CN117970037A - SOD change-based multiple lightning identification method for power transmission line - Google Patents

Abstract

The present invention relates to a method for identifying multiple lightning strikes on a power transmission line based on SOD changes, and belongs to the field of intelligent manufacturing and relay protection of new power systems. When a protected transmission line is struck by lightning and a fault occurs, the SOD change of the current waveform of the lightning fault phase is performed to obtain the SOD change result of the fault phase current waveform within the recording time window. ; Then, the SOD change is applied to the current waveform of a non-fault cycle in the recording window of S1 to obtain the SOD change result of the non-fault phase current waveform in the same cycle. ; Then by comparing and The abnormal point of the current waveform in the recording window is determined by the result; finally, the corresponding abnormal section is determined by the abnormal point, so as to judge the number of lightning strikes on the protected transmission line. The present invention only processes and compares the fault phase current information of the line after the lightning strike, without considering the other information of the current and the information of other electrical quantities. The judgment criterion is simple and the result is reliable.

Description

A method for identifying multiple lightning strikes on power transmission lines based on SOD changes

Technical Field

The invention relates to a transmission line multiple lightning identification method based on SOD changes, and belongs to the field of new power system intelligent manufacturing and relay protection.

Background technique

As an important part of the domestic power system, 110kV overhead transmission lines are of great significance in ensuring the stable and safe transmission of electric energy. Lightning current is an extremely strong electromagnetic pulse current. When thunderclouds discharge, they will form transient overvoltages on transmission lines. The main research direction of many scholars at home and abroad is to calculate and analyze the fault component caused by the first lightning strike, but ignore the impact of subsequent lightning strikes. According to statistical data analysis, the number of faults such as lightning tripping of lines above 110kV voltage level accounts for more than 60% of the total number of faults, and according to data from the lightning monitoring system, more than 70% of ground lightning strikes are multiple lightning strikes.

However, due to the lack of corresponding monitoring devices, it is currently difficult to identify and analyze subsequent lightning currents, and the actual operation is relatively difficult. It is difficult to determine whether the overhead transmission line is caused by a single lightning strike or multiple lightning strikes. There is an urgent need for a simple and reliable method that can accurately distinguish whether it is a single lightning strike or multiple lightning strikes after a lightning strike fault, which can play a reliable basic role in the targeted analysis of lightning protection for transmission lines.

Therefore, a multiple lightning identification method for transmission lines based on SOD changes is proposed to address the above problems.

Summary of the invention

The purpose of the present invention is to solve the shortcomings of the lack of corresponding monitoring devices, the difficulty of identifying and analyzing subsequent lightning currents, the difficulty of practical operation, and the difficulty in determining whether the overhead transmission line is caused by a single lightning strike or multiple lightning strikes, etc., from the perspective of intelligent manufacturing and relay protection of new power systems. Based on the identification of lightning faults by protection devices, the present invention proposes a method of identifying single lightning strikes and multiple lightning strikes by comparing the similarity of current waveforms in each time window.

Based on the above considerations, a multiple lightning identification method for transmission lines based on SOD changes is proposed.

A method for identifying multiple lightning strikes on a power transmission line based on SOD changes, characterized in that: collecting three-phase current signals of the power transmission line after a fault, and performing identification according to the following steps:

S1: When the protected transmission line is struck by lightning and a fault occurs, the SOD change of the lightning fault phase current waveform is performed to obtain the SOD change result of the fault phase current waveform within the recording time window ;

S2: Apply SOD change to the current waveform of a non-fault cycle in the recording time window of S1, and obtain the SOD change result of the non-fault phase current waveform in the same cycle ;

S3: By comparison With/> The abnormal point of the current waveform within the recording window is determined based on the result;

S4: Determine the corresponding abnormal section based on the abnormal point, so as to judge the number of times the protected transmission line is struck by lightning.

Preferably, the S1 specifically includes:

Take the fault phase current waveform in the short-time window and perform a fourth-order SOD change to obtain , the formula is:

;

in The original fault signal.

Preferably, S2 specifically includes:

Select a non-fault cycle in the recording window of S1, advance the margin of the recording window by 20ms, obtain the non-fault phase current waveform of the same cycle, perform SOD change on the waveform, and obtain .

Preferably, the S3 specifically includes:

Ⅰ. Adoption in principle;

Since the data needs to follow a normal distribution, In principle, /> The probability is 99.7%, so the distance to the average value The probability of a value other than , which belongs to very rare low-probability event data, so if it exceeds 3 times the standard deviation, it can be regarded as an outlier;

a1. Calculation The average value is: />

b1. Calculation The standard deviation of is:/>

II. By comparison With/> The difference between each item of data in the two arrays and /> The size of is used to determine the abnormal point of the current waveform within the recording window;

a2. If

Then the point is judged to be a normal point;

b2. If

Then the point is judged as an abnormal point.

Preferably, the S4 specifically includes:

a3. Connect the times corresponding to the abnormal points to determine the abnormal time period;

b3. If the time interval between two abnormal time periods is less than 1ms, the two abnormal time periods are merged into one abnormal time period;

c3. Count the number of abnormal time periods in the recording time window, record it as n, and judge that n lightning strikes occurred in the recording time window.

The present invention also discloses a transmission line multiple lightning identification system based on SOD changes, which is characterized by comprising:

Signal acquisition and processing module, used to acquire, process and store the current signal of the line;

Fault start module for comparing current rate of change The size of the setting value controls the start of the device;

A fault identification module is used to determine whether the fault is a lightning fault;

Lightning strike identification module, used to Based on the principle, the abnormal section of the current waveform within the recording time window is determined to identify single lightning strikes and multiple lightning strikes.

Preferably, the signal acquisition and processing module specifically includes:

Current transmitter unit, A/D converter unit and memory.

Preferably, the fault startup module specifically includes:

Current change rate monitoring unit, sampling device starting unit.

Preferably, the fault identification module specifically includes:

The lightning fault identification unit is used to determine whether the line fault is a lightning fault rather than other faults such as a short circuit or a broken line.

Preferably, the lightning strike identification module specifically includes:

The data calculation unit is used to perform SOD changes on the lightning fault phase current and the non-fault phase current waveform in the same period to obtain With/> ;

calculate The average value of and/> The standard deviation of ;

Lightning stroke type identification unit, used to Principles as a benchmark, by comparison/> With/> Based on the results, the abnormal section of the current waveform within the recording time window is determined to identify single lightning strikes and multiple lightning strikes;

The discrimination result output unit is used to output the lightning stroke type discrimination result.

The principle of the present invention is to utilize the fault current waveform collected by the monitoring device installed on the line, and adopt SOD change to the fault phase current waveform within the recording time window to Based on the principle, the abnormal section of the current waveform in the recording time window is determined, and the number of abnormal sections in the recording time window is counted to distinguish whether it is a single lightning strike or multiple lightning strikes.

The present invention has the following beneficial effects:

1. The method and system for identifying multiple lightning strikes on power transmission lines based on SOD changes of the present invention have an intuitive and simple principle, a clear physical concept, are easy to implement, and are suitable for practical engineering applications;

2. The method and system for identifying multiple lightning strikes on a power transmission line based on SOD changes of the present invention only processes and compares the fault phase current information of the line after the lightning strike, without considering the rest of the current information and the rest of the electrical quantity information, so the judgment criteria are simple and the results are reliable;

3. The method and system for identifying multiple lightning strikes on power transmission lines based on SOD changes of the present invention have simple signal processing and do not require the use of complex algorithms. It is only necessary to perform SOD changes on the fault phase current waveform within the recording time window, so the error probability is extremely low.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an AC system model;

Figure 2 is a tower model;

Figure 3 shows the differential form of the lightning fault current with a single lightning strike amplitude of 30kA at 20km from the head end;

Figure 4 shows the current differential form of a lightning fault with multiple lightning strokes of 30kA, 8kA, and 5kA at 20km from the head end;

Figure 5 shows the differential form of the lightning fault current with a single lightning stroke amplitude of 30kA at 100km from the head end;

Figure 6 shows the current differential form of a lightning fault with multiple lightning strokes of 30kA, 8kA, and 5kA at 100km from the head end;

FIG7 is a flow chart of multiple mine identification for transmission lines;

Figure 8 is a diagram of the multiple lightning identification system for transmission lines.

Detailed ways

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

When a lightning fault occurs in a power transmission line, the method and system of the present invention can accurately identify whether it is a single lightning strike or multiple lightning strikes. The process of identifying single lightning strikes and multiple lightning strikes on a power transmission line is shown in FIG7 , and the system is shown in FIG8 . The specific steps are as follows:

Step 1. When the current change rate When it is greater than the set value, the high-frequency data acquisition and wave recording device starts and records the current waveform before and after the fault;

Step 2: Determine whether it is a lightning fault by using a lightning fault identification method for transmission line traveling wave protection, wherein the lightning fault identification method for transmission line traveling wave protection is an existing method.

Step 3: When it is judged as a lightning fault, the SOD change of the lightning fault phase current waveform is performed to obtain the SOD change result of the fault phase current waveform within the recording time window. ;

Step 4: Apply SOD change to the current waveform of a non-fault cycle in the above recording time window to obtain the SOD change result of the non-fault phase current waveform in the same cycle. ;

Step 5. By comparison With/> The abnormal point of the current waveform within the recording window is determined based on the result of

Step 6, determine the corresponding abnormal segment based on the above abnormal points;

Step 7: Determine the number of lightning strikes on the protected transmission line through the abnormal section.

The example is as follows: According to the AC system model shown in FIG1 , the reliability of the present invention is verified by two sets of embodiments through simulation software:

Example 1:

110kV line, 300km, single lightning stroke with an amplitude of 30kA and multiple lightning strokes with amplitudes of 30kA, 8kA and 5kA respectively occur at 20km from the head end. The required current extreme value moment is measured at the protection installation at the station end and the lightning stroke severity is determined;

To ensure the reliability of the experiment, only one bus is built here to ensure that there is no impact caused by bus reflection and refracted waves of non-protected lines. The sampling rate is 100kHz.

Ⅰ. For single lightning strike

By performing SOD changes on the fault phase current waveform within the recording time window, the fourth-order SOD change is selected here, and its expression is:

Get the SOD change result of the fault phase current waveform within the recording time window and obtain .

The margin of the above recording time window is advanced by 20ms to obtain the current waveform of the phase without fault in the same period. The SOD change is performed on the waveform to obtain .

The average value is:

The standard deviation of is:

but

calculate , where /> The value of is recorded as the normal point; The value of is recorded as an outlier.

The moments corresponding to the selected abnormal points are connected to determine the abnormal time period as [1.00002, 1.00016], as shown in FIG3 .

In the recording time window, there is only one abnormal time period, so a single lightning strike occurred in the recording time window, and the judgment is accurate.

II. For multiple lightning strikes

By performing SOD changes on the fault phase current waveform within the recording time window, the fourth-order SOD change is selected here, and its expression is:

;

Get the SOD change result of the fault phase current waveform within the recording time window and obtain .

The margin of the above recording time window is advanced by 20ms to obtain the current waveform of the phase without fault in the same period. The SOD change is performed on the waveform to obtain .

The average value is:

The standard deviation of is:

but

calculate , where /> The value of is recorded as the normal point; The value of is recorded as an outlier.

The moments corresponding to the selected abnormal points are connected to determine the abnormal time periods as [1.00002, 1.00016], [1.00202, 1.00209], and [1.00272, 1.00276], as shown in FIG4 .

There are three abnormal time periods in the recording time window, so multiple lightning strikes occurred in the recording time window, and the number of lightning strikes is 3, which is an accurate judgment.

Example 2:

110kV line, 300km, single lightning stroke with amplitude of 30kA and multiple lightning stroke with amplitude of 30kA, 8kA and 5kA respectively occurred at 100km from the head end. The required current extreme value moment was measured at the protection installation at the station end and the lightning stroke severity was determined.

To ensure the reliability of the experiment, a busbar is built here to ensure that there is no impact caused by busbar reflection and refracted waves from non-protected lines. The sampling rate is 100kHz.

Ⅰ. For single lightning strike

According to the above steps, we can calculate:

The average value is:

The standard deviation of is:

but

calculate , where /> The value of is recorded as the normal point; The value of is recorded as an outlier.

The moments corresponding to the selected abnormal points are connected to determine the abnormal time period as [1.00029, 1.00045], as shown in FIG5 .

In the recording time window, there is only one abnormal time period, so a single lightning strike occurred in the recording time window, and the judgment is accurate.

II. For multiple lightning strikes

According to the above steps, we can calculate:

The average value is:

The standard deviation of is:

but

calculate , where /> The value of is recorded as the normal point; The value of is recorded as an outlier.

The moments corresponding to the selected abnormal points are connected to determine the abnormal time periods as [1.00029, 1.00045], [1.00229, 1.00235], and [1.00299, 1.00303], as shown in FIG6 .

There are three abnormal time periods in the recording time window, so multiple lightning strikes occurred in the recording time window, and the number of lightning strikes is 3, which is an accurate judgment.

Those skilled in the art will appreciate that the above embodiments are only used to illustrate the present invention and should not be considered to limit the scope of the present invention.

The results in the table and a large number of other simulation experiments show that the present invention is not only applicable to the determination of lightning strike types for existing transmission lines of various voltage levels, but also applicable to the determination of lightning strike types for long-distance, large-capacity, half-wavelength transmission lines with great development potential in the future. Therefore, the present invention can be well applied in engineering practice.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. A method for identifying multiple lightning strikes on a power transmission line based on SOD changes, characterized in that: collecting three-phase current signals of the power transmission line after a fault, and performing identification according to the following steps: S1: When the protected transmission line is struck by lightning and a fault occurs, the SOD change of the lightning fault phase current waveform is performed to obtain the SOD change result of the fault phase current waveform within the recording time window ; S2: Apply SOD change to the current waveform of a non-fault cycle in the recording time window of S1, and obtain the SOD change result of the non-fault phase current waveform in the same cycle ; S3: By comparison With/> The abnormal point of the current waveform within the recording window is determined based on the result of S4: Determine the corresponding abnormal section based on the abnormal point, so as to judge the number of times the protected transmission line is struck by lightning. 2. A method for identifying multiple lightning strikes on a power transmission line based on SOD changes according to claim 1, characterized in that: said S1 specifically comprises: Take the fault phase current waveform in the short-time window and perform a fourth-order SOD change to obtain , the formula is: ; in The original fault signal. 3. A method for identifying multiple lightning strikes on a power transmission line based on SOD changes according to claim 1, characterized in that: said S2 specifically comprises: Select a non-fault cycle in the recording window of S1, advance the margin of the recording window by 20ms, obtain the non-fault phase current waveform of the same cycle, perform SOD change on the waveform, and obtain . 4. A method for identifying multiple lightning strikes on a power transmission line based on SOD changes according to claim 1, characterized in that: said S3 specifically comprises: Ⅰ. Adoption in principle; a1. Calculation The average value is: /> ; b1. Calculation The standard deviation of is:/> ; II. By comparison With/> The difference between each item of data in the two arrays and /> The size of is used to determine the abnormal point of the current waveform in the recording window; a2. If ; Then the point is judged to be a normal point; b2. If ; Then the point is judged as an abnormal point. 5. According to claim 1, a method for identifying multiple lightning strikes on a power transmission line based on SOD changes, It is characterized in that: the S4 specifically includes: a3. Connect the times corresponding to the abnormal points to determine the abnormal time period; b3. If the time interval between two abnormal time periods is less than 1ms, the two abnormal time periods are merged into one abnormal time period; c3. Count the number of abnormal time periods in the recording time window, record it as n, and judge that n lightning strikes occurred in the recording time window. 6. A transmission line multiple lightning identification system based on SOD changes, characterized by comprising: A signal acquisition and processing module (1), used for acquiring, processing and storing the current signal of the line; Fault start module (2) for comparing the current change rate The size of the setting value controls the start of the device; A fault identification module (3) is used to determine whether the fault is a lightning fault; The lightning strike identification module (4) is used to Based on the principle, the abnormal section of the current waveform within the recording time window is determined to identify single lightning strikes and multiple lightning strikes. 7. A transmission line multiple lightning identification system based on SOD changes according to claim 6, characterized in that: the signal acquisition and processing module (1) specifically comprises: A current transmission unit (101), an A/D conversion unit (102) and a memory (103). 8. A transmission line multiple lightning identification system based on SOD changes according to claim 6, characterized in that: the fault start module (2) specifically comprises: A current change rate monitoring unit (201) and a sampling device starting unit (202). 9. A transmission line multiple lightning identification system based on SOD changes according to claim 6, characterized in that: the fault identification module (3) specifically comprises: The lightning fault determination unit (301) is used to determine whether the line fault is a lightning fault rather than other faults such as a short circuit or a broken line. 10. A transmission line multiple lightning identification system based on SOD changes according to claim 6, characterized in that: the lightning identification module (4) specifically comprises: The data calculation unit (401) is used to perform SOD changes on the lightning fault phase current and the non-fault phase current waveform in the same period to obtain With/> ; calculate The average value of and/> The standard deviation of ; A lightning stroke type identification unit (402) is used to Principles as a benchmark, by comparison/> With/> Based on the results, the abnormal section of the current waveform within the recording time window is determined to identify single lightning strikes and multiple lightning strikes; The discrimination result output unit (403) is used to output the lightning stroke type discrimination result.