Optimization method for number and size of openings of oil guide box of converter transformer

Abstract

The present application belongs to the technical field of transformer simulation, and particularly relates to a method for optimizing the number and size of openings of an oil guide box of a converter transformer, which calculates the no-load loss and load loss of the converter transformer; performs grid division on a physical model and imports the physical model into computational fluid dynamics software; sets parameters and conditions for simulation in the computational fluid dynamics software; and the computational fluid dynamics software statistically obtains the average temperature, hottest point temperature of the converter transformer grid-side winding, valve-side winding and voltage-regulating side winding, and the maximum oil flow speed of the transformer oil flow area; the variation law is obtained by changing one variable, the optimal optimization scheme is obtained, and the number and size of openings of the grid-side oil outlet hole, valve-side oil outlet hole and voltage-regulating side oil outlet hole are determined. The oil flow distribution of the grid side, valve side and voltage-regulating side is reasonably adjusted, so as to reduce the hottest point temperature and finally protect the operation safety of the converter transformer and prolong the service life of the converter transformer.

Description

Technical Field

[0001] This invention belongs to the field of transformer simulation technology, and in particular relates to a method for optimizing the number and size of openings in the oil guide box of a converter transformer. Background Technology

[0002] Large-capacity converter transformers have high requirements for heat dissipation and temperature control, and generally adopt a forced oil guiding structure. This structure requires an oil pump and an oil guide box to connect the oil circuit of the transformer body to the oil circuit of the cooling system. During transformer operation, the oil pump generates oil pressure, driving cooling oil from the cooling system's oil circuit into the oil guide box. From there, the oil flows through evenly distributed openings on the oil guide box into the oil circuit of the transformer body. Within this circuit, the cooling oil continuously exchanges heat with the winding coils and insulation materials, thereby cooling the windings and insulation.

[0003] The number and size of the openings in the oil guide box affect the oil flow resistance. If the design of the number and size of the openings is unreasonable, it will affect the flow distribution to the grid side, valve side, and voltage regulating side, thus affecting the oil flow velocity. If the oil flow velocity is too fast, it will cause the oil to become electrified, affecting the safe operation of the converter transformer; if the oil flow velocity is too slow, it will easily cause the temperature to exceed the limit, affecting the service life of the insulation material and ultimately damaging the service life of the converter transformer. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes an optimization method for the number and size of openings in the oil conductor box of a converter transformer. The aim is to rationally optimize the number and size of openings on the oil conductor box through simulation technology, thereby reducing the hottest spot temperature of the converter transformer and ultimately extending its service life. The technical solution adopted in this invention is as follows:

[0005] A method for optimizing the number and size of openings in the oil conductor box of a converter transformer includes the following steps:

[0006] Step 1: For the actual product, calculate the no-load loss and load loss of the converter transformer;

[0007] Step 2: Build an actual physical model based on the product drawings, mesh the physical model, and import the mesh into computational fluid dynamics software;

[0008] Step 3: In the computational fluid dynamics software, set the mass conservation equation, energy conservation equation, and momentum conservation equation; set the fluid region and solid region; input the physical properties of the fluid and solid; input the no-load loss and load loss from Step 1; and input the boundary conditions.

[0009] Step 4: The computational fluid dynamics software automatically solves the mass conservation equation, energy conservation equation, and momentum conservation equation based on all the conditions set in Step 3, and obtains the temperature and velocity of each grid. Then, it statistically obtains the average temperature, hottest temperature, and maximum oil flow velocity in the transformer oil flow region of the converter transformer grid-side winding, valve-side winding, and voltage regulating side winding.

[0010] Step 5: The number of openings for the mesh-side oil outlet, valve-side oil outlet, and pressure-regulating side oil outlet are N respectively. w N f and N t The opening dimensions are D w D f and D t For N w N f N t D w D f and D t Of these six variables, keep five constant and change only one variable, repeating steps 2-4 to calculate the average temperature, hottest spot temperature, and maximum oil flow velocity in the transformer oil flow region as a function of N for the grid-side winding, valve-side winding, and voltage regulating winding. w N f N t D w D f and D t The changing pattern;

[0011] Step 6: Based on the data obtained in Step 5, and taking into account the average temperature, hottest spot temperature, and maximum oil flow velocity of the grid-side winding, valve-side winding, and pressure-regulating winding, obtain the optimal solution and determine the number N of openings for the grid-side oil outlet, valve-side oil outlet, and pressure-regulating oil outlet. w N f and N t and the opening size D w D f and D t .

[0012] The beneficial effects of this invention are:

[0013] This invention proposes an optimization method for the number and size of openings in the oil guide box of a converter transformer. This method can optimize the number and size of openings in the oil guide box of the converter transformer, and reasonably adjust the oil flow distribution on the grid side, valve side and voltage regulating side, thereby reducing the hottest temperature on the grid side, valve side and voltage regulating side of the converter transformer, and ultimately protecting the operational safety of the converter transformer and extending its service life. Attached Figure Description

[0014] Figure 1This is a top view of the oil guide box structure according to an embodiment of the present invention;

[0015] Figure 2 This is a bottom view of the oil guide box structure according to an embodiment of the present invention;

[0016] Figure 3 This is a flowchart illustrating the steps of the optimization method according to an embodiment of the present invention.

[0017] In the diagram, 1 is the oil guide box inlet, 2 is the mesh side oil outlet, 3 is the valve side oil outlet, and 4 is the pressure regulating side oil outlet. Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] like Figure 1 The image shown is a top view of the oil guide box structure according to an embodiment of the present invention; as shown... Figure 2 The image shown is a bottom view of the oil guide box structure according to an embodiment of the present invention. The oil guide box of the converter transformer includes an oil guide box inlet 1, a grid-side oil outlet 2, a valve-side oil outlet 3, and a voltage-regulating side oil outlet 4. The oil guide box inlet 1 is connected to the grid-side oil outlet 2, the valve-side oil outlet 3, and the voltage-regulating side oil outlet 4, respectively. Transformer oil flows into the oil guide box from the oil guide box inlet 1 and flows from the grid-side oil outlet 2, the valve-side oil outlet 3, and the voltage-regulating side oil outlet 4 to the grid-side winding oil flow area, the valve-side winding oil flow area, and the voltage-regulating side winding oil flow area, respectively. The transformer oil continuously exchanges heat with the winding coils and insulating materials, thereby cooling the winding coils and insulating materials.

[0020] like Figure 3 The diagram shown is a flowchart of the optimization method according to an embodiment of the present invention. A method for optimizing the number and size of openings in the oil conductor box of a converter transformer includes the following steps:

[0021] Step 1: For actual products, taking a ±800kV converter transformer as an example, calculate the no-load loss and load loss of the converter transformer. The specific method is as follows:

[0022] The no-load loss of a converter transformer includes hysteresis loss, eddy current loss, and additional loss in the core.

[0023] Preferably, the no-load loss of the converter transformer can be obtained by the following empirical formula:

[0024]

[0025] Where: P0 is the no-load loss, in W;

[0026] K1 is the additional loss factor, which depends on the core diameter. Its value can be obtained by consulting the manufacturer's transformer manual.

[0027] P represents the unit loss of the iron core, expressed in W / kg. Its value can be obtained by consulting the material properties of the iron core manufacturer.

[0028] G represents the weight of the iron core, measured in kg.

[0029] Load losses include the resistance loss of the coil conductors, the additional losses of the coil (including eddy current damage and incomplete transposition loss of the conductors), lead losses, and stray losses in the structural components.

[0030] Preferably, the load loss of the converter transformer can be obtained by the following formula:

[0031]

[0032] Where: P r The resistance loss of the coil wire, measured in watts (W), can be calculated using the following formula:

[0033]

[0034] Where m is the number of phases of the converter transformer;

[0035] I represents the current per phase of the winding, in amperes (A).

[0036] r is the resistance of each phase of the winding, in Ω.

[0037] P f The additional loss of the coil, expressed in watts (W), can be calculated using the following empirical formula, considering the complexity of the additional loss:

[0038]

[0039] Among them, K f The percentage of additional losses in the coil conductors depends on the capacity of the converter transformer; the value can be found in the manufacturer's transformer manual.

[0040] P y Lead loss, expressed in watts (W), can be calculated using the following formula:

[0041]

[0042] Where m is the number of phases of the converter transformer;

[0043] I y This represents the current flowing through the lead, measured in amperes (A).

[0044] R y This represents the resistance of each phase in the lead wire, in Ω.

[0045] P z Let represent stray losses in structural components, expressed in W. Considering the complexity of stray losses, they can be calculated using the following empirical formula:

[0046]

[0047] Wherein, K2 is the stray loss factor, which depends on the capacity of the converter transformer. Its value can be found in the manufacturer's transformer manual.

[0048] This represents the main magnetic flux in the iron core under rated excitation, expressed in Wb.

[0049] U k Impedance voltage percentage at rated capacity, in percentage form;

[0050] H k The coil reactance height is in mm.

[0051] This is the circumference of the inner wall of the fuel tank, in mm;

[0052] A represents the length of the fuel tank, in mm;

[0053] B represents the width of the fuel tank, in mm;

[0054] M0 is the center distance of the iron core, in mm;

[0055] f is the frequency of the transformer, in Hz;

[0056] S represents the operating capacity of the transformer, measured in kVA.

[0057] S e This refers to the rated capacity of the transformer, expressed in kVA.

[0058] Step 2: Establish an actual physical model based on the product drawings, mesh the physical model, and import the mesh into computational fluid dynamics software. The specific process includes:

[0059] For this ±800kV converter transformer, a three-dimensional physical model was established based on the drawings. The physical model includes the transformer's tank, core, insulation materials, grid-side winding, valve-side winding, voltage-regulating winding, oil guide box, and oil flow section. The physical model can reflect the dimensions and connection relationships of the tank, core, insulation materials, grid-side winding, valve-side winding, voltage-regulating winding, oil guide box, and oil flow section.

[0060] Preferably, Fluent Meshing software is used to mesh the physical model. The purpose of meshing is to discretize the physical model so that it can be imported into computational fluid dynamics software for calculation.

[0061] Preferably, the oil tank, iron core, insulating material, grid-side winding, valve-side winding, voltage regulating side winding, and oil guide box adopt prismatic layer mesh; the oil flow section adopts tetrahedral mesh boundary layer mesh.

[0062] Preferably, the computational fluid dynamics software used is ANSYS Fluent.

[0063] Step 3: In the computational fluid dynamics software, set the mass conservation equation, energy conservation equation, and momentum conservation equation; set the fluid and solid regions; input the physical properties of the fluid and solid; input the no-load loss and load loss from Step 1; and input the boundary conditions. The specific process includes:

[0064] 3.1) Set the mass conservation equation, energy conservation equation, and momentum conservation equation in ANSYS Fluent software, and the software will automatically solve these equations iteratively.

[0065] The mass conservation equation is shown below:

[0066]

[0067] in, The density of the fluid is expressed in kg / m³. 3 ;

[0068] t represents time, measured in seconds (s).

[0069] u, v, and w are the components of the velocity vector in the x, y, and z directions, respectively.

[0070] The energy conservation equation is shown below:

[0071]

[0072] Where i is the internal energy of the fluid, in J;

[0073] The density of the fluid is expressed in kg / m³. 3 ;

[0074] C p Specific heat capacity, expressed in J / (kg·K);

[0075] T represents temperature, and the unit is K.

[0076] k is the heat transfer coefficient of the fluid, with units of W / (m³). 2 ·K);

[0077] u, v, and w are the components of the velocity vector in the x, y, and z directions, respectively.

[0078] S T This is the viscous dissipation term, in J.

[0079] The differential expressions of the momentum conservation equation in the x, y, and z directions are shown below:

[0080]

[0081] Where u, v, and w are the components of the velocity vector in the x, y, and z directions;

[0082] f b,x f b,y f b,z These are the components of the volume force vector in the x, y, and z directions;

[0083] S x S y S z These are the components of the viscous force vector in the x, y, and z directions.

[0084] 3.2) Set up fluid region and solid region; fluid region includes oil flow part; solid region includes oil tank, iron core, insulation material, grid side winding, valve side winding, pressure regulating side winding and oil guide box;

[0085] 3.3) Set the physical properties of the fluid. The fluid used is commonly used transformer oil. The physical properties of the transformer oil are various physical properties measured during the test, including the density, specific heat capacity, thermal conductivity and dynamic viscosity of the transformer oil at different temperatures.

[0086] 3.4) Set the physical properties of the solids. The physical properties of the oil tank, iron core, insulating material, grid-side winding, valve-side winding, voltage regulating side winding and oil guide box are various physical properties measured during the test, including density, specific heat capacity and thermal conductivity at different temperatures.

[0087] 3.5) Input the no-load loss and load loss calculated in step 1 into the ANSYS Fluent software;

[0088] 3.6) Input boundary conditions, including the initial velocity and initial temperature of the transformer oil; the initial velocity of the transformer oil is obtained based on the nameplate parameters of the selected oil pump; the initial temperature of the transformer oil is obtained based on the nameplate parameters of the selected pump and the ambient temperature.

[0089] Step 4: The computational fluid dynamics software automatically solves the mass conservation equation, energy conservation equation, and momentum conservation equation based on all the conditions set in Step 3, obtaining the temperature and velocity for each grid cell. Then, it statistically obtains the average temperature, hottest spot temperature, and maximum oil flow velocity in the transformer oil flow region for the grid-side winding, valve-side winding, and voltage regulating winding of the converter transformer. The specific process includes:

[0090] 4.1) Based on all the conditions set in step 3, the ANSYS Fluent software automatically solves the mass conservation equation, energy conservation equation, and momentum conservation equation to obtain the temperature and velocity of each grid.

[0091] 4.2) Statistically analyze the temperature of all grids in the grid-side winding of the converter transformer, average them, and obtain the average temperature of the grid-side winding. As shown in the following formula:

[0092]

[0093] in, This represents the average temperature of the grid-side winding, in Kelvin (K).

[0094] T w,j Temperature of a single grid in the grid-side winding, in Kelvin;

[0095] n w This represents the total number of grids in the mesh-side winding;

[0096] 4.3) Statistically analyze the temperature of all grids in the grid-side winding of the converter transformer, find the maximum value, and obtain the hottest temperature of the grid-side winding. As shown in the following formula:

[0097]

[0098] in, This is the hottest temperature of the grid-side winding, expressed in Kelvin (K).

[0099] T w,j Temperature of a single grid in the grid-side winding, in Kelvin;

[0100] 4.4) Repeat steps 4.2) and 4.3) above to obtain the average temperature of the valve-side winding. The hottest temperature of the valve-side winding Average temperature of the voltage regulating side winding The hottest temperature of the voltage regulating winding .

[0101] 4.5) Statistically calculate the velocity of all grids in the oil flow region of the converter transformer, find the maximum value, and obtain the maximum velocity of the oil flow region. As shown in the following formula:

[0102]

[0103] in, This represents the maximum velocity of all grid cells in the oil flow region, in m / s.

[0104] V j The velocity of a single grid cell in the oil flow region, in m / s;

[0105] n0 is the number of all grids in the oil flow region;

[0106] Step 5: The number of openings for the mesh-side oil outlet 2, the valve-side oil outlet 3, and the pressure regulating side oil outlet 4 are N respectively. w N f and N t The opening dimensions are D w D f and D t For N w N f N t D w D f and D t Of these six variables, keep five constant and change only one variable, repeating steps 2-4 to calculate the average temperature, hottest spot temperature, and maximum oil flow velocity in the transformer oil flow region as a function of N for the grid-side winding, valve-side winding, and voltage regulating winding. w N f N t D w D f D t The changing patterns and specific processes include:

[0107] 5.1) Keep N w N f N t D w D f Unchanged, changed D t Repeat steps 2-4 to calculate the average temperature, hottest spot temperature, and maximum oil flow velocity in the transformer oil flow region of the grid-side winding, valve-side winding, and voltage regulating winding as a function of D. t The changing pattern;

[0108] 5.2) Keep N w N f N t D w D t Unchanged, changed D f Repeat steps 2-4 to calculate the average temperature, hottest spot temperature, and maximum oil flow velocity in the transformer oil flow region of the grid-side winding, valve-side winding, and voltage regulating winding as a function of D.f The changing pattern;

[0109] 5.3) Keep N w N f N t D f D t Unchanged, changed D w Repeat steps 2-4 to calculate the average temperature, hottest spot temperature, and maximum oil flow velocity in the transformer oil flow region of the grid-side winding, valve-side winding, and voltage regulating winding as a function of D. w The changing pattern;

[0110] 5.4) Keep N w N f D w D f D t Unchanged, change N t Repeat steps 2-4 to calculate the average temperature, hottest spot temperature, and maximum oil flow velocity in the transformer oil flow region as a function of N for the grid-side winding, valve-side winding, and voltage regulating winding. t The changing pattern;

[0111] 5.5) Keep N w N t D w D f D t Unchanged, change N f Repeat steps 2-4 to calculate the average temperature, hottest spot temperature, and maximum oil flow velocity in the transformer oil flow region as a function of N for the grid-side winding, valve-side winding, and voltage regulating winding. f The changing pattern;

[0112] 5.6) Keep N f N t D w D f D t Unchanged, change N w Repeat steps 2-4 to calculate the average temperature, hottest spot temperature, and maximum oil flow velocity in the transformer oil flow region as a function of N for the grid-side winding, valve-side winding, and voltage regulating winding. w The changing pattern.

[0113] Step 6: Based on the data obtained in Step 5, and taking into account the average winding temperature, the hottest spot temperature, and the maximum oil flow velocity, the optimal optimization method is obtained to determine the number N of the openings for the mesh-side oil outlet 2, the valve-side oil outlet 3, and the pressure regulating side oil outlet 4. w N f and N t and the opening size D w D f and Dt The specific process for step 6 is as follows:

[0114] 6.1) For this ±800kV converter transformer, based on the data obtained in step 5, remove all schemes with a maximum oil flow velocity greater than 0.5m / s;

[0115] 6.2) Based on the data obtained in step 5, remove all schemes whose average winding temperature and hottest temperature do not meet the protocol requirements;

[0116] 6.3) Calculate the hottest temperature of the grid-side winding in all schemes. The hottest temperature of the valve-side winding and the hottest temperature of the voltage regulating side winding average As shown in the following formula:

[0117]

[0118] 6.4) The minimum number of openings N corresponds to w N f and N t， and the opening size D w D f and D t This is the final optimized solution.

[0119] Finally, it should be noted that the above embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit them. The scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention.

Claims

1. A method for optimizing the number and size of openings of an oil guide box of a converter transformer, the oil guide box comprising an oil guide box inlet (1), a grid side oil outlet hole (2), a valve side oil outlet hole (3) and a regulating side oil outlet hole (4), transformer oil flowing into the oil guide box from the oil guide box inlet (1) and flowing to a grid side winding oil flow area, a valve side winding oil flow area and a regulating side winding oil flow area from the grid side oil outlet hole (2), the valve side oil outlet hole (3) and the regulating side oil outlet hole (4) respectively; characterized in that The optimization method comprises the following steps: Step 1, for an actual product, calculate the no-load loss and load loss of the converter transformer; Step 2, establish an actual physical model according to the drawings of the product, divide the physical model into grids, and import the divided grids into a computational fluid dynamics software; Step 3, in the computational fluid dynamics software, set the mass conservation equation, the energy conservation equation and the momentum conservation equation, set the fluid region and the solid region, input the physical properties of the fluid and the solid, input the no-load loss and the load loss of step 1, and input the boundary conditions; Step 4, the computational fluid dynamics software automatically solves the mass conservation equation, the energy conservation equation and the momentum conservation equation according to all conditions set in step 3, and obtains the temperature and velocity of each grid; then, the average temperature, the hottest point temperature of the grid side winding, the valve side winding and the regulating side winding of the converter transformer and the maximum oil flow velocity of the transformer oil flow area are obtained by statistics; Step 5, the number of openings of the web side oil outlet hole (2), the valve side oil outlet hole (3) and the pressure regulating side oil outlet hole (4) are N w , N f and N t respectively, and the opening sizes are D w , D f and D t respectively, for the six variables N w , N f , N t , D w , D f and D t , keeping five of the six variables unchanged and changing only one of the six variables, repeating steps 2-4 to calculate the average temperature of the web side winding, the valve side winding and the pressure regulating side winding, the hottest point temperature and the maximum oil flow speed of the transformer oil flow area with the change of N w , N f , N t , D w , D f and D t . Step 6, according to the data obtained in step 5, the optimal optimization scheme is obtained by comprehensively considering the winding average temperature, the hottest spot temperature and the maximum oil flow velocity, to determine the opening number N of the net side oil outlet hole (2), the valve side oil outlet hole (3) and the pressure regulating side oil outlet hole (4) w , N f , and N t , and the opening size D w , D f , and D t .

2. The method of optimization of the number and size of openings of the oil duct of a converter transformer according to claim 1, characterized in that, The no-load loss of the converter transformer includes the magnetic hysteresis loss, the eddy current loss and the additional loss in the core, and the load loss of the converter transformer includes the resistance loss of the coil wire, the additional loss of the coil, the lead loss and the stray loss in the structural member.

3. The method of optimization of the number and size of openings of the oil duct of a converter transformer according to claim 1, characterized in that, The physical model includes the oil tank, the core, the insulating material, the grid side winding, the valve side winding, the regulating side winding, the oil guide box and the oil flow part of the converter transformer, and can reflect the size and connection relationship of the oil tank, the core, the insulating material, the grid side winding, the valve side winding, the regulating side winding, the oil guide box and the oil flow part; the purpose of grid division is to discretize the physical model so that it can be imported into the computational fluid dynamics software for calculation; the oil tank, the core, the insulating material, the grid side winding, the valve side winding, the regulating side winding and the oil guide box adopt prismatic layer grids, and the oil flow part adopts tetrahedral grid boundary layer grids.

4. The method of optimization of the number and size of openings of the oil duct of a converter transformer according to claim 3, characterized in that, The physical model is divided into grids by using the Fluent Meshing software, and the computational fluid dynamics software uses the ANSYS Fluent software.

5. The method of optimization of the number and size of openings of the oil duct box of a converter transformer according to claim 4, characterized in that, The specific process of step 3 includes: 3.1) In the ANSYS Fluent software, set the mass conservation equation, the energy conservation equation and the momentum conservation equation, and the software automatically iteratively solves these equations; 3.2) Set the fluid region and the solid region; the fluid region includes the oil flow part; the solid region includes the oil tank, the core, the insulating material, the grid side winding, the valve side winding, the regulating side winding and the oil guide box; 3.3) Set the physical properties of the fluid, the fluid uses common transformer oil, and the physical properties of the transformer oil are various physical properties measured during the test, including the density, specific heat capacity, thermal conductivity and dynamic viscosity of the transformer oil at different temperatures; 3.4) Set the physical properties of the solid, the physical properties of the oil tank, the core, the insulation material, the winding on the network side, the winding on the valve side, the winding on the pressure regulating side, and the oil guide box are various physical properties measured during the test process, including density, specific heat capacity, and thermal conductivity at different temperatures; 3.5) Input the no-load loss and load loss into the ANSYS Fluent software; 3.6) Input the boundary conditions, including the initial velocity and initial temperature of the transformer oil; the initial velocity of the transformer oil is obtained according to the nameplate parameters of the selected oil pump; the initial temperature of the transformer oil is obtained according to the nameplate parameters of the selected finned radiator and the ambient temperature.

6. The method of optimization of the number and size of openings of the oil duct of a converter transformer according to claim 4, characterized in that, The specific process of step 4 includes: 4.1) Based on all the conditions set in step 3, the ANSYS Fluent software automatically solves the mass conservation equation, the energy conservation equation, and the momentum conservation equation to obtain the temperature and velocity of each grid; 4.2) Statistics the temperature of all grids of the grid-side winding of the converter transformer, averages them to obtain the average temperature of the grid-side winding ; 4.3) Statistics of the temperature of all grids of the grid side winding of the converter transformer, maximum value is obtained, and the hottest point temperature of the grid side winding is obtained ; 4.4) repeating the above steps 4.2) and 4.3) to obtain the average temperature of the valve side winding , the hottest spot temperature of the valve side winding , the average temperature of the pressure regulating side winding , the hottest spot temperature of the pressure regulating side winding ; 4.5) Calculate the velocity of all the grids in the oil flow region, find the maximum value of them, and get the maximum velocity of the oil flow region .

7. The method of optimization of the number and size of openings of the oil duct of a converter transformer according to claim 4, characterized in that, The specific process of step 5 includes: 5.1) Keep N w , N f , N t , D w , D f unchanged, change D t , repeat steps 2~4, calculate the change rule of the average temperature of the grid-side winding, the valve-side winding, the voltage-regulation-side winding, the hottest point temperature, and the maximum oil flow velocity of the transformer oil flow area with D t ; 5.2) Keep N w , N f , N t , D w , D t unchanged, change D f , repeat steps 2~4, calculate the change rule of the average temperature of the grid-side winding, the valve-side winding, the voltage-regulation-side winding, the hottest point temperature, and the maximum oil flow velocity of the transformer oil flow area with D f ; 5.3) Keep N w , N f , N t , D f , D t unchanged, change D w , repeat steps 2~4, calculate the change rule of the average temperature, hottest point temperature of the grid side winding, valve side winding, voltage regulation side winding and the maximum oil flow velocity of the transformer oil flow area with D w ; 5.4) Keep N w , N f , D w , D f , D t unchanged, change N t , repeat steps 2~4, calculate the average temperature, hottest point temperature of the grid side winding, valve side winding, voltage regulating side winding and the maximum oil flow velocity of the transformer oil flow area with N t ; 5.5) Keep N w , N t , D w , D f , D t unchanged, change N f , repeat steps 2~4, calculate the average temperature, hottest point temperature of the grid side winding, valve side winding, voltage regulating side winding and the maximum oil flow velocity of the transformer oil flow area with N f ; 5.6) Keep N f , N t , D w , D f , D t unchanged, change N w , repeat steps 2~4, calculate the change rule of the average temperature of the grid-side winding, the valve-side winding, the voltage-regulation-side winding, the hottest point temperature, and the maximum oil flow velocity of the transformer oil flow area with N w .

8. The method of optimization of the number and size of openings of the oil duct of a converter transformer according to claim 4, characterized in that, The specific process of step 6 is as follows: 6.1) According to the data obtained in step 5, remove all schemes whose maximum oil flow velocity is greater than 0.5 m / s; 6.2) According to the data obtained in step 5, remove all schemes whose winding average temperature and hottest point temperature do not meet the protocol requirements; 6.3) Statistics of the average of the hottest spot temperature of the line side winding , the hottest spot temperature of the valve side winding and the hottest spot temperature of the voltage regulating side winding ;​ 6.4) Number of openings N corresponding to the minimum time w , N f and N t， and the opening size D w , D f and D t , i.e. the final determined optimization scheme.

9. The method of optimization of the number and size of openings of the oil duct of a converter transformer according to claim 1, characterized in that, The oil flow velocity requires that the maximum oil flow velocity of the oil flow part be not greater than 0.5 m / s.

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