Rapid calculation method and system for temperature field of oil-immersed transformer based on thermal circuit method

Abstract

The invention belongs to the field of electrical equipment state monitoring and thermal analysis, and discloses an oil-immersed transformer temperature field rapid calculation method and system based on a thermal circuit method, and the method comprises the steps: calculating the iron loss of an iron core and the copper loss of a winding according to the working condition of a transformer; the method comprises the following steps of: constructing a thermal circuit topology comprising three high-voltage winding nodes, three low-voltage winding nodes, three iron core column nodes and one oil tank environment node by adopting a 1 / 2 upper half part integral modeling scheme, and setting convection thermal resistors among windings, winding-iron core, winding-oil tank and iron core-oil tank, and radiation thermal resistors connected in parallel with the convection thermal resistors; according to the real-time temperature of the transformer oil, thermal physical characteristic parameters of the oil are obtained through linear interpolation, the optimized iron core and winding characteristic scales are combined, the convective heat transfer coefficient is corrected, and convective thermal resistance is calculated; and a thermal circuit matrix equation is established, a Newton-Raphson iteration method is adopted for solving, iteration convergence conditions are met, and the temperature of each node is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrical equipment state monitoring and thermal analysis, and particularly relates to an oil-immersed transformer temperature field fast calculation method and system based on a thermal circuit method. BACKGROUND

[0002] The oil-immersed transformer is the core equipment of the power system power transmission and distribution, and its operating temperature directly determines the insulation material aging rate (according to the "6 degree rule", the thermal aging rate doubles every 6℃ increase in temperature), thereby affecting the equipment life and power grid safety. At present, the new power system presents the characteristics of high proportion of new energy and high proportion of power electronic equipment, and the transformer faces dynamic working conditions such as light load, load, overload, and the like, and needs to grasp the internal temperature distribution in real time to support operation and maintenance decisions.

[0003] The current transformer temperature calculation mainly relies on finite element simulation and thermal circuit method: the finite element simulation has high accuracy, but needs to construct a complex three-dimensional model, and the grid subdivision and iterative solution take more than 30s, which cannot meet the real-time monitoring demand; the thermal circuit method is based on the thermal-electric analogy theory, and has high calculation efficiency, but the existing thermal circuit model has obvious limitations - most models do not fully consider the influence of the oil tank structure, oil flow characteristics and external environment on heat transfer, and have poor adaptability to non-rated conditions such as light load and overload, resulting in a temperature calculation error of more than 8%, which is difficult to match the dual demands of precision and efficiency in engineering application.

[0004] Defects and deficiencies of the prior art: (1) Poor working condition adaptability: the existing thermal circuit model is mostly designed for rated load, and does not consider the decrease in heat dissipation efficiency caused by low oil flow speed in light load, and does not correct the local heat accumulation caused by the sharp increase in copper loss in overload, and the temperature calculation deviation in non-rated conditions can reach 10%-15%, which cannot cover the dynamic load scenarios of the new power system.

[0005] (2) Low thermal resistance calculation accuracy: the calculation of the convection thermal resistance in the traditional model does not distinguish the change of the thermal physical properties (such as density and thermal conductivity) of the transformer oil with temperature, and the characteristic dimensions of the core and winding are not optimized, resulting in an error of more than 15% in the calculation of the convection thermal resistance, which directly affects the accuracy of the temperature result.

[0006] (3) Lack of multi-factor coupling: the heat dissipation differences of different parts (top, side wall, front / rear wall) of the oil tank are ignored, and the influence of radiation heat transfer on high temperature scenarios (oil temperature ≥ 60℃) is not coupled, and the temperature prediction deviation in actual operation is more than 5℃, which cannot support fault warning.

[0007] (4) Solution efficiency to be optimized: some thermal circuit models need to solve multiple-dimensional nonlinear equation sets, and the number of iterations is more than 20 times, and the calculation time is more than 5s, which is difficult to meet the engineering standard of real-time state monitoring of the transformer (requiring a delay of ≤1s). SUMMARY

[0008] To solve the problems in the prior art, the application provides a fast oil-immersed transformer temperature field calculation method and system based on the thermal circuit method, which realizes fast and accurate calculation of the transformer thermal circuit under multiple working conditions by the technical path of "accurate heat source calculation - thermal circuit topology optimization - dynamic correction of thermal resistance - fast iterative solution" based on the thermoelectric analogy theory and in combination with the internal heat generation and heat transfer mechanism of the oil-immersed transformer.

[0009] To achieve the above object, the application provides the following scheme. A fast oil-immersed transformer temperature field calculation method based on the thermal circuit method, the method comprising: calculating the core iron loss and winding copper loss according to the transformer working condition; adopting the 1 / 2 upper half integral modeling scheme to construct a thermal circuit topology comprising three high-voltage winding nodes, three low-voltage winding nodes, three core column nodes and one oil tank environment node, setting the convective thermal resistance between windings, between winding and core, between winding and oil tank, and between core and oil tank, and the radiation thermal resistance in parallel with the convective thermal resistance; acquiring the thermal physical property parameters of the oil by linear interpolation according to the real-time temperature of the transformer oil, correcting the convective heat transfer coefficient in combination with the optimized core and winding characteristic scales, and calculating the convective thermal resistance; establishing a thermal circuit matrix equation and solving it by the Newton-Raphson iteration method to obtain the temperature of each node under the condition of meeting the iteration convergence condition.

[0010] Preferably, the core iron loss calculation method comprises: obtaining the magnetic flux density B of the core corner area, T-shaped area and uniform area by the magnetic circuit model based on the core B-P curve, extracting the unit weight iron loss P by the cubic spline interpolation method, combining the core weight to obtain the total power of the iron loss ; The winding copper loss calculation method comprises: ; wherein, is the temperature of the transformer winding, is the effective value of the high / low-voltage winding current, is the high / low-voltage winding resistance at the reference temperature is the resistance temperature coefficient of copper, is the eddy current loss, is the stray loss.

[0011] Preferably, the radiation thermal resistance calculation formula is: ; ​wherein, is emissivity, is Boltzmann constant, is radiation area, is solid surface temperature, is oil tank ambient temperature.

[0012] Preferably, the convection heat transfer coefficient calculation method comprises: vertical surface: ; top surface: ; wherein, l is characteristic scale, ν is oil kinematic viscosity, Gr is Grashof number, Pr is Prandtl number, is oil thermal conductivity.

[0013] Preferably, the thermal circuit matrix equation is: ; wherein, G is the thermal conductance matrix, thermal conductance = 1 / thermal resistance; T is the node temperature vector; P is the node heat power vector, and the heat power of the high-voltage winding, the low-voltage winding and the core column is evenly divided according to the heat source quantization result.

[0014] The application also provides an oil-immersed transformer temperature field fast calculation system based on the thermal circuit method, which is used to realize the method and comprises a first calculation module, a construction module, a second calculation module and an iteration module. The first calculation module is used to calculate the core iron loss and the winding copper loss according to the transformer operating condition. The construction module is used to adopt a 1 / 2 upper half overall modeling scheme to construct a thermal circuit topology comprising three high-voltage winding nodes, three low-voltage winding nodes, three core column nodes and one oil tank ambient node, set the convection thermal resistance between windings, between windings and core, between windings and oil tank, and between core and oil tank, and the radiation thermal resistance in parallel with the convection thermal resistance. The second calculation module is used to obtain the thermal physical property parameters of the oil through linear interpolation according to the real-time temperature of the transformer oil, correct the convection heat transfer coefficient in combination with the optimized core and winding characteristic scales, and calculate the convection thermal resistance. The iteration module is used to establish a thermal circuit matrix equation, solve it by using the Newton-Raphson iteration method, meet the iteration convergence condition, and obtain the temperature of each node.

[0015] Preferably, the calculation method of the core iron loss comprises: Based on the core B-P curve, the magnetic flux density B of the core corner area, T-shaped area and uniform area is obtained through the magnetic circuit model, and the cubic spline interpolation method is used to extract the unit weight iron loss , the weight of the iron core , the total power of the iron loss ; The winding copper loss calculation method comprises: ; Wherein, is the temperature of the transformer winding, is the effective value of the high / low voltage winding current, is the high / low voltage winding resistance at the reference temperature is the resistance temperature coefficient of copper, is the eddy current loss, is the stray loss.

[0016] Preferably, the radiation resistance calculation formula is: ; Wherein, is the emissivity, is the Boltzmann constant, is the radiation area, is the solid surface temperature, is the oil tank ambient temperature.

[0017] Preferably, the convection heat transfer coefficient calculation method comprises: Vertical surface: ; Top surface: ; Wherein, l is the characteristic scale, ν is the oil kinematic viscosity, Gr is the Grashof number, Pr is the Prandtl number, is the oil thermal conductivity.

[0018] Preferably, the thermal circuit matrix equation is: ; Wherein, G is the thermal conductance matrix, thermal conductance=1 / thermal resistance; T is the node temperature vector; P is the node heat power vector, and the heat power of the high-voltage winding, the low-voltage winding and the iron core column is evenly distributed according to the heat source quantization result.

[0019] Compared with the prior art, the beneficial effects of the present application are: The present application has high calculation precision and strong working condition adaptability: ​(1) Multi-condition error control: light load (load rate 30%) temperature calculation error <=3%, load (100%) error <=2.5%, overload (150%) error <=4%, compared with the traditional model (error 8%-15%), the precision is improved by more than 60%, which meets the monitoring precision standard of GB / T 6451-2015 "Technical parameters and requirements of oil-immersed power transformer"; (2) Thermal resistance correction effect: after introducing the dynamic correction of transformer oil thermal physical properties, the calculation error of convective thermal resistance is reduced to within 5%, and the temperature deviation is reduced by 4-6℃ in the high temperature scene (oil temperature >=60℃) radiation heat exchange coupling.

[0020] The present application has high solving efficiency and strong engineering practicability: (1) Calculation speed: single-condition calculation time <=0.8s, compared with finite element simulation (>=30s), the efficiency is improved by 37 times, which meets the real-time state monitoring (delay <=1s) requirement of transformer; (2) Convenient operation: no complex modeling is needed, only the rated parameters of transformer (capacity, voltage, winding turns, etc.) and real-time working condition current need to be input, and then the temperature of each node can be output, which is suitable for the operation habit of field operation and maintenance personnel.

[0021] The present application has significant economic and social benefits: (1) Prolong the service life of equipment: through accurate temperature monitoring, the insulation aging caused by overheating is avoided, the expected service life of the transformer is prolonged by 3-5 years, and the replacement cost of a single device is saved by 50-100 million yuan; (2) Reduce operation and maintenance cost: real-time temperature data support preventive operation and maintenance, reduce the number of emergency repair, and reduce the annual operation and maintenance cost by 20%-30%; (3) Support power grid safety: adapt to the dynamic load of new power system, provide data basis for transformer overload warning and life evaluation, and ensure stable operation of power grid. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical scheme of the present application, the following briefly introduces the drawings needed to be used in the embodiments, obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating labor intensity.

[0023] Figure 1 The three views of the physical structure of the transformer model of the embodiment of the present application, wherein, (a) is the front view; (b) is the top view; (c) is the side view; Figure 2 The thermal road topology diagram of the embodiment of the present application; Figure 3The following is a comparison chart of temperatures under multiple operating conditions in an embodiment of the present invention. (a) is a comparison curve of the calculation results of the present method and the finite element simulation results under light load conditions; (b) is a comparison curve of the calculation results of the present method and the finite element simulation results under load conditions; and (c) is a comparison curve of the calculation results of the present method and the finite element simulation results under overload conditions. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1 like Figures 1-3 As shown, this invention provides a rapid calculation method for the temperature field of an oil-immersed transformer based on the thermal circuit method, the method comprising: Step 1: Heat source quantification calculation: Calculate the core iron loss and winding copper loss according to the transformer operating conditions (light load, load, overload). The iron loss is obtained by interpolation of the core BP curve. The copper loss takes into account the effective value of the current, the temperature coefficient of resistance and the correction of stray loss. Under the overload condition, the eddy current loss correction coefficient k (1.2-1.5) is introduced. Step 2: Equivalent thermal circuit topology construction: Using the 1 / 2 upper half overall modeling scheme, construct a thermal circuit topology including 3 high-voltage winding nodes, 3 low-voltage winding nodes, 3 core column nodes and 1 oil tank environment node. Set the convective thermal resistance between windings, winding-core, winding-oil tank, core-oil tank, and radiative thermal resistance in parallel with the convective thermal resistance. Step 3: Dynamic correction of thermal resistance: Based on the real-time temperature of the transformer oil, the thermophysical properties of the oil (thermal conductivity, kinematic viscosity, volume expansion coefficient) are obtained by linear interpolation. Combined with the optimized core and winding characteristic dimensions, the convective heat transfer coefficient is corrected and the convective thermal resistance is calculated. Step 4: Fast Iterative Solution: Establish the Thermal Path Matrix Equation The Newton-Raphson iterative method was used to solve the problem. The convergence condition of the iteration was that the temperature difference between two adjacent temperature intervals was ≤0.1℃ and the calculation time was ≤0.8s, thus obtaining the temperature of each node.

[0027] Step 1: Quantitative calculation of heat source (to solve the problem of inaccurate heat source input) The heat source includes core iron loss and winding copper loss, and the calculation method is as follows: (1) Iron loss calculation: based on the core B-P curve (magnetic flux density-loss curve), the magnetic flux density B of the core corner area, T-shaped area, and uniform area is obtained through the magnetic circuit model, and the cubic spline interpolation method is used to extract the unit weight iron loss , combined with the core weight , the total power of the iron loss is obtained ; (2) Copper loss calculation: considering the current effective value, resistance temperature coefficient, and stray loss, the formula is: Wherein, is the temperature of the transformer winding, is the temperature of the surrounding environment, the reference temperature, is the effective value of the high / low voltage winding current, is the resistance of the high / low voltage winding at the reference temperature (20℃), is the resistance temperature coefficient of copper (0.00393 / ℃), (eddy current loss) accounts for 5%-8% of copper loss, (stray loss) accounts for 3%-5% of copper loss; (3) Multi-working condition adaptation: when the load rate is less than or equal to 50%, the copper loss is reduced in proportion to the square of the load rate; when the load rate is greater than or equal to 120%, the copper loss is increased in proportion to the square of the load rate, and the eddy current loss correction coefficient k (1.2-1.5) is introduced.

[0028] Step 2: Equivalent thermal circuit topology construction (solve the problem of insufficient multi-factor coupling) Adopt "1 / 2 upper half integral modeling" (avoid heat transfer error caused by segmented core and winding), construct 9-node thermal circuit topology: Winding nodes: 3 high-voltage winding nodes (HV1-HV3), 3 low-voltage winding nodes (LV1-LV3); Core nodes: 3 core column nodes (CC1-CC3); Environment nodes: 1 oil tank environment node (T env , default 20℃); Key thermal resistance settings: Winding-to-winding thermal resistance : convective heat transfer between high and low voltage windings, set between HV and LV nodes; Winding-to-core thermal resistance : convective heat transfer between low-voltage winding and core column, set between LV and CC nodes; Winding-to-oil tank thermal resistance : convective heat transfer between high and low voltage windings and oil tank top. Core-oil tank thermal resistance : Convection heat transfer between the iron core column and the top of the oil tank; Radiative thermal resistance : Connected in parallel with the convective thermal resistance, it characterizes the radiative heat transfer between the solid surface (winding, core) and the tank wall, and the formula is: ; in, For emission rate (core 0.85, winding 0.75), For the radiation area, It is Boltzmann's constant. The solid surface temperature This refers to the ambient temperature of the fuel tank.

[0029] Step 3: Dynamic correction of thermal resistance (solving the problem of low accuracy in thermal resistance calculation) Based on the thermal circuit parameter calculation method, a dynamic correction of the transformer oil thermophysical properties is introduced: (1) Convection heat transfer coefficient Correction: Vertical surfaces (winding sidewalls, core columns): ; Top surface (winding top, core top): ; in, l ν is the characteristic scale, and ν is the kinematic viscosity of the oil. Gr Let Pr be a Grashof number and Pr be a Prandtl number. The thermal conductivity of oil; (2) Feature scale optimization: Core characteristic dimensions ( a For the thickness of the iron core column, b (Wide width of the iron core column). Winding characteristic scale ( e For the width of the oil passage, d (winding thickness); (3) Calculation of convection thermal resistance: ; in, A v This represents the heat dissipation area.

[0030] Step 4: Fast iterative solution (to solve the problem of low solution efficiency) (1) Establishment of thermal circuit equations: Based on the nodal temperature balance, matrix equations are constructed. Where: G is a 10×10 thermal conductivity matrix (thermal conductivity = 1 / thermal resistance), such as: ; T is the node temperature vector: ; wherein the 3 high-voltage winding node temperatures are respectively the 3 low-voltage winding node temperatures are respectively ; the 3 core column node temperatures are respectively ; and the oil tank environment node temperature is .

[0031] P is the node heat power vector: ; wherein the 3 high-voltage winding node heat powers are respectively the 3 low-voltage winding node heat powers are respectively ; the 3 core column node heat powers are respectively . (2) Solution algorithm: Newton-Raphson iteration method is adopted, the initial temperature is set to , the convergence condition is that the adjacent temperature difference is ≤0.1℃, the iteration number is ≤10 times, and the calculation time is ≤0.8s.

[0032] Alternative solution (adapt to different engineering scenarios) (1) Heat source calculation alternative: if the B-P curve is lacking, the IEEE standard iron loss formula can be used: ; wherein is the power frequency, is the maximum magnetic flux density of the core, is the hysteresis loss coefficient, is the eddy current loss coefficient, which is suitable for the scene without core experimental data; (2) Solution algorithm alternative: if the hardware resources are limited, Gauss-Seidel iteration method can be used, the calculation time is ≤1s, the precision is reduced by ≤3%, which meets the low-cost operation and maintenance demand.

[0033] Embodiment two This embodiment illustrates the specific implementation process of embodiment one through specific data: Transformer parameters: The transformer parameters are as follows: Rated capacity: 400kVA, high-voltage side rated voltage: 10.5kV, rated frequency: 50Hz; Core: core column cross-section thickness 200mm, window width 327mm, window height 604mm, material is silicon steel sheet, weight 500kg; Winding: Low-voltage winding turns 64 turns, inner diameter 145 mm, outer diameter 173 mm, height 404 mm; high-voltage winding turns 1386 turns, inner diameter 183 mm, outer diameter 220.2 mm, height 404 mm; Transformer oil: 25# transformer oil, ambient temperature T env = 20℃; Working condition: light load (load rate 30%, I H = 6.5A), load (100%, I H = 21.7A), overload (150%, I H = 32.6A).

[0034] Implementation step details: Step 1: heat source calculation (1) Iron loss: through the magnetic circuit model, the core uniform area B = 1.3T is obtained, and P = 0.5B2fA is obtained by checking the B-P curve, so P = 0.5*1.3T2*50Hz*0.5A = 1.5W, 3 core columns are divided, and each column has P = 0.5W; ; (2) Copper loss: Reference resistance: ; Load working condition: ; 3 high-voltage windings are divided (high-voltage winding loss ratio 60%), 3 low-voltage windings are divided: ; Light load / overload: adjust according to load rate square and correction coefficient, light load , overload .

[0035] Step 2: thermal resistance calculation and correction (take load working condition as an example) (1) Transformer oil parameters (oil temperature 60℃, k ; (2) Characteristic scale: ; (3) Convective heat transfer coefficient (top of winding): ; (4) Convective thermal resistance :Calculate the convection area and substitute it into the convection thermal resistance formula to get: ; ; ​(5) Radiative thermal resistance : ; After parallel connection ; Step 3: Solution of thermal circuit equation (1) Construct the thermal conductivity matrix G: , and other elements are filled according to the topology; (2) Iterative solution: Initial temperature , substitute , the 5th iteration converges (temperature difference ≤0.1℃), and the key node temperature of the load working condition is obtained: LV2 (intermediate phase low-voltage winding) 95.1℃, HV2 93.2℃, and CC2 90.6℃.

[0036] Step 4: Result verification: Compared with the finite element simulation result: the simulation temperature of LV2 node is 92.5℃, the calculation temperature by the method is 95.1℃, and the error is 2.8%, which is within the engineering allowable range.

[0037] Example Three The application further provides an oil-immersed transformer temperature field fast calculation system based on a thermal circuit method, which is used for realizing the method in Example One, and comprises a first calculation module, a construction module, a second calculation module and an iteration module. The first calculation module is used for calculating the core iron loss and winding copper loss according to the transformer working condition. The construction module is used for adopting a 1 / 2 upper half overall modeling scheme to construct a thermal circuit topology comprising three high-voltage winding nodes, three low-voltage winding nodes, three core column nodes and one oil tank environment node, setting the convective thermal resistance between windings, between winding and core, between winding and oil tank and between core and oil tank, and the radiative thermal resistance in parallel with the convective thermal resistance. The second calculation module is used for acquiring the thermal physical property parameters of the oil through linear interpolation according to the real-time temperature of the transformer oil, correcting the convective heat transfer coefficient in combination with the optimized core and winding characteristic dimensions, and calculating the convective thermal resistance. The iteration module is used for establishing a thermal circuit matrix equation, solving by using the Newton-Raphson iteration method, meeting the iteration convergence condition, and obtaining the temperature of each node.

[0038] In this embodiment, the calculation method of the core iron loss comprises: Based on the core B-P curve, the magnetic flux density B of the core corner area, T-shaped area and uniform area is obtained through a magnetic circuit model, and the unit weight iron loss P is extracted by using a cubic spline interpolation method. In combination with the core weight Total power of iron loss ; The methods for calculating winding copper losses include: ; in, The temperature of the transformer windings. These are the effective values ​​of the high / low voltage winding currents. Reference temperature High / low voltage winding resistance, is the temperature coefficient of resistance of copper. For eddy current losses, This is stray loss.

[0039] In this embodiment, the formula for calculating radiative thermal resistance is: ; in, For emission rate, It is Boltzmann's constant. For the radiation area, The solid surface temperature This refers to the ambient temperature of the fuel tank.

[0040] In this embodiment, the method for calculating the convective heat transfer coefficient includes: Vertical surfaces: ; Top surface: ; in, l As a feature scale, ν The kinematic viscosity of the oil. Gr For Grashof numbers, Pr For Prandtl numbers, The value represents the thermal conductivity of oil.

[0041] In this embodiment, the thermal path matrix equation is: ; Where G is the thermal conductivity matrix, thermal conductivity = 1 / thermal resistance; T is the node temperature vector; P is the node thermal power vector, and the thermal power of the high-voltage winding, low-voltage winding, and core column is evenly distributed according to the heat source quantization results.

[0042] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A rapid calculation method for the temperature field of an oil-immersed transformer based on the thermal circuit method, characterized in that, The method includes: Calculate the core iron loss and winding copper loss based on the transformer operating conditions; A 1 / 2 upper half overall modeling scheme is adopted to construct a thermal topology including 3 high-voltage winding nodes, 3 low-voltage winding nodes, 3 core column nodes and 1 oil tank environment node. The convective thermal resistance between windings, winding-core, winding-oil tank, core-oil tank and radiative thermal resistance in parallel with the convective thermal resistance are set. Based on the real-time temperature of the transformer oil, the thermophysical properties of the oil are obtained by linear interpolation. Combined with the optimized core and winding characteristic dimensions, the convective heat transfer coefficient is corrected and the convective thermal resistance is calculated. The thermal path matrix equation is established and solved using the Newton-Raphson iterative method. The iterative convergence condition is satisfied, and the temperature of each node is obtained.

2. The method according to claim 1, characterized in that, The calculation methods for core loss include: Based on the core BP curve, the magnetic flux density B in the core corner region, T-shaped region, and uniform region is obtained through a magnetic circuit model. The iron loss per unit weight is extracted using cubic spline interpolation. Combined with the weight of the iron core Total power of iron loss ; The methods for calculating winding copper losses include: ； in, The temperature of the transformer windings. These are the effective values ​​of the high / low voltage winding currents. Reference temperature High / low voltage winding resistance, is the temperature coefficient of resistance of copper. For eddy current losses, This is stray loss.

3. The method according to claim 1, characterized in that, The formula for calculating radiative thermal resistance is: ； in, For emission rate, It is Boltzmann's constant. For the radiation area, The solid surface temperature This refers to the ambient temperature of the fuel tank.

4. The method according to claim 1, characterized in that, Methods for calculating the convective heat transfer coefficient include: Vertical surfaces: ; Top surface: ; in, l As a feature scale, ν The kinematic viscosity of the oil. Gr For Grashof numbers, Pr For Prandtl numbers, The value represents the thermal conductivity of oil.

5. The method according to claim 1, characterized in that, The thermal path matrix equation is: ； Where G is the thermal conductivity matrix, thermal conductivity = 1 / thermal resistance; T is the node temperature vector; P is the node thermal power vector, and the thermal power of the high-voltage winding, low-voltage winding, and core column is evenly distributed according to the heat source quantization results.

6. A rapid calculation system for the temperature field of an oil-immersed transformer based on the thermal circuit method, the system being used to implement the method described in any one of claims 1-5, characterized in that, The system includes: a first computing module, a construction module, a second computing module, and an iteration module; The first calculation module is used to calculate the core iron loss and winding copper loss based on the transformer operating conditions; The construction module is used to construct a thermal topology that includes 3 high-voltage winding nodes, 3 low-voltage winding nodes, 3 core column nodes and 1 oil tank environment node by adopting a 1 / 2 upper half overall modeling scheme. It sets the convective thermal resistance between windings, between windings and cores, between windings and oil tanks, and between cores and oil tanks, as well as the radiative thermal resistance in parallel with the convective thermal resistance. The second calculation module is used to obtain the thermophysical property parameters of the transformer oil through linear interpolation based on the real-time temperature of the oil, and to correct the convective heat transfer coefficient and calculate the convective thermal resistance by combining the optimized core and winding characteristic scales. The iterative module is used to establish the thermal path matrix equation, solve it using the Newton-Raphson iterative method, satisfy the iterative convergence condition, and obtain the temperature of each node.

7. The system according to claim 6, characterized in that, The calculation methods for core loss include: Based on the core BP curve, the magnetic flux density B in the core corner region, T-shaped region, and uniform region is obtained through a magnetic circuit model. The iron loss per unit weight is extracted using cubic spline interpolation. Combined with the weight of the iron core Total power of iron loss ; The methods for calculating winding copper losses include: ； in, The temperature of the transformer windings. These are the effective values ​​of the high / low voltage winding currents. Reference temperature High / low voltage winding resistance, is the temperature coefficient of resistance of copper. For eddy current losses, This is stray loss.

8. The system according to claim 6, characterized in that, The formula for calculating radiative thermal resistance is: ； in, For emission rate, It is Boltzmann's constant. For the radiation area, The solid surface temperature This refers to the ambient temperature of the fuel tank.

9. The system according to claim 6, characterized in that, Methods for calculating the convective heat transfer coefficient include: Vertical surfaces: ; Top surface: ; in, l As a feature scale, ν The kinematic viscosity of the oil. Gr For Grashof numbers, Pr For Prandtl numbers, The value represents the thermal conductivity of oil.

10. The system according to claim 6, characterized in that, The thermal path matrix equation is: ； Where G is the thermal conductivity matrix, thermal conductivity = 1 / thermal resistance; T is the node temperature vector; P is the node thermal power vector, and the thermal power of the high-voltage winding, low-voltage winding, and core column is evenly distributed according to the heat source quantization results.

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