Method and system for observing sag of extra-high voltage direct current line with large rotation angle without containing strain string

Abstract

The invention discloses an extra-high voltage direct current line large-rotation-angle sag observation method and system without containing a strain string, and the method comprises the steps: extracting three-dimensional space coordinates of a lead suspension point of a tangent tower of an adjacent gear and a connection point of a strain string and a lead of a current gear through obtaining target laser point cloud data; calculating a projection distance between the two points on the horizontal plane and defining the projection distance as a traverse observation span; selecting a traverse point cloud in the target laser point cloud data, fitting according to a catenary model to generate a three-dimensional space vector line, extracting coordinates of a plurality of points on the vector line, and calculating an actually measured sag value by using an oblique parabola formula; and converting the design sag based on the full span into the design sag based on the lead observation span, comparing the actual measurement sag with the design sag, and calculating an error to complete sag state evaluation. According to the method, the strain insulator string interference can be effectively eliminated, the problem that the error of a traditional method exceeds the standard is solved, and the accuracy and reliability of ultra-high-voltage direct-current large-rotation-angle line sag observation are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of high-voltage transmission line technology, specifically providing a method and system for observing the sag of ultra-high-voltage direct current lines at large turning angles without tension string. Background Technology

[0002] This invention belongs to the field of construction and operation and maintenance technology of ultra-high voltage direct current (UHVDC) transmission lines, specifically relating to a method for observing conductor sag under the condition of tension towers with large turning angles. Sag is a key parameter for measuring the safe operation of overhead transmission lines, directly affecting conductor tension, distance to ground, and tower load. Especially in ±800kV UHVDC projects, its control accuracy is directly related to the safe and stable operation of the power grid. With the continuous expansion of the construction scale of UHVDC lines in my country, the line routes are becoming increasingly complex, and tension towers with large turning angles are frequently appearing. Traditional sag observation generally adopts the whole span observation method, simplifying the tension string into a straight bar model and using the design span as the calculation benchmark. However, the length of the tension string in UHV lines can reach more than 20 meters and the weight can exceed 10 tons. The catenary shape and the concentrated load of the diverter significantly change the stress state of the conductor. In addition, the large turning angle causes a significant deviation between the actual span and the design value at both poles, resulting in systematic errors in the traditional method for sag calculation. In recent years, conducting 3D modeling and sag inversion of conductors based on point cloud data acquired by UAV LiDAR has become a research hotspot. However, existing point cloud fitting methods have not effectively eliminated tension string interference and generally assume that the maximum sag is located in the center of the span, ignoring the sag offset effect caused by string weight. This results in the sag error of existing technologies significantly exceeding the standard under the large turning angle condition of UHVDC, making it difficult to meet the ±2.5% acceptance accuracy requirement of the "DL / T5235-2010" specification. There is an urgent need for a new sag observation method. Summary of the Invention

[0003] To address the technical problem that existing technologies, such as uncoupling and monitoring devices, cannot achieve real-time and accurate monitoring and early warning of load conditions, this invention provides a method for observing the sag of ultra-high voltage direct current lines at large turning angles without tension strings.

[0004] This invention provides a method for observing the sag of a large-angle UHVDC transmission line without tension string, the working steps of which include: Acquire target laser point cloud data, and based on the target laser point cloud data, extract the three-dimensional spatial coordinates of the suspension point B of the conductor of the adjacent straight tower and the connection point C between the tension string and the conductor of this span; Calculate the projected distance between point B and point C on the horizontal plane, and define the projected distance as the traverse observation span; In the target laser point cloud data, the point cloud data of the conductor from point B to point C is selected, and the selected conductor point cloud is fitted according to the catenary model to generate the three-dimensional spatial vector line of the conductor. Based on the three-dimensional spatial vector line, extract the spatial coordinates of several points, and calculate the measured sag value of the conductor under operating conditions using the parabolic curve formula based on the spatial coordinates of the several points. The design sag based on the entire span is converted into the design sag based on the observed span of the conductor; the measured sag value is compared with the design sag to obtain the sag error.

[0005] Furthermore, in the step of acquiring target laser point cloud data, the target laser point cloud data is collected by using a drone equipped with a lidar device.

[0006] Furthermore, in the step of extracting the three-dimensional spatial coordinates of the suspension point of the conductor of the adjacent straight tower and the connection point between the tension string and the conductor of this span, professional point cloud processing software is used to extract the three-dimensional spatial coordinates; when the point cloud data is noisy, manual positioning is used in the three-dimensional point cloud view to determine the three-dimensional spatial coordinates.

[0007] Furthermore, in the step of fitting the selected traverse point cloud according to the catenary model, the traverse points at both ends and the middle section of the span in the traverse point cloud are selected as fitting reference points for fitting.

[0008] Furthermore, calculating the projected distance between point B and point C on the horizontal plane includes: Based on the extracted three-dimensional spatial coordinates of points B and C, their first coordinate components and second coordinate components in the preset coordinate system on the horizontal plane are obtained respectively. The first coordinate difference is obtained by subtracting the first coordinate component of point C from the first coordinate component of point B; the second coordinate difference is obtained by subtracting the second coordinate component of point C from the second coordinate component of point B. Calculate the sum of the squares of the first coordinate difference and the squares of the second coordinate difference, then take the square root of the sum, and the result is defined as the observation span of the traverse.

[0009] Furthermore, in the step of converting the design sag based on the full span to the design sag based on the observed span of the conductor, the principle that the horizontal stress of the conductor is constant within the tension section is utilized, and the design horizontal stress corresponding to the full span is used as the conversion benchmark to complete the conversion.

[0010] Furthermore, in the step of calculating the sag error, the sag error is the percentage of the difference between the measured sag value and the converted design sag value relative to the converted design sag value.

[0011] This invention also provides a large-angle observation system for ultra-high voltage direct current lines without tension string sag, comprising: Point cloud acquisition module, used to acquire target laser point cloud data; The coordinate extraction module, connected to the point cloud acquisition module, is used to extract the three-dimensional spatial coordinates of the suspension point of the conductor of the adjacent straight tower and the connection point between the tension string and the conductor of this span based on the target laser point cloud data. The span calculation module, connected to the coordinate extraction module, is used to calculate the projected distance on the horizontal plane between the suspension point of the conductor of the adjacent straight tower and the connection point between the tension string and the conductor of the current span, and defines the projected distance as the conductor observation span. The point cloud fitting module is connected to the point cloud acquisition module and the coordinate extraction module respectively. It is used to select the conductor point cloud data from the suspension point of the conductor of the adjacent straight tower to the connection point of the tension string and the conductor in the target laser point cloud data, and to fit the selected conductor point cloud according to the catenary model to generate the three-dimensional spatial vector line of the conductor. The sag calculation module is connected to the point cloud fitting module. It is used to extract the spatial coordinates of several points on the fitted three-dimensional spatial vector line, and calculate the measured sag value of the conductor under the operating conditions based on the spatial coordinates of the several points using the parabolic curve formula. The sag comparison and evaluation module is connected to the span calculation module and the sag calculation module. It is used to convert the design sag based on the full span to the design sag based on the observed span of the conductor. It is also used to compare the measured sag value with the converted design sag, calculate the sag error, and complete the sag status evaluation.

[0012] Furthermore, the point cloud acquisition module includes a drone and a lidar sensor mounted on the drone, the lidar sensor being used to acquire the target lidar point cloud data.

[0013] Furthermore, the coordinate extraction module includes a software automatic extraction unit and a manual assisted positioning unit; the software automatic extraction unit is used to extract the three-dimensional spatial coordinates using professional point cloud processing software, and the manual assisted positioning unit is used to assist in positioning to determine the three-dimensional spatial coordinates when the point cloud data has high noise.

[0014] Beneficial effects The core innovation of this invention compared to existing technologies lies in proposing a novel method for sag observation without tension strings. This method accurately extracts the three-dimensional spatial morphology of the conductor using laser point cloud data and uses its projected length on the horizontal plane as the actual observation span. This completely eliminates the interference of span asymmetry caused by large turning angles, the catenary effect of the tension string's self-weight, and the concentrated load of the drain line on the conductor's stress state. Simultaneously, based on the mechanical principle that the horizontal stress of the conductor is constant within the tension section, the design horizontal stress is used as a bridge to recalculate the design sag of the section without tension strings, and this is accurately compared with the measured sag value obtained from point cloud fitting. This method fundamentally corrects the physical distortion problem of traditional full-span observation models, significantly improving the accuracy and reliability of sag observation for UHVDC large-angle lines, and keeping the error stably controlled within ±2.5% as allowed by regulations. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0016] Figure 1 This is a diagram illustrating the working steps of the UHVDC line large-angle sag observation method without tension string provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the sag observation method for a large-angle railway line provided in an embodiment of the present invention; Figure 3 The wire vectorization fitting diagram provided in the embodiments of the present invention; Figure 4 This is a schematic diagram of fitting and solving the sag of the parabola formula provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of an ultra-high voltage direct current line large-angle sag observation system without tension string, provided as another embodiment of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0019] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text implies three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied. Furthermore, the technical solutions of the various embodiments can be combined, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0020] In existing technologies, sag observation of UHVDC transmission lines generally adopts the whole-span observation method, simplifying the tension string into a straight bar model and using the designed span as the calculation benchmark. However, the length and weight of the tension string in UHV lines significantly alter the stress state of the conductor, and large turning angles lead to significant deviations between the actual span and the design value. Traditional methods introduce systematic errors in sag calculation. Existing lidar point cloud fitting methods do not effectively isolate tension string interference, assume that the maximum sag is located at the center of the span, and ignore the sag offset effect caused by string weight, resulting in observation errors that are difficult to meet acceptance accuracy requirements.

[0021] To address these issues, technicians discovered that traditional methods fail to consider the actual impact of the tension string on the conductor, leading to inaccurate sag calculation benchmarks. Analysis revealed that spatial differences in the connection points between the tension string and the conductor alter the actual suspension state of the conductor, and the asymmetrical distribution of spans at the two extremes further exacerbates the error under large turning angle conditions. Therefore, a proposed method involves precisely separating the tension string from the conductor, independently modeling the conductor, reconstructing the true stress pattern using three-dimensional spatial coordinates, and establishing a local span observation system, thereby eliminating the influence of the tension string on sag calculations.

[0022] refer to Figures 1-4 This embodiment provides a method for observing the sag of a large turning angle of an ultra-high voltage direct current transmission line without tension string, the working steps of which include: S1. Obtain target laser point cloud data, and based on the target laser point cloud data, extract the three-dimensional spatial coordinates of the suspension point B of the conductor of the adjacent straight tower and the connection point C between the tension string and the conductor of this span. S2. Calculate the projected distance between point B and point C on the horizontal plane, and define the projected distance as the traverse observation span; S3. In the target laser point cloud data, select the conductor point cloud data from point B to point C, and fit the selected conductor point cloud according to the catenary model to generate the three-dimensional spatial vector line of the conductor. S4. Based on the three-dimensional spatial vector line, extract the spatial coordinates of several points, and based on the spatial coordinates of the several points, calculate the measured sag value of the conductor under operating conditions using the parabolic curve formula. S5. Convert the design sag based on the entire span to the design sag based on the observed span of the conductor; compare the measured sag value with the design sag to obtain the sag error.

[0023] According to step S1, it should be noted that the acquisition of target laser point cloud data refers to the set of spatial coordinates of the conductor and its ancillary facilities obtained through a 3D scanning device. Specifically, a UAV equipped with a LiDAR can be used for multi-angle scanning, and the identifiability of the conductor features can be ensured through point cloud density control.

[0024] Furthermore, the UAV platform and LiDAR sensor are physically connected through an onboard integrated interface. The flight control system provides power to both and synchronizes their operation. The ground control terminal establishes two-way communication with the UAV through a 4G / 5G or OcuSync 3.0 image transmission link. On the one hand, it issues flight missions to the UAV, and on the other hand, it receives the POS (position and attitude) data transmitted back by the UAV in real time. After the flight is completed, the raw point cloud and image data are imported to the data processing workstation via USB or wirelessly.

[0025] refer to Figure 2 According to the traverse observation span described in step S2, it should be noted that the projection length l0 of the traverse observation span guide line (i.e., from the suspension point B of the adjacent straight tower to the connection point C between the tension string and the traverse in this span) on the horizontal plane is as follows: Based on the target laser point cloud data obtained in step S1, the three-dimensional spatial coordinates (Bx, Bᵧ, B) of points B and C are accurately extracted. z ) and (Cx,Cᵧ,C z ); Ignoring the height difference between the two points, only calculate the X-axis projection distance l0 on the horizontal plane (XY plane), and use this l0 value as the benchmark distance for subsequent sag calculation and error assessment.

[0026] By physically isolating the tension string, it is completely excluded from the observation system, thus effectively avoiding the problem of span asymmetry caused by large turning angles and the sag distortion caused by the tension string's own weight and the concentrated load of the drain line. This makes the observation benchmark closer to the mechanical behavior of the conductor itself, laying a geometric foundation for accurately assessing the conductor's sag state.

[0027] refer to Figure 3 As described in step S3, the selected traverse point cloud is fitted using a catenary model to generate a three-dimensional spatial vector line for the traverse. It should be noted that this step employs catenary fitting technology based on laser point cloud data to vectorize the traverse. This process is a crucial bridge connecting the original observation data with subsequent sag calculations, and its accuracy directly determines the reliability of the final sag evaluation result. The specific implementation steps are as follows: Import the pre-processed laser point cloud data into professional point cloud processing software (such as Pix4Dsurvey), manually select the point cloud corresponding to the target conductor (such as pole 1 or pole 2) in the 3D view, and ensure that the selected point cloud completely covers the entire conductor from the adjacent span suspension point B to the tension string connection point C.

[0028] Launch the point cloud processing software to perform catenary fitting, and perform curve fitting on the selected point cloud. To improve fitting accuracy and avoid the problems of complex point cloud structure and high noise in the tension string area, the lower conductor points at both ends and the middle section of the span are preferentially selected as the main fitting reference points (no less than 3), and the software is allowed to automatically iterate and optimize until the optimal fitting curve is obtained. The three-dimensional vector line generated in this step is the mathematical expression of the spatial morphology of the conductor under the current working conditions.

[0029] To verify the fitting effect and guide subsequent calculations, this step specifically compares and analyzes the two fitting modes: "with strings" and "without strings." For example... Figure 3 As shown, when the fitting range includes the tension string, due to the essential difference between the rigidity of the string structure and the flexibility of the conductor, the fitting curve will deviate significantly from the actual point cloud near the tension tower end; while when the fitting range is strictly limited to points B to C (i.e. excluding the tension string), the fit between the catenary model and the conductor point cloud is significantly improved, especially in the main body of the conductor where they almost completely overlap.

[0030] refer to Figure 4According to step S4, based on the three-dimensional spatial vector line, the spatial coordinates of several points are extracted. Based on the spatial coordinates of these points, the measured sag value of the conductor under operating conditions is calculated using the parabolic curve formula. It should be noted that after completing the conductor vectorization fitting, in order to achieve a fast and accurate solution for the sag value, this step uses the parabolic curve formula to perform a secondary analytical calculation on the catenary fitting result. On the generated three-dimensional vector line of the conductor, 20 spatial coordinate points are uniformly extracted at equal intervals to ensure coverage of the entire conductor (from point B to point C). After processing these discrete point coordinates, they are substituted into the parabolic curve arbitrary point sag calculation formula (1) for fitting and solving, and the measured sag value f of the conductor under the current operating conditions can be obtained. m0 ,like Figure 4 As shown.

[0031] (1) in, For the maximum sag, The horizontal distance from the left suspension point. After completing the vectorized fitting of the conductor, in order to achieve a fast and accurate solution for the sag value, this method uses the "parabolic curve formula" to perform secondary analytical calculation on the catenary fitting result. On the generated three-dimensional vector line of the conductor, 20 spatial coordinate points are uniformly extracted at equal intervals to ensure coverage of the entire conductor (from point B to point C); then, after processing the coordinates of these discrete points, they are substituted into the parabolic curve sag calculation formula (1) for fitting and solving, so as to quickly and stably obtain the measured sag value f of the conductor under the current working condition. m0 ,like Figure 4 As shown. Independent calculations were performed for two types of conductors: those with tension strings and those without, to provide a valid comparison. For sections with tension strings, the observation span was taken as the horizontal distance *l* from point A to point B, and the fitting range included the tension string region. The resulting sag value was denoted as *fm*, used to simulate the results of traditional observation methods. For sections without tension strings, the observation span was strictly taken as the horizontal distance *l0* from point B to point C, and the fitting range was limited to the conductor. The resulting sag value was denoted as *f*. m0 This is the actual measurement result.

[0032] According to step S5, the design sag based on the entire span is converted to the design sag based on the observed span of the conductor. It should be noted that when querying the allowable horizontal stress used by the conductor in the design, the basic force principle that the horizontal stress of the conductor is equal in the tension section is used to convert the allowable horizontal stress provided in the design stage. As a bridge, it realizes the accurate conversion from the design value with tension string to the design value without tension string. The measured sag value obtained by point cloud fitting (also based on the section without tension string) is compared with the corresponding design value. Finally, the sag error under various conditions is calculated by formula (2).

[0033] (2) in, To fit and solve the sag for conductors without tension strings, Calculate the sag for conductors without tension strings.

[0034] refer to Figure 5 The present invention also provides another embodiment, a large-angle observation system for ultra-high voltage direct current transmission lines without tension string sag, comprising: Point cloud acquisition module, used to acquire target laser point cloud data; The coordinate extraction module, connected to the point cloud acquisition module, is used to extract the three-dimensional spatial coordinates of the suspension point of the conductor of the adjacent straight tower and the connection point between the tension string and the conductor of this span based on the target laser point cloud data. The span calculation module, connected to the coordinate extraction module, is used to calculate the projected distance on the horizontal plane between the suspension point of the conductor of the adjacent straight tower and the connection point between the tension string and the conductor of the current span, and defines the projected distance as the conductor observation span. The point cloud fitting module is connected to the point cloud acquisition module and the coordinate extraction module respectively. It is used to select the conductor point cloud data from the suspension point of the conductor of the adjacent straight tower to the connection point of the tension string and the conductor in the target laser point cloud data, and to fit the selected conductor point cloud according to the catenary model to generate the three-dimensional spatial vector line of the conductor. The sag calculation module is connected to the point cloud fitting module. It is used to extract the spatial coordinates of several points on the fitted three-dimensional spatial vector line, and calculate the measured sag value of the conductor under the operating conditions based on the spatial coordinates of the several points using the parabolic curve formula. The sag comparison and evaluation module is connected to the span calculation module and the sag calculation module. It is used to convert the design sag based on the full span to the design sag based on the observed span of the conductor. It is also used to compare the measured sag value with the converted design sag, calculate the sag error, and complete the sag status evaluation.

[0035] Furthermore, the point cloud acquisition module includes a drone and a lidar sensor mounted on the drone, the lidar sensor being used to acquire the target lidar point cloud data.

[0036] Furthermore, the coordinate extraction module includes a software automatic extraction unit and a manual assisted positioning unit; the software automatic extraction unit is used to extract the three-dimensional spatial coordinates using professional point cloud processing software, and the manual assisted positioning unit is used to assist in positioning to determine the three-dimensional spatial coordinates when the point cloud data has high noise.

[0037] Through the above embodiments, the present invention effectively overcomes the adverse effects of point cloud data noise on coordinate extraction accuracy in the complex environment of UHV lines, ensures the positioning reliability of the three-dimensional coordinates of the tension string connection point, provides accurate benchmark data support for subsequent sag calculation, and meets the engineering requirements of high-precision sag observation.

[0038] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (devices), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0039] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0040] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0041] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for observing the sag of a large turning angle in an ultra-high voltage direct current (UHVDC) line without tension string, characterized in that, The work steps include: Acquire target laser point cloud data, and based on the target laser point cloud data, extract the three-dimensional spatial coordinates of the suspension point B of the conductor of the adjacent straight tower and the connection point C between the tension string and the conductor of this span; Calculate the projected distance between point B and point C on the horizontal plane, and define the projected distance as the traverse observation span; In the target laser point cloud data, the point cloud data of the conductor from point B to point C is selected, and the selected conductor point cloud is fitted according to the catenary model to generate the three-dimensional spatial vector line of the conductor. Based on the three-dimensional spatial vector line, extract the spatial coordinates of several points, and calculate the measured sag value of the conductor under operating conditions using the parabolic curve formula based on the spatial coordinates of the several points. The design sag based on the entire span is converted into the design sag based on the observed span of the conductor; the measured sag value is compared with the design sag to obtain the sag error, and the sag status assessment is completed.

2. The method for observing the large turning angle of an ultra-high voltage direct current line without tension string sag, as described in claim 1, is characterized in that... In the step of acquiring target laser point cloud data, the target laser point cloud data is collected by using a drone equipped with a lidar device.

3. The method for observing the large turning angle of an ultra-high voltage direct current line without tension string sag, as described in claim 1, is characterized in that... In the step of extracting the three-dimensional spatial coordinates of the suspension point of the conductor of the adjacent straight tower and the connection point between the tension string and the conductor of the current span, point cloud processing software is used to extract the three-dimensional spatial coordinates; when the point cloud data is noisy, the three-dimensional spatial coordinates are determined by manual positioning in the three-dimensional point cloud view.

4. The method for observing the large turning angle of an ultra-high voltage direct current line without tension string sag according to claim 1, characterized in that, In the step of fitting the selected traverse point cloud according to the catenary model, the traverse points at both ends and the middle section of the traverse point cloud are selected as the fitting reference points for fitting.

5. The method for observing the large turning angle of an ultra-high voltage direct current line without tension string sag according to claim 1, characterized in that, The calculation of the projected distance between point B and point C on the horizontal plane includes: Based on the extracted three-dimensional spatial coordinates of points B and C, their first coordinate components and second coordinate components in the preset coordinate system on the horizontal plane are obtained respectively. The first coordinate difference is obtained by subtracting the first coordinate component of point C from the first coordinate component of point B; the second coordinate difference is obtained by subtracting the second coordinate component of point C from the second coordinate component of point B. Calculate the sum of the squares of the first coordinate difference and the squares of the second coordinate difference, then take the square root of the sum, and the result is defined as the observation span of the traverse.

6. The method for observing the large turning angle of an ultra-high voltage direct current line without tension string sag according to claim 1, characterized in that, In the step of converting the design sag based on the full span to the design sag based on the observed span of the conductor, the principle that the horizontal stress of the conductor is constant within the tension section is used to complete the conversion by taking the design horizontal stress corresponding to the full span as the conversion benchmark.

7. The method for observing the large turning angle of an ultra-high voltage direct current line without tension string sag according to claim 1, characterized in that, In the step of calculating the sag error, the sag error is the percentage of the difference between the measured sag value and the converted design sag value relative to the converted design sag value.

8. A large-angle observation system for ultra-high voltage direct current transmission lines without tension string sag, characterized in that, include: Point cloud acquisition module, used to acquire target laser point cloud data; The coordinate extraction module, connected to the point cloud acquisition module, is used to extract the three-dimensional spatial coordinates of the suspension point of the conductor of the adjacent straight tower and the connection point between the tension string and the conductor of this span based on the target laser point cloud data. The span calculation module, connected to the coordinate extraction module, is used to calculate the projected distance on the horizontal plane between the suspension point of the conductor of the adjacent straight tower and the connection point between the tension string and the conductor of the current span, and defines the projected distance as the conductor observation span. The point cloud fitting module is connected to the point cloud acquisition module and the coordinate extraction module respectively. It is used to select the conductor point cloud data from the suspension point of the conductor of the adjacent straight tower to the connection point of the tension string and the conductor in the target laser point cloud data, and to fit the selected conductor point cloud according to the catenary model to generate the three-dimensional spatial vector line of the conductor. The sag calculation module is connected to the point cloud fitting module. It is used to extract the spatial coordinates of several points on the fitted three-dimensional spatial vector line, and calculate the measured sag value of the conductor under the operating conditions based on the spatial coordinates of the several points using the parabolic curve formula. The sag comparison and evaluation module is connected to the span calculation module and the sag calculation module. It is used to convert the design sag based on the full span to the design sag based on the observed span of the conductor. It is also used to compare the measured sag value with the converted design sag, calculate the sag error, and complete the sag status evaluation.

9. The UHVDC transmission line large-angle sag observation system without tension string as described in claim 8, characterized in that, The point cloud acquisition module includes a drone and a lidar sensor mounted on the drone. The lidar sensor is used to acquire the target lidar point cloud data.

10. The UHVDC transmission line large-angle sag observation system without tension string as described in claim 8, characterized in that, The coordinate extraction module includes a software automatic extraction unit and a manual assisted positioning unit; the software automatic extraction unit is used to extract the three-dimensional spatial coordinates through point cloud processing software, and the manual assisted positioning unit is used to assist in positioning to determine the three-dimensional spatial coordinates when the point cloud data has high noise.

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