Method for identifying overheating position of oil-immersed transformer winding

Abstract

The invention discloses a method for identifying an overheating position of an oil-immersed transformer winding, which comprises the following steps of: 1) performing finite element division on a transformer magnetic field-circuit coupling simulation model by taking magnetic field loss of a winding area as a heat source, and constructing a transformer magnetic field finite element model; 2) setting material attributes of the transformer and the low-voltage winding; 3) setting boundary conditions, and performing bidirectional coupling calculation between a temperature field and a flow field by using finite element simulation software to obtain a temperature rise parameter of the transformer; 4) setting a temperature analysis point, and setting an overheat point at the position of a middle turn wire of each layer of winding; 5) constructing an overheating position '0-1' identification matrix based on the analysis point temperature matrix and the overheating temperature threshold matrix; and if the (i + 1) th element in the overheating position 0-1 identification matrix is 1 and the (i-1) th element is 0, judging that the ith layer of the winding is locally overheated. The invention provides a simulation calculation method for oil-immersed transformer winding hot-spot temperature rise.

Description

Technical Field

[0001] The invention relates to the technical field of transformers, and in particular to a method for identifying an overheated position of an oil-immersed transformer winding. Background Art

[0002] Oil-immersed transformers are important equipment in power systems and play a key role in the stability of the system. Windings are the most critical components of transformers, and their temperature rise characteristics can affect the service life of transformers. Faults such as local overheating of the windings will cause the hot spot temperature of the windings to rise, which is an important factor causing transformer failure and shutdown.

[0003] However, since the calculation of the temperature rise of transformer windings and other components and oil flow is a multidisciplinary problem, and the structure of the transformer is complex and there are many factors affecting heat transfer, it is difficult to calculate the temperature rise of each point inside the power transformer.

[0004] At present, there are two main methods for transformer winding hot spot temperature rise: direct measurement and indirect calculation. Direct measurement is to install optical fiber temperature measurement equipment inside the transformer to directly collect the temperature of the observation point. This method has a fixed temperature measurement point, and it is difficult to obtain the local hot spot temperature due to the uncertainty of the hot spot position. The indirect calculation method mainly includes numerical simulation method, guideline method, thermal circuit model method and analytical calculation method. Among them, numerical simulation method has become an important method for studying transformer temperature field in recent years. Excessive temperature rise will cause the insulation material to age prematurely and reduce the insulation performance, shorten the service life, and thus affect the efficiency and normal operation of the power transformer. Therefore, it is necessary to accurately calculate the winding temperature rise and accurately determine the overheating position when the winding is locally overheated. Summary of the invention

[0005] The object of the present invention is to provide a method for identifying the overheating position of an oil-immersed transformer winding, comprising the following steps:

[0006] 1) Obtain the initial parameters of the oil-immersed transformer, and establish a transformer magnetic field-circuit coupling simulation model based on finite element simulation software to obtain the magnetic field distribution and loss in the winding area;

[0007] 2) Taking the magnetic field loss in the winding area as the heat source, the transformer magnetic field-circuit coupling simulation model is divided by finite element method to construct a transformer magnetic field finite element model;

[0008] 3) Set the material properties of the transformer and low-voltage winding;

[0009] 4) Set boundary conditions and use finite element simulation software to perform bidirectional coupling calculations between the temperature field and the flow field. During the calculation process, iterate according to the changes in the material properties of the transformer and low-voltage winding with temperature and flow velocity until the convergence conditions are met, thereby obtaining the transformer temperature rise parameters;

[0010] 5) According to the number of winding layers, the winding is divided into several layers, and a temperature analysis point is set at the outlet of each layer of winding, and a hot spot is set at the position of the middle turn conductor of each layer of winding;

[0011] 6) Constructing the analysis point temperature matrix;

[0012] 7) Constructing an overheating temperature threshold matrix for determining whether the winding is locally overheated;

[0013] 8) Based on the analysis point temperature matrix and the overheating temperature threshold matrix, an overheating position “0-1” identification matrix is ​​constructed;

[0014] If the i+1th element in the overheating position "0-1" identification matrix is ​​1 and the i-1th element is 0, it is determined that local overheating occurs in the i-th layer of the winding.

[0015] Furthermore, the initial parameters of the oil-immersed transformer include transformer capacity, rated voltage, and physical structural parameters of the internal components of the transformer.

[0016] Further, the steps of establishing a transformer magnetic field-circuit coupling simulation model include:

[0017] s1) Each conductor turn in each coil of the low voltage winding is configured as a single rectangular cross section;

[0018] s2) Determine the rated current flowing through each turn of the low-voltage winding through the rated capacity S and rated voltage U of the transformer Thus, a transformer magnetic field-circuit coupling simulation model is established;

[0019] s3) Based on the magnetic field-circuit coupling simulation model, the magnetic field distribution of the low-voltage winding is obtained, namely:

[0020]

[0021] B=μ·H (2)

[0022]

[0023] In the formula, I 每匝 is the current per turn of the conductor; N is the number of turns of the low-voltage winding; H is the magnetic field strength; l is the average length of the magnetic circuit; B is the magnetic flux density; μ is the magnetic permeability of the material.

[0024] Further, the material properties of the transformer include transformer oil density, thermal conductivity, dynamic viscosity, and specific heat capacity at constant pressure;

[0025] The material properties of the low voltage winding include density, specific heat capacity and thermal conductivity.

[0026] Further, the steps of setting boundary conditions include:

[0027] Set the oil flow inlet boundary conditions: stipulate that the inlet oil flow is uniform, and set the inflow velocity and oil flow temperature;

[0028] Set the oil outlet pressure to 0Pa;

[0029] When the oil flows, the oil flow is set to a no-slip wall boundary condition at the wire cake and insulation boundary.

[0030] Furthermore, the expression for the bidirectional coupling calculation is as follows:

[0031]

[0032]

[0033] Where: ρ is the fluid density; v is the velocity vector; p is the fluid pressure; τ is the viscous stress tensor; F is the external force; g is the gravitational acceleration; c p is the constant pressure heat capacity; T is the temperature; k t is the thermal conductivity; Q is the internal heat source; is the Hamiltonian operator; t is the time;

[0034] Among them, the internal heat source Q is as follows:

[0035] Q(t)=Q0[1+α(T s -T0)] (4)

[0036] Where: Q0 is the winding loss at the initial temperature T0, T s is the real-time temperature obtained by iterative solution, and α is the resistance correction temperature factor.

[0037] Further, when setting the temperature analysis points, each layer of winding includes two temperature analysis points.

[0038] Furthermore, the i-th element in the analysis point temperature matrix is ​​the temperature of the temperature analysis point i when the winding partition i is overheated.

[0039] Furthermore, when constructing the overheating temperature threshold matrix, when the i-th layer of the winding is overheated, the minimum overheating temperature rise of the upper adjacent temperature analysis point is used as the threshold for judging whether the i-th layer is locally overheated.

[0040] Furthermore, when constructing the overheat position "0-1" identification matrix, if the i-th element of the analysis point temperature matrix is ​​less than the i-th element of the overheat temperature threshold matrix, the i-th element of the overheat position "0-1" identification matrix is ​​set to 0, otherwise it is set to 1.

[0041] The technical effect of the present invention is undoubted, and the beneficial effects of the present invention are:

[0042] (1) The simulation calculation method of the transformer winding temperature rise characteristics described in the present invention is based on the finite element method, fluid mechanics and computational heat transfer, and uses a temperature-flow field coupled numerical calculation model using simulation software to propose a simulation calculation method for the hot spot temperature rise of an oil-immersed transformer winding.

[0043] (2) The use of distributed sensing optical fiber is expensive, and the process of embedding it into the transformer winding is relatively complicated. This patent provides a method for dividing the winding into zones and layers to obtain the local overheating position of the winding. The overheating temperature threshold of each layer is obtained by dividing the winding area into zones and layers, and an overheating temperature threshold matrix can be constructed. If the state quantity of the upper analysis point of a certain layer of winding is 1, and the state quantity of the lower analysis point is 0, it can be determined that the layer has local overheating. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a two-dimensional plane model of oil-immersed transformer.

[0045] Figure 2 It is the three-dimensional model of the low-voltage winding of oil-immersed transformer.

[0046] Figure 3 This is the calculation process for temperature field simulation.

[0047] Figure 4 It is the two-dimensional model of the low-voltage winding of the oil-immersed transformer and the simulation results of the temperature field.

[0048] Figure 5 Identify the flow field for superheat locations.

[0049] Figure 6 The typical location is selected.

[0050] Figure 7 Shown are the simulation results of the temperature field at the selected typical locations. DETAILED DESCRIPTION

[0051] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0052] Embodiment 1:

[0053] See also Figures 1 to 7 , a method for identifying the overheating position of an oil-immersed transformer winding, comprising the following steps,

[0054] 1) Obtain the initial parameters of the oil-immersed transformer, and establish a transformer magnetic field-circuit coupling simulation model based on finite element simulation software to obtain the magnetic field distribution and loss in the winding area;

[0055] 2) Taking the magnetic field loss in the winding area as the heat source, the transformer magnetic field-circuit coupling simulation model is divided by finite element method to construct a transformer magnetic field finite element model;

[0056] 3) Set the material properties of the transformer and low-voltage winding;

[0057] 4) Set boundary conditions and use finite element simulation software to perform bidirectional coupling calculations between the temperature field and the flow field. During the calculation process, iterate according to the changes in the material properties of the transformer and low-voltage winding with temperature and flow velocity until the convergence conditions are met, thereby obtaining the transformer temperature rise parameters;

[0058] 5) According to the number of winding layers, the winding is divided into several layers, and a temperature analysis point is set at the outlet of each layer of winding, and a hot spot is set at the position of the middle turn conductor of each layer of winding;

[0059] 6) Constructing the analysis point temperature matrix;

[0060] 7) Constructing an overheating temperature threshold matrix for determining whether the winding is locally overheated;

[0061] 8) Based on the analysis point temperature matrix and the overheating temperature threshold matrix, an overheating position “0-1” identification matrix is ​​constructed;

[0062] If the i+1th element in the overheat position "0-1" identification matrix is ​​1 and the i-1th element is 0, it is determined that local overheating occurs in the i-th layer of the winding. Local overheating occurs when the temperature of the upper area exceeds a certain threshold (the state quantity is 1) and the lower area does not exceed the threshold (the state quantity is 0).

[0063] The initial parameters of oil-immersed transformers include transformer capacity, rated voltage, and physical structural parameters of transformer internal components.

[0064] The steps to establish a transformer magnetic field-circuit coupling simulation model include:

[0065] s1) Each conductor turn in each coil of the low voltage winding is configured as a single rectangular cross section;

[0066] s2) Determine the rated current flowing through each turn of the low-voltage winding through the rated capacity S and rated voltage U of the transformer Thus, a transformer magnetic field-circuit coupling simulation model is established;

[0067] s3) Based on the magnetic field-circuit coupling simulation model, the magnetic field distribution of the low-voltage winding is obtained, namely:

[0068]

[0069] B=μ·H (2)

[0070]

[0071] In the formula, I 每匝 is the current per turn of the conductor; N is the number of turns of the low-voltage winding; H is the magnetic field strength; l is the average length of the magnetic circuit; B is the magnetic flux density; μ is the magnetic permeability of the material.

[0072] The material properties of the transformer include transformer oil density, thermal conductivity, dynamic viscosity and specific heat capacity at constant pressure;

[0073] The material properties of the low voltage winding include density, specific heat capacity and thermal conductivity.

[0074] The steps to set boundary conditions include:

[0075] Set the oil flow inlet boundary conditions: stipulate that the inlet oil flow is uniform, and set the inflow velocity and oil flow temperature;

[0076] Set the oil outlet pressure to 0Pa;

[0077] When the oil flows, the oil flow is set to a no-slip wall boundary condition at the wire cake and insulation boundary.

[0078] The expression for the two-way coupling calculation is as follows:

[0079]

[0080] Where: ρ is the fluid density; v is the velocity vector; p is the fluid pressure; τ is the viscous stress tensor; F is the external force; g is the gravitational acceleration; c p is the constant pressure heat capacity; T is the temperature; k t is the thermal conductivity; Q is the internal heat source; is the Hamiltonian operator; t is the time;

[0081] Among them, the internal heat source Q is as follows:

[0082] Q(t)=Q0[1+α(T s -T0)] (4)

[0083] Where: Q0 is the winding loss at the initial temperature T0, T s is the real-time temperature obtained by iterative solution, and α is the resistance correction temperature factor.

[0084] When setting the temperature analysis point, each partition corresponds to a layer of winding, and each layer of winding includes two temperature analysis points. Through this arrangement, each layer has an independent temperature analysis point (upper and lower), which can accurately detect local overheating. Specifically, it can be divided into 10 layers of windings, and the partition granularity is finer, which can monitor the temperature changes of each layer in more detail, discover potential problems, and ensure the overall stability and safety of the winding. The judgment standard is: there are two temperature analysis points on each layer of winding, one above and one below. If the upper state quantity is 1 and the lower state quantity is 0, it is judged as local overheating.

[0085] The i-th element in the analysis point temperature matrix is ​​the temperature of the temperature analysis point i when the winding partition i is overheated.

[0086] When constructing the overheating temperature threshold matrix, the minimum overheating temperature rise of the upper adjacent temperature analysis point when the i-th layer of the winding is overheated is used as the threshold for judging whether the i-th layer has local overheating.

[0087] When constructing the overheating position "0-1" identification matrix, if the i-th element of the analysis point temperature matrix is ​​less than the i-th element of the overheating temperature threshold matrix, the i-th element of the overheating position "0-1" identification matrix is ​​set to 0, otherwise it is set to 1.

[0088] Embodiment 2:

[0089] A method for identifying an overheated position of an oil-immersed transformer winding comprises the following steps:

[0090] 1) Obtain the initial parameters of the oil-immersed transformer, and establish a transformer magnetic field-circuit coupling simulation model based on finite element simulation software to obtain the magnetic field distribution and loss in the winding area;

[0091] 2) Taking the magnetic field loss in the winding area as the heat source, the transformer magnetic field-circuit coupling simulation model is divided by finite element method to construct a transformer magnetic field finite element model;

[0092] 3) Set the material properties of the transformer and low-voltage winding;

[0093] 4) Set boundary conditions and use finite element simulation software to perform bidirectional coupling calculations between the temperature field and the flow field. During the calculation process, iterate according to the changes in the material properties of the transformer and low-voltage winding with temperature and flow velocity until the convergence conditions are met, thereby obtaining the transformer temperature rise parameters;

[0094] 5) According to the number of winding layers, the winding is divided into several layers, and a temperature analysis point is set at the outlet of each layer of winding, and a hot spot is set at the position of the middle turn conductor of each layer of winding;

[0095] 6) Constructing the analysis point temperature matrix;

[0096] 7) Constructing an overheating temperature threshold matrix for determining whether the winding is locally overheated;

[0097] 8) Based on the analysis point temperature matrix and the overheating temperature threshold matrix, an overheating position “0-1” identification matrix is ​​constructed;

[0098] If the i+1th element in the overheating position "0-1" identification matrix is ​​1 and the i-1th element is 0, it is determined that local overheating occurs in the i-th layer of the winding.

[0099] Embodiment 3:

[0100] A method for identifying the overheating position of an oil-immersed transformer winding, the technical content of which is the same as that of Example 2. Furthermore, the initial parameters of the oil-immersed transformer include the transformer capacity, the rated voltage, and the physical structural parameters of the internal components of the transformer.

[0101] Embodiment 4:

[0102] A method for identifying an overheated position of an oil-immersed transformer winding, the technical content of which is the same as any one of Embodiments 2-3, and further, the step of establishing a transformer magnetic field-circuit coupling simulation model comprises:

[0103] 1) Each conductor turn in each coil of the low-voltage winding is set to a single rectangular cross-section;

[0104] 2) Determine the rated current flowing through each turn of the low-voltage winding through the rated capacity S and rated voltage U of the transformer Thus, a transformer magnetic field-circuit coupling simulation model is established;

[0105] 3) Based on the magnetic field-circuit coupling simulation model, the magnetic field distribution of the low-voltage winding is obtained, namely:

[0106]

[0107] B=μ·H (2)

[0108]

[0109] In the formula, I 每匝 is the current per turn of the conductor; N is the number of turns of the low-voltage winding; H is the magnetic field strength; l is the average length of the magnetic circuit; B is the magnetic flux density; μ is the magnetic permeability of the material.

[0110] Embodiment 5:

[0111] A method for identifying an overheated position of an oil-immersed transformer winding, the technical content of which is the same as any one of embodiments 2-4, and further, the material properties of the transformer include transformer oil density, thermal conductivity, dynamic viscosity and constant-pressure specific heat capacity;

[0112] The material properties of the low voltage winding include density, specific heat capacity and thermal conductivity.

[0113] Embodiment 6:

[0114] A method for identifying an overheated position of an oil-immersed transformer winding, the technical content of which is the same as any one of Embodiments 2-5, and further, the step of setting boundary conditions comprises:

[0115] Set the oil flow inlet boundary conditions: stipulate that the inlet oil flow is uniform, and set the inflow velocity and oil flow temperature;

[0116] Set the oil outlet pressure to 0Pa;

[0117] When the oil flows, the oil flow is set to a no-slip wall boundary condition at the wire cake and insulation boundary.

[0118] Embodiment 7:

[0119] A method for identifying the overheating position of an oil-immersed transformer winding, the technical content of which is the same as any one of Embodiments 2-6, and further, the expression of the bidirectional coupling calculation is as follows:

[0120]

[0121] Where: ρ is the fluid density; v is the velocity vector; p is the fluid pressure; τ is the viscous stress tensor; F is the external force; g is the gravitational acceleration; c p is the constant pressure heat capacity; T is the temperature; k t is the thermal conductivity; Q is the internal heat source; is the Hamiltonian operator; t is the time;

[0122] Among them, the internal heat source Q is as follows:

[0123] Q(t)=Q0[1+α(T s -T0)] (4)

[0124] Where: Q0 is the winding loss at the initial temperature T0, T s is the real-time temperature obtained by iterative solution, and α is the resistance correction temperature factor.

[0125] Embodiment 8:

[0126] A method for identifying the overheating position of an oil-immersed transformer winding, the technical content of which is the same as any one of embodiments 2-7, and further, when setting the temperature analysis points, each layer of the winding includes two temperature analysis points.

[0127] Embodiment 9:

[0128] A method for identifying the overheating position of an oil-immersed transformer winding, the technical content of which is the same as any one of embodiments 2-8, and further, the i-th element in the analysis point temperature matrix is ​​the temperature of the temperature analysis point i when the winding partition i is overheated.

[0129] Embodiment 10:

[0130] A method for identifying the overheating position of an oil-immersed transformer winding, the technical content of which is the same as any one of Examples 2-9. Furthermore, when constructing an overheating temperature threshold matrix, the minimum overheating temperature rise of the upper adjacent temperature analysis point when the i-th layer of the winding is overheated is used as the threshold for judging whether local overheating occurs in the i-th layer.

[0131] Embodiment 11:

[0132] A method for identifying the overheating position of an oil-immersed transformer winding, the technical content of which is the same as any one of embodiments 2-10. Further, when constructing an overheating position "0-1" identification matrix, if the i-th element of the analysis point temperature matrix is ​​less than the i-th element of the overheating temperature threshold matrix, then the i-th element of the overheating position "0-1" identification matrix is ​​set to 0, otherwise it is set to 1.

[0133] Embodiment 12:

[0134] A method for identifying an overheated position of an oil-immersed transformer winding comprises the following steps:

[0135] Step 1: Obtain the initial parameters of the oil-immersed transformer, including transformer capacity, rated voltage, and physical structural parameters of the transformer's internal components. Establish a transformer magnetic field-circuit coupling simulation model based on finite element simulation software to obtain the magnetic field distribution and loss in the winding area.

[0136] Step 2: Use the adaptive meshing function of the software to perform finite element division on the model and apply the loss calculated in step 1 as a heat source to the simulation software.

[0137] Step 3: Set the transformer oil density, thermal conductivity, dynamic viscosity and specific heat at constant pressure, and set the material properties of the low-voltage winding, including density, specific heat and thermal conductivity.

[0138] Step 4: Set boundary conditions, including the inlet flow velocity of the oil channel, and use finite element simulation software to perform bidirectional coupling calculations between the temperature field and the flow field. Iterate according to the changes in material properties with temperature and flow velocity until the convergence conditions are met, and the temperature rise characteristics of the transformer can be obtained.

[0139] Step 5: Set the local overheating of the winding: set temperature analysis points at the exit of each partition, a total of 11 temperature analysis points, each layer contains two temperature analysis points, a total of 10 layers, and set overheating points at the middle turn conductor position of each layer, a total of 10 overheating points, based on this to study the influence of local overheating of the winding on the distribution of temperature rise.

[0140] Step 6: Construct the analysis point temperature matrix. The first element in the analysis point temperature matrix is ​​the temperature of temperature analysis point 1 (increased to 11 in sequence) when winding partition 1 is overheated to a certain extent.

[0141] Step 7: Construct an overheating temperature threshold matrix for judging local overheating of the winding. When a certain layer of the winding is overheated, the minimum overheating temperature rise of the adjacent temperature analysis point above it is used as the threshold for judging whether the layer is locally overheated, and construct an overheating temperature threshold matrix.

[0142] Step 8: Construct an overheating position "0-1" identification matrix. The constructed overheating position "0-1" identification matrix is ​​the analysis point temperature matrix minus the corresponding value in the overheating temperature threshold matrix. The first element in the matrix is ​​the state quantity at the temperature analysis point 1 (increased to 11 in sequence), which is used to determine whether local overheating occurs below this point.

[0143] In step 1, a two-dimensional axisymmetric physical model is established in the finite element simulation software. During this modeling process, each turn of conductor in each coil in the low-voltage winding is set to a single rectangular cross-section. The rated current flowing through each turn of conductor in the low-voltage winding is determined by the rated capacity and rated voltage of the transformer. Finally, a magnetic field-circuit coupling simulation model of the transformer is established to obtain the magnetic field distribution of the low-voltage winding.

[0144] The mathematical model for the bidirectional coupling calculation described in step 4 is:

[0145]

[0146]

[0147] Where: ρ is the fluid density; v is the velocity vector; p is the fluid pressure; τ is the viscous stress tensor; F is the external force; g is the gravitational acceleration; c p is the constant pressure heat capacity; T is the temperature; k t is the thermal conductivity; Q is the internal heat source; is the Hamiltonian operator.

[0148] Step 4 also includes the step of winding loss correction, and the winding loss correction is achieved by:

[0149] Q(t)=Q0[1+α(T s -T0)] (4)

[0150] Where: Q0 is the winding loss at the initial temperature T0, T s is the real-time temperature obtained by iterative solution, α is the resistance correction temperature factor, which is 234.5K for copper.

[0151] Step 7 specifically includes:

[0152] First, select the typical positions of each layer. Overheating at different positions has different effects on the temperature rise of the analysis point. Overheating at positions close to the analysis point has a greater impact on the temperature rise of the analysis point. Complete the temperature rise calculation of the analysis point when overheating occurs at each typical position, and select the minimum overheating temperature rise as the threshold for judging whether local overheating occurs in the layer. That is, if the threshold is exceeded, it is judged that local overheating occurs below the layer. It is necessary to combine step 8 to judge which layer below the layer has local overheating.

[0153] Step 8 specifically includes:

[0154] When an element in the analysis point temperature matrix is ​​smaller than the corresponding element in the overheat temperature matrix, the state quantity is set to 0, indicating that the adjacent layer below the temperature analysis point i corresponding to the element has not been locally overheated; conversely, the state quantity is set to 1, indicating that the adjacent layer below the temperature analysis point i corresponding to the element has been locally overheated. Therefore, when the state quantity at the adjacent temperature analysis point above a layer is 1 and the state quantity at the temperature analysis point below is 0, local overheating occurs in the layer of the winding.

[0155] Embodiment 13:

[0156] A method for identifying an overheated position of an oil-immersed transformer winding comprises the following steps:

[0157] Step 1: Obtain the initial parameters of the oil-immersed transformer, including transformer capacity, rated voltage, and physical structural parameters of the transformer's internal components. Establish a transformer magnetic field-circuit coupling simulation model based on finite element simulation software to obtain the magnetic field distribution and loss in the winding area.

[0158] Step 2: Use the adaptive meshing function of the software to perform finite element division on the model and apply the loss calculated in step 1 as a heat source to the simulation software.

[0159] Step 3: Set the transformer oil density, thermal conductivity, dynamic viscosity and specific heat at constant pressure, and set the material properties of the low-voltage winding, including density, specific heat and thermal conductivity.

[0160] Step 4: Set boundary conditions, including the inlet flow velocity of the oil channel, and use finite element simulation software to perform bidirectional coupling calculations between the temperature field and the flow field. Iterate according to the changes in material properties with temperature and flow velocity until the convergence conditions are met, and the temperature rise characteristics of the transformer can be obtained.

[0161] The mathematical model for the bidirectional coupling calculation described in step 4 is as follows:

[0162]

[0163] Step 4 also includes the step of winding loss correction, and the winding loss correction is achieved by:

[0164] Q(t)=Q0[1+α(T s -T0)] (11)

[0165] Where: Q0 is the winding loss at the initial temperature T0, T s is the real-time temperature obtained by iterative solution, α is the resistance correction temperature factor, which is 234.5K for copper.

[0166] Step 5: Set the local overheating of the winding: set temperature analysis points at the exit of each partition, a total of 11 temperature analysis points, each layer contains two temperature analysis points, a total of 10 layers, and set overheating points at the middle turn conductor position of each layer, a total of 10 overheating points, based on this to study the influence of local overheating of the winding on the distribution of temperature rise.

[0167] Step 6: Construct the analysis point temperature matrix. The first element in the analysis point temperature matrix is ​​the temperature of temperature analysis point 1 (increased to 11 in sequence) when winding partition 1 is overheated to a certain extent.

[0168] Step 7: Construct an overheating temperature threshold matrix for judging local overheating of the winding. When a certain layer of the winding is overheated, the minimum overheating temperature rise of the adjacent temperature analysis point above it is used as the threshold for judging whether the layer is locally overheated, and construct an overheating temperature threshold matrix.

[0169] Step 7 specifically includes: first, selecting typical positions of each layer. Overheating at different positions has different effects on the temperature rise of the analysis point. Overheating at positions close to the analysis point has a greater impact on the temperature rise of the analysis point. This article takes layer 7 as an example to complete the temperature rise calculation of the analysis point when overheating occurs at each typical position, and selects the minimum overheating temperature rise as the threshold for judging whether local overheating occurs in the layer. That is, if the threshold is exceeded, it is judged that local overheating occurs below the layer, and it is necessary to combine step 8 to judge which layer below the layer has local overheating.

[0170] Step 8: Construct an overheating position "0-1" identification matrix. The constructed overheating position "0-1" identification matrix is ​​obtained by subtracting the corresponding value in the overheating temperature threshold matrix from the analysis point temperature matrix. The first element in the matrix is ​​the state quantity at the temperature analysis point 1 (increased to 11 in sequence), which is used to determine whether local overheating occurs below this point. When a certain layer of the winding has local overheating, the temperature rise of the temperature analysis point above it increases while the temperature rise of the temperature analysis point below it remains basically unchanged. Therefore, the size of the corresponding position elements of the analysis point temperature matrix and the overheating temperature matrix can be compared to make a judgment. When an element in the analysis point temperature matrix is ​​smaller than the corresponding element in the overheating temperature matrix, the state quantity is set to 0, indicating that the adjacent layer below the temperature analysis point i corresponding to the element has not undergone local overheating; otherwise, the state quantity is set to 1, indicating that the adjacent layer below the temperature analysis point i corresponding to the element has undergone local overheating. Therefore, when a certain layer of the winding has local overheating, the state quantity at the adjacent temperature analysis point above the layer is 1 and the state quantity at the temperature analysis point below the layer is 0. Based on this feature, the overheating position can be identified.

[0171] This embodiment provides a method for identifying the overheating position of the oil-immersed transformer winding, which can accurately determine the local overheating position of the winding.

Claims

1. A method for identifying the overheated position of an oil-immersed transformer winding, characterized in that: The following steps are included: 1) Obtain the initial parameters of the oil-immersed transformer, and establish a transformer magnetic field-circuit coupling simulation model based on finite element simulation software to obtain the magnetic field distribution and loss in the winding area. 2) Taking the magnetic field loss in the winding area as the heat source, the transformer magnetic field-circuit coupling simulation model is divided by finite element method to construct a transformer magnetic field finite element model; 3) Set the material properties of the transformer and low-voltage winding; 4) Set boundary conditions and use finite element simulation software to perform bidirectional coupling calculations between the temperature field and the flow field. During the calculation process, iterate according to the changes in the material properties of the transformer and low-voltage winding with temperature and flow velocity until the convergence conditions are met, thereby obtaining the transformer temperature rise parameters; 5) According to the number of winding layers, the winding is divided into several layers, and a temperature analysis point is set at the outlet of each winding layer, and a hot spot is set at the position of the middle turn conductor of each winding layer; 6) Constructing the analysis point temperature matrix; 7) Constructing an overheating temperature threshold matrix for determining whether the winding is locally overheated; 8) Based on the analysis point temperature matrix and the overheating temperature threshold matrix, an overheating position "0-1" identification matrix is ​​constructed; If the i+1th element in the overheating position "0-1" identification matrix is ​​1 and the i-1th element is 0, it is determined that local overheating occurs in the i-th layer of the winding.

2. The method for identifying the overheated position of an oil-immersed transformer winding according to claim 1, characterized in that: The initial parameters of oil-immersed transformers include transformer capacity, rated voltage, and physical structural parameters of transformer internal components.

3. The method for identifying the overheated position of an oil-immersed transformer winding according to claim 2, characterized in that: The steps to establish a transformer magnetic field-circuit coupling simulation model include: 1) Each conductor turn in each coil of the low-voltage winding is set to a single rectangular cross-section; 2) Determine the rated current flowing through each turn of the low-voltage winding through the rated capacity S and rated voltage U of the transformer Thus, a transformer magnetic field-circuit coupling simulation model is established; 3) Based on the magnetic field-circuit coupling simulation model, the magnetic field distribution of the low-voltage winding is obtained, namely: B=μ·H (2) In the formula, I 每匝 is the current per turn of the conductor; N is the number of turns of the low-voltage winding; H is the magnetic field strength; l is the average length of the magnetic circuit; B is the magnetic flux density; μ is the magnetic permeability of the material.

4. The method for quickly calculating the temperature rise of oil-immersed transformer windings according to claim 1, characterized in that: The material properties of the transformer include transformer oil density, thermal conductivity, dynamic viscosity and specific heat capacity at constant pressure; The material properties of the low voltage winding include density, specific heat capacity and thermal conductivity.

5. The method for quickly calculating the temperature rise of oil-immersed transformer windings according to claim 1, characterized in that: The steps to set boundary conditions include: Set the oil flow inlet boundary conditions: stipulate that the inlet oil flow is uniform, and set the inflow velocity and oil flow temperature; Set the oil outlet pressure to 0Pa; When the oil flows, the oil flow is set to a no-slip wall boundary condition at the wire cake and insulation boundary.

6. The method for quickly calculating the temperature rise of oil-immersed transformer windings according to claim 1, characterized in that: The expression for the two-way coupling calculation is as follows: Where: ρ is the fluid density; v is the velocity vector; p is the fluid pressure; τ is the viscous stress tensor; F is the external force; g is the gravitational acceleration; c p is the constant pressure heat capacity; T is the temperature; k t is the thermal conductivity; Q is the internal heat source; is the Hamiltonian operator; t is the time; Among them, the internal heat source Q is as follows: Q(t)=Q0[1+α(Ts-T0)] (7) Where: Q0 is the winding loss at the initial temperature T0, T s is the real-time temperature obtained by iterative solution, and α is the resistance correction temperature factor.

7. The method for quickly calculating the temperature rise of oil-immersed transformer windings according to claim 1, characterized in that: When setting the temperature analysis points, each layer of winding includes two temperature analysis points.

8. The method for quickly calculating the temperature rise of oil-immersed transformer windings according to claim 1, characterized in that: The i-th element in the analysis point temperature matrix is ​​the temperature of the temperature analysis point i when the winding partition i is overheated.

9. The method for quickly calculating the temperature rise of oil-immersed transformer windings according to claim 1, characterized in that: When constructing the overheating temperature threshold matrix, the minimum overheating temperature rise of the upper adjacent temperature analysis point when the i-th layer of the winding is overheated is used as the threshold for judging whether the i-th layer has local overheating.

10. The method for quickly calculating the temperature rise of oil-immersed transformer windings according to claim 1, characterized in that: When constructing the overheating position "0-1" identification matrix, if the i-th element of the analysis point temperature matrix is ​​less than the i-th element of the overheating temperature threshold matrix, the i-th element of the overheating position "0-1" identification matrix is ​​set to 0, otherwise it is set to 1.

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