Electromagnetic transient modeling and calculation method for overvoltage of air gap and conductor insulator string in lightning backflashover

Abstract

This invention discloses an electromagnetic transient modeling and calculation method for the overvoltage of air gaps and conductor insulator strings in overhead lines during lightning backflashovers. Currently, it is impossible to obtain the voltage of the air gap between the conductor and ground wire at the point of impact and the voltage of the conductor insulator strings of adjacent towers at the instant of a lightning strike on an overhead line. This invention performs electromagnetic transient simulation modeling on the structural and material parameters of the overhead line, the actual structural parameters of the towers, and the lightning current. It also performs electromagnetic transient simulation modeling on the normal operation of the power system and the actual lightning fault situation. Considering different peak values ​​and wavefront times of the lightning current, the maximum value of the lightning overvoltage of the air gap between the conductor and ground wire at the point of impact and the conductor insulator strings of adjacent towers after a lightning strike is calculated using electromagnetic transient simulation software. This provides a reference for the selection of air gaps between the conductor and ground wire and the insulation coordination design for lightning current intrusion into overhead lines, and lays the foundation for the design evaluation of various line types and tower selections.

Description

Technical Field

[0001] This invention belongs to the field of power grid transmission and transformation technology, and relates to the calculation of air gap overvoltage. Specifically, it is an electromagnetic transient modeling and calculation method for the overvoltage of air gap and conductor insulator string in a lightning backflashover line. Background Technology

[0002] High-voltage transmission lines are developing towards higher voltage levels and larger transmission capacities. Overhead lines are susceptible to extreme weather conditions during operation, including frequent lightning strikes that cause lightning current to enter the lines. This is especially true in areas with frequent lightning strikes, long spans, and long spans of overhead lines, where the probability of line tripping due to lightning faults is significant.

[0003] Because lightning strikes occur on the order of microseconds, existing online monitoring devices cannot continuously monitor voltage information at the lightning strike point. Furthermore, the large-scale installation of on-site online monitoring devices would also reduce the economic efficiency of power grid operation. Currently, the characteristics of overvoltage in the air gap between conductors and ground wires caused by lightning current backflashover at the center of the ground wire span, as well as the overvoltage characteristics of the insulators on the upper conductors, are unclear. It is impossible to obtain the instantaneous voltage values ​​of the air gap between conductors and ground wires at the lightning strike point, and the voltage values ​​of the insulator strings on adjacent towers, at the moment of the lightning strike on the overhead line. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the defects of the prior art and provide an electromagnetic transient modeling and calculation method for the overvoltage of the air gap and conductor insulator string in a lightning backflashover line. This method obtains the maximum values ​​of the overvoltage of the air gap and the overvoltage of the conductor insulator string through electromagnetic transient calculation, thereby providing a reference for the selection of the air gap and insulation coordination design of the conductor and ground wire in overhead lines when lightning current invades the line, and laying the foundation for the design evaluation of various line types and tower types.

[0005] Therefore, the present invention adopts the following technical solution: an electromagnetic transient modeling and calculation method for overvoltage of air gap and conductor insulator string in lightning backflashover, comprising the following steps:

[0006] a) Establish an overhead line model in electromagnetic transient simulation software;

[0007] b) Establish the tower model in the electromagnetic transient simulation software;

[0008] c) Establish a power supply model in the electromagnetic transient simulation software based on the normal operating parameters of the power system;

[0009] d) Obtain the air gap between the conductor and ground wire and the dry arc distance between the conductor and insulator string on site, and establish the air gap model and the insulator string model respectively;

[0010] e) Obtain the location of the lightning strike fault point and the magnitude of the lightning current on site, and establish a lightning current model in the electromagnetic transient simulation software;

[0011] f) The overhead line model, tower model, power supply model, and insulator string model described above are connected to the ABC three-phase conductors in the electromagnetic transient simulation software;

[0012] The lightning current model described in g) is connected to the overhead line model via a single-phase conductor in the electromagnetic transient simulation software, and the lightning current is injected into the ground wire of the overhead line model via the single-phase conductor.

[0013] h) The conductor-to-ground air gap model described above is connected to the conductor and ground wire in the overhead line model by a single-phase conductor in the electromagnetic transient simulation software;

[0014] i) Set different lightning currents and wavefront times in the electromagnetic transient simulation software, and use the electromagnetic transient simulation software to perform electromagnetic transient calculations to obtain the maximum values ​​of the air gap overvoltage of the conductor and the insulator string overvoltage of the conductor.

[0015] Further, in step a), by obtaining the actual spatial location and model of the overhead line on site, the structural parameters and material parameters of the overhead line are obtained based on the model, thereby establishing the overhead line model in the electromagnetic transient simulation software; the actual spatial location of the overhead line includes the height of the ABC three-phase lines from the ground and the distance from the center crossarm of the tower, as well as the height of the ground wire from the ground and the distance from the center crossarm of the tower; the structural parameters include the outer diameter, inner diameter, number of splits, and split spacing of the conductors of the ABC three-phase lines, as well as the outer diameter, inner diameter, number of splits, and split spacing of the conductor of the ground wire; the material parameters include the DC resistance of the conductors of the ABC three-phase lines and the DC resistance of the conductor of the ground wire.

[0016] Further, in step b), by obtaining the actual dimensions and model of the tower on site, the tower structural parameters are obtained based on the model, and the tower wave impedance parameters are calculated, thereby establishing the tower model in the electromagnetic transient simulation software; the actual dimensions of the tower include the ground height of each crossarm, the equivalent radius of each main member, and the equivalent radius of each crossarm; the tower wave impedance parameters include the wave impedance of each main member, the wave impedance of each diagonal member, and the wave impedance of each crossarm.

[0017] Furthermore, in step c), the normal operating parameters of the power system include the effective value of the power system operating voltage, the power system operating phase angle, and the power system operating frequency.

[0018] Furthermore, in step d), the conductor-to-ground air gap model and the insulator string model are constructed using the intersection method.

[0019] Furthermore, in step e), the location of the lightning fault point includes the distance from the lightning fault point to the left tower and the distance from the lightning fault point to the right tower; the lightning current model parameters include the peak value, wavefront time and half-peak time of the lightning current, and the lightning current is described using a double exponential function model.

[0020] Furthermore, step f) specifically includes:

[0021] f1) The overhead line model includes a first overhead line model and a second overhead line model; the tower model includes a first tower model and a second tower model; the power supply model includes a first power supply model and a second power supply model; the insulator string model includes a first insulator string model and a second insulator string model.

[0022] f2) The first power source model, the first insulator string model, the first overhead line model, the second overhead line model, the second insulator string model, and the second power source model are connected in series with ABC three-phase conductors.

[0023] f3) The ABC three-phase connection points of the first insulator string model and the first tower model are connected in series in sequence, and the ABC three-phase connection points of the second insulator string model and the second tower model are connected in series in sequence.

[0024] f4) The first grounding point, the first overhead line model, the second overhead line model, and the second grounding point are connected in series using single-phase conductors in the software.

[0025] f5) The first grounding point is connected in parallel with the ground wire suspension point of the first tower model, and the second grounding point is connected in parallel with the ground wire suspension point of the second tower model;

[0026] In the f6 software, both the first and second grounding points are at zero potential and are considered to be the same point electrically.

[0027] Furthermore, in step g), when using a single-phase conductor to connect the lightning current model and the overhead line model, the overhead line model is connected by a ground wire.

[0028] Furthermore, in step h), when using a single-phase conductor to connect the air gap model of the conductor and the overhead line model, the overhead line model selects the ground wire and the A-phase conductor among the ABC three-phase conductors.

[0029] Further, in step i), the maximum values ​​of the air gap overvoltage of the conductor and the overvoltage of the conductor insulator string are obtained through the following steps:

[0030] i1) The voltage monitoring points are set up for the conductor-to-ground wire air gap model and the insulator string model described in step d).

[0031] i2) Based on common lightning current parameters in the atmosphere, different lightning current peak values ​​and wavefront times are set in the electromagnetic transient simulation software, and the conductor-to-ground air gap voltage and conductor-to-insulator string overvoltage values ​​are recorded under each working condition.

[0032] i3) After the electromagnetic transient simulation software has finished running repeatedly, the overvoltage values ​​of the air gap between the conductor and the ground wire and the overvoltage values ​​of the conductor insulator string are compared respectively to obtain the maximum overvoltage values ​​of the air gap between the conductor and the ground wire and the maximum overvoltage values ​​of the conductor insulator string:

[0033] ,

[0034] ,

[0035] in, , These are the maximum overvoltage values ​​of the air gap between the conductor and ground wire, and the maximum overvoltage values ​​of the conductor insulator string, respectively. i Representing the i One lightning current peak value; j Representing the j One wave head time; , These are the overvoltage values ​​of the air gap between the conductor and the ground wire, and the overvoltage values ​​of the conductor insulator string, respectively.

[0036] This invention performs electromagnetic transient simulation modeling on the structural and material parameters of overhead lines and the actual structural parameters of towers, performs electromagnetic transient simulation modeling on lightning current, and performs electromagnetic transient modeling on normal operation of the power system and actual lightning fault conditions. After considering different peak values ​​and wavefront times of lightning current, the maximum value of lightning overvoltage at the conductor-to-ground air gap at the lightning strike point and the conductor insulator string of adjacent towers is calculated by electromagnetic transient simulation software. This provides a reference for the selection of conductor-to-ground air gap and insulation coordination design for lightning current intrusion into overhead lines, and lays the foundation for the design evaluation of various line types and tower selections. Attached Figure Description

[0037] Figure 1 This is a flowchart of an electromagnetic transient modeling and calculation method for overvoltage of air gap and conductor insulator string in a lightning backflashover line, according to the present invention.

[0038] Figure 2 This is a flowchart illustrating the process of obtaining the calculation results for the air gap overvoltage of conductors and the overvoltage of conductor insulator strings, considering different peak lightning currents and wavelengths.

[0039] Figure 3 This is a schematic diagram of the tower structure parameters in a specific embodiment of the present invention;

[0040] Figure 4This is a schematic diagram of the tower wave impedance parameters in a specific embodiment of the present invention;

[0041] Figure 5 The above diagram shows the waveforms of overvoltage in the air gap of the conductor and overvoltage in the conductor insulator string in a specific embodiment of the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be explained and described below with reference to the accompanying drawings. However, the following embodiments are only preferred embodiments of the present invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present invention.

[0043] This embodiment presents an electromagnetic transient modeling and calculation method for overvoltage of air gaps and conductor insulator strings in lightning backflashover lines. Figure 1 As shown. The steps are as follows:

[0044] a) Obtain the actual spatial location and model of the overhead line on site, and obtain the structural and material parameters of the overhead line based on the model. Establish the overhead line model in the electromagnetic transient simulation software.

[0045] b) Obtain the actual dimensions and model of the tower on site, obtain the tower structural parameters based on the model, calculate the tower wave impedance parameters, and establish the tower model in the electromagnetic transient simulation software;

[0046] c) Establish a power supply model in the electromagnetic transient simulation software based on the normal operating parameters of the power system;

[0047] d) Obtain the air gap between the conductor and ground wire and the dry arc distance between the conductor and insulator string on site, and establish the air gap model and the insulator string model;

[0048] e) Obtain the location of the lightning strike fault point and the magnitude of the lightning current on site, and establish a lightning current model in the electromagnetic transient simulation software;

[0049] f) The overhead line model, tower model, power supply model, and insulator string model described above are connected to the ABC three-phase conductors in the electromagnetic transient simulation software;

[0050] The lightning current model described in g) is connected to the overhead line model via a single-phase conductor in the electromagnetic transient simulation software, and the lightning current is injected into the ground wire of the overhead line model via the single-phase conductor.

[0051] h) The conductor-to-ground air gap model described above is connected to the conductor and ground wire in the overhead line model by a single-phase conductor in the electromagnetic transient simulation software;

[0052] i) Set different lightning currents and wavefront times in the electromagnetic transient simulation software, and use the electromagnetic transient simulation software to perform electromagnetic transient calculations to obtain the maximum values ​​of the air gap overvoltage of the conductor and the insulator string overvoltage of the conductor.

[0053] Specifically, in step a), the actual spatial location of the overhead line includes the height of the ABC three-phase lines from the ground and their distance from the center crossarm of the tower, as well as the height of the ground wire from the ground and its distance from the center crossarm of the tower.

[0054] Specifically, in step a), the structural parameters include: the outer diameter, inner diameter, number of splits, and split spacing of the conductors of the ABC three-phase circuit, and the outer diameter, inner diameter, number of splits, and split spacing of the conductor of the ground wire; the material parameters include: the DC resistance of the conductors of the ABC three-phase circuit, and the DC resistance of the conductor of the ground wire.

[0055] Specifically, in step b), the actual dimensions of the tower include the ground clearance of each crossarm section, the equivalent radius of each main material section, and the equivalent radius of each crossarm section.

[0056] Specifically, in step b), the tower wave impedance parameters, including the wave impedance of each main member segment, each diagonal member segment, and each crossarm segment, are calculated through the following steps:

[0057] b1) Obtain the actual dimensions of the tower, including the ground clearance of each crossarm, the equivalent radius of each main material, and the equivalent radius of each crossarm.

[0058] b2) The wave impedance of each section of the main material of the tower is calculated as shown in equation (1).

[0059] (1)

[0060] In the formula, Z Tk For the first k Equivalent wave impedance of main material of the tower section, Ω; h k For the first k The height of the crossarm above the ground, in meters; r Tk For the first k Equivalent radius of the main material of the tower section, in meters.

[0061] b3) The wave impedance of each section of the inclined material of the tower is calculated as shown in equation (2).

[0062] (2)

[0063] In the formula, Z Lk For the first k Equivalent wave impedance of the inclined member of the tower section, Ω.

[0064] b4) The wave impedance of each crossarm of the tower is calculated as shown in equation (3).

[0065] (3)

[0066] In the formula, Z Ak For the first k Equivalent wave impedance of crossarm segment, Ω; r Ak For the first k The equivalent radius of the crossarm is m.

[0067] Specifically, in step c), the normal operating parameters of the power system include the effective value of the operating voltage of the power system, the operating phase angle of the power system, and the operating frequency of the power system.

[0068] Specifically, in step d), the conductor-to-ground air gap model and the insulator string model are constructed using the intersection method, and are obtained through the following steps:

[0069] d1) Obtain the air gap of the conductor and ground wire L air Dry arc distance of conductor insulator string L insulator ;

[0070] d2) Construct the volt-second characteristic curve of the air gap between the conductor and the ground wire (i.e., the air gap model of the conductor and the ground wire), as shown in equation (4).

[0071] (4)

[0072] In the formula, The voltage-second characteristic curve of the air gap between the conductor and ground wire is given in kV; t is the flashover time in μs. L air The air gap for the conductor / ground wire is in meters (m).

[0073] d3) Construct the volt-second characteristic curve of the insulator string (i.e., the insulator string model), as shown in equation (5).

[0074] (5)

[0075] In the formula, The figure shows the volt-second characteristic curve of the insulator string, in kV; t is the flashover time, in μs. L insulator The distance between the dry arcs of the conductor insulator string is in meters (m).

[0076] Specifically, in step e), the location of the lightning strike fault point includes the distance from the lightning strike fault point to the left tower and the distance from the lightning strike fault point to the right tower.

[0077] Specifically, in step e), the lightning current model parameters include the peak value of the lightning current, the wavefront time, and the half-peak time. The lightning current is described using a double exponential function model, as shown in equations (6) and (7).

[0078] (6)

[0079] in, Indicates lightning current; This represents the initial peak lightning current, in kA. This is the peak current correction factor; t Indicates time, in seconds; This refers to the wavefront time coefficient; The half-peak time coefficient; e It is a natural constant;

[0080] (7)

[0081] in, The peak value of the lightning current is determined by... , and Jointly decided; wave head timing is determined by The decision was made that the half-peak time would be determined by... Decide.

[0082] Specifically, step f) includes:

[0083] f1) The overhead line model includes the first overhead line model and the second overhead line model; the tower model includes the first tower model and the second tower model; the power supply model includes the first power supply model and the second power supply model; the insulator string model includes the first insulator string model and the second insulator string model.

[0084] f2) The first power source model, the first insulator string model, the first overhead line model, the second overhead line model, the second insulator string model, and the second power source model are connected in series with ABC three-phase conductors.

[0085] f3) The ABC three-phase connection points of the first insulator string model and the first tower model are connected in series in sequence, and the ABC three-phase connection points of the second insulator string model and the second tower model are connected in series in sequence.

[0086] f4) The first grounding point, the first overhead line model, the second overhead line model, and the second grounding point are connected in series using single-phase conductors in the software.

[0087] f5) The first grounding point is connected in parallel with the ground wire suspension point of the first tower model, and the second grounding point is connected in parallel with the ground wire suspension point of the second tower model;

[0088] In the f6 software, both the first and second grounding points are at zero potential and are considered to be the same point electrically.

[0089] Specifically, in step g), when using a single-phase conductor to connect the lightning current model and the overhead line model, the overhead line model is connected by a ground wire.

[0090] Specifically, in step h), when using a single-phase conductor to connect the air gap model of the conductor and the overhead line model, the overhead line model selects the ground wire and the A-phase conductor among the ABC three-phase conductors.

[0091] Specifically, in step i), the maximum values ​​of the air gap overvoltage of the conductor and the insulator string overvoltage are obtained as follows: Figure 2 As shown, it is obtained through the following steps:

[0092] i1) The voltage monitoring points are set up for the conductor-to-ground wire air gap model and the insulator string model described in step d).

[0093] i2) Based on common lightning current parameters in the atmosphere, different lightning current peak values ​​and wavefront times are set in the electromagnetic transient simulation software, and the conductor-to-ground air gap voltage and conductor-to-insulator string overvoltage values ​​are recorded under each working condition.

[0094] i3) After the electromagnetic transient simulation software has been run repeatedly, the overvoltage values ​​of the air gap between the conductor and the ground wire and the overvoltage values ​​of the conductor insulator string are compared respectively to obtain the maximum overvoltage values ​​of the air gap between the conductor and the ground wire and the maximum overvoltage values ​​of the conductor insulator string, as shown in equations (8) and (9).

[0095] (8)

[0096] (9)

[0097] in, , These are the maximum overvoltage values ​​of the air gap between the conductor and ground wire, and the maximum overvoltage values ​​of the conductor insulator string, respectively. i This represents the peak value of the i-th lightning current; j This represents the time of the j-th wavehead; , These are the overvoltage values ​​of the air gap between the conductor and the ground wire, and the overvoltage values ​​of the conductor insulator string, respectively.

[0098] Taking a 220kV lightning strike line fault as an example, the electromagnetic transient modeling and calculation method of the lightning backflashover line air gap and conductor insulator string overvoltage of this invention is used to obtain the overvoltage values ​​of the conductor-to-ground wire air gap and conductor insulator string of this line. The specific steps are as follows:

[0099] 1) Obtain the actual spatial location and model of the overhead line on site, obtain the structural and material parameters of the overhead line, and establish the overhead line model in the electromagnetic transient simulation software;

[0100] 1.1) Obtain the actual spatial location of the overhead lines, including: the heights of the three phases ABC above the ground are 21m, 27.5m, and 34m, respectively, and the distances from the center crossarm of the tower are 4.2m, 2.2m, and 2.2m, respectively; and the height of the ground wire above the ground is 38.5m, and the distance from the center crossarm of the tower is 7.6m.

[0101] 1.2) Obtain the actual overhead line conductor model JL / G1A-300 / 40 on site, and obtain the structural and material parameters of the corresponding overhead line model. The structural parameters include: the outer diameter of the conductor of the ABC three-phase line is 2.394m, the inner diameter of the conductor is 0m, the number of splits is 4, and the split spacing is 400mm; the outer diameter of the conductor of the ground wire is 1.52m, the inner diameter of the conductor is 0m, the number of splits is 0, and the split spacing is 0mm. The material parameters include: the DC resistance of the conductor of the ABC three-phase line is 0.0960Ω / km, and the DC resistance of the conductor of the ground wire is 0.274Ω / km.

[0102] 1.3) Establish an overhead line model in the simulation software ATP-EMTP.

[0103] 2) Obtain the actual dimensions and model of the tower on site, obtain the tower structural parameters, calculate the tower wave impedance parameters, and establish the tower model in the electromagnetic transient simulation software;

[0104] 2.1) Obtain the actual dimensions of the tower, such as... Figure 3 As shown, the ground clearance of the first to fourth crossarms of the tower is h1=21m, h2=27.5m, h3=34m, and h4=38.5m, respectively; the equivalent radii of the first to fourth main members are respectively... r T1 =0.85m r T2 =0.75m r T3 =0.5m r T4 =0.32m; the equivalent radii of the first to fourth crossarms are respectively r A1 =2.2m r A2 =4.2m r A3 =2.2m r A4 =1.6m;

[0105] 2.2) The tower wave impedance parameters are calculated, such as... Figure 4As shown, the wave impedances of the main materials of the tower from the first to the fourth section are respectively... Z T1 =98.3Ω Z T2 =109.4Ω Z T3 =95.4Ω Z T4 =69.5Ω; the wave impedances of the first to fourth sections of the tower's inclined members are respectively Z L1 =884.5Ω Z L2 =984.7Ω Z L3 =858.8Ω Z L4 =625.9Ω; the crossarm wave impedances of the first to fourth sections of the tower are respectively Z A1 =461.8Ω Z A2 =454.3Ω Z A3 =426.5Ω Z A4 =410.3Ω;

[0106] 2.3) Establish the tower model in the simulation software ATP-EMTP.

[0107] 3) Obtain normal operating parameters of the power system and establish a power supply model in the electromagnetic transient simulation software;

[0108] 3.1) Obtain the normal operating parameters of the power system, including: the effective value of the power system operating voltage is 127.017kV, the power system operating phase angle is -151.95°, and the power system operating frequency is 50Hz;

[0109] 3.2) Establish a power supply model in the simulation software ATP-EMTP.

[0110] 4) Obtain the air gap between the conductor and ground wire and the dry arc distance between the conductor and insulator string on site, and establish the air gap model and the insulator string model;

[0111] 4.1) Obtain the air gap between the conductor and ground wire and the dry arc distance between the conductor and insulator string, including: air gap between the conductor and ground wire 9.31m, dry arc distance between the conductor and insulator string 2.044m;

[0112] 4.2) Establish the volt-second characteristic curve of the air gap between the conductor and ground wire, for Establish the volt-second characteristic curve of the insulator string, for ;

[0113] 4.3) Establish the air gap model of the conductor and ground wire and the insulator string model in the simulation software ATP-EMTP.

[0114] 5) Obtain the location of the lightning strike fault and the magnitude of the lightning current, and establish a lightning current model in the electromagnetic transient simulation software;

[0115] 5.1) Obtain the location of the lightning strike fault point, including: the distance from the lightning strike fault point to the left tower is 420m, and the distance from the lightning strike fault point to the right tower is 283m;

[0116] 5.2) Obtain the lightning current model parameters, including: peak lightning current -100kA, wavefront time 2.6μs, and half-peak time 50μs;

[0117] 5.3) Establish a lightning current model in the simulation software ATP-EMTP.

[0118] 6) Connect the overhead line model, tower model, power supply model, and insulator string model with the ABC three-phase conductors in the simulation software ATP-EMTP;

[0119] 7) Connect the overhead line model, tower model, power supply model, and insulator string model with the ABC three-phase conductors in the simulation software ATP-EMTP;

[0120] 8) Connect the lightning current model to the overhead line model using a single-phase conductor in the simulation software ATP-EMTP, and inject the lightning current into the ground wire of the overhead line model through the single-phase conductor.

[0121] 9) Connect the conductor and ground wire in the single-phase conductor of the overhead line model in the simulation software ATP-EMTP to the conductor and ground wire of the air gap model.

[0122] 10) In the electromagnetic transient simulation software, different lightning current peak values ​​were set to 50kA, 80kA, 100kA, 120kA, 150kA, and 200kA, with wavefront times of 1.2μs, 2.6μs, 5μs, and 10μs. Electromagnetic transient calculations were performed in the simulation software ATP-EMTP. The calculation results are shown in Tables 1 and 2. The overvoltage waveform is as follows: Figure 5 As shown.

[0123] According to Tables 1 and 2, the maximum overvoltage of the air gap between the conductor and ground wire is 9190.8kV, and the maximum overvoltage of the conductor insulator string is 5883.7kV.

[0124] Table 1 Overvoltage under different peak lightning currents

[0125]

[0126] Table 2 Overvoltage at different wavefront times

[0127]

[0128] Table 1 shows that, keeping the wavefront / half-peak time constant at 2.6 / 50 μs, the breakdown voltage of the air gap between the conductor and ground gradually increases with the increase of the peak lightning current. When the peak lightning current increases from 50 kA to 200 kA, the breakdown voltage increases from 3003.9 kV to 9005.5 kV, a 3.0-fold increase. Table 1 also shows that, keeping the wavefront / half-peak time constant, the overvoltage of the upper phase insulator is positively correlated with the peak lightning current. When the peak lightning current gradually increases from 80 kA to 200 kA, the overvoltage of the upper phase insulator increases from 2853.2 kV to 5741.2 kV, a 2.0-fold increase.

[0129] As shown in Table 2, keeping the peak lightning current constant, the overvoltage values ​​of the air gap between the conductor and ground wire and the overvoltage values ​​of the upper phase insulator gradually decrease with the increase of the wavefront time. When the wavefront time gradually increases from 1.2 μs to 10 μs, the overvoltage of the air gap between the conductor and ground wire decreases from 9190.8 kV to 1720.7 kV, a reduction of 81.28%; the overvoltage of the upper phase insulator decreases from 5883.7 kV to 209.4 kV, a reduction of 96.44%.

[0130] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A method for electromagnetic transient modeling and calculation of lightning back striking line air gap and conductor insulator string overvoltage, characterized in that, The method comprises the steps of: a) establishing an overhead line model in electromagnetic transient simulation software; b) establishing a tower model in electromagnetic transient simulation software; c) establishing a power supply model in electromagnetic transient simulation software according to normal operation parameters of a power system; d) obtaining an air gap of a ground wire and a dry arc distance of a conductor insulator string, and establishing an air gap model of the ground wire and an insulator string model; e) obtaining a lightning fault point position and a lightning current size, and establishing a lightning current model in the electromagnetic transient simulation software; f) connecting the overhead line model, the tower model, the power supply model and the insulator string model with ABC three-phase conductors in the electromagnetic transient simulation software; g) connecting the lightning current model with the ground wire of the overhead line model through a single-phase conductor in the electromagnetic transient simulation software, and injecting the lightning current into the ground wire of the overhead line model through the single-phase conductor; h) connecting the air gap model of the ground wire with the conductor and the ground wire in the overhead line model through a single-phase conductor in the electromagnetic transient simulation software; i) setting different lightning currents and wave head times in the electromagnetic transient simulation software, and performing electromagnetic transient calculation to obtain maximum overvoltage of the air gap of the ground wire and overvoltage of the conductor insulator string; in step d), the air gap model of the ground wire and the insulator string model are constructed by an intersection method; the specific content of step f) comprises: f1) the overhead line model comprises a first overhead line model and a second overhead line model; the tower model comprises a first tower model and a second tower model; the power supply model comprises a first power supply model and a second power supply model; and the insulator string model comprises a first insulator string model and a second insulator string model; f2) the first power supply model, the first insulator string model, the first overhead line model, the second overhead line model, the second insulator string model and the second power supply model are connected in series by ABC three-phase conductors; f3) the first insulator string model and the ABC three-phase hanging point of the first tower model are connected in series, and the second insulator string model and the ABC three-phase hanging point of the second tower model are connected in series; f4) the first grounding point, the first overhead line model, the second overhead line model and the second grounding point are connected in series by a single-phase conductor in the software; f5) the first grounding point is connected in parallel with the ground wire hanging point of the first tower model, and the second grounding point is connected in parallel with the ground wire hanging point of the second tower model; f6) the first grounding point and the second grounding point are both zero potential and are electrically regarded as the same point.

2. The electromagnetic transient modeling and calculation method of lightning back striking line air gap and conductor insulator string overvoltage according to claim 1, characterized in that, in step a), the actual spatial position and the type of the overhead line are obtained, the structure parameters and the material parameters of the overhead line are obtained according to the type of the overhead line, and thus the overhead line model in the electromagnetic transient simulation software is established; the actual spatial position of the overhead line comprises the height from the ground and the distance from the tower center cross arm of the ABC three-phase line, and the height from the ground and the distance from the tower center cross arm of the ground wire; the structure parameters comprise the outer diameter of the conductor, the inner diameter of the conductor, the number of branches and the branch spacing of the ABC three-phase line, and the outer diameter of the conductor, the inner diameter of the conductor, the number of branches and the branch spacing of the ground wire; and the material parameters comprise the direct current resistance of the conductor of the ABC three-phase line and the direct current resistance of the conductor of the ground wire.

3. The electromagnetic transient modeling and computational method of lightning back striking line air gap and conductor insulator string overvoltage according to claim 1, characterized in that, In step b), the tower model in the electromagnetic transient simulation software is established by obtaining the actual size and model of the tower on site, obtaining the tower structure parameters according to the model, and calculating the tower wave impedance parameters, wherein the actual size of the tower includes the height of each cross arm of the tower, the equivalent radius of each main material, and the equivalent radius of each cross arm; and the tower wave impedance parameters include the wave impedance of each main material of the tower, the wave impedance of each inclined material, and the wave impedance of each cross arm.

4. The electromagnetic transient modeling and computational method of lightning back striking line air gap and conductor insulator string overvoltage according to claim 1, characterized in that, In step c), the normal operation parameters of the power system include the effective value of the operation voltage of the power system, the operation phase angle of the power system, and the operation frequency of the power system.

5. The electromagnetic transient modeling and computational method of lightning back striking line air gap and conductor insulator string overvoltage according to claim 1, wherein, In step e), the lightning stroke fault point position includes the distance from the lightning stroke fault point to the left tower and the distance from the lightning stroke fault point to the right tower; the lightning current model parameters include the peak value of the lightning current, the wave head time, and the half-peak time, and the lightning current is described by using a double exponential function model.

6. The electromagnetic transient modeling and computational method of lightning back striking line air gap and conductor insulator string overvoltage according to claim 1, wherein, In step g), when the lightning current model and the overhead line model are connected by using a single-phase conductor, the overhead line model is connected by using a ground wire.

7. The electromagnetic transient modeling and computational method of lightning back striking line air gap and conductor insulator string overvoltage according to claim 1, characterized in that, In step h), when the conductor-ground wire air gap model and the overhead line model are connected by using a single-phase conductor, the overhead line model is connected by using a ground wire and an A-phase conductor in the ABC three-phase conductor.

8. The electromagnetic transient modeling and computational method of lightning back striking line air gap and conductor insulator string overvoltage according to claim 1, characterized in that, In step i), the maximum values of the conductor-ground wire air gap overvoltage and the conductor insulator string overvoltage are obtained by the following steps: i1) in the conductor-ground wire air gap model and the insulator string model in step d), voltage monitoring points are respectively set; i2) in the electromagnetic transient simulation software, different peak values of the lightning current and wave head times are set, and the conductor-ground wire air gap overvoltage value and the conductor insulator string overvoltage value under each working condition are recorded; i3) after the electromagnetic transient simulation software is repeatedly run, the conductor-ground wire air gap overvoltage value and the conductor insulator string overvoltage value are compared, and the maximum values of the conductor-ground wire air gap overvoltage and the conductor insulator string overvoltage are obtained: ， ， wherein, , are the maximum air gap overvoltage of the conductor-to-ground and the maximum insulator string overvoltage of the conductor, respectively; i represents the first i peak of the lightning current; j represents the first j wave front time; , are the air gap overvoltage and the insulator string overvoltage, respectively.

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