Lightning strike risk assessment method for wind turbines in complex terrain

Abstract

The invention discloses a method for assessing the lightning strike risk of wind turbines under complex terrain. The method first uses the finite element method to determine point by point whether the downward leader of each lightning current amplitude interval at each coordinate position can hit a certain wind power generator, and then calculates the lightning interception area of ​​the wind turbine. Finally, the area is multiplied by the local ground lightning density to obtain the number of downward lightning strikes suffered by the wind turbine per year, and the number of lightning strikes is used as the basis for the lightning strike risk assessment of the wind turbine. When calculating the potential distribution between the lightning strike target point and the downward leader head, the present invention takes into account the influence of terrain factors, which can reflect the physical process of lightning connection of wind turbines under different terrain structures, and the results are more accurate. At the same time, it overcomes the disadvantage that the existing method cannot reflect the influence of the geometric shape of the target object on the lightning connection process, and provides a theoretical analysis method for analyzing the lightning strike risk of wind turbines in complex environments.

Description

Technical Field

[0001] The invention belongs to the field of wind power generation lightning protection, and in particular relates to a method for assessing the lightning strike risk of a wind turbine generator under complex terrain. Background Art

[0002] As an important renewable energy, wind energy has the characteristics of abundant reserves, renewable, wide distribution and no pollution. Compared with traditional coal-fired or oil-fired power generation, wind power generation can reduce pollution and smoke, and is one of the main directions of renewable energy development. At the same time, wind energy, as the cleanest energy that can be market-oriented except for hydropower, has been recognized and developed by various countries and regions in the world, and is playing an increasingly important role in the global energy structure.

[0003] Most wind farms are located in open areas. Wind turbines are very susceptible to lightning strikes due to their terrain and tall structures. Most of the damage caused by lightning to wind turbines is irreparable. The blade damage and downtime caused by lightning are the most serious. The economic losses generated far exceed the sum of other failures, which has become a key factor restricting the large-scale development of wind power. It can be seen that it is of great practical significance to conduct lightning risk assessment on wind turbines and wind farms, find out the weak points of lightning strikes, and propose the most economical lightning protection measures for wind turbines in inland wind farms.

[0004] At present, the empirical formula recommended by IEC61400-24 is mainly used to calculate the number of downward lightning strikes on wind turbines. This method uses three times the height of the unit as the equivalent lightning radius of the unit, determines the circular lightning interception area centered on the unit, and the product of the ground lightning density and the area of ​​the circular area is the average annual number of lightning strikes on the unit. This method regards the wind turbine as a lightning rod with a height equal to the sum of the cabin height and the impeller radius, but this method has obvious shortcomings: it is separated from the actual physical process of lightning strikes, and cannot reflect the influence of lightning current amplitude and the geometric shape of the wind turbine on the size of the lightning interception area of ​​the unit. In addition, the geometric shape of wind turbines is more complex than that of traditional ground targets such as lightning rods. Therefore, the accuracy of the IEC recommended method needs further research and verification. In addition, traditional wind turbine lightning risk assessment methods are based on the establishment of wind turbines in flat and open terrain, while the actual situation is that most wind turbines are established on mountain tops or hillsides with high wind speeds, ignoring the influence of factors such as terrain on lightning risk.

[0005] In recent years, the basic research on lightning strike termination of ground targets has made great progress. The self-consistent leader inception and propagation model (SLIM) proposed by Becerra and Cooray does not have the problem that the electro geometrical model (EGM) cannot consider the oncoming leader, and overcomes the shortcomings of the electro geometrical model and the collection volume method (CVM) based on the leader method that cannot reflect the influence of the geometric shape of the target on the lightning strike termination process. It can be used for the calculation of the downward lightning strike risk of ground targets and the distribution analysis of lightning attachment points. Its main shortcomings include:

[0006] 1. The model has too much computational effort, which is not conducive to its use in actual engineering.

[0007] 2. The parameter settings of the model for judging whether the various conditions are hit are based on statistical data. However, with the development of wind power generation, the scale of wind turbines is also expanding, so the accuracy of these parameters needs further research and verification. Summary of the invention

[0008] The technical problem to be solved by the present invention is that the existing wind turbine lightning strike risk assessment method does not take into account the actual terrain location of the wind turbine, and proposes a wind turbine lightning strike risk assessment method to assess the lightning strike risk of a single wind turbine under different terrain factors, so as to find out the weak points of lightning strike and propose the most economical lightning strike protection measures for wind turbines.

[0009] The object of the present invention is achieved in this way. The present invention proposes a method for assessing the lightning strike risk of a wind turbine generator under complex terrain, comprising the following steps:

[0010] Step 1, setting of evaluation parameters;

[0011] Select any wind turbine in the wind turbine generator set to be evaluated, denoted as wind turbine D, and construct equal-angle rays in the horizontal direction with the center of wind turbine D as the starting point. Assume that the angles of two adjacent rays are both β, and a total of F rays are obtained. The length of the ray is the average distance R between wind turbines in the wind farm where wind turbine D is located. On each of the F rays, points are taken from the starting point outward at equal intervals j, and M points are obtained for one ray, and a total of F×M points are obtained for F rays. With the center of the wind turbine as the pole, record the polar coordinates of F×M points, and form a polar coordinate set of the position of the downlink leader, denoted as set A, A={(r a ,θ b )|r a =a×j,θb =b×β,a=1,2,3...M; b=1,2,3...F}

[0012] Among them, r m is the polar radius of any point in set A, θ b is the polar angle of any point in set A, and a is the polar diameter r m The serial number of b is the polar angle θ b Serial number;

[0013] According to the known observation data, the lightning current amplitude range is set to 0-300KA, and 0-300KA is divided into G intervals. The lightning current amplitude of the median of each interval is used as the lightning current amplitude of the evaluation point in the interval. The lightning current amplitudes of the evaluation points in the G intervals are obtained and form a set of lightning current amplitudes, which is recorded as set B, B = {I Py |I Py =y×v, y=1,2,3...G;}, where v is the equally divided lightning current amplitude range 0-

[0014] 300KA interval length, v = 300 / G, I Py is the lightning current amplitude of any interval evaluation point in set B, y is the lightning current amplitude I Py The corresponding serial number;

[0015] Step 2, obtain the terrain data of the location of wind turbine D; select any point in the set A obtained in step 1 as point X, and record the vertical distance from the head of the downward leader to the ground at the position of point X as height H1; select any lightning current amplitude I of an interval evaluation point in the set B obtained in step 1 Py , the finite element method is used to calculate the wind turbine D in the terrain data and the lightning current amplitude I Py When , the following two sets of data at the point X position: the potential distribution U1(l) of the line between the lightning target point and the downward leader head in the state of streamer generation and the potential distribution U2(l) of the line between the lightning target point and the downward leader head in the state of no streamer generation, where l is the distance from any point on the line between the downward leader head and the lightning target point to the downward leader head; two potential distribution curves are used to express the potential distribution U1(l) and the potential distribution U2(l), where the potential distribution curve in the state of streamer generation is recorded as potential distribution curve 1, and the potential distribution curve in the state of no streamer generation is recorded as potential distribution curve 2;

[0016] The lightning strike target point is the tip of the wind turbine blade, and the value range of the height H1 is 0-1000m;

[0017] Step 3: record the straight-line distance from the head of the descending leader at point X to the lightning target point as distance H2. If H2

[0018] Step 4: Based on the potential distribution curve 1 and the potential distribution curve 2 obtained in step 2, determine whether there is a stable oncoming leader at the lightning strike target point. If there is a stable oncoming leader, determine that the downward leader at the position of point X hits the wind turbine D. Otherwise, reduce the height H1 and return to step 2. The specific determination steps of step 4 are as follows:

[0019] Step 4.1, determine whether a streamer is generated at the lightning strike target point, if a streamer is generated, proceed to step 4.2, otherwise reduce the height H1 and return to step 2; the lightning strike target point having a streamer means that the potential distribution curve 1 and the potential distribution curve 2 in step 2 have an intersection;

[0020] Step 4.2, judging whether the streamer in step 4.1 is transformed into a leader, if the streamer is transformed into a leader, proceeding to step 4.3, otherwise lowering the height H1 and returning to step 2; the requirement for the streamer to be transformed into a leader is that the space charge ΔQ generated in the streamer reaches 1μC, that is, if ΔQ ≥ 1μC, it is determined that the streamer is transformed into a leader;

[0021] The calculation formula for the space charge ΔQ generated in the streamer is:

[0022]

[0023] In the formula, K Q is the geometric factor, take K Q =3.5×10 -11 , l s is the length of the initial streamer, l s =0.02m;

[0024] Step 4.3, determine whether the leader described in step 4.2 develops into a stable oncoming leader. If the leader develops into a stable oncoming leader, determine that the downward leader at point X hits the fan D, and go to step 5. Otherwise, reduce the height H1 and return to step 2.

[0025] The requirement for the leader to develop into a stable oncoming leader is: the length L of the oncoming leader obtained by n iterations (n) >2 meters, where the number of iterations n is the number of times the height H1 is reduced;

[0026] Step 5: According to the method from step 2 to step 4, the downward leader of each point in set A is determined point by point at the lightning current amplitude I Py ​After all the points in set A are judged, the outermost points of all the points where the up and down leader of F rays hits wind turbine D are connected to form a closed boundary. The area enclosed by the boundary is the lightning current amplitude I Py The lightning interception area of ​​the wind turbine generator is A(I Py );

[0027] Step 6: According to the method of steps 2 to 5, determine whether the downlink leader can hit the wind turbine D at the lightning current amplitude of each interval evaluation point in set B, and record it; after all the interval evaluation points in set B are determined, the number of lightning strikes N of the wind turbine D is calculated according to the following formula, and the number of lightning strikes N of the wind turbine is used as the basis for the lightning strike risk assessment of the wind turbine:

[0028]

[0029] In the formula, P(I P y) is the lightning current amplitude I P The probability density distribution of lightning current amplitude at time y, N G is the ground-to-ground lightning density at the wind turbine location, N G =0.04T d 1.25 , where T d is the number of thunderstorm days at the location of the wind turbine.

[0030] Preferably, the terrain data in step 2 includes the height of the terrain where the wind turbine is located, the inclination of the ground where the wind turbine is located, and the location of the wind turbine, wherein the height of the terrain where the wind turbine is located ranges from 0 to 100 m, and the inclination of the ground where the wind turbine is located ranges from 0° to 45°; the inclination of the ground where the wind turbine is located is the inclination formed by the ground where the wind turbine is located and the horizontal plane, and the location of the wind turbine takes into account two situations: the wind turbine is located on the top of a mountain and on a hillside; the method for obtaining the height of the terrain where the wind turbine is located is: draw a circle with the wind turbine as the center and R as the radius, and obtain the altitude difference between each point in the circular area and the wind turbine, and the altitude difference is the height of the terrain where the wind turbine is located.

[0031] Preferably, when a streamer is generated at the lightning strike target point in step 2, the field strength in the space where the streamer occurs is E=450KV / m.

[0032] Preferably, the length L of the oncoming leader obtained by n iterations in step 4.3 is (n) The steps include:

[0033] Step 4.3.1, calculate the space charge Q generated by the streamer after the nth iteration using the following formula: n , and make a judgment, if Q n >0, go to step 4.3.2, otherwise reduce the height H1 and repeat step 4.3.1;

[0034]

[0035] Where, L (n-1) is the length of the oncoming leader calculated at the n-1th iteration, and the initial length of the oncoming leader L (0) =0.02m, is the initial streamer length at the nth iteration, U 1n (l) is the potential distribution of the line between the lightning strike target point and the head of the downward leader obtained by the nth iteration calculation, U 1(n-1) (l) is the potential distribution of the line between the lightning strike target point and the head of the downward leader obtained by the n-1th iteration calculation;

[0036] Step 4.3.2, calculate the length L of the oncoming leader obtained through n iterations (n) ;

[0037] L (n) =L (n-1) +Q n / q L

[0038] Among them, q L is the space charge required per unit length of the oncoming leader, and q L =65C / m.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1. It can reflect the physical process of wind turbine lightning protection under different terrain structures, and the results are more accurate.

[0041] 2. It not only takes into account the problem of oncoming leaders, but also reflects the shortcomings of the geometric shape of the target object on the lightning connection process, making the calculation results more convincing.

[0042] 3. This method has a clearer physical meaning, and the model has been applied in the lightning protection design of transmission lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a flow chart of the present invention.

[0044] Figure 2 It is a potential distribution diagram between the lightning strike target point and the downward leader head when streamer occurs and when streamer does not occur in the present invention.

[0045] Figure 3 It is a plane schematic diagram of the medium-angle F-ray distribution and the lightning strike interception area of ​​the wind turbine generator according to the present invention.

[0046] Figure 4 It is a three-dimensional schematic diagram of the lightning interception area of ​​wind turbines in complex terrain. DETAILED DESCRIPTION

[0047] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0048] Figure 1 : is a flow chart of a method for assessing the lightning strike risk of a wind turbine generator under complex terrain of the present invention. As can be seen from the figure, a method for assessing the lightning strike risk of a wind turbine generator under complex terrain of the present invention comprises the following steps:

[0049] Step 1, setting of evaluation parameters;

[0050] Select any wind turbine in the wind turbine generator set to be evaluated, denoted as wind turbine D, and construct equal-angle rays in the horizontal direction with the center of wind turbine D as the starting point. Assume that the angles of two adjacent rays are both β, and a total of F rays are obtained. The length of the ray is the average distance R between wind turbines in the wind farm where wind turbine D is located. On each of the F rays, points are taken from the starting point outward at equal intervals j, and M points are obtained for one ray, and a total of F×M points are obtained for F rays. With the center of the wind turbine as the pole, record the polar coordinates of F×M points, and form a polar coordinate set of the position of the downlink leader, denoted as set A, A={(r a ,θ b )|r a =a×j,θ b =b×β, a=1, 2, 3...M; b=1, 2, 3...F}

[0051] Among them, r m is the polar radius of any point in set A, θ b is the polar angle of any point in set A, and a is the polar diameter r m The serial number of b is the polar angle θ b The serial number of the

[0052] The distribution of F equiangular rays can be seen Figure 3 .

[0053] According to the known observation data, the lightning current amplitude range is set to 0-300KA, and 0-300KA is divided into G intervals. The lightning current amplitude of the median of each interval is used as the lightning current amplitude of the evaluation point in the interval. The lightning current amplitudes of the evaluation points in the G intervals are obtained and form a set of lightning current amplitudes, which is recorded as set B, B = {I Py |I Py=y×v, y=1, 2, 3...G;}, where v is the length of the interval that equally divides the lightning current amplitude range from 0 to 300KA, v=300 / G, I Py is the lightning current amplitude of any interval evaluation point in set B, y is the lightning current amplitude I Py The corresponding serial number.

[0054] Step 2, obtain the terrain data of the location of wind turbine D; select any point in the set A obtained in step 1 as point X, and record the vertical distance from the head of the downward leader to the ground at the position of point X as height H1; select any lightning current amplitude I of an interval evaluation point in the set B obtained in step 1 Py , the finite element method is used to calculate the wind turbine D in the terrain data and the lightning current amplitude I Py When , the following two sets of data at point X are obtained: the potential distribution U1(l) of the line between the lightning target point and the downward leader head in the state of streamer generation and the potential distribution U2(l) of the line between the lightning target point and the downward leader head in the state of no streamer generation, where l is the distance from any point on the line between the downward leader head and the lightning target point to the downward leader head; two potential distribution curves are used to express the potential distribution U1(l) and the potential distribution U2(l), where the potential distribution curve in the state of streamer generation is recorded as potential distribution curve 1, and the potential distribution curve in the state of no streamer generation is recorded as potential distribution curve 2. It can be seen from the potential distribution curve 1 and the potential distribution curve 2 Figure 2 .

[0055] The lightning strike target point is the tip of the wind turbine blade, and the height H1 has a value range of 0-1000m.

[0056] In step 2, the terrain data includes the height of the terrain where the wind turbine is located, the inclination of the ground where the wind turbine is located, and the location of the wind turbine, wherein the height of the terrain where the wind turbine is located ranges from 0 to 100 m, and the inclination of the ground where the wind turbine is located ranges from 0° to 45°; the inclination of the ground where the wind turbine is located is the inclination formed by the ground where the wind turbine is located and the horizontal plane, and the location of the wind turbine takes into account two situations: the wind turbine is located on the top of a mountain and on a hillside; the method for obtaining the height of the terrain where the wind turbine is located is: draw a circle with the wind turbine as the center and R as the radius, and obtain the altitude difference between the lowest point in the circular area and the wind turbine, and the altitude difference is the height of the terrain where the wind turbine is located.

[0057] In step 2, when a streamer is generated at the lightning strike target point, the field strength in the space where the streamer occurs is taken as E=450KV / m.

[0058] Step 3, record the straight-line distance from the head of the descending leader at point X to the lightning strike target point as distance H2. If H2

[0059] Step 4: Based on the potential distribution curve 1 and the potential distribution curve 2 obtained in step 2, determine whether there is a stable oncoming leader at the lightning strike target point. If there is a stable oncoming leader, determine that the downward leader at point X hits wind turbine D. Otherwise, reduce the height H1 and return to step 2.

[0060] The specific judgment steps of step 4 are as follows:

[0061] Step 4.1, determine whether a streamer is generated at the lightning strike target point. If a streamer is generated, proceed to step 4.2, otherwise lower the height H1 and return to step 2; the generation of a streamer at the lightning strike target point means that the potential distribution curve 1 and the potential distribution curve 2 in step 2 have an intersection. Figure 2 The state where the potential distribution curve 1 and the potential distribution curve 2 intersect at the 0 point is shown.

[0062] Step 4.2, determine whether the streamer in step 4.1 is transformed into a leader. If the streamer is transformed into a leader, go to step 4.3, otherwise reduce the height H1 and return to step 2; the requirement for the streamer to transform into a leader is: the amount of space charge ΔQ generated in the streamer reaches 1μC, that is, if ΔQ ≥ 1μC, it is determined that the streamer is transformed into a leader.

[0063] The calculation formula for the space charge ΔQ generated in the streamer is:

[0064]

[0065] In the formula, K Q is the geometric factor, take K Q =3.5×10 -11 , l s is the length of the initial streamer, l s =0.02m.

[0066] Step 4.3, determine whether the leader described in step 4.2 develops into a stable oncoming leader. If the leader develops into a stable oncoming leader, determine that the downward leader at point X hits fan D, and go to step 5. Otherwise, reduce the height H1 and return to step 2.

[0067] The requirement for the leader to develop into a stable oncoming leader is: the length L of the oncoming leader obtained by n iterations (n) >2 meters, where n is the number of iterations, and the number of iterations n is the number of times the height H1 is lowered.

[0068] ​Specifically, the length L of the oncoming leader obtained after n iterations is (n) The calculation steps are as follows:

[0069] Step 4.3.1, calculate the space charge Q generated by the streamer after the nth iteration using the following formula: n , and make a judgment, if Q n >0, go to step 4.3.2, otherwise reduce the height H1 and repeat step 4.3.1.

[0070]

[0071] Where, L (n-1) is the length of the oncoming leader calculated at the n-1th iteration, and the initial length of the oncoming leader L (0) =0.02m, is the initial streamer length at the nth iteration, U 1n (l) is the potential distribution of the line between the lightning strike target point and the head of the downward leader obtained by the nth iteration calculation, U 1(n-1) (l) is the potential distribution of the line between the lightning strike target point and the downward leader head obtained by the n-1th iteration calculation.

[0072] Step 4.3.2, calculate the length L of the oncoming leader obtained through n iterations (n) ;

[0073] L (n) =L (n-1) +Q n / q L

[0074] Among them, q L is the space charge required per unit length of the oncoming leader, and q L =65C / m.

[0075] Step 5: According to the method from step 2 to step 4, the downward leader of each point in set A is determined point by point at the lightning current amplitude I Py After all the points in set A are judged, the outermost points of all the points where the up and down leader of F rays hits wind turbine D are connected to form a closed boundary. The area enclosed by the boundary is the lightning current amplitude I Py The lightning interception area of ​​the wind turbine generator is A(I Py ).

[0076] Figure 3 The lightning interception area A(I Py ) Plan view, Figure 4 The lightning interception area A(I Py) 3D schematic diagram.

[0077] Step 6: According to the method of steps 2 to 5, determine whether the downlink leader can hit the wind turbine D at each interval of the lightning current amplitude in set B, and record it; after all intervals in set B are determined, the number of lightning strikes N of the wind turbine D is calculated according to the following formula, and the number of lightning strikes N of the wind turbine is used as the basis for the lightning strike risk assessment of the wind turbine:

[0078]

[0079] In the formula, P(I P y) is the lightning current amplitude I P The probability density distribution of lightning current amplitude at time y, N G is the ground-to-ground lightning density at the wind turbine location, N G =0.04T d 1.25 , where T d is the number of thunderstorm days at the location of the wind turbine.

Claims

1. A method for assessing lightning strike risk of wind turbines in complex terrain, characterized in that: Including the following steps: Step 1, setting of evaluation parameters; Arbitrarily select a wind turbine in the wind farm wind turbines to be evaluated, denoted as wind turbine D. Taking the center of wind turbine D as the starting point, construct equiangular rays in the horizontal direction. Let the angle between two adjacent rays be β, and a total of F rays are obtained. The length of the rays is the average distance R between the wind turbines in the wind farm where wind turbine D is located. On each of the F rays, take points at equal intervals j outward from the starting point. One ray gets M points, and a total of F×M points are obtained for the F rays. Taking the wind turbine center as the pole, record the polar coordinates of the F×M points and form a set of polar coordinates of the positions where a downward leader is located, denoted as set A. A={(r a ,the b )|r a =a×j,θ b =b×β,a=1,2,3...M;b=1,2,3...F} Among them, r a is the polar radius of any point in set A, θ b is the polar angle of any point in set A, and a is the polar diameter r a The serial number of b is the polar angle θ b Serial number; According to the known observation data, the lightning current amplitude range is set to 0-300KA, and 0-300KA is divided into G intervals. The lightning current amplitude of the median of each interval is used as the lightning current amplitude of the evaluation point in the interval. The lightning current amplitudes of the evaluation points in the G intervals are obtained and form a set of lightning current amplitudes, which is recorded as set B, B = {I Py |I Py =y×v, y=1,2,3...G;}, where v is the length of the interval that equally divides the lightning current amplitude range from 0 to 300KA, v=300 / G, I Py is the lightning current amplitude of any interval evaluation point in set B, y is the lightning current amplitude I Py The corresponding serial number; Step 2, obtain the terrain data of the location of wind turbine D; select any point in the set A obtained in step 1 as point X, and record the vertical distance from the head of the descending leader to the ground at the position of point X as the height H1 of the descending leader head to the ground; select any lightning current amplitude I of an interval evaluation point in the set B obtained in step 1 Py , the finite element method is used to calculate the wind turbine D in the terrain data and the lightning current amplitude I Py When , the following two sets of data at the point X position: the potential distribution U1(l) of the line between the lightning target point and the downward leader head in the state of streamer generation and the potential distribution U2(l) of the line between the lightning target point and the downward leader head in the state of no streamer generation, where l is the distance from any point on the line between the downward leader head and the lightning target point to the downward leader head; two potential distribution curves are used to express the potential distribution U1(l) and the potential distribution U2(l), where the potential distribution curve in the state of streamer generation is recorded as potential distribution curve 1, and the potential distribution curve in the state of no streamer generation is recorded as potential distribution curve 2; The lightning strike target point is the position of the tip of the wind turbine blade, and the value range of the height H1 is 0 - 1000m. Step 3, record the straight-line distance from the head of the downward leader at the position of point X to the lightning strike target point as the distance H2 from the head of the downward leader to the target point. If H2 < H1, enter Step 4; if H2 ≥ H1, it is determined that the downward leader at the position of point X cannot strike wind turbine D, and enter Step 5. Step 4, based on the potential distribution curve 1 and potential distribution curve 2 obtained in Step 2, judge whether there is a stable oncoming leader at the lightning strike target point. If there is a stable oncoming leader, it is determined that the downward leader at the position of point X strikes wind turbine D; otherwise, reduce the height H1 and return to Step 2. The specific judgment steps of Step 4 are as follows: Step 4.1, judge whether there is a streamer generated at the lightning strike target point. If there is a streamer generated, enter Step 4.2; otherwise, reduce the height H1 and return to Step 2. The generation of a streamer at the lightning strike target point means that there is an intersection between the potential distribution curve 1 and potential distribution curve 2 described in Step 2. Step 4.2, judge whether the streamer in Step 4.1 transforms into a leader. If the streamer transforms into a leader, enter Step 4.3; otherwise, reduce the height H1 and return to Step 2. The requirement for the streamer to transform into a leader is that the space charge amount △Q generated in the streamer reaches 1 μC, that is, if △Q ≥ 1 μC, it is determined that the streamer transforms into a leader. The calculation formula for the space charge amount △Q generated in the streamer is: In the formula, K Q is the geometric factor, take K Q =3.5×10 -11 , l s is the length of the initial streamer, l s =0.02m; Step 4.3, judge whether the leader in Step 4.2 develops into a stable oncoming leader. If the leader develops into a stable oncoming leader, it is determined that the downward leader at the position of point X strikes wind turbine D and enter Step 5; otherwise, reduce the height H1 and return to Step 2. The requirement for the leader to develop into a stable oncoming leader is: the length L of the oncoming leader obtained by n iterations (n) >2 meters, where the number of iterations n is the number of times the height H1 is lowered; Step 5: According to the method from step 2 to step 4, the downward leader of each point in set A is determined point by point at the lightning current amplitude I Py After all the points in set A are judged, the outermost points of all the points where the up and down leaders of F rays hit wind turbine D are connected to form a closed boundary. The area enclosed by the boundary is the lightning current amplitude I Py The lightning interception area of ​​the wind turbine generator is A(I Py ); Step 6, judge whether the downward leader can strike wind turbine D when evaluating the lightning current amplitude of each interval evaluation point in set B one by one according to the method from Step 2 to Step 5, and make a record. After all the interval evaluation points in set B are judged, calculate the lightning strike times N of wind turbine D according to the following formula, and use the lightning strike times N of this wind turbine as the basis for the lightning strike risk assessment of the wind turbine: In the formula, P(I Py ) is the lightning current amplitude I Py The probability density distribution of lightning current amplitude is N G is the ground-to-ground lightning density at the wind turbine location, N G =0.04T d 1.25 , where T d is the number of thunderstorm days at the location of the wind turbine; The terrain data in step 2 include the height of the terrain where the wind turbine is located, the inclination of the ground where the wind turbine is located, and the location of the wind turbine, wherein the height of the terrain where the wind turbine is located varies from 0 to 100m, and the inclination of the ground where the wind turbine is located varies from 0° to 45°; the inclination of the ground where the wind turbine is located is the inclination formed by the ground where the wind turbine is located and the horizontal plane, and the location of the wind turbine takes into account the two situations where the wind turbine is located on the top of the mountain and on the hillside; the method for obtaining the height of the terrain where the wind turbine is located is: draw a circle with the wind turbine as the center and R as the radius, and obtain the altitude difference between the lowest point in the circular area and the wind turbine, and the altitude difference is the height of the terrain where the wind turbine is located; The length L of the oncoming leader obtained by n iterations in step 4.3 is (n) The steps include: Step 4.3.1, calculate the space charge Q generated by the streamer after the nth iteration using the following formula: n , and make a judgment, if Q n >0, go to step 4.3.2, otherwise reduce the height H1 and repeat step 4.3.1; Where, L (n-1) is the length of the oncoming leader calculated at the n-1th iteration, and the initial length of the oncoming leader L (0) =0.02m, is the initial streamer length at the nth iteration, U 1n (l) is the potential distribution of the line between the lightning strike target point and the head of the downward leader obtained by the nth iteration calculation, U 1(n-1) (l) is the potential distribution of the line between the lightning strike target point and the head of the downward leader obtained by the n-1th iteration calculation; Step 4.3.2, calculate the length L of the oncoming leader obtained through n iterations (n) ; L (n) =L (n-1) +Q n / q L Among them, q L is the space charge required per unit length of the oncoming leader, and q L =65C / m.

2. The method for assessing lightning strike risk of wind turbines in complex terrain according to claim 1, characterized in that: When a streamer is generated at the lightning strike target point in step 2, the field strength in the space where the streamer occurs is taken as E=450KV / m.

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