Flexible grounding active power distribution network single-phase earth fault line selection method and system

Abstract

The invention discloses a flexible grounding active power distribution network single-phase earth fault line selection method and system, and the method comprises the steps: detecting that the protection is started, and the fault of a flexible grounding active power distribution network does not disappear before a neutral point parallel small resistor RN is switched on, and starting a line selection process: i, switching on the neutral point parallel small resistor RN; ii, extracting zero-sequence current of each feeder line, zero-sequence current of a neutral line and zero-sequence voltage of a bus in a power frequency period before / after the input of the parallel small resistor RN; iii, calculating the ratio of the zero-sequence admittance of each feeder line to the zero-sequence admittance of the neutral line before / after the input of the parallel small resistor RN; iv, calculating a zero-sequence admittance ratio amplitude multiplication coefficient of each feeder line; and v, obtaining a line selection analysis criterion. The fault line can be accurately selected, the line selection logic is simple, and the transition resistance tolerance is high.

Description

Technical Field

[0001] The invention relates to the technical field of distribution network protection, and in particular to a fault line selection method for a flexible grounding active distribution network. Background Art

[0002] An active distribution network refers to a distribution network that has a large number of distributed power sources connected and power flows in both directions. When the distributed power grid-connected transformer adopts a mixed grounding method of ungrounded or grounded via a small grid-connected resistor, when a permanent single-phase grounding fault occurs in the distribution network, the fault line selection method of the traditional distribution network is difficult to directly apply. Therefore, this field urgently needs a technical solution for accurately selecting the fault line to quickly remove the grounding fault, thereby solving the problems raised by the background technology. Technological innovation in this area is crucial to improving power supply reliability and safe operation of power systems. Summary of the invention

[0003] In view of the problems existing in the above-mentioned traditional technologies, the present invention aims to propose a single-phase grounding fault line selection method and system for a flexible grounding active distribution network, which realizes a selection strategy for the line fault line containing distributed power sources based on the feeder zero-sequence admittance and the neutral line inductive zero-sequence admittance.

[0004] The present invention is achieved by the following technical solutions:

[0005] In a first aspect, the present invention proposes a line selection method for a single-phase grounding fault in a flexible grounding active distribution network, the line selection method comprising:

[0006] Detected neutral point zero sequence current I n , at the neutral point zero sequence current I n Greater than the start value I 0set In the case of, the protection starts;

[0007] When a small resistor R is connected in parallel to the neutral point N Before the flexible grounding active distribution network is put into use, the fault of the flexible grounding active distribution network has not disappeared. The fault of the flexible grounding active distribution network further includes busbar fault, line fault without distributed power supply, and line fault with distributed power supply. Specifically, the line without distributed power supply is a Class I feeder, and the line containing distributed power supply and all distributed power supply are not grounded is a Class II feeder. The line containing distributed power supply and all distributed power supply are connected to the grid through the small grounding resistance R of the distributed power supply grid transformer. DG The grounded line is a Class III feeder, and the distributed power source is not grounded and connected to the distributed power source through a small resistor R DG The line with grounding is a Class IV feeder. The feeders include Class I feeders, Class II feeders, Class III feeders and Class IV feeders, which are gathered at the busbar and the line selection analysis process begins:

[0008] i. Connect a small resistor R in parallel with the neutral point N ;

[0009] ii. Extract the small parallel resistor R N Zero-sequence current of each feeder, zero-sequence current of neutral line, and zero-sequence voltage of busbar within one power frequency cycle before / after being put into operation;

[0010] iii. According to the parallel small resistor R N Before the neutral line is put into operation, the zero-sequence admittance of each feeder to the ground is calculated by connecting a small resistor R in parallel N The ratio of the zero-sequence admittance of each feeder before being put into operation to the zero-sequence admittance of the neutral line, and the small parallel resistor R N After the neutral line is put into operation, the zero-sequence admittance of each feeder is calculated by connecting a small resistor R in parallel N The ratio of the zero-sequence admittance of each feeder line to the zero-sequence admittance of the neutral line after being put into operation;

[0011] iv. According to the small parallel resistor obtained in step iii, put it into R N The zero-sequence admittance ratio of each feeder to the neutral line before and after commissioning, and the zero-sequence admittance ratio amplitude multiplication coefficient of each feeder are calculated Among them, Y i ' -n Indicates a small resistor R in parallel with the neutral point N After being put into operation, the ratio of the zero-sequence admittance of each feeder to the neutral line, Y i-n Indicates a small resistor R in parallel with the neutral point N Before being put into operation, the ratio of the zero-sequence to-ground admittance of each feeder relative to the neutral line;

[0012] v. Based on the zero-sequence admittance ratio amplitude multiplication coefficient of each feeder in the active distribution network as the line selection analysis criterion, k i >1 indicates a faulty line, otherwise it is a healthy line.

[0013] In some embodiments, in step iii, the parallel small resistor R N Zero-sequence admittance Y of the neutral line before switching on n The zero-sequence admittance Y of each feeder 1 , Y 2 , Y 3 , Y 4 The calculation method is as follows:

[0014]

[0015] in, Represents the zero-sequence current of each feeder, Indicates the neutral line zero sequence current, Indicates bus zero sequence voltage, C 1 , C 2 , C 3 , C 4Represents the equivalent capacitance of each feeder to ground, C 0∑ Represents the sum of the system's equivalent capacitance to ground, x 1 、x 2 、x 3 Respectively represent the feeder line l 1 , l 2 , l 3 The small resistor R DG The number of grounded distributed generation sources, R DG represents the small grounding resistance of the distributed power grid-connected transformer, v represents the detuning compensation degree of the arc suppression coil, j represents an imaginary number, ω represents the angular frequency, and L s Indicates the flexible grounding mode with R N Arc suppression coils connected in parallel.

[0016] In some embodiments, in step iii, the parallel small resistor R N The ratio of the zero-sequence admittance of each feeder before operation to the zero-sequence admittance of the neutral line Y 1-n , Y 2-n , Y 3-n , Y 4-n The calculation method is as follows:

[0017]

[0018] Among them, Y n Represents a small parallel resistor R N The zero-sequence admittance to ground of the neutral line before being put into operation.

[0019] In some embodiments, in step iii, the parallel small resistor R N Zero-sequence admittance Y of the neutral line after switching on n ′ and the zero-sequence admittance to ground Y of each feeder 1 ′、Y 2 ′、Y 3 ′、Y 4 ' is calculated as follows:

[0020]

[0021] In some embodiments, in step iii, the parallel small resistor R N The ratio of the zero-sequence admittance of each feeder to the inductive zero-sequence admittance of the neutral line after being put into operation Y 1 ' -n , Y 2 ' -n , Y 3 ' -n , Y 4 ' -n The expression is as follows:

[0022] .

[0024] In some implementations, the zero-sequence admittance ratio amplitude multiplication factor k of each feeder is 1 , k 2 , k 3 , k 4 The expression is as follows:

[0025] .

[0027] 1. In a second aspect, the present invention implements a flexible grounding active distribution network single-phase grounding fault system for executing a flexible grounding active distribution network single-phase grounding fault line selection method in any embodiment, the line selection system comprising a protection start detection module and a line selection analysis module;

[0028] The protection start detection module is used to detect the neutral point zero sequence current I n , at the neutral point zero sequence current I n Greater than the start value I 0set In the case of, the protection starts;

[0029] The line selection analysis module is used to connect a small resistor R in parallel with the neutral point. N Before the flexible grounding active distribution network is put into use, the fault of the flexible grounding active distribution network has not disappeared. The fault of the flexible grounding active distribution network further includes busbar fault, line fault without distributed power supply, and line fault with distributed power supply. Specifically, the line without distributed power supply is a Class I feeder, and the line containing distributed power supply and all distributed power supply are not grounded is a Class II feeder. The line containing distributed power supply and all distributed power supply are connected to the grid through the small grounding resistance R of the distributed power supply grid transformer. DG The grounded line is a Class III feeder, and the distributed power source is not grounded and connected to the distributed power source through a small resistor R DG The line with grounding is a Class IV feeder. The feeders include Class I feeders, Class II feeders, Class III feeders and Class IV feeders, which are gathered at the busbar and the line selection analysis process begins:

[0030] i. Connect a small resistor R in parallel with the neutral point N ;

[0031] ii. Extract the small parallel resistor R N Zero-sequence current of each feeder, zero-sequence current of neutral line, and zero-sequence voltage of busbar within one power frequency cycle before / after being put into operation;

[0032] iii. According to the parallel small resistor R N Before the neutral line is put into operation, the zero-sequence admittance of each feeder to the ground is calculated by connecting a small resistor R in parallel N The ratio of the zero-sequence admittance of each feeder before being put into operation to the zero-sequence admittance of the neutral line, and the small parallel resistor R NAfter the neutral line is put into operation, the zero-sequence admittance of each feeder is calculated by connecting a small resistor R in parallel N The ratio of the zero-sequence admittance of each feeder line to the zero-sequence admittance of the neutral line after being put into operation;

[0033] iv. According to the small parallel resistor obtained in step iii, put it into R N The zero-sequence admittance ratio of each feeder to the neutral line before and after commissioning, and the zero-sequence admittance ratio amplitude multiplication coefficient of each feeder are calculated Among them, Y i ' -n Indicates a small resistor R in parallel with the neutral point N After being put into operation, the ratio of the zero-sequence admittance of each feeder to the neutral line, Y i-n Indicates a small resistor R in parallel with the neutral point N Before being put into operation, the ratio of the zero-sequence to-ground admittance of each feeder relative to the neutral line;

[0034] v. Based on the zero-sequence admittance ratio amplitude multiplication coefficient of each feeder in the active distribution network as the line selection analysis criterion, k i >1 indicates a faulty line, otherwise it is a healthy line.

[0035] In a third aspect, the present invention proposes an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, it implements a single-phase grounding fault line selection method for a flexible grounding active distribution network according to any one of claims 1 to 6.

[0036] In a fourth aspect, the present invention proposes a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements a single-phase grounding fault line selection method for a flexible grounding active distribution network according to any one of claims 1 to 6.

[0037] Compared with the prior art, the present invention has the advantages of:

[0038] The advantage of the present invention is that the method for selecting a line for a single-phase grounding fault in a flexible grounding active distribution network can accurately select the fault line when a permanent single-phase grounding fault occurs in the distribution network, by simply counting the number of distributed power sources grounded via a grid-connected small resistance in each feeder line, when the distributed power grid-connected transformer adopts a mixed grounding method of ungrounded or grid-connected small resistance grounding. The line selection logic is simple and the ability to tolerate transition resistance is strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A topological structure diagram of a 10kV distribution network provided in an embodiment of the present invention;

[0040] Figure 2It is an overall flow chart of a single-phase grounding fault line selection method for a flexible grounding active distribution network of the present invention;

[0041] Figure 3 A module diagram of a single-phase ground fault line selection system for a flexible grounding active distribution network of the present invention;

[0042] Figure 4 It is the zero-sequence current diagram of each feeder and neutral line when a single-phase metallic grounding fault occurs at point f;

[0043] Figure 5 It is the bus zero-sequence voltage when a single-phase metallic grounding fault occurs at point f. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0045] In order to enable those skilled in the art to better understand the present invention, a specific implementation method of the present invention is further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly describe the technical solution of the present invention.

[0046] The present invention proposes a method for selecting a line for a single-phase grounding fault in a flexible grounding active distribution network. The flexible grounding active distribution network fault further includes a busbar fault, a line fault without a distributed power source, and a line fault with a distributed power source. Specifically, a line without a distributed power source is a Class I feeder, a line with a distributed power source and all distributed power sources are not grounded is a Class II feeder, and a line with a distributed power source and all distributed power sources are connected to the grid through a small grounding resistor R DG The grounded line is a Class III feeder, and the distributed power source is not grounded and connected to the distributed power source through a small resistor R DG The line that is grounded at the same time is a Class IV feeder. The various feeders include Class I feeders, Class II feeders, Class III feeders and Class IV feeders, which converge at the busbar.

[0047] like Figure 1 In the topological structure of the 10 kV distribution network system of the embodiment of the present invention shown in FIG. 1 , l 2 , l 3 , l 4 Four feeders, of which feeder l 1 There is only one type of feeder without distributed power supply, feeder l 2 The neutral point of the grid-connected transformer of the upper distributed power supply is not grounded, which is a Class II feeder. 3 The upper distributed power grid-connected transformer is connected to the grid through a small resistor R DG (R DG =10Ω) grounding is Class III feeder, feeder l 4One of the grid-connected transformers in the distributed power supply is not grounded, and the other grid-connected transformer is connected to the ground through a small resistor R DG Grounding is for Class IV feeder, l 1 , l 2 , l 3 , l 4 Gather at the busbar. Set the system to have a permanent metallic single-phase grounding fault at t = 0.2s, and connect a small resistor R in parallel to the neutral point. N (R N =10Ω) is put into operation at t=1.2s.

[0048] definition A small resistor R is connected in parallel with the neutral point N The ratio of the zero-sequence admittance of each feeder i to the zero-sequence admittance of the neutral line before being put into operation; A small resistor R is connected in parallel with the neutral point N The ratio of the zero-sequence admittance of each feeder i to the inductive zero-sequence admittance of the neutral line after being put into operation, is the multiplication factor of the zero-sequence admittance ratio amplitude of each feeder; where Y i ' -n Indicates a small resistor R in parallel with the neutral point N After being put into operation, the ratio of the zero-sequence admittance of each feeder to the neutral line, Y i-n Indicates a small resistor R in parallel with the neutral point N Before commissioning, the ratio of the zero-sequence admittance of each feeder to the neutral line, i represents the feeder number, and i=1,2,3,4, n refers to the system neutral line.

[0049] like Figure 2 As shown in FIG. 1 , a single-phase ground fault line selection method for a flexible grounding active distribution network of the present invention is shown, and the specific implementation process is as follows:

[0050] Step 1: Detect the neutral point zero-sequence current I n Greater than the start value I 0set When the protection starts, if the small resistance R N (10Ω) Before input, the neutral point zero sequence current I n If it returns to normal and the fault disappears, the line selection process ends; otherwise, continue to step 2;

[0051] Step 2: After determining that it is a permanent ground fault, connect a small parallel resistor R N , and simultaneously sample the small parallel resistor R N Zero-sequence current I of each feeder within one power frequency cycle before being put into operation i0 (i represents the feeder type, i = 1, 2, 3, 4), neutral line zero sequence current I 0 and busbar zero-sequence voltage U 0, and the zero-sequence admittance to ground of the neutral line and each feeder is calculated from this, the expression is as follows:

[0052]

[0053] Among them, C i represents the equivalent capacitance to ground of the ith feeder, C 0∑ Represents the sum of the system's equivalent capacitance to ground, x 1 、x 2 、x 3 Respectively represent the feeder line l 1 , l 2 , l 3 The number of distributed power sources connected to the grid with small resistance grounding is included in the above figure. DG Indicates the small grounding resistance of the distributed power grid-connected transformer. Indicates the detuning compensation degree of the arc suppression coil, which is generally -10% to -5%, indicating that the system is in an over-compensation state. j represents an imaginary number, ω represents the angular frequency, and L s Indicates the flexible grounding mode with R N Arc suppression coils connected in parallel.

[0054] Step 3: According to the formula Calculate the small parallel resistor R N Ratio of zero-sequence admittance of each feeder to zero-sequence admittance of neutral line before operation Y 1-n , Y 2-n , Y 3-n , Y 4-n , the expression is as follows:

[0055]

[0056] Step 4: Connect a small resistor R in parallel N Then, the fast Fourier algorithm is used to obtain the zero-sequence current of each outgoing line in one power frequency cycle after a delay of 0.05s. Neutral zero sequence current and bus zero sequence voltage The small parallel resistance R is calculated from this N After being put into operation, the zero-sequence admittance of the neutral line and each feeder to ground is expressed as follows:

[0057]

[0058] Step 5: According to the formula Calculate the small parallel resistor R N The ratio of the zero-sequence admittance of each feeder to the inductive zero-sequence admittance of the neutral line after being put into operation:

[0059]

[0060] Step 6: According to the small parallel resistors obtained in steps 3 and 5, put them into R N Calculate the zero-sequence admittance ratio of each feeder before and after and the neutral line. Calculate the amplitude multiplication factor of the zero-sequence admittance ratio of each feeder.

[0061]

[0062] According to the zero-sequence admittance ratio amplitude multiplication coefficient of Class I feeders, Class II feeders, Class III feeders and Class IV feeders in the active distribution network as the line selection analysis criterion,

[0063] k i >1 indicates a faulty line, otherwise it is a healthy line.

[0064] like Figure 3 As shown, a flexible grounding active distribution network single-phase grounding fault line selection system for executing the above-mentioned flexible grounding active distribution network single-phase grounding fault line selection method is provided. The line selection system includes a protection start detection module 100 and a line selection analysis module 200;

[0065] The protection start detection module 100 is used to detect the neutral point zero sequence current I n , at the neutral point zero sequence current I n Greater than the start value I 0set In the case of, the protection starts;

[0066] The line selection analysis module 200 is used to connect a small resistor R in parallel to the neutral point. N Before the flexible grounding active distribution network is put into use, the fault of the flexible grounding active distribution network has not disappeared. The fault of the flexible grounding active distribution network further includes busbar fault, line fault without distributed power supply, and line fault with distributed power supply. Specifically, the line without distributed power supply is a Class I feeder, and the line containing distributed power supply and all distributed power supply are not grounded is a Class II feeder. The line containing distributed power supply and all distributed power supply are connected to the grid through the small grounding resistance R of the distributed power supply grid transformer. DG The grounded line is a Class III feeder, and the distributed power source is not grounded and connected to the distributed power source through a small resistor R DG The line with grounding is a Class IV feeder. The feeders include Class I feeders, Class II feeders, Class III feeders and Class IV feeders, which are gathered at the busbar and the line selection analysis process begins:

[0067] i. Connect a small resistor R in parallel with the neutral point N ;

[0068] ii. Extract the small parallel resistor R N Zero-sequence current of each feeder, zero-sequence current of neutral line, and zero-sequence voltage of busbar within one power frequency cycle before / after being put into operation;

[0069] iii. According to the parallel small resistor RN Before the neutral line is put into operation, the zero-sequence admittance of each feeder to the ground is calculated by connecting a small resistor R in parallel N The ratio of the zero-sequence admittance of each feeder before being put into operation to the zero-sequence admittance of the neutral line, and the small parallel resistor R N After the neutral line is put into operation, the zero-sequence admittance of each feeder is calculated by connecting a small resistor R in parallel N The ratio of the zero-sequence admittance of each feeder line to the zero-sequence admittance of the neutral line after being put into operation;

[0070] iv. According to the small parallel resistor obtained in step iii, put it into R N The zero-sequence admittance ratio of each feeder to the neutral line before and after commissioning, and the zero-sequence admittance ratio amplitude multiplication coefficient of each feeder are calculated Among them, Y i ' -n Indicates a small resistor R in parallel with the neutral point N After being put into operation, the ratio of the zero-sequence admittance of each feeder to the neutral line, Y i-n Indicates a small resistor R in parallel with the neutral point N Before being put into operation, the ratio of the zero-sequence to-ground admittance of each feeder relative to the neutral line;

[0071] v. Based on the zero-sequence admittance ratio amplitude multiplication coefficient of each feeder in the active distribution network as the line selection analysis criterion, k i >1 indicates a faulty line, otherwise it is a healthy line.

[0072] Combined with Figure 1 The topology structure shown in FIG. 1 and the specific embodiment of the line selection method are described as follows:

[0073] Assumption: Due to the feeder l 1 , l 2 , l 3 The zero-sequence admittance ratio amplitude multiplication factor does not exceed 1, so it is determined that the feeder l 1 , l 2 , l 3 Improve the line;

[0074] And, analyze the feeder l 4 :

[0075] Known R N =R DG =10Ω, then

[0076]

[0077] Since the maximum ground capacitance current of a single line in a 10kV distribution system does not exceed 50A, the ground capacitance current of the system is generally not greater than 200A. l4 ≤2.9mS,ωC 0Σ ≤11.6mS, -vωC0Σ ≤1.16mS. Neutral point grounding resistance R N is 10Ω, which is commonly used in engineering practice, then ω(C l4 -C 0Σ )≤4.06mS. And according to the premise, x l1 +x l2 +x l3 ≥0 and rounded. Therefore:

[0078]

[0079] Obviously, all feeders in the active distribution network except the fault line 1 , l 2 , l 3 The number of DGs in small and medium resistance grounding mode (x 1 +x 2 +x 3 ≥0) affects k 4 The value also affects the line selection criteria. For example:

[0080]

[0081] In this example, x 1 =x 2 =0,x 3 =1, there are k 4 ≥1.99, i.e. l 4 The zero-sequence admittance ratio amplitude multiplication factor of the feeder exceeds 1, which satisfies the line selection criterion. 4 For fault line.

[0082] In addition, based on similar inventive concepts, an embodiment of the present invention further provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the above method when executing the computer program.

[0083] In addition, based on similar inventive concepts, an embodiment of the present invention further provides a non-transitory computer-readable storage medium on which a computer program is stored, and the computer program implements the above method when executed by a processor.

[0084] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0085] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0086] For those skilled in the art, improvements and changes can be made according to the above invention content. Any modification, improvement and change made on the basis of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for selecting a single-phase ground fault line in a flexible grounding active distribution network, characterized in that: The line selection method includes: Detected neutral point zero sequence current I n , at the neutral point zero sequence current I n Greater than the start value I 0set In the case of, the protection starts; When a small resistor R is connected in parallel to the neutral point N Before the flexible grounding active distribution network is put into use, the fault of the flexible grounding active distribution network has not disappeared. The fault of the flexible grounding active distribution network further includes busbar fault, line fault without distributed power supply, and line fault with distributed power supply. Specifically, the line without distributed power supply is a Class I feeder, and the line containing distributed power supply and all distributed power supply are not grounded is a Class II feeder. The line containing distributed power supply and all distributed power supply are connected to the grid through the small grounding resistance R of the distributed power supply grid transformer. DG The grounded line is a Class III feeder, and the distributed power source is not grounded and connected to the distributed power source through a small resistor R DG The line with grounding is a Class IV feeder. The feeders include Class I feeders, Class II feeders, Class III feeders and Class IV feeders, which are gathered at the busbar and the line selection analysis process begins: i. Connect a small resistor R in parallel with the neutral point N ; ii. Extract the small parallel resistor R N Zero-sequence current of each feeder, zero-sequence current of neutral line, and zero-sequence voltage of busbar within one power frequency cycle before / after being put into operation; iii. According to the parallel small resistor R N Before the neutral line is put into operation, the zero-sequence admittance of each feeder to the ground is calculated by connecting a small resistor R in parallel N The ratio of the zero-sequence admittance of each feeder before being put into operation to the zero-sequence admittance of the neutral line, and the small parallel resistor R N After the neutral line is put into operation, the zero-sequence admittance of each feeder is calculated by connecting a small resistor R in parallel N The ratio of the zero-sequence admittance of each feeder line to the zero-sequence admittance of the neutral line after being put into operation; iv. According to the small parallel resistor obtained in step iii, put it into R N The zero-sequence admittance ratio of each feeder to the neutral line before and after commissioning, and the zero-sequence admittance ratio amplitude multiplication coefficient of each feeder are calculated Among them, Y i ' -n Indicates a small resistor R in parallel with the neutral point N After being put into operation, the ratio of the zero-sequence admittance of each feeder to the neutral line, Y i-n Indicates a small resistor R in parallel with the neutral point N Before being put into operation, the ratio of the zero-sequence to-ground admittance of each feeder relative to the neutral line; v. Based on the zero-sequence admittance ratio amplitude multiplication coefficient of each feeder in the active distribution network as the line selection analysis criterion, k i >1 indicates a faulty line, otherwise it is a healthy line.

2. A method for selecting a single-phase ground fault line in a flexible grounding active distribution network as claimed in claim 1, characterized in that: In step iii, the parallel small resistor R N Zero-sequence admittance Y of the neutral line before switching on n The calculation method of the zero-sequence ground admittance Y1, Y2, Y3, and Y4 of each feeder is as follows: in, Represents the zero-sequence current of each feeder, Indicates the neutral line zero sequence current, represents the busbar zero-sequence voltage, C1, C2, C3, C4 represent the equivalent capacitance to ground of each feeder, C 0∑ represents the sum of the equivalent ground capacitance of the system, and x1, x2, and x3 represent the capacitance of the feeder lines l1, l2, and l3 respectively through a small resistor R DG The number of grounded distributed generation sources, R DG represents the small grounding resistance of the distributed power grid-connected transformer, v represents the detuning compensation degree of the arc suppression coil, j represents an imaginary number, ω represents the angular frequency, and L s Indicates the flexible grounding mode with R N Arc suppression coils connected in parallel.

3. A method for selecting a single-phase ground fault line in a flexible grounding active distribution network as claimed in claim 1, characterized in that: In step iii, the parallel small resistor R N The ratio of the zero-sequence admittance of each feeder before operation to the zero-sequence admittance of the neutral line Y 1-n , Y 2-n , Y 3-n , Y 4-n The calculation method is as follows: Among them, Y n Represents a small parallel resistor R N The zero-sequence admittance to ground of the neutral line before being put into operation.

4. A method for selecting a single-phase ground fault line in a flexible grounding active distribution network as claimed in claim 1, characterized in that: In step iii, the parallel small resistor R N Zero-sequence admittance Y of the neutral line after switching on n The calculation method of the zero-sequence admittance to ground Y1′, Y2′, Y3′, and Y4′ of each feeder is as follows:

5. A method for selecting a single-phase ground fault line in a flexible grounding active distribution network as claimed in claim 1, characterized in that: In step iii, the parallel small resistor R N The ratio of the zero-sequence admittance of each feeder to the inductive zero-sequence admittance of the neutral line after being put into operation is Y1′ -n , Y2′ -n , Y3′ -n , Y4′ -n The expression is as follows:

6. A method for selecting a single-phase ground fault line in a flexible grounding active distribution network according to claim 1, characterized in that: In step iv, the expressions of the zero-sequence admittance ratio amplitude multiplication coefficients k1, k2, k3, and k4 of each feeder are as follows:

7. A flexible grounding active distribution network single-phase grounding fault system implementing a flexible grounding active distribution network single-phase grounding fault line selection method as claimed in any one of claims 1 to 6, characterized in that: The line selection system includes a protection start detection module and a line selection analysis module; The protection start detection module is used to detect the neutral point zero sequence current I n , at the neutral point zero sequence current I n Greater than the start value I 0set In the case of, the protection starts; The line selection analysis module is used to connect a small resistor R in parallel with the neutral point. N Before the flexible grounding active distribution network is put into use, the fault of the flexible grounding active distribution network has not disappeared. The fault of the flexible grounding active distribution network further includes busbar fault, line fault without distributed power supply, and line fault with distributed power supply. Specifically, the line without distributed power supply is a Class I feeder, and the line containing distributed power supply and all distributed power supply are not grounded is a Class II feeder. The line containing distributed power supply and all distributed power supply are connected to the grid through the small grounding resistance R of the distributed power supply grid transformer. DG The grounded line is a Class III feeder, and the distributed power source is not grounded and connected to the distributed power source through a small resistor R DG The line with grounding is a Class IV feeder. The feeders include Class I feeders, Class II feeders, Class III feeders and Class IV feeders, which are gathered at the busbar and the line selection analysis process begins: i. Connect a small resistor R in parallel with the neutral point N ; ii. Extract the small parallel resistor R N Zero-sequence current of each feeder, zero-sequence current of neutral line, and zero-sequence voltage of busbar within one power frequency cycle before / after being put into operation; iii. According to the parallel small resistor R N Before the neutral line is put into operation, the zero-sequence admittance of each feeder to the ground is calculated by connecting a small resistor R in parallel N The ratio of the zero-sequence admittance of each feeder before being put into operation to the zero-sequence admittance of the neutral line, and the small parallel resistor R N After the neutral line is put into operation, the zero-sequence admittance of each feeder is calculated by connecting a small resistor R in parallel N The ratio of the zero-sequence admittance of each feeder line to the zero-sequence admittance of the neutral line after being put into operation; iv. According to the small parallel resistor obtained in step iii, put it into R N The zero-sequence admittance ratio of each feeder to the neutral line before and after commissioning, and the zero-sequence admittance ratio amplitude multiplication coefficient of each feeder are calculated Among them, Y i ' -n Indicates a small resistor R in parallel with the neutral point N After being put into operation, the ratio of the zero-sequence admittance of each feeder to the neutral line, Y i-n Indicates a small resistor R in parallel with the neutral point N Before being put into operation, the ratio of the zero-sequence to-ground admittance of each feeder relative to the neutral line; v. Based on the zero-sequence admittance ratio amplitude multiplication coefficient of each feeder in the active distribution network as the line selection analysis criterion, k i >1 indicates a faulty line, otherwise it is a healthy line.

8. An electronic device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, a method for selecting a single-phase grounding fault line in a flexible grounding active distribution network according to any one of claims 1 to 6 is implemented.

9. A non-transitory computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed by a processor, a method for selecting a single-phase grounding fault line in a flexible grounding active distribution network according to any one of claims 1 to 6 is implemented.

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