Method for improving and transforming ice resistance of power transmission line based on four-split conductor transformation and double-split

Abstract

The invention discloses a power transmission line ice resistance improving and transforming method based on four-split conductor transformation and double-split. The method comprises the steps that a line mechanical structure and electrical parameters needed in the power transmission line transforming process are collected; preliminarily selecting a modified double split conductor section according to an economic current density method; s2, verifying the selected wire cross section based on a heating condition, and if the heating verification is not passed, entering the step S2 again, and selecting a larger cross section; the diameter of the selected wire is verified based on the corona condition, and if the corona verification-free condition is not met, the corresponding corona inception field intensity Es is calculated to serve as the constraint condition in the step S5; based on mechanical and electrical safety constraint conditions, optimized design is carried out on the split spacing and the phase spacing of the remodeled wire; and S6, simulation verification of the ice resistance improvement effect after modification is carried out, and a new thought is provided for ultrahigh-voltage power transmission line wires in medium and heavy ice areas and structural form selection thereof through extraction of the lowest surface electric fields of different double-bundle conductor structural forms.

Description

Technical Field

[0001] This invention relates to the field of disaster prevention and mitigation technology for overhead transmission lines. More specifically, it relates to a method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors into double-split conductors. Based on relevant GB standards and mechanical and electrical safety constraints, the method optimizes the design of parameters such as conductor cross-section, split spacing, and phase spacing during the line modification process, providing a reference for the design of improving the anti-icing capability of ultra-high voltage transmission lines in medium and severe icing areas. Background Technology

[0002] In the field of power transmission, the design of overhead conductors is crucial for ensuring the stable operation of the power system. Especially in areas prone to icing, the conductors' anti-icing capability directly affects the reliability of power supply; traditional four-section overhead conductors face numerous challenges when dealing with icing conditions.

[0003] When encountering icy weather, due to the structural characteristics of the four-section conductor, each sub-conductor will adhere to the ice layer, resulting in a significant increase in the overall weight. The large amount of ice not only puts the conductor itself under huge gravitational load, but also increases the possibility of conductor galloping. This puts great pressure on the tower structure supporting the conductor, which can easily lead to serious accidents such as tower collapse, resulting in large-scale power outages and seriously affecting social production and life.

[0004] To improve the performance of overhead conductors in icing environments, changing from a four-phase to a two-phase configuration is a promising optimization approach. From a mechanical perspective, reducing the number of sub-conductors directly reduces the overall icing load on the conductor. Reduced icing on each phase conductor means a significant reduction in the vertical and horizontal loads acting on the towers, thereby improving tower stability and enhancing the overall transmission line's anti-icing capability under icing conditions. Furthermore, the two-phase configuration simplifies the conductor structure to some extent, reducing galloping caused by the complex aerodynamic interactions between multiple sub-conductors and lowering the risk of phase-to-phase short circuits and other faults due to conductor galloping.

[0005] In practical applications, for some transmission lines located in heavy icing areas, converting four-section conductors to two-section conductors can significantly improve the survivability of the lines under severe weather conditions. For example, in mountainous areas and other regions with complex terrain, variable climate, and a high risk of severe icing, using two-section conductors can effectively reduce the damage of ice storms to the transmission system and ensure a continuous power supply. Summary of the Invention

[0006] The purpose of this method is to propose a method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors. By artificially setting boundaries far from the solution domain, the open-domain problem is transformed into a finite-domain problem. Using the ANSYS finite element method platform and the proposed mathematical model for optimizing the split conductor structure, the optimal form of the double-split conductor structure is finally achieved, with the maximum electric field value on the conductor surface as the optimization index and the split spacing and phase spacing as optimization variables. This addresses the problem in ultra-high voltage transmission lines in medium- and severe icing areas where traditional four-split conductors experience a significant increase in overall weight and a higher probability of conductor galloping when iced, placing immense pressure on the tower structure and easily leading to serious accidents such as tower collapse and large-scale power outages. By modifying the four-split conductor to a double-split conductor, while ensuring electrical safety (meeting conditions such as heating and corona discharge), the structural parameters such as conductor split spacing and phase spacing are optimized, improving the anti-icing capability of the transmission line under icing and de-icing conditions, reducing the damage of ice disasters to the transmission system, and ensuring continuous power supply.

[0007] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows: a method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors into double-split conductors, comprising the following steps:

[0008] S1: Collect the mechanical structure and electrical parameters of the power transmission line required for the power transmission line renovation process;

[0009] S2: The cross section of the modified double-split conductor is initially selected according to the economic current density method;

[0010] S3: Verify the selected conductor cross-section based on the heating condition. If the heating check fails, re-enter step S2 and select a larger cross-section.

[0011] S4: Verify the selected conductor diameter based on corona conditions. If the corona exemption condition is not met, calculate the corresponding corona initiation field strength E. s As a constraint in step S5;

[0012] S5: Optimize the design of conductor splitting spacing and phase spacing based on mechanical and electrical safety constraints;

[0013] S6: Simulation verification of the improved ice resistance after modification.

[0014] Furthermore, the mechanical structural parameters of the line mentioned in step S1 include: the span length, elevation difference, and mechanical parameters of the conductor before modification of the line in the icing zone. The mechanical parameters of the conductor before modification include: actual cross-sectional area, elastic modulus, rated breaking force, and mass per unit length. The electrical parameters of the line include: rated voltage, maximum transmission power, economic current density, and rated power factor.

[0015] Furthermore, in step S2, the economic current density method uses the following economic current density formula to initially select the cross-section of the modified double-split conductor:

[0016]

[0017] In the formula: S is the cross-sectional area of ​​the conductor (mm²) 2 P is the maximum transmission power (kW); J is the economic current density (A / mm²). 2 );U N This is the line's rated voltage (kV).

[0018] Furthermore, the modified economic conductor cross section obtained from equation (1) needs to take into account the skin effect characteristics of steel-cored aluminum stranded wire. The aluminum cross section with low resistivity mainly plays the role of current carrying, while the mechanical load is mainly borne by the steel wire in the core. Therefore, the aluminum cross section of the selected conductor should be slightly larger than the economic cross-sectional area S calculated by equation (1.1). Combined with the current standard "GB / T1179-2017 Round Wire Concentric Stranded Overhead Conductor", the corresponding conductor cross section and its nominal cross-sectional area S1 can be determined.

[0019] Furthermore, in step S3, the following formula is used to verify whether the selected conductor cross-section meets the heating limitation condition:

[0020]

[0021] In the formula: S1 is the nominal cross-sectional area (mm²) of the conductor selected in step 1. 2 ); other parameters have the same meaning as in equation (1).

[0022] Furthermore, the specific verification method is as follows: I obtained from equation (2) max Given the operating current under maximum load, and referring to the standard "Calculation Method for Performance of Concentric Stranded Overhead Conductors", obtain the allowable current carrying capacity I corresponding to the nominal cross-sectional area S1. If I ≥ I max If the current is positive, it indicates that even if the conductor operates under the maximum load current for a long time, it is far below its allowable current carrying capacity, so the conductor cross-section can meet the requirements of the heating conditions; otherwise, re-enter step S2 to select a larger conductor cross-section.

[0023] Furthermore, in step S4, the following method is used to verify whether the selected cross-section meets the corona safety constraint conditions:

[0024] The "Design Code for 110kV~750kV Overhead Transmission Lines" provides a reference value for the minimum outer diameter of steel-cored aluminum stranded wires that do not require corona verification. If the wire selected in step S3 does not meet the verification exemption requirements shown in Table 1, the corresponding corona initiation field strength E can be calculated according to Pick's formula (3). s For optimization and verification in step S5:

[0025]

[0026] In the formula: δ is the relative density of air considering the local altitude; m is the surface roughness coefficient of the stranded wire; R is the outer radius of the conductor (cm).

[0027] Furthermore, in step S5, the following steps are used to optimize the design of the modified conductor splitting spacing B and phase spacing L1;

[0028] S51. Based on the aforementioned structural and electrical parameters of the line, establish the mechanical-electrical constraints regarding the conductor splitting distance B and phase spacing L1:

[0029] S52. Constructing a mathematical model for the optimization of split conductor structures:

[0030] The purpose of optimizing the split conductor structure is to find the splitting distance B and phase spacing L1 that minimize the maximum electric field value on the modified two-split surface. Based on optimization theory, the corresponding mathematical model can be expressed as follows:

[0031]

[0032] In the formula: E max is the maximum electric field strength on the conductor surface; B and L1 are design variables, parameters involved in structural optimization design; s i (B, L1) are the specific conditions involved in the above mechanical-electrical constraints;

[0033] S53. Solving the optimized model of the split conductor structure yields the split spacing B and phase spacing L1 of the modified conductor.

[0034] Furthermore, the solution to the optimization model of the S53 split conductor structure is as follows:

[0035] (1) Construction of a simplified two-dimensional finite element calculation model:

[0036] The two-dimensional cross-sectional model of the transmission line specifically includes three-phase overhead conductors, lightning protection wires, OPGW optical cable ground wires, the ground, and the surrounding air; however, to facilitate rapid simulation calculation and analysis, the following simplifications are made:

[0037] ①The earth is an infinitely large conductor surface with a potential of 0;

[0038] ② The conductor is an infinitely long, straight, smooth cylinder parallel to the ground, and the surface of the conductor is an equipotential surface;

[0039] ③ The influence of towers, fittings and nearby objects is ignored, as are the end effects and sag effects of conductors and lightning protection wires; the average height to ground is used when specifically calculating the surface electric field of conductors and ground wires.

[0040] ④ The power system frequency is 50Hz, which is in the very low frequency (ELF) range. The electromagnetic fields can be considered to be independent of each other and do not interfere with each other. Therefore, it can be further simplified to a quasi-electrostatic field problem, and its effects can be analyzed using the general concept of electrostatic field.

[0041] (2) Setting boundary conditions:

[0042] Geometric boundary conditions: For areas far from the solution domain, an open domain problem is transformed into a finite domain problem by artificially setting a boundary. For conventional high-voltage transmission lines, the inner boundary is selected as 60m and the outer boundary as 120m. The inner boundary is the solution domain, which is partitioned using quadratic triangular elements. The air layer between the inner and outer boundaries simulates an infinite region. Using infinite elements for partitioning can meet the accuracy requirements.

[0043] Electric field boundary conditions: In actual operating conditions, the voltage magnitude and phase within the three-phase conductors alternate with time. Therefore, when the voltage is given, the obtained electric field strength is the instantaneous value at a certain moment. Here, with a phase angle of 0° as the loading condition, the maximum surface electric field strength is obtained in the middle phase B. From this, the conductor potential distribution conditions in the calculation model can be determined as follows: the voltage of the middle phase B is the peak value. The voltages of phases A and C are The surface potential of the dual ground wires is 0;

[0044] (3) Solution method:

[0045] The improved gradient method built into ANSYS was used to perform sensitivity analysis of the surface electric field strength of the conductor with respect to the splitting distance B and the phase distance L1. When the sensitivity is less than 1%, it can be considered that it has converged to the optimal value.

[0046] Furthermore, in step S6, the following steps are used to simulate and verify the improvement in the anti-icing capability of the modified line:

[0047] S61: Based on the collected mechanical structure parameters of the transmission line, construct the corresponding tower-conductor-ground wire geometric models before and after the modification in ANSYS;

[0048] S62: Based on the "stretchable but not compressible" flexible cable characteristics of overhead lines, Link10 elements are selected as overhead line elements; based on the beam element characteristics of the main tower material and the truss rigidity of each component mainly bearing axial forces, a truss-beam hybrid finite element model of the transmission tower is constructed; and the calculation model of the overhead line tower-line coupling system is constructed through the CP coupling command.

[0049] S63: Perform form-finding analysis on the tower-line coupling system to obtain the stress and spatial distribution of the conductor and tower before and after the modification in the un-iced state;

[0050] S64: Based on the equivalent icing thickness of the selected line in the icy area, convert it into the corresponding icing density;

[0051] S65: Change the conductor density parameter to the linear density after icing, perform the corresponding static analysis, and obtain the stress and spatial distribution of the conductor and tower under icing conditions before and after the modification.

[0052] S66: Change the conductor density parameter from the linear density after icing to the bare conductor linear density before icing, conduct the corresponding transient analysis, and obtain the maximum de-icing jump height under 100%, 50%, and 10% de-icing conditions before and after the modification.

[0053] S67: Calculate the comprehensive vibration reduction rate Ri of the de-icing jump after the modification, as shown in the following formula (6).

[0054]

[0055] In the formula: i = 1, 2, 3 correspond to the three de-icing conditions of 100%, 50%, and 10%, respectively; H ai H represents the maximum jump height (m) under de-icing condition i after modification; bi The maximum jump height (m) is under de-icing condition i before the modification.

[0056] Compared with existing technologies, this invention has the following advantages: Based on the large-scale commercial finite element calculation platform ANSYS, and based on the mechanical and electrical safety constraints of split conductors clearly specified in the existing domestic GB standards, this invention analyzes the surface electric field distribution characteristics of conductors under different combinations of split spacing and phase spacing. By extracting the minimum surface electric field under different double-split conductor structural forms, a general method for obtaining the optimal structural form under given conditions is established, providing a new approach for the selection of conductors and their structural forms for ultra-high voltage transmission lines in medium and severe icy areas. Attached Figure Description

[0057] Figure 1 This is a flowchart of the present invention;

[0058] Figure 2 This is a schematic diagram of the calculation domain for the electric field in a two-dimensional cross section.

[0059] Figure 3 Flowchart for the optimized design of split conductor structures. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0062] like Figure 1 As shown, a method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors includes the following steps:

[0063] S1: Collect the mechanical structure and electrical parameters of the power transmission line required for the power transmission line renovation process;

[0064] S2: The cross section of the modified double-split conductor is initially selected according to the economic current density method;

[0065] S3: Verify the selected conductor cross-section based on the heating condition. If the heating check fails, re-enter step S2 and select a larger cross-section.

[0066] S4: Verify the selected conductor diameter based on corona conditions. If the corona exemption condition is not met, calculate the corresponding corona initiation field strength E. s As a constraint in step S5;

[0067] S5: Optimize the design of conductor splitting spacing and phase spacing based on mechanical and electrical safety constraints;

[0068] S6: Simulation verification of the improved ice resistance after modification.

[0069] In step S1, the mechanical structural parameters of the line include: the span length, elevation difference, and detailed parameters of the modified lead conductor (ground) of the line in the icing zone. The detailed parameters of the modified lead conductor (ground) include: actual cross-sectional area, elastic modulus, rated breaking force, mass per unit length, etc. The electrical parameters of the line include: rated voltage of the line, maximum transmission power of the line, economic current density, and rated power factor, etc.

[0070] In step S2, the cross-section of the modified double-split conductor is initially selected using the following economic current density formula:

[0071]

[0072] In the formula: S is the cross-sectional area of ​​the conductor (mm²) 2 P is the maximum transmission power (kW); J is the economic current density (A / mm²). 2 );U N This is the line's rated voltage (kV).

[0073] It should be further explained that the modified economic conductor cross section obtained by formula (1) needs to take into account the skin effect characteristics of steel-cored aluminum stranded wire (the aluminum cross section with low resistivity mainly plays the role of current carrying, while the mechanical load is mainly borne by the steel wire in the core). Therefore, the aluminum cross section (nominal cross section) of the selected conductor should be slightly larger than the economic cross-sectional area S calculated by formula (1.1). Combined with the current standard "GB / T1179-2017 Round Wire Concentric Stranded Overhead Conductor", the corresponding conductor cross section and its nominal cross-sectional area S1 can be determined.

[0074] In step S3, the following formula is used to verify whether the selected conductor cross-section meets the heating limitation condition:

[0075]

[0076] In the formula: S1 is the nominal cross-sectional area (mm²) of the conductor selected in step 1. 2 Other parameters have the same meaning as in equation (1);

[0077] The specific verification method is as follows: I obtained from equation (2) max Given the operating current under maximum load, and referring to the standard "Calculation Method for Performance of Concentric Stranded Overhead Conductors", the allowable current carrying capacity I corresponding to the nominal cross-sectional area S1 (at the highest long-term allowable operating temperature of 70℃ in my country) can be obtained. If I ≥ I max If the current is positive, it indicates that even if the conductor operates under the maximum load current for a long time, it is far below its allowable current carrying capacity, so the conductor cross-section can meet the requirements of the heating conditions; otherwise, re-enter step S2 to select a larger conductor cross-section.

[0078] In step S4, the following method is used to verify whether the selected cross-section meets the corona safety constraint conditions:

[0079] The "Design Code for 110kV~750kV Overhead Transmission Lines" provides reference values ​​for the minimum outer diameter of steel-cored aluminum stranded wires that do not require verification of corona conductors, as shown in Table 1 below.

[0080] Table 1 Minimum outer diameter of wires that do not require corona verification.

[0081]

[0082] If the conductor selected in step S3 does not meet the verification exemption requirements shown in Table 1, the corresponding corona initiation field strength E can be calculated according to Pick's formula (3). s For optimization and verification in step S5:

[0083]

[0084] In the formula: δ is the relative density of air considering the local altitude; m is the surface roughness coefficient of the stranded wire; R is the outer radius of the conductor (cm).

[0085] In step S5, the following steps are used to optimize the design of the modified conductor splitting spacing B and phase spacing L1;

[0086] like Figure 3 As shown, the optimization design process for the split conductor structure is as follows:

[0087] S51. Based on the aforementioned structural and electrical parameters of the line, establish the mechanical-electrical constraints regarding the conductor splitting distance B and phase spacing L1:

[0088] Mechanical-electrical constraint 1: Maintaining sufficient distance between split conductors can prevent secondary span oscillation. According to domestic and international research: when the ratio of the split spacing S0 to the diameter d of the sub-conductor is greater than 16, secondary span oscillation can be avoided; when it is less than 10, it is not advisable; when it is between 10 and 16, damping spacers must be installed to solve the problem.

[0089] Mechanical-Electrical Constraint 2: Protection angle of ground wire to side conductor on single-circuit towers in medium-ice zones: 330kV transmission lines and 220kV transmission lines with double ground wires should adopt about 15° - "DLT5440-2009 Technical Specification for Design of Overlapping Ice Overhead Transmission Lines";

[0090] Mechanical-Electrical Constraint 3: For spans shorter than 1000m, the horizontal distance D between lines should be calculated using the following formula – 《Design Code for 110kV~750kV Overhead Transmission Lines》

[0091]

[0092] In the formula: k i is the suspension insulator string coefficient; D is the horizontal distance between conductors (m); L is the length of the suspension insulator string (m); U is the nominal voltage of the system (kV); f c The maximum sag of the conductor is (m).

[0093] Mechanical-electrical constraint 4: Considering the cost of modification, without expanding the original tower structure, the phase spacing should be less than or equal to half of the crossarm span;

[0094] Mechanical-electrical constraint 5: The maximum electric field strength on the conductor surface is lower than the corona initiation field strength E. s (If the outer diameter does not meet the corona exemption requirements shown in Table 1).

[0095] S52. Constructing a mathematical model for the optimization of split conductor structures:

[0096] The purpose of optimizing the split conductor structure is to find the splitting distance B and phase spacing L1 that minimize the maximum electric field value on the modified two-split surface. Based on optimization theory, the corresponding mathematical model can be expressed as follows:

[0097]

[0098] In the formula: E max is the maximum electric field strength on the conductor surface; (B, L1) are design variables, parameters involved in structural optimization design; s i (B, L1) represents the specific conditions involved in the aforementioned mechanical-electrical constraints.

[0099] S53. Solving the optimization model of the split conductor structure:

[0100] (1) Construction of a simplified two-dimensional finite element calculation model:

[0101] Figure 2 A two-dimensional cross-sectional model of the transmission line is shown, which specifically includes the three-phase overhead conductors, lightning protection wires, OPGW optical cable ground wires, the earth, and the surrounding air. Detailed explanations of the parameters in the model are shown in Table 2 below.

[0102] Table 2 shows the meanings of each parameter.

[0103]

[0104] Meanwhile, to facilitate rapid simulation calculation and analysis, the following simplifications are made:

[0105] ①The earth is an infinitely large conductor surface with a potential of 0;

[0106] ② The conductor is an infinitely long, straight, smooth cylinder parallel to the ground, and the surface of the conductor is an equipotential surface;

[0107] ③ The influence of nearby objects such as towers and fittings is ignored, as are the end effects and sag effects of conductors and lightning protection wires. The average height to ground is used when calculating the surface electric field of conductors and ground wires.

[0108] ④ The power frequency of my country's power system is 50Hz, which is in the extremely low frequency (ELF) range. The electromagnetic fields can be considered to be independent of each other and do not interfere with each other. Therefore, it can be further simplified to a quasi-electrostatic field problem, and its effects can be analyzed using the general concept of electrostatic field.

[0109] (2) Setting boundary conditions:

[0110] Geometric boundary conditions: For areas far from the solution domain, an open domain problem is transformed into a finite domain problem by artificially setting a boundary. For conventional high-voltage transmission lines, the inner boundary is selected as 60m and the outer boundary as 120m. The inner boundary part is the solution domain, which is partitioned using quadratic triangular elements. The air layer between the inner and outer boundaries simulates an infinite region. Using infinite elements for partitioning can meet the accuracy requirements.

[0111] Electric field boundary conditions: In actual operating conditions, the magnitude and phase of the voltage in the three-phase conductors alternate with time. Therefore, when the voltage is given, the obtained electric field strength is the instantaneous value at a certain moment. Here, with a phase angle of 0° as the loading condition, the maximum surface electric field strength is obtained in the middle phase B. From this, the conductor potential distribution conditions in the calculation model can be determined as follows: the voltage of the middle phase B is the peak value. The voltages of phases A and C are The surface potential of the dual ground wire is 0.

[0112] (3) Solution method:

[0113] The improved gradient method built into ANSYS (the gradient is also known as sensitivity because it represents the relative change of the objective function to the change of the design variable) is used to perform sensitivity analysis of the surface electric field of the conductor with respect to the splitting spacing B and the phase spacing L1. When the sensitivity is less than 1%, it can be considered that it has converged to the optimal value.

[0114] In step S6, the following steps are used to simulate and verify the improvement in the anti-icing capability of the modified line:

[0115] S61: Based on the collected mechanical structure parameters of the transmission line, construct the corresponding tower-conductor-ground wire geometric models before and after the modification in ANSYS;

[0116] S62: Based on the "stretchable but not compressible" flexible cable characteristics of overhead lines, Link10 elements are selected as overhead line elements; based on the beam element characteristics of the main tower material and the truss rigidity of each component mainly bearing axial forces, a truss-beam hybrid finite element model of the transmission tower is constructed; and the calculation model of the overhead line tower-line coupling system is constructed through the CP coupling command.

[0117] S63: Perform form-finding analysis on the tower-line coupling system to obtain the stress and spatial distribution of the conductor and tower before and after the modification in the un-iced state;

[0118] S64: Based on the equivalent icing thickness of the selected line in the icy area, convert it into the corresponding icing density;

[0119] S65: Change the conductor density parameter to the linear density after icing, perform the corresponding static analysis, and obtain the stress and spatial distribution of the conductor and tower under icing conditions before and after the modification.

[0120] S66: Change the conductor density parameter from the linear density after icing to the bare conductor linear density before icing, conduct the corresponding transient analysis, and obtain the maximum de-icing jump height under 100%, 50%, and 10% de-icing conditions before and after the modification.

[0121] S67: Calculate the comprehensive vibration reduction rate Ri of the de-icing jump after the modification, as shown in the following formula (6).

[0122]

[0123] In the formula: i = 1, 2, 3 correspond to the three de-icing conditions of 100%, 50%, and 10%, respectively; H ai H represents the maximum jump height (m) under de-icing condition i after modification; bi The maximum jump height (m) is under de-icing condition i before the modification.

[0124] 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 or improvements 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 improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors, characterized in that: Includes the following steps: S1: Collect the mechanical structure and electrical parameters of the power transmission line required for the power transmission line renovation process; S2: The cross section of the modified double-split conductor is initially selected according to the economic current density method; S3: Verify the selected conductor cross-section based on the heating condition. If the heating check fails, re-enter step S2 and select a larger cross-section. S4: Verify the selected conductor diameter based on corona conditions. If the corona exemption condition is not met, calculate the corresponding corona initiation field strength E. s As a constraint in step S5; S5: Optimize the design of conductor splitting spacing and phase spacing based on mechanical and electrical safety constraints; S6: Simulation verification of the improved ice resistance after modification.

2. The method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors according to claim 1, characterized in that: The mechanical structural parameters of the line in step S1 include: the span length, elevation difference, and mechanical parameters of the conductor before modification of the line in the icing zone. The mechanical parameters of the conductor before modification include: actual cross-sectional area, elastic modulus, rated breaking force, and mass per unit length. The electrical parameters of the line include: rated voltage, maximum transmission power, economic current density, and rated power factor.

3. The method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors according to claim 1, characterized in that: In step S2, the economic current density method uses the following economic current density formula to initially select the cross-section of the modified double-split conductor: In the formula: S is the cross-sectional area of ​​the conductor (mm²) 2 P is the maximum transmission power (kW); J is the economic current density (A / mm²). 2 );U N This is the line's rated voltage (kV).

4. The method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors according to claim 3, characterized in that: The modified economic conductor cross section obtained from equation (1) needs to further consider the skin effect characteristics of steel-cored aluminum stranded wire. The aluminum cross section with low resistivity mainly plays the role of current carrying, while the mechanical load is mainly borne by the steel wire in the core. Therefore, the aluminum cross section of the selected conductor should be slightly larger than the economic cross-sectional area S calculated by equation (1.1). Combined with the current standard "GB / T1179-2017 Round Wire Concentric Stranded Overhead Conductor", the corresponding conductor cross section and its nominal cross-sectional area S1 can be determined.

5. The method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors according to claim 4, characterized in that: In step S3, the following formula is used to verify whether the selected conductor cross-section meets the heating limitation condition: In the formula: S1 is the nominal cross-sectional area (mm²) of the conductor selected in step 1. 2 ); other parameters have the same meaning as in equation (1).

6. The method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors according to claim 5, characterized in that: The specific verification method is as follows: I obtained from equation (2) max Given the operating current under maximum load, and referring to the standard "Calculation Method for Performance of Concentric Stranded Overhead Conductors", obtain the allowable current carrying capacity I corresponding to the nominal cross-sectional area S1. If I ≥ I max This indicates that even if the conductor operates under the maximum load current for a long time, it is still far below its allowable current carrying capacity, so the conductor cross-section can meet the requirements of the heating conditions. Otherwise, re-enter step S2 to select a larger conductor cross-section.

7. The method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors according to claim 1, characterized in that: In step S4, the following method is used to verify whether the selected cross-section meets the corona safety constraint conditions: The "Design Code for 110kV~750kV Overhead Transmission Lines" provides a reference value for the minimum outer diameter of steel-cored aluminum stranded wire that does not require corona verification. If the wire selected in step S3 does not meet the exemption requirements shown in Table 1, the corresponding corona initiation field strength E can be calculated according to Pick's formula (3). s For optimization and verification in step S5: In the formula: δ is the relative density of air considering the local altitude; m is the surface roughness coefficient of the stranded wire; R is the outer radius of the conductor (cm).

8. The method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors according to claim 1, characterized in that: In step S5, the following steps are used to optimize the design of the modified conductor splitting spacing B and phase spacing L1; S51. Based on the aforementioned structural and electrical parameters of the line, establish the mechanical-electrical constraints regarding the conductor splitting distance B and phase spacing L1: S52. Constructing a mathematical model for the optimization of split conductor structures: The purpose of optimizing the split conductor structure is to find the splitting distance B and phase spacing L1 that minimize the maximum electric field value on the modified two-split surface. Based on optimization theory, the corresponding mathematical model can be expressed as follows: In the formula: E max is the maximum electric field strength on the conductor surface; (B, L1) are design variables, parameters involved in structural optimization design; s i (B, L1) are the specific conditions involved in the above mechanical-electrical constraints; S53. Solving the optimized model of the split conductor structure yields the split spacing B and phase spacing L1 of the modified conductor.

9. A method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors, as described in claim 8, is characterized in that: Solution of the S53 split conductor structure optimization model: (1) Construction of a simplified two-dimensional finite element calculation model: The two-dimensional cross-sectional model of the transmission line specifically includes three-phase overhead conductors, lightning protection wires, OPGW optical cable ground wires, the ground, and the surrounding air; however, to facilitate rapid simulation calculation and analysis, the following simplifications are made: ①The earth is an infinitely large conductor surface with a potential of 0; ② The conductor is an infinitely long, straight, smooth cylinder parallel to the ground, and the surface of the conductor is an equipotential surface; ③ Ignore the influence of nearby objects on towers and fittings, and ignore the end effects and sag effects of conductors and lightning protection wires; when specifically calculating the surface electric field of conductors and ground wires, use the average height to ground; ④ The power system frequency is 50Hz, which is in the very low frequency (ELF) range. The electromagnetic fields can be considered to be independent of each other and do not interfere with each other. Therefore, it can be further simplified to a quasi-electrostatic field problem, and its effects can be analyzed using the general concept of electrostatic field. (2) Setting boundary conditions: Geometric boundary conditions: For areas far from the solution domain, an open domain problem is transformed into a finite domain problem by artificially setting a boundary. For conventional high-voltage transmission lines, the inner boundary is selected as 60m and the outer boundary as 120m. The inner boundary is the solution domain, which is partitioned using quadratic triangular elements. The air layer between the inner and outer boundaries simulates an infinite region. Using infinite elements for partitioning can meet the accuracy requirements. Electric field boundary conditions: In actual operating conditions, the voltage magnitude and phase within the three-phase conductors alternate with time. Therefore, when the voltage is given, the obtained electric field strength is the instantaneous value at a certain moment. Here, with a phase angle of 0° as the loading condition, the maximum surface electric field strength is obtained in the middle phase B. From this, the conductor potential distribution conditions in the calculation model can be determined as follows: the voltage of the middle phase B is the peak value. The voltages of phases A and C are The surface potential of the dual ground wires is 0; (3) Solution method: The improved gradient method built into ANSYS was used to perform sensitivity analysis of the surface electric field strength of the conductor with respect to the splitting distance B and the phase distance L1. When the sensitivity is less than 1%, it can be considered that it has converged to the optimal value.

10. The method for improving the anti-icing capability of transmission lines based on the modification of four-split conductors to double-split conductors according to claim 9, characterized in that: In step S6, the following steps are used to simulate and verify the improvement in the anti-icing capability of the modified line: S61: Based on the collected mechanical structure parameters of the transmission line, construct the corresponding tower-conductor-ground wire geometric models before and after the modification in ANSYS; S62: Based on the "stretchable but not compressible" flexible cable characteristics of overhead lines, Link10 element is selected as the overhead line element; based on the beam element characteristics of the main tower material and the truss rigidity of each component mainly bearing axial force, a truss-beam hybrid transmission tower finite element model is constructed; and the calculation model of the overhead line tower-line coupling system is constructed through the CP coupling command. S63: Perform form-finding analysis on the tower-line coupling system to obtain the stress and spatial distribution of the conductor and tower before and after the modification in the un-iced state; S64: Based on the equivalent icing thickness of the selected line in the icy area, convert it into the corresponding icing density; S65: Change the conductor density parameter to the linear density after icing, perform the corresponding static analysis, and obtain the stress and spatial distribution of the conductor and tower under icing conditions before and after the modification. S66: Change the conductor density parameter from the linear density after icing to the bare conductor linear density before icing, conduct the corresponding transient analysis, and obtain the maximum de-icing jump height under 100%, 50%, and 10% de-icing conditions before and after the modification. S67: Calculate the comprehensive vibration reduction rate Ri of the de-icing jump after the modification, as shown in the following formula (6); In the formula: i = 1, 2, 3 correspond to the three de-icing conditions of 100%, 50%, and 10%, respectively; H ai H represents the maximum jump height (m) under de-icing condition i after modification; bi The maximum jump height (m) is under de-icing condition i before the modification.

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