A method for simulating bolt connection reliability in circuit breaker operation process

Abstract

The present application belongs to the technical field of bolt connection simulation, and particularly relates to a simulation method for bolt connection reliability in the operation process of a circuit breaker. The method specifically comprises the following steps: determining the basic structural parameters of the bolt connection, and preliminarily evaluating the bolt connection design based on the bolt structure design standard; after meeting the evaluation standard, modeling the three-dimensional model of the bolt connection and the main parts of the circuit breaker; establishing a bolt connection reliability simulation model for the three-dimensional model, and determining the parts to be included in the entire analysis and the bolt connection to be focused on; the bolt connection included in the bolt connection reliability simulation model is modeled according to the modeling standard to establish a bolt connection grid model; the bolt connection reliability simulation model is subjected to load and simulation solving, and then comprehensive evaluation is performed according to the bolt load standard; if the evaluation meets the standard, the design of the bolt connection is completed. The method can comprehensively predict the failure mode of the bolt connection in the breaking and closing process of the circuit breaker.

Description

Technical Field

[0001] This invention belongs to the field of bolt connection simulation technology, specifically relating to a method for simulating the reliability of bolt connections during circuit breaker operation. Background Technology Circuit breakers generate significant instantaneous impact loads during repeated mechanical operations, which can easily lead to mechanical structure and connection failures. As circuit breaker design voltage levels gradually increase, more and more double-acting self-energized circuit breakers are being used. These circuit breakers generate even greater impact loads due to their faster opening and closing speeds, significantly increasing the risk of structural and connecting component failures. Bolted connections, as a primary connection method in mechanical structures, should be prevented from failing during repeated opening and closing operations in the transmission system. There are many failure modes for bolted connections, including overload fracture, fatigue fracture, bolt slippage, shear failure loosening, and thread stripping. If bolted connection failure occurs during circuit breaker opening and closing operations, it will further lead to test failures, resulting in increased testing costs, project delays, and a series of other serious consequences. Therefore, employing appropriate evaluation methods to ensure the reliability of bolted connections in the early design stages is of paramount importance for circuit breaker engineering.

[0002] Currently, with the development of computer simulation technology, there are increasingly more evaluation methods for bolted connections, but these methods are often relatively one-sided. First, they involve relatively little structural assessment of bolted connections before simulation calculations. Second, regarding the establishment of simulation models, most bolted connection models are not detailed enough, either lacking the definition of the effective compression zone, failing to define cross-sections, or having inconsistent mesh standards, etc. Third, regarding the simulation process, current simulation analyses of bolted connections often fail to consider the changes in clamping force and relaxation stability after bolt tightening, and the load application is basically based on multi-load step steady-state application using static or random vibration loads.

[0003] For the bolted connections in the transmission system of a double-acting self-powered arc-extinguishing chamber, the main loads are a series of impact loads generated during the high-speed opening and closing of the circuit breaker. Therefore, traditional steady-state load application methods cannot accurately simulate the impact loads during circuit breaker operation, thus failing to accurately assess the reliability of the bolted connections. Moreover, most methods for evaluating simulation results only consider bolt loosening or bolt breakage as a single failure assessment criterion. However, the failure modes of actual bolted connections are diverse, and the evaluation criteria are too simplistic, failing to comprehensively consider all bolt failure modes. Summary of the Invention

[0004] The purpose of this invention is to provide a simulation method for the reliability of bolted connections during circuit breaker operation, which solves the problem that existing technologies cannot accurately simulate the impact of impact loads during circuit breaker operation, thus making it impossible to accurately assess the reliability of bolted connections.

[0005] This invention is achieved through the following technical solution: This invention discloses a method for simulating the reliability of bolted connections during circuit breaker operation, comprising the following steps: S1. Determine the basic structural parameters of the bolted connection and conduct a preliminary evaluation of the bolted connection design based on bolted structure design standards; S2. After meeting the evaluation criteria of S1, a three-dimensional model is created for the bolted connection and the main components of the circuit breaker. A reliability simulation model for bolted connections is established based on the 3D model to determine the components to be included in the entire analysis and the bolted connections that are of key concern. The bolt connections included in the bolt connection reliability simulation model are modeled according to the modeling standards to create a bolt connection mesh model. S3. Apply loads to the bolt connection reliability simulation model and perform simulation solutions. Then, conduct a comprehensive evaluation based on the bolt load standard. If the evaluation meets the standard, the bolt connection design is completed.

[0006] Furthermore, in S1, the basic structural parameters of the bolted connection include bolt stiffness, connector stiffness, effective engagement length of the thread, nominal diameter of the bolt, total connection length, bolt preload, and area of ​​the effective contact area between the washer and the connected parts. In S1, a preliminary evaluation of the bolt connection design is conducted based on the bolt structure design standard. Specifically, this includes checking the stiffness ratio of the bolt connection, checking the thread engagement ratio of the bolt connection, checking the ratio of the bolt elongation length to the nominal diameter, and checking the contact stress between the bolt head and the washer.

[0007] Furthermore, the stiffness ratio of a bolted connection is the ratio of the bolt stiffness to the bolted connection stiffness, and the bolted connection stiffness is the sum of the bolt stiffness and the stiffness of the connecting parts. The expression is: ,in For bolt stiffness, For the stiffness of the connector; The formula for calculating bolt stiffness is as follows: ; in, The elastic modulus of the bolt material. The cross-sectional area of ​​the bolt shank connecting the bolt head. L R The length of the bolt rod; C h This is the stiffness coefficient of the bolt head;D The nominal diameter of the bolt; C t This is the stiffness coefficient of the threaded joint; A S This is the effective cross-sectional area of ​​the threaded joint. In the formula Pitch This is the distance between the two threads.

[0008] Furthermore, the thread engagement ratio of a bolted connection is the ratio of the effective engagement length of the thread to its nominal diameter, and the formula is as follows: In the formula, For effective spin length, D This is the nominal diameter of the bolt.

[0009] Furthermore, the ratio of bolt elongation length to nominal diameter must be greater than 2; The contact stress between the bolt head and the washer should be less than 1.1 times the compressive yield strength of the connected parts. The specific calculation formula is as follows: ; In the formula, This represents the contact stress between the bolt head and the washer. This is the maximum preload of the bolt. This refers to the area of ​​the effective contact area between the gasket and the connected component.

[0010] Furthermore, in S2, a bolt connection mesh model is established according to the modeling standards, specifically including the following process: Topological partitioning and full hexahedral mesh generation are performed on bolted connections, and the requirements for the number of bolt mesh layers and the number of elements are defined. The definition requirements for the number of bolt mesh layers and the number of units include the division criteria for bolt heads, washers, bolt tension areas, engagement areas, transition areas, and connectors. Define the contact surfaces of the bolt connection simulation model: including the contact between the bolt head and the washer, the contact between the washer and the connector, and the contact between the connectors; Define the cross-section of the bolt connection simulation model: including the cross-section of the bolt head, the cross-section of the engagement position, and the cross-section of the preload applied; Define the output node set of the bolt connection simulation model: including the node set between the bolt head and the washer, the node set between the washer and the connector, and the node set between the connectors.

[0011] Furthermore, in S2, when establishing the reliability simulation model of bolted connections, all components included in the model are divided into hexahedral meshes, the number of meshes is controlled, and different material properties are defined for each component; the bolts and moving parts that are of particular interest are defined as elastoplastic materials, and non-moving parts are defined as rigid materials.

[0012] Furthermore, in S2, when establishing a reliability simulation model for bolted connections, in addition to setting the contact relationships and connection forms of bolted connections, the contact relationships and connection forms between other transmission components and fasteners must also be included. The contact relationship is as follows: a contact surface is established between components that may generate collision force, while retaining an initial gap. The contact type is surface-to-surface symmetrical contact. The connection method is as follows: the connecting bearings are defined using a rotating pair, and the structural welding adopts a common node connection method; When establishing a simulation model for the reliability of bolted connections, it is also necessary to establish the boundary conditions of the model, which specifically include: setting all the constrained degrees of freedom of the fastener; setting the translational pair of the stationary arc contact so that the stationary arc contact can only move along the axial direction.

[0013] Furthermore, in S3, the process of applying loads to the bolt connection reliability simulation model and performing simulation solutions specifically includes three analysis steps: Step-1 is the implicit steady-state analysis step: apply the minimum bolt preload at the center section of each bolted connection; Step-2 is the implicit steady-state analysis step: the relaxation stability of the bolt is simulated by fixing the length of the bolt; Step-3 is the explicit transient analysis step; the conversion between implicit and explicit algorithms is completed by defining curves; and a load is applied to perform transient analysis to simulate the opening and closing operation process of the entire transmission system under the condition that the bolts have been tightened and then relaxed and stabilized. The conversion between implicit and explicit algorithms is accomplished by defining a curve, specifically as follows: The total analysis time for the bolt connection reliability simulation model is set to T seconds. The first t1 seconds are set to 1, which represents implicit analysis, indicating that the bolt preload is applied and self-relaxed within t1 seconds. The last t2 seconds are set to 0, which represents explicit algorithm for transient analysis, indicating that the mechanism completes the opening and closing operation within t2 seconds. The specific process of applying loads for transient analysis is as follows: The opening and closing load characteristic speed curve is applied to the bolt connection reliability simulation model as a forced speed to drive the transient opening and closing motion of the bolt connection reliability simulation model; A clamping force curve is applied to the end of the stationary arc contact to simulate the clamping resistance generated by the stationary arc contact during opening and closing. The opening and closing load characteristic speed curves and clamping force curves were obtained after polynomial fitting.

[0014] Furthermore, in S3, a comprehensive evaluation is conducted based on the bolt load standard, specifically including the following aspects: Check residual preload: This is used to ensure that the residual preload of the axial force bolted connection output in the simulation is greater than zero; Check the slippage assessment of bolted connections: Transverse shear force causes bolt slippage and loosening. The slippage between the bolt head and the connector is assessed by calculating the ratio of the external shear load to the shear resistance at the bolt contact. Check the total tensile stress of bolts in bolted connections: compare the total tensile stress of bolts obtained from simulation calculations with the yield strength to assess the permanent deformation of the bolts; The formula for calculating the total tensile stress of a bolt is: , A s The effective cross-sectional area of ​​the screw thread. D The nominal diameter of the bolt; The total tensile force of the bolt; In the formula Pitch The distance between the two threads; The formula for calculating the total tensile force of a bolt is: ; In the formula, For maximum preload, F ext For external loads, For bolt stiffness, The height of the connector; Verify the axial stress range and the equivalent bending stress range: The axial stress range is used to evaluate the amount of stress change generated when a bolted connection is subjected to an applied external load, reflecting the fatigue failure mode of the bolt; the equivalent bending stress range combines the effects of cyclic axial stress and bending stress on the bolt, reflecting the fatigue failure mode of the bolt.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a simulation method for the reliability of bolted connections during circuit breaker operation. First, a preliminary evaluation of the bolted connection design is conducted based on structural design standards. After confirming the design is reasonable, a standard simulation model is established for further simulation evaluation. Using simulation software technology, a nonlinear bolted connection mesh model and a bolted connection reliability simulation model are established according to modeling standards. A load analysis step is set for the bolted connection reliability simulation model, and loads are applied for simulation solving. Finally, the reliability of the bolted connection is comprehensively evaluated based on load standards. This method can accurately predict whether bolted connections will fail during actual opening and closing operations. This method can comprehensively predict the failure modes of bolted connections during circuit breaker opening and closing, thereby effectively evaluating the reliability of bolted connections in the circuit breaker drive system under actual opening and closing impact loads. The actual load conditions considered in this invention are closer to reality. This invention uses structural design standard simulation and load standards to conduct a more comprehensive evaluation of the bolts, enabling a more accurate assessment of the reliability of the bolted connections with higher precision.

[0016] Furthermore, the bolt modeling method in this invention is more detailed, with clear mesh and modeling requirements. This modeling method is not limited to bolt modeling of the arc-extinguishing chamber transmission system, but can also be applied to bolt simulation modeling of other structures, making it more versatile.

[0017] Furthermore, when setting the load analysis step for the simulation model, the implicit and explicit phase conversion calculation method is used. First, the implicit algorithm is used to apply the preload to the bolt and calculate the steady-state relaxation. Then, the experimental characteristics and clamping force are used as load inputs, and the explicit algorithm is used to perform transient calculations of opening and closing. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating a method for simulating the reliability of bolt connections during circuit breaker operation, as proposed in this invention. Figure 2 These are the basic structural parameters for bolted connections; Figure 3 The definition diagram of the effective conical compression region of a bolted connection when modeling a simulation model of a bolted connection; Figure 4 A standard drawing for modeling bolted connection mesh models; Figure 5 A schematic diagram showing the contact surface settings of a bolted connection when modeling a simulation model of a bolted connection. Figure 6 The definition of bolt cross-section when modeling a bolted connection simulation model; Figure 7 When modeling bolted connections, the definition of the bolt output node set is provided. Figure 8The structural diagram included in the dynamic analysis model of the bolted connection should include the main bolted connection, the static side structure of the arc-extinguishing chamber, and related non-moving components. Figure 9 The curve is defined to enable the conversion between implicit and explicit algorithms. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0020] The detailed description of the embodiments of the present invention provided in the following figures is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the figures and embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0022] During the development of circuit breakers, various tests are required, including those for temperature rise, insulation, and reliability. During these tests, the operating mechanism often drives the dynamic and static transmission systems to perform opening and closing operations. With increasing voltage levels and the adoption of double-acting arc-extinguishing chambers, the operating power of the entire system is greater than before, and the opening and closing speeds are higher, generating significant opening and closing impact loads. Bolted connections, as a primary connection method in circuit breakers, are more prone to loosening, overload, and fatigue fracture under these large impact loads. This can lead to serious consequences such as test failures and project delays. Therefore, to ensure the reliability of bolted connections, a comprehensive evaluation of bolts during the design phase is crucial.

[0023] Currently, the evaluation of bolted connections in circuit breakers lacks preliminary assessment, often relying directly on simulation analysis. Furthermore, most simulation methods remain at the static analysis stage, and there is a lack of clear definition standards for modeling bolted connections. During actual installation, bolts need to be tightened first, followed by a self-relaxation stabilization process. After installation, the circuit breaker's opening and closing operations are a high-speed transient process. Existing technologies sometimes fail to account for bolt preload and self-relaxation, and sometimes fail to consider transient operating conditions, resulting in significant discrepancies with reality and making it difficult to guarantee simulation accuracy.

[0024] Therefore, this invention proposes a simulation method for the reliability of bolted connections during circuit breaker operation. First, a preliminary assessment of the design based on structural standards is conducted. Then, a standard bolted connection simulation model is established, considering bolt preload and self-relaxation. Next, transient analysis of the opening and closing cycles is performed on the entire simulation. Finally, the simulation results are used for evaluation to comprehensively reflect the reliability of the bolted connections. Compared with existing technologies, this invention is more comprehensive, more realistic, and has greater versatility.

[0025] This invention discloses a method for simulating the reliability of bolted connections during circuit breaker operation, comprising the following steps: S1. Determine the basic structural parameters of the bolted connection and conduct a preliminary evaluation of the bolted connection design based on bolted structure design standards; S2. After meeting the evaluation criteria of S1, a three-dimensional model is created for the bolted connection and the main components of the circuit breaker. A reliability simulation model for bolted connections is established based on the 3D model to determine the components to be included in the entire analysis and the bolted connections that are of key concern. The bolt connections included in the bolt connection reliability simulation model are modeled according to the modeling standards to create a bolt connection mesh model. S3. Apply loads to the bolt connection reliability simulation model and perform simulation solutions. Finally, conduct a comprehensive evaluation based on the bolt load standard. If the evaluation meets the standard, the bolt connection design is completed.

[0026] In S1, determine as follows Figure 2 The basic structural parameters of the bolted connection are shown, and a preliminary evaluation of the bolted connection is performed based on bolt structure design standards. The specific steps are as follows: Figure 2 In this context, D represents the nominal diameter of the bolt; D H L1 represents the bolt hole diameter; L2 represents the bolt non-threaded transition length; L3 represents the bolt thread non-engaged length; L represents the bolt engaged length; L J This represents the bolt extension length.

[0027] The structural design standards for bolts specifically include the following four points: 1.1 Check the stiffness ratio of the bolted connection. The formula is: ,in For bolt stiffness, This refers to the stiffness of the connecting parts. The smaller the stiffness ratio of the bolted connection, the less external load is absorbed by the bolts. Generally, this value is required to be less than 30%.

[0028] Bolt stiffness Bolt stiffness is determined by three components: bolt shank stiffness, bolt head stiffness, and bolt thread stiffness. Under load, the bolt head and the first few engaged threads all affect bolt stiffness. And participate in bolt stiffness The calculation.

[0029] The stiffness of the bolt rod can be calculated using the formula... To demolish, among which, The axial tensile force acting on the bolt. This refers to the amount of deformation after being subjected to tensile force. The elastic modulus of the bolt material. This refers to the cross-sectional area of ​​the bolt shank connecting the bolt head. If the bolt shank has different cross-sectional areas... Then the stiffness of the bolt rod needs to be increased. K R Perform segmented calculations; L R The length of the bolt rod. L R= L1+L2+L3.

[0030] Bolt head stiffness can be determined by formula Perform the calculation, where, C h Let be the stiffness coefficient of the bolt head, taken as 0.4; D This is the nominal diameter of the bolt.

[0031] Bolt thread stiffness can be achieved through Perform calculations. In the formula Pitch The distance between the two threads. A S This is the effective cross-sectional area of ​​the threaded joint. C t The stiffness coefficient of the threaded joint is 0.6.

[0032] After calculating the stiffness of the bolt shank, bolt head, and threads, the final formula for calculating bolt stiffness is: .

[0033] The key to stiffness calculation of connectors is to determine the effective compression cone region. The evaluation method for the effective compression region can be found in [reference needed]. Figure 3 Define the stiffness of the connector. .in, The elastic modulus of the connecting material; The projected area of ​​the effective compression cone region of the connector; This represents the bolt extension length.

[0034] In addition to the above formula calculations, the stiffness of bolts and connectors can also be calculated by applying a single axial tensile force to the finite element bolt model.

[0035] 1.2. Check the thread engagement ratio. The formula is: In the formula, The effective spin length is Figure 2 L3 in D This is the nominal diameter of the bolt. This value is typically used to ensure that the threaded engagement area is not the weakest point of the connection, prioritizing sufficient strength for the internal threads. Generally, when components are made of aluminum, bolt connections require a value greater than 2; when components are made of steel, bolt connections require a value greater than 1.5.

[0036] 1.3. Check the contact stress between the bolt head and the washer. The contact stress should be less than 1.1 times the stress of the bolt head. The compressive yield strength of the joint. The formula for calculating the contact stress is: In the formula, This is the maximum preload of the bolt. This refers to the area of ​​the effective contact area between the gasket and the connected component.

[0037] The formula for calculating the preload of a bolt is as follows: , T To tighten the torque, k T As the torque coefficient, when calculating the maximum preload, K T Take 0.1; when calculating the minimum preload, K T Take 0.2.

[0038] 1.4. Verify the ratio of bolt elongation to nominal diameter. Bolt elongation is the length from the bottom of the bolt head to the first effective engagement position. This invention requires this value to be greater than 2. Ensuring the bolt elongation can reduce the loss of preload, prevent bolt loosening, and effectively reduce the dynamic stress transmitted to the bolt by external loads.

[0039] In S2, after a preliminary assessment that meets the above structural standards, 3D solid models of the bolted connections and main components of the circuit breaker are created using modeling software such as UG. The model should include the main moving parts during the opening and closing operations of the arc-extinguishing chamber, as well as the related non-moving parts that provide support and constraints for the moving parts.

[0040] Using simulation software technology, a bolt connection mesh model is established according to certain modeling standards. Specifically, ANSA or Hypermesh is used for discretization modeling, and the bolts are divided into full hexahedral meshes.

[0041] When meshing, the size of the effective compression region of the 30° cone needs to be defined, refer to... Figure 3 The conical region can be drawn using two sets of lines. The first set of lines is drawn at a 30° angle from the bottom of the bolt head and the outside of the contact surface with the washer. The second set of lines is drawn at a 30° angle from the depth of the threaded hole at 0.8 times the nominal diameter of the bolt. By extending, intersecting, or reaching the edge of the component, the conical compression region can be obtained.

[0042] For standards on mesh modeling of bolts, please refer to Figure 4 Four layers of mesh should be established in the axial direction of the bolt head, and 16 to 24 elements should be included in the circumferential direction. The mesh in the bolt tension area should be no less than eight layers, and the mesh in the bolt engagement area should be no less than six layers. Common nodes should be set for the bolt engagement area and the connector. Two layers of mesh should be set for the gasket. A 1mm non-contact area should be set on the outer ring of the effective compression area.

[0043] The contact surface settings for bolted connections should refer to Figure 5 Set up diagrams a and b in the diagram, and establish a set of contact surfaces 1 between the bolt head and the washer, 2 between the washer and the connector, and 3 between the connectors.

[0044] Bolt head cross-section definition reference Figure 6 The definitions are as follows: Figure a shows a schematic diagram of the bolt cross-section, and Figure b shows a three-dimensional schematic diagram of the bolt cross-section. Specifically, the bolt head is defined as being offset downwards by 1mm, the tension section is defined as being located at the middle of the bolt tension region, and the engagement section is defined as being offset upwards by 1mm.

[0045] The definition of the output node set of bolts can be found in [reference]. Figure 7 Define, such as Figure 7 As shown in Figures a and b, output node set 1 is defined on the contact surface between the bolt head and the washer, output node set 2 is defined on the contact surface between the washer and the connector, and output node set 3 is defined on the contact surface between the connectors.

[0046] Using simulation technology, a reliability simulation model for bolted connections is established according to mesh modeling standards. A specific example can be found here. Figure 8 Mesh modeling was performed, using hexahedral meshes throughout. The model included key bolt connections, such as beam connection bolts and static arc contact connection bolts, and the bolt modeling method described in step 3 was used.

[0047] Specifically, the simulation model for the reliability of bolted connections includes defining the models of each transmission component, setting a rotating pair at the bearing location, setting the frictional contact between the contact surfaces of each component while retaining the initial clearance, and setting the friction type to double-sided symmetrical contact. A common node connection method is also set between welded parts.

[0048] The definition of bolt materials should consider nonlinearity and define them as elasto-plastic materials. Major moving transmission components, such as shift forks, racks, and push rod pins, should be made of elasto-plastic materials. Non-moving components should be made of rigid materials, used only for load transmission, to reduce computational resources. The positions of the mounting flange bolt holes in the entire stationary circuit breaker transmission system should constrain all degrees of freedom. A translational pair should be provided at the end of the stationary arc contact, allowing only axial translation of the stationary arc contact.

[0049] In S3, loads are applied to the bolt connection reliability simulation model for simulation and solution. Specifically, load analysis steps are first set for the bolt connection reliability simulation model. Specifically, Ls-Dyna is used to define the load steps, which include a total of three analysis steps: Step-1 is the implicit steady-state analysis step, where the minimum bolt preload is applied to the center section of the bolt. The minimum preload can be obtained using the formula in Step-1. The minimum preload is usually used to evaluate the shear resistance of the bolted connection, the connection gap, and the bolt's ability to withstand cyclic loads, while the maximum stress is used to evaluate the contact stress.

[0050] Step-2 is the implicit steady-state analysis step. After the bolt is preloaded in step-1, it will produce axial elastic deformation. By fixing the length of the bolt, the self-relaxation and stable state of the bolt after the preload is tightened can be simulated, which is more consistent with the actual installation state of the bolt.

[0051] Step-3 is the explicit transient analysis step: the conversion between implicit and explicit algorithms is completed by defining curves, and a load is applied to perform transient analysis to simulate the opening and closing operation process of the entire transmission system under the condition that the bolts have been tightened and then relaxed and stabilized.

[0052] The conversion between implicit and explicit algorithms is achieved by defining a curve. Specifically, the conversion curve can be found in the following reference: Figure 9 The total model analysis time is 1.04 seconds. Setting the value to 1 for the first second indicates implicit analysis, meaning the bolt preload application and self-relaxation are completed within 1 second. Setting the value to 0 for the next 40 seconds indicates explicit algorithm-based transient analysis, meaning the mechanism completes the tripping operation within 40 seconds. Curve conversion is achieved through the control card *CONTROL_IMPLICIT_GENERAL.

[0053] Transient analysis is performed by applying loads. Specifically, after 1 second of analysis time, the opening and closing load characteristic speed curve is applied to the moving side transmission component. After the moving side component moves for a period of time, it drives the stationary side transmission component, such as the pull rod, fork, and rack, to move and complete the opening and closing process of the final stationary arc contact. The clamping force curve is applied to the end of the stationary arc contact to simulate the clamping resistance experienced by the stationary arc contact during the opening and closing process.

[0054] Once the model is set up, you can use Ls-Run to perform simulation and obtain simulation results.

[0055] Among them, the speed curve of opening and closing load characteristics and the clamping force curve can be obtained by actual measurement. After the obtained measured curves are smoothed by polynomial fitting, they are applied to the simulation model for solution.

[0056] In S3, a comprehensive evaluation is conducted based on the bolt load standard, specifically including the following points: Check residual preload: The distribution of external load is evaluated by calculating the residual preload on the contact surface using simulation. The residual preload must be greater than zero. If the residual preload is less than zero, it indicates that the bolt is no longer tightened after bearing the load and no longer has shear resistance; in this case, the external load is entirely borne by the bolt. If this requirement is not met, a higher tightening torque or a larger stiffness ratio can be used to increase the residual preload.

[0057] Verify the slippage assessment of bolted connections: The shear resistance is calculated by multiplying the residual preload output from the bolt simulation model contact pair by the coefficient of friction. The slippage assessment formula for bolted connections is also provided. , The external shear load obtained on the contact pair. That is, shear resistance. The coefficient of friction is typically taken as 0.05 to 0.1.

[0058] Bolt slippage typically occurs at the bolt head contact pair and the contact pair between two connecting parts. For the bolt head contact pair, the external shear load divided by the shear resistance should be less than 30%; for the contact pair between two connecting parts, the external shear load divided by the shear resistance should be less than 95%. If either condition is met, the bolt is considered highly likely to slip, leading to bolt loosening and failure. Slippage assessments for each bolt head and connecting part should be performed separately. If the slippage assessment requirements are not met, using more bolts or a higher tightening torque, increasing the friction coefficient of the connecting parts, or increasing the stiffness ratio can all improve shear resistance.

[0059] Check the total tensile stress of the bolts in the bolted connection: Comparing the total tensile stress and yield strength of the bolt obtained from simulation calculations reveals that if the stress exceeds the yield strength, the bolt will undergo permanent deformation, potentially leading to loosening or breakage. The total tensile stress of the bolt can also be easily verified using the following empirical formula: [Formula for calculating the total tensile force of a bolt is missing from the original text]. In the formula, For maximum preload, F ext For external loads, This refers to the height of the connector. When an external load is applied to a bolted connection, part of it is borne by the bolts, and part is unloaded by the connector.

[0060] The formula for calculating the total tensile stress of a bolt is: , In the formula Pitch The distance between the two threads. A s The effective cross-sectional area of ​​the screw thread. D This is the nominal diameter of the bolt.

[0061] Simulation results often take into account elastic deformation and changes in stress cross-section, making them more accurate than empirical formulas. The total tensile stress of the bolts should be less than the yield strength. If this requirement is not met, optimization can be achieved by using more bolts or bolts with higher strength, or by reducing the stiffness ratio to lower the stress.

[0062] Check the axial stress range and equivalent bending stress range: The stress variation range of a bolted connection under applied external load is evaluated, reflecting the fatigue failure mode of the bolt. First, the axial stress range and the equivalent bending stress range need to be obtained. For the axial stress range, simulation can obtain the axial external load borne by the bolt. Dividing this by the simulated cross-sectional area of ​​the bolt yields the axial stress range, as shown in the theoretical formula. ;in , This represents the axial external load borne by the bolt. A s This refers to the effective cross-sectional area of ​​the threaded joint. For 10.9 grade bolts, the axial stress range is generally required to be less than 100 MPa.

[0063] Similarly, the equivalent bending stress range can be obtained from the bolt bending moment obtained through simulation, and the calculation formula is as follows: ,in, M Represents the bolt bending moment. For the moment of inertia, The diameter representing the effective tensile zone of the bolt. . D This refers to the nominal diameter of the bolt.

[0064] Based on the axial stress range and the bending stress range, the equivalent bending stress range can be checked. The formula for calculating the equivalent bending stress range is as follows: For grade 10.9 bolts, this value is generally required to be less than 150 MPa. This value ensures that the bolt meets fatigue requirements. Failure to meet this requirement may lead to fatigue failure, accompanied by crack initiation, crack growth, crack propagation, and eventually bolt fracture. Optimization can be achieved by using more and larger bolts or reducing the stiffness ratio.

[0065] Once the bolt load standard is fully evaluated and meets the requirements, the bolt design can be completed and subsequent testing and verification can be carried out.

[0066] In summary, the simulation method for bolt connection reliability during circuit breaker operation in this invention begins with a preliminary assessment of the bolt structure design based on defined structural design standards. A standard bolt connection simulation model is then established, and a combination of implicit and explicit calculation methods fully considers the application and relaxation stability of bolt preload. The reliability of the bolts under circuit breaker opening and closing conditions is calculated. Finally, a comprehensive evaluation is conducted using load standards to ensure that the bolt connection meets design requirements and that the circuit breaker will not fail during subsequent tests.

[0067] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for simulating the reliability of bolted connections during circuit breaker operation, characterized in that, Includes the following steps: S1. Determine the basic structural parameters of the bolted connection and conduct a preliminary evaluation of the bolted connection design based on bolted structure design standards; S2. After meeting the evaluation criteria of S1, a three-dimensional model is created for the bolted connection and the main components of the circuit breaker. A reliability simulation model for bolted connections is established based on the 3D model to determine the components to be included in the entire analysis and the bolted connections that are of key concern. The bolt connections included in the bolt connection reliability simulation model are modeled according to the modeling standards to create a bolt connection mesh model. S3. Apply loads to the bolt connection reliability simulation model and perform simulation solutions. Then, conduct a comprehensive evaluation based on the bolt load standard. If the evaluation meets the standard, the bolt connection design is completed. In S3, the process of applying loads to the bolt connection reliability simulation model and performing simulation solutions specifically includes three analysis steps: Step-1 is the implicit steady-state analysis step: apply the minimum bolt preload at the center section of each bolted connection; Step-2 is the implicit steady-state analysis step: the relaxation stability of the bolt is simulated by fixing the length of the bolt; Step-3 is the explicit transient analysis step; the conversion between implicit and explicit algorithms is completed by defining curves; and a load is applied to perform transient analysis to simulate the opening and closing operation process of the entire transmission system under the condition that the bolts have been tightened and then relaxed and stabilized. The conversion between implicit and explicit algorithms is accomplished by defining a curve, specifically as follows: The total analysis time for the bolt connection reliability simulation model is set to T seconds. The first t1 seconds are set to 1, which represents implicit analysis, indicating that the bolt preload is applied and self-relaxed within t1 seconds. The last t2 seconds are set to 0, which represents explicit algorithm for transient analysis, indicating that the mechanism completes the opening and closing operation within t2 seconds. The specific process of applying loads for transient analysis is as follows: The opening and closing load characteristic speed curve is applied to the bolt connection reliability simulation model as a forced speed to drive the transient opening and closing motion of the bolt connection reliability simulation model; A clamping force curve is applied to the end of the stationary arc contact to simulate the clamping resistance generated by the stationary arc contact during opening and closing. The opening and closing load characteristic speed curves and clamping force curves were obtained after polynomial fitting.

2. The method for simulating the reliability of bolted connections during circuit breaker operation according to claim 1, characterized in that, In S1, the basic structural parameters of bolted connections include bolt stiffness, connecting member stiffness, effective engagement length of the thread, nominal diameter of the bolt, total connection length, bolt preload, and area of ​​effective contact area between the washer and the connected member. In S1, a preliminary evaluation of the bolt connection design is conducted based on the bolt structure design standard. Specifically, this includes checking the stiffness ratio of the bolt connection, checking the thread engagement ratio of the bolt connection, checking the ratio of the bolt elongation length to the nominal diameter, and checking the contact stress between the bolt head and the washer.

3. The method for simulating the reliability of bolted connections during circuit breaker operation according to claim 2, characterized in that, The thread engagement ratio of a bolted connection is the ratio of the effective engagement length of the thread to its nominal diameter, expressed by the formula: In the formula, For effective spin length, D This is the nominal diameter of the bolt.

4. The method for simulating the reliability of bolted connections during circuit breaker operation according to claim 2, characterized in that, The ratio of bolt elongation to nominal diameter must be greater than 2; The contact stress between the bolt head and the washer should be less than 1.1 times the compressive yield strength of the connected parts. The specific calculation formula is as follows: ; In the formula, This represents the contact stress between the bolt head and the washer. This is the maximum preload of the bolt. This refers to the area of ​​the effective contact area between the gasket and the connected component.

5. The method for simulating the reliability of bolted connections during circuit breaker operation according to claim 1, characterized in that, In S2, a bolt connection mesh model is created according to the modeling standards, which specifically includes the following process: Topological partitioning and full hexahedral mesh generation are performed on bolted connections, and the requirements for the number of bolt mesh layers and the number of elements are defined. The definition requirements for the number of bolt mesh layers and the number of units include the division criteria for bolt heads, washers, bolt tension areas, engagement areas, transition areas, and connectors. Define the contact surfaces of the bolt connection simulation model: including the contact between the bolt head and the washer, the contact between the washer and the connector, and the contact between the connectors; Define the cross-section of the bolt connection simulation model: including the cross-section of the bolt head, the cross-section of the engagement position, and the cross-section of the preload applied; Define the output node set of the bolt connection simulation model: including the node set between the bolt head and the washer, the node set between the washer and the connector, and the node set between the connectors.

6. The method for simulating the reliability of bolted connections during circuit breaker operation according to claim 1, characterized in that, In S2, when establishing a reliability simulation model for bolted connections, all components included in the model are divided into hexahedral meshes, the number of meshes is controlled, and different material properties are defined for each component; the bolts and moving parts are defined as elastoplastic materials, while non-moving parts are defined as rigid materials.

7. The method for simulating the reliability of bolted connections during circuit breaker operation according to claim 1, characterized in that, In S2, when establishing a reliability simulation model for bolted connections, in addition to setting the contact relationships and connection forms of bolted connections, the contact relationships and connection forms between other transmission components and fixed components must also be included. The contact relationship is as follows: a contact surface is established between components that may generate collision force, while retaining an initial gap. The contact type is surface-to-surface symmetrical contact. The connection method is as follows: the connecting bearings are defined using a rotating pair, and the structural welding adopts a common node connection method; When establishing a simulation model for the reliability of bolted connections, it is also necessary to establish the boundary conditions of the model, which specifically include: setting all the constrained degrees of freedom of the fastener; setting the translational pair of the stationary arc contact so that the stationary arc contact can only move along the axial direction.

8. The method for simulating the reliability of bolted connections during circuit breaker operation according to claim 1, characterized in that, In S3, a comprehensive evaluation is conducted based on bolt load standards, specifically including the following aspects: Check residual preload: This is used to ensure that the residual preload of the axial force bolted connection output in the simulation is greater than zero; Check the slippage assessment of bolted connections: Transverse shear force causes bolt slippage and loosening. The slippage between the bolt head and the connector is assessed by calculating the ratio of the external shear load to the shear resistance at the bolt contact. Check the total tensile stress of bolts in bolted connections: compare the total tensile stress of bolts obtained from simulation calculations with the yield strength to assess the permanent deformation of the bolts; The formula for calculating the total tensile stress of a bolt is: , A s The effective cross-sectional area of ​​the screw thread. D The nominal diameter of the bolt; The total tensile force of the bolt; In the formula Pitch The distance between the two threads; The formula for calculating the total tensile force of a bolt is: ; In the formula, For maximum preload, F ext For external loads, For bolt stiffness, For the stiffness of the connector; Verify the axial stress range and the equivalent bending stress range: The axial stress range is used to evaluate the amount of stress change generated when a bolted connection is subjected to an applied external load, reflecting the fatigue failure mode of the bolt; the equivalent bending stress range combines the effects of cyclic axial stress and bending stress on the bolt, reflecting the fatigue failure mode of the bolt.

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