location method based on cosine similarity.

[0017] Fourthly, the present invention provides a computer-readable storage medium storing computer-executable instructions that, when executed by a processor, implement the steps of the cosine similarity single-phase ground fault location method.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention starts immediately when the zero-sequence voltage exceeds the threshold, avoiding delays; the cosine similarity comparison method is used to measure the difference between the polarity of the zero-sequence current and the derivative of the zero-sequence voltage, without the need to determine the equivalent capacitance value; a comprehensive detection criterion based on the synergistic effect of the main criterion and the auxiliary criterion is constructed, which takes into account the simplification error of the line model, has good reliability when a high-resistance grounding fault occurs, and does not require filtering of the zero-sequence current, maintaining consistent discrimination for high resistance, noise, and arc suppression coil compensation. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the overall process of a single-phase ground fault location method based on cosine similarity according to an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram illustrating the specific process of a single-phase ground fault location method based on cosine similarity according to an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of the zero-sequence equivalent network under a single-phase grounding fault in a single-phase grounding fault selection method based on cosine similarity according to an embodiment of the present invention.

[0023] Figure 4 This is a schematic diagram of the amplitude-frequency and phase-frequency characteristics of the input impedance in a single-phase ground fault location method based on cosine similarity, as described in an embodiment of the present invention.

[0024] Figure 5 In a single-phase ground fault location method based on cosine similarity according to an embodiment of the present invention, the zero-sequence resistance pair A schematic diagram illustrating the influence of phase frequency characteristics. Detailed Implementation

[0025] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0026] Example 1, referring to Figure 1 As an embodiment of the present invention, a method for selecting a single-phase ground fault based on cosine similarity is provided, comprising: S100: Acquire the real-time signal of the zero-sequence current and voltage of the bus; S200: Compare the rated voltage of the bus with the real-time voltage, and based on the comparison results, determine whether to initiate fault line selection; S300: If started, it samples and acquires the zero-sequence current of each line and the zero-sequence voltage of the bus in the first cycle after the fault. S400: Calculate the cosine similarity coefficient of each line based on the acquired data; S500: Construct the main criterion to distinguish faulty lines from non-faulty lines by comparing the signs of the cosine similarity coefficients; S600: If the cosine similarity coefficient does not meet the primary criterion, then a secondary criterion is constructed to determine the faulty line.

[0027] It should be noted that although the existing technology has high accuracy, it relies on complex parameter optimization; it has poor reliability and high cost under extreme conditions such as high-resistance grounding and strong noise, and does not meet the judgment of some practical applications.

[0028] Therefore, through the above steps S100-S600, based on the fault characteristics under single-phase grounding fault, the zero-sequence voltage derivative reflecting the capacitance characteristics is compared with the measured zero-sequence voltage, the zero-sequence current is identified from the perspective of similarity and distance, and the faulty line is detected by using the cosine similarity comparison method.

[0029] Example 2, refer to Figures 1-5 As an embodiment of the present invention, based on the above embodiment, a method for selecting single-phase ground faults using cosine similarity is provided.

[0030] Before explaining the solution, we first analyze the fault characteristics under single-phase grounding faults to reveal the importance of the differences in equivalent line models in distinguishing faulty and non-faulty lines.

[0031] (1) Characteristics of single-phase grounding fault The zero-sequence equivalent network of a single-phase ground fault occurring at 5 points on the feeder in a resonant grounding system is as follows: Figure 3 As shown. Assume a fault occurs at point f. This represents the equivalent capacitance of a non-faulty circuit. , The equivalent capacitance upstream and downstream of the fault point; This serves as a zero-sequence virtual voltage source for the fault point. This is expressed as 3 times the equivalent inductance of the arc suppression coil; It is the sum of the upstream modulus, zero modulus, and 3 times the transition resistance of the faulty line.

[0032] according to Figure 3 As shown, taking non-faulty line 1 as an example, the zero-sequence voltage of the bus is... Zero-sequence current of non-faulty line 1 The differential equation can be expressed as: (1) in, The capacitance to ground of line 1 is represented by equation (1). The zero-sequence currents of non-faulted lines are approximately equal, and their amplitudes are proportional to the equivalent capacitances and in the same direction.

[0033] Similarly, the differential equation between the zero-sequence voltage of the bus and the zero-sequence current i05 of the faulted line 5 can be expressed as: (2) in, This represents the sum of the capacitances to ground of the other four non-faulty lines. Non-faulty lines can be equivalent to capacitors within their characteristic frequency bands, while faulty lines include equivalent resistance, equivalent inductance, equivalent zero-sequence capacitance, and a virtual voltage source at the fault point. Therefore, faulty and non-faulty lines can be distinguished by determining whether the line conforms to a capacitance model.

[0034] According to equation (1), subtracting the capacitor current in the right-hand term, equation (1) can be rewritten as: (3) Similarly, equation (2) can also be transformed, that is: (4) The left-hand side of equations (3) and (4) represents the error calculated based on the measured zero-sequence current and capacitive current, where the capacitive current is obtained by multiplying the derivative of the zero-sequence voltage by the equivalent capacitance. The calculation errors for non-faulty lines and faulty lines are respectively set as... and As shown in (5): (5) According to equation (5), when a single-phase ground fault occurs in a resonant grounding system, for the non-faulty lines, A value of 0 indicates that the magnitude and polarity of the derivative of the measured zero-sequence current and zero-sequence voltage multiplied by the equivalent capacitance are consistent. For faulty circuits, since the inductive current cannot completely compensate for the capacitive current, especially during transient processes, If it is not equal to 0, it indicates that the measured zero-sequence current is inconsistent with the amplitude and polarity of the corresponding capacitor current.

[0035] (2) Line impedance phase frequency characteristics In a low-current grounding system's zero-sequence network, when the end of the line is open-circuited, the input impedance of the line... for: (6) In equation (6), The wave impedance of the line, For the propagation coefficient, Where is the line length; then The phase frequency and amplitude frequency characteristics are as follows Figure 4 As shown.

[0036] When a single-phase ground fault occurs, the frequency range of the transient component is typically greater than 200Hz, where the zero-sequence resistance... It is much smaller than the reactance. Therefore, when analyzing the zero-sequence impedance at the input end of the line, the effect of the zero-sequence resistance is ignored. Then, the zero-sequence impedance at the fault point can be expressed as: (7) In equation (7), , These are the zero-sequence capacitance and zero-sequence inductance of the circuit.

[0037] like Figure 5 As shown, when series and parallel resonances occur, the zero-sequence resistance can be considered or ignored. right The phase frequency characteristics are almost unaffected; therefore, the zero-sequence resistance can be ignored when analyzing the phase frequency characteristics of the impedance. The impact, among which, .

[0038] like Figure 4 and Figure 5 As shown, when the frequency is When the impedance varies within a certain range, the input impedance of the line is capacitive; when At this time, the impedance at the input of the line exhibits alternating inductive and capacitive changes, with intervals between the changes being [missing information]. When composure transforms into sensibility, When the amplitude-frequency characteristic of the circuit is at its minimum, it indicates series resonance; when the circuit changes from inductive to capacitive, its amplitude-frequency characteristic is at its maximum, indicating parallel resonance.

[0039] As can be seen from the above, as the frequency increases, series or parallel resonance will occur on the line, generating transient resonant current. The amplitude of the transient current is affected by the excitation source. The virtual power source at the fault point, acting as the excitation source, monotonically decreases in amplitude with increasing frequency, starting from the power frequency. Therefore, the transient current amplitude generated at the minimum resonant frequency of series or parallel resonance is the largest. The characteristic frequency band is defined as the frequency range from 0 (or the 3rd harmonic for a resonant grounding system) to the minimum value of the first resonant frequency of all healthy lines.

[0040] The above is an analysis of fault characteristic quantities for subsequent solutions. This invention is not limited to single-phase grounding faults, and the calculation errors of non-faulty lines and faulty lines are also considered. and The former equals 0, while the latter does not. This characteristic can be used for fault analysis.

[0041] In this embodiment of the application, the real-time signal of the bus zero-sequence current voltage is acquired in step S100; In one alternative implementation, the data can be acquired via an electronic current transformer using the open delta voltage of the main PT and the zero-sequence CT output.

[0042] In another alternative implementation, high-precision synchronous acquisition modules, such as GPS and PTP, can be deployed inside the bus PT and each line FTU to acquire data synchronously.

[0043] In the embodiments of this application, reference is made to Figures 1-2 In step S200, the rated voltage of the bus is compared with the real-time voltage. Based on the comparison result, it is determined whether to initiate fault selection, including the following steps A1-A2: A1: Set the startup threshold coefficient ; A2: If the bus real-time voltage Greater than If the fault is detected, then the faulty line should be selected; where, This is the rated voltage.

[0044] Specifically, the startup threshold coefficient It is generally taken as 0.15 based on actual needs.

[0045] In another alternative implementation, based on the above implementation, a second criterion can also be set, for example: calculating the instantaneous zero-sequence power. , The direction is positive (flowing into the busbar) or negative (flowing out of the busbar) and the amplitude is greater than the set value; the line selection is started when both criteria are met; this method can eliminate false starts such as PT disconnection and resonance.

[0046] In this embodiment of the application, if the process is started in step S300, the zero-sequence current of each line and the zero-sequence voltage of the bus are sampled and acquired in the first cycle after the fault. Specifically, in S200 Greater than When the condition is met for the first time, the current sampling point is recorded as the fault start time. At this time, synchronous sampling is started, and the period time can be set. For example, starting from the fault start time, the sampling data of the next 20ms (50Hz) is continuously buffered to ensure that the period is completely after the fault occurs. The zero-sequence voltage of the bus and the zero-sequence current of multiple lines are extracted.

[0047] In another optional implementation, after the data is extracted in S300 based on the above implementation, a data alignment and integrity verification step can be added to check whether all channels have collected the complete cycle. If there are any missing points or communication abnormalities, the current cycle can be abandoned and the next cycle can be re-collected.

[0048] In the embodiments of this application, reference is made to Figure 2 In step S400, based on the acquired data, the cosine similarity coefficient of each line is calculated, including the following steps B1-B2: B1: Calculate the derivatives of the measured zero-sequence current and the normalized zero-sequence current and zero-sequence voltage after similarity comparison; In this embodiment of the application, the derivatives of the zero-sequence current and the zero-sequence current and zero-sequence voltage calculated and measured in B1 after normalization based on similarity comparison are expressed as follows: (8) in, and This indicates the normalized first phase after a single-phase ground fault. The derivatives of the zero-sequence current of the line and the zero-sequence voltage of the bus; Indicates the first The instantaneous value of the zero-sequence current of the line; Represents the absolute value function; This represents the measured value of the zero-sequence voltage at the busbar. Represented as at discrete time points The zero-sequence voltage value of the bus at the location; Represents a time variable; Indicates the time of occurrence of a single-phase ground fault; This indicates the period of the zero-sequence current.

[0049] B2: Based on the derivatives of zero-sequence current and zero-sequence voltage, the cosine similarity coefficient of each line is calculated. Specifically, B2 is represented as: (9) in, It is the total number of sampling points for zero-sequence current within half a cycle.

[0050] It should be noted that, ignoring the amplitude of the time series, cosine similarity can effectively measure the relative direction of two time series signals, thus eliminating the need to determine the equivalent capacitance under single-phase-to-ground fault conditions. Furthermore, the zero-sequence current and zero-sequence voltage derivatives of non-faulty lines have the same polarity, while those of faulty lines have opposite polarities. Therefore, the zero-sequence current and zero-sequence voltage derivatives of non-faulty lines... The calculated value is positive, while the faulty line's... The calculated value is negative. By comparing the signs of these coefficients, faulty lines can be detected.

[0051] It should also be noted that, since line impedance alternates between capacitance and inductance across the entire frequency band, the calculation of faulty and non-faulty lines... Strictly speaking, the sign difference exists only within the characteristic frequency band. Considering that the measured zero-sequence current includes multiple frequency components, including high-frequency components, fundamental components, and attenuated DC components, they need to be filtered to obtain the frequency components within the characteristic frequency band.

[0052] However, due to the extremely weak zero-sequence current, the complex fault transient process, and the inability of the fixed range of characteristic frequency bands to adapt to all fault conditions, the performance of existing filtering methods in practical applications is not ideal. To ensure the reliability of detection results under single-phase grounding faults, this invention constructs the following comprehensive detection criteria based on the synergistic effect of the main criterion and auxiliary criterion, which takes into account the simplification error of the line model and does not require filtering of the zero-sequence current.

[0053] In this embodiment of the application, the main criterion in step S500 includes: for fault line selection under a single-phase ground fault, if only one feeder exhibits a negative cosine similarity coefficient, then the corresponding feeder is identified as the faulty line, as expressed as: (10) By comparing the signs of the calculated cosine similarity coefficients, faulty lines and non-faulty lines can be distinguished.

[0054] It should be noted that, due to the influence of network parameters, fault conditions, measurement errors, and background noise on the zero-sequence signal, in practical applications, the calculated circuit... Equation (10) may not be satisfied. In particular, the transient zero-sequence current of the faulted line decays rapidly under high-resistance ground faults, and the measured zero-sequence current used for similarity calculations will include a steady-state component; furthermore, if an inappropriate time window is selected, the calculated value of the faulted line will be affected. It may be positive, and the main criterion cannot accurately identify the faulty line.

[0055] Therefore, in order to accurately identify faulty circuits, it is necessary to introduce the following auxiliary criteria to improve the reliability of the detection results and ensure that the identification process remains robust even under extreme fault conditions.

[0056] In this embodiment of the application, if the cosine similarity coefficient does not meet the primary criterion in step S600, a secondary criterion is constructed to determine the faulty line, including steps C1-C3: C1: Based on the cosine similarity coefficient of each line, identify the minimum cosine similarity value; Specifically, the cosine similarity coefficient of each line can still be obtained using formulas (8) and (9); the minimum cosine similarity value can be directly identified by comparison. ; C2: Calculate the average similarity coefficient of the remaining lines excluding the line with the minimum similarity value. ; C3: Based on the average similarity coefficient and the minimum cosine similarity value, the waveform similarity distance is calculated. .

[0057] Specifically, C1-C3 can be represented as: (11) In this embodiment of the application, if the cosine similarity coefficient does not meet the primary criterion in step S600, a secondary criterion is constructed to determine the faulty line, which further includes: Set distance threshold ; Specifically, distance threshold It can be set to 0.6.

[0058] If the calculated waveform similarity distance is greater than the distance threshold, then the line with the minimum cosine similarity value is a faulty line. Otherwise, it indicates a busbar fault.

[0059] It should be noted that waveform similarity distance It is a quantitative indicator of the difference in cosine similarity between the zero-sequence current waveform of a faulty line and that of a group of healthy lines, used to quantitatively determine the faulty line.

[0060] In summary, this invention, by analyzing the fault characteristics of grounding faults, derives the relationship between the original measured zero-sequence current and the derivative of the zero-sequence voltage, which reflects capacitance characteristics, and uses this relationship to reveal the model differences between faulty and non-faulty lines. Since non-faulty lines can be modeled using capacitance, the measured zero-sequence current is similar to the capacitive current calculated by multiplying the derivative of the zero-sequence voltage by the equivalent capacitance, where the difference is small and their polarities are the same. Conversely, faulty lines do not conform to the capacitance model, resulting in a significant difference between the measured zero-sequence current and the calculated capacitive current. Next, cosine similarity comparison is used to describe the polarity difference between the measured feeder zero-sequence current and the derivative of the zero-sequence voltage on the bus after the initial single-phase grounding fault, without calculating the equivalent capacitance parameters. Based on a comprehensive detection criterion that combines the main and auxiliary criteria, this criterion considers the simplification error of the line model, has good reliability even in the event of high-resistance grounding faults, and eliminates the need for filtering the zero-sequence current.

[0061] Example 3 illustrates a schematic scheme for a single-phase ground fault location method based on cosine similarity. It should be noted that the technical solution of this cosine similarity single-phase ground fault location system belongs to the same concept as the technical solution of the cosine similarity single-phase ground fault location method described above. Details not described in detail in this example of the cosine similarity single-phase ground fault location system can be found in the description of the cosine similarity single-phase ground fault location method described above.

[0062] This embodiment also provides another single-phase ground fault location system based on cosine similarity, including: The first acquisition module is used to acquire the real-time signals of the zero-sequence current and voltage of the bus. The first judgment module is used to compare the rated voltage of the bus with the real-time voltage, and based on the comparison result, to determine whether to activate the fault line selection. The second acquisition module is used to sample and acquire the zero-sequence current of each line and the zero-sequence voltage of the bus in the first cycle after the fault if it is started. The first calculation module is used to calculate the cosine similarity coefficient of each line based on the acquired data; The second judgment module is used to construct the main criterion, which distinguishes faulty lines from non-faulty lines by comparing the signs of the cosine similarity coefficients. The second calculation module is used to construct a secondary criterion to determine the faulty line if the cosine similarity coefficient does not meet the primary criterion.

[0063] This embodiment also provides a computer device applicable to a single-phase ground fault location method based on cosine similarity, comprising: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to implement the single-phase ground fault location method based on cosine similarity as proposed in the above embodiment.

[0064] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements a single-phase ground fault location method based on cosine similarity as proposed in the above embodiments.

[0065] The storage medium proposed in this embodiment and the single-phase ground fault selection method for implementing cosine similarity proposed in the above embodiments belong to the same inventive concept. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0066] From the above description of the implementation methods, those skilled in the art will clearly understand that the present invention can be implemented using software and necessary general-purpose hardware. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0067] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A single phase to ground fault line selection method of cosine similarity characterized in that, The method comprises the following steps: acquiring real-time signals of bus zero sequence current and voltage; comparing bus rated voltage with real-time voltage, and judging whether to start fault line selection based on the comparison result; if starting, sampling and acquiring zero sequence current of each line and bus zero sequence voltage in the first cycle after fault; calculating cosine similarity coefficients of each line based on the acquired data; constructing a main criterion, and distinguishing fault lines and non-fault lines by comparing signs of the cosine similarity coefficients; if the cosine similarity coefficients do not conform to the main criterion, constructing a secondary criterion to determine the fault line.

2. A single phase to ground fault line selection method of cosine similarity as claimed in claim 1 wherein, The method for calculating cosine similarity coefficients of each line based on the acquired data comprises the following steps: calculating derivatives of the measured zero sequence current and the normalized zero sequence current and zero sequence voltage for similarity comparison; calculating the cosine similarity coefficients of each line based on the derivatives of the zero sequence current and the zero sequence voltage.

3. A single phase to ground fault line selection method of cosine similarity as claimed in claim 2, wherein, The main criterion is constructed by the following steps: for fault line selection under single-phase grounding fault, if only one feeder shows a negative value of the cosine similarity coefficient, the corresponding feeder is identified as the fault line, which is represented as:

4. A single phase to ground fault line selection method of cosine similarity as claimed in claim 3 wherein, the fault line and the non-fault line are distinguished by comparing the signs of the calculated cosine similarity coefficients. If the cosine similarity coefficients do not conform to the main criterion, the secondary criterion is constructed to determine the fault line, which comprises the following steps: identifying the minimum value of the cosine similarity based on the cosine similarity coefficients of each line; calculating the average similarity coefficient of the remaining lines except the line with the minimum value of the cosine similarity; 5. A single phase to ground fault line selection method of cosine similarity as claimed in claim 4, wherein, calculating the waveform similarity distance based on the average similarity coefficient and the minimum value of the cosine similarity. If the cosine similarity coefficients do not conform to the main criterion, the secondary criterion is constructed to determine the fault line, which further comprises the following steps: setting a distance threshold; if the calculated waveform similarity distance is greater than the distance threshold, the line with the minimum value of the cosine similarity is the fault line; 6. A single phase to ground fault line selection method of cosine similarity as claimed in claim 5 wherein, otherwise, it is a bus fault. Setting the start threshold coefficient ; If the real-time bus voltage is greater than , it is determined that the fault line selection is started; wherein, is the rated voltage.

7. A single phase to ground fault line selection method of cosine similarity as claimed in claim 6, wherein, The method for comparing bus rated voltage with real-time voltage, and judging whether to start fault line selection based on the comparison result comprises the following steps: in and This indicates the normalized first phase after a single-phase ground fault. The derivatives of the zero-sequence current of the line and the zero-sequence voltage of the bus; Indicates the first The instantaneous value of the zero-sequence current of the line; Represents the absolute value function; This represents the measured value of the zero-sequence voltage at the busbar. Represented as at discrete time points The zero-sequence voltage value of the bus at the location; Represents a time variable; Indicates the time of occurrence of a single-phase ground fault; This indicates the period of the zero-sequence current.

8. A single-phase earth fault line selection system of cosine similarity, applying the method according to any one of claims 1 to 7, characterized in that, the calculation of the derivatives of the measured zero sequence current and the normalized zero sequence current and zero sequence voltage for similarity comparison is represented as: The method comprises the following steps: a first acquisition module is configured to acquire real-time signals of bus zero sequence current and voltage; a first judgment module is configured to compare bus rated voltage with real-time voltage, and judge whether to start fault line selection based on the comparison result; a second acquisition module is configured to sample and acquire zero sequence current of each line and bus zero sequence voltage in the first cycle after fault if starting; a first calculation module is configured to calculate cosine similarity coefficients of each line based on the acquired data; a second judgment module is configured to construct a main criterion, and distinguish fault lines and non-fault lines by comparing signs of the cosine similarity coefficients; 9. A computer device, comprising: a second calculation module is configured to construct a secondary criterion to determine the fault line if the cosine similarity coefficients do not conform to the main criterion. The method comprises the following steps: a memory and a processor; the memory is configured to store computer executable instructions, and the processor is configured to execute the computer executable instructions, so as to realize the steps of the single-phase grounding fault line selection method based on cosine similarity according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer executable instructions stored in the computer readable medium are executed by the processor to implement the steps of the single-phase-to-ground fault line selection method based on cosine similarity according to any one of claims 1 to 7.

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