Low-current single-phase fault grounding discrimination method and system based on zero-sequence transient quantity

Abstract

The invention discloses a low-current single-phase fault grounding judgment method and system based on zero-sequence transient quantity. The method comprises the following steps: collecting a zero-sequence voltage signal and a zero-sequence current signal which consider the transition resistance of a grounding point and are based on the characteristics of the zero-sequence transient quantity; respectively performing scale decomposition on the zero-sequence voltage signal and the zero-sequence current signal according to frequency by adopting a wavelet algorithm, and extracting waveforms of each frequency range; searching a first half wave in the waveform of each frequency range; according to the positioned first half-wave, the first half-wave polarities of the zero-sequence voltage signal and the zero-sequence current signal are judged respectively; and comparing the polarities of the zero-sequence voltage signal and the zero-sequence current signal, and carrying out single-phase fault grounding positioning. The position of a fault point is obtained through qualitative analysis, and the fault positioning precision is high.

Description

Technical Field

[0001] The present invention relates to the technical field of fault grounding identification, and in particular to a method and system for identifying a small current single-phase fault grounding based on a zero-sequence transient quantity. Background Art

[0002] During the operation of the power grid, due to human factors such as construction and natural factors such as bad weather, power transmission may cause faults in long-distance line transmission. Among them, single-phase fault grounding is the most common in line faults. However, due to the small changes in voltage and current in the single-phase fault grounding system through the neutral arc suppression coil grounding system, or when the grounding resistance is large, if the effective values ​​of the zero-sequence voltage and zero-sequence current calculated by the steady-state method do not reach the range of variation of the conventional power protection action setting, the protection action cannot be triggered. Therefore, it is very important to achieve effective small-current single-phase grounding fault identification.

[0003] The transient method is more effective in capturing the sudden change characteristics of fault phases, so the transient method is generally used for small current fault identification. However, there is still room for improvement in the use of the transient method to determine single-phase grounding faults, and the accuracy of the judgment needs to be improved. The traditional method is based on a simplified model to analyze transient time domain characteristics, but its conclusion is not perfect, especially the influence of the transition resistance at the connection point is not considered enough. However, if the transition resistance is taken into account, the zero-sequence voltage and current of the collected signal will be particularly small, and the conventional transient method.

[0004] In the prior art, the invention patent with the patent publication number CN102854437A discloses a method for fault line selection of a small current grounding system using the time-frequency atomic decomposition theory. The method is mainly based on the time-frequency atomic decomposition theory, and the zero-sequence current data is sparsely decomposed in the Gabor overcomplete atomic library, and then the matching attenuated sinusoidal quantity atoms are obtained by optimizing and solving the relevant parameters. The time-frequency atomic decomposition method can accurately obtain the disturbance characteristics such as the start and end time, amplitude, frequency and change law of the fundamental wave and each harmonic, and can effectively filter out the interference signal. According to the energy entropy of the atoms after the time-frequency atomic decomposition, they are arranged from large to small, and the zero-sequence transient current fundamental wave atoms are removed, and the phase angles (polarity) of the atoms with similar zero-sequence current frequencies of each line are compared: if the atomic phase angles (polarity) of the line zero-sequence transient frequency are similar to those of other lines, it is a fault line; if the atomic phase angles (polarity) corresponding to each line are the same, it is a busbar fault, and the comparison results of the atomic phase angles of each frequency are combined to determine the fault line. However, the focus of this patent is on line selection for ground faults.

[0005] The paper "Analysis of Transient Traveling Waves in Distribution Lines and Research on Grounding Line Selection" discloses the propagation law and characteristics of transient current traveling waves generated after single-phase grounding of distribution lines based on traveling wave theory. Wavelet transform is used as a tool to characterize the grounding fault characteristics of the traveling wave and finds that the initial transient current traveling wave generated at the moment of single-phase grounding is independent of the grounding method, thus opening up new ideas for grounding line selection. The modulus maximum of wavelet transform at different scales is used in this paper to represent the traveling wave information in different frequency bands, which is used as a line selection criterion. In this paper, wavelet transform at different scales is used for fault line selection. Summary of the invention

[0006] The technical problem to be solved by the present invention is to solve the problem that the current single-phase fault grounding judgment does not take into account the transition resistance of the grounding point, and the fault grounding judgment is not accurate.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A method for distinguishing a small current single-phase fault grounding based on zero-sequence transient quantity, comprising:

[0009] Collect zero-sequence voltage signal and zero-sequence current signal based on zero-sequence transient quantity characteristics taking into account the transition resistance of the grounding point;

[0010] The wavelet algorithm is used to decompose the zero-sequence voltage signal and the zero-sequence current signal according to the frequency, and the waveforms of each frequency range are extracted;

[0011] Find the first half wave in the waveform of each frequency range;

[0012] According to the located first half wave, the polarity of the first half wave of the zero-sequence voltage signal and the zero-sequence current signal is judged respectively;

[0013] The polarities of the zero-sequence voltage signal and the zero-sequence current signal are compared to locate the single-phase ground fault.

[0014] In one embodiment of the present invention, the zero-sequence voltage signal and the zero-sequence current signal based on the zero-sequence transient quantity characteristics are collected, including: simulation signal collection, derived waveform collection, and device direct collection;

[0015] Among them, the simulation signal acquisition is based on the establishment of a transient model with the transition resistance of the grounding point added;

[0016] Exporting recording collection is to read and collect data through actual fault recording collection;

[0017] Direct device collection is to directly use data collection products for online collection;

[0018] The data collected by the simulated signal is used as the training set, the data collected by the exported recording is used as the test set, and the data directly collected by the device is used as the verification set.

[0019] In one embodiment of the present invention, the frequencies of the simulated analog signal acquisition and the device direct acquisition are synchronously set according to the frequencies of the derived wave recording acquisition.

[0020] In one embodiment of the present invention, the waveform of each frequency range is extracted, including: using the wavelet algorithm to perform five-layer decomposition using the wavelet function db10:

[0021] The original frequency signal frequency is: 0~Org-Fre;

[0022] First layer decomposition: The first layer low frequency signal is: 0~Org-Fre*0.5; the first layer high frequency signal is: Org-Fre*0.5~Org-Fre;

[0023] Second layer decomposition: The second layer low frequency signal is: 0~Org-Fre / 2 2 ; The second layer high frequency signal is: Org-Fre / 2 2 ~Org-Fre / 2;

[0024] The third layer decomposition: The third layer low frequency signal is: 0~Org-Fre / 2 3 ; The third layer high frequency signal is: Org-Fre / 2 3 ~Org-Fre / 2 2 ;

[0025] Fourth layer decomposition: The fourth layer low frequency signal is: 0~Org-Fre / 2 4 ; The fourth layer high frequency signal is: Org-Fre / 2 4 ~Org-Fre / 2 3 ;

[0026] Fifth layer decomposition: The fifth layer low frequency signal is: 0~Org-Fre / 2 5 ; The fifth layer high frequency signal is: Org-Fre / 2 5 ~Org-Fre / 2 4 .

[0027] In one embodiment of the present invention, when searching for the first half wave in the waveform of each frequency range, maximum value comparison is performed based on using high frequency signals of each layer.

[0028] In one embodiment of the present invention, searching for the first half wave in the waveform of each frequency range includes:

[0029] Select one cycle for the first half-wave verification signal, and compare it with the signal position of the previous cycle, set the error range, and when the signal value exceeds the error range, determine it as the first half-wave position, and record the time when the signal value is at this time.

[0030] In one embodiment of the present invention, if the first half-wave does not appear in the cycle, it is determined that a single-phase grounding fault does not occur in the cycle.

[0031] In one embodiment of the present invention, the first half-wave polarities of the zero-sequence voltage signal and the zero-sequence current signal are judged respectively, including:

[0032] It is determined that the slope changes at least three times after the first half wave appears, and at least two identical changes are taken as the basis for determining the polarity of the first half wave. At this time, if the slope is positive, the polarity of the zero-sequence voltage signal or the zero-sequence current signal is positive, and if the slope is negative, the polarity of the zero-sequence voltage signal or the zero-sequence current signal is negative.

[0033] In one embodiment of the present invention, the polarities of the zero-sequence voltage signal and the zero-sequence current signal are compared to locate the single-phase ground fault, including:

[0034] If the polarities of the zero-sequence voltage signal and the zero-sequence current signal are opposite, it is determined that the fault point is located downstream of the acquisition position. If the polarities of the zero-sequence voltage signal and the zero-sequence current signal are the same, it is determined that the fault point is located upstream of the acquisition position.

[0035] A system for distinguishing a small current single-phase fault grounding based on zero-sequence transient quantity, using the above-mentioned method for distinguishing a small current single-phase fault grounding based on zero-sequence transient quantity, comprises:

[0036] A signal acquisition module is used to acquire zero-sequence voltage signals and zero-sequence current signals based on zero-sequence transient quantity characteristics while taking into account the transition resistance of the grounding point;

[0037] The waveform frequency extraction module is used to use the wavelet algorithm to scale the zero-sequence voltage signal and the zero-sequence current signal according to the frequency, and extract the waveforms of each frequency range;

[0038] The first half-wave positioning module is used to find the first half-wave in the waveform of each frequency range;

[0039] The polarity judgment module is used to judge the polarity of the first half wave of the zero-sequence voltage signal and the zero-sequence current signal respectively according to the located first half wave;

[0040] The fault location module is used to compare the polarities of the zero-sequence voltage signal and the zero-sequence current signal to locate the single-phase grounding fault.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention adopts a wavelet algorithm to directly analyze the collected transient quantities of zero-sequence voltage and zero-sequence current. When a single-phase fault occurs to ground, the voltage and current waveforms will undergo sudden changes. The wavelet algorithm is used to detect the time when the first half-wave appears, the polarity of the first half-wave is determined, and the location of the fault point is obtained through qualitative analysis.

[0042] Considering the characteristics after the transition resistance at the docking location, the collected signal zero-sequence voltage and current will become much smaller than without adding it. The calculation using the steady-state method will be displayed within the error range, and it is impossible to make a fault judgment. Therefore, the present invention performs multi-scale decomposition on the zero-sequence voltage and zero-sequence current collected after adding the transition resistance at the docking location, and considers the detection mutation characteristics, which belongs to the high-frequency band part. Therefore, the high-frequency signals of each layer are used for maximum value comparison. The mutation characteristics of the layer signal with the largest maximum value are the most obvious, and it is selected as the first half-wave verification signal for determining the signal mutation.

[0043] The present invention adopts wavelet algorithm and selects wavelet function db10, which has the following advantages:

[0044] (1) It has a compact support set, which is non-zero in a finite interval and zero elsewhere. It is very suitable for processing signals with finite length or local characteristics;

[0045] (2) It has regularity and can effectively capture smooth changes and reduce the impact of noise;

[0046] (3) Symmetry reduces the impact of edge effects;

[0047] (4) It can be used for multi-resolution analysis, decomposing the signal into different frequency components, which is suitable for signal compression, denoising and feature extraction;

[0048] (5) It has 10 vanishing moments and can capture the 10th-order polynomial features in the signal. The features that can be captured are complex enough to support fault identification;

[0049] (6) It is localized in time and frequency, which is very suitable for analyzing signals whose statistical properties change over time.

[0050] The line selection accuracy for large resistance grounding faults is not high, and there are also problems with adaptability to different types of transmission lines and the ability to cope with complex fault conditions. Different fault location methods such as fault traveling wave location method and multi-branch radiation network fault location method have their own advantages and disadvantages, and it is necessary to select a suitable method according to the specific conditions of the actual circuit. The present invention, based on the wavelet algorithm, uses the first half-wave transient quantity characteristics to determine the fault location, which improves the accuracy and efficiency of small current single-phase fault grounding discrimination. Compared with the existing discrimination method, it is more reliable. The device of this method is deployed in each section of the line, and only the zero-sequence voltage and zero-sequence current need to be collected to locate the fault, which is more concise and clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The present invention is a flowchart of a method for distinguishing a small current single-phase fault grounding based on a zero-sequence transient quantity according to an embodiment of the present invention.

[0052] Figure 2 Schematic diagram of signal decomposition using a wavelet algorithm according to an embodiment of the present invention.

[0053] Figure 3 It is a schematic diagram of the first half wave of positioning according to an embodiment of the present invention.

[0054] Figure 4 The present invention is a block diagram of a small current single-phase fault grounding determination system based on zero-sequence transient quantity according to an embodiment of the present invention. DETAILED DESCRIPTION

[0055] In order to facilitate those skilled in the art to understand the technical solution of the present invention, the technical solution of the present invention is further described in conjunction with the accompanying drawings of the specification.

[0056] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0057] See also Figure 1 As shown, the present invention provides a method for distinguishing a small current single-phase fault grounding based on a zero-sequence transient quantity, comprising:

[0058] S10, collecting zero-sequence voltage signals and zero-sequence current signals based on zero-sequence transient quantity characteristics taking into account the transition resistance of the grounding point.

[0059] In one embodiment of the present invention, there are three ways to collect zero-sequence voltage signals and zero-sequence current signals: simulation signal collection, derived waveform collection, and device direct collection. Among them, simulation signal collection is based on the establishment of a transient model with a transition resistance at the grounding point. In this embodiment, the specific structure of the transient model with a transition resistance at the grounding point is not limited. Derived waveform collection is to read data through actual fault waveform collection, and device direct collection is to directly use data collection products for online collection.

[0060] In this embodiment, specifically, the data collected by the simulated analog signal is used as a training set, the data collected by the derived recording is used as a test set, and the data directly collected by the device is used as a verification set, so as to train, test and verify the method.

[0061] In this embodiment, the collection of zero-sequence voltage signals and zero-sequence current signals is mainly divided into two types, one is to directly collect zero-sequence voltage and zero-sequence current data, and the other is to obtain zero-sequence voltage and zero-sequence current by calculating the sum of three-phase voltage and three-phase current vectors, which is called self-generated zero-sequence voltage and self-generated zero-sequence current. In this embodiment, the specific type is not limited, and any one or a combination of the two can be selected.

[0062] In this embodiment, according to the frequency of the derived wave recording collection, the frequencies of the simulated signal collection and the direct collection of the device are synchronously set. Specifically, in the derived wave recording collection, the data is read through the actual fault wave recording collection, and the actual fault wave recording data is sampled at 6400Hz. Since the national regulations stipulate that the operating frequency of power transmission is 50Hz, the number of sampling points per cycle is 128 points, which is a power of two and meets the requirements. The sampling frequency can be set for both the simulated signal collection and the direct collection of the device. Therefore, the sampling frequency of the signal per cycle is set to 128 points in the example of the present invention.

[0063] S20, using wavelet algorithm, scales and decomposes the zero-sequence voltage signal and the zero-sequence current signal according to the frequency, and extracts the waveforms of each frequency range.

[0064] In one embodiment of the present invention, the waveforms of each frequency range are extracted, and the wavelet algorithm is adopted and implemented using the wavelet function db10. The wavelet algorithm can decompose the collected waveforms by frequency, extract the waveform changes of each frequency range, and amplify the waveform changes of each frequency range. In the single-phase fault grounding judgment, the collected zero-sequence voltage signal and zero-sequence current signal can be subjected to wavelet transformation, and the frequency range with the largest change (modulus maximum value embodiment) can be extracted to perform fault judgment. The transformed signal has the same basic law as the original signal, and the amplitude change is larger, which is easy to capture transient characteristics and facilitates the positioning and polarity judgment of the first half wave.

[0065] See also Figure 2 As shown, in this embodiment, the wavelet function db10 refers to a member of the Daubechies wavelet family, which has 10 filter coefficients. The signal is decomposed into five levels of approximate coefficients and detail coefficients through a series of low-pass and high-pass filters. Specifically, in this embodiment, the collected zero-sequence voltage signal and zero-sequence current signal are decomposed into five layers respectively:

[0066] The frequency of the original frequency signal is: 0~Org-Fre. In this embodiment, the original frequency signal is a zero-sequence voltage signal and a zero-sequence current signal with a cycle acquisition frequency of two powers.

[0067] The first layer of decomposition: The first layer of low-frequency signal is: 0~Org-Fre*0.5; the first layer of high-frequency signal is: Org-Fre*0.5~Org-Fre.

[0068] Second layer decomposition: The second layer low frequency signal is: 0~Org-Fre / 2 2 ; The second layer high frequency signal is: Org-Fre / 2 2 ~Org-Fre / 2.

[0069] The third layer decomposition: The third layer low frequency signal is: 0~Org-Fre / 2 3 ; The third layer high frequency signal is: Org-Fre / 2 3 ~Org-Fre / 2 2 .

[0070] Fourth layer decomposition: The fourth layer low frequency signal is: 0~Org-Fre / 2 4 ; The fourth layer high frequency signal is: Org-Fre / 2 4 ~Org-Fre / 2 3 .

[0071] Fifth layer decomposition: The fifth layer low frequency signal is: 0~Org-Fre / 2 5 ; The fifth layer high frequency signal is: Org-Fre / 2 5 ~Org-Fre / 2 4 .

[0072] In this embodiment, the collected signal is subjected to five-layer wavelet decomposition to obtain low-frequency signals and high-frequency signals of each layer after decomposition. Since the detection mutation characteristics belong to the high-frequency band, the high-frequency signals of each layer are used to compare the maximum values. The mutation characteristics of the layer signal with the largest maximum value are most obvious, and the first half-wave verification signal is selected to simplify the calculation complexity, filter noise, and achieve faster and more accurate waveform identification.

[0073] S30, searching for the first half wave in the waveform of each frequency range.

[0074] In one embodiment of the present invention, the first half-wave is searched for the zero-sequence voltage signal and the zero-sequence current signal after decomposition at different scales, and the first half-wave is compatible with the situation at the beginning and within the cycle. Specifically, for the processed cycle, the first half-wave verification signal is used, and it is compared with the signal position of the previous cycle, and the error range is set. After the signal value exceeds the error range, it is judged for more than three times in a row, and it is determined to be the position where the first half-wave appears, and the time at which the signal value is at this time is recorded, such as Figure 3 As shown, the horizontal axis is time, the vertical axis is signal value, the part circled by the box is the position where the first half-wave appears, and the time corresponding to the position where this half-wave appears is recorded. Since the value range of the zero-sequence voltage signal and the zero-sequence current signal is quite different, the error range of the zero-sequence voltage signal and the zero-sequence current signal is set separately to meet actual needs.

[0075] In this embodiment, if the first half-wave does not appear in the cycle, it is determined that no single-phase grounding fault occurs in the cycle.

[0076] S40, judging the polarities of the first half-waves of the zero-sequence voltage signal and the zero-sequence current signal respectively according to the located first half-wave.

[0077] In one embodiment of the present invention, after locating the first half wave, the polarities of the first half waves of the two signals are judged respectively. Specifically, the change trend of the first half wave is judged, mainly the positive and negative of the slope is judged, if the slope is positive, it is positive, if the slope is negative, it is negative, and at least three changes of the slope after the first half wave appear are judged, and at least two identical changes are taken as the basis for determining the polarity of the first half wave. The number of slope changes can be adjusted according to actual needs.

[0078] S50, comparing the polarities of the zero-sequence voltage signal and the zero-sequence current signal to locate the single-phase ground fault.

[0079] In one embodiment of the present invention, the polarities of the two signals (zero-sequence voltage signal and zero-sequence current signal) are compared to locate the single-phase ground fault. If the polarities are opposite, it is determined that the fault point is located downstream of the acquisition position. If the polarities are the same, it is determined that the fault point is located upstream of the acquisition position. If no first half-wave appears, it is determined that no single-phase ground fault occurs in the cycle, thereby realizing the small current single-phase ground fault discrimination based on the zero-sequence transient quantity characteristics.

[0080] See also Figure 4 As shown, the present invention also provides a small current single-phase fault grounding judgment system based on zero-sequence transient quantity, which applies the small current single-phase fault grounding judgment method based on zero-sequence transient quantity described above, including:

[0081] The signal acquisition module is used to acquire zero-sequence voltage signals and zero-sequence current signals based on zero-sequence transient quantity characteristics while taking into account the transition resistance of the grounding point.

[0082] The waveform frequency extraction module is used to use the wavelet algorithm to scale the zero-sequence voltage signal and the zero-sequence current signal according to the frequency, and extract the waveforms of each frequency range.

[0083] The first half-wave positioning module is used to find the first half-wave in the waveform of each frequency range.

[0084] The polarity judgment module is used to judge the polarity of the first half wave of the zero-sequence voltage signal and the zero-sequence current signal respectively according to the located first half wave.

[0085] The fault location module is used to compare the polarities of the zero-sequence voltage signal and the zero-sequence current signal to locate the single-phase grounding fault.

[0086] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting from any point of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any reference numerals in the claims should not be regarded as limiting the claims involved.

[0087] The embodiments described above only represent implementation methods of the invention. The protection scope of the present invention is not limited to the embodiments described above. For those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for distinguishing small current single-phase fault grounding based on zero-sequence transient quantity, characterized in that: include: Collect zero-sequence voltage signal and zero-sequence current signal based on zero-sequence transient quantity characteristics taking into account the transition resistance of the grounding point; The wavelet algorithm is used to decompose the zero-sequence voltage signal and the zero-sequence current signal according to the frequency, and the waveforms of each frequency range are extracted; Find the first half wave in the waveform of each frequency range; According to the located first half wave, the polarity of the first half wave of the zero-sequence voltage signal and the zero-sequence current signal is judged respectively; The polarities of the zero-sequence voltage signal and the zero-sequence current signal are compared to locate the single-phase ground fault.

2. The method for distinguishing small current single-phase ground fault based on zero-sequence transient quantity according to claim 1 is characterized in that: Collect zero-sequence voltage signals and zero-sequence current signals based on zero-sequence transient quantity characteristics, including: simulation signal collection, derived waveform collection, and device direct collection; Among them, the simulation signal acquisition is based on the establishment of a transient model with the transition resistance of the grounding point added; Exporting recording collection is to read and collect data through actual fault recording collection; Direct device collection is to directly use data collection products for online collection; The data collected by the simulated signal is used as the training set, the data collected by the exported recording is used as the test set, and the data directly collected by the device is used as the verification set.

3. The method for distinguishing a small current single-phase ground fault based on zero-sequence transient quantity according to claim 2 is characterized in that: According to the frequency of the exported recorded wave collection, the frequency of the simulated analog signal collection and the direct collection of the device are set synchronously.

4. The method for distinguishing a small current single-phase ground fault based on zero-sequence transient quantity according to claim 1 is characterized in that: Extract the waveform of each frequency range, including: Wavelet algorithm uses wavelet function db10 to perform five-layer decomposition: The original frequency signal frequency is: 0~Org-Fre; First layer decomposition: The first layer low frequency signal is: 0~Org-Fre*0.5; the first layer high frequency signal is: Org-Fre*0.5~Org-Fre; Second layer decomposition: The second layer low frequency signal is: 0~Org-Fre / 2 2 ; The second layer high frequency signal is: Org-Fre / 2 2 ~Org-Fre / 2; The third layer decomposition: The third layer low frequency signal is: 0~Org-Fre / 2 3 ; The third layer high frequency signal is: Org-Fre / 2 3 ~Org-Fre / 2 2 ; Fourth layer decomposition: The fourth layer low frequency signal is: 0~Org-Fre / 2 4 ; The fourth layer high frequency signal is: Org-Fre / 2 4 ~Org-Fre / 2 3 ; Fifth layer decomposition: The fifth layer low frequency signal is: 0~Org-Fre / 2 5 ; The fifth layer high frequency signal is: Org-Fre / 2 5 ~Org-Fre / 2 4 .

5. The method for distinguishing small current single-phase ground fault based on zero-sequence transient quantity according to claim 4 is characterized in that: When searching for the first half wave in the waveform of each frequency range, maximum value comparison is performed based on the use of high-frequency signals of each layer.

6. The method for determining a small current single-phase ground fault based on zero-sequence transient quantity according to claim 5 is characterized in that: Find the first half wave in each frequency range, including: Select one cycle for the first half-wave verification signal, and compare it with the signal position of the previous cycle, set the error range, and when the signal value exceeds the error range, determine it as the first half-wave position, and record the time when the signal value is at this time.

7. The method for determining a small current single-phase ground fault based on zero-sequence transient quantity according to claim 6 is characterized in that: If the first half wave does not appear in the cycle, it is determined that no single-phase grounding fault occurs in the cycle.

8. The method for distinguishing a small current single-phase ground fault based on zero-sequence transient quantity according to claim 1 is characterized in that: The first half-wave polarity of the zero-sequence voltage signal and the zero-sequence current signal are judged respectively, including: It is determined that the slope changes at least three times after the first half wave appears, and at least two identical changes are taken as the basis for determining the polarity of the first half wave. At this time, if the slope is positive, the polarity of the zero-sequence voltage signal or the zero-sequence current signal is positive, and if the slope is negative, the polarity of the zero-sequence voltage signal or the zero-sequence current signal is negative.

9. The method for distinguishing a small current single-phase ground fault based on zero-sequence transient quantity according to claim 1, characterized in that: The polarities of the zero-sequence voltage signal and the zero-sequence current signal are compared to locate the single-phase ground fault, including: if the polarities of the zero-sequence voltage signal and the zero-sequence current signal are opposite, it is determined that the fault point is located downstream of the collection position; if the polarities of the zero-sequence voltage signal and the zero-sequence current signal are the same, it is determined that the fault point is located upstream of the collection position.

10. A small current single-phase fault grounding identification system based on zero-sequence transient quantity, characterized in that: The method for distinguishing a small current single-phase ground fault based on a zero-sequence transient quantity according to any one of claims 1 to 9 is applied, comprising: A signal acquisition module is used to acquire zero-sequence voltage signals and zero-sequence current signals based on zero-sequence transient quantity characteristics while taking into account the transition resistance of the grounding point; The waveform frequency extraction module is used to use the wavelet algorithm to scale the zero-sequence voltage signal and the zero-sequence current signal according to the frequency, and extract the waveforms of each frequency range; The first half-wave positioning module is used to find the first half-wave in the waveform of each frequency range; The polarity judgment module is used to judge the polarity of the first half wave of the zero-sequence voltage signal and the zero-sequence current signal respectively according to the located first half wave; The fault location module is used to compare the polarities of the zero-sequence voltage signal and the zero-sequence current signal to locate the single-phase grounding fault.

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