Direct-current grounding fault positioning method for secondary circuit of transformer substation

Abstract

The invention relates to the technical field of electric power, in particular to a direct-current grounding fault positioning method for a secondary circuit of a transformer substation. The method comprises the following steps: acquiring fault traveling wave information, determining two traveling wave detection terminals which firstly detect fault traveling waves, determining the time when the two traveling wave detection terminals detect the fault traveling wave information, determining a fault occurrence range, and if a direct-current grounding fault occurs on a line between the two first detection terminals, determining the fault occurrence range; if yes, determining the position of the direct-current grounding fault according to the time when the two first detection terminals detect the fault traveling waves; if the DC grounding fault occurs on a cross node between the two first detection terminals or on a line outside the two first detection terminals, determining two traveling wave detection terminals closest to the two first detection terminals, and recording the two traveling wave detection terminals as second detection terminals; and determining the time when the two second detection terminals detect the fault traveling wave to determine the position of the DC grounding fault. The traveling wave detection terminal is arranged at the tail end of the line, the fault is rapidly and accurately detected and positioned, and rapid response of the fault is achieved.

Description

Technical Field

[0001] The invention relates to the field of electric power technology, and in particular to a method for locating a DC grounding fault in a secondary circuit of a transformer substation. Background Art

[0002] In the power system, the secondary circuit is the key part connecting the primary equipment and the control center, and undertakes the important task of monitoring, controlling and protecting the primary equipment. With the continuous development and expansion of the power system, higher requirements are put forward for the maintenance and fault diagnosis of the secondary circuit. Although traditional fault detection methods such as manual inspection and regular testing can ensure the stability of the system to a certain extent, they are inefficient and easy to miss, and can no longer meet the needs of modern power grids.

[0003] Based on the above problems, the invention patent with publication number CN115436865A discloses a current transformer secondary circuit monitoring system and method based on infrared thermal imaging. The secondary equipment is scanned by infrared thermal imaging, and the location of possible faults is determined by temperature anomalies. However, this method can only detect heating problems caused by overload, and cannot fully cover all types of faults (such as poor contact, etc.).

[0004] The invention patent with publication number CN112910089A proposes a method and system for visualizing fault logic of secondary equipment in a substation. The online monitoring device is used to collect the current and voltage signals in the secondary circuit in real time, and the signal characteristic changes are analyzed to detect faults. Although this method can improve the accuracy and timeliness of detection to a certain extent, the lack of accurate positioning capability of the specific DC grounding fault makes subsequent maintenance work still difficult.

[0005] In view of the fact that both of the above-mentioned two existing technologies have their own limitations, the present application aims to solve the following technical problems: how to effectively improve the accuracy and timeliness of secondary circuit fault detection, reduce false alarms or missed alarms caused by improper detection methods, and how to achieve a more comprehensive and in-depth diagnosis of secondary circuit faults. Summary of the invention

[0006] The present application provides a method for locating faults in a secondary circuit of a substation, which accurately locates the fault point by capturing and analyzing the changing characteristics of a traveling wave signal, thereby providing reliable protection for the safe and stable operation of the power system.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] A method for locating a DC grounding fault in a secondary circuit of a substation, wherein a traveling wave detection terminal is provided at the line end of the secondary circuit of the substation for detecting a fault traveling wave on the line; the method comprises: obtaining fault traveling wave information detected by the traveling wave detection terminal; determining two traveling wave detection terminals that first detect the fault traveling wave according to the fault traveling wave information detected by the traveling wave detection terminal, both of which are recorded as first detection terminals; respectively obtaining the time when the two first detection terminals detect the fault traveling wave information, and determining the fault occurrence range, including the line between the two first detection terminals, the intersection node between the two first detection terminals, or the line outside the two first detection terminals; if the DC grounding fault occurs on the line between the two first detection terminals, determining the DC grounding fault position according to the time when the two first detection terminals detect the fault traveling wave; if the DC grounding fault occurs on the intersection node between the two first detection terminals or on the line outside the two first detection terminals, determining two traveling wave detection terminals closest to the two first detection terminals, both of which are recorded as second detection terminals; determining the time when the two second detection terminals detect the fault traveling wave, and determining the DC grounding fault position in combination with the time when the first detection terminal detects the fault traveling wave.

[0009] In one possible implementation, each line end in the secondary circuit is provided with a traveling wave detection terminal; the fault traveling waves detected by the traveling wave detection terminal include current traveling waves and voltage traveling waves;

[0010] The traveling wave detection terminal detects fault traveling waves on the line, including:

[0011] Collect the three-phase current and zero-sequence current of the line;

[0012] Determine whether the zero-sequence current collected by the line is greater than the set current threshold;

[0013] If so, current recording is performed to obtain the current traveling wave;

[0014] Collect three-phase voltage and zero-sequence voltage;

[0015] Determine whether the zero-sequence voltage collection amount is greater than the set voltage threshold;

[0016] If the zero-sequence voltage acquisition amount is greater than the set voltage threshold, voltage recording is performed to obtain the voltage traveling wave.

[0017] In one possible implementation, the fault traveling wave information includes fault characteristics and wave head arrival time; the wave head arrival time is the arrival time of the first wave head when the traveling wave detection terminal performs current recording and voltage recording, and the fault characteristics are determined by the waveforms of the current recording and voltage recording.

[0018] In one possible implementation, determining the arrival time of the first wave head includes:

[0019] The fault traveling wave detected by the traveling wave detection terminal is transformed by continuous wavelet transform, which is expressed as:

[0020]

[0021] Where a is the expansion factor, b is the translation factor, Ψa,b(x) is the wavelet function corresponding to a and b of the selected base wavelet Ψ(x); f(x) represents the fault traveling wave signal detected by the traveling wave detection terminal; ψ * is the complex conjugate of the wavelet function;

[0022] Get the modulus maximum point |fw(a0,b0)| of the wavelet transform, which satisfies that at any scale a0, there exists a point (a0,b0), and for any point b in a neighborhood of b0, |fw(a0,b)|≤|fw(a0,b0)|;

[0023] According to the modulus maximum moment corresponding to the modulus maximum point |fw(a0,b0)|, the arrival time of the first wave head is determined.

[0024] In one possible implementation, obtaining the time when the two first detection terminals detect the fault traveling wave information and determining the fault occurrence range includes:

[0025] Determine the distances l1 and l2 from the two first detection terminals to the cross node between the two first detection terminals, and the propagation speed v of the fault traveling wave;

[0026] Obtaining the time difference between the two first detection terminals detecting the fault traveling wave information, and determining whether the time difference is equal to a preset threshold; wherein the preset threshold is expressed as (l1-l2) / v;

[0027] If the time difference is equal to the preset threshold (l1-l2) / v, it is determined that the fault occurrence range is the cross node between the two first detection terminals or the line outside the two first detection terminals;

[0028] If the time difference is greater than a preset threshold value (l1-l2) / v, or if the time difference is less than the preset threshold value (l1-l2) / v, it is determined that the fault occurrence range is the line between the two first detection terminals.

[0029] In one possible implementation, determining the DC grounding fault location according to the time when the two first detection terminals detect the fault traveling waves includes:

[0030] Determine the line midpoint of the two first detection terminals;

[0031] The first detection terminal which first detects the fault traveling wave among the two first detection terminals is determined, the DC grounding fault position is located between the first detection terminal which first detects the fault traveling wave and the midpoint of the line, and the distance from the DC grounding fault position to the midpoint of the line is half of the product of the absolute value of the time difference between the two first detection terminals detecting the fault traveling wave and the propagation speed v of the fault traveling wave.

[0032] In one possible implementation, determining the DC grounding fault location according to the time when the two second detection terminals detect the fault traveling waves and the time when the two first detection terminals detect the fault traveling waves includes:

[0033] Determine the second detection terminal among the two second detection terminals which first detects the fault traveling wave;

[0034] Determine that the fault occurrence range is a line formed by the second detection terminal that first detects the fault traveling wave and an adjacent cross node; wherein the adjacent cross node is a cross node between the second detection terminal that first detects the fault traveling wave and the first detection terminal that is closest to the second detection terminal that first detects the fault traveling wave;

[0035] The DC grounding fault position is determined according to the time when the second detection terminal that first detects the fault traveling wave detects the fault traveling wave and the time when the first detection terminal that is closest to the second detection terminal that first detects the fault traveling wave detects the fault traveling wave.

[0036] In one possible implementation, after the traveling wave detection terminal is set to detect the fault traveling wave on the line, the clock of each traveling wave detection terminal is corrected to correct the time reference of each traveling wave detection terminal. The method includes:

[0037] Inject different fault traveling waves at two known locations in the secondary circuit;

[0038] Respectively obtain a first detection time and a second detection time when the traveling wave detection terminal detects two types of fault traveling waves;

[0039] Calculating a first standard deviation between a first detection time and a first theoretical time, and a second standard deviation between a second detection time and a second theoretical time;

[0040] Determining whether the first standard deviation or the second standard deviation is greater than a second preset threshold;

[0041] If the first standard deviation or the second standard deviation is greater than the second preset threshold, the clock of the traveling wave detection terminal is corrected to control the first standard deviation and the second standard deviation to be less than or equal to the second preset threshold.

[0042] In one possible implementation, the clock of the traveling wave detection terminal is corrected to control the second standard deviation to be less than or equal to the second preset threshold, including:

[0043] adjusting the second detection time according to the difference between the first detection time and the first theoretical time;

[0044] Comparing the adjusted second detection time with the second theoretical time to determine a corrected standard deviation between the adjusted second detection time and the second theoretical time;

[0045] Determine whether the corrected standard deviation is less than a second preset threshold; if so, the correction is completed;

[0046] If the corrected standard deviation is greater than or equal to the second preset threshold, different fault signals are injected into the other two positions of the secondary loop to correct the clock of the traveling wave detection terminal.

[0047] In one possible implementation, the clock of the traveling wave detection terminal is corrected to control the first standard deviation to be less than or equal to the second preset threshold, including:

[0048] Adjusting the first detection time according to the difference between the second detection time and the second theoretical time;

[0049] Comparing the adjusted first detection time with the first theoretical time to determine a corrected standard deviation between the adjusted first detection time and the first theoretical time;

[0050] Determine whether the corrected standard deviation is less than a second preset threshold; if so, the correction is completed;

[0051] If the corrected standard deviation is greater than or equal to the second preset threshold, different fault signals are injected into the other two positions of the secondary loop to correct the clock of the traveling wave detection terminal.

[0052] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0053] The technical solution of the present application can detect and locate faults quickly and accurately by setting a traveling wave detection terminal at the end of the line, thereby significantly improving the reliability and safety of the power system. Once a fault occurs, the traveling wave detection terminal can immediately detect the fault traveling wave and achieve a rapid response to the fault.

[0054] By analyzing the time recorded by the two traveling wave detection terminals that first detected the fault traveling wave, the area where the fault occurred can be accurately determined, whether it is the line between the two detection terminals, the cross node or the line outside the terminal. Accurate fault location helps to quickly repair the fault, thereby reducing power outage time and ensuring the continuity of power supply. Improve safety: Timely and accurate fault location and repair can reduce safety risks caused by faults and ensure the safe operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a schematic diagram of the topological structure of a secondary circuit of a substation provided in Example 1 of the present application.

[0056] Figure 2 This is a flow chart of a fault detection method for a substation secondary circuit provided in Example 2 of the present application.

[0057] Figure 3 This is a fault diagram provided in Example 2 of the present application in which a DC grounding fault occurs between two traveling wave detection terminals.

[0058] Figure 4 This is a fault diagram provided in Example 2 of the present application in which a DC grounding fault occurs between cross nodes between two first detection terminals.

[0059] Figure 5 This is a fault diagram provided in Example 2 of the present application in which a DC grounding fault occurs on a line outside the two first detection terminals.

[0060] Figure 6 A flow chart of a method for locating a DC grounding fault in a secondary circuit of a substation provided in Example 3 of the present application. DETAILED DESCRIPTION

[0061] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0062] In the following description, many specific details are set forth to facilitate a full understanding of the present application, but the present application may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0063] When a DC ground fault occurs in the secondary circuit, a sudden voltage will appear at the fault point. Under the action of this sudden voltage, moving voltage and current traveling waves will appear on the line. These traveling waves are caused by line faults and contain rich fault information. They can be used as the basis for fault detection and are called fault traveling waves.

[0064] Fault traveling waves have transient characteristics and are non-repeatable. They are generated at the moment of fault occurrence and mainly reflect the nature of the fault point. Regardless of the nature of the fault, the severity of the fault, or the wiring method of the system, fault traveling waves will appear. Therefore, the correct use of fault traveling waves is of great significance to improving fault detection technology.

[0065] In the following, in combination with specific embodiments, the fault location method for the secondary circuit of a substation based on the traveling wave tracing theory provided by the present application is described in detail.

[0066] Embodiment 1:

[0067] After a DC ground fault occurs in a distribution line, the traveling wave generated at the fault point is transmitted from the fault point to both ends. During the transmission of the traveling wave, refraction and reflection will occur at the wave impedance discontinuity point. Therefore, in the embodiment of the present application, a traveling wave detection terminal is installed on the distribution line to monitor the traveling wave head and locate and detect the line fault of the secondary circuit of the substation.

[0068] Specifically, see Figure 1 , which is a schematic diagram of the topological structure of a secondary circuit of a substation provided in Example 1 of the present application.

[0069] like Figure 1 As shown in , each line end A~H in the secondary circuit is provided with a traveling wave detection terminal, including traveling wave detection terminal A~traveling wave detection terminal H. Figure 1 a to f in the figure are cross nodes of the line. The distances between the detection terminals A to H and their respective adjacent cross nodes and the distances between adjacent cross nodes can be measured in advance.

[0070] For example, the distance between intersection node a and intersection node b is l ab , the distance between the intersection node b and the intersection node c is l bc , the distance between the intersection node c and the intersection node d is l cd , the distance between the intersection node d and the intersection node e is l de , the distance between the intersection node e and the intersection node f is l ef , the distance between the detection terminal A and the cross node a can be recorded as l Aa , the distance between the detection terminal B and the cross node a can be recorded as l Ba, the distance between the detection terminal C and the cross node b can be recorded as l Cb , the distance between the detection terminal D and the cross node d can be recorded as l Dd , the distance between the detection terminal E and the cross node d can be recorded as l Ed , the distance between the detection terminal F and the cross node f can be recorded as l Ff , the distance between the detection terminal G and the cross node f can be recorded as l Gf , the distance between the detection terminal H and the cross node e can be recorded as l He .

[0071] Furthermore, the distance between any two traveling wave detection terminals can also be determined. For example, the distance between detection terminal A and detection terminal B is l Aa +l Ba , the distance between detection terminal A and detection terminal C is l Aa +l ab +l Cb , the distance between detection terminal A and detection terminal D is l Aa +l ab +l bc +l cd +l Dd , the distance between detection terminal A and detection terminal E is l Aa +l ab +l bc +l cd +l Ed , the distance between detection terminal A and detection terminal F is l Aa +l ab +l bc +l ce +l ef +l Ff , the distance between detection terminal A and detection terminal G is l Aa +l ab +l bc +l ce +l ef +l Gf , the distance between detection terminal A and detection terminal H is l Aa +l ab +l bc +l ce +l He According to the above method, the distance between any two detection terminals can be determined in sequence.

[0072] After a DC grounding fault occurs, a corresponding transient traveling wave signal will be generated in the line of the secondary circuit, and the transient traveling wave signal propagates along the shortest path in the line of the secondary circuit. Therefore, the position of the DC grounding fault in the line of the secondary circuit can be determined based on the transient traveling wave signal detected by the traveling wave detection terminal A to the traveling wave detection terminal H, combined with the distance between the traveling wave detection terminal A to the traveling wave detection terminal H and their respective adjacent cross nodes.

[0073] Specifically, in the technical solution provided in Example 1 of the present application, when a traveling wave signal is generated at a fault point and spreads outward, each traveling wave detection terminal located upstream and downstream of the fault point will record the time of signal arrival. By comparing the differences in the arrival times of the traveling wave signals detected by each terminal, combined with the pre-calibrated distance information between the terminals, the propagation speed and direction of the traveling wave signal can be calculated. Based on these data, the specific location of the DC grounding fault can be accurately located, thereby guiding maintenance personnel to quickly find and handle the fault point.

[0074] Embodiment 2

[0075] See also Figure 2 , is a flow chart of a fault detection method for a substation secondary circuit provided in the second embodiment of the present application. The fault detection method provided in the second embodiment of the present application is implemented based on the substation secondary circuit provided in the first embodiment. Figure 2 As shown in , the specific implementation steps of the above method include:

[0076] Step 201: Acquire fault traveling wave information detected by each traveling wave detection terminal.

[0077] Among them, the fault traveling wave information includes fault characteristics and wave head arrival time.

[0078] The transient traveling wave generated by the line after a fault occurs has mutation and singularity. The traditional Fourier transform analysis method and time domain analysis method will produce large errors, while wavelet analysis has good detection ability for the mutation of the signal.

[0079] Specifically, the fault feature may be determined based on the waveform feature of the fault traveling wave, and the wave head arrival time may be the time when the first wave head is detected.

[0080] Assume Ψ(x) as the base wavelet, fw(a,b) represents the continuous wavelet transform of the fault traveling wave signal f(x)∈L2(R) detected by the traveling wave detection terminal, which can be expressed as

[0081]

[0082] In the formula, a is the expansion factor, b is the translation factor, Ψ a,b (x) is the wavelet function corresponding to a and b of the selected base wavelet Ψ(x), ψ* is the complex conjugate of the wavelet function.

[0083] Suppose that under a certain scale a0 of wavelet transform, there exists a point (a0, b0) such that for any point b in a certain neighborhood of b0, |fw(a0, b)|≤|fw(a0, b0)|, then (a0, b0) is called the modulus maximum point of wavelet transform, |f w (a0,b0)| is the modulus maximum corresponding to the modulus maximum point.

[0084] The modulus maximum point of the wavelet transform corresponds to the transient traveling wave mutation point one by one. The wavelet modulus maximum point indicates that the signal has the largest rate of change at this point. The time when the initial wave head of the traveling wave signal arrives at the detection end corresponds to the first modulus maximum moment of the wavelet transform of the traveling wave signal, thereby determining the wave head arrival time of the fault traveling wave at each fault detection terminal.

[0085] In addition, the embodiment of the present application takes into account that the modulus maxima of the fault traveling wave and the noise signal have different performances under wavelet transform. The modulus maxima of the fault traveling wave signal increases with the increase of scale, and the modulus maxima of the noise signal decreases with the increase of scale. Therefore, a larger scale wavelet transform is selected to avoid the influence of noise on the detection of the traveling wave head.

[0086] Step 202: According to the fault traveling wave information detected by each traveling wave detection terminal, two traveling wave detection terminals that first detect the fault traveling wave are determined, and both are recorded as first detection terminals.

[0087] Specifically, the first two first detection terminals detecting the faulty traveling waves are determined according to the time when each traveling wave detection terminal detects the first wave head of the faulty traveling wave, and the time when the first two first detection terminals detecting the faulty traveling waves detect the faulty traveling waves are set to be t1 and t2 respectively.

[0088] Step 203 , preliminarily determine the fault occurrence range according to the times t1 and t2 when the first detection terminal detects the fault traveling wave.

[0089] For example, the distances between the two first detection terminals and the cross node between them are l1 and l2 respectively, and the propagation speed of the fault traveling wave is v. If the difference between t1 and t2 is equal to the preset threshold, the DC grounding fault occurs at the cross node between the two first detection terminals, or occurs on the line outside the two first detection terminals. If the difference between t1 and t2 is greater than or less than the preset threshold, the DC grounding fault occurs on the line between the two first detection terminals. Among them, the preset threshold can be (l1-l2) / v. Of course, the preset threshold can also be set according to the actual situation, and the embodiment of the present application does not make specific limitations.

[0090] In a specific scenario, see Figure 3If a DC grounding fault occurs between detection terminal A and detection terminal B, the fault traveling wave first reaches detection terminal A and detection terminal B from the fault location. Detection terminal A and detection terminal B are the first two detection terminals to detect the fault traveling wave. After that, the fault traveling wave reaches other traveling wave detection terminals.

[0091] The time when the traveling wave detection terminal A detects the fault traveling wave is t1, and the time when the detection terminal B detects the fault traveling wave is t2. The difference between t1 and t2 is (l A故 -l Ba -l B故 ) / v. Among them, l A故 is the distance between the traveling wave detection terminal A and the fault point, l B故 is the distance between the traveling wave detection terminal B and the fault point. That is, when the DC grounding fault occurs between the traveling wave detection terminal A and the traveling wave detection terminal B, the difference between t1 and t2 is not equal to the preset threshold value (l Aa -l Ba ) / v.

[0092] In another scenario, see Figure 4 , the DC grounding fault occurs between the cross node a and the cross node b, and the fault traveling wave first reaches the traveling wave detection terminal B and the traveling wave detection terminal C from the fault location. That is, the traveling wave detection terminal B and the traveling wave detection terminal C are the two detection terminals that first detect the fault traveling wave, and then the fault traveling wave reaches other traveling wave detection terminals.

[0093] The time when the traveling wave detection terminal B detects the fault traveling wave is t3, and the time when the detection terminal C detects the fault traveling wave is t4. The difference between t3 and t4 is less than (l Ba +l ab -l Cb ) / v, or the difference between t3 and t4 is less than (l ab +l Cb -l Ba That is, when the fault point is located on the line between the traveling wave detection terminal B and the traveling wave detection terminal C, the difference between t3 and t4 is not equal to the preset threshold value (l Ba +l ab -l Cb ) / v or (l ab +l Cb -l Ba ) / v.

[0094] In some other embodiments, see Figure 5 , the DC grounding fault occurs between the cross node b and the cross node c, and the fault traveling wave first reaches the traveling wave detection terminal B and the traveling wave detection terminal C from the fault location.

[0095] The time when the traveling wave detection terminal B detects the fault traveling wave is t5, and the time when the detection terminal C detects the fault traveling wave is t6. The difference between t5 and t6 is equal to (l b故 +l Cb -l b故 -l ab -l Bb ) / v or (l b故 +l ab +l Bb -l b故 -l Cb ) / v, that is, the difference between t5 and t6 is equal to (l Cb -l ab -l Bb ) / v or (l ab +l Bb -l Cb ) / v, indicating that the fault point is located at the cross node between detection terminal B and detection terminal C, or occurs on the line outside the two first detection terminals.

[0096] Step 204: If the DC grounding fault occurs on the line between the two first detection terminals, the DC grounding fault position is determined according to the time when the two first detection terminals detect the fault traveling waves.

[0097] Specifically, the line midpoints of the two first detection terminals are first determined. Then, the first detection terminal that first detects the fault traveling wave among the two first detection terminals is determined. It can be determined that the DC grounding fault position is located between the first detection terminal that first detects the fault traveling wave and the line midpoint, and the distance from the DC grounding fault position to the line midpoint is half of the product of the absolute value of the time difference between the two first detection terminals detecting the fault traveling wave and the propagation speed v of the fault traveling wave.

[0098] For example, Figure 3 In, l Aa , l Ba , t1, t2 and v are all known, then the fault location is: taking the midpoint of line AaB as the reference, the distance to the midpoint is half of the product of the absolute value of the difference between t1 and t2 and v. If t1 is less than t2, the fault point is located on the side of the midpoint close to the detection terminal A; if t1 is greater than t2, the fault point is located on the side of the midpoint close to the detection terminal B.

[0099] For example, Figure 4 In, l Ba , l ab , l Cb, t3, t4 and v are all known, then the fault location is: with the midpoint of line BabC as the reference, the distance to the midpoint is half the product of the absolute value of the difference between t3 and t4 and v. If t3 is less than t4, the fault point is located on the side of the midpoint close to detection terminal B. If t3 is greater than t4, the fault point is located on the side of the midpoint close to detection terminal C.

[0100] Step 205: If the DC grounding fault occurs at a cross node between two first detection terminals, or occurs on a line outside the two first detection terminals, two traveling wave detection terminals closest to the first two first detection terminals are determined and recorded as second detection terminals.

[0101] Step 206, determining the time when the two second detection terminals detect the fault traveling waves, and determining the DC grounding fault location according to the time when the two second detection terminals detect the fault traveling waves and the time when the two first detection terminals detect the fault traveling waves.

[0102] Specifically, first determine the second detection terminal that first detects the fault traveling wave among the two second detection terminals. Then determine that the fault occurrence range is the line formed by the second detection terminal that first detects the fault traveling wave and the adjacent cross node. Among them, the adjacent cross node is the cross node between the second detection terminal that first detects the fault traveling wave and the first detection terminal that is closest to the second detection terminal that first detects the fault traveling wave. Finally, determine the DC grounding fault location based on the time when the second detection terminal that first detects the fault traveling wave detects the fault traveling wave and the time when the first detection terminal that is closest to the second detection terminal that first detects the fault traveling wave detects the fault traveling wave.

[0103] For example, Figure 5 In FIG. 1 , it is assumed that the two second detection terminals are traveling wave detection terminal A and traveling wave detection terminal H. The time when traveling wave detection terminal A detects the wave head is t7, and the time when traveling wave detection terminal H detects the wave head is t8. Then Ba , l ab , l Cb , l Aa , l He , l ce , l bc , t5, t6, t7, t8 and v are all known, then the fault location is:

[0104] If t7 is earlier than t8 , the fault is located on line Aa. The specific location of the fault is determined based on t7 and t5 . For the specific method, refer to step 204 .

[0105] If t7 is later than t8 , the fault is located on line bceH. The specific location of the fault is determined based on t8 and t6 . For the specific method, refer to step 204 .

[0106] Compared with the prior art, the technical solution provided in the second embodiment of the present application has the following beneficial effects:

[0107] The technical solution of the present application can detect and locate faults quickly and accurately by setting a traveling wave detection terminal at the end of the line, thereby significantly improving the reliability and safety of the power system. Once a fault occurs, the traveling wave detection terminal can immediately detect the fault traveling wave and achieve a rapid response to the fault.

[0108] By analyzing the time recorded by the two traveling wave detection terminals that first detected the fault traveling wave, the area where the fault occurred can be accurately determined, whether it is the line between the two detection terminals, the cross node or the line outside the terminal. Accurate fault location helps to quickly repair the fault, thereby reducing power outage time and ensuring the continuity of power supply. Improve safety: Timely and accurate fault location and repair can reduce safety risks caused by faults and ensure the safe operation of the power system.

[0109] Embodiment 3

[0110] See also Figure 6 , is a flow chart of a method for locating a DC grounding fault in a secondary circuit of a substation provided in Embodiment 3 of the present application. Embodiment 3 further refines the process of detecting a faulty traveling wave by a traveling wave detection terminal.

[0111] Traveling wave detection terminals (such as sensors or monitoring devices) are installed at key locations in substations to capture traveling wave information when a fault occurs. The traveling wave signals are transmitted to the server in real time through a network (such as industrial Ethernet, optical fiber communication, wireless communication, etc.).

[0112] The server receives data from each traveling wave detection terminal, including but not limited to traveling wave arrival time difference (TDOA), traveling wave amplitude change and other information, and then calculates the location of the fault point

[0113] Specifically, Figure 6 As shown in , the specific implementation steps of the above method may include:

[0114] Step 601, determining the connection relationship and distance between each traveling wave detection terminal and the cross node in the line of the secondary loop.

[0115] Among them, the connection relationship between each traveling wave detection terminal and the intersection node is: the line identifier of each detection terminal, the adjacent relationship between each traveling wave detection terminal, the line identifier corresponding to each intersection node, the adjacent relationship between the traveling wave detection terminal and the intersection node, etc.

[0116] The distances between the various traveling wave detection terminals and the cross nodes include: the distance between the cross nodes and the distance between the traveling wave detection terminals and the cross nodes.

[0117] Step 602: Determine the distance between any two traveling wave detection terminals according to the above connection relationship and distance.

[0118] Step 603: After the traveling wave detection terminal detects the fault traveling wave, it sends the fault traveling wave information to the server.

[0119] In this embodiment, the process of the traveling wave detection terminal detecting fault traveling waves is: collecting the three-phase current and zero-sequence current of the line, when the zero-sequence current collection amount exceeds the set current threshold, the traveling wave detection terminal performs current recording; collecting the three-phase voltage and zero-sequence voltage, when the zero-sequence voltage collection amount exceeds the set voltage threshold, the traveling wave detection terminal performs voltage recording.

[0120] The traveling wave detection terminal determines the arrival time of the first wave head based on the current recording and voltage recording, with specific reference to the above content, and determines the fault characteristics based on the waveforms of the current recording and voltage recording, and sends the terminal identification, arrival time and fault characteristics to the server.

[0121] Specifically, the traveling wave detection terminal converts the terminal identification, arrival time and fault characteristics into relatively concise information (e.g., hexadecimal information) using preset rules, and then generates a sequence of these concise information in the order of terminal identification, arrival time and fault characteristics and sends it to the server for efficient transmission. After receiving this sequence, the server extracts the concise information of the terminal identification, arrival time and fault characteristics from it, and then converts the concise information into the information of the terminal identification, arrival time and fault characteristics themselves according to the preset rules.

[0122] The server converts the sequence of the same traveling wave detection terminal into a vector in advance, and calculates the distance between the two vectors of the same traveling wave detection terminal at adjacent moments. If the distance is less than the first preset threshold, it means that the two sequences of the same traveling wave detection terminal at adjacent moments are the same, and the sequence of the previous moment can be used for fault location, and there is no need to process the sequence of the next moment.

[0123] Step 604: The server determines the first two detection terminals that detect the faulty traveling waves according to the faulty traveling wave information sent by each traveling wave detection terminal.

[0124] Step 605: If the DC grounding fault occurs on the line between the two first detection terminals, the location of the fault is determined according to the time when the two first detection terminals detect the fault traveling waves.

[0125] Step 606: If the DC ground fault occurs at a cross node between the first detection terminals, or occurs on a line outside the two first detection terminals, then based on the distance between any two detection terminals determined in step 602, determine the two second detection terminals closest to the first two first detection terminals that detected the fault traveling waves.

[0126] Step 607, determining the time when the two second detection terminals detect the fault traveling waves, and determining the DC grounding fault location according to the time when the two second detection terminals detect the fault traveling waves and the time when the two first detection terminals detect the fault traveling waves.

[0127] In some embodiments, the server simulates and displays the fault location information through a display. For example, a simulated screen of the secondary circuit is generated, and after the DC grounding fault location is determined, a fault icon is generated at the corresponding position in the simulated screen. After the user places the mouse on the fault icon, an animation is generated that displays the fault characteristics, the DC grounding fault location, and the fault time. The animation can also display the historical faults at the DC grounding fault location, which can facilitate the management personnel to have a more intuitive and clear grasp of the faults in the secondary circuit.

[0128] In addition, in order to improve the accuracy of fault location, the method provided in this embodiment further includes correcting the clock of each traveling wave detection terminal so that the time reference of each traveling wave detection terminal is consistent.

[0129] Specifically, different fault traveling waves are injected at two known positions of the secondary circuit. When the traveling wave detection terminals A to H detect two fault traveling waves respectively, the first detection time and the second detection time when the traveling wave detection terminals A to H detect the two fault traveling waves respectively are recorded. Each first detection time and the second detection time are compared with the first theoretical time and the second theoretical time (the theoretical time is the time obtained according to theoretical calculation).

[0130] The first detection time corresponds to the first theoretical time, and the second detection time corresponds to the second theoretical time. Calculate the first standard deviation between the first detection time of each traveling wave detection terminal and the first theoretical time, and the second standard deviation between the second detection time of each traveling wave detection terminal and the second theoretical time. If the first standard deviation and the second standard deviation are both less than or equal to the second preset threshold, it is not necessary to correct the clock of each detection terminal. If at least one of the first standard deviation and the second standard deviation is greater than the second preset threshold, it is necessary to correct the clock of each detection terminal so that the standard deviation is less than or equal to the second preset threshold. Optionally, the above-mentioned second preset threshold can be set according to actual conditions, and this application does not make specific limitations.

[0131] Furthermore, the correction process is as follows: adjust the second detection time according to the difference between the first detection time and the first theoretical time. Compare the adjusted second detection time with the second theoretical time, and calculate the second standard deviation between the adjusted second detection time and the second theoretical time (the second standard deviation recalculated after adjustment). If the second standard deviation is less than the second preset threshold, the correction is completed. If the second standard deviation is greater than or equal to the second preset threshold, inject different fault signals at two known positions of the secondary circuit (different from the last position) again, and repeat the above steps.

[0132] In other embodiments, the correction can also be performed by adjusting the first detection time according to the difference between the second detection time and the second theoretical time. The adjusted first detection time is compared with the first theoretical time, and the first standard deviation of the adjusted first detection time and the first theoretical time is calculated (the first standard deviation recalculated after adjustment). If the first standard deviation is less than the second preset threshold, the correction is completed. If the first standard deviation is greater than or equal to the second preset threshold, different fault signals are injected again at two known positions of the secondary circuit (different from the last position), and the above steps are executed cyclically.

[0133] Optionally, the above correction process may be performed once at regular intervals, for example, once a week. Alternatively, the above correction process may be performed once after the presence detection terminal is powered off and restarted, which is not specifically limited in the embodiments of the present application.

[0134] Compared with the prior art, the technical solution provided by the embodiment of the present application has the following beneficial effects:

[0135] The present application first establishes the connection relationship and distance database between each traveling wave detection terminal and the cross node in the line of the secondary circuit, and then determines the distance between any two traveling wave detection terminals. After the detection terminal detects the fault traveling wave, the information of the fault traveling wave is sent to the server. The server determines the first two first detection terminals that detect the fault traveling wave based on the information of the fault traveling wave sent by the detection terminal. If the DC grounding fault occurs on the line between the two first detection terminals, the location of the fault is determined according to the time when the two first detection terminals detect the fault traveling wave. If the DC grounding fault occurs at the cross node between the two first detection terminals, or occurs on the line outside the two first detection terminals, determine the two second detection terminals closest to the first two first detection terminals that detect the fault traveling wave, determine the time when the two second detection terminals detect the fault traveling wave, and determine the DC grounding fault location based on the time when the two second detection terminals detect the fault traveling wave and the time when the two first detection terminals detect the fault traveling wave.

[0136] By setting a detection terminal at the end of each line to detect the fault traveling wave, the location of the fault in the secondary circuit can be determined based on the time when the detection terminal detects the fault traveling wave and the position and connection relationship of the detection terminal. It is no longer necessary to conduct regular inspections and tests on the secondary circuit line through manual observation or the use of special testing equipment. Line faults can be discovered at the first time, saving manpower and improving fault detection efficiency and accuracy.

[0137] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for locating a DC grounding fault in a secondary circuit of a substation, wherein a traveling wave detection terminal is provided at the end of the line of the secondary circuit of the substation for detecting a fault traveling wave on the line, characterized in that: include: Obtaining fault traveling wave information detected by the traveling wave detection terminal; According to the fault traveling wave information, the two traveling wave detection terminals which first detect the fault traveling wave are determined, and both are recorded as the first detection terminals; Respectively obtain the time when the two first detection terminals detect the fault traveling wave information, and determine the fault occurrence range, including the line between the two first detection terminals, the cross node between the two first detection terminals, or the line outside the two first detection terminals; If a DC grounding fault occurs on the line between two first detection terminals, the DC grounding fault position is determined according to the time when the two first detection terminals detect the fault traveling waves; If the DC grounding fault occurs at a cross node between two first detection terminals or occurs on a line outside the two first detection terminals, two traveling wave detection terminals closest to the two first detection terminals are determined and both are recorded as second detection terminals; The time when the two second detection terminals detect the fault traveling waves is determined, and the DC grounding fault position is determined in combination with the time when the first detection terminal detects the fault traveling wave.

2. A method for locating a DC grounding fault in a secondary circuit of a substation according to claim 1, characterized in that: A traveling wave detection terminal is provided at each line end in the secondary circuit; The fault traveling waves detected by the traveling wave detection terminal include current traveling waves and voltage traveling waves; The traveling wave detection terminal detects fault traveling waves on the line, including: Collect the three-phase current and zero-sequence current of the line; Determine whether the zero-sequence current collected by the line is greater than the set current threshold; If so, current recording is performed to obtain the current traveling wave; Collect three-phase voltage and zero-sequence voltage; Determine whether the zero-sequence voltage collection amount is greater than the set voltage threshold; If the zero-sequence voltage acquisition amount is greater than the set voltage threshold, voltage recording is performed to obtain the voltage traveling wave.

3. A method for locating a DC grounding fault in a secondary circuit of a substation according to claim 2, characterized in that: The fault traveling wave information includes fault characteristics and wave head arrival time; the wave head arrival time is the arrival time of the first wave head when the traveling wave detection terminal performs current recording and voltage recording, and the fault characteristics are determined by the waveforms of the current recording and voltage recording.

4. A method for locating a DC grounding fault in a secondary circuit of a substation according to claim 3, characterized in that: Determine the arrival time of the first wave head, including: The fault traveling wave detected by the traveling wave detection terminal is transformed by continuous wavelet transform, which is expressed as: In the formula, a is the expansion factor, b is the translation factor, Ψ a,b (x) is the wavelet function corresponding to a and b of the selected base wavelet Ψ(x); f(x) represents the fault traveling wave signal detected by the traveling wave detection terminal; ψ * is the complex conjugate of the wavelet function; Get the modulus maximum point of wavelet transform |f w (a0,b0)|, which satisfies that at any scale a0, there exists a point (a0,b0) such that for any point b in a neighborhood of b0, |f w (a0,b)|≤|fw(a0,b0)|; According to the modulus maximum point |f w (a0,b0)|The corresponding modulus maximum moment determines the arrival time of the first wave head.

5. A method for locating a DC grounding fault in a secondary circuit of a substation according to claim 1, characterized in that: Obtaining the time when the two first detection terminals detect the fault traveling wave information and determining the fault occurrence range includes: Determine the distances l1 and l2 from the two first detection terminals to the cross node between the two first detection terminals, and the propagation speed v of the fault traveling wave; Obtaining a time difference between two first detection terminals detecting fault traveling wave information, and determining whether the time difference is equal to a preset threshold; wherein the preset threshold is expressed as (l1-l2) / v; If the time difference is equal to the preset threshold (l1-l2) / v, it is determined that the fault occurrence range is the cross node between the two first detection terminals or the line outside the two first detection terminals; If the time difference is greater than a preset threshold value (l1-l2) / v, or if the time difference is less than the preset threshold value (l1-l2) / v, it is determined that the fault occurrence range is the line between the two first detection terminals.

6. A method for locating a DC grounding fault in a secondary circuit of a substation according to claim 1, characterized in that: Determining the DC grounding fault position according to the time when the two first detection terminals detect the fault traveling waves includes: Determine the line midpoint of the two first detection terminals; The first detection terminal which first detects the fault traveling wave among the two first detection terminals is determined, the DC grounding fault position is located between the first detection terminal which first detects the fault traveling wave and the midpoint of the line, and the distance from the DC grounding fault position to the midpoint of the line is half of the product of the absolute value of the time difference between the two first detection terminals detecting the fault traveling wave and the propagation speed v of the fault traveling wave.

7. A method for locating a DC grounding fault in a secondary circuit of a substation according to claim 1, characterized in that: Determining the DC grounding fault position according to the time when the two second detection terminals detect the fault traveling waves and the time when the two first detection terminals detect the fault traveling waves includes: Determine the second detection terminal among the two second detection terminals which first detects the fault traveling wave; Determine that the fault occurrence range is a line formed by the second detection terminal that first detects the fault traveling wave and an adjacent cross node; wherein the adjacent cross node is a cross node between the second detection terminal that first detects the fault traveling wave and the first detection terminal that is closest to the second detection terminal that first detects the fault traveling wave; The DC grounding fault position is determined according to the time when the second detection terminal that first detects the fault traveling wave detects the fault traveling wave and the time when the first detection terminal that is closest to the second detection terminal that first detects the fault traveling wave detects the fault traveling wave.

8. A method for locating a DC grounding fault in a secondary circuit of a substation according to claim 1, characterized in that: After the traveling wave detection terminal is set to detect the fault traveling wave on the line, the method further includes correcting the clock of each traveling wave detection terminal to correct the time reference of each traveling wave detection terminal. The method includes: Inject different fault traveling waves at two known locations in the secondary circuit; Respectively obtain a first detection time and a second detection time when the traveling wave detection terminal detects two types of fault traveling waves; Calculating a first standard deviation between a first detection time and a first theoretical time, and a second standard deviation between a second detection time and a second theoretical time; Determining whether the first standard deviation or the second standard deviation is greater than a second preset threshold; If the first standard deviation or the second standard deviation is greater than the second preset threshold, the clock of the traveling wave detection terminal is corrected to control the first standard deviation and the second standard deviation to be less than or equal to the second preset threshold.

9. A method for locating a DC grounding fault in a secondary circuit of a substation according to claim 8, characterized in that: Correcting the clock of the traveling wave detection terminal to control the second standard deviation to be less than or equal to the second preset threshold includes: adjusting the second detection time according to the difference between the first detection time and the first theoretical time; Comparing the adjusted second detection time with the second theoretical time to determine a corrected standard deviation between the adjusted second detection time and the second theoretical time; Determine whether the corrected standard deviation is less than a second preset threshold; if so, the correction is completed; If the corrected standard deviation is greater than or equal to the second preset threshold, different fault signals are injected into the other two positions of the secondary loop to correct the clock of the traveling wave detection terminal.

10. A method for locating a DC grounding fault in a secondary circuit of a substation according to claim 8, characterized in that: Correcting the clock of the traveling wave detection terminal to control the first standard deviation to be less than or equal to the second preset threshold includes: Adjusting the first detection time according to the difference between the second detection time and the second theoretical time; Comparing the adjusted first detection time with the first theoretical time to determine a corrected standard deviation between the adjusted first detection time and the first theoretical time; Determine whether the corrected standard deviation is less than a second preset threshold; if so, the correction is completed; If the corrected standard deviation is greater than or equal to the second preset threshold, different fault signals are injected into the other two positions of the secondary loop to correct the clock of the traveling wave detection terminal.

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