Power distribution network fault diagnosis method and system based on traveling wave ranging and recording screening

Abstract

The invention provides a power distribution network fault diagnosis method and system based on traveling wave distance measurement recording screening, and the method comprises the steps: integrating a traveling wave distance measurement unit in a distribution network feeder terminal unit (FTU), and carrying out the communication with the FTU through a serial port, a network port or other modes, thereby forming a traveling wave distance measurement FTU device; one IO port of the traveling wave distance measurement unit MCU is connected with an IO port of the FTU master control MCU, and real-time level signals are received; the FTU and the traveling wave distance measurement unit share a GPS signal to ensure time synchronization; fault time calculation is realized in the FTU, after a line fault is confirmed, fault starting time is calculated by using power frequency recording and sent to the traveling wave distance measurement unit, and the traveling wave distance measurement unit screens traveling wave main waves according to the calculated fault starting time and uploads the traveling wave main waves to a main station for distance measurement. According to the invention, high reliability of fault diagnosis of the FTU and high precision of fault positioning of the traveling wave fault location unit are combined together; the traveling wave distance measurement unit is integrated in the FTU to form the traveling wave distance measurement terminal, so that the main wave of the fault traveling wave is accurately screened out, and the engineering installation cost is not increased.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network fault detection, and in particular to a distribution network fault diagnosis method and system based on traveling wave ranging and recording screening. Background Art

[0002] Most distribution networks in my country use a low-current grounding system. When a single-phase grounding fault occurs, the handling strategy is to continue operation without power outage and inspect the grounding point. More than 80% of faults in distribution networks are single-phase grounding faults [1]. Therefore, fast and accurate positioning of the fault point is of great significance for the small-scale isolation and rapid maintenance of the fault, which is of great significance to the safe, stable and efficient operation of the distribution network.

[0003] Traveling wave ranging technology has been maturely applied in transmission networks, but it has not been put into use on a large scale in distribution networks due to technical and cost limitations. With the improvement of the national economic living standards, the requirements for the operation level of distribution networks are also increasing. The country has also increased its investment in distribution network construction and maintenance. At the same time, breakthroughs in high-frequency sensing technology, high-precision GPS timing technology, high-speed 4G / 5G communication technology and high-frequency synchronous sampling technology have also promoted the realization of distribution network traveling wave ranging technology. In addition, the trend of primary and secondary equipment integration has also greatly reduced the investment in the installation of traveling wave acquisition devices. Therefore, my country's distribution network has the conditions for applying traveling wave ranging technology. However, the traveling wave unit will start recording for a variety of reasons, including lightning strikes, switch operations, load fluctuations, transient faults and permanent faults. According to statistics, about 70% of single-phase grounding faults in my country's distribution network are transient grounding faults. How to confirm that the traveling wave is started by a fault and how to select the main wave (i.e., the initial traveling wave of the fault) from multiple traveling wave recordings of a fault for ranging are a major problem in the application of traveling wave ranging technology to distribution network lines.

[0004] To solve this problem, there are three existing technical solutions:

[0005] Increase the reset time of the traveling wave start to ensure that the traveling wave unit is started only when the initial traveling wave arrives. This method can solve the problem to a certain extent, but there is a risk that the fault will not be reset when the initial traveling wave arrives after the disturbance starts, which is more common in the case of developing faults. This method also has the problem of not being able to distinguish non-fault starting traveling waves.

[0006] According to the statistical characteristics of the fault traveling waves, they are screened locally and then uploaded to the master station. This method can distinguish the start of traveling waves caused by lightning strikes, switch operations, etc., but it cannot filter out the main wave from multiple traveling waves in a single fault, and it has high requirements on the local computing power of the terminal, which is difficult to meet with terminal resources.

[0007] All recorded waves are uploaded to the main station for screening. This method is the current mainstream practice, but there are the following problems in the implementation process: first, instantaneous faults will generate a large number of recorded waves, which will cause great pressure on wireless communication and main station processing, and in severe cases will cause the main station server to crash; second, the fault analysis time is greatly increased, and the main station cannot quickly give fault location results; third, there are high requirements for the main station algorithm, and each main wave needs to be correctly screened out from multiple groups of recorded waves uploaded by multiple terminals on multiple lines for ranging, and often human intervention is required due to screening failures. Summary of the invention

[0008] To solve the above problems, the present invention aims to propose a distribution network fault diagnosis method and system based on traveling wave ranging and recording screening. Based on the mature feeder terminal product FTU, the high reliability of FTU fault diagnosis and the high precision of traveling wave ranging unit fault location are combined together; the traveling wave ranging unit is integrated in the FTU to form a traveling wave ranging terminal, so as to accurately screen out the main traveling wave of the fault without increasing the engineering installation cost.

[0009] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0010] A distribution network fault diagnosis method based on traveling wave ranging and recording screening includes the following steps:

[0011] S1. Integrate the traveling wave ranging unit into the distribution network feeder terminal FTU, and communicate with the FTU via a serial port, network port or other means to form a traveling wave ranging FTU device;

[0012] S2, an IO port of the traveling wave ranging unit MCU is connected to the IO port of the FTU main control MCU to receive the real-time level signal;

[0013] S3, FTU and the traveling wave ranging unit share GPS signals to ensure time synchronization, where FTU receives the NEMA message of the GPS module through the serial port, parses it to obtain the year, month, day, hour, minute, second and millisecond information, and the traveling wave ranging unit receives the second pulse signal from the GPS module, and obtains the information below the second level of the fault time after counting by the crystal oscillator, which is accurate to nanoseconds. The information above the second level is sent by the FTU through the communication port;

[0014] S4. FTU implements fault time estimation internally. After confirming the line fault, it uses the power frequency recording to estimate the fault start time and sends it to the traveling wave ranging unit. The traveling wave ranging unit selects the main traveling wave according to the estimated fault start time and uploads it to the master station for ranging.

[0015] Furthermore, the line fault includes a ground fault and a short circuit fault.

[0016] Furthermore, the ground fault diagnosis process includes the following steps:

[0017] Step 1: The FTU collects zero-sequence voltage in real time at a relatively low sampling rate, and takes the zero-sequence voltage exceeding the upper limit as a starting condition, and records the wave after starting; the traveling wave ranging unit collects three-phase current traveling waves in real time at a relatively high sampling rate, and takes whether the current traveling waves exceed the upper limit as a starting condition, and records the wave after starting;

[0018] Step 2: If the FTU detects that the zero-sequence voltage exceeds the upper limit and the over-limit time exceeds the set value, the IO port level connected to the traveling wave ranging unit is flipped, and the sampled data within a certain range before and after the moment is recorded; the traveling wave ranging unit detects that the IO port level is flipped and the lock is started. At this time, the current traveling wave at the initial moment of the fault has been recorded by the traveling wave ranging unit for screening;

[0019] Step 3: After the FTU completes the recording, it calculates the fault time of the recorded zero-sequence voltage channel, slides from left to right in a 20ms time window, and the sliding step can be set. Perform a full-cycle Fourier analysis on the data in the window to obtain the fundamental amplitude. The first mutation point of the fundamental amplitude is the fault time.

[0020] The full-cycle discrete Fourier transform formula is as follows:

[0021]

[0022] In the above formula, N is the number of sampling points per cycle, x(n) is a single sampling point, real(k) is the real part of the kth harmonic, and imag(k) is the imaginary part of the kth harmonic. Therefore, the fundamental amplitude can be calculated by the following formula:

[0023]

[0024] Step 4: FTU sends the estimated fault time to the traveling wave ranging unit;

[0025] Step 5: After detecting the IO port level flip, the traveling wave ranging unit is ready to receive the fault time sent by the FTU, and replies with a confirmation frame after receiving the fault time; the time range for filtering the recording wave is determined according to the received time, and the main wave of the fault traveling wave is filtered out from the cached recording wave data;

[0026] Step 6: The traveling wave ranging unit uploads the selected traveling wave main wave to the main station.

[0027] Furthermore, in step one, the FTU adopts a sampling rate of 6.4kHz and the traveling wave ranging unit adopts a sampling rate of 1MHz; in step two, the FTU recording time range is 12 cycles in total, namely the first 4 and the last 8 cycles; in step three, the time window length is 2ms; in step five, the time range for screening recording determined by the traveling wave ranging unit is the received fault time ±1ms.

[0028] Furthermore, in step 4, in the communication protocol between the FTU and the traveling wave ranging unit, time information including normal synchronization time and fault time is sent in a frame structure; the traveling wave ranging unit replies and confirms with a corresponding frame structure.

[0029] Furthermore, the short circuit fault diagnosis process includes the following steps:

[0030] Step 1: FTU collects line voltage in real time at a lower sampling rate, and takes the line voltage exceeding the lower limit as the starting condition, and records the wave after starting; collects the AB and CB line voltages, and the AC line voltage is obtained by calculation, and its calculation derivation process is shown in formula (3); the traveling wave ranging unit collects the three-phase current traveling wave in real time at a higher sampling rate, and takes whether the current traveling wave exceeds the upper limit as the starting condition, and records the wave after starting;

[0031]

[0032] Step 2: If the FTU detects that the line voltage exceeds the lower limit and the over-limit time exceeds the set value, the IO port level connected to the traveling wave ranging unit is flipped, and the sampled data within a certain range before and after the moment is recorded; the traveling wave ranging unit detects that the IO port level is flipped and the lock is started. At this time, the current traveling wave at the initial moment of the fault has been recorded by the traveling wave ranging unit for screening;

[0033] Step 3: After the FTU completes the waveform recording, the fault time is estimated for the line voltage channel that exceeds the lower limit in the waveform recording. If AB is short-circuited, use U AB Channel, if BC is short-circuited, use U BC Channel, if AC is short-circuited, then the U synthesized by (1) AC Channel, if the three phases are short-circuited, use U AB Channel; slide from left to right with a time window of 20ms per cycle, and the sliding step can be set. Perform full-cycle Fourier analysis on the data in the window to obtain the fundamental amplitude. The first mutation point of the fundamental amplitude is detected as the fault moment;

[0034] Step 4: FTU sends the estimated fault time to the traveling wave ranging unit;

[0035] Step 5: After detecting the IO port level flip, the traveling wave ranging unit is ready to receive the fault time sent by the FTU, determines the time range for filtering the recording according to the received time, and filters out the main wave of the fault traveling wave from the cached recording data;

[0036] Step 6: The traveling wave ranging unit uploads the selected traveling wave main wave to the main station.

[0037] Furthermore, in the step one, the FTU adopts a sampling rate of 6.4kHz; in the step two, the FTU recording time range is 12 cycles in total, namely the first 4 and the last 8; in the step three, the time window length is 2ms; in the step four, the FTU and the traveling wave ranging unit communicate in a frame structure to send time information, including normal synchronization time and fault time; the traveling wave ranging unit replies and confirms with a corresponding frame structure, and in the step five, the time range for screening recording determined by the traveling wave ranging unit is the received fault time ±1ms.

[0038] In order to achieve the above object, the present invention also provides a distribution network fault diagnosis system based on traveling wave ranging and recording screening, comprising the following modules:

[0039] Traveling wave ranging FTU module: used to integrate the traveling wave ranging unit into the distribution network feeder terminal FTU, and communicate with the FTU through the serial port, network port or other methods to form a traveling wave ranging FTU device;

[0040] Traveling wave ranging connection module: used to connect an IO port of the traveling wave ranging unit MCU with the IO port of the FTU main control MCU to receive real-time level signals;

[0041] Traveling wave ranging synchronization module: used for FTU and traveling wave ranging unit to share GPS signal to ensure time synchronization, wherein FTU receives NEMA message from GPS module through serial port, parses to get year, month, day, hour, minute, second and millisecond information, traveling wave ranging unit receives second pulse signal from GPS module, gets information below second level of fault time after crystal oscillator counting, accurate to nanosecond, information above second level is sent by FTU through communication port;

[0042] Traveling wave ranging calculation module: used to realize fault time calculation inside FTU. After confirming the line fault, the fault start time is calculated using the power frequency recording wave and sent to the traveling wave ranging unit. The traveling wave ranging unit selects the main traveling wave according to the calculated fault start time and uploads it to the master station for ranging.

[0043] Beneficial effects: The present invention is based on the mature feeder terminal product FTU, which combines the high reliability of FTU fault diagnosis with the high precision of traveling wave ranging unit fault location; the traveling wave ranging unit is integrated into the FTU to form a traveling wave ranging terminal, which can accurately screen out the main traveling wave of the fault without increasing the engineering installation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0045] Figure 1It is a flowchart of the main algorithm of the distribution network fault diagnosis method based on traveling wave ranging and recording screening according to an embodiment of the present invention;

[0046] Figure 2 It is a schematic diagram of the structure of a traveling wave ranging FTU device in a distribution network fault diagnosis method based on traveling wave ranging and recording screening according to an embodiment of the present invention;

[0047] Figure 3 A schematic diagram of zero-sequence voltage recording fault time estimation in a distribution network fault diagnosis method based on traveling wave ranging recording screening according to an embodiment of the present invention;

[0048] Figure 4 A schematic diagram of line voltage recording fault time estimation in a distribution network fault diagnosis method based on traveling wave ranging recording screening according to an embodiment of the present invention;

[0049] Figure 5 It is a structural schematic diagram of a distribution network fault diagnosis system based on traveling wave ranging and recording screening according to an embodiment of the present invention. DETAILED DESCRIPTION

[0050] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0051] Example 1

[0052] See also Figure 1-4 :A distribution network fault diagnosis method based on traveling wave ranging and recording screening includes the following steps:

[0053] S1. Integrate the traveling wave ranging unit into the distribution network feeder terminal FTU, and communicate with the FTU via a serial port, network port or other means to form a traveling wave ranging FTU device;

[0054] S2, an IO port of the traveling wave ranging unit MCU is connected to the IO port of the FTU main control MCU to receive the real-time level signal;

[0055] S3, FTU and the traveling wave ranging unit share GPS signals to ensure time synchronization, where FTU receives the NEMA message of the GPS module through the serial port, parses it to obtain the year, month, day, hour, minute, second and millisecond information, and the traveling wave ranging unit receives the second pulse signal from the GPS module, and obtains the information below the second level of the fault time after counting by the crystal oscillator, which is accurate to nanoseconds. The information above the second level is sent by the FTU through the communication port;

[0056] S4. FTU implements fault time estimation internally. After confirming the line fault, it uses the power frequency recording to estimate the fault start time and sends it to the traveling wave ranging unit. The traveling wave ranging unit selects the main traveling wave according to the estimated fault start time and uploads it to the master station for ranging.

[0057] This embodiment is based on the mature feeder terminal product FTU, which combines the high reliability of FTU fault diagnosis and the high accuracy of traveling wave ranging unit fault location. The traveling wave ranging unit is integrated into the FTU to form a traveling wave ranging terminal, which can accurately screen out the main traveling wave of the fault without increasing the engineering installation cost.

[0058] In a specific example, the line fault includes a ground fault and a short circuit fault.

[0059] In a specific example, the ground fault diagnosis process includes the following steps:

[0060] Step 1: The FTU collects zero-sequence voltage in real time at a relatively low sampling rate, and takes the zero-sequence voltage exceeding the upper limit as a starting condition, and records the wave after starting; the traveling wave ranging unit collects three-phase current traveling waves in real time at a relatively high sampling rate, and takes whether the current traveling waves exceed the upper limit as a starting condition, and records the wave after starting;

[0061] Step 2: If the FTU detects that the zero-sequence voltage exceeds the upper limit and the over-limit time exceeds the set value, the IO port level connected to the traveling wave ranging unit is flipped, and the sampled data within a certain range before and after the moment is recorded; the traveling wave ranging unit detects that the IO port level is flipped and the lock is started. At this time, the current traveling wave at the initial moment of the fault has been recorded by the traveling wave ranging unit for screening;

[0062] Step 3: After the FTU completes the recording, the fault time is estimated for the recorded zero-sequence voltage channel. Figure 3 As shown in the figure, a time window with a cycle of 20ms is slid from left to right, and the sliding step size can be set (2ms is recommended). The data in the window is subjected to full-cycle Fourier analysis to obtain the fundamental amplitude. The first mutation point of the fundamental amplitude is detected as the fault moment.

[0063] The full-cycle discrete Fourier transform formula is as follows:

[0064]

[0065] In the above formula, N is the number of sampling points per cycle, x(n) is a single sampling point, real(k) is the real part of the kth harmonic, and imag(k) is the imaginary part of the kth harmonic. Therefore, the fundamental amplitude can be calculated by the following formula:

[0066]

[0067] Step 4: FTU sends the estimated fault time to the traveling wave ranging unit;

[0068] Step 5: After detecting the IO port level flip, the traveling wave ranging unit is ready to receive the fault time sent by the FTU, and replies with a confirmation frame after receiving the fault time; the time range for filtering the recording wave is determined according to the received time, and the main wave of the fault traveling wave is filtered out from the cached recording wave data;

[0069] Step 6: The traveling wave ranging unit uploads the selected traveling wave main wave to the main station.

[0070] In a specific example, in step one, the FTU uses a 6.4kHz sampling rate and the traveling wave ranging unit uses a 1MHz sampling rate; in step two, the FTU recording time range is 4 cycles in front and 8 cycles in the back, totaling 12 cycles (240ms); in step three, the time window length is 2ms, and in step five, the time range for screening recording determined by the traveling wave ranging unit is the received fault time ±1ms.

[0071] In a specific example, in step 4, in the communication protocol between the FTU and the traveling wave ranging unit, time information including normal synchronization time and fault time is sent in the frame structure shown in Table 1; the traveling wave ranging unit replies with the corresponding frame structure shown in Table 2 for confirmation.

[0072] In a specific example, the short circuit fault diagnosis process includes the following steps:

[0073] Step 1: FTU collects line voltage in real time at a lower sampling rate, and takes the line voltage exceeding the lower limit as the starting condition, and records the wave after starting; collects the AB and CB line voltages, and the AC line voltage is obtained by calculation, and its calculation derivation process is shown in formula (3); the traveling wave ranging unit collects the three-phase current traveling wave in real time at a higher sampling rate, and takes whether the current traveling wave exceeds the upper limit as the starting condition, and records the wave after starting;

[0074]

[0075] Step 2: If the FTU detects that the line voltage exceeds the lower limit and the over-limit time exceeds the set value, the IO port level connected to the traveling wave ranging unit is flipped, and the sampled data within a certain range before and after the moment is recorded; the traveling wave ranging unit detects that the IO port level is flipped and the lock is started. At this time, the current traveling wave at the initial moment of the fault has been recorded by the traveling wave ranging unit for screening;

[0076] Step 3: After the FTU completes the waveform recording, the fault time is estimated for the line voltage channel that exceeds the lower limit in the waveform recording. If AB is short-circuited, use U Ab Channel, if BC is short-circuited, use U bc Channel, if AC is short-circuited, then the U synthesized by (1) ac Channel, if the three phases are short-circuited, use U AB channel; Figure 4 As shown, a time window with a cycle of 20ms is slid from left to right, and the sliding step size can be set (2ms is recommended). The data in the window is subjected to full-cycle Fourier analysis (refer to equations (1) and (2)) to obtain the fundamental amplitude. The first mutation point of the fundamental amplitude is detected as the fault moment.

[0077] Step 4: FTU sends the estimated fault time to the traveling wave ranging unit;

[0078] Step 5: After detecting the IO port level flip, the traveling wave ranging unit is ready to receive the fault time sent by the FTU, determines the time range for filtering the recording according to the received time, and filters out the main wave of the fault traveling wave from the cached recording data;

[0079] Step 6: The traveling wave ranging unit uploads the selected traveling wave main wave to the main station.

[0080] In a specific example, in step one, the FTU adopts a sampling rate of 6.4kHz; in step two, the FTU recording time range is 12 cycles (240ms) in total, namely the first 4 and the last 8; in step three, the time window length is 2ms; in step four, in the communication protocol between the FTU and the traveling wave ranging unit, time information is sent in the frame structure shown in Table 1, including normal synchronization time and fault time; the traveling wave ranging unit replies and confirms with the corresponding frame structure shown in Table 2, and in step five, the time range for screening recording determined by the traveling wave ranging unit is the received fault time ±1ms.

[0081] In a specific implementation, it also includes a traveling wave recording screening method when a distribution line grounding fault occurs, comprising the following steps:

[0082] Step 1: The FTU collects the zero-sequence voltage of the distribution line in real time at a sampling rate of 6.4kHz, and takes the zero-sequence voltage exceeding the upper limit as the starting condition, and records the wave after starting; the traveling wave ranging unit collects the three-phase current traveling wave in real time at a sampling rate of 1MHz, and takes whether the current traveling wave exceeds the upper limit as the starting condition, and records the wave after starting;

[0083] Step 2: If the FTU detects that the zero-sequence voltage exceeds the upper limit and the over-limit time exceeds the set value, the IO port level connected to the traveling wave ranging unit is flipped, and the sampling data of 12 cycles (240ms) before and after the 4th and 8th time are recorded. The traveling wave ranging unit detects that the IO port level is flipped and the lock is started. At this time, the current traveling wave at the initial moment of the fault has been recorded by the traveling wave ranging unit for screening;

[0084] In this step, since the initial traveling wave (main wave) of the fault is at the initial moment of the fault, the main wave has been recorded by the traveling wave ranging unit when the FTU detects that the zero voltage exceeds the limit. The FTU flips the IO port level to lock the traveling wave ranging unit to start, avoiding the traveling wave ranging unit from competing for resources with its startup thread when screening the recording, and also reducing the number of interference recordings;

[0085] Step 3: After the FTU completes the recording, the fault time of the recorded zero-sequence voltage channel is estimated. A time window of 20ms is slid from left to right with a sliding step of 2ms. The data in the window is subjected to a full-cycle Fourier analysis to obtain the fundamental amplitude. The time corresponding to the first mutation point of the fundamental amplitude is detected to be 11:30:21:566 ms on July 21, 2024, which is the fault time.

[0086] Step 4: FTU frames the estimated fault time of 11:30:21:566 ms on July 21, 2024 to the traveling wave ranging unit according to the communication protocol;

[0087] Step 5: After detecting the IO port level flip, the traveling wave ranging unit is ready to receive the fault time sent by the FTU, and replies with a confirmation frame after receiving the fault time. According to the received time of 11:30:21:566 ms on July 21, 2024, the time range for filtering the recording is determined to be 11:30:21:565 ms on July 21, 2024 to 11:30:21:567 ms on July 21, 2024, and the main wave of the fault traveling wave is filtered out from the cached recording data;

[0088] Step 6: The traveling wave ranging unit uploads the selected traveling wave main wave to the main station.

[0089] In a specific implementation, it also includes a traveling wave recording screening method when the AB phase of the distribution line is short-circuited, comprising the following steps:

[0090] Step 1: The FTU collects the line voltage of the distribution line in real time at a sampling rate of 6.4kHz, and takes the line voltage exceeding the lower limit as the starting condition, and records the wave after starting; the traveling wave ranging unit collects the three-phase current traveling wave in real time at a sampling rate of 1MHz, and takes whether the current traveling wave exceeds the upper limit as the starting condition, and records the wave after starting;

[0091] Step 2: If the FTU detects that the line voltage exceeds the lower limit and the over-limit time exceeds the set value, the IO port level connected to the traveling wave ranging unit is flipped, and the sampling data of 12 cycles (240ms) before and after the 4 and 8 times of the moment are recorded. The traveling wave ranging unit detects that the IO port level is flipped and the lock is started. At this time, the current traveling wave at the initial moment of the fault has been recorded by the traveling wave ranging unit for screening;

[0092] In this step, since the initial traveling wave (main wave) of the fault occurs at the initial moment of the fault, the main wave has been recorded by the traveling wave ranging unit when the FTU detects that the line voltage exceeds the limit. The FTU flips the IO port level to lock the traveling wave ranging unit to start, avoiding the traveling wave ranging unit from competing for resources with its startup thread when screening the recording, and also reducing the number of interference recordings;

[0093] Step 3: After the FTU completes the recording, the fault time of the recorded AB line voltage channel is estimated. A time window of 20ms is slid from left to right with a sliding step of 2ms. The data in the window is subjected to full-cycle Fourier analysis to obtain the fundamental amplitude. The time corresponding to the first mutation point of the fundamental amplitude is detected to be 11:32:51:218 ms on July 21, 2024, which is the fault time.

[0094] Step 4: FTU frames and sends the estimated fault time of 11:32:51:218 ms on July 21, 2024 to the traveling wave ranging unit according to the communication protocol;

[0095] Step 5: After detecting the IO port level flip, the traveling wave ranging unit is ready to receive the fault time sent by the FTU, and replies with a confirmation frame after receiving the fault time. According to the received time of 11:32:51:218 ms on July 21, 2024, the time range for filtering the recording is determined to be 11:32:51:217 ms to 11:32:51:219 ms on July 21, 2024, and the main wave of the fault traveling wave is filtered out from the cached recording data;

[0096] Step 6: The traveling wave ranging unit uploads the selected traveling wave main wave to the main station.

[0097] In a specific implementation, it also includes a traveling wave recording screening method when an AC phase short circuit fault occurs in a distribution line, comprising the following steps:

[0098] Step 1: The FTU collects the line voltage of the distribution line in real time at a sampling rate of 6.4kHz, and takes the line voltage exceeding the lower limit as the starting condition, and records the wave after starting; the traveling wave ranging unit collects the three-phase current traveling wave in real time at a sampling rate of 1MHz, and takes whether the current traveling wave exceeds the upper limit as the starting condition, and records the wave after starting;

[0099] Step 2: If the FTU detects that the line voltage exceeds the lower limit and the over-limit time exceeds the set value, the IO port level connected to the traveling wave ranging unit is flipped, and the sampling data of 12 cycles (240ms) before and after the 4 and 8 times of the moment are recorded. The traveling wave ranging unit detects that the IO port level is flipped and the lock is started. At this time, the current traveling wave at the initial moment of the fault has been recorded by the traveling wave ranging unit for screening;

[0100] In this step, since the initial traveling wave (main wave) of the fault occurs at the initial moment of the fault, the main wave has been recorded by the traveling wave ranging unit when the FTU detects that the line voltage exceeds the limit. The FTU flips the IO port level to lock the traveling wave ranging unit to start, avoiding the traveling wave ranging unit from competing for resources with its startup thread when screening the recording, and also reducing the number of interference recordings;

[0101] Step 3: After the FTU completes the recording, it generates AC line voltage recording data according to formula (3) to calculate the fault time. It slides from left to right with a time window of 20ms per cycle, with a sliding step of 2ms. It performs a full-cycle Fourier analysis on the data in the window to obtain the fundamental amplitude. The time corresponding to the first mutation point of the fundamental amplitude is 11:32:51:218 ms on July 21, 2024, which is the fault time.

[0102] Step 4: FTU frames the estimated fault time of 11:52:11:112 ms on July 21, 2024, and sends it to the traveling wave ranging unit according to the communication protocol;

[0103] Step 5: After detecting the IO port level flip, the traveling wave ranging unit is ready to receive the fault time sent by the FTU, and replies with a confirmation frame after receiving the fault time. According to the received time of 11:52:11:112 milliseconds on July 21, 2024, the time range for filtering the recording is determined to be 11:52:11:111 milliseconds on July 21, 2024 to 11:52:11:113 milliseconds on July 21, 2024, and the main wave of the fault traveling wave is filtered out from the cached recording data;

[0104] Step 6: The traveling wave ranging unit uploads the selected traveling wave main wave to the main station.

[0105] In summary, the fault diagnosis, wave recording and other functions mentioned in this embodiment are inherent functions of the terminal and do not require additional development. It is only necessary to implement the fault time estimation algorithm on this basis, which is simple to implement and has low development and verification costs.

[0106] The traveling wave main wave screening algorithm proposed in this embodiment can effectively solve the main wave selection problem in the current distribution network traveling wave ranging technology, realize the local distribution terminal's accurate screening of traveling wave main waves in the case of ground fault and short circuit fault, greatly reduce the communication and storage pressure of the master station, and is a great help to the distribution network to quickly and accurately locate faults and promote traveling wave ranging technology in the distribution network.

[0107] Table 1 FTU transmission protocol frame structure

[0108]

[0109] Table 2 Traveling wave ranging unit reply protocol frame structure

[0110]

[0111]

[0112] Example 2

[0113] To achieve the above purpose, see Figure 5 :This embodiment also provides a distribution network fault diagnosis system based on traveling wave ranging and recording screening, including the following modules:

[0114] Traveling wave ranging FTU module: used to integrate the traveling wave ranging unit into the distribution network feeder terminal FTU, and communicate with the FTU through the serial port, network port or other methods to form a traveling wave ranging FTU device;

[0115] Traveling wave ranging connection module: used to connect an IO port of the traveling wave ranging unit MCU with the IO port of the FTU main control MCU to receive real-time level signals;

[0116] Traveling wave ranging synchronization module: used for FTU and traveling wave ranging unit to share GPS signal to ensure time synchronization, wherein FTU receives NEMA message from GPS module through serial port, parses to get year, month, day, hour, minute, second and millisecond information, traveling wave ranging unit receives second pulse signal from GPS module, gets information below second level of fault time after crystal oscillator counting, accurate to nanosecond, information above second level is sent by FTU through communication port;

[0117] Traveling wave ranging calculation module: used to realize fault time calculation inside FTU. After confirming the line fault, the fault start time is calculated using the power frequency recording wave and sent to the traveling wave ranging unit. The traveling wave ranging unit selects the main traveling wave according to the calculated fault start time and uploads it to the master station for ranging.

[0118] The distribution network fault diagnosis system based on traveling wave ranging and recording screening of this embodiment has the same advantages as the distribution network fault diagnosis method based on traveling wave ranging and recording screening described above over the prior art, which will not be repeated here.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A distribution network fault diagnosis method based on traveling wave ranging and recording screening, characterized in that: The process includes the following steps: S1. Integrate the traveling wave ranging unit into the distribution network feeder terminal FTU, and communicate with the FTU via a serial port, network port or other means to form a traveling wave ranging FTU device; S2, an IO port of the traveling wave ranging unit MCU is connected to the IO port of the FTU main control MCU to receive the real-time level signal; S3, FTU and the traveling wave ranging unit share GPS signals to ensure time synchronization, where FTU receives the NEMA message of the GPS module through the serial port, parses it to obtain the year, month, day, hour, minute, second and millisecond information, and the traveling wave ranging unit receives the second pulse signal from the GPS module, and obtains the information below the second level of the fault time after counting by the crystal oscillator, which is accurate to nanoseconds. The information above the second level is sent by the FTU through the communication port; S4. FTU implements fault time estimation internally. After confirming the line fault, it uses the power frequency recording to estimate the fault start time and sends it to the traveling wave ranging unit. The traveling wave ranging unit selects the main traveling wave according to the estimated fault start time and uploads it to the master station for ranging.

2. The distribution network fault diagnosis method based on traveling wave ranging and recording screening according to claim 1 is characterized in that: The line fault includes a ground fault and a short circuit fault.

3. The distribution network fault diagnosis method based on traveling wave ranging and recording screening according to claim 2 is characterized in that: The ground fault diagnosis process includes the following steps: Step 1: The FTU collects zero-sequence voltage in real time at a relatively low sampling rate, and takes the zero-sequence voltage exceeding the upper limit as a starting condition, and records the wave after starting; the traveling wave ranging unit collects three-phase current traveling waves in real time at a relatively high sampling rate, and takes whether the current traveling waves exceed the upper limit as a starting condition, and records the wave after starting; Step 2: If the FTU detects that the zero-sequence voltage exceeds the upper limit and the over-limit time exceeds the set value, the IO port level connected to the traveling wave ranging unit is flipped, and the sampled data within a certain range before and after the moment is recorded; the traveling wave ranging unit detects that the IO port level is flipped and the lock is started. At this time, the current traveling wave at the initial moment of the fault has been recorded by the traveling wave ranging unit for screening; Step 3: After the FTU completes the recording, it calculates the fault time of the recorded zero-sequence voltage channel, slides from left to right in a 20ms time window, and the sliding step can be set. Perform a full-cycle Fourier analysis on the data in the window to obtain the fundamental amplitude. The first mutation point of the fundamental amplitude is the fault time. The full-cycle discrete Fourier transform formula is as follows: In the above formula, N is the number of sampling points per cycle, x(n) is a single sampling point, real(k) is the real part of the kth harmonic, and imag(k) is the imaginary part of the kth harmonic. Therefore, the fundamental amplitude can be calculated by the following formula: Step 4: FTU sends the estimated fault time to the traveling wave ranging unit; Step 5: After detecting the IO port level flip, the traveling wave ranging unit is ready to receive the fault time sent by the FTU, and replies with a confirmation frame after receiving the fault time; the time range for filtering the recording wave is determined according to the received time, and the main wave of the fault traveling wave is filtered out from the cached recording wave data; Step 6: The traveling wave ranging unit uploads the selected traveling wave main wave to the main station.

4. The method for diagnosing distribution network faults based on traveling wave ranging and recording screening according to claim 3 is characterized in that: In the step one, the FTU adopts a sampling rate of 6.4kHz and the traveling wave ranging unit adopts a sampling rate of 1MHz; in the step two, the FTU recording time range is 12 cycles in total, namely the first 4 and the last 8 cycles; in the step three, the time window length is 2ms, and in the step five, the time range for screening recording determined by the traveling wave ranging unit is the received fault time ±1ms.

5. The distribution network fault diagnosis method based on traveling wave ranging and recording screening according to claim 3 is characterized in that: In step 4, the FTU sends time information including normal synchronization time and fault time in a frame structure in the communication protocol with the traveling wave ranging unit; the traveling wave ranging unit responds and confirms with a corresponding frame structure.

6. The method for diagnosing distribution network faults based on traveling wave ranging and recording screening according to claim 2 is characterized in that: The short circuit fault diagnosis process includes the following steps: Step 1: FTU collects line voltage in real time at a lower sampling rate, and takes the line voltage exceeding the lower limit as the starting condition, and records the wave after starting; collects the AB and CB line voltages, and the AC line voltage is obtained by calculation, and its calculation derivation process is shown in formula (3); the traveling wave ranging unit collects the three-phase current traveling wave in real time at a higher sampling rate, and takes whether the current traveling wave exceeds the upper limit as the starting condition, and records the wave after starting; Step 2: If the FTU detects that the line voltage exceeds the lower limit and the over-limit time exceeds the set value, the IO port level connected to the traveling wave ranging unit is flipped, and the sampled data within a certain range before and after the moment is recorded; the traveling wave ranging unit detects that the IO port level is flipped and the lock is started. At this time, the current traveling wave at the initial moment of the fault has been recorded by the traveling wave ranging unit for screening; Step 3: After the FTU completes the waveform recording, the fault time is estimated for the line voltage channel that exceeds the lower limit in the waveform recording. If AB is short-circuited, use U AB Channel, if BC is short-circuited, use U BC Channel, if AC is short-circuited, then the U synthesized by (1) AC Channel, if the three phases are short-circuited, use U AB Channel; slide from left to right with a time window of 20ms per cycle, and the sliding step can be set. Perform full-cycle Fourier analysis on the data in the window to obtain the fundamental amplitude. The first mutation point of the fundamental amplitude is detected as the fault moment; Step 4: FTU sends the estimated fault time to the traveling wave ranging unit; Step 5: After detecting the IO port level flip, the traveling wave ranging unit is ready to receive the fault time sent by the FTU, determines the time range for filtering the recording according to the received time, and filters out the main wave of the fault traveling wave from the cached recording data; Step 6: The traveling wave ranging unit uploads the selected traveling wave main wave to the main station.

7. The method for diagnosing distribution network faults based on traveling wave ranging and recording screening according to claim 6 is characterized in that: In the step 1, the FTU adopts a sampling rate of 6.4kHz; in the step 2, the FTU recording time range is 12 cycles in total, namely the first 4 and the last 8 cycles; in the step 3, the time window length is 2ms; in the step 4, the FTU and the traveling wave ranging unit communicate in a frame structure to send time information, including normal synchronization time and fault time; the traveling wave ranging unit replies and confirms with a corresponding frame structure, and in the step 5, the time range for screening recording determined by the traveling wave ranging unit is the received fault time ±1ms.

8. A distribution network fault diagnosis system based on traveling wave ranging and recording screening, characterized in that: Includes the following modules: Traveling wave ranging FTU module: used to integrate the traveling wave ranging unit into the distribution network feeder terminal FTU, and communicate with the FTU through the serial port, network port or other methods to form a traveling wave ranging FTU device; Traveling wave ranging connection module: used to connect an IO port of the traveling wave ranging unit MCU with the IO port of the FTU main control MCU to receive real-time level signals; Traveling wave ranging synchronization module: used for FTU and traveling wave ranging unit to share GPS signal to ensure time synchronization, wherein FTU receives NEMA message from GPS module through serial port, parses to get year, month, day, hour, minute, second and millisecond information, traveling wave ranging unit receives second pulse signal from GPS module, gets information below second level of fault time after crystal oscillator counting, accurate to nanosecond, information above second level is sent by FTU through communication port; Traveling wave ranging calculation module: used to realize fault time calculation inside FTU. After confirming the line fault, the fault start time is calculated using the power frequency recording wave and sent to the traveling wave ranging unit. The traveling wave ranging unit selects the main traveling wave according to the calculated fault start time and uploads it to the master station for ranging.

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