A method and system for detecting the sagging state of overhead lines based on magnetic sensors

Abstract

The present invention discloses a method and system for detecting the sag state of an overhead line based on a magnetic sensor, which belongs to the technical field of application of electromagnetic sensing theory in power systems; the detection method comprises: S1, constructing a three-dimensional magnetic field model of the overhead line in the sag state; S2, selecting the installation position of the magnetic sensor according to the verification result of the three-dimensional magnetic field model established in S1; S3, solving the final catenary coefficient through an iterative algorithm based on the magnetic field data calculated by the discretized three-dimensional magnetic field model and the magnetic field data collected by the magnetic sensor, thereby obtaining the sag size of the overhead line; the detection method of the present invention is a non-invasive detection means, and at the same time, the calculation speed can be greatly improved by discretizing the mathematical model, and can be widely used in the scenario of sag detection of overhead power lines of power grids, providing a guarantee for preventing the overhead line from causing faults such as short circuit to ground due to excessive sag, and improving the safety of stable operation of the power system.

Description

Technical Field

[0001] The present invention belongs to the technical field of application of electromagnetic sensing theory in power systems, and particularly relates to a method and system for detecting the drooping state of an overhead line based on a magnetic sensor. Background Art

[0002] Overhead transmission lines, as a vital component of the power grid, connect power sources at the generating end and loads at the receiving end. Ultra-high voltage AC and DC transmission lines, in particular, carry the crucial task of large-scale, cross-regional power transmission. Therefore, the condition of these lines directly determines the safe and stable operation of the entire power grid system. Furthermore, when long-distance, high-voltage transmission lines are installed outdoors in extreme weather conditions (such as high temperatures, strong winds, ice and snow), they can experience changes in their line configuration. The most common change is sag. This occurs when excessive current loads cause overheating, extending the length of the line conductor. This sag lowers the conductor to an unsafe height above the ground, potentially leading to safety incidents such as ground shorts.

[0003] Current methods for detecting transmission line sag primarily involve installing tension sensors on the line to directly measure sag and using drones to obtain sag measurements. However, installing tension sensors requires direct access to the transmission line, making installation and maintenance difficult. Drones are also very sensitive to weather conditions and cannot be used in inclement weather such as rain or snow. To address these challenges, a new method for detecting transmission line sag in real time is urgently needed. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a method and system for detecting the sagging state of an overhead line based on a magnetic sensor.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for detecting the sagging state of an overhead line based on a magnetic sensor comprises the following steps:

[0007] S1, constructing a three-dimensional magnetic field model of the overhead line under sagging state;

[0008] S2, selecting the installation location of the magnetic sensor based on the verification results of the three-dimensional magnetic field model established in S1;

[0009] S3, based on the magnetic field data calculated by the discretized three-dimensional magnetic field model and the magnetic field data collected by the magnetic sensor, the final catenary coefficient is solved through an iterative algorithm to obtain the sag size of the overhead line.

[0010] Furthermore, in said S1, the step of constructing a three-dimensional magnetic field model includes:

[0011] S11, derive the physical model of the overhead line sagging condition and conclude that the overhead line hanging between two towers is in the shape of a catenary;

[0012] S12, calculate the catenary equation of the overhead line;

[0013] There is a uniform load γ along the length of the overhead line, which is in a vertical downward direction. Under the action of the load γ, the overhead line takes on a curved shape. σ0 is the stress in the x-axis direction of the overhead line. Select a microelement σ Δ The force analysis in the x-axis and y-axis directions is carried out respectively, and the force balance equation of the overhead line is:

[0014] ∑X=0,σ Δ cosθ=σ0 (1)

[0015] ∑Y=0,σ Δ sinθ=γL Δ (2)

[0016] Combining the above equations, we can get the catenary equation of the overhead line:

[0017]

[0018] Among them, C1 and C2 are integration constants, whose values depend on the origin position of the coordinate system;

[0019] A droop state model of overhead transmission lines is established. The overhead lines are located in the ZOY plane. It can be seen that the lines between adjacent transmission towers satisfy the catenary equation:

[0020]

[0021] Where α is the catenary coefficient, which is the L is the distance between two adjacent towers, k is a constant;

[0022] S13, calculating the three-dimensional magnetic field model of the overhead line in the drooping state;

[0023] It can be seen that dz / dy=sinh(αy). In the three-dimensional coordinate system, Biot-Savart's law satisfies the following form:

[0024]

[0025] Where μ0 is the vacuum permeability, is the unit vector along the tangent direction of the overhead line, are the unit vectors in the x, y, and z axis directions respectively, and r is A direction vector pointing to a point P in space.

[0026] Assume that the coordinates of the magnetic field point P in the three-dimensional coordinate system are (x0, y0, z0), then the distance vector Combining the above formulas, we can get:

[0027]

[0028] Among them, B x , B y , B z are the magnetic induction intensities in the x, y, and z axis directions respectively.

[0029] Furthermore, in S11, it is assumed that the overhead line is a flexible cable chain without rigidity; and it is assumed that the load acting on the overhead line is evenly distributed along the length of the line.

[0030] Furthermore, in S2, the installation position of the magnetic sensor is determined. It is necessary to compare the power frequency magnetic fields of different topological structures based on the three-dimensional magnetic field model to determine the points with consistent characteristics, and it is also necessary to use the magnetic field correction coefficient of the magnetic conductive material to correct the magnetic field near the installation point.

[0031] Furthermore, in S2, the magnetic sensor is installed on the tower.

[0032] Furthermore, in S3, the iterative operation steps include:

[0033] S31, discretizing the three-dimensional magnetic field model established in S1;

[0034] S32, setting an initial value of a catenary coefficient and bringing it into the discretized three-dimensional magnetic field model to calculate and obtain a set of periodic magnetic field data;

[0035] S33, calculating the root mean square error between the magnetic field data collected by the magnetic sensor and the magnetic field data solved by the discretized three-dimensional magnetic field model; each iteration recalculates the root mean square error between the magnetic field data solved by different catenary coefficients and the sensor collected data until the root mean square error is less than a set threshold, and then the iteration is stopped;

[0036] S34, after the iteration stops, the magnetic field data solved by the discretized three-dimensional magnetic field model at this time is selected, and the corresponding catenary coefficient is obtained, so that the sag of the overhead line can be obtained.

[0037] Furthermore, the discretization processing result of the three-dimensional magnetic field model is:

[0038] X-axis magnetic field model, for B in equation (8) x The formula after discretization is:

[0039]

[0040] Y-axis direction magnetic field model, for B in Equation (8) y The formula after discretization is as follows:

[0041]

[0042] Z-axis direction magnetic field model, for B in Equation (8) z The formula after discretization is as follows:

[0043] [[ID=!4]]

[0044] where, -L / 2 < t i < L / 2, i = 1, 2, 3…, n, and Δt is the spacing between adjacent t i intervals.

[0045] Furthermore, the evaluation index of each iteration algorithm is the root mean square error of two groups of data:

[0046]

[0047] where, N is the number of data, X i is the data group collected by the magnetic sensor, and x i is the data group calculated in each iteration.

[0048] An overhead line sag state detection system based on magnetic sensors, comprising:

[0049] Model construction module: used to construct a three-dimensional magnetic field model under the sag state of the overhead line;

[0050] Sensor position determination module: to select the installation position of the magnetic sensor according to the verification result of the three-dimensional magnetic field model;

[0051] Iterative operation module: based on the magnetic field data calculated by the discretized three-dimensional magnetic field model and the magnetic field data collected by the magnetic sensor, solve the final catenary coefficient through an iterative algorithm, so as to obtain the sag size of the overhead line.

[0052] Advantages of the present invention:

[0053] 1. The overhead line detection method adopted by the present invention is a novel non-intrusive detection method, which does not require any operation on the overhead line and has the advantages of convenient installation and maintenance compared with traditional detection methods;

[0054] 2. The present invention uses magnetic sensors for detection. Magnetic sensors have developed rapidly and are widely used in various fields at present. This is because magnetic sensors have higher stability and can be used in weather such as high temperature, rain, snow, and strong wind, and have a longer service life, which can greatly save costs;

[0055] 3. The iterative algorithm used in the present invention discretizes the integral equation and converts the integral into a summation, which can greatly improve the calculation time and thus realize the real-time detection function of the overhead line;

[0056] 4. The present invention can be applied to safety detection scenarios of power systems to reduce the possibility of overhead line failures, thereby improving the power safety and reliability of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0058] Figure 1 is a schematic diagram of overhead line sag detection according to the present invention;

[0059] Figure 2 It is the overhead line suspension curve stress diagram of the present invention;

[0060] Figure 3 It is a schematic diagram of the drooping state of the overhead transmission line of the present invention;

[0061] Figure 4 It is a flow chart of the iterative algorithm of the present invention. DETAILED DESCRIPTION

[0062] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0063] like Figure 1 The figure shows a schematic diagram of overhead line sag detection. A method for detecting the sag state of an overhead line based on a magnetic sensor includes the following steps:

[0064] S1, constructing a three-dimensional magnetic field model of the overhead line under sagging state;

[0065] The specific steps include:

[0066] S11, derive the physical model of the overhead line sagging condition and conclude that the overhead line hanging between two towers is in the shape of a catenary;

[0067] To simplify the problem, we first assume that the overhead line is a flexible cable chain with no rigidity. This is because the span of the overhead transmission line is much larger than the cross-sectional dimensions of the overhead line, that is, the length of the entire overhead line is much greater than its diameter. At the same time, overhead lines are often twisted wires composed of multiple strands of fine metal wires, so the rigidity of the overhead line has little effect on the shape of the curve in the suspension space. Based on this assumption, the overhead line can only withstand tension but not bending moment. Secondly, we assume that the load acting on the overhead line is evenly distributed along its length.

[0068] Based on the above assumptions, it is believed that the overhead line hanging between the two towers is in the shape of a catenary.

[0069] S12, calculate the catenary equation of the overhead line;

[0070] like Figure 2 In the example of an overhead line, A and B are the two suspension points. A uniform specific load γ is applied along the length of the line, in a vertically downward direction. Under the action of the specific load γ, the line takes on a curved shape. There is an axial stress at any point along the axis of the line, such as Figure 2 As shown in the figure, at the suspension points A and B, the axial stresses of the overhead line are σ A and σ B ; Establish as Figure 2 The yox coordinate system is shown, σ0 is the stress in the x-axis direction of the overhead line, and a microelement σ is selected. Δ The force analysis in the x-axis and y-axis directions is carried out respectively, and the force balance equation of the overhead line is:

[0071] ∑X=0,σ Δ cosθ=σ0 (1)

[0072] ∑Y=0,σ Δ sinθ=γL Δ (2)

[0073] Combining the above equations, we can get the catenary equation of the overhead line:

[0074]

[0075] Among them, C1 and C2 are integration constants, whose values depend on the origin position of the coordinate system;

[0076] According to the above formula (3), assuming that the two ends of the transmission line are at the same height, and the lowest point of the sag of the overhead line at the same height is located at the center of the span, this point is taken as the coordinate origin. Then, when x = 0, y = 0, dy / dx = 0, the conditions are met. Substituting into formula (3) to obtain C1 and C2:

[0077]

[0078] According to the above derived formula (4), we can establish Figure 3The droop state model of the overhead transmission line is shown in the figure. In the figure, L is the span, H is the sag, and the overhead line is located in the ZOY plane. It can be seen that the line between adjacent transmission towers satisfies the catenary equation:

[0079]

[0080] Where α is the catenary coefficient, which is the Related to the conductor sag, L is the span (the distance between two adjacent towers), and k is a constant.

[0081] The conductor sag formula is:

[0082]

[0083] S13, calculating the three-dimensional magnetic field model of the overhead line in the drooping state;

[0084] It can be seen that dz / dy=sinh(αy). In the three-dimensional coordinate system, Biot-Savart's law satisfies the following form:

[0085]

[0086] Where μ0 is the vacuum permeability, is the unit vector along the tangent direction of the overhead line, are the unit vectors in the x, y, and z axis directions respectively, and r is A direction vector pointing to a point P in space.

[0087] Assume that the coordinates of the magnetic field point P in the three-dimensional coordinate system are (x0, y0, z0), then the distance vector

[0088] Combining the above formulas, we can get:

[0089]

[0090] Among them, B x , B y , B z are the magnetic induction intensities in the x, y, and z axis directions respectively.

[0091] S2, selecting the installation location of the magnetic sensor based on the verification results of the three-dimensional magnetic field model established in S1;

[0092] To determine the installation position of the magnetic sensor, it is necessary to compare the power frequency magnetic fields of different topological structures based on the three-dimensional magnetic field model obtained above to determine the points with relatively consistent characteristics. In addition, since the magnetic field at the detection point is closely related to the shape of the surrounding magnetic conductive metal, the traditional analytical model cannot accurately model the complex magnetic circuit. Therefore, it is also necessary to use the magnetic field correction coefficient of the magnetic conductive material to correct the magnetic field near the installation point. Ultimately, the number of magnetic sensitive elements installed in different transmission cable topologies and their respective installation positions are reasonably determined, and the optimal positioning criteria for magnetic elements in the magnetic state detection of transmission cables are established. Specifically study the influence of factors such as tower type (stem-shaped tower, upper-shaped tower, gate-shaped tower, V-shaped tower, T-shaped tower, wine glass-shaped tower, stem-shaped tower, etc.), basic parameters (foundation, terrain, span, wire diameter, height, etc.), material properties, temperature distribution, etc. on the magnetic field at the installation point of the magnetic sensitive element;

[0093] In the present invention, the installation position of the magnetic sensor is selected on the tower. Although the sag in the middle of the overhead line is the largest, in reality, due to the certain height of the overhead line, the sensor cannot be installed in mid-air. Moreover, according to the established three-dimensional magnetic field model, the magnetic field on the ground is much smaller than the magnetic field on the tower. Therefore, the benefit of installing the sensor on the tower is the greatest.

[0094] S3, based on the magnetic field data calculated by the discretized three-dimensional magnetic field model and the magnetic field data collected by the magnetic sensor, the final catenary coefficient is solved through an iterative algorithm to obtain the sag of the overhead line;

[0095] like Figure 4 As shown, the specific steps of the iterative algorithm are:

[0096] S31, discretizing the three-dimensional magnetic field model established in S1;

[0097] Since the three-dimensional magnetic field model established previously is in integral form, discretization is used to greatly improve the calculation speed. It has been verified that the discretized magnetic field data is very close to the magnetic field obtained by integration and meets the requirements. The specific discretization results are:

[0098] X-axis magnetic field model, for B in equation (8) x The formula after discretization is:

[0099]

[0100] Y-axis magnetic field model, for B in equation (7) y The formula after discretization is:

[0101]

[0102] Z - axis magnetic field model. For B in Equation (7), z The formula after discretization is:

[0103]

[0104] where, -L / 2 < t i < L / 2, i = 1, 2, 3…, n. The larger n is, the more accurate the discretized result is. Δt is the spacing between adjacent t i values.

[0105] S32. Set an initial value of the catenary coefficient and substitute it into the discretized three - dimensional magnetic field model to calculate a set of periodic magnetic field data. During the iterative operation process, by continuously changing the catenary coefficient, different magnetic field data can be obtained;

[0106] S33. The magnetic sensor also collects a set of periodic magnetic field data, and calculates the root - mean - square error between the magnetic field data collected by the magnetic sensor and the magnetic field data solved by the discretized three - dimensional magnetic field model. Each iteration recalculates the root - mean - square error value between the magnetic field data solved by different catenary coefficients and the data collected by the sensor until the root - mean - square error is less than the set threshold, and the iteration stops;

[0107] The evaluation index of each iteration algorithm is the root - mean - square error of the two sets of data:

[0108]

[0109] where, N is the number of data, X i is the data set collected by the magnetic sensor, and x i is the data set calculated for each iteration;

[0110] S34. After the iteration stops, select the magnetic field data solved by the discretized three - dimensional magnetic field model at this time, and correspondingly obtain the catenary coefficient, then the sag size of the overhead line can be obtained.

[0111] In the description of this specification, the descriptions referring to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0112] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for detecting the sagging state of an overhead line based on a magnetic sensor, characterized in that: The following steps are involved: S1, constructing a three-dimensional magnetic field model of the overhead line under sagging state; S2, selecting the installation location of the magnetic sensor based on the verification results of the three-dimensional magnetic field model established in S1; S3, based on the magnetic field data calculated by the discretized three-dimensional magnetic field model and the magnetic field data collected by the magnetic sensor, the final catenary coefficient is solved through an iterative algorithm to obtain the sag of the overhead line; In S1, the step of constructing a three-dimensional magnetic field model includes: S11, derive the physical model of the overhead line sagging condition and conclude that the overhead line hanging between two towers is in the shape of a catenary; S12, calculate the catenary equation of the overhead line; There is a uniform load γ along the length of the overhead line, which is in a vertical downward direction. Under the action of the load γ, the overhead line takes on a curved shape. σ0 is the stress in the x-axis direction of the overhead line. Select a microelement σ Δ The force analysis in the x-axis and y-axis directions is carried out respectively, and the force balance equation of the overhead line is: ∑X=0,σ Δ cosθ=σ0 (1) ∑Y=0,σ Δ sinθ=γL Δ (2) Combining the above equations, we can get the catenary equation of the overhead line: Among them, C1 and C2 are integration constants, whose values depend on the origin position of the coordinate system; A droop state model of overhead transmission lines is established. The overhead lines are located in the ZOY plane. It can be seen that the lines between adjacent transmission towers satisfy the catenary equation: Where α is the catenary coefficient, which is the L is the distance between two adjacent towers, k is a constant; S13, calculating the three-dimensional magnetic field model of the overhead line in the drooping state; It can be seen that dz / dy=sinh(αy). In the three-dimensional coordinate system, Biot-Savart's law satisfies the following form: Where μ0 is the vacuum permeability, is the unit vector along the tangent direction of the overhead line, are the unit vectors in the x, y, and z axis directions respectively, and r is A direction vector pointing to a point P in space; Assume that the coordinates of the magnetic field point P in the three-dimensional coordinate system are (x0, y0, z0), then the distance vector Combining the above formulas, we can get: Among them, B x , B y , B z are the magnetic induction intensities in the x, y, and z axis directions respectively; In S3, the iterative operation steps include: S31, discretizing the three-dimensional magnetic field model established in S1; S32, setting an initial value of a catenary coefficient and bringing it into the discretized three-dimensional magnetic field model to calculate and obtain a set of periodic magnetic field data; S33, calculating the root mean square error between the magnetic field data collected by the magnetic sensor and the magnetic field data solved by the discretized three-dimensional magnetic field model; each iteration recalculates the root mean square error between the magnetic field data solved by different catenary coefficients and the sensor collected data until the root mean square error is less than a set threshold, and then the iteration is stopped; S34, after the iteration stops, the magnetic field data solved by the discretized three-dimensional magnetic field model at this time is selected, and the corresponding catenary coefficient is obtained, so as to obtain the sag of the overhead line; The discretization result of the three-dimensional magnetic field model is: X-axis magnetic field model, for B in equation (8) x The formula after discretization is: The Y-axis magnetic field model, for B in equation (8) y The formula after discretization is: The magnetic field model in the Z-axis direction is used to calculate the B in equation (8). z The formula after discretization is: where, -L / 2 < t i < L / 2, i = 1, 2, 3…, n, and Δt is the spacing between adjacent t i values.

2. The method for detecting the sagging state of an overhead line based on a magnetic sensor according to claim 1, characterized in that: In the above S11, it is assumed that the overhead line is a flexible cable chain without rigidity; and it is assumed that the load acting on the overhead line is evenly distributed along the length of the line.

3. The method for detecting the sagging state of an overhead line based on a magnetic sensor according to claim 1, characterized in that: In S2, the installation position of the magnetic sensor is determined. It is necessary to compare the power frequency magnetic fields of different topological structures based on the three-dimensional magnetic field model to determine the points with consistent characteristics, and it is also necessary to use the magnetic field correction coefficient of the magnetic conductive material to correct the magnetic field near the installation point.

4. The method for detecting the sagging state of an overhead line based on a magnetic sensor according to claim 3, characterized in that: In S2, the magnetic sensor is installed on the tower.

5. The method for detecting the sagging state of an overhead line based on a magnetic sensor according to claim 1, characterized in that: The evaluation index of each iterative algorithm is the root mean square error of the two sets of data: Among them, N is the number of data, X i The data set collected by the magnetic sensor, x i The data set calculated for each iteration.

6. A system for detecting the sagging state of an overhead line based on a magnetic sensor, which implements the method for detecting the sagging state of an overhead line based on a magnetic sensor according to any one of claims 1 to 5, characterized in that: include: Model building module: used to build a three-dimensional magnetic field model of the overhead line in the drooping state; Sensor position determination module: selects the installation location of the magnetic sensor based on the verification results of the three-dimensional magnetic field model; Iterative calculation module: Based on the magnetic field data calculated by the discretized three-dimensional magnetic field model and the magnetic field data collected by the magnetic sensor, the final catenary coefficient is solved through an iterative algorithm to obtain the sag of the overhead line.

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