A method and system for selecting fault lines in a flexible grounding system

Abstract

The present invention discloses a flexible grounding system fault line selection method system, the method comprising: after a grounding fault occurs in the distribution network, calculating the zero-sequence current amplitude ratio ρ between the neutral point and each outgoing line in the arc suppression coil compensation stage n‑j , and the zero-sequence current amplitude ratio ρ′ between the neutral point and each outgoing line after the neutral point parallel small resistance is put into operation n‑j , where j=1,2...N, N is the number of outgoing lines of the distribution network; the fault line is judged according to the variation characteristics of the zero-sequence current amplitude ratio. The present invention is simple to implement, reliable and highly applicable.

Description

Technical Field

[0001] The invention belongs to the technical field of medium voltage distribution network relay protection, and relates to a fault line selection method and system for a flexible grounding system. Background Art

[0002] my country's 10-35kV medium-voltage distribution network mainly adopts the neutral point ungrounded or resonant grounding operation mode. The resonant grounding method can effectively extinguish the instantaneous arc and prevent the arc from reigniting, but the overvoltage level after the fault is high and the fault line selection is difficult. In order to quickly handle the grounding fault, many urban distribution networks adopt the neutral point through a small resistor grounding method. This method can quickly remove the fault and suppress the overvoltage, but the protection tripping rate is high and the neutral point equipment is easily damaged. The flexible grounding method of arc suppression coil and small resistor has the advantages of both the resonant grounding method and the grounding method through a small resistor. It has developed rapidly and has been promoted and applied in many places in my country.

[0003] At present, most flexible grounding systems still use the zero-sequence overcurrent protection used in low-resistance grounding systems to deal with single-phase grounding faults. The zero-sequence overcurrent protection is set according to the maximum capacitive current of the line, and the set value is generally 40 to 60A, and the maximum grounding resistance can only be detected at around 140Ω. However, the surrounding environment of the distribution network is complex and the overhead distance of the line is low. High-resistance grounding faults caused by direct contact between exposed live wires and non-ideal conductors such as cement, sand, and grass often occur. The zero-sequence current may be less than the set value, causing the protection to fail to operate. Therefore, it is an urgent problem for technical researchers in this field to study the line selection method for single-phase high-resistance grounding faults in flexible grounding systems and accurately identify and cut off the faulty feeder. Summary of the invention

[0004] In order to solve the problem of high-resistance grounding fault protection refusing to operate in a flexible grounding system, the present invention provides a flexible grounding system fault line selection method and system, which are simple to implement, reliable and highly applicable.

[0005] The technical solution provided by the present invention is:

[0006] A flexible grounding system fault line selection method is used to calculate the zero-sequence current amplitude ratio ρ between the neutral point and each outgoing line in the arc suppression coil compensation stage after a ground fault occurs in the distribution network. n-j , and the zero-sequence current amplitude ratio ρ′ between the neutral point and each outgoing line after the neutral point parallel small resistance is put into operation n-j , where j is the number of the distribution network outgoing line, j = 1, 2, ..., N, N is the number of distribution network outgoing lines; the fault line is determined according to the change characteristics of the zero-sequence current amplitude ratio.

[0007] Furthermore, if the neutral point zero-sequence current amplitude suddenly changes, that is, the difference between the neutral point zero-sequence current amplitudes of the previous and next sampling points exceeds the set threshold value I set ;, it is determined that a ground fault occurs in the distribution network.

[0008] Furthermore, if the neutral point zero-sequence current amplitude suddenly changes and the fault still exists after a period of time (the difference Δ3I between the current sampling point and the neutral point zero-sequence current amplitude before the fault occurs) n Exceeding the set threshold I set ), a small resistor is connected in parallel to the neutral point to avoid interference from instantaneous ground faults.

[0009] Furthermore, the period of time is 2.0s to 5.0s.

[0010] Furthermore, the method for determining the fault line according to the change of the zero-sequence current amplitude ratio is:

[0011] First, combining ρ n-j and ρ′ n-j Calculate the multiplication factor of each outgoing line, that is:

[0012] λ j =ρ′ n-j / ρ n-j

[0013] Among them, λ j It represents the multiplication factor of the jth outgoing line of the distribution network;

[0014] Then, we will satisfy λ j <λ set The outgoing line is judged as a faulty line, otherwise it is judged as a sound line.

[0015] Furthermore, after the neutral point is connected in parallel with a small resistor, for the line whose zero-sequence current amplitude is less than the minimum working current of the primary side of the zero-sequence current transformer, ρ n-j Indirect solution of the ratio of the neutral point and line zero-sequence current amplitude ρ′ after the small resistor is put into operation n-j For lines where the zero-sequence current amplitude is greater than or equal to the minimum primary operating current of the zero-sequence current transformer, the direct measurement method is used to calculate ρ′ n-j .

[0016] Further, the use of n-j Indirect solution of the ratio of the neutral point and line zero-sequence current amplitude ρ′ after the small resistor is put into operation n-j The formula is:

[0017]

[0018] Among them, R n A small resistor is connected in parallel with the neutral point, X L It is the zero-sequence equivalent reactance of the arc suppression coil.

[0019] Furthermore, the direct measurement method uses a zero-sequence current transformer to collect the zero-sequence current of the neutral point of the distribution network and each outgoing line, and calculates the zero-sequence current amplitude of the neutral point of the distribution network and each outgoing line.

[0020] Furthermore, the minimum operating current of the primary side of the zero-sequence current transformer is 1A.

[0021] Furthermore, the zero-sequence current amplitude is three times the amplitude of the steady-state power frequency component of the zero-sequence current measured by the zero-sequence current transformer; since the zero-sequence current transformer collects three times the zero-sequence current, directly taking three times the zero-sequence current here can reduce the amount of calculation and shorten the fault processing time.

[0022] A flexible grounding system fault line selection system, comprising a data acquisition module and a control module;

[0023] The data acquisition module is used to collect the zero-sequence current of the neutral point of the distribution network and each outgoing line;

[0024] The control module calculates the zero-sequence current amplitude ratio between the neutral point and each outgoing line during the arc suppression coil compensation stage and the zero-sequence current amplitude ratio between the neutral point and each outgoing line after a small resistor is connected in parallel to the neutral point based on the data obtained by the data acquisition module after a ground fault occurs in the distribution network, and determines the faulty line according to the changing characteristics of the zero-sequence current amplitude ratio.

[0025] Furthermore, the data acquisition module is a zero-sequence current transformer, including zero-sequence current transformers installed on the neutral line and each outgoing line of the distribution network, which are used to collect zero-sequence currents of the neutral point and each outgoing line respectively.

[0026] Furthermore, the workflow of the control model to implement fault line judgment refers to the various steps in the above-mentioned flexible grounding system fault line selection method.

[0027] The beneficial effects achieved by the present invention are:

[0028] (1) The present invention selects the fault line only based on the zero-sequence current amplitude of the neutral point and the outgoing line of the distribution network before and after the small parallel resistor is put into operation. There is no need to introduce zero-sequence voltage and it is not affected by the reverse polarity of the zero-sequence current transformer and the disconnection of the zero-sequence voltage transformer (PT). (2) Considering that the zero-sequence current of some healthy lines may be relatively weak after the small resistor is put into operation, and the zero-sequence current transformer has accuracy limitations (that is, the minimum working current of the primary side of the zero-sequence current transformer can only reach a specific value, and the zero-sequence current transformer can accurately measure it), it is impossible to accurately measure certain weak currents. The present invention proposes an indirect solution method for the zero-sequence current amplitude ratio of the neutral point and the outgoing line after the small resistor is put into operation. For the zero-sequence current amplitude For lines with a current smaller than the minimum working current of the primary side of the zero-sequence current transformer, there is no need to directly measure the weak zero-sequence current of some healthy lines after the small resistor is put into operation through the zero-sequence current transformer. Instead, the zero-sequence current amplitude of the neutral point and the outgoing line after the small resistor is put into operation is indirectly solved by the zero-sequence current amplitude ratio of the neutral point and the outgoing line before the small resistor is put into operation in parallel, thereby avoiding the problem of calculation error caused by the inability of the zero-sequence current transformer to accurately measure certain weak currents; (3) The line selection method proposed in the present invention is theoretically not affected by the transition resistance. Even considering the accuracy limitation of the zero-sequence current transformer, it can be fully applicable to the ground fault line selection with a transition resistance within 3000Ω; (4) The principle is simple, reliable and highly applicable. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Attached Figure 1 Schematic diagram of a single-phase grounding fault in a flexible grounding system according to an embodiment of the present invention.

[0030] Attached Figure 2 It is a zero-sequence equivalent network for single-phase grounding fault in the flexible grounding system in the embodiment of the present invention.

[0031] Attached Figure 3 It is a line selection flow chart of an embodiment of the present invention.

[0032] Attached Figure 4 Schematic diagram of a flexible grounding system simulation model according to an embodiment of the present invention.

[0033] Attached Figure 5 1 is a line selection result diagram when the transition resistance of the embodiment of the present invention is 200Ω, Figure 5 (a) is the ratio of the neutral point to each line zero-sequence current amplitude, Figure 5 (b) is the multiplication factor. DETAILED DESCRIPTION

[0034] The present invention is described below in conjunction with the accompanying drawings and simulation examples.

[0035] Embodiment 1:

[0036] The technical solution provided by this embodiment is:

[0037] 1) The neutral point zero-sequence current transformer (zero-sequence CT) is used to sample the neutral point zero-sequence current of the distribution network in real time and calculate the neutral point zero-sequence current amplitude 3I n , if the neutral point zero-sequence current amplitude changes suddenly, that is, the difference between the neutral point zero-sequence current amplitudes of the previous and next sampling points Δ3I n Exceeding the set threshold I set ;, it is determined that a ground fault occurs in the distribution network;

[0038] 2) In the arc suppression coil compensation stage, the zero-sequence current transformer is used to collect the zero-sequence current of the neutral point and each outgoing line of the distribution network, and the zero-sequence current amplitude of the neutral point and each outgoing line of the distribution network is calculated, which is recorded as 3I n and 3I 0j ,j=1,2…N, where 3I 0j It represents the zero-sequence current amplitude of the jth outgoing line of the distribution network, N is the number of outgoing lines of the distribution network, and then calculates the zero-sequence current amplitude ratio between the neutral point and each outgoing line, which is recorded as ρ n-j ,j=1,2…N, where ρ n-j It represents the zero-sequence current amplitude ratio between the neutral point of the distribution network and the jth outgoing line;

[0039] 3) Connect a small resistor in parallel to the neutral point, and calculate the zero-sequence current amplitude ratio between the neutral point and each outgoing line after the small resistor is connected, denoted as ρ′ n-j ,j=1,2…N, where ρ′ n-j It represents the zero-sequence current amplitude ratio between the neutral point of the distribution network and the jth outgoing line;

[0040] 4) Combined with ρ n-j and ρ′ n-j Calculate the multiplication factor of each outgoing line, i.e. λ j =ρ′ n-j / ρ n-j ,j=1,2,…,N,where λ j represents the multiplication factor of the jth outgoing line of the distribution network, satisfying λ j <λ set The outgoing line is judged as a faulty line, otherwise it is judged as a sound line.

[0041] The line selection method proposed in the above embodiment 1 is applied to the attached Figure 1 The flexible grounding system shown in the attached Figure 1 As shown, the distribution network contains N outgoing lines (see Figure 1 The lines L1 to L N ), assuming that the transition resistance of the Nth outgoing line in the figure is R f Single-phase ground fault. P is the arc suppression coil inductance, and the arc suppression coil is in an over-compensated state. nis a small resistor connected in parallel with the neutral point. According to the actual operation experience of the flexible grounding system, this embodiment sets R n =10Ω. S is a small parallel resistance input switch. When S is disconnected, the system is in a resonant grounding state. When S is closed, the system is in an arc suppression coil and small resistance grounding state.

[0042] Will attach Figure 1 Simplified to Figure 2 The single-phase ground fault zero-sequence equivalent network of the flexible grounding system shown in the figure is C 0k (k=1,2,…,N-1) is the zero-sequence capacitance to ground of a sound line, It is the zero-sequence current at the outlet of a healthy line. C 0N is the zero-sequence capacitance of the fault line to ground, is the zero-sequence current at the fault line outlet. L =3ωL P is the zero-sequence equivalent reactance of the arc suppression coil, is the neutral point zero sequence current. is the bus zero-sequence voltage, It is a virtual power supply at the fault point.

[0043] Before connecting a small parallel resistor: According to Kirchhoff's current law, the zero-sequence current of the line should be Fault line zero sequence current Neutral point zero sequence current satisfy:

[0044]

[0045] Where: j is the imaginary unit, ω is the angular frequency, C 0∑ is the sum of all line-to-ground capacitances, v is the system detuning degree, which is generally -10% to -5%, and satisfies 1 / (3ωL P )=(1-v)ωC 0∑ .

[0046] Before the small parallel resistor is put into use: the ratio of the zero-sequence current amplitude between the neutral point and the sound line ρ n-k , the ratio of the zero-sequence current amplitude between the neutral point and the fault line ρ n-f satisfy:

[0047]

[0048] After the small parallel resistor is put into use: According to Kirchhoff's current law, the zero-sequence current of the line is improved Fault line zero sequence current Neutral point zero sequence current satisfy:

[0049]

[0050] After the small parallel resistor is put into use: the amplitude ratio of the zero-sequence current at the neutral point and the sound line ρ′ n-k , the ratio of the zero-sequence current amplitude between the neutral point and the fault line ρ′ n-f satisfy:

[0051]

[0052] In order to quantitatively characterize the change characteristics of the neutral point and line zero-sequence current amplitude ratio before and after the small parallel resistor is put into the flexible grounding system, and to construct the line selection criterion based on this, the multiplication coefficient λ is introduced j =ρ′ n-j / ρ n-j (j=1,2,…,N).

[0053] According to equations (2) and (4), the robust line multiplication factor λ can be obtained: k for:

[0054]

[0055] From formula (5), we can know that the system ground capacitance current is 200A (C 0∑ Maximum), when the overcompensation is 10% (v minimum), the multiplication factor of the healthy line is the smallest, which is 2.81. In other cases, the multiplication factor is larger.

[0056] The above analysis shows that: before and after the small parallel resistor is put into use, the ratio of the zero-sequence current amplitude of the neutral point and the sound line increases. At the same time, the multiplication factor of the sound line decreases with the increase of the distribution network scale and overcompensation degree.

[0057] According to equations (2) and (4), the fault line multiplication factor λ can be obtained: f for:

[0058]

[0059] Analysis (6) shows that when C 0N -vC 0∑ =(1-v)C 0∑ That is, when there is only one outgoing line in the distribution network, the multiplication factor of the fault line is the largest, which is 1, and the multiplication factor is smaller in other cases.

[0060] The above analysis shows that: before and after the small parallel resistor is put into use, the ratio of the zero-sequence current amplitude between the neutral point and the fault line decreases. At the same time, the multiplication factor of the fault line is related to the scale of the distribution network, the degree of overcompensation and the capacitance of the fault line to the ground.

[0061] In order to improve the reliability of the line selection method, in this embodiment, the fault line selection criterion threshold value λ set Set to

[0062]

[0063] Therefore, the fault line selection criterion is: when the line multiplication factor satisfies λ j <λ set When λ j >λ set When , it is judged as a healthy line.

[0064] Taking the "Technical Solution for the Integration of Primary and Secondary Power Distribution Equipment of the State Grid Corporation" as a reference, the minimum operating current of the primary side of the existing zero-sequence current transformer is 1A (the minimum current that can be accurately measured). When a small resistor is connected in parallel to the neutral point, especially when a high transition resistance grounding fault occurs, the bus zero-sequence voltage will be greatly reduced, resulting in a zero-sequence current amplitude of 3I' on some healthy lines. 0k If it fails to reach 1A, the zero-sequence current transformer will not be able to accurately collect the zero-sequence current of this part of the healthy line, which will lead to ρ′ n-k The calculation accuracy is insufficient. For this reason, a ρ′ is used n-k The indirect solution method does not require direct measurement of the weak zero-sequence current of some healthy lines after the small resistor is put into operation.

[0065] Before the parallel small resistance is put into use, the neutral point and line zero sequence current can be directly measured, so that ρ can be accurately solved. n-k , according to formula (2)ρ n-k In the solution expression, the sound line capacitance to ground C 0k satisfy:

[0066]

[0067] Substituting equations (2) and (8) into equation (4), ρ′ n-k In the solution expression of , simplify it, then ρ′ n-k satisfy:

[0068]

[0069] According to formula (9), for a healthy line where the amplitude of the zero-sequence current is less than 1A after the small resistor is put into operation, the value of n-k To indirectly solve ρ′ n-k , while for lines with zero-sequence current amplitude greater than 1A, it is directly obtained through the zero-sequence current transformer, and then ρ′ is solved n-k .

[0070] At the same time, since the zero-sequence current of the fault line and the zero-sequence current of the neutral point are much larger than the zero-sequence current of the healthy line, when the transition resistance R f =3000Ω high resistance ground fault, 3I′ n ≈3I′ 0f≈2A, and the smaller the transition resistance, the larger the zero-sequence current amplitude of the neutral point and each line; therefore, for the case where the transition resistance is within 3kΩ, the zero-sequence current amplitude of the fault line and the neutral point must be greater than 2A, and the corresponding zero-sequence current amplitude will not be less than 1A. The zero-sequence current of the fault line and the neutral point can be accurately collected by the zero-sequence current transformer, and the zero-sequence current amplitude ratio of the neutral point and the fault line can be directly calculated. Therefore, the proposed line selection method is fully applicable to high-resistance grounding faults with a transition resistance of less than 3000Ω, and even for high-resistance grounding faults with a transition resistance slightly greater than 3000Ω, as long as the zero-sequence current amplitude of the fault line and the neutral point is greater than 1A, the line selection method proposed by the present invention can also be applied.

[0071] Simulation example:

[0072] Attached Figure 4 This is a schematic diagram of a simulation model of a flexible grounding system according to an embodiment of the present invention. The system includes two pure cable lines (L1, L4) and two overhead-cable hybrid lines (L2, L3). The length of each line is marked in the figure. P The overcompensation is 8%. The load at the end of each line is (400+j20)Ω, and the model is a three-phase symmetrical linear load.

[0073] In the embodiment, the line parameters are set to be the same, and the specific line parameters are:

[0074] Cable:

[0075] The positive sequence parameters are: R1 = 0.27Ω / km, L1 = 0.255mH / km, C1 = 0.376μF / km;

[0076] The zero-sequence parameters are: R0=2.7Ω / km, L0=1.109mH / km, C0=0.276μF / km.

[0077] Overhead lines:

[0078] The positive sequence parameters are: R1 = 0.17Ω / km, L1 = 1.017mH / km, C1 = 0.115μF / km;

[0079] The zero-sequence parameters are: R0=0.32Ω / km, L0=3.56mH / km, C0=0.0062μF / km.

[0080] The cable line L4 is set to have a single-phase grounding fault with a transition resistance of 200Ω at 0.06s. The fault point is 4km away from the fault line exit. The parallel small resistor is put into use 1.0s after the fault occurs to avoid instantaneous faults. Figure 5 This is a diagram of line selection results when the transition resistance is 200Ω in an embodiment of the present invention.

[0081] Attached Figure 5 (a) is the ratio of the neutral point to the zero-sequence current amplitude of each line. Figure 5 As shown in (a), before and after the small parallel resistor is put into operation, the amplitude ratio of the zero-sequence current of the neutral point and the sound line increases, while the amplitude ratio of the zero-sequence current of the neutral point and the fault line decreases. The simulation results are consistent with the theoretical analysis.

[0082] Attached Figure 5 (b) is the multiplication factor calculated by the ratio of the neutral point to the line zero-sequence current amplitude 2.5 power frequency cycles (0.9s to 0.95s) before the parallel small resistor is put into operation and 2.5 power frequency cycles (1.1s to 1.15s) after the parallel small resistor is put into operation. Figure 5 As shown in (b), the multiplication coefficient of the faulty line L4 is 0.306, and the multiplication coefficients of the other sound lines are 7.467. The multiplication coefficient of the faulty line is less than the threshold value 1.91 set by the line selection criterion, and the multiplication coefficient of the sound line is greater than the threshold value 1.91 set by the line selection criterion, which can accurately identify the faulty line L4.

[0083] A large number of simulations were carried out on single-phase grounding faults with different transition resistances, which verified that before and after the small resistance was put into use, the zero-sequence current amplitude ratio between the neutral point and the sound line increased, while the zero-sequence current amplitude ratio between the neutral point and the faulty line decreased. At the same time, the line multiplication factor was not affected by the transition resistance, and the simulation results were consistent with the theoretical analysis.

[0084] A large number of simulations were carried out on single-phase grounding faults with different fault distances, which verified that before and after the small resistor was put into operation, the zero-sequence current amplitude ratio between the neutral point and the sound line increased, while the zero-sequence current amplitude ratio between the neutral point and the faulty line decreased. At the same time, the line multiplication factor was not affected by the fault distance, and the simulation results were consistent with the theoretical analysis.

[0085] In order to verify the influence of different transition resistance grounding on the line selection results of this method, the cable line L4 is taken at a distance of 4 km from the fault point to the fault line exit, and single-phase grounding faults with transition resistances of 5Ω, 200Ω, 500Ω, 1000Ω, 2000Ω, and 3000Ω occur respectively. The line selection results are shown in Table 1.

[0086] In order to verify the influence of different fault distances to grounding on the line selection results of this method, when the transition resistance of cable line L1 is 3000Ω, single-phase grounding faults with fault points at distances of 0km, 4km, 8km, 12km, 16km, and 20km from the fault line exit occur respectively, and the line selection results are shown in Table 2.

[0087] Table 1 Line selection results under different transition resistances

[0088]

[0089] Table 2 Line selection results at different fault distances

[0090]

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for selecting a fault line in a flexible grounding system, characterized in that: After a ground fault occurs in the distribution network, the zero-sequence current amplitude ratio ρ between the neutral point and each outgoing line in the arc suppression coil compensation stage is calculated. n-j , and the zero-sequence current amplitude ratio between the neutral point and each outgoing line after the neutral point parallel small resistance is put into operation ρ n ' -j , where j = 1, 2, ..., N, N is the number of outgoing lines of the distribution network; After the neutral point parallel small resistance is put into use, for the line whose zero-sequence current amplitude is less than the minimum working current of the primary side of the zero-sequence current transformer, use ρ n-j Indirect solution of ρ n ' -j , the formula is: Where R n A small resistor is connected in parallel with the neutral point, X L is the zero-sequence equivalent reactance of the arc suppression coil; for the line whose zero-sequence current amplitude is greater than or equal to the minimum working current of the primary side of the zero-sequence current transformer, the direct measurement method is used to calculate ρ n ' -j； The fault line is judged according to the change characteristics of the zero-sequence current amplitude ratio, including: First, combining ρ n-j and ρ n ' -j Calculate the multiplication factor of each outgoing line, that is: l j =ρ n ′ -j / r n-j Among them, λ j It represents the multiplication factor of the jth outgoing line of the distribution network; Then, we will satisfy λ j <λ set The outgoing line is judged as a faulty line, otherwise it is judged as a sound line.

2. The method for selecting a fault line in a flexible grounding system according to claim 1, characterized in that: If the neutral point zero-sequence current amplitude suddenly changes, that is, the difference between the neutral point zero-sequence current amplitudes obtained by the previous and next sampling points exceeds the set threshold value I set ; It is determined that a ground fault occurs in the distribution network.

3. The method for selecting a fault line in a flexible grounding system according to claim 1, characterized in that: If the amplitude of the zero-sequence current at the neutral point suddenly changes and the fault still exists after a period of time, a small resistor is connected in parallel with the neutral point.

4. The method for selecting a fault line in a flexible grounding system according to claim 3, characterized in that: The period of time is 2.0s to 5.0s.

5. The method for selecting a fault line in a flexible grounding system according to claim 1, characterized in that: The direct measurement method uses a zero-sequence current transformer to collect the zero-sequence current of the neutral point of the distribution network and each outgoing line, and calculates the zero-sequence current amplitude of the neutral point of the distribution network and each outgoing line.

6. The method for selecting a fault line in a flexible grounding system according to claim 1, characterized in that: The zero-sequence current is three times the steady-state power frequency component of the zero-sequence current measured by the zero-sequence current transformer.

7. A flexible grounding system fault line selection system, characterized in that: Used to implement the method according to any one of claims 1 to 6, comprising a data acquisition module and a control module; The data acquisition module is used to collect the zero-sequence current of the neutral point of the distribution network and each outgoing line; The control module calculates the zero-sequence current amplitude ratio between the neutral point and each outgoing line during the arc suppression coil compensation stage and the zero-sequence current amplitude ratio between the neutral point and each outgoing line after a small resistor is connected in parallel to the neutral point based on the data obtained by the data acquisition module after a ground fault occurs in the distribution network, and determines the faulty line according to the changing characteristics of the zero-sequence current amplitude ratio.

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