Method and system for establishing dynamic response and damage model of dry casing under earthquake influence

Abstract

The invention belongs to the technical field of electrical equipment, and discloses a dry-type bushing dynamic response calculation and core crack damage model establishment method under the earthquake action, and after vibration response simulation of a transformer bushing under the earthquake working condition is completed, various important data can be obtained; according to the method, related data such as acceleration response, displacement response, actual stress, deformation degree, stress concentration and the like are acquired, so that various parameters of the structure and the material can be adjusted, and corresponding optimization can be carried out. Through the simulation, the conditions of various physical effects in the 110kV impregnated paper dry-type bushing can be predicted, and the service life of the material in an actual scene can be accurately determined. According to the method, two fracture phase field models are established, crack propagation simulation is carried out on the thin plate under different loading conditions, numerical calculation is carried out by establishing the phase field model of the isotropic plate fracture problem and utilizing finite element analysis software, and the crack propagation process of the thin plate with the initial crack under the action of stretching and shearing loads is researched. And the influence of each parameter on crack propagation is calculated.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrical equipment, and in particular relates to a method and system for calculating the dynamic response of a dry bushing under earthquake action and establishing a core crack damage model. Background Art

[0002] Dry-type bushing has the characteristics of stable electrical performance, oil-free flame retardant, small size, light weight, etc. Compared with oil-impregnated paper bushing, it has good fire and explosion resistance. In the context of the development of power grids and power equipment with increasingly higher requirements for safety and performance, the application of dry-type bushing is increasing, but its manufacturing process is complex and difficult, especially for large-sized bushings. In the production process, improper process control will produce defects such as bubbles, cracks and foreign matter. These defects often have little effect on the overall insulation performance of the bushing in the early stage, but in extreme working conditions such as earthquakes, its internal tiny defects are easily affected by strong loads and develop rapidly, causing serious damage to the core, thereby posing a great threat to the safety of the power system, and ultimately leading to reduced insulation performance or breakdown, thus affecting the safe and stable operation of the power grid.

[0003] Transformer bushing is a key substation equipment for the normal operation of the power transmission and transformation system. It is mainly composed of two parts: the transformer box and the insulating bushing. The box structure is complex and the bushing structure is slender. Statistics of major earthquakes at home and abroad show that: because the natural frequency of the transformer is close to the frequency of seismic waves, it is severely damaged in high-intensity earthquake areas, which not only causes direct economic losses, but also brings serious secondary disasters. At present, there is little research on the dynamics of dry bushings under special working conditions, and the electrical characteristics of dry bushings under earthquake conditions still need to be further studied.

[0004] The transformer-bushing system is one of the important equipment in the power system and is severely damaged in earthquakes. The existing numerical models have simplified the original structure a lot, especially the simulation of the connection position between the bushing flange and the riser has a great influence on the bushing response results. At the same time, due to the large size of the high-voltage transformer, it is difficult to implement the vibration table test of the transformer prototype structure under the existing conditions. Therefore, in order to establish a reasonable high-voltage transformer-bushing system seismic performance analysis method, optimize the seismic design of the transformer-bushing system, establish a high-voltage transformer-bushing system finite element model, and calculate and analyze its dynamic response under earthquake action, it is necessary.

[0005] Through the above analysis, the problems and defects of the prior art are as follows:

[0006] The transformer-bushing system is one of the important equipment in the power system and is severely damaged in earthquakes. The existing numerical models have simplified the original structure a lot, especially the simulation of the connection position between the bushing flange and the riser has a great influence on the bushing response results. At the same time, due to the large size of the high-voltage transformer, it is difficult to implement the vibration table test of the transformer prototype structure under the existing conditions. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a method for calculating the dynamic response of a dry casing under earthquake action and establishing a core crack damage model.

[0008] The present invention is implemented in this way: a method for calculating the dynamic response of dry casing under earthquake action and establishing a core crack damage model comprises:

[0009] Step 1, establishing a transformer-bushing system simulation model;

[0010] Transformer-elevator-bushing model, the insulating bushing is connected to the oil tank through the elevator, where the transformer side plate and bottom plate are 15mm thick, the top plate is 20mm thick, the elevator is 1600mm long, the wall thickness is 20mm, the inclination angle is 20°, and the structure is Q235 steel; the overall height of the bushing is 2840mm, the maximum outer diameter at the flange is 200mm, and the air side height is 1450mm;

[0011] Step 2, seismic wave selection and loading method;

[0012] According to the actual glue-impregnated paper dry casing, a finite element model was established for simulation analysis. The overall force distribution characteristics of the casing under the simulated base vibration load were analyzed using the time history analysis method to study the influence of mechanical vibration load on the force distribution.

[0013] Step 3: Analysis of transformer-bushing vibration response under earthquake conditions;

[0014] Step 4: Establish crack extension model.

[0015] Furthermore, the seismic wave selection and loading method:

[0016] (1) For electrical equipment with an axisymmetric structure and arranged vertically, a single horizontal earthquake test shall be conducted; for electrical equipment with an asymmetric structure, two horizontal earthquake tests shall be considered; for electrical equipment with long cantilevers or large spans, vertical earthquake tests shall also be considered;

[0017] (2) The test response spectrum TRS generated by the vibration table should envelope the required response spectrum RRS. If a small number of single points in the TRS are outside the tolerance band and offset from the resonant frequency of the test equipment, it is acceptable. Considering that the maximum displacement of some vibration tables is limited and the lower frequency part has little effect on the equipment, the tolerance of the spectrum value below 0.7 times the natural frequency of the equipment can be uncontrolled.

[0018] Further, the transformer-bushing vibration response analysis under the earthquake condition:

[0019] 1) Modal analysis;

[0020] Firstly, the modal analysis of the whole model is carried out to obtain the natural frequencies and vibration modes of the first 20 modal modes of the model. The 1st to 6th modal vibration modes are mainly concentrated on the side wall of the oil tank, showing the form of alternating absorption and expansion. At the same time, there will be a small local buckling at the upper end of the casing. The 7th modal vibration mode casing shows an upward bending shape, the 12th modal vibration mode casing shows a rightward bending shape, and the 16th to 20th modal casings all show large deformations. The vibration modes of each order are mainly concentrated in the slender structure on the upper part of the casing and the side plate of the oil tank.

[0021] 2) Analysis of acceleration response of dry casing at different positions;

[0022] Since the bushing is a slender structure, it is connected to the transformer box through a riser. In order to study the acceleration response of the bushing under different earthquake levels, the earthquake response of different levels is studied respectively; the acceleration response values ​​of the top, flange and bottom of the bushing are extracted and analyzed respectively;

[0023] 3) Analysis of displacement response of dry casing at different positions;

[0024] 4) Analysis of stress response of dry casing at different positions.

[0025] Furthermore, the displacement response analysis of the dry casing at different positions is as follows:

[0026] As the casing height increases, its displacement shows a significant upward trend, that is, the displacement at the top is greater than that at the middle and bottom. The maximum horizontal displacement at the top of the casing is most affected by the earthquake, while the maximum vertical displacement at the middle and bottom are most affected by the earthquake.

[0027] Further, the stress response analysis of the dry casing at different positions is as follows:

[0028] The maximum acceleration, maximum displacement and maximum stress of the bushing vibration response under different earthquake levels were extracted respectively. With the increase of earthquake level, the peak values ​​of various responses showed an upward trend. When the earthquake level reached 8, the maximum acceleration peak of the bushing was 163.83m / s2, the displacement peak was 25.35mm, and the stress peak was 4.55MPa. Under this earthquake level, the top acceleration was 4.3 times that of the bottom, posing a great safety hazard to the mechanical properties of the transformer bushing. Since the epoxy core is a brittle material, its tensile and compressive strengths are much lower than those of other components.

[0029] Further, the crack propagation model is established:

[0030] Two fracture phase field models are established to simulate the crack propagation of thin plates under different loading conditions. By establishing a phase field model for the isotropic plate fracture problem and using finite element analysis software for numerical calculations, the crack propagation process of a thin plate with an initial crack under tensile and shear loads is studied, and the influence of various parameters on crack propagation is calculated.

[0031] Another object of the present invention is to provide a method system for calculating the dynamic response of dry casing under earthquake action and establishing a core crack damage model, comprising:

[0032] Simulation model building module, used for transformer-bushing system simulation model building;

[0033] Loading module, used for seismic wave selection and loading method;

[0034] Response analysis module, used for transformer-bushing vibration response analysis under earthquake conditions;

[0035] Extension model building module, used for crack extension model building.

[0036] Another object of the present invention is to provide a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method for calculating the dynamic response of the dry casing under earthquake action and establishing the core crack damage model.

[0037] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to execute the steps of the method for calculating the dynamic response of the dry casing under earthquake action and establishing a core crack damage model.

[0038] Another object of the present invention is to provide an information data processing terminal, which is used to implement the dry casing dynamic response calculation and core crack damage model establishment method system under earthquake action.

[0039] Another object of the present invention is to provide a method system for calculating the dynamic response of dry casing under earthquake action and establishing a core crack damage model, comprising:

[0040] A simulation model module of transformer-elevator-dry bushing is established, in which the transformer is connected to the oil tank through the elevator. The structural parameters of the bushing are as follows: the overall height of the bushing is 2840 mm, the maximum outer diameter at the flange is 200 mm, the air side height is 1450 mm, the length of the elevator is 1600 mm, the wall thickness is 20 mm, the inclination angle is 20°, and the model is made of Q235 steel.

[0041] The seismic wave loading module simulates the vibration of the base by loading actual seismic waves based on the time history analysis method, and analyzes the influence of mechanical vibration load on the stress distribution of the casing;

[0042] Dynamic response analysis module, used to calculate the dynamic response of the transformer-bushing system under seismic loads, including displacement, velocity, acceleration and stress distribution;

[0043] The crack propagation model module is used to predict the generation and propagation path of cracks in dry casing under earthquake action through simulation analysis of stress concentration areas.

[0044] Furthermore, the system also includes an acceleration response analysis module for analyzing the acceleration responses of the top, flange and bottom of the dry casing under different earthquake levels, and outputting the acceleration distribution characteristics of each casing position under different earthquake conditions.

[0045] Furthermore, the system also includes a displacement response analysis module for analyzing the displacement response of the dry casing under different seismic loads, and outputting the displacement change trends of the top, middle and bottom ends, especially the displacement response of the top in the horizontal direction and the middle and bottom in the vertical direction.

[0046] Furthermore, the system also includes a crack propagation analysis module, which simulates the crack propagation path through finite element calculation, outputs the casing crack generation and propagation process under different seismic conditions, and evaluates the impact of crack propagation on the casing structure.

[0047] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0048] First, after completing the vibration response simulation of the transformer bushing under earthquake conditions, the present invention can obtain various important data, such as acceleration response, displacement response, actual force, deformation degree, stress concentration and other related data, so that various parameters of the structure and materials can be adjusted and optimized accordingly. Through this simulation, the various physical effects in the 110kV glue-impregnated paper dry bushing can be predicted, and the service life of the material in the actual scene can be accurately determined.

[0049] The present invention establishes two fracture phase field models, simulates crack propagation of thin plates under different loading conditions, establishes a phase field model of isotropic plate fracture problem, and uses finite element analysis software to perform numerical calculations to study the crack propagation process of a thin plate with an initial crack under tensile and shear loads, and calculates the influence of various parameters on crack propagation.

[0050] Second, as auxiliary evidence of the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0051] (1) The expected benefits and commercial value of the technical solution of the present invention after transformation are:

[0052] (2) The technical solution of the present invention fills the technical gap in the industry at home and abroad:

[0053] At present, there are few studies on the vibration response characteristics of 110kV dry bushings at home and abroad, and the defects that may be caused by earthquakes have not been studied. This paper studies the dynamic response of bushings under earthquake conditions, extracts the core stress distribution, applies it as an external load to the crack propagation model of epoxy core thin plates, and studies the accelerated evolution process of crack defects under earthquakes.

[0054] (3) Whether the technical solution of the present invention solves the technical problems that people have been eager to solve but have not been able to solve successfully:

[0055] The dry casing is large in size, and field tests are difficult and the working conditions are complex. It is difficult to reflect the internal stress and defect distribution law of the dry casing core under different working conditions. By simulating extreme working conditions through simulation calculation, the dynamic response of the casing and the development of crack damage under different earthquake levels are studied, and the weak stress areas and damage mechanisms of the dry casing are revealed, which provides a research basis for the structural optimization of the dry casing and provides a research basis for improving the risk prevention and control of dry casing operation and maintenance.

[0056] (4) Whether the technical solution of the present invention overcomes technical prejudice: BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a flow chart of a method for calculating the dynamic response of a dry casing under earthquake action and establishing a core crack damage model provided by an embodiment of the present invention.

[0058] Figure 2 It is a system structure block diagram of a method for calculating the dynamic response of a dry casing under earthquake action and establishing a core crack damage model provided by an embodiment of the present invention.

[0059] Figure 3 It is a transformer-bushing model diagram provided in an embodiment of the present invention.

[0060] Figure 4 It is a standard response spectrum curve diagram provided by an embodiment of the present invention.

[0061] Figure 5 It is an artificial response spectrum curve diagram provided by an embodiment of the present invention.

[0062] Figure 6 It is a time history curve diagram of different seismic wave accelerations provided by an embodiment of the present invention.

[0063] Figure 7 The modal vibration shape diagrams provided by the embodiments of the present invention are (a) 1st order and (b) 16th order.

[0064] Figure 8 It is a diagram corresponding to the model mode and frequency provided by an embodiment of the present invention.

[0065] Fig. 9 It is an acceleration response diagram of different positions of the casing provided by an embodiment of the present invention.

[0066] Fig.10 This is a maximum acceleration distribution diagram of different positions of the casing provided by an embodiment of the present invention.

[0067] Fig.11 It is an x-direction displacement diagram provided by an embodiment of the present invention.

[0068] Fig.12 It is a y-direction displacement diagram provided by an embodiment of the present invention.

[0069] Fig.13 This is a z-direction displacement diagram provided by an embodiment of the present invention.

[0070] Fig.14 This is a displacement response distribution diagram of the casing at different positions provided by an embodiment of the present invention.

[0071] Fig.15 This is a distribution diagram of maximum displacements of the casing at different positions provided by an embodiment of the present invention.

[0072] Fig.16 This is a stress distribution diagram of the casing provided by an embodiment of the present invention.

[0073] Fig.17 This is a stress distribution diagram of the core flange provided by an embodiment of the present invention.

[0074] Fig.18 This is a core stress distribution diagram provided by an embodiment of the present invention.

[0075] Fig.19 This is a stress distribution diagram of a transformer bushing provided by an embodiment of the present invention.

[0076] Fig. 20 It is a distribution diagram of various parameters of vibration response under different earthquake levels provided by an embodiment of the present invention.

[0077] Fig.21 1 is a diagram of a crack growth model provided by an embodiment of the present invention. (a) Tensile load model (b) Shear load model.

[0078] Fig. 22 1 is a crack propagation path diagram under tensile stress provided by an embodiment of the present invention. (a) initiation (b) propagation (c) fracture.

[0079] Fig.23 It is a crack extension stress distribution diagram under different earthquake levels provided by an embodiment of the present invention.

[0080] Fig.24 It is a diagram of the crack rapid expansion starting time and maximum stress distribution provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0081] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0082] like Figure 1 As shown, a method for calculating the dynamic response of a dry casing under earthquake action and establishing a core crack damage model provided by an embodiment of the present invention includes the following steps:

[0083] S101, establishment of transformer-bushing system simulation model;

[0084] Transformer-elevator-bushing model, the insulating bushing is connected to the oil tank through the elevator, where the transformer side plate and bottom plate are 15mm thick, the top plate is 20mm thick, the elevator is 1600mm long, the wall thickness is 20mm, the inclination angle is 20°, and the structure is Q235 steel; the overall height of the bushing is 2840mm, the maximum outer diameter at the flange is 200mm, and the air side height is 1450mm;

[0085] S102, seismic wave selection and loading method;

[0086] According to the actual glue-impregnated paper dry casing, a finite element model was established for simulation analysis. The overall force distribution characteristics of the casing under the simulated base vibration load were analyzed using the time history analysis method to study the influence of mechanical vibration load on the force distribution.

[0087] S103, analysis of transformer-bushing vibration response under earthquake conditions;

[0088] S104, crack extension model establishment.

[0089] The seismic wave selection and loading method provided by the embodiment of the present invention is as follows:

[0090] (1) For electrical equipment with an axisymmetric structure and arranged vertically, a single horizontal earthquake test shall be conducted; for electrical equipment with an asymmetric structure, two horizontal earthquake tests shall be considered; for electrical equipment with long cantilevers or large spans, vertical earthquake tests shall also be considered;

[0091] (2) The test response spectrum TRS generated by the vibration table should envelope the required response spectrum RRS. If a small number of single points in the TRS are outside the tolerance band and offset from the resonant frequency of the test equipment, it is acceptable. Considering that the maximum displacement of some vibration tables is limited and the lower frequency part has little effect on the equipment, the tolerance of the spectrum value below 0.7 times the natural frequency of the equipment can be uncontrolled.

[0092] The transformer-bushing vibration response analysis under earthquake conditions provided by the embodiment of the present invention is as follows:

[0093] 1) Modal analysis;

[0094] Firstly, the modal analysis of the whole model is carried out to obtain the natural frequencies and vibration modes of the first 20 modal modes of the model. The 1st to 6th modal vibration modes are mainly concentrated on the side wall of the oil tank, showing the form of alternating absorption and expansion. At the same time, there will be a small local buckling at the upper end of the casing. The 7th modal vibration mode casing shows an upward bending shape, the 12th modal vibration mode casing shows a rightward bending shape, and the 16th to 20th modal casings all show large deformations. The vibration modes of each order are mainly concentrated in the slender structure on the upper part of the casing and the side plate of the oil tank.

[0095] 2) Analysis of acceleration response of dry casing at different positions;

[0096] Since the bushing is a slender structure, it is connected to the transformer box through a riser. In order to study the acceleration response of the bushing under different earthquake levels, the earthquake response of different levels is studied respectively; the acceleration response values ​​of the top, flange and bottom of the bushing are extracted and analyzed respectively;

[0097] 3) Analysis of displacement response of dry casing at different positions;

[0098] 4) Analysis of stress response of dry casing at different positions.

[0099] Analysis of displacement responses of dry casing at different positions provided by the embodiment of the present invention:

[0100] As the casing height increases, its displacement shows a significant upward trend, that is, the displacement at the top is greater than that at the middle and bottom. The maximum horizontal displacement at the top of the casing is most affected by the earthquake, while the maximum vertical displacement at the middle and bottom are most affected by the earthquake.

[0101] Analysis of stress responses of dry casing at different positions provided by the embodiment of the present invention:

[0102] The maximum acceleration, maximum displacement and maximum stress of the casing vibration response under different earthquake levels were extracted respectively. With the increase of earthquake level, the peak values ​​of each response showed an upward trend. When the earthquake level reached 8, the maximum acceleration peak value of the casing was 163.83m / s 2The peak displacement is 25.35mm and the peak stress is 4.55MPa. Under this earthquake level, the top acceleration is 4.3 times that of the bottom, posing a huge safety hazard to the mechanical properties of the transformer bushing. Since the epoxy core is a brittle material, its tensile and compressive strengths are much lower than those of other components.

[0103] The crack propagation model provided by the embodiment of the present invention is established:

[0104] Two fracture phase field models are established to simulate the crack propagation of thin plates under different loading conditions. By establishing a phase field model for the isotropic plate fracture problem and using finite element analysis software for numerical calculations, the crack propagation process of a thin plate with an initial crack under tensile and shear loads is studied, and the influence of various parameters on crack propagation is calculated.

[0105] like Figure 2 As shown, the embodiment of the present invention provides a system for calculating the dynamic response of dry bushings under earthquake action and establishing a crack damage model. The system includes four main modules: a simulation model establishment module is used to create a simulation model of the transformer-bushing system; a loading module is used to select and load seismic waves; a response analysis module is responsible for analyzing the vibration response of the transformer-bushing under earthquake conditions; and a crack extension model establishment module is used to simulate crack extension behavior, so as to perform more accurate damage analysis.

[0106] Another object of the present invention is to provide a computer device, which includes a memory and a processor. The memory stores a corresponding computer program, and when the processor executes the program, all steps of the dry casing dynamic response calculation and crack damage model establishment method provided by the present invention can be implemented. This computer device can effectively simulate the stress and damage of the casing under earthquake conditions and provide a scientific analysis basis.

[0107] In addition, the present invention also proposes a computer-readable storage medium, in which a computer program stored, when executed by a processor, enables the processor to perform dry casing dynamic response calculation and crack propagation related steps. Through this storage medium, the simulation method can be easily transplanted to different computing environments, improving the application flexibility of the system.

[0108] The present invention also proposes an information data processing terminal, which is specially used to realize the dynamic response calculation of dry casing under earthquake conditions and the establishment of crack growth model. The terminal can complete the entire process from data input, seismic wave loading, response analysis to crack growth simulation through the collaborative work of the above modules, providing a scientific basis for engineering design.

[0109] In the specific implementation, the establishment of the simulation model starts with the physical model of the transformer-bushing system. The insulating bushing is connected to the oil tank through a riser. The thickness of the transformer side plate and bottom plate is 15mm, the thickness of the top plate is 20mm, the length of the riser is 1600mm, the wall thickness is 20mm, the inclination angle is 20°, and the structural material is Q235 steel. The overall height of the bushing is 2840mm, the maximum outer diameter at the flange is 200mm, and the air side height is 1450mm. The model ignores the influence of the radiator and aluminum foil, and the core is equivalent to the epoxy impregnated paper core.

[0110] When modeling, the insulating oil in the tank is evenly distributed on the side wall of the tank as an additional mass, and the damping ratio of the model is determined to be 2% according to the "Electric Power Facilities Seismic Design Code". The material parameters required for simulation are set through standardized mechanical properties to ensure the accuracy and reliability of the simulation results.

[0111] Table 1 Main material properties

[0112] Material <![CDATA[Density [kg / m 3 > <![CDATA[Young's modulus GPa > Poisson's ratio Steel frame 7850 210 0.3 Flange 2700 70 0.33 Outer sheath 870 20 0.47 Core 1200 4.5 0.38 Copper guide rod 8940 126 0.34

[0113] In order to study the operating conditions of dry bushings subjected to complex environmental dynamics such as mechanical vibration and reduce the probability of accidents of transformer dry bushings, a finite element model was established with reference to the actual glue-impregnated paper type dry bushing for simulation analysis. The time history analysis method was used to analyze the overall force distribution characteristics of the bushing under simulated base vibration load, and the influence of mechanical vibration load on the force distribution was studied.

[0114] The calculation is carried out in accordance with the requirements of the seismic input in the "Code for Seismic Design of Power Facilities" (GB50260-2013), "Technical Code for Seismic Design of Ultra-high Voltage Porcelain Insulated Electrical Equipment and Installation and Maintenance of Shock Absorption Devices" (Q / GDW11132-2013) and "Technical Code for Seismic Test of High Voltage Pillar Electrical Equipment" (Q / GDW11391-2015). The specific requirements are as follows:

[0115] (1) Electrical equipment with an axisymmetric structure and vertical arrangement can be subjected to a single horizontal earthquake test; electrical equipment with an asymmetric structure should consider two horizontal earthquake tests; electrical equipment with long cantilevers or large spans should also consider vertical earthquake tests. According to the requirements of the Technical Specifications for Seismic Design of UHV Porcelain Insulated Electrical Equipment and Installation and Maintenance of Shock Absorption Devices, when considering vertical earthquake effects, the vertical earthquake load combination coefficient is taken as 0.8, and the seismic motions in both directions must meet the requirements of the correlation specified in the current specifications.

[0116] (2) The test response spectrum (TRS) generated by the vibration table should envelope the required response spectrum (RRS). It is acceptable if a small number of single points in the TRS are outside the tolerance band and offset from the resonant frequency of the test equipment. In addition, considering that the maximum displacement of some vibration tables is limited and the lower frequency part has little effect on the equipment, the tolerance of the spectrum value below 0.7 times the natural frequency of the equipment can be uncontrolled.

[0117] According to the above requirements, and considering that the actual engineering sites are all within the Class III sites, the present invention selects artificial synthetic seismic motion and two measured seismic motions, El-centro wave and Taft wave, for earthquake simulation vibration simulation calculation. The artificial synthetic seismic motion is generated by fitting the response spectrum (referred to as "standard response spectrum") specified in the "Technical Regulations for Seismic Design of Ultra-High Voltage Porcelain Insulated Electrical Equipment and Installation and Maintenance of Shock Absorption Devices" (QIGDW 11132-2013). The characteristic period of the standard response spectrum is 0.9s, which can almost cover Class I to Class III sites in my country; El-centro wave and Taft wave are typical representatives of seismic motion of Class II or Class III sites. During seismic calculation, the damping ratio of electrical equipment should be determined according to the measured damping ratio. When there is a lack of measured data, the damping ratio can be taken as 2%. The artificial seismic response spectrum has a high degree of fit with the standard response spectrum, and the spectrum envelope range is wider than that of El-centro wave and Taft wave. The influence of the vibration response spectrum characteristics of various places on the seismic response of transformer bushings is analyzed.

[0118] This study on the vibration response and crack extension of casing under earthquake conditions was conducted. The earthquake occurrence area was selected as Guangdong. By querying the magnitude and intensity of earthquakes in different regions of the country, the seismic fortification intensity of different provinces and cities in Guangzhou can be basically divided into three levels, namely: the seismic fortification intensity is 6 degrees, and the design basic earthquake acceleration value is 0.05g; the seismic fortification intensity is 7 degrees, and the design basic earthquake acceleration value is 0.10g; the seismic fortification intensity is 8 degrees, and the design basic earthquake acceleration value is 0.20g. According to the situation in different regions, the earthquake level of this study is set as a rare earthquake of 6-8 degrees, the design earthquake group is the first group, and the site category is Class II. According to the "Code for Seismic Design of Buildings" GB50011-2010 and the seismic fortification intensity of various places in Guangdong Province, four artificial wave response spectrum curves corresponding to these four different earthquake levels are generated based on the standard response spectrum as shown in the figure, and two actual seismic waves are used as the control group. The present invention selects artificial synthetic ground motion and two measured ground motions-El-centro wave and Taft wave for earthquake simulation. Artificial synthetic seismic motion is generated by fitting the response spectrum specified in the technical regulations for seismic design of electrical equipment and installation and maintenance of shock-absorbing devices, namely the "standard response spectrum". The figure below shows that the artificial wave is highly consistent with the standard response spectrum, which verifies the validity of the artificial wave data. Among them, El-centro wave and Taft wave are typical representatives of seismic motion for Class II or Class I sites. According to the provisions of relevant specifications such as GB 50260-2013 and O / GDW11132-2013, the damping ratio of electrical equipment should be determined based on the measured damping ratio during seismic calculation. When there is a lack of measured data, the damping ratio can be taken as 2%.

[0119] During the simulation calculation, accelerations with a scale factor of 1:1:0.8 in the x, y, and z directions are applied to the bottom of the transformer at the same time, in order to simulate the vibration response of the transformer structure under actual earthquake action. The acceleration curves in the x direction under different earthquake levels are shown in the figure below. When applying the acceleration load, it is applied at a ratio of 1:1:0.8. The scale factors in the x and y directions are equal, reflecting the earthquake effect on the horizontal plane, while the scale factor in the z direction is slightly lower, considering that the earthquake acceleration in the vertical direction is usually small. The figure shows the acceleration time history curve converted according to the above response spectrum. Figure 6 Time history curves of different seismic wave accelerations.

[0120] After completing the simulation of the vibration response of the transformer bushing under earthquake conditions, various important data can be obtained, such as acceleration response, displacement response, actual force, deformation degree, stress concentration and other related data, so that various parameters of the structure and materials can be adjusted and optimized accordingly. Through this simulation, the various physical effects in the 110kV glue-impregnated paper dry-type bushing can be predicted, and the service life of the material in the actual scenario can be accurately determined.

[0121] Analysis of transformer-bushing vibration response under earthquake conditions.

[0122] First, the modal analysis of the overall model was performed to obtain the natural frequencies and vibration modes of the first 20 modal modes of the model. The 1st to 6th modal modes are mainly concentrated on the side wall of the oil tank, showing an alternating absorption and expansion pattern. At the same time, a small local buckling will occur at the upper end of the casing. The 7th modal mode casing has an upward bending shape, the 12th modal mode casing has a rightward bending shape, and the 16th to 20th modal casings have large deformations. Each modal mode is mainly concentrated in the slender structure on the upper part of the casing and the side plate of the oil tank.

[0123] Figure 7 Mode shape diagram

[0124] Figure 8 Model mode and frequency correspondence diagram

[0125] As shown in the figure, the transformer bushing system model mode and frequency correspondence diagram, the model base frequency is 3.8057Hz, the model first 9 order frequencies are almost all between 1 and 10Hz, close to the earthquake frequency, and it is very easy to produce resonance under the action of earthquakes. Resonance refers to the phenomenon that when the natural frequency of the structure matches the external excitation frequency, the vibration amplitude will increase significantly, which may lead to structural damage. Therefore, it is necessary to study the vibration response characteristics of the transformer bushing system under the influence of earthquakes.

[0126] 3.2 Analysis of acceleration response of dry casing at different positions

[0127] Since the bushing is a slender structure, it is connected to the transformer box through a lifting seat. In order to study the acceleration response of the bushing under different earthquake levels, the present invention studies the earthquake response of different levels. The acceleration response values ​​at the top, flange and bottom of the bushing are extracted for analysis. The following analysis takes a magnitude 7 earthquake as an example.

[0128] Fig. 9 Acceleration response of casing at different positions

[0129] As shown in the figure, the vibration response distribution diagram of the casing under a magnitude 7 earthquake. The peak value of the acceleration response in the y direction of the casing top is the largest, and increases with time. The acceleration in the x, y, and z directions shows an oscillating downward trend, which is consistent with the distribution trend of the seismic motion. The acceleration response amplitude of the casing in the y direction is the largest, followed by the x direction, and the acceleration response amplitude in the z direction is relatively small, indicating that the casing is greatly affected by the horizontal seismic motion. In the y direction, the maximum acceleration of the casing top is 43.4m / s2, which occurs at 15.76s, corresponding to the rapid acceleration rise stage in the seismic wave response spectrum. In the acceleration distribution curve at the flange, that is, the middle position of the casing, the acceleration in the y direction is the largest, followed by the x direction, indicating that the middle part of the casing is still greatly affected by the horizontal seismic motion. There is a figure showing the acceleration distribution curve at the bottom of the casing, that is, at the position of the equalizing cover at the bottom of the casing. Similar to the distribution trend of the upper and middle ends, the acceleration in the y direction is the largest, followed by the x direction, indicating that the casing is still greatly affected by the horizontal y direction seismic motion.

[0130] Fig.10 Maximum acceleration distribution at different positions of casing

[0131] As shown in the figure, the maximum response acceleration distribution curves in the x, y, and z directions at different positions of the top, middle, and bottom of the casing are shown. Due to the slender structure of the casing, the acceleration of the top of the casing is greater than that of the middle and bottom. Since the casing is greatly affected by the horizontal earthquake, the acceleration response in the y direction is the largest, which is greater than that in the z direction and greater than that in the x direction.

[0132] In the displacement response analysis of dry casing at different positions, with the rapid change of ground motion, the displacement of the top of the casing reaches the maximum value in the y direction, followed by the z direction, indicating that the horizontal ground motion has a greater impact on the displacement of the top. In contrast, the displacement of the middle end is significantly lower than that of the top, and the maximum displacement value is about half of that of the top, showing that there are significant differences in the impact of ground motion on casings at different positions. The displacement of the bottom of the casing further decreases, with the total displacement in the z direction being the largest, followed by the y direction, and the smallest displacement in the x direction.

[0133] As the height of the casing increases, the displacement shows a significant upward trend, with the top end having the largest displacement, followed by the middle end, and the bottom end having the smallest displacement. In the horizontal direction, the maximum displacement of the top end of the casing is most significantly affected by the earthquake, while the maximum displacement of the middle end and the bottom end is more significantly affected by the earthquake in the vertical direction. This shows that the casing is subjected to different forces at different heights, and especially under earthquake conditions, the displacement responses at each position are significantly different.

[0134] In the stress response analysis, the maximum stress value of the casing reached 17MPa, which appeared at the connection between the flange and the silicone rubber sheath. Since the epoxy core is a brittle material, it is subject to greater stress and its stress intensity is significantly higher than other parts. The analysis shows that the stress is concentrated in the connection area between the core and the flange. The stress of the core under seismic motion is 1.6MPa, which is significantly higher than the stress under gravity conditions alone, becoming a stress concentration area.

[0135] The vibration response parameters under different earthquake levels show that with the increase of earthquake level, the displacement, acceleration and stress response of the casing all have a significant increasing trend. These responses are concentrated at the connection between the flange and the core. Especially under high-level earthquake conditions, the stress of the casing presents a higher safety hazard.

[0136] The maximum acceleration, maximum displacement and maximum stress of the bushing vibration response under different earthquake levels are extracted respectively. As the earthquake level increases, the peak values ​​of each response show an upward trend. When the earthquake level reaches 8, the maximum acceleration peak of the bushing is 163.83m / s2, the displacement peak is 25.35mm, and the stress peak is 4.55MPa. Under this earthquake level, the top acceleration is 4.3 times larger than the bottom, which poses a great safety hazard to the mechanical properties of the transformer bushing. Since the epoxy core is a brittle material, the tensile and compressive strengths are much lower than those of other components, so the crack propagation model of the epoxy core will be studied below.

[0137] Aiming at the brittle fracture problem of epoxy resin thin plates, the present invention establishes two fracture phase field models, simulates the crack propagation of thin plates under different loading conditions, establishes a phase field model of the isotropic plate fracture problem, and uses finite element analysis software for numerical calculation to study the crack propagation process of thin plates with initial cracks under tensile and shear loads, and calculates the influence of various parameters on crack propagation.

[0138] like Fig.19 The figure shows the establishment of a casing core crack model dominated by tensile stress. A time-varying displacement u is applied to the upper end of the model. The displacement increment u = 10-5mm, Young's modulus E = 15GPa, and Poisson's ratio is 0.38 at each time step under the initial working condition. Three main modules, solid mechanics module, historical variable module and phase field module, are established through solid mechanics and mathematical interfaces to conduct transient research on crack extension. Fig.21 The crack growth model.

[0139] The crack extension state at different extension periods is shown in the figure below. In the crack initiation stage, the phase field change is observed at the end of the prefabricated crack in the phase field distribution, but its value is less than 1, and strain concentration occurs at the end of the crack. Before the crack starts, high strain concentration first appears at the tip of the prefabricated crack, and micro-strain is formed in the high strain area. As the load increases, the phase field and principal strain values ​​of the crack rupture zone gradually increase. When the phase field value reaches 1, the principal strain also reaches the critical value. At this time, the specimen reaches the critical state of crack initiation. Then the loading continues, the crack starts, and an obvious phase field crack is observed at the front end of the prefabricated crack in the phase field distribution, and new micro-damage appears at the crack tip. Crack extension is the result of continuous accumulation of micro-damage caused by stress concentration, and finally the crack continues to evolve until it penetrates the specimen. When the crack first appears, its width changes slowly. When the internal stress of the specimen accumulates to a certain stage, the appearance of macro cracks causes the crack width to increase rapidly, and then the crack width increases at a relatively fast rate until the crack penetrates the thin plate model.

[0140] As shown in the figure below, the core crack extension direction under the dominance of tensile stress develops forward along the original crack direction. Through the curve diagram of loading displacement and equivalent stress of the loading point, it is found that as the crack expands, the crack tip continues to move forward, and the position of the stress concentration area also moves forward accordingly.

[0141] Fig. 22 Crack propagation path under tensile stress

[0142] When the deformation energy released by crack expansion is equal to or greater than the energy required for crack expansion, the crack will expand unstably and break. When the crack expands forward by a unit length from a certain end point, the energy released per unit thickness of the plate is the critical energy release rate. The law of crack expansion is summarized through the curve of the loading displacement and von Mises equivalent stress of the loading point. The stress-displacement curve under tensile load and shear load shows a trend of increasing first and then decreasing. The area where stress increases rapidly is the crack initiation stage, and then the crack expands rapidly, and the stress value begins to decrease until the crack expansion ends.

[0143] Based on the above research, the maximum stress on the surface of the epoxy core under earthquake conditions was extracted as the condition for applying the crack boundary load, and the crack propagation law under different earthquake levels was studied.

[0144] Fig.23 Crack extension stress distribution under different earthquake levels

[0145] When the deformation energy released by crack expansion is equal to or greater than the energy required for crack expansion, the crack will expand unstably and break. When the crack expands forward by a unit length from a certain end point, the energy released per unit thickness of the plate is the critical energy release rate. The law of crack expansion is summarized through the curve of the loading displacement and von Mises equivalent stress of the loading point. The stress-displacement curve under the tensile load shows a trend of increasing first and then decreasing. The area where stress increases rapidly is the crack initiation stage, and then the crack expands rapidly, and the stress value begins to decrease until the crack expansion ends.

[0146] Fig.24 The starting time of rapid crack growth and the maximum stress distribution

[0147] As the earthquake magnitude increases, the crack boundary load increases, resulting in a decrease in the critical energy release rate for crack extension, a decrease in the maximum stress that the material can withstand, a decrease in the energy required for fracture, a decrease in the stress accumulation time in the crack initiation stage, and a decrease in the time to reach the rapid expansion stage. The expansion rate increases significantly, and the crack will expand at an earlier time.

[0148] 1. Specific application fields or related products of the present invention.

[0149] Can be applied to the research on structural optimization of power equipment

[0150] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. It can be understood by a person of ordinary skill in the art that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0151] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for calculating the dynamic response of dry casing under earthquake action and establishing a core crack damage model, characterized in that: The following steps are involved: Step 1, establishing a simulation model of a transformer-elevator-dry bushing, wherein the transformer is connected to the oil tank through the elevation seat; Step 2, select the actual seismic wave and load it, analyze the stress distribution of the casing under the mechanical vibration load through the finite element model, and use the time history analysis method to simulate the influence of the base vibration on the force of the casing; Step 3: Analyze the vibration response of the transformer-bushing system under earthquake conditions and calculate the dynamic response characteristics of the system under earthquake loads, including displacement, velocity, acceleration and stress distribution; Step 4: Establish a crack propagation model based on simulation analysis, and predict the generation and propagation path of cracks in dry casing under earthquake action through stress analysis of local stress concentration areas.

2. The method for calculating the dynamic response of dry casing under earthquake action and establishing the core crack damage model as claimed in claim 1, characterized in that: The seismic wave selection and loading method: (1) For electrical equipment with an axisymmetric structure and arranged vertically, a single horizontal earthquake test shall be conducted; for electrical equipment with an asymmetric structure, two horizontal earthquake tests shall be considered; for electrical equipment with long cantilevers or large spans, vertical earthquake tests shall also be considered; (2) The test response spectrum TRS generated by the vibration table should envelope the required response spectrum RRS. If a small number of single points in the TRS are outside the tolerance band and offset from the resonant frequency of the test equipment, it is acceptable. Considering that the maximum displacement of some vibration tables is limited and the lower frequency part has little effect on the equipment, the tolerance of the spectrum value below 0.7 times the natural frequency of the equipment can be uncontrolled.

3. The method for calculating the dynamic response of dry casing under earthquake action and establishing the core crack damage model as claimed in claim 1, characterized in that: Analysis of transformer-bushing vibration response under the earthquake condition: 1) Modal analysis; Firstly, the modal analysis of the whole model is carried out to obtain the natural frequencies and vibration modes of the first 20 modal modes of the model. The 1st to 6th modal vibration modes are mainly concentrated on the side wall of the oil tank, showing the form of alternating absorption and expansion. At the same time, there will be a small local buckling at the upper end of the casing. The 7th modal vibration mode casing shows an upward bending shape, the 12th modal vibration mode casing shows a rightward bending shape, and the 16th to 20th modal casings all show large deformations. The vibration modes of each order are mainly concentrated in the slender structure on the upper part of the casing and the side plate of the oil tank. 2) Analysis of acceleration response of dry casing at different positions; Since the bushing is a slender structure, it is connected to the transformer box through a riser. In order to study the acceleration response of the bushing under different earthquake levels, the earthquake response of different levels is studied respectively; the acceleration response values ​​of the top, flange and bottom of the bushing are extracted and analyzed respectively; 3) Analysis of displacement response of dry casing at different positions; 4) Analysis of stress response of dry casing at different positions.

4. The method for calculating the dynamic response of dry casing under earthquake action and establishing the core crack damage model as claimed in claim 3, characterized in that: Analysis of displacement response of dry casing at different positions: As the casing height increases, its displacement shows a significant upward trend, that is, the displacement at the top is greater than that at the middle and bottom. The maximum horizontal displacement at the top of the casing is most affected by the earthquake, while the maximum vertical displacement at the middle and bottom are most affected by the earthquake.

5. The method for calculating the dynamic response of dry casing under earthquake action and establishing the core crack damage model as claimed in claim 3, characterized in that: Analysis of stress response of dry casing at different positions: The maximum acceleration, maximum displacement and maximum stress of the bushing vibration response under different earthquake levels were extracted respectively. With the increase of earthquake level, the peak values ​​of various responses showed an upward trend. When the earthquake level reached 8, the maximum acceleration peak of the bushing was 163.83m / s2, the displacement peak was 25.35mm, and the stress peak was 4.55MPa. Under this earthquake level, the top acceleration was 4.3 times that of the bottom, posing a great safety hazard to the mechanical properties of the transformer bushing. Since the epoxy core is a brittle material, its tensile and compressive strengths are much lower than those of other components.

6. The method for calculating the dynamic response of dry casing under earthquake action and establishing the core crack damage model as claimed in claim 1, characterized in that: The crack growth model is established: Two fracture phase field models are established to simulate the crack propagation of thin plates under different loading conditions. By establishing a phase field model for the isotropic plate fracture problem and using finite element analysis software for numerical calculations, the crack propagation process of a thin plate with an initial crack under tensile and shear loads is studied, and the influence of various parameters on crack propagation is calculated.

7. A method system for calculating the dynamic response of dry casing under earthquake action and establishing a core crack damage model according to any one of claims 1 to 6, characterized in that: include: A simulation model module of transformer-elevator-dry bushing is established, in which the transformer is connected to the oil tank through the elevator. The structural parameters of the bushing are as follows: the overall height of the bushing is 2840 mm, the maximum outer diameter at the flange is 200 mm, the air side height is 1450 mm, the length of the elevator is 1600 mm, the wall thickness is 20 mm, the inclination angle is 20°, and the model is made of Q235 steel. The seismic wave loading module simulates the vibration of the base by loading actual seismic waves based on the time history analysis method, and analyzes the influence of mechanical vibration load on the stress distribution of the casing; Dynamic response analysis module, used to calculate the dynamic response of the transformer-bushing system under seismic loads, including displacement, velocity, acceleration and stress distribution; The crack propagation model module is used to predict the generation and propagation path of cracks in dry casing under earthquake action through simulation analysis of stress concentration areas.

8. The system according to claim 7, characterized in that The system also includes an acceleration response analysis module for analyzing the acceleration responses of the top, flange and bottom of the dry casing under different earthquake levels, and outputting the acceleration distribution characteristics of each position of the casing under different earthquake conditions.

9. The system according to claim 8, characterized in that The system also includes a displacement response analysis module for analyzing the displacement response of the dry casing under different seismic loads, and outputting the displacement change trends of the top, middle and bottom ends, especially the displacement response of the top in the horizontal direction and the middle and bottom in the vertical direction.

10. The system according to claim 9, characterized in that The system also includes a crack propagation analysis module, which simulates the crack propagation path through finite element calculation, outputs the casing crack generation and propagation process under different earthquake conditions, and evaluates the impact of crack propagation on the casing structure.

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