Dry-type transformer turn-to-turn short circuit multi-physical field simulation analysis method considering insulation aging and harmonic influence

Abstract

The invention provides a dry-type transformer turn-to-turn short circuit multi-physical field simulation analysis method considering insulation aging and harmonic influence, and relates to the technical field of simulation analysis, and the method comprises the following steps: constructing a physical simulation model of a to-be-tested dry-type transformer; setting physical parameters and multi-physical field operation conditions of the physical simulation model; calculating a corresponding physical field operation calculation result under each physical field operation condition; performing post-processing on the physical field operation calculation result; by establishing a detailed simulation model and accurately assigning physical property parameters of each component, physical property changes of the turn-to-turn insulating material at different aging stages and under different temperature and frequency conditions are emphatically considered; turn-to-turn short circuit fault modeling is further introduced, magnetic-thermal-flow coupling simulation calculation is carried out under multi-harmonic excitation, the multi-physical field distribution characteristics of the dry-type transformer during different turn-to-turn short circuit faults are explored, and a reliable basis is provided for design optimization and safety evaluation.

Description

Technical Field

[0001] The present invention relates to the technical field of simulation analysis, and more specifically, to a multi-physical field simulation analysis method for inter-turn short circuit of dry-type transformers considering insulation aging and harmonic effects. Background Art

[0002] Good winding insulation is an important basis for ensuring the normal operation of dry-type transformers and safe and stable power supply. Since dry-type transformers use solid insulation materials, their insulation performance directly affects the equipment's short-circuit resistance, overload resistance, and high-temperature resistance. During actual operation, dry-type transformers are also affected by factors such as switching surges, long-term overload, local overvoltage, high ambient temperature, and harmonic interference, which cause the inter-turn insulation of the winding to gradually deteriorate, thereby increasing local electric field stress and temperature rise. In severe cases, it may lead to local insulation breakdown or inter-turn short circuit faults.

[0003] Inter-turn short circuit is one of the most destructive fault types in dry-type transformers. Its occurrence not only causes local current distortion and severe distortion of the electromagnetic field in the winding, but also generates intense local overheating and arc effects, causing further damage to the insulation structure, and even leading to equipment burnout and power grid accidents. Especially under the dual action of harmonic excitation and insulation aging, the evolution process of inter-turn short circuit is more concealed and complex, posing a severe challenge to the safety of transformers.

[0004] However, in the current related research on inter-turn short circuit faults of dry-type transformers, there are still many limitations. Most analysis methods only start from the perspective of the electromagnetic field, set fixed inter-turn short circuit positions and electrical parameters, and discuss the effects of inter-turn faults on the distribution of current, voltage, and magnetic field under idealized material properties and basic power frequency excitation conditions. Such research generally ignores the performance degradation of insulation materials under long-term thermal and electrical stresses during actual operation, and fails to reflect the deep influence of the aging process on the evolution of inter-turn short circuit behavior. Moreover, using a sinusoidal power frequency source as the excitation signal, there is a lack of modeling and analysis of complex excitation scenarios containing a large number of high-order harmonics in the actual operation environment. This simplified treatment cannot reveal the coupling relationship between harmonic frequency, amplitude, and inter-turn electrical stress, nor can it capture the local electromagnetic disturbances and non-uniform temperature rise phenomena caused by harmonics.

[0005] Therefore, there is an urgent need to construct a multi-physical field coupling simulation method for dry-type transformers that has the ability to input multi-frequency harmonic excitation, supports the modeling of inter-turn short circuit fault conditions, and integrates the insulation aging response mechanism. With high-precision parameter assignment and visualization post-processing, quantitative analysis of temperature rise distribution, electromagnetic stress, and heat dissipation characteristics under fault scenarios can be achieved, providing theoretical support and technical basis for equipment condition diagnosis, structural optimization, and operation reliability assessment. Summary of the Invention

[0006] In view of this, the present invention provides a multi-physical field simulation analysis method for inter-turn short circuit of dry-type transformers considering insulation aging and harmonic effects. Based on the traditional magnetic-thermal-fluid coupling simulation, this method first introduces the modeling of the inter-turn short circuit fault state, constructs a local short circuit path, and simulates the electromagnetic-thermal-fluid field evolution process after the fault occurs. By establishing a high-precision simulation model including aging insulation material parameters and multi-frequency harmonic excitation sources, phenomena such as current density redistribution, local hot spot migration, and magnetic flux anomaly are studied under fault scenarios, realizing the accurate prediction of the physical field changes of dry-type transformers in typical inter-turn short circuit fault states. It provides theoretical support and simulation basis for fault identification, structural optimization, and thermal failure assessment.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A multi-physical field simulation analysis method for inter-turn short circuit of dry-type transformers considering insulation aging and harmonic effects, comprising the following steps:

[0009] S1: Construct a physical simulation model of the dry-type transformer to be tested;

[0010] S2: Set the physical parameters and multi-physical field operating conditions of the physical simulation model;

[0011] S3: Calculate the corresponding physical field operation calculation results under each physical field operating condition;

[0012] S4: Post-process the physical field operation calculation results.

[0013] Preferably, the S1 includes:

[0014] The physical simulation model includes a three-dimensional model of the dry-type transformer and a two-dimensional model of the dry-type transformer under different inter-turn short circuit faults, wherein the three-dimensional model of the dry-type transformer includes a core model, a high-voltage winding model, and a low-voltage winding model;

[0015] Set the inter-turn short circuit fault scenario in the two-dimensional model of the dry-type transformer, and simulate different inter-turn short circuit fault states by applying short circuit path conditions at specific positions of the winding.

[0016] Preferably, the S1 further includes:

[0017] Set the inter-turn short circuit fault scenario in the two-dimensional model of the dry-type transformer, and simulate different inter-turn short circuit fault states by applying short circuit path conditions at specific positions of the winding. This fault model can adjust parameters such as the short circuit position and inter-turn resistance to adapt to various typical working condition analyses;

[0018] Set up a multi-factor aging test to test the insulation material of the dry-type transformer to be tested and obtain the insulation material characteristic parameters;

[0019] Modify the attribute parameters of the inter-turn insulation material of the physical simulation model according to the characteristic parameters of the insulation material.

[0020] The present invention further expands the modeling method of the insulation material of dry-type transformers, and focuses on considering the physical property changes of the inter-turn insulation material at different aging stages and under different temperature and frequency conditions. For common Nomex insulation paper, a function model of material parameters such as thermal conductivity, relative permittivity, and specific heat capacity changing with the aging state and working conditions is established.

[0021] In the modeling stage of the present invention, the idea of partitioned modeling in the insulation aging stage is introduced. The insulation area is divided into three areas: "unaged area", "mild aging area", and "severe aging area", and different material characteristic parameters are assigned respectively to realize the joint expression of the spatial non-uniformity and time evolution of the insulation performance.

[0022] Preferably, the S2 includes:

[0023] S21: According to the actual material properties of each component in the dry-type transformer to be measured, assign electromagnetic parameters, thermal parameters, and fluid parameters to the three-dimensional model and two-dimensional model of the dry-type transformer.

[0024] S22: Add the operating conditions of the electromagnetic, thermal, and fluid physical fields to the three-dimensional model and two-dimensional model of the dry-type transformer after assignment respectively.

[0025] Preferably, in the S22, the operating conditions of the physical field include: the coupling condition of the electromagnetic physical field and the magnetic field, the thermal field condition, and the flow field condition.

[0026] Preferably, the S3 includes:

[0027] S31: Set the coupling condition of the electromagnetic physical field and the magnetic field, construct the corresponding circuit topology model of the dry-type transformer to be measured, and set the circuit environment that can realize the fundamental wave superposition and multi-frequency harmonic excitation at the same time, and calculate the corresponding electromagnetic loss calculation result.

[0028] S32: Set the thermal field condition and temperature parameters, and combine the electromagnetic loss calculation result and the physical simulation model to obtain the temperature rise distribution of the dry-type transformer to be measured.

[0029] S33: Set the flow field condition and the corresponding boundary condition, simulate the natural convection cooling condition, and analyze the cooling capacity of the physical simulation model.

[0030] Preferably, the S3 further includes:

[0031] S34: Conduct the magneto-thermal-fluid multi-physics field coupling calculation of the dry-type transformer under test with different harmonic excitation methods superimposed on the fundamental wave;

[0032] S35: Construct a live simulation current based on the harmonic current content rates of each frequency in the actual operating environment, and use it as the excitation source to input into the turn-to-turn short-circuit fault model of the dry-type transformer, and analyze the comprehensive operating condition responses under different degrees of turn-to-turn short-circuit faults.

[0033] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a multi-physics field simulation analysis method for turn-to-turn short circuits of dry-type transformers considering insulation aging and harmonic effects, integrating turn-to-turn short-circuit fault modeling, multi-frequency harmonic excitation, and insulation performance evolution mechanisms, constructing a magneto-thermal-fluid multi-physics field coupling simulation model suitable for complex operating conditions, analyzing characteristics such as the redistribution of current density, magnetic flux distortion, and hot spot migration under different fault states, and improving the performance prediction accuracy of dry-type transformers under fault conditions.

[0034] At the same time, the present invention proposes a method for correcting material characteristic parameters based on experimental measurement data. By establishing an experimental-dominated material parameter update mechanism, the dynamic response and quantitative accuracy of material modeling are realized, and accurate modeling and material parameter assignment are achieved. Combining the coupled calculations of the electromagnetic field, thermal field, and flow field, the present invention can accurately simulate the electromagnetic losses, temperature rise, and flow field distribution of dry-type transformers under different types of turn-to-turn short-circuit fault conditions with fundamental wave superimposed multi-harmonic excitation. Especially when considering the changes in the turn-to-turn insulation structure and insulation performance parameters, it can effectively predict the electric field distribution and temperature rise under the influence of harmonics, avoiding the problems of neglect or insufficient consideration of turn-to-turn insulation in traditional methods. Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0036] Figure 1 It is the overall flowchart of a multi-physics field simulation analysis method for turn-to-turn short circuits of dry-type transformers considering insulation aging and harmonic effects provided by the present invention;

[0037] Figure 2 It is the three-dimensional model diagram of the dry-type transformer established in the embodiment of the present invention;

[0038] Figure 3 It is the two-dimensional model diagram of the dry-type transformer established in the embodiment of the present invention;

[0039] Figure 4It is a schematic diagram of the modeling of inter-turn short-circuit faults in a transformer in an embodiment of the present invention;

[0040] Figure 5 It is a schematic diagram of an electro-thermal combined aging test scheme for inter-turn insulation materials provided by the present invention;

[0041] Figure 6 It is a schematic diagram of heat transfer in a dry-type transformer in an embodiment of the present invention;

[0042] Figure 7 It is a magnetic field distribution diagram near the short-circuit point of a dry-type transformer under different inter-turn short-circuit fault conditions in an embodiment of the present invention;

[0043] Figure 8 It is a magnetic field distribution diagram of a dry-type transformer under normal conditions in an embodiment of the present invention;

[0044] Figure 9 It is a temperature field distribution diagram of a dry-type transformer under normal conditions in an embodiment of the present invention;

[0045] Figure 10 It is a flow field distribution diagram of a dry-type transformer under normal conditions in an embodiment of the present invention. Specific embodiments

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0047] See Figure 1 As shown, an embodiment of the present invention discloses a multi-physical field simulation analysis method for inter-turn short circuits in a dry-type transformer considering insulation aging and harmonic effects, including the following steps:

[0048] S1: Construct a physical simulation model of the dry-type transformer to be tested;

[0049] S2: Set the physical parameters and multi-physical field operating conditions of the physical simulation model;

[0050] S3: Calculate the corresponding physical field operation calculation results under each physical field operating condition;

[0051] S4: Post-process the physical field operation calculation results.

[0052] In a specific embodiment, S1 includes:

[0053] The physical simulation model includes a three-dimensional model of a dry-type transformer and two-dimensional models of the dry-type transformer under different inter-turn short-circuit faults. The three-dimensional model of the dry-type transformer includes an iron core model, a high-voltage winding model, and a low-voltage winding model;

[0054] In the two-dimensional model of the dry-type transformer, inter-turn short-circuit fault scenarios are set, and different inter-turn short-circuit fault states are simulated by applying short-circuit path conditions at specific positions of the windings.

[0055] Specifically, in the two-dimensional model of the dry-type transformer, using the symmetry characteristics of the dry-type transformer, a one-half single-phase model of the dry-type transformer is built using the two-dimensional rotation model tool in COMSOL Multiphysics software;

[0056] For the construction of the model winding part, certain optimization measures are adopted. In the three-dimensional model of the dry-type transformer, it is assumed that the simulation model of the three-phase transformer is axially symmetric about the center. Hollow cylinders are respectively constructed as the high-voltage winding and the low-voltage winding of the winding part; in the two-dimensional model of the dry-type transformer, the method of modeling by turns is adopted to finely describe the distribution, thickness, and arrangement of the insulating materials between each turn;

[0057] For the iron core structure, the structure is appropriately optimized on the basis of considering the magnetism and temperature dependence of the iron core. In the two-dimensional rotation model, the iron core is regarded as a cylinder, and in the three-dimensional model, a laminated iron core model is constructed according to the actual design parameters;

[0058] Due to the huge amount of three-dimensional finite element calculations, in the three-dimensional geometric model of the dry-type transformer, only the key components of the dry-type transformer (iron core, high-voltage winding, low-voltage winding) are considered, and the influence of mechanical structure parts such as bolts and structural parts on the physical field distribution is ignored;

[0059] For the two-dimensional model of the dry-type transformer, it is assumed that the dry-type transformer is composed of an iron core, a high-voltage winding, a low-voltage winding, inter-turn insulation, inter-layer insulation, insulating lining, heat dissipation air ducts, and cooling air around the dry-type transformer, etc. The positions and sizes of each component are set according to the actual structure of the dry-type transformer. For the specific model schematic diagram, see Figures 2-3 as shown.

[0060] See Figure 4 as shown. In the two-dimensional model of the dry-type transformer, inter-turn short-circuit fault scenarios are set. By adding a section of conductor at the short-circuit point between the short-circuited turns, different turn coils are paralleled to form a short-circuited turn to apply short-circuit path conditions and simulate different inter-turn short-circuit fault states. This fault model can adjust parameters such as the short-circuit position and inter-turn resistance to adapt to various typical working condition analyses.

[0061] In a specific embodiment, S1 further includes:

[0062] Set up a multi-factor aging test to test the insulating materials of the dry-type transformer to be tested and obtain the characteristic parameters of the insulating materials;

[0063] Modify the attribute parameters of the inter-turn insulating materials in the physical simulation model according to the characteristic parameters of the insulating materials.

[0064] Specifically, in the two-dimensional model of the dry-type transformer, use the sub-turn modeling method and set the materials of the inter-turn insulation, inter-layer insulation, insulating lining, etc. according to the actual structure of the dry-type transformer. For the materials not built in the software material library, use the method of adding blank materials and setting parameters, and set the material properties according to the actual parameters of the materials.

[0065] The insulating material can be Nomex insulating paper, and the specific test process can include the following steps:

[0066] (1) Experimentally test the characteristic parameters of the inter-turn insulating materials at different aging stages

[0067] Obtain Nomex insulating paper at different aging stages through a multi-factor aging test, and respectively test the following material parameters:

[0068] a. Thermal conductivity test: Use the HotDisk TPS method to test and obtain the thermophysical properties of the material varying with temperature;

[0069] b. Relative permittivity test: Use FDS (Frequency Domain Dielectric Spectroscopy Test System) to test and analyze the variation relationship of the material under different frequencies and temperature conditions;

[0070] c. Specific heat capacity test: Use a synchronous thermal analyzer (DSC-TGA) to test and obtain the curve of specific heat capacity varying with temperature.

[0071] (2) Modeling dimension: Import the function relationships obtained from the above experiments into the COMSOL multi-physics simulation platform, define them as temperature / frequency-dependent material property parameters; and establish an aging stage identifier through the module embedded function to call the material data in different aging states to achieve the "adaptive parameter update" of the simulation model.

[0072] Among them, as shown in Figure 5 In a multi-factor combined aging test mentioned in the embodiment of the present invention, a signal generator is used to edit the test voltage waveform of the superimposed harmonic, output it to a high-voltage amplifier that can simultaneously meet the high-frequency and high-voltage output, and load it onto the inter-turn insulation specimen in the electrothermal blast drying oven. By controlling variables such as temperature, humidity, and voltage frequency, simulate the aging environment under different operating conditions of the dry-type transformer.

[0073] In the modeling stage of the embodiment of the present invention, the idea of partition modeling in the insulation aging stage is introduced. According to the internal temperature field distribution and current density distribution of the transformer, the insulation area is divided into three regions: "unaged area", "lightly aged area", and "severely aged area", and different material property parameters are assigned based on the data obtained from experiments to realize the joint expression of the spatial non-uniformity and time evolution of the insulation performance.

[0074] Through the thermal conductivity, specific heat capacity, and relative permittivity curves obtained from the above tests in the embodiment of the present invention, they are input into the physical simulation model of the dry-type transformer to correct the property parameters of the inter-turn insulation material. Combining the data of different aging stages, the influence of aging on the physical fields (electromagnetic field, temperature field, flow field) of the transformer is analyzed; by inputting the variation relationships of the material property parameters with temperature and frequency, the accuracy of the simulation calculation is further optimized, making the model calculation results more real and reliable.

[0075] In a specific embodiment, S2 includes:

[0076] S21: According to the actual material properties of each component in the dry-type transformer to be measured, electromagnetic parameters, thermal parameters, and fluid parameters are assigned to the three-dimensional model and two-dimensional model of the dry-type transformer. The core material of the dry-type transformer to be measured uses silicon steel sheets, the winding material uses copper, the inter-turn insulation material uses NOMEX insulation paper, the inter-layer insulation material uses polyimide film, the insulation support material uses epoxy resin, and other parts of the dry-type transformer to be measured are regarded as air. The density, thermal conductivity, and constant-pressure specific heat capacity of each material are defined. For magnetic materials, their conductivity, relative permittivity, and relative permeability also need to be set. For flowing media, their dynamic viscosity parameters need to be set;

[0077] Regarding the electromagnetic parameters of the winding and the core, the influence of temperature on the conductivity of the winding is relatively large, so it is represented by a function of temperature and defined as shown in Equation (1). The relative permeability of the core is represented by the pre-set function B-H curve of the software, as Figure 2 shown;

[0078]

[0079] In the formula, T0 and α0 are the reference temperature and its corresponding conductivity respectively, which are selected according to the ambient temperature and the material library attributes; T and α(T) are the actual temperature of the winding and its corresponding conductivity respectively; ξ is the temperature compensation coefficient, and its value is 0.00393 / °C;

[0080] S22: Add the operating conditions of the electromagnetic, thermal, and fluid physical fields to the three-dimensional model and two-dimensional model of the dry-type transformer after assignment respectively, and set the coupling relationships between different physical fields and between different multi-physical fields according to various heat transfer methods in the actual operating environment of the dry-type transformer.

[0081] In a specific embodiment, in S22, the operating conditions of the physical field include: the coupling conditions of the electromagnetic physical field and the magnetic field, the thermal field conditions, and the flow field conditions.

[0082] Specifically, the "magnetic field" and the "solid and fluid heat transfer" physical fields are used as the coupling interfaces of the "electromagnetic heat" multi-physical field; the "laminar flow" physical field is coupled with the heat transfer interface as the coupling interface of the "non-isothermal flow" multi-physical field; and a set of "surface-to-surface radiation heat transfer" multi-physical field interfaces are supplemented according to the actual heat transfer environment. Through the above measures, magnetic-thermal coupling and flow-thermal coupling are respectively realized to achieve magnetic-thermal-flow multi-physical field coupling.

[0083] In the "magnetic field" physical field, the Ampere's law boundary condition in the solid is set for the iron core, the magnetization model is set as the B-H curve, and the magnetic field modulus and the magnetic co-energy density both come from the material properties; the conduction model is set as the conductivity, the coil boundary condition is set for the winding part, and the coil length multiplication factor and the coil area multiplication factor are set according to the actual size of the dry-type transformer to make the electromagnetic field analysis and calculation of the model consistent with the actual situation. The relative magnetic permeability is used to set the magnetization model of the winding coil, and the loss calculation modules are added to the winding coil and the iron core respectively to accurately calculate the losses of each part;

[0084] In the three-dimensional model, a uniform multi-turn wire is used as the wire model of the coil, which can be consistent with the optimization measures for the winding part of the transformer three-dimensional model mentioned in S1; in the two-dimensional model, the winding coil part is set as a single wire and a coil group to realize the sub-turn modeling of the winding; in the two-dimensional model, the "axisymmetric" boundary condition is added to the central axis of the iron core to meet the requirements of the two-dimensional rotation and model optimization of the dry-type transformer, and the "magnetic insulation" boundary condition is added to the outer air edge part of the transformer; the "Ampere's law in the fluid" boundary condition is added to the air outside the conductor to realize the electromagnetic conduction inside the air.

[0085] In a specific embodiment, S3 includes:

[0086] S31: Set the coupling conditions of the electromagnetic physical field and the magnetic field, construct the circuit topology model corresponding to the dry-type transformer to be measured, and at the same time set the circuit environment that can realize the fundamental wave superposition and multi-frequency harmonic excitation, and calculate the corresponding electromagnetic loss calculation results;

[0087] S32: Set the thermal field conditions and temperature parameters, and combine the electromagnetic loss calculation results and the physical simulation model to obtain the temperature rise distribution of the dry-type transformer to be measured;

[0088] S33: Set the flow field conditions and the corresponding boundary conditions, simulate the natural convection cooling conditions, and analyze the cooling capacity of the physical simulation model.

[0089] Specifically, S31 may further include: when setting the transient solver parameters for field-circuit coupling in the three-dimensional model of the dry-type transformer, select to solve the physical fields and variables of "magnetic field" and "circuit", and set the output step size and start and end times; generally speaking, solving the electromagnetic field does not require excessive computer memory and calculation time, so select the full-coupling solution method in the transient solver, and set the non-linear method and the maximum number of iterations;

[0090] Couple the "circuit" physical field with the "magnetic field" physical field to construct a "field-circuit" coupling simulation environment for the dry-type transformer model; in the "circuit" physical field, add a superimposable three-phase voltage source as the excitation part of the three-phase dry-type transformer; and use the "External Ivs U" component to convert the potential of each corresponding node in the circuit into circuit current as the coil current excitation in the winding coil;

[0091] According to the actual operating environment of the dry-type transformer, conduct a quantitative analysis of the harmonic current with a large content, apply a power supply excitation including fundamental waves and higher harmonics (such as 5th, 7th, 11th, 13th, etc.) in the "circuit" physical field, and use the spectrum superposition method to ensure the simultaneous presence of multi-frequency signals;

[0092] Perform mesh division on the dry-type transformer calculation model. Since the electromagnetic distribution of the winding part is relatively uniform, use free triangular meshing for the upper end of the winding hollow cylinder and swept meshing for the cylindrical surface, and use free tetrahedral meshing with higher calculation efficiency for the rest of the dry-type transformer;

[0093] In the electromagnetic physical environment analysis module, based on the basic simulation environment of field-circuit coupling, calculate the three-dimensional electromagnetic field and losses of the dry-type transformer. According to the basic theory of Maxwell's electromagnetic field, during the operation of the dry-type transformer, the generation of temperature rise mainly stems from core losses and winding losses, and these losses are released in the form of heat energy, resulting in an increase in the internal temperature of the transformer.

[0094] For the core part, the Steinmetz formula and the Bertotti formula are often used to calculate the hysteresis loss and eddy current loss respectively. Specifically, the Steinmetz formula reveals the functional relationship between the core loss density, the maximum magnetic flux density reached in the core, the material's inherent characteristic parameters, and the magnetization frequency. Its mathematical expression is usually written as:

[0095]

[0096] In the formula, P C is the total loss power of the core; k is a constant related to the material properties, called the Steinmetz coefficient; B β mis the maximum magnetic flux density in the iron core; f is the power supply frequency; α and β are empirical constants related to material properties obtained by fitting experimental data. Common values are α≈1, indicating a linear relationship between losses and frequency, while β≈1.6 means that the losses follow a power-law relationship with the maximum magnetic flux density.

[0097] For windings, in the low-frequency operating state, due to the skin effect and proximity effect, the additional losses are small, and the current is relatively uniformly distributed within the conductor cross-section. Therefore, the energy loss in the conductor mainly comes from resistive heat dissipation. The calculation formula for the winding resistance loss density is:

[0098] P Cu =∫ V ρ(r)·J 2 (r)dV (3)

[0099] In the formula, P Cu represents the winding loss density, ρ(r) is the resistivity of the conductor at position r, J(r) represents the current density at that position, and V is the total volume of the conductor. In the case of only considering resistive losses, the overall loss of the transformer winding can also be simplified to:

[0100] P Cu =I 2 ·R (4)

[0101] In the formula, I represents the rated current of the transformer, and R is the total resistance of the winding;

[0102] According to formula (2) and formula (4), transient field calculations are performed in the electromagnetic physical environment analysis module to obtain the core loss, high-voltage winding loss, and low-voltage winding volume loss density within each electrical cycle. Then, the cycle-averaged loss study is used to calculate the average loss of the volume loss density within a single electrical cycle.

[0103] The possible effects of multi-frequency harmonic excitation on dry-type transformers are as follows: Harmonic components of different frequencies will cause distortion of the magnetic field in the transformer core, resulting in uneven distribution of the magnetic flux density, thereby affecting the magnetic saturation degree and loss characteristics of the core; The existence of harmonic currents may lead to local overheating and uneven electromagnetic forces, affecting the mechanical stress and thermal stress of the winding; The high-frequency components caused by harmonics will increase the copper loss and iron loss of the transformer, may trigger local hot spots, change the internal temperature field distribution of the transformer, and thus affect the life of the insulating material. By introducing fundamental waves and different harmonic excitation methods in the simulation, the effects of harmonics on the performance of dry-type transformers can be comprehensively evaluated, providing a scientific basis for design optimization and safety assessment.

[0104] S32 may also include: constructing a "solid and fluid heat transfer" physical field for the two-dimensional model of the dry-type transformer, defining the thermal properties for the model respectively according to the material properties of each component, such as defining the air part as fluid and the rest as solid; setting the initial temperature value as the operating environment temperature of the dry-type transformer; adding a thermal symmetry boundary condition to the central axis of the iron core of the two-dimensional rotating model;

[0105] According to the basic principles of heat transfer, air is a medium for convective and radiative heat transfer, and the selection of its thermal properties and boundary conditions has an important impact on the accuracy of the simulation results. Its density, thermal conductivity and specific heat capacity take the values in the material library; the convective heat transfer boundary condition of air is set as external natural convection, and the upper side of the horizontal plate, the lower side of the horizontal plate and the vertical wall are set respectively according to its position on the outer surface of the transformer;

[0106] The principle of air convective heat transfer refers to q = h·(T surface -T ambient ), where q is the heat flux density per unit area; T surface is the surface temperature; T ambient is the ambient temperature; the value of the heat transfer coefficient h entirely depends on the heat transfer mode and flow state. According to the empirical formula, the heat transfer coefficient of air under natural convection is about 10 W / (m 2 ·K).

[0107] For the periodic average losses of the iron core, high-voltage winding and low-voltage winding calculated in the field-circuit coupling in S31 for the three-dimensional model of the dry-type transformer, set to be presented in the form of a three-dimensional drawing group, and draw the surface data on the three-dimensional model to reflect the values at each point within the domain of each component;

[0108] Export the surface drawing data of the periodic average loss density of different components calculated for the three-dimensional model under different fundamental wave superposed with different harmonic excitation conditions into a text data format, and screen the data in the data processing tool, take the data average value as the loss values of the iron core, high-voltage winding and low-voltage winding, and add them to the temperature physical field analysis module as the heat source values of different components.

[0109] See Figure 6 As shown, S33 specifically further includes: according to the actual temperature rise process of the dry-type transformer, it can be known that the temperature rise inside the transformer mainly comes from the iron core loss and winding loss. The heat generated by the heat source of the dry-type transformer, part of which raises the temperature of the transformer itself, and the other part dissipates heat according to different heat conduction methods. It mainly includes conduction heat transfer, convective heat transfer and radiative heat transfer, and dissipates to the outer surface surrounded by cold air according to the Figure 6 shown heat dissipation methods and heat dissipation paths.

[0110] Set the boundary conditions in the flow field analysis module according to the heat transfer method. In addition to the convective heat transfer of air mentioned in S6, there is self-heat conduction inside the dry-type transformer, which is the transfer of energy between adjacent particles. According to Fourier's law, the heat flux density is proportional to the temperature gradient, indicating that heat is transferred from the region with higher temperature to the region with lower temperature, and the heat flow direction is always from the high-temperature region to the low-temperature region. This process mainly occurs in the solid heat transfer medium, that is, the energy transfer between the various components inside the transformer (such as the iron core, winding, insulation layer, etc.);

[0111] When considering the insulation of the dry-type transformer, the dry-type transformer usually adopts a laminated winding structure. There is an insulating medium or epoxy resin between the windings and between the windings and the iron core. The thermal resistance of these materials (R = L / (k·A), where R is the thermal resistance; L is the length of the heat conduction path; k is the thermal conductivity of the material, and A is the heat transfer area) acts in series, resulting in a high thermal resistance layer in the overall heat conduction path, making the heat dissipation in some areas slower and the temperature prone to local increase;

[0112] Radiative heat transfer refers to the process by which an object transfers heat to the outside through electromagnetic waves (mainly infrared radiation). During the operation of the dry-type transformer, there is radiative heat transfer between different components inside it and between the components and the surrounding air, resulting in the non-contact dissipation of energy to the outside;

[0113] Specifically, the thermal radiation of the dry-type transformer is mainly manifested in the following aspects: First, a large amount of heat is generated in the iron core of the transformer during long-term operation due to hysteresis loss and eddy current loss, and this heat is transferred to the surrounding low-voltage windings by radiation; Second, due to the temperature difference between the high-voltage and low-voltage windings, significant radiative heat transfer also occurs on the surface of the windings, causing some heat to be transferred from the winding with higher temperature to the winding with lower temperature in the form of radiation; In addition, the outer surface of the high-voltage winding is directly exposed to the air environment, and its surface temperature is usually higher than the temperature of the surrounding air, so the process of radiative heat dissipation to the air occurs.

[0114] When considering the impact of thermal radiation on the overall thermal management of the dry-type transformer, it is necessary to introduce Stefan-Boltzmann's law for quantitative analysis, and its radiative heat transfer power can be calculated by the following formula:

[0115]

[0116] In the formula, q is the radiative heat transfer flux density; σ is the Stefan-Boltzmann constant, with a value of 5.67×10-8W / (m 2 ·K 4 ); ε is the surface emissivity; A is the radiative surface area; T1 and T2 are the absolute temperatures of the radiator and the environment respectively;

[0117] In the simulation calculation, by combining the three mechanisms of conduction heat transfer, convective heat transfer, and radiative heat transfer, a comprehensive heat transfer equation is established in the temperature physical field analysis module to ensure the accuracy of the simulation results. The specific calculation uses the following heat balance equation:

[0118]

[0119] In the formula, ρ is the material density; C p is the specific heat capacity; is the temperature gradient, representing the direction and magnitude of temperature change; k is the thermal conductivity; v is the air flow velocity; Q is the heat source term; h c is the convective heat transfer coefficient; T ∞ is the ambient temperature; this formula simultaneously considers the heat conduction inside the transformer the convective heat transfer of the air medium h c (T ∞ -T), and the radiative heat transfer on the iron core, winding, and transformer surface

[0120] In the temperature physical field analysis module, a "surface-to-surface radiation" physical field is constructed for the two-dimensional model of the dry-type transformer. The surfaces between the iron core and the low-voltage winding, between the low-voltage winding and the high-voltage winding, and between the high-voltage winding and the external air are set as diffuse reflection surfaces, and the emission radiation direction is the positive normal direction; the surface emissivity ε and the environmental radiation rate ε amb are both 0.9.

[0121] In a specific embodiment, S3 further includes:

[0122] S34: Perform magnetic-thermal-fluid multi-physics field coupling calculation on the dry-type transformer to be tested under different harmonic excitation modes superimposed on the fundamental wave.

[0123] Specifically, for the magnetic-thermal-fluid multi-physics field coupling problem of the dry-type transformer under different harmonic excitation conditions superimposed on the fundamental wave, a separated-step solution strategy is adopted to improve the calculation efficiency and accuracy. During the solution process, the overall calculation is divided into three modules: electromagnetic calculation, fluid-thermal calculation, and thermal radiation calculation, and the solution conditions are set respectively to ensure that the calculations of each physical field can be carried out independently and interact with each other through the coupling boundary conditions.

[0124] The electromagnetic calculation module is mainly used to solve the magnetic field distribution of the transformer and consider the influence of different harmonic excitations on the magnetic field. The fluid-thermal calculation module is used to solve the flow field, pressure field, and temperature field distributions of the air inside and around the transformer, and at the same time, combined with the thermal resistance characteristics of the insulating medium and epoxy resin, analyze the influence of harmonic excitation on the local temperature rise. The thermal radiation calculation module optimizes the heat transfer process through the radiosity calculation of the upper and lower surfaces, combines the radiation heat transfer theory, and improves the accuracy of the overall steady-state calculation.

[0125] For each separation step, a PARDISO direct solver with high solution efficiency is uniformly used for steady-state solution, enabling the calculation to run stably under conditions of large memory requirements and long calculation times, and ensuring the accuracy and reliability of the calculation results of different physical fields.

[0126] In a specific embodiment, S3 further includes:

[0127] S35: Construct an actual simulation current based on the harmonic current content rates of each frequency in the actual operating environment, and use it as an excitation source to input into the turn-to-turn short-circuit fault model of the dry-type transformer, and analyze the comprehensive operating condition responses under different degrees of turn-to-turn short-circuit faults.

[0128] Specifically, in the simulation model, select a local area of the winding to construct a turn-to-turn short-circuit path, and simulate different degrees of short-circuit fault states by adjusting the short-circuit impedance value or connection nodes; in the excitation setting, according to the harmonic current content rate in the actual operating environment of the transformer, edit the actual simulation non-sinusoidal current waveform with multiple typical harmonic components superimposed, and input it into the winding circuit model to achieve in-depth coupled calculation between the electro-magnetic-thermal multi-physical fields.

[0129] Specifically, S4 further includes: After the multi-physical field coupled solution of the present invention is completed, the calculation results are further systematically post-processed to extract key physical quantities, analyze the influence of harmonic excitation and insulation characteristics on the internal physical field distribution of the dry-type transformer, and optimize the operating performance of the transformer.

[0130] See Figures 7-8 As shown, in the post-processing module, first analyze the calculation results of the electromagnetic field, extract the magnetic induction intensity distribution of key parts such as the transformer core and winding, and compare the magnetic field distortion conditions under the superposition excitation of the fundamental wave and harmonics to evaluate the influence of harmonics on the magnetic flux distribution. At the same time, perform spectral analysis on the harmonic components of the coil current and voltage to obtain the influence degree of different frequency harmonics on the electrical performance.

[0131] Under the condition of considering the turn-to-turn short-circuit fault condition, the magnetic field analysis is also applicable to evaluating the perturbation characteristics of local faults on the overall magnetic field distribution of the transformer. In the post-processing module, key positions such as the fault area and its surrounding windings and core can be selected to extract physical quantities such as magnetic induction intensity and magnetic field energy density, and analyze the local magnetic flux aggregation, non-uniform distribution and possible saturation trend caused by the short circuit. At the same time, use the equipotential line distribution map and vector field map to visualize the change of the magnetic field direction and the local field enhancement area. By combining the two analysis methods of the time domain and the frequency domain, the dynamic response characteristics of the magnetic field under the short-circuit state can be further evaluated, providing a basis for the research on the influence mechanism of turn-to-turn faults and the magnetic field optimization design.

[0132] See Figure 9As shown, in the post-processing of the temperature field calculation results, the temperature distribution data of key parts such as the transformer winding, iron core, inter-turn short-circuit point, and insulation structure are extracted. Combining with the temperature rise change trends under different harmonic excitation conditions and different inter-turn short-circuit fault conditions, the effects of harmonics and inter-turn short-circuit faults on the thermal characteristics of the transformer are evaluated. For the local overheating area, the relationship between it and the electromagnetic loss distribution and insulation characteristics is further analyzed to reveal the hot spot effect that may be caused by harmonic excitation and its potential impact on insulation aging.

[0133] See Figure 10 As shown, in the fluid mechanics analysis part, the flow field characteristics of the cooling medium inside and around the transformer are visualized, including the velocity field, pressure field, and streamline distribution. Combining with the temperature field calculation results, the cooling effect and heat exchange efficiency under different harmonic excitation conditions and different inter-turn short-circuit fault conditions are analyzed. By comparing the flow field structures under different conditions, the influence of the insulation material and the cooling channel design on the heat dissipation performance is evaluated, and an optimized improvement plan is proposed.

[0134] To ensure the comprehensiveness and reliability of the calculation results, the present invention also conducts statistical analysis on the solution data, extracts the maximum value, minimum value, average value, and change trend of each key physical quantity, and compares them with the test data or engineering standards to verify the rationality of the simulation results. Based on the post-processing analysis results, the insulation structure, heat dissipation design, and harmonic suppression measures of the transformer can be further optimized to improve the operation stability and service life of the dry-type transformer in a complex power system.

[0135] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0136] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-physical field simulation analysis method for inter-turn short circuit of dry-type transformers considering insulation aging and harmonic effects, characterized in that, It includes the following steps: S1: Construct a physical simulation model of the dry-type transformer to be tested; S2: Set the physical parameters and multi-physical field operating conditions of the physical simulation model; S3: Calculate the corresponding physical field operation calculation results under each physical field operating condition; S4: Post-process the physical field operation calculation results.

2. The multi-physical field simulation analysis method for inter-turn short circuit of a dry-type transformer considering insulation aging and harmonic influence according to claim 1, characterized in that, The S1 includes: The physical simulation model includes a three-dimensional model of the dry-type transformer and a two-dimensional model of the dry-type transformer under different turn-to-turn short-circuit faults. The three-dimensional model of the dry-type transformer includes a core model, a high-voltage winding model, and a low-voltage winding model; Set the turn-to-turn short-circuit fault scenario in the two-dimensional model of the dry-type transformer, and simulate different turn-to-turn short-circuit fault states by applying short-circuit path conditions at specific positions of the winding.

3. A multi-physical field simulation analysis method for inter-turn short circuit of dry-type transformers considering insulation aging and harmonic effects according to claim 2, characterized in that, The S1 also includes: Set up a multi-factor aging test to test the insulating material of the dry-type transformer to be tested and obtain the characteristic parameters of the insulating material; Modify the attribute parameters of the turn-to-turn insulating material of the physical simulation model according to the characteristic parameters of the insulating material.

4. A multi-physical field simulation analysis method for inter-turn short circuit of dry-type transformers considering insulation aging and harmonic effects according to claim 2, characterized in that, The S2 includes: S21: Assign electromagnetic parameters, thermal parameters, and fluid parameters to the three-dimensional model of the dry-type transformer and the two-dimensional model of the dry-type transformer according to the actual material properties of each component in the dry-type transformer to be tested; S22: Add electromagnetic, thermal, and fluid physical field operating conditions to the three-dimensional model of the dry-type transformer and the two-dimensional model of the dry-type transformer after assignment respectively.

5. A multi-physical field simulation analysis method for inter-turn short circuit of dry-type transformers considering insulation aging and harmonic effects according to claim 4, characterized in that, In the S22, the physical field operating conditions include: electromagnetic physical field and magnetic field coupling conditions, thermal field conditions, and flow field conditions.

6. A multi-physical field simulation analysis method for inter-turn short circuit of dry-type transformers considering insulation aging and harmonic effects according to claim 4, characterized in that, The S3 includes: S31: Set the electromagnetic physical field and magnetic field coupling conditions, construct the corresponding circuit topology model of the dry-type transformer to be tested, and set a circuit environment that can realize fundamental wave superposition of multi-frequency harmonic excitation, and calculate the corresponding electromagnetic loss calculation results; S32: Set the thermal field conditions and temperature parameters, and combine the electromagnetic loss calculation results and the physical simulation model to obtain the temperature rise distribution of the dry-type transformer to be tested; S33: Set the flow field conditions and the corresponding boundary conditions, simulate the natural convection cooling conditions, and analyze the cooling capacity of the physical simulation model.

7. A multi-physical field simulation analysis method for inter-turn short circuit of dry-type transformers considering insulation aging and harmonic effects according to claim 6, characterized in that, The S3 also includes: S34: Conduct magnetic-thermal-fluid multi-physical field coupling calculation of the dry-type transformer to be tested under different harmonic excitation modes of fundamental wave superposition; S35: Construct a live simulation current based on the harmonic current content rate of each frequency in the actual operating environment, and input it as an excitation source into the turn-to-turn short-circuit fault model of the dry-type transformer to analyze the comprehensive operating condition response under different turn-to-turn short-circuit fault degrees.

Images