Identification method, system and equipment for tail current of current transformer and medium

Abstract

The invention discloses a current transformer trailing current identification method, system, device and medium, and the method comprises the steps: obtaining the Frechet distance F of the exciting current of a current transformer after a circuit breaker is cut off due to the fault of a power system; according to the complementary set Fs of the Frechet distance F, calculating an improved similarity Fst; and acquiring a fundamental wave amplitude # imgabs0 # and a direct current component amplitude # imgabs1 # of the current transformer, and judging that the trailing of the current transformer occurs when the conditions of # imgabs2 # imgabs3 # or # imgabs4 # are met. According to the invention, the tail current after the circuit breaker trips off can be quickly and accurately identified, and maloperation of circuit breaker failure protection is effectively avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of relay protection of electric power systems, and in particular relates to a method, system, equipment and medium for identifying tail current of a current transformer. Background Art

[0002] When a fault occurs in the power system, the relay protection device operates and trips the corresponding circuit breaker, the fault is isolated, the fault current disappears, and the protection is restored. However, due to the presence of an inductor in the CT secondary current circuit, part of the electrical energy is stored in the inductor at the moment of tripping. After the circuit breaker is disconnected, the CT's excitation winding, secondary winding, and CT secondary protection and measurement circuits form a loop and release the energy stored in the inductor. At this time, the protection may still measure the decaying non-periodic DC component (i.e., tail current). When the initial amplitude of the tail current is high and the time constant is large, the protection may cause the failure protection to malfunction due to the continuous satisfaction of the current criterion, thereby expanding the scope of the power outage and having a greater impact on the system. Summary of the invention

[0003] The purpose of the present invention is to provide a method, system, device and medium for identifying the tail current of a current transformer, which can quickly and accurately identify the tail current after the circuit breaker is tripped, and effectively avoid the false operation of the circuit breaker failure protection.

[0004] In order to achieve the above object, the solution of the present invention is:

[0005] A method for identifying tail current of a current transformer, comprising:

[0006] After the circuit breaker is tripped due to a power system fault, the Fréchet distance F of the current transformer excitation current is obtained;

[0007] The complement F of F according to the Fréchet distance s , calculate the improved similarity F st :

[0008] F st =F s ×ε(Δt-ΔT set )

[0009] Among them, ε is the indicator function; ΔT set is the zero-crossing time threshold; Δt is F s The value is greater than the threshold F s set Length of time;

[0010] Get the fundamental amplitude of the current transformer and the DC component amplitude

[0011] judge or When it is satisfied, it is determined that current transformer tailing occurs.

[0012] Among them, the Fréchet distance F of the current transformer excitation current is obtained, including:

[0013] After the circuit breaker is opened, the current transformer current curve is obtained, and the curve L with a window width ΔT is intercepted. a , and the curve L a Connect the first and last points of to get a straight line L b , where ΔT = j*(1 / 4)T, T is 1 cycle;

[0014] When j = 1, 2, 3, ..., the Fréchet distance is calculated according to the following steps:

[0015] On the curve L a Take m points from above and get the point set L a0 ={p1,…,p m}; On the straight line L b Take n points on the top and get the point set L b0 ={q1,…,q n}, thus obtaining the point pair L: (p ka ,q kb ), ka=1,2,…,m, kb=1,2,…,n;

[0016] Get the path from the starting point (p1, q1) to the end point (p m ,q n ) and calculate the maximum distance ||L|| of each point-to-point path;

[0017] The minimum value among all the distances between points on the path is taken as the Fréchet distance.

[0018] Among them, the threshold According to the following method,

[0019]

[0020] Among them, K rel The value is 1.15~1.3, F s theory =1.

[0021] Among them, get the fundamental amplitude of the current transformer and the DC component amplitude include,

[0022] List the following matrix,

[0023]

[0024] Among them, T1, T2, T3 are set values; ω is the power frequency angular frequency; α1 is the initial phase angle of the power frequency component;

[0025] Deformation obtained,

[0026]

[0027] in,

[0028] Where Y a is the DC filter coefficient; Y b is the cosine filter coefficient; Y c is the sinusoidal filter coefficient;

[0029] So we get,

[0030] I1=|Y c X+jY b X

[0031] I0=|Y a X|

[0032] in, is the power frequency component amplitude I1; is the DC component amplitude I0.

[0033] This also includes setting the circuit breaker failure protection action time t delay for:

[0034] t delay =t1+t2+t3+t4

[0035] Among them, t1 is the action time of the intelligent substation protection device after passing through the operation box; t2 is the circuit breaker breaking time; t3 is the return time of the current element; t4 is the time coordination margin.

[0036] A current transformer tail current identification system, comprising:

[0037] A Fréchet distance acquisition module is configured to acquire the Fréchet distance F of the current transformer excitation current after the circuit breaker is tripped due to a power system fault;

[0038] Improved similarity acquisition module, configured as the complement F of Fréchet distance F s , calculate the improved similarity F st :

[0039] F st =F s ×ε(Δt-ΔT set )

[0040] Among them, ε is the indicator function; ΔTset is the zero-crossing time threshold; Δt is F s Value greater than threshold Length of time;

[0041] Amplitude acquisition module, configured to obtain the fundamental amplitude of the current transformer and the DC component amplitude as well as,

[0042] The tail current judgment module is configured to judge or When it is satisfied, it is determined that current transformer tailing occurs.

[0043] A computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor; when the processor executes the computer program, the steps of the method for identifying the tail current of a current transformer as described above are implemented.

[0044] A computer-readable storage medium stores a computer program; wherein the computer program, when executed by a processor, implements the steps of the method for identifying the tail current of a current transformer as described above.

[0045] After adopting the above scheme, the present invention can quickly and accurately identify the tail current after the circuit breaker is tripped based on the three-point window algorithm of the least squares method and the Fréchet distance algorithm, and construct a comprehensive criterion for rapid identification of tail current in combination with the tail criterion, so as to effectively avoid the false operation of the circuit breaker failure protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is the equivalent circuit diagram of current transformer;

[0047] Figure 2(a) shows the single-phase circuit breaker failure protection logic based on tail current identification;

[0048] Figure 2(b) shows the three-phase circuit breaker failure protection logic based on tail current identification;

[0049] Figure 3 The following are the sampling current waveform, Fréchet calculation result and the least squares three-point window algorithm calculation result when the fault is removed and the CT generates tail current;

[0050] Figure 4 The following are the sampling current waveform, Fréchet calculation result and least squares three-point window algorithm calculation result when the fault is not removed and the CT does not generate tail current;

[0051] Figure 5It is the sampling current waveform, Fréchet calculation result and least squares three-point window algorithm calculation result diagram when the fault current is saturated and the fault is removed, and the CT generates tail current;

[0052] FIG6 is a diagram showing the initial sampling current waveform of the simulated fault current, the Fréchet calculation result, and the calculation result of the least squares three-point window algorithm;

[0053] Among them, (a) is a DC ratio of 60%, (b) is a DC ratio of 85%, and (c) is a DC ratio of 135%;

[0054] FIG7 is a comparison diagram of the sampling current waveform and the algorithm;

[0055] Among them, (a) is the case without noise, (b) is the case with noise;

[0056] Figure 8 is the tail current F st value;

[0057] Fig. 9 It is the amplitude-frequency response of the three-point window filter at different frequencies. DETAILED DESCRIPTION

[0058] The technical solutions and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0059] The present invention provides a method for identifying tail current of a current transformer, which is described from the following aspects.

[0060] First, the formation mechanism of tail current and the impact of tail current on failure protection are analyzed as follows:

[0061] The equivalent circuit diagram of current transformer (CT) is as follows Figure 1 As shown, R1 and L1 represent the primary side resistance and inductance of the current transformer, R2 and L2 represent the secondary side resistance and inductance of the current transformer, R m , L m Respectively represent the current transformer excitation resistance and excitation inductance, I1, I2, I m They represent the primary current, secondary current and excitation current of CT respectively. When the circuit breaker CF is disconnected, the corresponding energy stored in the inductor will flow through the secondary flow path, that is, the CT current tailing phenomenon occurs.

[0062] When the circuit breaker CF is disconnected, the corresponding energy stored in the inductor will flow through the secondary flow path, that is, the CT current tailing phenomenon occurs. The secondary flow path is the RL loop, and the attenuation current expression is:

[0063]

[0064] Where: i m(0) represents the initial value of the excitation current; T represents the decay time constant; i2(t) represents the decay current; t represents the time constant.

[0065] T=(L2+L m ) / (R2+R m +R L ) (2)

[0066] The setting of the failure protection delay time mainly considers the circuit breaker opening time and the reliable return time of the current element. Considering the CT current tailing phenomenon, the current element return time may be longer. In order to prevent the failure protection from false start and expand the fault range, the failure protection delay setting time is longer, generally set to 0.2~0.3s.

[0067] However, if the current tailing phenomenon is serious, the current element does not return within the specified time, and the failure protection will still be falsely activated, causing a large area of ​​switches to trip. Although the re-voltage criterion can avoid false startup to a certain extent, it still cannot solve all problems, such as the transformer low-voltage side fault but the high-voltage side switch failure, the line end fault bus voltage fluctuation is small, etc. Moreover, in the case of 2 / 3 connection, the re-voltage criterion is no longer set.

[0068] The Fréchet distance algorithm is constructed as follows:

[0069] After the circuit breaker CF is opened, a curve L with a window width ΔT is intercepted on the CT current curve. a , and the curve L a Connect the first and last points of to get a straight line L b , in L a Take m points from above and get the point set L a0 ={p1,…,p m}; in L b Take n points on the top and get the point set L b0 ={q1,…,q n}, thus obtaining the point pair L: (p ka ,q kb ), ka=1,2,…,m, kb=1,2,…,n.

[0070] Get the path from the starting point (p1, q1) to the end point (p m ,q n ), where each point-to-point path contains several point pairs, and when moving from a point to the next point on the path, you can choose a or L b Go up one point or keep the current point;

[0071] For example, given a point set L a0= {p1, p2, p3} and L b0 ={q1,q2,q3,q4}, we want to find all possible point-to-point paths from the starting point (p1,q1) to the end point (p3,q4), and several paths are listed below:

[0072] Path 1: (p1,q1)→(p2,q2)→(p2,q3)→(p3,q3)→(p3,q4)

[0073] Path 2: (p1,q1)→(p1,q2)→(p2,q2)→(p2,q3)→(p3,q4)

[0074] Path 3: (p1,q1)→(p2,q1)→(p2,q2)→(p3,q3)→(p3,q4)

[0075] Path 4: (p1,q1)→(p2,q1)→(p3,q2)→(p3,q3)→(p3,q4)

[0076] Path 5: (p1,q1)→(p1,q2)→(p2,q3)→(p3,q3)→(p3,q4)

[0077] Path 6: (p1,q1)→(p2,q2)→(p3,q3)→(p3,q4)

[0078] Path 7: (p1,q1)→(p1,q2)→(p1,q3)→(p2,q3)→(p3,q4)

[0079] Path 8: (p1,q1)→(p2,q1)→(p3,q2)→(p3,q4)

[0080] Path 9: (p1,q1)→(p1,q2)→(p1,q3)→(p2,q3)→(p2,q4)→(p3,q4)

[0081] Path 10: (p1,q1)→(p2,q2)→(p3,q2)→(p3,q3)→(p3,q4)

[0082] Each point-to-point path has a maximum distance between point pairs, expressed as:

[0083]

[0084] Where: ||L|| represents L a With L b The length value between;

[0085] The minimum value of the distances between all point pairs is taken as the Fréchet distance, and the calculated value of the Fréchet distance is:

[0086] F(L a ,L b )=min||L|| (4)

[0087] When the sampling current is a tail current, the F value between its normalized sampling current sequence and the template straight waveform sequence theoretically tends to 0. In order to facilitate practical engineering applications, the complement set F of the F value is used. s As the basis for setting, that is, after obtaining the Fréchet distance value F, according to F s (j)=1-F(j), j=1,2,3…, calculate the corresponding F s Value, where ΔT=j*(1 / 4)T, T is 1 cycle.

[0088] The setting principles are as follows:

[0089]

[0090] Where K rel Generally, it is between 1.15 and 1.3. s theory =1, let's take K rel =1.2, then F s set =0.83; F s set is the threshold value;

[0091] When the F is calculated using a window width less than or equal to 1 / 2 cycle s value, which is greater than the threshold F s set The Δt value of some parts is small, generally below 30ms, so the improved similarity F can be obtained. st Value is

[0092] F st =F s ×ε(Δt-ΔT set ) (6)

[0093] Where ε is the indicator function, which is used to ensure that F is calculated when Δt meets the conditions st , when Δt does not meet the conditions, ε is 0; ΔT set is the zero-crossing time threshold, take ΔT set =30ms. Due to the improved similarity F st The calculation is just to discard the sampling current F s The value is the characteristic point when its Δt value does not meet the condition, so the improved similarity F of the tail current is judged. st Threshold value is the same as F s set ,Right now Then the improved new criterion for tail current identification is obtained:

[0094]

[0095] In this embodiment, a least squares three-point window algorithm needs to be constructed as follows:

[0096] Assume that the preset model of the input signal is:

[0097]

[0098] Where: x(t) is the real-time value; I0 is the amplitude of the DC component; I1 is the amplitude of the power frequency component; ω is the angular frequency of the power frequency; α1 is the initial phase angle of the power frequency component.

[0099] Then we have:

[0100] x(t)=I0+I1 sin(ωt)cosα1+I1cos(ωt)sinα1 (9)

[0101] When t is T1, T2 and T3, we can get:

[0102]

[0103] The unknown matrix can be solved from equation (10), as shown in equations (11) and (12).

[0104]

[0105]

[0106] Where: Y a is the DC filter coefficient; Y b is the cosine filter coefficient; Y c are the sinusoidal filter coefficients.

[0107] The formula for the three-point window sine and cosine filter is:

[0108] I1=|Y c X+jY b X| (13)

[0109] The formula for the three-point window DC filter is:

[0110] I0=|Y a X| (14)

[0111] According to the amplitude-frequency response of the three-point window cosine, sine and DC filters, and following the DC component ratio braking principle based on the full-cycle Fourier algorithm, the three-point window DC component ratio braking criterion based on the least squares method can be obtained as follows:

[0112]

[0113] In the formula, is the fundamental wave amplitude, that is, the power frequency component amplitude I1 calculated by formula (13); is the DC component amplitude I0 calculated by formula (14); K set.3 For the ratio braking criterion setting, this embodiment takes a certain margin into consideration and takes it as 1.2.

[0114] Based on the above content, the comprehensive criterion for rapid identification of tail current is constructed as follows:

[0115] Combining the least squares three-point window algorithm with the Fréchet distance algorithm, a comprehensive criterion for rapid identification of tail current is proposed:

[0116]

[0117] The current transformer tail current identification method provided by the present invention can also be combined with the existing circuit breaker failure protection criterion to achieve the purpose of both identifying the tail current and performing circuit breaker failure protection. The improved circuit breaker failure protection logic is shown in Figure 2 (a) and Figure 2 (b), in which: Represents phase current; I n Indicates the rated current of the secondary side; I set Indicates the failure current value; T Ⅰ Indicates the three time settings of failure protection; T Ⅱ is the failure protection time constant. The improved single-phase circuit breaker failure protection logic shown in Figure 2(a) adds a single-phase tail current mark on the basis of the original criterion to quickly identify whether the fault has been removed; the three-phase circuit breaker failure protection logic shown in Figure 2(b) adds a tail current mark or a no-current criterion by phase on the basis of the original criterion to quickly determine whether the three-phase fault has been removed. After adopting the improved circuit breaker failure protection logic, when the circuit breaker trips normally, if current transformer tailing occurs, the improved protection logic can accurately identify the tail current within 20ms, and the circuit breaker failure protection action condition is not met; if current transformer tailing does not occur, the full-cycle Fourier phase current criterion of the improved single-phase circuit breaker failure protection Return, the single-phase circuit breaker failure protection action conditions are not met.

[0118] This embodiment also optimizes the failure protection action delay as follows:

[0119] The action time of circuit breaker failure protection mainly considers three factors: circuit breaker breaking time, current element return time and time coordination margin.

[0120] t delay =t1+t2+t3+t4 (17)

[0121] where t delay is the action time of circuit breaker failure protection; t1 is the action time after the intelligent substation protection device exits and passes through the operation box; t2 is the circuit breaker opening time; t3 is the return time of the current element; t4 is the time coordination margin.

[0122] The embodiment of the present invention further provides a system for identifying tail current of a current transformer, comprising:

[0123] A Fréchet distance acquisition module is configured to acquire the Fréchet distance F of the current transformer excitation current after the circuit breaker is tripped due to a power system fault;

[0124] Improved similarity acquisition module, configured as the complement F of Fréchet distance F s , calculate the improved similarity F st :

[0125] F st =F s ×ε(Δt-ΔT set )

[0126] Among them, ε is the indicator function; ΔT set is the zero-crossing time threshold; Δt is F s The value is greater than the threshold F s set Length of time;

[0127] Amplitude acquisition module, configured to obtain the fundamental amplitude of the current transformer and the DC component amplitude as well as,

[0128] The tail current judgment module is configured to judge or When it is satisfied, it is determined that current transformer tailing occurs.

[0129] A specific embodiment is provided below to illustrate the technical solution and effects of the present invention.

[0130] The experiment simulates a 220kV line in a 220kV substation with a phase A ground fault at t = 0.1s, the line main protection operates correctly at t = 0.11s, and the corresponding circuit breaker correctly cuts off the fault and fails. The simulation time of the example is 0.3s, the current sampling frequency is 80 points per cycle, and the 1 / 4 cycle window length is selected for the Fréchet distance algorithm, and its action threshold value is The setting is 0.83. Table 1 shows the use of failure protection action time in enterprises of various countries.

[0131] Table 1 Investigation of failure protection action time

[0132]

[0133] from Figure 3 It can be seen from the figure that when the fault is removed and the CT generates tail current, after the judgment is started, F before t = 0.18s st The values ​​are all less than the threshold value F s set ; At t = 0.18s, that is, about 1 / 4 cycle after the circuit breaker is disconnected, F st The value rises rapidly above the threshold value, meeting the criterion, and determining that a tail current is generated on the secondary side of the CT within the sampling interval. After the fault is removed, the DC component of the tail current generated is large, and the power frequency component tends to 0, so the amplitude ratio of the DC component to the power frequency component is large. At t = 0.195s, the logic flag becomes 1, and the least squares three-point window algorithm determines that a tail current is generated on the secondary side of the CT within the sampling interval.

[0134] from Figure 4 It can be seen from the figure that when the fault is not removed and the CT does not generate tail current, after the judgment is started, its F st The calculated value is less than the threshold value The tail current criterion is not met, and it is determined that the CT secondary side does not generate tail current within the sampling interval. Its logic flag is 0, the amplitude ratio of the DC component and the power frequency component is not greater than 1, and the least squares three-point window algorithm is used to determine that the CT secondary side does not generate tail current within the sampling interval.

[0135] from Figure 5 It can be seen from the figure that when the fault current is saturated and the fault is removed, and the CT generates tail current, after the judgment is started, the F of the fault current saturation period st The calculated values ​​are all less than the threshold value F s set ; At t = 0.18s (circuit breaker trips about 1 / 4 cycle) F st The calculated value quickly rises above the threshold value, meeting the criterion, and it is determined that the CT secondary side has generated a tail current within the sampling interval. The DC component of the tail current is large, and the power frequency component tends to 0, so the amplitude ratio of the DC component to the power frequency component is large. At t = 0.195s, the logic flag becomes 1, and the least squares three-point window algorithm is used to determine that the CT secondary side has generated a tail current within the sampling interval.

[0136] As can be seen from Figure 6, as the proportion of DC in the initial fault increases, the improved similarity F st The value of the sequence increases during the fault period, but is still less than the threshold value F s set; About 5ms after the fault circuit breaker is disconnected, F st The sequence value rises rapidly to the threshold value F s set The above shows that the CT generates a tail current. After the fault occurs, the DC component of the tail current is large, and the power frequency component tends to 0, so the amplitude ratio of the DC component to the power frequency component is large. At t = 0.195s, the logic flag becomes 1, and the least squares three-point window algorithm is used to determine that the CT secondary side generates a tail current within the sampling interval. Therefore, it can be seen that even if the DC ratio reaches 135% at the initial stage of the fault, the criterion proposed by the present invention can still be judged without misjudgment, indicating that the proposed criterion is not affected by the DC component of the fault.

[0137] In order to verify the advantage of the proposed algorithm in identifying the tail current time, the proposed algorithm is compared with the three-point window algorithm based on the least squares method and the Fréchet distance algorithm. The comparison results are shown in Figure 7. Setting τ to 30ms, the influence of the decaying non-periodic tail current on the current element of the improved circuit breaker failure protection is analyzed. During the simulation, the initial tail current is set to the maximum value of 20I. n consider.

[0138] As can be seen from Figure 7(a), in various cases, the three-point window algorithm based on the least squares method takes a long time to identify the tail current, while the proposed algorithm and the Fréchet distance algorithm are approximately 1 / 4 cycle after the circuit breaker is disconnected. st The value rises rapidly above the threshold value, meeting the criterion, and it is determined that a tail current is generated on the secondary side of the CT within the sampling interval.

[0139] The proposed algorithm is compared with the three-point window algorithm based on the least squares method and the Fréchet distance algorithm. Some noise is added to the tail current used in the test. The comparison results are shown in Figure 7(b).

[0140] from Figure 8 It can be seen that in all cases, the Fréchet distance algorithm cannot stably identify the tail current. The main reason is that the Fréchet distance algorithm has no filtering process. Noise interference will cause the similarity Fst value to fluctuate around the threshold, and the tail current identification is unstable. The specific situation is as follows Figure 8 shown.

[0141] Relatively speaking, in various cases, the proposed algorithm and the least squares three-point window algorithm can accurately and stably identify the tail current. The main reason is that the cosine filter and sine filter of the least squares three-point window algorithm can filter out the DC component well, while the DC filter can filter out the fundamental component well, avoiding the interference of noise on the identification of the tail current. The amplitude-frequency response of the three-point window filter in different frequency ranges is shown in Figure 2. Fig. 9 shown.

[0142] An embodiment of the present invention further provides another computer device, including a processor and a memory configured to store a computer program that can be run on the processor; wherein, when the processor is configured to run the computer program, the method steps in the aforementioned embodiment are executed.

[0143] In practical applications, the processor includes a field programmable gate array (FPGA), and the processor may be a central processing unit (CPU) or a digital signal processor (DSP). It is understandable that for different devices, the electronic device used to implement the function of the processor may be other, and the embodiment of the present invention does not specifically limit it.

[0144] The above-mentioned memory can be a volatile memory (volatile memory), such as a random access memory (RAM); or a non-volatile memory (non-volatile memory), such as a read-only memory (ROM), a flash memory, a hard disk (HDD) or a solid-state drive (SSD); or a combination of the above-mentioned types of memory, and provide instructions and data to the processor.

[0145] In an exemplary embodiment, an embodiment of the present invention further provides a computer-readable storage medium for storing a computer program.

[0146] Optionally, the computer-readable storage medium can be applied to any one of the methods in the embodiments of the present invention, and the computer program enables the computer to execute the corresponding processes implemented by the processor in each method in the embodiments of the present invention. For the sake of brevity, they are not described here.

[0147] In the several embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as: multiple units or components can be combined, or can be integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the components shown or discussed can be through some interfaces, and the indirect coupling or communication connection of the devices or units can be electrical, mechanical or other forms.

[0148] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The schemes in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0149] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0150] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0151] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0152] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0153] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for identifying tail current of a current transformer, characterized in that: include, After the circuit breaker is tripped due to a power system fault, the Fréchet distance F of the current transformer excitation current is obtained; The complement F of F according to the Fréchet distance s , calculate the improved similarity F st : F st =F s ×ε(Δt-ΔT set ) Among them, ε is the indicator function; ΔT set is the zero-crossing time threshold; Δt is F s Value greater than threshold Length of time; Get the fundamental amplitude of the current transformer and the DC component amplitude judge or When it is satisfied, it is determined that current transformer tailing occurs.

2. The method according to claim 1, characterized in that: Obtain the Fréchet distance F of the current transformer excitation current, including, After the circuit breaker is opened, the current transformer current curve is obtained, and the curve L with a window width ΔT is intercepted. a , and the curve L a Connect the first and last points of to get a straight line L b , where ΔT = j*(1 / 4)T, T is 1 cycle; When j = 1, 2, 3, ..., the Fréchet distance is calculated according to the following steps: On the curve L a Take m points from above and get the point set L a0 ={p1,…,p m }; On the straight line L b Take n points on the top and get the point set L b0 ={q1,…,q n }, thus obtaining the point pair L: (p ka ,q kb ), ka=1,2,…,m, kb=1,2,…,n; Get the path from the starting point (p1, q1) to the end point (p m ,q n ) and calculate the maximum distance ||L|| of each point-to-point path; The minimum value among all the distances between points on the path is taken as the Fréchet distance.

3. The method according to claim 2, characterized in that: Threshold According to the following method, Among them, K rel The value ranges from 1.15 to 1.

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4. The method according to claim 1, characterized in that: Get the fundamental amplitude of the current transformer and the DC component amplitude include, List the following matrix, Among them, T1, T2, T3 are set values; ω is the power frequency angular frequency; α1 is the initial phase angle of the power frequency component; Deformation obtained, in, Where Y a is the DC filter coefficient; Y b is the cosine filter coefficient; Y c is the sinusoidal filter coefficient; So we get, I1=|Y c X+yY b X| I0=|Y a X| in, is the power frequency component amplitude I1; is the DC component amplitude I0.

5. The method according to claim 1, characterized in that: Also includes setting the circuit breaker failure protection action time t delay for: t delay =t1+t2+t3+t4 Among them, t1 is the action time of the intelligent substation protection device after passing through the operation box; t2 is the circuit breaker breaking time; t3 is the return time of the current element; t4 is the time coordination margin.

6. A current transformer tail current identification system, characterized in that: include, A Fréchet distance acquisition module is configured to acquire the Fréchet distance F of the current transformer excitation current after the circuit breaker is tripped due to a power system fault; Improved similarity acquisition module, configured as the complement F of Fréchet distance F s , calculate the improved similarity F st : F st =F s ×ε(Δt-ΔT set ) Among them, ε is the indicator function; ΔT set is the zero-crossing time threshold; Δt is F s Value greater than threshold Length of time; Amplitude acquisition module, configured to obtain the fundamental amplitude of the current transformer and the DC component amplitude as well as, The tail current judgment module is configured to judge or When it is satisfied, it is determined that current transformer tailing occurs.

7. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor; characterized in that: When the processor executes the computer program, the steps of the method for identifying the tail current of a current transformer as described in any one of claims 1 to 5 are implemented.

8. A computer-readable storage medium storing a computer program; characterized in that: When the computer program is executed by a processor, the steps of the method for identifying the tail current of a current transformer as claimed in any one of claims 1 to 5 are implemented.

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