Line protection fault identification method and system

Abstract

The invention relates to the technical field of fault identification, in particular to a line protection fault identification method and system, which can sample current on two sides of a target line in real time in the target line to obtain a sampling current sequence on the opposite side; sampling value integration is carried out on a sampling current sequence obtained through sampling, and a corresponding integral current sequence is obtained; calculating a three-phase current correlation coefficient of the integral current sequences on the two sides by using a waveform similarity algorithm; and if the current correlation coefficient of a certain phase meets a protection criterion, the phase is a fault phase, otherwise, the phase is a non-fault phase. It can be understood that the technical scheme removes the influence of high-frequency components by performing short-time integral sampling on the current, is not restricted by small amplitude of fault current in a new energy scene, has strong adaptability to transition resistance, and has better high-frequency endurance capability than a common waveform similarity algorithm; fault maloperation outside a line protection area can be prevented in the scene that the high-frequency content of a new energy transmission line is large.

Description

Technical Field

[0001] This invention relates to the field of fault identification technology, and specifically to a method and system for identifying line protection faults. Background Technology

[0002] Due to the fault characteristics of new energy power sources, the amplitude of the fault current output by new energy sources is limited and the phase angle is controlled. Furthermore, under the low-pass control strategy that suppresses negative sequence current, only positive sequence current is output, and there is no zero sequence or negative sequence current. The reliability of traditional current protection and differential protection is affected to a certain extent. In the context of dual high-voltage power grid access, the power flow of the grid flows in both directions and varies greatly. The topology is complex, and the reverse current of adjacent line faults can easily cause overcurrent protection to malfunction. The traditional power frequency and transient analysis methods based on synchronous generator power sources are no longer applicable.

[0003] Waveform similarity algorithm is an algorithm that measures the degree of similarity between different waveforms or sequences. Because it is not constrained by waveform amplitude, waveform similarity algorithm has obvious advantages in distinguishing waveforms in different states. Therefore, experts at home and abroad have conducted a lot of research on the use of waveform similarity algorithm in line protection of power systems, and the method of using transient waveform similarity to identify faults has become an effective means.

[0004] However, most existing waveform similarity algorithms rely on low-pass filters installed in protection systems to reduce the impact of high-frequency quantities from new energy sources, or require wavelet transform for data preprocessing, which involves a large amount of computation. Considering the high high-frequency content of new energy sources, existing algorithms are prone to malfunctions when facing faults outside the protection zone. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a line protection fault identification method and system to solve the problem that the waveform similarity algorithm in the prior art has the problem of false operation of external faults under the influence of high frequency of new energy when facing external faults.

[0006] According to a first aspect of the present invention, a method for identifying line protection faults is provided, comprising: In the target line, the current on the first side and the second side of the target line are sampled in real time to obtain the sampling current sequence of the first side and the sampling current sequence of the second side. The sampled current sequences from the first and second sides are integrated to obtain the integrated current sequences from the first and second sides, respectively. Using a waveform similarity algorithm, the three-phase current correlation coefficients of the first-side integral current sequence and the second-side integral current sequence are calculated. If the current correlation coefficient of a certain phase meets the protection criterion, then that phase is a faulty phase; otherwise, that phase is a non-faulty phase.

[0007] Preferably, the sampling values ​​of the first-side sampled current sequence and the second-side sampled current sequence are integrated, including: Using a quarter-cycle sampling time window, the sampled current sequences of the first and second sides are integrated respectively.

[0008] Preferably, the sampling values ​​of the first-side sampled current sequence and the second-side sampled current sequence are integrated, including: The sampled current sequences from the first and second sides are integrated using the following formula:

[0009] Where k is the current sampling point, X(k) is the sampled value corresponding to point k, X'(k) is the integrated value of point k, and i is the lag index relative to the current sampling point k within the integration window; N Int The number of integration points; If the integration data window is 1 / 4 of the fundamental frequency, the number of integration points is calculated using the following formula:

[0010] in, N b The number of sampling points in one period. f s Sampling frequency, f b This is the fundamental frequency.

[0011] Preferably, a waveform similarity algorithm is used to calculate the three-phase current correlation coefficient between the first-side integral current sequence and the second-side integral current sequence, including: The three-phase current correlation coefficient between the first-side integral current sequence and the second-side integral current sequence is calculated using the following formula:

[0012] x ={ x 1, x 2, ..., x n} y ={ y 1, y 2, ..., y n} in, r ( x , y ) is a variable x and variables y The degree of relevance, n This represents the number of sampling points.

[0013] Preferably, when sampling the current on the first and second sides of the target line in real time, the method further includes: The sampling frequency is less than 1.5 kHz.

[0014] Preferably, the protection criterion is: at the same time, if the current correlation coefficient of the same phases on both sides is between -0.9 and +1, then the phase is the faulty phase.

[0015] Preferably, the target line is a power transmission line from a new energy power station, with the first side being the power station side and the second side being the system side.

[0016] Preferably, the line protection fault identification method further includes: After the faulty phase is identified, the output line issues an alarm for the fault within the zone and activates the protection of the faulty phase. If the correlation coefficients of the three-phase currents do not meet the protection criteria, the fault is judged to be outside the protection zone, and the protection is reset.

[0017] According to a second aspect of the present invention, a line protection fault identification system is provided, comprising: A first microcomputer protection device installed on the first side of the target line is used to sample the current on the first side of the target line in real time to obtain the sampled current sequence on the first side. A second microprocessor-based protection device is installed on the second side of the target line to sample the current on the second side of the target line in real time and obtain the sampled current sequence on the second side. The calculation and identification module is used to integrate the sampled current sequences of the first side and the second side respectively to obtain the integrated current sequences of the first side and the second side. Using a waveform similarity algorithm, the three-phase current correlation coefficient of the integrated current sequences of the first side and the second side is calculated. If the current correlation coefficient of a certain phase meets the protection criterion, then the phase is a faulty phase; otherwise, the phase is a non-faulty phase.

[0018] Preferably, in the line protection fault identification system, both the first microcomputer protection device and the second microcomputer protection device are equipped with a low-pass filter to filter out high-frequency components with a frequency greater than or equal to the sampling frequency.

[0019] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects: It is understood that the technical solution presented in this invention can sample the current on both sides of the target line in real time, obtaining the sampled current sequence on each side; integrate the sampled current sequence to obtain the corresponding integrated current sequence; and calculate the three-phase current correlation coefficient of the integrated current sequence on both sides using a waveform similarity algorithm. If the current correlation coefficient of a certain phase meets the protection criterion, then that phase is a faulty phase; otherwise, that phase is a non-faulty phase. It is understood that this technical solution removes the influence of high-frequency components by performing short-time integral sampling of the current, is not constrained by the small amplitude of fault current in new energy scenarios, has strong adaptability to excessive resistance, and has better high-frequency tolerance than ordinary waveform similarity algorithms. It can prevent false tripping of faults outside the line protection zone in scenarios with high high-frequency content in new energy transmission lines.

[0020] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0022] Figure 1 This is a schematic diagram illustrating the steps of a line protection fault identification method according to an exemplary embodiment; Figure 2 This is a schematic diagram of the power transmission line of a new energy power station, according to an exemplary embodiment. Figure 3 This is a schematic diagram of the original current sampling sequence on the opposite side of a fault within the zone, according to an exemplary embodiment. Figure 4 This is a schematic diagram of the original current sampling sequence on the opposite side of an external fault, according to an exemplary embodiment. Figure 5 This is a schematic diagram of the original sampled waveform of an intra-area fault, according to an exemplary embodiment. Figure 6 This is a schematic diagram of the original sampled waveform of an external fault, according to an exemplary embodiment. Figure 7 This is a schematic diagram of an intra-area fault integral sampling waveform according to an exemplary embodiment; Figure 8 This is a schematic diagram of an out-of-area fault integral sampling waveform according to an exemplary embodiment; Figure 9 This is a schematic diagram illustrating the similarity of fault waveforms within a region according to an exemplary embodiment. Figure 10 This is a schematic diagram illustrating the waveform similarity of an external fault according to an exemplary embodiment. Detailed Implementation

[0023] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0024] In one embodiment, Figure 1 This is a schematic diagram illustrating the steps of a line protection fault identification method according to an exemplary embodiment. The method includes: Step S11: In the target line, the current on the first side and the second side of the target line are sampled in real time to obtain the sampling current sequence of the first side and the sampling current sequence of the second side.

[0025] Step S12: Integrate the sampled current sequences of the first side and the second side respectively to obtain the integrated current sequences of the first side and the integrated current sequences of the second side.

[0026] Step S13: Using a waveform similarity algorithm, calculate the three-phase current correlation coefficient between the first-side integral current sequence and the second-side integral current sequence.

[0027] Step S14: If the current correlation coefficient of a certain phase meets the protection criterion, then the phase is a faulty phase; otherwise, the phase is a non-faulty phase.

[0028] It is understood that the technical solution shown in this embodiment can sample the current on both sides of the target line in real time to obtain the sampled current sequence on each side; integrate the sampled current sequence to obtain the corresponding integrated current sequence; and use a waveform similarity algorithm to calculate the three-phase current correlation coefficient of the integrated current sequences on both sides. If the current correlation coefficient of a certain phase meets the protection criterion, then that phase is a faulty phase; otherwise, that phase is a non-faulty phase. It is understood that this technical solution removes the influence of high-frequency components by performing short-time integral sampling of the current, is not constrained by the small amplitude of fault current in new energy scenarios, has strong adaptability to excessive resistance, and has better high-frequency tolerance than ordinary waveform similarity algorithms. It can prevent false tripping of faults outside the line protection zone in scenarios with high high-frequency content in new energy transmission lines.

[0029] In a preferred embodiment, see Figure 2 The target line is a power transmission line from a new energy power station, with the first side being the power station side and the second side being the system side. Figure 2The diagram mainly shows the grid connection of new energy power plants via transmission lines, which consists of the power plant side, the system side, and the transmission lines.

[0030] When a fault occurs in the transmission line, the transient current characteristics on the system side are similar to those of a synchronous generator fault, and the transient current waveform on this side is a decaying fundamental frequency sine wave. The transient current characteristics on the power station side are determined by the fault characteristics of the new energy power source, and the transient current waveform on this side is a decaying non-fundamental frequency sine wave or a waveform without a specific change pattern, that is, it is no longer a fundamental frequency sine wave.

[0031] When an external fault occurs on the transmission line, Kirchhoff's current law states that, neglecting line capacitance current, the same current flows through both the system side and the station side. If the positive direction of the current is defined as the flow from the busbar to the line, then... Figure 2 As indicated by the arrow, the transient current waveforms on both sides are completely opposite.

[0032] Based on the above analysis, it can be found that the correlation between the transient current waveforms on both sides is weak when the fault occurs within the transmission line's fault zone, but strong when the fault occurs outside the fault zone. Therefore, a longitudinal protection principle based on the correlation of transient current waveforms can be constructed.

[0033] In practice, during step S11, the devices set on both sides of the power transmission line of the new energy power station sample the current sequence in real time, and the device on this side samples the current sequence in real time. I x And simultaneously receive the sampling current sequence sent by the other device. I y Record the protection activation time as zero time, and the current as... I x (0), I y (0). This side: usually refers to the power station side (the outlet side of the new energy power station); the opposite side: usually refers to the system side (the substation side connected to the power grid or the external system side).

[0034] Then, step S12 is performed to integrate the sampled values.

[0035] It should be noted that in step S12, the sampled current sequences from the first and second sides are integrated, including: Using a quarter-cycle sampling time window, the sampled current sequences from the first and second sides are integrated using the following formula:

[0036] Where k is the current sampling point, X(k) is the sampled value corresponding to point k, X'(k) is the integrated value of point k, and i is the lag index relative to the current sampling point k within the integration window; N Int The number of integration points; If the integration data window is 1 / 4 of the fundamental frequency, the number of integration points is calculated using the following formula:

[0037] in, N b The number of sampling points in one period. f s Sampling frequency, f b The fundamental frequency of the system during normal operation is given by [value], and the fundamental period is given by [value]. .

[0038] After integrating the sampled values ​​using the above formula, the station's integrated current sequence can be obtained. I x 'and system-side integrated current sequence I y ', can be merged into a new sampling sequence, denoted as ( I x ', I y ').

[0039] The technical solution shown in this embodiment takes into account the problem that the current of the new energy power grid will inevitably have large harmonics, which will reduce the correlation of the current waveforms on both sides when an external fault occurs on the line. The similarity calculation results will be unstable and may lead to unstable action results. Therefore, this embodiment proposes to perform integral filtering on the waveforms on both sides of the line for a period of time before calculating the waveform correlation, forming a new sampling sequence, and then performing waveform correlation calculation on it. This can improve the correlation of the current waveforms on both sides of the external fault under high harmonics and reduce the probability of protection maloperation.

[0040] After obtaining the new sampling sequence ( I x ', I y After that, step S13 is executed to calculate the correlation coefficient of the three-phase current using the waveform similarity algorithm.

[0041] The formula for calculating waveform similarity is as follows:

[0042] x ={ x 1, x 2, ..., x n} y ={ y 1, y 2, ..., y n} in, r ( x , y ) is a variable x and variables y The degree of relevance, n This represents the number of sampling points.

[0043] Waveform similarity algorithms use the Pearson correlation coefficient to measure the correlation between two variables using covariance and variance, as shown in the formula above. For two variables whose amplitudes and variation patterns are independent, the Pearson correlation coefficient is unaffected by the magnitude of the variable amplitudes and can effectively measure the correlation between two transient current waveforms.

[0044] In the above formula, when r ( x, y When )=-1, it indicates that the variable x and y The two waveforms exhibiting completely opposite patterns of change and a negative correlation are the strongest; when r ( x , y When )=1, it indicates that the two waveforms have completely identical changing patterns and the correlation is strongest, being positive; when r ( x , y When the absolute value is close to 0, it indicates that the two waveforms have significantly different patterns of change and a weak correlation.

[0045] After calculating the correlation coefficient of the three-phase current, proceed to step S14.

[0046] In step S14, the first step is to construct the protection criterion.

[0047] The waveform similarity algorithm calculation formula illustrates the waveform similarity principle. Under ideal conditions, without considering the effects of high frequency and capacitive current, it can be seen from the current relationship between the longitudinal protection and the opposite side that, for faults outside the zone, the current direction on the opposite side of the line is opposite, and the waveform similarity is -1. For faults within the zone, the waveform similarity is between -1 and 1. Therefore, let the similarity protection setting be r. set The criteria for determining protective actions are:

[0048] in, i W For the transient current on the station side, i S For system-side transient current, r for Phase current correlation coefficient.

[0049] If the correlation coefficient of a certain phase current satisfies the protection criterion, that is:

[0050] If a fault occurs in the transmission line within the zone, that phase is the faulty phase, and its protection will activate. Phases that do not meet the criteria are judged as non-faulty phases, and the corresponding protection will not activate.

[0051] However, the above protection criteria should also be adjusted for similarity protection settings.

[0052] The impact of similarity protection settings involves two aspects. First, the existing Pearson waveform similarity algorithm has a correlation coefficient of -1 for faults outside the protection zone, which is obtained by ignoring the line capacitive current. However, during transient processes, the line capacitive current is affected by high-frequency components, reaching several times the steady-state capacitive current. Therefore, the influence of transient capacitive current needs to be considered in the construction of protection criteria. Second, there is the transmission error of the current transformer.

[0053] Regarding the first aspect, when a fault occurs outside the system side of the transmitting line, the fault traveling wave propagates to the transmitting line after refraction at the system-side bus, forming a transient capacitive current. Considering the large inductance of the main transformer at the substation, the refractive index at the system-side bus is close to 1, so the amplitude of the transient capacitive current is very small in this case. The same applies when a fault occurs outside the substation side of the transmitting line. However, when a fault occurs near the outside of either side of the zone, such as... Figure 2 For K1 and K5, the fault point is still located inside the two busbars. The transient capacitive current is an unrefractive fault traveling wave with a large amplitude, and its impact needs to be analyzed.

[0054] Taking a fault at point K5 as an example, the frequency of the minimum frequency component of the transient capacitive current experienced on both sides of the line at this time satisfies:

[0055] In the above formula, L It is the length of the transmission line; v It is the speed of travel wave propagation, approximately 300,000 km / s.

[0056] To save on investment costs, the transmission lines from new energy power plants are often connected to nearby regional substations, with line lengths generally kept under 100km. Therefore... f min Not less than 750Hz. In addition, to prevent spectral aliasing, the microcomputer protection device sets a low-pass filter before sampling to filter out high-frequency components with a frequency of half or more than the sampling frequency. Therefore, as long as the sampling frequency is not greater than 1.5kHz, it can be assumed that high-frequency components of 750Hz and above will be filtered out by the low-pass filter.

[0057] Therefore, in a preferred embodiment, when sampling the current on the first and second sides of the target line in real time, the sampling frequency is less than 1.5 kHz. When the device sampling frequency is less than 1.5 kHz, the influence of transient capacitive current on this algorithm can be ignored.

[0058] Regarding the second aspect, the current transformer is the core device for acquiring current signals. In actual operation, factors such as core saturation and accuracy level can cause a slight deviation between the acquired current signal and the actual current, preventing the correlation coefficient during external faults from perfectly reaching -1. To avoid protection maloperation due to current transformer errors, a certain margin needs to be left in the setpoint: the ideal value of -1 is corrected to -0.9, i.e., the similarity protection setting value r... set =-0.9.

[0059] In summary, the protection is equipped with a "waveform correlation coefficient setting" (the setting range is -1 to +1). When the similarity of the integrated waveforms of the fault currents of the same phases on both sides is between -0.9 and +1 at the same time, the protection will activate and report "longitudinal waveform protection activation".

[0060] Therefore, in a preferred embodiment, the protection criterion is: at the same time, if the current correlation coefficient of the same phases on both sides is between -0.9 and +1, then the phase is a faulty phase.

[0061] In one embodiment, the line protection fault identification method further includes: After the faulty phase is identified, the output line issues an in-zone fault warning and activates the protection for the faulty phase. If the correlation coefficients of the three-phase currents do not meet the protection criteria, the fault is judged to be outside the zone, and the protection resets.

[0062] To verify the tolerance of the proposed current integral waveform similarity to high-frequency signals, high-order harmonics were superimposed on the field fault recording for simulation analysis and verification.

[0063] See Figure 3 and Figure 4 The original current sampling sequences of the faults inside and outside the zone when superimposed with the 7th harmonic are respectively. It can be seen that when there is no fault (the first cycle) or when there is a fault outside the zone, the waveform is symmetrical about the x-axis and has a strong correlation. When there is a fault inside the zone (the second and third cycles), the waveform pattern is disrupted and the correlation decreases.

[0064] See Figure 5 , Figure 6 , Figure 7 and Figure 8 .right Figure 3 and Figure 4 The waveform shown is obtained by integral sampling after superimposing high-frequency harmonics. Figure 7 and Figure 8The integral sampling waveform shown is accompanied by the original sampling waveform for comparison. Figure 5 and Figure 6 .

[0065] By calculating the waveform similarity between the original sampled waveform and the current integral sampled waveform, a comparison of the waveform similarity between faults within and outside the fault zone can be obtained. (See [link to relevant documentation]). Figure 9 and Figure 10 .

[0066] Figure 9 and Figure 10 The calculation results of integral similarity and simple similarity proposed in this embodiment were compared. As can be seen from the figure, when high-frequency harmonics are superimposed, the calculation results of integral similarity and simple similarity are similar when there is a fault within the zone, and both can correctly identify the fault. However, when there is a fault outside the zone, the calculation results of simple similarity are less stable, and the calculation results of multiple points are greater than -0.9, which poses a risk of false operation. On the other hand, the calculation results of integral similarity are more stable, and there are no points that meet the protection criteria, so there is no risk of false operation.

[0067] Based on the above simulations, it can be seen that the longitudinal current integral waveform similarity fault identification method proposed in this embodiment can operate correctly at different locations and with different fault types in the transmission lines of new energy power plants, and is not affected by the magnitude of the fault current. It has strong resistance tolerance and has a good high-frequency resistance compared with ordinary waveform similarity identification methods.

[0068] Understandably, this invention addresses the problem of power frequency transient quantity failure in the protection of new energy transmission lines. Building upon conventional waveform similarity algorithms, it proposes a fault identification method based on longitudinal current integral waveform similarity. This method utilizes a quarter-cycle sampling time window to perform integral sampling processing on the current sampling sequence of the opposite side, then calculates waveform similarity. A waveform correlation coefficient greater than -0.9 is used as the criterion for faults within the protection zone. This method is not constrained by the small amplitude of fault currents in new energy scenarios and exhibits strong adaptability to excessive resistance. Fault waveform simulations have verified the effectiveness of this method, demonstrating better high-frequency tolerance than conventional waveform similarity algorithms. It can prevent false tripping due to faults outside the protection zone in scenarios with high high-frequency content in new energy transmission lines.

[0069] In another embodiment, a line protection fault identification system is provided, comprising: A first microcomputer protection device installed on the first side of the target line is used to sample the current on the first side of the target line in real time to obtain the sampled current sequence on the first side. A second microprocessor-based protection device is installed on the second side of the target line to sample the current on the second side of the target line in real time and obtain the sampled current sequence on the second side. The calculation and identification module is used to integrate the sampled current sequences of the first side and the second side respectively to obtain the integrated current sequences of the first side and the second side. Using a waveform similarity algorithm, the three-phase current correlation coefficient of the integrated current sequences of the first side and the second side is calculated. If the current correlation coefficient of a certain phase meets the protection criterion, then the phase is a faulty phase; otherwise, the phase is a non-faulty phase.

[0070] Preferably, in the line protection fault identification system, both the first microcomputer protection device and the second microcomputer protection device are equipped with a low-pass filter to filter out high-frequency components with a frequency greater than or equal to the sampling frequency.

[0071] It is understood that the same or similar parts in the above embodiments can be referred to each other, and the contents not described in detail in some embodiments can be referred to the same or similar contents in other embodiments.

[0072] It should be noted that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means at least two.

[0073] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0074] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0075] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0076] Furthermore, the functional units in the various embodiments of the present invention can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0077] The storage media mentioned above can be read-only memory, disk, or optical disk, etc.

[0078] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0079] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for identifying line protection faults, characterized in that, include: In the target line, the current on the first side and the second side of the target line are sampled in real time to obtain the sampling current sequence of the first side and the sampling current sequence of the second side. The sampled current sequences from the first and second sides are integrated to obtain the integrated current sequences from the first and second sides, respectively. Using a waveform similarity algorithm, the three-phase current correlation coefficients of the first-side integral current sequence and the second-side integral current sequence are calculated. If the current correlation coefficient of a certain phase meets the protection criterion, then that phase is a faulty phase; otherwise, that phase is a non-faulty phase.

2. The line protection fault identification method according to claim 1, characterized in that, Integrating the sampled current sequences from the first and second sides respectively, including: Using a quarter-cycle sampling time window, the sampled current sequences of the first and second sides are integrated respectively.

3. The line protection fault identification method according to claim 2, characterized in that, Integrating the sampled current sequences from the first and second sides respectively, including: The sampled current sequences from the first and second sides are integrated using the following formula: Where k is the current sampling point, X(k) is the sampled value corresponding to point k, X'(k) is the integrated value of point k, and i is the lag index relative to the current sampling point k within the integration window; N Int The number of integration points; If the integration data window is 1 / 4 of the fundamental frequency, the number of integration points is calculated using the following formula: in, N b The number of sampling points in one period. f s Sampling frequency, f b This is the fundamental frequency.

4. The line protection fault identification method according to claim 1, characterized in that, Using a waveform similarity algorithm, the three-phase current correlation coefficients of the first-side integral current sequence and the second-side integral current sequence are calculated, including: The three-phase current correlation coefficient between the first-side integral current sequence and the second-side integral current sequence is calculated using the following formula: x ={ x 1， x 2，…， x n} y ={ y 1， y 2，…， y n} in, r ( x , y ) is a variable x and variables y The degree of relevance, n This represents the number of sampling points.

5. The line protection fault identification method according to claim 1, characterized in that, When sampling the current on the first and second sides of the target line in real time, it also includes: The sampling frequency is less than 1.5 kHz.

6. The line protection fault identification method according to claim 1, characterized in that, The protection criterion is as follows: at the same time, if the current correlation coefficient of the same phases on both sides is between -0.9 and +1, then the phase is the faulty phase.

7. The line protection fault identification method according to claim 1, characterized in that, The target line is a power transmission line from a new energy power station, with the first side being the power station side and the second side being the system side.

8. The line protection fault identification method according to claim 1, characterized in that, Also includes: After the faulty phase is identified, the output line issues an alarm for the fault within the zone and activates the protection of the faulty phase. If the correlation coefficients of the three-phase currents do not meet the protection criteria, the fault is judged to be outside the protection zone, and the protection is reset.

9. A line protection fault identification system, characterized in that, include: A first microcomputer protection device installed on the first side of the target line is used to sample the current on the first side of the target line in real time to obtain the sampled current sequence on the first side. A second microprocessor-based protection device is installed on the second side of the target line to sample the current on the second side of the target line in real time and obtain the sampled current sequence on the second side. The calculation and identification module is used to integrate the sampled current sequences of the first side and the second side respectively to obtain the integrated current sequence of the first side and the integrated current sequence of the second side. Using a waveform similarity algorithm, the three-phase current correlation coefficients of the first-side integral current sequence and the second-side integral current sequence are calculated. If the current correlation coefficient of a certain phase meets the protection criterion, then the phase is a faulty phase; otherwise, the phase is a non-faulty phase.

10. The line protection fault identification system according to claim 9, characterized in that, Both the first microcomputer protection device and the second microcomputer protection device are equipped with a low-pass filter to filter out high-frequency components with a frequency greater than or equal to the sampling frequency.

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