Temperature rise calculation method for liquid-immersed transformer

Abstract

The invention provides a temperature rise calculation method for a liquid-immersed transformer. The liquid-immersed transformer temperature rise calculation method comprises the steps that S1, a thermal circuit calculation model of the average oil temperature of a transformer and an electromagnetic and fluid coupling calculation model are established; s2, the thermal resistance R, the total heat capacity sigma CSUM and a heat source of the transformer are obtained, so that the average oil temperature theta om of the transformer is obtained, then the oil temperature theta bo of an oil outlet of a radiator of the transformer is obtained, and the oil temperature theta bo of the oil outlet of the radiator serves as the open boundary incoming flow temperature in the coupling calculation model; s3, acquiring a temperature distribution condition on the transformer, and obtaining a temperature value T2 on a coil grid unit of the transformer according to the temperature distribution condition; s4, judging whether the conductivity is corrected or not; and S5, after the conductivity is corrected, the steps S2, S3 and S4 are repeated until the temperature distribution is in a convergence state. According to the invention, the problems of low calculation efficiency and poor accuracy of the temperature rise calculation method of the liquid-immersed transformer in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of high voltage power transmission and distribution, and in particular to a method for calculating the temperature rise of a liquid immersed transformer. Background Art

[0002] At present, liquid-immersed transformers are the most important equipment in high-voltage power transmission and distribution systems. With the gradual increase in my country's investment in ultra-high voltage long-distance power transmission and the rapid increase in the capacity of a single liquid-immersed transformer, the local overheating caused by losses has become increasingly prominent, and higher requirements have been placed on the reliability of liquid-immersed transformers. Specifically, the temperature rise of the transformer is the most important indicator, which is directly related to the life of the transformer and the safety of the power system. As the temperature rises, the deterioration rate of the transformer oil-paper insulation system will be greatly accelerated, which is prone to insulation failure. At the same time, for every 6°C that the hot spot temperature in the liquid-immersed transformer exceeds the design value, the transformer's operating life will be halved. Therefore, it is very important to accurately control the temperature rise of the transformer during the design process. At the same time, the temperature rise calculation of the liquid-immersed transformer (especially the calculation of the hot spot temperature rise) is also a difficult point in the transformer design process.

[0003] In the prior art, the temperature rise of the transformer is usually obtained by using engineering analysis method, thermal circuit model method and numerical calculation method. However, the above three temperature rise calculation methods all have certain problems or limitations, making it difficult to achieve efficient and accurate transformer temperature rise calculation. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for calculating the temperature rise of a liquid-immersed transformer, so as to solve the problem that the method for calculating the temperature rise of a liquid-immersed transformer in the prior art has low calculation efficiency and poor accuracy.

[0005] In order to achieve the above object, the present invention provides a method for calculating the temperature rise of a liquid-immersed transformer, comprising: step S1: establishing a thermal circuit calculation model for the average oil temperature of the transformer and establishing a coupling calculation model of the electromagnetic and fluid of the transformer; step S2: obtaining the thermal resistance R and the total heat capacity ∑C of the transformer SUM And the heat source, according to the thermal resistance R, total heat capacity ∑C SUM And the heat source to obtain the average transformer oil temperature θ om , and according to the average oil temperature of the transformer θ om The oil temperature of the transformer radiator outlet is obtained as θ bo , and then the radiator oil outlet oil temperature θ boAs the open boundary in the coupled calculation model, flow temperature; step S3: obtaining the temperature distribution on the transformer to obtain the temperature value T2 on the coil grid unit of the transformer according to the temperature distribution; step S4: judging whether the conductivity needs to be corrected according to the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value ε; step S5: after correcting the conductivity, repeating steps S2, S3 and S4 until the temperature distribution on the transformer converges.

[0006] Furthermore, according to the thermal resistance R, the total heat capacity ∑C SUM And the heat source to obtain the average transformer oil temperature θ om The method includes: According to the equation: It is obtained that; among them, θ om,1 is the initial average oil temperature within a calculation period, θ om,2 is the final average oil temperature within a calculation period, q Fe is the transformer core loss, q Cu is the transformer coil ohmic loss, q St is the stray loss in other metal components of the transformer; Lost The heat dissipated by the transformer into the air; the core loss q of the transformer is obtained through simulation based on the electromagnetic parameters of the transformer Fe , transformer coil ohmic loss q Cu and stray losses q in other metal parts of the transformer St .

[0007] Furthermore, the transformer core loss q is calculated by simulation based on the electromagnetic parameters of the transformer. Fe , transformer coil ohmic loss q Cu and stray losses q in other metal parts of the transformer St The method comprises: step S01: establishing a magnetic field simulation model according to the electromagnetic design parameters of the transformer; step S02: inputting material properties into the magnetic field simulation model; step S03: using the current when the voltage is minimum tapped as the excitation of the magnetic field simulation model.

[0008] Further, the total heat capacity ∑C is obtained SUM The method includes: According to the equation: ∑C SUM =0.132×(m A +m T )+0.58×m O It is concluded that, among them, m A is the mass of the core and coil, m T is the mass of the fuel tank and accessories, m O is the oil mass in the transformer; or, according to the equation: ∑C SUM =wtank Cp tank M tank +w core Cp core M core +w Cu Cp Cu M Cu +w oil Cp oil M oil It is concluded that, among them, w tank Fuel tank + w insulation Cp insulation M insulation Heat capacity correction factor, w core is the core heat capacity correction factor, w Cu is the coil heat capacity correction factor, w oil is the correction factor for the heat capacity of the transformer oil, w insulation is the thermal capacity correction factor of the insulation material, M tank is the weight of the fuel tank, Cp tank is the specific heat capacity of the oil tank, M core is the core weight, Cp core is the core specific heat capacity, M Cu is the coil weight, Cp Cu is the specific heat capacity of the coil, M oil is the weight of oil in transformer, Cp oil is the specific heat capacity of the oil in the transformer, M insulation is the weight of the insulation material, Cp insulation is the specific heat capacity of the insulating material.

[0009] Furthermore, the temperature rise calculation method of the liquid-immersed transformer further includes: Step S11: obtaining the oil tank weight M of the transformer tank 、Core weight M core , Coil weight M Cu 、Transformer oil weight M oil , Insulation material weight M insulation And as input data, obtain the actual measured value of the heat capacity of the transformer and use it as output data; Step S12: construct a BP neural network, and train the BP neural network multiple times to establish a total heat capacity model.

[0010] Furthermore, the BP neural network's neuron net input Net in and neuron output y satisfy: y=f(Net in -θ); where x i For each input data, w i is the heat capacity correction factor, and θ is the threshold value.

[0011] Furthermore, the temperature rise calculation method of the liquid-immersed transformer further includes a step S110 between step S11 and step S12: calculating the oil tank weight M obtained in step S11 tank 、Core weight M core , Coil weight M Cu 、Transformer oil weight M oil , Insulation material weight M insulation And the measured value of the thermal capacity of the transformer is normalized.

[0012] Further, the method of obtaining the thermal resistance R of the transformer includes: according to the equation: It is obtained that; where h is the heat transfer coefficient and satisfies: Nu is the Nusselt number and satisfies: Nu=C·[Gr·Pr] n , C is the convective heat transfer correlation coefficient, L is the characteristic length, k is the thermal conductivity, S is the heat dissipation area, Gr is the Grashof number and satisfies: Pr is the Prandtl number and satisfies: ρ is the density, μ is the dynamic viscosity, g is the acceleration due to gravity, β is the rate of volume change, and Δθ is the temperature difference.

[0013] Furthermore, according to the average oil temperature of the transformer θ om The oil temperature of the transformer radiator outlet is obtained as θ bo The method includes: According to the equation: It is obtained that; among them, θ co is the temperature difference between the inlet and outlet of the transformer radiator and satisfies: θ co =2(0.2θ om +Δτ), Δτ is the correction function of the coil center height and the heat sink center height.

[0014] Furthermore, the method for obtaining the temperature distribution on the transformer includes: calculating the temperature distribution on the transformer using a fluid-solid coupling physical field.

[0015] By applying the technical solution of the present invention, a thermal circuit calculation model of the average oil temperature of the transformer is first established, and a coupling calculation model of the electromagnetic and fluid of the transformer is established, and then the thermal resistance R and the total heat capacity ∑C of the transformer are obtained. SUM And the heat source, according to the thermal resistance R, total heat capacity ∑C SUM And the heat source to obtain the average transformer oil temperature θ om , and according to the average oil temperature of the transformer θ om The oil temperature of the transformer radiator outlet is obtained as θ bo , and then the radiator oil outlet oil temperature θ boAs the open boundary in the coupled calculation model, the flow temperature is obtained. After that, the temperature distribution on the transformer is obtained to obtain the temperature value T2 on the coil grid unit of the transformer according to the temperature distribution, and then the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value ε is used to determine whether the conductivity needs to be corrected. If the conductivity needs to be corrected, after correcting the conductivity, the oil temperature θ of the radiator outlet of the transformer is recalculated. bo , and then the radiator oil outlet oil temperature θ bo As the open boundary flow temperature in the coupled calculation model, the temperature distribution on the transformer is re-obtained, and the temperature value T2 on the coil grid unit of the transformer is obtained according to the temperature distribution. Then, according to the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value ε, it is determined whether the conductivity needs to be corrected. This is repeated until the temperature distribution on the transformer converges. In this way, the transformer temperature rise calculation method is based on the thermal path method and the numerical calculation method, which realizes the efficient and accurate calculation of the transformer temperature rise and the accurate positioning of the hot spot temperature rise position, making up for many problems of the traditional liquid-immersed transformer temperature rise calculation, and thus solving the problem of low calculation efficiency and poor accuracy of the transformer temperature rise calculation method in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0017] Figure 1 A flow chart showing an embodiment of a method for calculating temperature rise of a liquid immersed transformer according to the present invention is shown;

[0018] Figure 2 Shows Figure 1 Thermal circuit calculation model diagram of transformer average oil temperature in the temperature rise calculation method of liquid-immersed transformer;

[0019] Figure 3 Shows Figure 1 BP neural network model diagram of the temperature rise calculation method of liquid immersed transformer in;

[0020] Figure 4 Shows Figure 1 BP neural network analysis flow chart of temperature rise calculation method of liquid immersed transformer in;

[0021] Figure 5 Shows Figure 1 The temperature distribution cloud diagram calculated by the temperature rise calculation method of liquid-immersed transformer in;

[0022] Figure 6 The temperature distribution cloud diagram calculated by the traditional numerical calculation method is shown;

[0023] Figure 7 A comparison chart of temperature rise test results is shown. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0025] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs.

[0026] In the present invention, unless otherwise specified, the directional words used, such as "up" and "down", usually refer to the directions shown in the drawings, or to the vertical, perpendicular or gravity directions; similarly, for ease of understanding and description, "left" and "right" usually refer to the left and right shown in the drawings; "inside" and "outside" refer to the inside and outside relative to the outline of each component itself, but the above directional words are not used to limit the present invention.

[0027] In order to solve the problem of low calculation efficiency and poor accuracy of the temperature rise calculation method of a liquid-immersed transformer in the prior art, the present application provides a temperature rise calculation method of a liquid-immersed transformer.

[0028] like Figure 1 As shown in the figure, the temperature rise calculation method of liquid immersed transformer includes:

[0029] Step S1: establishing a thermal circuit calculation model for the average oil temperature of the transformer and establishing a coupling calculation model for the electromagnetic and fluid of the transformer;

[0030] Step S2: Obtain the thermal resistance R and total heat capacity ∑C of the transformer SUM And the heat source, according to the thermal resistance R, total heat capacity ∑C SUM And the heat source to obtain the average transformer oil temperature θ om , and according to the average oil temperature of the transformer θ om The oil temperature of the transformer radiator outlet is obtained as θ bo , and then the radiator oil outlet oil temperature θ bo Flow temperature as an open boundary in the coupled computational model;

[0031] Step S3: obtaining the temperature distribution on the transformer, so as to obtain the temperature value T2 on the coil grid unit of the transformer according to the temperature distribution;

[0032] Step S4: judging whether the conductivity needs to be corrected according to the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value ε;

[0033] Step S5: After correcting the conductivity, repeat steps S2, S3 and S4 until the temperature distribution on the transformer is in a convergent state.

[0034] Applying the technical solution of this embodiment, first establish a thermal circuit calculation model for the average oil temperature of the transformer, establish an electromagnetic and fluid coupling calculation model for the transformer, and then obtain the thermal resistance R and total heat capacity ∑C of the transformer. SUM And the heat source, according to the thermal resistance R, total heat capacity ∑C SUM And the heat source to obtain the average transformer oil temperature θ om , and according to the average oil temperature of the transformer θ om The oil temperature of the transformer radiator outlet is obtained as θ bo , and then the radiator oil outlet oil temperature θ bo As the open boundary in the coupled calculation model, the flow temperature is obtained. After that, the temperature distribution on the transformer is obtained to obtain the temperature value T2 on the coil grid unit of the transformer according to the temperature distribution, and then the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value ε is used to determine whether the conductivity needs to be corrected. If the conductivity needs to be corrected, after correcting the conductivity, the oil temperature θ of the radiator outlet of the transformer is recalculated. bo , and then the radiator oil outlet oil temperature θ bo As the open boundary flow temperature in the coupled calculation model, the temperature distribution on the transformer is re-obtained, and the temperature value T2 on the coil grid unit of the transformer is obtained according to the temperature distribution. Then, according to the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value ε, it is determined whether the conductivity needs to be corrected. This is repeated until the temperature distribution on the transformer converges. In this way, the transformer temperature rise calculation method is based on the thermal path method and the numerical calculation method, which realizes the efficient and accurate calculation of the transformer temperature rise and the accurate positioning of the hot spot temperature rise position, making up for many problems of the traditional liquid-immersed transformer temperature rise calculation, and thus solving the problem of low calculation efficiency and poor accuracy of the liquid-immersed transformer temperature rise calculation method in the prior art.

[0035] In this embodiment, the electromagnetic and fluid coupling calculation model of the transformer is established by determining the electromagnetic design parameters and structural design parameters of the transformer (including the main structural parameters of the transformer, the materials used for the main components, and the size and quantity of the external plate heat sink, etc.).

[0036] like Figure 2 As shown, according to the oil circulation process in the transformer and the principle of energy balance, a thermal circuit calculation model for the average oil temperature of the transformer is established.

[0037] In this embodiment, from the physical process of transformer heat dissipation, when the oil flow temperature and speed reach stability, the temperature of the core and coil and other components no longer continues to rise, and all the excess heat is transferred to the external environment through the thermal cycle. At this point, the heating and cooling of the transformer are balanced. At this time, the hot spot temperature in the transformer usually appears at the upper part of the coil, and the hot spot temperature is one of the most critical factors that limit the transformer load capacity and evaluate the transformer life.

[0038] In this embodiment, the dynamic thermal circuit model is used to calculate the average oil temperature of the transformer θ om , according to the average oil temperature θ om Calculate the oil temperature θ at the radiator outlet entering the transformer coil bo , the radiator outlet oil temperature θ bo Taking the incoming flow temperature of the open boundary as the input temperature, the traditional closed self-circulating transformer fluid-solid coupling calculation model is simplified into an internal fluid-solid coupling calculation model with an open boundary. This greatly simplifies the solution process and shortens the calculation time while ensuring that the calculation accuracy is met.

[0039] In this embodiment, the variable step length method is used to calculate the average oil temperature of the transformer θ om Thus, since the specific heat capacity, thermal conductivity, viscosity and density of the insulating oil are all quantities that change with temperature, a dynamic equation is required to calculate the average oil temperature when a steady state is reached.

[0040] In this embodiment, the temperature distribution is calculated by the physical field of fluid-solid coupling, and the conductivity is corrected to recalculate the temperature rise distribution in the coil. The process is repeated until the temperature rise value reaches the convergence requirement, and the calculation is completed. Specifically, a thermal circuit calculation model of the average oil temperature of the transformer is first established, and a calculation method of the total heat capacity in the transformer containing a correction factor is proposed. Combined with the test data of the previous transformer (especially for special insulating medium transformers, such as natural ester insulating oil transformers), the heat capacity correction factor of different characteristic parameters is obtained through the BP neural network, so as to improve the calculation accuracy of the total heat capacity, and make this average oil temperature thermal circuit model applicable to special liquid insulation transformers. In this way, according to the calculation method of the transformer self-circulation physical process and characteristic temperature, a combination of the thermal circuit method and the numerical calculation method is proposed to simplify the traditional transformer self-circulation calculation model, that is, to simplify the self-circulation calculation model into a calculation model with an open boundary, which greatly improves the engineering efficiency and ensures the calculation accuracy.

[0041] In this embodiment, a numerical calculation model of the fluid in the body is established. The calculation model only includes the body of the transformer, that is, the low-voltage coil, the high-voltage coil, the voltage regulating coil and the corresponding insulation structure. The insulation structure includes a paper tube, an electrostatic plate, a pressure plate and an oil guide plate in the coil. The boundary condition is an open boundary, which can automatically allocate the flow in and out of the boundary. The temperature of the incoming flow entering the calculation domain is the oil temperature θ of the radiator outlet. bo .

[0042] In this embodiment, according to the thermal resistance R, the total heat capacity ∑C SUM And the heat source to obtain the average transformer oil temperature θ om The methods include:

[0043] According to the equation: We can get: om,1 is the initial average oil temperature within a calculation period, θ om,2 is the final average oil temperature within a calculation period, q Fe is the core loss of the transformer, q Cu is the transformer coil ohmic loss, q St is the stray loss in other metal components of the transformer; Lost The heat dissipated by the transformer into the air; the core loss q of the transformer is obtained through simulation based on the electromagnetic parameters of the transformer Fe , transformer coil ohmic loss q Cu and stray losses q in other metal parts of the transformer St .

[0044] In this embodiment, the core loss q of the transformer is obtained by simulation calculation based on the electromagnetic parameters of the transformer. Fe , transformer coil ohmic loss q Cu and stray losses q in other metal parts of the transformer St The methods include:

[0045] Step S01: establishing a magnetic field simulation model according to the electromagnetic design parameters of the transformer;

[0046] Step S02: inputting material properties into the magnetic field simulation model;

[0047] Step S03: using the current when the voltage is at the minimum tap as the excitation of the magnetic field simulation model.

[0048] Specifically, a natural ester insulating oil transformer is used as an example, the model is SWZ-100000 / 220, the transformer includes a transformer oil storage cabinet, a coupling pipe, a radiator, a high-voltage bushing, a neutral point bushing and a transformer oil tank, and the basic performance parameters are shown in Table 1. In step S01, a magnetic field simulation model is established according to the finite element method. In step S02, the material properties include the coil material, the core material and the material of other metal structural parts, and the specific material property settings are shown in Table 2. At the same time, the transformer in this embodiment is an on-load tap-changing transformer, and the heat source during the temperature rise test is the loss generated when the voltage is minimum tapped (the current is the largest at this time, and the loss during the operation of the transformer is also the largest), so the input excitation is the current when the voltage is minimum tapped, and at this time there is a loss density distribution in the low-voltage coil, the high-voltage coil and the voltage regulating coil.

[0049] Table 1 Basic performance parameters of SWZ-100000 / 220 transformer

[0050]

[0051]

[0052] Table 2 Magnetic field calculation material properties of SWZ-100000 / 220 transformer

[0053] Material Magnetic Permeability Conductivity [S / m] Electrical Copper 1 46700000 Silicon steel sheet Nonlinear BH curve 1 Air 1 1

[0054] Among them, the coil material is electrical copper, the core material is silicon steel sheet and its magnetic permeability follows the BH curve, and the material of other metal structural parts is A3 steel and its magnetic permeability also follows the BH curve.

[0055] Optionally, obtain the total heat capacity ∑C SUM The methods include:

[0056] According to the equation: ∑C SUM =0.132×(m A +m T )+0.58×m O In which, m A is the mass of the core and coil, m T is the mass of the fuel tank and accessories, m O is the oil mass in the transformer; or, according to the equation: ∑C SUM =w tank Cp tank M tank +w core Cp core M core +w Cu Cp Cu M Cu +w oil Cp oilM oil We can get: tank Fuel tank + w insulation Cp insulation M insulation Heat capacity correction factor, w core is the core heat capacity correction factor, w Cu is the coil heat capacity correction factor, w oil is the correction factor for the heat capacity of the transformer oil, w insulation is the thermal capacity correction factor of the insulation material, M tank is the weight of the fuel tank, Cp tank is the specific heat capacity of the oil tank, M core is the core weight, Cp core is the core specific heat capacity, M Cu is the coil weight, Cp Cu is the specific heat capacity of the coil, M oil is the weight of oil in transformer, Cp oil is the specific heat capacity of the oil in the transformer, M insulation is the weight of the insulation material, Cp insulation is the specific heat capacity of the insulating material. Thus, the above arrangement makes the total heat capacity ∑C SUM The calculation methods are more diverse to meet different usage requirements and working conditions.

[0057] In this embodiment, the total heat capacity ∑C SUM According to the equation:

[0058] ∑C SUM =wt ank Cp tank M tank +w core Cp core M core +w Cu Cp Cu M Cu +w oil Cp oil M oil +w insulation Cp insulation M insulation Conclude.

[0059] In this embodiment, the temperature rise calculation method of the liquid immersed transformer also includes:

[0060] Step S11: Obtain the oil tank weight M of the transformer tank 、Core weight M core , Coil weight M Cu 、Transformer oil weight M oil , Insulation material weight M insulation and as input data, obtain the measured value of the heat capacity of the transformer and as output data;

[0061] Step S12: construct a BP neural network, and train the BP neural network multiple times to establish a total heat capacity model.

[0062] Specifically, the weight of the transformer oil tank M tank 、Core weight M core , Coil weight M Cu 、Transformer oil weight M oil , Insulation material weight M insulation The measured value of the transformer's thermal capacity is used as the network input and the network output. Based on the historical experimental data of these characteristic parameters, sample learning is performed on the implicit relationship between them and the total thermal capacity of the transformer to establish a transformer-specific total thermal capacity model.

[0063] In this embodiment, the neuron net input Net of the BP neural network in And the neuron output y satisfies:

[0064]

[0065] y=f(Net in -θ). Among them, x i For each input data, w i is the heat capacity correction factor, and θ is the threshold value.

[0066] like Figure 3 As shown in the neural network model, for any neuron, x1, x2, ..., x n is the input of the neuron, which is often the independent variable that has a key impact on the system model (i.e., the tank weight M tank 、Core weight M core , Coil weight M Cu 、Transformer oil weight M oil , Insulation material weight M insulation ), w1, w2, …, w n The weight ratio of each input is adjusted for the connection weight. There are many ways to combine the signals and input them to the neuron. The most convenient linear weighted summation can be used to obtain the neuron net input Net in Among them, the neuron will be activated only when the information received by the neuron reaches the threshold θ, so the Net in It is compared with θ and then processed through the activation function to produce the neuron output y.

[0067] In this embodiment, the transfer function used by the BP neural network is a nonlinear transformation function Sigmoid function, which is characterized in that the function itself and its derivatives are continuous, and the activation function equation is:

[0068]

[0069] In this embodiment, the process of solving the correction factor of the transformer thermal capacity by using the BP neural network is as follows: Figure 4 As shown in the figure, the weight of each input independent variable solved by the algorithm is the heat capacity correction factor of each item, which is calculated by equation ∑C SUM =w tank Cp tank M tank +w core Cp core M core +w Cu Cp Cu M Cu +w oil Cp oil M oil +w insulation Cp insulation M insulation The corrected thermal capacity of the transformer can be obtained. The transformer in this embodiment is a natural ester insulating oil transformer.

[0070] In this embodiment, the temperature rise calculation method of the liquid-immersed transformer further includes a step S110 between step S11 and step S12: calculating the oil tank weight M obtained in step S11. tank 、Core weight M core , Coil weight M Cu 、Transformer oil weight M oil , Insulation material weight M insulation And the measured value of the thermal capacity of the transformer is normalized.

[0071] In this embodiment, the method for obtaining the thermal resistance R of the transformer includes:

[0072] According to the equation: Where h is the heat transfer coefficient and satisfies: Nu is the Nusselt number and satisfies: Nu=C·[Gr·Pr] n , C is the convective heat transfer correlation coefficient, L is the characteristic length, k is the thermal conductivity, S is the heat dissipation area, Gr is the Grashof number and satisfies: Pr is the Prandtl number and satisfies: ρ is the density, μ is the dynamic viscosity, g is the acceleration due to gravity, β is the volume change rate, and Δθ is the temperature difference.

[0073] Specifically, the calculation equation of the heat transfer coefficient h is as follows:

[0074]

[0075] In this embodiment, according to the average oil temperature θ of the transformer omThe oil temperature of the transformer radiator outlet is obtained as θ bo The methods include:

[0076] According to the equation: We can get: co is the temperature difference between the inlet and outlet of the transformer radiator and satisfies: θ co =2(0.2θ om +Δτ), Δτ is the correction function of the coil center height and the heat sink center height.

[0077] Specifically, since the specific heat capacity, thermal conductivity, viscosity and density of the insulating oil are all quantities that change with temperature, a dynamic equation is needed to calculate the temperature when the average oil temperature reaches a steady state. In order to realize the dynamic average oil temperature calculation, the differential equation that establishes the mathematical model is used, and the variable step size method is used to calculate the average oil temperature of the transformer. The average transformer oil temperature θ at steady state is calculated. om .

[0078] In this embodiment, the temperature rise calculation method of the liquid immersed transformer further includes step S04 after step S03:

[0079] The calculation results of the electromagnetic module are coupled to the fluid calculation module, and the relevant material parameters are input.

[0080] Specifically, Table 3 lists the material properties of solid materials, such as density, thermal conductivity, and specific heat capacity, and Table 4 lists the material properties of fluid materials, such as viscosity, density, thermal conductivity, and specific heat capacity.

[0081] Table 3 Solid material properties

[0082]

[0083] Table 4 Fluid material properties

[0084]

[0085]

[0086] In this embodiment, the method for obtaining the temperature distribution on the transformer includes: calculating the temperature distribution on the transformer using a fluid-solid coupling physical field.

[0087] Specifically, the fluid-temperature field calculation adopts the convection heat dissipation calculation model and the heat conduction model. The overall temperature inside the transformer is relatively low, and the effect of thermal radiation on heat dissipation can be ignored. After multiple conductivity corrections, the temperature rise inside the transformer body reaches convergence. The temperature distribution cloud diagram obtained by using the temperature rise calculation method of the liquid-immersed transformer of this embodiment and the traditional numerical calculation method is as follows: Figure 5 and Figure 6As shown, the temperature distribution is basically the same. The hot spot temperature obtained by the temperature rise calculation method of the liquid-immersed transformer in this embodiment is 123°C, that is, the temperature rise is 103K, and the hot spot temperature obtained by the traditional method is 124°C, that is, the temperature rise is 104K.

[0088] Experimental verification: The results of the temperature rise experiment are as follows Figure 7 As shown, all results are converted into temperature rise, and the comparison of temperature rise calculation results is shown in Table 5.

[0089] Table 5 Comparison of temperature rise calculation results

[0090]

[0091] Specifically, the calculation time comparison between the temperature rise calculation method of the liquid-immersed transformer of this embodiment and the traditional two-dimensional axisymmetric calculation method is shown in Table 6.

[0092] Table 6 Comparison of calculation time

[0093]

[0094] Among them, the calculation result of the temperature rise calculation method of the liquid-immersed transformer in this embodiment has a small error with the measured value, is extremely accurate, and greatly shortens the calculation time, thereby improving engineering efficiency.

[0095] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0096] First, establish the thermal circuit calculation model of the average oil temperature of the transformer, establish the electromagnetic and fluid coupling calculation model of the transformer, and then obtain the thermal resistance R and total heat capacity ∑C of the transformer. SUM And the heat source, according to the thermal resistance R, total heat capacity ∑C SUM And the heat source to obtain the average transformer oil temperature θ om , and according to the average oil temperature of the transformer θ om The oil temperature of the transformer radiator outlet is obtained as θ bo , and then the radiator oil outlet oil temperature θ bo As the open boundary in the coupled calculation model, the flow temperature is obtained. After that, the temperature distribution on the transformer is obtained to obtain the temperature value T2 on the coil grid unit of the transformer according to the temperature distribution, and then the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value ε is used to determine whether the conductivity needs to be corrected. If the conductivity needs to be corrected, after correcting the conductivity, the oil temperature θ of the radiator outlet of the transformer is recalculated. bo , and then the radiator oil outlet oil temperature θ boAs the open boundary flow temperature in the coupled calculation model, the temperature distribution on the transformer is re-obtained, and the temperature value T2 on the coil grid unit of the transformer is obtained according to the temperature distribution, and then the conductivity needs to be corrected according to the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value ε, and this is repeated until the temperature distribution on the transformer converges. In this way, the temperature rise calculation method of the liquid-immersed transformer is based on the thermal path method and the numerical calculation method, which realizes the efficient and accurate calculation of the temperature rise of the liquid-immersed transformer and the accurate positioning of the hot spot temperature rise position, making up for many problems of the traditional liquid-immersed transformer temperature rise calculation, and thus solving the problem of low calculation efficiency and poor accuracy of the temperature rise calculation method of the liquid-immersed transformer in the prior art.

[0097] Obviously, the above-described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0098] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0099] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating the temperature rise of a liquid immersed transformer, characterized in that: include: Step S1: establishing a thermal circuit calculation model for the average oil temperature of the transformer and establishing a coupling calculation model for the electromagnetic and fluid of the transformer; Step S2: Obtain the thermal resistance R and total heat capacity ∑C of the transformer SUM and a heat source, according to the thermal resistance R, the total heat capacity ∑C SUM The heat source is used to obtain the average transformer oil temperature θ om , and according to the transformer average oil temperature θ om The oil temperature of the transformer radiator outlet is obtained as θ bo , and then the oil temperature of the radiator outlet is bo Flow temperature as an open boundary in the coupled computational model; Step S3: obtaining the temperature distribution on the transformer, so as to obtain the temperature value T2 on the coil grid unit of the transformer according to the temperature distribution; Step S4: judging whether the conductivity needs to be corrected according to the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value ε; Step S5: after correcting the conductivity, repeating the steps S2, S3 and S4 until the temperature distribution on the transformer is in a convergent state.

2. The temperature rise calculation method of a liquid immersed transformer according to claim 1 is characterized in that: According to the thermal resistance R, the total heat capacity ΣC SUM The heat source is used to obtain the average transformer oil temperature θ om The methods include: According to the equation: to conclude; Among them, θ om,1 is the initial average oil temperature within a calculation period, θ om,2 is the final average oil temperature within a calculation period, q Fe is the core loss of the transformer, q Cu is the transformer coil ohmic loss, q St is the stray loss in other metal components of the transformer; Lost The heat dissipated by the transformer into the air; the core loss q of the transformer is obtained through simulation based on the electromagnetic parameters of the transformer Fe , transformer coil ohmic loss q Cu and stray losses q in other metal parts of the transformer St .

3. The temperature rise calculation method of a liquid immersed transformer according to claim 1 is characterized in that: The transformer core loss q is obtained by simulation based on the electromagnetic parameters of the transformer. Fe , transformer coil ohmic loss q Cu and stray losses q in other metal parts of the transformer St The methods include: Step S01: establishing a magnetic field simulation model according to the electromagnetic design parameters of the transformer; Step S02: inputting material properties into the magnetic field simulation model; Step S03: using the current when the voltage is at the minimum tap as the excitation of the magnetic field simulation model.

4. The temperature rise calculation method of a liquid immersed transformer according to claim 1 is characterized in that: Get the total heat capacity ∑C SUM The methods include: According to the equation: ∑C SUM =0.132×(m A +m T )+0.58×m O to conclude; Among them, m A is the mass of the core and coil, m T is the mass of the fuel tank and accessories, m O is the oil quality in the transformer; Or, according to the equation: to conclude; Among them, w tank is the tank heat capacity correction factor, w core is the core heat capacity correction factor, w Cu is the coil heat capacity correction factor, w oil is the correction factor for the heat capacity of the transformer oil, w insulation is the thermal capacity correction factor of the insulation material, M tank is the weight of the fuel tank, Cp tank is the specific heat capacity of the oil tank, M core is the core weight, Cp core is the core specific heat capacity, M Cu is the coil weight, Cp Cu is the specific heat capacity of the coil, M oil is the weight of oil in transformer, Cp oil is the specific heat capacity of the oil in the transformer, M insulation is the weight of the insulation material, Cp insulation is the specific heat capacity of the insulating material.

5. The temperature rise calculation method of a liquid immersed transformer according to claim 1 is characterized in that: The temperature rise calculation method of the liquid immersed transformer also includes: Step S11: Obtain the oil tank weight M of the transformer tank 、Core weight M core , coil weight M Cu 、Transformer oil weight M oil , Insulation material weight M insulation and as input data, obtain the measured value of the heat capacity of the transformer and as output data; Step S12: constructing a BP neural network, and training the BP neural network multiple times to establish a total heat capacity model.

6. The temperature rise calculation method of a liquid immersed transformer according to claim 5, characterized in that: The neuron net input Net of the BP neural network in and neuron output y satisfy: y=f(Net in -θ); Among them, x i For each input data, w i is the heat capacity correction factor, and θ is the threshold value.

7. The method for calculating the temperature rise of a liquid immersed transformer according to claim 5, characterized in that: The method for calculating the temperature rise of a liquid-immersed transformer further includes a step S110 located between the step S11 and the step S12: The fuel tank weight M obtained in step S11 tank 、Core weight M core , Coil weight M Cu 、Transformer oil weight M oil , Insulation material weight M insulation And the measured value of the thermal capacity of the transformer is normalized.

8. The temperature rise calculation method of a liquid immersed transformer according to claim 1, characterized in that: Methods for obtaining the thermal resistance R of the transformer include: According to the equation: to conclude; Where h is the heat transfer coefficient and satisfies: Nu is the Nusselt number and satisfies: Nu=C·[Gr·Pr] n , C is the convective heat transfer correlation coefficient, L is the characteristic length, k is the thermal conductivity, S is the heat dissipation area, Gr is the Grashof number and satisfies: Pr is the Prandtl number and satisfies: ρ is the density, μ is the dynamic viscosity, g is the acceleration due to gravity, β is the rate of volume change, and Δθ is the temperature difference.

9. The method for calculating the temperature rise of a liquid immersed transformer according to claim 1, characterized in that: According to the average transformer oil temperature θ om The oil temperature of the transformer radiator outlet is obtained as θ bo The methods include: According to the equation: to conclude; Among them, θ co is the temperature difference between the inlet and outlet of the transformer radiator and satisfies: θ co =2(0.2θ om +Δτ), Δτ is the correction function of the coil center height and the heat sink center height.

10. The method for calculating the temperature rise of a liquid immersed transformer according to claim 1, characterized in that: The method for obtaining the temperature distribution on the transformer includes: The temperature distribution on the transformer is calculated using the physics of fluid-structure interaction.

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