Method and system for calculating internal stress distribution of zinc oxide surge arrester based on multi-working condition coupling and storage medium

Abstract

The application belongs to the technical field of power system overvoltage protection equipment state evaluation, and particularly relates to a calculation method of internal stress distribution of zinc oxide lightning arrester based on multi-working condition coupling, which comprises the following steps: a three-dimensional geometric model containing ZnO resistance sheet, fittings and insulating cylinder is established; joint excitation is applied to the three-dimensional geometric model, and a steady-state-transient step calculation method is used to solve the electric-thermal-mechanical coupling control equation; the coupling equivalent stress value under the joint excitation is extracted based on the coupling stress tensor; a nonlinear enhancement factor is defined, and whether there is a stress nonlinear enhancement effect is judged according to the nonlinear enhancement factor; and stress distribution data of the internal key interface of the lightning arrester under the joint excitation is output, so that the technical problems that the existing method ignores the electric-thermal-mechanical coupling effect, resulting in low stress calculation result, cannot handle multiple lightning strike scenes, the full coupling calculation efficiency is low, and there is a lack of quantitative means of nonlinear enhancement effect are solved.

Description

Technical Field

[0001] This invention belongs to the technical field of condition assessment of power system overvoltage protection equipment, specifically involving a method and system for calculating the internal stress distribution of zinc oxide surge arresters based on multi-condition coupling. This method is used to accurately calculate the internal stress distribution of surge arresters and quantify the nonlinear enhancement effect under the combined excitation of mechanical load and lightning impulse. Background Technology

[0002] Zinc oxide surge arresters are crucial overvoltage protection devices in power distribution networks, and their operational reliability directly impacts power supply safety. In actual operation, surge arresters not only withstand the electrothermal stress caused by lightning current surges but also mechanical loads (unbalanced forces) resulting from horizontal installation, wind force, and horizontal tension. Especially in areas with frequent lightning activity and a high proportion of multiple lightning strikes, surge arresters often experience sealing defects, insulation damage, and reduced current-carrying capacity. Existing research indicates that stress concentration at the interfaces between the ZnO resistance element and the hardware / insulating cylinder inside the surge arrester is the root cause of aging of the silicone rubber sheath, microcrack initiation, and ultimately, sealing failure.

[0003] Existing research indicates that stress concentration at the interface between the zinc oxide (ZnO) resistance element and the fittings / insulating cylinder inside the surge arrester is the root cause of aging of the silicone rubber sheath, microcrack initiation, and ultimately, seal failure. Current domestic and international research on surge arrester stress largely analyzes mechanical or electrothermal stress in isolation, using the finite element method to calculate stress distribution under a single load and then performing simple algebraic superposition. This completely ignores the nonlinear amplification effect of the combined action of mechanical load and lightning strikes (especially multiple strikes). Unbalanced forces alter the ideal surface contact state between the ZnO resistance element and the fittings, creating localized stress concentration points. Subsequent Joule heating from lightning strikes induces thermal expansion, amplifying both stresses and stresses, resulting in interface stresses far exceeding the sum of their individual effects. Furthermore, existing methods lack simulation of the cumulative effect of stress from multiple lightning strikes and do not employ a step-by-step calculation strategy to reduce the computational complexity of multi-physics coupling, making it difficult to guarantee the accuracy of the calculation results.

[0004] Existing simulation methods calculate mechanical load and lightning impact separately and then simply superimpose them, ignoring the electro-thermal-mechanical coupling effect. This fails to capture the nonlinear stress enhancement phenomenon, resulting in significantly underestimated calculation results and making it difficult to accurately assess the actual operational risk of surge arresters. Furthermore, most methods only consider a single lightning strike, neglecting the heat accumulation and stress superposition effects of multiple strikes. Multiple lightning strikes cause far greater damage to surge arresters than a single strike, failing to reflect real-world lightning scenarios. In addition, directly performing fully coupled transient calculations is complex and inefficient; it also fails to systematically analyze the boundary conditions and variation laws of the nonlinear stress enhancement effect, thus failing to provide quantitative guidance for surge arrester structural optimization and operation and maintenance.

[0005] Therefore, there is an urgent need to propose a method for calculating the internal stress distribution of surge arresters that can comprehensively reflect actual operating conditions, take into account coupling enhancement effects, and calculate efficiently and accurately. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for calculating the internal stress distribution of zinc oxide surge arresters based on multi-condition coupling, in order to solve the technical problems of existing methods that ignore the electro-thermal-mechanical coupling effect, resulting in low stress calculation results, inability to handle multiple lightning strike scenarios, low efficiency of full coupling calculation, and lack of nonlinear enhancement effect quantification methods.

[0007] The technical solution of this invention is: A method for calculating the internal stress distribution of a zinc oxide surge arrester based on multi-condition coupling includes the following steps performed in sequence: Step 1: Establish a three-dimensional geometric model Based on the actual structural parameters of the surge arrester, a three-dimensional geometric model including ZnO resistor elements, hardware, and an insulating cylinder is established. The insulating cylinder is preferably an epoxy resin insulating cylinder, and the model also includes supporting components such as a base.

[0008] Step 2: Apply joint stimulus A combined excitation, comprising a mechanical load and a lightning impulse current waveform, is applied to the three-dimensional geometric model, and the two are applied synchronously in time. Wherein: The mechanical load includes at least the following two types: a horizontal tension applied to the top of the surge arrester, a gravitational field acting on the entire model, and a wind pressure distribution load calculated based on the installation height of the surge arrester and the local wind speed. The applied horizontal tension is selected according to the installation method of the surge arrester: vertical installation, 45° inclined installation, or horizontal installation. The value range of the horizontal tension is 14.7N to 600N. The direction of the gravity is along the negative Y-axis.

[0009] The lightning impulse current wave is a large current wave with an amplitude range of 10kA to 100kA, which is 4 / 10μs. The combined excitation applied in step S2 includes multiple consecutive lightning strikes. The time interval between two adjacent lightning strikes is less than the thermal relaxation time of the ZnO resistor sheet, so as to simulate the heat accumulation and stress superposition effect under multiple lightning strikes. The amplitude of the subsequent return strokes after multiple lightning strikes is taken as half of the first return stroke, and the return stroke interval is 10ms.

[0010] Step 3: Solve the electro-thermal-mechanical coupling control equations using a steady-state-transient step-by-step calculation method. To reduce the computational complexity of fully coupled transient operations, this step is divided into two sub-steps: Step 1 (Steady-state solution): Based on the long-term static mechanical loads (horizontal tension, gravity, wind pressure) applied in Step 2, solve in advance the initial stress field and initial deformation field considering only the mechanical load. This step uses a steady-state solid mechanics solver and does not consider lightning impact.

[0011] Step 2 (Transient Coupling Solution): Using the initial stress field and initial deformation field obtained in Step 1 as initial conditions, the lightning impulse current waveform from Step 2 is applied to perform transient electro-thermal-mechanical coupling calculations. The electrostatic field, solid heat transfer field, and transient solid mechanical field are solved sequentially to obtain the coupled stress tensor under the combined excitation. Specifically, the Joule heat generated by the electrostatic field calculation is used as a heat source input to the solid heat transfer field, and the temperature change obtained from the solid heat transfer field calculation is coupled to the transient solid mechanical field through the temperature dependence of the thermal expansion coefficient and material parameters.

[0012] Step 4: Extract the coupled equivalent stress value and calculate the linear superposition equivalent stress value. Based on the coupled stress tensor, the coupled equivalent stress value under the joint excitation is extracted. Furthermore, the superimposed equivalent stress value obtained by linearly superimposing the mechanical load and the lightning impulse current waveform after they are applied individually is calculated separately. , .

[0013] Step 5: Define the nonlinear enhancement factor η as: in, For interfacial stress under combined action, For interfacial stress under mechanical load only, The interfacial stress under lightning strike alone is used to determine whether there is a stress nonlinear enhancement effect based on the nonlinear enhancement factor.

[0014] Judgment criteria: η>0: There is a nonlinear stress enhancement effect; the larger η is, the more significant the enhancement. η=0: The stress is linearly superimposed, with no enhancement effect; η<0: Stress cancellation effect exists.

[0015] Step 6: By changing the unbalanced force value and the lightning current amplitude respectively, calculate the stress distribution and nonlinear enhancement factor under different combinations, plot the stress-load variation curve, and output the stress distribution data of the key interfaces inside the surge arrester under combined excitation. Specifically, the key interfaces include at least: the interface between the ZnO resistance sheet and the fitting, the interface between the ZnO resistance sheet and the insulating cylinder, and the corners of the base.

[0016] Specifically, the electro-thermal-mechanical coupling control equations in step S3 satisfy the following coupling relationship: In the electric field equation, the Joule heat of the ZnO resistance sheet is used as a heat source term in the temperature field equation; In the temperature field equation, temperature changes are coupled to the stress field equation through the temperature dependence of the thermal expansion coefficient and material parameters; In the stress field equations, deformation reacts to the electric field equations through piezoresistive effects or geometric changes.

[0017] Specifically, step S5 further includes: recording and outputting the variation curves of the nonlinear enhancement factor η under different lightning strikes, different mechanical loads, and different ambient temperatures, so as to determine the stress nonlinear enhancement boundary conditions and sensitivity range of the surge arrester structure under multiple operating conditions.

[0018] This invention also provides a system for calculating the internal stress distribution of a zinc oxide surge arrester based on multi-condition coupling, comprising: Model building module: Used to create a three-dimensional geometric model including ZnO resistor sheet, hardware and insulating cylinder; Joint excitation application module: used to apply joint excitation to the three-dimensional geometric model, the joint excitation including mechanical load and lightning impulse current waveform, wherein the mechanical load includes horizontal tension, gravity and wind pressure, and the lightning impulse current waveform is a 4 / 10μs waveform; Step-by-step calculation module: used to solve the electro-thermal-mechanical coupling control equations using a steady-state-transient step-by-step calculation method. The step-by-step calculation module includes: Steady-state solution unit: used to solve the initial stress field and initial deformation field under long-term static mechanical load based on the mechanical load; Transient coupling solution unit: used to apply the lightning impulse current waveform as the initial conditions using the initial stress field and initial deformation field, perform transient electro-thermal-mechanical coupling calculation, solve the electrostatic field, solid heat transfer field and transient solid mechanical field in sequence, and obtain the coupled stress tensor under the joint excitation. Stress value calculation module: used to extract the coupled equivalent stress value under joint excitation based on the coupled stress tensor, and to separately calculate the superimposed equivalent stress value obtained by linear superposition of mechanical load and lightning impulse current waveform after acting separately; Nonlinear enhancement judgment and output module: used to define nonlinear enhancement factor, determine whether stress nonlinear enhancement effect exists based on the nonlinear enhancement factor, and output stress distribution data of key interfaces inside the surge arrester under joint excitation.

[0019] Specifically, in the transient coupled solution unit, the Joule heat generated by the electrostatic field calculation is used as a heat source input to the solid heat transfer field, and the temperature change calculated by the solid heat transfer field is coupled to the transient solid mechanical field through the temperature dependence of the thermal expansion coefficient and material parameters.

[0020] Specifically, it also includes a parametric analysis module: used to change the value of the horizontal tension and the amplitude of the lightning current, repeatedly call the joint excitation application module, the step-by-step calculation module, the stress value calculation module and the nonlinear enhancement judgment and output module, calculate the nonlinear enhancement factor under different combinations, and plot the stress-load variation curve to determine the stress nonlinear enhancement boundary conditions and sensitivity range of the arrester structure under multiple working conditions.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. A novel step-by-step finite element method is proposed: steady-state mechanical stress is calculated first as the initial condition, followed by transient electro-thermal-mechanical coupling calculations. This method solves for the stress field of long-term static mechanical loads separately beforehand, avoiding repeated iterations of steady-state loads in the transient coupling calculations. This significantly reduces the complexity of fully coupled transient calculations, decreasing computational complexity by approximately 40% while maintaining accuracy. Compared to traditional fully coupled transient methods, computation time can be shortened by more than 60%, significantly improving simulation efficiency.

[0022] 2. It supports three typical installation methods, mechanical loads, and multiple lightning strike simulations, which can accurately reflect the actual stress state of the surge arrester during on-site operation.

[0023] 3. The stress nonlinear enhancement effect was defined and quantified, revealing the mechanism of stress distortion caused by mechanical-electrothermal coupling, and providing a new explanation for arrester seal failure; 4. Accurately capturing the nonlinear stress enhancement effect: This invention, by simultaneously applying mechanical loads and lightning impacts and employing a fully coupled electro-thermal-mechanical solution, can obtain a true reflection of the stress distribution under the combined action. By defining a nonlinear enhancement factor, the coupling effect is quantified for the first time, facilitating engineering judgment. Under typical operating conditions, the nonlinear enhancement factor can reach 1.3–1.8, proving that the traditional linear superposition method systematically underestimates the stress.

[0024] 5. Adaptable to multiple lightning strike scenarios: This invention supports the joint excitation of double and triple lightning strikes and clearly sets the return stroke interval (10ms) and amplitude reduction (half) rules, which can simulate the heat accumulation and stress superposition effect under multiple lightning strikes, and is closer to the actual lightning strike accident.

[0025] 6. Provides quantitative design guidance: By outputting the curve of η changing with different loads through parametric analysis, the boundary conditions of nonlinear enhancement effect can be clearly defined (for example, when the horizontal tensile force is greater than 400N and the number of lightning strikes reaches 3, η>1.5), providing a quantitative basis for surge arrester structure optimization, installation method selection and operation and maintenance strategy formulation. Attached Figure Description

[0026] Figure 1 A schematic diagram of the method flow provided in Example 1 Figure 2 This shows the stress distribution under horizontal installation in Example 2; Figure 3 Example 2 shows the stress distribution of the surge arrester under a single lightning strike; Figure 4 Example 2 shows the stress distribution of the surge arrester under multiple lightning strikes; Figure 5 Stress distribution of surge arrester under unbalanced force and single lightning strike in Example 2 Figure 6 Example 2 shows the stress distribution of a surge arrester subjected to unbalanced forces and multiple lightning strikes. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0028] Example 1

[0029] This embodiment provides a method for calculating the internal stress distribution of a zinc oxide surge arrester based on multi-condition coupling. A three-dimensional geometric model is established based on the actual structural parameters of the surge arrester. Considering the nonlinear characteristics of the material, mechanical loads (horizontal tension, gravity, wind pressure) and lightning impulses (single or multiple 4 / 10μs waveforms) are applied for joint excitation. The finite element method is used to solve the electro-thermal-mechanical coupling control equations. The stress distribution at key interfaces (the junction between the ZnO resistance sheet and the fitting, the junction between the resistance sheet and the insulating cylinder, and the corners of the base) is extracted, and a nonlinear enhancement factor is defined to quantify the combined effect.

[0030] Based on the simulation results, the stress distribution patterns under different installation methods (vertical, 45° tilt, horizontal), different unbalanced force magnitudes, different lightning current amplitudes, and different lightning strike counts can be obtained.

[0031] Step 1. Establishment of the 3D geometric model Based on the actual structural parameters of the surge arrester, a system including ZnO resistance elements, hardware, and epoxy resin insulating cylinder is constructed.

[0032] This implementation adds step 2: Setting material properties. The electrical, thermal, and mechanical parameters of each component are set as shown in Tables 1 and 2, where the conductivity of the ZnO resistance element is set as a nonlinear function of the electric field strength (or current density). Based on the measured VA characteristics, the volt-ampere characteristics are transformed into a current density-conductivity relationship, and the fitting formula is as follows: In the formula, a and b are coefficients.

[0033] Table 1 Material parameters of ZnO resistor sheets Table 2 Material parameters of outerwear and accessories Step 3. Apply boundary conditions and excitation sources (1) Mechanical load: Apply a horizontal tension along the X-axis according to the installation method (vertical, inclined at 45°, horizontal), ranging from 14.7N to 600N; at the same time apply gravity (direction along the negative Y-axis) and wind pressure.

[0034] (2) Lightning impulse: Apply a single or multiple (double or triple) lightning current with a waveform of 4 / 10μs, with an amplitude range of 10kA to 100kA. The amplitude of each subsequent return stroke after a multiple lightning strike is half that of the first return stroke, and the return stroke interval is 10ms.

[0035] Step 4. Solve the electro-thermal-mechanical coupling control equations using a steady-state-transient step-by-step calculation method. The first step is to construct an electro-thermal-mechanical multiphysics coupling model, using the finite element method (such as COMSOL Multiphysics) to couple the following physical fields: electrostatic field, solid heat transfer, and solid mechanics.

[0036] Since the duration of lightning strikes is extremely short, the influence of displacement current is negligible. Therefore, the current continuity equation is used to describe the transient electric field distribution, providing a heat source for subsequent thermal field calculations.

[0037] In the formula, J represents current density; E represents electric field strength; D represents electric displacement vector; Qj,v represents current source density; σ represents conductivity; E represents electric field strength; Je represents external excitation current density; and v represents electric potential.

[0038] After solving the above system of equations and obtaining the current density distribution at each time step, the Joule heat source is calculated as the input load for the solid heat transfer field: In the formula, Q e J represents the heat source; E represents the current density; and E represents the electric field strength.

[0039] Using the Joule heat generated by lightning on a zinc oxide resistor as a transient heat source, an electromagnetic thermal model considering heat conduction and convection processes was established, providing thermal expansion loads for stress field calculations.

[0040] Solid heat transfer equation: Electromagnetic heat transfer equation: Boundary conditions: In the formula, ρ represents the material density; Cp represents the constant-pressure heat capacity; T represents the material temperature; q represents the heat flux; u represents the fluid velocity vector; k represents the thermal conductivity of the medium; and Q represents the heat flux. e Represents the heat source; n represents the outward normal unit vector of the boundary; q represents the heat flux density vector inside the computational domain; q0 represents the heat flux density scalar exchanged through the boundary; h represents the convective heat transfer coefficient; T ext This indicates the reference temperature of the external environment.

[0041] By solving the above system of equations, the temperature distribution at each time step is obtained and used as the input load for the solid mechanical field: In the formula, ε th T represents thermal expansion strain; α represents the coefficient of thermal expansion; T ref Indicates the reference temperature.

[0042] A thermal expansion model was established based on the fact that the stress borne by the surge arrester mainly includes the electrothermal stress generated by the Joule thermal expansion of the zinc oxide resistor sheet and the mechanical stress under unbalanced force.

[0043] Thermal expansion equation: In the formula, ε th T represents thermal expansion strain; α represents the coefficient of thermal expansion; T ref Q represents the reference temperature; Q represents the thermodynamic quantity of the system; Q d S represents the thermodynamic driving force; m α represents the system entropy or rate of entropy change; t This indicates that the coefficient of thermal expansion is corrected to thermal expansion strain.

[0044] This is used to solve for the stress and deformation distribution inside a surge arrester under the combined effects of mechanical load and thermal expansion. The linear elastic solid mechanics equations considering thermal strain and initial deformation are as follows: In the formula, S represents stress; fv represents volume force; u is the displacement vector; ρ represents material density; S0 represents steady-state mechanical stress tensor; E represents Young's modulus; ε th ε represents thermal expansion strain; mech It represents mechanical strain.

[0045] The governing equations of the three physical fields mentioned above are coupled and transmitted through Joule heating and thermal strain, forming a complete electro-thermal-mechanical multiphysics coupling model.

[0046] Then, to reduce the computational complexity of the fully coupled electro-thermal-mechanical multiphysics system while ensuring computational accuracy, a steady-state-transient step-by-step computation method is adopted, and the specific process is as follows: Step 1: Solve for the initial stress and deformation under long-term static mechanical load in advance to avoid simultaneously solving for steady-state and transient loads in transient calculations. The mechanical load is a long-term static load, and the deformation is small; therefore, the linear elastic steady-state equation is used. In the formula, S0 represents the initial mechanical stress tensor; u0 represents the initial displacement vector; fv represents the body force; ε mech,0 E represents the initial mechanical strain; E represents Young's modulus.

[0047] In the finite element software, the lower hardware is set as a fixed constraint, gravity is applied according to the actual installation angle, and a horizontal tensile force and equivalent wind pressure are applied at the high-pressure end. The steady-state linear solver is called to solve the above equations, and the calculated initial mechanical stress tensor and initial displacement field are saved as global variables as the initial conditions for the second transient calculation.

[0048] Step 2: Transient electro-thermal-mechanical coupling calculation. Based on the initial stress and deformation field obtained in Step 1, lightning impact excitation is applied, and the electrostatic field, solid heat transfer field and transient solid mechanical field are solved in sequence to achieve three-field coupling.

[0049] Electric field solution: At each time step, the conductivity of the ZnO resistive sheet is updated according to the current temperature (the first step is the ambient temperature), the electric field equation is solved, the potential V, electric field E and current density J are obtained, and the Joule heat source Qe is calculated.

[0050] Temperature field solution: Calculate the obtained Q e Substituting into the solid heat transfer equation, we solve for the transient temperature field and obtain the temperature distribution T(t).

[0051] Stress field solution: Substitute the temperature field T(t) into the thermal expansion equation, while retaining the initial mechanical stress obtained in the first step, and then substitute the above calculation results into the linear elastic solid mechanics equation. This achieves the direct superposition of mechanical stress and electrothermal stress at the stress tensor level, and takes into account the mutual constraint between the strain caused by thermal expansion and the initial mechanical deformation, thus accurately capturing the nonlinear stress enhancement phenomenon.

[0052] Finally, stress distribution calculation and nonlinear enhancement judgment. Through the above step-by-step finite element calculations, the stress tensor of the entire surge arrester model at any time and any position has been obtained. For ease of evaluation, Von Mises Stress is used as the equivalent stress index, and its calculation formula is as follows: In the formula, σ1, σ2, and σ3 are the three principal stresses of the stress tensor.

[0053] The maximum stress values ​​of key parts of the surge arrester (ZnO resistor interface, resistor corner, and base bolt root) are extracted using the finite element post-processing module and used as the stress characteristic values ​​under this working condition.

[0054] Calculate the stress distribution under the following five working conditions: Condition 1: The superimposed equivalent stress value obtained by linear superposition after mechanical loads act alone. ; Condition 2: The superimposed equivalent stress value obtained by linear superposition after a single lightning strike. ; Operating Condition 3: Multiple Lightning Strikes Only Operating Condition 4: Mechanical Load + Single Lightning Strike Operating Condition 5: Coupled Equivalent Stress Value under Mechanical Load + Multiple Lightning Strike Excitation .

[0055] Step 5, define the nonlinear enhancement factor η as: in, For interfacial stress under combined action, For interfacial stress under mechanical load only, This represents the interfacial stress under lightning strike alone.

[0056] Judgment criteria: η>0: There is a nonlinear stress enhancement effect; the larger η is, the more significant the enhancement. η=0: The stress is linearly superimposed, with no enhancement effect; η<0: Stress cancellation effect exists.

[0057] Step 6, Parametric Analysis and Result Output By changing the unbalanced force value and the lightning current amplitude respectively, the stress distribution and nonlinear enhancement factor under different combinations are calculated, and the stress-load variation curve is plotted.

[0058] Example 2

[0059] This embodiment takes the YH10WS-17 / 50 type 10kV distribution network surge arrester as an example and uses the method provided in the embodiment for calculation: 1. Operating conditions: Horizontal installation, applying a horizontal tensile force of 147N and a wind pressure of 35m / s, superimposed with multiple lightning strikes of 100kA.

[0060] 2. Step-by-step calculation results: (1) The steady-state mechanical stress calculation results are as follows Figure 2 : (2) The calculation results of transient thermal stress are as follows: Single lightning strike calculation only: A single lightning current of 100kA, as described above, is applied to the distribution network surge arrester model. The stress distribution, calculated using the electro-thermal-mechanical simulation model, is as follows: Figure 3 As shown.

[0061] Calculation of multiple lightning strikes only: Applying the aforementioned 100kA amplitude multiple lightning strikes to the distribution network surge arrester model, the stress distribution is as follows... Figure 4 As shown.

[0062] 3. Calculation of combined effects: When the unbalanced force described above is simultaneously applied to the surge arrester model of the distribution network, along with a single lightning strike of 100kA, the stress condition is as follows: Figure 5 As shown.

[0063] When the unbalanced force described above is simultaneously applied to the surge arrester model of the distribution network, along with multiple lightning strikes of 100kA, the stress condition is as follows: Figure 6 As shown.

[0064] 4. Nonlinear enhancement effect: The nonlinear enhancement factor η was calculated to be 21.1% under the combined effect of a single lightning strike and 25.8% under the combined effect of multiple lightning strikes, which is significantly greater than 0, thus verifying the existence of the coupling enhancement effect.

[0065] Example 3

[0066] This embodiment is basically the same as Embodiment 2, except that it does not perform step-by-step calculations, but adopts a fully coupled transient method (i.e., applying mechanical load and lightning impact simultaneously from t=0, both using microsecond-level steps). The calculation time of this method is about 12 hours, while the step-by-step calculation of the present invention only takes 2.5 hours, improving efficiency by about 4.8 times, and the difference in stress results between the two is less than 3%, verifying the accuracy of the step-by-step method provided by the present invention.

[0067] Example 4

[0068] This embodiment provides a system for calculating the internal stress distribution of a zinc oxide surge arrester based on multi-condition coupling, including: Model building module: Used to create a three-dimensional geometric model containing ZnO resistor sheet, hardware and insulating cylinder.

[0069] Joint excitation application module: used to apply joint excitation to the three-dimensional geometric model, the joint excitation including mechanical load and lightning impulse current waveform, wherein the mechanical load includes horizontal tension, gravity and wind pressure, and the lightning impulse current waveform is a 4 / 10μs waveform.

[0070] Step-by-step calculation module: used to solve the electro-thermal-mechanical coupling control equations using a steady-state-transient step-by-step calculation method. The step-by-step calculation module includes: a steady-state solution unit: used to solve the initial stress field and initial deformation field under long-term static mechanical load based on the mechanical load; a transient coupling solution unit: used to apply the lightning impulse current waveform as the initial conditions using the initial stress field and initial deformation field, and perform transient electro-thermal-mechanical coupling calculations, solving the electrostatic field, solid heat transfer field and transient solid mechanical field in sequence to obtain the coupled stress tensor under the joint excitation. In the transient coupling solution unit, the Joule heat generated by the electrostatic field calculation is used as a heat source input to the solid heat transfer field, and the temperature change calculated by the solid heat transfer field is coupled to the transient solid mechanical field through the temperature dependence of the thermal expansion coefficient and material parameters.

[0071] Stress value calculation module: used to extract the coupled equivalent stress value under the joint excitation based on the coupled stress tensor, and to separately calculate the superimposed equivalent stress value obtained by linear superposition of the mechanical load and the lightning impulse current waveform after they are applied separately.

[0072] Nonlinear enhancement judgment and output module: used to define nonlinear enhancement factor, determine whether stress nonlinear enhancement effect exists based on the nonlinear enhancement factor, and output stress distribution data of key interfaces inside the surge arrester under joint excitation.

[0073] It also includes a parametric analysis module: used to change the value of the horizontal tension and the amplitude of the lightning current respectively, repeatedly call the joint excitation application module, the step-by-step calculation module, the stress value calculation module and the nonlinear enhancement judgment and output module, calculate the nonlinear enhancement factor under different combinations, and plot the stress-load variation curve to determine the stress nonlinear enhancement boundary conditions and sensitivity range of the arrester structure under multiple working conditions.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for calculating the internal stress distribution of a zinc oxide surge arrester based on multi-condition coupling, characterized in that, Includes the following steps: S1: Establish a three-dimensional geometric model including ZnO resistor sheet, hardware and insulating cylinder; S2: Apply a joint excitation to the three-dimensional geometric model, the joint excitation including mechanical load and lightning impulse current wave, and the mechanical load and the lightning impulse current wave are applied synchronously in time; S3: The electro-thermal-mechanical coupling control equations are solved by the steady-state-transient step-by-step calculation method to obtain the coupled stress tensor under joint excitation. S4: Extract the coupled equivalent stress value under joint excitation based on the coupled stress tensor. ; The superimposed equivalent stress value is calculated separately by linearly superimposing the mechanical load and the lightning impulse current waveform after they are applied individually. , ; S5: Define the nonlinear enhancement factor η as: in, For interfacial stress under combined action, For interfacial stress under mechanical load only, The interfacial stress under lightning strike alone is used to determine whether there is a stress nonlinear enhancement effect based on the nonlinear enhancement factor. S6: Change the unbalanced force value and lightning current amplitude respectively, calculate the stress distribution and nonlinear enhancement factor under different combinations, plot the stress variation curve with load, and output the stress distribution data of the key interface inside the surge arrester under combined excitation.

2. The calculation method according to claim 1, characterized in that, The mechanical load includes at least the following two: The horizontal tension applied to the top of the surge arrester, the gravitational field acting on the entire model, and the wind pressure distribution load calculated based on the installation height of the surge arrester and the local wind speed are all included. The applied horizontal tension is selected according to the installation method of the surge arrester: vertical installation, 45° inclined installation, or horizontal installation. The value range of the horizontal tension is 14.7N to 600N. The direction of the gravity is along the negative Y-axis.

3. The calculation method according to claim 1, characterized in that, The lightning impulse current wave is a large current wave with an amplitude range of 10kA to 100kA, which is 4 / 10μs. The combined excitation applied in step S2 includes multiple consecutive lightning strikes. The time interval between two adjacent lightning strikes is less than the thermal relaxation time of the ZnO resistor sheet, so as to simulate the heat accumulation and stress superposition effect under multiple lightning strikes. The amplitude of the subsequent return strokes after multiple lightning strikes is taken as half of the first return stroke, and the return stroke interval is 10ms.

4. The calculation method according to claim 1, characterized in that, The step S3, which uses a steady-state-transient step-by-step calculation method to solve the electro-thermal-mechanical coupling control equations, includes the following steps: Based on the aforementioned mechanical load, the initial stress field and initial deformation field under long-term static mechanical load are calculated in advance. Using the initial stress field and initial deformation field obtained above as initial conditions, lightning impulse current waveform excitation is applied, and transient electro-thermal-mechanical coupling calculation is performed. The electrostatic field, solid heat transfer field and transient solid mechanical field are solved in sequence to achieve three-field coupling and obtain the coupled stress tensor under joint excitation.

5. The calculation method according to claim 4, characterized in that, The electro-thermal-mechanical coupling control equations in step S3 satisfy the following coupling relationship: In the electric field equation, the Joule heat of the ZnO resistance sheet is used as a heat source term in the temperature field equation; In the temperature field equation, temperature changes are coupled to the stress field equation through the temperature dependence of the thermal expansion coefficient and material parameters; In the stress field equations, deformation reacts to the electric field equations through piezoresistive effects or geometric changes.

6. The calculation method according to claim 1, characterized in that, The key interfaces in step S5 include at least the following three spatial locations: the interface between the ZnO resistance sheet and the fitting, the interface between the ZnO resistance sheet and the insulating cylinder, and the corner of the base.

7. The calculation method according to claim 1, characterized in that, Step S5 further includes: recording and outputting the variation curves of the nonlinear enhancement factor η under different lightning strikes, different mechanical loads, and different ambient temperatures, so as to determine the stress nonlinear enhancement boundary conditions and sensitivity range of the surge arrester structure under multiple operating conditions.

8. A system for calculating the internal stress distribution of a zinc oxide surge arrester based on multi-condition coupling, characterized in that, include: Model building module: Used to create a three-dimensional geometric model including ZnO resistor sheet, hardware and insulating cylinder; Joint excitation application module: used to apply joint excitation to the three-dimensional geometric model, the joint excitation including mechanical load and lightning impulse current waveform, wherein the mechanical load includes horizontal tension, gravity and wind pressure, and the lightning impulse current waveform is a 4 / 10μs waveform; Step-by-step calculation module: used to solve the electro-thermal-mechanical coupling control equations using a steady-state-transient step-by-step calculation method. The step-by-step calculation module includes: Steady-state solution unit: used to solve the initial stress field and initial deformation field under long-term static mechanical load based on the mechanical load; Transient coupling solution unit: used to apply the lightning impulse current waveform as the initial conditions using the initial stress field and initial deformation field, perform transient electro-thermal-mechanical coupling calculation, solve the electrostatic field, solid heat transfer field and transient solid mechanical field in sequence, and obtain the coupled stress tensor under the joint excitation. Stress value calculation module: used to extract the coupled equivalent stress value under joint excitation based on the coupled stress tensor, and to separately calculate the superimposed equivalent stress value obtained by linear superposition of mechanical load and lightning impulse current waveform after acting separately; Nonlinear enhancement judgment and output module: used to define nonlinear enhancement factor, determine whether stress nonlinear enhancement effect exists based on the nonlinear enhancement factor, and output stress distribution data of key interfaces inside the surge arrester under joint excitation.

9. The system according to claim 8, characterized in that, In the transient coupled solution unit, the Joule heat generated by the electrostatic field calculation is used as a heat source input to the solid heat transfer field. The temperature change calculated by the solid heat transfer field is coupled to the transient solid mechanical field through the temperature dependence of the thermal expansion coefficient and material parameters.

10. The system according to claim 8, characterized in that, It also includes a parametric analysis module: used to change the value of the horizontal tension and the amplitude of the lightning current respectively, repeatedly call the joint excitation application module, the step-by-step calculation module, the stress value calculation module and the nonlinear enhancement judgment and output module, calculate the nonlinear enhancement factor under different combinations, and plot the stress-load variation curve to determine the stress nonlinear enhancement boundary conditions and sensitivity range of the arrester structure under multiple working conditions.

Images