Transformer iron core vibration characteristic analysis method based on multi-physics field coupling

Abstract

A transformer iron core vibration characteristic analysis method based on multi-physics field coupling comprises the steps that firstly, a three-dimensional transient electromagnetic field finite element model is established on a Maxwell module of an ANSYS platform based on the transformer no-load state, then an external circuit is edited to simulate magnetizing inrush current, coupling of an electric field and a magnetic field is achieved, and the iron core flux density and harmonic conditions are observed. The method comprises the following steps of: performing modal analysis, analyzing the inherent frequency and the vibration mode of an iron core by virtue of a Modal module, finding out a weak link of an iron core structure, and introducing the volume force density of a no-load iron core under excitation surge current by utilizing a Transient Structural Module transient structure module so as to realize coupling of electricity, magnetism and a structural field. And finally, coupling the vibration deformation condition into an nCode Design-Life module in combination with a material fatigue curve, so that the sequential coupling analysis of electricity-magnetism-structure-fatigue is realized, the fatigue analysis is performed on the transformer iron core, and the fatigue life of the iron core is predicted. And a theoretical basis and an analysis path are provided for the structural optimization design of the transformer, so that relay protection maloperation events caused by excitation inrush current are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of transformer core vibration characteristic analysis, and in particular relates to a transformer core vibration characteristic analysis method based on multi-physical field coupling. Background Art

[0002] The transformers in the power system are mainly three-phase transformers. The normal operation of the transformer is of special significance to maintaining the stability and safety of the system. When the transformer is operating normally, its excitation current is generally 3% to 5% of the rated current. By setting the appropriate threshold value, the transformer differential protection can accurately distinguish between internal faults and external faults. However, when the transformer is closed at no-load or an external fault is removed and an excitation surge current appears, the transformer core will be severely saturated, the magnetostriction of the core silicon steel sheet will aggravate the core vibration, and the distorted excitation current will produce harmonics. In severe cases, the transformer structure will loosen, which may lead to mechanical fatigue failure and severe consequences. In addition, when the transformer generates an excitation surge current, the excitation current is very large. If there are no appropriate protection measures, this transient process will inevitably lead to the misoperation of the differential protection.

[0003] Therefore, analyzing the vibration characteristics of the core and fatigue life warning when the transformer has an excitation surge current is of great significance to the safe and stable operation of the power station. At the same time, the design method of transformer structure optimization through multi-physical field coupling analysis can also help reduce the false operation of relay protection caused by excitation surge current, improve equipment utilization, and reduce cost losses.

[0004] Based on the above analysis, the technical problem to be solved by the present invention is: 1. The second harmonic method is simple and easy to implement, but when a serious fault occurs in a large transformer, the differential protection may fail to operate due to resonance, making it impossible to effectively and accurately analyze the excitation current under the excitation surge.

[0005] 2. With the continuous improvement of transformer core materials, when the residual magnetism and closing angle meet certain conditions, the second harmonic method may cause the differential protection to malfunction, making it impossible to accurately judge the vibration characteristics of the core under the excitation surge current.

[0006] 3. The selection of the threshold value of the second harmonic method is often difficult to determine, and the setting standards of different manufacturers are different, making it impossible to apply to transformers of different manufacturers in power stations. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a transformer core vibration characteristic analysis method based on multi-physical field coupling, which can realize the analysis of the core vibration characteristics and fatigue life warning when the transformer has an excitation surge current, and provide a theoretical basis and analysis path for the structural optimization design of the transformer, thereby reducing the relay protection false operation events caused by the excitation surge current.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: A transformer core vibration characteristic analysis method based on multi-physics field coupling, the steps are: Establish a three-dimensional transient electromagnetic field finite element model to realize electromagnetic field coupling; Conduct structural field analysis to achieve electric-magnetic-structural field coupling; Perform fatigue analysis to achieve electro-magnetic-structural-fatigue sequential coupling; Combined with the material fatigue curve, the vibration deformation situation is coupled to the nCode Design-Life (fatigue durability simulation software) module, realizing the sequential coupling analysis of electro-magnetic-structural-fatigue, performing fatigue analysis on the transformer core, and predicting the fatigue life of the core.

[0009] Preferably, the three-dimensional transient electromagnetic field finite element model is established by: establishing a three-dimensional transient electromagnetic field finite element model in the Maxwell (motor low-frequency electromagnetic simulation) module of the ANSYS platform based on the no-load state of the transformer, and then editing the external circuit to simulate the excitation inrush current, realize the coupling of the electric field and the magnetic field, and observe the core magnetic flux density and harmonic conditions.

[0010] Preferably, the Maxwell (motor low-frequency electromagnetic simulation) calculation and analysis equations are: ; ; In the formula, E Indicates the electric field strength in V / m. H Indicates the magnetic field strength, unit A / m, B Indicates the magnetic induction intensity, unit T, J Indicates current density, unit A / m2, Indicates the conductivity of the medium, unit S / m.

[0011] Preferably, when a 10A DC current flows into the no-load transformer, the moments 0.985s and 0.995s are selected to correspond to the amplitude moments of the positive half-cycle and the negative half-cycle respectively; the excitation inrush current causes the core magnetic density of the positive half-cycle to reach the saturation section of the magnetization curve, resulting in a significant increase in the core magnetic density of the positive half-cycle; the no-load current of the transformer is 1% of the rated current, and when the excitation inrush current occurs, the transformer excitation current becomes an asymmetric waveform, and distorted harmonics appear; each harmonic component increases significantly, among which the second harmonic component increases significantly.

[0012] Preferably, when performing structural field analysis, the Modal (modal analysis) module is used to analyze the natural frequency and vibration mode of the core to find the weak links of the core structure.

[0013] Preferably, when the excitation current contains more harmonics, in addition to the basic magnetic flux, a large amount of harmonic flux will be generated, which aggravates the vibration of the transformer. When analyzing the vibration of the transformer, the core is first subjected to modal analysis; the modal analysis provides a basis for avoiding resonance between the natural frequency of the core and the main frequency of vibration; the strength distribution characteristics of the vibration deformation provide a basis for real-time monitoring of the transformer vibration and selection of the optimal measuring point location; the transient structural module is used to introduce the volume force density of the unloaded core under the excitation surge current to achieve the coupling of the electric-magnetic-structural field.

[0014] Preferably, the Transient Structural module is a transient structural module of the Workbench (simulation platform) workbench platform. The volume force density of the no-load core of the transformer when the excitation surge current is introduced into the Transient Structural module, and the volume force density is used as the excitation of the structural field to realize the coupling of the electric-magnetic-structural field, and then the transient dynamic analysis is performed; through the simulation analysis, the vibration deformation of the transformer core is observed; and post-processing is performed: core equivalent stress, total acceleration, total deformation.

[0015] Preferably, the fatigue analysis realizes the sequential coupling of electro-magnetic-structural-fatigue by coupling the vibration deformation obtained in the transient dynamics module in the ANSYS (large-scale general finite element software) platform to the nCode Design-Life module, thereby realizing the sequential coupling analysis of electro-magnetic-structural-fatigue.

[0016] A transformer core vibration characteristic analysis system based on multi-physics field coupling, the system comprising: Model building unit: used to establish a three-dimensional transient electromagnetic field finite element model to achieve electromagnetic field coupling; Structural field analysis unit: used to perform structural field analysis and thus realize electric-magnetic-structural field coupling; Fatigue analysis unit: used to perform fatigue analysis and realize the sequential coupling of electric-magnetic-structural-fatigue; Prediction output unit: It is used to combine the material fatigue curve and couple the vibration deformation to the nCode Design-Life module, realizing the sequential coupling analysis of electro-magnetic-structural-fatigue, performing fatigue analysis on the transformer core, and predicting the fatigue life of the core.

[0017] A computer device comprising: one or more processors; The processor is used to store one or more programs; When the one or more programs are executed by the one or more processors, a transformer core vibration characteristic analysis method based on multi-physical field coupling as described in any one of claims 1 to 8 is implemented.

[0018] The present invention can achieve the following beneficial effects: The present invention analyzes the vibration characteristics of the core and warns of fatigue life when a transformer has an excitation surge current. Compared with other prediction methods, this method couples the electric-magnetic-structural-fatigue multi-physical fields and has higher accuracy. This method provides a theoretical basis and analysis path for the structural optimization design of the transformer, thereby reducing relay protection malfunction events caused by the excitation surge current. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 A simulation diagram of a three-dimensional transient electromagnetic field finite element model of a transformer in an embodiment of the present invention; Figure 2 It is a simulation diagram of the core magnetic flux density of no-load excitation inrush current in an embodiment of the present invention; Figure 3 This is a harmonic diagram of the A-phase current of the transformer no-load excitation inrush current in an embodiment of the present invention; Figure 4 A simulation diagram of the core volume force density of no-load excitation inrush current in an embodiment of the present invention; Figure 5 It is a simulation diagram of each order mode vibration shape of the core in the embodiment of the present invention; Figure 6 It is a bar graph of the natural frequencies of each order of the core modal in the embodiment of the present invention; Figure 7 It is a simulation diagram of equivalent stress of the core under the excitation surge current in the embodiment of the present invention; Figure 8 It is a simulation diagram of the total acceleration of the core under the excitation inrush current in an embodiment of the present invention; Fig. 9 It is a simulation diagram of the total deformation of the core under the excitation surge current in the embodiment of the present invention; Fig.10 This is a simulation diagram of the fatigue life of the core under the excitation surge current in an embodiment of the present invention; Fig.11 This is a simulation diagram of core fatigue damage under excitation surge current in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The preferred solution is Figures 1 to 11 As shown in FIG. 1 , a transformer core vibration characteristic analysis method based on multi-physics field coupling is shown in FIG. 1 . The specific method is as follows: 1. Establish a three-dimensional transient electromagnetic field finite element model to realize electromagnetic field coupling; The high-voltage transformer used in a hydropower station is the same as the main transformer, and both use the YD11 wiring method, with only differences in capacity and transformation ratio. The present invention establishes a transformer simulation model with parameters of rated power 50MVA, rated voltage 110 / 38.5 / 10.5kV, turns ratio 78 / 165 / 472 / 48, no-load current 1%, and connection group YD11. Its calculation and analysis satisfy the Maxwell equations: ; In the formula, E Indicates the electric field strength V / m, H Indicates the magnetic field strength A / m, B represents the magnetic induction intensity T, J Indicates the current density A / m2, Indicates the conductivity of the medium S / m, ; When a 10A DC current flows into an unloaded transformer, the selected moments are 0.985s and 0.995s, which correspond to the amplitude moments of the positive half cycle and the negative half cycle respectively. The excitation inrush current makes the core magnetic flux of the positive half cycle reach the saturation section of the magnetization curve, resulting in a significant increase in the core magnetic flux of the positive half cycle.

[0021] The transformer no-load current is 1% of the rated current. When the excitation inrush current occurs, the transformer excitation current becomes an asymmetric waveform and distorted harmonics appear. Each harmonic component increases significantly, among which the second harmonic component increases significantly.

[0022] 2. Structural field analysis realizes electric-magnetic-structural field coupling; When the excitation current contains more harmonics, in addition to the basic magnetic flux, a large amount of harmonic flux will be generated, which aggravates the vibration of the transformer. Therefore, it is necessary to analyze the vibration deformation of the transformer.

[0023] When the transformer has an excitation inrush current, the core magnetic flux density shows obvious asymmetry in the positive and negative half cycles. Magnetostriction is the phenomenon that when the core is excited, the size of the silicon steel sheet increases along the magnetic force line and decreases perpendicular to the magnetic force line. Due to magnetostriction, the core vibrates periodically with the excitation frequency, and the increase in magnetic flux density increases the magnetostriction rate of the core. Magnetostriction is expressed by magnetostriction rate. Therefore, magnetostriction under excitation inrush current will cause the transformer to vibrate violently.

[0024] Modal analysis is performed with the help of the Modal module of the ANSYS Workbench platform. In order to be consistent with the actual situation, the bottom of the transformer core is fixed as a constraint condition to analyze the natural frequency and vibration mode of the transformer core.

[0025] Through modal analysis, the natural frequency and vibration mode of the core structure can be obtained, and the weak links of the core structure can be found. When analyzing transformer vibration, modal analysis of the core must be performed. Modal analysis provides a theoretical basis for avoiding resonance between the natural frequency of the core and the main vibration frequency. The distribution characteristics of the strength of vibration deformation can provide a theoretical basis for real-time monitoring of transformer vibration and selection of the optimal measurement point location. The maximum total deformation and the maximum deformation location of each mode are shown in Table 1.

[0026] Table 1 Maximum total deformation and maximum deformation location of each mode;

[0027] The volume force density of the transformer core under no-load condition during magnetizing inrush current is introduced in the transient structural module of the Workbench platform. It is used as the excitation of the structural field to realize the coupling of the electric-magnetic-structural field and further conduct transient dynamic analysis. Through simulation analysis, the vibration deformation of the transformer core is observed. After post-processing, the equivalent stress, total acceleration and total deformation of the core are shown as follows: Figure 7 , 8 , as shown in Figure 9.

[0028] From the distribution of equivalent stress, it can be seen that the maximum stress is located at the lower part of the side yoke, the core top angle vibrates most violently, and shows a tendency to bend. The part with the greatest stress is the most vulnerable part and is the weak link of the transformer core structure.

[0029] 3. Fatigue analysis realizes the sequential coupling of electric-magnetic-structural-fatigue Combined with the material fatigue curve, the transformer core was fatigue analyzed and the fatigue life of the core was predicted. Generally, structural fatigue occurs in the area of ​​stress concentration. The lower part of the core yoke is subjected to the greatest force, which is likely to cause fatigue damage. The vibration deformation obtained in the transient dynamics module of ANSYS software is coupled to the nCode Design-Life module to achieve the sequential coupling analysis of electro-magnetic-structural-fatigue.

[0030] The fatigue life of the core under the excitation surge current, such as Fig.10 As shown in Figure 2, the fatigue damage of the core under the excitation surge current is as follows: Fig.11 As shown, the degree of fatigue damage in the lower part of the side yoke can be clearly seen. The red area of ​​the core fatigue damage is located in the lower part of the side yoke, which is a weak area. The fatigue failure of the transformer core first occurs in the lower part of the side yoke, and it is very likely that cumulative damage will occur, leading to cracks and damage. Fatigue failure seriously affects the stable operation of the transformer and has an adverse effect on the safe and stable operation of the power station. In further improvement plans, it is possible to consider improving the structure of the transformer core to reduce the impact of the excitation surge current on vibration fatigue.

[0031] 4. Combined with the material fatigue curve, the vibration deformation is coupled to the nCode Design-Life module to achieve the sequential coupling analysis of electro-magnetic-structural-fatigue, perform fatigue analysis on the transformer core, and predict the fatigue life of the core.

[0032] The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A transformer core vibration characteristics analysis method based on multi-physics field coupling, characterized in that The following steps are involved: Establish a three-dimensional transient electromagnetic field finite element model to realize electromagnetic field coupling; Conduct structural field analysis to achieve electric-magnetic-structural field coupling; Perform fatigue analysis to achieve electro-magnetic-structural-fatigue sequential coupling; Combined with the material fatigue curve, the vibration deformation situation is coupled to the fatigue durability simulation module, realizing the sequential coupling analysis of electro-magnetic-structural-fatigue, performing fatigue analysis on the transformer core, and predicting the fatigue life of the core.

2. The transformer core vibration characteristic analysis method based on multi-physical field coupling according to claim 1 is characterized in that: The three-dimensional transient electromagnetic field finite element model is established by: establishing a three-dimensional transient electromagnetic field finite element model in the motor low-frequency electromagnetic simulation module based on the no-load state of the transformer, and then editing the external circuit to simulate the excitation surge current, realize the coupling of the electric field and the magnetic field, and observe the core magnetic flux density and harmonic conditions.

3. The transformer core vibration characteristic analysis method based on multi-physical field coupling according to claim 2 is characterized in that: The calculation and analysis equations of the motor low-frequency electromagnetic simulation module are: ； ； In the formula, ▽ is the gradient operator, E represents the electric field strength, H represents the magnetic field strength, B represents the magnetic induction intensity, J represents the current density, Indicates the conductivity of the medium.

4. The transformer core vibration characteristic analysis method based on multi-physical field coupling according to claim 2 is characterized in that: When a 10A DC current flows into the no-load transformer, the moments 0.985s and 0.995s are selected to correspond to the amplitude moments of the positive half-cycle and the negative half-cycle respectively; the excitation inrush current makes the core magnetic density of the positive half-cycle reach the saturation section of the magnetization curve, resulting in a significant increase in the core magnetic density of the positive half-cycle; the no-load current of the transformer is 1% of the rated current. When the excitation inrush current occurs, the transformer excitation current becomes an asymmetric waveform and distorted harmonics appear; each harmonic component increases significantly, among which the second harmonic component increases significantly.

5. The transformer core vibration characteristic analysis method based on multi-physical field coupling according to claim 2 is characterized in that: When performing structural field analysis, the modal analysis module is used to analyze the natural frequency and vibration mode of the core to find the weak links in the core structure.

6. The transformer core vibration characteristic analysis method based on multi-physical field coupling according to claim 5 is characterized in that: When the excitation current contains more harmonics, in addition to the basic magnetic flux, a large amount of harmonic flux will also be generated, which aggravates the vibration of the transformer. When analyzing the vibration of the transformer, the core is first subjected to modal analysis; modal analysis provides a basis for avoiding resonance between the natural frequency of the core and the main frequency of vibration; the strength distribution characteristics of vibration deformation provide a basis for real-time monitoring of the transformer vibration and selection of the optimal measuring point location; the transient dynamics module is used to introduce the volume force density of the no-load core under the excitation surge current to achieve the coupling of the electric-magnetic-structural field.

7. The transformer core vibration characteristic analysis method based on multi-physical field coupling according to claim 6 is characterized in that: The transient dynamics module is a transient structural module of the simulation platform working platform. The volume force density of the no-load core of the transformer during the excitation inrush current is introduced into the transient dynamics module, and the volume force density is used as the excitation of the structural field to realize the coupling of the electric-magnetic-structural field, and then the transient dynamics analysis is carried out; through the simulation analysis, the vibration deformation of the transformer core is observed; post-processing is carried out: core equivalent stress, total acceleration, and total deformation.

8. The transformer core vibration characteristic analysis method based on multi-physical field coupling according to claim 1 is characterized in that: The fatigue analysis realizes the sequential coupling of electro-magnetic-structural-fatigue by coupling the vibration deformation obtained in the transient dynamics module in the large-scale general finite element software platform to the fatigue durability simulation module, thereby realizing the sequential coupling analysis of electro-magnetic-structural-fatigue.

9. A transformer core vibration characteristics analysis system based on multi-physical field coupling, characterized in that: The system includes: Model building unit: used to establish a three-dimensional transient electromagnetic field finite element model to achieve electromagnetic field coupling; Structural field analysis unit: used to perform structural field analysis and thus realize electric-magnetic-structural field coupling; Fatigue analysis unit: used to perform fatigue analysis and realize the sequential coupling of electric-magnetic-structural-fatigue; Prediction output unit: It is used to combine the material fatigue curve and couple the vibration deformation into the fatigue durability simulation module, thus realizing the sequential coupling analysis of electro-magnetic-structural-fatigue, performing fatigue analysis on the transformer core and predicting the fatigue life of the core.

10. A computer device, characterized in that: include: one or more processors; The processor is used to store one or more programs; When the one or more programs are executed by the one or more processors, a transformer core vibration characteristic analysis method based on multi-physical field coupling as described in any one of claims 1 to 8 is implemented.

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