A method for extracting topographic parameters of an EGM model of a transmission line lightning shielding failure

Abstract

The application discloses a kind of transmission line lightning shielding failure EGM model topographic and geomorphic parameter extraction methods, comprising: determining the ground point cloud sample of a certain calculation point;Conductor height extraction;Conductor height h is calculated c ;Ground inclination extraction;The ground point cloud after screening is projected to section, linear fitting is carried out, and the linear equation is z=ky+b;The fitting deviation of the elevation of the ground below conductor is calculated, and the protruding object discrimination condition equation is constructed;If the deviation does not exceed threshold value, determine that the topography of the calculation point does not contain protruding object, calculate ground inclination;When the deviation is greater than threshold value, calculate ground inclination.The application distinguishes flat terrain from protruding object terrain, quantitatively describes the influence of significant protruding object with the help of ground inclination parameter;It can independently identify the conductor to be evaluated and screen the sample point cloud required for parameter extraction, and can realize the automatic extraction and pairing of the conductor to be evaluated and the lightning conductor according to the spatial position, improve the measurement accuracy and efficiency of line structure parameters.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power transmission, and particularly relates to a method for extracting topographic and geomorphic parameters of an EGM model of lightning shielding failure of a power transmission line. BACKGROUND

[0002] Lightning shielding failure is one of the main threats to the safe operation of ultra-high voltage overhead lines. With the continuous construction and operation of ultra-high voltage lines, lightning shielding failure prevention has attracted great attention from power grid companies. The "differentiated lightning protection" concept considers that lightning shielding failure risk assessment based on different factors such as topography, line structure, and lightning activity can help to identify weak points in line lightning protection and improve the technical and economic efficiency of lightning shielding failure prevention. Phase-differentiated and full-channel refined lightning shielding failure risk assessment is of great significance to lightning protection of ultra-high voltage lines.

[0003] Currently, the widely used lightning shielding failure risk quantitative calculation model is the electro-geometric model (EGM), which comprehensively considers the influence of line structure and topography by means of geometric parameters. In the past, ground elevation database and tower drawings were used as data sources for parameter extraction, and the accuracy and refinement of geometric parameters were limited, which no longer meets the needs of differentiated and refined lightning shielding failure risk assessment. Research on advanced parameter extraction algorithms is a necessary condition for realizing differentiated and refined lightning shielding failure risk assessment.

[0004] With the continuous development of three-dimensional real scene reconstruction technology, the point cloud data collected by airborne LiDAR can achieve centimeter-level accuracy, providing technical support for accurate digital description of power transmission channels. LiDAR has been applied in many spatial intelligent measurement fields such as power line reconstruction and tower inclination measurement, and has shown considerable adaptability, research value and application potential in the field of EGM model geometric parameter extraction. However, in actual engineering, the parameter extraction based on LiDAR has the following difficulties: LiDAR produces a large amount of discrete and irregular point cloud data, and the accuracy of parameter extraction is difficult to ensure; full-channel refined assessment requires parameter extraction at a large number of positions, and manual operation will greatly limit the assessment refinement. In view of the above problems, some scholars have carried out preliminary research: modeling the line and ground point cloud, and then extracting parameters; the set cross section is less, which reduces the calculation amount, but the high-precision point cloud data is not fully utilized. As can be seen from the above, the current research on parameter extraction based on LiDAR point cloud is relatively less, and the intelligentization is not deep enough. How to accurately and finely extract geometric parameters based on power transmission channel point cloud data has become an urgent engineering problem.

[0005] In view of this, in order to fully utilize the advantages of laser radar technology and promote the differentiation and refinement of the risk assessment of the lightning shielding failure, on the basis of the existing research results, an intelligent extraction algorithm of the geometric parameters of the EGM model based on the point cloud of the power transmission channel is proposed, and the accuracy, universality and stability of the algorithm are verified through the example of a 500kV line in a mountainous area. SUMMARY

[0006] The purpose of the present application is to provide a method for extracting topographic and geomorphic parameters of an EGM model for lightning shielding failure of a power transmission line, in order to solve the problems raised in the background art.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical solution: a method for extracting topographic and geomorphic parameters of an EGM model for lightning shielding failure of a power transmission line, comprising the following steps:

[0008] S1: determining the ground point cloud sample of a certain calculation point, the space being centered on the section where the calculation point is located and having a width of W;

[0009] S2: extraction of the height of the conductor relative to the ground: screening the ground point cloud in the W*W square centered on the horizontal projection of the conductor point from the ground point cloud sample of the calculation point;

[0010] S3: calculating the average elevation of the screened point cloud to obtain the ground elevation z g under the conductor c ;

[0011] S4: extraction of the ground inclination: based on the ground point cloud sample of the calculation point, a certain margin is set according to the coordinates of the conductor calculation point, and the ground point cloud outside the conductor is screened;

[0012] S5: projecting the screened ground point cloud onto the section and performing linear fitting to obtain the linear equation z=ky+b;

[0013] S6: calculating the fitting deviation of the ground elevation under the conductor and constructing the protrusion discrimination condition equation;

[0014] S7: if the deviation does not exceed the threshold value, it is determined that the topography of the calculation point does not contain protrusions, and the ground inclination is calculated;

[0015] S8: when the deviation is greater than the threshold value, it is determined that the topography of the calculation point contains protrusions, the ground point cloud outside the W*W square not containing the ground under the conductor is screened, the highest point coordinates (y t , z t ) of the protrusions are extracted based on the elevation sorting of the z coordinates, and the ground inclination is calculated.

[0016] Preferably, in step S1, the ground point cloud sample of a certain calculation point is determined by the following formula

[0017] | x - x | i | < W / 2.

[0018] Preferably in any of the above solutions, in step S2, the calculation point ground point cloud samples are screened by the following formula

[0019] | y - y | c | < W / 2.

[0020] Preferably in any of the above solutions, in step S3, the calculation traverse-to-ground height h c The following formula is used

[0021] h c = z c - z g .

[0022] Preferably in any of the above solutions, in step S4, the ground point cloud outside the traverse is screened by the following formula

[0023]

[0024] Preferably in any of the above solutions, in step S6, the fitting deviation of the ground elevation under the calculation traverse is calculated by the following formula

[0025] E = | ky c + b - z g | > E0.

[0026] Preferably in any of the above solutions, in step S7, the ground inclination calculation formula is

[0027]

[0028] Preferably in any of the above solutions, in step S8, the ground inclination calculation formula is

[0029]

[0030] Preferably in any of the above solutions, in step S8, the ground point cloud outside the W*W grid under the traverse is screened by the following formula

[0031]

[0032] Technical effects and advantages of the present application: The power line lightning shielding EGM model topographic and geomorphic parameter extraction method distinguishes between flat terrain and protruding terrain, and quantitatively describes the influence of significant protrusions with the help of ground inclination parameters; it can independently identify the evaluation conductor and screen the sample point cloud required for parameter extraction, and can realize automatic extraction and pairing of the evaluation conductor and the ground wire according to the spatial position, thereby improving the measurement accuracy and efficiency of the line structure parameters. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Ground point cloud for calculating ground elevation under conductor;

[0034] Figure 2 Ground point cloud for calculating ground inclination;

[0035] Figure 3 Flow chart for ground inclination extraction;

[0036] Figure 4 Rolling calculation chart;

[0037] Figure 5 Parameter extraction automation flow chart. DETAILED DESCRIPTION

[0038] The specific embodiments of the present application will be further described below with reference to the accompanying drawings. It should be noted that the description of these embodiments is intended to help understand the present application, but does not constitute a limitation on the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0039] Topographic parameter extraction

[0040] The ground point cloud mainly includes pure ground, vegetation, buildings, etc. The previous method uses pure ground to extract topographic parameters, and in fact, the accessories such as vegetation and buildings also have a certain lightning attraction effect. In this paper, pure ground and its accessories are considered as equivalent ground.

[0041] Unlike the line structure, the topography is very complex, and it is difficult to model, and it will inevitably lose part of the information. Therefore, this paper directly takes the ground point cloud as the object to carry out topographic parameter extraction. Due to the complexity of the actual terrain, the ground area that effectively shields the conductor calculation point is usually not limited to the cross-section range, and it is more reasonable to sample the ground point cloud in the three-dimensional space around the conductor calculation point. This direct sampling method can also avoid the modeling error brought by the modeling and sampling method. The ground point cloud samples of a calculation point are determined according to the following formula, and the space is centered on the cross-section where the calculation point is located, and the width is W. It should be noted that in order to avoid too few point clouds in the sampling space or even sampling holes, the value of W here should be set appropriately large.

[0042] |x-x i |<W / 2.

[0043] Conductor-to-ground height extraction

[0044] Because the terrain micro-variation sometimes contradicts the overall trend of the terrain, the EGM risk assessment model pays more attention to the overall trend of the terrain, and it is more engineering meaningful to extract the average ground elevation within a certain range around the ground point under the conductor than to strictly extract the ground point under the conductor. According to the following formula, the ground point cloud within the W*W grid centered on the horizontal projection of the conductor point is obtained by screening the ground point cloud samples of the calculation point, as shown in Figure 1 .

[0045] |y-y c |<W / 2.

[0046] The average elevation of the screened point cloud is calculated to obtain the ground elevation z g under the conductor, which is combined with the conductor elevation z g extracted in section 2.1 of this paper to calculate the height h c of the conductor to the ground by the following formula.

[0047] h c =z c -z g .

[0048] Ground inclination extraction

[0049] Based on the ground point cloud samples of the calculation point, for a certain side conductor object, a certain margin (W / 2) is set according to the coordinates of the conductor calculation point, and the ground point cloud outside the conductor is screened by the following formula, as shown in Figure 2 .

[0050]

[0051] The standard classifies the terrain of the cross-line of the transmission channel into typical terrains such as valley, peak, along slope, and flat ground. In fact, protrusions such as trees, rocks, and buildings can also have a shielding effect on the line. The traditional EGM model does not consider protrusions, and the related research on protrusions is not perfect. The IEEE Working Group 1410-2004 standard

[21] The calculation results show that the height of the protrusion itself affects its shielding effect, and higher significant protrusions have a stronger shielding effect. Therefore, smaller protrusions can be ignored, and significant protrusions should be handled separately, but existing research lacks a method for handling significant protrusions.

[0052] In order to facilitate engineering application, this paper constructs a protrusion discrimination condition to distinguish between flat terrain and protrusion terrain, and uses the ground inclination parameter to quantitatively describe the influence of significant protrusions, as follows:

[0053] Project the screened ground point cloud onto the cross section, and perform linear fitting to obtain the linear equation

[0054] z=ky+b.

[0055] The fitting deviation of the ground elevation under the wire is calculated by the following formula, and the protrusion discrimination condition equation is constructed.

[0056] E = |ky c +b-z g |>E0.

[0057] If the deviation does not exceed the threshold value, it is determined that the terrain at the calculation point does not contain protrusions, and the ground inclination calculation formula is

[0058]

[0059] When the deviation is greater than the threshold value, it is determined that the terrain at the calculation point contains protrusions, and the conventional ground inclination calculation method cannot reflect the shielding effect of the protrusions. The outer ground point cloud not containing the W*W grid under the wire is screened by the following formula, and the highest point coordinates (y t , z t ) of the protrusions are extracted based on the z coordinate elevation sorting.

[0060]

[0061] The equivalent ground inclination calculation formula considering the protrusion correction is

[0062]

[0063] In the formula, θ is defined as positive for uphill and negative for downhill outside the wire; k is the slope of the ground contour line obtained by fitting.

[0064] For continuous wire-ground spatial curves, cross-section points are used, and for discrete ground point cloud data, three-dimensional sampling is used. This makes parameter extraction feasible at any position in the full channel, and direct measurement can effectively improve the accuracy of parameter extraction, meeting the basic conditions for full-channel small-granularity traversal evaluation.

[0065] For the wire to be evaluated, a series of calculation points are set along the positive direction of the X-axis in small granularity Q (such as 1 m) along the route direction, forming a parameter extraction calculation queue. The sampling width W is set to be greater than the calculation point granularity Q, so that there is an overlapping part in the terrain sampling of adjacent calculation points, thereby realizing full-channel terrain parameter extraction without omission.

[0066] Further, lightning discharge has randomness, and real lightning shielding is not strictly in a single section. For a certain conductor calculation point, the lightning development path that causes shielding tends to pass through the space above the weak shielding terrain. In order to more comprehensively consider the shielding effect of the terrain around the conductor, a "one-to-many" shielding risk rolling calculation method is used, that is, the line structure of a certain calculation point and the terrain parameters of adjacent P calculation points are combined in turn, and the EGM model is calculated multiple times, and the maximum value of the evaluation results is taken as the shielding risk of the conductor calculation point, as shown in Figure 4 , in which P = 3 is set.

[0067] The shielding risk of the i-th conductor point is calculated by the following formula.

[0068] S F = max{S F1 ,S F2 ,S F3}

[0069] In the formula, S F1 S F2 ,S F3 are the shielding flashover rates calculated by combining the i+1th, i-th and i-1th terrain parameters with the i-th line structure parameter, respectively.

[0070] Full-channel coverage and fine evaluation without omission mean that the number of sections is extremely large, and the current manual operation is no longer applicable. The design of the automatic operation process is shown in Figure 5 , in which the input transmission channel point cloud can complete the automatic operation of parameter extraction and obtain the geometric parameters of the phase conductor in the full channel. The automatic process realizes the parameter extraction of phase precision and full-channel refinement by generating a calculation queue for each conductor object in turn and traversing all calculation queues.

[0071] After completing the small particle size automatic traversal of parameter extraction and shielding risk evaluation, the research results can be used as data support for shielding risk grading analysis. The previous shielding risk evaluation is evaluated by each span / tower, and the algorithm in this paper can realize the fine division of risk levels at different positions in each span.

[0072] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A method for extracting topographic parameters of an EGM model for a transmission line lightning shielding failure, characterized in that: The method comprises the following steps: S1: determining a ground point cloud sample of a certain calculation point, a spatial range of the ground point cloud sample being centered on a section where the calculation point is located and having a width of W; S2: extraction of the height of the traverse with respect to the ground: screening the ground point cloud sample of the calculation point to obtain the ground point cloud within a W*W square centered on the horizontal projection of the traverse point; S3: Obtain the average value of the elevation of the screened point cloud, and get the ground elevation z under the traverse g , calculate the height of the traverse above the ground h c ; S4: extraction of the ground inclination: on the basis of the ground point cloud sample of the calculation point, a certain margin is set according to the coordinates of the calculation point of the traverse object, and the ground point cloud outside the traverse is screened; S5: projecting the screened ground point cloud to the section, performing linear fitting, and obtaining a linear equation z=ky+b; S6: calculating the fitting deviation of the ground elevation below the traverse, and constructing a protrusion discrimination condition equation; S7: if the deviation does not exceed a threshold value, it is determined that the terrain of the calculation point does not contain a protrusion, and the ground inclination is calculated; S8: When the deviation is greater than the threshold value, it is determined that the terrain at the calculation point contains a protrusion, the outside ground point cloud not containing the W*W grid under the traverse is screened, the highest point coordinates (y t , z t ) of the protrusion are extracted based on z coordinate elevation ordering, and the ground inclination is calculated; In step S6, the fitting deviation of the ground elevation below the traverse is calculated by the following formula E = |ky c + b - z g | > E0.

2. The method according to claim 1, characterized in that: In step S1, the ground point cloud sample x-x of a certain calculation point is determined by the following formula i | < W / 2.

3. The method of claim 1, wherein the method comprises: In step S2, the computed point ground point cloud samples are filtered by the following formula |y-y c |<W / 2.

4. The method of claim 1, wherein the method comprises: In step S3, the calculation of the height of the conductor above ground hcuses the following equation h c = z c - z g .

5. The method of claim 1, wherein the method is characterized by: In step S4, the ground point cloud outside the conductor is filtered by the following formula 6. The method of claim 1, wherein the method is characterized by: In step S7, the ground inclination calculation formula is 7. The method of claim 1, wherein the method is characterized by: In step S8, the ground inclination calculation formula is 8. The method of claim 1, wherein the method is characterized by: In step S8, the outside ground point cloud not containing the W*W grid under the wire is screened by the following formula

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