Gas insulated power transmission equipment insulator surface discrete charge spot numerical calculation method and system

Abstract

The invention relates to a numerical calculation method and system for discrete charge spots on the surface of an insulator of gas insulated power transmission equipment. The numerical calculation method for the discrete charge spots on the surface of the insulator of the gas-insulated power transmission equipment comprises the following steps: firstly, collecting parameter data of the gas-insulated power transmission equipment; building a three-dimensional electro-thermal coupling multi-physical simulation system containing surface traps according to the parameter data in combination with the operating environment of the gas insulated power transmission equipment; and then, a mapping algorithm is utilized to subdivide the mesh of the solution domain, and iterative solution is carried out on the established simulation system to obtain the development characteristics of the discrete charge spots on the surface of the insulator. Compared with the prior art, the method has the advantages that the accuracy and analyzability of simulation results are enhanced, the calculation cost is reduced, and the calculation efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of insulation performance of electrical equipment, and in particular to a method and system for numerically calculating discrete charge spots on the surface of an insulator of a gas-insulated power transmission equipment. Background Art

[0002] Due to the uneven distribution of primary energy between the east and west, my country has been prompted to carry out long-distance and large-capacity power transmission projects. As a new form of power transmission, gas-insulated transmission equipment can meet the rigid requirements of power transmission in many aspects, such as low electromagnetic radiation level, large transmission capacity, low loss, and strong environmental compatibility. At present, gas-insulated switches have been widely recognized and applied. Unlike AC gas-insulated switches, DC gas-insulated switches cannot achieve safe and stable operation at present. One of the main reasons is that during the long-term operation of DC gas-insulated switches, accumulated charges will be generated on the surface of the insulator, which distorts the surface electric field of the insulator and greatly increases the risk of insulator flashover. In addition, the formation of discrete charge spots in the later stage of surface accumulation greatly reduces the insulation characteristics of the equipment. However, the current research on surface charge accumulation is still immature, and the experimental measurement methods are limited, so it is impossible to effectively observe the entire process of charge transport on the surface of the insulator.

[0003] With the widespread application of numerical simulation as an auxiliary research method in electrical engineering, it has been increasingly used to reveal the mechanism of charge accumulation on the surface of insulators and the characteristics of insulation failure in DC gas-insulated transmission equipment. In particular, the auxiliary research of numerical simulation is particularly important in describing the relationship between the macroscopic operating conditions and the microscopic charge transport and injection behavior of carriers under electrostatic fields. However, existing studies usually ignore the influence of microscopic defects on the charge accumulation process when using multi-physics simulation models including electrostatic fields, resulting in the incomplete spatiotemporal evolution characteristics of the surface charge of insulators obtained by simulation calculations.

[0004] The invention patent with publication number CN117634248A discloses a numerical simulation method for calculating the surface charge accumulation of insulators of gas insulated switchgear (GIS). By building a three-dimensional simulation model, this method can accurately simulate the spatial distribution characteristics of the surface charge, strengthen the corroboration relationship with the experimental observation results, and provide convenience for researchers to deeply explore the diverse mechanisms of charge behavior. However, it does not consider the influence of surface traps on charge behavior, and its simulation results cannot accurately restore the uneven conduction process of the surface charge accumulation of insulators of DC gas insulated transmission equipment to form discrete charge spots, which makes its results lack accuracy. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a method and system for numerically calculating discrete charge spots on the surface of insulators of gas-insulated power transmission equipment.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] According to one aspect of the present invention, a method for numerically calculating discrete charge spots on the surface of an insulator of a gas-insulated power transmission equipment is provided, the method steps comprising:

[0008] S1. Collect parameter data of gas-insulated transmission equipment;

[0009] S2. Combined with the operating environment of gas-insulated transmission equipment, a three-dimensional electric-thermal coupling multi-physics simulation system with surface traps is built based on parameter data;

[0010] S3. Using the mapping algorithm, the grid of the solution domain is divided, and the established simulation system is iteratively solved to obtain the development characteristics of discrete charge spots on the insulator surface.

[0011] As a preferred technical solution, the parameter data in S1 includes geometric parameters, thermal parameters of each component, electrostatic parameters and characteristic parameters of the operating environment.

[0012] As a preferred technical solution, the geometric parameters include the insulator surface geometry, curvature, material thickness, gas insulation area size and cavity size; the thermal parameters include thermal conductivity, specific heat capacity and density; the electrostatic parameters include relative dielectric constant and conductivity; the characteristic parameters of the operating environment include external temperature, gas type and pressure, insulating gas flow rate, gas humidity and operating voltage under stable operating conditions.

[0013] As a preferred technical solution, the three-dimensional electro-thermal coupled multi-physics simulation system in S2 includes a three-dimensional geometric model and a physical field model, wherein the physical field model includes a solid heat transfer model, an electrostatic field model and a surface trap model.

[0014] As a preferred technical solution, the surface trap model is jointly established by the Schottky emission equation, the carrier trapping and carrier de-trapping probability equations.

[0015] As a preferred technical solution, the Schottky emission equation characterizes the injection of carriers at the gas-solid interface, and its specific formula is:

[0016]

[0017]

[0018] Where j(0,t) is the current density generated when the carriers are injected at the cathode; j(d,t) is the current density generated when the carriers are injected at the anode; A is the Richardson constant; E is the electric field strength; E in(h) is the built-in electric field strength, ε0 is the air dielectric constant; ε r is the relative dielectric constant; k B is the Boltzmann constant; T is the temperature.

[0019] As a preferred technical solution, the probability equations for carrier trapping and carrier detrapping in surface traps are specifically:

[0020] P tr =q e N t μ0 / ε0ε r

[0021] P de =v ATE exp(-E t / k B T)

[0022] Where P tr is the carrier trapping probability; P de is the carrier detrapping probability; q e is the electron charge; μ0 is the mobility; N t is the trap density; ε0 is the empty dielectric constant; ε r is the relative dielectric constant ν ATE is the escape frequency of carriers; E t is the trap depth; k B is the Boltzmann constant; T is the temperature.

[0023] As a preferred technical solution, the mesh generation in S3 adopts a non-uniform mesh generation algorithm, and the specific process of the mesh generation is as follows: first, a coarse regular tetrahedral global mesh is generated, and then the area requiring fine mesh is encrypted and the boundary is adapted based on the geometric curvature, so as to make the insulator part the focus of the calculation of this model; when the solution accuracy requirement is high, the original unstructured grid points are mapped to the grid points of the structured grid through a mapping algorithm to form a uniform regular tetrahedral grid structure, and the entire insulator is uniformly divided through a sweeping algorithm.

[0024] As a preferred technical solution, the development characteristics of discrete charge spots on the insulator surface in S3 include the distribution of charges at each point on the insulator surface, the electric field, the surface charge density and the surface injection current characteristics. The specific process of iteratively solving the established simulation system is: first, solving the simulation system through a solver to obtain its electric field distribution and potential distribution, then setting the surface charge boundary conditions, and iteratively solving the simulation system under the boundary conditions. In each iteration, the electric field distribution is updated and the surface charge density is calculated, and the error is calculated synchronously. The iteration is stopped when the error threshold or the change in the electric field is less than the preset value.

[0025] According to another aspect of the present invention, a system for numerical calculation of discrete charge spots on the surface of insulators of gas-insulated power transmission equipment is provided. The system works by applying a method for numerical calculation of discrete charge spots on the surface of insulators of gas-insulated power transmission equipment as described above. The system includes a data collection module, a system building module and an iterative solution module.

[0026] Among them, the data collection module is used to collect parameter data of gas-insulated transmission equipment; the system construction module is used to combine the operating environment of gas-insulated transmission equipment, and build a three-dimensional electric-thermal coupling multi-physics simulation system containing surface traps based on parameter data; the iterative solution module is used to use the mapping algorithm to divide the grid of the solution domain, and iteratively solve the established simulation system to obtain the development characteristics of discrete charge spots on the insulator surface.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. In the numerical calculation method of discrete charge spots on the surface of insulators of gas-insulated power transmission equipment of the present invention, the parameter data of the gas-insulated power transmission equipment is first collected; then, in combination with the operating environment of the gas-insulated power transmission equipment, a three-dimensional electric-thermal coupling multi-physics simulation system containing surface traps is built based on the parameter data; then, the mapping algorithm is used to divide the grid of the solution domain, and the established simulation system is iteratively solved to obtain the development characteristics of discrete charge spots on the surface of the insulator. It can accurately restore the uneven conduction process of the charge accumulation on the surface of the insulator of the DC gas-insulated power transmission equipment to form discrete charge spots, and obtain the refined development characteristics of the charge spot morphology on the insulator surface from seconds to hours in a three-dimensional perspective, thereby improving the accuracy and analytical nature of the simulation results.

[0029] 2. The present invention establishes a three-dimensional electro-thermal coupling multi-physics simulation system, in which the physical field models include a solid heat transfer model, an electrostatic field model and a surface trap model, wherein the electrostatic field model is jointly established by the Poisson equation, gas conductivity and solid conductivity; the surface trap model is jointly established by the Schottky emission equation, the carrier trap equation and the carrier de-trap equation; the solid heat transfer model is jointly established by the Fourier heat transfer, the Navier-Stokes equation and the energy emission equation. By combining the solid heat transfer model, the electrostatic field model and the surface trap model, the complex physical processes occurring inside the gas-insulated power transmission equipment can be fully described, making the simulation closer to the actual working conditions.

[0030] 3. The meshing method of the present invention adopts a non-uniform meshing algorithm, and the specific meshing process is as follows: first, a rough regular tetrahedron global mesh is generated, and then the area requiring fine mesh is encrypted and adapted to the boundary based on the geometric curvature, so as to focus on the calculation of the insulator part of the model; when the solution accuracy requirement is high, the original unstructured grid points are mapped to the grid points of the structured grid through the mapping algorithm to form a uniform regular tetrahedral grid structure, and the entire insulator is uniformly meshed through the sweeping algorithm. The calculation efficiency is improved and the calculation cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the method steps for numerically calculating discrete charge spots on the surface of an insulator of a gas-insulated power transmission equipment in the present invention;

[0032] Figure 2 A schematic diagram of the logic framework of a simulation system for a numerical simulation method for calculating charge accumulation on the surface of an insulator of a GIS device in the present invention;

[0033] Figure 3a Schematic diagram of the three-dimensional geometric model for numerical calculation of discrete charge spots on the surface of insulators of gas-insulated power transmission equipment proposed in the present invention

[0034] Figure 3b A mesh division diagram of a three-dimensional geometric model for numerical calculation of discrete charge spots on the surface of an insulator of a gas-insulated power transmission equipment proposed by the present invention;

[0035] Figure 4a Schematic diagram of three-dimensional simulated surface charge spots when the discrete charge spots develop when the simulation time is 120s in the embodiment;

[0036] Figure 4b Schematic diagram of three-dimensional simulated surface charge spots when the discrete charge spots develop when the simulation time is 4080s in the embodiment;

[0037] Figure 4c Schematic diagram of three-dimensional simulated surface charge spots when the discrete charge spots develop when the simulation time is 9960s in the embodiment;

[0038] Figure 5a Schematic diagram of the three-dimensional simulated surface electric field distribution of the discrete charge spots when the simulation time is 120s in the embodiment;

[0039] Figure 5b Schematic diagram of the three-dimensional simulated surface electric field distribution of the discrete charge spots when the simulation time is 4080s in the embodiment;

[0040] Figure 5c Schematic diagram of the three-dimensional simulated surface electric field distribution of the discrete charge spots when the simulation time is 9960s in the embodiment;

[0041] Figure 6a This is a numerical distribution diagram of the charge injection rate at the gas-solid interface along the radial direction when the simulation time of the embodiment is 120s;

[0042] Figure 6b This is a numerical distribution diagram of the charge injection rate at the gas-solid interface along the radial direction when the simulation time is 4080s in the embodiment;

[0043] Figure 6c It is a numerical distribution diagram of the charge injection rate at the gas-solid interface along the radial direction when the simulation time is 9960s in the embodiment. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0045] Due to the uneven distribution of primary energy between the east and west, my country has been prompted to carry out long-distance and large-capacity power transmission projects. As a new form of power transmission, gas-insulated transmission equipment can meet the rigid requirements of power transmission in many aspects, such as low electromagnetic radiation level, large transmission capacity, low loss, and strong environmental compatibility. At present, gas-insulated switches have been widely recognized and applied. Unlike AC gas-insulated switches, DC gas-insulated switches cannot achieve safe and stable operation at present. One of the main reasons is that during the long-term operation of DC gas-insulated switches, accumulated charges will be generated on the surface of the insulator, which distorts the surface electric field of the insulator and greatly increases the risk of insulator flashover. In addition, the formation of discrete charge spots in the later stage of surface accumulation greatly reduces the insulation characteristics of the equipment. However, the current research on surface charge accumulation is still immature, and the experimental measurement methods are limited, so it is impossible to effectively observe the entire process of charge transport on the surface of the insulator.

[0046] With the widespread application of numerical simulation as an auxiliary research method in electrical engineering, it has been increasingly used to reveal the mechanism of charge accumulation on the surface of insulators and the characteristics of insulation failure in DC gas-insulated transmission equipment. In particular, the auxiliary research of numerical simulation is particularly important in describing the relationship between the macroscopic operating conditions and the microscopic charge transport and injection behavior of carriers under electrostatic fields. However, when using multi-physics simulation models including electrostatic fields, existing studies usually ignore the influence of microscopic defects on the charge accumulation process, resulting in the incomplete spatiotemporal evolution characteristics of the insulator surface charge obtained by simulation calculation. Therefore, the numerical simulation method for the behavior of charge accumulation on the surface of insulators in DC gas-insulated transmission equipment to generate discrete charge spots needs to be further improved.

[0047] Example 1

[0048] In this embodiment, a numerical calculation method for discrete charge spots on the surface of gas-insulated switchgear insulators is applied to analyze the development of discrete charge spots on the surface of insulators of actual gas-insulated transmission equipment, and trap defects and thermal field distribution of the insulator surface material are added to establish an electric-thermal coupling model to obtain the charge and electric field intensity distribution on the insulator surface, thereby providing guidance for the insulation optimization design of DC gas-insulated transmission equipment.

[0049] The present embodiment uses a method for numerically calculating discrete charge spots on the surface of an insulator of a gas-insulated power transmission device. The method steps are as follows: Figure 1 As shown, including:

[0050] S1. Collect parameter data of gas-insulated transmission equipment;

[0051] S2. Combined with the operating environment of gas-insulated transmission equipment, a three-dimensional electric-thermal coupling multi-physics simulation system with surface traps is built based on parameter data;

[0052] S3. Using the mapping algorithm, the grid of the solution domain is divided, and the established simulation system is iteratively solved to obtain the development characteristics of discrete charge spots on the insulator surface.

[0053] In this method, the parameter data in S1 include geometric parameters, thermal parameters of each component, electrostatic parameters and characteristic parameters of the operating environment.

[0054] In the method, the geometric parameters include the insulator surface geometry, curvature, material thickness, gas insulation area size and cavity size; the thermal parameters include thermal conductivity, specific heat capacity and density; the electrostatic parameters include relative dielectric constant and conductivity; the characteristic parameters of the operating environment include external temperature, gas type and pressure, insulating gas flow velocity, gas humidity and operating voltage under stable operating conditions.

[0055] In this method, the three-dimensional electro-thermal coupling multi-physics simulation system in S2 includes a three-dimensional geometric model and a physical field model, wherein the physical field model includes a solid heat transfer model, an electrostatic field model and a surface trap model. The surface trap model is jointly established by the Schottky emission equation, the carrier trapping and the carrier de-trapping probability equations.

[0056] Among them, the Schottky emission equation characterizes the injection of carriers at the gas-solid interface, and its specific formula is:

[0057]

[0058] Where j(0,t) is the current density generated when the carriers are injected at the cathode; j(d,t) is the current density generated when the carriers are injected at the anode; A is the Richardson constant; E is the electric field strength; E in(h) is the built-in electric field strength, ε0 is the air dielectric constant; ε r is the relative dielectric constant; k B is the Boltzmann constant; T is the temperature.

[0059] Among them, the probability equations of carrier trapping and carrier detrapping in surface traps are specifically:

[0060] P tr =q e N t μ0 / ε0ε r

[0061] P de =v ATE exp(-E t / k B T)

[0062] Where P tr is the carrier trapping probability; P de is the carrier detrapping probability; q e is the electron charge; μ0 is the mobility; N t is the trap density; ε0 is the empty dielectric constant; ε r is the relative dielectric constant ν ATE is the escape frequency of carriers; E t is the trap depth; k B is the Boltzmann constant; T is the temperature.

[0063] In this method, the mesh generation in S3 adopts a non-uniform mesh generation algorithm, and the specific process of mesh generation is as follows: first, a coarse regular tetrahedral global mesh is generated, and then the area requiring fine mesh is encrypted and the boundary is adapted based on the geometric curvature, so as to make the insulator part the focus of the calculation of this model; when the solution accuracy requirement is high, the original unstructured grid points are mapped to the grid points of the structured grid through the mapping algorithm to form a uniform regular tetrahedral grid structure, and the entire insulator is uniformly divided through the sweeping algorithm.

[0064] In this method, the development characteristics of discrete charge spots on the insulator surface in S3 include the distribution of charges at each point on the insulator surface, the electric field, the surface charge density and the surface injection current characteristics. The specific process of iteratively solving the established simulation system is as follows: first, the simulation system is solved by a solver to obtain its electric field distribution and potential distribution, and then the surface charge boundary conditions are set, and the simulation system is iteratively solved under the boundary conditions. In each iteration, the electric field distribution is updated and the surface charge density is calculated, and the error is calculated synchronously. The iteration is stopped when the error threshold or the change in the electric field is less than the preset value.

[0065] In this embodiment, firstly, according to the high-voltage gas-insulated power transmission equipment actually put into operation, key geometric parameters, thermal parameters of each component, electrostatic parameters and characteristic parameters of the operating environment are collected and recorded; then, according to the key parameter data obtained, a three-dimensional electric-thermal coupling multi-physics field simulation model is built according to the specific operating environment of the gas-insulated power transmission equipment, including a solid heat transfer model, an electrostatic field model, a surface trap model and a charge injection model; then, according to the key parameter data and the three-dimensional electric-thermal coupling multi-physics field simulation model, the boundary conditions, initial operating conditions and model constraints of the three-dimensional electric-thermal coupling model are set to determine the calculation accuracy range of the simulation; finally, according to the characteristics of charge accumulation and development, the grid of the solution domain is evenly divided through a mapping algorithm, the established mathematical model is numerically solved, and the distribution of surface charges at each point on the surface of the insulator is gradually calculated. The electric field, surface charge density, and the corresponding surface injection current characteristics are solved by an iterative method.

[0066] In this embodiment, important geometric parameters include the surface geometry, curvature, material thickness, gas insulation area size, and cavity size of the insulator; thermal parameters and electrostatic parameters of various components of the GIS equipment, thermal parameters include thermal conductivity, specific heat capacity, density, etc.; electrostatic parameters include relative dielectric constant, electrical conductivity, etc.; operating environment characteristic parameters include external temperature, gas type and pressure, insulating gas flow rate, gas humidity, and operating voltage under stable operating conditions.

[0067] In this embodiment, COMSOL Multiphysics multi-physics field simulation software is used to establish a GIS insulator three-dimensional electric-thermal multi-physics field coupling system that meets the actual engineering application size; the structure of the three-dimensional electric-thermal multi-physics field coupling system is as follows: Figure 2 As shown, it specifically includes: electrostatic field model, solid heat transfer model, bulk conductivity model in solid dielectrics, charge transfer model of gas-solid interface, Schottky emission model, and charge transfer model including electron traps.

[0068] Among them, the electrostatic field model is jointly established by Poisson's equation, gas conductivity and solid conductivity; the surface trap model is jointly established by Schottky emission equation, carrier trapping equation and carrier detrapping equation; the solid heat transfer model is jointly established by Fourier heat transfer, Navier-Stokes equations and energy emission equation.

[0069] The charge accumulation mechanism on the insulator surface can be expressed by the first-order kinetic equation:

[0070]

[0071] Where σ represents the charge density per unit surface area; J In and J Gn are the normal current density on the solid side and the gas side respectively; E r is the tangential component of the electric field at the gas-solid interface; γ s is the surface conductivity of the insulator.

[0072] Among them, the expression of the charge injected into the solid side of the insulator gas-solid interface is:

[0073]

[0074] γ vi (E) = γ g e βE

[0075] In the formula, J I is the current density on the solid side; E is the electric field intensity; D is the electric displacement vector on the solid side; γ vi is the conductivity of the solid block; β is the electric field strength coefficient of the conductivity on the solid side, which is taken as 0.1mm / kV.

[0076] Among them, the expression of charge generation and diffusion on the gas side is:

[0077]

[0078] Where D is the electric displacement vector; e is the unit charge, which is 1.6×10 -19 C;n + and n - is the density of positive and negative ions; b+ and b - is the mobility of positive and negative ions; k r is the composite coefficient, taking 2.27×10 -13 m 3 / s; N IP is the natural ionization coefficient, taking 29cm -3 s -1 .

[0079] The electric field distribution in the cavity is expressed by the Laplace equation:

[0080]

[0081] In the formula, is the electric potential at that point, E is the electric field strength at that point, n + and n - is the number of positive and negative charges, ρ is the charge density;

[0082] The Schottky thermoelectric emission equation characterizes the injection of carriers at the gas-solid interface, and the expression is as follows:

[0083]

[0084] In addition, the behaviors of carrier entry and de-entrapment probabilities in surface traps are described by the following formula:

[0085]

[0086] P tr =q e N t μ0 / ε0ε r

[0087] P de =v ATE exp(-E t / k B T)

[0088] Where j(0,t) and j(d,t) are the current densities generated when carriers are injected into the cathode / anode, A / m 2 , A is the Richardson constant; q trap and q free It is divided into trapped charge and free charge density in the solid surface layer; P tr and P de are the capture probability and de-trapping probability of carriers, respectively; ν ATE is the carrier escape frequency, s -1 . N t is the trap density, eV -1 m -3; Et is the trap depth, eV; K is the temperature; h is Planck's constant, J·s; k B is the Boltzmann constant, J.K. -1 .

[0089] Among them, the heat transfer between solid and fluid is expressed by the following expression:

[0090]

[0091]

[0092] Where u is the gas flow rate, m·s -1 ; Q is the heat source generated by the central conductor, W·m -3 ; P is the gas pressure, Pa; μ is the dynamic viscosity coefficient, Pa·s; g is the gravitational acceleration, m / s 2 ; Sulfur hexafluoride gas density ρ(kg / m 3 ) is calculated by (14); M is the average molar mass of sulfur hexafluoride, kg / mol; R is the gas constant.

[0093] As shown in Figure 3, Figure 3a Schematic diagram of the three-dimensional geometric model for numerical calculation of discrete charge spots on the surface of insulators of gas-insulated transmission equipment. Figure 3b This is a mesh division diagram of the three-dimensional geometric model for the numerical calculation of discrete charge spots on the surface of insulators of gas-insulated transmission equipment. In the figure, the mesh division adopts uniform division to remove the discrete charge spot results caused by the influence of the mesh.

[0094] Figure 4a , 4b and 4c are schematic diagrams of the three-dimensional simulated surface charge spots when the discrete charge spots develop at simulation times of 120 s, 4080 s, and 9960 s, respectively; Figure 5a , 5b and 5c are schematic diagrams of the three-dimensional simulated surface electric field distribution of the discrete charge spots when the simulation time is 120s, 4080s and 9960s respectively; Figure 6a , 6b 6c are the numerical distributions of the charge injection rate along the radial direction at the gas-solid interface when the simulation time is 120s, 4080s and 9960s respectively. As shown in Figures 4, 5 and 6, the electric-thermal multi-physics field coupling model of charge accumulation on the insulator surface can accurately simulate the drift and diffusion of charged particles in the insulating gas, the charge accumulation morphology on the insulator surface at the time scale of seconds to hours, the temporal and spatial distribution characteristics of the electric field distortion induced by charge accumulation on the insulator surface, the generation and development process of charge spots on the gas-solid interface surface, and output three-dimensional visualized calculation results, which is helpful to analyze the uneven conduction process on the insulator surface and the influencing mechanism of charge spot formation.

[0095] In summary, this method can accurately restore the uneven conduction process of charge accumulation on the insulator surface of DC gas-insulated transmission equipment to form discrete charge spots, and obtain the refined development characteristics of the charge spot morphology on the insulator surface from seconds to hours in a three-dimensional perspective, which improves the accuracy and analytical nature of the simulation results and further deepens the depth and breadth of theoretical research.

[0096] Example 2

[0097] In this embodiment, a numerical calculation system for discrete charge spots on the surface of insulators of gas-insulated switchgear is applied to analyze the development of discrete charge spots on the surface of insulators of actual gas-insulated transmission equipment, and trap defects and thermal field distribution of the insulator surface material are added to establish an electric-thermal coupling model to obtain the charge and electric field intensity distribution on the insulator surface, thereby providing guidance for the insulation optimization design of DC gas-insulated transmission equipment.

[0098] The system includes a data collection module, a system building module and an iterative solution module. The data collection module is used to collect parameter data of gas-insulated transmission equipment; the system building module is used to combine the operating environment of gas-insulated transmission equipment and build a three-dimensional electric-thermal coupling multi-physics simulation system with surface traps based on parameter data; the iterative solution module is used to use a mapping algorithm to divide the grid of the solution domain and iteratively solve the established simulation system to obtain the development characteristics of discrete charge spots on the insulator surface.

[0099] In this embodiment, firstly, according to the high-voltage gas-insulated power transmission equipment actually put into operation, key geometric parameters, thermal parameters of each component, electrostatic parameters and characteristic parameters of the operating environment are collected and recorded; then, according to the key parameter data obtained, a three-dimensional electric-thermal coupling multi-physics field simulation model is built according to the specific operating environment of the gas-insulated power transmission equipment, including a solid heat transfer model, an electrostatic field model, a surface trap model and a charge injection model; then, according to the key parameter data and the three-dimensional electric-thermal coupling multi-physics field simulation model, the boundary conditions, initial operating conditions and model constraints of the three-dimensional electric-thermal coupling model are set to determine the calculation accuracy range of the simulation; finally, according to the characteristics of charge accumulation and development, the grid of the solution domain is evenly divided through a mapping algorithm, the established mathematical model is numerically solved, and the distribution of surface charges at each point on the surface of the insulator is gradually calculated. The electric field, surface charge density, and the corresponding surface injection current characteristics are solved by an iterative method.

[0100] In this embodiment, important geometric parameters include the surface geometry, curvature, material thickness, gas insulation area size, and cavity size of the insulator; thermal parameters and electrostatic parameters of various components of the GIS equipment, thermal parameters include thermal conductivity, specific heat capacity, density, etc.; electrostatic parameters include relative dielectric constant, electrical conductivity, etc.; operating environment characteristic parameters include external temperature, gas type and pressure, insulating gas flow rate, gas humidity, and operating voltage under stable operating conditions.

[0101] In this embodiment, COMSOL Multiphysics multi-physics field simulation software is used to establish a GIS insulator three-dimensional electric-thermal multi-physics field coupling system that meets the actual engineering application size; the structure of the three-dimensional electric-thermal multi-physics field coupling system is as follows: Figure 2 As shown, it specifically includes: electrostatic field model, solid heat transfer model, bulk conductivity model in solid dielectrics, charge transfer model of gas-solid interface, Schottky emission model, and charge transfer model including electron traps.

[0102] Among them, the electrostatic field model is jointly established by Poisson's equation, gas conductivity and solid conductivity; the surface trap model is jointly established by Schottky emission equation, carrier trapping equation and carrier detrapping equation; the solid heat transfer model is jointly established by Fourier heat transfer, Navier-Stokes equations and energy emission equation.

[0103] The charge accumulation mechanism on the insulator surface can be expressed by the first-order kinetic equation:

[0104]

[0105] Where σ represents the charge density per unit surface area; J In and J Gn are the normal current density on the solid side and the gas side respectively; E r is the tangential component of the electric field at the gas-solid interface; γ s is the surface conductivity of the insulator.

[0106] Among them, the expression of the charge injected into the solid side of the insulator gas-solid interface is:

[0107]

[0108] γ vi (E) = γ g e βE

[0109] In the formula, J I is the current density on the solid side; E is the electric field intensity; D is the electric displacement vector on the solid side; γ vi is the conductivity of the solid block; β is the electric field strength coefficient of the conductivity on the solid side, which is taken as 0.1mm / kV.

[0110] Among them, the expression of charge generation and diffusion on the gas side is:

[0111]

[0112] Where D is the electric displacement vector; e is the unit charge, which is 1.6×10 -19 C;n + and n - is the density of positive and negative ions; b + and b - is the mobility of positive and negative ions; k r is the composite coefficient, taking 2.27×10 -13 m 3 / s; N IP is the natural ionization coefficient, taking 29cm -3 s -1 .

[0113] The electric field distribution in the cavity is expressed by the Laplace equation:

[0114]

[0115] In the formula, is the electric potential at that point, E is the electric field strength at that point, n + and n - is the number of positive and negative charges, ρ is the charge density;

[0116] The Schottky thermoelectric emission equation characterizes the injection of carriers at the gas-solid interface, and the expression is as follows:

[0117]

[0118] In addition, the behaviors of carrier entry and de-entrapment probabilities in surface traps are described by the following formula:

[0119]

[0120] P tr =q e N t μ0 / ε0ε r

[0121] P de =v ATE exp(-E t / k B T)

[0122] Where j(0,t) and j(d,t) are the current densities generated when carriers are injected into the cathode / anode, A / m 2 , A is the Richardson constant; q trap and q freeIt is divided into trapped charge and free charge density in the solid surface layer; P tr and P de are the capture probability and de-trapping probability of carriers, respectively; ν ATE is the carrier escape frequency, s -1 . N t is the trap density, eV -1 m -3 ; Et is the trap depth, eV; K is the temperature; h is Planck's constant, J·s; k B is the Boltzmann constant, J.K. -1 .

[0123] Among them, the heat transfer between solid and fluid is expressed by the following expression:

[0124]

[0125] Where u is the gas flow rate, m·s -1 ; Q is the heat source generated by the central conductor, W·m -3 ; P is the gas pressure, Pa; μ is the dynamic viscosity coefficient, Pa·s; g is the gravitational acceleration, m / s 2 ; Sulfur hexafluoride gas density ρ(kg / m 3 ) is calculated by (14); M is the average molar mass of sulfur hexafluoride, kg / mol; R is the gas constant.

[0126] As shown in Figure 3, Figure 3a Schematic diagram of the three-dimensional geometric model for numerical calculation of discrete charge spots on the surface of insulators of gas-insulated transmission equipment. Figure 3b This is a mesh division diagram of the three-dimensional geometric model for the numerical calculation of discrete charge spots on the surface of insulators of gas-insulated transmission equipment. In the figure, the mesh division adopts uniform division to remove the discrete charge spot results caused by the influence of the mesh.

[0127] Figure 4a , 4b and 4c are schematic diagrams of the three-dimensional simulated surface charge spots when the discrete charge spots develop at simulation times of 120 s, 4080 s, and 9960 s, respectively; Figure 5a , 5b and 5c are schematic diagrams of the three-dimensional simulated surface electric field distribution of the discrete charge spots when the simulation time is 120s, 4080s and 9960s respectively; Figure 6a , 6b6c are the numerical distributions of the charge injection rate along the radial direction at the gas-solid interface when the simulation time is 120s, 4080s and 9960s respectively. As shown in Figures 4, 5 and 6, the electric-thermal multi-physics field coupling model of charge accumulation on the insulator surface can accurately simulate the drift and diffusion of charged particles in the insulating gas, the charge accumulation morphology on the insulator surface at the time scale of seconds to hours, the temporal and spatial distribution characteristics of the electric field distortion induced by charge accumulation on the insulator surface, the generation and development process of charge spots on the gas-solid interface surface, and output three-dimensional visualized calculation results, which is helpful to analyze the uneven conduction process on the insulator surface and the influencing mechanism of charge spot formation.

[0128] In summary, this system can accurately restore the uneven conduction process of charge accumulation on the insulator surface of DC gas-insulated transmission equipment to form discrete charge spots, and obtain the refined development characteristics of the charge spot morphology on the insulator surface from seconds to hours in a three-dimensional perspective, which improves the accuracy and analytical nature of the simulation results and further deepens the depth and breadth of theoretical research.

[0129] The above is only a specific embodiment 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 various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for numerically calculating discrete charge spots on the surface of insulators of gas-insulated power transmission equipment, characterized in that: The method steps include: S1. Collect parameter data of gas-insulated transmission equipment; S2. Combined with the operating environment of gas-insulated transmission equipment, a three-dimensional electric-thermal coupling multi-physics simulation system with surface traps is built based on parameter data; S3. Using the mapping algorithm, the grid of the solution domain is divided, and the established simulation system is iteratively solved to obtain the development characteristics of discrete charge spots on the insulator surface.

2. The method for numerically calculating discrete charge spots on the surface of insulators of gas-insulated power transmission equipment according to claim 1, characterized in that: The parameter data in S1 include geometric parameters, thermal parameters of each component, electrostatic parameters and characteristic parameters of the operating environment.

3. The method for numerically calculating discrete charge spots on the surface of insulators of gas-insulated power transmission equipment according to claim 2, characterized in that: The geometric parameters include the insulator surface geometry, curvature, material thickness, gas insulation area size and cavity size; the thermal parameters include thermal conductivity, specific heat capacity and density; the electrostatic parameters include relative dielectric constant and conductivity; the characteristic parameters of the operating environment include external temperature, gas type and pressure, insulating gas flow rate, gas humidity and operating voltage under stable operating conditions.

4. The method for numerically calculating discrete charge spots on the surface of insulators of gas-insulated power transmission equipment according to claim 1, characterized in that: The three-dimensional electro-thermal coupled multi-physics simulation system in S2 includes a three-dimensional geometric model and a physical field model, wherein the physical field model includes a three-dimensional geometric model and a physical field model; wherein the physical field model includes a solid heat transfer model, an electrostatic field model and a surface trap model.

5. The method for numerically calculating discrete charge spots on the surface of insulators of gas-insulated power transmission equipment according to claim 4, characterized in that: The electrostatic field model is jointly established by Poisson's equation, gas conductivity and solid conductivity; the surface trap model is jointly established by Schottky emission equation, carrier trapping equation and carrier detrapping equation; The solid heat transfer model is jointly established by Fourier heat transfer, Navier-Stokes equations and energy emission equations.

6. A method for numerically calculating discrete charge spots on the surface of insulators of gas-insulated power transmission equipment according to claim 5, characterized in that: The Schottky emission equation characterizes the injection of carriers at the gas-solid interface, and its specific formula is: Where j(0,t) is the current density generated when the carriers are injected at the cathode; j(d,t) is the current density generated when the carriers are injected at the anode; A is the Richardson constant; E is the electric field strength; E in(h) is the built-in electric field strength, ε0 is the air dielectric constant; ε r is the relative dielectric constant; k B is the Boltzmann constant; T is the temperature.

7. The method for numerically calculating discrete charge spots on the surface of insulators of gas-insulated power transmission equipment according to claim 5, characterized in that: The probability equations of carrier trapping and carrier detrapping in the surface trap are specifically: P tr =q e N t m0 / e0e r P de =v ATE exp(-E t / k B T) Where P tr is the carrier trapping probability; P de is the carrier detrapping probability; q e is the electron charge; μ0 is the mobility; N t is the trap density; ε0 is the empty dielectric constant; ε r is the relative dielectric constant ν ATE is the escape frequency of carriers; E t is the trap depth; k B is the Boltzmann constant; T is the temperature.

8. The method for numerically calculating discrete charge spots on the surface of insulators of gas-insulated power transmission equipment according to claim 1, characterized in that: The mesh generation in S3 adopts a non-uniform mesh generation algorithm, and the specific process of the mesh generation is as follows: first, a rough regular tetrahedral global mesh is generated, and then the area requiring a fine mesh is encrypted and the boundary is adapted based on the geometric curvature, so that the insulator part is the focus of the calculation of this model; when the solution accuracy requirement is high, the original unstructured grid points are mapped to the grid points of the structured grid through a mapping algorithm to form a uniform regular tetrahedral grid structure, and the entire insulator is uniformly divided through a sweeping algorithm.

9. The method for numerically calculating discrete charge spots on the surface of insulators of gas-insulated power transmission equipment according to claim 1, characterized in that: The development characteristics of discrete charge spots on the insulator surface in S3 include the distribution of charges at each point on the insulator surface, the electric field, the surface charge density and the surface injection current characteristics. The specific process of iteratively solving the established simulation system is as follows: first, solving the simulation system through a solver to obtain its electric field distribution and potential distribution, then setting the surface charge boundary conditions, and iteratively solving the simulation system under the boundary conditions. In each iteration, the electric field distribution is updated and the surface charge density is calculated, and the error is calculated synchronously. The iteration is stopped when the error threshold or the change in the electric field is less than the preset value.

10. A numerical calculation system for discrete charge spots on the surface of insulators of gas-insulated power transmission equipment, characterized in that: The system works by applying a method for numerically calculating discrete charge spots on the surface of an insulator of a gas-insulated power transmission equipment as described in claims 1 to 9, and the system includes a data collection module, a system building module and an iterative solution module; The data collection module is used to collect parameter data of the gas-insulated power transmission equipment; The system building module is used to build a three-dimensional electric-thermal coupling multi-physics simulation system containing surface traps based on parameter data in combination with the operating environment of the gas-insulated power transmission equipment; The iterative solution module is used to utilize a mapping algorithm to divide the grid of the solution domain, and to iteratively solve the established simulation system to obtain the development characteristics of discrete charge spots on the surface of the insulator.

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