A method for design checking and optimization of outer insulation of extra-high voltage bushing in complex environment

Abstract

This invention belongs to the field of power technology and relates to a method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments. The method includes: acquiring parameters; constructing a finite element model; simulating the electric field under normal operating conditions; determining key locations; extracting the peak electric field intensity at key locations under three complex operating conditions; and judgment and optimization. This invention accurately simulates real operating environments such as high humidity and contamination by constructing simulation models for three typical complex operating conditions: discontinuous water film, a wet contamination layer containing a dry strip, and a locally wet contamination layer. It effectively characterizes the abrupt changes in the dielectric properties of the dielectric material under complex environments and the resulting solid-liquid-gas three-phase interface effect. Simultaneously, by comparing the peak electric field intensity under complex operating conditions with the preset critical discharge electric field intensity, it scientifically assesses the deterioration impact of complex environments on high-risk areas, accurately determines whether the original design meets the insulation safety requirements under complex operating conditions, and optimizes designs with potential safety hazards.

Description

Technical Field

[0001] This invention belongs to the field of power technology and relates to a method for design verification and optimization of external insulation of ultra-high voltage bushings under complex environments. Background Technology

[0002] With the rapid development of ultra-high voltage power systems, bushings, as the core insulating connection components between key equipment such as transformers, reactors, and GIS and lines, undertake multiple functions of conductive conduction, insulation isolation, and mechanical support. Their external insulation performance directly determines the safety margin and operational reliability of the entire power transmission and transformation system.

[0003] Currently, conventional design methods for the external insulation of ultra-high voltage bushings all assume a clean, dry, and interference-free ideal atmospheric environment as the simulation premise. They conduct two-dimensional / three-dimensional electric field numerical simulations by constructing a homogeneous insulating medium model, and calculate the insulation margin and determine the insulation structure parameters based on the uniform electric field distribution law.

[0004] However, this design method has many shortcomings: First, it ignores complex environmental factors such as high humidity, dirt adhesion, and discontinuous water film, resulting in significant deviations between simulation verification results and actual on-site operating conditions, thus losing its reference accuracy; Second, it does not consider environmentally induced abrupt changes in dielectric properties and solid-liquid-gas three-phase interface effects, making it impossible to accurately predict the risk of local electric field concentration and flashover discharge in actual operation, which can easily lead to conservative insulation design or insufficient safety margin; Third, it does not locate the key area of ​​peak electric field intensity of the outer insulation of the bushing, making it difficult to specifically analyze the deterioration effect of complex environment on high-risk parts and to accurately identify potential insulation safety hazards. Summary of the Invention

[0005] The purpose of this invention is to provide a method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments. This method can couple complex environmental factors to carry out electric field simulation, locate the key region of electric field intensity peak, quantify the electric field distortion law, and construct an operating condition benchmarking mechanism to achieve accurate verification and optimization of the bushing external insulation design.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows: A method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments includes the following steps: Obtain the core structural parameters and material properties of the casing.

[0007] A finite element model of the casing is constructed based on the core structural parameters and material property parameters.

[0008] Electric field boundary conditions and voltage loads are applied to the finite element model of the bushing, and the model is meshed to obtain a complete discretized model under normal operating conditions.

[0009] Electric field simulation analysis was performed on the complete discretized model under normal operating conditions to obtain the electric field intensity distribution map under normal operating conditions. Based on the electric field intensity distribution map under normal operating conditions, the key location with the maximum electric field intensity was determined.

[0010] Three complex simulation models were constructed on the umbrella skirt surface at the key location with the greatest electric field intensity, including discontinuous water film, wet and dirty layer with dry zone, and local wet and dirty condition. The boundary conditions and mesh generation were kept consistent with the normal condition. Electric field simulation analysis was performed on the three complex simulation models in turn, and the peak electric field intensity at the key location under the three complex conditions was extracted.

[0011] The peak electric field strength at key locations under three complex operating conditions is compared with the preset critical discharge electric field strength. If the peak electric field strength at key locations under all three complex operating conditions is less than the preset critical discharge electric field strength, the original design of the bushing is deemed to meet the insulation safety requirements under complex operating conditions. If any one of the peak electric field strengths at key locations under the three complex operating conditions is greater than or equal to the preset critical discharge electric field strength, the original design of the bushing has an insulation safety hazard, and the original design is optimized.

[0012] The invention is further characterized by: When performing electric field simulation analysis on the complete discretized model under normal operating conditions, the analysis is based on the principles of electrostatic field or quasi-static current field, and uses a generalized current conduction equation. The generalized current conduction equation is as follows: , In the formula, σ ( r ) is in spatial location r conductivity at that point j The imaginary unit, ω The angular frequency of alternating current. ε 0 is the vacuum permittivity. ε r ( r ) is in spatial location r The relative permittivity of the material at that location, φ ( r ) is in spatial location r The electric potential at that point.

[0013] When extracting the peak electric field intensity at key locations under three complex operating conditions, the following formula is used to determine it: , In the formula, E i In the first i Peak electric field intensity extracted under complex working conditions i=0,1,2,3 correspond to normal operating conditions, discontinuous water film operating conditions, wet fouling layer operating conditions containing dry zones, and locally wet fouling operating conditions, respectively. E ( r || represents the electric field intensity vector. E ( r ) modulus, Ω key This is the key location where the electric field strength is greatest.

[0014] When constructing a simulation model of discontinuous water film working conditions on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, a discontinuous water film with a thickness of 0.3mm to 0.8mm is set on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, and a local dry area with a length of 0.5mm to 5mm is reserved between the water films to obtain the simulation model of discontinuous water film working conditions.

[0015] When constructing a simulation model of a wet contamination layer containing a dry strip on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, a wet contamination layer with a thickness of 0.3 mm to 1.0 mm is set on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, and a dry strip with a length of 0.5 mm to 10 mm and a thickness of 0.1 mm to 1.5 mm is set in the wet contamination layer to obtain a simulation model of a wet contamination layer containing a dry strip.

[0016] When constructing a simulation model of localized wet and polluted conditions on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, a continuous, gapless localized wet and polluted layer with a length of 5mm to 30mm and a thickness of 0.35mm to 1mm is set on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, thus obtaining the simulation model of localized wet and polluted conditions.

[0017] When determining the key location with the largest electric field intensity based on the electric field intensity distribution map under normal operating conditions, the reference value of the electric field intensity at the key location is extracted, and the grid independence of the reference value is verified. By comparing the reference values ​​of the electric field intensity under different grid densities, it is ensured that its rate of change meets the preset requirements.

[0018] The original design of the bushing had insulation safety hazards. When optimizing the original design, the electric field distortion coefficient under the three complex working conditions was determined based on the electric field strength benchmark value and the peak electric field strength at the key location under the three complex working conditions. The insulation safety hazards were classified according to the largest electric field distortion coefficient, and corresponding optimizations were carried out for different levels of safety hazards.

[0019] The electric field distortion coefficient is determined by the following formula: , In the formula, K X The electric field distortion coefficient is... E XThe peak electric field intensity at key locations under three complex operating conditions is represented by X=1, 2, and 3, which correspond to the discontinuous water film condition, the wet fouling layer condition containing a dry zone, and the locally wet fouling condition, respectively. E 0 represents the reference value for electric field strength.

[0020] The insulation safety hazard is classified according to the electric field distortion coefficient. When optimization is performed for different levels of safety hazards, the maximum electric field distortion coefficient is considered. K Xmax When the value is greater than 1.5, the insulation safety hazard is judged as high-risk, and structural or material modifications are made to the bushing. When the value is less than 1.2... K Xmax When the value is ≤1.5, the insulation safety hazard is judged to be of medium risk. Surface treatment and process strengthening measures are implemented for the bushing. K Xmax When the value is ≤1.2, the insulation safety hazard is determined to be low risk, and the bushing is subjected to operation monitoring and maintenance.

[0021] The present invention provides a method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments, which has the following advantages: This invention constructs simulation models for three typical complex operating conditions: a discontinuous water film, a wet contamination layer containing a dry strip, and a locally wet contamination layer. These models accurately simulate real operating environments such as high humidity and contamination adhesion, effectively characterizing the abrupt changes in the dielectric properties of the medium under complex conditions and the resulting solid-liquid-gas three-phase interface effect. Simultaneously, it achieves the location of the critical position with the maximum electric field intensity on the outer insulation surface of the bushing and quantitative analysis of the electric field distortion characteristics. By comparing the peak electric field intensity under complex operating conditions with the preset critical discharge electric field intensity, it scientifically assesses the deterioration impact of complex environments on high-risk areas, accurately determines whether the original design meets the insulation safety requirements under complex operating conditions, and optimizes designs with potential safety hazards. This effectively improves the reliability and safety of the outer insulation of ultra-high voltage bushings operating in real complex environments. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall process of the present invention.

[0023] Figure 2 This is a schematic diagram of the finite element model of the sleeve in this invention.

[0024] Figure 3 This is a local mesh division diagram of the casing in this invention.

[0025] Figure 4 This is a schematic diagram of the surface electric field extraction path in this invention.

[0026] Figure 5 This is a magnified view of a portion of the GIS composite sleeve.

[0027] Figure 6 This is a finite element model of a GIS composite sleeve.

[0028] Figure 7 This is a diagram showing the grid division results for the GIS composite sleeve.

[0029] Figure 8 This is a diagram showing the electric field distribution of a GIS composite bushing under normal operating conditions.

[0030] Figure 9 A simulation distribution diagram of the discontinuous water film condition in the key area of ​​the GIS composite casing.

[0031] Figure 10 This is a simulation distribution map of the wet contamination layer containing dry sections in the key areas of the GIS composite casing.

[0032] Figure 11 This is a simulation distribution map of the key areas of the GIS composite sleeve under localized wet and contaminated conditions. Detailed Implementation

[0033] The technical solutions of the present invention will now be described clearly and in detail with reference to the accompanying drawings. In the description of the embodiments of the present invention, unless otherwise stated, " / " indicates "or," for example, A / B can mean A or B. "And / or" in the text is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. Furthermore, in the description of the embodiments of the present invention, "multiple" refers to two or more. The terms "first" and "second" are used for descriptive purposes only and should not be construed as implying or suggesting relative importance or implicitly indicating the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0034] like Figure 1 , Figure 2 As shown, this invention provides a method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments, comprising the following steps: Obtain the core structural parameters and material properties of the casing.

[0035] A finite element model of the casing is constructed based on the core structural parameters and material property parameters.

[0036] Electric field boundary conditions and voltage loads are applied to the finite element model of the bushing, and the model is meshed to obtain a complete discretized model under normal operating conditions.

[0037] Electric field simulation analysis was performed on the complete discretized model under normal operating conditions to obtain the electric field intensity distribution map under normal operating conditions. Based on the electric field intensity distribution map under normal operating conditions, the key location with the maximum electric field intensity was determined.

[0038] Three complex simulation models were constructed on the umbrella skirt surface at the key location with the greatest electric field intensity, including discontinuous water film, wet and dirty layer with dry zone, and local wet and dirty condition. The boundary conditions and mesh generation were kept consistent with the normal condition. Electric field simulation analysis was performed on the three complex simulation models in turn, and the peak electric field intensity at the key location under the three complex conditions was extracted.

[0039] The peak electric field strength at key locations under three complex operating conditions is compared with the preset critical discharge electric field strength. If the peak electric field strength at key locations under all three complex operating conditions is less than the preset critical discharge electric field strength, the original design of the bushing is deemed to meet the insulation safety requirements under complex operating conditions. If any one of the peak electric field strengths at key locations under the three complex operating conditions is greater than or equal to the preset critical discharge electric field strength, the original design of the bushing has an insulation safety hazard, and the original design is optimized.

[0040] In summary, this invention obtains the core structural parameters and material property parameters of the bushing. Based on these parameters, a finite element model of the bushing is constructed. Electric field boundary conditions and voltage loads are applied to the finite element model, and a mesh is generated to obtain a complete discretized model under normal operating conditions. Electric field simulation analysis is performed on this model to obtain the electric field intensity distribution map under normal operating conditions. Based on the electric field intensity distribution map, the key locations with the maximum electric field intensity are determined. At these key locations, simulation models for three complex operating conditions are constructed on the skirt surface: a discontinuous water film condition, a wet fouling layer condition containing a dry zone, and a locally wet fouling condition. While maintaining consistent boundary conditions and mesh generation with normal operating conditions, electric field simulation analysis was performed on the simulation models of three complex operating conditions in sequence. The peak electric field intensity at key locations under the three complex operating conditions was extracted, and the peak electric field intensity at key locations under the three complex operating conditions was compared with the preset critical discharge electric field intensity. If the peak electric field intensity at key locations under the three complex operating conditions is less than the preset critical discharge electric field intensity, it is determined that the original design scheme of the bushing meets the insulation safety requirements under complex operating conditions. If any one of the peak electric field intensity at key locations under the three complex operating conditions is greater than or equal to the preset critical discharge electric field intensity, the original design scheme of the bushing has an insulation safety hazard, and the original design scheme is optimized. This invention constructs simulation models for three typical complex operating conditions: a discontinuous water film, a wet contamination layer containing a dry strip, and a locally wet contamination layer. These models accurately simulate real operating environments such as high humidity and contamination adhesion, effectively characterizing the abrupt changes in the dielectric properties of the medium under complex conditions and the resulting solid-liquid-gas three-phase interface effect. Simultaneously, it achieves the location of the critical position with the maximum electric field intensity on the outer insulation surface of the bushing and quantitative analysis of the electric field distortion characteristics. By comparing the peak electric field intensity under complex operating conditions with the preset critical discharge electric field intensity, it scientifically assesses the deterioration impact of complex environments on high-risk areas, accurately determines whether the original design meets the insulation safety requirements under complex operating conditions, and optimizes designs with potential safety hazards. This effectively improves the reliability and safety of the outer insulation of ultra-high voltage bushings operating in real complex environments.

[0041] The core structural parameters include key geometric parameters such as the tube's rated voltage level, sheath outer / inner diameter, sheath length, insulation layer thickness, and flange position and dimensions. The material property parameters include the relative permittivity of various parts such as the air domain, silicone rubber sheath, epoxy tube, insulating rod, inner and outer shielding layers, center conductor, metal flange, and insulating gas.

[0042] When applying electric field boundary conditions and voltage loads to the finite element model of the bushing, in order to simulate the electric field distribution of the bushing under normal operating conditions, it is necessary to reasonably set the electric field boundary conditions and voltage loads. According to the rated voltage level of the bushing, the corresponding rated voltage is applied to the high-voltage end of the bushing. The outer shielding layer and flange are grounded structures and set as zero potential boundaries. The air domain adopts the "electrically insulated boundary" condition, and the size is five times the diameter of the bushing model to eliminate the influence of boundary effects.

[0043] like Figure 3 As shown, when meshing the finite element model of the sleeve, in order to balance the calculation accuracy and efficiency, a free triangular mesh is used to discretize the model, and local refinement is implemented for electric field sensitive areas (such as the tip of the umbrella skirt and the material interface) to improve the simulation accuracy.

[0044] In the electric field simulation analysis of the complete discretized model under normal operating conditions, the principle of electrostatic field or quasi-static current field is used, and a generalized current conduction equation is adopted for the electric field simulation analysis. The generalized current conduction equation is as follows: .

[0045] In the formula, σ ( r ) is in spatial location r The electrical conductivity at that location varies depending on the region of the material. j The imaginary unit satisfies j 2 =−1, used to characterize the phase relationship in an alternating electric field. ω The angular frequency of alternating current. ε 0 is the vacuum permittivity. ε r ( r ) is in spatial location r The relative permittivity of the material at that location, φ ( r ) is in spatial location r The electric potential at that point.

[0046] The electric field simulation includes normal operating conditions, discontinuous water film operating conditions, wet fouling layer operating conditions with dry zone, and local wet fouling operating conditions.

[0047] Under the power frequency of 50Hz, for most insulated areas and contamination layers with finite conductivity, a DC steady-state approximation can be used, and the above generalized current conduction equation simplifies to: .

[0048] In the formula, κ ( r ) represents spatial location rThe equivalent conductivity at a given point, under DC or low-frequency approximation, comprehensively reflects the electrical conductivity and dielectric polarization characteristics of a material. For good insulators, its value is extremely low. φ ( r ) is in spatial location r The electric potential at that point.

[0049] The electric field strength is determined by the following formula: .

[0050] In the formula, E ( r Let be the electric field intensity vector at spatial location r, whose value is the negative gradient with respect to the electric potential. φ ( r ) is in spatial location r The electric potential at that point.

[0051] When extracting the peak electric field intensity at key locations under three complex operating conditions, the following formula is used to determine it: .

[0052] In the formula, E i In the first i Peak electric field intensity extracted under complex working conditions i =0,1,2,3 correspond to normal operating conditions, discontinuous water film operating conditions, wet fouling layer operating conditions containing dry zones, and locally wet fouling operating conditions, respectively. E ( r || represents the electric field intensity vector. E ( r ) modulus, Ω key This is the key location where the electric field strength is greatest.

[0053] The differences in simulation for each operating condition ultimately lie in the material property functions within the aforementioned generalized current conduction equation. ε r ( r )and σ ( r In terms of the specific spatial distribution, different relative permittivity and conductivity values ​​are only set in the step of defining the model material.

[0054] In the process of constructing a simulation model of discontinuous water film working conditions on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, a discontinuous water film with a thickness of 0.3 mm to 0.8 mm is set on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, and a local dry area with a length of 0.5 mm to 5 mm is reserved between the water films to obtain the simulation model of discontinuous water film working conditions. The thickness of the discontinuous water film is preferably 0.5 mm.

[0055] In the simulation model of the wet contamination layer containing dry strips on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, a wet contamination layer with a thickness of 0.3 mm to 1.0 mm is set on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, and a dry strip with a length of 0.5 mm to 10 mm and a thickness of 0.1 mm to 1.5 mm is set in the wet contamination layer to obtain the simulation model of the wet contamination layer containing dry strips. The thickness of the wet contamination layer is preferably 0.5 mm.

[0056] In constructing a simulation model of localized wet and polluted conditions on the surface of the umbrella skirt at the critical location where the electric field strength is greatest, a continuous, gapless localized wet and polluted layer with a length of 5mm to 30mm and a thickness of 0.35mm to 1mm is set on the surface of the umbrella skirt at the critical location where the electric field strength is greatest, to obtain the simulation model of localized wet and polluted conditions.

[0057] Specifically, when determining the key location with the largest electric field intensity based on the electric field intensity distribution map under normal operating conditions, the reference value of the electric field intensity at the key location is extracted, and the grid independence of the reference value is verified. By comparing the reference values ​​of the electric field intensity under different grid densities, it is ensured that its rate of change meets the preset requirements.

[0058] like Figure 4 As shown, based on the principles of electrostatic fields or quasi-static current fields, and using the generalized current conduction equation, an electric field simulation analysis is performed to obtain the electric field distribution of the bushing under normal operating conditions, resulting in an electric field intensity distribution map. The key locations with the maximum electric field intensity are identified from the simulation results, and along... Figure 4 The maximum electric field strength at the surface of the outer insulating sheath of the bushing is extracted, and the reference value of the electric field strength at that location is recorded. E 0.

[0059] In verifying the mesh independence of the electric field intensity reference value, to avoid errors in the electric field value caused by excessively large mesh size and to improve the reliability of the simulation data, electric field reference values ​​under different mesh densities were specifically designed. E The grid density is compared with 0 to ensure that the rate of change is less than 2%, which is a requirement of grid independence. When this requirement is met, it indicates that the grid density can accurately capture the characteristics of electric field distribution, and there is no need to further refine the grid, thus ensuring that the error of the electric field strength data is within an acceptable range.

[0060] Among them, the preset critical electric field strength for discharge E C It is set to 4.5kV / cm.

[0061] The original design of the bushing had insulation safety hazards. When optimizing the original design, the electric field distortion coefficient under the three complex working conditions was determined based on the electric field strength benchmark value and the peak electric field strength at the key location under the three complex working conditions. The insulation safety hazards were classified according to the largest electric field distortion coefficient, and corresponding optimizations were carried out for different levels of safety hazards.

[0062] like Figure 1 As shown, the electric field distortion coefficient is determined by the following formula: .

[0063] In the formula, K X The electric field distortion coefficient is... E X The peak electric field intensity at key locations under three complex operating conditions is represented by X=1, 2, and 3, which correspond to the discontinuous water film condition, the wet fouling layer condition containing a dry zone, and the locally wet fouling condition, respectively. E 0 represents the reference value for electric field strength.

[0064] like Figure 1 As shown, insulation safety hazards are classified according to the electric field distortion coefficient. When optimizing for different levels of safety hazards, the maximum electric field distortion coefficient is... K Xmax When the value is greater than 1.5, the insulation safety hazard is judged as high-risk, and structural or material modifications are made to the bushing. When the value is less than 1.2... K Xmax When the value is ≤1.5, the insulation safety hazard is judged to be of medium risk. Surface treatment and process strengthening measures are implemented for the bushing. K Xmax When the value is ≤1.2, the insulation safety hazard is determined to be low risk, and the bushing is subjected to operation monitoring and maintenance.

[0065] When making structural or material modifications to the bushing, the shape and spacing of the skirts can be redesigned to improve the electric field distribution; a long-lasting hydrophobic coating (such as RTV or PRTV) can be applied to the surface of the sheath to suppress the continuous formation of water film; and the outer insulation can be reshaped using high dielectric constant and high hydrophobic composite materials.

[0066] Among these measures, when performing surface treatment and process enhancement on the sleeve, the surface of the sheath can be treated with superhydrophobicity; the smoothness and cleanliness of the umbrella skirt or sheath surface can be optimized to reduce the points of dirt adhesion.

[0067] When monitoring and maintaining the casing, this area can be marked as a key inspection point to increase the frequency of inspections.

[0068] Example 1 like Figure 5As shown, a 1000kV GIS composite bushing in the northern part of the Yangtze River Delta was selected, and the verification and optimization method of this invention was applied as follows: 1) Obtain the core structural parameters and material property parameters of the GIS composite sleeve, such as... Figure 5 And as shown in Table 1 below.

[0069] Table 1 shows the material and relative permittivity values ​​for various parts of the GIS composite sleeve. 2) Based on the core structural parameters and material property parameters, a finite element model of the GIS composite sleeve is constructed.

[0070] like Figure 6 As shown, a finite element model of the GIS composite sleeve was built based on finite element simulation software, according to the core structural parameters and material property parameters obtained.

[0071] 3) Boundary condition settings and mesh generation.

[0072] like Figure 7 As shown, a rated phase voltage of 635kV is applied to the center conductor, the outer shielding layer and flange are set as zero potential boundaries, and the air domain adopts the "electrically insulated boundary" condition. Then, the finite element model is meshed to obtain a complete discretized model under normal operating conditions.

[0073] 4) such as Figure 8 As shown, solving the complete discretized model under normal operating conditions reveals that the electric field strength reaches its peak at the interface between the insulating rod and the shielding layer; this area is designated as the critical region. Meanwhile, as shown in Table 2, four mesh schemes were designed, and simulations were performed on the electric field strength at the tip of the umbrella skirt in the critical region under each scheme. The results show that when the number of meshes increases from 190,000 to 790,000, the calculated electric field strength increases from 3.56 kV / cm to 3.94 kV / cm. Further increasing to 3.81 million meshes, the electric field strength stabilizes at 3.99 kV / cm, with a variation of less than 2%, verifying mesh independence. Scheme 4 is ultimately selected as the optimal meshing scheme to ensure computational accuracy. E 0 = 3.99 kV / cm.

[0074] Table 2 shows the electric field intensity values ​​of key regions under four grid schemes. 5) Electric field simulation analysis under complex environmental conditions.

[0075] Water film condition: A discontinuous water film with a thickness of 0.5 mm is set on the surface of the sheath at key locations, with a 3 mm local dry area reserved between the water films. Simulation results. Figure 9 As shown, the peak electric field intensity of the line is extracted. E 1 = 5.2 kV / cm EC =4.5kV / cm.

[0076] Working condition with wet contamination layer containing dry tape: A 0.5mm thick contamination layer is set on the surface of the sheath at critical locations, with a dry tape area in the middle. Simulation results are as follows. Figure 10 As shown, the peak electric field intensity of the line is extracted. E 2 = 4.9 kV / cm E C =4.5kV / cm.

[0077] Localized wet contamination condition: A 0.5mm thick localized wet contamination layer was applied to the surface of the sheath at critical locations. Simulation results are as follows: Figure 11 As shown, the peak electric field intensity of the line is extracted. E 3 = 4.1 kV / cm E C =4.5kV / cm.

[0078] 6) Comparison of simulation results and judgment of design rationality.

[0079] because E 0 = 3.99 kV / cm E 1 = 5.2 kV / cm E 2 = 4.9 kV / cm E 3 = 4.1 kV / cm. Wherein, E 1> E C , E 2> E C , E 3< E C This indicates that the electric field at critical locations of the bushing's external insulation is significantly distorted under water film and polluted dry conditions, reaching the discharge threshold. The original design has insulation safety hazards and needs to be optimized.

[0080] Calculate the electric field distortion coefficient K 1 = 1.30 K 2 = 1.23, then K Xmax = K 1 = 1.30.

[0081] Therefore, based on K Xmax The value classifies the critical area of ​​the casing as a medium-risk zone (1.2 < K Xmax≤1.5): The electric field is significantly distorted, posing a potential risk. The optimization plan can prioritize low-cost and easy-to-implement surface treatment and process enhancement measures: superhydrophobic treatment of the sheath surface; optimization of the smoothness and cleanliness process of the umbrella skirt or sheath surface to reduce dirt adhesion points.

[0082] It is understood that this invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of this invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this invention are within the protection scope of this invention.

Claims

1. A method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments, characterized in that, Includes the following steps: Obtain the core structural parameters and material properties of the casing; A finite element model of the casing is constructed based on the core structural parameters and material property parameters; Electric field boundary conditions and voltage loads are applied to the finite element model of the bushing, and the model is meshed to obtain a complete discretized model under normal operating conditions. Electric field simulation analysis was performed on the complete discretized model under normal operating conditions to obtain the electric field intensity distribution map under normal operating conditions. Based on the electric field intensity distribution map under normal operating conditions, the key location with the maximum electric field intensity was determined. Three complex simulation models were constructed on the umbrella skirt surface at the key location with the greatest electric field intensity, including discontinuous water film, wet and dirty layer with dry zone, and local wet and dirty condition. The boundary conditions and mesh generation were kept consistent with the normal condition. Electric field simulation analysis was performed on the three complex simulation models in turn, and the peak electric field intensity at the key location under the three complex conditions was extracted. The peak electric field strength at key locations under three complex operating conditions is compared with the preset critical discharge electric field strength. If the peak electric field strength at key locations under all three complex operating conditions is less than the preset critical discharge electric field strength, the original design of the bushing is deemed to meet the insulation safety requirements under complex operating conditions. If any one of the peak electric field strengths at key locations under the three complex operating conditions is greater than or equal to the preset critical discharge electric field strength, the original design of the bushing has an insulation safety hazard, and the original design is optimized.

2. The method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments as described in claim 1, characterized in that, When performing electric field simulation analysis on a complete discretized model under normal operating conditions, the electric field simulation analysis is based on the principles of electrostatic field or quasi-static current field, and a generalized current conduction equation is used. The generalized current conduction equation is as follows: ， In the formula, σ ( r ) is in spatial location r conductivity at that point j The imaginary unit, ω The angular frequency of alternating current. ε 0 is the vacuum permittivity. ε r ( r ) is in spatial location r The relative permittivity of the material at that location, φ ( r ) is in spatial location r The electric potential at that point.

3. The method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments as described in claim 1, characterized in that, When extracting the peak electric field intensity at key locations under three complex operating conditions, the following formula is used: ， In the formula, E i In the first i Peak electric field intensity extracted under complex working conditions i =0,1,2,3 correspond to normal operating conditions, discontinuous water film operating conditions, wet fouling layer operating conditions containing dry zones, and locally wet fouling operating conditions, respectively. E ( r || represents the electric field intensity vector. E ( r ) modulus, Ω key This is the key location where the electric field strength is greatest.

4. The method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments as described in claim 1, characterized in that, When constructing a simulation model of discontinuous water film working conditions on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, a discontinuous water film with a thickness of 0.3mm to 0.8mm is set on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, and a local dry area with a length of 0.5mm to 5mm is reserved between the water films to obtain the simulation model of discontinuous water film working conditions.

5. The method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments according to claim 1, characterized in that, When constructing a simulation model of a wet contamination layer containing a dry strip on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, a wet contamination layer with a thickness of 0.3 mm to 1.0 mm is set on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, and a dry strip with a length of 0.5 mm to 10 mm and a thickness of 0.1 mm to 1.5 mm is set in the wet contamination layer to obtain a simulation model of a wet contamination layer containing a dry strip.

6. The method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments according to claim 1, characterized in that, When constructing a simulation model of localized wet and polluted conditions on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, a continuous, gapless localized wet and polluted layer with a length of 5mm to 30mm and a thickness of 0.35mm to 1mm is set on the surface of the umbrella skirt at the critical location where the electric field strength is the greatest, thus obtaining the simulation model of localized wet and polluted conditions.

7. The method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments as described in claim 1, characterized in that, When determining the key location with the largest electric field intensity based on the electric field intensity distribution map under normal operating conditions, the reference value of the electric field intensity at the key location is extracted, and the grid independence of the reference value is verified. By comparing the reference values ​​of the electric field intensity under different grid densities, it is ensured that its rate of change meets the preset requirements.

8. The method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments according to claim 7, characterized in that, The original design had insulation safety hazards. When optimizing the original design, the electric field distortion coefficient under the three complex working conditions was determined based on the electric field strength benchmark value and the peak electric field strength at key locations under the three complex working conditions. The insulation safety hazards were classified according to the largest electric field distortion coefficient, and corresponding optimizations were carried out for different levels of safety hazards.

9. The method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments according to claim 8, characterized in that, The electric field distortion coefficient is determined by the following formula: ， In the formula, K X The electric field distortion coefficient is... E X The peak electric field intensity at key locations under three complex operating conditions is represented by X=1, 2, and 3, which correspond to the discontinuous water film condition, the wet fouling layer condition containing a dry zone, and the locally wet fouling condition, respectively. E 0 represents the reference value for electric field strength.

10. The method for verifying and optimizing the external insulation design of ultra-high voltage bushings under complex environments according to claim 9, characterized in that, Insulation safety hazards are classified according to the electric field distortion coefficient. When optimizing for different levels of safety hazards, the maximum electric field distortion coefficient is... K Xmax When the value is greater than 1.5, the insulation safety hazard is judged as high-risk, and structural or material modifications are made to the bushing. When the value is less than 1.2... K Xmax When the value is ≤1.5, the insulation safety hazard is judged to be of medium risk. Surface treatment and process strengthening measures are implemented for the bushing. K Xmax When the value is ≤1.2, the insulation safety hazard is determined to be low risk, and the bushing is subjected to operation monitoring and maintenance.

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