Transformer coil drying control parameter calculation method

Abstract

The invention relates to a transformer coil drying control parameter calculation method, in order to enable direct current heating of a dry-type transformer coil to achieve rapid coil drying and not to exceed the hot spot temperature, a heating device model is established, the heating device model comprises an oven, and modeling is conducted on the dry-type transformer coil; the heating device model and the coil model are imported into three-dimensional finite element analysis software, the coil model is arranged in the heating device, and grid division is conducted on the coil model; heat conductivity coefficients of corresponding materials are set for the used materials of all the parts in the coil model; the current introduced into the coil is changed under the condition of constant oven temperature, and temperature distribution corresponding to all parts of the coil is detected; the temperature of the oven is changed under the condition of constant current, and temperature distribution corresponding to all parts of the coil is detected; through temperature distribution, optimal control parameters which not only can ensure that heat damage is not generated when the coil is heated, but also can greatly improve the heating efficiency are found.

Description

Technical Field

[0001] The invention relates to a transformer coil drying control parameter calculation method, belonging to the electrical technical field. Background Art

[0002] After the transformer coil is cast, or during transportation or storage, it is necessary to dry the coil inside the dry-type transformer before putting it into use due to moisture or rain. The traditional drying device has a drying room. The coil is placed in the drying room, and the temperature in the drying room is increased to dry the coil inside the transformer. If the oven temperature is too high, the hottest point temperature in the coil exceeds a certain range, which will pose a serious threat to the safe operation of the transformer. If the temperature is too low, the coil is not easy to dry quickly. Without an optimal drying control parameter, it is difficult to use this method to safely and quickly dry the coil. Therefore, a method to determine the optimal drying control parameters is very important.

[0003] The patent document with authorization announcement number CN215176543U discloses an oven and a drying mechanism arranged inside the oven. By arranging a main drying rod that can move along the outer circumference of the coil and an auxiliary drying rod that can move along the inner circumference of the coil, the outer wall and the inner wall of the coil are dried respectively by the heating elements on the main drying rod and the auxiliary drying rod, so that the inner and outer walls of the coil are heated more evenly. However, this scheme only involves the device structure and does not consider the corresponding relationship between the heating time, the temperature rise curve and the maximum hot spot temperature of the coil, nor does it provide an optimal, safe and efficient temperature control strategy. Summary of the invention

[0004] The purpose of the present invention is to provide a method for calculating transformer coil drying control parameters, so as to solve the problem of how to provide a method for calculating transformer coil drying control parameters.

[0005] To achieve the above object, the solution of the present invention includes:

[0006] A transformer coil drying control parameter calculation method of the present invention comprises the following steps:

[0007] 1) Establish a heating device model, which includes a furnace and a dry-type transformer coil model;

[0008] 2) Import the heating device model and the coil model into the three-dimensional finite element analysis software, place the coil model inside the heating device, and mesh the coil model; set the thermal conductivity of the corresponding material for each part of the coil model;

[0009] 3) When the furnace temperature is changed, the temperature distribution corresponding to each part of the detection coil is detected; the optimal drying control parameters are obtained according to the temperature distribution.

[0010] By importing the modeling into the three-dimensional finite element analysis software, the temperature distribution under different furnace temperatures is analyzed and the optimal control parameters are obtained to ensure that the coil is dried under safe and efficient setting conditions.

[0011] Furthermore, in step 3), the current passed through the coil is changed while the oven temperature is kept constant, and the temperature distribution of each part of the coil is detected; the oven temperature is changed while the current is kept constant, and the temperature distribution of each part of the coil is detected.

[0012] Applying different currents to the coil will cause different degrees of heating of the coil. Therefore, by further setting the constant furnace temperature, changing the current passed through the coil and under the conditions of constant current and changing furnace temperature, an optimal drying control parameter is analyzed.

[0013] Furthermore, it also includes detecting the temperature distribution corresponding to each part of the coil when the wire is a round wire and a square wire respectively under a constant oven temperature and a constant current.

[0014] By further setting the other conditions unchanged and the wires being round wires and square wires respectively, another optimal drying parameter is analyzed.

[0015] Furthermore, in step 2), the coil model is a three-dimensional finite element model with quarter-plane symmetry.

[0016] The design of a three-dimensional finite element model with quarter-surface symmetry ensures the correctness of the structure and saves simulation time.

[0017] Furthermore, in step 2), the coil model includes a conductor, an air slot plate and an insulating paint part; and mesh division is set using a free tetrahedral mesh for the conductor, the air slot plate and the insulating paint.

[0018] The method of dividing the area into different densities is adopted to achieve a balance between calculation accuracy and speed, and can accurately reflect the temperature field distribution inside the heating device.

[0019] Furthermore, in step 2), the three-dimensional finite element analysis software is COMSOL.

[0020] Furthermore, in step 3), the optimal drying control parameter is the control parameter when all parts in the coil do not exceed the corresponding preset maximum tolerance and the drying time is the shortest.

[0021] By obtaining the optimal drying control parameters, the coil can be dried under a safe and efficient control method. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of a DC heating system in this embodiment;

[0023] Figure 2 This is a schematic diagram of the dry-type transformer coil being placed in a drying furnace for heating in this embodiment;

[0024] Figure 3 It is the structural diagram of the dry-type transformer in this embodiment;

[0025] Figure 4 is the three-dimensional finite element model in this embodiment;

[0026] Figure 5 This is the temperature field calculation process in this embodiment;

[0027] Figure 6 is a grid division diagram of the DC heating device in this embodiment;

[0028] Figure 7 : is the temperature field distribution diagram in this embodiment;

[0029] Figure 8 is the hottest point temperature when different currents are applied in this embodiment;

[0030] Fig. 9 is the hottest temperature of each oven temperature and current in this embodiment;

[0031] Fig.10 3 is a temperature field distribution diagram when the conductor is a round conductor in this embodiment. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0033] In order to make the DC heating of dry-type transformer coils achieve rapid drying of internal materials without exceeding the hot spot temperature, according to the DC heating principle of dry-type transformer coils, such as Figure 1 As shown, combined with the drying box device, a current heating and drying model of the corresponding dry-type transformer is built. When the direct current heats the winding, the corresponding relationship between the current and the maximum hot spot temperature of the winding is calculated according to the thermal characteristics of the coil insulation and the covering layer, etc., providing current and temperature correlation data for the temperature control method of the heating system.

[0034] Based on multi-physics field finite element software, the temperature field simulation calculation of the dry-type transformer was carried out, and the corresponding temperature field distribution cloud map and hot spot temperature change when different currents were applied under different furnace temperatures and wire types were calculated. The results show that the hot spot temperature of the dry-type transformer coil will increase with the increase of the applied current and the furnace temperature, and the wire type has a certain influence on the temperature field distribution. The results provide a certain reference value for the design and heat dissipation of DC heating of dry-type transformers.

[0035] By calculating the temperature rise curve, the withstand temperature, heat capacity characteristics and thermal conductivity of the insulation material, as well as the heat transfer process, a temperature control strategy for DC heating is designed and studied to find a heating temperature control strategy that can ensure that the winding heating does not cause thermal damage to the internal material of the coil and greatly improve the heating efficiency of the dry-type transformer coil.

[0036] A transformer coil drying control parameter calculation method embodiment 1:

[0037] like Figure 2 As shown, in this embodiment, a dry-type transformer coil is placed in a drying furnace to construct a heating device model, and the model includes a drying furnace, and current is applied to the dry-type transformer coil in the drying furnace.

[0038] Dry-type transformer coil structure diagram Figure 3 As shown in the figure, a three-dimensional finite element model of the dry-type transformer coil is constructed. Figure 4 As shown, the dry-type transformer coil is composed of a conductor, insulating varnish and an air slot plate. The conductor has two types: a square conductor and a round conductor. The conductor is made of nine layers of copper wire by firing, and insulating varnish is poured between the conductors.

[0039] In this embodiment, in order to restore the actual structure of the dry-type transformer coil DC heating device as much as possible and take into account the speed of simulation calculation, a Figure 4 The three-dimensional finite element coil model with quarter-plane symmetry shown in the figure not only ensures the correctness of the actual structure but also saves simulation calculation time.

[0040] like Figure 5 The temperature field calculation process shown in the figure is as follows:

[0041] Model import after modeling: import the heater model and coil model into COMSOL, where the coil model is located inside the heater model.

[0042] Material property setting: Set the thermal conductivity of the material according to the materials used in each part of the actual dry-type transformer DC heating device, as shown in Table 1:

[0043] Table 1 Material properties of various heated parts of dry-type transformers

[0044]

[0045] The load conditions applied in the simulation calculation mainly include the current excitation applied to the wire when the device is heated and the furnace temperature. Since the equivalent resistance of the wire remains unchanged, if the magnitude of the applied current needs to be changed, the magnitude of the potential in the initial value can be changed.

[0046] Meshing: Meshing plays a very important role in finite element calculations. Finite element meshes are divided on the basis of geometric models, and the finite element calculation process is performed on the basis of meshes. After meshing is completed, the finite element calculation process is performed on the basis of meshes. For two-dimensional meshing, COMSOL discretizes the region using triangular or quadrilateral meshes. For curved boundaries, the mesh units are approximately equivalent to the real geometry, and the geometrically defined boundary units are discretized into boundary units. Under three-dimensional conditions, the software discretizes the region using tetrahedrons, hexahedrons, prismatic mesh units, etc. In the software, you can directly use free tetrahedral meshes to mesh three-dimensional entities. Free tetrahedral meshes have the best adaptability to geometry, so they are also the default three-dimensional meshing form of COMSOL.

[0047] The current heating model is relatively complex, and multiple meshing methods need to be used when meshing. The size of the mesh determines the accuracy of the simulation results. The finer the mesh, the more accurate the calculation results, but the higher the requirements for the computer. In actual processing, different density partitioning methods are often used in different regions to achieve a balance between calculation accuracy and speed. In order to accurately reflect the temperature field distribution inside the current heating device, different mesh sizes are set for the conductors, air trough plates and insulating paint. The meshing settings for the conductors, air trough plates and insulating paint use free tetrahedral meshes; the partitioning results include "19036076" domain units, 5079528 boundary units and 347310 edge units; the number of vertex units: 1806; the number of edge units: 347310; the number of boundary units: 5079528; this model is divided into 19036076 mesh units in total, such as Figure 6 shown.

[0048] Set the result analysis under different conditions:

[0049] In this simulation, the dry-type transformer coil is heated by changing the furnace temperature without applying current, and the temperature distribution inside the coil is obtained when the furnace temperature is continuously changed.

[0050] Simulate the temperature field distribution characteristics when current is applied to the heating device at a certain oven temperature, such as Figure 7 The figure shows the overall temperature field distribution diagram of the heating device when the conductor is a square conductor, the oven temperature is 80°C, and the applied current is 40A. It can be seen that the temperature changes basically from high to low in the positive direction of the y-axis, while the temperature increases first and then decreases in the positive direction of the x-axis. The temperature in the middle of the insulating paint is higher than the temperature on both sides of it. The highest temperature point, that is, the hottest point, is located near the innermost insulating paint, and its value is 96°C. Therefore, the heat dissipation effect needs to be strengthened on the inside of the device.

[0051] When the applied current is constant at 40A, the furnace temperature is continuously changed to observe the change in the hottest point temperature. As shown in Table 2, the hottest point temperature increases with the increase in the furnace temperature. Therefore, the change in the furnace temperature has a certain effect on the hottest point temperature of the DC heating device. When using the DC heating device to heat the dry-type transformer, it should be done at a lower furnace temperature to prevent the device from overheating.

[0052] Table 2 Hottest point temperature at different oven temperatures

[0053]

[0054] Generally, according to Joule's law, the heat generated in the wire is positively correlated with the current. The greater the applied current, the more heat is generated and the faster the temperature rises. At an oven temperature of 80°C, different current excitations are applied, such as Figure 8 The figure shows how the hottest point temperature of the heating device changes with the applied current. It can be seen that as the current increases, the hottest point temperature rises sharply, which is consistent with the theoretical situation. When the excitation exceeds 70A, the hottest point temperature will exceed 180°C, which will pose a serious threat to the safe operation of the transformer. The device has higher requirements for heat dissipation. Therefore, when a certain current is applied for excitation heating, the heat dissipation effect of the device needs to be strengthened, and the applied current should not be too high.

[0055] At a certain oven temperature, when different current excitations are applied to the DC device, the temperature of its hottest point will rise sharply. When heating, attention should be paid to the control of the current size. Under the condition of applying a certain current, the hottest point temperature of the DC device will increase with the increase of the oven temperature. The size of the applied current excitation and the oven temperature can affect the temperature field distribution of the device. In order to ensure the normal heating of the dry-type transformer by the DC device, the current size cannot be too high and it is not suitable to heat at too high an oven temperature.

[0056] like Fig. 9 As shown, when the oven temperature is 27℃-100℃, the hottest point temperature increases sharply with the increase of oven temperature and current excitation. This is mainly due to the Joule heat generated by the current in the wire, which causes the sharp rise in temperature. When increasing the current excitation, it is necessary to prevent the device from overheating and causing accidents.

[0057] The wire type is changed to round wire. To further simplify the calculation and speed up the calculation, the model ignores the air slot plate. When the oven temperature is set to 80℃ and 40A current is applied, the temperature field distribution diagram of the heating device is as follows: Fig.10 As shown in the figure, the temperature of the insulating varnish is significantly higher than that of the round conductor. The hottest point temperature is located near the insulating varnish between the two layers of conductor, which is 92°C, slightly lower than the hottest point temperature of the square conductor. Therefore, after changing to a round conductor, the distribution of the temperature field is affected to a certain extent.

[0058] Under the same conditions, after replacing the square wire with a round wire, the hottest point temperature of the heating device is slightly reduced, the temperature of the insulating paint is higher than that of the round wire, and the hottest point temperature is located near the insulating paint between the two layers of wire. The wire type has a certain influence on the distribution of the temperature field.

[0059] Temperature field calculation: Based on the analysis results under the above-mentioned various setting conditions, it can be concluded that the control parameters when each part of the coil does not exceed the corresponding preset maximum tolerance and the drying time is the shortest are the optimal control parameters.

[0060] It should be noted that: in this embodiment, it is not limited to obtaining the optimal control parameters under any one or more set conditions.

Claims

1. A method for calculating transformer coil drying control parameters, characterized in that: The steps include: 1) Establishing a heating device model, wherein the heating device model includes a drying furnace and also models a dry-type transformer coil; 2) Importing the heating device model and the coil model into a three-dimensional finite element analysis software, placing the coil model inside the heating device, and meshing the coil model; setting the thermal conductivity of the corresponding material for each part of the coil model; 3) When the furnace temperature is changed, the temperature distribution corresponding to each part of the detection coil is detected; and the optimal drying control parameters are obtained according to the temperature distribution.

2. The transformer coil drying control parameter calculation method according to claim 1 is characterized in that: In the step 3), the current passed through the coil is changed while the oven temperature is kept constant, and the temperature distribution of each part of the coil is detected; the oven temperature is changed while the current is kept constant, and the temperature distribution of each part of the coil is detected.

3. The transformer coil drying control parameter calculation method according to claim 2 is characterized in that: It also includes the temperature distribution corresponding to each part of the detection coil when the wire is a round wire and a square wire respectively under a constant oven temperature and a constant current.

4. The transformer coil drying control parameter calculation method according to claim 1, characterized in that: In step 2), the coil model is a three-dimensional finite element model with quarter-plane symmetry.

5. The transformer coil drying control parameter calculation method according to claim 1, characterized in that: In step 2), the coil model includes a conductor, an air slot plate and an insulating paint part; and mesh division is set using a free tetrahedral mesh for the conductor, the air slot plate and the insulating paint.

6. The transformer coil drying control parameter calculation method according to claim 1, characterized in that: In step 2), the three-dimensional finite element analysis software is COMSOL.

7. The transformer coil drying control parameter calculation method according to any one of claims 1 to 3, characterized in that: In step 3), the optimal drying control parameter is the control parameter when each part in the coil does not exceed the corresponding preset maximum tolerance and the drying time is the shortest.

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