Overhead transmission line sag online monitoring method fusing real-time image and laser point cloud information

Abstract

The invention provides an overhead transmission line sag online monitoring method fusing real-time images and laser point cloud information, and the method comprises the steps: obtaining an internal parameter matrix and a distortion vector of a camera through the calibration of the camera; after a camera is installed on site and the view field angle is adjusted, a shot picture and three-dimensional laser point cloud data of the power transmission channel are subjected to homonymy feature point matching, and a three-dimensional space and a monitoring image coordinate transformation matrix are established; extracting the center line of the ground wire in the real-time shot picture; and iteratively calculating a sigma / gamma value by comparing the difference between the projection of the three-dimensional ground wire and the center line of the image ground wire, and finally calculating the sag of the ground wire. According to the method, real-time monitoring of the ground wire sag can be realized only by using the image information acquired by the on-site camera, the on-site workload is small, the requirement on a shooting site is avoided, and the applicability is high.

Description

Technical Field

[0001] The invention relates to the technical field of online monitoring of power transmission lines, and in particular to a method for real-time monitoring of the sag size of a power transmission line through a visualization system. Background Art

[0002] The sag of transmission lines is an important indicator for line design and operation and maintenance. Whether the sag is controlled within the specified design tolerance directly affects the safe and stable operation of the line. Design departments, construction units, and operation and maintenance units should all ensure that the sag of overhead power lines is controlled within a reasonable range from the perspective of economy and safety. Real-time monitoring of the sag changes of transmission lines can not only promptly discover the hidden dangers of insufficient safe crossing distances caused by excessive sag, but also provide important data support for dynamic capacity expansion of lines under high temperature and high load; calculate the equivalent ice thickness of the line during the icing period to provide support for line melting and de-icing work. Traditional sag monitoring methods require the observation of many physical quantities and the calculation process is cumbersome.

[0003] As the cost of manufacturing reliable large-area electronic photosensitive devices becomes lower and lower, images have become a low-cost, information-rich, and highly reliable data source. However, the traditional image-based sag measurement method, due to the lack of depth information and shooting angle, causes distortion of the transmission line image, large measurement errors, and limited application occasions. Summary of the invention

[0004] The purpose of the present invention is to provide an online monitoring method for the sag of overhead transmission lines that integrates real-time images and laser point cloud information. The catenary of the ground conductor in three-dimensional space is projected onto the two-dimensional image through a transformation relationship matrix between the three-dimensional point cloud and the two-dimensional image calculated in advance. The projection curve is made to coincide with the ground conductor monitored in real time by a method of correcting the σ / γ value, and the sag value of the transmission line is calculated. The method has the advantages of fast on-site monitoring speed, high efficiency and accurate results.

[0005] In order to achieve the above object, the present invention comprises the following steps:

[0006] An online monitoring method for sag of overhead transmission lines integrating real-time images and laser point cloud information comprises the following steps:

[0007] (1) Calibrate the camera to obtain the camera internal parameter matrix and distortion vector to correct the two-dimensional image captured by the camera in real time;

[0008] (2) Install the camera on the tower, adjust the field of view angle and fix it;

[0009] (3) After installation, the camera takes a photo, matches the same-name feature points with the three-dimensional laser point cloud data of the power transmission channel, calculates the three-dimensional coordinates and the two-dimensional coordinate transformation matrix, and projects the three-dimensional point cloud to the plane where the photo is located for comparison between the three-dimensional ground conductor and the ground conductor in the photo;

[0010] (4) The camera takes real-time photos at the site at a set time interval to extract the center line of the ground wire;

[0011] (5) Set the initial value of σ / γ and calculate the trajectory curve of the ground conductor in the three-dimensional coordinate system according to the catenary equation, where σ is the horizontal stress of the ground conductor and γ is the specific load;

[0012] (6) Project the ground wire trajectory curve into a two-dimensional coordinate system and compare it with the center line of the ground wire in the photo. If the maximum pixel difference between the two in the vertical direction is greater than 10, change the σ / γ value and repeat this step until the maximum pixel difference between the two in the vertical direction is within 10.

[0013] (7) Calculate the sag value of the ground wire according to the maximum sag calculation formula.

[0014] Furthermore, the step (1) of calibrating the camera is as follows: using Zhang's calibration method to calibrate the camera's intrinsic parameter matrix and distortion vector, the intrinsic parameter matrix is ​​used for coordinate transformation, and the distortion vector is used to correct the two-dimensional image captured by the camera.

[0015] Furthermore, in step (2), the camera is installed on the pole tower on site, and the field of view angle is adjusted and fixed. The camera is firmly installed on the main material 8 meters above the pole tower foundation, aimed at the transmission channel, and ensured to capture images of more than half of the total length of a transmission line, including the hanging point of the opposite end of the ground wire and the lowest point of the sag.

[0016] Furthermore, in step (3), the camera takes a photo after installation, and matches the feature points with the three-dimensional laser point cloud data of the power transmission channel. The specific steps are as follows: the camera takes an image of the power transmission channel, selects more than 20 pairs of feature points with the same name on the image and in the three-dimensional laser point cloud data, obtains the corresponding coordinate values, and calculates the three-dimensional coordinate and two-dimensional coordinate transformation matrix, including 1 rotation matrix and 1 translation vector.

[0017] Furthermore, the specific steps for extracting the center line of the ground wire in step (4) are as follows: for the ground wire monitored in real time, firstly, edge detection is performed using the Sobel operator; secondly, binarization and filtering are performed; then, complex backgrounds such as the ground are filtered by selecting a region of interest; and finally, the center line of the ground wire is obtained through refinement and deburring.

[0018] Furthermore, the specific steps of calculating the trajectory curve of the ground conductor in the three-dimensional coordinate system according to the catenary equation in step (5) are as follows: obtaining the height of the ground conductor hanging points at both ends of the monitoring gear, the gear spacing and other information through the transmission line ledger, obtaining the three-dimensional coordinates of the hanging points at both ends of the ground conductor in the laser point cloud data, setting the initial value of σ / γ (), and calculating the trajectory curve of the ground conductor in the three-dimensional coordinate system according to the catenary equation.

[0019] Furthermore, in the step (6), the three-dimensional ground wire trajectory curve is projected to a two-dimensional coordinate system, and the specific steps of curve comparison are: according to the three-dimensional coordinate and two-dimensional coordinate transformation matrix, the three-dimensional trajectory curve point set is projected to the real-time image two-dimensional coordinate system, and compared with the curve of step (4); if the error is greater than the preset value, the σ / γ value is changed, and the ground wire trajectory curve point set in the three-dimensional coordinate system is recalculated, and then the projection and comparison are performed until the error is less than the preset value.

[0020] Furthermore, the specific steps of calculating the ground wire in step (7) are as follows: according to the maximum sag formula Calculate the sag value, where l is the span, β is the height difference angle of the two ends of the ground wire. Δh is the height difference between the hanging points at both ends of the ground wire.

[0021] The advantages of the present invention are:

[0022] 1. Through Zhang’s calibration method and matching of feature points with the same name, the camera internal parameters, distortion vector and 3D / 2D transformation matrix are pre-calibrated and calculated, which solves the problems of inconvenience, low accuracy and difficulty in obtaining transformation matrix on site after installation using traditional methods.

[0023] 2. Obtain the spatial trajectory curve of the ground wire through an iterative method, then project the curve onto a two-dimensional plane, compare it with the real-time line two-dimensional image to obtain the σ / γ value, and finally calculate the sag of the ground wire. The currently commonly used sag measurement angle method requires measuring the sag angle, hanging point angle, and on-site temperature, and also needs to obtain information such as conductor stress and specific load to calculate the sag value. The amount of on-site measurement data is large and the measurement process is complicated. At present, the transmission line channels above 220 kV have basically collected three-dimensional laser point cloud data, and channel video (image) online monitoring equipment is installed. The present invention does not need to add additional measuring equipment, and accurate sag data can be obtained by analyzing real-time image information through software, which has good real-time performance and lays the foundation for subsequent ground wire icing analysis, cross-span analysis and other applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of coordinate transformation in an embodiment of the present invention;

[0025] Figure 2 A schematic plan view of a ground wire trajectory in an embodiment of the present invention;

[0026] Figure 3 The present invention is a flowchart of an online monitoring method for sag of overhead transmission lines that integrates real-time images and laser point cloud information. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention.

[0028] like Figure 3 As shown, an embodiment of the present invention provides an online monitoring method for sag of overhead transmission lines by integrating real-time images and laser point cloud information, comprising the following steps:

[0029] Step P101: The camera calibration step is: use Zhang's calibration method to calibrate the camera's intrinsic parameter matrix and distortion vector, such as Figure 1 As shown. The internal parameter calibration formula is:

[0030]

[0031] Where α is the scale factor on the x-axis, β is the scale factor on the y-axis, u0 and v0 are the origin offsets in the coordinate transformation, and K is the intrinsic parameter matrix.

[0032] Distortion vector calibration includes radial distortion parameters (k1, k2, k3) and tangential distortion parameters (p1, p2). The following formula is used to correct the captured photos:

[0033]

[0034] Where (u c ,v c ) is the corrected pixel point, and r is the distance between the point (u, v) and the center (u0, v0).

[0035] Step P102: On-site installation and adjustment of the camera. The specific steps are as follows: The camera is firmly installed on the main material 8 meters above the tower foundation, and is aimed at the transmission channel to ensure that it can capture more than half of the image of the full length of the first-stage transmission line, including the lowest point of the ground wire. In the subsequent real-time monitoring of the ground wire sag, the camera installation position and angle cannot be changed.

[0036] Step P103: After installation, the camera takes an image of the power transmission channel, selects more than 20 pairs of feature points with the same name on the image and in the three-dimensional laser point cloud data, obtains the corresponding coordinate values, and calculates the three-dimensional coordinate and two-dimensional coordinate transformation matrix, including 1 rotation matrix and 1 translation vector. The formula is:

[0037]

[0038] Where R is the rotation matrix and T is the translation vector. Considering that there are 12 unknowns in the above equation, each set of 3D / 2D feature points with the same name corresponds to 2 equations, so at least 6 sets of matching points are required to solve R and T. By selecting more sets of matching points and optimizing the algorithm, the accuracy of R and T can be improved.

[0039] Step P104: Extract the center line of the ground wire. The specific steps are as follows: for the ground wire monitored in real time, first use the Sobel operator to perform edge detection; then perform binarization and filtering; then filter the complex background such as the ground by selecting the region of interest; and finally obtain the center line of the ground wire through refinement and deburring.

[0040] Step P105: Calculate the trajectory curve of the ground conductor in the three-dimensional coordinate system according to the catenary equation. The specific steps are as follows: obtain the three-dimensional coordinates of the two end hanging points of the ground conductor in the laser point cloud data. The plane where the trajectory curve of the ground conductor is located is the vertical plane where the line connecting the two end hanging points is located. With one of the hanging points as the center of the circle, the trajectory curve of the ground conductor on this plane is:

[0041]

[0042] Where l is the span, set the initial value of σ / γ (σ is the horizontal stress of the line, γ is the specific load), and solve the trajectory curve of the ground wire according to the above catenary equation. Considering the coordinate correspondence between the trajectory curve and the line connecting the two hanging points in three-dimensional space, as shown in Figure 2 As shown, the trajectory curve coordinate values ​​are converted into three-dimensional coordinate values.

[0043] Step P106: The three-dimensional ground wire trajectory curve is projected onto a two-dimensional coordinate system. The specific steps for curve comparison are as follows: based on the three-dimensional coordinate and two-dimensional coordinate transformation matrix, the three-dimensional trajectory curve point set is projected onto the real-time image two-dimensional coordinate system, and compared with the curve of step P104. If the error is greater than the preset value, the σ / γ value is changed, and the ground wire trajectory curve point set in the three-dimensional coordinate system is recalculated, and then projection and comparison are performed again until the error is less than the preset value.

[0044] Step P107: The specific steps for calculating the sag of the ground wire are as follows: According to the maximum sag formula:

[0045]

[0046] Where β is the height difference angle, unit is degree, and the sag value can be calculated.

[0047] The present invention can realize real-time monitoring of the sag of the ground wire by only utilizing the image information collected by the on-site camera, with small on-site workload, no requirements on the shooting location, and strong applicability.

[0048] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by technicians in this technical field within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for online monitoring of sag of overhead transmission lines by integrating real-time images and laser point cloud information, characterized in that The steps include: (1) Calibrate the camera to obtain the camera internal parameter matrix and distortion vector to correct the two-dimensional image captured by the camera in real time; (2) Install the camera on the tower, adjust the field of view angle and fix it; (3) After installation, the camera takes a photo, matches the same-name feature points with the three-dimensional laser point cloud data of the power transmission channel, calculates the three-dimensional coordinates and the two-dimensional coordinate transformation matrix, and projects the three-dimensional point cloud to the plane where the photo is located for comparison between the three-dimensional ground conductor and the ground conductor in the photo; (4) The camera takes real-time photos at the site at a set time interval to extract the center line of the ground wire; (5) Set the initial value of σ / γ and calculate the trajectory curve of the ground conductor in the three-dimensional coordinate system according to the catenary equation, where σ is the horizontal stress of the ground conductor and γ is the specific load; (6) Project the ground wire trajectory curve into a two-dimensional coordinate system and compare it with the center line of the ground wire in the photo. If the maximum pixel difference between the two in the vertical direction is greater than 10, change the σ / γ value and repeat this step until the maximum pixel difference between the two in the vertical direction is within 10. (7) Calculate the sag value of the ground wire according to the maximum sag calculation formula.

2. The method for online monitoring of sag of overhead power transmission lines by integrating real-time images and laser point cloud information according to claim 1, characterized in that: The step (1) of calibrating the camera is as follows: using Zhang's calibration method to calibrate the camera's intrinsic parameter matrix and distortion vector, the intrinsic parameter matrix is ​​used for coordinate transformation, and the distortion vector is used to correct the two-dimensional image captured by the camera.

3. The method for online monitoring sag of overhead power transmission lines by integrating real-time images and laser point cloud information according to claim 1, characterized in that: The step (2) of installing the camera on the pole tower on site, adjusting the field of view angle and fixing the camera are as follows: the camera is firmly installed on the main material 8 meters above the pole tower foundation, aimed at the transmission channel, and ensured that more than half of the image of the entire length of a transmission line can be captured, including the hanging point of the opposite end of the ground wire and the lowest point of the sag.

4. The method for online monitoring of sag of overhead power transmission lines by integrating real-time images and laser point cloud information according to claim 1, characterized in that: The specific steps of step (3) are as follows: the camera takes a photo after installation, and matches the feature points with the three-dimensional laser point cloud data of the power transmission channel. The camera takes an image of the power transmission channel, selects more than 20 pairs of feature points with the same name on the image and in the three-dimensional laser point cloud data, obtains the corresponding coordinate values, and calculates the three-dimensional coordinate and two-dimensional coordinate transformation matrix, including 1 rotation matrix and 1 translation vector.

5. The method for online monitoring of sag of overhead power transmission lines by integrating real-time images and laser point cloud information according to claim 1, characterized in that: The specific steps of extracting the center line of the ground conductor in step (4) are as follows: for the ground conductor monitored in real time, firstly, edge detection is performed using the Sobel operator; secondly, binarization and filtering are performed; then, complex backgrounds such as the ground are filtered by selecting an area of ​​interest; and finally, the center line of the ground conductor is obtained through refinement and deburring.

6. The method for online monitoring of sag of overhead power transmission lines by integrating real-time images and laser point cloud information according to claim 1, characterized in that: The specific steps of calculating the trajectory curve of the ground conductor in the three-dimensional coordinate system according to the catenary equation in step (5) are as follows: obtaining the height of the ground conductor hanging points at both ends of the monitoring gear, the gear spacing and other information through the transmission line ledger, obtaining the three-dimensional coordinates of the hanging points at both ends of the ground conductor in the laser point cloud data, setting the initial value of σ / γ (), and calculating the trajectory curve of the ground conductor in the three-dimensional coordinate system according to the catenary equation.

7. The method for online monitoring sag of overhead power transmission lines by integrating real-time images and laser point cloud information according to claim 1, characterized in that: In the step (6), the three-dimensional ground wire trajectory curve is projected onto a two-dimensional coordinate system, and the specific steps of curve comparison are: according to the three-dimensional coordinate and two-dimensional coordinate transformation matrix, the three-dimensional trajectory curve point set is projected onto the real-time image two-dimensional coordinate system, and compared with the curve of step (4); if the error is greater than the preset value, the σ / γ value is changed, and the ground wire trajectory curve point set in the three-dimensional coordinate system is recalculated, and then the projection and comparison are performed again until the error is less than the preset value.

8. The method for online monitoring sag of overhead power transmission lines by integrating real-time images and laser point cloud information according to claim 1, characterized in that: The specific steps for calculating the ground wire in step (7) are as follows: according to the maximum sag formula Calculate the sag value, where l is the span, β is the height difference angle of the two ends of the ground wire. Δh is the height difference between the hanging points at both ends of the ground wire.

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