Method for analyzing damage of high-conductivity fiber grounding body under large current based on multi-field coupling

Abstract

The invention relates to a multi-field coupling-based high-conductivity fiber grounding body damage analysis method under large current. The method comprises the following steps of 1, constructing a lightning stroke thermoelectric coupling mathematical model: representing the damage area and the damage depth of a high-conductivity fiber grounding body by adopting temperature field distribution; 2, constructing a quasi-static arc adhesion sound model of the high-conductivity fiber grounding body: analyzing electro-thermal coupling of quasi-static arc damage of the high-conductivity fiber grounding body; and step 3, establishing a multi-field coupling model of lightning arc damage of the high-conductivity fiber grounding body: performing electro-magnetic-thermal-mechanical coupling analysis on material damage of the high-conductivity fiber grounding body under long-duration lightning current arc, and representing thermal fluid dynamic characteristics of the lightning current arc. Obtaining a damage mechanism of the high-conductivity fiber grounding body under the action of the lightning current arc; the method has the advantages that the electro-thermal multi-physical field coupling model is constructed based on thermoelectric coupling, and the damage mechanism rule is analyzed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of transmission line grounding damage analysis, and particularly relates to a high-conductivity fiber grounding body damage analysis method under large current based on multi-field coupling. BACKGROUND

[0002] The electric power construction planning will force the transmission line to be built in large quantities in the high-resistivity barren mountainous areas and the basic farmland areas in rural areas, which poses new challenges to the operation reliability of the transmission line tower grounding body. Challenge one: in the mountainous areas with high soil resistivity (the soil resistivity is generally more than 1500Ω·m), the high resistivity causes the current to not be discharged to the ground in time when a large current is impacted, the lightning resistance level of the transmission line is significantly reduced, and the trip-out accident is easily caused. Challenge two: the gradient stress generated by the lightning current impact in the high-resistivity area accelerates the damage and deterioration of the grounding body, and the electrochemical corrosion and oxygen absorption corrosion are easily caused at the metal connection of the grounding body in the acidic soil in the mountainous areas, resulting in the problem of "land loss" of the transmission line tower. The above new problems will cause the electrical connection failure of the transmission line grounding, the trip-out accident caused by the large current impact is frequent, and the operation safety of the power system is seriously threatened. Therefore, it is necessary to analyze the electro-thermal coupling of the high-conductivity fiber grounding body under the large current (including the lightning current) impact, find out the damage mechanism, and realize the effective and reliable application control of the new high-conductivity fiber grounding body material. Therefore, it is very necessary to provide a high-conductivity fiber grounding body damage analysis method under large current based on multi-field coupling, which is based on thermal-electric coupling, constructs an electro-thermal multi-physical field coupling model, and analyzes the damage mechanism law. SUMMARY

[0003] The application aims to overcome the deficiencies of the prior art and provide a high-conductivity fiber grounding body damage analysis method under large current based on multi-field coupling, which is based on thermal-electric coupling, constructs an electro-thermal multi-physical field coupling model, and analyzes the damage mechanism law.

[0004] The application is achieved in the following manner: the high-conductivity fiber grounding body damage analysis method under large current based on multi-field coupling comprises the following steps:

[0005] Step 1: constructing a lightning strike thermal-electric coupling mathematical model: adopting the temperature field distribution to represent the damage area and damage depth of the high-conductivity fiber grounding body;

[0006] Step 2: constructing a high-conductivity fiber grounding body quasi-static arc adhesion response model: analyzing the electro-thermal coupling of the quasi-static arc damage of the high-conductivity fiber grounding body;

[0007] Step 3: Establishing a multi-field coupling model of lightning arc damage of high-conductivity fiber grounding body: The electric-magnetic-thermal-mechanical coupling analysis of the material damage of the high-conductivity fiber grounding body under the long-duration lightning current arc, the thermal fluid dynamics characteristics of the lightning current arc are characterized, and the damage mechanism of the high-conductivity fiber grounding body under the lightning current arc is obtained.

[0008] The step 1 of constructing a lightning thermal coupling mathematical model includes the following steps:

[0009] Step 1.1: Electric-thermal coupling basic control equation;

[0010] Step 1.2: Heat balance equation;

[0011] Step 1.3: Boundary conditions;

[0012] Step 1.4: Pyrolysis kinetics model of high-conductivity fiber grounding body material: From the perspective of the electrical properties of the high-conductivity fiber grounding body material, the electrical conductivity that can characterize the electrical properties of the material is selected, a combined model of the pyrolysis degree and electrical conductivity of the high-conductivity fiber grounding body material is established, the action process of the high-conductivity fiber grounding body material and the lightning current is described, the influence of the material pyrolysis process on the electrical properties of the material is analyzed, and then the lightning damage behavior of the material is obtained.

[0013] The electric-thermal coupling basic control equation in step 1.1 is specifically: the electric field of the high-conductivity fiber grounding body during lightning is controlled by the Maxwell equation set, assuming that the current is a steady-state direct current, i.e. In the formula, V is the unit volume; J is the unit current density; S is the unit cross-sectional area; r c is the unit charge density; n is the outer normal of the surface S; the Ohm's law form of the current density is: In the formula, E is the electric field strength; is the potential energy; σ is the electrical conductivity; x is the unit length of the high-conductivity fiber grounding body; using Ohm's law, the conservation control equation is written as a variational form, and the electric field finite element model control equation is obtained: In the formula, is the control unit volume current density; δ is the variational fitting function of the potential; the Joule heat energy power P ec of the current in the conductor can be described as:

[0014] The heat balance equation in step 1.2 is specifically: the heat generated by the lightning current needs to be conducted and diffused inside the high-conductivity fiber grounding body material, and the steady-state Fourier heat conduction law is used to describe the heat conduction process. From the steady-state Fourier heat conduction equation, we can get: Where, p is the material density; Q is the material internal energy; w is the temperature variation fitting function; k is the thermal conductivity coefficient; q is the inflow heat flow per unit area; r is the heat generated per unit volume element.

[0015] The boundary condition in the step 1.3 is specifically: the third boundary condition of heat transfer is as follows: q r = F B (θ B -θ z ) 4 -F(θ-θ z ) 4 , wherein θ is the surface temperature of the high-conductivity fiber grounding body material; θ B is the ambient temperature; θ z is the absolute zero value of the temperature scale; q r is the surface heat flow density; F B and F are the radiation constants of the environment and the surface of the high-conductivity fiber grounding body.

[0016] The high-conductivity fiber grounding body quasi-static arc adhesion response model in the step 2 comprises the following steps.

[0017] Step 2.1: lightning current waveform: including the first return stroke current component, the continuous current component between return strokes, the long-duration continuous current component, and the subsequent return stroke current component.

[0018] Step 2.2: constitutive equation: the electromagnetic field adopts Maxwell equations to describe the current transmission process and the potential distribution characteristics, and the thermal field adopts the Joule law and the heat conduction equation to describe the generation and transmission process of arc heat.

[0019] The lightning current waveform in the step 2.1 is specifically: the lightning current is calculated by using a double exponential model, and the lightning impulse current is as follows: Wherein, I peak is the peak value of the lightning current; η is a correction coefficient; α is a parameter representing the decay of the tail of the lightning current; and β is a parameter representing the rising speed of the front of the lightning current.

[0020] The constitutive equation in the step 2.2 is specifically: in the three-dimensional finite element modeling process of the high-conductivity fiber grounding body, the electrical and thermal parameters of each unit structure are represented in the form of a vector matrix, and the current density can be represented by Ohm's law; meanwhile, in the vector matrix calculation process, the current continuity equation in the Maxwell equations is used to constrain the current density distribution in the finite element model: Wherein, is a vector differential operator; the magnetic field characteristics of the high-conductivity fiber grounding body can be calculated according to the differential equation of Ampere's loop law, and the expression is as follows: Where B is the magnetic induction vector matrix; μ is the material permeability; the lightning current energy conducted in the high-conductivity fiber grounding body will be converted into heat energy in the form of Joule heat, according to Joule's law, the electric power dissipated by the current flowing through the conductor, that is, the Joule heat source Q of the high-conductivity fiber grounding body in the finite element model, can be expressed as Q = P ec = J · E = (σE) · E (15), according to the Fourier heat conduction equation, the control equation of the temperature field can be expressed as: Where ρ is the material density; C p is the constant-pressure heat capacity; T is the thermodynamic temperature of the material; k is the thermal conductivity of the material.

[0021] The multi-field coupling model established in step 3 is an electric-magnetic-thermal-mechanical coupling control equation, specifically: the long-duration lightning component discharge arc is a thermal-magnetic fluid with a current of hundreds of amperes, including a plasma central discharge arc column with a local thermodynamic equilibrium state characteristic LTE and a near-cathode / anode discharge area with a non-local thermodynamic equilibrium state characteristic NLTE; the numerical analysis equation of the LTE state plasma discharge includes the mass conservation equation, momentum conservation equation and energy conservation equation of the fluid, and the coupling thereof with the Maxwell equation describing the electromagnetic field and the heat conduction equation describing the third type of boundary condition; wherein the mass conservation equation is: According to the Navier-Stokes equation, the radial and axial momentum conservation equations of the fluid are established:

[0022] The energy conservation equation in the material-arc interaction process is: Where v r and v z respectively represent the radial and axial velocities of the plasma; ρ is the density of the plasma; P is the pressure in the arc column area; η is the viscosity of the plasma; F r and F z respectively represent the radial and axial electromagnetic forces in the arc column area; g is the acceleration of gravity; h is the plasma enthalpy; κ is the thermal conductivity of the plasma; c p is the constant-pressure heat capacity of the plasma; Q J is the Joule heat source in the arc column area; Q E is the heat exchange caused by the electron energy level transition in the arc column area; Q R is the thermal radiation loss in the arc column area; the Maxwell equation set is solved for the current density, magnetic induction intensity and electric field intensity: Where E r and E z are the radial and axial electric field intensity components, respectively; μ is the magnetic permeability.

[0023] The heat flux of the near-cathode anode discharge area, i.e. the cathode / anode sheath area, the cathode sheath area in the NLTE needs to be analyzed and calculated by considering the energy transfer process shown in the following formula: In the formula, is the heat flux of the plasma arc column and the calculation domain of the cathode; is the unit normal vector; J i and J e are the ion current density and the electron current density; V i is the ionization potential of the air medium; φ cathode is the work function of the cathode material; ε cathode is the radiation coefficient of the cathode material; T cathode is the temperature of the cathode; the heat flux calculation of the anode sheath area needs to consider the energy transfer process shown in the following formula: In the formula, T anode is the temperature of the anode; |J|φ anode represents the electron energy absorbed by the anode; represents the heat loss generated by the thermal radiation of the anode.

[0024] Advantages of the present application: the present application is a high-conductivity fiber grounding body damage analysis method based on multi-field coupling under large current, in use, the present application uses the multi-field coupling theory to construct an electric-thermal multi-physical field coupling model of the high-conductivity fiber grounding material under the impact of large current (including lightning current), analyzes the steady-state electrical characteristics (static electrical characteristics) and transient thermal characteristics of the conductive concrete grounding body under the impact of lightning current based on the thermal-electric coupling principle, obtains the electric-thermal generation process and conduction law, understands the temperature gradient distribution and the corresponding thermal stress distribution in the material and the electrical distribution characteristics in the material; the present application reveals the electric field and thermal field distribution of the new high-conductivity fiber grounding material under the impact of large current or lightning current from the mechanism, and proves the damage law of the new material; the present application has the advantages of thermal-electric coupling, constructing an electric-thermal multi-physical field coupling model, and analyzing the damage mechanism law. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is the lightning ablation analysis flowchart of the present application.

[0026] Figure 2 It is the schematic diagram of the lightning current waveform of the lightning direct effect test of the present application.

[0027] Figure 3 It is the lightning arc damage multi-field coupling model calculation flowchart of the present application. DETAILED DESCRIPTION

[0028] The novel high-conductivity fiber grounding material is a composite material mainly composed of novel carbon fiber conductive material and supplemented with other materials. Its conductivity is far superior to that of graphite composite grounding materials, and its performance is more stable. As a functional composite material, the novel high-conductivity fiber grounding material has a variety of excellent properties and has attracted widespread attention from researchers. Considering that adding a certain amount of conductive components to ordinary commercial concrete can greatly improve its conductivity, it can become a conductor with good conductivity. As a natural grounding device, the key to meeting the grounding resistance design requirements of concrete foundations is the conductive material. Therefore, in order to ensure the safe and stable operation of facilities, meet environmental protection requirements, and facilitate construction, novel high-conductivity fibers are added to concrete to form a concrete grounding body. This invention is the first to elucidate the electric field and thermal field distribution characteristics and variation laws of conductive concrete grounding bodies with added high-conductivity fiber grounding material under high current or lightning current impact from the perspective of a multi-field coupling model. A multi-field coupling model is built, and based on the model calculation results, the multi-field coupling damage mechanism of impact current on high-conductivity fiber grounding body material is further explored, and the electric field and thermal field variation laws of novel high-conductivity fiber grounding body material under high current impact are solved, laying a theoretical foundation for exploring the damage mechanism.

[0029] The present invention will now be further described with reference to the accompanying drawings.

[0030] Example 1

[0031] like Figures 1-3 As shown, a damage analysis method for high-conductivity fiber grounding conductors under high current conditions based on multi-field coupling is described. The method includes the following steps:

[0032] Step 1: Construct a mathematical model of lightning thermoelectric coupling: Use temperature field distribution to characterize the damage area and damage depth of the high-conductivity fiber grounding body;

[0033] In this embodiment, specifically: ① Basic governing equations for electrothermal coupling: During a lightning strike, the electric field of the high-conductivity fiber grounding electrode is controlled by Maxwell's equations (i.e., the electric field in the high-conductivity fiber grounding electrode material obeys Maxwell's charge conservation equation). Assuming the current is a steady-state DC current, that is: In the formula, V is the unit volume; J is the unit current density; S is the unit cross-sectional area; r c Let n be the unit charge volume density; n be the outward normal of surface S; Ohm's law form for current density is: In the formula, E is the electric field strength; Let be the electric potential energy; σ be the electrical conductivity; and x be the unit length of the high-conductivity fiber grounding electrode. Using Ohm's law, the conservation control equations are written in variational form, yielding the control equations for the finite element model of the electric field as follows: In the formula, where δ is the variational fitting function of potential; P is the Joule heat energy power of current in the conductor ec The control equation of the electric field finite element model can be described as:

[0034] The derivation process of the control equation of the electric field finite element model is as follows: on the basis of the Maxwell equation group, according to the divergence theorem, the following equation can be obtained: Since the volume is arbitrary, the following equation can be obtained: An arbitrary electric potential field variable is introduced The following equation can be obtained: According to the chain rule and the divergence theorem, the following equation can be obtained: Then, the control equation of the electric field finite element model is obtained in combination with Ohm's law.

[0035] ②Heat balance equation: the heat generated by lightning current needs to be conducted and diffused in the high-conductivity fiber grounding body material. The steady-state Fourier heat conduction law is used to describe the heat conduction process. The steady-state Fourier heat conduction equation is as follows: In the formula, p is the material density; Q is the internal energy of the material; w is the variational fitting function of temperature; k is the thermal conductivity; q is the inflow heat flow per unit area; and r is the heat generated per unit volume element. The derivation process is as follows: according to the Joule law, the Joule heat energy power P of current in the conductor ec is as follows: formula, in the transient analysis process, the heat P generated by the current through the conductor in the time increment Δt ec is as follows: In the formula, E1 and σ are the values at time t+Δt; ΔE is the electric field density increment in the time increment Δt; and r is the energy released as an internal energy source, that is, r = η v P ec , in which η v is the energy conversion factor; based on the energy balance equation and Ohm's law, the heat conduction equation can be obtained.

[0036] ③Boundary condition: the heat transfer between the surface of the high-conductivity fiber grounding body material and the surrounding environment is in the form of heat conduction and heat radiation. Since the lightning current releases a large amount of heat to the high-conductivity fiber grounding body material in a very short time, a large temperature difference is formed between the high-conductivity fiber grounding body material and the surrounding environment, so under the lightning environment, the heat transfer between the surface of the high-conductivity fiber grounding body material and the surrounding environment is mainly in the form of heat radiation. The third boundary condition of heat transfer is as follows: q r = F B (θ B -θ z ) 4 -F(θ-θ z) 4 , where θ is the surface temperature of the high-conductivity fiber grounding body material; θ B is the ambient temperature; θ z is the temperature scale absolute zero value; q r is the surface heat flux; F B , and F is the radiation constant of the ambient and the surface of the high-conductivity fiber grounding body material.

[0037] ④ Pyrolysis kinetics model of the high-conductivity fiber grounding body material: from the perspective of the electrical properties of the high-conductivity fiber grounding body material, the electrical conductivity that can represent the electrical properties of the material is selected, a combined model of the pyrolysis degree and the electrical conductivity of the high-conductivity fiber grounding body material is established, the interaction process of the high-conductivity fiber grounding body material and the lightning current is described, σ1 is defined as the electrical conductivity in the laying direction, σ2 is defined as the electrical conductivity perpendicular to the laying direction, and σ3 is defined as the electrical conductivity in the thickness direction, where σ1 is the largest; α(T) is defined as the pyrolysis degree of the material at the thermodynamic temperature T corresponding to the material temperature θ, and the relationship between the electrical conductivity σ i (i = 1, 2, 3) of the material in the two directions and the pyrolysis degree of the material is σ i (θ) = σ i (θ0) + α(T)(σ i (θ p ) - σ i (θ0)) (6), where σ2(θ0) and σ3(θ0) are the electrical conductivities of the material in the longitudinal direction and the thickness direction at room temperature θ0; the pyrolysis temperature of the material is defined as θ p , when the temperature of the material rises to θ p , the electrical conductivities in the two directions are σ2(θ p ) and σ3(θ p ) respectively; during the pyrolysis process of the material, chemical bond breaking occurs, which is a molecular level change and has chemical kinetics characteristics, and the pyrolysis process can be described by an n-order chemical kinetics rate equation, where t is the pyrolysis time at a rising temperature; n is the reaction order of the pyrolysis process; k(T) is the pyrolysis reaction rate constant, where A is the frequency factor; R is a constant; T is the thermodynamic temperature; E a is the pyrolysis reaction activation energy; the surface temperature of the material during the lightning stroke process rises rapidly in a very short time, and this very rapid rising process can be regarded as a linear rising process with a very large rising rate v, and the relationship between the surface temperature of the material and the rising time t can be approximately linearly expressed as T = T0 + vt, where T0 is the thermodynamic temperature corresponding to the room temperature and is also the initial thermodynamic temperature of the material, T0 = 273.15 + θ0, and the above equations can be combined to obtain: Two-end integration can obtain: In the formula, T0 is the initial temperature of the material; T1 is a certain temperature at which the material can undergo pyrolysis; by solving the above formula, the relationship between the degree of pyrolysis α(T) and temperature T can be further obtained: According to the above formula, the degree of material pyrolysis α(T) at temperature T can be obtained; according to formula (6), the electrical conductivity σ(T) of the material corresponding to the degree of pyrolysis α(T) can be obtained. In this way, the influence of the material pyrolysis process on the electrical performance parameters of the material can be analyzed, and the lightning damage behavior of the material can be studied more realistically.

[0038] In summary, this invention utilizes ABAOUS software to perform electro-thermal coupled finite element analysis on a high-conductivity fiber grounding specimen. The process is as follows: Figure 1 As shown, the electro-thermal coupling analysis results of lightning currents with different peak values ​​and the same waveform indicate that the higher the peak value, the larger the damage area and the greater the damage depth; the damage area along 0° and 90° is greater than that along 45° and -45° directions; the electro-thermal coupling analysis results of conductivity in different directions indicate that the greater the conductivity along the laying direction, the smaller the damage depth; the change in conductivity perpendicular to the laying direction has no significant effect on the lightning ablation damage results; the greater the conductivity in the thickness direction, the smaller the damage area and the greater the damage depth; the electro-thermal coupling analysis results of different densities indicate that the greater the density, the enhanced heat absorption and dissipation capacity of the composite material per unit volume, and the smaller the damage area and damage depth; the electro-thermal coupling analysis results of different specific heats indicate that specific heat has a significant impact on the damage area and damage depth. When the specific heat increases, its heat absorption and dissipation capacity is enhanced, the temperature rise is smaller, and the ablation damage area and depth decrease.

[0039] Step 2: Construct a quasi-static arc adhesion response model for high-conductivity fiber grounding conductors: Analyze the electro-thermal coupling of quasi-static arc damage to high-conductivity fiber grounding conductors;

[0040] In this embodiment, ① the lightning current waveform includes the first return stroke current component (A component), the inter-return stroke continuous current component (B component), the long-duration continuous current component (C component), and the subsequent return stroke current component (D component). The waveform, amplitude, integral of action, and charge of different lightning current components are all different. The lightning current waveform in the direct lightning effect test is as follows: Figure 2 As shown; the double-exponential model is the most widely used model in lightning current analysis and calculation, and its lightning impulse current is: In the formula, I peak η is the peak value of the lightning current; α is the correction coefficient; α is the parameter characterizing the attenuation of the lightning current tail; β is the parameter characterizing the rise velocity of the lightning current wavefront; in addition, the lightning impulse current can also be expressed as: In the formula, I0 is the current constant; α1 is the reciprocal of the wave tail time constant; β1 is the reciprocal of the wave front time constant; and t1 is the duration of the lightning current wave.

[0041] The main factor causing damage is the joule heat effect of lightning current. The huge energy generated by lightning discharge is conducted to the surface of the material instantaneously, causing pyrolysis of the surface of the material and phase change expansion of the interior. Therefore, the thermal-electric coupling analysis of lightning quasi-static arc damage is performed. The current transmission process and potential distribution characteristics are described by Maxwell equations. The joule law and heat conduction equation are used to describe the generation and transmission process of arc heat (described in detail above). In the process of three-dimensional finite element modeling of the high-conductivity fiber grounding body, the electrical and thermal parameters of each unit structure are characterized as a vector matrix. The current density can be expressed as J = σE (12) by Ohm's law, where J is the current density vector matrix, σ is the material conductivity, and E is the electric field intensity vector matrix.

[0042] Meanwhile, in the vector matrix calculation process, the current continuity equation in Maxwell's equations is used to constrain the current density distribution in the finite element model: where is the vector differential (Nabla) operator. The magnetic field characteristics of the high-conductivity fiber grounding body can be calculated according to the differential equation of Ampere's loop law, and the expression is: where B is the magnetic induction intensity vector matrix, μ is the material magnetic permeability, and the lightning current energy conducted in the high-conductivity fiber grounding body is converted into heat energy in the form of joule heat. According to the joule law, the electric power dissipated by the current flowing through the conductor is the joule heat source Q of the high-conductivity fiber grounding body in the finite element model, which can be expressed as Q = J · E = (σE) · E (15). According to the Fourier heat conduction equation, the temperature field control equation can be expressed as: where ρ is the material density, C p is the constant-pressure heat capacity, T is the thermodynamic temperature of the material, and k is the material thermal conductivity.

[0043] Step 3: Establish a multi-field coupling model of lightning arc damage to the high-conductivity fiber grounding body: Perform an electric-magnetic-thermal-mechanical coupling analysis of the material damage of the high-conductivity fiber grounding body under long-duration lightning current arcs to characterize the thermal-fluid dynamic characteristics of lightning current arcs and obtain the damage mechanism of the high-conductivity fiber grounding body under lightning current arcs.

[0044] In summary, the transfer law of lightning damage in the lightning process, the temperature of the high-conductivity fiber grounding body material surface and the damage depth along the normal direction of the lightning position increase rapidly in the initial stage of lightning; when the lightning current amplitude reaches the maximum, the temperature rise and the damage depth increase rate gradually slow down, the temperature rise change law of the material surface layer is basically the same as the applied lightning current change law, that is, the lightning damage development law has certain similarity with the lightning current amplitude change law; by changing the amplitude of the same lightning current waveform, it is found that the maximum temperature and damage depth of the material surface will increase with the increase of the lightning current amplitude, and within a certain current range, the damage degree is approximately linearly positively correlated with the applied lightning current amplitude; when the length-width ratio of the high-conductivity fiber grounding body specimen is close to 1, the high-conductivity fiber grounding body damage area is often concentrated in the quasi-static arc attachment, and compared with other length-width ratios, the damage area is smaller, but the damage depth is deeper.

[0045] The application is a high-conductivity fiber grounding body damage analysis method based on multi-field coupling under large current. In use, the application uses the multi-field coupling theory to construct an electric-thermal multi-physical field coupling model of the high-conductivity fiber grounding material under the impact of large current (including lightning current) for the conductive concrete grounding body prepared by the high-conductivity fiber grounding material with the best ratio, analyzes the steady-state electrical characteristics (static electrical characteristics) and transient thermal characteristics of the conductive concrete grounding body under the impact of lightning current based on the thermal-electric coupling principle, obtains the electric-thermal generation process and conduction law, and understands the temperature gradient distribution and the corresponding thermal stress distribution in the material and the electrical distribution characteristics in the material. The application reveals the electric field and thermal field distribution of the new high-conductivity fiber grounding body material under the impact of large current or lightning current from the mechanism, and proves the damage law of the new material. The application has the advantages of thermal-electric coupling, construction of an electric-thermal multi-physical field coupling model, and analysis of the damage mechanism law.

[0046] Example 2

[0047] As shown in Figures 1-3 the high-conductivity fiber grounding body damage analysis method based on multi-field coupling under large current, the method comprises the following steps:

[0048] Step 1: Construct a lightning thermal-electric coupling mathematical model: adopt temperature field distribution to represent the damage area and damage depth of the high-conductivity fiber grounding body;

[0049] Step 2: Construct a quasi-static arc attachment response model of the high-conductivity fiber grounding body: analyze the electric-thermal coupling of the quasi-static arc damage of the high-conductivity fiber grounding body;

[0050] Step 3: Establishing a multi-field coupling model of lightning arc damage of high-conductivity fiber grounding body: The electric-magnetic-thermal-mechanical coupling analysis of material damage of high-conductivity fiber grounding body under long-duration lightning current arc, the thermal fluid dynamics characteristics of lightning current arc are characterized, and the damage mechanism of high-conductivity fiber grounding body under lightning current arc is obtained.

[0051] In this embodiment, the electric-magnetic-thermal-mechanical coupling control equation: the discharge arc of long-duration lightning component (C component) is a thermal magnetic fluid with a current of hundreds of amperes, and the thermal magnetic fluid structure mainly includes a plasma central discharge arc column with a local thermodynamic equilibrium state characteristic (LTE) and a near-cathode / anode discharge area with a non-local thermodynamic equilibrium state characteristic (NLTE); in the discharge area in LTE, the electron temperature in the plasma is approximately equal to the temperature of heavy particles (including ions, neutral atoms, etc.), the arc can be treated as an incompressible Newtonian fluid with laminar flow characteristics, and the optical thinness property is satisfied, and the reabsorption of radiation is negligible compared to the total radiation loss; in the near-cathode / anode discharge area (i.e. the cathode / anode sheath area) in NLTE, the differential action of the cathode / anode pair on electrons and heavy particles makes the ion density in this area much larger than the electron density, and the ion temperature is much lower than the electron temperature, resulting in a sharp change in temperature, electric field strength, etc. in the sheath area; the numerical analysis equation of the plasma discharge in LTE mainly includes the mass conservation equation, the momentum conservation equation and the energy conservation equation of the fluid, and the coupling of the Maxwell equation describing the electromagnetic field and the heat conduction equation describing the third type of boundary condition; in the modeling analysis, the above control equation is converted and solved in cylindrical coordinates to obtain the following control equation; wherein the mass conservation equation is as follows: According to the Navier-Stokes equation, the radial and axial momentum conservation equations of the fluid are as follows:

[0052] The energy conservation equation in the process of material-arc interaction is as follows: In the formula, v r and v z respectively represent the radial and axial velocities of the plasma; p is the density of the plasma; P is the pressure of the arc column area; η is the viscosity of the plasma; F r and F z respectively represent the radial and axial electromagnetic forces of the arc column area, F r =-J z B θ , F z =-J r B θ , (wherein J r and Jz B represents the radial and axial current density components, respectively; θ (where g is the tangential component of the magnetic flux density); g is the gravitational acceleration; h is the plasma enthalpy; κ is the thermal conductivity of the plasma; c p Q is the constant-pressure heat capacity of the plasma; J Q is the Joule heat source for the arc column region; E Heat exchange caused by electronic level transitions in the arc column region; Q R For thermal radiation loss in the arc column region; Q J Q E Q R The calculation is as follows: Q R =-4πε N In the formula, ρ is the conductivity; k B Boltzmann constant; e is the electron charge; ε N is the thermal emissivity.

[0053] Solve for the current density, magnetic induction, and electric field strength by simultaneously applying Maxwell's equations: In the formula, E r and E z denoted as radial and axial electric field intensity components, respectively; μ is the magnetic permeability.

[0054] In the cathode / anode sheath region, the electrical conductivity is consistent with that of the near-cathode / anode region, while the thermal conductivity, constant-pressure heat capacity, viscosity, and other parameters are consistent with those of the arc column region. Considering the microscopic transport characteristics of electrons-heavy particles and their heat transfer features in the sheath region, the heat flux in the cathode sheath region needs to be analyzed and calculated by further considering the energy transfer process shown in the following equation: In the formula, For the heat flux of the plasma arc column and cathode computational domain; J is the unit normal vector; i and J e V represents the ion current density and the electron current density. i φ is the ionization potential of the air medium. cathode ε is the work function of the cathode material; cathode T is the emissivity of the cathode material; cathode The temperature of the cathode; J i V i The term represents the energy generated by ions bombarding the cathode; J e φ cathode The term represents the energy required for the cathode to emit electrons; The term represents the heat loss caused by cathode thermal radiation; J i and J e Satisfy: |Ji |+|J e |=|J|;The thermal field electron emission of the cathode can be calculated using the Richardson-Dushman formula: In the formula, A R φ is the thermionic emission constant (Richardson constant) of the cathode surface; eff The effective work function of the cathode material; based on the Richardson current density J R Calculate ion current density J i and thermal electron flux density J e ,as follows: The calculation of heat flux in the anode sheath region needs to consider the energy transfer process shown in the following equation: In the formula, T anode The temperature of the anode; |J|φ anode The term represents the energy of electrons absorbed by the anode; The term represents the heat loss caused by anodic thermal radiation.

[0055] To analyze the temperature distribution and corresponding thermal stress distribution changes of materials under lightning arcs, the equivalent heat capacity method is used to treat the local melting phase change heat transfer process of high-conductivity fiber grounding electrode materials. That is, the heat capacity of the material in the solid-liquid two-phase coexistence region is expressed as the equivalent heat capacity c. p,eff As shown below: In the formula, c p,s c p,1 θ represents the solid phase heat and liquid phase heat of the material; L represents the latent heat of phase change of the material; θ s θ1 represents the solid fraction and liquid fraction, which characterize the degree of phase transformation of the material, satisfying θ s = 1 - θ1; ​​α is an intermediate variable; θ1 and α are calculated as follows: In the formula, H(x) is the smoothed Heaviside step function; T s T1 represents the solidus temperature and liquidus temperature during a non-isothermal phase transition.

[0056] After local melting, the high-conductivity fiber grounding material is mainly affected by two forces: one is the surface tension related to the surface profile curvature; the other is the Marangoni effect introduced by the temperature gradient along the surface of the molten pool. Therefore, based on the radial momentum conservation equation (Equation (18)), the Marangoni force M needs to be considered. A The effect on material damage is calculated as follows: In the formula, σ represents the surface tension of the liquid material.

[0057] In summary, based on the magnetic hydrodynamics of the electric arc and the joint analysis of the cathode-arc-anode when discharging, the application establishes an electric-magnetic-thermal-force coupling model of material damage under the long duration lightning current arc, studies the thermal hydrodynamic characteristics of the lightning current arc, calculates the damage depth of the material under the lightning current arc, analyzes the damage characteristics of the material under the joint action of the Lorentz force, the pressure difference gradient force, the surface tension of the molten material and the Marangoni force, obtains the damage mechanism of the high-conductivity fiber grounding body material, and finds that the heat conduction of the arc and the absorbed electron energy of the material surface are the main causes of the damage.

[0058] The application is a high-conductivity fiber grounding body damage analysis method based on multi-field coupling under large current. In use, the application uses the multi-field coupling theory to construct an electric-thermal multi-physical field coupling model of the high-conductivity fiber grounding material under the impact of large current (including lightning current), analyzes the steady-state electrical characteristics (static electrical characteristics) and transient thermal characteristics of the conductive concrete grounding body under the impact of lightning current based on the thermal-electric coupling principle, obtains the electric-thermal generation process and conduction law, understands the internal temperature gradient distribution and the corresponding thermal stress distribution of the material and the internal electrical distribution characteristics of the material, and reveals the electric field and thermal field distribution of the new high-conductivity fiber grounding body material under the impact of large current or lightning current and proves the damage law of the new material. The application has the advantages of thermal-electric coupling, construction of an electric-thermal multi-physical field coupling model, and analysis of the damage mechanism law.

Claims

1. A method for analyzing damage of a high-conductivity fiber grounding body under high current based on multi-field coupling, characterized in that: The method comprises the following steps: Step 1: constructing a lightning thermal-electric coupling mathematical model: adopting a temperature field distribution to represent the damage area and damage depth of the high-conductivity fiber grounding body; Step 2: constructing a high-conductivity fiber grounding body quasi-static arc adhesion response model: analyzing the electric-thermal coupling of the high-conductivity fiber grounding body quasi-static arc damage; Step 3: establishing a multi-field coupling model of the high-conductivity fiber grounding body lightning arc damage: analyzing the electric-magnetic-thermal-mechanical coupling of the high-conductivity fiber grounding body material damage under a long-duration lightning current arc, representing the thermal fluid dynamics characteristics of the lightning current arc, and obtaining the damage mechanism of the high-conductivity fiber grounding body under the action of the lightning current arc.

2. The method for ground body damage analysis of high conductance fiber under high current based on multi-field coupling according to claim 1, wherein: The step 1 of constructing the lightning thermal-electric coupling mathematical model comprises the following steps: Step 1.1: basic control equation of electric-thermal coupling; Step 1.2: heat balance equation; Step 1.3: boundary condition; Step 1.4: pyrolysis kinetics model of the high-conductivity fiber grounding body material: from the perspective of the electric property of the high-conductivity fiber grounding body material, the conductivity representing the electric property of the material is selected, a combined model of the pyrolysis degree and the conductivity of the high-conductivity fiber grounding body material is established, the action process of the high-conductivity fiber grounding body material and the lightning current is described, the influence of the material pyrolysis process on the electric property parameters of the material is analyzed, and then the lightning damage behavior of the material is obtained.

3. The method for damage analysis of high conductance grounding body under high current based on multi-field coupling according to claim 2, characterized in that: The electric heat coupling basic control equation in step 1.1 is specifically: the electric field of the high-conductivity fiber grounding body in the lightning process is controlled by Maxwell equation group, assuming that the current is steady-state direct current, namely: In the formula, V is a unit volume; J is a unit current density; S is a unit cross-sectional area; r c is a unit charge density; n is an outer normal of the surface S; the Ohm law form of the current density is: In the formula, E is an electric field intensity; is an electric potential energy; sigma is an electric conductivity; x is a unit length of the high-conductivity fiber grounding body; the conservation control equation is written into a variation form by using the Ohm law, and the electric field finite element model control equation is obtained as: In the formula, is a control unit volume current density; delta is a variation fitting function of the electric potential; in the Joule law, the Joule heat energy power P ec of the current in the conductor can be described as:

4. The method for damage analysis of high conductance grounding body under high current based on multi-field coupling according to claim 2, characterized in that: The heat balance equation in step 1.2, specifically: the heat generated by lightning current needs to be conducted and diffused inside the high-conductivity fiber grounding body material, and the steady-state Fourier heat conduction law is used to describe the heat conduction process. From the steady-state Fourier heat conduction equation, we can get: In the formula, ρ is the material density; Q is the internal energy of the material; w is the variational fitting function of temperature; k is the thermal conductivity coefficient; q is the inflow heat flow per unit area; r is the heat generated per unit volume element.

5. The multi-field coupling based ground body damage analysis method for high conductance fiber under high current of claim 2, wherein: The boundary condition in step 1.3, specifically: using a heat transfer third boundary condition as shown in the following formula: q r = F (θ - θ B ) B - θ z ) 4 - F (θ - θ z ) 4 , wherein θ is the surface temperature of the high-conductivity fiber grounding body material; θ B is the ambient temperature; θ z is the absolute zero value of the temperature scale; q r is the surface heat flux; and F B and F are the radiation constants of the environment and the surface of the high-conductivity fiber grounding body material.

6. The multi-field coupling based ground body damage analysis method for high conductance fiber under high current of claim 1, wherein: The step 2 of constructing the high-conductivity fiber grounding body quasi-static arc adhesion response model comprises the following steps: Step 2.1: lightning current waveform: including a first return stroke current component, a continuous current component between return strokes, a long-duration continuous current component, and a subsequent return stroke current component; Step 2.2: constitutive equation: the electromagnetic field adopts Maxwell equations to describe the current transmission process and the potential distribution characteristics, and the thermal field adopts the Joule law and the heat conduction equation to describe the generation and transmission process of the arc heat.

7. The method for ground fault analysis of high conductance fiber ground based on multi-field coupling at high current according to claim 6, characterized in that: The lightning current waveform in the step 2.1 is specifically: the lightning current is calculated by using a double exponential model, and the lightning impulse current is: In the formula, I peak is a lightning current peak value; η is a correction coefficient; α is a parameter for representing a tail decay of the lightning current; and β is a parameter for representing a rising speed of a wave front of the lightning current.

8. The multi-field coupling based ground body damage analysis method for high conductance fiber under high current of claim 6, wherein: The constitutive equation in step 2.2 is: in the process of three-dimensional finite element modeling of high-conductivity fiber grounding body, the electrical and thermal parameters of each unit structure are characterized as a vector matrix, and the current density can be expressed by Ohm's law; at the same time, in the process of vector matrix calculation, the current continuity equation in Maxwell's equation set is used to constrain the current density distribution in the finite element model: Where, is a vector differential operator; the magnetic field characteristics of the high-conductivity fiber grounding body can be calculated according to the differential equation of Ampere's law, and the expression is: Where, B is the magnetic induction intensity vector matrix; μ is the material permeability; the lightning current energy conducted in the high-conductivity fiber grounding body will be converted into heat energy in the form of Joule heat, according to Joule's law, the electric power dissipated by the current flowing through the conductor, that is, the Joule heat source Q of the high-conductivity fiber grounding body in the finite element model, can be expressed as Q=P ec =J·E=(σE)·E(15), according to Fourier's heat conduction equation, the control equation of the temperature field can be expressed as: Where, ρ is the material density; C p is the constant-pressure heat capacity; T is the thermodynamic temperature of the material; k is the thermal conductivity of the material.

9. The multi-field coupling based ground body damage analysis method for high conductance fiber under high current of claim 1, wherein: The multi-field coupling model established in step 3 is an electric-magnetic-thermal-force coupling control equation, specifically: the discharge arc of the long duration lightning component is a thermal magnetic fluid with a current of hundreds of amperes, including a plasma central discharge arc column with a local thermodynamic equilibrium state characteristic LTE and a near cathode / anode discharge area with a non-local thermodynamic equilibrium state characteristic NLTE; the numerical analysis equation of the LTE state plasma discharge includes the mass conservation equation, momentum conservation equation and energy conservation equation of the fluid, and the coupling thereof with the Maxwell equation describing the electromagnetic field and the heat conduction equation describing the third type boundary condition; wherein the mass conservation equation is: According to the Navier-Stokes equation, the radial and axial momentum conservation equations of the fluid are established: The energy conservation equation in the material-arc interaction process is: where v r and v z denote the radial and axial velocity of the plasma, respectively; p is the density of the plasma; P is the pressure in the arc column region; η is the viscosity of the plasma; F r and F z denote the radial and axial electromagnetic forces in the arc column region, respectively; g is the gravitational acceleration; h is the plasma enthalpy; κ is the thermal conductivity of the plasma; c p is the constant pressure heat capacity of the plasma; Q J is the Joule heat source in the arc column region; Q E is the heat exchange due to electron energy level transitions in the arc column region; Q R is the thermal radiation loss in the arc column region; Maxwell's equations are solved simultaneously for the current density, the magnetic induction, and the electric field strength: where E r and E z are the radial and axial electric field strength components, respectively; μ is the magnetic permeability.

10. The method for ground fault analysis of high conductance fiber ground based on multi-field coupling at high current according to claim 9, characterized in that: The near-cathode anode discharge area in the NLTE, i.e. the cathode / anode sheath area, the heat flux of the cathode sheath area needs to be analyzed and calculated by considering the energy transmission process shown in the following formula: where, is the heat flux of the plasma arc column, cathode computational domain; is the unit normal vector; J i and J e are the ion current density and electron current density; V i is the ionization potential of the air medium; φ cathode is the work function of the cathode material; ε cathode ε is the emissivity of the cathode material; T cathode T is the temperature of the cathode; The heat flux calculation for the anode sheath region needs to take into account the energy transfer process shown in the following equation: where T anode T is the temperature of the anode; |J|φ anode The term represents the electron energy absorbed by the anode; The term represents the heat loss due to anode thermal radiation.

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