An optimization method for the tower head clearance of transmission line towers considering the requirements of lightning strike tripping rate limits

Abstract

The present invention relates to a method for optimizing the tower head gap of a transmission line tower considering the requirement of a lightning trip rate limit, comprising: obtaining relevant data of the transmission line tower to be optimized; constructing an air gap flashover model based on a pilot development method; establishing a complete transmission line electromagnetic transient simulation calculation model; calculating the back-strike trip rate and shielding trip rate of the transmission line; obtaining the overall lightning trip rate of the transmission line; judging whether the overall lightning trip rate of the transmission line is greater than a set lightning trip rate limit; if the judgment result is no, reducing the tower head air gap length X by Δx and returning to step (1); otherwise, outputting the optimized tower head air gap. The present invention utilizes a pilot method as a tower head air gap breakdown judgment method to calculate the lightning trip rates corresponding to different gap distances, thereby gradually approaching the transmission line tower head gap distance corresponding to the premise of not exceeding the lightning trip rate, guiding the specific tower lightning overvoltage gap value, and optimizing the tower design.

Description

Technical Field

[0001] The present invention relates to the field of high voltage and insulation technology, and in particular to a method for optimizing the clearance between transmission line tower heads taking into account a lightning trip rate limit requirement. Background Art

[0002] Lightning strikes on transmission lines remain one of the main causes of power line tripping accidents. Lightning-related failures in power systems typically account for approximately 50%. Furthermore, the higher the voltage level and the greater the transmission capacity of a transmission line, the greater the importance and reliability requirements of the line. However, this increases the height of the towers and the length of the line corridor, significantly increasing the lightning attraction capacity and the probability of lightning strikes. Therefore, stricter technical measures for lightning protection are required. Lightning-induced tripping of transmission lines not only impacts power supply reliability and the safe and stable operation of the power grid, but also disrupts the normal production and daily life of the public. In severe cases, it can cause significant losses to the national economy.

[0003] Current transmission line engineering design primarily relies on the volt-second characteristic curve of insulators under standard lightning waveforms, using the intersection method as the flashover criterion to calculate the line's lightning trip-out rate. However, the impact of lightning overvoltage flashover across the tower head air gap is less considered. In reality, lightning tripping occurs not only along insulator flashovers, but also through air flashovers, which contribute significantly to the overall line trip-out rate. Air flashovers are also expected to impact the overall line trip-out rate and warrant significant attention. Furthermore, accurately determining the lightning gap for towers of 500kV and above, or for taller towers, is crucial for optimizing tower size and reducing construction costs. The intersection method, which compares the overvoltage across the gap with its corresponding volt-second characteristic curve, has the disadvantage of requiring a suitable volt-second characteristic curve, a relatively difficult requirement.

[0004] The patent, Publication No. CN116186983A, entitled "System for Simulating Tower Head Gap and Model Parameter Determination of Overhead Transmission Lines," simulates tower head gap discharge using rod-electrode discharge, replacing the tower head air gap with the rod-electrode gap to experimentally measure the tower head gap breakdown voltage, achieving tower head gap breakdown voltage measurement. However, this method only obtains the tower head gap breakdown voltage, but does not provide the distance parameter for the tower head gap breakdown under breakdown conditions. This lacks consideration for determining tower head gap parameters. Summary of the Invention

[0005] In order to solve the problem that the current selection of tower head gap distance under lightning overvoltage conditions is only based on 0.8 times the lightning flashover voltage of the insulator string, without clear guidance and lack of theoretical support, the purpose of the present invention is to provide a transmission line tower head gap optimization method that takes into account the lightning trip rate limit requirements, which is of great significance to the actual lightning resistance level evaluation of the entire line and the tower indicators.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for optimizing the clearance between transmission line tower heads taking into account the lightning trip rate limit requirement, the method comprising the following steps in sequence:

[0007] (1) Select a section of transmission line as the research object and obtain relevant data of the transmission line tower to be optimized;

[0008] (2) Construct an air gap flashover model based on the pilot development method;

[0009] (3) Based on the air gap flashover model and the relevant data obtained in step (1), a complete electromagnetic transient simulation calculation model for the transmission line is established;

[0010] (4) Calculate the lightning resistance level of the transmission line I according to the electromagnetic transient simulation calculation model of the transmission line c , Shielding lightning protection level I min ;

[0011] (5) Using transmission line lightning protection level I c , calculate the transmission line back-tripping rate N1; according to the transmission line shielding lightning resistance level I min , calculate the transmission line shielding failure trip rate N2;

[0012] (6) Add the transmission line back-strike trip rate N1 and the transmission line shielding failure trip rate N2 to obtain the overall transmission line lightning trip rate;

[0013] (7) Determine whether the overall lightning trip rate of the transmission line is greater than the set lightning trip rate limit. If the judgment result is no, reduce the tower head air gap length X by △x and return to step (1). Otherwise, output the optimized tower head air gap.

[0014] In step (1), the relevant data include the average height of the transmission line lightning conductor above the ground, the average height of the three-phase conductors A, B, and C above the ground, the protection angle of the three-phase lightning conductors A, B, and C, and the annual number of thunderstorm days in the area where the transmission line is located.

[0015] In step (2), the leader development method refers to: starting from the physical process of gas discharge, it is considered that the leader development speed is related to the instantaneous voltage applied to both ends of the insulator string and the leader development length, and whether flashover occurs is determined by calculating the leader development length;

[0016] Integrating the leader development speed over time t yields the leader development length S:

[0017]

[0018] Where: k is the coefficient to be corrected, v1 is the leader development speed, u(t) is the voltage across the tower head air gap, d g is the length of the air gap at the tower head, d1 is the length of the developed leader; E0 is the minimum electric field strength at which the leader can continue to develop, and its value is 23KV / cm; E z is the electric field strength of the leader channel;

[0019] Assume that at time t0, the leader starts to grow from length 0 and growth speed 0. At time t0+△t, the leader growth speed is:

[0020]

[0021] Formula (1) and formula (2) together constitute the air gap flashover model based on the pilot development method;

[0022] The leader development speed is integrated from time t0 to time t0+△t to obtain the length of the leader development in this time period. When △t is small enough, it is assumed that the leader development speed remains unchanged in this time period, and the leader development length in each △t is accumulated. When the leader development length is greater than or equal to the tower head air gap or insulation gap, it is considered to be a breakdown.

[0023] The step (5) specifically refers to: using the transmission line to strike back the lightning resistance level I c , as well as the number of lightning strikes N, arcing rate η, and pole striking rate g in the transmission line corridor, calculate the transmission line back-strike tripping rate N1:

[0024] N1=N×g×η×P IC (3)

[0025]

[0026] Where, P IC To appear higher than the counterattack lightning resistance level I c probability;

[0027] According to the transmission line shielding lightning protection level I min Calculate the transmission line shielding failure trip rate N2:

[0028]

[0029] Where N g is the density of ground-to-ground lightning, I max is the maximum shielding failure current, f(I) is the probability density of lightning current amplitude, D(I) is the projection distance of the exposed arc of the conductor on the ground, and I is the lightning current.

[0030] The step (7) specifically means: if the overall lightning trip rate of the transmission line corresponding to the tower head air gap length X is less than the set lightning trip rate limit, then the tower head air gap length is reduced by Δx as a unit length each time until the overall lightning trip rate of the transmission line corresponding to the i-th time is greater than the lightning trip rate limit. At this time, the optimized tower head air gap is output as: X-(i-1)Δx.

[0031] It can be seen from the above technical solution that the beneficial effects of the present invention are as follows: First, the present invention takes the lightning trip rate limit specified by the State Grid as the standard line, uses the pilot method as the tower head air gap breakdown judgment method, calculates the lightning trip rate corresponding to different tower head air gap distances, and gradually approaches the transmission line tower head air gap distance corresponding to the premise of not exceeding the lightning trip rate, guides the specific tower lightning overvoltage gap value, and can optimize the tower design; Second, since the higher the voltage level, the higher the transmission line tower height, the higher the project cost, reducing the tower head air gap distance on the premise that the lightning protection performance meets the requirements can save material usage and reduce the project budget from an economic point of view; Third, a reasonable tower head air gap distance is of great significance to the actual lightning resistance level evaluation of the entire line and the tower indicators; Fourth, the lightning trip rate can not only be used as a tool to evaluate the lightning resistance level of the transmission line, but also can be used as a tool to optimize the tower height, opening up a new path for tower optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a flow chart of the method of the present invention;

[0033] Figure 2 Schematic diagram comparing the overall trip rate and trip rate limit corresponding to different gap distances. DETAILED DESCRIPTION

[0034] like Figure 1 As shown, a method for optimizing the clearance between transmission line tower heads considering the limit requirement of lightning trip rate is provided. The method comprises the following steps in sequence:

[0035] (1) Select a section of transmission line as the research object and obtain relevant data of the transmission line tower to be optimized;

[0036] (2) Use the MODELS module in the electromagnetic transient simulation software to construct an air gap flashover model based on the pilot development method;

[0037] (3) Based on the air gap flashover model and the relevant data obtained in step (1), a complete electromagnetic transient simulation calculation model for the transmission line is established;

[0038] (4) Calculate the lightning resistance level of the transmission line I according to the electromagnetic transient simulation calculation model of the transmission line c , Shielding lightning protection level I min ;

[0039] (5) Using transmission line lightning protection level I c , calculate the transmission line back-tripping rate N1; according to the transmission line shielding lightning resistance level I min , calculate the transmission line shielding failure trip rate N2;

[0040] (6) Add the transmission line back-strike trip rate N1 and the transmission line shielding failure trip rate N2 to obtain the overall transmission line lightning trip rate;

[0041] (7) Determine whether the overall lightning trip rate of the transmission line is greater than the set lightning trip rate limit. If the judgment result is no, reduce the tower head air gap length X by △x and return to step (1). Otherwise, output the optimized tower head air gap.

[0042] In step (1), the relevant data include the average height of the transmission line lightning conductor above the ground, the average height of the three-phase conductors A, B, and C above the ground, the protection angle of the three-phase lightning conductors A, B, and C, and the annual number of thunderstorm days in the area where the transmission line is located.

[0043] In step (2), the leader development method refers to: starting from the physical process of gas discharge, it is considered that the leader development speed is related to the instantaneous voltage applied to both ends of the insulator string and the leader development length, and whether flashover occurs is determined by calculating the leader development length;

[0044] Integrating the leader development speed over time t yields the leader development length S:

[0045]

[0046] Where: k is the coefficient to be corrected, v1 is the leader development speed, u(t) is the voltage across the tower head air gap, d g is the length of the air gap at the tower head, d1 is the length of the developed leader; E0 is the minimum electric field strength at which the leader can continue to develop, and its value is 23KV / cm; E z is the electric field strength of the leader channel;

[0047] Assume that at time t0, the leader starts to grow from length 0 and growth speed 0. At time t0+△t, the leader growth speed is:

[0048]

[0049] Formula (1) and formula (2) together constitute the air gap flashover model based on the pilot development method;

[0050] The leader development speed is integrated from time t0 to time t0+△t to obtain the length of the leader development in this time period. When △t is small enough, it is assumed that the leader development speed remains unchanged in this time period, and the leader development length in each △t is accumulated. When the leader development length is greater than or equal to the tower head air gap or insulation gap, it is considered to be a breakdown.

[0051] The step (5) specifically refers to: using the transmission line to strike back the lightning resistance level I c , as well as the number of lightning strikes N, arcing rate η, and pole striking rate g in the transmission line corridor, calculate the transmission line back-strike tripping rate N1:

[0052] N1=N×g×η×P IC (3)

[0053]

[0054] Where, P IC To appear higher than the counterattack lightning resistance level I c probability;

[0055] According to the transmission line shielding lightning protection level I min Calculate the transmission line shielding failure trip rate N2:

[0056]

[0057] Where N g is the density of ground-to-ground lightning, I max is the maximum shielding failure current, f(I) is the probability density of lightning current amplitude, D(I) is the projection distance of the exposed arc of the conductor on the ground, and I is the lightning current.

[0058] The step (7) specifically means: if the overall lightning trip rate of the transmission line corresponding to the tower head air gap length X is less than the set lightning trip rate limit, then the tower head air gap length is reduced by Δx as a unit length each time until the overall lightning trip rate of the transmission line corresponding to the i-th time is greater than the lightning trip rate limit. At this time, the optimized tower head air gap is output as: X-(i-1)Δx.

[0059] Example 1

[0060] The transmission line tower is determined as the main research object and the relevant data of the tower is obtained. In this embodiment, a 1000KV double-circuit transmission line with two lightning conductors on the same tower is selected. The total height of the tower is 110m. Some of its main parameters are shown in Table 1.

[0061] Table 1 Partial parameters of 1000KV double-circuit line tower

[0062]

[0063] The initial tower head air gap length is set to 8.795 meters.

[0064] The calculated back-strike lightning resistance level I corresponding to the 8.795m tower head air gap is c The lightning protection level of phase A is 274KA, the lightning protection level of phase B is 37KA, the lightning protection level of phase C is 17.6KA, and the lightning protection level of phase C is 28.7KA. The calculated back-strike tripping rate N1 of the transmission line is 0.015379 times / (100KM·a), and the transmission line shielding tripping rate N2 is 0.03515 times / (100KM·a). By adding the back-strike tripping rate N1 and the transmission line shielding tripping rate N2, the overall lightning tripping rate of the transmission line corresponding to the tower head air gap length of 8.795m is 0.05053 times / (100KM·a).

[0065] The calculated overall lightning trip-out rate for the transmission line, 0.05053 times / (100 km·a), is compared with the established lightning trip-out rate limit. This data indicates that the trip-out rate is lower than the standard in the "Guidelines for Lightning Protection of Overhead Transmission Lines" (Q / GDW11452-2015). The lightning trip-out rate limit for 1000 kV towers is 0.1 times / (100 km·a), so the tower head air clearance distance can be further reduced.

[0066] Reduce the tower head air gap distance, taking 1m as the node for reduction. When the tower head air gap is reduced to 5.395m, the overall lightning trip rate of the transmission line is 0.10176 times / (100km·a), and when the tower head air gap is reduced to 5.795m, the overall lightning trip rate of the transmission line is 0.08584 times / (100km·a). It can be concluded that the tower head air gap distance that meets the lightning trip rate limit requirements is between 5.395 and 5.795. It is finely divided, as shown in Table 2 below. The trip rate of each finely divided section is calculated and compared with the trip rate limit to select the appropriate gap distance.

[0067] Table 2 Lightning trip rate corresponding to different gaps

[0068]

[0069]

[0070] The output finally satisfies the trip rate limit by setting the tower head air gap length X=5.495m.

[0071] like Figure 2As shown in the figure, the horizontal axis is the tower head air gap distance, the vertical axis is the lightning trip rate, the yellow line represents the process of the total lightning trip rate increasing during the process of reducing the tower head air gap, and the gray line represents the lightning trip rate limit specified for 1000KV transmission lines. Figure 2 It can be seen that when the tower head air gap is 5.495m, the lightning trip rate does not exceed the trip rate limit, and when it is 5.395m, the lightning trip rate exceeds the trip rate limit. Therefore, the tower head air gap distance that meets the lightning trip rate limit is 5.495m.

[0072] In summary, the present invention uses the lightning trip rate limit specified by the State Grid as the standard line, utilizes the pilot method as the tower head air gap breakdown judgment method, and combines it with the ATP-EMPT simulation software to calculate the lightning trip rate corresponding to different gap distances, thereby gradually approximating the transmission line tower head gap distance corresponding to the premise of not exceeding the lightning trip rate, guiding the specific tower lightning overvoltage gap value, and optimizing the tower design. Since the higher the voltage level, the taller the transmission line tower, the higher the project cost. From an economic perspective, reducing the tower head gap distance while meeting the lightning protection performance requirements can save material usage and reduce project budgets. A reasonable gap distance is of great significance to the actual lightning resistance level assessment of the entire line and the tower indicators. This makes the lightning trip rate not only a tool for evaluating the lightning resistance level of the transmission line, but also a tool for optimizing the tower height, opening up a new path for tower optimization.

Claims

1. A method for optimizing the clearance between transmission line towers and tower heads considering the lightning trip rate limit requirement, characterized by: The method comprises the following steps in the following order: (1) Select a section of transmission line as the research object and obtain relevant data of the transmission line tower to be optimized; (2) Construct an air gap flashover model based on the pilot development method; (3) Based on the air gap flashover model and the relevant data obtained in step (1), a complete electromagnetic transient simulation calculation model for the transmission line is established; (4) Calculate the lightning resistance level of the transmission line I according to the electromagnetic transient simulation calculation model of the transmission line c , Shielding lightning protection level I min ; (5) Using transmission line lightning protection level I c , calculate the transmission line back-tripping rate N1; according to the transmission line shielding lightning resistance level I min , calculate the transmission line shielding failure trip rate N2; (6) Add the transmission line back-strike trip rate N1 and the transmission line shielding failure trip rate N2 to obtain the overall transmission line lightning trip rate; (7) Determine whether the overall lightning trip rate of the transmission line is greater than the set lightning trip rate limit. If the judgment result is no, reduce the tower head air gap length X by △x and return to step (1). Otherwise, output the optimized tower head air gap. In step (2), the leader development method refers to: starting from the physical process of gas discharge, it is considered that the leader development speed is related to the instantaneous voltage applied to both ends of the insulator string and the leader development length, and whether flashover occurs is determined by calculating the leader development length; Integrating the leader development speed over time t yields the leader development length S: Where: k is the coefficient to be corrected, v1 is the leader development speed, u(t) is the voltage across the tower head air gap, d g is the length of the air gap at the tower head, d1 is the length of the developed leader; E0 is the minimum electric field strength at which the leader can continue to develop, and its value is 23KV / cm; E z is the electric field strength of the leader channel; Assume that at time t0, the leader starts to grow from length 0 and growth speed 0. At time t0+△t, the leader growth speed is: Formula (1) and formula (2) together constitute the air gap flashover model based on the pilot development method; The leader development speed is integrated from time t0 to time t0+△t to obtain the leader development length in this time period. When △t is small enough, it is assumed that the leader development speed is constant in this time period. The leader development length in each △t is accumulated. When the leader development length is greater than or equal to the tower head air gap or insulation gap, it is considered to be breakdown. The step (5) specifically refers to: using the transmission line to strike back the lightning resistance level I c , as well as the number of lightning strikes N, arcing rate η, and pole striking rate g in the transmission line corridor, calculate the transmission line back-strike tripping rate N1: N1=N×g×η×P IC (3) Where, P IC To appear higher than the counterattack lightning resistance level I c probability; According to the transmission line shielding lightning protection level I min Calculate the transmission line shielding failure trip rate N2: Where N g is the density of ground-to-ground lightning, I max is the maximum shielding failure current, f(I) is the probability density of lightning current amplitude, D(I) is the projection distance of the exposed arc of the conductor on the ground, and I is the lightning current.

2. The method for optimizing the transmission line tower head clearance considering the lightning trip rate limit requirement according to claim 1 is characterized in that: In step (1), the relevant data include the average height of the transmission line lightning conductor above the ground, the average height of the three-phase conductors A, B, and C above the ground, the protection angle of the three-phase lightning conductors A, B, and C, and the annual number of thunderstorm days in the area where the transmission line is located.

3. The method for optimizing the transmission line tower head clearance considering the lightning trip rate limit requirement according to claim 1, characterized in that: The step (7) specifically means: if the overall lightning trip rate of the transmission line corresponding to the tower head air gap length X is less than the set lightning trip rate limit, then the tower head air gap length is reduced by Δx as a unit length each time until the overall lightning trip rate of the transmission line corresponding to the i-th time is greater than the lightning trip rate limit. At this time, the optimized tower head air gap is output as: X-(i-1)Δx.

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