Method for calculating average height of overhead line wire during wind load calculation

Abstract

The invention discloses a method for calculating the average height of an overhead line wire during wind load calculation, and the method comprises the steps: determining a curve equation for describing the shape of an overhead line, and determining a function relation between the height h of the wire in a gear and the horizontal position x; in a calculation formula of the wind load, representing a parameter related to the height as a function related to the horizontal position x; listing an integral equation of the equivalent height and the actual height according to an equal load principle; and solving the integral equation to obtain an analytic solution or an approximate solution of the equivalent height, namely a calculation formula of the average height of the overhead line wire during wind load calculation. According to the scheme, aiming at the characteristics of a load calculation formula, the function of the influence of the height on the load is established, the equivalent height is calculated by using a full-range'equal load 'method, the method is closer to an actual model of wind load calculation, and the method has more significance and value in actual application.

Description

Technical Field

[0001] The invention belongs to the technical field of overhead power transmission line design, and in particular relates to a method for calculating the average height of overhead line wires when calculating wind loads. Background Art

[0002] The main specifications for overhead line design are "110kV~750kV Overhead Transmission Line Design Specification" (GB50545-2010), "Overhead Transmission Line Load Specification" (DLT5551-2018), "Overhead Transmission Line Electrical Design Code" (DL / T 5582-2020). The industry calls "110kV~750kV Overhead Transmission Line Design Specification" (GB 50545-2010) the old specification, and "Overhead Transmission Line Load Specification" (DLT5551-2018) and "Overhead Transmission Line Electrical Design Code" (DL / T 5582-2020) the new specification. The old and new specifications have major changes in the wind load calculation formula, but because the new specification is an industry standard, it cannot completely replace the national standard (old specification) at the regulatory management level. The calculation of wind loads on wires in both the old and new standards involves the "wind pressure height variation coefficient", whose purpose is to characterize the effect of wind loads, which increases with the change in the height of the structure. Since the shape of the hanging wires is a "catenary" or "parabola", the actual height of the wires varies with their location. In order to simplify engineering calculations, the concept of average wire hanging height is introduced, that is, the hanging height of the wires in the section is equivalent to a constant, which is convenient for calculation.

[0003] The current method for calculating the average hanging height of the conductor is to use the "equal area" principle. Assuming a straight line parallel to the ground, when the area formed by the straight line and the ground is exactly equal to the area formed by the conductor curve and the ground, the height of the parallel straight line at this time is the average hanging height of the conductor. The shape of the conductor curve is a hyperbolic cosine function according to theoretical deduction, that is, the "catenary" shape in mathematics. In actual engineering, a "parabola" is generally used for approximate and simplified calculations. Using the parabola function formula combined with the "equal area" principle, it can be deduced that the average height of the conductor h eq = Height of the lowest point of the conductor + 1 / 3×maximum sag f of the conductor. In this "equal area" method, the horizontal and vertical axes corresponding to the area are both distances in space. It is an average height based on equal area and cannot reflect the physical meaning, i.e. the load situation. The actual wind load on the wires in the gear should be that the wind at different heights acts on the wire micro-element to form a load micro-element. The total load of the wires in the gear is formed by summing up the load micro-elements at various positions in the gear. Since the wires are curved, the height of the wire micro-element changes with the position, and the wind pressure also changes with the height. Therefore, the equivalent height of the wire used for load calculation should be equivalent based on the principle of equal load. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for calculating the average height of overhead line wires when calculating wind loads, so as to solve the problem that the existing calculation method cannot reflect the physical meaning, that is, the load action situation. The present invention aims at the characteristics of the load calculation formula, establishes a function of the influence of height on load, and uses the full-file "equal load" method to calculate the equivalent height, which is closer to the load action mechanism.

[0005] According to the technical solution of the present invention, the present invention provides a method for calculating the average height of overhead line wires when calculating wind load, comprising the following steps: Step S1, determining the curve equation describing the shape of the overhead wire, and determining the functional relationship between the height h of the wire in the section and the horizontal position x; Step S2, in the calculation formula of the wind load, the parameter related to the height is expressed as a function related to the horizontal position x; Step S3, according to the "equal load" principle, the integral equation of the equivalent height and the actual height is listed; wherein the "equal load" principle means that for a certain level of wire, it is assumed that there is a line with an equivalent height h eq The wind load of the straight line is equal to the sum of the loads of each load element of the wire in the curve shape; Step S4, solving the integral equation to obtain an analytical solution or an approximate solution of the equivalent height, which is a calculation formula for the average height of overhead line wires used in wind load calculation.

[0006] Furthermore, in step S2, after expressing the height-related parameters as functions related to the horizontal position x, the general wind load calculation formula is obtained as follows: W X (h)=g(h)•L p •C; Among them, g(h) is the height correlation calculation function, L p is the horizontal span of the tower, C is the calculation coefficient; Then in step S3, let any small segment of any wire element be Δx, the horizontal position of the wire element be x, the height corresponding to the wire element be h(x), and the wind load of the wire element be: ΔW = g(h(x))•Δx•C; For a line with an equivalent height h eq The wind load of the straight line is: ; The sum of the loads of each load element of the wire under the curve shape is: ; Where L is the span, and its value in this formula is equal to the horizontal span L of the tower. p ; Then, according to the “equal load” principle, the integral equation is: .

[0007] Furthermore, in step S1, the curve equation describing the shape of the overhead wire is a parabola equation or a catenary equation.

[0008] Furthermore, in step S2, the parameters related to the height include at least one of a wind pressure height variation coefficient and a turbulence intensity at an average height of the conductor.

[0009] In one embodiment, in step S2, the calculation formula of wind load is: W X =a·W O ·μ z ·μ sc β o ·d·L p ·B·sin 2 θ; W O =V 2 / 1600; Where: W X is the standard value of horizontal wind load perpendicular to the conductor and ground wire; a is the wind pressure unevenness coefficient; β o μ is the wind load adjustment factor for 500kV and 750kV line conductors and ground wires; z is the wind pressure height variation coefficient; μ sc is the body coefficient of the conductor or ground wire; d is the outer diameter of the conductor or ground wire or the calculated outer diameter when covered with ice; L p is the horizontal spacing of the tower; B is the wind load increase factor when covered with ice; θ is the angle between the wind direction and the conductor or ground wire direction; W O is the standard value of the reference wind pressure; V is the wind speed at a reference height of 10m; Then in step S3, the integral equation obtained is: ; Where: L is the gear distance; h eq is the equivalent height, i.e. the average height of overhead line wires used in wind load calculation; m α is the wind pressure correction factor.

[0010] Furthermore, in step S4, the analytical solution is obtained from the integral equation: ; Where: h eqis the equivalent height, i.e., the average height of overhead line wires used for wind load calculation; h0 is the height of the lowest point of the conductor in the section; f is the maximum sag in the section; α is the ground roughness coefficient.

[0011] Furthermore, the ground roughness categories include: Class A refers to near-sea surfaces and islands, coasts, lakeshores and desert areas; Class B refers to fields, villages, jungles, hills, and towns and urban suburbs with relatively sparse houses; Class C refers to urban areas with densely packed buildings; and Class D refers to urban areas with densely packed buildings and taller houses. For Class A, Class B, Class C, and Class D terrains, the ground roughness coefficient α is 0.12, 0.16, 0.22, and 0.30, respectively.

[0012] In another embodiment, in step S2, the calculation formula of the wind load is: W X =β c α L ·W O ·μ z ·μ sc ·d·L p ·B l ·sin 2 θ; β c =γ c (1+2g·I z ); ; ; ; W O =V O 2 / 1600; Where: W X is the standard value of wind load perpendicular to the conductor and ground wire; β c is the ground line gust coefficient; α L W is the gear spacing reduction coefficient; O is the reference wind pressure; μ z is the wind pressure height variation coefficient; μ sc is the body coefficient of the conductor or ground wire; d is the outer diameter of the conductor or ground wire or the calculated outer diameter when covered with ice; L p is the horizontal span of the tower; B l is the ice-covered wind load increase factor for the ground wire; θ is the angle between the wind direction and the conductor or ground wire direction; γ c is the wind load reduction factor of the ground wire; g is the peak factor; I z is the turbulence intensity at the average height of the conductor; I 10is the nominal turbulence intensity at 10m height; Z is the average height of the conductor and ground wire; α is the ground roughness index; ε c is the reduction factor of wind load pulsation of ground wire; δ L L is the span correlation integration factor; X is the integration length of the horizontal correlation function; e is a natural constant; V O is the basic wind speed; Then in step S3, the integral equation obtained is: ; Where: L is the gear distance; h eq is the equivalent height, i.e. the average height of overhead line wires used in wind load calculation; m α is the wind pressure correction factor.

[0013] Furthermore, in step S4, the approximate solution is obtained from the integral equation: ; Where: h eq is the equivalent height, i.e., the average height of overhead line wires used for wind load calculation; h0 is the height of the lowest point of the conductor in the section; f is the maximum sag in the section; α is the ground roughness coefficient; g(α) is the equivalent height calculation coefficient.

[0014] Furthermore, the ground roughness categories include: Class A refers to near-sea surfaces and islands, coasts, lakeshores and desert areas; Class B refers to fields, villages, jungles, hills, and towns and urban suburbs with relatively sparse houses; Class C refers to urban areas with densely packed buildings; and Class D refers to urban areas with densely packed buildings and taller houses. For Class A, Class B, Class C, and Class D terrains, the ground roughness coefficient α is 0.12, 0.15, 0.22, and 0.30, respectively, and the equivalent height calculation coefficient g(α) is 19.5%, 21%, 23.5%, and 26.5%, respectively.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The method for calculating the average height of overhead line wires during wind load calculation of the present invention is based on the definition formula for overhead line load calculation in the new and old design specifications, and from the perspective of being more suitable for the load action mechanism, based on the load action principle, and using formula derivation combined with approximate calculation to propose a recommended calculation formula. The existing calculation method is derived based on the "equal area" method formed by the curve and the ground. The horizontal axis and vertical axis corresponding to this area are both distances in space, which is an average height in a mathematical relationship and cannot reflect the physical meaning, that is, the load action situation. The present invention, based on the characteristics of the load calculation formula, establishes a function of the influence of height on load, and uses the full-scale "equal load" method to calculate the equivalent height, so it is more helpful for wind load calculation, closer to the actual model of wind load calculation, and has more significance and value for practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a method flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The present invention provides a method for calculating the average height of overhead line wires when calculating wind loads, solving the problem that the existing calculation method cannot reflect the physical meaning, that is, the load action. Affected by gravity, the natural hanging shape of the wires of the overhead line is actually a "catenary" or "parabola" rather than a horizontal line. The present invention is based on the characteristics of the load calculation formula, from the perspective of being more suitable for the load action mechanism, and establishes a function of the influence of height on load, and uses the full-file "equal load" method to calculate the equivalent height.

[0018] A method for calculating the average height of overhead line wires when calculating wind loads of the present invention comprises the following steps: Step S1, determine the curve equation describing the shape of the overhead wire, and determine the functional relationship h(x) between the height h of the wire in the section and the horizontal position x; the curve equation describing the shape of the overhead wire can be selected as a parabola equation or a catenary equation; for example, the parabola equation is: h(x)=k·x 2 , x∈[-L / 2,L / 2]; where k is the coefficient of the quadratic term.

[0019] Step S2, analyzing the calculation formula of wind load in the specification, in which the parameters related to height are expressed as functions related to the horizontal position x; the parameters related to height include, for example, at least one of the wind pressure height variation coefficient and the turbulence intensity at the average height of the conductor, that is, the wind pressure height variation coefficient μ(h) related to height and the turbulence intensity Iz(h) at the average height are expressed as functions μ(h(x)) and Iz(h(x)) related to the horizontal position x; taking the functional relationship h(x) between the height h of the wire in the gear and the horizontal position x as an example, the specific process is as follows: ; Among them, m α is the wind pressure correction coefficient, which is determined according to the terrain types A, B, C, and D. Specifically, according to the national standard, the corresponding ground roughness values ​​for types A, B, C, and D are 1.379, 1.000, 0.616, and 0.318, respectively; according to the industry standard, the corresponding ground roughness values ​​for types A, B, C, and D are 1.284, 1.000, 0.544, and 0.262, respectively; m α In the subsequent integral equation, both sides can be eliminated; ; Among them, α is the surface roughness index, I 10 is the nominal turbulence intensity at 10m height; All height-related parameters in the calculation formula for wind load are expressed as functions.

[0020] Step S3, according to the "equal load" principle, list the integral equations of the equivalent height and the actual height. The actual wind load on the wires in the gear should be that the wind at different heights acts on the wire microelement to form a load microelement, and the total load of the wires in the gear is formed by summing up the load microelement at each position in the gear. Since the wires are curved, the height of the wire microelement changes with the position, and the wind pressure also changes with the height. Therefore, the equivalent height of the wire used for load calculation should be equivalent based on the principle of equal load. The "equal load" principle of the present invention means that for a certain gear of wires, it is assumed that there is a height of equivalent height h eq The straight line whose wind load is equal to the sum of the loads of each load element of the wire under the curve shape. The key point of this method is that the wires at different locations have different heights, which leads to different wind pressure height variation coefficients, and thus different wind loads. Based on the principle of equal load, a constant equivalent height is used to replace the changing curve height.

[0021] Step S4, solving the integral equation to obtain an analytical solution or an approximate solution of the equivalent height, which is a recommended formula for calculating the average height of overhead line wires for wind load calculation.

[0022] More specifically, for the calculation formula of the wind load in the specification described in step S2, in Example 1, the content recorded in the "110kV~750kV Overhead Transmission Line Design Specification" (GB 50545-2010) is as follows: W X =a·W O ·μ z ·μ sc β o ·d·L p ·B·sin 2 θ; W O =V 2 / 1600; Where: W X is the standard value of horizontal wind load perpendicular to the conductor and ground wire (kN); a is the wind pressure unevenness coefficient, which should be determined according to the design basic wind speed and the provisions of Table 10.1.18-1. When checking the electrical clearance of the tower, the value of a changes with the horizontal span and is determined according to the provisions of Table 10.1.18-2; β o β is the wind load adjustment factor for conductors and ground wires of 500kV and 750kV lines, which is only used to calculate the wind loads on conductors and ground wires acting on towers (excluding the calculation of conductor and ground wire tension sag and wind deflection angle). oIt should be determined according to the provisions of Table 10.1.18-1. For lines of other voltage levels, β o Take 1.0; μ z is the wind pressure height variation coefficient. The wind pressure height variation coefficient with a reference height of 10m shall be determined according to the provisions of Table 10.1.22; μ sc It is the body factor of the conductor or ground wire. When the wire diameter is less than 17mm or covered with ice (regardless of the wire diameter), μ sc =1.2; wire diameter is greater than or equal to 17mm, μ sc Take 1.1; d is the outer diameter of the conductor or ground wire or the calculated outer diameter when covered with ice; for a split conductor, the sum of the outer diameters of all sub-conductors is taken (m); L p is the horizontal span of the tower (m); B is the wind load increase factor when covered with ice, which is 1.1 for 5 mm ice area and 1.2 for 10 mm ice area; θ is the angle between the wind direction and the conductor or ground wire direction (°); W O is the standard value of the base wind pressure (kN / m 2 ); V is the wind speed (m / s) at a reference height of 10m.

[0023] Table 10.1.18-1 Wind pressure unevenness coefficient a and ground wire wind load adjustment coefficient β o

[0024] Note: For jumper calculations, a should be 1.0.

[0025] Table 10.1.18-2 Values ​​of wind pressure non-uniformity coefficient a as a function of horizontal span

[0026] In Example 2, the contents recorded in the "Overhead Transmission Line Load Specification" (DLT5551-2018) and the "Overhead Transmission Line Electrical Design Code" (DL / T 5582-2020) are as follows: W X =β c α L ·W O ·μ z ·μ sc ·d·L p ·B l ·sin 2 θ; β c =γ c (1+2g·Iz ); ; ; ; W O =V O 2 / 1600; Where: W X is the standard value of wind load perpendicular to the conductor and ground wire (kN); β c is the ground line gust coefficient; α L is the gear spacing reduction factor; W O is the reference wind pressure (kN / m 2 ); μ z is the wind pressure height variation coefficient. The wind pressure height variation coefficient with a reference height of 10m shall be determined according to the provisions of Table 6.1.1-1; μ sc It is the body factor of the conductor or ground wire. When the wire diameter is greater than or equal to 17 mm, it is 1.0. When the wire diameter is less than 17 mm, it is 1.1. d is the outer diameter of the conductor or ground wire or the calculated outer diameter when covered with ice. For split conductors, the sum of the outer diameters of all sub-conductors is taken (m); L p is the horizontal span of the tower (m); B l It is the coefficient of wind load increase for ground wire due to ice coating. For various situations designed with ice, it is 1.1 for 5mm ice area, 1.2 for 10mm ice area, and 1.0 for no ice situation. It is 1.0 when calculating tension. θ is the angle between the wind direction and the conductor or ground wire direction (°); γ c is the wind load reduction factor of the ground wire, which is taken as 0.9; g is the peak factor, which is 2.5; I z is the turbulence intensity at the average height z of the conductor; I 10 is the nominal turbulence intensity at 10m height, which can be 0.12, 0.14, 0.23 and 0.39 for the ground roughness of types A, B, C and D respectively; Z is the average height of the conductor and ground wire (m); α is the surface roughness index, which is 0.12, 0.15, 0.22, and 0.3 for landforms of types A, B, C, and D, respectively; ε cis the reduction coefficient of wind load fluctuation of ground wire, which should be taken as 0 when calculating the tension of ground wire, and the value specified in Table 6.1.1-2 when calculating the wind load of ground wire (for tower structure design); δ L is the span correlation integral factor, which should be calculated according to the above formula for the ground wire and can be taken as 1.0 when calculating the jumper wire; L X is the integration length of the horizontal correlation function, which can be taken as 50m; e is a natural constant, which can be taken as 2.71828; V O is the basic wind speed (m / s).

[0027] Table 6.1.1-1 Wind pressure height variation coefficient μ z

[0028] Note 1: Among the ground roughness categories: Category A refers to areas near the sea, islands, coasts, lakeshores and desert areas; Category B refers to fields, villages, jungles, hills, towns with relatively sparse houses and urban suburbs; Category C refers to urban areas with densely packed buildings; Category D refers to urban areas with densely packed buildings and taller houses.

[0029] Note 2: For overhead transmission lines located in the open sea and on islands, the wind pressure height variation coefficient should be appropriately increased.

[0030] Table 6.1.1-2 Ground wind load pulsation reduction factor ε c

[0031] Note: For coastal areas affected by typhoons, 0.7 can be used.

[0032] In the above formula, for a certain gear spacing L p Wire, parameters a, W O , μ sc , β o , d, B, θ, B1 are all constants; and the parameter μ z , β c , α L It is related to the height. The specification uses specific values ​​for calculation. In this method, it is expressed as a function μ that changes with the height h. z (h), β c (h), α L (h); then the load of the wire is expressed as a function of h W X (h): For Example 1 (national standard), W X (h) = μ z (h)•L p•C1; C1 is the first calculation coefficient, C1= a•W O •μ sc •β o •d•B•sin 2 θ; For Example 2 (row standard), W X (h) = β c (h)•α L (h)•μ z (h)•L p •C2; where C2 is the second calculation coefficient, C2=W O •μ sc •d•B l •sin 2 θ.

[0033] Furthermore, it can be transformed into a general wind load calculation formula: W X (h)=g(h)•L p •C; Wherein g(h) is the height correlation calculation function, and C is the calculation coefficient; for Example 1: g(h)=μ z (h), C = C1; for Example 2: g(h) = β c (h)•α L (h)•μ z (h), C=C2.

[0034] Then in step S3, let any small segment of any wire S be Δx, the horizontal position of the wire element be x, the height corresponding to the wire element be h(x), and the wind load of the wire element be: ΔW = g(h(x))•Δx•C; Wherein, g(h(x)) is a height-dependent calculation function with respect to a horizontal position x.

[0035] According to the "equal load" principle, for a certain wire, suppose there is a line with a height of h eq The wind load of the straight line is equal to the sum of the loads of each load element of the wire in the curve shape: For a line with an equivalent height h eq The wind load of the straight line is: ; Among them, g(h eq ) is the height and takes the equivalent height h eq The value of the highly correlated calculation function when ; The wind load of the curve (the sum of the loads of each load element of the wire under the curve shape) is: ; Where L is the span, and its value in this formula is equal to the horizontal span L of the tower. p ; Let the wind load on the line be W X直 = Wind load on curve W X曲 , the relationship between the equivalent height and the actual height is obtained, that is, the integral equation of the equal load principle is: .

[0036] For example, for Example 1, the integral equation of the equal load principle is: ; Where: L is the span, that is, the upper and lower limits of the change of the microelement dx, and the value in this formula is equal to the horizontal span L of the tower p . m α is the wind pressure correction factor.

[0037] Then, in step S4, the analytical solution of the equivalent height of the wire is obtained from the integral equation: ; Where: h eq is the equivalent height, i.e., the average height of overhead line wires used for wind load calculation in this method (m); f is the maximum sag in the gear (m); the calculation formula for the maximum sag f in the gear is: , g is the load ratio of the wire in the gear, L is the gear distance, and T is the tension of the wire in the gear; h0 is the height of the lowest point of the conductor in the section (m); the height of the lowest point of the conductor in the section h0 can be determined according to the maximum sag f in the section and the height of the suspension point h x Calculated, the calculation formula is h0=h x -f, suspension point height h x is a known value for the project; α is the surface roughness coefficient, and the values ​​of A, B, C and D terrain types are 0.12, 0.16, 0.22 and 0.30 respectively; among the surface roughness categories: Category A refers to near-sea surfaces and islands, coasts, lakeshores and desert areas; Category B refers to fields, villages, jungles, hills, towns and urban suburbs with relatively sparse houses; Category C refers to urban areas with densely packed buildings; and Category D refers to urban areas with densely packed buildings and taller houses.

[0038] For Example 2, the integral equation of the equal load principle is: ; Where: L is the span, that is, the upper and lower limits of the change of the microelement dx, and the value in this formula is equal to the horizontal span L of the tower p .

[0039] Then in step S4, the integral equation is difficult to solve, and an approximate solution of the equivalent height can be obtained by using an approximate numerical value: ; Where: h eq is the equivalent height, i.e., the average height of overhead line wires used for wind load calculation in this method (m); h0 is the height of the lowest point of the conductor in the section (m); f is the maximum sag in the range (m); α is the surface roughness coefficient, which is 0.12, 0.15, 0.22, and 0.30 for A, B, C, and D terrain types, respectively; g(α) is the equivalent height calculation coefficient, which is 19.5%, 21%, 23.5% and 26.5% for A, B, C and D terrains respectively.

[0040] It should be noted that in the above two embodiments, the functional relationship h(x) between the height h of the wire in the gear and the horizontal position x adopts a parabolic equation. The above two embodiments are examples of calculation of the present invention. The focus of the present invention is to use the "equal load" method for calculation instead of the existing "equal area" method. For new specifications that appear in the future, or other related specifications / standards that require the calculation of the average height of overhead line wires, the solution of the present invention can also be adopted.

[0041] In order to more clearly highlight the innovation of the present invention, as a supplementary explanation, the calculation process of the existing "equal area" method is as follows: When the lowest point of the wire is taken as 0 meters, the following equation can be listed (the wire curve shape takes a parabola as an example): ; The area enclosed by the inner curve and the flat ground = Average height of wires (h eq )×gear distance (L): .

[0042] In summary, the calculation method of the average height of overhead line wires used in wind load calculation of the present invention is based on the definition formula of overhead line load calculation in the new and old design specifications, and from the perspective of being more suitable for the load action mechanism, based on the load action principle, and using formula derivation combined with approximate calculation, a recommended calculation formula is proposed. The existing calculation method is derived based on the "equal area" method formed by the curve and the ground. The horizontal axis and vertical axis corresponding to this area are both distances in space, which is an average height in a mathematical relationship and cannot reflect the physical meaning, that is, the load action situation. The present invention, based on the characteristics of the load calculation formula, establishes a function of the influence of height on load, and uses the full-file "equal load" method to calculate the equivalent height, which is closer to the actual model of wind load calculation and has more significance and value for practical application.

Claims

1. A method for calculating the average height of overhead line wires for wind load calculation, characterized in that: The steps include: Step S1, determining the curve equation describing the shape of the overhead wire, and determining the functional relationship between the height h of the wire in the section and the horizontal position x; Step S2, in the calculation formula of the wind load, the parameter related to the height is expressed as a function related to the horizontal position x; Step S3, according to the "equal load" principle, the integral equation of the equivalent height and the actual height is listed; wherein the "equal load" principle means that for a certain level of wire, it is assumed that there is a line with an equivalent height h eq The wind load of the straight line is equal to the sum of the loads of each load element of the wire in the curve shape; Step S4, solving the integral equation to obtain an analytical solution or an approximate solution of the equivalent height, which is a calculation formula for the average height of overhead line wires used in wind load calculation.

2. The method for calculating the average height of overhead line wires for wind load calculation according to claim 1, characterized in that: In step S2, after expressing the height-related parameters as functions related to the horizontal position x, the general wind load calculation formula is obtained as follows: W X (h)=g(h)•L p •C; Among them, g(h) is the height correlation calculation function, L p is the horizontal span of the tower, C is the calculation coefficient; Then in step S3, let any small segment of any wire element be Δx, the horizontal position of the wire element be x, the height corresponding to the wire element be h(x), and the wind load of the wire element be: ΔW = g(h(x))•Δx•C; For a line with an equivalent height h eq The wind load of the straight line is: ； The sum of the loads of each load element of the wire under the curve shape is: ； Where L is the span, and its value in this formula is equal to the horizontal span L of the tower. p ; Then, according to the "equal load" principle, the integral equation is: 。 3. The method for calculating the average height of overhead line wires for wind load calculation according to claim 1 or 2, characterized in that: In step S1, the curve equation describing the shape of the overhead power line is a parabola equation or a catenary equation.

4. The method for calculating the average height of overhead line wires for wind load calculation according to claim 1 or 2, characterized in that: In step S2, the parameters related to the height include at least one of the wind pressure height variation coefficient and the turbulence intensity at the average height of the conductor.

5. The method for calculating the average height of overhead line wires for wind load calculation according to claim 1, characterized in that: In step S2, the calculation formula of wind load is: W X =a·W O ·m z ·m sc ·b o ·d·L p ·B·sin 2 I; W O =V 2 / 1600; Where: W X is the standard value of horizontal wind load perpendicular to the conductor and ground wire; a is the wind pressure unevenness coefficient; β o μ is the wind load adjustment factor for 500kV and 750kV line conductors and ground wires; z is the wind pressure height variation coefficient; μ sc is the body coefficient of the conductor or ground wire; d is the outer diameter of the conductor or ground wire or the calculated outer diameter when covered with ice; L p is the horizontal spacing of the tower; B is the wind load increase factor when covered with ice; θ is the angle between the wind direction and the conductor or ground wire direction; W O is the standard value of the benchmark wind pressure; V is the wind speed at a benchmark height of 10m; Then in step S3, the integral equation obtained is: ； Where: L is the gear distance; h eq is the equivalent height, i.e. the average height of overhead line wires used in wind load calculation; m α is the wind pressure correction factor.

6. The method for calculating the average height of overhead line wires for wind load calculation according to claim 5, characterized in that: In step S4, the analytical solution is obtained from the integral equation: ； Where: h eq is the equivalent height, i.e., the average height of overhead line wires used for wind load calculation; h0 is the height of the lowest point of the conductor in the section; f is the maximum sag in the section; α is the ground roughness coefficient.

7. The method for calculating the average height of overhead line wires for wind load calculation according to claim 6, characterized in that: The ground roughness categories include: Class A refers to near-sea surfaces and islands, coasts, lakeshores and desert areas; Class B refers to fields, villages, jungles, hills, towns and urban suburbs with relatively sparse houses; Class C refers to urban areas with densely packed buildings; and Class D refers to urban areas with densely packed buildings and taller houses. For Class A, Class B, Class C and Class D terrains, the ground roughness coefficient α is 0.12, 0.16, 0.22 and 0.30 respectively.

8. The method for calculating the average height of overhead line wires for wind load calculation according to claim 1, characterized in that: In step S2, the calculation formula of wind load is: W X =b c ·a L ·W O ·m z ·m sc ·d·L p ·B l ·sin 2 I; b c =c c (1+2g·I z ); ； ； ； W O =V O 2 / 1600; Where: W X is the standard value of wind load perpendicular to the conductor and ground wire; β c is the ground line gust coefficient; α L W is the gear spacing reduction coefficient; O is the reference wind pressure; μ z is the wind pressure height variation coefficient; μ sc is the body coefficient of the conductor or ground wire; d is the outer diameter of the conductor or ground wire or the calculated outer diameter when covered with ice; L p is the horizontal span of the tower; B l is the ice-covered wind load increase factor for the ground wire; θ is the angle between the wind direction and the conductor or ground wire direction; γ c is the wind load reduction factor of the ground wire; g is the peak factor; I z is the turbulence intensity at the average height of the conductor; I 10 is the nominal turbulence intensity at 10m height; Z is the average height of the conductor and ground wire; α is the ground roughness index; ε c is the reduction factor of wind load pulsation of ground wire; δ L is the span correlation integration factor; L X is the integration length of the horizontal correlation function; e is a natural constant; V O is the basic wind speed; Then in step S3, the integral equation obtained is: ； Where: L is the gear distance; h eq is the equivalent height, i.e. the average height of overhead line wires used in wind load calculation; m α is the wind pressure correction factor.

9. The method for calculating the average height of overhead line wires for wind load calculation according to claim 8, characterized in that: In step S4, the approximate solution is obtained from the integral equation: ； Where: h eq is the equivalent height, i.e., the average height of overhead line wires used for wind load calculation; h0 is the height of the lowest point of the conductor in the section; f is the maximum sag in the section; α is the ground roughness coefficient; g(α) is the equivalent height calculation coefficient.

10. The method for calculating the average height of overhead line wires for wind load calculation according to claim 9, characterized in that: The ground roughness categories include: Class A refers to near-sea surfaces and islands, coasts, lakeshores and desert areas; Class B refers to fields, villages, jungles, hills, towns and urban suburbs with relatively sparse houses; Class C refers to urban areas with densely packed buildings; Class D refers to urban areas with densely packed buildings and taller houses; for Class A, Class B, Class C and Class D terrains, the ground roughness coefficient α is 0.12, 0.15, 0.22 and 0.30 respectively, and the equivalent height calculation coefficient g(α) is 19.5%, 21%, 23.5% and 26.5% respectively.

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