A method for optimizing lightning overvoltage in AC transmission lines converted to DC operation

Abstract

This invention discloses a method for optimizing lightning overvoltage in AC transmission lines converted to DC operation, comprising the following steps: analyzing the relevant configuration selection for long-span sections after the AC line is converted to DC operation, and determining the parameter selection range of the relevant configuration; establishing an electromagnetic transient simulation model of the DC-converted transmission line based on the determined parameter selection range of the relevant configuration; establishing a constraint model with the minimum lightning overvoltage of the transmission line in the span section as the objective function; calling the electromagnetic transient simulation model and the constraint model, and optimizing the lightning overvoltage of the long-span section line using an adaptive particle swarm optimization algorithm to obtain the minimum lightning overvoltage value of the AC transmission line converted to DC operation that meets the line insulation configuration requirements, thus filling the research gap in the changes of lightning overvoltage in transmission lines, especially in long-span sections, and the insulation coordination scheme of long-span sections after the DC conversion.

Description

Technical Field

[0001] This invention belongs to the field of power technology and relates to a method for optimizing lightning overvoltage of transmission lines, particularly a method for optimizing lightning overvoltage of AC transmission lines converted to DC operation. Background Technology

[0002] With the rapid growth in electricity demand, the relatively lagging investment in power transmission and distribution infrastructure has made it difficult for existing AC transmission lines to meet development requirements, with some lines nearing saturation. However, time, cost, and land resources limit the feasibility of building new transmission line corridors. DC transmission, compared to AC transmission, has the advantages of large transmission capacity and low losses. Converting AC lines to DC lines can significantly increase the transmission capacity of existing lines while substantially reducing construction investment, making it a promising application.

[0003] Converting AC transmission lines to DC operation can greatly alleviate the power shortage in some areas and help change the current situation of tight transmission corridors and increasingly serious electromagnetic coupling within the corridors. However, current research focuses more on capacity expansion schemes and DC transmission structures when converting AC to DC operation. There is still a lack of effective research on the changes in lightning overvoltage of transmission lines, especially long-span sections, and insulation coordination schemes for long-span sections after conversion to DC operation. Summary of the Invention

[0004] In view of the above-mentioned shortcomings in the prior art, the lightning overvoltage optimization method for converting AC transmission lines to DC operation provided by the present invention solves the problem that there is still a lack of effective research on the change of lightning overvoltage in long-span sections and the insulation coordination scheme of long-span sections.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for optimizing lightning overvoltage in AC transmission lines converted to DC operation is provided, comprising the following steps:

[0006] S1. Analyze the relevant configuration selection for long-span sections after the AC line is converted to DC operation, and determine the parameter selection range for the relevant configuration;

[0007] S2. Based on the determined parameter selection range of the relevant configuration, establish an electromagnetic transient simulation model of the modified DC transmission line;

[0008] S3. Establish a constraint model with the minimum lightning overvoltage of the crossing section of the transmission line as the objective function;

[0009] S4. Call the electromagnetic transient simulation model and constraint model, and optimize the lightning overvoltage of the long-span line using the adaptive particle swarm algorithm to obtain the minimum lightning overvoltage value of the AC transmission line converted to DC operation that meets the line insulation configuration requirements.

[0010] Further, step S1 includes the following sub-steps:

[0011] S11. Preliminarily determine the selection of insulators, conductors, and ground wires for DC operation of transmission lines, and the selection of lightning protection wires to match them, and complete the relevant configuration selection;

[0012] S12. Based on the relevant configuration selection, obtain the mechanical strength data and average operating stress value of the conductor and ground wire, and determine the lightning resistance requirements of the center of the line span.

[0013] S13. Based on the lightning resistance requirements of the center of the line span, the mechanical strength data of the conductor and ground wire, and the average operating stress value, determine the parameter selection range of the relevant configuration.

[0014] Further: In step S13, it is necessary to determine the parameter selection range for the relevant configuration, including the range of the number of insulator discs, the range of the distance between conductors and ground wires under DC operation, and the selection range of grounding resistance under DC operation; wherein, the specific method for determining the range of the number of insulator discs is as follows:

[0015] Calculate the DC-AC pollution accumulation ratio K of DC suspension insulators under the same average wind speed pollution accumulation conditions. p The specific formula is as follows:

[0016] K p =77.8(v*d) -1.06

[0017] Where v is the average wind speed during the period of pollution accumulation, and d is the particle size of the pollutants with a 50% probability of accumulation.

[0018] According to the DC / AC pollution accumulation ratio K of DC suspension insulators p The equivalent salt deposit density of insulators under AC operation was calculated to obtain the equivalent salt deposit density under DC voltage operation under the same operating conditions. The mathematical expression for this is:

[0019] ESDD DC =ESDD AC .K p

[0020] Among them, ESDD DC The equivalent salt deposition density of the charged DC reference insulator in the field is ESDD. AC The equivalent salt density on-site for energized AC reference insulators;

[0021] Using the reference specified in IEC 60507: at a given reference: ESDD DC Under these conditions, the artificial soiling tolerance voltage U was obtained by repeated experiments more than 10 times using the constant voltage rise and fall method. 50 The maximum fouling withstand voltage U was calculated from the artificial fouling withstand voltage obtained. w Its mathematical expression is:

[0022] U w =(1-3σ)U 50

[0023] Where σ is the standard deviation, which is a constant of 7%;

[0024] The number of suspension insulators M in DC operation is determined using the pollution withstand voltage method. The specific formula is as follows:

[0025]

[0026] Among them, U m This is the maximum voltage during system operation;

[0027] The method for determining the distance range between conductors and ground wires under DC operation is as follows:

[0028] Adjust the sag of the conductor and lightning protection wire, taking into account local temperature conditions. When the temperature is ±15℃ and there is no wind, the distance between the central conductor and the ground wire in the span must meet the requirement of S≥0.012L+1.5.

[0029] Where S is the distance between the conductor and the ground wire, and L is the span length, in meters;

[0030] The method for determining the selection range of grounding resistance under DC operation is as follows:

[0031] Determine the grounding resistance value based on soil resistivity:

[0032] When the soil resistivity is not greater than 100 Ω·m, the grounding resistance is selected as 10 Ω.

[0033] When the soil resistivity is greater than 100 Ω·m and not greater than 500 Ω·m, the grounding resistance should be 15 Ω.

[0034] When the soil resistivity is greater than 500 Ω·m but not greater than 1000 Ω·m, the grounding resistance should be 20 Ω.

[0035] When the soil resistivity is greater than 1000 Ω·m but not greater than 2000 Ω·m, the grounding resistance should be 25 Ω.

[0036] When the soil resistivity is greater than 2000 Ω·m, the grounding resistance should be 30 Ω.

[0037] Further: In step S2, the specific method for establishing the electromagnetic transient simulation model of the modified DC transmission line is as follows:

[0038] An electromagnetic transient simulation model of a lightning channel is established using a double exponential function, and its specific formula is as follows:

[0039] U t =A(e-at -e -bt )

[0040] Among them, U t Let A be the magnitude of the lightning current, a and b be the time constants related to the wavefront and wave tail, e be the natural constant, and t be the lightning current time.

[0041] The method for establishing the electromagnetic transient simulation model of the long-span tower is as follows: the tower is divided into crossarms of different heights, and the distortion of traveling waves with different wave impedances in different sections is simulated equivalently.

[0042] The method for establishing an electromagnetic transient simulation model of an overhead transmission line is as follows: In the LCC simulation module, input the required sets of parameter data for each actual line conductor, and the LCC module will automatically calculate and establish the model.

[0043] The method for establishing the electromagnetic transient simulation model of the air gap in an insulator is as follows: the electromagnetic transient simulation model of the air gap in an insulator is calculated using the volt-second characteristics of the air gap, and the specific formula is as follows:

[0044]

[0045] Among them, U b U is the flashover voltage. ∞ U0 is the flashover voltage when the wavefront time is long enough, U0 is the flashover voltage when the wavefront time is very short, and τ is the time constant when fitting the volt-second characteristic to a curve, which is taken as 8×10-7s.

[0046] Further: In step S3, the constraint model with the minimum lightning overvoltage of the crossing section transmission line as the objective function specifically includes: DC insulator length range constraint:

[0047] N min ≤N≤N max

[0048] Where N is the insulator length range, N max N min These are the set maximum and minimum values, respectively.

[0049] Grounding resistance range constraints:

[0050] R min ≤R≤R max

[0051] Where R is the grounding resistance of the tower, R max R min These are the set maximum and minimum values, respectively.

[0052] Distance range constraints between conductors and ground wires:

[0053] Smin ≤S≤S max

[0054] Where S is the distance between the conductor and ground wire of the transmission line, S max S min These are the set maximum and minimum values, respectively.

[0055] Calling simulation models in MATLAB:

[0056] U min =f(R,S,N)

[0057] Among them, U min This represents the minimum value of lightning overvoltage.

[0058] Furthermore, step S4 includes the following sub-steps:

[0059] S41. Call the constraint model and select a random number within the parameter constraint range as the initial position of the particle swarm.

[0060] S42. Call the electromagnetic transient simulation model of the modified DC transmission line, input the initial position of the particle swarm and run it to obtain the new positions of the particles and the particle swarm.

[0061] S43. Update the new position of the particle using adaptive inertia weights, and adjust the new position of the particle using a constraint model;

[0062] S44. Determine if the maximum number of iterations has been reached:

[0063] If so, proceed to step S45;

[0064] If not, return to step S42;

[0065] S45, the position of the output particle, serves as the minimum lightning overvoltage value to meet the line insulation configuration requirements.

[0066] Further: In step S43, the formula for calculating the adaptive inertia weight w is:

[0067]

[0068] Among them, T max w represents the maximum number of iterations. max For the maximum inertia weight, w min The minimum inertia weight is t, where t is the current iteration number.

[0069] The beneficial effects of this invention are as follows:

[0070] 1. By combining adaptive changes in weight coefficients, the adaptive changes in parameters can effectively balance local and global searches, solving the problem of difficulty in finding the global optimum caused by particle inertia and individual extrema in the later stages of iteration.

[0071] 2. By employing an adaptive particle swarm optimization algorithm, the lightning overvoltage method for transmission lines described in this invention achieves higher accuracy and better stability;

[0072] 3. It fills the research gaps in the study of changes in lightning overvoltage, especially in long-span sections, and insulation coordination schemes for long-span sections after the conversion to DC operation. Attached Figure Description

[0073] Figure 1 This is a flowchart of the lightning overvoltage optimization method described in this invention. Detailed Implementation

[0074] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0075] like Figure 1 As shown, in one embodiment of the present invention, the following steps are included:

[0076] S1. Analyze the relevant configuration selection for long-span sections after the AC line is converted to DC operation, and determine the parameter selection range for the relevant configuration;

[0077] S2. Based on the determined parameter selection range of the relevant configuration, establish an electromagnetic transient simulation model of the modified DC transmission line;

[0078] S3. Establish a constraint model with the minimum lightning overvoltage of the crossing section of the transmission line as the objective function;

[0079] S4. Call the electromagnetic transient simulation model of the modified DC transmission line and the constraint model with the minimum lightning overvoltage of the crossing section as the objective function. Optimize the lightning overvoltage of the long-span section line using the adaptive particle swarm optimization algorithm to obtain the minimum lightning overvoltage value of the AC transmission line converted to DC operation and its corresponding configuration parameters.

[0080] Step S1 in this embodiment includes the following sub-steps:

[0081] S11. Preliminarily determine the selection of insulators, conductors, and ground wires for DC operation of transmission lines, and the selection of lightning protection wires to match them, and complete the relevant configuration selection;

[0082] S12. Based on the relevant configuration selection, obtain the mechanical strength data and average operating stress value of the conductor and ground wire, and determine the lightning resistance requirements of the center of the line span.

[0083] S13. Based on the lightning resistance requirements of the center of the line span, the mechanical strength data of the conductor and ground wire, and the average operating stress value, determine the parameter selection range of the relevant configuration.

[0084] In step S13 of this embodiment, the parameter selection range for the relevant configuration needs to be determined, including the range of the number of insulator discs, the range of the distance between conductors and ground wires under DC operation, and the range of the grounding resistance under DC operation. Specifically, the method for determining the range of the number of insulator discs is as follows: Calculate the DC-AC pollution accumulation ratio K of the DC suspension insulator under the same average wind speed pollution accumulation conditions. p The specific formula is as follows:

[0085] K p =77.8(v*d) -1.06

[0086] Where v is the average wind speed during the period of pollution accumulation, and d is the particle size of the pollutants with a 50% probability of accumulation.

[0087] According to the DC / AC pollution accumulation ratio K of DC suspension insulators p The equivalent salt deposit density of insulators under AC operation was calculated to obtain the equivalent salt deposit density under DC voltage operation under the same operating conditions. The mathematical expression for this is:

[0088] ESDD DC =ESDD AC .K p

[0089] Among them, ESDD DC The equivalent salt deposition density of the charged DC reference insulator in the field is ESDD. AC The equivalent salt density on-site for energized AC reference insulators;

[0090] Using the reference specified in IEC 60507: at a given reference: ESDD DC Under these conditions, the artificial soiling tolerance voltage U was obtained by repeated experiments more than 10 times using the constant voltage rise and fall method. 50 The maximum fouling withstand voltage U was calculated from the artificial fouling withstand voltage obtained. w Its mathematical expression is:

[0091] U w =(1-3σ)U 50

[0092] Where σ is the standard deviation, which is a constant of 7%;

[0093] The number of suspension insulators M in DC operation is determined using the pollution withstand voltage method. The specific formula is as follows:

[0094]

[0095] Among them, U m This is the maximum voltage during system operation;

[0096] Due to the long spans and high towers of long-span transmission lines, the lightning resistance requirements are higher in the center of the span. DC lines should avoid lightning backflashover in the center of the span, therefore, a certain distance should be maintained between conductors and ground wires. Considering the lightning resistance requirements in the center of the span and the mechanical properties and strength of the conductors, a reasonable range for the distance between conductors and ground wires is determined. The method for determining the distance range between conductors and ground wires under DC operation is as follows:

[0097] Adjust the sag of the conductor and lightning protection wire, taking into account local temperature conditions. When the temperature is ±15℃ and there is no wind, the distance between the central conductor and the ground wire in the span must meet the requirement of S≥0.012L+1.5.

[0098] Where S is the distance between the conductor and the ground wire, and L is the span length, in meters;

[0099] The method for determining the selection range of grounding resistance under DC operation is as follows:

[0100] Determine the grounding resistance value based on soil resistivity:

[0101] When the soil resistivity is not greater than 100 Ω·m, the grounding resistance is selected as 10 Ω.

[0102] When the soil resistivity is greater than 100 Ω·m and not greater than 500 Ω·m, the grounding resistance should be 15 Ω.

[0103] When the soil resistivity is greater than 500 Ω·m but not greater than 1000 Ω·m, the grounding resistance should be 20 Ω.

[0104] When the soil resistivity is greater than 1000 Ω·m but not greater than 2000 Ω·m, the grounding resistance should be 25 Ω.

[0105] When the soil resistivity is greater than 2000 Ω·m, the grounding resistance should be 30 Ω.

[0106] In step S2 of this embodiment, the specific method for establishing the electromagnetic transient simulation model of the modified DC transmission line is as follows:

[0107] An electromagnetic transient simulation model of a lightning channel is established using a double exponential function. The specific formula is as follows:

[0108] U t =A(e -at-e -bt )

[0109] Among them, U t Let A be the magnitude of the lightning current, a and b be the time constants related to the wavefront and wave tail, e be the natural constant, and t be the lightning current time.

[0110] The method for establishing the electromagnetic transient simulation model of the long-span tower is as follows: the tower is divided into crossarms of different heights, and the distortion of traveling waves with different wave impedances in different sections is simulated equivalently.

[0111] The method for establishing an electromagnetic transient simulation model of an overhead transmission line is as follows: In the LCC simulation module, input the required sets of parameter data for each actual line conductor, and the LCC module will automatically calculate and establish the model.

[0112] The method for establishing the electromagnetic transient simulation model of the air gap in an insulator is as follows: the electromagnetic transient simulation model of the air gap in an insulator is calculated using the volt-second characteristics of the air gap, and the specific formula is as follows:

[0113]

[0114] Among them, U b U is the flashover voltage. ∞ U0 is the flashover voltage when the wavefront time is long enough, U0 is the flashover voltage when the wavefront time is very short, and τ is the time constant when fitting the volt-second characteristic to a curve, which is taken as 8×10-7s.

[0115] In step S3 of this embodiment, the constraint model with the minimum lightning overvoltage of the crossing section transmission line as the objective function specifically includes: DC insulator length range constraint:

[0116] N min ≤N≤N max

[0117] Where N is the insulator length range, N max N min These are the set maximum and minimum values, respectively.

[0118] Grounding resistance range constraints:

[0119] R min ≤R≤R max

[0120] Where R is the grounding resistance of the tower, R max R min These are the set maximum and minimum values, respectively.

[0121] Distance range constraints between conductors and ground wires:

[0122] S min≤S≤S max

[0123] Where S is the distance between the conductor and ground wire of the transmission line, S max S min These are the set maximum and minimum values, respectively.

[0124] Calling simulation models in MATLAB:

[0125] U min =f(R,S,N)

[0126] Among them, U min This represents the minimum value of lightning overvoltage.

[0127] In step S4 of this embodiment, there are the following sub-steps:

[0128] S41. Call the constraint model and select a random number within the parameter constraint range as the initial position of the particle swarm.

[0129] S42. Call the electromagnetic transient simulation model of the modified DC transmission line, input the initial position of the particle swarm and run it to obtain the new positions of the particles and the particle swarm.

[0130] S43. Update the new position of the particle using adaptive inertia weights, and adjust the new position of the particle using a constraint model;

[0131] S44. Determine if the maximum number of iterations has been reached:

[0132] If so, proceed to step S45;

[0133] If not, return to step S42;

[0134] S45, the position of the output particle, serves as the minimum lightning overvoltage value to meet the line insulation configuration requirements.

[0135] In step S43 of this embodiment, the formula for calculating the adaptive inertia weight w is:

[0136]

[0137] Among them, T max w represents the maximum number of iterations. max For the maximum inertia weight, w min The minimum inertia weight is t, where t is the current iteration number.

[0138] This is a linearly decreasing inertia weight, which can better balance global search and local search capabilities. Generally, w max Taking 0.9, a larger value for w is more beneficial for global search capabilities. minGenerally, a value of 0.4 is chosen. In the convergence state, a smaller value of w is more conducive to searching for the local optimum. Compared with constant inertia weight, adaptive inertia weight can better balance the search capability according to the number of iterations.

[0139] In the description of this invention, it should be understood that the terms "center," "thickness," "upper," "lower," "horizontal," "top," "bottom," "inner," "outer," and "radial," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying the relative importance or the number of technical features implicitly specified. Therefore, a feature defined by "first," "second," and "third" may explicitly or implicitly include one or more of that feature.

[0140] This invention provides a method for optimizing lightning overvoltage when converting AC transmission lines to DC operation, filling the research gap in the changes in lightning overvoltage, especially in long-span sections, and the insulation coordination schemes for long-span sections after the conversion to DC operation.

Claims

1. A method for optimizing lightning overvoltage of AC line operated in DC mode, characterized in that, Includes the following steps: S1. Analyze the relevant configuration selection for long-span sections after the AC line is converted to DC operation, and determine the parameter selection range for the relevant configuration; S2. Based on the determined parameter selection range, establish an electromagnetic transient simulation model for the modified DC transmission line; S3. Establish a constraint model with the minimum lightning overvoltage of the crossing section of the transmission line as the objective function; S4. Call the electromagnetic transient simulation model and constraint model, and optimize the lightning overvoltage of the long-span line using the adaptive particle swarm algorithm to obtain the minimum lightning overvoltage value of the AC transmission line converted to DC operation that meets the line insulation configuration requirements. In step S1 It includes the following steps: S11. Preliminarily determine the selection of insulators, conductors, and ground wires for DC operation of transmission lines, and complete the relevant configuration selection; S12. Based on the relevant configuration selection, obtain the mechanical strength data and average operating stress value of the conductor and ground wire, and determine the lightning resistance requirements of the center of the line span. S13. Based on the lightning resistance requirements of the center of the line span, the mechanical strength data of the conductor and ground wire, and the average operating stress value, determine the parameter selection range of the relevant configuration. The parameter selection range in step S13 includes the range of the number of insulator discs, the range of the distance between conductors and ground wires under DC operation, and the range of the grounding resistance under DC operation. The specific method for determining the range of the number of insulator discs is as follows: Calculate the DC-AC pollution accumulation ratio of DC suspension insulators under the same average wind speed pollution accumulation conditions. K p The specific formula is as follows: in, v The average wind speed during the period of sewage accumulation. d The particle size of contaminants with a cumulative probability of 50%; Based on the DC / AC pollution accumulation ratio of DC suspension insulators K p The equivalent salt deposit density of insulators under AC operation was calculated to obtain the equivalent salt deposit density under DC voltage operation under the same operating conditions. The mathematical expression for this is: in, The equivalent salt density on-site for a charged DC reference insulator. The equivalent salt density on-site for energized AC reference insulators; Using the reference specified in IEC 60507: Under these conditions, the artificial soiling tolerance voltage was obtained by repeated experiments more than 10 times using the constant voltage rise and fall method. The maximum fouling withstand voltage was calculated by obtaining the artificial fouling withstand voltage. Its mathematical expression is: Where σ is the standard deviation, which is a constant of 7%; The number of suspension string insulators for DC operation is determined using the pollution withstand voltage method. M The specific formula is as follows: in, This is the maximum voltage during system operation; The method for determining the distance range between conductors and ground wires under DC operation is as follows: Adjust the sag of the conductors and lightning protection wires, taking into account local temperature conditions. When the temperature is ±15℃ and there is no wind, adjust the distance between the central conductor and the ground wire in the span, and the distance between the conductor and the ground wire under DC operation. S satisfy ,in, L This refers to the distance between the gears. The method for determining the selection range of grounding resistance under DC operation is as follows: Determine the grounding resistance value based on soil resistivity: When the soil resistivity is not greater than 100 Ω·m, the grounding resistance is selected as 10 Ω. When the soil resistivity is greater than 100 Ω·m and not greater than 500 Ω·m, the grounding resistance should be 15 Ω. When the soil resistivity is greater than 500 Ω·m but not greater than 1000 Ω·m, the grounding resistance should be 20 Ω. When the soil resistivity is greater than 1000 Ω·m but not greater than 2000 Ω·m, the grounding resistance should be 25 Ω. When the soil resistivity is greater than 2000 Ω·m, the grounding resistance should be 30 Ω.

2. The method for optimizing lightning overvoltage when converting AC transmission lines to DC operation according to claim 1, characterized in that: In step S2, the method for establishing the electromagnetic transient simulation model of the modified DC transmission line is as follows: The electromagnetic transient simulation model of the lightning channel is established using a double exponential function, and the specific formula is: in, Where A is the magnitude of the lightning current, and A is the amplitude of the lightning current. a and b The time constant related to the wavefront and wavetail. e It is a natural constant. t For lightning current time; The method for establishing the electromagnetic transient simulation model of the long-span tower is as follows: the tower is divided into crossarms of different heights, and the distortion of traveling waves with different wave impedances in different sections is simulated equivalently. The method for establishing an electromagnetic transient simulation model of an overhead transmission line is as follows: In the LCC simulation module, input the required sets of parameter data for each actual line conductor, and the LCC module will automatically calculate and establish the model. The method for establishing the electromagnetic transient simulation model of the air gap in an insulator is as follows: the electromagnetic transient simulation model of the air gap in an insulator is calculated using the volt-second characteristics of the air gap, and the specific formula is as follows: in, This is the flashover voltage. This is the flashover voltage when the wavefront time is sufficiently long. This refers to the flashover voltage when the wavefront time is very short. The time constant for fitting the volt-second characteristic to a curve is taken as 8 × 10⁻⁷ s.

3. The method for optimizing lightning overvoltage when converting AC transmission lines to DC operation according to claim 2, characterized in that: In step S3, the constraint model uses the minimum lightning overvoltage of the crossing section transmission line as the objective function. ,in, This is the minimum value of lightning overvoltage. R The value of the tower grounding resistance. S The distance between the conductors and ground wires of the transmission line. N This is the length of the insulator; Insulator length N Range constraints: in, , These are the set maximum and minimum values, respectively. Tower grounding resistance R Range constraints: in, , These are the set maximum and minimum values, respectively. Distance between conductors and ground wires of transmission lines S Range constraints: in, , These are the set maximum and minimum values, respectively.

4. The method for optimizing lightning overvoltage in AC transmission lines converted to DC operation according to claim 3, characterized in that: Step S4 includes the following sub-steps: S41. Call the constraint model and select a random number within the parameter constraint range as the initial position of the particle swarm. S42. Call the electromagnetic transient simulation model of the modified DC transmission line, input the initial position of the particle swarm and run it to obtain the new positions of the particles and the particle swarm. S43. Update the new position of the particle using adaptive inertia weights, and adjust the new position of the particle using a constraint model; S44. Determine if the maximum number of iterations has been reached: If so, proceed to step S45; If not, return to step S42; S45, the position of the output particle, serves as the minimum lightning overvoltage value to meet the line insulation configuration requirements.

5. The method for optimizing lightning overvoltage when converting AC transmission lines to DC operation according to claim 4, characterized in that: In step S43, adaptive inertia weights w The calculation formula is: in, The maximum number of iterations, For maximum inertia weight, For minimum inertia weight, t This represents the current iteration number.

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