A method for determining the current of an overhead three-phase transmission line based on geophysical data

Abstract

This invention provides a method for determining the current of an overhead three-phase transmission line based on geophysical data. The method involves investigating the underground dielectric structure of the area where the overhead three-phase transmission line is to be constructed; measuring and recording the parameter information of the overhead three-phase transmission line; modeling the overhead three-phase transmission line using the parameter information and performing a pre-forward model based on the investigated underground dielectric structure; designing magnetic field observation points based on the pre-model results; measuring the magnetic field response of the overhead three-phase transmission line at the observation points; and using the measured magnetic field response data and the constructed transmission line model, inverting the current of the overhead three-phase transmission line. The beneficial effects of this invention are: it provides a theoretical basis and technical guidance for the quantitative analysis and research of the power frequency electromagnetic response generated by power lines; and it fully considers the design parameters and sag morphology of actual overhead transmission lines during the current inversion process, making the overhead three-phase transmission line model more realistic and greatly improving the accuracy of the results.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration technology, and in particular to a method for determining the current of an overhead three-phase transmission line based on geophysical data. Background Technology

[0002] In geophysics, electromagnetic radiation from power transmission lines is often considered noise, but it can also serve as an electromagnetic signal for geophysical exploration. Both eliminating and utilizing its effects require quantitative analysis and research into the electromagnetic response characteristics of power transmission lines, which necessitates knowledge of the current flowing through them. In the power sector, the current in transmission lines can be measured using current sensors. However, current sensors suffer from drawbacks such as large size and installation difficulties, making current measurement virtually impossible for geophysicists. Currently, no method for measuring the current in power transmission lines has been proposed in the geophysical community. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for determining the current of overhead three-phase transmission lines based on geophysical data. This method fully considers the design parameters and sag characteristics of actual overhead transmission lines, making the constructed power line model more consistent with reality and significantly improving the accuracy of the results. This method for determining the current of overhead three-phase transmission lines based on geophysical data mainly includes:

[0004] S1: Investigate the underground dielectric electrical structure of the area where the overhead three-phase transmission line to be studied is erected, and confirm whether there is a large-scale low-resistivity electrical structure in the shallow part. If so, the geological model is a layered model with different resistivity considering the low-resistivity electrical structure. If not, the geological model is a uniform half-space model with different resistivity.

[0005] S2: Measure and record the parameter information of the overhead three-phase transmission line;

[0006] S3: Use the parameter information obtained in step S2 to model the overhead three-phase transmission line to obtain the overhead three-phase transmission line model. Combine it with the geological model established in step S1 to perform pre-forward modeling. Then, design magnetic field observation points based on the pre-forward modeling results.

[0007] S4: Measure the magnetic field response of the overhead three-phase transmission line at each magnetic field observation point designed in step S3;

[0008] S5: Using the measured magnetic field response data and the overhead three-phase transmission line model constructed in step S3, the current of the transmission line is inverted to obtain the final current of the overhead three-phase transmission line.

[0009] Furthermore, the parameter information includes the number of spans, circuits, and splits of the target transmission line (i.e., the actual overhead three-phase transmission line), the height and coordinates of the suspension points at both ends of each transmission line within each span and any point or points 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] Furthermore, a total station is used 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 or points 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.

[0011] Furthermore, the process of modeling the overhead three-phase transmission line based on the aforementioned parameter information is as follows:

[0012] For a single drooping split electric field line within each span of each phase conductor in each circuit, it can be considered as a catenary, and its coordinates can be transformed to the xOy plane. Assuming that the coordinates of the suspension points O and B at both ends of the catenary are (0, 0) and (l, h) respectively after the transformation, the equation of the catenary can be expressed as:

[0013]

[0014] In the formula, T0 is the horizontal tension at the lowest point A of the catenary, ρ is the linear density of the catenary, g is the acceleration due to gravity, and a is the x-coordinate of the lowest point A, satisfying the following:

[0015]

[0016] By inversely transforming the overall coordinates of the catenary to the original coordinate system, the coordinates of each point on the power line can be obtained.

[0017] Furthermore, the method for calculating the electromagnetic response of the overhead three-phase transmission line model in the pre-forward modeling is as follows:

[0018] Each single drooping split power line in each phase of each circuit is divided into a finite number of straight sub-conductor segments in different directions. The electromagnetic response of a single sub-conductor segment is calculated using the open-source software Dipole1D. The electromagnetic response excited by the drooping split power line is approximately the superposition of the responses excited by each sub-conductor. Finally, the electromagnetic responses excited by the power lines in all spans of all three phases of all circuits are superimposed to obtain the total electromagnetic response excited by the entire transmission line.

[0019] Furthermore, the electromagnetic response was measured using a fluxgate magnetometer.

[0020] Furthermore, the electromagnetic response includes a magnetic field component perpendicular to the direction of the transmission line and a magnetic field component perpendicularly downward.

[0021] Furthermore, the optimization problem describing the inversion of the current in an overhead three-phase transmission line is expressed as:

[0022] In an overhead three-phase transmission line with M circuits, the current J loaded on any split sub-conductor of the q-th phase conductor in the m-th circuit is... mq Represented as:

[0023]

[0024] Where j is the imaginary unit, I m Let α be the amplitude of the current applied to any split sub-conductor of any phase conductor in the m-th loop. mq Let be the phase of the current applied to any split sub-conductor of the q-th phase conductor in the m-th loop;

[0025] I m With α mq These are all decision variables in the inversion optimization process, because the phases of the three-phase conductors in each loop have the following relationship:

[0026]

[0027] The number of decision variables can be reduced to 2M;

[0028] The objective function of the inversion optimization problem is set as follows:

[0029]

[0030] Where F1, F2, F3, and F4 are four objective functions, N is the total number of measurement points, and |H n |and|H n* | represents the magnetic field strength amplitude calculated by forward modeling at measurement point n and the actual measured magnetic field strength amplitude, respectively. and These are the magnetic field strength phase calculated by forward modeling at measurement point n and the actual measured magnetic field strength phase, respectively. The subscripts TL and z represent the component perpendicular to the transmission line and the vertically downward component, respectively.

[0031] The final optimization problem for inverting the current of an overhead three-phase transmission line is:

[0032]

[0033] And consider the constraints:

[0034]

[0035] Among them, I min and I max I m The upper and lower limits.

[0036] Furthermore, the process of solving the optimization problem of inverting the current of an overhead three-phase transmission line using a non-dominated sorting genetic algorithm with an elitist strategy is as follows:

[0037] (1) Set the maximum number of iterations;

[0038] (2) Set C initial current amplitude and phase decision vectors And use it as the initial parent population, where, in I min and I max Randomly distributed among them, Randomly distributed between -180° and 180° and According to equation (4), the current iteration number gen is set to 1;

[0039] (3) Genetic algorithm is used to generate a new generation of subpopulation, and the number of individuals in the subpopulation is also C;

[0040] (4) Merge the child population with the parent population. After merging, the population size becomes 2C.

[0041] (5) Perform non-dominated sorting on the merged population to generate a series of non-dominated sets, and calculate the crowding degree.

[0042] (6) Select individuals in descending order of non-dominated set hierarchy to form a new parent population. When the number of individuals in the population exceeds C after adding a non-dominated set of a certain level, compare the crowding of individuals in the non-dominated set and fill the new parent population with individuals with higher crowding until the population size reaches C.

[0043] (7) Determine whether the number of iterations exceeds the set maximum number. If yes, terminate the iteration and output the population. If no, gen = gen + 1 and return to step (3) to perform the operations of steps (3)-(7).

[0044] The beneficial effects of the technical solution provided by this invention are:

[0045] 1. A method for determining the current of overhead three-phase transmission lines is proposed for the field of geophysics, which can provide a theoretical basis and technical guidance for the quantitative analysis and research of the power frequency electromagnetic response generated by power lines.

[0046] 2. The inversion process fully considers the design parameters and droop shape of actual overhead transmission lines, making the power line model more realistic and greatly improving the accuracy of the results. Attached Figure Description

[0047] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0048] Figure 1 This is a flowchart of a method for determining the current of an overhead three-phase transmission line based on geophysical data, as described in an embodiment of the present invention.

[0049] Figure 2 This is a model diagram of the forward simulation experiment in the embodiments of the present invention;

[0050] in Figure 2 (a) is a schematic diagram of a uniform half-space model. The half-space resistivity of the five models J01, J1, J10, J100 and J1000 are 0.1, 1, 10, 100 and 1000 Ω·m, respectively.

[0051] Figure 2 (b) is a schematic diagram of a two-layer model. The resistivity of the first layer and the second layer are 1 and 100 Ω·m, respectively. The thickness of the first layer of the two models G1 and G2 is 1 m and 50 m, respectively.

[0052] Figure 2 (c) is a schematic diagram of a two-layer model. The resistivity of the first layer and the second layer are 100 and 1 Ω·m, respectively. The thickness of the first layer of models D1 and D2 is 1 m and 50 m, respectively.

[0053] Figure 2 (d) shows the overhead three-phase transmission line model and the line survey diagram.

[0054] Figure 3 This is a graph showing the results of the forward simulation experiment in an embodiment of the present invention.

[0055] Figure 4 This is a schematic diagram of the segmentation of the catenary and drooping electric field lines in an embodiment of the present invention;

[0056] in, Figure 4 (a) is a schematic diagram of a catenary;

[0057] Figure 4 (b) is a schematic diagram of a drooping electric field line divided into a finite number of straight conductor segments in different directions;

[0058] Figure 5 This is a flowchart of the overhead three-phase transmission line current inversion using the non-dominated sorting genetic algorithm (NSGA-II) with elitist strategy in an embodiment of the present invention. Detailed Implementation

[0059] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0060] The embodiments of the present invention provide a method for determining the current of an overhead three-phase transmission line based on geophysical data.

[0061] Please refer to Figure 1 , Figure 1 This is a flowchart of a method for determining the current of an overhead three-phase transmission line based on geophysical data, as described in an embodiment of the present invention, specifically including:

[0062] S1. Investigate the underground dielectric electrical structure of the area where the overhead three-phase transmission line to be studied is located, and confirm whether there is a large-scale low-resistivity electrical structure in the shallow part. If so, use a layered model (formed by a uniform half-space model after incorporating the low-resistivity electrical structure) with different resistivities as the geological model. If not, use a uniform half-space model with different resistivities as the geological model. If the vertical scale of the low-resistivity electrical structure is not less than the preset vertical scale, it is a large-scale low-resistivity electrical structure. Otherwise, it is a small-scale low-resistivity electrical structure. The preset vertical scale varies depending on the resistivity of the specific low-resistivity electrical structure and should be determined based on the actual application scenario.

[0063] According to forward simulation experiments (forward model such as...) Figure 2 As shown, the forward modeling results are as follows: Figure 3 As shown), when there are no low-resistivity electrical structures (resistivity greater than 1 Ω·m) in the shallow underground layer, or when the longitudinal scale of such structures is small, the magnetic field measured near the center of an overhead three-phase transmission line is almost unaffected by the underground dielectric structure, and is determined solely by the transmission line's design parameters and the applied current. Figure 3 The magnetic field responses based on the five models J10, J100, J1000, G1, and D2 show a very good match within a range of approximately 40 meters. Therefore, the current of the transmission line can be inverted using the magnetic field data within this range without considering the electrical structure of the underground medium. However, if there are low-resistivity electrical structures in the shallow underground layer and their longitudinal scale is large, the magnetic field response measured near the center of the overhead three-phase transmission line will be affected by them, such as... Figure 3 Based on the magnetic field response of models J01, J1, G2, and D1, if the current of the transmission line is to be inverted using the magnetic field data, the influence of low-resistivity structures must be fully considered. Therefore, when determining the current of the transmission line, it is necessary to first consult existing geological data of the area where the transmission line is to be erected or conduct shallow resistivity sounding to determine whether there are large-scale low-resistivity structures in the shallow underground of the area (in this example, a low-resistivity structure with a longitudinal thickness of not less than 100 meters is considered a large-scale low-resistivity structure) in order to determine the geological model. Generally speaking, only a few underground media (such as seawater intrusion into aquifers) have resistivity lower than 1 Ω·m.

[0064] S2. Measure and record the parameter information of the overhead three-phase transmission line.

[0065] Actual overhead three-phase transmission lines involve many design parameters, such as transmission structure, number of circuits, and branching patterns, and also exhibit a certain degree of sag due to gravity and other factors. A thorough consideration of these parameters and an accurate description of the sag pattern of overhead transmission lines (which is described by treating them as catenaries and using the catenary equation) are crucial for accurately simulating actual power line radiation.

[0066] First, record the number of spans, circuits, and splits of the overhead three-phase transmission line to be studied; these parameters are all visually perceptible. Then, use a total station to measure and record the height and coordinates of the suspension points at both ends of each transmission line within each span. Next, randomly select another point on the same transmission line (excluding the suspension points) and measure its height and coordinates. Although this height and coordinate information can be used to calculate the phase spacing of the three-phase conductors, the split spacing of the split conductors, and the span size, to save subsequent indoor work and for verification purposes, it is advisable to directly measure this information using a total station. Furthermore, it is recommended to select multiple points on the same transmission line for height and coordinate measurements to provide more usable data and verification information for subsequent simulations of sag power lines.

[0067] S3. Based on the transmission line parameter information measured in step S2, model the overhead three-phase transmission line to obtain the overhead three-phase transmission line model. Using the overhead three-phase transmission line model as the emission source, excite electromagnetic signals to perform pre-forward modeling on the geological model obtained in step S1. Design magnetic field observation points based on the pre-forward modeling results.

[0068] Using the parameter information of the overhead three-phase transmission line obtained in step S2, the target transmission line (i.e., the actual overhead three-phase transmission line) can be accurately modeled. The specific process is as follows:

[0069] For a single drooping split electric field line within each span of each phase conductor in each loop, it can be described using the catenary equation. For example... Figure 4 As shown in (a), assuming the coordinates of the suspension points O and B at both ends of a catenary are (0, 0) and (l, h) respectively, the equation of the catenary is:

[0070]

[0071] In the formula, T0 is the horizontal tension at the lowest point A of the catenary, ρ is the linear density of the catenary, g is the acceleration due to gravity, and a is the x-coordinate of the lowest point A, satisfying the following conditions:

[0072]

[0073] 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 measured to transform it to the xOy plane where the catenary equation lies. Note that the catenary equation contains a coefficient k, which is related to the conductor type and load of the electric line and is difficult to measure. It can be considered an unknown quantity, and the coordinates of a point on the electric line other than the suspension point (after coordinate transformation) can be substituted into equation (1) to obtain the coefficient k. After obtaining the catenary equation satisfied by the electric line, the coordinates of the additional measured points can be substituted into the equation to verify its correctness. After confirming the accuracy of the equation, an inverse coordinate transformation is performed to restore it to the original coordinate system. At this point, the coordinates of every point on the electric line are known.

[0074] Next, a pre-forward modeling is performed. The purpose of the pre-forward modeling is to roughly understand the range within which the overhead three-phase transmission line is unaffected by underground geoelectric structures, so as to deploy measuring points within this range. During the pre-forward modeling, the constructed overhead three-phase transmission line model is used as the emission source, and the electromagnetic response excited by the overhead three-phase transmission line model is calculated based on the geological model obtained in step S1. The method for calculating the electromagnetic response is as follows: for each single drooping split electric field line in each phase conductor of each circuit, it is divided into a finite number of straight sub-conductor segments in different directions, such as... Figure 4 As 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 lines across all spans of the three-phase conductors in all loops, the total electromagnetic response induced by the entire transmission line is obtained. Furthermore, since the current conditions on the overhead three-phase transmission line are unknown, the amplitude and phase of the applied current can be arbitrarily set during pre-modeling without significantly affecting the determination of the aforementioned range.

[0075] Finally, based on the pre-forward modeling results, the range of overhead three-phase transmission lines that are not affected by underground geoelectric structures is determined, and a layout scheme for measuring points is designed accordingly.

[0076] S4. Measure the magnetic field response of the transmission line at the measuring point determined in step S3.

[0077] The magnetic field response is measured at the measurement point determined in step S3, including the magnetic field component perpendicular to the transmission line direction and the vertically downward magnetic field component. A fluxgate magnetometer can be used for magnetic field measurement.

[0078] S5. Using the measured magnetic field data and the constructed transmission line model, invert the current of the transmission line.

[0079] For an overhead three-phase transmission line with multiple circuits, each circuit can be energized independently, therefore the current in each circuit is generally different. Within each circuit, if the circuit is operating normally, the current amplitude on each phase conductor is the same, and their phases differ by 120°. When split conductors exist, the current on the split sub-conductors is an average distribution of the current in the corresponding phase conductors. In an overhead three-phase transmission line with M circuits, the current J loaded on any split sub-conductor of the q-th phase conductor in the m-th circuit is... mq It can be represented as

[0080]

[0081] Where j is the imaginary unit, I m Let α be the amplitude of the current applied to any split sub-conductor of any phase conductor in the m-th loop. mq Let be the phase of the current applied to any split sub-conductor of the q-th phase conductor in the m-th loop.

[0082] I m With α mq All of these are decision variables in the inversion optimization process. For the above-mentioned overhead three-phase transmission line with M loops, the number of decision variables in the inversion optimization problem should be 4M, but because the phases of the three-phase conductors in each loop have the following relationship:

[0083]

[0084] The number of decision variables can be reduced to 2M.

[0085] The objective function of the inversion optimization problem is set as follows:

[0086]

[0087] Where F1, F2, F3, and F4 are four objective functions, N is the total number of measurement points, and |H n |and|H n* | These represent the magnetic field strength amplitude calculated by forward modeling at measurement point n and the magnetic field strength amplitude actually measured in step S4, respectively. and These represent the magnetic field strength phase calculated from the forward model at measurement point n and the actual magnetic field strength phase measured in step S4, respectively. The subscripts TL and z represent the component perpendicular to the transmission line direction and the vertically downward component, respectively. The transmission line model used in the forward model is the overhead three-phase transmission line model constructed in step S3, and the calculation method for the electromagnetic response of the transmission line is the same as the calculation method for the electromagnetic response of the transmission line in the pre-forward model in step S3.

[0088] Therefore, the optimization problem of the current in an overhead three-phase transmission line can be expressed as:

[0089]

[0090] And consider the constraints:

[0091]

[0092] Among them, I min and I max I m The upper and lower limits.

[0093] The problem described by equation (6) is a multi-objective optimization problem, which can be solved in two ways. The first is to use traditional optimization algorithms (such as weighted methods, linear programming methods, principal objective methods, etc.), the core idea of ​​which is to first transform the multi-objective function into a single-objective function, and then use a single-objective optimization algorithm to solve the multi-objective optimization problem; the second is to use intelligent optimization algorithms (such as evolutionary algorithms, particle swarm optimization, etc.) to directly solve the multi-objective optimization problem. This invention uses the most common non-dominated sorting genetic algorithm with elitist strategy (NSGA-II) among many multi-objective intelligent optimization algorithms to solve the problem. The algorithm flowchart is as follows. Figure 5 As shown, the specific implementation steps are as follows:

[0094] (1) Set the maximum number of iterations.

[0095] (2) Set C initial current amplitude and phase decision vectors And use it as the initial parent population. in I min and I max Randomly distributed among them, Randomly distributed between -180° and 180° and Calculated according to equation (4). The current iteration number gen is set to 1.

[0096] (3) Generate a new generation of offspring populations using a genetic algorithm (selection, crossover, and mutation of the parent population). The number of individuals in the offspring population is also C.

[0097] (4) Merge the child population with the parent population. After merging, the population size becomes 2C.

[0098] (5) Perform non-dominated sorting on the merged population to generate a series of non-dominated sets, and calculate the crowding degree.

[0099] (6) Select individuals in descending order of non-dominated set hierarchy to form a new parent population. When the number of individuals in the population exceeds C after adding a non-dominated set of a certain level, compare the crowding of individuals in the non-dominated set and fill the new parent population with individuals with higher crowding until the population size reaches C.

[0100] (7) Determine whether the number of iterations exceeds the set maximum number. If yes, terminate the iteration and output the population. If no, then gen = gen + 1 and return to step (3) to perform the operations of steps (3)-(7).

[0101] The beneficial effects of this invention are:

[0102] 1. A method for determining the current of overhead three-phase transmission lines is proposed for the field of geophysics, which can provide a theoretical basis and technical guidance for the quantitative analysis and research of the power frequency electromagnetic response generated by power lines.

[0103] 2. The inversion process fully considers the design parameters and droop shape of actual overhead transmission lines, making the overhead three-phase transmission line model more realistic and greatly improving the accuracy of the results.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the current of an overhead three-phase transmission line based on geophysical data, characterized in that: include: S1: Investigate the underground dielectric electrical structure of the area where the overhead three-phase transmission line to be studied is erected, and confirm whether there is a large-scale low-resistivity electrical structure in the shallow part. If so, the geological model is a layered model with different resistivity considering the low-resistivity electrical structure. If not, the geological model is a uniform half-space model with different resistivity. S2: Measure and record the parameter information of the overhead three-phase transmission line; S3: Use the parameter information obtained in step S2 to model the overhead three-phase transmission line to obtain the overhead three-phase transmission line model. Combine it with the geological model established in step S1 to perform pre-forward modeling. Then, design magnetic field observation points based on the pre-forward modeling results. S4: Measure the magnetic field response of the overhead three-phase transmission line at each magnetic field observation point designed in step S3; S5: Using the measured magnetic field response data and the overhead three-phase transmission line model constructed in step S3, the current of the transmission line is inverted to obtain the final current of the overhead three-phase transmission line. In step S2, the parameter information includes the number of spans, the number of circuits, the number of splits of the overhead three-phase transmission line, the height and coordinates of the suspension points at both ends of each transmission line within each span and any point or points 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. In step S5, the optimization problem describing the inversion of the overhead three-phase transmission line current is expressed as: In an overhead three-phase transmission line with M circuits, the current loaded on any split sub-conductor of the q-th phase conductor in the m-th circuit is... Represented as: Where j is the imaginary unit, Let be the amplitude of the current applied to any split sub-conductor of any phase conductor in the m-th loop. Let be the phase of the current applied to any split sub-conductor of the q-th phase conductor in the m-th loop; and These are all decision variables in the inversion optimization process, because the phases of the three-phase conductors in each loop have the following relationship: The number of decision variables has been reduced to 2M. The objective function of the inversion optimization problem is set as follows: in, , , , There are four objective functions, where N is the total number of measurement points. and These represent the magnetic field strength amplitude calculated by forward modeling at measurement point n and the actual measured magnetic field strength amplitude, respectively. and These represent the phase of the magnetic field strength calculated by forward modeling at measurement point n and the phase of the magnetic field strength actually measured, respectively. (Subscripts are also provided.) and These represent the component perpendicular to the direction of the transmission line and the vertically downward component, respectively. The final optimization problem for inverting the current of an overhead three-phase transmission line is: And consider the constraints: in, and They are respectively The upper and lower limits.

2. The method for determining the current of an overhead three-phase transmission line based on geophysical data as described in claim 1, characterized in that: In step S2, a total station is used 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 or points 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.

3. The method for determining the current of an overhead three-phase transmission line based on geophysical data as described in claim 1, characterized in that: In step S3, the process of modeling the overhead three-phase transmission line based on the parameter information is as follows: For a single drooping split electric field line within each span of each phase conductor in each circuit, treat it as a catenary and transform its coordinates to... x O y In a plane, assuming the coordinates of the suspension points O and B at both ends of the catenary after transformation are respectively... and The equation of the catenary is then expressed as: In the formula, , 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: Then, the coordinates of the entire catenary are inversely transformed back to the original coordinate system to obtain the coordinates of each point on the power line.

4. The method for determining the current of an overhead three-phase transmission line based on geophysical data as described in claim 1, characterized in that: The method for calculating the electromagnetic response of the overhead three-phase transmission line model in step S3 pre-forward modeling is as follows: Each single drooping split power line in each phase of each circuit is divided into a finite number of straight sub-conductor segments in different directions. The electromagnetic response of a single sub-conductor segment is calculated using the open-source software Dipole1D. The electromagnetic response excited by the drooping split power line is approximately the superposition of the responses excited by each sub-conductor. Finally, the electromagnetic responses excited by the power lines in all spans of all three phases of all circuits are superimposed to obtain the total electromagnetic response excited by the entire transmission line.

5. The method for determining the current of an overhead three-phase transmission line based on geophysical data as described in claim 1, characterized in that: In step S4, a fluxgate magnetometer is used to measure the electromagnetic response.

6. The method for determining the current of an overhead three-phase transmission line based on geophysical data as described in claim 1, characterized in that: In step S4, the electromagnetic response includes a magnetic field component perpendicular to the direction of the transmission line and a magnetic field component perpendicularly downward.

7. The method for determining the current of an overhead three-phase transmission line based on geophysical data as described in claim 6, characterized in that: The process of solving the optimization problem of inverting the current of an overhead three-phase transmission line using a non-dominated sorting genetic algorithm with an elitist strategy is as follows: (1) Set the maximum number of iterations; (2) Settings C Initial current amplitude and phase decision vector And use it as the initial parent population, where, exist and Randomly distributed among them, Randomly distributed between -180° and 180° and According to equation (4), the current iteration number gen is set to 1; (3) Using a genetic algorithm, a new generation of offspring is generated, with the number of individuals in the offspring population also being... C ; (4) Merge the child population with the parent population. After merging, the population size becomes 2. C ; (5) Perform non-dominated sorting on the merged population to generate a series of non-dominated sets, and calculate the crowding degree; (6) Select individuals in descending order of non-dominated set hierarchy to form a new parent population; when a non-dominated set of a certain level is added, the number of individuals in the population exceeds... C If the population size reaches a certain threshold, then the crowding density of individuals in the non-dominant set is compared, and individuals with higher crowding density are added to the new parent population until the population size reaches a certain threshold. C ; (7) Determine whether the number of iterations exceeds the set maximum number. If yes, terminate the iteration and output the population; otherwise, gen = gen + 1 and return to step (3).

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