CN112595938B - Method for evaluating adaptability of graphite-based flexible grounding device of pole tower of overhead transmission line - Google Patents
Method for evaluating adaptability of graphite-based flexible grounding device of pole tower of overhead transmission line Download PDFInfo
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Abstract
The invention discloses an evaluation method of adaptability of a grounding device of a pole tower of an overhead transmission line, which comprises the steps of establishing a power frequency finite element model and a lightning impulse finite element model of the grounding device and the environment soil where the grounding device is positioned; acquiring the power frequency grounding resistance and the impact grounding resistance of the grounding device according to the model; if the power frequency grounding resistance does not meet the grounding design requirement, the grounding device is not suitable for the overhead transmission line tower under the corresponding voltage level; if the voltage level is met, inputting the power frequency grounding resistor and the impact grounding resistor into an overhead transmission line model under the corresponding voltage level of the grounding device, and obtaining a single-phase power frequency short circuit and current passing through the grounding device when the tower is struck by lightning; and taking the current as a boundary condition, performing simulation calculation to obtain the temperature rise of the grounding device, wherein if the temperature rise of the grounding device meets the design requirement, the grounding device is suitable for the overhead transmission line tower, otherwise, the grounding device is not suitable for the overhead transmission line tower. The invention aims to evaluate the adaptability of a grounding device in the application of an overhead transmission line pole tower.
Description
Technical Field
The invention belongs to the technical field of lightning protection grounding, and particularly relates to an evaluation method for adaptability of a graphite-based flexible grounding device of an overhead transmission line tower.
Background
The grounding body of the tower is an important ring in lightning protection of the overhead transmission line, and the over-high grounding resistance can reduce the lightning-resistant level of the line and increase the flashover rate of the line, so that the safe and stable operation of the power system is affected. Conventional grounding materials such as galvanized steel, copper-clad steel and the like have been widely used in the grounding of power systems, but in actual operation, conventional grounding bodies have problems of poor corrosion resistance, poor contact with soil, susceptibility to artificial damage and the like. Aiming at the defects of the traditional material grounding body in practical application, the graphite-based flexible material with excellent corrosion resistance and soil compatibility is gradually applied to the grounding body of the pole tower of the overhead transmission line, but the application of the graphite-based flexible grounding device in the line still has the adaptability problem.
Specifically, at first, the self resistivity of the graphite-based flexible grounding device is larger than that of the traditional metal grounding material, and the main body resistance is higher, so that the power frequency grounding resistance and the impact grounding resistance of the tower can be influenced. Secondly, overhead transmission line is because the voltage grade is high, and transport capacity is big, and when taking place single-phase through shaft tower ground short circuit, the electric current through the grounding body is great, and the circuit erects in the field easily to suffer the thunderbolt simultaneously, has high-amplitude lightning current to flow through the shaft tower grounding body. The graphite-based flexible grounding device contains chemical fibers, adhesives and the like, and the working temperature is not suitable to exceed 160 ℃, so that the temperature rise of the graphite-based flexible grounding device when a large current passes through the graphite-based flexible grounding device must be estimated. However, at present, no method for adaptively evaluating the type and design of the graphite-based flexible grounding device exists, so that whether the graphite-based flexible grounding device is suitable for the corresponding voltage class power transmission line tower cannot be judged.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an evaluation method for the adaptability of the graphite-based flexible grounding device of the overhead transmission line tower, which aims at evaluating the adaptability of the graphite-based flexible grounding device in the application of the overhead transmission line tower and provides a basis for the selection and design optimization of the graphite-based flexible grounding device.
In order to solve the technical problems, the invention is realized by the following technical scheme:
an evaluation method for adaptability of a graphite-based flexible grounding device of an overhead transmission line tower, comprising the following steps:
establishing a power frequency finite element model comprising a graphite-based flexible grounding device and the environment soil where the graphite-based flexible grounding device is located, and establishing a lightning impulse finite element model comprising the graphite-based flexible grounding device and the environment soil where the graphite-based flexible grounding device is located;
acquiring a power frequency grounding resistance of the graphite-based flexible grounding device according to the power frequency finite element model, and acquiring a lightning impulse grounding resistance of the graphite-based flexible grounding device according to the lightning impulse finite element model;
comparing the power frequency grounding resistance with a design value of the power frequency grounding resistance of the graphite-based flexible grounding device under a voltage level corresponding to the graphite-based flexible grounding device; when the power frequency grounding resistance is larger than the design value of the power frequency grounding resistance, the graphite-based flexible grounding device is not suitable for the overhead transmission line tower under the corresponding voltage level; when the power frequency grounding resistance is not larger than the design value of the power frequency grounding resistance, inputting the power frequency grounding resistance and the impact grounding resistance into an overhead transmission line model under the corresponding voltage level of a graphite-based flexible grounding device;
acquiring current of the overhead transmission line passing through the graphite-based flexible grounding device when a single-phase power frequency is short-circuited and current of the overhead transmission line passing through the graphite-based flexible grounding device when a tower is struck by lightning according to the overhead transmission line model;
taking the current passing through the graphite-based flexible grounding device when the single-phase power frequency is short-circuited as the terminal boundary condition of the power frequency finite element model to obtain a first volume loss density; taking the current passing through the graphite-based flexible grounding device when the tower is struck by lightning as the terminal boundary condition of the lightning impulse finite element model to obtain second volumetric loss density;
calculating a first temperature rise of the graphite-based flexible grounding device according to the first volumetric loss density and the specific heat capacity of the graphite-based flexible grounding device; calculating a second temperature rise of the graphite-based flexible grounding device according to the second volumetric loss density and the specific heat capacity of the graphite-based flexible grounding device;
comparing the first temperature rise and the second temperature rise with temperature rise thresholds of the graphite-based flexible grounding device; when at least one of the first temperature rise and the second temperature rise is greater than the temperature rise threshold, the graphite-based flexible grounding device is not suitable for the overhead transmission line tower under the corresponding voltage level; when the first temperature rise and the second temperature rise are not greater than the temperature rise threshold, the graphite-based flexible grounding device is suitable for the overhead transmission line tower under the corresponding voltage level.
Further, the establishment process of the power frequency finite element model and the lightning impulse finite element model is as follows:
and establishing a three-dimensional model of the graphite-based flexible grounding device, introducing the three-dimensional model into finite element simulation software, and establishing a model of the environment soil where the graphite-based flexible grounding device is positioned by utilizing the finite element simulation software according to the burying depth of the graphite-based flexible grounding device to obtain the power frequency finite element model and the lightning impulse finite element model.
Further, the method for obtaining the power frequency grounding resistance of the graphite-based flexible grounding device according to the power frequency finite element model comprises the following steps: and setting the resistivity of the environment soil where the graphite-based flexible grounding device is positioned as a fixed value, and solving the power frequency grounding resistance in a frequency domain by adopting an electric current field.
Further, the method for obtaining the impulse grounding resistance of the graphite-based flexible grounding device according to the lightning impulse finite element model comprises the following steps:
and setting the resistivity of the environment soil where the graphite-based flexible grounding device is positioned as a layered interpolation function related to the electric field strength, and solving in a time domain by adopting a plurality of physical fields of electric field and magnetic field coupling to obtain the impact grounding resistance.
Further, the method for establishing the overhead transmission line model comprises the following steps:
establishing the overhead transmission line model by using ATP-EMTP;
the overhead transmission line model comprises an overhead line, a tower and a lightning current source, wherein the overhead line adopts a JMARti frequency response model in an LCC module in ATP-EMTP, the tower adopts a multi-wave impedance model, and the lightning current source is simulated by adopting a double-index model.
Further, calculating the first temperature rise of the graphite-based flexible grounding device according to the first volume loss density and the specific heat capacity of the graphite-based flexible grounding device, wherein the specific formula is as follows:
wherein P is max Maximum bulk loss density of graphite material in unit W/m in graphite-based flexible earthing device 3 ；
Δt-the duration of the power frequency short-circuit current, unit s;
c m specific heat capacity of graphite material, unit J/(kg. Deg.C);
density of rho-graphite material in kg/m 3 。
Further, calculating a second temperature rise of the graphite-based flexible grounding device according to the second volumetric loss density and the specific heat capacity of the graphite-based flexible grounding device, wherein the specific formula is as follows:
wherein P is i -bulk loss density in W/m for the ith time step of the graphite material in a graphite-based flexible earthing device 3 ；
N is the total number of time steps,t is the duration of the lightning current in s;
Δt-time domain simulation time step, unit s;
c m specific heat capacity of graphite material, unit J/(kg. Deg.C);
density of rho-graphite material in kg/m 3 。
Further, the finite element simulation software is COMSOL Mutiphysics finite element simulation software.
Compared with the prior art, the invention has at least the following beneficial effects: the invention provides an evaluation method for the adaptability of a graphite-based flexible grounding device of an overhead transmission line tower, which is characterized in that before the graphite-based flexible grounding device is not embedded for application, the power frequency grounding resistance, the impact grounding resistance and the current passing through the graphite-based flexible grounding device when a single-phase power frequency is short-circuited of the graphite-based flexible grounding device and the temperature rise under the current passing through the graphite-based flexible grounding device when the tower is struck by lightning are subjected to simulation calculation according to the actual engineering conditions of the graphite-based flexible grounding device. The modeling calculation can be carried out on any type of graphite-based flexible grounding device by combining the calculation advantages of finite element simulation software and electromagnetic transient simulation software, and the adaptability is wider. The evaluation method can carry out calculation evaluation on the whole set of complete graphite-based flexible grounding device, and has the advantages of low cost, flexibility, convenience, design and construction rationality assurance and the like compared with the test which has high cost and is difficult to implement and can only evaluate part of the structure of the graphite-based flexible grounding device. The optimization and improvement of the shape selection and design of the graphite grounding device are facilitated to a certain extent before engineering construction, and the optimization and improvement of the shape selection and design of the graphite grounding device are significant in reducing the lightning flashover rate of overhead transmission lines and avoiding unreasonable engineering construction.
In order to make the above objects, features and advantages of the present invention more comprehensible, preferred embodiments accompanied with figures are described in detail below.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for evaluating the adaptability of a graphite-based flexible grounding device of an overhead transmission line tower according to the present invention;
fig. 2 is a three-dimensional model diagram of a graphite-based flexible grounding device according to an embodiment of the present invention;
FIG. 3 is a schematic diagram showing the relationship between the soil conductivity and the soil electric field intensity according to the embodiment of the present invention;
fig. 4 is a 220kV overhead transmission line model provided by an embodiment of the present invention.
In the figure: 1-armoured down-lead; 2-spark-ignition grounding module; 3-graphite resistance-reducing cloth; 4-horizontal flexible grounding body.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As a specific embodiment of the invention, the method for evaluating the adaptability of the graphite-based flexible grounding device of the pole tower of the overhead transmission line comprises the following steps:
establishing a power frequency finite element model comprising a graphite-based flexible grounding device and the environment soil where the graphite-based flexible grounding device is located, and establishing a lightning impulse finite element model comprising the graphite-based flexible grounding device and the environment soil where the graphite-based flexible grounding device is located;
specifically, the building process of the power frequency finite element model and the lightning impulse finite element model is as follows: and establishing a three-dimensional model of the graphite-based flexible grounding device by utilizing Solidworks, introducing the three-dimensional model into finite element simulation software, and establishing a model of the environment soil where the graphite-based flexible grounding device is positioned by utilizing the finite element simulation software according to the burying depth of the graphite-based flexible grounding device to obtain a power frequency finite element model and a lightning impulse finite element model.
The power frequency grounding resistance of the graphite-based flexible grounding device is obtained according to a power frequency finite element model, and the specific obtaining method comprises the following steps: setting the resistivity of the environment soil where the graphite-based flexible grounding device is positioned as a fixed value, and solving in a frequency domain by adopting an electric current field to obtain the power frequency grounding resistance.
According to the lightning impulse finite element model, the impulse grounding resistance of the graphite-based flexible grounding device is obtained, and the specific obtaining method comprises the following steps: the resistivity of the environment soil where the graphite-based flexible grounding device is arranged is a layered interpolation function related to the electric field strength, and the impact grounding resistance is obtained by solving a plurality of physical fields of electric field and magnetic field coupling in a time domain.
The three-dimensional model diagram of the near-zone pole tower grounding device of the 220kV overhead transmission line shown in fig. 2 is built in Solidworks software, and the graphite-based flexible grounding device is applied to a region with the soil resistivity of 0-300 omega-m, and the maximum allowable power frequency grounding resistance is 10 omega. The graphite-based flexible grounding device mainly comprises an armored graphite down-lead 1, a horizontal flexible grounding body 4, graphite resistance-reducing cloth 3 and a spark-thorn grounding module 2, and the model is simplified in engineering according to the actual sizes of the parts.
The three-dimensional model of the graphite-based flexible grounding device was imported into COMSOL Mutiphysics finite element software, with a soil field disposed around the grounding device. When current passes through the grounding body, the graphite-based flexible grounding device is used as the center, the current uniformly disperses to the surrounding soil, the soil area is arranged in a hemispherical shape, and the grounding device is buried below the soil surface by 0.6m. The radius of the soil area is set to be more than 10 times of the maximum diagonal length of the grounding device, so that the calculation result can be basically accurate, and the radius is set to be 500m in the embodiment.
The hemispherical surface of the soil area is set to be a ground potential, and the upper end of the armored downlead is used as a current injection point. The conductivity, relative permittivity and relative permeability of the graphite in this embodiment are respectively 5×10 4 S/m, 15 and 1. When the power frequency grounding resistance is calculated, the soil conductivity is considered to be a fixed value which does not change along with the field intensity and is 0.00333S/m; when the impact grounding resistance is calculated, the soil conductivity is set to change along with the field intensity, and the relationship between the soil conductivity and the soil field intensity is shown in figure 3. The power frequency grounding resistance is 9.256 omega and the impact grounding resistance is 7.234 omega.
Comparing the power frequency grounding resistance with a design value of the power frequency grounding resistance under the voltage level corresponding to the graphite-based flexible grounding device; when the power frequency grounding resistance is larger than the design value of the power frequency grounding resistance, the graphite-based flexible grounding device is not suitable for the overhead transmission line tower under the corresponding voltage level; when the power frequency grounding resistance is not larger than the design value of the power frequency grounding resistance, inputting the power frequency grounding resistance and the impact grounding resistance into an overhead transmission line model under the corresponding voltage level of the graphite-based flexible grounding device; the overhead line adopts a JMARti frequency response model in an LCC module in the ATP-EMTP, the tower adopts a multi-wave impedance model, and the lightning current source adopts a double-index model for simulation.
And acquiring the current of the overhead transmission line passing through the graphite-based flexible grounding device when the single-phase power frequency is short-circuited and the current of the overhead transmission line passing through the graphite-based flexible grounding device when the tower is struck by lightning.
The power frequency grounding resistance of the graphite-based flexible grounding device is 9.256 Ω and is smaller than the design value of the power frequency grounding resistance. And constructing a 220kV overhead transmission line model in ATP-EMTP electromagnetic transient calculation software as shown in fig. 4. In the embodiment, the parameters of the 220kV overhead transmission line are selected for investigation. The length of the overhead transmission line is 200km, and the transmission capacity is 121MW. The line tower is a single-loop straight tower, the tower is simulated by adopting a multi-wave impedance model, and the grounding device is simulated by adopting a grounding resistance. When a single-phase power frequency short circuit occurs to the circuit, the grounding resistance is set to 9.256 omega; when the tower is struck by lightning, the grounding resistance is set to 7.234 omega. Through simulation calculation, the single-phase power frequency short-circuit current amplitude value passing through the graphite-based flexible grounding device is 1743A, the lightning current amplitude value passing through the graphite-based flexible grounding device is 176.250kA, and the waveform is 2.8/10.7 mu s. The double exponential function of lightning current is:
I＝-389620×(e -547679t -e -145777t )。
taking the current passing through the graphite-based flexible grounding device during single-phase power frequency short circuit as the terminal boundary condition of a power frequency finite element model to obtain a first volume loss density; and taking the current passing through the graphite-based flexible grounding device when the tower is struck by lightning as a terminal boundary condition of the lightning impulse finite element model to obtain the second volumetric loss density.
Calculating a first temperature rise of the graphite-based flexible grounding device according to the first volumetric loss density and the specific heat capacity of the graphite-based flexible grounding device; and calculating a second temperature rise of the graphite-based flexible grounding device according to the second volumetric loss density and the specific heat capacity of the graphite-based flexible grounding device.
The terminal current amplitude of the power frequency finite element model is set to 1743A, and the terminal current of the lightning impulse finite element model is set to be a double exponential function with current amplitude of 189.020kA and waveform of 2.8/10.7 mu s. Graphite has a specific heat capacity of 710J/(. Degree.C.kg) and a density of 2000kg/m 3 . Short-circuit current and lightning strike current have short action time, so different materials can be regarded as absolute materialsA thermal state. The maximum power frequency short-circuit current lasts for 0.5s, and the simulation result shows that the maximum value of the first volume loss density is 7.6x10 7 W/m 3 The first temperature rise maximum value is:
the lightning current lasts for 50 mu s, the time-domain simulation time step is 1 mu s, then
The second maximum temperature rise is:
under the power frequency short-circuit current with the duration of 0.04s, the maximum temperature rise of the graphite grounding device is not more than 26.761 ℃; under the lightning impulse current, the maximum temperature rise of the graphite grounding device is not more than 74.360 ℃.
Comparing the first temperature rise and the second temperature rise with temperature rise threshold values of the graphite-based flexible grounding device; when at least one of the first temperature rise and the second temperature rise is larger than a temperature rise threshold value, the graphite-based flexible grounding device is not suitable for the overhead transmission line tower under the corresponding voltage level; when the first temperature rise and the second temperature rise are not greater than the temperature rise threshold, the graphite-based flexible grounding device is suitable for the overhead transmission line tower under the corresponding voltage level.
The graphite-based flexible grounding device in the embodiment is applicable to near-area towers of 220kV overhead transmission lines, and the temperature rise of the graphite-based flexible grounding device under power frequency short circuit and lightning stroke heavy current is not more than 120 ℃.
Finally, it should be noted that: the above examples are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention, but it should be understood by those skilled in the art that the present invention is not limited thereto, and that the present invention is described in detail with reference to the foregoing examples: any person skilled in the art may modify or easily conceive of the technical solution described in the foregoing embodiments, or perform equivalent substitution of some of the technical features, while remaining within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention, and are intended to be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (8)
1. The method for evaluating the adaptability of the graphite-based flexible grounding device of the pole tower of the overhead transmission line is characterized by comprising the following steps of:
establishing a power frequency finite element model comprising a graphite-based flexible grounding device and the environment soil where the graphite-based flexible grounding device is located, and establishing a lightning impulse finite element model comprising the graphite-based flexible grounding device and the environment soil where the graphite-based flexible grounding device is located;
acquiring a power frequency grounding resistance of the graphite-based flexible grounding device according to the power frequency finite element model, and acquiring a lightning impulse grounding resistance of the graphite-based flexible grounding device according to the lightning impulse finite element model;
comparing the power frequency grounding resistance with a design value of the power frequency grounding resistance of the graphite-based flexible grounding device under a voltage level corresponding to the graphite-based flexible grounding device; when the power frequency grounding resistance is larger than the design value of the power frequency grounding resistance, the graphite-based flexible grounding device is not suitable for the overhead transmission line tower under the corresponding voltage level; when the power frequency grounding resistance is not larger than the design value of the power frequency grounding resistance, inputting the power frequency grounding resistance and the impact grounding resistance into an overhead transmission line model under the corresponding voltage level of a graphite-based flexible grounding device;
acquiring current of the overhead transmission line passing through the graphite-based flexible grounding device when a single-phase power frequency is short-circuited and current of the overhead transmission line passing through the graphite-based flexible grounding device when a tower is struck by lightning according to the overhead transmission line model;
taking the current passing through the graphite-based flexible grounding device when the single-phase power frequency is short-circuited as the terminal boundary condition of the power frequency finite element model to obtain a first volume loss density; taking the current passing through the graphite-based flexible grounding device when the tower is struck by lightning as the terminal boundary condition of the lightning impulse finite element model to obtain second volumetric loss density;
calculating a first temperature rise of the graphite-based flexible grounding device according to the first volumetric loss density and the specific heat capacity of the graphite-based flexible grounding device; calculating a second temperature rise of the graphite-based flexible grounding device according to the second volumetric loss density and the specific heat capacity of the graphite-based flexible grounding device;
comparing the first temperature rise and the second temperature rise with temperature rise thresholds of the graphite-based flexible grounding device; when at least one of the first temperature rise and the second temperature rise is greater than the temperature rise threshold, the graphite-based flexible grounding device is not suitable for the overhead transmission line tower under the corresponding voltage level; when the first temperature rise and the second temperature rise are not greater than the temperature rise threshold, the graphite-based flexible grounding device is suitable for the overhead transmission line tower under the corresponding voltage level.
2. The method for evaluating the adaptability of the graphite-based flexible grounding device of the overhead transmission line tower according to claim 1, wherein the establishing process of the power frequency finite element model and the lightning impulse finite element model is as follows:
and establishing a three-dimensional model of the graphite-based flexible grounding device, introducing the three-dimensional model into finite element simulation software, and establishing a model of the environment soil where the graphite-based flexible grounding device is positioned by utilizing the finite element simulation software according to the burying depth of the graphite-based flexible grounding device to obtain the power frequency finite element model and the lightning impulse finite element model.
3. The method for evaluating the adaptability of the graphite-based flexible grounding device of the overhead transmission line tower according to claim 1, wherein the method for acquiring the power frequency grounding resistance of the graphite-based flexible grounding device according to the power frequency finite element model is as follows: and setting the resistivity of the environment soil where the graphite-based flexible grounding device is positioned as a fixed value, and solving the power frequency grounding resistance in a frequency domain by adopting an electric current field.
4. The method for evaluating the adaptability of the graphite-based flexible grounding device of the overhead transmission line tower according to claim 1, wherein the method for acquiring the impulse grounding resistance of the graphite-based flexible grounding device according to the lightning impulse finite element model is as follows:
and setting the resistivity of the environment soil where the graphite-based flexible grounding device is positioned as a layered interpolation function related to the electric field strength, and solving in a time domain by adopting a plurality of physical fields of electric field and magnetic field coupling to obtain the impact grounding resistance.
5. The method for evaluating the adaptability of the graphite-based flexible grounding device of the pole tower of the overhead transmission line according to claim 1, wherein the method for establishing the model of the overhead transmission line is as follows:
establishing the overhead transmission line model by using ATP-EMTP;
the overhead transmission line model comprises an overhead line, a tower and a lightning current source, wherein the overhead line adopts a JMARti frequency response model in an LCC module in ATP-EMTP, the tower adopts a multi-wave impedance model, and the lightning current source is simulated by adopting a double-index model.
6. The method for evaluating the adaptability of the graphite-based flexible grounding device of the pole tower of the overhead transmission line according to claim 1, wherein the first temperature rise of the graphite-based flexible grounding device is calculated according to the first volumetric loss density and the specific heat capacity of the graphite-based flexible grounding device, and the specific formula is as follows:
wherein P is max Maximum bulk loss density of graphite material in unit W/m in graphite-based flexible earthing device 3 ；
Δt-the duration of the power frequency short-circuit current, unit s;
c m specific heat capacity of graphite material, unit J/(kg. Deg.C);
density of rho-graphite material in kg/m 3 。
7. The method for evaluating the adaptability of the graphite-based flexible grounding device of the overhead transmission line tower according to claim 1, wherein the second temperature rise of the graphite-based flexible grounding device is calculated according to the second volumetric loss density and the specific heat capacity of the graphite-based flexible grounding device, and the specific formula is as follows:
wherein P is i -bulk loss density in W/m for the ith time step of the graphite material in a graphite-based flexible earthing device 3 ；
N is the total number of time steps,t is the duration of the lightning current in s;
Δt-time domain simulation time step, unit s;
c m specific heat capacity of graphite material, unit J/(kg. Deg.C);
density of rho-graphite material in kg/m 3 。
8. The method for evaluating the adaptability of the graphite-based flexible grounding device of the pole tower of the overhead transmission line according to claim 2, wherein the finite element simulation software is COMSOL Mutiphysics finite element simulation software.
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