Ground fault detection method and system for power distribution network

Abstract

The application relates to the technical field of ground fault detection, in particular to a ground fault detection method and system for a power distribution network. The method comprises the following steps: acquiring zero sequence currents on each feeder in the power distribution network; acquiring transient energy sudden increase characteristics of each feeder in the power distribution network, and obtaining five harmonic distinguishability of each feeder in the power distribution network according to the deviation degree of each harmonic amplitude, so as to obtain fault harmonic characteristic values of each feeder; obtaining fault confidence weights of each feeder in the power distribution network according to the consistency degree of harmonic amplitude and harmonic energy sudden change characteristics of the zero sequence currents on each feeder in the power distribution network, so as to obtain ground fault recognition degrees of each feeder in the power distribution network, and to obtain a ground fault detection result of the power distribution feeder. The application can improve the ground fault detection precision.

Description

Technical Field

[0001] This application relates to the field of grounding fault detection technology, specifically to grounding fault detection methods and systems for power distribution networks. Background Technology

[0002] Distribution networks mostly operate with an ungrounded neutral point and overhead conductors. In rural and mountainous areas, single-phase grounding faults are common on overhead lines, especially during severe weather conditions such as winter snowstorms or summer thunderstorms. Single-phase grounding faults are prone to occur in distribution networks, and since they cannot form a circuit, the network's protection devices cannot activate. Furthermore, single-phase grounding faults pose a serious threat to the safety and reliability of the power supply. If not addressed promptly, they can even escalate into short-circuit faults, further exacerbating the negative impact on the distribution network. Therefore, it is crucial to detect and resolve grounding faults in distribution networks quickly and accurately to improve their safety and reliability.

[0003] In existing technologies for detecting ground faults in distribution network feeders, the zero-sequence current of each feeder in the distribution network is monitored, and single-phase ground faults are quickly detected by utilizing the directional and amplitude characteristics of the transient zero-sequence current, aiming to improve the efficiency of ground fault detection in distribution networks. However, when a ground fault occurs in a distribution network feeder, a fifth harmonic component is generated in the transient zero-sequence current. Existing technologies do not fully exploit the characteristic changes of this fifth harmonic component, leading to poor accuracy in detecting ground faults in distribution network feeders and a tendency for false detections. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this application is to provide a grounding fault detection method and system for power distribution networks. The specific technical solution adopted is as follows: This application provides a ground fault detection method for power distribution networks, including the following steps: Obtain the zero-sequence current on each feeder in the distribution network; By measuring the increase in zero-sequence current in the frequency domain over a short period of time among the harmonic energies of each feeder in the distribution network, the transient energy surge of each feeder in the distribution network is obtained. Based on the deviation of each harmonic amplitude, the fifth harmonic distinctiveness of each feeder in the distribution network is obtained. Then, combined with the transient energy surge, the fault harmonic characteristic value of each feeder is obtained. Based on the consistency of the abrupt change characteristics of the harmonic amplitude and harmonic energy of the zero-sequence current on each feeder in the frequency domain, the fault confidence weight of each feeder in the distribution network is obtained, and combined with the fault harmonic characteristic value, the ground fault identification degree of each feeder in the distribution network is obtained. Anomaly detection is performed on the ground fault identification rate of all feeders in the distribution network to obtain the ground fault detection results of the distribution network feeders.

[0005] Preferably, the zero-sequence currents on each feeder are arranged in time sequence to form the zero-sequence current sequence of each feeder. A sliding window is set on the zero-sequence current sequence, wherein each sliding window corresponds to a transient stage. The zero-sequence currents in each sliding window form the transient current sequence of each transient stage. The transient current sequence is transformed in the frequency domain. The frequency corresponding to the largest amplitude value in the amplitude spectrum of the positive frequency part of each transient stage is recorded as the fundamental frequency. The amplitude and energy corresponding to five times the fundamental frequency in the amplitude spectrum and power spectrum in the frequency domain are respectively used as the fifth harmonic amplitude and fifth harmonic energy of each transient stage.

[0006] Preferably, the process for obtaining the transient energy surge of each feeder in the distribution network is as follows: In the formula, For the transient energy surge of the j-th feeder in the distribution network, To determine the number of transient phases, It is an exponential function with the natural constant as its base. and These are the fifth harmonic energies of the b-th and b-1-th transient stages of the j-th feeder, respectively.

[0007] Preferably, the process for obtaining the fifth harmonic distinctiveness of each feeder in the distribution network is as follows: In the formula, To distinguish the fifth harmonic of the j-th feeder in the distribution network, Let be the fifth harmonic amplitude of the j-th feeder in the s-th transient stage in the distribution network. Let be the average of the fifth harmonic amplitudes of all feeders except the j-th feeder in the distribution network during the s-th transient phase.

[0008] Preferably, the fault harmonic characteristic value of each feeder is the sum of the normalized result of the transient energy surge of each feeder and the normalized result of the fifth harmonic distinctiveness.

[0009] Preferably, the fifth harmonic amplitude and fifth harmonic energy of all transient stages of each feeder are arranged in time sequence to form the harmonic amplitude sequence and harmonic energy sequence of each feeder, and the mutation position sequence set of the fifth harmonic amplitude and the mutation position sequence set of the fifth harmonic energy of each feeder are extracted by the BG segmentation algorithm.

[0010] Preferably, the process of obtaining the fault confidence weight of each feeder in the distribution network is as follows: calculate the similarity between the fifth harmonic amplitude and the mutation position set of the fifth harmonic energy of each feeder, count the sum of the similarity and a preset constant greater than zero, and use the normalized result of the product of the sum and the maximum value of the harmonic energy sequence of each feeder as the fault confidence weight of each feeder in the distribution network.

[0011] Preferably, the process for obtaining the ground fault identification degree of each feeder in the distribution network is as follows: In the formula, Let the ground fault identification degree of the j-th feeder in the distribution network be denoted as . Let J be the fault confidence weight of the j-th feeder in the distribution network. Let be the fault harmonic characteristic value on the j-th feeder in the distribution network.

[0012] Preferably, the ground fault identification degree of all feeders in the distribution network is used as the input of the 3Sigma anomaly detection method, and the distribution network feeders corresponding to the ground fault identification degree that are not in the 3Sigma range are counted as the ground fault feeders in the distribution network.

[0013] This application also provides a ground fault detection system for power distribution networks, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of any of the above-described ground fault detection methods for power distribution networks.

[0014] As can be seen from the above, the ground fault detection method and system for power distribution networks provided in this application have at least the following beneficial effects: This application extracts the fifth harmonic energy and amplitude of the zero-sequence current in each transient stage using Fourier transform. The fifth harmonic energy and amplitude are used to distinguish the sudden increase in transient energy and the fifth harmonic characteristics on the red feeder of the distribution network, thereby highlighting the sudden increase in transient energy in the fifth harmonic component after a single-phase ground fault and the difference between the feeder with a single-phase ground fault and the feeder in normal operation. This is beneficial for accurately identifying the fifth harmonic characteristics of the feeder ground fault in the distribution network. Meanwhile, by considering the abrupt change characteristics of the simultaneity between the amplitude and energy of the fifth harmonic in the zero-sequence current, as well as the prominence of the energy of the fifth harmonic in the zero-sequence current, this application accurately measures the reliability of the fifth harmonic current generated by a single-phase ground fault. This facilitates more accurate and rapid detection of ground faults in the distribution network and avoids the problem of false detection of ground faults in the distribution network feeders. This application fully explores the characteristic changes of the fifth harmonic component in the transient zero-sequence current, and combines the fault confidence weight and fault harmonic characteristic value of each feeder in the distribution network to measure and identify single-phase grounding faults on each feeder in the distribution network. It also combines anomaly detection algorithms to accurately detect grounding faults on feeders in the distribution network, thereby solving the problem of false detection of grounding faults in distribution network feeders and improving the accuracy of detecting grounding faults in distribution network feeders. Attached Figure Description

[0015] To more clearly illustrate the technical solutions and advantages in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 The flowchart of the ground fault detection method for power distribution networks provided in this application is shown. Detailed Implementation

[0017] To further illustrate the technical means and effects adopted by this application to achieve the intended purpose of the invention, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of the grounding fault detection method and system for power distribution networks proposed in this application. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0018] Unless otherwise specified and limited, terms such as “comprising,” “including,” or any other variations thereof are intended to cover a non-exclusive inclusion, such that a circuit structure, article, or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase “comprising one…” does not exclude the presence of other identical elements in the article or device that includes said element. Furthermore, the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items. All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0019] The following description, in conjunction with the accompanying drawings, details the specific scheme of the grounding fault detection method and system for power distribution networks provided in this application.

[0020] Please see Figure 1The diagram illustrates a flowchart of a ground fault detection method for power distribution networks according to an embodiment of this application, including the following steps: Step 1: Obtain the zero-sequence current on each feeder in the distribution network.

[0021] To improve the accuracy of detecting ground faults in distribution network feeders, it is necessary to consider the fifth harmonic component of the transient zero-sequence current when a ground fault occurs in the distribution network feeder, and fully explore the characteristic changes of the fifth harmonic component of the transient zero-sequence current. This will enable rapid and accurate detection of ground faults in distribution network feeders and avoid the problem of false detection of ground faults in distribution network feeders.

[0022] Zero-sequence current transformers are installed on each feeder in the distribution network. The zero-sequence current on each feeder in the distribution network is monitored in real time through the zero-sequence current transformers. The sampling frequency of the zero-sequence current is 10kHz, which enables the capture of the zero-sequence current characteristics during high-frequency transient processes. This is suitable for fault analysis of grounding faults in the distribution network feeders.

[0023] Furthermore, in order to facilitate the analysis of the zero-sequence current characteristics of each feeder in the distribution network, preferably, in this embodiment, the zero-sequence currents collected per second on each feeder are arranged in chronological order to form a sequence, which is denoted as the zero-sequence current sequence of each feeder in the distribution network.

[0024] Step 2: By measuring the increase in zero-sequence current among harmonic energies in the frequency domain over a short period of time on each feeder of the distribution network, the transient energy surge of each feeder in the distribution network is obtained. Based on the deviation of each harmonic amplitude, the fifth harmonic distinctiveness of each feeder in the distribution network is obtained. Then, combined with the transient energy surge, the fault harmonic characteristic value of each feeder is obtained.

[0025] Typically, when a single-phase ground fault occurs on a distribution network feeder, the fifth harmonic component of the transient zero-sequence current increases, and the fifth harmonic component of the zero-sequence current on the feeder with the single-phase ground fault is larger than that on the feeder without the fault. Therefore, in order to more accurately detect ground faults in the distribution network, it is necessary to fully explore the changes in the fifth harmonic characteristics of the transient zero-sequence current when a ground fault occurs in the distribution network.

[0026] To facilitate the analysis of the transient characteristics of zero-sequence current on each feeder in the distribution network over a short period of time, a sliding window is set on the zero-sequence current sequence of the distribution network feeders. Each sliding window corresponds to a transient stage. Preferably, in this embodiment, the time length of the sliding window is 20 milliseconds, and the sliding step size is equal to the size of the sliding window. The sequence of zero-sequence current in each sliding window is recorded as the transient current sequence of each transient stage, reflecting the transient characteristics of zero-sequence current on each feeder over a short period of time. This is beneficial for analyzing the transient characteristics of the distribution network after a ground fault.

[0027] Therefore, in order to extract the fifth harmonic characteristics in the transient zero-sequence current, the transient current sequence of each transient stage is used as the input of the Fourier transform. The Fourier transform can be either the discrete Fourier transform or the fast Fourier transform. In this embodiment, the fast Fourier transform is used to extract the amplitude spectrum and power spectrum of the positive frequency part of each transient stage. In the amplitude spectrum and power spectrum, the horizontal axis is frequency, and the vertical axis is amplitude and energy, respectively. The Fourier transform is a well-known technique, and the specific process will not be described in detail.

[0028] Furthermore, in the amplitude spectrum of the positive frequency portion of each transient stage, the frequency corresponding to the maximum amplitude is recorded as the fundamental frequency, and the amplitude and energy corresponding to five times the fundamental frequency in the amplitude spectrum and power spectrum are recorded as the fifth harmonic amplitude and fifth harmonic energy of each transient stage, respectively.

[0029] After a single-phase ground fault occurs on a distribution network feeder, the fifth harmonic component in the transient zero-sequence current will suddenly increase, causing a sudden increase in the energy of the fifth harmonic component. If the sudden increase in the energy of the fifth harmonic on a certain distribution network feeder is more prominent, then the feeder will better reflect the sudden increase in the transient energy of the fifth harmonic component after a single-phase ground fault.

[0030] Based on the above analysis, the transient energy surge of each feeder in the distribution network is calculated: In the formula, For the transient energy surge of the j-th feeder in the distribution network, To determine the number of transient phases, It is an exponential function with the natural constant as its base. and These are the fifth harmonic energies of the b-th and b-1-th transient stages of the j-th feeder, respectively.

[0031] As can be understood from the above process, the transient energy surge reflects the sudden increase in transient energy in the fifth harmonic component after a single-phase ground fault. The greater the transient energy surge, the more sudden the increase in the transient fifth harmonic energy after a single-phase ground fault is reflected in the feeder of the distribution network. Therefore, the feeder of the distribution network is more likely to experience a single-phase ground fault at this time.

[0032] Meanwhile, since the fifth harmonic component of the zero-sequence current on a feeder experiencing a single-phase ground fault is larger than that on a feeder without a fault, if the fifth harmonic component on a certain distribution network feeder differs significantly from the fifth harmonic amplitude on other feeders, it more reliably indicates that a single-phase ground fault has occurred on the distribution network feeder, making a clear distinction between feeders with single-phase ground faults and feeders in normal operation.

[0033] Therefore, the fifth harmonic distinctiveness of each feeder in the distribution network is calculated: In the formula, To distinguish the fifth harmonic of the j-th feeder in the distribution network, Let be the fifth harmonic amplitude of the j-th feeder in the s-th transient stage in the distribution network. Let be the average of the fifth harmonic amplitudes of all feeders except the j-th feeder in the distribution network during the s-th transient phase.

[0034] It should be noted that, in the above process, the fifth harmonic distinctiveness reflects the difference in the fifth harmonic amplitude between the distribution network feeder experiencing a single-phase ground fault and other normally operating feeders. The greater the fifth harmonic distinctiveness, the more it reflects the fifth harmonic current characteristics of the distribution network feeder experiencing a single-phase ground fault, thus producing a clear distinction between the feeder experiencing a single-phase ground fault and the normally operating feeder.

[0035] Based on the above analysis, the energy characteristics and amplitude characteristics of the fifth harmonic after a single-phase ground fault occur on the feeder of the distribution network are extracted by using Fourier transform, so as to obtain the transient energy surge and the fifth harmonic distinctiveness of each feeder in the distribution network.

[0036] To avoid false detections of grounding faults in the distribution network, in this preferred embodiment, the transient energy surge and the fifth harmonic distinctiveness of each feeder in the distribution network are exponentially normalized. The sum of the exponentially normalized transient energy surge and the fifth harmonic distinctiveness is denoted as the fault harmonic characteristic value of each feeder in the distribution network. The fault harmonic characteristic value reflects the magnitude of the fifth harmonic current after a single-phase grounding fault. A larger fault harmonic characteristic value indicates a more prominent fifth harmonic energy and amplitude characteristic of the fifth harmonic current after a single-phase grounding fault, suggesting a higher probability of a single-phase grounding fault occurring on the distribution network feeder.

[0037] Step 3: Based on the consistency of the abrupt change characteristics of the harmonic amplitude and harmonic energy of the zero-sequence current on each feeder in the frequency domain, obtain the fault confidence weight of each feeder in the distribution network, and combine it with the fault harmonic characteristic value to obtain the ground fault identification degree of each feeder in the distribution network.

[0038] Under normal circumstances, the fifth harmonic current in the zero-sequence current of the distribution network feeder is relatively small. At this time, the relationship between the fifth harmonic amplitude and the fifth harmonic energy is weak. However, if a single-phase ground fault occurs on the distribution network feeder, the fifth harmonic current in the zero-sequence current will increase. At this time, the fifth harmonic amplitude and the fifth harmonic energy will exhibit a simultaneous abrupt change, which strengthens the relationship between the fifth harmonic amplitude and the fifth harmonic energy.

[0039] Therefore, the fifth harmonic amplitude and energy of all transient stages of each feeder in the distribution network are arranged into a sequence according to time order, which is denoted as the harmonic amplitude sequence and harmonic energy sequence of each feeder in the distribution network. The harmonic amplitude sequence and harmonic energy sequence of each feeder in the distribution network are respectively used as the BG (Bernaola Galvan, non-stationary time series mutation detection) segmentation algorithm. The mutation bit sequence set of the fifth harmonic amplitude and the mutation bit sequence set of the fifth harmonic energy of each feeder in the distribution network are obtained by the Bernaola Galvan segmentation algorithm. The Bernaola Galvan segmentation algorithm is a well-known technology, and the specific process will not be described in detail.

[0040] Generally, the more prominent the fifth harmonic energy characteristics of the fifth harmonic current on a certain distribution network feeder, and the more consistent the abrupt change characteristics of the fifth harmonic amplitude and the fifth harmonic energy, the greater the credibility of the fifth harmonic current generated by the single-phase grounding fault on the distribution network feeder.

[0041] Therefore, the similarity between the fifth harmonic amplitude and the abrupt change sequence set of the fifth harmonic energy of each feeder is statistically analyzed. Preferably, in this embodiment, the Jaccard similarity coefficient between the fifth harmonic amplitude and the abrupt change sequence set of the fifth harmonic energy of each feeder in the distribution network is calculated. In practical applications, implementers can also use other existing similarity coefficients to measure the similarity between the fifth harmonic amplitude and the abrupt change sequence set of the fifth harmonic energy of each feeder, such as cosine similarity, Pearson correlation coefficient, etc. This embodiment does not impose any special restrictions on this.

[0042] Furthermore, the sum of the Jaccard similarity coefficient and a preset positive constant (denoted as the first product factor in this embodiment for ease of description) is used as the exponentially normalized result of the product of the first product factor and the maximum value of the harmonic energy sequence of each feeder. This result serves as the fault confidence weight for each feeder in the distribution network. The larger the fault confidence weight, the greater the credibility of the fifth harmonic current generated by a single-phase ground fault on the feeder of the distribution network. It should be noted that in the calculation of the first product factor, the addition of the preset positive constant to the Jaccard similarity coefficient is to avoid the product factor being 0. The preset positive constant has a value range of (0.01, 0.1) and its impact on the calculation result is small and can be ignored. In this embodiment, the value is 0.05.

[0043] Furthermore, by combining the fault confidence weights and fault harmonic characteristic values ​​of each feeder in the distribution network, single-phase grounding faults on each feeder in the distribution network are measured and identified, thereby enabling more accurate and rapid detection of grounding faults in the distribution network.

[0044] Based on the above analysis, the ground fault identification rate of each feeder in the distribution network is calculated: In the formula, Let the ground fault identification degree of the j-th feeder in the distribution network be denoted as . Let J be the fault confidence weight of the j-th feeder in the distribution network. Let be the fault harmonic characteristic value on the j-th feeder in the distribution network.

[0045] As can be understood from the above analysis process in this embodiment, the ground fault identification degree reflects the characteristic magnitude of single-phase ground faults occurring on each feeder in the distribution network. If the abnormal characteristics of single-phase ground faults occurring on the feeder of the distribution network are more prominent, it indicates that the feeder of the distribution network deviates more from the zero-sequence current characteristics of the feeder of the distribution network under normal operation, and the feeder of the distribution network is more likely to experience a single-phase ground fault.

[0046] Step 4: Perform anomaly detection on the grounding fault identification of all feeders in the distribution network to obtain the grounding fault detection results of the distribution network feeders.

[0047] Furthermore, to enable rapid and accurate detection of ground faults in the distribution network, preferably, in this embodiment, the 3Sigma anomaly detection method is used to detect the ground fault identification rate of all feeders in the distribution network, thereby obtaining the ground fault detection results on the distribution network feeders. Specifically, the ground fault identification rate of all feeders in the distribution network is used as the input of the 3Sigma anomaly detection method. The 3Sigma anomaly detection method is used to obtain the distribution network feeders whose ground fault identification rates are not within the 3Sigma range, and these feeders are identified as ground fault feeders in the distribution network, thus realizing the ground fault detection of the distribution network feeders. The 3Sigma anomaly detection method is a known technology, and its specific process will not be described in detail.

[0048] Based on the same inventive concept as the above method, this application also provides a ground fault detection system for power distribution networks, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of any of the above-described ground fault detection methods for power distribution networks.

[0049] It is understood that the order of the embodiments described above is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. Furthermore, the above description focuses on specific embodiments of this specification. Additionally, the processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired results. In some implementations, multitasking and parallel processing are possible or may be advantageous.

[0050] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0051] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Any equivalent structural or procedural transformations made based on the description and drawings of this application, or direct or indirect applications in other related technical fields, are similarly included within the protection scope of this application.

Claims

1. A ground fault detection method for power distribution networks, characterized in that, Includes the following steps: Obtain the zero-sequence current on each feeder in the distribution network; By measuring the increase in zero-sequence current in the frequency domain over a short period of time among the harmonic energies of each feeder in the distribution network, the transient energy surge of each feeder in the distribution network is obtained. Based on the deviation of each harmonic amplitude, the fifth harmonic distinctiveness of each feeder in the distribution network is obtained. Then, combined with the transient energy surge, the fault harmonic characteristic value of each feeder is obtained. Based on the consistency of the abrupt change characteristics of the harmonic amplitude and harmonic energy of the zero-sequence current on each feeder in the frequency domain, the fault confidence weight of each feeder in the distribution network is obtained, and combined with the fault harmonic characteristic value, the ground fault identification degree of each feeder in the distribution network is obtained. Anomaly detection is performed on the ground fault identification rate of all feeders in the distribution network to obtain the ground fault detection results of the distribution network feeders.

2. The grounding fault detection method for distribution networks as described in claim 1, characterized in that, The zero-sequence currents on each feeder are arranged in time sequence to form the zero-sequence current sequence of each feeder. A sliding window is set on the zero-sequence current sequence, where each sliding window corresponds to a transient stage. The zero-sequence currents in each sliding window form the transient current sequence of each transient stage. The transient current sequence is then transformed in the frequency domain. The frequency corresponding to the largest amplitude value in the positive frequency part of the amplitude spectrum of each transient stage is recorded as the fundamental frequency. The amplitude and energy corresponding to five times the fundamental frequency in the amplitude spectrum and power spectrum in the frequency domain are respectively used as the fifth harmonic amplitude and fifth harmonic energy of each transient stage.

3. The grounding fault detection method for distribution networks as described in claim 2, characterized in that, The process for obtaining the transient energy surge of each feeder in the distribution network is as follows: In the formula, For the transient energy surge of the j-th feeder in the distribution network, To determine the number of transient phases, It is an exponential function with the natural constant as its base. and These are the fifth harmonic energies of the b-th and b-1-th transient stages of the j-th feeder, respectively.

4. The grounding fault detection method for distribution networks as described in claim 2, characterized in that, The process for obtaining the fifth harmonic distinctiveness of each feeder in the distribution network is as follows: In the formula, To distinguish the fifth harmonic of the j-th feeder in the distribution network, Let be the fifth harmonic amplitude of the j-th feeder in the s-th transient stage in the distribution network. Let be the average of the fifth harmonic amplitudes of all feeders except the j-th feeder in the distribution network during the s-th transient phase.

5. The grounding fault detection method for distribution networks as described in claim 1, characterized in that, The fault harmonic characteristic value of each feeder is the sum of the normalized result of the transient energy surge of each feeder and the normalized result of the fifth harmonic distinctiveness.

6. The grounding fault detection method for distribution networks as described in claim 2, characterized in that, The fifth harmonic amplitude and fifth harmonic energy of all transient stages of each feeder are arranged in time sequence to form the harmonic amplitude sequence and harmonic energy sequence of each feeder. The mutation position sequence set of the fifth harmonic amplitude and the mutation position sequence set of the fifth harmonic energy of each feeder are extracted by the BG segmentation algorithm.

7. The grounding fault detection method for distribution networks as described in claim 6, characterized in that, The process of obtaining the fault confidence weight of each feeder in the distribution network is as follows: calculate the similarity between the fifth harmonic amplitude and the mutation position set of the fifth harmonic energy of each feeder, count the sum of the similarity and a preset constant greater than zero, and use the normalized result of the product of the sum and the maximum value of the harmonic energy sequence of each feeder as the fault confidence weight of each feeder in the distribution network.

8. The grounding fault detection method for distribution networks as described in claim 1, characterized in that, The process of obtaining the ground fault identification degree of each feeder in the distribution network is as follows: In the formula, Let the ground fault identification degree of the j-th feeder in the distribution network be denoted as . Let J be the fault confidence weight of the j-th feeder in the distribution network. Let be the fault harmonic characteristic value on the j-th feeder in the distribution network.

9. The grounding fault detection method for distribution networks as described in claim 1, characterized in that, The ground fault identification degree of all feeders in the distribution network is used as the input of the 3Sigma anomaly detection method. The distribution network feeders whose ground fault identification degree is not within the 3Sigma range are counted and regarded as ground fault feeders in the distribution network.

10. A ground fault detection system for power distribution networks, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the ground fault detection method for power distribution networks as described in any one of claims 1-9.

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