Lightning stroke windage yaw coupling risk assessment method for power transmission line under strong wind condition

Abstract

The invention discloses a lightning stroke windage yaw coupling risk assessment method for a power transmission line under a strong wind condition. The method comprises the following steps: acquiring meteorological parameters, line parameters and ground-to-ground lightning density; calculating the minimum air gap distance of each base tower under different windage yaw conditions; constructing an insulator string and air gap flashover criterion pilot model based on a pilot method; calculating the minimum wind speed value of the lightning resistance level and the gap flashover of each base tower; the electrical geometric model is improved based on a Monte Carlo algorithm, and the lightning trip-out rate is calculated; and evaluating a line risk level according to a calculation result of the lightning trip-out rate. According to the power transmission line lightning stroke windage yaw coupling risk assessment method under the strong wind condition, the accuracy of lightning stroke risk calculation can be improved, and a reference is provided for power transmission line lightning stroke windage yaw coupling risk assessment.

Description

Technical Field

[0001] The invention relates to the field of transmission line lightning strike wind deflection coupling risk assessment, in particular to a transmission line lightning strike wind deflection coupling risk assessment method under strong wind conditions. Background Art

[0002] In recent years, extreme weather has occurred frequently, which has significantly increased the probability of transmission lines facing thunderstorms and strong winds. The safe operation of transmission lines has been seriously threatened. How to finely evaluate the risk of lightning-wind coupling has become a topic that needs to be studied and solved urgently. There is a lack of high-density wind speed data during line design, and the design wind speed used to determine the minimum air gap between the live part of the line and the tower components under lightning overvoltage is usually an empirical value, which makes it difficult to ensure the rationality of the tower head air gap design under different terrain and coupled meteorological conditions. In addition, most of the existing transmission line lightning wind deflection coupling risk assessment methods focus on simply calculating the impact of the relative position change of the conductor and the ground wire on the lightning shielding failure, without considering the breakdown of the air gap at the tower head, such as the literature [1]: Chen Guoqing, Sun Caixin, Zhang Zhijin, et al. Research on the calculation model of the lightning protection performance of 500kV double-circuit transmission line with wind speed [J]. Proceedings of the CSEE, 2003, 23(5): 109-112+116. Literature [2]: Zhou Kun, Han Hao, Xia Zeju. Evaluation of lightning protection performance of UHV transmission line based on improved electrical geometry model considering comprehensive factors [J]. Insulators and Lightning Arrester, 2018, 286(6): 69-73+80. Transmission line wind deflection flashover is usually considered to be caused by the air gap between the live conductor and the tower being unable to withstand the power frequency voltage, and the tower head gap flashover fault under lightning overvoltage is rarely considered. Summary of the invention

[0003] The purpose of the present invention is to analyze the influence of wind deviation on the lightning strike risk of transmission lines, and propose a method for assessing the wind-deviated coupling risk of lightning strikes on transmission lines under strong wind conditions, which can improve the accuracy of lightning strike risk calculation and provide a reference for the assessment of the wind-deviated coupling risk of lightning strikes on transmission lines.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A method for assessing the risk of lightning strike-wind coupling of a transmission line under strong wind conditions comprises the following steps:

[0006] Step 1: Obtain meteorological parameters, line parameters and ground-to-ground lightning density;

[0007] Step 2: Calculate the minimum air gap distance of each base tower under different wind deviation conditions;

[0008] Step 3: Construct the pilot model of insulator string and air gap flashover criterion based on the pilot method;

[0009] Step 4: Calculate the lightning resistance level of each tower and the minimum wind speed value of gap flashover;

[0010] Step 5: Improve the electrical geometry model based on the Monte Carlo algorithm and calculate the lightning trip rate;

[0011] Step 6: Evaluate the line risk level based on the calculated results of the lightning tripping rate.

[0012] In step 1, meteorological parameters include wind speed and wind direction data; line parameters include tower height, call height, cross arm length, insulator string length, span, sag, and ground wire model; ground lightning density refers to the number of ground lightning strikes per square kilometer and per year.

[0013] In step 2, the minimum air gap distance of each base tower is the minimum air gap distance of the tower corresponding to different voltage levels.

[0014] 4. A method for assessing the risk of lightning and wind deflection coupling of a power transmission line under strong wind conditions according to claim 1, characterized in that: in said step 2, a finite element model of the transmission line and the insulator string is established based on the line point cloud data to calculate the wind deflection displacement change of the insulator string and each local point of the line, thereby calculating the minimum air gap distance;

[0015] The initial deformation of the transmission line is described by the catenary equation, which is calculated as follows:

[0016]

[0017] Where z is the sag, H is the horizontal running tension, q is the unit force, L is the span, α and β are the tangent angles at both ends of the catenary, c is the span hanging point position difference, and x is the distance from the starting point to each point per unit length.

[0018] In step 3, a pilot model for flashover criterion of insulator string and air gap is constructed based on the pilot method, and the pilot method is selected as the flashover criterion of insulator string and air gap; the pilot development speed is related to the voltage value and the pilot development length, and the pilot development speed calculation formula recommended by CIGRE is:

[0019]

[0020] In the formula, v z is the leader development speed; k is the leader development coefficient; U(t) is the instantaneous voltage value of the insulator string and the air gap; s is the developed length of the leader, L1 is the minimum distance between the insulator string and the tower head air gap, and E0 is the starting field strength threshold of the leader.

[0021] In step 4, since both the insulator string and the tower head air gap are simulated and calculated using the leader model, when the applied lightning current makes the leader development distance greater than the final jump distance h f When the lightning current is at the lightning withstand level, it is considered that the lightning current is at the lightning withstand level. Since the flashover voltage of the insulator string is not affected by the wind speed, as the wind speed increases, the tower head air gap will gradually decrease, and the withstand voltage value will also decrease. Therefore, when the lightning withstand level changes, it can be considered that the air gap is broken down. Based on this, the lightning withstand level of each base tower of the line is calculated. The corresponding wind speed value at this time is the minimum wind speed when the tower air gap is broken down.

[0022]

[0023] In the formula, h f is the final transition distance; l is the insulator string length.

[0024] In step 5, the electrical geometry model is improved based on the Monte Carlo algorithm to calculate the lightning tripping rate. When calculating the shielding tripping rate, firstly, according to the swing amplitude range of the conductor and the ground wire, the Monte Carlo algorithm combined with the probability density function is used to randomly select points to determine the coordinate values ​​of the conductor and the ground wire in the Cartesian two-dimensional coordinate system; secondly, combined with the electrical geometry model, the shielding tripping rate is calculated for multiple cycles until the number of cycles k meets the total number of cycles k s Then, the average value of the tripping rate is solved; finally, based on the above process, the lightning tripping rate is calculated for each tower.

[0025] Based on the statistical results of the line wind deviation points and considering the influence of local line galloping, a probability density formula for the line wind deviation points is proposed to improve the efficiency of the calculation of lightning-wind deviation coupling risk.

[0026]

[0027] Where f(x) is the probability density function; x is a random number in the range of (0,1); k, b and c are correlation coefficients.

[0028] The lightning trip rate includes the bypass trip rate and the counter-strike trip rate.

[0029] The calculation process of the shielding failure trip rate includes the following steps:

[0030] 1) Calculate the spatial position of the bottom of the insulator string and the connection point of the conductor:

[0031]

[0032] Where: G x , G y is the x and y coordinates of point G at the bottom of the insulator string; L c is the cross arm length, h cis the wire height, is the wind deflection angle of the suspension insulator string, l is the length of the insulator string;

[0033] 2) Based on the Monte Carlo algorithm, calculate the coordinate values ​​of the conductor and ground wire at each point in the Cartesian coordinate system:

[0034]

[0035] Where: X c is the horizontal coordinate of the wire in the Cartesian coordinate system, f c is the conductor sag, f(x) is the probability density function of the conductor windage position, ξ i Y is the wind deflection angle of the conductor; c is the ordinate of the wire in the Cartesian coordinate system;

[0036]

[0037] Where: X s is the horizontal coordinate of the wire in the Cartesian coordinate system, L s is the length of the ground wire cross arm, f s is the ground wire sag, γ i is the ground line wind deflection angle, Y s is the ordinate of the wire in the Cartesian coordinate system, H s is the ground line height;

[0038] 3) Select the lightning resistance level I of the air gap c As the lower limit of the calculation of the shielding rate integral, calculate the shielding rate:

[0039]

[0040] Where: P α is the lightning strike rate, φ is the lightning incident angle, I max is the maximum lightning current amplitude that causes flashover; x is the probability of shielding failure, and f(I) is the lightning current amplitude probability density function;

[0041] 4) Calculate the shielding failure trip rate:

[0042] P r =N1ηP α (9);

[0043] Where: P r is the tripping rate of circuit breaker failure, N1 is the density of ground lightning, η is the arcing rate;

[0044] The calculation process of the counter-tripping rate includes the following steps:

[0045] The calculation formula of the back-tripping rate is:

[0046] P f=N1ηg (10);

[0047] Where P f is the strike-back tripping rate; N1 is the number of lightning strikes; η is the arcing rate; g is the probability of lightning current directly hitting the tower; P is the probability of flashover.

[0048] In step 6,

[0049] According to the calculation results of the counter-attack tripping rate and the shielding failure tripping rate, the risk level of the transmission line is divided. The risk level classification standard is shown in Table 1;

[0050] Table 1 Lightning risk level classification standards

[0051]

[0053] In the above table: P r0 and P f0 are the average counter-attack tripping rate and the average shielding tripping rate when wind deviation is not considered, P f is the counter-tripping rate; P r is the circuit breaker tripping rate.

[0054] The present invention provides a method for assessing the risk of lightning-wind coupling of power transmission lines under strong wind conditions, which has the following technical effects:

[0055] 1) Compared with the traditional lightning risk assessment method, the present invention takes into account the risk of tower head gap flashover under lightning overvoltage, establishes a pilot model for insulator string and air gap flashover criteria, and uses the Monte Carlo algorithm to improve the electrical geometry model. It also considers the influence of ground inclination and lightning incident angle, thereby improving the accuracy of lightning risk calculation and being more in line with the actual operating conditions of lightning-struck transmission lines.

[0056] 2) In step 1 of the present invention, the meteorological parameters are derived from the actual monitoring data of the meteorological station; the line parameters are obtained based on the line point cloud data, and the data accuracy is high;

[0057] 3) The minimum air gap distances under different wind deviation conditions in step 2 of the present invention are obtained by simulation calculation of a finite element model established based on actual data, and the calculation results are reliable;

[0058] 4) The pilot development model established in step 3 of the present invention has high accuracy in simulating the flashover of insulator strings and air gaps. It can better reflect the physical process of long gap discharge and overcome the U 50％ Disadvantages of the intersection method and the method of intersection.

[0059] 5) The lightning resistance level calculated in step 4 of the present invention includes the situation of air gap flashover, and the calculation result is more accurate;

[0060] 6) In step 5 of the present invention, the Monte Carlo algorithm is used to improve the electrical geometry model, and the calculation is repeated multiple times to improve the accuracy of the trip rate calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0062] Figure 1 It is the finite element model of transmission line and insulator string.

[0063] Figure 2 It is a tower and pilot model.

[0064] Figure 3 To improve the electrical geometry model.

[0065] Figure 4 The density distribution of ground-to-ground lightning is 300#-320#.

[0066] Figure 5 This is the calculation flow chart of the shielding failure tripping rate.

[0067] Figure 6(a) shows the calculation results of the lightning resistance level of the insulator string and tower head gap under different wind speed conditions (back-strike lightning resistance level).

[0068] Figure 6(b) is the calculation result of the lightning protection level of the insulator string and tower head gap under different wind speed conditions (shielding lightning protection level).

[0069] Figure 7 This is the result diagram of the back-strike tripping rate when the wind speed is greater than 17m / s.

[0070] Figure 8 This is the result diagram of the circuit breaker tripping rate when the wind speed is greater than 13m / s.

[0071] Fig. 9 This is a risk level classification diagram for the back-strike tripping rate of each tower at different wind speeds.

[0072] Fig.10 The risk level classification diagram of the shielding failure tripping rate of each tower at different wind speeds.

[0073] Fig.11 This is a schematic diagram of the line windage displacement value. DETAILED DESCRIPTION

[0074] A method for assessing the risk of lightning strike-wind coupling of a transmission line under strong wind conditions comprises the following steps:

[0075] Step 1: Obtain meteorological parameters based on the micro-meteorological station monitoring device, obtain line parameters through line point cloud data, and obtain ground-to-ground lightning density based on lightning data;

[0076] The meteorological parameters that need to be obtained include wind speed and wind direction data.

[0077] The line parameters that need to be obtained include tower height, call height, crossarm length, insulator string length, span, sag, and ground wire model.

[0078] The ground-to-ground lightning density refers to the number of lightning strikes on the ground per square kilometer per year.

[0079] Step 2: Calculate the minimum air gap distance of each tower under different wind deviation conditions.

[0080] The present invention establishes a finite element model of a transmission line and an insulator string based on line point cloud data, which is used to calculate the wind deflection angle of the insulator string and the wind deflection displacement change of each local point of the line, so as to calculate the minimum air gap distance. The finite element model of the transmission line and the insulator string is as follows: Figure 1 shown.

[0081] In the modeling process, the top of the insulator string is set as a fixed hinge, and the Link8 unit in the NASYS software is used to simulate the insulator string, and the Link10 unit is used to simulate the transmission line. The initial deformation of the transmission line is described by the catenary equation. The calculation method of the catenary equation is shown in formula (1):

[0082]

[0083] Wherein, z is the sag, unit: m; L is the span, unit: m; c is the span hanging point position difference, unit: m; H is the horizontal running tension, unit: N; x is the distance from the starting point to each point per unit length, unit: m; α and β are the tangent angles at both ends of the catenary, unit: °; q is the unit force, unit: N / M.

[0084] Through the calculation results of wind deflection angle and tower structure parameters, the minimum air gap of the tower head can be calculated using the following formula:

[0085]

[0086] Where, L1 is the minimum air gap distance; m is the cross arm length; l is the insulator string length; η is the angle between the tower body and the cross arm; is the wind deflection angle of the suspension insulator string.

[0087] The parameters that need to be obtained are the minimum air gap distance of the tower under the corresponding voltage level, as shown in Table 2.

[0088] Table 2 Minimum air gap distance of towers at various voltage levels

[0089]

[0090] Step 3: Use the pilot method to establish the pilot model of the flashover criterion of the insulator string and the air gap;

[0091] The pilot method proposed by CIGRE can better reflect the physical process of long gap discharge and overcome the U 50％ The present invention can better characterize the change of air gap length by using the pilot method. Therefore, the pilot method is selected as the criterion for flashover of insulator string and air gap.

[0092] The leader development speed is related to the voltage value and the leader development length. The leader development speed calculation formula recommended by CIGRE is:

[0093]

[0094] In the formula, v z is the leader development speed; k is the leader development coefficient; U(t) is the instantaneous voltage value of the insulator string and the air gap; s is the developed length of the leader, unit: m; L1 is the minimum distance between the insulator string and the tower head air gap, unit: m; E0 is the starting field strength threshold of the leader.

[0095] Step 4: Calculate the lightning resistance level of each base tower and the minimum wind speed value of the tower head air gap flashover;

[0096] The lightning resistance level of a transmission line refers to the maximum lightning current value that will not cause insulation flashover when lightning strikes the line, measured in kA.

[0097] Since the insulator string and the tower head air gap are simulated by the leader model, when the applied lightning current makes the leader development distance greater than the final jump distance h f When the lightning current is considered to be at the lightning withstand level. Since the flashover voltage of the insulator string is not affected by wind speed, as the wind speed increases, the tower head air gap will gradually decrease, and the withstand voltage value will also decrease. Therefore, when the lightning withstand level changes, it can be considered that the air gap is broken down. Based on this, the lightning withstand level of each base tower of the line is calculated, and the corresponding wind speed value at this time is the minimum wind speed when the tower air gap breaks down.

[0098]

[0099] In the formula, h f is the final transition distance, unit: m; D is the insulator string length, unit: m.

[0100] The wind speed here is a prerequisite for calculation. Under the condition that a certain wind speed is known, the corresponding minimum air gap distance can be calculated through finite element simulation and the minimum air gap distance formula. If the air gap of the transmission line is broken down by lightning at this time, it means that the wind speed at this time is the minimum wind speed when the air gap of the tower is broken down.

[0101] Step 5: Improve the electrical geometry model based on the Monte Carlo algorithm and calculate the lightning tripping rate.

[0102] The Monte Carlo algorithm solves complex problems through random sampling and statistical inference, and is applicable to numerical calculations and probability analysis in many fields.

[0103] Figure 3 Schematic diagram of electrical geometry model, electrical geometry model is used to calculate the shielding failure trip rate. The specific calculation process of the method for calculating the shielding failure trip rate can refer to step 5.

[0104] When calculating the shielding failure trip rate, firstly, Figure 3 The swing amplitude range of the conductor and the ground wire is determined by randomly selecting points using the Monte Carlo algorithm combined with the probability density function to determine the coordinate values ​​of the conductor and the ground wire in the Cartesian two-dimensional coordinate system. Secondly, combined with the electrical geometry model, the shielding failure trip rate is calculated multiple times until the number of cycles k meets the total number of cycles k. s Finally, based on the above process, the lightning trip rate is calculated for each tower. The specific calculation process is as follows: Figure 5 shown.

[0105] Based on the randomness of the Monte Carlo algorithm and combined with the probability density function (4), it can be ensured that the random points can be consistent with the actual wire displacement distribution on the basis of simulating the random swing of the wire. Fig.11 .

[0106] According to existing research and finite element simulation, when the simulation time limit is set to 600s, the wind deviation dancing trajectory of the line within the span is crescent-shaped. Based on the statistical results of the line wind deviation position and considering the influence of the local line dancing, the probability density formula of the line wind deviation position is proposed to improve the efficiency of the calculation of the lightning wind deviation coupling risk.

[0107]

[0108] Where f(x) is the probability density function; x is a random number in the range of (0,1); k, b and c are correlation coefficients.

[0109] After considering the influence of wind speed, the insulator string will be deflected by wind. The spatial position of the bottom of the insulator string and the conductor connection point can be calculated by formula (5):

[0110]

[0111] Where: G x , G y is the x and y coordinates of point G at the bottom of the insulator string; L c is the cross arm length, unit: m; h c is the conductor height, unit: m; is the wind deflection angle of the suspension insulator string, unit: °; l is the length of the insulator string, unit: m.

[0112] Based on the Monte Carlo algorithm, the coordinate values ​​of the conductor and ground wire at each point on the Cartesian coordinate system can be calculated using the following formulas (6) and (7).

[0113]

[0114] Where: X c is the horizontal coordinate of the wire in the Cartesian coordinate system; f c is the conductor sag, f(x) is the probability density function of the conductor windage position; ξ i Y is the wind deflection angle of the conductor; c is the ordinate of the wire in the Cartesian coordinate system.

[0115]

[0116] Where: X s L is the horizontal coordinate of the wire in the Cartesian coordinate system, unit: m; s is the length of the ground wire cross arm, f s is the ground wire sag, unit: m; γ i Y is the ground line wind deflection angle, unit: °; s H is the ordinate of the wire in the Cartesian coordinate system, unit: m; s is the ground line height, unit: m;

[0117] When calculating the shielding failure rate, it involves determining the range of lightning current amplitude values. Since the present invention is to explore the lightning strike characteristics of the tower head air gap, the air gap lightning resistance level I is selected. c As the lower limit of the calculation of the bypass rate integral, the bypass rate calculation formula is:

[0118]

[0119] Where: P α is the lightning strike rate, φ is the lightning incident angle, I max is the maximum lightning current amplitude that causes flashover; x is the probability of shielding failure, and f(I) is the lightning current amplitude probability density function.

[0120] The calculation formula of the shielding failure trip rate is:

[0121] P r =N1ηP α (9);

[0122] Where P r is the shielding failure tripping rate; N1 is the number of lightning strikes; η is the arcing rate; g is the probability of lightning current directly hitting the tower; P is the probability of flashover.

[0123] The calculation process of the counter-tripping rate includes the following steps:

[0124] The calculation formula of the back-tripping rate is:

[0125] P f =N1ηgP (10);

[0126] Where P f is the strike-back tripping rate; N1 is the number of lightning strikes; η is the arcing rate; g is the probability of lightning current directly hitting the tower; P is the probability of flashover.

[0127] Step 6: Determine the line risk level based on the risk level assessment criteria.

[0128] According to the calculation results of the counter-attack tripping rate and the shielding failure tripping rate, the risk level of the transmission line is divided. The risk level classification standard is shown in Table 1. r0 and P f0 are the average counter-attack tripping rate and the average shielding tripping rate when wind deviation is not considered, P f is the counter-tripping rate; P r is the circuit breaker tripping rate.

[0129] Based on the line point cloud data, micro gas station data and ground lightning density, the pilot model of insulator string and air gap flashover criterion was established, and the lightning resistance level of each base tower and the minimum wind speed value of tower head air gap flashover were calculated. The electrical geometry model was improved based on the Monte Carlo algorithm to achieve quantitative analysis of the coupling risk of lightning strike and wind deviation.

[0130] Example 1

[0131] This paper uses a 330kV transmission line as an example to analyze the risk of lightning strike and wind deflection coupling disaster. There are lightning strike and wind deflection threats in multiple tower sections of this line. Based on historical fault data, this paper selects the 300#-320# section as the research object. The average altitude of this section is 4500m, and the ground lightning density level distribution is as follows Figure 4 As shown. The models of the straight tower and the tension tower are ZBC 250 and JG 150 respectively, the conductor model is 3×LGJ-240 / 30, the left and right models of the ground wire are 1×19-11.5-1270, OPGW-120, and the insulator model is FXBW-330 / 160-1. In addition, since the tension towers 302# and 311# in this section have been installed with hard drain wires and windproof insulator strings, the air gap between the jumper and the tower body has changed little after calculation, so only the straight tower is taken as the research object below.

[0132] According to the line parameters and terrain parameters obtained from the point cloud data, the lightning resistance level of the line section is calculated, and the minimum wind speed for air gap flashover to occur on each base tower is obtained.

[0133] According to the flashover mechanism of the insulator string, the lightning resistance level of the insulator string is not affected by the wind speed. If the lightning resistance level changes under the influence of wind deviation, it can be considered as air gap breakdown. The calculation results of the counter-strike lightning resistance level of the insulator and the air gap are shown in Figure 6(a), and the calculation results of the shielding lightning resistance level of the insulator and the air gap are shown in Figure 6(b). As shown in Figure 6(a), when the wind speed is less than 12m / s, the counter-strike lightning resistance level of the tower remains unchanged. However, as the wind speed increases, the lightning resistance level of some towers begins to decrease. When the wind speed reaches 17m / s, the counter-strike lightning resistance level of all towers decreases to varying degrees. Similarly, as shown in Figure 6(b), when the wind speed is less than 11m / s, the shielding lightning resistance level does not change. When the wind speed reaches 13m / s, the shielding lightning resistance level of all towers decreases.

[0134] Table 3 Minimum wind speed value when air gap flashes over

[0135]

[0136] Since the withstand voltage of the insulator string is not affected by wind speed, while the withstand voltage of the tower head air gap decreases with increasing wind speed, by comparing the changes in the lightning strike resistance level and the shielding lightning resistance level of each base tower, the minimum wind speed value of the tower air gap flashover under lightning overvoltage can be determined. The specific wind speed values ​​are shown in Table 3.

[0137] It can be seen from Table 3 that when the wind speed is greater than 17m / s, if the tower strikes back, there is a risk of air gap breakdown at the tower head. According to wind speed statistics, the maximum wind speed is 24m / s, so wind speeds of 18m / s, 20m / s, 22m / s, and 24m / s are selected to calculate the strike back trip rate, and a wind speed of 0m / s is selected as the control group. The specific results are as follows: Figure 7 shown.

[0138] Depend on Figure 7 It can be seen that the greater the wind speed, the higher the tripping rate of the tower head gap flashover caused by the backlash. Its essence is that it is due to the reduction of the air gap, which causes the withstand voltage value of the tower head air gap to decrease.

[0139] Similarly, when the wind speed is greater than 13m / s, if the tower fails, there is a risk of air gap breakdown at the tower head. This paper selects wind speeds of 14m / s, 16m / s, 18m / s, 20m / s, 22m / s, and 24m / s to calculate the trip rate of the failure, and also selects a wind speed of 0m / s as the control group to explore the influence of wind speed on the trip rate.

[0140] Depend on Figure 8 It can be seen that with the increase of wind speed, the air gap at the tower head continues to decrease and the shielding failure rate continues to increase, which is the fundamental reason for the increase of shielding failure tripping rate. The shielding failure tripping rate is quite different between wind speeds 0 and 14m / s, which is caused by the large difference in the shielding failure rates of the two.

[0141] According to the calculation results of lightning tripping rate under different wind speeds, combined with the risk level classification standard, the back-strike risk and shielding risk level of each base tower are divided. The results are as follows: Fig. 9 and Fig.10 shown.

[0142] According to the flashover mechanism of insulator strings, when the wind speed is less than 13m / s, the risk of tower strikeback will not change. The risk of strikeback will only increase when the wind speed exceeds the air gap flashover speed.

[0143] Depend on Fig. 9 It can be seen that when the wind speed is 18m / s, the risk level of multiple towers increases, because some towers have reached the minimum wind speed for air gap breakdown under this wind speed condition. In addition, it is calculated that when the wind speed is 20m / s, the backlash risk level of all towers reaches D risk.

[0144] Depend on Fig.10 It can be seen that as the wind speed increases, the number of towers with the risk of shielding increases significantly. When the wind speed is 14m / s, the number of towers with level D risk increases by 13, and when the wind speed is 18m / s, the risk of shielding of all towers reaches level D.

Claims

1. A method for assessing the risk of lightning-wind coupling in power transmission lines under strong wind conditions, characterized in that: The following steps are involved: Step 1: Obtain meteorological parameters, line parameters and ground-to-ground lightning density; Step 2: Calculate the minimum air gap distance of each base tower under different wind deviation conditions; Step 3: Construct the pilot model of insulator string and air gap flashover criterion based on the pilot method; Step 4: Calculate the lightning resistance level of each tower and the minimum wind speed value of gap flashover; Step 5: Improve the electrical geometry model based on the Monte Carlo algorithm and calculate the lightning trip rate; Step 6: Evaluate the line risk level based on the calculated results of the lightning tripping rate.

2. The method for assessing the risk of lightning strike and wind deflection coupling of power transmission lines under strong wind conditions according to claim 1 is characterized in that: In step 1, meteorological parameters include wind speed and wind direction data; line parameters include tower height, call height, cross arm length, insulator string length, span, sag, and ground wire model; ground lightning density refers to the number of ground lightning strikes per square kilometer and per year.

3. The method for assessing the risk of lightning strike and wind deflection coupling of power transmission lines under strong wind conditions according to claim 1 is characterized in that: In step 2, the minimum air gap distance of each base tower is the minimum air gap distance of the tower corresponding to different voltage levels.

4. The method for assessing the risk of lightning strike and wind deflection coupling of power transmission lines under strong wind conditions according to claim 1, characterized in that: In the step 2, based on the line point cloud data, a finite element model of the transmission line and the insulator string is established to calculate the windage displacement change of the insulator string and each local point of the line, so as to calculate the minimum air gap distance; The initial deformation of the transmission line is described by the catenary equation, which is calculated as follows: Where z is the sag, H is the horizontal running tension, q is the unit force, L is the span, α and β are the tangent angles at both ends of the catenary, c is the span hanging point position difference, and x is the distance from the starting point to each point per unit length.

5. The method for assessing the risk of lightning strike and wind deflection coupling of power transmission lines under strong wind conditions according to claim 1, characterized in that: In step 3, a pilot model for flashover criterion of insulator string and air gap is constructed based on the pilot method, and the pilot method is selected as the flashover criterion of insulator string and air gap; the pilot development speed is related to the voltage value and the pilot development length, and the pilot development speed calculation formula recommended by CIGRE is: In the formula, v z is the leader development speed; k is the leader development coefficient; U(t) is the instantaneous voltage value of the insulator string and the air gap; s is the developed length of the leader, L1 is the minimum distance between the insulator string and the tower head air gap, and E0 is the starting field strength threshold of the leader.

6. The method for assessing the risk of lightning strike and wind deflection coupling of power transmission lines under strong wind conditions according to claim 1, characterized in that: In step 4, since both the insulator string and the tower head air gap are simulated and calculated using the leader model, when the applied lightning current makes the leader development distance greater than the final jump distance h f When the lightning current is at the lightning withstand level, it is considered that the lightning current is at the lightning withstand level. Since the flashover voltage of the insulator string is not affected by the wind speed, as the wind speed increases, the tower head air gap will gradually decrease, and the withstand voltage value will also decrease. Therefore, when the lightning withstand level changes, it can be considered that the air gap is broken down. Based on this, the lightning withstand level of each base tower of the line is calculated. The corresponding wind speed value at this time is the minimum wind speed when the tower air gap is broken down. In the formula, h f is the final transition distance; D is the insulator string length.

7. The method for assessing the risk of lightning strike and wind deflection coupling of power transmission lines under strong wind conditions according to claim 1, characterized in that: In step 5, the electrical geometry model is improved based on the Monte Carlo algorithm to calculate the lightning tripping rate. When calculating the shielding tripping rate, firstly, according to the swing amplitude range of the conductor and the ground wire, the Monte Carlo algorithm combined with the probability density function is used to randomly select points to determine the coordinate values ​​of the conductor and the ground wire in the Cartesian two-dimensional coordinate system; secondly, combined with the electrical geometry model, the shielding tripping rate is calculated for multiple cycles until the number of cycles k meets the total number of cycles k s Then, the average value of the tripping rate is solved; finally, based on the above process, the lightning tripping rate is calculated for each tower.

8. The method for assessing the risk of lightning strike and wind deflection coupling of power transmission lines under strong wind conditions according to claim 7, characterized in that: Based on the statistical results of the line wind deviation points and considering the influence of local line galloping, a probability density formula for the line wind deviation points is proposed to improve the efficiency of the calculation of lightning-wind deviation coupling risk. Where f(x) is the probability density function; x is a random number in the range of (0,1); k, b and c are correlation coefficients.

9. The method for assessing the risk of lightning strike and wind deflection coupling of power transmission lines under strong wind conditions according to claim 8, characterized in that: The lightning trip rate includes the bypass trip rate and the counter-strike trip rate. The calculation process of the shielding failure trip rate includes the following steps: 1) Calculate the spatial position of the bottom of the insulator string and the connection point of the conductor: Where: G x , G y is the x and y coordinates of point G at the bottom of the insulator string; L c is the cross arm length, h c is the wire height, is the wind deflection angle of the suspension insulator string, l is the length of the insulator string; 2) Based on the Monte Carlo algorithm, calculate the coordinate values ​​of the conductor and ground wire at each point in the Cartesian coordinate system: Where: X c is the horizontal coordinate of the wire in the Cartesian coordinate system, f c is the conductor sag, f(x) is the probability density function of the conductor windage position, ξ i Y is the wind deflection angle of the conductor; c is the ordinate of the wire in the Cartesian coordinate system; Where: X s is the horizontal coordinate of the wire in the Cartesian coordinate system, L s is the length of the ground wire cross arm, f s is the ground wire sag, γ i Y is the ground line wind deflection angle, s is the ordinate of the wire in the Cartesian coordinate system, H s is the ground line height; 3) Select the lightning resistance level I of the air gap c As the lower limit of the calculation of the shielding rate integral, calculate the shielding rate: Where: P α is the lightning strike rate, φ is the lightning incident angle, I max is the maximum lightning current amplitude that causes flashover; x is the probability of shielding failure, and f(I) is the lightning current amplitude probability density function; 4) Calculate the shielding failure trip rate: P r =N1ηP α (9); Where: P r is the tripping rate of circuit breaker failure, N1 is the density of ground lightning, η is the arcing rate; The calculation process of the counter-tripping rate includes the following steps: The calculation formula of the back-tripping rate is: P f =N1ηgP (10); Where P f is the strike-back tripping rate; N1 is the number of lightning strikes; η is the arcing rate; g is the probability of lightning current directly hitting the tower; P is the probability of flashover.

10. The method for assessing the risk of lightning strike and wind deflection coupling of power transmission lines under strong wind conditions according to claim 1, characterized in that: In step 6, the risk level of the transmission line is divided according to the calculation results of the counter-attack tripping rate and the shielding failure tripping rate. The risk level classification standard is shown in Table 1; Table 1 Lightning risk level classification standards In the above table: P r0 and P f0 are the average counter-attack tripping rate and the average shielding tripping rate when wind deviation is not considered, P f is the counter-tripping rate; P r is the circuit breaker tripping rate.

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