PT secondary circuit N-phase multipoint grounding monitoring method and system

Abstract

The invention belongs to the technical field of relay protection secondary alternating current circuits, and particularly relates to a PT secondary circuit N-phase multipoint grounding monitoring method and system. The system comprises a high-precision current sensor, a distributed acquisition terminal and a background system. The acquisition terminal carries out synchronous acquisition and calculation processing on the PT secondary circuit N-phase ground point current acquired by the high-precision current sensor and each branch current, and then transmits the current to the background system through the communication network for further judgment. The method for judging the PT secondary circuit N-phase multi-point grounding mainly comprises the steps that N-phase grounding wire currents are detected, when it is judged that two-point or multi-point grounding faults occur, similarity analysis based on the Hausdorff distance is adopted, the similarity of the N-phase grounding wire currents and the similarity of currents of all branches are compared, and the fault branches are further judged. According to the method, the detection accuracy of the PT secondary circuit N-phase multipoint grounding fault branch can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary AC circuits of relay protection, and particularly relates to a method and system for monitoring multi-point grounding of the N phase in a PT secondary circuit. Background Art

[0002] The secondary AC circuit of the relay protection PT is a key component of the power secondary system. With the increase in the scale of the power grid, the number of defects such as two-point grounding and multi-point grounding in the PT secondary AC circuit has been increasing due to reasons such as cable insulation and manual misoperation.

[0003] When two-point or multi-point grounding occurs in the N phase of the PT secondary circuit, it will cause the phase shift of the neutral point voltage of the PT secondary circuit, thereby affecting the amplitude and phase of the phase voltage and zero-sequence voltage, and resulting in incorrect operation of the protection.

[0004] When two-point or multi-point grounding occurs in the N phase of the PT secondary circuit, the secondary protection device cannot judge, and the operation and maintenance personnel can only judge through analysis after the protection malfunctions.

[0005] At present, in order to avoid power grid accidents caused by faults in the secondary circuit of relay protection, each power grid company needs to dispatch team technicians to the substation site to gradually check it every year or even every quarter. The workload is large, consuming a lot of manpower and material resources, and the inspection efficiency is low.

[0006] For the multi-point grounding insulation fault of the PT secondary circuit, mainly detect the effective value of the current on the grounding wire of the PT secondary side. If the current detected on the grounding wire is greater than a certain value (for example: 50 mA), it is determined that there is two-point or multi-point grounding in the N phase, and then gradually detect the effective value of the N-phase current on each branch to judge and locate the fault branch.

[0007] The existing technologies have the following problems:

[0008] (1) According to the detection requirements of each power grid company, when the current on the grounding wire of the PT secondary side reaches a certain value (for example: 50 mA), it is further determined that there is two-point or multi-point grounding in the N phase. If the potential difference between the two grounding points of the N phase at the site is relatively low, and when two-point or multi-point grounding occurs, the grounding wire current does not reach the threshold value, it cannot be judged and processed in time, and long-term tracking and observation are required;

[0009] (2) When two-point or multi-point grounding in the N phase of the PT secondary circuit is detected, it is necessary to sequentially measure the N-phase current of each branch for investigation; and there is unbalanced current on the neutral line due to reasons such as inconsistent PT parameters and inconsistent voltages. If there is two-point or multi-point grounding in the N phase, the current is superimposed. Due to the phase relationship of the vectors, it may not be possible to determine the branch position of the fault grounding point through the measurement of the effective value on the N line;

[0010] (3) Since manual inspection is carried out regularly, there is a time difference between the manual inspection and the occurrence of two or more points of grounding on the N phase of the PT secondary circuit. If a grounding fault occurs in a line during this period, it will lead to incorrect operation of the protection.

[0011] In view of the existing PT secondary AC circuit, when two or more points of grounding occur on the N phase, it is necessary to conduct long-term manual inspections, it is impossible to judge small grounding circulating currents, and it is difficult to locate the fault branch of the grounding point. The present invention is proposed. Summary of the Invention

[0012] This patent mainly solves the problems of rapid judgment of two or more points of grounding on the N phase of the PT secondary circuit and fault location of the grounding point branch; through the waveform similarity analysis method, it judges the insulation fault and the fault location of the grounding point branch when the grounding circulating current is small during two or more points of grounding on the N phase; when two or more points of grounding occur on the N phase, the grounding circulating current and the neutral line unbalanced current of the branch are superimposed, and the effective value cannot accurately reflect the fault of the grounding point branch. Through the waveform similarity analysis method, the judgment of the fault location of the grounding point branch is carried out.

[0013] As a preferred scheme of a method for monitoring multiple points of grounding on the N phase of a PT secondary circuit according to the present invention, wherein: collecting data of each current sensor to form a periodic data point set and calculating the effective value;

[0014] Comparing the neutral line grounding current with a threshold value to judge whether there are two or more points of grounding;

[0015] According to the judgment result, similarity analysis and comparison are carried out to obtain the fault branch of the grounding point.

[0016] As a preferred scheme of a method for monitoring multiple points of grounding on the N phase of a PT secondary circuit according to the present invention, wherein: the collecting of data of each current sensor includes the neutral line grounding current and the N-phase current of each PT secondary circuit.

[0017] As a preferred scheme of a method for monitoring multiple points of grounding on the N phase of a PT secondary circuit according to the present invention, wherein: the calculation of the effective value is expressed as:

[0018]

[0019] Wherein, I rms is the effective value of the current of the collected line, N is the number of points collected in a period, and i1 to i N are the instantaneous values of the currents of the collected points.

[0020] As a preferred scheme of a method for monitoring multiple points of grounding on the N phase of a PT secondary circuit according to the present invention, wherein: the comparing of the neutral line grounding current with a threshold value includes,

[0021] If the effective value of the neutral line grounding current is greater than or equal to the high threshold, it is determined that there are two or more points of grounding;

[0022] If the effective value of the neutral line grounding current is less than or equal to the low threshold, it is determined that there are no two or more points of grounding;

[0023] If the effective value of the neutral line grounding current is greater than the low threshold and less than the high threshold, the similarity analysis values of the neutral line grounding current and the currents of each branch are compared.

[0024] As a preferred scheme of a method for monitoring N-phase multi-point grounding in a PT secondary circuit according to the present invention, wherein: the similarity analysis comparison according to the judgment result includes,

[0025] When it is determined that there are two or more points of grounding, the similarity analysis of each branch is performed, and the similarity analysis comparison is performed with the neutral line grounding current waveform to obtain the faulty branch of the grounding point;

[0026] If the neutral line grounding current is greater than the low threshold, the faulty branch of the grounding point is judged through the similarity analysis values of these two paths.

[0027] As a preferred scheme of a method for monitoring N-phase multi-point grounding in a PT secondary circuit according to the present invention, wherein: the similarity analysis is expressed as,

[0028] For the neutral line grounding current, a set of sampling points in one cycle is selected, denoted as I NF ={i E1 ,i E2 ,…,i Em}; for each branch, a set of sampling points in the same cycle is selected. Here, taking branch 1 as an example, it is denoted as I N1 ={i 11 ,i 12 ,…,i 1m}, then the Hausdorff distance between the neutral line grounding current I NE and the current I N1 of branch 1 is expressed as:

[0029] H(I NE ,I N1 )=max(h(I NE ,I N1 ),h(I N1 ,I NE ))

[0030] Wherein:

[0031]

[0032] where ||·|| represents the Euclidean distance between the neutral line grounding current point set and the branch 1 current point set. The distances from the point i NE in the neutral line grounding current point set I Ex to all points in the branch 1 current point set I N1 are arranged in ascending order, and the minimum value is denoted as d i , then d i is the minimum distance corresponding to i Ex . The minimum distances d NE corresponding to all points i Ex in the neutral line grounding current point set I i are obtained respectively. The combined set is denoted as D. The elements in D are arranged in ascending order. Among them, the maximum value is h(I NE , I N1 ), which is called the one-way Hausdorff distance from the neutral line grounding current point set I NE to the branch 1 current point set I N1 . The one-way Hausdorff distance h(I N1 , I NE ) from the branch 1 current point set I N1 to the neutral line grounding current point set I NE is obtained. H(I NE , I N1 ) is the larger value of the two, which is used as the waveform similarity discrimination.

[0033] As a preferred solution of a method for monitoring N-phase multi-point grounding of a PT secondary circuit according to the present invention, wherein: the similarity analysis and comparison are performed according to the judgment result, and the grounding fault branch obtained includes,

[0034] Calculate the Hausdorff distances H(I NE , I N1 ), H(I NE , I N2 ),..., H(I NE , I NX ), where I NE is the sampling point set of the neutral point grounding current in one cycle, and I N1 , I N2 ,..., I NX are the sampling point sets of one cycle of branch 1, branch 2,..., branch X respectively.

[0035] If a certain Hausdorff distance is less than the set value, it is determined that the neutral line grounding current waveform and the current waveform of this branch have similarity, thereby obtaining the grounding fault branch.

[0036] If the detected value cannot be accurately judged, and at the same time, the neutral line grounding current is greater than the low threshold, it is determined that there is a multi-point grounding fault, and continue to calculate the Hausdorff distance H(I NE ,I N1 +I N2 ), H(I NE ,I N1 +I N3 ), ……, and judge the multi-point connection fault branch.

[0037] As a preferred solution of a PT secondary circuit N-phase multi-point grounding monitoring system according to the present invention, it includes a grounding measurement device, a distributed acquisition terminal, and a background device.

[0038] A computer device includes a memory and a processor. The memory stores a computer program. It is characterized in that when the processor executes the computer program, it implements the steps of any one of the methods in a PT secondary circuit N-phase multi-point grounding monitoring method.

[0039] A computer-readable storage medium stores a computer program thereon. It is characterized in that when the computer program is executed by a processor, it implements the steps of any one of the methods in a PT secondary circuit N-phase multi-point grounding monitoring method.

[0040] The beneficial effects of the present invention: High-precision current sensors are installed on the N-phase grounding wires of the PT secondary circuit and each branch. Through on-line current acquisition, numerical calculation, and analysis, it is possible to quickly judge the two-point or multi-point grounding situation of the N-phase of the PT secondary circuit and locate the fault branch of the grounding point; avoid regular manual inspections, and prevent incorrect actions of relay protection during the fault due to time differences;

[0041] Traditionally, relying on the effective value of the N-phase current of the branch to judge the N-phase grounding point fault of the branch. Since there is unbalanced current in the N-phase during normal operation, the superposition of the N-phase current of the branch will be caused by multi-point grounding of the N-phase. Simply relying on detecting the effective value cannot fully guarantee the accuracy of fault branch location; this patent adopts the waveform similarity analysis method, which can accurately locate the fault branch.

[0042] For the situation where the grounding circulating current is small, the traditional method cannot accurately judge and can only perform long-term tracking and monitoring. This patent adopts waveform similarity analysis. By monitoring the waveform similarity between the grounding wire current and the N-phase current of each branch, it is possible to accurately judge whether there is multi-point grounding of the N-phase of the PT secondary circuit. Description of the Drawings

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0044] Figure 1 It is a schematic diagram of the PT secondary circuit N-phase multi-point grounding monitoring for a PT secondary circuit N-phase multi-point grounding monitoring method provided by an embodiment of the present invention.

[0045] Figure 2 It is a schematic diagram of the PT secondary circuit N-phase two-point grounding monitoring for a PT secondary circuit N-phase multi-point grounding monitoring method provided by an embodiment of the present invention. Figure 1 。

[0046] Figure 3 It is a schematic diagram of the PT secondary circuit N-phase two-point grounding monitoring for a PT secondary circuit N-phase multi-point grounding monitoring method provided by an embodiment of the present invention. Figure 2 。

[0047] Figure 4 It is a schematic diagram of the PT secondary circuit N-phase multi-point grounding monitoring for a PT secondary circuit N-phase multi-point grounding monitoring method provided by an embodiment of the present invention.

[0048] Figure 5 It is a flow chart of the PT secondary circuit two-point / multi-point grounding monitoring for a PT secondary circuit N-phase multi-point grounding monitoring method provided by an embodiment of the present invention. Detailed implementation manners

[0049] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will make a detailed description of the specific implementation manners of the present invention in conjunction with the accompanying drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0050] Embodiment 1

[0051] Refer to Figures 1-4 , which is the first embodiment of the present invention. This embodiment provides a PT secondary circuit N-phase multi-point grounding monitoring method, including:

[0052] It should be noted that, as Figure 1 shown, there should be only one grounding point in the PT secondary circuit. A high-precision current sensor is connected to the grounding wire to measure the current I 地 。

[0053] High-precision current sensors are connected to each branch in the figure to measure I1 to I7 respectively.

[0054] The current of the high-precision current sensor is connected to the distributed acquisition terminal for calculation and processing in the terminal.

[0055] The calculation results in the terminal are transmitted to the background system through the communication network for further analysis and judgment, as well as human-computer interaction.

[0056] It should be noted that under normal conditions, as Figure 1 shown, I 地 is a very small leakage current, about a few milliamperes, which can be ignored;

[0057] I1 to I7 are the N-phase currents of each PT branch respectively, which are unbalanced currents; generally, the rated capacity of the PT secondary side is dozens of volt-amperes (for example: if the rated capacity of the PT secondary side is 50 VA, the rated working current is 865 mA). Due to reasons such as incomplete consistency of the three-phase voltages and incomplete consistency of the PT parameters, unbalanced currents will occur in the N-phase of the secondary side of each branch PT.

[0058] The waveforms of the N-phase of the secondary side of each branch PT reflected by I1 to I7 have a high degree of similarity.

[0059] The waveforms of the N-phase of the secondary side of each branch PT reflected by I1 to I7 have a high degree of similarity within each of their respective cycles.

[0060] It should be noted that when two-point grounding occurs and the grounding loop current is large, as Figure 2 shown, when another point of N-phase grounding occurs at point K of branch 7, due to the potential difference between the two points, I 地 and I7 both change significantly in waveform and value.

[0061] I 地 The effective value changes significantly, and it can be judged that two-point or multi-point grounding has occurred.

[0062] When measuring the currents of I1 to I7, among them, the current values of I1 to I6 do not change significantly. Through waveform similarity analysis, compared with their previous current waveforms and the current waveforms among them, they all have a high degree of waveform similarity, and it is judged that they are not the fault branches of the grounding point.

[0063] When measuring the current of I7, if the current value of I7 increases significantly compared with before, it is basically judged that branch 7 is the fault branch of the grounding point; if the increase in the current value of I7 is not obvious, but the waveform changes greatly, then each characteristic point of the I7 acquisition cycle data set should be stripped of the corresponding characteristic point values of the corresponding cycle before the change, and then compared with I 地 for waveform similarity analysis to judge the fault branch of the grounding point.

[0064] It should be noted that when two-point grounding occurs and the grounding loop current is small, such as Figure 3 As shown, when another point of N-phase grounding occurs at point M on branch 1, due to the low potential difference between the two points or the large grounding resistance, I 地 and I1 change in waveform and value, but the change is small.

[0065] Detect I 地 The effective value does not exceed the threshold specified by the standard, but there is a certain increase, and it can be initially judged that two-point grounding has occurred.

[0066] Since the potential difference between the two points is mainly the fundamental wave and the third harmonic, and the parameter between the two points is mainly resistive, the waveform after the superposition of the generated loop current and the I1 unbalanced current, the corresponding periodic waveform before I1, and the corresponding periodic waveforms of I2 to I7 have a low similarity. Furthermore, it is comprehensively judged that N-phase two-point grounding has occurred, and the grounding fault branch is branch 1.

[0067] Furthermore, when multi-point grounding occurs, such as Figure 4 As shown, when multi-point grounding of N-phase occurs at point M on branch 1 and point K on branch 7, at this time, I 地 、I1 and I7 change in both waveform and value.

[0068] I 地 The change in the effective value is large, and it can be judged that two-point or multi-point grounding has occurred.

[0069] When measuring the currents of I1 to I7, among them, the current values of I2 to I6 do not change significantly. Through waveform similarity analysis, there is a high waveform similarity with their respective previous current waveforms and the current waveforms between them, and it is judged that they are not the grounding fault branches.

[0070] When measuring the currents of I1 and I7, if the current value is larger than before, it can be judged that there is a grounding fault in this branch.

[0071] For further judgment, compare the corresponding characteristic values of the waveforms within the periods of I1 and I7 with those of the previous periods, and the waveform similarity is found to be low.

[0072] Furthermore, subtract the corresponding characteristic values of the waveforms within the previous periods from the characteristic values within the periods of I1 and I7 to form a new set of characteristic points of I1 and I7, and there is a high waveform similarity with the I 地 Characteristic point set calculation, and it can be judged that branch 1 and branch 7 are the grounding fault branches, thus resulting in multi-point grounding of N-phase in the PT secondary circuit.

[0073] Regarding Figure 4 , the specific description of a single measurement for the three-point grounding situation of the PT secondary circuit is as follows:

[0074] ①. Collect the current signals of each branch in real time to form a periodic data set I 地 and I1 - I7;

[0075] ②. Calculate the 地 effective value of I. If the result is greater than 50 mA, it is judged that there are two or more points grounded;

[0076] ③. Measure the currents of I1 - I7 to obtain a periodic feature data set, and perform similarity analysis with the periodic data set collected during normal times respectively;

[0077] ④. Compare the waveform similarities of the periodic feature data sets of the current waveforms of I1 - I7 pairwise;

[0078] ⑤. According to ③ and ④, it is obtained that there are no significant changes in the current waveforms of branches I2 - I6, and there is a high waveform similarity, excluding them as the grounded fault branches of the grounding point; for the current waveforms of I1 and I7, whether comparing the corresponding characteristic values of the waveforms within the period with those in the previous period or comparing them pairwise, the waveform similarities are all low;

[0079] ⑥. For the periodic feature data sets of the currents of I1 and I7, subtract the corresponding characteristic values of the waveforms in the previous period from the characteristic values within the periods of I1 and I7 to form new characteristic point sets of I1 and I7;

[0080] ⑦. Compare the characteristic point sets of I1 and I7 with the 地 characteristic point set of I respectively, and perform waveform similarity comparison between I1 and I7, and obtain a high waveform similarity;

[0081] ⑧. Judge that branch 1 and branch 7 are the grounded fault branches of the grounding point.

[0082] Embodiment 2

[0083] As Figure 1 and Figure 5 shown, this is the first embodiment of the present invention. This embodiment provides a method for monitoring multi - point grounding of the N - phase of the PT secondary circuit, including:

[0084] It should be noted that the detection process as Figure 5 shown is as follows:

[0085] The first step: Through current sensors of each path, the controller collects the current data of each path, including the neutral - line grounding current and the N - phase currents of each PT secondary circuit, generates periodic data point sets respectively, and performs effective - value calculation;

[0086] The second step: Two thresholds are designed in the controller, one is a high threshold (for example: 50 mA), and the other is a low threshold (for example: 20 mA), and compare the neutral - line grounding current with the high threshold value;

[0087] Step 3: If the neutral line grounding current is greater than or equal to the high threshold, then judge two-point or multi-point grounding;

[0088] Step 4: On the basis of Step 3, by performing similarity analysis on each branch and comparing it with the waveform of the neutral line grounding current, obtain the faulty branch of the grounding point;

[0089] Step 4: On the basis of Step 2, if the neutral line grounding current is less than the high threshold, then compare the neutral line grounding current with the low threshold;

[0090] Step 5: If the neutral line grounding current is less than or equal to the low threshold, then judge that there is no two-point or multi-point grounding;

[0091] Step 6: On the basis of Step 4, if the neutral line grounding current is greater than the low threshold, then perform similarity analysis on each branch and compare it with the waveform of the neutral line grounding current;

[0092] Step 7: If each similarity analysis value is less than the set value, then judge that there is no two-point or multi-point grounding;

[0093] Step 8: On the basis of Step 6, if there is a similarity analysis value greater than or equal to the set value, then judge the faulty branch of the grounding point through the similarity analysis values of these two paths.

[0094] Adopting waveform similarity analysis based on the Hausdorff distance algorithm is an algorithm that measures the similarity between two point sets based on the overall shape characteristics of spatial targets and has good anti-interference ability.

[0095] The algorithm principle is as follows:

[0096] For the neutral line grounding current, select a set of sampling points for one cycle, denoted as I NE ={i E1 , i E2 , …, i Em}; for each branch, select the same set of sampling points for the same cycle. Here, taking Branch 1 as an example, denoted as I N1 ={i 11 , i 12 , …, i 1m}, then the Hausdorff distance between the neutral line grounding current I NE and the current of Branch 1 I N1 is expressed as:

[0097] H(I NE , I N1 ) = max(h(I NE , I N1 ), h(I N1 , I NE ))

[0098] Wherein:

[0099]

[0100] In the formula, ||·|| represents the Euclidean distance between the neutral - line grounding current point set and the branch - 1 current point set. The points i in the neutral - line grounding current point set I NE to all points in the branch - 1 current point set I Ex are arranged in ascending order of distance. The minimum value is denoted as d N1 . Then d i is the minimum distance corresponding to i i . The minimum distances d Ex corresponding to all points i in the neutral - line grounding current point set I NE are obtained respectively. The combined set is denoted as D. The elements in D are arranged in ascending order. Among them, the maximum value is h(I Ex , I i ), which is called the one - way Hausdorff distance from the neutral - line grounding current point set I NE to the branch - 1 current point set I N1 . The one - way Hausdorff distance h(I NE , I N1 ) from the branch - 1 current point set I N1 to the neutral - line grounding current point set I NE is obtained. H(I N1 , I NE ) is the larger value of the two, which is used as the waveform similarity discrimination. NE , I N1 ) is the larger value of the two, which is used as the waveform similarity discrimination.

[0101] Specifically, for using the Hausdorff - distance algorithm to solve the monitoring of multiple - point grounding of the N - phase of the PT secondary circuit, the main method is as follows:

[0102] Protection criterion based on the Hausdorff - distance algorithm:

[0103] The Hausdorff - distance algorithm uses the feature - point sets of two waveforms for similarity recognition. The current sequences i1 and i2 collected by high - precision current sensors form a two - dimensional point set with time as the abscissa and current quantity as the ordinate, and each point in the point set can be used as a feature point in the algorithm.

[0104] Taking the PT secondary circuit Figure 1 as an example, the sampling - value sequences of the grounding - wire current sensor and the sensors on the N - lines of each branch are I 地And I1 to I7. For each sequence, a two-dimensional point set is formed with time as the abscissa and current value as the ordinate, mainly for detecting the phase. To eliminate the influence of amplitude, the waveform is first normalized. The maximum and minimum values of the current sequence are extracted within the determined time window and denoted as i max and i min , and used as a reference. The amplitude of each point in the sequence is compressed so that each point of the current sequence falls within the range of [0, 1], thus obtaining the normalized current sequence. The compression method is as follows:

[0105]

[0106] The current I 地 and I1 to I7 are respectively normalized, and the Hausdorff distance value corresponding to the mismatch degree between the two sequences is calculated. Then the H value must fall within the range of [0, 1].

[0107] Selection of data window and sampling frequency:

[0108] The selection of the data window length is related to the reliability of the criterion. For the Hausdorff distance algorithm, since it only involves the distance calculation of two feature points between point sets, considering that the ground loop current is mainly affected by power frequency or harmonic electromotive force, a power frequency period of 20 ms is selected as the length of the data window.

[0109] Criterion setting: When a ground fault occurs at point K in branch 7, the normalized current sequences of I 地 and I7 are basically completely coincident. Considering that there is unbalanced current in branch 7 during normal operation, I7 needs to subtract the corresponding feature point value of the same period before and then be normalized, and the H value calculated in this way is approximately 0.

[0110] For other branches, the similarity with I 地 is very low. Generally, if it is greater than a certain set value, it can be judged that there is no waveform similarity between the two.

[0111] Embodiment 3

[0112] The third embodiment of the present invention provides a PT secondary circuit N-phase multi-point ground monitoring system, which is characterized in that it includes:

[0113] Ground measurement device: mainly high-precision current sensors are connected to the N-phase grounding wire of the PT secondary circuit and the N-lines of each branch;

[0114] Distributed acquisition terminal: synchronously acquires and calculates the currents measured by multiple high-precision current sensors;

[0115] Backend device: transmits the calculation data of the distributed acquisition terminal to the backend system through the communication network for further analysis and judgment, as well as human-computer interaction.

[0116] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered by the scope of the claims of the present invention.

[0117] Embodiment 4

[0118] The fourth embodiment of the present invention is different from the previous three embodiments in that:

[0119] If the above functions are implemented in the form of software function units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, the essence of the technical solution of the present invention, or the part that contributes to the prior art, or part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0120] The logic and / or steps represented in the flowchart or described in other ways herein, for example, can be considered as a definite sequence list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch instructions from the instruction execution system, apparatus, or device and execute the instructions), or in combination with these instruction execution systems, apparatuses, or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device.

[0121] More specific examples (a non-exhaustive list) of computer-readable media include the following: an electrical connection (electronic device) having one or more wirings, a portable computer diskette (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable media can even be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpretation, or other suitable processing as necessary, and then storing it in a computer memory.

[0122] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: a discrete logic circuit having logic gate circuits for implementing logical functions on data signals, an application specific integrated circuit having suitable combinational logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

Claims

1. A monitoring method for multi-point grounding of the N-phase in the PT secondary circuit, characterized in that: including Collecting data from various current sensors to form a periodic data point set and performing effective value calculation Comparing the neutral line grounding current with a threshold value to determine whether there are two or more points of grounding Performing similarity analysis and comparison based on the judgment result to obtain the faulty branch of the grounding point 2. The N-phase multi-point grounding monitoring method for the PT secondary circuit according to claim 1, characterized in that: The collecting data from various current sensors includes the neutral line grounding current and the N-phase current of each PT secondary circuit 3. A method for monitoring multi-point grounding of the N-phase of a PT secondary circuit according to claim 2, characterized in that: The effective value calculation is expressed as Among them, I rms is the effective value of the neutral line grounding current of the acquisition line, N is the number of points collected within a period, and i1 to i N are the instantaneous values of the currents at each collected point.

4. A method for monitoring N-phase multi-point grounding of a PT secondary circuit according to claim 3, characterized in that: The comparing the neutral line grounding current with a threshold value includes If the effective value of the neutral line grounding current is greater than or equal to the high threshold value, it is judged that there are two or more points of grounding If the effective value of the neutral line grounding current is less than or equal to the low threshold value, it is judged that there are no two or no more points of grounding If the effective value of the neutral line grounding current is greater than the low threshold value and less than the high threshold value, compare the similarity analysis values of the neutral line grounding current and the currents of each branch 5. A monitoring method for multi-point grounding of the N-phase in the PT secondary circuit according to claim 4, characterized in that: The performing similarity analysis and comparison based on the judgment result includes When it is judged that there are two or more points of grounding, by performing similarity analysis between each branch and performing similarity analysis and comparison with the neutral line grounding current waveform, the faulty branch of the grounding point is obtained If the neutral line grounding current is greater than the low threshold value, judge the faulty branch of the grounding point through the similarity analysis values of the neutral line grounding current and the currents of each branch 6. A method for monitoring multi-point grounding of the N phase of a PT secondary circuit according to claim 5, characterized in that: The similarity analysis is expressed as For the neutral line grounding current, a set of sampling points in a period is selected, \(I\) NE =\(\{i\) E1 、\(i\) E2 、…、\(i\) Em \}\); for a branch, a set of sampling points in a period is selected, \(I\) N1 =\(\{i\) 11 、\(i\) 12 、…、\(i\) 1m \}, then the Hausdorff distance between the neutral line grounding current \(I\) NE and the branch current \(I\) N1 is expressed as: H(I NE ,I N1 ) = max(h(I NE ,I N1 ), h(I N1 ,I NE )) wherein where ||·|| represents the Euclidean distance between the neutral line grounding current point set and the branch current point set. For the neutral line grounding current point set I NE the point i Ex in it to all points in the branch 1 current point set I N1 are arranged in ascending order of distance. The minimum value is denoted as d i , then d i is the minimum distance corresponding to i Ex . The minimum distances d NE corresponding to all points i Ex in the neutral line grounding current point set I i are obtained respectively. The combined set is denoted as D. The elements in D are arranged in ascending order. Among them, the maximum value is h(I NE ,I N1 ), which is called the one-way Hausdorff distance from the neutral line grounding current point set I NE to the branch 1 current point set I N1 . The one-way Hausdorff distance h(I N1 from the branch current point set I NE to the neutral line grounding current point set I N1 is obtained. H(I NE ,I NE ,I N1 ) is used as the waveform similarity discrimination.

7. A PT secondary circuit N-phase multi-point grounding monitoring method according to claim 6, characterized in that: The performing similarity analysis and comparison based on the judgment result to obtain the faulty branch of the grounding point includes If the Hausdorff distance is less than the set value, it is judged that the neutral line grounding current waveform and the current waveform of the branch have similarity, and the faulty branch of the grounding fault is obtained If the detected value cannot be accurately judged, and at the same time, the neutral line grounding current is greater than the threshold value, it is judged that there is a multi-point grounding fault, and continue to calculate the Hausdorff distances H(I NE ,I N1 +I N2 ), H(I NE ,I N1 +I N3 ), ……, and judge the multi-point contact fault branch; Among them, I N2 refers to the set of current points of branch 2, and I N3 refers to the set of current points of branch 3.

8. A system for a PT secondary circuit N-phase multi-point grounding monitoring method according to any one of claims 1-7, characterized in that: including a grounding measurement device, a distributed acquisition terminal, and a background device 9. A computer device, comprising a memory and a processor, the memory storing a computer program, characterized in that, When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented 10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, the steps of the method according to any one of claims 1 to 7 are implemented

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