Power transmission line design system

Abstract

To provide a power transmission line design system for efficiently designing a power transmission line by reducing manual work.SOLUTION: A power transmission line design system is a system for designing a power transmission line including a tower and an overhead wire, and includes a tower selection unit that selects a type of tower, an overhead wire design unit that designs an overhead wire to be attached to the selected tower, a design unit that calculates a design item based on the selected tower and the designed overhead wire, and a design standard determination unit that determines whether the design item satisfies a design standard. When the design standard determination part determines that the design standard is not satisfied, a steel tower selection part selects the type of the steel tower again, or the overhead wire design part designs the overhead wire again, and the design part calculates the design item again.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a power transmission line design system. [Background technology]

[0002] The design of a power transmission line (power transmission system) is carried out, for example, in the following order.

[0003] First, a designer uses a power transmission line route planning system to plan and profile the power transmission line according to the terrain, and then determines the power transmission line route.

[0004] Next, the designers manually create the basic design and detailed design, referring to various design guidelines and based on conditions such as the horizontal angle of the transmission line and the type of wire.

[0005] Basic design is the process of determining the design specifications for each tower (for example, the number of insulators and required separation distance depending on the transmission line voltage and number of circuits) before construction, such as the installation of a new extra-high voltage transmission line. Detail design is the process of conducting detailed studies based on the basic design (for example, determining whether or not to use standard towers and the maximum usable tension).

[0006] Patent Document 1 discloses a tower pole design support system. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-99664 Summary of the Invention [Problem to be solved by the invention]

[0008] In the implementation design of conventional transmission line design methods, designers manually calculate and evaluate appropriate values ​​and select equipment to satisfy all the criteria for each design item. Therefore, the implementation design takes a lot of time and is prone to design errors. Furthermore, if changes occur after the implementation design is completed (for example, if a change in the transmission line route requires a change in span length or tower height), a lot of time is required to redesign.

[0009] An object of the present invention is to provide a power transmission line design system that performs efficient power transmission line design. [Means for solving the problem]

[0010] A power transmission line design system according to a first aspect of the present invention is a system for designing a power transmission line including a pylon and an overhead line. The power transmission line design system includes a tower selection unit that selects a type of pylon, an overhead line design unit that designs an overhead line to be attached to the selected pylon, a design unit that calculates design items based on the selected pylon and the designed overhead line, and a design criteria determination unit that determines whether the design items satisfy design criteria. If the design criteria determination unit determines that the design criteria are not satisfied, the tower selection unit reselects a type of pylon or the overhead line design unit redesigns the overhead line, and then the design unit redesigns the design items.

[0011] In this system, the tower type is reselected or the overhead line is redesigned until the design items meet the design criteria. In other words, the calculation and judgment of the design items and the above conditions are repeatedly changed. As a result, the system repeats calculation and judgment until the design item criteria in the detailed design are met, automatically selecting appropriate values ​​and equipment specifications, providing a transmission line design system that performs efficient transmission line design.

[0012] In a power transmission line design system according to a second aspect of the present invention, the design criteria include at least one of an insulation design criteria, a pole design criteria, and an ice and snow resistance design criteria. If the design criteria determination unit determines that at least one of the insulation design criteria, the pole design criteria, and the ice and snow resistance design criteria is not satisfied, the tower selection unit reselects the type of tower.

[0013] This system provides a power transmission line design system that performs efficient power transmission line design.

[0014] In a power transmission line design system according to a third aspect of the present invention, the design criteria include a separation design criterion. The overhead line includes a power line and an overhead ground wire. If the design criteria determination unit determines that the separation design criterion is not satisfied, the overhead line design unit redesigns at least one of the power line and the overhead ground wire.

[0015] This system provides a power transmission line design system that performs efficient power transmission line design.

[0016] In the power transmission line design system according to the fourth aspect of the present invention, if the sag ratios of the power line and the overhead ground wire are outside a predetermined range, the overhead line design unit increases or decreases the maximum usable tension of at least one of the power line and the overhead ground wire to bring the sag ratios of the power line and the overhead ground wire within the predetermined range.

[0017] In this system, the maximum usable tension of the power line or the overhead ground wire is set so as to realize a sag ratio within a predetermined range.

[0018] In the power transmission line design system according to the fifth aspect of the present invention, if the amount of take-in of the overhead ground wire when it is connected is less than a predetermined value, the overhead line design unit reduces the maximum usable tension of the overhead ground wire to make the amount of take-in of the overhead ground wire when it is connected equal to or greater than the predetermined value.

[0019] In this system, the maximum usable tension of the overhead ground wire is set so that the amount of take-in of the overhead ground wire when it is fastened is equal to or greater than a predetermined value.

[0020] In a power transmission line design system according to a sixth aspect of the present invention, if the safety factor in the strength design of the power line is not achieved, the overhead line design unit reduces the maximum usable tension of the power line to achieve the safety factor in the strength design of the power line.

[0021] In this system, the maximum working tension of the power line is set so that the safety factor in the strength design of the power line is achieved.

[0022] In the power transmission line design system according to the seventh aspect of the present invention, if the safety factor in the strength design of the overhead ground wire is not achieved, the overhead line design unit reduces the maximum usable tension of the overhead ground wire to achieve the safety factor in the strength design of the overhead ground wire.

[0023] In this system, the maximum working tension of the overhead ground wire is set so that the safety factor in the strength design of the overhead ground wire is achieved. [Effects of the Invention]

[0024] According to the present invention, a power transmission line design system that performs efficient power transmission line design is provided. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic diagram showing a steel tower and surrounding structures that are the design targets of the power transmission line design system of the present invention. FIG. [Figure 2] FIG. 2 is a block diagram showing a control configuration of the power transmission line design system of the present invention. [Figure 3] 1 is a flowchart showing a basic control operation of the power transmission line design system. [Figure 4] 10 is a first flowchart showing the overhead line design operation by the overhead line design unit. [Figure 5] 10 is a second flowchart showing the overhead line design operation by the overhead line design unit. DETAILED DESCRIPTION OF THE INVENTION

[0026] 1. Overview of this embodiment The power transmission line design system 11 (Fig. 2) is a system that automatically performs the calculations and judgments of basic and detailed designs for power transmission lines, as well as the creation of construction schedules and budget statements, which have traditionally been performed by engineers.

[0027] The power transmission line design system 11 takes in data on the power transmission line route created by a power transmission line route review system (not shown) and utilizes it in combination with data on various design standards.

[0028] The power transmission line design system 11 algorithmizes the trial and error process that was previously performed by designers, and automatically repeats it to arrive at appropriate design values ​​and equipment specifications. As a result, it is possible to build equipment that takes into account economy and ease of construction.

[0029] 2. Features of this embodiment The power transmission line design system 11 has the following features: Note that the power transmission line design system 11 does not necessarily have to have all of the following features.

[0030] 1) The power transmission line design system 11 determines each item (initial value) of the basic design using the power transmission line route selection result and the manually input design condition data as input values.

[0031] 2) The power transmission line design system 11 repeats calculations and judgments until all the criteria for multiple design items (for example, tower selection, overhead line design) in the detailed design are satisfied, and automatically selects appropriate values ​​and equipment specifications.

[0032] 3) The power transmission line design system 11 determines values ​​that satisfy the design criteria in the examination of each design item of the detailed design.

[0033] 4) The power transmission line design system 11 outputs a construction schedule summarizing the results of the basic design and the detailed design, and outputs construction costs and material costs other than temporary construction items based on the specifications.

[0034] 3. Effects of this embodiment The effects of the power transmission line design system 11 are as follows: Note that the power transmission line design system 11 does not necessarily have to achieve all of the following effects.

[0035] 1) The time required for basic design, detailed design, construction schedules, and budget calculations after the transmission line route is selected will be reduced.

[0036] 2) Multiple transmission line routes can be compared in a short time, making it possible to select the optimal transmission line route taking into account ease of construction and economic efficiency.

[0037] 3) Manual design errors (human error) and variations in quality between designers are eliminated.

[0038] 4. Specific Description of the Present Embodiment Hereinafter, an embodiment of the present invention will be specifically described with reference to FIGS.

[0039] Figure 1 is a schematic diagram showing the structure of a transmission line that is the target of design by the transmission line design system of the present invention. In Figure 1, the transmission line 1 has a steel tower 2, one overhead ground wire 3 (overhead wire), and multiple power lines (overhead wires) 4. The multiple power lines 4 are supported by the steel tower 2 via multiple insulators 5. The steel tower 2 is installed on a foundation 6.

[0040] 2 is a block diagram showing the control configuration of a transmission line design unit of the transmission line design system of the present invention. In FIG. 2, a transmission line design system 11 designs a transmission line 1 including a steel tower 2 and overhead lines (overhead ground wires 3 and power lines 4).

[0041] The power transmission line design system 11 will be described with reference to FIG. The power transmission line design system 11 is a computer system having a processor (e.g., CPU), a storage device (e.g., ROM, RAM, HDD, SSD, etc.), and various interfaces (e.g., A / D converter, D / A converter, communication interface, etc.). The power transmission line design system 11 performs various control operations by executing programs stored in a storage unit (corresponding to part or all of the storage area of ​​the storage device).

[0042] The power transmission line design system 11 may be configured with a single processor, or may be configured with multiple independent processors for each control.

[0043] Some or all of the functions of each element of the power transmission line design system 11 may be realized as a program executable by a computer system constituting a control unit. Alternatively, some of the functions of each element of the power transmission line design system 11 may be configured by a custom IC.

[0044] The power transmission line design system 11 includes a basic design unit 12. The basic design unit 12 designs initial values ​​(basic design results) based on input values ​​(route selection results, design initial conditions).

[0045] The power transmission line design system 11 has a tower selection unit 13, an overhead line design unit 14, an insulation design unit 15, a pole design unit 16, a clearance design unit 17, an ice and snow resistance design unit 18, a tower design unit 19, and a foundation and site design unit 20, which are collectively referred to as an implementation design unit 25.

[0046] The tower selection unit 13 selects a standard tower type and provisionally selects the cross arm shape.

[0047] The overhead line design unit 14 designs the overhead line (at least one of the power line and the overhead ground wire) to be attached to the selected steel tower. Specifically, the maximum usable tension of the power line and the overhead ground wire is determined. Furthermore, the support point tension and EDS are considered, and the insulator device is selected. Furthermore, the insulator suspension type is selected, and the maximum load of the suspension device is considered.

[0048] The insulation design department 15 performs insulation design based on the selected tower and designed overhead line. Specifically, it considers clearance, support insulators, conductor spacing (wind breath), and allowable catenary angle. Furthermore, the insulation design department 15 also functions as a design criteria evaluation department, determining whether the designed insulation (design item) satisfies the design criteria.

[0049] The pole design unit 16 designs the pole based on the selected tower and designed overhead line. Specifically, it considers the planar clearance and the safety distance during work. Furthermore, it considers lateral vibration due to wind and determines the cross arm shape. Furthermore, the pole design unit 16 functions as one of the design criteria judgment units and judges whether the designed pole (design item) satisfies the design criteria.

[0050] The separation design unit 17 performs separation design based on the selected tower and designed overhead line. Specifically, the height of the power line above ground is determined. Furthermore, separation from other structures, trees, and overhead power lines is considered. Furthermore, the separation design unit 17 functions as a design criteria determination unit, determining whether the separation (design item) satisfies the design criteria.

[0051] The ice and snow resistance design unit 18 performs ice and snow resistance design based on the selected tower and designed overhead line. Specifically, tip-off studies and sleet jump studies are carried out. Furthermore, galloping studies and ring damper installation studies are carried out. Furthermore, the ice and snow resistance design unit 18 functions as a design criteria judgment unit, and judges whether the ice and snow resistance (design item) meets the design criteria.

[0052] The tower design department 19 designs the tower based on the selected tower and the designed overhead line. Specifically, the design conditions (design load span, horizontal angle, vertical angle) are considered. Furthermore, the expected load and foundation load are calculated. Furthermore, stress calculations and component selection are performed.

[0053] The foundation and site design unit 20 designs the foundation and site based on the selected steel tower and the designed overhead line. Specifically, the stability of the standard steel tower foundation is calculated, and the one-side joint and post joint are considered. Further consideration is carried out using the site design system.

[0054] The power transmission line design system 11 includes a construction schedule creation unit 21 and a budget creation unit 22.

[0055] The construction schedule creation unit 21 creates a construction schedule based on the design results of the detailed design unit 25.

[0056] The budget preparation section 22 prepares a budget based on the design results of the detailed design section 25.

[0057] The power transmission line design system 11 is connected to a reception unit 23 and an output unit 24.

[0058] The receiving unit 23 receives input values ​​(route selection results, design initial conditions) from a power transmission line route review system (not shown) and transmits them to the basic design unit 12.

[0059] The output unit 24 outputs data from the construction schedule creation unit 21 and the budget creation unit 22 to the outside.

[0060] 5. Outline of the detailed design In the implementation design, the implementation design section 25 repeats calculations and judgments based on input values ​​(route selection results, initial design conditions) and initial values ​​(basic design results) until all the criteria for each design item required for the implementation design (for example, tower selection, overhead line design) are satisfied, and derives appropriate values ​​and equipment specifications.

[0061] Please refer to Figure 3 for the overall system overview flow diagram.

[0062] The control flowcharts described below are merely examples, and steps can be omitted or replaced as necessary. Furthermore, multiple steps can be executed simultaneously, or some or all of the steps can be executed in an overlapping manner.

[0063] Furthermore, each block in the control flowchart is not limited to a single control operation, but can be replaced with a plurality of control operations represented by a plurality of blocks.

[0064] In step S1, the results of the basic design (route selection result, design initial conditions, basic design) are output from the basic design unit 12 to the detailed design unit 25.

[0065] Next, in the detailed design, calculations and judgments are repeated to consider appropriate equipment specifications and design values ​​so as to satisfy the standards of the basic design results. The detailed design is carried out by the Tower Selection Department 13, Overhead Wiring Design Department 14, Insulation Design Department 15, Pole Design Department 16, Clearance Design Department 17, Ice and Snow Resistance Design Department 18, Tower Design Department 19, and Foundation and Site Design Department 20 of the Detailed Design Department 25.

[0066] In step S2, the tower selection unit 13 selects a tower.

[0067] In step S3, the overhead line design unit 14 designs the overhead line.

[0068] In step S4, the insulation design unit 15 designs the insulation. If the design conditions are not met in this step, the process returns to step S2, where tower selection (S2), overhead line design (S3), and insulation design (S4) are performed. In other words, if the insulation design unit 15 (design criteria determination unit) determines that the insulation design criteria are not met, the tower selection unit 13 selects the tower type again, and the overhead line design unit 14 designs the overhead line again. Note that only one of the tower reselection (S2) and overhead line redesign (S3) may be performed.

[0069] In step S5, the pole design unit 16 designs the pole. If the design conditions are not met in this step, the process returns to step S2, and tower selection (S2), overhead line design (S3), insulation design (S4), and pole design (S5) are performed again. In other words, if the pole design unit 16 determines that the pole design criteria are not met, the tower selection unit 13 selects the tower type again, and the overhead line design unit 14 designs the overhead line again. Note that only one of the tower selection reselection (S2) and overhead line design redesign (S3) may be performed.

[0070] In step S6, the clearance design unit 17 designs the clearance. If the design conditions are not met in this step, the process returns to step S3, and the overhead line design (S3), insulation design (S4), pole design (S5), and clearance design (S6) are performed again. In other words, if the clearance design unit 17 (design criteria determination unit) determines that the clearance design criteria are not met, the overhead line design unit 14 designs the overhead line again.

[0071] In step S7, the ice and snow resistant design unit 18 designs ice and snow resistance. If the design conditions are not met in this step, the process returns to step S2, and after tower selection (S2), overhead line design (S3), insulation design (S4), and pole design (S5) are performed, ice and snow resistant design (S7) is performed. In other words, if the ice and snow resistant design unit 18 determines that the ice and snow resistant design standards are not met, the tower selection unit 13 selects the tower type again, and the overhead line design unit 14 designs the overhead line again. Note that only one of the tower reselection (S2) and overhead line redesign (S3) may be performed.

[0072] In step S8, the tower design unit 19 designs the tower.

[0073] In step S9, the foundation and site design unit 20 designs the foundation and site.

[0074] In step S10, the construction schedule creation unit 21 creates and outputs a construction schedule, and the budget creation unit 22 creates and outputs a budget. In addition, a list of the detailed design results and supporting documents for the detailed design results are also output.

[0075] 6.Detailed design flow chart In order to satisfy the design standards, even when examining each design item (such as determining the maximum usable tension of power lines and overhead ground wires in the overhead line design), appropriate values ​​and equipment specifications are derived through repeated trial and error.

[0076] As an example, we will explain how to determine the maximum usable tension of power lines and overhead ground wires.

[0077] The maximum working tension of power lines and overhead ground wires must satisfy all three of the following conditions:

[0078] First condition: The sag ratio (the ratio of overhead ground wire sag to power line sag) must be approximately 80% (specifically, the sag ratio must be between 65% and 95%).

[0079] Second condition: Wiring must be possible (specifically, the difference between the diagonal distance between the towers and the wire support points on the towers and the actual length of the wire between the wire support points must be 0.10 m or more at a temperature of 0°C).

[0080] Third condition: The strength of the overhead lines and insulators must satisfy the safety factor (specifically, the above conditions are: a) the safety factor of the power lines, overhead ground wires, and insulators must be 2.5 or more during high and low temperature seasons, b) the safety factor must be 1.05 or more for 95% of the minimum tensile load of the power lines and overhead ground wires when snow has accumulated, and c) under normal conditions, the ratio of the support point tension of the power lines and overhead ground wires to the minimum tensile load must be 25% or less, and the ratio of the support point tension to the strength of the insulators must be 25% or less). The following flow is executed by the overhead contact line design unit 14.

[0081] In step S11, the sag of the power lines and overhead ground wires is calculated using the maximum tensions used in the basic design (input values). Then, the process proceeds to step S12.

[0082] In step S12, it is determined whether the sag ratio is equal to or greater than 65% and equal to or less than 95%. If the determination result is YES, the process proceeds to step S13. If the determination result is NO, the process proceeds to step S14.

[0083] In step S14, it is determined whether the sag ratio is less than 65%. If the determination result is NO, the process proceeds to step S15. If the determination result is YES, the process proceeds to step S16.

[0084] In step S15, the maximum usable tension of the overhead ground wire is reduced by 980 N. The process then returns to step S11, i.e., the sag calculation (step S11) and the determination of the sag ratio (step S12) are subsequently performed.

[0085] In step S16, the maximum usable tension of the overhead ground wire is increased by 980 N. The process then returns to step S11, which means that the sag calculation (step S11) and the determination of the sag ratio (step S12) are subsequently performed.

[0086] As described above, if the sag ratios of the power lines and the overhead ground wires are outside the predetermined range (NO in step S12), the overhead line design unit 14 increases or decreases the maximum usable tension of the overhead ground wires (steps S15 and S16) to bring the sag ratios of the power lines and the overhead ground wires within the predetermined range (YES in step S12). More specifically, by repeating the sag ratio determination (S12) and the sag ratio increase or decrease (steps S15 and S16), the sag ratio of 65% to 95% is satisfied (YES in step S12). In other words, as a method for bringing the sag ratio within the predetermined range (65 to 95%), rather than calculating the maximum usable tension to be changed (for example, the maximum usable tension that will bring the sag ratio to 80%), the maximum usable tension is increased or decreased by a predetermined value to bring it within the predetermined range. This minimizes the amount of change in the maximum usable tension and reduces the impact on the preceding and following spans.

[0087] As a result of the above, the first condition is satisfied. Note that, if the sag ratios of the power lines and the overhead ground wire are outside the predetermined ranges, the overhead line design unit 14 may increase or decrease the maximum usable tension of the power lines, or may increase or decrease the maximum usable tension of both the power lines and the overhead ground wire.

[0088] In step S13, it is determined whether the take-in amount of the overhead ground wire at the time of installation is 0.10 m or more. The take-in amount at the time of installation refers to the diagonal distance between the pylons and the pylon's electric wire support points and the actual length of the electric wire between the pylons. This determination is necessary because if the take-in amount at the time of installation is less than 0.10 m, it may not be possible to actually install the electric wire. If the determination result is YES, the process proceeds to step S19 (Figure 5). In other words, in this case, the second condition is satisfied. If the determination result is NO, the process proceeds to step S17.

[0089] In step S17, the maximum usable tension of the overhead ground wire is reduced by 980 N. The process then proceeds to step S18.

[0090] In step S18, the sag of the overhead ground wire is calculated, after which the process returns to step S13.

[0091] As described above, if the amount of take-in of the overhead ground wire when it is connected is less than a predetermined value (NO in step S13), the overhead line design unit 14 reduces the maximum usable tension of the overhead ground wire (step S17) so that the amount of take-in of the overhead ground wire when it is connected is equal to or greater than the predetermined value.

[0092] In step S19, it is determined whether the sag ratio is between 65% and 95%. The reason for determining the sag ratio in step S19 following step S12 is because the sag ratio may have been changed as a result of step S17. If the determination result is YES, the process proceeds to step S20. If the determination result is NO, the process proceeds to step S24.

[0093] In step S24, the maximum usable tension of the power line is reduced by 980 N. The process then proceeds to step S25.

[0094] In step S25, the power line sag is calculated, after which the process returns to step S19.

[0095] In step S20, it is determined whether the strength of the power line insulator device satisfies the safety factor. If the determination is YES, the process proceeds to step S21. If the determination is NO, the process proceeds to step S26.

[0096] In step S26, the maximum usable tension of the power line is reduced by 980 N. The process then returns to step S20.

[0097] As described above, if the safety factor in the strength design of the power line is not achieved (NO in step S20), the overhead line design unit 14 reduces the maximum usable tension of the power line (step S26) to achieve the safety factor in the strength design of the power line.

[0098] In step S21, it is determined whether the strength of the overhead ground wire satisfies the safety factor. If the determination is YES, the process proceeds to step S22. In this case, the third condition is satisfied. If the determination is NO, the process proceeds to step S27.

[0099] In step S27, the maximum usable tension of the overhead ground wire is reduced by 980 N. The process then returns to step S21.

[0100] As described above, if the safety factor in the strength design of the overhead ground wire is not achieved (NO in step S21), the overhead line design unit 14 reduces the maximum usable tension of the overhead ground wire (step S27) to achieve the safety factor in the strength design of the overhead ground wire.

[0101] In step S22, it is determined whether the strength of the power line and the overhead ground wire does not satisfy the safety factor and therefore the maximum usable tension of the power line or the overhead ground wire has been changed (decreased). If the maximum usable tension has not been changed, the process proceeds to step S23. If the maximum usable tension of the power line or the overhead ground wire has been changed, the process returns to step S19. Redesign and evaluation are carried out. The reason is that if the maximum usable tension of the power line or the overhead ground wire has been changed, the sag ratio must be checked again.

[0102] In step S23, the maximum usable tension of the power line and the overhead ground wire is determined.

[0103] As described above, by repeatedly increasing or decreasing the maximum usable tension of the power line and overhead ground wire through trial and error until all three conditions are satisfied, it is possible to derive an appropriate tension, which takes into account both workability and economy.

[0104] 7. Other Embodiments Although several embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the invention. In particular, several embodiments and modifications described in this specification can be arbitrarily combined as necessary. [Explanation of symbols]

[0105] 1: Power lines 2: Steel tower 3: Overhead ground wire 4: Power lines 11: Transmission line design system 13: Tower Selection Department 14: Catenary Design Department 15: Insulation Design Department (Design Department, Design Standards Evaluation Department) 16:Column design department (design department, design standard judgment department) 17: Separation design department (design department, design standard judgment department) 18: Ice and Snow Resistance Design Department (Design Department, Design Standards Evaluation Department) 19: Tower Design Department 20: Site Design Department 25: Detail Design Department

Claims

1. A power transmission line design system for designing a power transmission line including a steel tower and an overhead line, a tower selection unit that selects the type of tower; an overhead line design department that designs overhead lines to be attached to the selected towers; The design department calculates the design items based on the selected tower and designed overhead line. a design criteria determination unit that determines whether the design items satisfy design criteria, If the design criteria determination unit determines that the design criteria are not satisfied, the tower selection unit reselects the type of tower or the overhead line design unit redesigns the overhead line, and then the design unit recalculates the design items. Transmission line design system.

2. The design standards include at least one of insulation design standards, column design standards, and ice and snow resistance design standards, 2. The power transmission line design system according to claim 1, wherein if the design criteria determination unit determines that at least one of the insulation design criteria, the pole design criteria, and the ice and snow resistance design criteria is not satisfied, the tower selection unit reselects a type of tower.

3. the design criteria include separation design criteria; The overhead line includes a power line and an overhead ground wire, 3. The power transmission line design system according to claim 1, wherein if the design standard determination unit determines that the separation design standard is not satisfied, the overhead line design unit redesigns at least one of the power line and the overhead ground wire.

4. The overhead line design unit 4. The power transmission line design system according to claim 3, wherein, if the sag ratios of the power line and the overhead ground wire are outside a predetermined range, the maximum usable tension of at least one of the power line and the overhead ground wire is increased or decreased to bring the sag ratios of the power line and the overhead ground wire within the predetermined range.

5. The overhead line design unit 4. The power transmission line design system according to claim 3, wherein, if an amount of take-in of the overhead ground wire when it is connected is less than a predetermined value, the maximum usable tension of the overhead ground wire is reduced so that the amount of take-in of the overhead ground wire when it is connected is made equal to or greater than the predetermined value.

6. The overhead line design unit 4. The power transmission line design system according to claim 3, wherein if a safety factor in the strength design of the power line is not achieved, the safety factor in the strength design of the power line is achieved by reducing a maximum usable tension of the power line.

7. The overhead line design unit 4. The power transmission line design system according to claim 3, wherein if a safety factor in the strength design of the overhead ground wire is not achieved, the safety factor in the strength design of the overhead ground wire is achieved by reducing a maximum usable tension of the overhead ground wire.

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