Self-adaptive power distribution network fault line selection protection method and device based on neutral point grounding mode

Abstract

The invention is suitable for the technical field of fault identification, and provides a self-adaptive power distribution network fault line selection protection method and device based on a neutral point grounding mode, and the method comprises the steps: collecting a transient signal and a steady-state signal after a fault occurs; neutral point ground impedance characteristics and system parameters are calculated based on the transient state signals and the steady state signals, the current grounding mode is judged, and the grounding mode comprises an arc suppression coil grounding mode, a high-resistance grounding mode and a non-grounding mode; selecting a corresponding fault criterion combination according to the identified grounding mode, and when the grounding mode is arc suppression coil grounding, if the extracted harmonic features and the transient time-frequency features point to the same line, determining that the line is a fault line; when the grounding mode is non-grounding or high-resistance grounding, judging based on transient energy distribution and polarity inversion characteristics, and determining that the line with the maximum transient energy and opposite polarity is a fault line; and the fault line number is output according to the identified fault line, and the alarm signal is triggered, so that the accuracy of fault identification is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fault identification, and particularly to an adaptive distribution network fault line selection and protection method and device based on the neutral point grounding method. Background Art

[0002] As the core link of the power system facing the user side, the safe and stable operation of the distribution network is directly related to the power supply reliability and power consumption quality. The single-phase grounding fault is the most common fault type in the distribution network. Especially in the system adopting the small current grounding method, the fault current is weak and the characteristics are complex, resulting in a significant increase in the difficulty of fault detection and line selection. Although the small current grounding system allows short-time operation with faults, problems such as overvoltage and arc re-ignition caused by faults may lead to equipment insulation breakdown, cable fires and even personal electric shock accidents.

[0003] In the prior art, most systems are designed for a single grounding method, such as only applicable to the arc suppression coil grounding or ungrounded system. However, the actual distribution network may need to switch the grounding method due to operating conditions. Due to the lack of a dynamic recognition mechanism in the system, it cannot adaptively adjust the criterion, resulting in the failure of line selection. In addition, relying on a single feature is vulnerable to interference under complex working conditions. For example, the fifth harmonic method may fail due to harmonic suppression when the arc suppression coil is overcompensated, and the transient energy method is prone to misjudgment when the cable capacitance distribution is uneven, etc. In this way, errors or mistakes are likely to occur in fault identification.

[0004] In view of this, an adaptive distribution network fault line selection and protection method and device based on the neutral point grounding method are needed. Summary of the Invention

[0005] The embodiments of the present application provide an adaptive distribution network fault line selection and protection method and device based on the neutral point grounding method, which are used to solve the problem of errors or mistakes in fault identification.

[0006] The first aspect of the embodiments of the present application provides an adaptive distribution network fault line selection and protection method based on the neutral point grounding method, including:

[0007] Real-time monitor the neutral point voltage of the distribution network and the zero-sequence current of each feeder, and collect the transient signal and steady-state signal after the fault occurs;

[0008] Based on the transient signal and steady-state signal, calculate the neutral point-to-earth impedance characteristic and system parameters, and determine the current grounding method. The grounding methods include grounding through an arc suppression coil, grounding through a high resistance and ungrounded method;

[0009] Select the corresponding fault criterion combination according to the identified grounding method. The fault criterion combination includes:

[0010] When the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and transient time-frequency characteristics point to the same line, it is determined as the faulty line;

[0011] When the grounding method is ungrounded or high-resistance grounded, the determination is made based on the transient energy distribution and polarity reversal characteristics. The line with the maximum transient energy and opposite polarities is the faulty line;

[0012] Output the faulty line number according to the identified faulty line and trigger an alarm signal.

[0013] Furthermore, calculating the neutral point-to-earth impedance characteristics and system parameters based on the transient signal and steady-state signal to determine the current grounding method, where the grounding methods include grounding through an arc suppression coil, high-resistance grounding, and ungrounded, includes:

[0014] If the neutral point-to-earth impedance characteristic is inductive and the overcompensation degree in the system parameters meets the preset overcompensation condition, it is determined as grounding through an arc suppression coil;

[0015] If the neutral point-to-earth impedance characteristic is negative and the grounding resistance value in the system parameters exceeds the first threshold, it is determined as high-resistance grounded;

[0016] If the amplitude of the neutral point impedance is greater than the second threshold and the relative difference between the zero-sequence voltage and zero-sequence current is the preset phase characteristic, it is determined as the ungrounded method.

[0017] Furthermore, when the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and transient time-frequency characteristics point to the same line, it is determined as the faulty line, including:

[0018] Calculate the fifth harmonic amplitude and phase of the zero-sequence current of each line through windowed Fourier transform;

[0019] If the fifth harmonic amplitude of the first line exceeds 1.2 times the maximum amplitude of the other lines except the first line, and the phase difference between the first line and the other lines is greater than or equal to 150 degrees, mark the first line as a candidate faulty line for harmonic characteristics.

[0020] Furthermore, when the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and transient time-frequency characteristics point to the same line, it is determined as the faulty line, and further includes:

[0021] Perform four-layer decomposition on the zero-sequence current signal using the Coj4 wavelet basis and extract the modulus maximum value of the third-layer detail coefficient;

[0022] If the modulus maximum value amplitude of the first line exceeds 60% of the sum of the modulus maximum values of all lines, and the polarity of the first line is opposite to that of the other lines except the first line, mark the first line as a candidate faulty line for transient time-frequency characteristics.

[0023] Further, when the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and the transient time-frequency characteristics point to the same line, it is determined as the faulty line, and it further includes:

[0024] When the harmonic characteristic candidate faulty line and the transient time-frequency characteristic candidate faulty line are the same line, it is determined that the first line is the faulty line;

[0025] When the harmonic characteristic candidate faulty line and the transient time-frequency characteristic candidate faulty line point to different lines, select the transient time-frequency characteristic candidate line as the faulty line;

[0026] When no line satisfies the harmonic characteristic and the transient time-frequency characteristic conditions simultaneously, it is determined as a bus fault.

[0027] Further, when the grounding method is ungrounded or high-resistance grounded, the determination is based on the transient energy distribution and the polarity reversal characteristic, and the line with the maximum transient energy and opposite polarities is the faulty line, including:

[0028] Perform four-layer decomposition on the zero-sequence current signal using Sym6 wavelet packet, and calculate the energy integral within the preset frequency band;

[0029] If the energy value of the first line exceeds 1.5 times the maximum energy value of other lines except the first line, mark the first line as a high-energy candidate line.

[0030] Further, when the grounding method is ungrounded or high-resistance grounded, the determination is based on the transient energy distribution and the polarity reversal characteristic, and the line with the maximum transient energy and opposite polarities is the faulty line, and it further includes:

[0031] Determine the initial polarity of the zero-sequence current waveform within 2 milliseconds after the fault;

[0032] If the polarity of the first line is opposite to the polarities of other lines except the high-energy candidate line, mark the first line as a polarity reversal candidate line;

[0033] When the high-energy candidate line and the polarity reversal candidate line are the same, it is determined that the first line is the faulty line.

[0034] Further, when the grounding method is ungrounded or high-resistance grounded, the determination is based on the transient energy distribution and the polarity reversal characteristic, and the line with the maximum transient energy and opposite polarities is the faulty line, and it further includes:

[0035] If there are multiple lines whose energy values exceed 1.5 times the maximum energy value of other lines, select the line corresponding to the maximum energy value as the high-energy candidate line;

[0036] If the selected high-energy candidate line does not have a polarity inversion, select the line with the second highest energy and a polarity inversion as the high-energy candidate line;

[0037] If none of the lines have a polarity inversion, it is determined as a bus fault.

[0038] Furthermore, the outputting the fault line number according to the identified fault line and triggering an alarm signal includes:

[0039] Encoding the identified fault line number into a message in a specific format, where the message at least includes the line number, the fault occurrence time, and the fault type code;

[0040] Uploading the message to the distribution network automation master station in real time through a wireless communication module;

[0041] Driving the alarm indicator in the local audible and visual alarm device to flash at a preset frequency, and dynamically displaying the fault line number and the processing guide on the display screen.

[0042] The second aspect of the embodiment of the present application provides an adaptive distribution network fault line selection and protection device based on the neutral grounding method, including:

[0043] A signal acquisition module, configured to monitor the neutral point voltage of the distribution network and the zero-sequence current of each feeder in real time, and collect transient signals and steady-state signals after a fault occurs;

[0044] A grounding method determination unit, configured to calculate the neutral point-to-earth impedance characteristic and system parameters based on the transient signal and the steady-state signal, and determine the current grounding method, where the grounding method includes grounding through an arc suppression coil, grounding through a high resistance, and non-grounding;

[0045] A fault criterion combination selection unit, configured to select a corresponding fault criterion combination according to the identified grounding method. The fault criterion combination includes: when the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and the transient time-frequency characteristics point to the same line, it is determined as the fault line; when the grounding method is non-grounding or grounding through a high resistance, it is determined based on the transient energy distribution and the polarity inversion characteristic, and the line with the maximum transient energy and opposite polarities is the fault line;

[0046] A fault line alarm unit, configured to output the fault line number according to the identified fault line and trigger an alarm signal.

[0047] From the above technical solutions, it can be seen that the embodiments of the present invention have the following advantages:

[0048] After collecting the transient signals and steady-state signals after a fault occurs, the present invention calculates the neutral point-to-earth impedance characteristics and system parameters based on the collected data, determines the current grounding method of the system, where the grounding methods include grounding through an arc suppression coil, grounding through a high resistance, and non-grounding; selects the corresponding fault criterion combination according to the identified grounding method; and finally outputs the fault line number of the identified fault line and triggers an alarm signal. The present invention adapts to the multi-mode grounding operation requirements of the distribution network by automatically switching the optimal criterion combination, solves the problem of line selection failure caused by the switching of the grounding method; and greatly improves the accuracy of fault identification by double verification to suppress interference such as arc re-ignition and transition resistance fluctuation. Brief Description of the Drawings

[0049] Figure 1 It is a schematic flowchart of an embodiment of an adaptive distribution network fault line selection protection method based on the neutral point grounding method in the present invention. Detailed Embodiments

[0050] The terms "first", "second", "third", "fourth", etc. (if any) in the specification, claims and above-mentioned drawings of the present invention are used to distinguish similar objects and do not necessarily have to be used to describe a specific order or sequence. It should be understood that such data used can be interchanged under appropriate circumstances so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "corresponding to" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0051] Embodiment 1

[0052] In this embodiment, the implementation method can be implemented in a system, can be implemented on a server, or can be implemented on a terminal, and no specific limitation is made. Next, from the perspective of system implementation, the adaptive distribution network fault line selection protection method based on the neutral point grounding method in the present application will be introduced. Please refer to Figure 1 , the method provided in the embodiment of the present application includes the following steps:

[0053] S11. Monitor the neutral point voltage of the distribution network and the zero-sequence current of each feeder in real time, and collect the transient signals and steady-state signals after a fault occurs;

[0054] Install a capacitive voltage divider or a resistive voltage divider at the neutral point to measure the neutral point-to-ground voltage U0 in real time. The sensor should have a wide-band response, such as 0.1 Hz - 10 kHz, and be able to capture transient signals and steady-state signals. Install zero-sequence current transformers at the outlet of each feeder to collect the zero-sequence current I of each feeder 0i . Signal conditioning is performed on the collected signals through a signal conditioning circuit, including a low-pass filter and an amplifier circuit.

[0055] Set a voltage mutation threshold, such as |ΔU0 / dt| > 1 kV / ms. When a fault is detected, high-speed sampling (100 kSPS) is used to capture high-frequency components within 0 - 20 ms after the fault occurs. At this time, the signal is a transient signal. After 20 ms after the fault, a conventional sampling rate (10 kSPS) is used to record the power frequency component (50 Hz) and low-order harmonics. At this time, the signal is a steady-state signal.

[0056] S12. Calculate the neutral point-to-ground impedance characteristics and system parameters based on the transient signal and the steady-state signal, and determine the current grounding method. The grounding methods include grounding through an arc suppression coil, grounding through a high resistance, and non-grounding;

[0057] In this embodiment, the neutral point-to-ground impedance characteristics include impedance amplitude and impedance angle. Among them, the impedance amplitude: where I0 = ∑I 0i is the zero-sequence current in the system. Impedance angle: The phase difference θ between U0 and I0 is obtained through FFT analysis <∠U0 - ∠I0. The specific definition of system parameters: The over-compensation degree p is the ratio of the inductive current of the arc suppression coil to the capacitive current of the system, The preset over-compensation condition is p ≥ 5%; the grounding resistance threshold R n is the engineering experience value of a typical high-resistance grounding system. The first threshold R n ≥ 100 Ω; the impedance threshold Z of the non-grounding system n characterizes the approximate open-circuit state of the neutral point. The second threshold |Z n | ≥ 100 kΩ. The neutral point-to-ground impedance characteristic is inductive, that is, the impedance angle θ satisfies 80° ≤ θ ≤ 100°. The neutral point-to-ground impedance characteristic is capacitive, that is, the impedance angle θ satisfies θ ≤ 10°; the preset phase characteristic is set as the phase difference θ between U0 and I0 = 90° ± 5°.

[0058] Specifically, the current grounding method is judged as follows:

[0059] 1. If the neutral point-to-ground impedance characteristic is inductive and the over-compensation degree in the system parameters meets the preset over-compensation condition, that is, 80° ≤ θ ≤ 100° and p ≥ 5%, it is determined to be grounded through an arc suppression coil;

[0060] 2. If the neutral point-to-ground impedance characteristic is capacitive and the grounding resistance value in the system parameters exceeds the first threshold, that is, θ ≤ 10° and Rn ≥100 Ω, it is determined to be grounded through a high resistance;

[0061] 3. If the magnitude of the neutral point impedance to the ground is greater than the second threshold and the relative difference between the zero - sequence voltage and the zero - sequence current is a preset phase characteristic, that is, |Z n |≥100 kΩ and θ = 90°±5°, it is determined to be an ungrounded mode.

[0062] S13. Select the corresponding fault criterion combination according to the identified grounding mode. The fault criterion combination includes: when the grounding mode is grounded through an arc suppression coil, if the extracted harmonic characteristics and the transient time - frequency characteristics point to the same line, then it is determined to be the fault line; when the grounding mode is ungrounded or grounded through a high resistance, it is determined based on the transient energy distribution and the polarity inversion characteristics. The line with the maximum transient energy and opposite polarity is the fault line;

[0063] 1. When the grounding mode is grounded through an arc suppression coil, if the extracted harmonic characteristics and the transient time - frequency characteristics point to the same line, then it is determined to be the fault line; here the first line is a set line, including the following:

[0064] Calculate the fifth - harmonic amplitude and phase of the zero - sequence current of each line through windowed Fourier transform;

[0065] If the fifth - harmonic amplitude of the first line exceeds 1.2 times the maximum amplitude of the other lines except the first line, and the phase difference between the first line and the other lines is greater than or equal to 150 degrees, then mark the first line as a candidate fault line for harmonic characteristics.

[0066] Specifically, here the harmonic characteristic is the fifth - harmonic. Extract it through FFT and set the amplitude threshold K1 = 1.2 and the phase - difference condition θ≥150° to ensure that the criterion is quantifiable. Calculate the fifth - harmonic amplitude I 5i and phase θ 5i of each line. If a certain line meets the following conditions: I 5i >K1max(I 5j ), and the phase difference |θ 5i ―θ 5j |≥150° with the non - fault lines, then mark this line as a candidate fault line for harmonic characteristics.

[0067] Use the Coj4 wavelet basis to decompose the zero - sequence current signal into four layers and extract the modulus maxima of the third - layer detail coefficients;

[0068] If the modulus - maximum amplitude of the first line exceeds 60% of the sum of the modulus maxima of all lines, and the polarity of the first line is opposite to that of the other lines except the first line, then mark the first line as a candidate fault line for transient time - frequency characteristics.

[0069] Specifically, the frequency band corresponding to the third-layer detail coefficient is 312.5 Hz - 625 Hz, and the modulus maximum value is W max , if the value of a certain route W max ≥K2·∑W max,j (K2 = 0.6), and the polarity is opposite to that of the non-faulty line, then mark this line as a candidate faulty line for transient time-frequency characteristics.

[0070] When the candidate faulty line for harmonic characteristics and the candidate faulty line for transient time-frequency characteristics are the same line, determine that the first line is the faulty line;

[0071] When the candidate faulty line for harmonic characteristics and the candidate faulty line for transient time-frequency characteristics point to different lines, select the candidate line for transient time-frequency characteristics as the faulty line;

[0072] When no line simultaneously meets the conditions of harmonic characteristics and transient time-frequency characteristics, it is determined as a bus fault.

[0073] 2. When the grounding method is ungrounded or high-resistance grounded, make a determination based on the transient energy distribution and polarity reversal characteristics. Then, the line with the maximum transient energy and opposite polarity is the faulty line, including the following:

[0074] Use Sym6 wavelet packet to decompose the zero-sequence current signal into four layers, and calculate the energy integral within the preset frequency band;

[0075] If the energy value of the first line exceeds 1.5 times the maximum energy value of the other lines except the first line, then mark the first line as a high-energy candidate line.

[0076] Specifically, the preset frequency band is the sub-band coefficient of 312.5 Hz - 1562.5 Hz. Square and sum each sub-band coefficient to obtain the transient energy value of each line where W i,k is the coefficient of the i-th line in the k-th sub-band. If the transient energy E i of a certain line satisfies E i ≥K3·max(E j ), where K3 = 1.5, then mark this line as a high-energy candidate line.

[0077] Determine the initial polarity of the zero-sequence current waveform within 2 milliseconds after the fault;

[0078] If the polarity of the first line is opposite to that of the other lines except the high-energy candidate line, then mark the first line as a polarity reversal candidate line;

[0079] When the high-energy candidate line and the polarity reversal candidate line are the same, determine that the first line is the faulty line.

[0080] Specifically, extract the zero-sequence current transient waveform within the time window of 0.5 ms - 2 ms after the fault occurs, calculate the initial polarity (positive / negative) of the transient waveforms of each line. If the polarity of a certain line is opposite to that of at least 80% of the non-faulty lines, it is determined as a candidate line for polarity inversion. When the high-energy candidate line coincides with the candidate line for polarity inversion, confirm that this line is the faulty line.

[0081] If the energy values of multiple lines exceed 1.5 times the maximum energy value of other lines, select the line corresponding to the maximum energy value as the high-energy candidate line;

[0082] If the selected high-energy candidate line does not have a polarity inversion, select the line with the second-highest energy and a polarity inversion as the high-energy candidate line;

[0083] If none of the lines have a polarity inversion, it is determined as a bus fault.

[0084] Specifically, if multiple lines satisfy E i ≥K3·max(E j ), select the line with the maximum transient energy value; if the line with the maximum transient energy value does not meet the polarity inversion condition, select the line with the second-highest energy and a polarity inversion; if no line meets the polarity inversion condition, it is determined as a bus fault.

[0085] S14. Output the faulty line number based on the identified faulty line and trigger an alarm signal.

[0086] Step S14 includes the following:

[0087] 1. Encode the identified faulty line number into a message in a specific format. The message should at least include the line number, the fault occurrence time, and the fault type code;

[0088] Here, the message format includes the line number, timestamp, and fault type code, ensuring that the information is structured and facilitating quick parsing by the master station.

[0089] 2. Upload the message to the distribution network automation master station in real time through a wireless communication module;

[0090] Use the limited 4G / LoRa dual-mode communication to balance long-distance transmission and high-bandwidth requirements and adapt to complex distribution network environments. The communication protocol supports IEC61850 or MQTT to ensure compatibility with existing automation systems.

[0091] 3. Drive the alarm indicator in the local audible and visual alarm device to flash at a preset frequency, and the display screen dynamically shows the faulty line number and the processing guide.

[0092] The acoustic-optic alarm device sounds at a frequency of 2 Hz through a buzzer, and the LED indicator flashes alternately in red and blue to provide intuitive warnings; the OLED screen displays the fault line number and suggested operations, such as "Fault line: L05", such as "Please check the cable insulation of section L05", to improve the on-site handling efficiency.

[0093] Through the above embodiments, by dynamically identifying the neutral point to ground impedance characteristics and combining the multi-criterion fusion strategy of harmonic characteristics, high-frequency transient time-frequency characteristics and transient energy distribution, the line selection accuracy and reliability in complex grounding scenarios are significantly improved.

[0094] Embodiment 2

[0095] An embodiment of an adaptive distribution network fault line selection and protection device based on the neutral point grounding method in the present invention includes the following steps:

[0096] A signal acquisition module for real-time monitoring of the neutral point voltage of the distribution network and the zero-sequence current of each feeder, and collecting transient signals and steady-state signals after a fault occurs;

[0097] A grounding method determination unit for calculating the neutral point to ground impedance characteristics and system parameters based on transient signals and steady-state signals, and determining the current grounding method. The grounding methods include grounding through an arc suppression coil, grounding through a high resistance, and non-grounding;

[0098] A fault criterion combination selection unit for selecting a corresponding fault criterion combination according to the identified grounding method. The fault criterion combinations include: when the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and transient time-frequency characteristics point to the same line, it is determined as the fault line; when the grounding method is non-grounding or high-resistance grounding, it is determined based on the transient energy distribution and polarity reversal characteristics, and the line with the maximum transient energy and opposite polarity is the fault line;

[0099] A fault line alarm unit for outputting the fault line number according to the identified fault line and triggering an alarm signal.

[0100] The specific functions and uses of the units in this embodiment are correspondingly similar to the steps in the first embodiment described above, and will not be elaborated here.

[0101] Those of ordinary skill in the art can realize that the units of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. To clearly illustrate the interchangeability of hardware and software, the components of each example have been generally described according to their functions in the above description. Whether these functions are executed in hardware or software depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0102] In the embodiments provided by the present invention, it should be understood that the division of units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored, etc. In addition, in each embodiment of the present invention, the functional units can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

[0103] If the above-mentioned integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, read-only memories (ROMs), random access memories (RAMs), mobile hard disks, magnetic disks, or optical discs that can store program codes.

[0104] It can be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the various embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention.

Claims

1. An adaptive fault line selection and protection method for a distribution network based on the neutral grounding method, characterized in that Including: Real-time monitor the neutral point voltage of the distribution network and the zero-sequence current of each feeder, and collect the transient signals and steady-state signals after a fault occurs; Calculate the neutral point to ground impedance characteristics and system parameters based on the transient signals and steady-state signals, and determine the current grounding method, where the grounding method includes grounding through an arc suppression coil, grounding through a high resistance, and non-grounding; Select the corresponding fault criterion combination according to the identified grounding method, and the fault criterion combination includes: When the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and transient time-frequency characteristics point to the same line, it is determined as the faulty line; When the grounding method is non-grounding or grounding through a high resistance, it is determined based on the transient energy distribution and polarity inversion characteristics. The line with the maximum transient energy and opposite polarity is the faulty line; Output the faulty line number according to the identified faulty line and trigger an alarm signal.

2. The adaptive distribution network fault line selection protection method based on the neutral point grounding method according to claim 1, characterized in that The calculating the neutral point to ground impedance characteristics and system parameters based on the transient signals and steady-state signals, and determining the current grounding method, where the grounding method includes grounding through an arc suppression coil, grounding through a high resistance, and non-grounding, includes: If the neutral point to ground impedance characteristic is inductive and the over-compensation degree in the system parameters meets the preset over-compensation condition, it is determined as grounding through an arc suppression coil; If the neutral point to ground impedance characteristic is negative and the grounding resistance value in the system parameters exceeds the first threshold, it is determined as grounding through a high resistance; If the amplitude of the neutral point impedance is greater than the second threshold and the relative difference between the zero-sequence voltage and the zero-sequence current is the preset phase characteristic, it is determined as the non-grounding method.

3. The adaptive distribution network fault line selection and protection method based on the neutral grounding mode according to claim 1, characterized in that The when the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and transient time-frequency characteristics point to the same line, it is determined as the faulty line, includes: Calculate the fifth harmonic amplitude and phase of the zero-sequence current of each line through windowed Fourier transform; If the fifth harmonic amplitude of the first line exceeds 1.2 times the maximum amplitude of the other lines except the first line, and the phase difference between the first line and the other lines is greater than or equal to 150 degrees, mark the first line as the harmonic characteristic candidate faulty line.

4. The adaptive distribution network fault line selection and protection method based on the neutral point grounding method according to claim 3, characterized in that, The when the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and transient time-frequency characteristics point to the same line, it is determined as the faulty line, further includes: Perform four-layer decomposition on the zero-sequence current signal using the Coj4 wavelet basis and extract the modulus maximum value of the third-layer detail coefficient; If the modulus maximum value amplitude of the first line exceeds 60% of the sum of the modulus maximum values of all lines, and the polarity of the first line is opposite to that of the other lines except the first line, mark the first line as the transient time-frequency characteristic candidate faulty line.

5. The adaptive distribution network fault line selection and protection method based on the neutral grounding mode according to claim 4, characterized in that, The when the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and transient time-frequency characteristics point to the same line, it is determined as the faulty line, further includes: When the harmonic characteristic candidate faulty line and the transient time-frequency characteristic candidate faulty line are the same line, determine the first line as the faulty line; When the harmonic characteristic candidate faulty line and the transient time-frequency characteristic candidate faulty line point to different lines, select the transient time-frequency characteristic candidate line as the faulty line; When no line satisfies the harmonic characteristic and transient time-frequency characteristic conditions simultaneously, it is determined as a bus fault.

6. The adaptive distribution network fault line selection and protection method based on the neutral grounding mode according to claim 1, characterized in that When the grounding method is ungrounded or high-resistance grounded, the determination is based on the transient energy distribution and polarity reversal characteristics. The line with the maximum transient energy and opposite polarities is the faulty line, including: Perform four-layer decomposition on the zero-sequence current signal using Sym6 wavelet packet and calculate the energy integral within a preset frequency band; If the energy value of the first line exceeds 1.5 times the maximum energy value of other lines except the first line, mark the first line as a high-energy candidate line.

7. The adaptive distribution network fault line selection and protection method based on the neutral point grounding method according to claim 6, wherein When the grounding method is ungrounded or high-resistance grounded, the determination is based on the transient energy distribution and polarity reversal characteristics. The line with the maximum transient energy and opposite polarities is the faulty line, and it also includes: Determine the initial polarity of the zero-sequence current waveform within 2 milliseconds after the fault; If the polarity of the first line is opposite to that of other lines except the high-energy candidate lines, mark the first line as a polarity reversal candidate line; When the high-energy candidate line is consistent with the polarity reversal candidate line, determine the first line as the faulty line.

8. The adaptive distribution network fault line selection and protection method based on the neutral point grounding method according to claim 7, characterized in that, When the grounding method is ungrounded or high-resistance grounded, the determination is based on the transient energy distribution and polarity reversal characteristics. The line with the maximum transient energy and opposite polarities is the faulty line, and it also includes: If the energy values of multiple lines exceed 1.5 times the maximum energy value of other lines, select the line corresponding to the maximum energy value as the high-energy candidate line; If the selected high-energy candidate line does not reverse in polarity, select the line with the second-highest energy and polarity reversal as the high-energy candidate line; If none of the lines reverse in polarity, it is determined as a bus fault.

9. The adaptive distribution network fault line selection and protection method based on the neutral point grounding method according to claim 1, characterized in that Outputting the faulty line number according to the identified faulty line and triggering an alarm signal includes: Encode the identified faulty line number into a message in a specific format. The message at least includes the line number, the fault occurrence time, and the fault type code; Upload the message to the distribution network automation master station in real time through a wireless communication module; Drive the alarm indicator in the local audible and visual alarm device to flash at a preset frequency, and the display screen dynamically displays the faulty line number and the handling guide.

10. An adaptive distribution network fault line selection and protection device based on the neutral point grounding method, characterized in that, Including: A signal acquisition module for real-time monitoring of the neutral point voltage of the distribution network and the zero-sequence current of each feeder, and collecting transient signals and steady-state signals after the fault occurs; A grounding method determination unit for calculating the neutral point-to-earth impedance characteristics and system parameters based on the transient signal and steady-state signal, and determining the current grounding method. The grounding method includes grounding through an arc suppression coil, grounding through a high resistance, and ungrounded; A fault criterion combination selection unit for selecting the corresponding fault criterion combination according to the identified grounding method. The fault criterion combination includes: when the grounding method is grounding through an arc suppression coil, if the extracted harmonic characteristics and transient time-frequency characteristics point to the same line, it is determined as the faulty line; when the grounding method is ungrounded or high-resistance grounded, the determination is based on the transient energy distribution and polarity reversal characteristics. The line with the maximum transient energy and opposite polarities is the faulty line; A faulty line alarm unit for outputting the faulty line number according to the identified faulty line and triggering an alarm signal.

Images