Direction pilot protection method and system suitable for new energy alternating current transmission line

Abstract

The invention discloses a direction pilot protection method and system suitable for a new energy alternating current transmission line, and the method comprises the steps: simulating a plurality of fault scenes based on a two-end system, and obtaining the three-phase current sampling data of an M end and an N end in each fault scene; utilizing a principal component analysis method to obtain a first classification criterion for dividing the plurality of simulation scenes into M-end forward faults and M-end reverse faults, and obtaining a second classification criterion for dividing the plurality of simulation scenes into N-end forward faults and N-end reverse faults; judging to-be-analyzed fault current data by combining the first classification criterion of the M end and the second classification criterion of the N end; if the classification criterion of the M end and the classification criterion of the N end are both forward faults, the fault to be analyzed occurs on a line between the M end and the N end, and protection action is performed; otherwise, the protection does not act. The method is not influenced by new characteristics of fault electrical quantity after the alternating current transmission line has a fault, the fault is reliably identified, and the fault is effectively isolated.

Description

Technical Field

[0001] The present invention relates to the technical field of transmission lines and directional longitudinal protection of new energy stations, and in particular to a directional longitudinal protection method and system suitable for new energy AC transmission lines. Background Art

[0002] With the increasing consumption of fossil energy and environmental problems, the development and utilization of clean and renewable energy such as wind and solar energy has developed rapidly. Wind power, photovoltaic and other new energy stations are connected to the traditional AC power grid on a large scale. Clean energy such as wind power and solar energy has uncertainty, so wind power, photovoltaic and other new energy stations cannot be directly connected to the power grid, and need to be connected to the traditional AC power grid through the corresponding grid-connected circuit. The grid-connected methods of photovoltaic stations are as follows: Figure 1 As shown in the figure, the inverter converts the electricity generated by the photovoltaic cells into industrial frequency AC and injects it into the power grid. Figure 2 As shown, the rectifier rectifies the electricity generated by the wind farm into direct current, and then the inverter inverts the direct current into industrial frequency alternating current and injects it into the grid.

[0003] The existing methods for determining whether an AC transmission line fault has occurred include: current differential protection method and directional longitudinal protection method.

[0004] (1) The current differential protection method is based on Kirchhoff's current law. Figure 3 (a) Figure 3 As shown in (b), when there is no fault in the line or the fault occurs outside the line, the current is measured on the left side of the line. Measure current with the right side of the line should be equal, and the sum of the two phase quantities should be 0 or a very small phase quantity. When a fault occurs on the line, such as Figure 3 As shown in (b), because there is a fault branch, the current measured on the left side of the line Measure current with the right side of the line The sum of the two phase quantities is a larger phase quantity. Based on the above differences, the current differential protection can determine whether the fault occurs on the protected line. The basic criterion of current differential protection can be written as: In the formula, I set is a threshold value greater than 0.

[0005] (2) Directional longitudinal protection method: The directional element or power direction measurement element is the key element in the directional comparison type longitudinal protection. The fault components of the power frequency voltage and current are usually used to form the directional element.

[0006] Define the direction from the busbar to the line as the positive direction. For a double-terminal power transmission line, when a short circuit occurs in the positive direction of the protection, the relationship between the voltage and current at the protection installation is: In the formula, They are the power frequency fault component voltage and current at the protection installation, Z s It is the impedance of the equivalent power source on the back bus of the back line where the protection is installed. When the protection is short-circuited in the reverse direction, the relationship between the voltage and current at the protection installation is:

[0007] It can be seen that by comparing the phase relationship of the fault component voltage and current, the direction of the fault can be clearly determined. In order to facilitate the determination of the voltage and current phase relationship, the actual directional element compares the fault component voltage and the fault component current in the simulated impedance Z. r The phase relationship between the voltages generated on r , Z s and Z s ′ is equal, so when there is a positive fault, the power direction is positive, that is:

[0008] Considering the influence of various factors, the power direction criterion corresponding to the positive direction fault is:

[0009] In case of reverse fault, the power direction is negative, that is:

[0010] Considering the influence of various factors, the power direction criterion corresponding to the reverse direction fault is:

[0011] However, after the new energy station is connected to the traditional AC power grid through the transmission line, affected by the new energy station's own control strategy, after the AC transmission line fails, the fault electrical quantity shows new change characteristics, such as the fault current amplitude on the new energy station side is limited, the phase is controlled to show weak feedback characteristics, and the harmonic content increases.

[0012] For the current differential protection method, the fault current injected into the system side may be much larger than the fault current injected into the renewable energy side. The fault of the transmission line is similar to the fault of the single-ended power line. The sensitivity of the differential protection (the ratio of the differential current to the braking current) is reduced, and even refusal to operate may occur. For the directional longitudinal protection method, according to the principle of the directional element, the direction of the directional element determines the equivalent impedance of the system on both sides of the line. When the back side of the protection installation is a renewable energy power source, the phase of its equivalent impedance is no longer fixed due to the influence of the renewable energy power source control strategy on the fault response, which may cause the protection to refuse to operate.

[0013] In view of this, this application is hereby filed. Summary of the invention

[0014] The technical problem to be solved by the present invention is that after a fault occurs in the AC transmission line of a new energy station, the sensitivity of the current differential protection decreases due to factors such as the limited amplitude of the fault current on the new energy station side and the controlled phase, and even causes the current differential protection to refuse to operate; due to the influence of the new energy station's own control strategy on the fault response, the phase of the equivalent impedance is no longer fixed, which may cause problems such as protection refusal to operate.

[0015] The purpose of the present invention is to provide a directional longitudinal protection method and system suitable for new energy AC transmission lines. The present invention adopts a directional longitudinal protection based on principal component analysis. This protection method can reliably identify asymmetric faults occurring on the protected line and effectively isolate the faults without being affected by new characteristics of fault electrical quantities after a fault in the AC transmission line.

[0016] The present invention is achieved through the following technical solutions:

[0017] In a first aspect, the present invention provides a directional longitudinal protection method applicable to a new energy AC transmission line, the method comprising:

[0018] Based on the two-terminal system, multiple fault scenarios are simulated and the three-phase current sampling data at the M and N terminals under each fault scenario are obtained; the M terminal of the two-terminal system is connected to the power grid system, and the N terminal is connected to the new energy system;

[0019] Based on the three-phase current data sampled at the M-terminal, the three-phase current data is processed using the principal component analysis (PCA) method to obtain a first classification criterion for dividing multiple simulation scenarios into forward faults at the M-terminal and reverse faults at the M-terminal;

[0020] Based on the three-phase current data obtained by sampling at the N-terminal, the three-phase current data is processed using the principal component analysis (PCA) method to obtain a second classification criterion for dividing multiple simulation scenarios into N-terminal forward faults and N-terminal reverse faults;

[0021] Combined with the first classification criterion of the M terminal and the second classification criterion of the N terminal, the fault current data to be analyzed is judged; if the classification criterion of the M terminal and the classification criterion of the N terminal are both forward faults, the fault to be analyzed occurs on the line between the M terminal and the N terminal, and the protection is activated; if one end of the classification criterion of the M terminal and the classification criterion of the N terminal is a forward fault and the other end is a reverse fault, the fault to be analyzed does not occur on the line between the M terminal and the N terminal, and the protection is not activated.

[0022] Furthermore, multiple failure scenarios include:

[0023] For the fault occurring on the back side of the M terminal, i.e., the fault at F1: a total of k1 fault scenarios are simulated based on different fault types, different transition resistances, and different fault moments;

[0024] For the fault occurring on the line between the M terminal and the N terminal, i.e., the fault at F2: a total of k2 fault scenarios are simulated based on different fault types, different fault transition resistances, different fault times, and different distances between the fault point and the measurement point at the M terminal;

[0025] For the fault on the back side of the N terminal, i.e., the fault at F3: a total of k3 fault scenarios are simulated based on different fault types, different transition resistances, and different fault moments;

[0026] There are K different fault scenarios in total: K = k1 + k2 + k3;

[0027] Among them, different fault types include phase A ground fault, phase B ground fault, phase C ground fault, AB two-phase short circuit fault, BC two-phase short circuit fault, CA two-phase short circuit fault, AB two-phase ground short circuit fault, BC two-phase ground short circuit fault, CA two-phase ground short circuit fault and ABC three-phase short circuit fault.

[0028] Different transition resistances include 0Ω, 10Ω, 50Ω and 100Ω, etc.

[0029] Different fault times include 2ms, 4ms, 6ms, 8ms and 10ms;

[0030] The different distances between the fault point and the M-end measurement point include 10km, 50km, 125km, 225km, etc.

[0031] Furthermore, based on the three-phase current data sampled at the M terminal, the three-phase current data is processed using the principal component analysis method to obtain a first classification criterion for dividing multiple simulation scenarios into M terminal forward faults and M terminal reverse faults, including:

[0032] Based on the three-phase current data sampled at the M terminal, the instantaneous values ​​sampled in each fault scenario are spliced ​​together in the order of the instantaneous value of the A phase current, the instantaneous value of the B phase current, and the instantaneous value of the C phase current to form a first fault column vector;

[0033] According to the first fault column vector, the first fault column vectors obtained by simulating different fault mode scenarios are combined into a first fault matrix;

[0034] Based on the first fault matrix, obtaining a first matrix required for calculation;

[0035] Find the first characteristic root of the first matrix, take the largest characteristic root and the second largest characteristic root from all the characteristic roots, and find the eigenvectors corresponding to the largest characteristic root and the second largest characteristic root to form the first dimension reduction matrix P M ;

[0036] Based on the first dimension reduction matrix P M, perform dimensionality reduction processing on the first fault matrix to obtain a first dimensionality-reduced matrix;

[0037] Using the elements of the first row of the matrix after the first dimensionality reduction as the horizontal coordinates and the elements of the second row as the vertical coordinates, the first distance of each coordinate point from the coordinate origin is calculated;

[0038] The magnitude relationship between the first distance and the first criterion threshold value is used as a first classification criterion for M-end forward faults and M-end reverse faults.

[0039] Furthermore, the expression of the first fault matrix X is:

[0040] X=[x1x2…x K ]

[0041] x k =[i Ak i Bk i Ck ] T

[0042]

[0043] Where K is the total number of simulated fault scenarios; x k is the first fault column vector, the subscript k takes any integer value from 1 to K, i Ak is the instantaneous value of phase A current sampled under the kth fault scenario, i Bk is the instantaneous value of phase B current sampled under the kth fault scenario, i Ck is the instantaneous value of the C phase current sampled under the Kth fault scenario; N is the number of sampling points, and N=20 can be calculated based on the sampling frequency of 4 kHz and the sampling time window length of 5 ms.

[0044] Furthermore, the magnitude relationship between the first distance and the first criterion threshold value is used as a first classification criterion for the M-end forward fault and the M-end reverse fault, including:

[0045] If the first distance is greater than the first criterion threshold, it is considered that a forward fault has occurred at the M end;

[0046] If the first distance is less than or equal to the first criterion threshold value, it is considered that a reverse fault occurs at the M end.

[0047] Furthermore, based on the three-phase current data sampled at the N-terminal, the three-phase current data is processed using the principal component analysis method to obtain a second classification criterion for dividing multiple simulation scenarios into N-terminal forward faults and N-terminal reverse faults, including:

[0048] Based on the three-phase current data sampled at the N terminal, the instantaneous values ​​sampled in each fault scenario are spliced ​​together in the order of the instantaneous value of the A phase current, the instantaneous value of the B phase current and the instantaneous value of the C phase current to form a second fault column vector;

[0049] According to the second fault column vector, the second fault column vectors obtained by simulating different fault mode scenarios are used to form a second fault matrix;

[0050] Based on the second fault matrix, obtaining a second matrix required for calculation;

[0051] Obtain the second characteristic root of the second matrix, take the largest characteristic root and the second largest characteristic root from all the characteristic roots, and obtain the eigenvectors corresponding to the largest characteristic root and the second largest characteristic root to form the second dimension reduction matrix P N ;

[0052] Based on the second dimension reduction matrix P N , perform dimensionality reduction processing on the second fault matrix to obtain a second dimensionality-reduced matrix;

[0053] The elements of the first row of the matrix after the second dimensionality reduction are used as the horizontal coordinates, and the elements of the second row are used as the vertical coordinates, and the second distance of each coordinate point from the coordinate origin is calculated;

[0054] The magnitude relationship between the second distance and the second criterion threshold value is used as a second classification criterion for N-end forward faults and N-end reverse faults.

[0055] Furthermore, the magnitude relationship between the second distance and the second criterion threshold value is used as a second classification criterion for the N-end forward fault and the N-end reverse fault, including:

[0056] If the second distance is greater than the second criterion threshold, it is considered that a forward fault has occurred at the N end;

[0057] If the second distance is less than or equal to the second criterion threshold value, it is considered that a reverse fault has occurred at the N end.

[0058] In a second aspect, the present invention further provides a directional longitudinal protection system applicable to a new energy AC transmission line, the system comprising:

[0059] Construct a simulation scenario to simulate multiple fault scenarios based on the two-terminal system and obtain the three-phase current sampling data at the M and N terminals under each fault scenario; the M terminal of the two-terminal system is connected to the power grid system, and the N terminal is connected to the new energy system;

[0060] A first criterion obtaining unit is used to process the three-phase current data obtained by sampling at the M terminal using a principal component analysis method to obtain a first classification criterion for dividing multiple simulation scenarios into M terminal forward faults and M terminal reverse faults;

[0061] A second criterion obtaining unit is used to process the three-phase current data obtained by sampling at the N-terminal using a principal component analysis method to obtain a second classification criterion for dividing the multiple simulation scenarios into N-terminal forward faults and N-terminal reverse faults;

[0062] The line fault judgment and protection unit is used to judge the fault current data to be analyzed by combining the first classification criterion of the M terminal and the second classification criterion of the N terminal; if the classification criterion of the M terminal and the classification criterion of the N terminal are both forward faults, the fault to be analyzed occurs on the line between the M terminal and the N terminal, and the protection is activated; if one end of the classification criterion of the M terminal and the classification criterion of the N terminal is a forward fault and the other end is a reverse fault, the fault to be analyzed does not occur on the line between the M terminal and the N terminal, and the protection is not activated.

[0063] Furthermore, the first criterion obtaining unit includes:

[0064] The instantaneous current splicing subunit is used to splice the instantaneous values ​​sampled in each fault scenario in the order of the instantaneous value of the A phase current, the instantaneous value of the B phase current and the instantaneous value of the C phase current based on the three-phase current data sampled at the M terminal to form a first fault column vector;

[0065] A fault matrix forming subunit is used to form a first fault matrix by combining the first fault column vectors obtained by simulating different fault mode scenarios according to the first fault column vector;

[0066] A first calculation subunit, used for obtaining a first matrix required for calculation based on a first fault matrix;

[0067] The dimension reduction matrix forming subunit is used to obtain the first characteristic root of the first matrix, take the largest characteristic root and the second largest characteristic root from all characteristic roots, and obtain the eigenvectors corresponding to the largest characteristic root and the second largest characteristic root to form the first dimension reduction matrix P M ;

[0068] A dimensionality reduction processing subunit is used to process the first dimensionality reduction matrix P M , perform dimensionality reduction processing on the first fault matrix to obtain a first dimensionality-reduced matrix;

[0069] A second calculation subunit is used to use each element of the first row of the matrix after the first dimension reduction as a horizontal coordinate and each element of the second row as a vertical coordinate to calculate a first distance between each coordinate point and the coordinate origin;

[0070] The first classification criterion obtaining subunit is used to use the magnitude relationship between the first distance and the first criterion threshold value as the first classification criterion for M-end forward fault and M-end reverse fault.

[0071] In a third aspect, the present invention further provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the above-mentioned directional longitudinal protection method applicable to new energy AC transmission lines is implemented.

[0072] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0073] 1. The present invention is applicable to the directional longitudinal protection method and system of the new energy AC transmission line. The present invention adopts the directional longitudinal protection based on the principal component analysis method. The protection method can reliably identify the asymmetric faults occurring on the protected line and effectively isolate the faults without being affected by the new characteristics of the fault electrical quantity after the AC transmission line fails;

[0074] 2. The present invention is applicable to the directional longitudinal protection method and system for the new energy AC transmission line. It can be seen from the process step 21 of obtaining the classification criterion of the M end and the process step 41 of the fault determination that the sampling window required by the present invention is 5ms. Compared with the half-cycle (10ms) or full-cycle (20ms) sampling window required by the current differential protection and the traditional longitudinal follower protection, the sampling window required by the present invention is shorter and faster;

[0075] 3. The present invention is applicable to the directional longitudinal protection method and system for the new energy AC transmission line. It can be seen from the fault judgment process steps 42 and 43 that most of the operations of the present invention are only simple addition and multiplication operations of the current sampling values, and do not involve the extraction of the phasor amplitude and phase using discrete Fourier transform. Therefore, compared with the current differential protection, the present invention is not affected by the limited current amplitude and the controlled current phase, and has higher sensitivity. At the same time, the present invention does not involve impedance calculation. Therefore, compared with the traditional directional longitudinal protection, the present invention is not affected by the change of the equivalent impedance of the back side system of the line, and is more reliable in identifying faults in the new energy transmission line. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0077] Figure 1 This is a schematic diagram of photovoltaic grid connection;

[0078] Figure 2 This is a schematic diagram of wind power grid connection;

[0079] Figure 3 Schematic diagram of line current at different fault locations, (a) line without fault, (b) fault outside the line, (c) fault on the line;

[0080] Figure 4 This is a schematic diagram of a simple two-terminal system structure of the present invention;

[0081] Figure 5 This is a flow chart of the directional longitudinal protection method applicable to the new energy AC transmission line of the present invention;

[0082] Figure 6 This is a structural block diagram of the directional longitudinal protection system applicable to the new energy AC transmission line of the present invention. DETAILED DESCRIPTION

[0083] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0084] In view of the problem that after a fault occurs in a new energy AC transmission line, the new characteristics of the fault electrical quantity change cause the protection performance of the traditional AC line to deteriorate, and the present invention designs an AC line protection method, namely, a directional longitudinal protection method suitable for new energy AC transmission lines, which can be unaffected by the new characteristics of the fault electrical quantity change, reliably identify asymmetric faults occurring on the protected line, and effectively isolate the faults.

[0085] by Figure 4 Taking the simple two-terminal system shown in the figure as an example, the locations where faults occur can be divided into three categories, namely F1, F2 and F3 as shown in the figure. F1 represents a fault on the back side of the M end, F2 represents a fault on the line, and F3 represents a fault on the back side of the N end. For the M end and the N end, the three types of faults can be divided into forward faults and reverse faults. From the M end, F2 and F3 are forward faults, and F1 is a reverse fault; from the N end, F1 and F2 are forward faults, and F3 is a reverse fault. The M end of the two-terminal system is connected to the power grid system, and the N end is connected to the new energy system.

[0086] The technical concept of the method of the present invention is: for the above three types of faults, based on the two-terminal system, multiple fault scenarios are simulated and the three-phase current sampling data at the M terminal and the N terminal under each fault scenario are obtained;

[0087] Based on the three-phase current data sampled at the M-terminal, the three-phase current data is processed using the principal component analysis (PCA) method to obtain a first classification criterion for dividing multiple simulation scenarios into forward faults at the M-terminal and reverse faults at the M-terminal;

[0088] Based on the three-phase current data obtained by sampling at the N-terminal, the three-phase current data is processed using the principal component analysis (PCA) method to obtain a second classification criterion for dividing multiple simulation scenarios into N-terminal forward faults and N-terminal reverse faults;

[0089] Combined with the first classification criterion of the M terminal and the second classification criterion of the N terminal, the fault current data to be analyzed is judged; if the classification criterion of the M terminal and the classification criterion of the N terminal are both forward faults, the fault to be analyzed occurs on the line between the M terminal and the N terminal, and the protection is activated; if one end of the classification criterion of the M terminal and the classification criterion of the N terminal is a forward fault and the other end is a reverse fault, the fault to be analyzed does not occur on the line between the M terminal and the N terminal, and the protection is not activated.

[0090] Example 1

[0091] like Figure 1 As shown, the present invention is applicable to a directional longitudinal protection method for a new energy AC transmission line, the method comprising:

[0092] Step 1: Based on the two-terminal system, multiple fault scenarios are simulated and the three-phase current sampling data at the M terminal and the N terminal under each fault scenario are obtained; the M terminal of the two-terminal system is connected to the power grid system, and the N terminal is connected to the new energy system;

[0093] In this embodiment, for the line to be protected, the systems on both sides can always be equivalent to two power supplies and the electromagnetic transient simulation software can be used to establish the following Figure 4 In the established simulation model, different fault scenarios of the fault locations represented by F1, F2 and F3 in the simulation diagram are simulated, and the three-phase current at the measurement point at the M end is sampled with a sampling frequency of 4kHz and a sampling time window length of 5ms.

[0094] Different failure scenarios can be described as follows:

[0095] (1) For the fault occurring on the back side of the M terminal, i.e., the fault at F1: three fault scenarios are simulated based on different fault types (i.e., A-phase grounding fault, BC-phase short-circuit fault, CA-phase grounding short-circuit fault), different transition resistances (i.e., 0Ω, 5Ω, 25Ω, 50Ω, 75Ω, 100Ω), and different fault times (i.e., 20km, 50km, 80km, 125km, 170km, 210km, 225km);

[0096] (2) For the fault occurring on the line between the M and N terminals, i.e., the fault at F2: a total of 26 fault scenarios were simulated based on different fault types, different fault transition resistances, different fault times, and different distances between the fault point and the measurement point at the M terminal (e.g., 10 km, 50 km, 125 km, 225 km, etc.);

[0097] (3) For the fault occurring on the back side of the N terminal, i.e., the fault at F3: three fault scenarios are simulated based on different fault types, different transition resistances, and different fault moments;

[0098] There are 32 different fault scenarios in total: K=3+26+3.

[0099] Step 2: Based on the three-phase current data sampled at the M terminal, the three-phase current data is processed using a principal component analysis (PCA) method to obtain a first classification criterion for dividing multiple simulation scenarios into M-terminal forward faults and M-terminal reverse faults;

[0100] In this embodiment, step 2 specifically includes:

[0101] Step 21, based on the three-phase current data sampled at the M terminal, the instantaneous values ​​sampled in each fault scenario in step 1 are spliced ​​together in the order of the instantaneous value of the current of phase A, the instantaneous value of the current of phase B, and the instantaneous value of the current of phase C to form a first fault column vector vector x k , whose expression is:

[0102] x k =[i Ak i Bk i Ck ] T

[0103] In the formula, x k The subscript “k” of can be an integer from 1 to K, corresponding to different fault scenarios in step 1; the vector i Ak 、i Bk and i Ck The expression is:

[0104]

[0105] In the formula, the elements in each vector represent the instantaneous value of the sample, N is the number of sampling points, and N = 20 can be calculated from the sampling frequency of 4kHz and the sampling time window length of 5ms; i Ak is the instantaneous value of phase A current sampled under the kth fault scenario, i Bk is the instantaneous value of phase B current sampled under the kth fault scenario, i Ck is the instantaneous value of the C phase current sampled under the Kth fault scenario;

[0106] Step 22: According to the first fault column vector x k , the first fault column vectors obtained by simulating different fault mode scenarios are used to form the first fault matrix X, which is expressed as follows:

[0107] X=[x1x2…x K ]

[0108] In the formula, the subscripts represent different fault scenarios, K is the K mentioned in step 1, and is the total number of simulated fault scenarios.

[0109] Step 23, based on the first fault matrix X, obtain the first matrix M required for calculation, and the expression of M is as follows:

[0110]

[0111] Combined with the first fault column vector x k The expression of The expression is:

[0112]

[0113] In the formula, μ l (l=1,2,…,60) is the average value of each row of the first fault matrix X.

[0114] Step 24, find the first eigenvalue of the first matrix M, take the largest eigenvalue and the second largest eigenvalue from the first eigenvalue, and record them as λ1 and λ2; use λ1 and λ2 to find the eigenvectors ξ1 and ξ2 corresponding to the largest eigenvalue and the second largest eigenvalue, ξ1 and ξ2 are the vector basis required for dimensionality reduction, and use the eigenvectors ξ1 and ξ2 to form the first dimensionality reduction matrix P M , the first dimension reduction matrix P M As shown below:

[0115] P M =[ξ1 ξ2] T

[0116] Step 25, based on the first dimension reduction matrix P M , perform dimensionality reduction processing on the first fault matrix X, and obtain the first reduced-dimensional matrix X P , the processing formula is as follows:

[0117] X P =PX

[0118] From step 22 and step 24, we can know that the first dimension reduction matrix P M is a 2×60 matrix, and the first fault matrix X is a 60×K matrix, so X P is a 2×K-order matrix. The first reduced-dimensional matrix X P Specifically, it can be expressed as:

[0119]

[0120] Where K is the K mentioned in step 1 and is the total number of simulated fault scenarios.

[0121] Step 26: transform the first dimension-reduced matrix X P The elements in the first row are used as the horizontal coordinates, and the elements in the second row are used as the vertical coordinates. The first distance of each coordinate point from the origin of the coordinate is calculated. The first distance can be calculated as follows:

[0122]

[0123] Wherein, the subscript “k” can be an integer from 1 to K, corresponding to different fault scenarios in step 1.

[0124] Step 27, using the magnitude relationship between the first distance and the first criterion threshold value as a first classification criterion for the M-end forward fault and the M-end reverse fault.

[0125] According to the distribution of the corresponding points of the back fault of the M end and the corresponding points of the forward fault of the M end, the first judgment threshold value L is set. setM , the first classification criterion, that is, the relationship between the first distance and the first criterion threshold value: L k >L setM If the criterion is met, it is considered that a forward fault has occurred at the M end; otherwise, it is considered that a reverse fault has occurred at the M end.

[0126] Step 3, based on the three-phase current data sampled at the N-terminal, the three-phase current data is processed using a principal component analysis (PCA) method to obtain a second classification criterion for dividing the multiple simulation scenarios into N-terminal forward faults and N-terminal reverse faults;

[0127] In this embodiment, the first dimension reduction matrix P obtained at the M end M And the first criterion threshold value L setM Similarly, similar calculations and derivations are performed on the N end to obtain the second dimension reduction matrix P of the N end N And the second criterion threshold value L setN .

[0128] Step 3 specifically includes:

[0129] Step 31, based on the three-phase current data sampled at the N terminal, the instantaneous values ​​sampled in each fault scenario are spliced ​​together in the order of the instantaneous value of the A phase current, the instantaneous value of the B phase current and the instantaneous value of the C phase current to form a second fault column vector;

[0130] Step 32, according to the second fault column vector, the second fault column vectors obtained by simulating different fault mode scenarios are used to form a second fault matrix;

[0131] Step 33, based on the second fault matrix, obtaining a second matrix required for calculation;

[0132] Step 34, obtain the second characteristic root of the second matrix, take the largest characteristic root and the second largest characteristic root from all the characteristic roots, and obtain the eigenvectors corresponding to the largest characteristic root and the second largest characteristic root to form a second dimension reduction matrix P N ;

[0133] Step 35, based on the second dimension reduction matrix P N , perform dimensionality reduction processing on the second fault matrix to obtain a second dimensionality-reduced matrix;

[0134] Step 36, using each element in the first row of the matrix after the second dimension reduction as the horizontal coordinate and each element in the second row as the vertical coordinate, and calculating the second distance of each coordinate point from the coordinate origin;

[0135] Step 37, using the magnitude relationship between the second distance and the second criterion threshold value as a second classification criterion for N-end forward fault and N-end reverse fault.

[0136] Step 4, combining the first classification criterion of the M terminal and the second classification criterion of the N terminal, judge the fault current data to be analyzed; if the classification criterion of the M terminal and the classification criterion of the N terminal are both forward faults, the fault to be analyzed occurs on the line between the M terminal and the N terminal, and the protection is activated; if one end of the classification criterion of the M terminal and the classification criterion of the N terminal is a forward fault and the other end is a reverse fault, the fault to be analyzed does not occur on the line between the M terminal and the N terminal, and the protection is not activated.

[0137] In this embodiment, the first dimension reduction matrix P of the M end is obtained in step 4 M And the first criterion threshold value L setM , the second dimension reduction matrix P at the N end N And the second criterion threshold value L setN After that, the fault determination process is as follows:

[0138] Step 41: After a fault occurs, the three-phase currents at the M and N terminals are sampled, and the current sampling values ​​are spliced ​​according to the method in step 21 in the above process to obtain the M terminal fault vector x FM , N-side fault vector x FN .

[0139] Step 42: Get the fault vector x FM 、x FN Then, using the first dimension reduction matrix P at the M end M and the second dimension reduction matrix P at the N end N Calculate the corresponding two-dimensional coordinate points. The specific calculation formula is as follows:

[0140]

[0141]

[0142] Step 43: Get the corresponding coordinate point (x FM ,y FM )、(x FN ,y FN ), calculate the distance L from the origin of the coordinate system FM and L FN , the specific calculation formula is as follows:

[0143]

[0144]

[0145] Step 44: Get L FM and L FN Then, L FM and L FN and the first criterion threshold L setM and the second criterion threshold value L setN For comparison, if there is L FM Greater than the first criterion threshold L setM And L FN Greater than the second criterion threshold L setN , it is considered that the fault occurs on the line and the protection is activated; otherwise, the protection does not operate.

[0146] The present invention has the following advantages:

[0147] (1) It can be seen from step 21 of obtaining the M-end classification criteria and step 41 of the fault judgment process that the sampling window required by the present invention is 5 ms. Compared with the current differential protection and the traditional longitudinal follower protection which require a half-cycle (10 ms) or full-cycle (20 ms) sampling window, the sampling window required by the present invention is shorter and faster.

[0148] (2) It can be seen from steps 42 and 43 of the fault determination process that most of the operations of the present invention are only simple addition and multiplication operations of the current sampling values, and do not involve the extraction of the phase amplitude and phase using discrete Fourier transform. Therefore, compared with current differential protection, the present invention is not affected by the limited current amplitude and controlled current phase, and has higher sensitivity. At the same time, the present invention does not involve impedance calculation, so compared with traditional directional longitudinal protection, the present invention is not affected by the change of the equivalent impedance of the back side system of the line, and is more reliable in identifying faults in new energy transmission lines.

[0149] Example 2

[0150] like Figure 6 As shown, the difference between this embodiment and embodiment 1 is that this embodiment provides a directional longitudinal protection system applicable to a new energy AC transmission line, and the system corresponds to the directional longitudinal protection method applicable to a new energy AC transmission line in embodiment 1 in a one-to-one manner; the system includes:

[0151] Construct a simulation scenario to simulate multiple fault scenarios based on the two-terminal system and obtain the three-phase current sampling data at the M and N terminals under each fault scenario; the M terminal of the two-terminal system is connected to the power grid system, and the N terminal is connected to the new energy system;

[0152] A first criterion obtaining unit is used to process the three-phase current data obtained by sampling at the M terminal using a principal component analysis method to obtain a first classification criterion for dividing multiple simulation scenarios into M terminal forward faults and M terminal reverse faults;

[0153] A second criterion obtaining unit is used to process the three-phase current data obtained by sampling at the N-terminal using a principal component analysis method to obtain a second classification criterion for dividing the multiple simulation scenarios into N-terminal forward faults and N-terminal reverse faults;

[0154] The line fault judgment and protection unit is used to judge the fault current data to be analyzed by combining the first classification criterion of the M terminal and the second classification criterion of the N terminal; if the classification criterion of the M terminal and the classification criterion of the N terminal are both forward faults, the fault to be analyzed occurs on the line between the M terminal and the N terminal, and the protection is activated; if one end of the classification criterion of the M terminal and the classification criterion of the N terminal is a forward fault and the other end is a reverse fault, the fault to be analyzed does not occur on the line between the M terminal and the N terminal, and the protection is not activated.

[0155] As a further implementation, the first criterion obtaining unit includes:

[0156] The instantaneous current splicing subunit is used to splice the instantaneous values ​​sampled in each fault scenario in the order of the instantaneous value of the A phase current, the instantaneous value of the B phase current and the instantaneous value of the C phase current based on the three-phase current data sampled at the M terminal to form a first fault column vector;

[0157] A fault matrix forming subunit is used to form a first fault matrix by combining the first fault column vectors obtained by simulating different fault mode scenarios according to the first fault column vector;

[0158] A first calculation subunit, used for obtaining a first matrix required for calculation based on a first fault matrix;

[0159] The dimension reduction matrix forming subunit is used to obtain the first characteristic root of the first matrix, take the largest characteristic root and the second largest characteristic root from all characteristic roots, and obtain the eigenvectors corresponding to the largest characteristic root and the second largest characteristic root to form the first dimension reduction matrix P M ;

[0160] A dimensionality reduction processing subunit is used to process the first dimensionality reduction matrix P M , perform dimensionality reduction processing on the first fault matrix to obtain a first dimensionality-reduced matrix;

[0161] A second calculation subunit is used to use each element of the first row of the matrix after the first dimension reduction as a horizontal coordinate and each element of the second row as a vertical coordinate to calculate a first distance between each coordinate point and the coordinate origin;

[0162] The first classification criterion obtaining subunit is used to use the magnitude relationship between the first distance and the first criterion threshold value as the first classification criterion for M-end forward fault and M-end reverse fault.

[0163] Among them, the execution process of each unit can be executed according to the process steps of the directional longitudinal protection method applicable to the new energy AC transmission line in Example 1, and will not be repeated one by one in this embodiment.

[0164] At the same time, the present invention also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the above-mentioned directional longitudinal protection method applicable to the new energy AC transmission line is implemented.

[0165] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0166] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes 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 generate 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.

[0167] 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 including 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.

[0168] 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.

[0169] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A directional longitudinal protection method applicable to new energy AC transmission lines, characterized in that: The method includes: Based on a two-terminal system, multiple fault scenarios are simulated and three-phase current sampling data at the M terminal and the N terminal under each fault scenario is obtained; the M terminal of the two-terminal system is connected to the power grid system, and the N terminal is connected to the new energy system; Based on the three-phase current data sampled at the M terminal, the three-phase current data is processed using the principal component analysis method to obtain a first classification criterion for dividing multiple simulation scenarios into forward faults at the M terminal and reverse faults at the M terminal; Based on the three-phase current data obtained by sampling at the N-terminal, the three-phase current data is processed by using the principal component analysis method to obtain a second classification criterion for dividing multiple simulation scenarios into N-terminal forward faults and N-terminal reverse faults; Combined with the first classification criterion of the M terminal and the second classification criterion of the N terminal, the three-phase current data of the fault to be analyzed is judged; if the classification criterion of the M terminal and the classification criterion of the N terminal are both forward faults, the fault to be analyzed occurs on the line between the M terminal and the N terminal, and the protection is activated; if one end of the classification criterion of the M terminal and the classification criterion of the N terminal is a forward fault and the other end is a reverse fault, the fault to be analyzed does not occur on the line between the M terminal and the N terminal, and the protection does not operate.

2. The directional longitudinal protection method applicable to the new energy AC transmission line according to claim 1 is characterized in that: Multiple failure scenarios, including: For the fault occurring on the back side of the M terminal, i.e., the fault at F1: a total of k1 fault scenarios are simulated based on different fault types, different transition resistances, and different fault moments; For the fault occurring on the line between the M terminal and the N terminal, i.e., the fault at F2: a total of k2 fault scenarios are simulated based on different fault types, different fault transition resistances, different fault times, and different distances between the fault point and the measurement point at the M terminal; For the fault occurring on the back side of the N terminal, i.e., the fault at F3: a total of k3 fault scenarios are simulated based on different fault types, different transition resistances, and different fault moments; There are K different fault scenarios in total: K = k1 + k2 + k3; Among them, different fault types include phase A ground fault, phase B ground fault, phase C ground fault, AB two-phase short circuit fault, BC two-phase short circuit fault, CA two-phase short circuit fault, AB two-phase ground short circuit fault, BC two-phase ground short circuit fault, CA two-phase ground short circuit fault and ABC three-phase short circuit fault.

3. The directional longitudinal protection method applicable to the new energy AC transmission line according to claim 1 is characterized in that: Based on the three-phase current data sampled at the M terminal, the three-phase current data is processed using the principal component analysis method to obtain the first classification criterion for dividing multiple simulation scenarios into M terminal forward faults and M terminal reverse faults, including: Based on the three-phase current data sampled at the M terminal, the instantaneous values ​​sampled in each fault scenario are spliced ​​together in the order of the instantaneous value of the A phase current, the instantaneous value of the B phase current, and the instantaneous value of the C phase current to form a first fault column vector; According to the first fault column vector, the first fault column vectors obtained by simulating different fault mode scenarios are used to form a first fault matrix; Based on the first fault matrix, obtaining a first matrix required for calculation; Obtain the first characteristic root of the first matrix, take the largest characteristic root and the second largest characteristic root from all the characteristic roots, and obtain the eigenvectors corresponding to the largest characteristic root and the second largest characteristic root to form the first dimension reduction matrix P M ; Based on the first dimension reduction matrix P M , performing dimensionality reduction processing on the first fault matrix to obtain a first dimensionality-reduced matrix; Using the elements of the first row of the matrix after the first dimensionality reduction as the horizontal coordinates and the elements of the second row as the vertical coordinates, the first distance of each coordinate point from the coordinate origin is calculated; The magnitude relationship between the first distance and the first criterion threshold value is used as a first classification criterion for M-end forward faults and M-end reverse faults.

4. The directional longitudinal protection method applicable to the new energy AC transmission line according to claim 3 is characterized in that: The expression of the first fault matrix X is: X=[x1 x2…x K ] x k =[i Ak i Bk i Ck ] T Where K is the total number of simulated fault scenarios; x k is the first fault column vector, the subscript k takes any integer value from 1 to K, i Ak is the instantaneous value of phase A current sampled under the kth fault scenario, i Bk is the instantaneous value of phase B current sampled under the kth fault scenario, i Ck is the instantaneous value of the C phase current sampled under the Kth fault scenario; N is the number of sampling points.

5. The directional longitudinal protection method applicable to the new energy AC transmission line according to claim 3 is characterized in that: The relationship between the first distance and the first criterion threshold value is used as a first classification criterion for M-end forward fault and M-end reverse fault, including: If the first distance is greater than the first criterion threshold value, it is considered that a forward fault has occurred at the M terminal; If the first distance is less than or equal to the first criterion threshold value, it is considered that a reverse fault occurs at the M end.

6. The directional longitudinal protection method applicable to the new energy AC transmission line according to claim 1 is characterized in that: Based on the three-phase current data sampled at the N-terminal, the three-phase current data is processed using the principal component analysis method to obtain a second classification criterion for dividing multiple simulation scenarios into N-terminal forward faults and N-terminal reverse faults, including: Based on the three-phase current data sampled at the N terminal, the instantaneous values ​​sampled in each fault scenario are spliced ​​together in the order of the instantaneous value of the A phase current, the instantaneous value of the B phase current and the instantaneous value of the C phase current to form a second fault column vector; According to the second fault column vector, second fault column vectors obtained by simulating different fault mode scenarios are used to form a second fault matrix; Based on the second fault matrix, obtaining a second matrix required for calculation; Obtain the second characteristic root of the second matrix, take the largest characteristic root and the second largest characteristic root from all the characteristic roots, and obtain the eigenvectors corresponding to the largest characteristic root and the second largest characteristic root to form the second dimension reduction matrix P N ; Based on the second dimension reduction matrix P N , performing dimensionality reduction processing on the second fault matrix to obtain a second dimensionality reduced matrix; The elements of the first row of the matrix after the second dimensionality reduction are used as the horizontal coordinates, and the elements of the second row are used as the vertical coordinates, and the second distance of each coordinate point from the coordinate origin is calculated; The magnitude relationship between the second distance and the second criterion threshold value is used as a second classification criterion for N-terminal forward faults and N-terminal reverse faults.

7. The directional longitudinal protection method applicable to the new energy AC transmission line according to claim 6 is characterized in that: The magnitude relationship between the second distance and the second criterion threshold value is used as a second classification criterion for N-end forward fault and N-end reverse fault, including: If the second distance is greater than the second criterion threshold value, it is considered that a forward fault at the N end has occurred; If the second distance is less than or equal to the second criterion threshold value, it is considered that a reverse fault occurs at the N end.

8. Applicable to the directional longitudinal protection system of the new energy AC transmission line, characterized by: The system includes: Construct a simulation scenario for simulating multiple fault scenarios based on a two-terminal system and obtaining three-phase current sampling data at the M terminal and the N terminal under each fault scenario; the M terminal of the two-terminal system is connected to the power grid system, and the N terminal is connected to the new energy system; A first criterion obtaining unit is used to process the three-phase current data obtained by sampling at the M terminal using a principal component analysis method to obtain a first classification criterion for dividing multiple simulation scenarios into M terminal forward faults and M terminal reverse faults; A second criterion obtaining unit is used to process the three-phase current data obtained by sampling at the N-terminal using a principal component analysis method to obtain a second classification criterion for dividing the multiple simulation scenarios into N-terminal forward faults and N-terminal reverse faults; The line fault judgment and protection unit is used to judge the fault current data to be analyzed by combining the first classification criterion of the M terminal and the second classification criterion of the N terminal; if the classification criterion of the M terminal and the classification criterion of the N terminal are both forward faults, the fault to be analyzed occurs on the line between the M terminal and the N terminal, and the protection is activated; if one end of the classification criterion of the M terminal and the classification criterion of the N terminal is a forward fault and the other end is a reverse fault, the fault to be analyzed does not occur on the line between the M terminal and the N terminal, and the protection is not activated.

9. The directional longitudinal protection system applicable to the new energy AC transmission line according to claim 8 is characterized in that: The first criterion obtaining unit comprises: The instantaneous current splicing subunit is used to splice the instantaneous values ​​sampled in each fault scenario in the order of the instantaneous value of the A phase current, the instantaneous value of the B phase current and the instantaneous value of the C phase current based on the three-phase current data sampled at the M terminal to form a first fault column vector; A fault matrix forming subunit is used to form a first fault matrix by simulating first fault column vectors obtained by simulating different fault mode scenarios according to the first fault column vector; A first calculation subunit, configured to obtain a first matrix required for calculation based on the first fault matrix; The dimension reduction matrix forming subunit is used to obtain the first characteristic root of the first matrix, take the largest characteristic root and the second largest characteristic root from all the characteristic roots, and obtain the eigenvectors corresponding to the largest characteristic root and the second largest characteristic root to form the first dimension reduction matrix P M ; A dimensionality reduction processing subunit is used to process the first dimensionality reduction matrix P M , performing dimensionality reduction processing on the first fault matrix to obtain a first dimensionality-reduced matrix; A second calculation subunit is used to use each element of the first row of the matrix after the first dimension reduction as a horizontal coordinate and each element of the second row as a vertical coordinate to calculate a first distance between each coordinate point and the coordinate origin; The first classification criterion obtaining subunit is used to use the magnitude relationship between the first distance and the first criterion threshold value as the first classification criterion for M-end forward fault and M-end reverse fault.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the directional longitudinal protection method applicable to a new energy AC transmission line as described in any one of claims 1 to 7 is implemented.

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