Method for calculating internal pressure rise of oil-immersed current transformer

Abstract

The invention discloses a method for calculating the internal pressure rise of an oil-immersed current transformer, and the method comprises the following steps: obtaining the structural parameters of the oil-immersed current transformer, and building a short-circuit arcing calculation model; setting a position of an arc heat source configured with a predetermined volume; calculating arc heat source power according to the volume of the arc heat source; performing grid division on the short-circuit arcing calculation model to obtain a finite element calculation model of the oil-immersed current transformer; and in finite element simulation software with boundary conditions, loading a calculation result of the power of the arc heat source to the position of the arc heat source as an energy source item of the finite element simulation software, and solving pressure rise distribution in the oil-immersed current transformer by adopting a coupling algorithm of temperature and a fluid field. According to the method, the electric arc is equivalent to a heat source with a fixed volume, and the internal short-circuit arcing pressure rise of the oil-immersed current transformer is solved by utilizing a Coupled algorithm in fluid simulation software, so that a reference can be provided for the safety protection design of the oil-immersed current transformer.

Description

Technical Field

[0001] The invention relates to the field of current sensors, and in particular to a method for calculating the internal pressure rise of an oil-immersed current transformer. Background Art

[0002] Oil-immersed current transformer is one of the common equipment in power transmission and distribution systems and is widely used in power systems. Its safe and reliable operation is the basis for ensuring the stable operation of power systems.

[0003] However, due to environmental, process and insulation aging issues, arc faults are very likely to occur inside the shell. The high-temperature arc quickly vaporizes and decomposes the surrounding insulating oil, producing a large amount of hydrocarbon mixed gas in a short period of time. The expansion inertia of the surrounding insulating oil causes a huge pressure difference on the gas-liquid interface, which propagates outward in the form of pressure waves. The pressure level inside the shell rises suddenly, and even causes an explosion, which seriously threatens the safety of surrounding equipment.

[0004] Therefore, it is very important to effectively evaluate the internal pressure characteristics of oil-immersed current transformers for their safety protection design. At present, the research on the pressure characteristics of oil-immersed current transformers mainly relies on experiments, but the experiments have the disadvantages of being time-consuming, costly, and polluting the environment.

[0005] The disclosure of the above background technology content is only used to assist in understanding the concept and technical solution of the present application. It does not necessarily belong to the prior art of the present application, nor does it necessarily provide technical guidance. In the absence of clear evidence that the above content has been disclosed before the filing date of the present application, the above background technology should not be used to evaluate the novelty and creativity of the present application. Summary of the invention

[0006] The object of the present invention is to provide a method for calculating the internal pressure rise of an oil-immersed current transformer by establishing a temperature-fluid field coupling calculation model by treating an electric arc as a heat source of fixed volume.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for calculating the internal pressure rise of an oil-immersed current transformer comprises the following steps:

[0009] Obtain the structural parameters of the oil-immersed current transformer and establish a short-circuit arcing calculation model for the oil-immersed current transformer;

[0010] Setting the location of an arc heat source, wherein the arc heat source is configured with a preset shape and size;

[0011] Calculating the volume of the arc heat source according to its shape and size, and calculating the power of the arc heat source according to the volume;

[0012] Meshing the short-circuit arcing calculation model to obtain a finite element calculation model of the oil-immersed current transformer;

[0013] In the finite element simulation software with boundary conditions set, the calculation result of the arc heat source power is loaded to the position of the arc heat source as the energy source item of the finite element simulation software, and the coupling algorithm of temperature and fluid field is used to solve the pressure rise distribution inside the oil-immersed current transformer.

[0014] Further, based on any one of the above-mentioned technical solutions or a combination of multiple technical solutions, when establishing a short-circuit arcing calculation model of an oil-immersed current transformer, one or more of the following simplified processing is performed on the structure of the oil-immersed current transformer:

[0015] Define and ignore the components that have little effect on the internal pressure rise of the transformer, including one or more of the transformer's secondary junction box, wire, base, porcelain sleeve, oil drain valve, oil storage cabinet, internal support bar, spacer, and outer insulation paper of the winding coil;

[0016] Ignore the heat exchange process of the transformer casing;

[0017] Ignore the thickness of the transformer casing;

[0018] Ignore the gaps on the surface of the transformer housing and assume that the housing is a fully enclosed structure;

[0019] The secondary winding and core of the transformer are simplified into a ring;

[0020] The primary conductor of the transformer is simplified into a solid cylinder;

[0021] The primary conductor of the transformer passing through the secondary winding is simplified to a solid cylinder passing through a ring, and the central axes of the two coincide.

[0022] Further, based on any one of the above-mentioned technical solutions or a combination of multiple technical solutions, the arc heat source power is calculated by the following calculation method:

[0023] Conduct short-circuit arcing test on oil-immersed current transformer in advance to detect short-circuit current and corresponding arc voltage;

[0024] The arc heat source power is calculated using the following formula: Among them, W arc is the arc heat source power, I arc The short-circuit current obtained by the short-circuit arc test of the transformer, U arc The arc voltage obtained by the short-circuit arc test of the transformer, V arc is the volume of the arc heat source.

[0025] Further, based on any one of the above-mentioned technical solutions or a combination of multiple technical solutions, boundary conditions are set in the finite element simulation software in the following manner:

[0026] The fluid field boundary conditions in the short-circuit arcing calculation model of the oil-immersed current transformer are set: using v wall = 0 defines that the solid component surface and the shell of the transformer are all non-slip walls, where v wall is the gas velocity near the wall;

[0027] The temperature field boundary conditions in the short-circuit arcing calculation model of the oil-immersed current transformer are set: the surface of the solid component of the transformer is set as a coupled boundary condition, and the shell of the transformer is set as an adiabatic boundary.

[0028] Furthermore, based on any one of the technical solutions or a combination of multiple technical solutions described above, the fluid dynamics equation and the heat conduction equation are coupled to solve the pressure of the flow field at each position of the grid and the velocity in each direction, and the pressure rise inside the oil-immersed current transformer is calculated through the velocity gradient of the flow field.

[0029] Further, based on any one of the above-mentioned technical solutions or a combination of multiple technical solutions, the method for calculating the internal pressure rise of an oil-immersed current transformer provided by the present invention further includes: setting the time step to T in the finite element simulation software step , T is used in the finite element simulation software step The pressure rise distribution is iteratively calculated for the time step, and the pressure of the flow field at each position of the grid and the velocity in each direction are updated until the preset convergence criterion is met.

[0030] Further, based on any one of the technical solutions or a combination of multiple technical solutions described above, the method for calculating the internal pressure rise of an oil-immersed current transformer provided by the present invention also includes setting solid material parameters and / or fluid material parameters of the oil-immersed current transformer, wherein the solid material parameters include material property parameters of the solid components inside the current transformer including the primary winding and / or the secondary winding, and the material property parameters include one or more of density, thermal conductivity, and constant-pressure heat capacity; the fluid material parameters include physical property parameters of the gas area around the arc heat source of the current transformer and the insulating oil medium, and the physical property parameters include one or more of density, constant-pressure specific heat, thermal conductivity, viscosity coefficient, and thermal expansion coefficient;

[0031] The influence of the solid material parameters and / or the fluid material parameters on the coupling of the fluid dynamics equation and the heat conduction equation is evaluated to optimize the coupling result.

[0032] Further, based on any one of the above-mentioned technical solutions or a combination of multiple technical solutions, the calculation formula for coupling the fluid dynamics equation and the heat conduction equation is:

[0033] in:

[0034]

[0035] Calculate the unknown matrix using the above formula The element p in i ', which represents the pressure of the grid in the i-th row;

[0036] In the formula, i represents the row number of the grid, j represents the column number of the grid, and A ij Represents the average value matrix of coefficients of momentum equation in fluid dynamics equation;

[0037] u i ' is the velocity component in the x-axis direction corresponding to the i-th row of grids, v i ' is the velocity component in the y-axis direction corresponding to the i-th row of grids, w i 'Represents the velocity component in the z-axis direction corresponding to the i-th row of grids;

[0038] represents the residual matrix, represents the residual of the grid pressure in the i-th row, represents the velocity residual in the x-axis direction corresponding to the i-th row of grids, represents the velocity residual in the y-axis direction corresponding to the i-th row of grids, Represents the velocity residual in the z-axis direction corresponding to the i-th row of grids;

[0039] a ij It represents the average value of the coefficients of the momentum equation at the grid at the i-th row and j-th column position. Among the superscript parameters, p represents pressure, u represents velocity in the x-axis direction, v represents velocity in the y-axis direction, and w represents velocity in the z-axis direction.

[0040] The beneficial effects brought by the technical solution provided by the present invention are as follows:

[0041] a. Based on the theory of fluid dynamics, the arc is equivalent to a fixed volume heat source, and a temperature-fluid field coupling calculation model is established to calculate the internal short-circuit arc pressure rise of the oil-immersed current transformer;

[0042] b. Using the Coupled algorithm in the fluid simulation software to solve the pressure rise can provide a reference for the safety protection design of oil-immersed current transformers;

[0043] c. The changes in the physical parameters of the insulating oil are taken into account in the calculation, and the arc is equivalent to a heat source of a fixed volume, ignoring its complex physical properties, which greatly reduces the complexity of the calculation. This patent can provide a reference for the safety protection design of oil-immersed current transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0045] Figure 1 A schematic flow chart of a method for calculating the internal pressure rise of an oil-immersed current transformer provided by an exemplary embodiment of the present invention;

[0046] Figure 2 A schematic diagram of setting the position of an arc heat source provided for an exemplary embodiment of the present invention;

[0047] Figure 3 A schematic diagram of a simplified short-circuit arcing calculation model provided for an exemplary embodiment of the present invention;

[0048] Figure 4 A pressure rise curve of a first monitoring point provided for an exemplary embodiment of the present invention;

[0049] Figure 5 A pressure rise curve of a second monitoring point provided for an exemplary embodiment of the present invention;

[0050] Figure 6 A pressure rise cloud diagram at time zero provided for an exemplary embodiment of the present invention;

[0051] Figure 7 A pressure rise cloud diagram at a time of 25 ms is provided for an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of 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.

[0053] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention 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 data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, device, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0054] The present invention aims to propose a simulation calculation method for the internal pressure rise of an oil-immersed current transformer, so as to provide reliable guidance for the structural strength and safety design of the oil-immersed current transformer on the basis of reducing the test cost.

[0055] In one embodiment of the present invention, a method for calculating the internal pressure rise of an oil-immersed current transformer is provided. Figure 1 As shown, the calculation method includes the following steps:

[0056] The first step is to obtain the structural parameters of the oil-immersed current transformer and establish a short-circuit arcing calculation model for the oil-immersed current transformer.

[0057] The oil-immersed current transformer is actually an electrical device with a complex structure, which causes considerable difficulty in establishing its corresponding short-circuit arcing calculation model. In a specific embodiment, when establishing the short-circuit arcing calculation model of the oil-immersed current transformer, the structure of the oil-immersed current transformer can be simplified as follows to greatly reduce the difficulty of establishing the short-circuit arcing calculation model:

[0058] Simplified processing method ①: Conventional oil-immersed current transformers include many components that have little to do with the internal pressure rise of the transformer, such as the transformer's secondary junction box, wires, base, porcelain sleeve, oil drain valve, oil storage cabinet, internal support bars, pads, outer insulation paper of the winding coil, etc. When building the model, the modeling of these solid components can be ignored;

[0059] Simplified processing method ②: Ignore the heat exchange process of the transformer shell, or ignore the thickness of the transformer shell, that is, assume that the heat dissipated from the shell to the air is zero;

[0060] Simplified processing method ③: Ignore the gaps on the surface of the transformer shell and assume that the shell is a fully enclosed structure;

[0061] Simplified processing method ④: The secondary winding and the iron core of the transformer are simplified into a ring, and the primary conductor of the transformer is simplified into a solid cylinder. The solid cylinder passes through the ring, and the central axes of the two are (roughly) coincident.

[0062] Step 2: Figure 2 As shown, the position of the arc heat source is set, and the arc heat source is configured with a preset shape and size.

[0063] The third step is to calculate the volume of the arc heat source according to its shape and size, and calculate the power of the arc heat source according to the volume.

[0064] Specifically, a short-circuit arc test is performed on the oil-immersed current transformer in advance to detect the short-circuit current and the corresponding arc voltage;

[0065] The arc heat source power is calculated using the following formula: Among them, W arc is the arc heat source power, I arc The short-circuit current obtained by the short-circuit arc test of the transformer, U arc The arc voltage obtained by the short-circuit arc test of the transformer, V arc is the volume of the arc heat source.

[0066] The fourth step is to mesh the short-circuit arcing calculation model to obtain a finite element calculation model of the oil-immersed current transformer.

[0067] Step 5. In the finite element simulation software with boundary conditions set, the calculation result of the arc heat source power is loaded to the position of the arc heat source as the energy source item of the finite element simulation software, and the coupling algorithm of temperature and fluid field is used to solve the pressure rise distribution inside the oil-immersed current transformer.

[0068] Specifically, the fifth step can be divided into the following steps:

[0069] S5.1. Initialization: Set the initial conditions in the finite element simulation software, including loading the arc heat source power calculated in the third step to the heat source position set in the second step. You can also set boundary conditions, such as the pressure, velocity and temperature of the initial state grid, to ensure the uniqueness of the calculation results.

[0070] Setting boundary conditions in the finite element simulation software can be divided into setting the fluid field boundary conditions and the temperature field boundary conditions in the short-circuit arcing calculation model of the oil-immersed current transformer:

[0071] Using v wall = 0 defines that the solid component surface and the shell of the transformer are all non-slip walls, where v wall is the gas velocity near the wall;

[0072] The surface of the solid part of the transformer is set as the coupled boundary condition, and the outer shell of the transformer is set as the adiabatic boundary, that is, Where T is temperature.

[0073] S5.2, coupled solution: set the time step to T in the finite element simulation software step , for example, 20μs, coupling the fluid dynamics equation and the heat conduction equation, solving the pressure of the flow field at each position of the grid and the velocity in each direction, and calculating the pressure rise inside the oil-immersed current transformer through the velocity gradient of the flow field;

[0074] In the finite element simulation software, T step The pressure rise distribution is iteratively calculated for the time step, and the pressure of the flow field at each position of the grid and the velocity in each direction are updated until the preset convergence criterion is met.

[0075] In a specific embodiment, the influence of the solid material parameters and fluid material parameters of the oil-immersed current transformer on the coupling of the fluid dynamics equation and the heat conduction equation is also considered to optimize the coupling result, wherein the solid material parameters include material property parameters of the solid components inside the current transformer including the primary winding and / or the secondary winding, and the material property parameters include one or more of density, thermal conductivity, and constant pressure heat capacity, as shown in Table 1 below:

[0076] Table 1 Material property parameter table

[0077]

[0078] The fluid material parameters include the physical property parameters of the gas region around the arc heat source of the current transformer and the insulating oil medium, wherein the physical property parameters include one or more of density, specific heat at constant pressure, thermal conductivity, viscosity coefficient, and thermal expansion coefficient;

[0079] The influence of the solid material parameters and / or fluid material parameters on the pressure parameters and velocity parameters in the fluid dynamics equation or the heat conduction equation is evaluated to optimize the coupling result.

[0080] The coupled algorithm can solve the momentum equation and the continuity equation at the same time. The coupled algorithm realizes a completely implicit coupled solution by implicitly discretizing some terms in the solution equation. The expressions involved can be written in the form of a matrix: In this specific embodiment, the calculation formula for coupling the fluid dynamics equation and the heat conduction equation is:

[0081] in:

[0082]

[0083] Calculate the unknown matrix using the above formula The element p in i ', which represents the pressure of the i-th row of grids.

[0084] In the above formula, i represents the row number of the grid, j represents the column number of the grid, and A ij Represents the average value matrix of coefficients of momentum equation in fluid dynamics equation;

[0085] u i ' is the velocity component in the x-axis direction corresponding to the i-th row of grids, v i ' is the velocity component in the y-axis direction corresponding to the i-th row of grids, w i 'Represents the velocity component in the z-axis direction corresponding to the i-th row of grids;

[0086] represents the residual matrix, represents the residual of the grid pressure in the i-th row, represents the velocity residual in the x-axis direction corresponding to the i-th row of grids, represents the velocity residual in the y-axis direction corresponding to the i-th row of grids, Represents the velocity residual in the z-axis direction corresponding to the i-th row of grids;

[0087] a ij represents the average value of the coefficients of the momentum equation at the grid at the i-th row and j-th column position. Among the superscript parameters, p represents pressure, u represents velocity in the x-axis direction, v represents velocity in the y-axis direction, and w represents velocity in the z-axis direction, that is, represents the average value of the coefficients of the momentum equation for the pressure at the grid position in the i-th row and j-th column, Represents the average value of the coefficients of the momentum equation for the velocity-pressure coupling in the x-axis direction at the grid at the i-th row and j-th column position, Represents the average value of the coefficients of the momentum equation for the coupling of velocity and pressure in the y-axis direction at the grid position of the i-th row and j-th column, Represents the average value of the coefficients of the momentum equation for the coupling of velocity and pressure in the z-axis direction at the grid at the i-th row and j-th column position; Represents the average value of the coefficients of the momentum equation for the coupling between the pressure and the velocity in the x-axis direction at the grid position in the i-th row and j-th column, The average value of the coefficients of the momentum equation representing the velocity in the x-axis direction at the grid position in the i-th row and j-th column, The average value of the coefficients of the momentum equation for the coupling of the velocity in the y-axis direction and the velocity in the x-axis direction at the grid position in the i-th row and j-th column, The average value of the coefficients of the momentum equation for the coupling between the velocity in the z-axis direction and the velocity in the x-axis direction at the grid at the i-th row and j-th column position; represents the average value of the coefficients of the momentum equation for the coupling between the pressure and the velocity in the y-axis direction at the grid position in the i-th row and j-th column, The average value of the coefficients of the momentum equation for the coupling of the velocity in the x-axis direction and the velocity in the y-axis direction at the grid position in the i-th row and j-th column, The average value of the coefficients of the momentum equation representing the velocity in the y-axis direction at the grid position in the i-th row and j-th column, The average value of the coefficients of the momentum equation for the coupling between the velocity in the z-axis direction and the velocity in the y-axis direction at the grid at the i-th row and j-th column position; The average value of the coefficients of the momentum equation for the coupling between the pressure and the velocity in the z-axis direction at the grid position in the i-th row and j-th column, The average value of the coefficients of the momentum equation for the coupling of the velocity in the x-axis direction and the velocity in the z-axis direction at the grid at the i-th row and j-th column position, The average value of the coefficients of the momentum equation for the coupling between the velocity in the y-axis direction and the velocity in the z-axis direction at the grid position in the i-th row and j-th column, The average value of the coefficients of the momentum equation for the velocity in the z-axis direction at the grid position at the i-th row and j-th column.

[0088] S5.3. Calculation of unknown matrix The pressure p of the element in the i-th row of the grid i ', that is, the pressure of the flow field at each position of the grid and the velocity in each direction are calculated through the velocity gradient of the flow field, and then the pressure rise inside the oil-immersed current transformer is calculated through the velocity gradient of the flow field.

[0089] Throughout the calculation process, the Coupled algorithm fully considers the mutual influence between fluid movement and temperature field, and can more accurately describe the pressure rise. The calculation takes into account the changes in the physical parameters of the insulating oil, and the arc is equivalent to a heat source of a fixed volume, ignoring its complex physical properties, which greatly reduces the calculation complexity. This patent can provide a reference for the safety protection design of oil-immersed current transformers.

[0090] The specific calculation example is as follows: In an embodiment in which the oil-immersed current transformer is simplified into a two-dimensional axisymmetric model, Figure 3 The part (half) above the axis of symmetry is shown. The radius of the closed container is Figure 3 The length of the middle AD is / the length of the BC, that is, 300mm; the height is the length of the AB side / the length of the CD side, that is, 500mm; add a volume heat source with a radius of 20mm at the center of the symmetry axis AB ( Figure 3 MNGL area in the figure), and add a gas domain with a radius of 50 mm around the volume heat source ( Figure 3 HIJK region in the

[0091] Set the HI-IJ-JK and MN-NL-LG boundary conditions as Coupled Boundaries, the outer wall of the container (AD-DC-CB) as an adiabatic boundary, and a no-slip wall boundary condition, and the material is copper. The arc uses an air arc, and the gas domain uses H2, which has the largest proportion of gas generated in the arc (85%). Set the dielectric physical properties of the air arc, H2, and insulating oil, including density, specific heat at constant pressure, thermal conductivity, viscosity coefficient, and thermal expansion coefficient.

[0092] Take the arc voltage as 0.8kV, the effective value of the short-circuit current as 20kA, and calculate the energy power per unit volume W based on the volume of the arc in the model. arc .

[0093] exist Figure 3 In the simplified model shown in the figure, two monitoring points P1 and P2 are set to calculate the pressure rise during short-circuit arcing within 25ms, and the oil pressure rise growth curve corresponding to the monitoring point P1 is obtained as follows: Figure 4 As shown, the oil pressure rise growth curve corresponding to the monitoring point P2 is as follows Figure 5 shown.

[0094] The pressure rise cloud at time 0 is as follows Figure 6 As shown, the pressure rise cloud diagram at the time of 25ms is as follows Figure 7 As shown, from Figure 7 The pressure rise information at each location in the grid can be determined.

[0095] In view of the shortcomings and deficiencies of the prior art, the present invention, based on the theory of fluid dynamics, equates the electric arc to a heat source of fixed volume, establishes a temperature-fluid field coupling calculation model, proposes a method for calculating the pressure rise of the internal short-circuit arc in an oil-immersed current transformer, and uses the Coupled algorithm in the fluid simulation software to solve the pressure rise, which can provide a reference for the safety protection design of the oil-immersed current transformer.

[0096] The changes in the physical parameters of the insulating oil are taken into account in the calculation, and the arc is equivalent to a heat source of a fixed volume, ignoring its complex physical properties, which greatly reduces the calculation complexity.

[0097] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0098] The above is only a specific implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A method for calculating the internal pressure rise of an oil-immersed current transformer, characterized in that: The following steps are involved: Obtain the structural parameters of the oil-immersed current transformer and establish a short-circuit arcing calculation model for the oil-immersed current transformer; Setting the location of an arc heat source, wherein the arc heat source is configured with a preset shape and size; Calculating the volume of the arc heat source according to its shape and size, and calculating the power of the arc heat source according to the volume; Meshing the short-circuit arcing calculation model to obtain a finite element calculation model of the oil-immersed current transformer; In the finite element simulation software with boundary conditions set, the calculation result of the arc heat source power is loaded to the position of the arc heat source as the energy source item of the finite element simulation software, and the coupling algorithm of temperature and fluid field is used to solve the pressure rise distribution inside the oil-immersed current transformer.

2. The method for calculating the internal pressure rise of an oil-immersed current transformer according to claim 1, characterized in that: When establishing the short-circuit arcing calculation model of the oil-immersed current transformer, one or more of the following simplified processing is performed on the structure of the oil-immersed current transformer: Define and ignore the components that have little effect on the internal pressure rise of the transformer, including one or more of the transformer's secondary junction box, wire, base, porcelain sleeve, oil drain valve, oil storage cabinet, internal support bar, spacer, and outer insulation paper of the winding coil; Ignore the heat exchange process of the transformer casing; Ignore the thickness of the transformer casing; Ignore the gaps on the surface of the transformer housing and assume that the housing is a fully enclosed structure; The secondary winding and core of the transformer are simplified into a ring; The primary conductor of the transformer is simplified into a solid cylinder; The primary conductor of the transformer passing through the secondary winding is simplified to a solid cylinder passing through a ring, and the central axes of the two coincide.

3. The method for calculating the internal pressure rise of an oil-immersed current transformer according to claim 1, characterized in that: The arc heat source power is calculated by the following calculation method: Conduct short-circuit arcing test on oil-immersed current transformer in advance to detect short-circuit current and corresponding arc voltage; The arc heat source power is calculated using the following formula: Among them, W arc is the arc heat source power, I arc The short-circuit current obtained by the short-circuit arc test of the transformer, U arc The arc voltage obtained by the short-circuit arc test of the transformer, V arc is the volume of the arc heat source.

4. The method for calculating the internal pressure rise of an oil-immersed current transformer according to claim 1, characterized in that: Set boundary conditions in the finite element simulation software by: The fluid field boundary conditions in the short-circuit arcing calculation model of the oil-immersed current transformer are set: using v wall = 0 defines that the solid component surface and the shell of the transformer are all non-slip walls, where v wall is the gas velocity near the wall; The temperature field boundary conditions in the short-circuit arcing calculation model of the oil-immersed current transformer are set: the surface of the solid component of the transformer is set as a coupled boundary condition, and the shell of the transformer is set as an adiabatic boundary.

5. The method for calculating the internal pressure rise of an oil-immersed current transformer according to any one of claims 1 to 4, characterized in that: The fluid dynamics equation and the heat conduction equation are coupled to solve the pressure of the flow field at each position of the grid and the velocity in each direction, and the pressure rise inside the oil-immersed current transformer is calculated through the velocity gradient of the flow field.

6. The method for calculating the internal pressure rise of an oil-immersed current transformer according to claim 5, characterized in that: Also includes: Set the time step to T in the finite element simulation software step , T is used in the finite element simulation software step The pressure rise distribution is iteratively calculated for the time step, and the pressure of the flow field at each position of the grid and the velocity in each direction are updated until the preset convergence criterion is met.

7. The method for calculating the internal pressure rise of an oil-immersed current transformer according to claim 5, characterized in that: It also includes setting solid material parameters and / or fluid material parameters of the oil-immersed current transformer, wherein the solid material parameters include material property parameters of the solid components inside the current transformer including the primary winding and / or the secondary winding, and the material property parameters include one or more of density, thermal conductivity, and constant-pressure heat capacity; the fluid material parameters include physical property parameters of the gas area around the arc heat source of the current transformer and the insulating oil medium, and the physical property parameters include one or more of density, constant-pressure specific heat, thermal conductivity, viscosity coefficient, and thermal expansion coefficient; The influence of the solid material parameters and / or the fluid material parameters on the coupling of the fluid dynamics equation and the heat conduction equation is evaluated to optimize the coupling result.

8. The method for calculating the internal pressure rise of an oil-immersed current transformer according to claim 5, characterized in that: The calculation formula that couples the fluid dynamics equation and the heat conduction equation is: in: Calculate the unknown matrix using the above formula The element p in i ', which represents the pressure of the grid in the i-th row; In the formula, i represents the row number of the grid, j represents the column number of the grid, and A ij Represents the average value matrix of coefficients of momentum equation in fluid dynamics equation; u i ' is the velocity component in the x-axis direction corresponding to the i-th row of grids, is the velocity component in the y-axis direction corresponding to the i-th row of grids, w i 'Represents the velocity component in the z-axis direction corresponding to the i-th row of grids; represents the residual matrix, represents the residual of the grid pressure in the i-th row, represents the velocity residual in the x-axis direction corresponding to the i-th row of grids, represents the velocity residual in the y-axis direction corresponding to the i-th row of grids, Represents the velocity residual in the z-axis direction corresponding to the i-th row of grids; a ij It represents the average value of the coefficients of the momentum equation at the grid at the i-th row and j-th column position. Among the superscript parameters, p represents pressure, u represents velocity in the x-axis direction, v represents velocity in the y-axis direction, and w represents velocity in the z-axis direction.

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