Line transient breakdown modeling method suitable for construction of distribution network traveling wave detection environment

Abstract

The invention relates to a line transient breakdown modeling method suitable for construction of a distribution network traveling wave detection environment. The line transient breakdown modeling method is used for solving the problem of transient fault modeling of experimental verification of a traveling wave distance measuring device at present. The method comprises the following steps: S1, constructing a black box Mayr model of an electric arc; considering that the diameter of the arc column is a constant value, the longer the distance between the section of the arc column and the circle center is, the lower the temperature is. S2, constructing a magnetohydrodynamic model; by means of a finite element method, grid division is conducted on the electric arc, solving is conducted through a multi-physical field coupling relation, and physical distribution characteristics in the electric arc are obtained; s3, constructing an instantaneous breakdown arc model; construction is carried out through a COMSOL system, the COMSOL system provides a geometric module, and drawing or structure size information of a line is utilized; s4, simulating to obtain instantaneous breakdown current and voltage waveform analysis; the metal shielding current is the arc current of the fault, and the wire core voltage is the arc voltage.

Description

Technical Field

[0001] This invention relates to a method for modeling instantaneous line breakdown in a distribution network traveling wave detection environment, which is used to solve the problem of instantaneous fault modeling in the experimental verification of current traveling wave ranging devices. Background Technology

[0002] Lean operation and maintenance with precise fault location in distribution networks is an important component of building smart distribution networks and realizing distribution network automation. Current verification schemes for precise location of instantaneous faults in distribution networks rely on on-site fault waveform playback, which cannot cover the verification of all types of line faults.

[0003] The instantaneous breakdown modeling technology for distribution network traveling wave detection environments has the following outstanding advantages: it simultaneously considers the complex interaction of electric, magnetic, and thermal fields inside the arc; it uses a black-box model combined with the differential equations of existing arc models to calculate the parameters of the arc model; it relies on the magnetohydrodynamic model of the finite element method to calculate the physical distribution characteristics inside the arc; it constructs a breakdown arc model through the COMSOL system to establish a two-dimensional model of the line; and it verifies the simulation results of the model according to the requirements for selecting the neutral grounding method of the distribution network.

[0004] With the rapid development of artificial intelligence model solving technology in recent years, it has been applied to the power system field. However, the current application level is low in the face of the problem of instantaneous line breakdown modeling in the distribution network traveling wave detection environment. There is an urgent need for a new modeling method to verify the ability to accurately locate instantaneous faults in the distribution network and improve the reliability of the distribution network. Summary of the Invention

[0005] This invention provides a method for modeling instantaneous line breakdown in a distribution network traveling wave detection environment. Belonging to the field of power system automation, it is used in new power operation and maintenance systems. It considers the complex interaction of electric, magnetic, and thermal fields within the arc. A black-box model is used in conjunction with the differential equations of existing arc models to calculate the parameters of the arc model. The magnetohydrodynamic model based on the finite element method is used to calculate the physical distribution characteristics within the arc. A breakdown arc model is constructed using the COMSOL system to establish a two-dimensional line model. The simulation results are verified according to the requirements for selecting the neutral grounding method of the distribution network, demonstrating good applicability and promotion potential.

[0006] A method for modeling instantaneous line breakdown suitable for setting up a traveling wave detection environment in a distribution network includes the following steps:

[0007] S1: Construct a black-box Mayr model of the electric arc;

[0008] The diameter of the arc column is considered as a constant value, the longer the distance between the arc column section and the center of the circle, the lower the temperature; the arc voltage acts on the arc column, and the energy transfer at the electrode and the energy change along the axial direction of the arc column are not considered; the arc transfers energy to the surrounding air through radiation and conduction, and the effect of convection is ignored;

[0009] S2: Construct a magnetohydrodynamic model;

[0010] By finite element method, the arc is meshed and solved through multi-physical field coupling relationship to obtain the physical distribution characteristics inside the arc; by applying appropriate boundary conditions, the electromagnetic field equation can be solved to determine the potential distribution; combined with the conductivity distribution, the current density distribution inside the arc can be further determined; at the same time, the combined action of the arc itself and the external magnetic field leads to the energy transfer inside the arc plasma;

[0011] S3: Construct a transient breakdown arc model;

[0012] The COMSOL system is used to construct the model, which provides a geometry module to establish a two-dimensional model of the line body or joint in the transient breakdown arc model module by using the drawing or structural size information of the line, and set defects; the defects are small air gaps in the insulation layer, so different sizes of air gap defects can be set in the insulation layer according to the development degree of early faults;

[0013] S4: Simulate to obtain transient breakdown current and voltage waveform analysis;

[0014] The metal shielding current is the arc current of the fault, and the wire core voltage is the arc voltage; when transient breakdown occurs, a short-time fault arc is generated, the current suddenly increases to a peak value, and then gradually decreases; the arc voltage waveform corresponds to the current level, the voltage rapidly decreases after breakdown, the higher the arc current, the lower the voltage, and with the gradual decrease of the current, the voltage gradually rises to a peak, and then the arc is extinguished, and the voltage returns to a sine wave.

[0015] In step S1, the scheme for constructing the black box Mayr model of the arc includes:

[0016] The arc can be simplified as a cylindrical structure composed of gas, and the arc conductance changes with the energy change of the arc column;

[0017] Because the resistance of the arc is small, the arc model is converted into the form of conductance;

[0018] The thermal ionization in the fixed arc is calculated according to the Saha formula.

[0019] Specifically, in step S1, the arc can be simplified as a cylindrical structure composed of gas, and the arc conductance changes with the energy change of the arc column, and the energy equation of the arc can be expressed as

[0020] (1)

[0021] wherein: : the rate of change of the stored energy in the arc per unit length;

[0022] : the arc current; : the arc voltage; : the dissipated power per unit length of the arc;

[0023] Since the arc has a small resistance, the arc model of equation (1) is converted into the form of conductance:

[0024] (2)

[0025] wherein: : the conductance per unit length of the arc; : the rate of change of the conductance per unit length of the arc;

[0026] The thermal ionization in the fixed arc is calculated according to the Saha formula:

[0027] (3)

[0028] wherein: : the conductance of the arc column without energy; : the energy of the arc; : the change of the energy in the arc column when the conductance of the arc changes by e times;

[0029] The derivative transformation of equation (3) can be obtained:

[0030] = = (4)

[0031] Substituting equation (4) into equation (2) can be obtained:

[0032] (5)

[0033] wherein: : the time constant of the arc, which has a physical meaning that when the conductance of the arc decreases to , the dissipated energy of the arc column is .

[0034] Specifically, in step S2, a magnetohydrodynamic model is constructed, including a mass conservation equation, a momentum conservation equation, an energy conservation equation, a gas state equation and an electromagnetic field equation group.

[0035] The mass conservation equation is:

[0036] (6)

[0037] where: : fluid density; : time; : velocity vector of fluid motion;

[0038] momentum conservation equation:

[0039] (7)

[0040] where: : pressure experienced by fluid; : dynamic viscosity of fluid; : identity matrix; : current density vector; : magnetic flux density vector;

[0041] energy conservation equation:

[0042] (8)

[0043] where: : plasma temperature; : constant pressure specific heat capacity; : thermal conductivity of fluid; : plasma electrical conductivity; : total volumetric radiation; : Boltzmann constant; : charge of an electron;

[0044] gas state equation:

[0045] (9)

[0046] where: R: ideal gas constant;

[0047] electromagnetic field equations:

[0048] (10)

[0049] (11)

[0050] (12)

[0051] (13)

[0052] where: : electric potential; : electric field intensity vector; : magnetic vector potential vector.

[0053] Specifically, the S3, the construction of the transient breakdown arc model includes:

[0054] Field equation set, the electric field of the intermittent arc can be represented by the charge conservation equation;

[0055] Magnetic field set the magnetic field equation of the intermittent arc;

[0056] Fluid heat transfer set temperature field equation in the analysis of heat transfer;

[0057] The arc plasma is in local thermal equilibrium heat source formula.

[0058] Field equation set, the electric field of the intermittent arc can be represented by the charge conservation equation:

[0059] (14)

[0060] In the formula: : current density vector; : charge density; : time;

[0061] The electric field intensity can be obtained from the potential:

[0062] (15)

[0063] In the formula: : electric field intensity; : potential;

[0064] The current density vector can be calculated by the electric field intensity:

[0065] (16)

[0066] In the formula: : conductivity.

[0067] Magnetic field set the magnetic field of the intermittent arc follows Ampere's law, its equation is:

[0068] (17)

[0069] In the formula: : magnetic field intensity vector

[0070] The magnetic flux density can be obtained from the magnetic field intensity:

[0071] (18)

[0072] In the formula: : magnetic flux density vector; : permeability

[0073] The relationship between the magnetic flux density and the magnetic vector potential is:

[0074] (19)

[0075] In the formula: : magnetic vector potential vector.

[0076] When analyzing heat transfer of the fluid heat transfer arrangement, the temperature field equation is used:

[0077] (20)

[0078] In the formula: : gas density; : heat capacity of the gas; : thermodynamic temperature of the gas; : velocity vector of the gas; : heat flux vector of the gas;

[0079] The heat flux can be obtained from the Fourier law:

[0080] (21)

[0081] In the formula: : thermal conductivity of the material.

[0082] In the multi-physical field coupling arrangement, the intermittent arc releases extremely high heat during the discharge process, which can be considered as a heat source; assuming that the arc plasma is in local thermal equilibrium, the formula of the heat source is:

[0083] (22)

[0084] In the formula: : heat generated by the equilibrium discharge heat source; : Boltzmann constant; : charge of an electron; : thermodynamic temperature of the arc plasma; : current density vector in the arc plasma; : electric field intensity vector in the arc plasma; : total volume radiation coefficient.

[0085] In the S4, the simulated transient arc can be considered as an ionized air plasma, the electric conductivity is affected by the degree of ionization, and the degree of ionization is closely related to the temperature, and the temperature is affected by the heat source of the arc current, the three interact and show a positive correlation.

[0086] Specifically, in step S4, the simulation transient arc generates a moment, the temperature of the arc column center point increases rapidly, and due to the approach to arc extinction, the arc discharge heat source power rapidly decreases, resulting in a rapid decrease in temperature near the critical point.

[0087] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0088] (1) The complex interaction of electric field-magnetic field-thermal field inside the arc is considered synchronously, and the black box model combines the differential equation of the existing arc model to calculate the parameters of the arc model.

[0089] (2) The physical distribution characteristics inside the arc are calculated by relying on the magnetohydrodynamic model of the finite element method.

[0090] (3) The breakdown arc model is constructed through the COMSOL system, and a two-dimensional model of the line is established.

[0091] (4) The simulation results of the model are verified according to the selection requirements of the neutral point grounding mode of the distribution network. BRIEF DESCRIPTION OF DRAWINGS

[0092] Figure 1 is the physical coupling relationship diagram of the transient breakdown arc of the distribution network line in the present application;

[0093] Figure 2 is the simulation circuit setting schematic diagram of the transient breakdown arc of the distribution network line in the present application;

[0094] Figure 3 is the transient breakdown schematic diagram of the distribution network line in the present application;

[0095] Figure 4 is the transient breakdown current waveform diagram of the line of the small grounding system in the present application;

[0096] Figure 5 is the transient breakdown voltage waveform diagram of the line of the small grounding system in the present application;

[0097] Figure 6 is the transient breakdown conductance waveform diagram of the line of the small grounding system in the present application;

[0098] Figure 7 is the arc column temperature change curve diagram of the transient breakdown arc of the line of the small grounding system in the present application. DETAILED DESCRIPTION

[0099] Referring to the accompanying Figures 1-7 , a line transient breakdown modeling method suitable for a distribution network traveling wave detection environment is built, which comprises the following steps:

[0100] S1: constructing a black box Mayr model of the arc;

[0101] The diameter of the arc column is considered as a constant value, the longer the distance between the arc column section and the center of the circle, the lower the temperature; the arc voltage acts on the arc column, and the energy transfer at the electrode and the energy change along the axial direction of the arc column are not considered; the arc transfers energy to the surrounding air through radiation and conduction, and the effect of convection is ignored;

[0102] S2: Constructing a magnetohydrodynamic model;

[0103] By relying on the finite element method, the arc is meshed and solved through the multi-physical field coupling relationship to obtain the physical distribution characteristics inside the arc; by applying appropriate boundary conditions, the electromagnetic field equation can be solved to determine the potential distribution; combined with the conductivity distribution, the current density distribution inside the arc can be further determined; at the same time, the combined action of the arc itself and the external magnetic field leads to the energy transfer inside the arc plasma;

[0104] S3: Constructing a transient breakdown arc model;

[0105] The COMSOL system is used for construction, and the COMSOL system provides a geometry module, which uses the drawing or structural size information of the line to establish a two-dimensional model of the line body or joint in the transient breakdown arc model module to set defects; the defects are small air gaps in the insulation layer, so different sizes of air gap defects can be set in the insulation layer according to the development degree of the early fault in the model;

[0106] S4: Simulation of transient breakdown current and voltage waveform analysis;

[0107] The metal shielding current is the arc current of the fault, and the wire core voltage is the arc voltage; when transient breakdown occurs, a short-time fault arc is generated, the current suddenly increases to a peak value, and then gradually decreases; the arc voltage waveform corresponds to the current level, the voltage rapidly decreases after breakdown, the higher the arc current, the lower the voltage, and with the gradual decrease of the current, the voltage gradually increases to a peak, and then the arc is extinguished, and the voltage returns to a sinusoidal wave.

[0108] In step S1, the black box Mayr model scheme of the arc is constructed.

[0109] Specifically, in step S1, the arc can be simplified as a cylindrical structure composed of gas, the arc conductance changes with the energy change of the arc column, and the energy equation of the arc can be expressed as

[0110] (1)

[0111] In the formula: : the change rate of the energy stored in the unit length of the arc;

[0112] : arc current; : arc voltage; : dissipated power per unit length of arc;

[0113] Since the resistance of the arc is small, the arc model of formula (1) is converted into the form of conductance:

[0114] (2)

[0115] In the formula: : conductance per unit length of arc; : rate of change of conductance per unit length of arc;

[0116] The thermal ionization in the fixed arc is calculated according to the Sahal formula:

[0117] (3)

[0118] In the formula: : conductance when the arc column does not contain energy; : energy of the arc; : change of energy in the arc column when the conductance of the arc changes e times;

[0119] The derivative transformation of formula (3) can be obtained:

[0120] (4)

[0121] Substituting formula (4) into formula (2) can be obtained:

[0122] (5)

[0123] In the formula: : time constant of the arc, which has the physical meaning that when the conductance of the arc decreases to , the dissipated energy of the arc column is .

[0124] Specifically, in step S2, a magnetohydrodynamic model is constructed, and a mass conservation equation is:

[0125] (6)

[0126] In the formula: : fluid density; : time; : velocity vector of fluid motion;

[0127] Momentum conservation equation:

[0128] (7)

[0129] ​​In the formula: : pressure experienced by the fluid; : dynamic viscosity of the fluid; : identity matrix; : current density vector; : magnetic flux density vector;

[0130] Energy conservation equation:

[0131] (8)

[0132] In the formula: : plasma temperature; : constant pressure specific heat capacity; : thermal conductivity of the fluid; : plasma conductivity; : total volume radiation; : Boltzmann constant; : charge amount of an electron;

[0133] Gas state equation:

[0134] (9)

[0135] In the formula: R: ideal gas constant;

[0136] Electromagnetic field equation set:

[0137] (10)

[0138] (11)

[0139] (12)

[0140] (13)

[0141] In the formula: : electric potential; : electric field intensity vector; : magnetic vector potential vector.

[0142] In the S3, a transient breakdown arc model is constructed, the field equation is set, the electric field of the intermittent arc can be expressed by the charge conservation equation, and the control equation is:

[0143] (14)

[0144] In the formula: : current density vector; : charge density; : time;

[0145] The electric field intensity can be obtained from the electric potential:

[0146] (15)

[0147] where: E: electric field intensity; V: electric potential;

[0148] The current density vector can be calculated from the electric field intensity:

[0149] (16)

[0150] where: σ: electrical conductivity

[0151] The magnetic field setup of the intermittent arc follows Ampere's law, whose equation is:

[0152] (17)

[0153] where: B: magnetic field intensity vector

[0154] The magnetic flux density can be obtained from the magnetic field intensity:

[0155] (18)

[0156] where: B: magnetic flux density vector; μ: magnetic permeability

[0157] The relationship between the magnetic flux density and the magnetic vector potential is:

[0158] (19)

[0159] where: A: magnetic vector potential vector

[0160] In the analysis of heat transfer, the temperature field equation is used when the fluid heat transfer is set:

[0161] (20)

[0162] where: ρ: gas density; Cp: heat capacity of the gas; T: thermodynamic temperature of the gas; v: velocity vector of the gas; q: heat flux vector of the gas;

[0163] The heat flux can be obtained from Fourier's law:

[0164] (21)

[0165] wherein: : thermal conductivity of the material

[0166] The intermittent arc in the discharge process releases extremely high heat to the outside, which can be considered as a heat source. Assuming that the arc plasma is in local thermal equilibrium, the formula of this heat source is:

[0167] (22)

[0168] wherein: : heat generated by the equilibrium discharge heat source; : Boltzmann constant; : charge of the electron; : thermodynamic temperature of the arc plasma; : current density vector in the arc plasma; : electric field intensity vector in the arc plasma; : total volume radiation coefficient.

[0169] In the S4, the simulated transient arc can be considered as an ionized air plasma, the electric conductivity is affected by the degree of ionization, and the degree of ionization is closely related to the temperature, and the temperature is affected by the heat source of the arc current, the three interact with each other, and show a positive correlation.

[0170] Specifically, in step S4, the temperature of the center point of the arc column increases rapidly due to the generation of the simulated transient arc, and the power of the arc discharge heat source rapidly decreases due to the approach to arc extinction, resulting in a rapid decrease in temperature near the critical point.

[0171] Embodiment

[0172] The black box Mayr model scheme and the magnetohydrodynamic model of the arc are constructed, and the physical coupling relationship diagram of the transient breakdown arc of the distribution network line is as shown in Figure 1 The initial temperature and pressure distribution determine the electric conductivity of the arc plasma. By applying appropriate boundary conditions, the electromagnetic field equation can be solved to determine the potential distribution. Combined with the conductivity distribution, the current density distribution in the arc can be further determined. The arc generates Joule heat, which is jointly determined by the conductivity and the current density, and is affected by the external magnetic field, generating electromagnetic force. Due to the influence of mechanics on the morphology of the arc, the energy transfer in the arc plasma is caused, and thus the new temperature and pressure distribution is obtained.

[0173] COMSOL system is used for construction, and the COMSOL system provides a geometry module, which uses the drawing or structural size information of the line to establish a two-dimensional model of the line body or joint in the module to set the defects. The schematic diagram of the simulation circuit setting of the transient breakdown arc of the distribution network line is as shown inFigure 2 As shown in the figure, generally, the power direction is from the power supply to the load through the three-core cable. The phase voltages of the three power supplies are connected in a node mode, and are equivalent to three two-port nodes using Thevenin theorem, one of which is ground and the other is voltage output. The voltage output node of the three two-port nodes is connected to the three cores of the three-core cable, which is connected to the load resistor and finally connected to the ground to form a loop. Due to the existence of defects, an additional loop is formed by the intermittent arc.

[0174] The simulation obtains the transient breakdown current and voltage waveform analysis. The schematic diagram of transient breakdown of distribution line is as shown in Figure 3 When the line fault occurs, the arc breaks the insulation layer to form a discharge channel, and the fault current flows through the arc and the metal shield layer, and flows into the ground at the grounding point at both ends of the line to form single-phase arc grounding. According to the comprehensive fault characteristics and relevant specifications, the transient breakdown arc in the fault current range of different neutral point grounding modes is simulated.

[0175] The waveform diagram of transient breakdown of small grounding system line is as shown in Figure 4 The metal shield current of the line is the arc current of the fault, and the core voltage is the arc voltage. From the waveform characteristics at a single fault current level, when the transient breakdown occurs, a short-time fault arc is generated, and its duration is about 1 / 4 of the power frequency cycle. The current suddenly increases to the peak value, and then gradually decreases, and the waveform is similar to 1 / 4 of the sine wave from the peak value of the positive half cycle to the near zero point. The arc voltage waveform corresponds to the current level. After breakdown, the voltage decreases rapidly, the higher the arc current, the lower the voltage, and as the current gradually decreases, the voltage gradually rises to the peak, and then the arc is extinguished, and the voltage returns to the sine wave. At this time, the voltage gradually decreases to 0 before the zero point of the positive half cycle of the waveform, so a sharp peak of arc extinction is formed. The current decreases to 0 at the same time as the time corresponding to the top of the peak of the arc extinction.

[0176] The arc can be regarded as ionized air plasma, and the conductivity is affected by the degree of ionization, which is closely related to the temperature, and the temperature is affected by the heat source of the arc current. The three interact with each other and show a positive correlation. The conductance waveform diagram of the transient breakdown of the small grounding system line is as shown in Figure 5 As shown in the figure, after the arc is generated, the temperature and the arc conductance both show a sharp peak due to the sudden increase in current. The conductance curve is similar to the trend of the metal shield current, and the conductance size of different fault current peaks has a significant difference. The higher the current, the higher the arc conductance.

[0177] The arc column temperature variation curve diagram of the transient breakdown of the small grounding system line is as shown in Figure 6As shown, the temperature of the center point of the arc column increases rapidly at the moment of arc generation. Due to the approach of arc extinction, the power of the arc discharge heat source decreases rapidly, resulting in a rapid decrease in temperature near the end point. After the end point, the decrease slows down.

[0178] The application provides a line transient breakdown modeling method suitable for a line traveling wave detection environment construction, which synchronously considers the mutual action of an internal complex electric field-magnetic field-thermal field of an arc, a black box model combines differential equations of existing arc models to calculate parameters of the arc model, relies on a magnetohydrodynamic model of a finite element method to calculate physical distribution characteristics in the arc, constructs a breakdown arc model through a COMSOL system, establishes a line two-dimensional model, and verifies simulation results of the model according to requirements selected according to a neutral point grounding mode of a distribution network.

Claims

1. A line transient breakdown modeling method suitable for a line traveling wave detection environment setup, characterized in that, It comprises the following steps: S1: Constructing a black box Mayr model of the electric arc; Considering that the diameter of the arc column of the electric arc is a constant value, the longer the distance between the arc column section and the center of the circle, the lower the temperature; the electric arc voltage is entirely applied to the arc column of the electric arc, and the energy transmission at the electrode and the energy change along the axial direction of the arc column are not considered; the electric arc transmits energy to the surrounding air through radiation and conduction, and the effect of convection is ignored; S2: Constructing a magnetohydrodynamic model; By means of the finite element method, the electric arc is meshed and solved through the multi-physical field coupling relationship to obtain the physical distribution characteristics inside the electric arc; by applying appropriate boundary conditions, the electromagnetic field equation can be solved to determine the electric potential distribution; in combination with the conductivity distribution, the current density distribution inside the electric arc can be further determined; meanwhile, the combined action of the electric arc itself and the external magnetic field leads to the energy transfer inside the electric arc plasma; S3: Constructing a transient breakdown arc model; The COMSOL system is used for construction, and the COMSOL system provides a geometry module, which utilizes the drawing or structural size information of the circuit to establish a two-dimensional model of the circuit body or joint in the transient breakdown arc model module to set a defect; The defect is a small air gap in the insulating layer; S4: Simulating to obtain the transient breakdown current and voltage waveform analysis; The metal shielding current is the fault arc current, and the wire core voltage is the arc voltage; after the transient breakdown occurs, a short-time fault arc is generated, the current suddenly increases to a peak value, and then gradually decreases; the arc voltage waveform corresponds to the current level, the voltage rapidly decreases after the breakdown, the higher the arc current, the lower the voltage, with the gradual decrease of the current, the voltage gradually increases to a peak, and then the arc is extinguished, and the voltage returns to a sinusoidal wave.

2. The line transient breakdown modeling method suitable for the environment of the distribution network traveling wave detection according to claim 1, characterized in that: In step S1, the scheme of constructing the black box Mayr model of the electric arc comprises: The electric arc can be simplified as a cylindrical structure composed of gas, and the electric arc conductance changes with the energy change of the arc column; Since the resistance of the electric arc is small, the electric arc model is converted into the form of electric conductance The thermal ionization in the fixed electric arc is calculated according to the Sahha formula.

3. The line transient breakdown modeling method suitable for the environment of the distribution network traveling wave detection according to claim 2, characterized in that: In step S1, the electric arc can be simplified as a cylindrical structure composed of gas, and the electric arc conductance changes with the energy change of the arc column, and the energy equation of the electric arc is represented as (1); In the formula: : rate of change of stored energy in the arc per unit length; : arc current; : arc voltage; : dissipated power per unit length of arc.

4. The line transient breakdown modeling method suitable for the environment of the distribution network traveling wave detection according to claim 2, characterized in that: Since the resistance of the electric arc is small, the electric arc model of formula (1) is converted into the form of electric conductance: (2); In the formulae: : the conductance of the arc per unit length; : the rate of change of the arc conductance per unit length.

5. The line transient breakdown modeling method suitable for the environment of the distribution network traveling wave detection according to claim 2, characterized in that: The thermal ionization in the fixed electric arc is calculated according to the Sahha formula: (3); wherein: : conductance of the arc column when the arc column contains no energy; : energy of the arc; : change in energy in the arc column when the conductance of the arc changes by a factor of e. The derivative of formula (3) is transformed to obtain: = = (4); Formula (4) is substituted into formula (2) to obtain: (5); In the formula: : Time constant of the arc, which has the physical meaning that when the arc conductance drops to the original , the dissipated energy of the arc column is .

6. The line transient breakdown modeling method suitable for the environment of the distribution network traveling wave detection according to claim 1, characterized in that: In step S2, a magnetohydrodynamic model is constructed, including: a mass conservation equation, a momentum conservation equation, an energy conservation equation, a gas state equation and an electromagnetic field equation group.

7. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 6, wherein, the mass conservation equation is: (6); wherein: : fluid density; : time; : velocity vector of fluid motion.

8. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 6, wherein, the momentum conservation equation is: (7); In the formulae: : pressure experienced by the fluid; : dynamic viscosity of the fluid; : identity matrix; : current density vector; : magnetic flux density vector.

9. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 6, wherein, the energy conservation equation is: (8); wherein: : plasma temperature; : constant pressure specific heat capacity; : fluid thermal conductivity; : plasma electrical conductivity; : total volumetric radiation; : Boltzmann constant; : charge of an electron.

10. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 6, wherein, the gas state equation is: (9); wherein, R: ideal gas constant.

11. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 6, wherein, the electromagnetic field equation group is: (10); (11); (12); (13); In the formulae: : electric potential; : electric field strength vector; : magnetic vector potential.

12. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 1, wherein, in step S3, the transient breakdown arc model is constructed, including: the field equation setting, the electric field of the intermittent arc can be represented by the charge conservation equation; the magnetic field setting, the magnetic field equation of the intermittent arc; the fluid heat transfer setting, the temperature field equation in the analysis of heat transfer; the formula of the heat source of the arc plasma under the local thermal equilibrium.

13. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 12, wherein, the field equation setting, the electric field of the intermittent arc can be represented by the charge conservation equation: (14); In the formulae: : current density vector; : charge density; : time; the electric field intensity can be obtained from the electric potential: (15); In the formulae: : electric field strength; : electric potential; the current density vector can be calculated from the electric field intensity: (16); In the formulae: : electrical conductivity.

14. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 12, wherein, the magnetic field setting, the magnetic field of the intermittent arc follows Ampere's law, and the equation is: (17); In the formulae: : magnetic field strength vector the magnetic flux density can be obtained from the magnetic field intensity: (18); In the formulae: : magnetic flux density vector; : magnetic permeability the relationship between the magnetic flux density and the magnetic vector potential is: (19); In the formulae: : magnetic vector potential.

15. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 12, wherein, the fluid heat transfer setting, the temperature field equation is used in the analysis of heat transfer: (20); wherein: : gas density; : heat capacity of the gas; : thermodynamic temperature of the gas; : velocity vector of the gas; : heat flux vector of the gas; the heat flux can be obtained from Fourier's law: (21); In the formulae: : thermal conductivity of the material.

16. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 12, wherein, the multi-physical field coupling setting, the intermittent arc releases extremely high heat during discharge, which can be considered as a heat source; the formula of the heat source of the arc plasma under the local thermal equilibrium is: (22); wherein: : heat generated by the equilibrium discharge heat source; : Boltzmann constant; : charge of an electron; : thermodynamic temperature of the arc plasma; : current density vector in the arc plasma; : electric field strength vector in the arc plasma; : total volume radiance coefficient.

17. The line transient breakdown modeling method suitable for the line traveling wave detection environment building of claim 1, wherein, in step S4, the simulation transient arc can be considered as ionized air plasma, the electric conductance is affected by the ionization degree, the ionization degree is closely related to the temperature, and the temperature is affected by the heat source of the arc current, the three interact with each other, and show a positive correlation.

18. The line transient breakdown modeling method suitable for building a network of traveling wave detection environment according to claim 17, characterized in that, In step S4, the temperature of the arc column center point increases sharply at the moment of simulating the transient arc generation. Because of the approach to arc extinction, the arc discharge heat source power rapidly decreases, resulting in a rapid decrease in temperature near the critical point.

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