A transformer phase change cooling simulation method and system considering gas phase insulation constraint

Abstract

The application discloses a transformer phase change cooling simulation method and system considering gas phase insulation constraints, establishes an electromagnetic field finite element model of a fluorocarbon liquid transformer to be simulated, calculates the distribution of electromagnetic loss and the distribution of electric field intensity in the transformer, performs heat-flow-phase change coupling simulation based on the distribution of electromagnetic loss, obtains phase change cooling result data in the transformer, identifies a gas-containing area in the transformer according to the phase change cooling result data, updates dielectric parameters and electric field intensity of the gas-containing area, and calculates a gas phase electric field stress accumulation amount, and comprehensively analyzes the phase change cooling effect and the gas phase insulation constraint condition of the fluorocarbon liquid transformer according to the phase change cooling result data and the gas phase electric field stress accumulation amount. The application has the advantages that the industry pain points that the traditional simulation cannot consider the cooling effect and the gas phase insulation constraint are solved, and a complete simulation framework is provided for collaborative optimization of the fluorocarbon liquid transformer.

Description

Technical Field

[0001] The present invention belongs to the technical field of multi-physics simulation for power transformers, and specifically relates to a transformer phase change cooling simulation method and system considering gas-phase insulation constraints. Background Art

[0002] As the core hub equipment of the power system transmission and distribution network, during the operation of a power transformer, winding copper loss, core iron loss and stray loss of metal structural parts will be continuously converted into heat energy. If the heat cannot be exported in time, internal overheating will be caused, which will greatly shorten the insulation life, and in severe cases, directly induce equipment insulation breakdown failure. Conventional mineral oil transformers rely on natural oil convection and forced oil circulation for heat dissipation. Restricted by the boiling point of mineral oil and the heat exchange limit, there is an obvious bottleneck in heat dissipation capacity in the scenarios of high-overload, compact, and high-frequency special transformers.

[0003] In order to break through the heat dissipation shortboard of traditional oil-immersed transformers, the industry gradually uses low-boiling-point fluorocarbon insulating media to replace mineral oil, and develops fluorocarbon liquid phase change cooling transformers. This type of equipment relies on the liquid-gas phase change latent heat of the fluorocarbon medium to achieve efficient heat exchange. When the temperature of the medium in the heating area rises to the saturation temperature under the current pressure, vaporization occurs. The gas-phase fluorocarbon medium migrates upward to the top condensation area driven by buoyancy and flow field pressure gradient, releases latent heat of vaporization and then re-liquefies, and returns to the heating area by gravity, forming a closed-loop phase change heat exchange cycle. It has the advantages of high heat exchange efficiency, compact equipment volume, and low risk of combustion and explosion, and has broad application prospects in scenarios such as large-capacity special transformers, transformers supporting offshore wind power converters, and indoor compact distribution transformers.

[0004] At the current stage, the mainstream simulation and analysis method for fluorocarbon liquid phase change cooling transformers adopts an electromagnetic-thermal-fluid unidirectional coupling simulation framework, and its general implementation process is: the first step is to establish an electromagnetic field finite element model to solve the global electromagnetic loss; the second step is to map the electromagnetic loss as a fixed heat source to the thermal-fluid coupling model to solve the internal temperature field, medium flow velocity field, pressure field and gas phase volume fraction distribution of the equipment; the third step is to qualitatively evaluate the phase change cooling performance of the equipment only based on the two indicators of the maximum temperature of the winding hot spot and the range of the internal vaporization area. This type of unidirectional coupling simulation method can only realize a single-dimensional evaluation of the heat exchange effect, and has fundamental defects in the aspect of insulation risk assessment, which are specifically reflected in the following three aspects: First, existing simulations neglect the electric field distortion effect caused by the difference in dielectric properties between the gaseous and liquid phases of fluorocarbon dielectrics. The dielectric constants and breakdown field strengths of the liquid and gaseous phases of fluorocarbon dielectrics differ significantly. When the gaseous dielectric accumulates in high-electric-field-sensitive areas such as winding ends, main insulation gaps, lead joints, bushing roots, and abrupt changes in structural dimensions, it alters the local equivalent dielectric constant, causing local electric field distortion and a sudden increase in field strength, directly compressing the insulation safety margin. However, traditional simulations only use the dielectric parameters of the pure liquid-phase fluorocarbon dielectric to calculate the initial electric field distribution, without updating the local dielectric electrical parameters in real time based on the gaseous phase distribution generated by the phase transition. This makes it impossible to reproduce the true electric field distribution under gaseous conditions, resulting in a significant deviation between the calculated electric field and the actual operating conditions of the equipment.

[0005] Second, there is a lack of quantitative indicators to simultaneously characterize the coupling risks between phase change heat transfer and gas-phase insulation. Existing technologies can only output three independent sets of simulation cloud maps: temperature, gas phase distribution, and electric field. They can only rely on manual comparison of the overlap between the gas phase region and the high electric field region. There are no standardized, quantifiable numerical indicators to measure the insulation stress risk caused by the accumulation of gas phase medium in the high electric field region. It is impossible to achieve an integrated quantitative evaluation of heat transfer performance and insulation constraints. At the same time, the manual comparison method is highly subjective and has large errors, making it difficult to support quantitative comparison and optimization under multiple loads and multiple structural schemes.

[0006] Third, it cannot provide guidance for the coordinated optimization of cooling and insulation structures. Traditional simulations can only adjust the condensation structure and dielectric flow channels when the temperature exceeds the limit, or optimize the insulation barrier and lead layout separately when the electric field exceeds the limit, thus severing the inherent coupling relationship between phase change heat transfer and gas phase insulation. In actual engineering, adjusting the condensation zone and gas phase guiding structure will simultaneously change the gas phase migration path and the distribution of gas-containing areas, thereby affecting the insulation stress in high electric field areas; simply thickening the insulation barrier will hinder dielectric flow and exacerbate local overheating. Existing simulation systems cannot predict the coupled side effects of these two types of optimization measures, making it difficult to provide an integrated structural improvement scheme that takes into account both heat dissipation and insulation.

[0007] Patent publication number CN110739138A discloses a phase-change cooled high-frequency high-voltage power electronic transformer. This patent uses a low-boiling-point H50 fluorocarbon phase-change dielectric to immerse the transformer body, relying on the latent heat of the liquid-gas phase change of the dielectric to achieve efficient heat dissipation of the windings. By limiting the physical structural parameters such as the insulation frame, winding arrangement, insulation distance, coil specifications, and core material, the power density and insulation withstand voltage level of the transformer are improved, which can reduce the size of the equipment, reduce the partial discharge, and adapt to high-frequency high-voltage power electronic conversion scenarios. However, it only completes the transformer hardware design from the level of physical structure and dielectric selection, and only relies on static insulation distance and the inherent withstand voltage of the dielectric to ensure insulation performance. It cannot construct a standardized quantitative index of gas phase electric field stress accumulation to characterize the insulation breakdown risk caused by gas phase accumulation; it cannot simultaneously and quantitatively evaluate the winding hot spot temperature rise cooling constraint and the gas phase insulation risk constraint, and cannot provide a quantitative simulation basis for the integrated and coordinated optimization of the gas phase migration path, condensation area, and insulation barrier of the fluorocarbon liquid transformer.

[0008] In summary, the industry urgently needs an integrated simulation analysis method that can simultaneously couple electromagnetic losses, heat-flow-phase transition, and electric fields with varying dielectric constants, and can quantitatively evaluate the phase change cooling effect and gas phase insulation constraints, filling the technical gap in existing unidirectional coupling simulations that cannot simultaneously consider the dual constraints of heat transfer and insulation. Summary of the Invention

[0009] The problem that this invention aims to solve is that existing simulations of phase change cooling for fluorocarbon liquid transformers cannot simultaneously take into account both heat transfer and insulation constraints.

[0010] The present invention solves the above-mentioned technical problems through the following technical means: A simulation method for transformer phase change cooling considering gas-phase insulation constraints includes the following steps: First, an electromagnetic field finite element model of the fluorocarbon liquid transformer to be simulated is established, and the distribution of electromagnetic loss and electric field intensity inside the transformer is calculated. Secondly, based on the electromagnetic loss distribution, a thermal-fluid-phase change coupled simulation was performed to obtain the phase change cooling result data inside the transformer; Next, based on the phase change cooling result data, identify the gas-containing region inside the transformer, update the dielectric parameters and electric field strength of the gas-containing region, and calculate the gas phase electric field stress accumulation. Finally, based on the phase change cooling results data and the gas phase electric field stress accumulation, a comprehensive analysis was conducted on the phase change cooling effect and gas phase insulation constraint of the fluorocarbon liquid transformer.

[0011] This invention breaks through the fragmented simulation mode of existing technologies that only solve heat transfer in one direction or calculate electric field separately by constructing a closed-loop simulation logic of electromagnetic-thermal-fluid phase change-gas-electric correction-comprehensive evaluation. It can simultaneously acquire two types of core performance data of transformer cooling and insulation, realize integrated analysis of phase change heat transfer and gas phase insulation risk, solve the industry pain point that traditional simulation cannot take into account both cooling effect and gas phase insulation constraint, and provide a complete simulation framework for the collaborative optimization of fluorocarbon liquid transformers.

[0012] Preferably, the electromagnetic field finite element model includes an electromagnetic loss calculation sub-model and an insulation electric field calculation sub-model; the electromagnetic loss distribution includes winding loss, core loss, and stray loss of metal structural components; the initial electric field intensity distribution includes the winding end, main insulation gap, lead connection area, bushing lead-out area, and local structural abrupt change area.

[0013] By subdividing the electromagnetic field into two sub-models, the system accurately covers all sources of transformer losses and key high-electric-field areas throughout the entire region. It can fully reproduce the transformer's actual electromagnetic heating and initial electric field distribution, avoiding simulation distortion caused by missed loss calculations and missing high-electric-field areas. This provides high-precision initial electromagnetic foundation data for subsequent phase transition simulations and correction of gas-containing electric fields.

[0014] Preferably, the heat-fluid-phase change coupling model includes a solid heat transfer region, a liquid-phase fluorocarbon medium region, a gaseous-phase fluorocarbon medium region, and a condensation region, and configures temperature-related physical property parameters of the fluorocarbon medium, latent heat of vaporization, the correspondence between saturation temperature and pressure, vaporization mass source terms, and condensation mass source terms; the phase change cooling result data includes temperature field, velocity field, and pressure field.

[0015] It fully divides the transformer into four major calculation regions: global heat transfer, two-phase medium, and condensation, and is equipped with temperature and pressure coupling properties and phase change source terms for fluorocarbon medium. It can accurately simulate the complete phase change cycle of vaporization and condensation of fluorocarbon medium, output multi-dimensional global field distribution data, fully restore the real heat exchange flow conditions inside the fluorocarbon liquid transformer, and improve the numerical accuracy of phase change cooling simulation.

[0016] Preferably, the heat-fluid-phase change coupled simulation process includes: calculating the vaporization mass source term when the medium temperature reaches the corresponding pressure saturation temperature; calculating the condensation mass source term when the gaseous medium enters the condensation zone and meets the condensation conditions; updating the internal pressure based on the vaporization and condensation mass, and iteratively updating the phase change source term and gas-liquid distribution region by correcting the saturation temperature.

[0017] The phase change simulation iteration update logic is limited to achieve real-time linkage correction of pressure, saturation temperature, and phase change source terms; it can dynamically match the transient change law of medium vaporization and condensation under different loads, solve the defect of traditional static phase change models that cannot adapt to variable operating conditions, and greatly improve the matching degree between transient phase change simulation results and actual equipment operating conditions.

[0018] Preferably, the method for identifying gas-containing regions is as follows: regions with a gas volume fraction not less than a preset threshold are determined to be gas-containing regions; the local equivalent dielectric constant of the gas-containing region satisfies the following formula: In the formula, For position ,time The equivalent dielectric constant; For position ,time The gas phase volume fraction; The dielectric constant of the gaseous fluorocarbon dielectric; The dielectric constant of the liquid-phase fluorocarbon medium is given. The equivalent dielectric parameter is loaded into the insulation electric field calculation sub-model to obtain the updated electric field intensity distribution under the gas-containing condition.

[0019] Based on the accurate identification of gas-containing regions by gas phase volume fraction, and the introduction of the two-phase equivalent dielectric constant formula to quantify the local dielectric electrical properties, the insulating dielectric parameters can be dynamically updated and the distorted electric field can be recalculated according to the degree of gas phase aggregation. This overcomes the shortcomings of existing technologies that only use the pure liquid phase dielectric constant and ignore the electric field distortion caused by the gas phase, and restores the true electric field distribution under gas-containing conditions.

[0020] Preferably, the region of insulating cooling medium with an updated electric field strength not less than a preset electric field threshold is designated as a high electric field interest region, and the gas phase volume fraction distribution and the electric field strength distribution under gas-containing conditions are unified to the same spatial coordinates and the same calculation time; the formula for calculating the gas phase electric field stress accumulation is: In the formula, For a moment The amount of gas phase electric field stress accumulation; Regions of interest with high electric fields; Volume of the region of interest in high electric field; To account for the electric field strength after considering the local gas phase distribution; This represents the breakdown field strength of the gaseous fluorocarbon medium under corresponding local temperature and pressure conditions.

[0021] The high electric field concern area is delineated and the spatiotemporal coordinates of multiple fields are unified. The amount of gas phase electric field stress accumulation is quantified by integral formula. A standardized quantitative index of insulation risk is formed to replace the qualitative analysis method of traditional manual comparison of cloud maps. It can quantitatively characterize the insulation breakdown risk caused by the superposition of gas phase and high electric field. The evaluation results are objective, quantifiable and convenient for horizontal comparison of multiple schemes.

[0022] Preferably, the phase change cooling effect of the fluorocarbon liquid transformer is analyzed based on the winding hot spot temperature, core temperature, vaporization region distribution, and condensation region distribution, and the gas phase insulation constraint is analyzed based on the gas phase volume fraction, gas-containing region location, and gas phase electric field stress accumulation.

[0023] Preferably, the maximum hot spot temperature of the winding and the maximum gas phase electric field stress accumulation within the phase change cooling simulation time range are obtained. When the maximum hot spot temperature of the winding is not higher than the preset temperature limit and the maximum gas phase electric field stress accumulation is not higher than the preset insulation risk limit, it is determined that the fluorocarbon liquid transformer simultaneously meets the phase change cooling constraint and the gas phase insulation constraint.

[0024] Preferably, when the maximum hot spot temperature of the winding exceeds the standard, the dielectric flow path, condensation area, or recirculation structure is adjusted; when the maximum gas phase electric field stress accumulation exceeds the standard, the gas phase migration path, condensation area, or local insulation structure is adjusted.

[0025] The present invention also discloses a transformer thermal stability evaluation system that adopts the above-mentioned transformer phase change cooling simulation method considering gas phase insulation constraints, including an electromagnetic field solution module, a phase change coupling simulation module, a gas-electric coupling correction module, and a comprehensive evaluation module. The electromagnetic field solving module is used to construct a finite element model of the transformer's electromagnetic field and output the electromagnetic loss distribution and the initial electric field distribution of the liquid phase. The phase change coupling simulation module is connected to the electromagnetic field solving module, receives electromagnetic loss as a heat source, and outputs global phase change cooling result data. The gas-electric coupling correction module is connected to the phase change coupling simulation module to identify gas-containing regions, update equivalent dielectric parameters, recalculate the electric field, and solve for the gas phase electric field stress accumulation. The comprehensive evaluation module is connected to the phase change coupling simulation module and the gas-electric coupling correction module, respectively. Based on the cooling data and stress accumulation, it completes the joint evaluation of cooling and insulation performance and outputs optimization and adjustment suggestions.

[0026] The advantages of this invention are: (1) The first electromagnetic-phase change-gas-electric correction integrated closed-loop simulation architecture breaks the limitation of the existing fluorocarbon liquid transformer simulation which only calculates the heat flow field and electric field independently. First, the global electromagnetic loss is solved as the heat source to drive the phase change simulation. Then, the gas phase distribution generated by the phase change is used back to replace the electric field model to dynamically correct the dielectric parameters, forming a complete multi-physics closed-loop calculation process. It can simultaneously reflect the equipment cooling heat transfer characteristics and the real working condition of the electric field distortion caused by the gas phase, solving the core pain point that traditional simulation cannot take into account both phase change cooling and gas phase insulation constraints. (2) Establish quantitative evaluation index of gas phase electric field stress accumulation: abandon the subjective qualitative analysis method of relying on manual comparison of gas phase and electric field cloud map in the industry, construct standardized gas phase electric field stress accumulation through global integral formula, unify the spatiotemporal dimensions of gas phase volume fraction, field strength and dielectric breakdown strength, objectively quantify the insulation breakdown risk caused by gas phase accumulation and high electric field superposition, and the unified index can be compared horizontally with multiple structural and multi-load working condition schemes, making the evaluation results more objective and the engineering practicality stronger; (3) Accurately reproduce the complete vaporization-condensation cycle of fluorocarbon medium: In the heat-fluid-phase change model, vaporization and condensation mass source terms are set. Through real-time mutual correction and iterative calculation of medium saturation temperature and internal pressure, the transient process of medium vaporization, floating, condensation and reflux under different loads is dynamically matched. The four major calculation regions of solid, liquid, gas and condensation are completely divided. Compared with the static phase change model, the simulation accuracy of temperature and gas phase distribution is greatly improved, which is close to the actual working condition of fluorocarbon liquid transformer. (4) Form a complete engineering design system of "dual threshold judgment + scenario-specific optimization": Set up simultaneous verification of dual safety limits for winding hot spot temperature and gas phase insulation stress, and judge whether the equipment meets the heat dissipation and insulation design requirements at the same time; provide differentiated optimization schemes for condensation flow channel, gas phase flow and local insulation for two types of problems: temperature exceeding the standard and insulation risk exceeding the standard, so as to realize the coordinated optimization of cooling structure and insulation structure, and directly guide the integrated structural design of transformer gas phase migration path, condensation zone and insulation barrier. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall process of a transformer phase change cooling simulation method considering gas phase insulation constraints according to Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of a fluorocarbon liquid transformer structure, which is a simulation method for transformer phase change cooling considering gas phase insulation constraints according to Embodiment 1 of the present invention.

[0028] In the picture: 1. Housing; 2. Gaseous fluorocarbon liquid; 3. Piping; 4. Condenser; 5. Liquid fluorocarbon liquid return chamber; 6. Radiator. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: To better illustrate the transformer phase-change cooling simulation method considering gas-phase insulation constraints of the present invention, a brief description of the fluorocarbon liquid transformer structure is provided first. (See reference...) Figure 2The fluorocarbon liquid phase change cooling transformer comprises a housing 1, pipes 3, a condenser 4, a liquid fluorocarbon liquid return chamber 5, and radiators 6, forming a closed-loop phase change cooling system. Specifically, the housing 1 is a sealed pressure-bearing shell, housing the transformer core, high and low voltage windings, and other core electrical components, and filled with a fluorocarbon insulating medium. The heat generated by the operation of the windings and core causes the submerged liquid fluorocarbon medium to heat up and vaporize, forming gaseous fluorocarbon liquid 2 that accumulates at the top of the housing. The gaseous fluorocarbon liquid 2, aided by buoyancy, is partially transported via pipes 3 to the condenser 4, and the remaining portion is transported to the radiators 6 located outside the housing 1. Multiple radiators 6 have input and output terminals connected to the interior of the housing 1, forming a circuit. The radiators 6 continuously remove the heat stored inside the gaseous fluorocarbon liquid 2 through air cooling or water cooling, and the cooled fluorocarbon liquid then returns to the interior of the housing 1. The high-temperature gaseous fluorocarbon liquid entering the condenser 4 releases its latent heat of vaporization and re-liquefies within the condenser 4. The liquefied low-temperature liquid fluorocarbon medium is collected in the liquid fluorocarbon liquid return chamber 5 at the bottom of the condenser, and then flows back to the bottom of the housing 1 by gravity to re-immerse the electrical components and participate in the next heat exchange cycle. The entire structure relies on the liquid-gas phase change cycle of the fluorocarbon medium to continuously remove the heat lost inside the transformer. At the same time, the gas and liquid two-phase fluorocarbon medium itself has insulating properties, which can ensure the electrical insulation performance of the energized areas such as windings and leads.

[0031] See Figure 1 The transformer phase change cooling simulation method considering gas phase insulation constraints of the present invention includes the following steps: S1, establishing an electromagnetic field finite element model of the fluorocarbon liquid transformer to be simulated, and calculating the electromagnetic loss distribution and electric field intensity distribution inside the transformer; S2, performing a heat-flow-phase change coupled simulation based on the electromagnetic loss distribution to obtain phase change cooling result data inside the transformer; S3, identifying the gas-containing region inside the transformer based on the phase change cooling result data, updating the dielectric parameters and electric field intensity distribution of the gas-containing region, and calculating the gas phase electric field stress accumulation; S4, comprehensively analyzing the phase change cooling effect and gas phase insulation constraint of the fluorocarbon liquid transformer based on the phase change cooling result data and the gas phase electric field stress accumulation.

[0032] This embodiment takes a 110 kV three-phase fluorocarbon liquid transformer as an example, with the following parameters: 590 turns of high-voltage winding; 98 turns of low-voltage winding; 705 mm inner diameter of low-voltage winding; 828 mm outer diameter of low-voltage winding; 920 mm inner diameter of high-voltage winding; 1102 mm outer diameter of high-voltage winding; and FC-40 fluorocarbon liquid as the replacement insulation medium.

[0033] The specific process is as follows: S1. Establish the electromagnetic field finite element model of the fluorocarbon liquid transformer to be simulated, and calculate the electromagnetic loss distribution and electric field intensity distribution inside the transformer.

[0034] The specific process of step S1 includes: 1. Geometric solid modeling A three-dimensional geometric model was constructed based on the actual structural dimensions of the transformer. High- and low-voltage windings, core, insulation frame, leads, bushings, and enclosure structure were built according to relevant parameters. The low-voltage winding has an inner diameter of 705mm and an outer diameter of 828mm, while the high-voltage winding has an inner diameter of 920mm and an outer diameter of 1102mm. The high-voltage winding has 590 turns, and the low-voltage winding has 98 turns. The core adopts a conventional silicon steel lamination structure for distribution transformers. The model fully recreates structural abrupt changes such as winding ends, main insulation gaps, lead connection nodes, bushing lead-out sections, and core corners. All key geometric areas prone to high electric fields and concentrated losses are preserved, eliminating simulation distortions caused by geometric simplification.

[0035] 2. Divide the model into two sub-models and assign corresponding material parameters. This step involves using an electromagnetic field finite element model, which includes a sub-model for calculating electromagnetic loss and a sub-model for calculating insulation electric field. Electromagnetic and dielectric property parameters are assigned to each component respectively. (1) Electromagnetic loss sub-model: The magnetization curve and iron loss curve of silicon steel sheet are entered into the iron core; the conductivity of copper conductor is set in the high and low voltage windings, and the conductivity parameters of steel are entered into the structural parts such as metal clamps and pull plates; the cooling medium filling area is filled with FC-40 fluorocarbon liquid, and the basic parameters of fluid thermal conductivity are only set in the loss calculation, and it does not participate in the electric field iteration. (2) Insulation electric field sub-model: The corresponding relative permittivity of solid insulating parts (epoxy insulating parts, paper insulation) is entered; the cooling medium in the whole domain is uniformly assigned the value according to pure liquid phase FC-40 fluorocarbon liquid, the relative permittivity of liquid phase fluorocarbon medium is taken as 1.9, and the vaporization to generate gas phase is not considered for the time being, so as to obtain the initial electric field reference under bubble-free working conditions.

[0036] 3. Refined mesh subdivision The mesh is refined for loss- and electric field-sensitive areas. High-order fine meshes are used for winding conductors, core laminations, winding ends, main insulation gaps, bushing roots, lead joints, and abrupt changes in structural chamfers; coarser meshes are used for the enclosure and external support structures to balance computational load and take into account both solution accuracy and simulation efficiency.

[0037] 4. Apply electromagnetic and electrical boundary conditions (1) Loss model excitation: Apply three-phase rated voltage and rated load current according to the rated operating conditions of 110kV transformer; set magnetic insulation boundaries on the outer contour of iron core and the outer surface of metal box to constrain the closed path of magnetic lines of force; (2) Electric field model boundary: The high voltage winding conductor is applied with a rated power frequency potential of 110kV, the low voltage winding is grounded, and the iron core, metal box and structural parts are grounded in a unified manner; a zero potential insulation boundary is set in the air domain outside the model to limit the electric field calculation solution domain.

[0038] 5. Finite element numerical solution Simultaneously initiate electromagnetic loss calculation and solve the static electric field of the insulation electric field, complete the iterative convergence calculation of the electromagnetic field equations, eliminate residuals to the preset convergence threshold, and ensure the stability and reliability of the numerical solution.

[0039] 6. Extract and export two types of globally distributed data. (1) Electromagnetic loss distribution data: Three types of loss fields are obtained by global analysis, namely the copper loss distribution of high and low voltage windings, the loss distribution of iron core hysteresis + eddy current iron, and the stray loss distribution of metal clamps, pull plates, and fasteners. The loss density cloud map data with spatial coordinate information is output, and the loss value corresponding to each spatial grid unit is recorded for subsequent mapping to the phase change model as a heat source. (2) Initial electric field intensity distribution data: The results of the electric field intensity of the whole domain under the pure liquid phase fluorocarbon medium are obtained. The field intensity values ​​of the winding end, main insulation gap, lead connection area, bushing lead-out area and local structural change area are extracted to form an initial electric field database with spatial coordinates, which serves as the benchmark for subsequent electric field correction calculation in gas-containing areas.

[0040] 7. Data format standardization preprocessing The electromagnetic loss distribution and initial electric field intensity distribution are uniformly transformed into a spatial grid coordinate format that matches the subsequent thermal-fluid-phase change coupling model, realizing a one-to-one mapping between data of multiple physics fields, and providing standardized basic data that can be directly called for step S2 heat source loading and step S3 dielectric parameter update.

[0041] S2. In this step, the global electromagnetic loss distribution output from S1 is used as a fixed heat source input to build a three-dimensional coupled transient simulation model of heat-flow-phase change. The complete cycle of vaporization, floating, condensation and reflux of fluorocarbon medium is solved, and the global phase change cooling field data is output.

[0042] The specific process of step S2 includes: 1. Reuse the geometric model and divide it into four major computational regions. Using the three-dimensional geometry of a 110kV transformer, the model is divided into four independent computational domains: the solid heat transfer region consisting of the core, high and low voltage windings, and metal structural components; the liquid fluorocarbon medium region consisting of the unvaporized FC-40 medium inside the tank; the gaseous fluorocarbon medium region consisting of the vaporized medium formed in the heat-generating region; and the condensation region consisting of the external condenser, liquid fluorocarbon return chamber, and radiator piping. This fully recreates the closed-loop circulation structure of the tank, piping, condenser, return chamber, and radiator.

[0043] 2. Assignment of global physical property parameters and phase transition constitutive relations For FC-40 fluorocarbon media, a temperature and pressure-related property library was configured, and curves showing the changes in density, dynamic viscosity, thermal conductivity, and specific heat capacity at constant pressure with temperature were entered. The latent heat of vaporization of the medium was calibrated, and a fitting relationship between saturation temperature and internal pressure was established. Control equations for vaporization mass source term and condensation mass source term were set respectively, limiting the activation of the vaporization source term only when the medium temperature exceeds the current pressure saturation temperature, and the activation of the condensation source term when the gaseous medium enters the condensation zone and the radiator removes sufficient heat. Solid thermal conductivity was entered for the core, windings, and epoxy insulation components, and air-cooled convection heat transfer boundary conditions were set for the radiator.

[0044] 3. S1 Electromagnetic Loss Spatial Mapping Loaded Heat Source Read the preprocessed winding loss, core loss, and metal stray loss data with unified spatial coordinates from S1, and apply the loss density as a volumetric heat source to the solid domains of the winding, core, and metal structure according to the mapping rule of one-to-one correspondence between grid cells; achieve precise spatial matching between electromagnetic heating and fluid heat transfer models, and avoid local temperature calculation distortion caused by heat source offset.

[0045] 4. Configure the transient simulation iterative solution control logic Transient multi-field coupled calculation is initiated, and iterative calculations are performed within each time step: ① The current unit medium temperature is read, compared with the saturation temperature under the same pressure, and the local vaporization mass source term is automatically calculated to update the gas phase volume fraction; ② The flow field of the gas phase fluorocarbon medium flowing along the pipe towards the condenser under the action of buoyancy and pressure gradient is tracked; ③ The gas phase medium is identified in the condenser region, and the condensation mass source term is solved according to the heat transfer rate of the radiator, and the liquefied medium flows into the liquid fluorocarbon liquid return cavity; ④ The internal pressure of the transformer tank is updated according to the difference between the total vaporization mass and the total condensation mass of the whole model; ⑤ The global medium saturation temperature is corrected again using the updated pressure, and it is substituted back into the vaporization and condensation source term equations to enter the next time step for iterative calculation until the temperature, pressure, and gas phase distribution reach a periodic steady state.

[0046] 5. Extraction and output of global phase change cooling result data After the simulation converges, all field data with spatial coordinates are exported, namely the phase change cooling result dataset, which includes: the whole-domain temperature field inside the transformer, the flow velocity field of the fluorocarbon medium, the pressure field of the tank and pipeline, the three-dimensional distribution cloud map of the gas phase volume fraction, the distribution of the vaporization region of the high-temperature medium, and the distribution of the liquefaction and condensation region inside the condenser. All field data maintain a spatial coordinate system that is completely consistent with the S1 electromagnetic field model, providing homologous matching data for S3 to identify gas-containing regions and correct dielectric parameters.

[0047] S3. This step takes the three-dimensional field data output from the transient thermal-fluid-phase change coupling simulation in S2 as input. Under the same spatial coordinates and the same calculation time, it sequentially completes six sub-processes: screening and identification of gas-containing regions, solving for the equivalent dielectric constant at the grid level, reloading and iterative calculation of the electric field model, delineation of high electric field danger zones, interpolation matching of gas phase breakdown field strength, and volume integral solution of gas phase electric field stress accumulation. This quantitatively characterizes the electric field distortion and insulation stress risk caused by gas phase accumulation.

[0048] The specific process of step S3 includes: 1. Spatiotemporal alignment of multiphysics data, enabling global traversal identification of gas-bearing regions. (1) Data source matching: retrieve the S2 output file and extract the gas phase volume fraction of each computational cell under the three-dimensional mesh. The fluid mesh is interpolated and mapped to the S1 electromagnetic field finite element mesh, so that the thermal phase transition field and the electric field share a set of three-dimensional spatial coordinates. This ensures that key positions such as the winding end, main insulation gap, lead joint, bushing root, and iron core chamfer correspond one-to-one, eliminating identification errors caused by misalignment of multiple field data.

[0049] (2) Preset gas phase judgment threshold: According to the FC-40 fluorocarbon dielectric insulation engineering standard, the gas phase volume fraction judgment threshold is set in advance (for example, 0.01, which can be customized according to the transformer voltage level and dielectric type); traverse all fluid calculation units filled with fluorocarbon dielectric inside the transformer box, and compare the gas phase volume fraction of each unit with the preset threshold.

[0050] (3) Partition marking and information archiving: If unit If the value is greater than or equal to the threshold, the unit is determined to be a gas-bearing unit and included in the gas-bearing region set. The unit's spatial coordinates, gas phase percentage, and local temperature and pressure are recorded simultaneously. If the unit... <Threshold: If the region is determined to be a pure liquid phase, the basic dielectric parameters of the liquid phase can be directly used without modification. (4) Output the gas-bearing region mesh set file: store the coordinates of all gas-bearing units, the gas phase ratio at the corresponding time, and the local temperature and pressure, as the input file for the next step of calculating the equivalent dielectric parameters.

[0051] 2. Solve the local equivalent dielectric constant of the gas-containing elements mesh by mesh to generate a global dynamic dielectric field. (1) Assignment of basic dielectric parameters: The inherent electrical parameters of the dielectric are entered in advance, and the relative permittivity of liquid FC-40 fluorocarbon dielectric is set. =1.9, relative permittivity of gaseous fluorocarbon dielectric This is a fixed low value (much smaller than the liquid phase); this parameter is the standard value for constant temperature and pressure calibration.

[0052] (2) Substitute the equivalent dielectric constant formula into each unit and calculate point by point: using the formula In the formula, For position ,time The equivalent dielectric constant; For position ,time The gas phase volume fraction; The dielectric constant of the gaseous fluorocarbon dielectric; The dielectric constant of the liquid-phase fluorocarbon medium. For all identified gas-containing units, the real-time gas volume fraction is retrieved. Substitute the values ​​into the formula to solve for the equivalent dielectric constant of the mesh element at the current time and current position. Direct assignment of pure liquid phase units .

[0053] (3) Global dielectric field reconstruction: The updated equivalent dielectric constant of each fluid mesh is mapped back to the finite element mesh of the S1 insulation electric field calculation sub-model, generating a three-dimensional time-varying equivalent dielectric constant field file that varies with the gas phase distribution. Each spatial unit corresponds to a set of dielectric parameters, accurately restoring the real medium layered structure of "liquid phase as the main component and local gas phase doping".

[0054] 3. Load the equivalent dielectric parameters into the electric field model and iteratively recalculate the gas-distorted electric field distribution. (1) Reuse electromagnetic field model boundary conditions: retain all settings of the insulation electric field calculation sub-model established by S1: apply 110kV power frequency rated potential to the high voltage winding, and ground the low voltage winding, iron core, metal clamps, and box shell; keep the dielectric parameters of solid insulation components (epoxy skeleton, insulating paper) unchanged, and only replace the dielectric constant field of the fluorocarbon dielectric filling area.

[0055] (2) Resolve the finite element electric field: Start the electrostatic field iterative calculation, set the potential convergence residual threshold, and carry out iterative calculation until the potential residual of the whole domain meets the convergence criterion; after the solution is completed, output the corrected electric field intensity distribution of the gas-bearing working condition. .

[0056] (3) Extraction of field strength in key areas: Export the local electric field values ​​at the winding end, main insulation gap, lead connection area, bushing lead-out section, and sharp corner of structural change separately, compare with the initial electric field results of pure liquid phase S1, quantify the electric field rise caused by gas phase accumulation, and record the grid positions with severe local field strength distortion.

[0057] 4. Define the region of interest with high electric field and match the temperature-pressure related breakdown field strength of the gaseous medium. (1) Setting a high electric field judgment threshold: Based on the insulation design standard of 110kV fluorocarbon transformer, a preset electric field strength judgment threshold is established; the corrected global electric field strength is then traversed. The set of all grid cells with an electric field strength ≥ this threshold within the fluorocarbon dielectric region is defined as the high electric field region of interest. Calculate the total volume of all grid cells in this region. .

[0058] (2) Interpolation matching of gas phase breakdown field strength: FC-40 gas phase fluorocarbon dielectric breakdown field strength The voltage and pressure exhibit a nonlinear relationship with local temperature and pressure. A temperature-pressure-breakdown field strength calibration database is pre-imported. For each grid cell within the high-electric-field region of interest, the real-time temperature and pressure output from S2 of that cell are retrieved. Using bilinear interpolation, the breakdown field strength of the gaseous medium under this condition is accurately obtained. This allows for the binding of three sets of parameters—gas volume fraction, distorted electric field strength, and dielectric breakdown field strength—to each grid cell.

[0059] 5. Calculate the gas-phase electric field stress accumulation using volume integral operations in high electric field regions. (1) Unified integration calculation benchmark: the high electric field region of interest Spatial coordinates of all grids within, , , Data is integrated into a single integrator to ensure that all physical quantities correspond to the same simulation time. .

[0060] (2) Substitute into the integral formula to perform three-dimensional volume integral calculation: In the formula, For a moment The amount of gas phase electric field stress accumulation; Regions of interest with high electric fields; Volume of the region of interest in high electric field; To account for the electric field strength after considering the local gas phase distribution; This represents the breakdown field strength of the gaseous fluorocarbon dielectric under corresponding local temperature and pressure conditions. The physical meaning of the formula is: normalized by the volume of the high electric field region, the integral sum of the squared ratio of the weighted gas phase proportion to the electric field breakdown margin quantifies the overall insulation stress risk formed by the gaseous dielectric in the high-field region; the calculation outputs the current moment... Corresponding gas phase electric field stress accumulation .

[0061] (3) Transient time-series data storage: This simulation uses two load coefficients of 0.8 and 1.0 for transient calculation. At each time step, the entire process of steps 1 to 5 of step S3 is repeated, and the data is recorded time by time. The time-series curves are used to extract the maximum gas-phase electric field stress accumulation during the entire simulation cycle, providing a unique quantitative evaluation index for the comprehensive analysis of the dual constraints of cooling and insulation in S4.

[0062] 6. Output a complete set of S3 analysis result files. After completing the single-moment or full-cycle calculation, three types of core data are output uniformly: ① spatial distribution cloud map and coordinate table of gas-bearing area; ② full-domain electric field intensity distribution data after gas correction; ③ full-time gas phase electric field stress accumulation numerical curve and peak value. All files maintain the same spatial reference as S1 and S2 and are directly connected to the comprehensive evaluation module in step S4.

[0063] S4. This step integrates the multi-field data of phase change cooling output from S2, the gas-containing region distribution, the corrected electric field distribution, and the time-series gas phase electric field stress accumulation index output from S3. It is divided into four sub-processes: phase change cooling effect sub-analysis, gas phase insulation constraint sub-analysis, joint judgment of dual constraint safety threshold, and differentiated structural optimization guidance for exceeding the standard working conditions. It simultaneously completes the integrated comprehensive assessment of heat dissipation performance and insulation risk, and provides feasible structural adjustment solutions for working conditions that do not meet the design limits.

[0064] The specific process of step S4 includes: 1. Based on the S2 phase change cooling results data, analyze the transformer phase change cooling effect item by item. (1) Extraction of core temperature indicators and evaluation of cooling performance: The full-time temperature field data of the S2 transient simulation was retrieved, and two types of key temperature feature values ​​were selected. The first is the temperature of all grids in the high and low voltage windings, and the maximum hot spot temperature of the windings during the simulation period was extracted. The second is the highest temperature of each lamination area of ​​the iron core. The temperature was compared with the preset temperature design limit of the equipment to determine whether the temperature rise of the windings and the iron core exceeded the standard. At the same time, the spatial coordinates of the hot spot were extracted to locate the high-temperature heating area inside the transformer and distinguish whether it was concentrated heating of the winding conductors, concentrated local loss of the iron core, or heat dissipation dead zone caused by poor medium flow.

[0065] (2) Phase change cycle heat transfer capacity analysis: retrieve three sets of field data from S2 output: gas phase volume fraction distribution, vaporization region distribution, and condensation region distribution. ①Analyze the vaporization area: Determine whether the high-temperature vaporization area is concentrated on the surface of the core heating components of the winding and iron core. If the vaporization area is too small, it indicates that the heat of the medium phase change is not fully utilized and the cooling capacity is insufficient. If the vaporization area spreads to high electric field components such as bushings and leads, the potential risk of gas phase intrusion into the insulation sensitive area should be predicted in advance. ②Analyze the heat exchange efficiency of the condensation zone: Statistically analyze the gas phase liquefaction range inside the condenser and the flow distribution of the liquid fluorocarbon liquid return cavity to determine whether the gaseous fluorocarbon medium can quickly complete the exothermic liquefaction and whether the low-temperature liquid medium can be uniformly returned to the heating zone at the bottom of the box by gravity; if the liquefaction in the condensation zone is insufficient and the return flow of the medium in the return cavity is obstructed, it is directly determined that there is a flow defect in the phase change cycle heat exchange loop.

[0066] (3) Overall rating of cooling performance Based on the winding hot spot temperature, the highest core temperature, and the degree of matching between vaporization or condensation areas, the cooling levels are qualitatively classified, and a cooling effect analysis report is generated.

[0067] 2. Based on the S3 gas-electric coupling calculation results, quantitatively analyze the gas phase insulation constraint. (1) Overview of basic characteristics of vapor phase accumulation insulation The coordinate file of the gas-bearing region and the cloud map of the global gas phase volume fraction distribution output by S3 were retrieved to statistically analyze two key pieces of information: first, the maximum gas phase volume fraction within the high electric field area of ​​interest, quantifying the degree of gas phase enrichment in the high field area; second, the overlap range between the gas-bearing region and other high electric field areas such as winding ends, main insulation gaps, lead joints, and bushing roots, visually determining the extent to which the gas phase medium intrudes into weak insulation areas. Taking this 110kV transformer embodiment as an example, the maximum gas phase volume fraction in the high field area is 0.041 when the load factor is 0.8, and rises to 0.068 when the load factor is 1.0. Increased load exacerbates the accumulation of gas phase in the high electric field area.

[0068] (2) Quantitative risk assessment of insulation stress Read the full-time gas phase electric field stress accumulation in S3 The curve extracts the maximum gas-phase electric field stress accumulation during the simulation period. This value is the core quantitative indicator characterizing the overall insulation risk. Simultaneously, the maximum electric field strength across the entire domain under the corrected gas-containing condition is retrieved and compared with the initial electric field result in the pure liquid phase to quantify the increase in electric field distortion caused by the gas phase. A larger value indicates a higher risk of insulation breakdown due to the superposition of the gas phase and the high electric field. In the example, a load of 0.8 corresponds to an accumulation of 0.017, while a load of 1.0 increases it to 0.031; the insulation risk increases synchronously with the increase in load.

[0069] 3. Safety assessment based on a dual threshold of phase change cooling constraint and gas phase insulation constraint. (1) Preset dual-dimensional design limit parameters: For 110kV fluorocarbon liquid transformer, two sets of judgment thresholds are pre-entered: the winding hot spot temperature preset temperature limit and the maximum gas phase electric field stress accumulation preset insulation risk limit. Both sets of limits are derived from the equipment insulation and heat dissipation design specifications.

[0070] (2) Simultaneously compare the two types of peak indicators and execute the joint judgment logic: extract the two core peak parameters in the entire simulation cycle, namely the maximum hot spot temperature of the winding and the maximum gas phase electric field stress accumulation, and complete the judgment under three working conditions: ① Condition 1: The maximum hot spot temperature of the winding is less than or equal to the temperature limit, and the maximum gas phase electric field stress accumulation is less than or equal to the insulation risk limit; it is determined that the transformer structure and phase change circulation arrangement scheme simultaneously meet the phase change cooling constraint and gas phase insulation constraint, and the heat dissipation and insulation performance meet the standards, and can be directly used for engineering prototype manufacturing. ② Operating Condition 2: The maximum hot spot temperature of the winding is greater than the temperature limit, but the gas phase electric field stress accumulation meets the standard; it is determined that there is only a heat dissipation defect and the insulation safety margin is sufficient. ③ Condition 3: The maximum gas phase electric field stress accumulation is greater than the insulation risk limit, and the winding hot spot temperature meets the standard; it is determined that there is only gas phase insulation risk, and the heat dissipation and heat exchange capacity meets the design requirements. ④ Condition 4: Both the winding hot spot temperature and the amount of gas phase electric field stress accumulation exceed the standard; it is determined that there are dual defects in heat dissipation and insulation, and the structural scheme needs to be fully optimized.

[0071] (3) Standardized archiving of judgment results: Record the current simulation load coefficient (0.8 / 1.0), double peak value, double threshold comparison result, and comprehensive judgment conclusion, and generate a standardized judgment data table to support the horizontal comparison and selection of the optimal design of multiple structural schemes.

[0072] 4. Differentiated structural optimization and adjustment scheme for output under excessive operating conditions Based on the joint judgment conclusion of process 3, targeted modification and optimization ideas are given for two types of defects, so as to achieve coordinated optimization design of cooling structure and insulation structure: (1) Only the winding hot spot temperature exceeds the standard (cooling is not up to standard, insulation is qualified): The root cause of the defect is insufficient phase change cycle heat dissipation capacity. The adjustment direction focuses on the medium flow and condensation heat exchange structure: optimize the medium flow guiding structure inside the box, adjust the condenser installation position, increase the heat exchange area of ​​the radiator, modify the flow channel size of the liquid fluorocarbon liquid return cavity, accelerate the low temperature liquid phase medium return speed, improve the phase change heat exchange efficiency of the heat-generating area, and reduce the local hot spot temperature of the winding and iron core.

[0073] (2) Only the amount of gas phase electric field stress accumulation exceeds the standard (insulation risk is too high, cooling is qualified): The root cause of the defect is that a large amount of gas phase medium accumulates in the high electric field insulation area. The adjustment direction focuses on the gas phase migration path and local insulation structure: add gas phase guide baffles to change the flow trajectory of gaseous fluorocarbon liquid and avoid gas phase accumulation in high electric field areas such as winding ends and bushings; adjust the condenser arrangement position to shorten the path of gas phase medium floating to the condensation area and accelerate the gas phase liquefaction elimination; thicken the insulation barrier and optimize the insulation chamfer structure in the area where the high electric field and gas phase overlap to reduce the degree of local electric field distortion.

[0074] (3) Temperature and insulation indicators both exceed the standard: The above two types of optimization measures are implemented simultaneously, taking into account the optimization of medium heat exchange cycle and gas phase migration and insulation structure modification, and eliminating overheating defects and gas phase insulation breakdown risks at the same time.

[0075] 5. Output the complete set of S4 comprehensive analysis results documents. After completing all analyses and judgments, a unified and complete simulation evaluation report is output. The report includes: temperature distribution cloud map of windings and core, distribution map of vaporization or condensation regions, superimposed cloud map of gas-containing regions and high electric field regions, time-series variation curve of gas phase electric field stress accumulation, judgment conclusion of dual threshold comparison, and suggestions for structural optimization and adjustment in different scenarios. The entire set of data fully inherits all simulation results from S1 to S3 and directly serves as the quantitative design basis for the gas phase migration path layout, condensation system design, and insulation structure optimization of 110kV fluorocarbon liquid transformer.

[0076] This embodiment takes a 110kV fluorocarbon liquid phase change cooling transformer as the object and includes four coupled simulation steps: The first step is to build an electromagnetic field finite element model, calculate the global electromagnetic loss and the initial electric field distribution of the pure liquid phase, and provide heat source and electric field benchmark for subsequent simulations; The second step maps the loss to the heat-flow-phase change coupled model, and iteratively solves the phase change cooling data such as temperature, flow field, and gas phase volume fraction based on the temperature-pressure correlation properties of the fluorocarbon medium and the vaporization-condensation source terms; The third step unifies the multi-field spatiotemporal coordinates to identify the gas-containing region, updates the equivalent parameters of the medium through the two-phase dielectric formula and recalculates the distorted electric field, and integrally calculates the gas phase electric field stress accumulation to quantify the insulation risk; The fourth step evaluates the cooling effect by combining temperature and phase change distribution, analyzes the insulation constraint based on the gas phase distribution and stress index, uses hot spot temperature and insulation stress dual thresholds to determine whether the equipment meets the standards, and provides condensation, gas phase conduction, and insulation structure optimization schemes for different non-compliant operating conditions. This invention achieves closed-loop coupled simulation of electromagnetic-phase-electric field, quantifies insulation risk with integral index, adapts the phase change model to transient conditions of variable load, and simultaneously verifies the dual constraints of cooling and insulation. It can directly guide the collaborative optimization of transformer structure, and the simulation accuracy and engineering practicality are significantly better than traditional unidirectional simulation methods.

[0077] Example 2: This embodiment further describes the system of the present invention based on Embodiment 1. This embodiment is a simulation system for phase change cooling of fluorocarbon liquid transformers considering gas phase insulation constraints. The system is mounted on a simulation computing workstation and includes four major functional modules: an electromagnetic field solution module, a phase change coupling simulation module, a gas-electric coupling correction module, and a comprehensive evaluation module.

[0078] 1. Electromagnetic field solution module It includes built-in sub-elements for geometric modeling, mesh generation, electromagnetic parameter assignment, and boundary condition setting, corresponding to execution method step S1. It can import the 3D structural dimensions of a transformer to build an electromagnetic field finite element model, run the electromagnetic loss sub-model and the insulation electric field sub-model respectively, and output global electromagnetic loss distribution and pure liquid phase initial electric field data with unified spatial coordinates, which are then standardized and transmitted to the phase change coupling simulation module.

[0079] 2. Phase Change Coupling Simulation Module It interfaces with the electromagnetic field solution module, receiving electromagnetic losses as a volumetric heat source, and executes step S2 accordingly. It includes a fluorocarbon medium property database, a vaporization or condensation mass source term solution unit, and a temperature and pressure iterative cycle controller. It divides the computation into four major domains: solid heat transfer, liquid, gaseous medium, and condensation. The transient solution outputs a complete set of phase change cooling field data, including temperature, velocity, pressure, and gas volume fraction, which is synchronously pushed to the gas-electric coupling correction module.

[0080] 3. Gas-electric coupling correction module The docking phase transition coupling simulation module is executed in step S3. This includes a gas-bearing region identification unit, an equivalent dielectric constant calculation unit, an electric field recalculation unit, and a high electric field integration solution unit. It automatically filters gas-rich regions, substitutes them into the two-phase dielectric formula to update the global dielectric parameters, recalculates the distorted electric field using the electromagnetic field model, retrieves the dielectric temperature and pressure breakdown data, integrates it to obtain the gas-phase electric field stress accumulation, and simultaneously sends the gas distribution, corrected electric field, and stress indicators to the comprehensive evaluation module.

[0081] 4. Comprehensive Evaluation Module The phase change coupling simulation module and the gas-electric coupling correction module are connected, and the corresponding method step S4 is executed. A built-in dual threshold database for temperature and insulation risk is used to automatically extract the maximum hot spot temperature of the winding and the peak gas phase electric field stress accumulation to complete a joint safety assessment. It distinguishes between three types of operating conditions: overheating exceeding limits, insulation risk exceeding limits, and dual exceeding limits, and automatically outputs suggestions for optimizing gas phase flow, condensation regions, and insulation structures. Finally, a visual simulation evaluation report is generated, including cloud maps of various field distributions, quantitative index curves, and optimization scheme text.

[0082] The operator completes the electromagnetic modeling and solution of the transformer in the electromagnetic field solution module → the data is automatically transferred to the phase change coupling simulation module to carry out transient phase change heat calculation → the gas-electric coupling correction module reads the gas phase data to complete dielectric update, electric field recalculation and insulation risk quantification → the comprehensive evaluation module integrates all field quantity data to complete the cooling and insulation dual constraint analysis and judgment and output the optimization scheme. The data of the four modules flows in a closed loop, and the integrated automatic simulation analysis of electromagnetic-thermal-flow phase change-gas-electric correction is fully realized.

[0083] In summary, the present invention has the following advantages: The simulation method and supporting system provided by this invention achieve closed-loop coupled calculation of electromagnetic, heat flow phase change, and electric field multi-physics fields, solving the shortcomings of traditional simulations where heat transfer and electric field calculations are separated and cannot simultaneously assess the risk of gas-phase insulation. This invention dynamically updates the equivalent dielectric parameters of the medium based on the gas phase distribution generated by phase change, accurately reproducing the electric field distortion caused by gas phase accumulation. It abandons the qualitative analysis method of manually comparing cloud maps and constructs a quantitative index of gas-phase electric field stress accumulation, objectively characterizing the insulation breakdown risk caused by the superposition of gas phase and high electric field. The phase change simulation adopts a temperature-pressure linkage iterative mechanism to fully reproduce the closed-loop cycle of vaporization and condensation of fluorocarbon media, adapting to different load transient operating conditions and significantly improving the simulation accuracy of temperature and gas phase distribution. This invention sets up a dual-threshold joint judgment system for winding temperature and insulation stress, simultaneously verifying the dual constraints of cooling and insulation, and providing differentiated structural optimization schemes for different exceeding conditions. The accompanying modular simulation system enables automatic data flow throughout the entire process, eliminating the need for manual processing of multiple data fields. It is easy to operate, has high calculation accuracy, and can directly guide the coordinated optimization of transformer gas phase conduction, condensation region, and insulation structure, demonstrating outstanding practical engineering value.

[0084] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Terms such as "upper," "lower," "left," "right," "front," and "rear" used in the invention are merely for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0085] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A simulation method for transformer phase change cooling considering gas-phase insulation constraints, characterized in that, Includes the following steps: First, an electromagnetic field finite element model of the fluorocarbon liquid transformer to be simulated is established, and the distribution of electromagnetic loss and electric field intensity inside the transformer is calculated. Secondly, based on the electromagnetic loss distribution, a thermal-fluid-phase change coupled simulation was performed to obtain the phase change cooling result data inside the transformer; Next, based on the phase change cooling result data, identify the gas-containing region inside the transformer, update the dielectric parameters and electric field strength of the gas-containing region, and calculate the gas phase electric field stress accumulation. Finally, based on the phase change cooling results data and the gas phase electric field stress accumulation, a comprehensive analysis was conducted on the phase change cooling effect and gas phase insulation constraint of the fluorocarbon liquid transformer.

2. The transformer phase change cooling simulation method considering gas phase insulation constraints according to claim 1, characterized in that, The electromagnetic field finite element model includes an electromagnetic loss calculation sub-model and an insulation electric field calculation sub-model; the electromagnetic loss distribution includes winding loss, core loss, and stray loss of metal structural components; the initial electric field intensity distribution includes the winding end, main insulation gap, lead connection area, bushing lead-out area, and local structural abrupt change area.

3. The transformer phase change cooling simulation method considering gas phase insulation constraints according to claim 1, characterized in that, The heat-fluid-phase change coupling model includes a solid heat transfer region, a liquid fluorocarbon medium region, a gaseous fluorocarbon medium region, and a condensation region. It configures the temperature-related physical properties of the fluorocarbon medium, latent heat of vaporization, the relationship between saturation temperature and pressure, vaporization mass source terms, and condensation mass source terms. The phase change cooling result data includes temperature field, velocity field, and pressure field.

4. The transformer phase change cooling simulation method considering gas phase insulation constraints according to claim 3, characterized in that, The coupled simulation process of heat-fluid-phase change includes: calculating the vaporization mass source term when the medium temperature reaches the corresponding pressure saturation temperature; calculating the condensation mass source term when the gaseous medium enters the condensation zone and meets the condensation conditions; updating the internal pressure based on the vaporization and condensation mass, and iteratively updating the phase change source term and gas-liquid distribution region by correcting the saturation temperature.

5. A transformer phase change cooling simulation method considering gas phase insulation constraints according to claim 1, characterized in that, The method for identifying gas-containing regions is as follows: regions with a gas volume fraction not less than a preset threshold are determined to be gas-containing regions; the local equivalent dielectric constant of the gas-containing region satisfies the following formula: In the formula, For position ,time The equivalent dielectric constant; For position ,time The gas phase volume fraction; The dielectric constant of the gaseous fluorocarbon dielectric; The dielectric constant of the liquid-phase fluorocarbon medium is given. The equivalent dielectric parameter is loaded into the insulation electric field calculation sub-model to obtain the updated electric field intensity distribution under the gas-containing condition.

6. A transformer phase change cooling simulation method considering gas phase insulation constraints according to claim 5, characterized in that, The region of insulating cooling medium with an updated electric field strength not less than a preset electric field threshold is designated as a high electric field interest region, and the gas phase volume fraction distribution and the electric field strength distribution under gas-containing conditions are unified to the same spatial coordinates and the same calculation time; the formula for calculating the gas phase electric field stress accumulation is: In the formula, For a moment The amount of gas phase electric field stress accumulation; Regions of interest with high electric fields; Volume of the region of interest in high electric field; To account for the electric field strength after considering the local gas phase distribution; This represents the breakdown field strength of the gaseous fluorocarbon medium under corresponding local temperature and pressure conditions.

7. A transformer phase change cooling simulation method considering gas phase insulation constraints according to claim 6, characterized in that, The phase change cooling effect of the fluorocarbon liquid transformer is analyzed based on the winding hot spot temperature, core temperature, vaporization region distribution, and condensation region distribution. The gas phase insulation constraint is analyzed based on the gas phase volume fraction, gas-containing region location, and gas phase electric field stress accumulation.

8. A transformer phase change cooling simulation method considering gas phase insulation constraints according to claim 7, characterized in that, The maximum hot spot temperature and the maximum gas phase electric field stress accumulation of the winding are obtained within the simulation time range of phase change cooling. When the maximum hot spot temperature of the winding is not higher than the preset temperature limit and the maximum gas phase electric field stress accumulation is not higher than the preset insulation risk limit, it is determined that the fluorocarbon liquid transformer simultaneously meets the phase change cooling constraint and the gas phase insulation constraint.

9. A transformer phase change cooling simulation method considering gas phase insulation constraints according to claim 8, characterized in that, When the maximum hot spot temperature of the winding exceeds the standard, adjust the medium flow path, condensation area, or recirculation structure; when the maximum gas phase electric field stress accumulation exceeds the standard, adjust the gas phase migration path, condensation area, or local insulation structure.

10. A transformer phase change cooling simulation system considering gas-phase insulation constraints, characterized in that, It includes an electromagnetic field solution module, a phase transition coupling simulation module, a gas-electric coupling correction module, and a comprehensive evaluation module; The electromagnetic field solving module is used to construct a finite element model of the transformer's electromagnetic field and output the electromagnetic loss distribution and the initial electric field distribution of the liquid phase. The phase change coupling simulation module is connected to the electromagnetic field solving module, receives electromagnetic loss as a heat source, and outputs global phase change cooling result data. The gas-electric coupling correction module is connected to the phase change coupling simulation module to identify gas-containing regions, update equivalent dielectric parameters, recalculate the electric field, and solve for the gas phase electric field stress accumulation. The comprehensive evaluation module is connected to the phase change coupling simulation module and the gas-electric coupling correction module respectively. It completes the joint evaluation of cooling and insulation performance based on cooling data and stress accumulation and outputs optimization and adjustment suggestions. The system executes the transformer phase change cooling simulation method considering gas phase insulation constraints as described in any one of claims 1 to 9.

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