Power distribution network single-phase earth fault line selection method based on hybrid arc extinction process

Abstract

The invention discloses a power distribution network single-phase earth fault line selection method based on a hybrid arc extinction process. And the waveform change characteristics of the transient-steady-state zero-sequence voltage and the transient-steady-state zero-sequence current of each line in the hybrid arc extinction process are comprehensively utilized to realize the preliminary identification, re-determination and line selection result verification of the fault line. According to the method, the grounding fault line selection is accurate, meanwhile, the rapid input of the arc extinguishing device can be ensured, and the problem that the fault information of a traditional fault line selection method is influenced by arc extinguishing is solved to a great extent. The method is good in fault line selection safety and high in reliability.

Description

Technical Field

[0001] The present invention relates to the field of single-phase grounding fault detection and protection of distribution networks, and specifically to a method for selecting a single-phase grounding fault line in a distribution network based on a hybrid arc extinguishing process. Background Art

[0002] As the "last mile" for electric energy to enter thousands of households, the distribution network is an important infrastructure for serving people's livelihood. Arc fault elimination and fault detection are important means to maximize the protection of people's lives and property safety. Most medium-voltage distribution networks in China adopt non-effective grounding methods. Single-phase grounding faults account for more than 80% of the total faults in the distribution network, and the grounding current is mainly capacitive current. After a single-phase grounding fault occurs in a small current grounding system, it can still operate with the fault for a period of time. However, due to the increasing complexity of the distribution network structure and the continuous increase of the system capacitive current compared with before, if there is a fault arc that cannot extinguish itself for a long time at the fault point, this may cause the expansion of the fault range, such as multi-point grounding, phase-to-phase short circuit, etc., and even seriously threaten personal safety and cause fire accidents. For example, the intermediate joint of a 35 kV cable in Xi'an exploded and caught fire, causing two substations to burn down, nearly 90,000 households to lose power, and the Samsung Xi'an semiconductor factory to lose about 10% of its productivity; after a 10 kV reserved diversion line in Xichang City, Liangshan Prefecture, Sichuan Province was grounded, arc extinguishing measures were not taken in time and the fault was not isolated, resulting in the fault point discharging continuously for 16 minutes, causing dozens of casualties, more than 700 hectares of forest being damaged, and direct economic losses of nearly 100 million yuan.

[0003] Distribution network grounding fault detection is an important means to minimize the fault scope, ensure the safety of distribution equipment, provide guidance for fault troubleshooting, and improve the efficiency of fault repair and power supply reliability. In recent years, the line selection technology for single-phase grounding faults (especially high-resistance grounding faults) has been the focus of distribution network fault protection. Existing fault line selection technologies can be mainly divided into passive line selection methods and active line selection methods. Among them, passive line selection methods can be further divided into steady-state and transient states according to signal characteristics. For single-phase grounding fault detection, the research of domestic and foreign experts and scholars mainly focuses on the fault stage before the arc suppression measures are taken, using the transient and steady-state electrical information caused by the fault or constructing line selection criteria by injecting non-arc suppression signals. The research on fault detection technology during the rapid input process of the arc suppression device after the fault occurs is relatively lacking, so it cannot meet the current demand for rapid arc suppression. On the other hand, the existing detection methods have poor tolerance to transition resistance. Especially, the transient and steady-state signals generated by high-resistance grounding faults are very weak, which is not conducive to signal acquisition and analysis. At the same time, the injection of non-arc suppression signals is not conducive to the safe operation of the power grid and may affect the self-extinguishing of the grounding arc, resulting in problems such as instantaneous faults developing into permanent faults. Through research, it is found that after the arc suppression device aimed at extinguishing the fault arc is put into operation (generating arc suppression signals), the transient process caused by it is very obvious and not easily affected by the size of the transition resistance. Therefore, making full use of the state information during the arc suppression process is the most direct and effective means to improve the reliability of fault detection and ensure the rapidity of arc suppression.

[0004] Through the retrieval of the existing technical field, it is found that the Chinese patent application number is 202411159030.7, the application publication number is CN118671517A, and the patent name is: A Fault Line Selection Method for Flexible DC Distribution Network Based on Improved Capsule Network. This patent uses an algorithm to process the fault information of the current and voltage of each line in the flexible DC distribution network, so as to intelligently determine the fault line, but does not consider the interference of actual distribution network arc suppression on fault information, and the detection accuracy is low.

[0005] The Chinese patent application number is 202411303011.7, the application publication number is CN119165293A, and the patent name is: Fault Line Selection Method Based on Gram Angle Field and Convolutional Neural Network. This patent collects the one-dimensional zero-sequence current time series data of each feeder when a single-phase grounding fault occurs in the distribution network for fault line selection, but does not consider the influence of three-phase asymmetry of distribution lines on the zero-sequence current of the line, resulting in a decrease in the sensitivity of line selection. Summary of the Invention

[0006] Technical Problem: The technical problem to be solved by the present invention is to provide a method for selecting the single-phase grounding fault line of a distribution network based on the hybrid arc suppression process, which can solve the problem that the traditional grounding fault line selection method cannot adapt to rapid arc suppression, and the fault signal is easily affected by the input of the arc suppression device, resulting in the failure of the fault line selection method.

[0007] Technical solution: To solve the above technical problems, the present invention proposes a single-phase grounding fault line selection method for a distribution network based on a hybrid arc suppression process. An arc suppression coil and an active arc suppression device are sequentially connected to the neutral point of the distribution network to form a multi-stage arc suppression process, thereby generating transient and steady-state information of the arc suppression process and realizing an accurate judgment of the fault feeder based on the hybrid arc suppression process.

[0008] A single-phase grounding fault line selection method for a distribution network based on a hybrid arc suppression process includes the following steps:

[0009] S1: When the distribution network is operating normally, measure the steady-state zero-sequence voltage value, denoted as Measure the steady-state zero-sequence current value of line n, denoted as

[0010] S2: After a grounding fault occurs in the distribution network at time t c , measure the steady-state zero-sequence voltage value, denoted as Measure the steady-state zero-sequence current value of line n, denoted as

[0011] S3: At time t0, connect a fully compensated arc suppression coil to the neutral point of the distribution network. The theoretical expression of the transient zero-sequence current waveform of line n, 3i 0n_tra (t) is:

[0012]

[0013] In the above formula, C n , G n are the total shunt capacitance and total shunt conductance to the ground of line n; u 0_tra (t) is the system transient zero-sequence voltage after the fully compensated arc suppression coil is put into operation;

[0014] S4: Record the actual value of the transient zero-sequence current of line n, 3i 0Cn_tra (t), and compare the magnitudes of 3i 0Cn_tra (t) and 3i 0n_tra (t) to preliminarily judge whether line n has a fault, including the following steps:

[0015] S4-1: If 3i 0Cn_tra (t0) = 3i 0n_tra (t0), then preliminarily judge that line n is normal;

[0016] S4-2: If 3i 0Cn_tra (t0) ≠ 3i 0n_tra (t0), then enter step S4-3;

[0017] S4-3: When u 0_tra (t0) > 0, 3i 0Cn_tra (t0) > 3i0n_tra (t0); or when u 0_tra (t0) < 0, 3i 0Cn_tra (t0) < 3i 0n_tra (t0), then initially judge that line n has a fault;

[0018] S5: At time t1, connect the active arc suppression device and the fully compensated arc suppression coil in parallel to the neutral point of the distribution network, record the transient zero-sequence voltage waveform and the transient zero-sequence current waveform of line n, and determine the faulty line according to the difference in the attenuation directions of the zero-sequence voltage and the zero-sequence current, including the following steps:

[0019] S5-1: If the attenuation directions of the transient zero-sequence voltage and the transient zero-sequence current waveform of line n are the same, and on the remaining lines except line n, the attenuation direction of the transient zero-sequence current is the same as the transient zero-sequence voltage, then further determine that line n is the faulty line;

[0020] S5-2: If the attenuation directions of the transient zero-sequence voltage and the transient zero-sequence current waveform of line n are opposite, then further determine that line n is a normal line;

[0021] S6: After the grounding current is completely suppressed to 0, measure the steady-state zero-sequence voltage value, denoted as Measure the steady-state zero-sequence current value of line n, denoted as

[0022] S7: According to the measured Construct a steady-state fault line selection criterion Υ to verify the accuracy of the faulty line selected in step S4 and step S5.

[0023] Furthermore, the time t0 when the fully compensated arc suppression coil is connected to the neutral point of the distribution network in step S3 satisfies:

[0024] t0 = t c +5T f Equation 2

[0025] In the above formula, T f is the power frequency period, and T f = 0.02s.

[0026] Furthermore, the time t1 when the fully compensated arc suppression coil is connected to the neutral point of the distribution network in step S5 satisfies:

[0027] t1 = t0 + 6τ Equation 3

[0028] In the above formula, τ is the time constant corresponding to the transient zero-sequence current in step S4.

[0029] Furthermore, in step S7, the steady-state fault line selection criterion Υ is:

[0030]

[0031] In the above formula, Y i is the total shunt admittance to ground of line n, and Y Σ is the total shunt admittance to ground of the system, and R E is the grounding resistance; the literal expression of the steady-state fault line selection criterion Υ is: based on the measured When the calculation formula are equal and equal to the total shunt admittance Y to ground of line n n , it is determined that line n is a normal line; when the calculation formula are not equal, and there is only equal to the total shunt admittance Y to ground of line n n , then it is determined that line n is a faulty line.

[0032] Advantageous effects: A single-phase grounding fault line selection method for a distribution network based on a hybrid arc suppression process proposed by the present invention can achieve accurate judgment of a faulty line while completely compensating the grounding current after a single-phase grounding fault occurs in the distribution network. This method ensures that fault arc suppression and fault line selection can be carried out synchronously, and can accurately judge the specific line where the grounding fault occurs while reliably suppressing the grounding current. Description of the Drawings

[0033] Figure 1 is a schematic diagram of equivalent operation for fault line selection in a multi-feeder distribution network;

[0034] Figure 2 is the waveforms of the transient zero-sequence voltage and transient zero-sequence current after the arc suppression coil is put into operation (the grounding resistance is set to 20 ohms);

[0035] Figure 3 is the waveforms of the transient zero-sequence voltage and transient zero-sequence current after the arc suppression coil is put into operation (the grounding resistance is set to 2000 ohms);

[0036] Figure 4 is the waveforms of the transient zero-sequence voltage and the transient zero-sequence currents of each line after the active arc suppression device is put into operation. Detailed Embodiments

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] Appendix Figure 1It is a schematic diagram of equivalent operation for fault line selection in a multi - feeder distribution network. There are n lines in this distribution network. C nA , C nB , C nC are the line - to - ground distributed capacitances of the A, B, and C phases of line n respectively; G nA , G nB , G nC are the line - to - ground distributed conductances of the A, B, and C phases of line n respectively, and R E is the grounding resistance. When a phase - A grounding fault occurs on the nth line of the distribution network, a method for single - phase grounding fault line selection in the distribution network based on the hybrid arc - suppression process is as follows.

[0039] Step S1: When the distribution network is operating normally, measure the steady - state zero - sequence voltage value, denoted as Measure the steady - state zero - sequence current value of line n, denoted as

[0040] Step S2: After a grounding fault occurs in the distribution network at time t c , measure the steady - state zero - sequence voltage value, denoted as Measure the steady - state zero - sequence current value of line n, denoted as

[0041] Step S3: Connect the fully compensated arc - suppression coil to the neutral point of the distribution network at time t0. The theoretical expression of the transient zero - sequence current waveform of line n, 3i 0n_tra (t) is:

[0042]

[0043] In the above formula, C n , G n are the total line - to - ground distributed capacitance and total line - to - ground distributed conductance of line n respectively; u 0_tra (t) is the system transient zero - sequence voltage after the fully compensated arc - suppression coil is put into operation. The time t0 when the fully compensated arc - suppression coil is connected to the neutral point of the distribution network satisfies:

[0044] t0 = t c +5T f Equation 6

[0045] In the above formula, T f is the power - frequency period, and T f = 0.02s.

[0046] Step S4: Record the actual value of the transient zero - sequence current of line n, 3i 0Cn_tra (t), and compare the magnitudes of 3i 0Cn_tra (t) and 3i 0n_tra (t) to preliminarily determine whether a fault has occurred on line n. The specific steps are as follows:

[0047] Step S4-1: If 3i 0Cn_tra (t0) = 3i 0n_tra (t0), then initially determine that line n is normal;

[0048] Step S4-2: If 3i 0Cn_tra (t0) ≠ 3i 0n_tra (t0), then proceed to Step S4-3;

[0049] Step S4-3: When u 0_tra (t0) > 0, 3i 0Cn_tra (t0) > 3i 0n_tra (t0); or when u 0_tra (t0) < 0, 3i 0Cn_tra (t0) < 3i 0n_tra (t0), then initially determine that line n has a fault;

[0050] Step S5: At time t1, connect the active arc suppression device and the fully compensated arc suppression coil in parallel to the neutral point of the distribution network, where the connection time t1 of the fully compensated arc suppression coil to the neutral point of the distribution network satisfies:

[0051] t1 = t0 + 6τ Equation 7

[0052] In the above formula, τ is the time constant corresponding to the transient zero-sequence current in Step S4.

[0053] Record the transient zero-sequence voltage waveform and the transient zero-sequence current waveform of line n, and determine the faulty line according to the difference in the attenuation directions of the zero-sequence voltage and zero-sequence current, including the following steps:

[0054] Step S5-1: If the attenuation directions of the transient zero-sequence voltage and the transient zero-sequence current waveform of line n are the same, and on the other lines except line n, the attenuation directions of the transient zero-sequence current and the transient zero-sequence voltage are the same, then further determine that line n is the faulty line;

[0055] Step S5-2: If the attenuation directions of the transient zero-sequence voltage and the transient zero-sequence current waveform of line n are opposite, then further determine that line n is a normal line;

[0056] Step S6: After the grounding current is completely suppressed to 0, measure the steady-state zero-sequence voltage value, denoted as Measure the steady-state zero-sequence current value of line n, denoted as

[0057] Step S7: According to the measured Construct the steady-state fault line selection criterion Υ, specifically:

[0058]

[0059] In the above formula, Y iis the total shunt admittance to ground of line n, Y Σ is the total shunt admittance to ground of the system, R E is the grounding resistance; the literal expression of the steady-state fault line selection criterion Υ is: based on the measured When the calculation formula are equal and equal to the total shunt admittance Y to ground of line n n , it is determined that line n is a normal line; when the calculation formula are not equal, and there is only equal to the total shunt admittance Y to ground of line n n , then it is determined that line n is a faulty line.

[0060] On the basis of Figure 1 , the MATLAB / Simulink simulation is used to verify a single-phase grounding fault line selection method for a distribution network based on the hybrid arc suppression process proposed by the present invention. The parameters of each line in the distribution network in the simulation are shown in Table 1. The equivalent inductance of the fully compensated arc suppression coil is L = 0.2528H, and the equivalent output current of the active arc suppression device is The grounding fault is set in phase A of line 3, and the grounding resistance R E is set to 20Ω and 2000Ω respectively. The simulation verification results of the fault line selection method based on hybrid arc suppression are shown in detail in Figure 2 , Figure 3 , Figure 4 and Tables 2, 3, and 4.

[0061] Table 1 Distribution network line shunt parameters to ground

[0062] Table 2 Preliminary line selection results when R E = 20Ω

[0063] Table 3 Preliminary line selection results when R E = 2000Ω

[0064] Table 4 Verification of line selection results based on steady-state information

[0065] As can be seen from Figure 2 and Table 2, when the grounding resistance R E = 20Ω (after the fully compensated arc suppression coil is put into operation), the zero-sequence current of line 1 satisfies: i 0C1_tra (0.142) = i 01_tra(0.142) = -0.702; The zero-sequence current of line 2 satisfies: i 0C2_tra (0.142) = i 02_tra (0.142) = -1.361; The zero-sequence current of line 3 satisfies: i 0C3_tra (0.142) = 29.503, i 03_tra (0.142) = -0.91. According to the line selection method described in step S4, if 3i 0Cn_tra (t0) = 3i 0n_tra (t0), then it is preliminarily determined that line n is normal. Therefore, it is preliminarily determined that line 1 and line 2 are normal, while line 3 has a grounding fault.

[0066] Similarly, from Appendix Figure 3 and Table 3, it can be seen that when the grounding resistance R E = 2000Ω (after the fully compensated arc suppression coil is put into operation), the zero-sequence current of line 1 satisfies: i 0C1_tra (0.152) = i 01_tra (0.152) = -2.080; The zero-sequence current of line 2 satisfies: i 0C2_tra (0.152) = i 02_tra (0.152) = -4.120; The zero-sequence current of line 3 satisfies: i 0C3_tra (0.152) = -3.168, i 03_tra (0.152) = -2.425. In addition, u 0_tra (0.152) = -2759.789 > 0, i 0C3_tra (0.152) < i 03_tra (0.152). Therefore, it is preliminarily determined that line 1 and line 2 are normal, while line 3 has a grounding fault.

[0067] From Appendix Figure 4 it can be seen that when the grounding resistance R E = 2000Ω (after the active arc suppression device is put into operation), the transient zero-sequence voltage of the system decays downward. Among the three lines, only the transient zero-sequence current of line 3 decays in the same direction as the transient zero-sequence voltage, both downward, while the transient zero-sequence currents of line 1 and line 2 decay in the opposite direction to the transient zero-sequence voltage, both upward. According to the fault line selection method described in step S5, the faulty line is determined to be line 3, while line 1 and line 2 are both normal lines.

[0068] From Table 4, it can be seen that when the grounding resistance R E = 20Ω, line 1 satisfies: ∠88.969°; Line 2 satisfies: Line 3 satisfies: According to the fault line selection criterion described in step S7, the faulty line can be determined to be line 3 again. Similarly, when the grounding resistance R E = 2000 Ω, line 1 satisfies: Line 2 satisfies: Line 3 satisfies: According to the fault line selection criterion described in step S7, the faulty line can be determined to be line 3 again.

Claims

1. A method for selecting a single-phase grounding fault line in a distribution network based on a hybrid arc extinguishing process, characterized in that: The selection of the fault line is realized by utilizing the difference of the transient steady-state zero-sequence voltage and zero-sequence current of each distribution line during the hybrid arc extinguishing process, including the following steps: S1: When the distribution network is operating normally, measure the steady-state zero-sequence voltage value, recorded as Measure the steady-state zero-sequence current value of line n, recorded as S2: at t c When a ground fault occurs in the distribution network, the steady-state zero-sequence voltage value is measured and recorded as Measure the steady-state zero-sequence current value of line n, recorded as S3: At time t0, the fully compensated arc suppression coil is connected to the neutral point of the distribution network. The transient zero-sequence current waveform of line n is theoretically expressed as 3i 0n_tra (t) is: In the above formula, C n , G n is the total distributed capacitance and conductance of line n to ground; u 0_tra (t) is the transient zero-sequence voltage of the system after the full compensation arc suppression coil is put into operation; S4: Record the actual value 3i of the transient zero-sequence current of line n 0Cn_tra (t), compare 3i 0Cn_tra (t) and 3i 0n_tra (t), to preliminarily determine whether line n has a fault, including the following steps: S4-1: If 3i 0Cn_tra (t0) = 3i 0n_tra (t0), it is preliminarily judged that line n is normal; S4-2: If 3i 0Cn_tra (t0)≠3i 0n_tra (t0), then proceed to step S4-3; S4-3: When u 0_tra When (t0)>0, 3i 0Cn_tra (t0)>3i 0n_tra (t0); or when u 0_tra When (t0)<0, 3i 0Cn_tra (t0)<3i 0n_tra (t0), it is preliminarily determined that line n is faulty; S5: At time t1, the active arc extinguishing device and the fully compensated arc extinguishing coil are connected in parallel to the neutral point of the distribution network, the transient zero-sequence voltage waveform and the transient zero-sequence current waveform of line n are recorded, and the fault line is determined according to the difference in the attenuation direction of the zero-sequence voltage and the zero-sequence current, including the following steps: S5-1: If the attenuation directions of the transient zero-sequence voltage and the transient zero-sequence current waveform of line n are the same, and the attenuation directions of the transient zero-sequence current and the transient zero-sequence voltage on the lines other than line n are the same, then line n is further determined to be the fault line; S5-2: If the attenuation directions of the transient zero-sequence voltage and the transient zero-sequence current waveform of line n are opposite, it is further determined that line n is a normal line; S6: After the ground current is completely suppressed to 0, measure the steady-state zero-sequence voltage value, recorded as Measure the steady-state zero-sequence current value of line n, recorded as S7: According to the measurement Construct a steady-state fault line selection criterion Y to verify the accuracy of the fault lines selected in step S4 and step S5.

2. A method for selecting a single-phase grounding fault line in a distribution network based on a hybrid arc extinguishing process according to claim 1, characterized in that: In step S3, the time t0 at which the full compensation arc suppression coil is connected to the neutral point of the distribution network satisfies: t0=t c +5T f Formula 2 In the above formula, T f is the power frequency period, and T f =0.02s.

3. The method for selecting a single-phase grounding fault line in a distribution network based on a hybrid arc extinguishing process according to claim 1 is characterized in that: In step S5, the time t1 at which the full compensation arc suppression coil is connected to the neutral point of the distribution network satisfies: t1=t0+6τ Formula 3 In the above formula, τ is the time constant corresponding to the transient zero-sequence current in step S4.

4. The method for selecting a single-phase grounding fault line in a distribution network based on a hybrid arc extinguishing process according to claim 1, characterized in that: In step S7, the steady-state fault line selection criterion Y is: In the above formula, Y i is the total distributed admittance of line n to ground, Y Σ is the total system-to-ground distributed admittance, R E is the grounding resistance; the textual expression of the steady-state fault line selection criterion Y is: based on the measured When the calculation Equal to and equal to the total distributed admittance Y of line n to ground n When , line n is determined to be a normal line; When the calculation Not equal, there is only one Equal to the total distributed admittance Y of line n to ground n When , line n is determined to be a faulty line.

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