A method for detecting underground lateral electric structure based on overhead three-phase transmission line

Abstract

The application discloses a kind of underground lateral electric structure detection methods based on overhead three-phase transmission line, including constructing overhead three-phase transmission line model, using forward numerical simulation to determine the distance of receiving and transmitting;According to the distance of receiving and transmitting determined, the electric field data along the direction of transmission line is measured;Based on overhead three-phase transmission line model, one-dimensional inversion is carried out on electric field data;The one-dimensional inversion results of all measuring points are combined, and the distribution of underground lateral geoelectric structure is determined by geophysical interpretation.This method provides a kind of method for detecting underground lateral electric structure by using overhead three-phase transmission line in geophysical field, not only more scientifically layout observation system, but also fully consider the design parameters and droop form of actual overhead three-phase transmission line in forward and inversion process, greatly improve the authenticity and accuracy of inversion result, provide positive reference and guiding role for the development of such work in future.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration, specifically to a method for detecting underground lateral electrical structures based on overhead three-phase power transmission lines. Background Technology

[0002] In the field of geophysics, the 50Hz power frequency electromagnetic field generated by power transmission lines easily overwhelms geophysical observation data. Most scholars consider it a form of electromagnetic noise and attempt to mitigate or eliminate its impact on geophysical data processing and interpretation. Meanwhile, some scholars view power transmission lines as a geophysical field source and utilize their electromagnetic radiation for underground electrical structure detection. However, current utilization of the electromagnetic field generated by power transmission lines is limited to simple field measurements and data processing. For example, when measuring the electromagnetic response of power transmission lines, the measurement points and lines are generally arranged based on the operator's experience, but the distance between the measurement points and the transmission line significantly affects the results. In the data processing stage, most studies currently only calculate the apparent resistivity from the measured electromagnetic response and then directly interpret it, without performing geophysical inversion, inevitably leading to discrepancies between the results and reality. Summary of the Invention

[0003] In view of this, the present invention proposes a method for detecting underground transverse electrical structures based on overhead three-phase transmission lines, comprising the following steps:

[0004] S1. Measure and record the parameters of the selected overhead three-phase transmission line, construct an overhead three-phase transmission line model based on the parameters, and determine the transmitting and receiving distance using forward numerical simulation.

[0005] S2. Measure the electric field data along the transmission line based on the determined transmit / receive distance;

[0006] S3. Construct a ground power model, and perform a single-point one-dimensional inversion of the electric field data based on the overhead three-phase transmission line model and the ground power model;

[0007] S4. Combine the one-dimensional inversion results of all measuring points to perform geophysical interpretation and determine the distribution of the underground lateral geoelectric structure.

[0008] Furthermore, step S1 specifically includes:

[0009] S11. Measure and record the design parameters and sag parameters of the selected overhead three-phase transmission line, including the number of spans, circuits and splits of the transmission line, and use a total station to measure the height and coordinates of the suspension points at both ends of each transmission line within each span and any point on the transmission line other than the suspension points, the phase spacing of the three-phase conductors, the split spacing of the split conductors and the span size.

[0010] S12. Model the overhead three-phase transmission line and perform forward modeling for different resistivity models. Using the transmission line parameter information obtained in step S11, accurately model the target transmission line. Treat a drooping split electric field line in each span of each phase conductor in each circuit as a catenary, and transform its coordinates to the xO plane. Let the coordinates of the suspension points O and B at both ends of the catenary after the transformation be (0,0) and (,h) respectively. Then the catenary can be expressed by the catenary equation as:

[0011]

[0012] In the formula, Let T0 be the suspension coefficient, T0 be the horizontal tension at the lowest point A of the catenary, ρ be the linear density of the catenary, g be the acceleration due to gravity, and a be the x-coordinate of the lowest point A, satisfying the following:

[0013]

[0014] The coordinates of each point on the power line are obtained by inverse transformation of the catenary coordinates to the original coordinate system. Forward modeling is performed using the constructed power line model and different resistivity models to determine the range within which the electromagnetic response of the target transmission line is unaffected by the underground geoelectric structure, and the transmitter-receiver distance is determined accordingly. The different resistivity models are overhead three-phase transmission lines with an infinitely long double-circuit drum-shaped structure along the y-axis as the transmitting source. The survey line is laid out along the x-axis for a total length of 4 km. The models are four uniform half-space models: J1, J10, J100, and J1000, with half-space resistivities of 1 Ω·m, 10 Ω·m, 100 Ω·m, and 1000 Ω·m, respectively.

[0015] Furthermore, step S3 specifically includes:

[0016] S31. Set the initial geoelectric model parameters, including the number of model layers N and the bottom interface depth z of the i-th layer. i and initial resistivity value The geoelectric model can then be expressed as:

[0017]

[0018] Where z0=0, z N =∞, where Iter is the current iteration number. Let Iter be the resistivity of the i-th layer in the Iter-th iteration; and set the maximum number of iterations Iter. max and the target fit difference χ * And set the current iteration number Iter to 1.

[0019] S32. Construct the roughness matrix δ and calculate δ T δ, the roughness matrix δ is an N×N matrix:

[0020]

[0021] S33. Calculate the forward response F[m] of the current model. Iter Jacobian matrix J Iter And update the model, F[m Iter The number of elements in the image is M, representing M forward data points;

[0022] Jacobian matrix J Iter Given an M×N matrix, satisfying:

[0023]

[0024] Among them, matrix elements It can be represented as:

[0025]

[0026] New model m Iter+1 The following formula can be used to calculate:

[0027] m Iter+1 =[μδ T δ+(WJ Iter ) T WJ Iter ] -1 (WJ Iter ) T Wd Iter (7)

[0028] In the formula, μ is the Lagrange multiplier, W and d Iter They respectively satisfy:

[0029]

[0030] d Iter =dF[m Iter ]+J Iter m Iter (9)

[0031] Where, σ j Let be the standard deviation of the j-th measured data, and d be the measured data.

[0032] S34. Calculate the degree of fit. And select an appropriate μ to make it as close as possible to the desired value. Minimum.

[0033] Fit The calculation formula is

[0034]

[0035] Where, ‖·‖ represents taking the L2 norm.

[0036] S35. Determine if Iter has reached Iter. max ,or Has χ been achieved? * 2 If so, stop the iteration and output the final inversion model m. Iter+1 Otherwise, Iter = Iter + 1, and repeat step S33.

[0037] The beneficial effects of the technical solution provided by this invention are:

[0038] The observation system was deployed more scientifically, and the electromagnetic response of the measured transmission lines was inverted. The design parameters and sag of the actual overhead transmission lines were fully considered during the inversion process, which greatly improved the authenticity and accuracy of the inversion results and provided positive reference and guidance for future geophysical exploration using transmission lines. Attached Figure Description

[0039] Figure 1 This is a flowchart of an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the forward modeling simulation experiment according to an embodiment of the present invention; wherein, the emission source is an overhead three-phase transmission line with an infinitely long double-circuit drum-shaped structure along the y-axis; the measuring line is laid out along the x-axis, with a total length of 4km; the model consists of four uniform half-space models J1, J10, J100 and J1000, with half-space resistivity of 1, 10, 100 and 1000Ω·m, respectively;

[0041] Figure 3 The results are the forward simulation experimental results of the embodiments of the present invention; wherein Figure 3 (a) E calculated based on models J1, J10, J100, and J1000 y The amplitude; Figure 3 (b) is the H calculated based on models J1, J10, J100, and J1000. x The amplitude; Figure 3 (c) H is calculated based on models J1, J10, J100, and J1000. Z The amplitude;

[0042] Figure 4 This is a schematic diagram illustrating the segmentation of a single drooping split power line within each span of each phase conductor in each circuit of the target transmission line according to an embodiment of the present invention. Figure 4 (a) is a schematic diagram of a catenary, in which Figure 4 (b) A schematic diagram showing the division of a single drooping split power line in each phase of each circuit of the target transmission line into straight sub-conductor segments in different directions.

[0043] Figure 5This is a flowchart illustrating the one-dimensional Occam inversion process in an embodiment of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0045] refer to Figure 1 , Figure 1 This is a flowchart of an embodiment of the present invention.

[0046] This invention provides a method for detecting underground transverse electrical structures based on overhead three-phase transmission lines, comprising the following steps:

[0047] S1. Construct an overhead three-phase transmission line model and use forward numerical simulation to determine the transmission and reception distance.

[0048] refer to Figure 2 , Figure 2 This is a forward simulation experimental model for an embodiment of the present invention. The emission source is an infinitely long, double-circuit, drum-shaped overhead three-phase transmission line along the y-axis; the measuring line is laid out along the x-axis, with a total length of 4 km; the model consists of four uniform half-space models J1, J10, J100, and J1000, with half-space resistivities of 1, 10, 100, and 1000 Ω·m, respectively. The forward simulation experimental results show that the electromagnetic field observed within a certain range around the center of the overhead three-phase transmission line exhibits a strong source effect. (Reference) Figure 3 , Figure 3 The results are from the forward simulation experiments of this invention. Figure 3 The results show that the amplitude curves of the primary field and the total field are in excellent agreement within this range. Since the electromagnetic response observed within the influence range of the source effect contains virtually no information about subsurface electrical properties, a suitable transmitter-receiver distance should be selected to avoid measurements within this range when using power lines for geophysical exploration. The transmitter-receiver distance can be determined using forward numerical simulation; furthermore, because the influence range of the source effect varies with the transmission line design parameters, constructing an accurate power line model that conforms to reality is crucial before forward simulation.

[0049] S11. Measure and record the design parameters and sag parameters of the selected overhead three-phase transmission line. Actual overhead three-phase transmission lines involve many design parameters, such as transmission structure, number of circuits, and branching configuration, and also exhibit a certain degree of sag due to gravity and other factors. Thorough consideration of these parameters and accurate description of the sag morphology of overhead transmission lines are crucial for accurately simulating actual power lines.

[0050] First, record the number of spans, circuits, and splits of the overhead three-phase transmission line to be studied. Then, use a total station to measure the height and coordinates of the suspension points at both ends of each transmission line within each span, as well as any point on the transmission line other than the suspension points, the phase spacing of the three-phase conductors, the split spacing of the split conductors, and the span size, among other parameters.

[0051] S12. Model the overhead three-phase transmission line and perform forward modeling for different resistivity models. Using the transmission line parameter information obtained in step S11, accurately model the target transmission line. A drooping split power line in each span of each phase conductor in each circuit can be regarded as a catenary. Figure 4 (a) is a schematic diagram of a catenary according to an embodiment of the present invention. The coordinates of the suspension points O and B at both ends of the catenary are (0,0) and (,h) respectively. The equation of the catenary is:

[0052]

[0053] In the formula, Let T0 be the suspension coefficient, T0 be the horizontal tension at the lowest point A of the catenary, ρ be the linear density of the catenary, g be the acceleration due to gravity, and a be the x-coordinate of the lowest point A, satisfying the following conditions:

[0054]

[0055] The above catenary equation restricts one endpoint of the catenary to the origin. For any drooping electric line, the coordinates and heights of the two suspension points can be used to transform it to the xOy plane where the catenary equation lies. Meanwhile, note that there is a coefficient k in the catenary equation, which is related to the conductor type and load of the electric line and is not easily measured. It can be considered an unknown quantity, and the coordinates of a point on the electric line other than the suspension point (already transformed) can be substituted into equation (1) to obtain the coefficient k. After obtaining the catenary equation satisfied by the electric line, an inverse coordinate transformation is performed on the entire line to restore it to the original coordinate system. At this point, the coordinates of every point on the electric line are known.

[0056] Next, forward modeling is performed using the constructed electric field line model and uniform half-space models with different resistivities. During the forward modeling process, each drooping split electric field line within each span of each phase conductor in each loop is divided into a finite number of straight sub-conductor segments in different directions, such as... Figure 4As shown in (b), the electromagnetic response induced by the power line can be approximated as the superposition of the responses induced by each sub-conductor. Clearly, the more sub-conductors used, the more accurate the approximation. The electromagnetic response of a single sub-conductor segment is calculated using the open-source software Dipole1D. The calculation requires information such as the center coordinates, length, inclination angle, and azimuth angle of the sub-conductor segment, all of which can be obtained from the coordinates of the two endpoints of the sub-conductor. Finally, by superimposing the electromagnetic responses induced by the power line across all spans of the three-phase conductors in all loops, the total electromagnetic response induced by the entire transmission line is obtained. Furthermore, the amplitude and phase of the current loaded on the power line can be arbitrarily set during forward modeling without significantly affecting the determination of the aforementioned range.

[0057] S13. Determine the approximate range of the source effect's influence based on the forward modeling results, ensuring that the minimum transmit / receive distance is greater than the aforementioned range. According to... Figure 3 The results show that the source effect of the electric field has a smaller range than that of the magnetic field, which means that there is a larger observation space. Therefore, the range of the source effect is based on the electric field.

[0058] S2. Measure the electric field data along the transmission line based on the determined transmitter-receiver distance. Since the transmitter-receiver distance is determined based on the range of influence of the electric field source effect, and the electric field is more sensitive to changes in the geoelectric structure than the magnetic field, this invention only measures the electric field component along the transmission line. The electric field response can be measured using conventional geophysical electromagnetic instruments.

[0059] S3. Construct a ground power model, and perform a single-point one-dimensional inversion of the electric field data based on the overhead three-phase transmission line model and the ground power model. The inversion process is as follows: Figure 5 As shown, the specific inversion steps are as follows:

[0060] S31. Set the initial geoelectric model parameters, including the number of model layers N and the bottom interface depth z of the i-th layer. i and initial resistivity value The geoelectric model can then be expressed as:

[0061]

[0062] Where z0 = 0, z N =∞, where Iter is the current iteration number. Let Iter be the resistivity of the i-th layer in the Iter-th iteration. Also set the maximum number of iterations, Iter. max and the target fit difference χ * And set the current iteration number Iter to 1.

[0063] S32. Construct the roughness matrix δ and calculate δ T δ, the roughness matrix δ is an N×N matrix:

[0064]

[0065] S33. Calculate the forward response F of the current model. Iter Jacobian matrix J Iter And update the model. F[ Iter The number of elements in the diagram is M, representing M forward modeling data. In this embodiment, the calculated forward modeling response is only the electric field strength along the direction of the overhead three-phase transmission line, therefore M = 1. The emission source used in the forward modeling is the actual overhead three-phase transmission line model constructed in step S12. During the forward modeling process, the drooping electric field line needs to be divided into a finite number of straight sub-conductor segments in different directions. The electromagnetic response of each straight sub-conductor segment is calculated using the open-source software Dipole1D. Then, the electromagnetic responses of all sub-conductors are superimposed to obtain the total electromagnetic response excited by the transmission line, referring to step S12.

[0066] Jacobian matrix J Iter Given an M×N matrix, satisfying:

[0067]

[0068] Among them, matrix elements It can be represented as:

[0069]

[0070] New model m Iter+1 The following formula can be used to calculate:

[0071] m Iter+1 =[μδ T δ+(WJ Iter ) T WJ Iter ] -1 (WJ Iter ) T Wd Iter (7) In the formula, μ is a Lagrange multiplier, W and d Iter Each satisfies

[0072]

[0073] d Iter =dF[m Iter ]+J Iter m Iter (9)

[0074] Where, σ j Let be the standard deviation of the j-th measured data, and d be the measured data (in this embodiment, the measured electric field strength).

[0075] S34. Calculate the degree of fit. And select an appropriate μ to make it as close as possible to the desired value. Minimum,

[0076] Fit The calculation formula is

[0077]

[0078] Here, ‖·‖ represents taking the L2 norm, and the optimal choice of μ can be obtained through linear search.

[0079] S35. Determine if Iter has reached Iter. max ,or Has χ been achieved? * 2 If so, stop the iteration and output the final inversion model m. Iter+1 Otherwise, Iter = Iter + 1, and repeat step S33.

[0080] S4. Combine the one-dimensional inversion results of all measuring points to perform geophysical interpretation and determine the distribution of the underground lateral geoelectric structure.

[0081] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting underground transverse electrical structures based on overhead three-phase transmission lines, characterized in that, Includes the following steps: S1. Measure and record the parameters of the selected overhead three-phase transmission line, construct an overhead three-phase transmission line model based on the parameters, and determine the transmitting and receiving distance using forward numerical simulation. S2. Measure the electric field data along the transmission line based on the determined transmit / receive distance; S3. Construct a ground power model, and perform a single-point one-dimensional inversion of the electric field data based on the overhead three-phase transmission line model and the ground power model; S4. Combine the one-dimensional inversion results of all measuring points to perform geophysical interpretation and determine the distribution of the underground lateral geoelectric structure; Step S3 is as follows: S31. Set the initial geoelectric model parameters, including the number of model layers. , No. Layer bottom interface depth and initial resistivity value The geoelectric model is represented as: in, , , This represents the current iteration number. For the first The second iteration The resistivity of the layer; and the maximum number of iterations. and target fit difference and the current iteration number Set to 1; S32. Constructing the roughness matrix and calculate Roughness matrix For one The matrix: S33. Calculate the forward response of the current model. Jacobian matrix And update the model, The number of elements in the middle is ,represent One orthogonal data; Jacobian matrix for A matrix that satisfies: Among them, matrix elements It can be represented as: New model The following formula can be used to calculate: In the formula, For Lagrange multipliers, and They respectively satisfy: in, For the first The standard deviation of each measured data point These are actual measured data; S34. Calculate the degree of fit. and select appropriate make Minimum; Fit The formula for calculation is: （10） in, This indicates taking the L2 norm; S35, Judgment Has it been achieved? ,or Has it been achieved? If so, stop the iteration and output the final inversion model. ;otherwise Repeat step S33.

2. The method for detecting underground transverse electrical structures based on overhead three-phase transmission lines according to claim 1, characterized in that, Step S1 is as follows: S11. Measure and record the design parameters and sag morphology parameters of the selected overhead three-phase transmission line, including the number of spans, circuits and splits of the transmission line, and use a total station to measure the height and coordinates of the suspension points at both ends of each transmission line within each span and any point on the transmission line other than the suspension points, the phase spacing of the three-phase conductors, the split spacing of the split conductors and the span size. S12. Using the transmission line parameter information obtained in step S11, accurately model the target transmission line. Treat a drooping split power line in each span of each phase conductor in each circuit as a catenary, and transform its coordinates to... In a plane, let the coordinates of the suspension points O and B at both ends of the catenary after the transformation be respectively... and Then the catenary can be expressed by the catenary equation as: In the formula, The suspension coefficient, The horizontal tension at the lowest point A of the catenary. The linear density of the catenary. It is the acceleration due to gravity. For the lowest point A x Coordinates and satisfy: The coordinates of each point on the power line are obtained by inverse transformation of the catenary coordinates to the original coordinate system. Forward modeling is performed using the constructed power line model and different resistivity models to determine the range within which the electromagnetic response of the target transmission line is unaffected by underground geoelectric structures, and thus determine the transmitter-receiver distance. The different resistivity models are based on an overhead three-phase transmission line with an infinitely long double-circuit drum-shaped structure along the y-axis as the transmitting source. The survey line is laid out along the x-axis, with a total length of 4 km. The models are four uniform half-space models: J1, J10, J100, and J1000, with half-space resistivities of 1... 10 100 and 1000 .

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