A flexible ground fault line selection method and system based on differentiated current characteristics

Abstract

The present invention discloses a flexible ground fault line selection method and system with differentiated current characteristics, including: after a fault occurs, collecting the zero-sequence current and zero-sequence voltage of each line in the circuit; preprocessing the zero-sequence current of each line; calculating the DTW of the preprocessed mapping quantity of each line to form a DTW matrix; judging the faulty line according to the comparison of elements in the matrix. Using a synchronous measurement unit, not only can the zero-sequence voltage and zero-sequence current signals of each line be collected, but also the collected signals can be marked with a synchronous time stamp, that is, rich signal resources can be utilized. The algorithm of the method in this paper is simple, does not require iteration, and has a small amount of calculation, and can judge the faulty line in a relatively short time.

Description

Technical Field

[0001] The present invention relates to the technical field of fault line selection in distribution networks, and in particular to a flexible ground fault line selection method and system with differentiated current characteristics. Background Art

[0002] At present, the resonant grounding method is conducive to arc extinguishing and inhibiting its reignition. With the increase in the proportion of cable application in urban distribution networks, the method of grounding through small resistance is widely adopted. When a fault occurs, the fault current is large, and the relay protection device can quickly start and cut off the fault line. At the same time, it can also reduce the system overvoltage level during the fault. In order to combine the advantages of the two grounding methods, the flexible grounding method is promoted and applied.

[0003] At present, the protection of flexible grounding system still uses the protection method of small resistance grounding system, which has limited ability to withstand transition resistance, and the characteristic amplitude is small when high resistance grounding fault occurs, resulting in large calculation error. Therefore, considering the difficulty of fault line selection in existing protection methods, the present invention proposes a flexible grounding fault line selection method with differentiated current characteristics. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by the present invention is the difficulty in selecting a line for a high-resistance grounding fault in an existing flexible grounding system.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a flexible ground fault line selection method with differentiated current characteristics, comprising:

[0007] After a fault occurs, the zero-sequence current and zero-sequence voltage of each line in the circuit are collected;

[0008] Pre-process the zero-sequence current of each line;

[0009] Calculate the DTW of each line mapping amount after preprocessing to form a DTW matrix;

[0010] Determine the faulty line by comparing the elements in the matrix.

[0011] As a preferred solution of the flexible ground fault line selection method with differentiated current characteristics described in the present invention, the fault occurs when the bus zero sequence voltage U0 satisfies U0≥kU N , then it is judged as a ground fault and line selection begins;

[0012] Where k is the reliability coefficient, which is set to 0.05; U N is the busbar rated voltage;

[0013] After the small parallel resistor is put into use, the bus zero-sequence voltage and each line zero-sequence current are collected.

[0014] As a preferred solution of the flexible grounding fault line selection method with differentiated current characteristics described in the present invention, the parallel small resistor includes, the access position is the neutral point, a switch S is set in parallel with the neutral point, when the switch S is closed, the small resistor is put into operation.

[0015] As a preferred solution of the flexible ground fault line selection method with differentiated current characteristics described in the present invention, wherein: the preprocessing includes mapping the zero-sequence current shown to the zero-sequence voltage shown, the zero-sequence current of the fault line and the zero-sequence current of the non-fault line;

[0016]

[0017] in, They represent the zero-sequence current of the fault line and the non-fault line, I 0f.P ,I 0h.P are the mapping quantities of zero-sequence current of fault line and non-fault line respectively.

[0018] As a preferred solution of the flexible ground fault line selection method with differentiated current characteristics of the present invention, wherein: the DTW of calculating the pre-processed line mapping amount includes: assuming that there are two time series T=(t1, t2, ..., t m ), R=(r1,r2,...,r n ), respectively representing the mapping quantities of the zero-sequence currents of the two lines;

[0019] Let A be a matrix A with m rows and n columns. m×n =(a ij ) m×n Represents the distance matrix between T and R. In the distance matrix, W = (w1, w2, ..., w k ) represents an optimal dynamic time bending path of time series T and R, so that the distance between the two sequences along the path is minimized;

[0020] where w k is the kth point in the curved path, is the coordinate in the optimal path, and w k =(t k ,r k ), i = 1, ..., k, k represents the number of nodes in the path;

[0021] DTW uses the sum of the distances between all similar points as the normalized path distance to measure the similarity between two time series, expressed as:

[0022]

[0023] Where DTW(T,R) is the dynamic time warping distance between time series T and R.

[0024] As a preferred solution of the flexible ground fault line selection method with differentiated current characteristics described in the present invention, wherein: the DTW matrix includes, for the zero-sequence current of lines a and b, calculating the dynamic time warping distance DTW(a, b) of the mapping quantity of each line after preprocessing;

[0025] According to the calculation results, the DTW matrix can be obtained:

[0026]

[0027] Wherein, DTW(n,b) represents the dynamic time warping distance between the mapping amount of line n and the mapping amount of line b; DTW(a,n) represents the dynamic time warping distance between the mapping amount of line a and the mapping amount of line n.

[0028] As a preferred solution of the flexible ground fault line selection method with differentiated current characteristics described in the present invention, the comparison of elements in the matrix includes defining D imax is the maximum value of the i-th row element in the DTW matrix, D isubmax is the second largest value in the i-th row;

[0029] If each row element in the DTW matrix satisfies D imax >D isubmax , it is determined to be a line fault; otherwise, it is determined to be a busbar fault;

[0030] If it is determined to be a line fault, the sum of the elements in the i-th row of the DTW matrix ∑D(i) is calculated respectively, and the maximum value ∑D(i) is found. max , then line i is determined to be a faulty line;

[0031] Among them, i=1,…,n.

[0032] A flexible ground fault line selection system using current characteristic differentiation according to any method of the present invention, characterized in that:

[0033] The synchronous measurement unit collects the zero-sequence current and zero-sequence voltage of each line in the circuit after a fault occurs;

[0034] A processing unit pre-processes the zero-sequence current of each line;

[0035] A matrix construction unit calculates the DTW of each line mapping amount after preprocessing to form a DTW matrix;

[0036] The judgment unit judges the faulty line according to the comparison of elements in the matrix.

[0037] A computer device comprises: a memory and a processor; the memory stores a computer program, wherein: the processor implements the steps of any one of the methods of the present invention when executing the computer program.

[0038] A computer-readable storage medium stores a computer program, wherein: when the computer program is executed by a processor, the steps of any one of the methods of the present invention are implemented.

[0039] Beneficial effects of the present invention: The flexible ground fault line selection method with differentiated current characteristics provided by the present invention collects high-precision signals through a synchronous measurement unit to achieve synchronous processing of fault data. Its current characteristic differentiation algorithm is simple and efficient, and can quickly locate high-resistance ground fault lines; combined with dynamic time bending distance, it improves the reliability of fault identification, is suitable for urban distribution networks with a high proportion of cables, and enhances system stability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0041] Figure 1 An overall flow chart of a flexible ground fault line selection method with differentiated current characteristics provided by a second embodiment of the present invention;

[0042] Figure 2 A relationship diagram of zero-sequence current and mapping quantity of a fault line and a non-fault line in a flexible ground fault line selection method with differentiated current characteristics provided by a second embodiment of the present invention;

[0043] Figure 3 A curved path diagram of two time series of a flexible ground fault line selection method with differentiated current characteristics provided by a second embodiment of the present invention;

[0044] Figure 4 A flexible grounding system fault equivalent circuit diagram of a flexible grounding fault line selection method with differentiated current characteristics provided by the first embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0046] Example 1, reference Figure 4 , which is an embodiment of the present invention, provides a flexible grounding fault line selection method with differentiated current characteristics, wherein the grounding fault characteristic analysis process of the flexible grounding system includes:

[0047] Figure 4 It is the equivalent circuit diagram of single-phase grounding fault in the flexible grounding system with n lines. i (i=1,2,…,n) is the zero-sequence capacitance of each line to ground, X L is the equivalent reactance of the arc suppression coil, is the fault virtual voltage source, R f is the transition resistance, R N A small resistor is connected in parallel to the neutral point, and S is a small resistor switching switch. During normal operation or fault occurrence, S is disconnected and the small resistor is not put into operation. If the fault still exists after a certain delay, S is closed, a small resistor is put into operation, and then the fault line is selected and removed according to the protection method. (If it is a transient fault, the small resistor is not put into operation; if the fault still exists after the delay, it means it is a permanent fault, so a small resistor needs to be put into operation to increase the short-circuit current to select the line and remove the fault line)

[0048] Before the small resistor is put into operation, that is, switch S is disconnected, the system impedance to ground is:

[0049]

[0050] In formula (1), j represents the imaginary part of the complex number, C 0∑ is the sum of the zero-sequence capacitance of all lines to ground, X L =3ωL is the equivalent reactance of the arc suppression coil. Then the bus zero-sequence voltage is:

[0051]

[0052] In formula (2), represents the fault virtual voltage source, R f is the transition resistance, and Z0 is the system impedance to ground. Therefore, the zero-sequence current of the fault line is:

[0053]

[0054] In formula (3), is the bus zero sequence voltage, C0∑ is the sum of the zero-sequence capacitance of all lines to ground, X L =3ωL is the equivalent reactance of the arc suppression coil. After the small resistor is put into operation, that is, the switch S is closed, the system impedance to ground changes relative to formula (1) to:

[0055]

[0056] In formula (4), R N A small resistor is connected in parallel with the neutral point, C 0∑ is the sum of the zero-sequence capacitance of all lines to ground, X L =3ωL is the equivalent reactance of the arc suppression coil, then the corresponding bus zero-sequence voltage value also changes. Therefore, compared with formula (3), the zero-sequence current of the fault line changes to:

[0057]

[0058] In formula (5), is the bus zero-sequence voltage, R N A small resistor is connected in parallel with the neutral point, C 0∑ is the sum of the zero-sequence capacitance of all lines to ground, X L =3ωL is the equivalent reactance of the arc suppression coil. The zero-sequence current of the non-fault line is not affected by the small resistor. Therefore, the analysis can be started from the change of the zero-sequence current of each line before and after the neutral point small resistor is put into operation. The access position is the neutral point, and a switch S is set at the neutral point in parallel. When the switch S is closed, the small resistor is put into operation.

[0059] The above analysis provides a basis for fault characteristic analysis.

[0060] Example 2, reference Figure 1-3 , which is an embodiment of the present invention, provides a flexible ground fault line selection method with differentiated current characteristics, comprising:

[0061] S1: When the bus zero-sequence voltage U0 satisfies U0 ≥ kU N , start line selection.

[0062] Where k is the reliability coefficient, which is set to 0.05, U N is the rated voltage of the busbar.

[0063] S2: After the small parallel resistor is put into use, the bus zero-sequence voltage and each line zero-sequence current are collected by the synchronous measurement unit. The zero-sequence current of each line is pre-processed.

[0064] Furthermore, the current characteristic preprocessing includes mapping the zero-sequence current to the zero-sequence voltage. The relationship diagram between the zero-sequence current of the fault line and the non-fault line and the mapping quantity is shown in FIG. Figure 2 shown.

[0065] according to Figure 2 As shown, They represent the zero-sequence current of the fault line and the non-fault line, I 0f.P ,I 0h.P are the mapping quantities of zero-sequence current of faulty line and non-faulty line respectively. According to the above analysis, we can get I 0f.P ,I 0h.P Specific calculation formula:

[0066]

[0067] According to formula (6), the zero-sequence current of each line can be preprocessed. Due to the addition of the resistive component, the mapping amount of the fault line is greater than that of the non-fault line. Therefore, this feature is used to identify the fault line.

[0068] Through mapping, the characteristic differences between the faulty lines and the non-faulty lines mentioned above are reflected. Figure 2 As shown, we can get:

[0069]

[0070] Therefore, we can get exist The mapping calculation formula is as follows:

[0071] S3: Mapping the dynamic time warping distance DTW(a, b) of each line after preprocessing, and forming a DTW matrix.

[0072] It should be said that the dynamic time warping distance (DTW) is a method to measure the similarity between two time series. In a time series, the lengths of the two time series that need to be compared for similarity may not be equal, which is manifested in the different speaking speeds of different people in the field of speech recognition. Moreover, the pronunciation speeds of different phonemes in the same word are also different. In addition, different time series may only have displacements on the time axis, that is, when the displacements are restored, the two time series are consistent. In these complex situations, the traditional Euclidean distance cannot effectively calculate the distance (or similarity) between the two time series.

[0073] DTW calculates the similarity between two time series by extending and shortening the time series. Figure 3 As shown in the figure, the two solid lines above and below represent two time series, and the dotted line between the time series represents the similar points between the two time series. Assume that there are two time series T = (t1, t2, ..., t m ), R=(r1,r2,…,r n ), respectively representing the mapping of the zero-sequence current of the two lines; let a matrix A with m rows and n columns m×n =(aij ) m×n Represents the distance matrix between T and R. In the distance matrix, W = (w1, w2, ..., w k ) represents an optimal dynamic time bending path of time series T and R, which minimizes the distance between the two sequences along the path; where w k is the kth point in the curved path, is the coordinate in the optimal path, and w k =(t k ,r k );i=1,...,k;k represents the number of nodes in the path. DTW uses the sum of the distances between all these similar points, called the WarpPathDistance, to measure the similarity between two time series, that is:

[0074]

[0075] Where: DTW(T,R) is the dynamic time warping distance between time series T and R.

[0076] For the zero-sequence current of lines a and b, according to formula (7), the dynamic time bending distance of the mapping quantity of each line after preprocessing, that is, DTW(a,b), is calculated. When a single-phase grounding fault occurs in the system, the mapping quantity of the faulty line is much larger than that of the non-faulty line, and the corresponding DTW(a,b) value is larger. When a fault occurs at the busbar, the amplitude of the mapping quantity of each line is similar and the polarity is consistent, then the corresponding DTW(a,b) value is smaller. According to the calculation results, the DTW matrix can be obtained:

[0077]

[0078] DTW(n,b) represents the dynamic time warping distance between the mapping amount of line n and the mapping amount of line b; DTW(a,n) represents the dynamic time warping distance between the mapping amount of line a and the mapping amount of line n.

[0079] S4: Compare the D of the elements in the i-th row of the matrix imax , D isubmax To identify line fault or bus fault.

[0080] From formula (8), we can see that the above matrix is ​​a real symmetric matrix. Define D imax is the maximum value of the i-th row element in the DTW matrix, D isubmax is the second largest value of the i-th row. According to the relationship between the two, the line fault or bus fault is determined, and the fault judgment criterion is:

[0081] D imax >D isubmax (9)

[0082] If all row elements in the DTW matrix satisfy equation (9), it is determined to be a line fault; otherwise, it is determined to be a bus fault.

[0083] If it is determined to be a line fault, the sum of the elements in the i-th row of the DTW matrix ∑D(i) (i=1,…,n) is calculated respectively, and the maximum value ∑D(i) is found. max , then line i is determined to be a faulty line.

[0084] Embodiment 3 is an embodiment of the present invention. This embodiment further provides a flexible ground fault line selection system with differentiated current characteristics, which includes:

[0085] The synchronous measurement unit collects the zero-sequence current and zero-sequence voltage of each line in the circuit after a fault occurs.

[0086] The processing unit pre-processes the zero-sequence current of each line.

[0087] The matrix construction unit calculates the DTW of each line mapping amount after preprocessing to form a DTW matrix.

[0088] The judgment unit judges the faulty line according to the comparison of elements in the matrix.

[0089] If the above functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the 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, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0090] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0091] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0092] 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-mentioned embodiments, a plurality of 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 by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0093] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A flexible ground fault line selection method with differentiated current characteristics, characterized in that: include: After a fault occurs, the zero-sequence current and zero-sequence voltage of each line in the circuit are collected; Pre-process the zero-sequence current of each line; Calculate the DTW of each line mapping amount after preprocessing to form a DTW matrix; Determine the faulty line by comparing the elements in the matrix.

2. The flexible ground fault line selection method based on current characteristic differentiation according to claim 1, characterized in that: The fault occurs when the bus zero sequence voltage U0 satisfies U0≥kU N , then it is judged as a ground fault and line selection begins; Where k is the reliability coefficient, which is set to 0.05; U N is the busbar rated voltage; After the small parallel resistor is put into use, the bus zero-sequence voltage and each line zero-sequence current are collected.

3. The flexible ground fault line selection method based on current characteristic differentiation according to claim 2, characterized in that: The parallel small resistor includes: the access position is the neutral point, and a switch S is set at the neutral point in parallel. When the switch S is closed, the small resistor is turned on.

4. The flexible ground fault line selection method based on current characteristic differentiation according to claim 3 is characterized in that: The pretreatment includes: Mapping the zero-sequence current shown to the zero-sequence voltage shown, zero-sequence current of the fault line and the non-fault line; in, They represent the zero-sequence current of the fault line and the non-fault line, I 0f.P ,I 0h.P are the mapping quantities of zero-sequence current of fault line and non-fault line respectively.

5. The flexible ground fault line selection method based on current characteristic differentiation according to claim 4 is characterized in that: The DTW of calculating the pre-processed mapping amount of each line includes: assuming that there are two time series T with sequence lengths of m and n respectively = (t1, t2, ..., t m ), R=(r1,r2,...,r n ), respectively representing the mapping quantities of the zero-sequence currents of the two lines; Let A be a matrix A with m rows and n columns. m×n =(a ij ) m×n Represents the distance matrix between T and R. In the distance matrix, W = (w1, w2, ..., w k ) represents an optimal dynamic time bending path of time series T and R, so that the distance between the two sequences along the path is minimized; where w k is the kth point in the curved path, is the coordinate in the optimal path, and w k =(t k ,r k ), i = 1, ..., k, k represents the number of nodes in the path; DTW uses the sum of the distances between all similar points as the normalized path distance to measure the similarity between two time series, expressed as: Where DTW(T,R) is the dynamic time warping distance between time series T and R.

6. The flexible ground fault line selection method based on current characteristic differentiation according to claim 5, characterized in that: The DTW matrix includes, for the zero-sequence current of lines a and b, calculating the dynamic time warping distance DTW(a,b) of the mapping quantity of each line after preprocessing; According to the calculation results, the DTW matrix can be obtained: Wherein, DTW(n,b) represents the dynamic time warping distance between the mapping amount of line n and the mapping amount of line b; DTW(a,n) represents the dynamic time warping distance between the mapping amount of line a and the mapping amount of line n.

7. The flexible ground fault line selection method based on current characteristic differentiation according to claim 6, characterized in that: The comparison of elements in the matrix includes defining D imax is the maximum value of the i-th row element in the DTW matrix, D isubmax is the second largest value in the i-th row; If each row element in the DTW matrix satisfies D imax >D isubmax , it is determined to be a line fault; otherwise, it is determined to be a busbar fault; If it is determined to be a line fault, the sum of the elements in the i-th row of the DTW matrix ∑D(i) is calculated respectively, and the maximum value ∑D(i) is found. max , then line i is determined to be a faulty line; Among them, i=1,…,n.

8. A flexible ground fault line selection system using current characteristic differentiation according to any one of the methods of claims 1 to 7, characterized in that: The synchronous measurement unit collects the zero-sequence current and zero-sequence voltage of each line in the circuit after a fault occurs; A processing unit pre-processes the zero-sequence current of each line; A matrix construction unit calculates the DTW of each line mapping amount after preprocessing to form a DTW matrix; The judgment unit judges the faulty line according to the comparison of elements in the matrix.

9. A computer device comprising: A memory and a processor; the memory stores a computer program, wherein the processor implements the steps of any method as claimed in claim 1 when executing the computer program.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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