A grounding evaluation method, medium and system for outdoor ring main unit

Abstract

The present invention provides a grounding evaluation method, medium and system for an outdoor ring network cabinet, which belongs to the technical field of outdoor ring network cabinets, and includes: obtaining grounding resistance measurement values ​​at multiple points around the outdoor ring network cabinet, operating data (voltage, current, power), temperature distribution when there is no ring network cabinet, and magnetic field data inside and outside the ring network cabinet. Based on these data, an equivalent grounding resistance model is established, and an electrothermal coupling equation group is established. Finite element method and time domain difference method are used for numerical solution to obtain numerical solutions of electric field intensity, current density, potential and temperature. At the same time, analytical methods are used to obtain analytical solutions of these physical quantities. Latin hypercube sampling is used to obtain the numerical range of grounding resistance, current, potential, impedance and temperature. Finally, a grounding evaluation model is established to judge the grounding state of the ring network cabinet according to the evaluation index. The present invention solves the technical problem that the existing method is too simple, the evaluation index is too single, and it cannot reflect the overall grounding performance status of the ring network cabinet.

Description

Technical Field

[0001] The present invention belongs to the technical field of outdoor ring network cabinets, and in particular, relates to a grounding evaluation method, medium and system for outdoor ring network cabinets. Background Art

[0002] The transmission and distribution network is one of the core infrastructures for modern urban power supply. Its stable and reliable operation is crucial to ensuring the supply of electricity for social production and life. As an important part of the transmission and distribution network, the outdoor ring main unit plays a key role in the power grid. The ring main unit is usually installed in an outdoor substation or switch station to play the role of power transmission, distribution and protection. Due to the complex and changeable outdoor environment, the ring main unit will be affected by various adverse factors, such as lightning strikes, moisture corrosion, temperature changes, etc., which poses a severe test to its operational reliability and safety. Among them, the grounding performance of the ring main unit is one of the key factors affecting its stable operation.

[0003] A good grounding system can not only effectively avoid external faults such as lightning strikes, but also ensure the safe operation of the equipment itself and prevent insulation failures and safety accidents caused by poor grounding. However, there are some problems and shortcomings in the existing grounding performance evaluation methods of ring main units. First, the method of measuring the grounding resistance value on site is too simple and cannot reflect the overall grounding performance of the ring main unit; second, the existing grounding performance evaluation indicators are too single and often only focus on the grounding resistance itself, while ignoring other important factors. Therefore, it is urgent to establish a more systematic and comprehensive grounding performance evaluation method for outdoor ring main units to better guide and serve the operation and maintenance of the transmission and distribution network. Summary of the invention

[0004] In view of this, the present invention provides an outdoor ring main unit grounding evaluation method, medium and system, which can solve the technical problems that the existing method for measuring the grounding resistance value is too simple, the evaluation index is too single, and it cannot reflect the overall grounding performance of the ring main unit.

[0005] The present invention is achieved in that:

[0006] A first aspect of the present invention provides a grounding assessment method for an outdoor ring main unit, comprising the following steps:

[0007] S10, obtaining the grounding resistance values ​​measured by the grounding resistance tester at multiple node resistance measurement points around the outdoor ring network cabinet; collecting the operation data of the outdoor ring network cabinet, including voltage, current, and power; obtaining the temperature distribution data obtained by thermal imaging scanning without the outdoor ring network cabinet; obtaining the magnetic field data inside and outside the outdoor ring network cabinet;

[0008] S20, using the multi-point grounding resistance measurement value and the geometric structure of the ring main unit, establishing the equivalent grounding resistance of the outdoor ring main unit;

[0009] S30. Establish the grounding electrothermal coupling equations, including Maxwell equations, Ohm's law equations, continuity equations, boundary condition equations and heat conduction equations:

[0010] S40, numerically solving the electrothermal coupling equations based on the finite element method and the time domain difference method to obtain multiple numerical solutions, specifically: a numerical solution for electric field intensity distribution, a numerical solution for current density distribution, a numerical solution for potential distribution, and a numerical solution for temperature distribution;

[0011] S50, using separation of variables method and series expansion to analytically solve the electrothermal coupling equations to obtain multiple analytical solutions, specifically: an analytical solution for electric field intensity, an analytical solution for current density, an analytical solution for potential, and an analytical solution for temperature;

[0012] S60, based on the multiple analytical solutions, using a Latin hypercube sampling method, obtaining multiple value ranges, specifically: a ground resistance range, a ground current range, a ground potential range, a ground impedance range, and a temperature range;

[0013] S70, establishing an outdoor ring main unit grounding assessment model, and substituting the multiple numerical solutions and multiple numerical ranges into the model to obtain a grounding assessment index;

[0014] S80: Determine the grounding status of the outdoor ring network cabinet according to the grounding evaluation index.

[0015] The equivalent grounding resistance of the outdoor ring network cabinet is specifically expressed as:

[0016]

[0017] Among them, R i is the ground resistance value of the i-th measuring point, n is the total number of measuring points, ρ is the soil resistivity, (x j ,y j ,z j ) is the spatial coordinate of the jth grounding point, m is the total number of grounding points, h is the equivalent burial depth, K s is the seasonal correction factor, L is the total length of the grounding body, and a and b are the length and width of the grounding grid respectively.

[0018] Wherein, the Maxwell equations are specifically expressed as:

[0019]

[0020] The Ohm's law equation is specifically expressed as:

[0021] J = σ(T)E + σ(T)v × B;

[0022] The continuity equation is specifically expressed as:

[0023]

[0024] The boundary condition equation is specifically expressed as:

[0025] n×(E2-E1)=0;

[0026] n·(D2-D1)=ρ s ;

[0027]

[0028] The heat conduction equation is specifically expressed as:

[0029]

[0030] Among them, E is the electric field intensity, H is the magnetic field intensity, J is the current density, D is the electric displacement, B is the magnetic induction intensity, ρ v is the volume charge density, σ(T) is the temperature-dependent conductivity, v is the carrier drift velocity, ρ s is the surface charge density, n is the interface normal vector, T is the temperature, ρ is the density, C p is the specific heat capacity, k(T) is the temperature-dependent thermal conductivity, Q J is the Joule heat source, Q e is the external heat source, Q r As a radiant heat source, and Represent the divergence and curl operations respectively.

[0031] The analytical solution of the electric field strength is specifically expressed as:

[0032]

[0033] In the formula, Represents the gradient operator.

[0034] The analytical solution of current density is specifically expressed as:

[0035] J(r,θ,φ)=σ(T)E(r,θ,φ);

[0036] Where J(r,θ,φ) is the current density vector, σ(T) is the temperature-dependent conductivity, E(r,θ,φ) is the electric field strength vector, r is the radial distance, θ is the polar angle, φ is the azimuth angle, and T is the temperature.

[0037] The potential analytical solution is specifically expressed as:

[0038]

[0039] where \(V(r,\theta,\varphi)\) is the electric potential function; \(\varepsilon_0\) is the vacuum permittivity; \(\int\) V \(dV'\) is a volume integral, where \(dV'\) is the volume element; is a closed surface integral, where \(dS'\) is the area element; \(\rho\) v \((r',\theta',\varphi')\) is the volume charge density; \(\rho\) s \((r',\theta',\varphi')\) is the surface charge density; \(r\) is the field point position vector; \(r'\) is the source point position vector; \(|r - r'|\) is the distance from the field point to the source point.

[0040] Among them, the temperature analytical solution is specifically expressed as:

[0041]

[0042] where \(T(r,t)\) is the temperature distribution function; \(T_0\) is the initial temperature; \(k\) is the thermal conductivity; \(t\) is the time; \(\tau\) is the time integration variable; \(Q(\tau)\) is the source intensity function; \(r\) is the radial distance; \(\alpha\) is the thermal diffusion coefficient; \(\exp()\): exponential function.

[0043] Among them, the outdoor ring main unit grounding evaluation model is specifically expressed as:

[0044]

[0045] where \(w\) i is the weight coefficient, \(f\) i \((x)\) is the nonlinear conversion function: \(R\) std is the standard grounding resistance value, \(I\) lim is the allowable grounding current limit value, \(V\) touch is the safe touch voltage, \(Z\) ref is the reference grounding impedance, \(T\) lim is the temperature limit value, \(k\) i and \(x\) 0i are the parameters of the sigmoid function; \(I\) g is the grounding current; \(V\) g is the grounding voltage; \(Z\) g is the grounding impedance; \(T\) max is the maximum temperature;

[0046] If \(G\leq0.6\), it indicates that the grounding state is good;

[0047] If \(0.6 < G\leq0.8\), it indicates that the grounding state is average and needs to be checked regularly;

[0048] If \(G > 0.8\), it indicates that the grounding state is poor and immediate improvement measures need to be taken.

[0049] A second aspect of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores program instructions, and when the program instructions are executed, they are used to execute the above-mentioned outdoor ring network cabinet grounding assessment method.

[0050] A third aspect of the present invention provides an outdoor ring main unit grounding assessment system, which includes the above-mentioned computer-readable storage medium.

[0051] Compared with the prior art, the grounding evaluation method, medium and system of an outdoor ring network cabinet provided by the present invention have the following beneficial effects: the method firstly measures the grounding resistance at multiple nodes around the ring network cabinet by using a grounding resistance tester, and collects the operating parameter data, thermal imaging data and magnetic field data of the ring network cabinet. Then, the equivalent grounding resistance model of the ring network cabinet is established by using these measurement data, and the influence of the geometric factors of the grounding body and the form of the grounding grid on the grounding performance is considered.

[0052] Next, the method constructs a grounded electrothermal coupling equation group including Maxwell's equations, Ohm's law equations, heat conduction equations, etc., and uses the finite element method and time-domain difference method to numerically solve them, obtaining numerical solutions to key physical quantities such as electric field intensity distribution, current density distribution, potential distribution, and temperature distribution. At the same time, the method also uses the separation of variables method and series expansion to analytically solve the above coupling equation group and obtain analytical solution expressions for these physical quantities.

[0053] Based on the above numerical and analytical solutions, this method further uses the Latin hypercube sampling method to obtain the numerical variation range of various parameters such as grounding resistance range, grounding current range, grounding potential range, grounding impedance range and temperature range. Finally, this method constructs a comprehensive grounding performance evaluation model, taking into account multiple factors such as grounding resistance, grounding current, grounding potential, grounding impedance and temperature, and judges the overall grounding status of the ring main unit based on the calculated grounding evaluation index.

[0054] Compared with the existing single grounding resistance measurement method, the comprehensive evaluation method proposed by the invention can diagnose the grounding performance of the outdoor ring network cabinet more comprehensively and accurately, taking into account both the electromagnetic environment factors and the thermal effect factors, providing a more reliable basis for evaluation for operation and maintenance personnel. It solves the technical problem that the existing method for measuring the grounding resistance value is too simple, the evaluation index is too single, and it cannot reflect the overall grounding performance of the ring network cabinet. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 A flow chart of the method provided by the present invention. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0057] like Figure 1 FIG. 1 is a flow chart of a grounding evaluation method for an outdoor ring network cabinet provided by the present invention. The method comprises the following steps:

[0058] S10, obtaining the grounding resistance values ​​measured by the grounding resistance tester at multiple node resistance measurement points around the outdoor ring network cabinet; collecting the operation data of the outdoor ring network cabinet, including voltage, current, and power; obtaining the temperature distribution data obtained by thermal imaging scanning without the outdoor ring network cabinet; obtaining the magnetic field data inside and outside the outdoor ring network cabinet;

[0059] S20, using the multi-point grounding resistance measurement value and the geometric structure of the ring main unit, establishing the equivalent grounding resistance of the outdoor ring main unit;

[0060] S30. Establish the grounding electrothermal coupling equations, including Maxwell equations, Ohm's law equations, continuity equations, boundary condition equations and heat conduction equations:

[0061] S40, numerically solving the electrothermal coupling equations based on the finite element method and the time-domain difference method to obtain multiple numerical solutions, specifically: a numerical solution for electric field intensity distribution, a numerical solution for current density distribution, a numerical solution for potential distribution, and a numerical solution for temperature distribution;

[0062] S50, using separation of variables method and series expansion to analytically solve the electrothermal coupling equations to obtain multiple analytical solutions, specifically: an analytical solution for electric field intensity, an analytical solution for current density, an analytical solution for potential, and an analytical solution for temperature;

[0063] S60, based on the multiple analytical solutions, using the Latin hypercube sampling method, obtaining multiple value ranges, specifically: a ground resistance range, a ground current range, a ground potential range, a ground impedance range, and a temperature range;

[0064] S70, establishing an outdoor ring main unit grounding assessment model, and substituting multiple numerical solutions and multiple numerical ranges to obtain a grounding assessment index;

[0065] S80. Determine the grounding status of the outdoor ring network cabinet according to the grounding evaluation index.

[0066] The specific implementation methods of the above steps are described in detail below:

[0067] Step S10, obtain the grounding resistance values ​​measured by the grounding resistance tester at multiple node resistance measurement points around the outdoor ring network cabinet, collect the operation data of the outdoor ring network cabinet, including voltage, current, power, obtain the temperature distribution data obtained by thermal imaging scanning without the outdoor ring network cabinet, and obtain the magnetic field data inside and outside the outdoor ring network cabinet. The purpose of this step is to collect various parameter data required for the evaluation of the grounding performance of the outdoor ring network cabinet.

[0068] The specific implementation is as follows:

[0069] 1) First, use a ground resistance tester to measure the ground resistance at multiple locations around the outdoor ring network cabinet. Usually, 10-20 measurement points evenly distributed around the ring network cabinet can be selected to obtain a more comprehensive ground resistance distribution. When measuring, it is necessary to ensure that the coordinate information of each measurement point is recorded.

[0070] 2) At the same time, the voltage, current, power and other parameter data of the outdoor ring network cabinet in normal operation are collected. These parameter data can be directly read from the monitoring system of the ring network cabinet or the field instrument.

[0071] 3) In the absence of a ring main unit, use a thermal imager to perform thermal imaging scans of the area around the ring main unit to obtain temperature distribution data of the area. These temperature data can provide important references for subsequent grounding performance analysis.

[0072] 4) Use a magnetic field meter to measure and collect magnetic field strength inside and outside the ring main unit. The magnetic field data can reflect the electromagnetic environment of the ring main unit and also has a certain reference value for evaluating the grounding performance.

[0073] Through the above steps, various parameter data required for the evaluation of the grounding performance of the outdoor ring network cabinet are obtained, laying the foundation for subsequent modeling and analysis. Among them, the grounding resistance value, operating parameter data, temperature distribution and magnetic field data are all key evaluation input information.

[0074] Step S20, using the multi-point grounding resistance measurement values ​​and the geometric structure of the ring main unit, establish the equivalent grounding resistance of the outdoor ring main unit. The purpose of this step is to establish an equivalent model of the overall grounding performance of the ring main unit based on the measured grounding resistance distribution.

[0075] The specific implementation is as follows:

[0076] 1) First calculate the equivalent value R of the ground resistance of multiple measurement points eq According to the principle of resistors in parallel, the formula can be used To calculate, where R i is the grounding resistance value of the i-th measuring point, and n is the total number of measuring points. In this way, the overall equivalent value of the grounding resistance around the ring network cabinet can be obtained.

[0077] 2) Next, consider the geometric shape of the grounding body. The grounding body of a general ring main unit can be approximated as a set of grounding electrodes, so the contribution of the geometric factor can be calculated using the Sverak formula. Where ρ is soil resistivity, (x j ,y j ,z j ) is the spatial coordinate of the jth grounding point, m is the total number of grounding points, and h is the equivalent burial depth.

[0078] 3) Finally, consider the factors affecting the grounding grid. For grounding bodies in the form of grounding grids, the Sverak-Riccioni formula can be used To calculate. Where K s is the seasonal correction factor, L is the total length of the grounding body, and a and b are the length and width of the grounding grid respectively.

[0079] 4) Adding the above three contributions together, we can get the equivalent grounding resistance R of the outdoor ring network cabinet. eq This equivalent grounding resistance can better reflect the overall condition of the actual grounding performance.

[0080] By establishing this equivalent grounding resistance model, the grounding resistance values ​​of multiple measurement points can be integrated into an equivalent value, and the influence of factors such as the geometric structure of the ring main unit and the form of the grounding grid can be taken into account. This provides an important basis for subsequent grounding performance analysis and evaluation.

[0081] Step S30, establishing a grounding electrothermal coupling equation group. The purpose of this step is to establish a complete mathematical model to describe the coupling relationship between physical quantities such as electric field, magnetic field, thermal field, etc. in the ring main cabinet grounding system.

[0082] The specific implementation is as follows:

[0083] 1) First, establish the Maxwell equations to describe the basic laws of the electromagnetic field. Maxwell equations include the curl equation, the divergence equation, and the continuity equation, covering the electric field intensity E, magnetic field intensity H, current density J, electric displacement D, magnetic induction intensity B, and body charge density ρ. v The relationship between basic electromagnetic quantities such as

[0084] 2) Next, Ohm's law equation is introduced to describe the relationship between current density J and electric field strength E, as well as carrier drift velocity v and magnetic induction intensity B. Among them, the conductivity σ(T) is related to the temperature T.

[0085] 3) In order to describe the coupling relationship between the electromagnetic field and the temperature field, the heat conduction equation needs to be introduced. The heat conduction equation describes the Joule heat effect Q J , external heat source Qe and the radiant heat source Q r The variation of the generated temperature T in time and space. Among them, the thermal conductivity k(T) is also related to the temperature T.

[0086] 4) At the same time, boundary condition equations need to be considered, including the continuity conditions of electric field intensity, electric displacement, current density on the interface, and boundary conditions of temperature field.

[0087] 5) Combining the above equations, a complete set of equations describing the grounding electrothermal coupling relationship is formed. The solution of this set of equations can obtain key physical quantities such as electric field intensity distribution, current density distribution, potential distribution and temperature distribution.

[0088] By establishing such a set of coupled equations, the interaction process between the electromagnetic field and the thermal field in the grounding system of the outdoor ring main unit can be fully described, which lays a solid mathematical foundation for subsequent numerical simulation and analytical analysis.

[0089] Step S40, numerically solving the electrothermal coupling equations based on the finite element method and the time domain difference method. The purpose of this step is to discretize and solve the grounding electrothermal coupling equations using numerical methods to obtain numerical solutions for electric field intensity distribution, current density distribution, potential distribution and temperature distribution.

[0090] The specific implementation is as follows:

[0091] 1) First, the finite element method is used to spatially discretize the computational domain. The entire computational domain is divided into multiple unit grids, and appropriate interpolation functions are selected on the grid nodes to discretize the field quantities.

[0092] 2) Next, the time-domain difference method is used to discretize the time derivative term. Here, the Newmark-β time integration method can be used to iteratively solve the changes of various field quantities during the time evolution process.

[0093] 3) The equations after spatial discretization and time discretization are assembled into a matrix form, that is, Where [M] is the mass matrix, [K] is the stiffness matrix, {u} is the unknown vector, and {F} is the load vector.

[0094] 4) In each time step, the matrix equation is solved using the Newmark-β method to obtain the value of the potential {u} at the next moment.

[0095] 5) Based on the obtained potential distribution, further calculate the electric field intensity distribution And the current density distribution J = σ(T)E.

[0096] 6) At the same time, the conduction equation of the temperature field is also discretized and coupled to the electric field and current field equations, and the temperature distribution T is obtained by iterative solution.

[0097] 7) Summarize the stiffness matrix [K] and load vector {F} of each unit in the entire computational domain to form a global matrix and vector, and modify them according to the boundary conditions.

[0098] 8) Finally, the potential distribution {u} on the entire calculation domain is solved, and then the electric field intensity distribution E, current density distribution J and temperature distribution T are calculated.

[0099] Specifically, step S40 is described by the following formula:

[0100] 1. Spatial discretization: Use the finite element method to divide the computational domain into grids and select a suitable interpolation function.

[0101] 2. Time discretization: The time derivative is discretized using the time domain difference method.

[0102] 3. Construct the discretized equation system:

[0103]

[0104] Where [M] is the mass matrix, [K] is the stiffness matrix, {u} is the unknown vector, and {F} is the load vector.

[0105] 4. Iterative solution: Use the Newmark-β method for time integration,

[0106]

[0107] Among them, β and γ are integral parameters, usually β = 0.25 and γ = 0.5.

[0108] 5. Solve the electric field intensity distribution:

[0109] 6. Solve the current density distribution: J = σ(T)E

[0110] 7. Solve the temperature distribution: solve iteratively through the heat conduction equation.

[0111] 8. Construct global matrices and vectors:

[0112]

[0113] Among them, N e is the number of units, [K e ] and {F e} are the element stiffness matrix and load vector respectively.

[0114] 9. Apply boundary conditions:

[0115] For Dirichlet boundary conditions: Modify [K global ] and {F global}

[0116] For Neumann boundary conditions: Modify {K global}

[0117] 10. Solve linear equations:

[0118] {u}=[K global ] -1 {F global}

[0119] 11. Post-processing:

[0120] Calculate the electric field strength:

[0121] Calculate the current density: J = σ(T)[B]{u}

[0122] Calculate temperature distribution: T = [N] {u T}

[0123] Where [B] is the strain-displacement matrix, [N] is the shape function matrix, {u T} is the temperature node value vector.

[0124] Through this numerical solution method based on the finite element method and the time-domain difference method, numerical solutions of various key physical quantities describing the grounding electrothermal coupling process can be obtained. These numerical solutions provide an important basis for further analysis and evaluation.

[0125] Step S50, using separation of variables method and series expansion, analytically solving the electrothermal coupling equations. The purpose of this step is to solve the grounding electrothermal coupling equations by analytical methods under certain simplified assumptions to obtain analytical solution expressions for electric field intensity, current density, potential and temperature.

[0126] The specific implementation is as follows:

[0127] 1) For the analytical solution of the electric field intensity distribution E, it can be assumed that the potential V satisfies the Laplace equation And the separation of variables method is used to solve it. Then the electric field strength can be calculated Analytical solution of .

[0128] 2) According to Ohm's law J = σ(T)E, we can further get the analytical solution expression of the current density distribution J. It is necessary to consider the linear change relationship between conductivity σ(T) and temperature.

[0129] 3) For the analytical solution of the potential distribution V, the Green function method can be used to calculate the volume charge density ρ v and surface charge density ρ s By integrating and solving the Laplace equation, we can obtain the expression of V(r,θ,φ).

[0130] 4) For the analytical solution of temperature distribution T, we can assume that the heat source is a point source and use the Green's function solution of the heat conduction equation Solve it. Where T0 is the initial temperature, k is the thermal conductivity, Q(τ) is the heat source intensity, and α is the thermal diffusion coefficient.

[0131] 5) When solving the analytical solution of electric field strength, the unknown coefficient A needs to be determined through boundary conditions. lm and B lm For example, the surface electric field strength can be used Solve for the condition that the potential is 0 at infinity.

[0132] 6) For the analytical solution of current density, it is necessary to consider the linear relationship between conductivity and temperature: σ(T) = σ0[1+α(T-T0)], where σ0 is the conductivity at the reference temperature T0 and α is the temperature coefficient.

[0133] 7) The calculation of the analytical solution of potential distribution involves the series expansion formula in the spherical coordinate system where r < =min(r,r′),r > =max(r,r′).

[0134] 8) The analytical solution of temperature distribution also requires processing time-varying heat sources, which can be converted into the integral form of Green's function using the convolution theorem.

[0135] The following is the derivation process of each analytical solution

[0136] 1. Derivation process of analytical solution of electric field strength:

[0137] Step 1: Start with Laplace's equation

[0138] Start with Laplace's equation for electrostatic fields:

[0139]

[0140] Where V is the electric potential, is the Laplace operator.

[0141] Step 2: Express Laplace's equation in spherical coordinates

[0142] In the spherical coordinate system (r,θ,φ), Laplace's equation can be written as:

[0143]

[0144] Step 3: Use the separation of variables method

[0145] Assume that the solution is of the form: V(r,θ,φ)=R(r)Y(θ,φ)

[0146] Substituting this form into Laplace's equation, we obtain:

[0147]

[0148] where l(l+1) is the separation constant.

[0149] Step 4: Solve the radial equation

[0150] The radial equation is:

[0151] The solution is: R(r) = Ar l +Br -(l+1)

[0152] Among them, A and B are constants.

[0153] Step 5: Solve the Angle Equation

[0154] The angle equation is:

[0155] The solutions to this equation are spherical harmonics

[0156] Step 6: Combine solutions

[0157] Combining the radial and angular solutions, and taking into account all possible values ​​of l and m, we obtain the general solution:

[0158]

[0159] Among them, A lm and B lm is a coefficient determined by the boundary conditions.

[0160] Step 7: Calculate the electric field strength The electric field strength is the negative gradient of the electric potential:

[0161]

[0162] In spherical coordinates, this gradient can be expressed as:

[0163]

[0164] 2. Derivation process of current density analytical solution:

[0165] Step 1: Use Ohm's Law The relationship between current density and electric field strength is given by Ohm's law:

[0166] J=σE

[0167] Here, σ is the conductivity.

[0168] Step 2: Consider the effect of temperature on conductivity

[0169] In practical situations, conductivity is usually a function of temperature and is therefore written as:

[0170] J(r,θ,φ)=σ(T)E(r,θ,φ)

[0171] Step 3: Substitute the electric field strength expression into

[0172] Substituting the electric field strength expression obtained previously, we obtain:

[0173]

[0174] Step 4: Expand the electric potential expression

[0175] Substituting the expanded form of the potential into the final expression for current density is:

[0176]

[0177] 3. Potential analytical solution derivation process:

[0178] Step 1: Start with Poisson's equation

[0179] In the presence of a charge distribution, the electric potential satisfies Poisson's equation:

[0180]

[0181] Where ρ is the charge density and ε0 is the dielectric constant of vacuum.

[0182] Step 2: Introducing Green's function

[0183] Define the Green function G(r,r′) to satisfy:

[0184]

[0185] Here, δ is the Dirac delta function.

[0186] Step 3: Use Green's Theorem

[0187] Applying Green's second theorem:

[0188]

[0189] Step 4: Substitute the Poisson equation and Green's function equation Substitute the Poisson equation and Green's function equation into the above equation to obtain:

[0190]

[0191] Step 5: Simplify the integral

[0192] Using the properties of the delta function, we can simplify the volume integral:

[0193]

[0194] Step 6: Choose an appropriate Green's function

[0195] In infinite space, the Green's function is:

[0196]

[0197] Step 7: Get the final solution

[0198] Substitute the Green's function and express the surface integral term as the surface charge density ρ s The final solution is obtained by integrating:

[0199]

[0200] 4. Temperature analytical solution derivation process:

[0201] Step 1: Start with the Heat Equation

[0202] The heat conduction equation is:

[0203]

[0204] Where ρ is the density, C p is the specific heat capacity, k is the thermal conductivity, and Q is the heat source term.

[0205] Step 2: Introducing Thermal Diffusivity

[0206] Defining Thermal Diffusivity The equation becomes:

[0207]

[0208] Step 3: Assume a point heat source

[0209] Assuming the heat source is a point source, it can be expressed as:

[0210]

[0211] Where Q(t) is the heat source intensity and δ(r) is the radial Dirac delta function.

[0212] Step 4: Introducing Green's function

[0213] Define the Green function G(r, t; r′, t′) to satisfy:

[0214]

[0215] Step 5: Solve for Green's function

[0216] In the spherically symmetric case, the solution of the Green's function is:

[0217]

[0218] Step 6: Solve for the temperature distribution using Green's function

[0219] The temperature distribution can be expressed as:

[0220]

[0221] Step 7: Simplify the integral

[0222] Using the properties of the delta function, we can simplify the spatial integral:

[0223]

[0224] This is the final analytical solution for the temperature distribution. In this solution, T0 is the initial temperature and the integral represents the contribution of the heat source to the temperature.

[0225] Through the above steps, the analytical expressions of key physical quantities such as electric field intensity, current density, potential and temperature can be obtained. These analytical solutions can more intuitively reflect the relationship between the various quantities and help to further analyze the mechanism of the grounding electrothermal coupling process.

[0226] Step S60, based on the Latin hypercube sampling method, obtain multiple value ranges, including ground resistance range, ground current range, ground potential range, ground impedance range and temperature range. The purpose of this step is to obtain the value variation range of each key parameter through random sampling method, so as to provide a basis for subsequent grounding performance evaluation.

[0227] Specific implementation of step S60:

[0228] 1) Divide the value range of each parameter into N intervals and randomly select a sample point in each interval.

[0229] 2) Randomly arrange the N sample points of each parameter, combine the sample points of different parameters, and obtain N groups of samples.

[0230] 3) For each parameter x i ,Convert the uniformly distributed random samples to the target distribution using the formula in is the inverse function of the cumulative distribution function of the ith parameter, π i is a uniform random number on [0,1]. This way, we can get a sample value y that meets the target distribution. i .

[0231] 4) The Iman-Conover method is used to adjust the correlation between samples, and the formula is Y adjusted =YP -1 C, where Y is the original sample matrix, P is the rank correlation matrix of y, and C is the Cholesky decomposition of the target correlation matrix.

[0232] 5) Finally, calculate the range and statistical characteristics of each parameter, including the minimum value x min , maximum value x max , mean μ and standard deviation σ.

[0233] Through this Latin hypercube sampling method, the value range of each evaluation parameter can be effectively sampled and the correlation between parameters can be considered, which provides an important data basis for the subsequent establishment of the grounding performance evaluation model.

[0234] Step S70: Establishing an outdoor ring main unit grounding evaluation model. The purpose of this step is to construct a comprehensive evaluation index to quantitatively evaluate the grounding performance of the ring main unit.

[0235] The specific implementation is as follows:

[0236] 1) The expression of the grounding assessment model is: Among them, w i is the weight coefficient of each evaluation factor, satisfying f i (x) is a nonlinear conversion function, and the sigmoid function can be selected

[0237] 2) R std is the standard grounding resistance value, I lim To allow the ground current limit, V touch is the safe contact voltage, Z ref is the reference ground impedance, T lim These reference quantities can be determined according to national standards or industry specifications.

[0238] 3) Weight coefficient w i It can be determined by the analytic hierarchy process (AHP). First, construct the judgment matrix A = (a ij ) 5×5 , where a ijIndicates the importance of factor i relative to factor j. Then calculate the maximum eigenvalue λ of the judgment matrix max and the corresponding eigenvector W. Finally, normalize the eigenvector to obtain the weight coefficient and perform a consistency test to ensure

[0239] 4) The parameter k of the non-linear transfer function f i (x) i and x 0i can be determined by historical data or expert experience. Among them, k i controls the steepness of the function, and x 0i is the midpoint. The formulas and can be used for calculation.

[0240] 5) The final grounding evaluation index G is obtained by weighted summation of the normalized values of each evaluation factor and the corresponding weight coefficients. Generally speaking, when G ≤ 0.6, the grounding state is good; when 0.6 < G ≤ 0.8, the grounding state is average and regular inspections are required; when G > 0.8, the grounding state is poor and immediate improvement measures need to be taken.

[0241] The weight coefficients are determined by the Analytic Hierarchy Process (AHP). The following gives the detailed calculation steps of the weight coefficients

[0242] 1. Construct the judgment matrix A = (a ij ) 5×5

[0243] 2. Calculate the eigenvector: AW = λ max W

[0244] 3. Consistency test: where

[0245] Determination of the parameters of the non-linear transfer function:

[0246] 1. For the sigmoid function

[0247] k i controls the steepness of the function, and x 0i is the midpoint.

[0248] 2. These parameters can be determined by historical data or expert experience:

[0249]

[0250] 3. The AHP calculation process of the weight coefficients:

[0251] a. Construct the judgment matrix A:

[0252] a ij Indicates the importance of factor i relative to factor j, usually using a 1-9 scale.

[0253] b. Calculate the maximum eigenvalue λ of the judgment matrix max and the corresponding eigenvector W:

[0254] (A - λ max I)W = 0

[0255] c. Normalize the eigenvector to obtain the weight:

[0256]

[0257] d. Consistency test:

[0258]

[0259] where RI is the random consistency index.

[0260] By constructing such a comprehensive grounding performance evaluation model, the grounding status of outdoor ring main units can be quantitatively evaluated, and corresponding maintenance or improvement measures can be taken in a timely manner according to the evaluation results. This provides an effective basis for improving the grounding reliability of ring main units.

[0261] Step S80: Determine the grounding status of the outdoor ring main unit according to the grounding evaluation index. The purpose of this step is to use the results of the aforementioned grounding evaluation model to make a final judgment and assessment of the grounding performance of the ring main unit.

[0262] The specific implementation method is as follows:

[0263] 1) Compare the calculated grounding evaluation index G with a pre-set threshold. As mentioned before, when G ≤ 0.6, the grounding status is good; when 0.6 < G ≤ 0.8, the grounding status is average and regular inspections are required; when G > 0.8, the grounding status is poor and improvement measures need to be taken immediately.

[0264] 2) According to the specific value of the evaluation index G, the specific situation of the grounding performance of the ring main unit can be further determined. For example, when G is close to 0, it indicates that the grounding status is very good; when G is close to 0.8, it indicates that the grounding status is critical and key attention is required; when G exceeds 0.8, it means that there are serious grounding problems and repair measures are urgently needed.

[0265] 3) In addition to the grounding evaluation index itself, the specific values of each evaluation factor can also be analyzed to determine the key factors affecting the grounding performance. For example, if the grounding resistance is too high or the temperature is too high is the main reason for the high G value, then these factors should be focused on for improvement.

[0266] 4) Comprehensive analysis of the value of the evaluation index G and the specific performance of each factor can more comprehensively diagnose the grounding performance of the ring network cabinet and provide a basis for subsequent maintenance and improvement work.

[0267] Through the above steps, the grounding status of the outdoor ring network cabinet can be quickly and accurately judged according to the specific value of the grounding evaluation index G, providing an important reference for network operation and maintenance management. At the same time, targeted improvement measures can be taken for the key factors affecting the grounding performance to improve the overall grounding reliability of the ring network cabinet.

[0268] In summary, the grounding evaluation method for outdoor ring main unit proposed in this invention comprehensively and systematically evaluates the grounding performance of the ring main unit from multiple perspectives, including key factors such as grounding resistance, grounding current, grounding potential, grounding impedance, and grounding thermal effect. By establishing an equivalent grounding resistance model and a set of grounding electrothermal coupling equations, using numerical and analytical methods to solve them, and using Latin hypercube sampling to obtain the numerical range of each parameter, a comprehensive grounding performance evaluation index is finally constructed, which provides effective technical support for the diagnosis and improvement of the grounding status of the ring main unit.

[0269] A second aspect of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores program instructions, and when the program instructions are executed, they are used to execute the above-mentioned outdoor ring network cabinet grounding assessment method.

[0270] A third aspect of the present invention provides an outdoor ring main unit grounding assessment system, which includes the above-mentioned computer-readable storage medium.

[0271] Specifically, the principle of the present invention is to establish a comprehensive grounding electrothermal coupling mathematical model and solve the model using both numerical and analytical methods to obtain the detailed distribution of key parameters in the ring main unit grounding system. This provides a solid technical foundation for subsequent comprehensive evaluation.

[0272] Firstly, this method establishes an equivalent grounding resistance model of the ring main unit through multi-point grounding resistance measurement and geometric parameter collection. This equivalent resistance model not only considers the grounding resistance value of a single measurement point, but also introduces the geometric factors of the grounding body and the form of the grounding grid, which more accurately reflects the overall status of the actual grounding performance.

[0273] Secondly, this method constructs a grounding electrothermal coupling mathematical model that includes Maxwell's equations, Ohm's law equations, heat conduction equations, etc. This coupling equation group not only describes the basic laws of the electromagnetic field, but also takes into account the influence of the temperature field, and can fully simulate the electromagnetic-thermal coupling process in the ring main unit grounding system.

[0274] For the above coupled equations, this method uses both numerical and analytical solutions. The numerical solution uses the finite element method and time domain difference method to obtain the numerical solutions of key physical quantities such as electric field intensity distribution, current density distribution and temperature distribution. The analytical solution uses the separation of variables method and series expansion to give the analytical solution expressions of these physical quantities. These two methods complement each other and provide strong support for a comprehensive understanding of the behavior mechanism of the ring main unit grounding system.

[0275] Based on the numerical and analytical solutions, the method further adopts the Latin hypercube sampling method to obtain the numerical variation range of each evaluation parameter. This random sampling method not only takes into account the correlation between parameters, but also better reflects the uncertainty of actual working conditions, laying a good data foundation for building a comprehensive grounding performance evaluation model.

[0276] Finally, this method establishes a comprehensive grounding performance evaluation model that integrates multiple factors such as grounding resistance, grounding current, grounding potential, grounding impedance and temperature. Through nonlinear transformation and weighted synthesis of various factors, the model can more accurately evaluate the overall grounding status of the ring main unit, provide a scientific basis for maintenance personnel, and guide improvement measures to address the problem.

[0277] In summary, the present invention uses advanced technical means such as systematic mathematical modeling, multivariate coupling analysis, and random sampling simulation to construct a complete outdoor ring network cabinet grounding performance evaluation method. Compared with the existing single grounding resistance measurement method, this method diagnoses the key indicators of the grounding system more comprehensively and accurately, providing strong support for improving the reliability and safety of the ring network cabinet operation.

[0278] In order to better understand and implement the present invention, an embodiment of a specific application scenario of the present invention is provided below: an outdoor ring main unit in a city's power transmission and distribution network is located in a substation and is mainly responsible for the power distribution task in the area. The ring main unit is exposed to the outdoor environment for a long time and is affected by natural factors such as rain, snow, temperature changes, and lightning strikes all year round. Its grounding performance has always been the focus of attention of operation and maintenance personnel. In order to comprehensively evaluate the grounding performance of the ring main unit, the power department decided to use the grounding evaluation method proposed in the present invention for diagnosis.

[0279] First, the operation and maintenance personnel selected 15 measurement points around the ring main unit to measure the grounding resistance value. The measurement results are shown in Table 1 below:

[0280] Table 1 Measurement point data table

[0281]

[0282]

[0283] It can be seen from the above table that the grounding resistance values ​​of the 15 measuring points around the ring network cabinet fluctuate between 2.7Ω and 3.2Ω, showing a relatively uniform distribution feature as a whole.

[0284] At the same time, the operation and maintenance personnel also collected the operating parameter data of the ring main unit under normal operation, including voltage of 10.5kV, current of 280A, and active power of 2.8MW. In addition, they also used a thermal imager to perform thermal imaging scans on the area around the ring main unit to obtain a temperature distribution map. From the temperature distribution map, it can be seen that the temperature of the ring main unit and its surrounding area is generally high, reaching a maximum of 45°C. This may be related to the combined effect of the internal heating of the ring main unit and the external ambient temperature.

[0285] In addition, the operation and maintenance personnel also used a magnetic field meter to measure the magnetic field strength inside and outside the ring main unit, and obtained the data in Table 2 as follows:

[0286] Table 2 Magnetic field measurement table

[0287] Measuring point number Magnetic field strength (A / m) 1 30 2 35 3 28 4 33 5 25

[0288] It can be seen from the magnetic field strength data that the magnetic field strength inside the ring main unit is significantly higher than that outside, which indicates that the electromagnetic environment of the ring main unit itself is relatively complex.

[0289] With the above-mentioned grounding resistance measurement data, operating parameter data, temperature distribution data and magnetic field strength data, operation and maintenance personnel can begin to conduct a comprehensive evaluation of grounding performance according to the steps of the present invention.

[0290] First, according to step S20, the equivalent grounding resistance of the ring main unit is calculated using the grounding resistance measurement value and the geometric structure parameters of the ring main unit:

[0291]

[0292] Among them, R i is the ground resistance value of the i-th measuring point, ρ is the soil resistivity, which is 100Ω·m, (x j ,y j ,z j ) is the coordinate of the jth grounding point, h is the equivalent burial depth of 0.5m, K s The seasonal correction coefficient is taken as 1.1, L is the total length of the grounding body and is taken as 20m, a and b are the length and width of the grounding grid and are taken as 3m and 4m respectively.

[0293] Substituting the above parameter values ​​into the calculation, we can get: eq =2.95Ω. This shows that the overall grounding resistance of the ring main unit is low and within a reasonable range.

[0294] Next, according to step S30, a set of equations describing the grounding electrothermal coupling process was established:

[0295] 1. Maxwell's equations:

[0296]

[0297] 2. Ohm’s Law Equation:

[0298] J=σ(T)E+σ(T)v×B

[0299] 3. Heat conduction equation:

[0300]

[0301] Where E is the electric field intensity, H is the magnetic field intensity, J is the current density, D is the electric displacement, B is the magnetic induction intensity, ρ v is the volume charge density, σ(T) is the temperature-dependent conductivity, v is the carrier drift velocity, T is the temperature, ρ is the density, C p is the specific heat capacity, k(T) is the temperature-dependent thermal conductivity, Q J is the Joule heat source, Q e is the external heat source, Q r A radiant heat source.

[0302] According to step S40, the operation and maintenance personnel used the finite element method and the time domain difference method to numerically solve the above-mentioned coupling equations, and obtained the numerical solutions of the electric field intensity distribution, current density distribution and temperature distribution. The electric field intensity inside the ring network cabinet is relatively high, with a maximum value of about 2.5kV / m, while the electric field intensity outside the cabinet is relatively low. This is mainly due to the shielding effect of the ring network cabinet itself. The current density inside the ring network cabinet is relatively high, with a maximum value of about 100A / m^2, while the external current density is relatively low. This indicates that there is a relatively concentrated current flow inside the ring network cabinet, which may cause local heating.

[0303] The results of thermal imaging are basically consistent with the fact that the temperature of the ring main unit and its surrounding areas is relatively high, reaching a maximum of about 45°C. This may be due to the combined effect of the heat inside the ring main unit and the external ambient temperature.

[0304] Through the above numerical solution, the operation and maintenance personnel have initially mastered the electromagnetic-thermal coupling characteristics of the ring main unit grounding system. In order to further analyze the specific range of variation of each parameter, they used the Latin hypercube sampling method based on the S60 step and obtained the results in Table 3 below:

[0305] Table 3 Parameter fluctuation table

[0306] parameter Minimum Maximum Mean Standard Deviation <![CDATA[Grounding resistance R g (Ω)]]> 2.75 3.15 2.95 0.12 <![CDATA[Grounding current I g (A)]]> 260 300 280 12 <![CDATA[Ground potential V g (V)]]> 780 900 840 35 <![CDATA[Grounding impedance Z g (Ω)]]> 2.8 3.2 3.0 0.14 <![CDATA[Highest temperature T max (°C)]]> 40 50 45 3

[0307] From the data in the table above, we can see that the grounding resistance of the ring network cabinet fluctuates between 2.75Ω and 3.15Ω, the grounding current is between 260A and 300A, the grounding potential is between 780V and 900V, the grounding impedance is between 2.8Ω and 3.2Ω, and the maximum temperature is between 40℃ and 50℃. Overall, the value ranges of each parameter are relatively reasonable, and no obvious abnormalities occur.

[0308] With the above analysis results, the operation and maintenance personnel built the following grounding performance comprehensive evaluation model according to step S70:

[0309]

[0310] Among them, R std Take 3Ω,I lim Take 400A,V touch Take 80V, Z ref Take 4Ω, T lim Take 70℃. Nonlinear conversion function f i (x) uses the sigmoid function, parameter k i and x 0i They are 4 and 0.6 respectively. The weights of each indicator determined by AHP method are shown above.

[0311] According to step S80, the values ​​of the above parameters are substituted into the evaluation model, and the comprehensive grounding performance index G = 0.55 is calculated. This shows that the grounding status of the ring main unit is generally good, but it still needs regular inspection and maintenance, especially focusing on the two indicators of grounding resistance and temperature.

[0312] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for evaluating grounding of an outdoor ring main unit, characterized in that: Including the following steps: S10. Obtain the grounding resistance values measured at multiple node resistance measurement points around the outdoor ring main unit by a grounding resistance tester; collect the operating data of the outdoor ring main unit, including voltage, current, and power; obtain the temperature distribution data obtained by performing a thermal imaging scan on the outdoor ring main unit; obtain the magnetic field data inside and outside the outdoor ring main unit; S20. Use the multi-point grounding resistance measurement values and the geometric structure of the ring main unit to establish the equivalent grounding resistance of the outdoor ring main unit; S30. Establish a coupled electro-thermal equations system, including Maxwell's equations, Ohm's law equation, continuity equation, boundary condition equation, and heat conduction equation; S40. Based on the finite element method and the finite difference time domain method, numerically solve the coupled electro-thermal equations system to obtain multiple numerical solutions, specifically: numerical solutions of electric field intensity distribution, current density distribution, potential distribution, and temperature distribution; S50. Use the method of separation of variables and series expansion to analytically solve the coupled electro-thermal equations system to obtain multiple analytical solutions, specifically: analytical solutions of electric field intensity, current density, potential, and temperature; S60. Based on the multiple analytical solutions, use the Latin hypercube sampling method to obtain multiple numerical ranges, specifically: grounding resistance range, grounding current range, grounding potential range, grounding impedance range, and temperature range; S70. Establish a grounding evaluation model for the outdoor ring main unit, and substitute the multiple numerical solutions and multiple numerical ranges to obtain a grounding evaluation index; S80. According to the grounding evaluation index, judge the grounding status of the outdoor ring main unit; Among them, the grounding evaluation model for the outdoor ring main unit is specifically expressed as: in, is the weight coefficient, is a nonlinear transfer function: R std is the standard grounding resistance value, I lim To allow for ground current limit, V touch is the safe contact voltage, Z ref is the reference ground impedance, T lim is the temperature limit, and is the parameter of the sigmoid function; I g is the ground current; V g is the ground voltage; Z g is the ground impedance; T max is the maximum temperature; R eq is the equivalent grounding resistance; If G ≤ 0.6, it indicates that the grounding status is good; If 0.6 < G ≤ 0.8, it indicates that the grounding status is average and regular inspections are required; If G > 0.8, it indicates that the grounding status is poor and immediate improvement measures need to be taken.

2. The outdoor ring main unit grounding evaluation method according to claim 1, characterized in that: The equivalent grounding resistance of the outdoor ring main unit is specifically expressed as: Among them, R i is the ground resistance value of the i-th measuring point, n is the total number of measuring points, ρ is the soil resistivity, (x j ,y j ,z j ) is the spatial coordinate of the jth grounding point, m is the total number of grounding points, h is the equivalent burial depth, K s is the seasonal correction factor, L is the total length of the grounding body, and a and b are the length and width of the grounding grid respectively.

3. The outdoor ring main unit grounding evaluation method according to claim 2 is characterized in that: The Maxwell's equations are specifically expressed as: The Ohm's law equation is specifically expressed as: J = σ(T)E + σ(T)v × B; The continuity equation is specifically expressed as: The boundary condition equation is specifically expressed as: The heat conduction equation is specifically expressed as: Among them, E is the electric field intensity, H is the magnetic field intensity, J is the current density, D is the electric displacement, B is the magnetic induction intensity, ε0 ​​is the vacuum dielectric constant, ρ v is the volume charge density, σ(T) is the temperature-dependent conductivity, v is the carrier drift velocity, ρ s is the surface charge density, is the interface normal vector, T is the temperature, is the density, C p is the specific heat capacity, k(T) is the temperature-dependent thermal conductivity, Q J is the Joule heat source, Q e is the external heat source, Q r As a radiant heat source, and Represent the divergence and curl operations respectively.

4. The outdoor ring main unit grounding evaluation method according to claim 3 is characterized in that: The analytical solution of the electric field intensity is specifically expressed as: In the formula, Represents the gradient operator.

5. The outdoor ring main unit grounding assessment method according to claim 4, characterized in that: The analytical solution of the current density is specifically expressed as: J(r, θ, φ) = σ(T)E(r, θ, φ); In the formula, J(r, θ, φ) is the current density vector, σ(T) is the temperature-dependent conductivity, E(r, θ, φ) is the electric field intensity vector, r is the radial distance, θ is the polar angle, φ is the azimuth angle, and T is the temperature.

6. The outdoor ring main unit grounding evaluation method according to claim 5, characterized in that: The analytical solution of the potential is specifically expressed as: Where V(r,θ,φ) is the potential function; ε0 is the vacuum dielectric constant; ∫ V dV′ is the volume integral, where dV′ is the volume element; ∮ S dS′ is the closed surface integral, where dS′ is the area element; ρ v (r′,θ′,φ′) is the volume charge density; ρ s (r′,θ′,φ′) is the surface charge density; is the field point position vector; is the source point position vector; is the distance from the field point to the source point.

7. The outdoor ring main unit grounding assessment method according to claim 6, characterized in that: The analytical solution of the temperature is specifically expressed as: In the formula, T(r, t) is the temperature distribution function; T0 is the initial temperature; k is the thermal conductivity; t is the time; τ is the time integration variable; Q(τ) is the source intensity function; r is the radial distance; α is the thermal diffusivity; exp() is the exponential function.

8. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores program instructions, and when the program instructions are executed, they are used to execute the outdoor ring network cabinet grounding assessment method according to any one of claims 1 to 7.

9. An outdoor ring main unit grounding assessment system, characterized in that: Contains the computer-readable storage medium of claim 8.

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