Method for identifying high-resistance grounding fault section of single-neutral-point small-resistance grounding active distribution network

Abstract

The invention discloses a method for identifying a high-resistance grounding fault section of a single-neutral-point small-resistance grounding active distribution network, which belongs to the technical field of power system protection and control, and comprises the following steps: S1, setting a high-resistance grounding fault direction judgment criterion of the single-neutral-point small-resistance grounding active distribution network; s2, setting a fault criterion in a high-resistance grounding fault area of the single-neutral-point small-resistance grounding active power distribution network; s3, setting an action process of the identification method for the high-resistance grounding fault section of the single-neutral-point small-resistance grounding active power distribution network; and S4, calculating the maximum allowable measurement error boundary. According to the method for identifying the high-resistance grounding fault section of the single-neutral-point small-resistance grounding active power distribution network, the reliability of line switch fault direction judgment during the single-phase high-resistance grounding fault of the single-neutral-point small-resistance grounding active power distribution network can be ensured, and the high-resistance grounding fault section can be effectively identified.

Description

Technical Field

[0001] The present invention relates to the technical field of power system protection and control, and in particular to a method for identifying a high-resistance grounding fault section of a single-neutral-point small-resistance grounded active distribution network. Background Technique

[0002] In the prior art, in recent years, with the development of social economy and the continuous expansion of urban scale, the number of cable accesses has increased rapidly, and the capacitive current of the distribution network has been increasing continuously. The small-resistance grounding method has gradually been popularized and applied in the distribution network. However, the setting value of the time-limited zero-sequence overcurrent protection commonly used at present is generally 40 - 60 A, and it can only detect single-phase grounding faults with a transition resistance of about 85 - 135 Ω at most. When a high-resistance grounding fault occurs, the protection will malfunction. For a distribution network using cables, its line capacitive current is large. Limited by the maximum system capacitive current to the ground, the setting value of the time-limited zero-sequence overcurrent protection is large, and the ability to detect the transition resistance is small. Moreover, cable lines are generally buried underground. When the cable insulation ages or is damaged, it will cause a single-phase grounding fault with a high transition resistance and a weak fault current, which is difficult to identify and troubleshoot. For a distribution network using overhead lines, single-phase grounding faults generally occur due to reasons such as conductor drooping, natural factors, and human electric shock, and the transition resistance can be as high as hundreds or thousands of ohms. Although the capacitive current to the ground is small, there are still problems such as a high tripping rate and difficulty in realizing high-resistance fault protection. Therefore, how to achieve rapid detection and accurate isolation of single-phase high-resistance grounding faults is of great significance for the safe and stable operation and application development of a system with a neutral point grounded through a small resistance.

[0003] With the proposal of the "dual carbon" goal, the penetration rate of distributed generation (DG) in the distribution network has been continuously increasing. The problem of detecting single-phase grounding faults in a neutral-point small-resistance grounded distribution system with a high proportion of DG access has also become the focus of attention in the industry. When the DG grid-connected transformer adopts different grounding methods, the equivalent zero-sequence network structure of the distribution network after a single-phase grounding fault has significant differences. In the investigation of actual projects, due to considerations of protection reliability and personal safety, the DG grid-connected transformers in the active distribution network generally adopt an ungrounded method. Defining the system with a small-resistance grounding method and the DG grid-connected transformer with an ungrounded method as a single-neutral-point small-resistance grounding method. Existing research on methods for detecting single-phase high-resistance grounding faults in a small-resistance grounded active distribution network often focuses on the identification of fault feeders and non-fault feeders, and there is less research on the single-neutral-point small-resistance grounding method. As the requirements for fault location in the distribution network are getting higher and higher, the existing detection methods that only identify single-phase high-resistance grounding fault feeders will not be able to meet the development needs of future new power systems, which is not conducive to the rapid location and treatment of high-resistance grounding in the distribution network.

[0004] Therefore, it is urgent to solve the problem of quickly and effectively identifying the single-phase high-resistance grounding fault section in an active distribution network with a single neutral point and small-resistance grounding, so as to meet the requirements of safe and reliable operation of the active distribution network with a single neutral point and small-resistance grounding and rapid handling of high-resistance grounding faults. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for identifying the high-resistance grounding fault section in an active distribution network with a single neutral point and small-resistance grounding, which can ensure the reliability of judging the fault direction of the line switch during a single-phase high-resistance grounding fault in the active distribution network with a single neutral point and small-resistance grounding, and effectively identify the high-resistance grounding fault section.

[0006] To achieve the above purpose, the present invention provides a method for identifying the high-resistance grounding fault section in an active distribution network with a single neutral point and small-resistance grounding, including the following steps:

[0007] S1. Set the criterion for judging the fault direction of high-resistance grounding in an active distribution network with a single neutral point and small-resistance grounding;

[0008] S2. Set the criterion for judging the fault within the high-resistance grounding fault area in an active distribution network with a single neutral point and small-resistance grounding;

[0009] S3. Set the action process of the method for identifying the high-resistance grounding fault section in an active distribution network with a single neutral point and small-resistance grounding;

[0010] S4. Calculate the boundary of the maximum allowable measurement error.

[0011] Preferably, in S1, it specifically includes the following steps:

[0012] S11. Define the symbols related to the criterion for judging the fault direction;

[0013] Define the amplitude of the zero-sequence voltage at the switch as U (0) , and the amplitude of the zero-sequence current as I (0) , the direction-representing voltage as U (0) -6R n I (0) , and define D as the fault direction;

[0014] S12. Configure the criterion for judging the fault direction based on the direction-representing voltage.

[0015] Preferably, in S12, it specifically includes the following steps:

[0016] S121. Set the resistance value R n of the small grounding resistance of the distribution network system;

[0017] S122. The criterion for judging the fault direction based on the direction-representing voltage is:

[0018]

[0019] During a positive-direction fault, the direction-characterizing voltage is less than zero, and D is 1; during a reverse-direction fault, the direction-characterizing voltage is greater than zero, and D is 0.

[0020] Preferably, in S2, it specifically includes the following steps:

[0021] S21. Classify the switch types around the section, which specifically includes the following steps:

[0022] S211. Taking the current flowing out of the bus as the positive current direction, define the switch closest to the system bus among the switches around the section as the upstream switch of the area, and define D 上游 as the judgment result of the fault direction of the only switch upstream of the area;

[0023] S212. Define the other switches around the section except the upstream switch of the area as the downstream switches of the area, and define as the sum of the judgment results of the fault directions of all the switches downstream; S22. Set the fault criterion within the high-resistance grounding fault area.

[0024] Preferably, in S22, taking the judgment result of the fault direction of the only switch upstream of the area as a positive-direction fault and the judgment results of the fault directions of all the switches downstream as reverse-direction faults as the fault criterion within the area, the fault criterion within the high-resistance grounding fault area is:

[0025]

[0026] Preferably, in S3, it specifically includes the following steps:

[0027] S31. Set the start criterion for the method of identifying the high-resistance grounding fault section in the single-neutral-point small-resistance grounded active distribution network;

[0028] S32. Set the judgment process of the fault directions of each switch after the high-resistance grounding fault in the single-neutral-point small-resistance grounded active distribution network;

[0029] S33. Set the identification process of the high-resistance grounding fault section in the single-neutral-point small-resistance grounded active distribution network.

[0030] Preferably, in S31, it includes the following steps:

[0031] S311. Let all switches collect zero-sequence voltage and current. When the zero-sequence voltage and current at a certain switch satisfy the start criterion of the sudden change of the zero-sequence current difference, start the method for identifying the single-phase grounding fault section;

[0032] S312. The start criterion of the sudden change of the zero-sequence current difference is:

[0033] ||i0(k)-i0(k-N)|-|i0(k-N)-i0(k-2N)||>ε;

[0034] Wherein, N is the number of sampling points per power frequency cycle, i0(k) is the sampled value of zero-sequence current, and ε is the threshold of the starting criterion for the sudden change of zero-sequence current;

[0035] In S32, the following steps are included:

[0036] S321. After the method is started, each switch collects the steady-state measurement values and judges the fault direction according to the fault direction discrimination criterion set in S1;

[0037] S322. Each switch uploads the fault direction judgment result to the master station;

[0038] In S33, the following steps are included:

[0039] S331. The master station collects the fault direction judgment results of the switches around the section to be discriminated;

[0040] S332. The master station judges the fault section of each section according to the fault criterion in the high-resistance grounding fault area set in S2; if the section to be discriminated meets the fault criterion in the high-resistance grounding fault area set, it is determined that a single-phase grounding fault has occurred in this section; otherwise, there is no fault in this section.

[0041] Preferably, in S4, the following steps are specifically included:

[0042] S41. Calculate the maximum allowable measurement error boundary of each switch at different transition resistances;

[0043] S42. Calculate the maximum allowable measurement error boundary of the whole network at different transition resistances, and select the accuracy of the measurement device according to the maximum allowable measurement error boundary of the whole network at different transition resistances.

[0044] Preferably, in S41, the following steps are included:

[0045] S411. Obtain the absolute value of the direction representation voltage at each switch during the fault of the edge endpoints of the distribution network at different transition resistances by one of the two methods of iterative calculation and simulation;

[0046] S412. Take the minimum value of the absolute value of the direction representation voltage at the switch during the fault of all the edge endpoints of the distribution network line as the maximum allowable measurement error boundary of the switch. The expression is as follows:

[0047] b = MIN|U (0) -6R n I (0) |;

[0048] Wherein, b is the maximum allowable measurement error boundary of this switch, and MIN|U (0) -6R n I (0)|It is the minimum value of the absolute value of the direction-characteristic voltage at the switch when a single-phase grounding fault occurs at all edge endpoints of the distribution network.

[0049] Preferably, in S42, the following steps are included:

[0050] S421: Take the minimum value of the maximum allowable measurement error boundaries of all switches that make up the section identification method for different transition resistances as the maximum allowable measurement error boundary B of the entire network for different transition resistances;

[0051] S422: When the absolute error Δ u of the zero-sequence voltage amplitude and the absolute error Δ i of the zero-sequence current amplitude measured at all switches satisfy the following formula:

[0052] Δ u +6R n Δ i <B;

[0053] It indicates that the fault section identification is accurate;

[0054] S423: The maximum allowable measurement error boundaries of the entire network are different for different transition resistances. Guide the selection of measurement equipment according to the maximum allowable measurement error for different magnitudes of transition resistances, that is, determine the measurement accuracy of the required measurement equipment according to the magnitude of the transition resistance to be tolerated.

[0055] Therefore, the beneficial effects of the present invention adopting the above-mentioned method for identifying high-resistance grounding fault sections in a single-neutral-point small-resistance grounded active distribution network are as follows:

[0056] (1) The method of the present invention aims at the problem of identifying high-resistance grounding fault sections in a small-resistance grounded active distribution network, and proposes a method for identifying high-resistance grounding fault sections in a single-neutral-point small-resistance grounded active distribution network based on direction-characteristic voltage, and details the judgment interval range and action criterion of the switch fault direction.

[0057] (2) The method of the present invention is not affected by the magnitude of the transition resistance and the arc discharge phenomenon during high-resistance grounding faults when the electrical quantities can be accurately measured.

[0058] (3) The method of the present invention considers the ungrounded mode of the distributed power grid grid-connected transformer, and the reliability of the method is not affected by the DG access situation.

[0059] (4) The calculation principle of the fault direction judgment interval of the method of the present invention is clear and easy to implement.

[0060] (5) The present invention proposes a maximum allowable measurement boundary method for the improved grounding fault section identification method, providing two-way guidance for practical engineering applications: determining the accuracy selection requirements of measurement equipment based on the target tolerance range of transition resistance; evaluating the transition resistance tolerance of the proposed method in combination with the actual accuracy of the installed equipment.

[0061] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Brief Description of the Drawings

[0062] Figure 1 is a schematic diagram of the wiring of a typical single-neutral-point low-resistance grounded active distribution network;

[0063] Figure 2 is a flowchart of the method for identifying high-resistance grounding fault sections in a single-neutral-point low-resistance grounded active distribution network of the present invention. Detailed Embodiments

[0064] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0065] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention pertains. The "first", "second" and similar terms used in the present invention do not denote any order, quantity or importance, but are only used to distinguish different components. The terms such as "comprising" or "including" mean that the elements or objects appearing before this term cover the elements or objects listed after this term and their equivalents, without excluding other elements or objects. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left" and "right" are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0066] Embodiment 1

[0067] The present invention provides a method for identifying high-resistance grounding fault sections in a single-neutral-point low-resistance grounded active distribution network. This method considers that the system adopts a low-resistance grounding method and the distributed power grid-connected transformer adopts an ungrounded method. According to the difference in the zero-sequence current-voltage characteristic relationship between the upstream and downstream of the fault point during a single-phase grounding fault in a single-neutral-point low-resistance grounding system, a direction-representing voltage is defined, and the direction of a single-phase grounding fault of the line switch is discriminated by the positive and negative of the direction-representing voltage. The in-zone fault is identified according to the criterion that the fault in the positive direction occurs at the only switch upstream of the section and the faults at the downstream switches are all in the reverse direction. Among them, in this embodiment, the positive direction of the current of each protection device is as Figure 1 shown.

[0068] A method for identifying high-resistance grounding fault sections in an active distribution network with a single neutral point and small-resistance grounding in this embodiment specifically includes the following steps:

[0069] S1. Set the criterion for judging the direction of high-resistance grounding faults in an active distribution network with a single neutral point and small-resistance grounding, including the following steps:

[0070] S11. Define the symbols related to the criterion for judging the direction of faults, specifically:

[0071] S111. Define the magnitude of the zero-sequence voltage at the switch as U (0) , and the magnitude of the zero-sequence current as I (0) , and the direction-characteristic voltage as U (0) -6R n I (0) .

[0072] S112. Define D as the fault direction. When the fault is in the positive direction, D is 1; when the fault is in the reverse direction, D is 0.

[0073] S12. Configure the criterion for judging the fault direction based on the direction-characteristic voltage, specifically:

[0074] S121. Set the resistance value R n of the small grounding resistance of the distribution network system to 10 Ω.

[0075] S122. The criterion for judging the fault direction based on the direction-characteristic voltage is:

[0076]

[0077] When the fault is in the positive direction, the direction-characteristic voltage is less than zero and D is 1; when the fault is in the reverse direction, the direction-characteristic voltage is greater than zero and D is 0.

[0078] S2. Set the criterion for judging faults within the high-resistance grounding fault area of an active distribution network with a single neutral point and small-resistance grounding, including the following steps:

[0079] S21. Classify the types of switches around the section, specifically:

[0080] S211. Taking the current flowing out of the bus as the positive direction of the current, define the switch FSW1 closest to the system bus among the switches around the section as the upstream switch of the area, and define D FSW1 as the judgment result of the fault direction of the only switch upstream of the area.

[0081] S212. Define the other switches FSW2, QSW1, and QSW2 around the section except the upstream switch of the area as the downstream switches of the area, and define D FSW2 +D QSW1 +D QSW2 as the sum of the judgment results of the fault directions of all the switches downstream.

[0082] S22. Set the fault criterion within the high-resistance grounding fault area, specifically as follows:

[0083] Taking the fault direction judgment result of the only switch upstream of the area as a positive-direction fault and the fault direction judgment results of all switches downstream as reverse-direction faults as the fault criterion within the area, the fault criterion within the high-resistance grounding fault area is:

[0084]

[0085] S3. Set the operation process of the method for identifying high-resistance grounding fault sections in a single-neutral-point small-resistance grounded active distribution network, as Figure 2 shown, specifically including the following steps:

[0086] S31. Set the startup criterion of the method for identifying high-resistance grounding fault sections in a single-neutral-point small-resistance grounded active distribution network, specifically as follows:

[0087] S311. Let all switches collect zero-sequence voltage and current. When the zero-sequence voltage and current at a certain switch satisfy the sudden change amount startup criterion of zero-sequence current difference, start the single-phase grounding fault section identification method.

[0088] S312. The sudden change amount startup criterion of zero-sequence current difference is:

[0089] ||i0(k) - i0(k - N)| - |i0(k - N) - i0(k - 2N)|| > ε

[0090] In the formula, N is the number of sampling points per power frequency cycle, i0(k) is the sampling value of zero-sequence current, and ε is the threshold of the sudden change amount startup criterion of zero-sequence current.

[0091] S32. Set the fault direction judgment process of each switch after a high-resistance grounding fault in a single-neutral-point small-resistance grounded active distribution network, specifically as follows:

[0092] S321. After the method starts, each switch collects steady-state measurement values and judges the fault direction according to the fault direction discrimination criterion set in S122.

[0093] S322. Each switch uploads the fault direction judgment result to the master station.

[0094] S33. Set the identification process of high-resistance grounding fault sections in a single-neutral-point small-resistance grounded active distribution network, specifically as follows:

[0095] S331. The master station collects the fault direction judgment results of the switches around a certain section.

[0096] S332. The master station judges the fault section for each section according to the fault criterion within the high-resistance grounding fault area set in S22. If a certain section meets the fault criterion within the high-resistance grounding fault area set, it is determined that a single-phase grounding fault has occurred within this section; otherwise, there is no fault within this section.

[0097] S4. Calculate the maximum allowable measurement error boundary, which specifically includes the following steps:

[0098] S41. Calculate the maximum allowable measurement error boundary for each switch at different transition resistances, specifically:

[0099] S411. Obtain the absolute value of the direction-characterizing voltage at each switch during the fault of the edge endpoints of the distribution network at different transition resistances through one of the two methods of iterative calculation and simulation.

[0100] S412. Take the minimum value of the absolute value of the direction-characterizing voltage at the switch during the fault of all edge endpoints of the distribution network line as the maximum allowable measurement error boundary of the switch.

[0101] b FSW1 =MIN|U (0) -6R n I (0) | FSW1.i

[0102] b FSW2 =MIN|U (0) -6R n I (0) | FSW2.i

[0103] b QSW1 =MIN|U (0) -6R n I (0) | QSW1.i

[0104] b QSW2 =MIN|U (0) -6R n I (0) | QSW2.i

[0105] i∈{k0,k5,k6,k7,k8}

[0106] In the formula, b FSW1 is the maximum allowable measurement error boundary of FSW1, b FSW2 is the maximum allowable measurement error boundary of FSW2, b QSW1 is the maximum allowable measurement error boundary of QSW1, b QSW2 is the maximum allowable measurement error boundary of QSW2, MIN|U (0) -6R nI (0) | FSW1.i is the minimum value of the absolute value of the direction characterization voltage at FSW1 when all edge endpoints of the line fail, MIN|U (0) -6R n I (0) | FSW2.i is the minimum value of the absolute value of the direction characterization voltage at FSW1 when all edge endpoints of the line fail, MIN|U (0) -6R n I (0) | QSW1.i is the minimum value of the absolute value of the direction characterization voltage at FSW1 when all edge endpoints of the line fail, MIN|U (0) -6R n I (0) | QSW2.i is the minimum value of the absolute value of the direction characterization voltage at FSW1 when all edge endpoints of the line fail, k0, k5, k6, k7, k8 are all edge endpoints of the line.

[0107] S42. Calculate the boundary of the maximum allowable measurement error of the entire network for different transition resistances, and select the accuracy of the measurement device according to the boundary of the maximum allowable measurement error of the entire network for different transition resistances. Specifically:

[0108] S421. Take the minimum value of the maximum allowable measurement error boundaries of all switches that make up the section identification method for different transition resistances as the boundary B of the maximum allowable measurement error of the entire network for different transition resistances. Taking FSW1, FSW2, QSW1, and QSW2 as examples, the calculation formula for B is as follows:

[0109] B = MIN(b FSW1 , b FSW2 , b QSW1 , b QSW2 )

[0110] S422. When the absolute error Δ u of the zero-sequence voltage amplitude and the absolute error Δ i of the zero-sequence current amplitude measured at all switches satisfy the following formula:

[0111] Δ u +6R n Δ i <B

[0112] Then it can be ensured that the proposed method accurately identifies the fault section.

[0113] S423. The maximum allowable measurement error boundaries of the entire network are different for different transition resistances. The selection of measurement equipment is guided by the maximum allowable measurement error for different magnitudes of transition resistances, that is, the measurement accuracy of the required measurement equipment is determined according to the magnitude of the transition resistance to be tolerated. When the measurement equipment is already installed and its accuracy is known, the ability of the single-phase grounding fault section identification method of this embodiment to tolerate the transition resistance can be determined according to the method of step S4.

[0114] Therefore, the present invention adopts the above-mentioned method for identifying high-resistance grounding fault sections in an active distribution network with a single neutral point and a small resistance grounding. This method can identify high-resistance grounding fault sections in an active distribution network with a single neutral point and a small resistance grounding, is not affected by the DG access situation, and is not affected by the magnitude of the transition resistance and the arc discharge phenomenon during high-resistance grounding faults when the electrical quantities can be accurately measured. Moreover, a method for the maximum allowable measurement boundary is proposed for the improved high-resistance grounding fault section identification method, providing two-way guidance for practical engineering applications: determining the accuracy selection requirements of the measurement equipment based on the target transition resistance range to be tolerated. Combining the actual accuracy of the installed equipment, evaluating the transition resistance tolerance ability of the proposed method.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for identifying high-resistance grounding fault sections in an active distribution network with a single neutral point grounded through a small resistor, characterized in that, It includes the following steps: S1. Set the discrimination criterion for the direction of high-resistance grounding faults in an active distribution network with a single neutral point and a small grounding resistance; S2. Set the discrimination criterion for faults within the high-resistance grounding fault area in an active distribution network with a single neutral point and a small grounding resistance; S3. Set the action process of the identification method for high-resistance grounding fault sections in an active distribution network with a single neutral point and a small grounding resistance; S4. Calculate the boundary of the maximum allowable measurement error.

2. The method for identifying a high-resistance grounding fault section of a single-neutral-point small-resistance grounded active distribution network according to claim 1, wherein: In S1, it specifically includes the following steps: S11. Define the symbols related to the discrimination criterion for the direction of fault; Define the zero-sequence voltage amplitude at the switch as U (0) , and the zero-sequence current amplitude as I (0) , and the direction-indicating voltage as U (0) -6R n I (0) , and define D as the fault direction; S12. Configure the discrimination criterion for the direction of fault based on the voltage representing the direction.

3. The method for identifying the high-resistance grounding fault section of a single-neutral-point small-resistance grounded active distribution network according to claim 2, characterized in that: In S12, it specifically includes the following steps: S121. Set the resistance value R of the grounding small resistor of the distribution network system n ; S122. The discrimination criterion for the direction of fault based on the voltage representing the direction is: In the case of a forward fault, the voltage representing the direction is less than zero, and D is 1; in the case of a reverse fault, the voltage representing the direction is greater than zero, and D is 0.

4. The method for identifying the high-resistance grounding fault section of an active distribution network with a single neutral point and small-resistance grounding according to claim 1, characterized in that: In S2, it specifically includes the following steps: S21. Classify the types of switches around the section, which specifically includes the following steps: S211. With the current flowing out from the busbar as the positive direction of the current, define the switch closest to the system busbar switch among the only switches around the section as the upstream switch of the area, and define D 上游 as the judgment result of the fault direction of the only switch upstream of the area; S212. Define other switches around the section except the upstream switch of the area as the downstream switches of the area, and define it as the sum of the judgment results of the fault directions of all switches defined as downstream; S22. Set the discrimination criterion for faults within the high-resistance grounding fault area.

5. The method for identifying the high-resistance grounding fault section of an active distribution network with a single neutral point grounded through a small resistor according to claim 4, characterized in that: In S22, taking the judgment result of the direction of the fault of the only switch upstream of the area as a forward fault and the judgment results of the directions of all switches downstream as reverse faults as the criterion for a fault occurring within the area, the discrimination criterion for faults within the high-resistance grounding fault area is:

6. The method for identifying high-resistance grounding fault sections in an active distribution network with a single neutral point and small-resistance grounding according to claim 1, wherein: In S3, it specifically includes the following steps: S31. Set the starting criterion for the identification method of high-resistance grounding fault sections in an active distribution network with a single neutral point and a small grounding resistance; S32. Set the judgment process for the directions of faults of each switch after a high-resistance grounding fault in an active distribution network with a single neutral point and a small grounding resistance; S33. Set the identification process for high-resistance grounding fault sections in an active distribution network with a single neutral point and a small grounding resistance.

7. The method for identifying the high-resistance grounding fault section of a single-neutral-point low-resistance grounded active distribution network according to claim 6, wherein: In S31, it includes the following steps: S311. Let all switches collect zero-sequence voltage and current. When the zero-sequence voltage and current at a certain switch satisfy the starting criterion for the sudden change of the zero-sequence current difference, start the identification method for single-phase grounding fault sections; S312. The starting criterion for the sudden change of the zero-sequence current difference is: ||i0(k)-i0(k-N)|-|i0(k-N)-i0(k-2N)||>ε; In the formula, N is the number of sampling points per power frequency cycle, i0(k) is the sampling value of the zero-sequence current, and ε is the threshold value of the starting criterion for the sudden change of the zero-sequence current; In S32, it includes the following steps: S321. After the method starts, each switch collects the steady-state measurement values and judges the direction of the fault according to the discrimination criterion for the direction of the fault set in S1; S322. Each switch uploads the judgment result of the direction of the fault to the master station; In S33, it includes the following steps: S331. The master station collects the judgment results of the directions of faults of the switches around the section to be discriminated; S332. The master station judges the fault sections of each section according to the discrimination criterion for faults within the high-resistance grounding fault area set in S2; if the section to be discriminated meets the discrimination criterion for faults within the high-resistance grounding fault area set, it is determined that a single-phase grounding fault has occurred within this section; otherwise, there is no fault within this section.

8. The method for identifying a high-resistance grounding fault section of an active distribution network with a single neutral point and small-resistance grounding according to claim 1, wherein: In S4, it specifically includes the following steps: S41. Calculate the boundary of the maximum allowable measurement error for each switch under different transition resistances; S42. Calculate the maximum allowable measurement error boundary of the entire network for different transition resistances, and select the accuracy of the measurement device according to the maximum allowable measurement error boundary of the entire network for different transition resistances.

9. The method for identifying a high-resistance grounding fault section of a single-neutral-point small-resistance grounded active distribution network according to claim 8, wherein: In S41, the following steps are included: S411. Obtain the absolute value of the direction-representing voltage at each switch during the fault of the edge endpoints of the distribution network for different transition resistances by one of the two methods of iterative calculation and simulation. S412. Take the minimum value of the absolute value of the direction-representing voltage at the switch during the fault of all edge endpoints of the distribution network line as the maximum allowable measurement error boundary of the switch. The expression is as follows: b = MIN|U (0) -6R n I (0) |; where b is the maximum allowable measurement error boundary of the switch, and MIN|U (0) -6R n I (0) | is the minimum value of the absolute value of the direction-characterizing voltage at the switch during single-phase grounding faults at all edge endpoints of the distribution network.

10. The method for identifying a high-resistance grounding fault section of a single-neutral-point small-resistance grounded active distribution network according to claim 8, wherein: In S42, the following steps are included: S421. Take the minimum value of the maximum allowable measurement error boundaries of all switches constituting the section identification method for different transition resistances as the maximum allowable measurement error boundary B of the entire network for different transition resistances. S422. When the absolute error Δ u of the zero-sequence voltage amplitude measured at all switches and the absolute error Δ i of the zero-sequence current amplitude satisfy the following formula: Δ u +6R n Δ i <B; It indicates that the fault section identification is accurate. S423. The maximum allowable measurement error boundaries of the entire network are different for different transition resistances. Guide the selection of measurement equipment according to the maximum allowable measurement error for different magnitudes of transition resistances, that is, determine the measurement accuracy of the required measurement equipment according to the magnitude of the transition resistance to be tolerated.

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