Method for improving shielding lightning protection performance of line in single-loop alternating-current to direct-current scene

Abstract

The invention relates to the technical field of lightning protection of high-voltage transmission lines, in particular to a method for improving shielding failure lightning protection performance of a line in a single-loop alternating-current to direct-current scene, which comprises the following steps of: configuring positive and negative leads and a return line of a direct-current line by utilizing three lead channels of an original alternating-current line tower, the configuration of the positive and negative wires and the return wire of the DC line comprises the following steps: determining three candidate arrangement modes of the wires: the return wire is located in a tower window, the positive wire is located in the tower window, and the negative wire is located in the tower window; based on the statistical characteristic that 90% of thunder and lightning is negative polarity, shielding failure flashover rates of the direct-current line in the three candidate arrangement modes are calculated by combining shielding failure differences of positive and negative thunder and lightning on the direct-current line; according to the shielding failure flashover rate, the arrangement mode with the lowest shielding failure flashover frequency is screened to serve as the shielding failure lightning prevention optimal wire arrangement scheme in the single-loop alternating-to-direct scene, and the excellent shielding failure lightning prevention effect can be achieved under the condition that an existing iron tower structure does not need to be changed.

Description

Technical Field

[0001] This application relates to the field of lightning protection technology for high-voltage transmission lines, and in particular to a method for improving the lightning protection performance of a line in a single-circuit AC-to-DC conversion scenario. Background Technology

[0002] With economic and social development, the conflict between power grid construction and land resources has become increasingly prominent. Making full use of existing transmission line corridors and improving transmission capacity through AC-to-DC conversion designs is of paramount importance. However, due to the long transmission distances of DC transmission lines, crossing areas with intense lightning activity is unavoidable, and lightning strikes are one of the main causes of DC transmission line failures.

[0003] Current research on improving the lightning protection performance of DC transmission lines only considers improving the ground wire protection angle, installing surge arresters, increasing insulator length, and lightning gaps. In reality, all of these technical measures come at the cost of increased engineering investment. Especially in the scenario of AC-to-DC conversion, the upgraded DC line is limited by the original AC line itself and external conditions, thus limiting the scope and effectiveness of improving lightning protection performance.

[0004] Therefore, this paper selects a single-circuit AC-to-DC conversion scenario and proposes a method to improve the lightning protection performance of DC lines against lightning strikes without changing the original transmission tower structure or increasing investment.

[0005] However, existing technologies still have the following problems:

[0006] Existing methods for improving the lightning protection performance of DC lines all require changes to the line structure or the addition of equipment, which leads to increased engineering investment. Especially in the case of AC-to-DC conversion, the implementation effect and scope of such measures are limited by the original line conditions, making it difficult to effectively improve lightning protection performance without increasing costs. Summary of the Invention

[0007] Therefore, this invention provides a method for improving the lightning protection performance of a line in a single-circuit AC-to-DC conversion scenario. This method overcomes the problem that existing methods for improving the lightning protection performance of DC lines all require changes to the line structure or the addition of equipment, leading to increased engineering investment. Especially in the AC-to-DC conversion scenario, the implementation effect and scope of such measures are limited by the existing line conditions, making it difficult to effectively improve lightning protection performance without increasing costs.

[0008] To achieve the above objectives, this invention provides a method for improving the lightning protection performance of power lines in a single-circuit AC-to-DC conversion scenario. The method includes:

[0009] Step S1: Using the three conductor channels of the original AC line tower, configure the positive and negative conductors and return line of the DC line. The configuration of the positive and negative conductors and return line of the DC line includes: determining three candidate arrangement methods of the conductors, namely, the return line is located inside the tower window, the positive conductor is located inside the tower window, and the negative conductor is located inside the tower window.

[0010] Step S2: Based on the statistical characteristic that 90% of lightning is negative polarity, and combined with the difference in the impact of positive and negative lightning on DC lines, calculate the flashover rate of DC lines under the three candidate arrangement methods.

[0011] Step S3: Select the arrangement with the lowest number of lightning strikes based on the lightning strike rate, and use it as the optimal conductor arrangement scheme for lightning protection against lightning strikes in a single-circuit AC-to-DC conversion scenario.

[0012] Furthermore, in step S1, the three conductor channels of the original AC line tower are utilized, including:

[0013] The original AC line tower's three conductor channels correspond to the positive conductor channel, negative conductor channel, and return line channel of the modified DC line, respectively, and the channel positions correspond one-to-one with the middle phase and side phase positions of the original AC line.

[0014] Furthermore, in step S3, based on the statistical characteristic that 90% of lightning is of negative polarity, the following is included:

[0015] Set the proportion of negative polarity lightning β=90% and the proportion of positive polarity lightning 1-β=10%. When calculating the flashover rate, the contribution of negative polarity lightning corresponding to β and the contribution of positive polarity lightning corresponding to 1-β are respectively included.

[0016] Further, in step S3, the flashover rate of the DC line under the three candidate arrangement methods is calculated using the EGM electrical geometry model, including:

[0017] Step S31: Input conductor and ground wire information, insulator string information and tower information to determine the geometric parameters of the EGM model;

[0018] Step S32: Consider the influence of the working voltage of the positive and negative poles of the DC line on the strike distance of the conductor, distinguish the instantaneous value of the working voltage on the positive and negative pole conductors from the lightning current, and determine the strike distance of the lightning on the positive and negative pole conductors.

[0019] Step S33: Based on the geometric function relationship between the grounding distance, conductor distance, and earthing distance and the lightning current, calculate the minimum lightning current value I for the positive and negative conductors respectively. min With the maximum winding conductor current I max ;

[0020] Step S34, combined with the line lightning withstand level I c The flashover rate SFFOR is calculated by integration.

[0021] Further, in the step S31, the conductor information includes: the outer diameter of the conductor, the hanging point position of the conductor, and the sag of the conductor; the insulator string information includes: the length of the insulator string and the flashover voltage of the insulator string; the tower information includes: the height of the tower cross arm, the equivalent radius of the tower body, and the width of the tower cross arm.

[0022] Further, in the step S34, by combining the lightning withstand level I c , the shielding failure flashover rate SFFOR is calculated by integral, including:

[0023] If Imin < Ic < Imax, the shielding failure flashover rate is calculated according to the following formula:

[0024] ;

[0025] where SFFOR is the shielding failure flashover rate, Ng is the ground flash density, P(I) is the probability density of lightning current amplitude, Z s is the ground projection distance of the exposed arc, Ic is the lightning withstand level of the transmission line, is the maximum current for shielding failure to strike the conductor, is the minimum lightning current value;

[0026] If Ic < Imin < Imax, the shielding failure flashover rate is calculated according to the following formula:

[0027] .

[0028] Further, the step S3 further includes: calculating the number of shielding failure flashovers, and the specific formula is:

[0029] N = N s η[β×SFFOR’+(1-β)×SFFOR’’];

[0030] where N is the number of shielding failure flashovers per 100 km per year, Ns is the number of lightning strikes per 100 km per year, η is the probability of arc formation for insulator lightning flashover, SFFOR' is the shielding failure flashover rate for negative lightning strikes, SFFOR'' is the shielding failure flashover rate for positive lightning strikes, is the proportion of negative lightning.

[0031] Further, in the step S4, the specific criteria for the optimal conductor arrangement scheme for shielding failure prevention in the single-circuit AC to DC conversion scenario are:

[0032] Compare the N values corresponding to the three candidate arrangement methods, and select the arrangement method with the smallest N value as the optimal scheme;

[0033] If the difference between the N values of the two arrangement methods is less than 5%, the arrangement method with the positive conductor located inside the tower window is preferentially selected.

[0034] Furthermore, in step S4, the optimal conductor arrangement scheme for preventing lightning strikes is as follows: the positive conductor of the DC line is arranged in the middle phase position of the original AC line, and the negative conductor of the DC line and the return line are arranged in the two side phase positions of the original AC line respectively.

[0035] Furthermore, in step S3, when calculating the flashover rate, the operating voltage of the return line is zero, and the strike distance of the return line is calculated based on zero voltage, which is the same as the strike distance to ground.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows: the positive conductor of the DC line is arranged in the middle phase position of the original AC line inside the tower window, and the negative conductor and return line of the DC line are arranged in the side phase positions of the original AC line. At the same time, the flashover rate is calculated by comprehensively considering the influence of positive and negative lightning to accurately evaluate the lightning protection effect of the two conductors of the DC line. This method does not require changing the original tower structure and can be directly implemented on the AC line towers undergoing AC-to-DC conversion. It can improve the line's lightning protection performance without increasing the investment in the conversion.

[0037] Furthermore, by precisely mapping the positive, negative, and return lines of the DC system to the original three AC channels, this invention avoids the need for tower structure modification, reinforcement, or reconstruction to adapt to new lines, reducing civil engineering and material costs, shortening the construction period, and achieving a comprehensive improvement in line transmission capacity and performance at the lowest possible modification cost. Since the positive conductor is at the highest risk in negative polarity thunderstorms, placing it in the most protected position can significantly reduce the flashover rate of the entire DC circuit at the system level, thereby directly improving the operational safety and power supply reliability of the line in lightning-prone areas.

[0038] Furthermore, by introducing key natural statistical parameters and a refined calculation model that conforms to the physical characteristics of DC, this invention improves the accuracy of lightning protection analysis, thereby providing an indispensable theoretical basis and core technical means for achieving optimal lightning protection performance with zero additional cost in AC-to-DC conversion projects.

[0039] Furthermore, this invention incorporates over ten key geometric and electrical parameters, including conductor outer diameter, hanging point location, sag, insulator string parameters, and detailed tower dimensions, to establish a refined, digital three-dimensional model that perfectly corresponds to the actual line in the lightning protection analysis for AC-to-DC conversion. This significantly improves the reliability and guiding value of the evaluation results. The risk of lightning strikes is not fixed but dynamically changes with the magnitude of the lightning current. By calculating the risk integral from the minimum lightning strike current I_min to the maximum lightning strike current I_max, the probability distribution of lightning strikes of different intensities is accurately captured. The invention clearly distinguishes between two scenarios for calculation, accurately determining the critical lightning current range leading to insulation flashover, providing a theoretical basis for differentiated protection strategies. By calculating I_min and I_max for the positive and negative conductors respectively, the invention achieves independent and accurate quantification of the lightning strike risk of the two conductors, providing crucial data support for systematically reducing loop risk through optimized arrangement. In AC-to-DC conversion projects, this invention provides reliable, accurate, and quantifiable core technical support for optimizing lightning protection performance without altering the tower structure.

[0040] Furthermore, this invention transforms the abstract flashover rate into the number of flashovers per 100 kilometers per year (N), making the lightning protection performance evaluation results more intuitive, measurable, and easy to compare across different line schemes, providing the most direct and clear basis for engineering decisions. By optimizing conductor arrangement to improve lightning protection performance, the N value calculated by this formula is the core indicator for measuring the optimization effect. By comparing the N values ​​under three candidate arrangement methods, the optimal scheme that minimizes the overall flashover risk of the line can be scientifically and objectively selected. This invention comprehensively considers multiple factors such as lightning current amplitude probability, lightning polarity, topography, and insulation level, and its predicted flashover number is closer to the actual operating performance after the line is put into operation. This provides accurate data support for power grid operation and maintenance departments to predict line risks and formulate scientific lightning protection operation and maintenance strategies.

[0041] Furthermore, this invention directly compares the quantitative index N value and selects the scheme with the smallest N value. When the calculation results of the two schemes are very close, their slight differences may already be within the range of model calculation error. Since 90% of lightning is negative polarity, and negative polarity lightning poses the greatest threat to positive polarity conductors, placing the positive polarity conductor within the tower window with the best shielding effect (the original middle phase position) is the optimal choice from the perspective of systemic risk control. This ensures that even when there are slight uncertainties in theoretical calculations, the highest-risk component can be proactively placed in the safest position, thereby optimizing the overall lightning protection performance of the system. By spatially rearranging the conductors, placing the most vulnerable target (positive polarity conductor) in the most robust shelter (within the tower window), it achieves the optimal allocation of lightning protection resources at zero cost. Attached Figure Description

[0042] Figure 1 This is a calculation flowchart of the method for improving the line's anti-flashover lightning performance in a single-circuit AC-to-DC conversion scenario according to an embodiment of this application;

[0043] Figure 2 This is a schematic diagram of the electrical geometry model of a DC line lightning strike protection system in the method for improving line protection against lightning strikes in a single-circuit AC-to-DC conversion scenario according to an embodiment of this application.

[0044] Figure 3 This is a structural schematic diagram of the arrangement of DC line pole conductors in a single-circuit AC-to-DC conversion scenario, which is part of the method for improving line anti-surge lightning performance in a single-circuit AC-to-DC conversion scenario according to an embodiment of this application.

[0045] In the diagram, 1 is the tower; 2 is the side phase support; 3 is the tower window; 4 is the return line; 5 is the negative conductor; and 6 is the positive conductor. Detailed Implementation

[0046] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0047] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0048] Please see Figures 1-3 As shown, Figure 1 This is a calculation flowchart of the method for improving the line's anti-flashover lightning performance in a single-circuit AC-to-DC conversion scenario according to an embodiment of this application; Figure 2 This is a schematic diagram of the electrical geometry model of a DC line lightning strike protection system in the method for improving line protection against lightning strikes in a single-circuit AC-to-DC conversion scenario according to an embodiment of this application. Figure 3 This is a structural schematic diagram of the arrangement of DC line pole conductors in a single-circuit AC-to-DC conversion scenario, which is part of the method for improving line anti-surge lightning performance in a single-circuit AC-to-DC conversion scenario according to an embodiment of this application.

[0049] The method for improving the line's protection against lightning strikes in a single-circuit AC-to-DC conversion scenario, as described in this application, includes:

[0050] Step S1, for the scenario of converting a single-circuit AC line into a DC line, utilize the three conductor channels of the original AC line tower to configure the positive and negative conductors and return line of the DC line, without changing the structure of the original AC line tower; wherein, configuring the positive and negative conductors and return line of the DC line includes: determining three candidate arrangement methods for the conductors, namely, the return line is located inside the tower window, the positive conductor is located inside the tower window, and the negative conductor is located inside the tower window;

[0051] Step S2: Based on the statistical characteristic that 90% of lightning is negative polarity, and combined with the difference in the impact of positive and negative lightning on DC lines, calculate the flashover rate of DC lines under the three candidate arrangement methods.

[0052] Step S3: Select the arrangement with the lowest number of lightning strikes based on the lightning strike rate, and use it as the optimal conductor arrangement scheme for lightning protection against lightning strikes in a single-circuit AC-to-DC conversion scenario.

[0053] This invention places the positive conductor of the DC line in the middle phase position of the original AC line inside the tower window, and places the negative conductor and return line of the DC line in the side phase positions of the original AC line. At the same time, it calculates the flashover rate by comprehensively considering the influence of positive and negative lightning to accurately evaluate the lightning protection effect of the two conductors of the DC line. This method does not require changing the original tower structure and can be directly implemented on AC line towers undergoing AC-to-DC conversion. It can improve the line's lightning protection performance without increasing the investment in the conversion.

[0054] Specifically, in step S1, the three conductor channels of the original AC line tower are utilized, including:

[0055] The original AC line tower's three conductor channels correspond to the positive conductor channel, negative conductor channel, and return line channel of the modified DC line, respectively, and the channel positions correspond one-to-one with the middle phase and side phase positions of the original AC line.

[0056] In this embodiment of the invention, a 500kV single-circuit AC transmission line is converted into a ±340kV DC line. The middle phase conductor channel of the original AC line is defined as the positive conductor channel of the converted DC line; the left phase conductor channel of the original AC line is defined as the negative conductor channel of the converted DC line; and the right phase conductor channel of the original AC line is defined as the return conductor channel of the converted DC line. The original three-phase AC conductors are removed, and the positive conductors of the ±340kV DC line are installed in the new positive conductor channel (original middle phase position); the negative conductors of the ±340kV DC line are installed in the new negative conductor channel (original left phase position); and the return conductor (or metal return conductor) of the DC system is installed in the new return conductor channel (original right phase position). Throughout the conversion process, the main structure, crossarm length, ground wire height, and position of the original AC line towers remain unchanged. Only the hardware and insulator strings of the conductors and ground wires are replaced as necessary to meet the requirements of DC electrical and mechanical performance.

[0057] This invention precisely maps the positive, negative, and return lines of the DC system to the original three AC channels, avoiding the need for tower structure modification, reinforcement, or reconstruction to adapt to new lines. This reduces civil engineering and material costs, shortens the construction period, and achieves a comprehensive improvement in line transmission capacity and performance at the lowest possible modification cost. Since the positive conductor is at the highest risk in negative polarity thunderstorms, placing it in the most protected position can significantly reduce the flashover rate of the entire DC circuit at the system level, thereby directly improving the operational safety and power supply reliability of the line in lightning-prone areas.

[0058] Specifically, in step S3, based on the statistical characteristic that 90% of lightning is negative polarity, the following is included:

[0059] Set the proportion of negative polarity lightning β=90% and the proportion of positive polarity lightning 1-β=10%. When calculating the flashover rate, the contribution of negative polarity lightning corresponding to β and the contribution of positive polarity lightning corresponding to 1-β are respectively included.

[0060] Specifically, in step S3, the flashover rate of the DC line under three candidate arrangement schemes is calculated using the EGM electrical geometry model, including:

[0061] Step S31: Input conductor and ground wire information, insulator string information and tower information to determine the geometric parameters of the EGM model;

[0062] Step S32: Consider the influence of the working voltage of the positive and negative poles of the DC line on the strike distance of the conductor, distinguish the instantaneous value of the working voltage on the positive and negative pole conductors from the lightning current, and determine the strike distance of the lightning on the positive and negative pole conductors.

[0063] Step S33: Based on the geometric function relationship between the grounding distance, conductor distance, and earthing distance and the lightning current, calculate the minimum lightning current value I for the positive and negative conductors respectively. min With the maximum winding conductor current I max ;

[0064] Step S34, combined with the line lightning withstand level I c The flashover rate SFFOR is calculated by integration.

[0065] This invention improves the accuracy of lightning protection analysis by introducing key natural statistical parameters and a refined calculation model that conforms to the physical characteristics of DC, thus providing an indispensable theoretical basis and core technical means for achieving optimal lightning protection performance with zero additional cost in AC-to-DC conversion projects.

[0066] Specifically, in step S31, the conductor and ground wire information includes: conductor and ground wire outer diameter, conductor and ground wire hanging point position, and conductor and ground wire sag; the insulator string information includes: insulator string length and insulator string flashover voltage; the tower information includes: tower crossarm height, tower body equivalent radius, and tower crossarm width.

[0067] Specifically, in step S34, by combining the lightning withstand level I of the line c , the shielding failure flashover rate SFFOR is calculated by integration, including:

[0068] If Imin < Ic < Imax, the shielding failure flashover rate is calculated by the following formula:

[0069] ;

[0070] where SFFOR is the shielding failure flashover rate, Ng is the ground flash density, P(I) is the probability density of lightning current amplitude, Z s is the ground projection distance of the exposed arc, Ic is the lightning withstand level of the transmission line, is the maximum current for shielding failure of the conductor, is the minimum lightning current value;

[0071] If Ic < Imin < Imax, the shielding failure flashover rate is calculated by the following formula:

[0072] .

[0073] In the embodiment of the present invention, an EGM electrical geometry model is established using geometric dimensions such as the suspension point positions of the conductor and ground wire, sag, insulator string length, cross-arm height, and cross-arm width. The lightning leader positioning position with a lightning current intensity of Ik is the curve CkAkBkDk. The arc segments CkAk and AkBk are arcs with the ground wire and conductor as the centers and the striking distance rsck of the conductor as the radius, and BkDk is a straight line parallel to the ground and with a height of the ground striking distance rsgk; the arc segment AkBk is the exposed arc segment of the transmission line, and a lightning strike located on AkBk will hit the conductor, Figure 2 where Dc is the exposed distance of the conductor. As the lightning current increases, the exposed arc segment becomes smaller and smaller. When it increases to a certain extent, the exposed arc is zero. As shown in Figure 2 , the lightning current corresponding to the curve CmAm(Bm)Dm is the maximum lightning current Imax that can cause shielding failure, and the corresponding striking distance is the maximum striking distance rmax. At this time, the conductor is completely shielded, that is, no more shielding failure occurs.

[0074] In the embodiment of the present invention, considering the influence of the positive and negative working voltages of the DC line on the striking distance of the conductor, the difference in shielding failure is distinguished between positive and negative. The instantaneous value of the working voltage on the conductor is , and the lightning current is . The striking distance of the lightning to the conductor with a working voltage thereon is determined by the following formula:

[0075] ;

[0076] According to the striking distance of the ground wire , the striking distance of the conductor and the striking distance to the ground and the geometric function relationship with the lightning current , respectively calculate the minimum lightning current values of the positive and negative conductors and the maximum shielding failure current .

[0077] Assume that Zs is the ground projection distance of the exposed arc, the probability density of the lightning current amplitude, the shielding failure flashover rate per 100 km per year for DC lines Then it can be calculated according to the following formula:

[0078] If Imin < Ic < Imax, the upper and lower limits of the integral for calculating the shielding failure flashover probability are taken as Ic and Imax, that is:

[0079] ;

[0080] If Ic < Imin < Imax, the upper and lower limits in the calculation formula are taken as Imin and Imax, that is:

[0081] ;

[0082] Among them, SFFOR is the shielding failure flashover rate, Ic is the lightning withstand level of the transmission line, is the minimum lightning current value, is the maximum shielding failure current.

[0083] In this invention, by incorporating more than a dozen key geometric and electrical parameters such as the outer diameter of the conductor and ground wire, the hanging point position, the sag, the parameters of the insulator string, and the detailed dimensions of the tower, a refined and digital three-dimensional model that can fully correspond to the actual line is established in the lightning protection analysis of AC to DC conversion, greatly improving the reliability and guiding value of the evaluation results; the shielding failure risk is not fixed, but changes dynamically with the magnitude of the lightning current. By calculating the risk integral from the minimum shielding failure current I_min to the maximum shielding failure current I_max, the shielding failure probability distribution of different intensities of lightning is accurately captured; by clearly distinguishing two situations for calculation, the critical lightning current range leading to insulation flashover is accurately determined, providing a theoretical basis for differential protection strategies; by calculating I_min and I_max for the positive and negative conductors respectively, the independent and accurate quantification of the shielding failure risk of the two conductors is achieved, providing key data support for systematically reducing the loop risk by optimizing the arrangement method in the future; realizing the optimization of the lightning protection performance without changing the tower structure in the AC to DC conversion project provides reliable, accurate, and quantifiable core technical support.

[0084] Specifically, step S3 further includes: calculating the number of shielding failure flashovers, and the specific formula is:

[0085] N = N sη[β×SFFOR'+(1-β)×SFFOR''];

[0086] Where N is the number of lightning strikes per 100 kilometers per year, Ns is the number of lightning strikes per 100 kilometers per year, η is the arc-establishment probability of lightning strikes on insulators, SFFOR' is the lightning strike flashover rate with negative polarity, and SFFOR'' is the lightning strike flashover rate with positive polarity. This represents the proportion of lightning with negative polarity.

[0087] In this embodiment of the invention, based on the flashover rate of each conductor and the proportion of lightning with negative polarity... Assuming 90% natural characteristics, calculate the number of flashovers per 100 kilometers per year in a DC circuit under positive and negative lightning currents:

[0088] N=N s η[β×SFFOR'+(1-β)×SFFOR''];

[0089] in, The proportion of lightning with negative polarity. η represents the number of lightning strikes per 100 kilometers per year, η is the probability of lightning flashover arcing of insulators, and SFFOR' and SFFOR'' are the negative and positive lightning flashover rates, respectively.

[0090] This invention transforms the abstract concept of flashover rate into the number of flashovers per 100 kilometers per year (N), making lightning protection performance assessment results more intuitive, measurable, and easy to compare across different line schemes. This provides the most direct and clear basis for engineering decisions. By optimizing conductor arrangement to improve lightning protection performance, the N value calculated by this formula is the core indicator for measuring the optimization effect. By comparing the N values ​​under three candidate arrangement methods, the optimal scheme that minimizes the overall flashover risk of the line can be scientifically and objectively selected. This invention comprehensively considers multiple factors such as lightning current amplitude probability, lightning polarity, topography, and insulation level. Its predicted flashover number is closer to the actual operating performance after the line is put into operation. This provides accurate data support for power grid operation and maintenance departments to predict line risks and formulate scientific lightning protection operation and maintenance strategies.

[0091] Specifically, in step S4, the specific criteria for the optimal conductor arrangement scheme for preventing lightning strikes in a single-loop AC-to-DC conversion scenario are as follows:

[0092] Compare the N values ​​corresponding to the three candidate permutations, and select the permutation with the smallest N value as the optimal solution;

[0093] If the difference in N values ​​between the two arrangements is less than 5%, the arrangement in which the positive conductor is located inside the tower window should be preferred.

[0094] In this embodiment of the invention, the calculation results of the three arrangement methods are compared horizontally. The results show that the calculated N value of the scheme with the return line inside the tower window is significantly higher than that of the other two schemes, and its lightning protection performance is the worst. Therefore, this scheme is first excluded. Among the remaining two schemes, the calculated N value of the scheme with the positive conductor inside the tower window is N_A, and the calculated N value of the scheme with the negative conductor inside the tower window is N_B. After comparison, the values ​​of N_A and N_B are very close, and the difference is less than the preset 5% threshold. Therefore, the arrangement method with the positive conductor inside the tower window is selected first.

[0095] Specifically, in step S4, the optimal conductor arrangement scheme for preventing lightning strikes is as follows: the positive conductor of the DC line is arranged in the middle phase position of the original AC line, and the negative conductor and return line of the DC line are arranged in the two side phase positions of the original AC line respectively.

[0096] Specifically, in step S3, when calculating the flashover rate, the operating voltage of the return line is zero, and the strike distance of the return line is calculated based on zero voltage, which is the same as the strike distance of the ground.

[0097] This invention directly compares the quantitative index N value and selects the scheme with the smallest N value. When the calculation results of the two schemes are very close, their slight differences may be within the range of model calculation error. Since 90% of lightning is negative polarity, and negative polarity lightning poses the greatest threat to positive conductors, placing the positive conductor in the tower window with the best shielding effect (the original middle phase position) is the optimal choice from the perspective of systemic risk control. This ensures that even when there are slight uncertainties in theoretical calculations, the highest-risk component can be proactively placed in the safest position, thereby optimizing the overall lightning protection performance of the system. By rearranging the conductors in space, placing the most vulnerable target (positive conductor) in the most robust shelter (inside the tower window), it achieves the optimal allocation of lightning protection resources at zero cost.

[0098] In this embodiment of the invention, based on the statistical characteristic that 90% of lightning is negative polarity, without changing the existing transmission tower structure or increasing investment, it is preferable to arrange the positive conductor 6 of the DC line in the middle phase position of the original AC line inside the tower window 3, and arrange the negative conductor 5 and return line 4 of the DC line in the side phase support 2 of the original AC line, which can effectively improve the lightning protection performance of the DC line.

[0099] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for improving the lightning protection performance of a line in a single-circuit AC-to-DC conversion scenario, characterized in that, Including: Step S1: Utilize the three conductor channels of the original AC line tower to configure the positive and negative conductors and the return line of the DC line. Among them, the configuration of the positive and negative conductors and the return line of the DC line includes: determining three candidate arrangements of the conductors, namely, the return line is located inside the tower window, the positive conductor is located inside the tower window, and the negative conductor is located inside the tower window. Step S2: Based on the statistical feature that 90% of lightning is negative polarity, and combined with the difference in shielding failure of positive and negative lightning to the DC line, calculate the shielding failure flashover rates of the DC line under the three candidate arrangements. Step S3: According to the shielding failure flashover rates, screen out the arrangement with the lowest number of shielding failure flashovers as the optimal conductor arrangement scheme for shielding failure prevention in the single-circuit AC-to-DC conversion scenario.

2. The method according to claim 1, characterized in that, In the said Step S1, the utilization of the three conductor channels of the original AC line tower includes: The three conductor channels of the original AC line tower respectively correspond to the positive conductor channel, the negative conductor channel, and the return line channel of the retrofitted DC line, and the channel positions correspond one-to-one with the middle phase and side phase positions of the original AC line.

3. The method according to claim 1, characterized in that, In the said Step S3, based on the statistical feature that 90% of lightning is negative polarity, it includes: Set the negative polarity lightning proportion β = 90%, and the positive polarity lightning proportion 1 - β = 10%. When calculating the shielding failure flashover rate, the contributions of negative polarity lightning corresponding to β and positive polarity lightning corresponding to 1 - β are respectively taken into account.

4. The method according to claim 1, characterized in that, In the said Step S3, the EGM (Electro-Geometric Model) is used to calculate the shielding failure flashover rates of the DC line under the three candidate arrangements, including: Step S31: Input the conductor and ground wire information, insulator string information, and tower information to determine the geometric parameters of the EGM model. Step S32: Considering the influence of the working voltages of the positive and negative poles of the DC line on the striking distance of the conductors, distinguish the instantaneous values of the working voltages on the positive and negative conductors and the lightning current, and determine the striking distances of lightning to the positive and negative conductors. Step S33: Based on the geometric function relationship between the grounding distance, conductor distance, and earthing distance and the lightning current, calculate the minimum lightning current value I for the positive and negative conductors respectively. min With the maximum winding conductor current I max ; Step S34, combined with the line lightning withstand level I c The flashover rate SFFOR is calculated by integration.

5. The method according to claim 4, characterized in that, In the said Step S31, the conductor and ground wire information includes: the outer diameter of the conductor and ground wire, the hanging point position of the conductor and ground wire, and the sag of the conductor and ground wire; the insulator string information includes: the length of the insulator string and the flashover voltage of the insulator string; the tower information includes: the height of the tower cross-arm, the equivalent radius of the tower body, and the width of the tower cross-arm.

6. The method according to claim 4, characterized in that, In step S34, the lightning withstand level I of the line is considered. c The flashover rate SFFOR is calculated by integration, including: If Imin < Ic < Imax, the shielding failure flashover rate is calculated according to the following formula: ； Where SFFOR is the lightning strike-on-the-loop rate, Ng is the ground flash density, P(I) is the probability density of lightning current amplitude, and Z is the lightning current amplitude probability density. s Ic is the ground projection distance of the exposed arc, and Ic is the lightning withstand level of the transmission line. For the maximum current of the winding conductor, This is the minimum lightning current value; If Ic < Imin < Imax, the shielding failure flashover rate is calculated according to the following formula: 。 7. The method according to claim 1, characterized in that, The said Step S3 also includes: calculating the number of shielding failure flashovers, and the specific formula is: N=N s η[β×SFFOR'+(1-β)×SFFOR'']; Where N is the number of lightning strikes per 100 kilometers per year, Ns is the number of lightning strikes per 100 kilometers per year, η is the arc-establishment probability of lightning strikes on insulators, SFFOR' is the lightning strike flashover rate with negative polarity, and SFFOR'' is the lightning strike flashover rate with positive polarity. This represents the proportion of lightning with negative polarity.

8. The method according to claim 7, characterized in that, In the said Step S4, the specific criteria for the optimal conductor arrangement scheme for shielding failure prevention in the single-circuit AC-to-DC conversion scenario are: Compare the N values corresponding to the three candidate arrangements, and select the arrangement with the smallest N value as the optimal scheme. If the difference between the N values of two arrangements is less than 5%, the arrangement with the positive conductor located inside the tower window is preferably selected.

9. The method according to claim 1, characterized in that, In the said Step S4, the optimal conductor arrangement scheme for shielding failure prevention is specifically: arrange the positive conductor of the DC line at the middle phase position of the original AC line, and arrange the negative conductor and the return line of the DC line at the two side phase positions of the original AC line respectively.

10. The method according to claim 4, characterized in that, In Step S3, when calculating the shielding failure flashover rate, for the return line, its working voltage is zero, and the striking distance of the return line is calculated based on zero voltage and is the same as the striking distance to the ground.

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