An internal arc fault oil flow velocity simulation method for an extra-high voltage converter transformer

Abstract

The application discloses a kind of ultra-high voltage converter transformer internal arc fault oil flow velocity simulation methods, obtain the operating parameter of ultra-high voltage converter transformer, structure data and material data;According to the operating parameter of ultra-high voltage converter transformer, structure data and material data, establish the simulation model of ultra-high voltage converter transformer;The tetrahedron mesh of ultra-high voltage converter transformer fluid region in model is divided;For the fluid domain after grid division setting dynamic grid, boundary condition;According to gas bubble boundary movement speed, set bubble-fluid coupling boundary condition;Using finite volume method, according to the arc energy of ultra-high voltage converter transformer when internal arc fault occurs, the oil flow velocity in the oil tank of ultra-high voltage converter transformer under arc fault is iteratively calculated in each time step.The application can accurately simulate the space-time distribution of oil flow velocity when arc fault occurs in converter transformer, especially, the oil flow velocity of gas relay installation place.

Description

Technical Field

[0001] This invention belongs to the technical field of short-circuit faults in power system equipment, and specifically relates to a simulation method for oil flow velocity during arc faults inside an ultra-high voltage converter transformer. Background Technology

[0002] In ultra-high voltage direct current (UHVDC) transmission system projects, converter transformers, as key main equipment constituting the DC transmission circuit, play a vital role in connecting AC and DC systems, providing short-circuit impedance, and supplying the required voltage to converter valves. As the single piece of equipment with the highest insulation requirements and the most complex manufacturing process within the converter station, the operational safety of the converter transformer largely determines the operational safety of the entire converter station and the reliability of the DC project. With the continuous development of DC transmission technology in my country and the continuous improvement of transmission levels and capacities, the capacity of converter transformers used has increased from 321 MVA in the Xiangjiaba-Shanghai UHVDC demonstration project to 510 MVA or even higher, posing more severe challenges to the design, manufacturing, and operation of converter transformers and their related components.

[0003] When a short-circuit fault occurs inside a converter transformer, a huge short-circuit current flows through the windings, causing severe vibration and insulation damage. In the initial stage of an arc fault inside the converter transformer, the insulating oil surrounding the arc vaporizes instantaneously due to the extremely high temperature of the arc, forming gas bubbles that gradually envelop the arc. Therefore, the pressure inside the gas bubbles interacts with the pressure of the external gas flow field, macroscopically manifesting as expansion and contraction of the bubbles. The dynamic growth of the gas bubbles compresses the surrounding insulating oil, causing an increase in internal pressure and oil flow surge. This overpressure from the fault causes significant damage to the converter transformer tank, easily damaging weak components. If the pressure is not released in time, it can quickly create static pressure exceeding the tank's capacity, leading to an explosion. With the increasing number of converter transformers in operation, explosions caused by internal short-circuit faults have become increasingly common, seriously threatening the stable operation of the power grid and the safety of people's lives. However, due to long-standing lack of understanding and the limitations of simulation methods, existing theoretical methods are unable to accurately describe the bubble dynamics of electric arcs in oil and the characteristics of oil flow velocity changes. Summary of the Invention

[0004] To overcome the problems in the prior art, the purpose of this invention is to provide a simulation method for oil flow velocity in an internal arc fault of an ultra-high voltage converter transformer. By setting bubble-fluid coupling boundary conditions, the finite volume method is used to calculate the oil flow velocity under fault conditions of the ultra-high voltage converter transformer, and on this basis, the spatiotemporal distribution of the oil flow velocity of the converter transformer is obtained, which can accurately describe the bubble dynamics behavior of the arc in the oil and the characteristics of oil flow velocity change.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A simulation method for oil flow velocity during internal arc faults in ultra-high voltage converter transformers includes the following steps:

[0007] Step 1: Obtain the operating parameters, structural data, and material data of the UHV converter transformer;

[0008] Step 2: Based on the operating parameters, structural data, and material data of the UHV converter transformer in Step 1, establish a simulation model of the UHV converter transformer.

[0009] Step 3: Perform tetrahedral meshing on the fluid region in the UHV converter transformer simulation model;

[0010] Step 4: Set the dynamic mesh, boundary conditions, and solver controller parameters for the fluid domain after mesh generation; set the bubble-fluid coupling boundary conditions according to the gas bubble boundary movement velocity; use the finite volume method to iteratively calculate the oil flow velocity inside the UHV converter transformer tank under the arc fault in each time step based on the arc energy of the UHV converter transformer when an internal arc fault occurs.

[0011] Furthermore, the operating parameters include: rated capacity, rated voltage, and rated frequency;

[0012] Structural data includes: fuel tank length, fuel tank width, fuel tank height, fuel tank radius, fuel tank length, and fuel tank wall thickness;

[0013] Material data includes: fluid material density, bulk modulus, and viscosity coefficient.

[0014] Furthermore, the dynamic mesh is set using the following formula:

[0015]

[0016] In the formula, ρ is the fluid density; Г is the diffusion coefficient; A is the area vector; S φ Represents the source term; φ is the boundary term. Scalar on the moving control volume V; u is the fluid velocity vector; u g This represents the grid movement speed.

[0017] Furthermore, the arc energy of an UHV converter transformer during an internal arc fault is calculated using the following formula:

[0018]

[0019] In the formula, W arc The electric arc energy is represented by t0, which is the fault initiation time; t is time; u is the electric arc energy. arc It is the arc voltage; i arcIt is electric arc current.

[0020] Furthermore, the arc voltage is calculated using the following formula:

[0021] u arc =E·l arc

[0022] In the formula, E is the electric field intensity of the arc column, l arc This is the length of the electric arc.

[0023] Furthermore, the boundary velocity of the gas bubble is calculated using the following formula:

[0024]

[0025] In the formula: R, and These are the gas bubble radius, the gas bubble boundary velocity, and the acceleration; r d It is the distance from the bubble to the boundary; p d It is the fluid boundary pressure; μ is the dynamic viscosity coefficient of the insulating oil; σ oil It is the surface tension coefficient of insulating oil.

[0026] Furthermore, the internal pressure P of the bubble b Calculated using the following formula:

[0027]

[0028] In the formula, γ is the specific heat ratio of the gas; V b It is the volume of the gas bubbles.

[0029] Furthermore, the internal energy U of the gas bubble b Calculated using the following formula:

[0030] U b =QW b +U0

[0031] In the formula, Q is the energy injected into the gas bubble; W b U0 is the work done by the bubble as it expands; U0 is the initial internal energy of the bubble.

[0032] Furthermore, using the finite volume method, based on the arc energy of the UHV converter transformer during an internal arc fault, the oil flow velocity inside the UHV converter transformer tank under the arc fault is iteratively calculated at each time step, thereby obtaining the oil flow velocity distribution, including the following steps:

[0033] The Navier-Stokes equations were numerically solved using the finite volume method to obtain the movement of insulating oil during an arc fault in a converter transformer.

[0034] Based on the movement of insulating oil during an arc fault in the converter transformer, the k-ε turbulence model is used to calculate the oil flow velocity inside the converter transformer tank during the fault.

[0035] Furthermore, the Navier-Stokes equations are:

[0036]

[0037] In the formula, f is the body force; p is the pressure; and ν is the fluid kinematic viscosity coefficient.

[0038] The k-ε turbulence model is:

[0039]

[0040] In the formula, k is the turbulent kinetic energy, and u i x is the i-th component of the fluid velocity vector u; i and x j ε is the spatial coordinate; μ is the turbulent dissipation rate; μ is the spatial coordinate. t For turbulent dynamic viscosity; G b and G k Y represents the turbulent kinetic energy generated by buoyancy and the average velocity gradient, respectively; M S represents the contribution of wave expansion in compressible turbulence to the total dissipation rate; k and S ε For the first and second source terms; C 1ε C 2ε and C 3ε σ represents the first, second, and third constants; k and σ ε These are the first and second Prandtl numbers for turbulence.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] This invention considers the dynamic behavior of gas bubbles during faults, enabling the calculation of gas bubble energy under continuous arc energy injection and bubble motion within a finite domain in spherical coordinates. This allows for accurate calculation of oil flow velocity under internal faults in UHV converter transformers. The invention considers the arc energy during internal arc faults in converter transformers, effectively and realistically reflecting the spatiotemporal distribution of oil flow velocity with high accuracy, achieving oil flow velocity calculation under different fault conditions. Numerical calculations based on the finite volume method ensure fast solution even with a large number of meshes and high parallel efficiency. By comprehensively considering the flow field boundary conditions, it more realistically simulates the actual situation of internal arc faults in converter transformers. Attached Figure Description

[0043] Figure 1The flowchart shows the simulation method for oil flow velocity in an internal arc fault of an ultra-high voltage converter transformer according to the present invention.

[0044] Figure 2 This is a geometric model diagram of an ultra-high voltage converter transformer according to an embodiment of the present invention.

[0045] Figure 3 This is a finite element model diagram of an ultra-high voltage converter transformer according to an embodiment of the present invention.

[0046] Figure 4 The following is a flow velocity cloud diagram of the internal fault oil in the UHV converter transformer according to an embodiment of the present invention, where (a) is 5 ms and (b) is 20 ms.

[0047] Figure 5 The image shows the oil flow and velocity waveform at the connection pipe of the ultra-high voltage converter transformer, as shown in an embodiment of the present invention. Detailed Implementation

[0048] The present invention will now be described in detail with reference to the accompanying drawings.

[0049] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0050] like Figure 1 As shown, the present invention provides a method for simulating the oil flow velocity during an internal arc fault in an ultra-high voltage converter transformer. The specific steps are as follows:

[0051] Step 1: Collect the operating parameters, structural data, and material data of the UHV converter transformer.

[0052] Operating parameters include: rated capacity, rated voltage, and rated frequency;

[0053] Structural data includes: fuel tank length, fuel tank width, fuel tank height, fuel tank radius, fuel tank length, and fuel tank wall thickness;

[0054] Material data includes: fluid material density, bulk modulus, and viscosity coefficient.

[0055] Step 2: Calculate the arc energy of the UHV converter transformer when an internal arc fault occurs.

[0056] The energy released by an internal arc fault in an ultra-high voltage converter transformer can be calculated as follows:

[0057]

[0058] In the formula, W arcThe electric arc energy is represented by t0, which is the fault initiation time; t is time; and P is the electric arc energy. arc It is the arc power; u arc It is the arc voltage; i arc It is electric arc current.

[0059] For ease of calculation, the arc voltage u can be considered as... arc The value is always positive. The arc energy of the UHV converter transformer during an internal arc fault is calculated using the following formula:

[0060]

[0061] If the voltage drop near the electrodes and the arc ignition and extinguishing peaks are ignored, the arc voltage can be considered to be only related to the arc length, and the arc voltage can be calculated by the following formula:

[0062] u arc =E·l arc

[0063] In the formula, E is the electric field intensity of the arc column, l arc This is the length of the electric arc.

[0064] Step 3: Based on the operating parameters, structural data, and material data of the UHV converter transformer collected in Step 1, the physical UHV converter transformer is reasonably simplified, and a simulation model of the UHV converter transformer is built based on the SpaceClaim tool modeling platform.

[0065] In this preferred example, the SpaceClaim tool is used to establish a three-dimensional fluid geometry model of the ultra-high voltage converter transformer, such as... Figure 2 As shown, measuring point 1 is the oil speed measuring point at the oil conservator connecting pipe.

[0066] Step 4: Using Meshing software, the fluid region of the UHV converter transformer simulation model is divided into tetrahedral meshes sequentially. The fluid region model has a large number of meshes and the overall mesh quality is high. Key parts are refined, and the number of nodes, elements, and mesh quality of the fluid domain are counted. The mesh quality is then checked and adjusted.

[0067] In this preferred embodiment, the mesh is divided as follows: Figure 3 As shown, from Figure 3 As can be seen, the fluid domain has a large number of grids per unit area, therefore the fluid model uses a high-density grid.

[0068] It is worth noting that technical personnel in the relevant field can determine the mesh density parameters based on the actual engineering application requirements, that is, determine the number of meshes per unit area of ​​the model.

[0069] Step 5: Set the dynamic mesh, boundary conditions, and solver controller parameters for the fluid domain after mesh generation. The oil flow during a converter transformer fault is driven by gas bubbles. The bubble dynamics equations are incorporated into a user-defined function (UDF) to describe bubble motion and set the bubble-fluid coupling boundary. Using the finite volume method in ANSYS software, based on the arc energy of the UHV converter transformer during an internal arc fault, the oil flow velocity at the gas relay installation location and the oil flow velocity inside the UHV converter transformer tank under arc fault conditions are iteratively calculated at each time step t, finally obtaining the oil flow velocity distribution. The specific process is as follows:

[0070] For the boundary is The scalar φ on the moving control body V is used to set the dynamic mesh using the following formula:

[0071]

[0072] In the formula, ρ is the fluid density; Г is the diffusion coefficient; A is the area vector; S φ Represents the source term; u is the fluid velocity vector; u g This represents the grid movement speed.

[0073] In the simulation model of the UHV converter transformer, the fluid at the outlet of the pressure relief valve and the oil conservator adopts the pressure-outlet boundary condition, with the outlet pressure set to atmospheric pressure, and the rest of the fluid domain is set as a wall.

[0074] Specifically, since the motion of the gas-fluid interface is determined by the bubble dynamics equations, a user-defined function (UDF) is used to describe the motion, assigning bubble pulsation behavior to the model's boundaries or nodes. A bubble-fluid coupling calculation process is designed to set the bubble-fluid boundary conditions. The DEFINE_GRID_MOTION macro is used to manipulate the motion of the mesh nodes to the greatest extent possible, combining the motion and deformation of the rigid body. The bubble dynamics equations are then incorporated into the UDF using the DEFINE_GRID_MOTION macro.

[0075] Specifically, with the continuous injection of electric arc energy, the internal energy of the gas bubble also changes accordingly, and the bubble pulsation behavior can be obtained from the following process:

[0076] According to the first law of thermodynamics, gas bubbles under the influence of electric arc energy satisfy the following thermodynamic equilibrium relationship, and the internal energy U of the gas bubble can be obtained from the following equation. b :

[0077] U b =QW b +U0

[0078] In the formula, Q is the energy injected into the gas bubble; W bU0 is the work done by the bubble as it expands; U0 is the initial internal energy of the bubble.

[0079] Based on the obtained internal energy U of the bubble b The internal pressure p of the bubble is calculated using the following formula. b :

[0080]

[0081] In the formula, γ is the specific heat ratio of the gas; V b It is the volume of the gas bubble;

[0082] Based on the obtained bubble internal pressure p b We can obtain the bubble dynamics equation in a finite domain in spherical coordinates. Solving this equation yields the boundary velocity of the gas bubble:

[0083]

[0084] In the formula: R, and These are the gas bubble radius, the gas bubble boundary velocity, and the acceleration; r d It is the distance from the bubble to the boundary; p d It is the fluid boundary pressure; μ is the dynamic viscosity coefficient of the insulating oil; σ oil It is the surface tension coefficient of insulating oil.

[0085] The boundary velocity of the gas bubble obtained by solving the bubble dynamics equation in spherical coordinate system User-defined functions (UDFs) are incorporated to control the movement of bubble boundary nodes and set bubble-fluid coupling boundary conditions.

[0086] Specifically, after setting the boundary conditions, assuming a fault occurs at t=0 ms, the oil flow velocity calculation under an arc fault in the UHV converter transformer begins. During the internal fault period of the converter transformer, the dynamic behavior of the insulating oil satisfies the Navier-Stokes (NS) equations and the k-ε turbulence equations. Driven by fault gas bubbles, the internal oil flow velocity of the converter transformer can be obtained by numerically solving the following equations using the finite volume method:

[0087] Navier-Stokes (NS) equations:

[0088]

[0089] In the formula, f is the body force; p is the pressure; and ν is the fluid kinematic viscosity coefficient.

[0090] The movement of insulating oil during an arc fault in a converter transformer is obtained using the Navier-Stokes equations. The flow velocity of the internal oil in the converter transformer during the fault is studied using a standard k-ε turbulence model, which has good numerical stability and computational accuracy.

[0091]

[0092]

[0093] In the formula, k is the turbulent kinetic energy, and u i x is the i-th component of the fluid velocity vector u; i and x j ε is the spatial coordinate; μ is the turbulent dissipation rate; μ is the spatial coordinate. t For turbulent dynamic viscosity; G b and G k Y represents the turbulent kinetic energy generated by buoyancy and the average velocity gradient, respectively; M S represents the contribution of wave expansion in compressible turbulence to the total dissipation rate; k and S ε For the first and second source terms; C 1ε C 2ε and C 3ε σ represents the first, second, and third constants; k and σ ε These are the first and second Prandtl numbers for turbulence.

[0094] The oil flow velocity is calculated within a simulation step t, and the oil flow velocity distribution inside the UHV converter transformer during arc faults is obtained through iteration. When the residual of the iteration step is less than a given threshold, the iteration step is considered to have converged. Then, t = t + Δt is set, and the calculation proceeds to the next time step. The new bubble boundary velocity is calculated again, and a bubble-fluid boundary is assigned, repeating the above calculation process. When the time step reaches t... max The calculation is considered complete at this point, and the project file and flow rate calculation results are saved.

[0095] This invention performs fault simulation calculations on a 415MVA / 500kV UHV converter transformer. The fault condition is an arc fault with a total energy of 1200kJ (i.e., arc energy) occurring in the middle of winding 2 of core column. The selected fluid material is a material with the chemical formula C. 16 H 29 The oil and gas mixture has a density of 895 kg / m³. 3 The bulk modulus is 140 MPa, and the viscosity coefficient is 0.00332 Pa·s. The simulation results of the spatiotemporal distribution and variation characteristics of the fault oil velocity in the UHV converter transformer are as follows: Figure 4 (a) and (b) and Figure 5 As shown. Figure 4 Images (a) and (b) are flow velocity contour maps of oil flow during arc faults inside an ultra-high voltage converter transformer. Figure 5 This is a graph showing the change in oil flow velocity at the connecting pipe. From... Figure 4 As can be seen in (a) and (b), in the initial few milliseconds after the fault begins, the bubbles expand rapidly due to the electric arc. Therefore, during this period, only the vicinity of the fault point experiences significant oil flow surge. It can be observed that at this time, an oil flow surge with a velocity of approximately 0.4 m / s appears on the front wall of the converter transformer near the fault point, while the flow velocity is lower elsewhere due to the oil's inertia. The bubbles continue to expand and reach their maximum value at t = 20 ms. At this time, the insulating oil flows rapidly to other parts of the converter transformer tank, and a flow velocity of approximately 1.5 m / s is generated locally at the fault point. The oil flow rate interruption relay is installed at the connecting pipe, from... Figure 5 It can be seen that in the initial 15ms, due to the large size of the converter transformer, the oil flow surge caused by the expansion of the fault bubble has not yet propagated to the connecting pipe, so the flow velocity at the connecting pipe is 0m / s during this period. Throughout the fault process, the oil flow velocity in the connecting pipe gradually increases, reaching approximately 1.1m / s at the end of the fault.

[0096] This invention can accurately simulate the spatiotemporal distribution of oil flow velocity during an arc fault inside a converter transformer, particularly the oil flow velocity at the gas relay installation location. This invention provides an accurate and reliable simulation method for studying the distribution of insulating oil velocity at the gas relay installation location during an arc fault in a converter transformer, offering valuable reference and guidance for researchers and engineers in related fields.

[0097] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0098] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for simulating oil flow velocity during internal arc faults in ultra-high voltage converter transformers, characterized in that, Includes the following steps: Step 1: Obtain the operating parameters, structural data, and material data of the UHV converter transformer; Step 2: Based on the operating parameters, structural data, and material data of the UHV converter transformer in Step 1, establish a simulation model of the UHV converter transformer. Step 3: Perform tetrahedral meshing on the fluid region in the UHV converter transformer simulation model; Step 4: Set the dynamic mesh, boundary conditions, and solver controller parameters for the fluid domain after mesh generation; set the bubble-fluid coupling boundary conditions according to the gas bubble boundary movement velocity; Using the finite volume method, the oil flow velocity inside the oil tank of the UHV converter transformer under the arc fault is iteratively calculated in each time step based on the arc energy when the UHV converter transformer experiences an internal arc fault. The velocity of the gas bubble boundary is calculated using the following formula: In the formula: R , and These are the gas bubble radius, the gas bubble boundary velocity, and the acceleration; r d It is the distance from the bubble to the boundary; p d It is the fluid boundary pressure; It is the dynamic viscosity coefficient of insulating oil; It is the surface tension coefficient of insulating oil; Using the finite volume method, based on the arc energy of an UHV converter transformer during an internal arc fault, the oil flow velocity inside the UHV converter transformer tank is iteratively calculated at each time step to obtain the oil flow velocity distribution. This includes the following steps: The Navier-Stokes equations were numerically solved using the finite volume method to obtain the movement of insulating oil during an arc fault in a converter transformer. Based on the movement of insulating oil during an arc fault in the converter transformer, use k - The turbulence model is used to calculate the oil flow velocity inside the converter oil tank during the fault.

2. The simulation method for oil flow velocity during internal arc faults in ultra-high voltage converter transformers according to claim 1, characterized in that, Operating parameters include: rated capacity, rated voltage, and rated frequency; Structural data includes: fuel tank length, fuel tank width, fuel tank height, fuel tank radius, fuel tank length, and fuel tank wall thickness; Material data includes: fluid material density, bulk modulus, and viscosity coefficient.

3. The simulation method for oil flow velocity during internal arc faults in ultra-high voltage converter transformers according to claim 1, characterized in that, The dynamic mesh is set using the following formula: In the formula, It is the fluid density; Γ is the diffusion coefficient; A It is an area vector; Indicates the source term; For the boundary mobile control body V scalars on; u For fluid velocity vector; u g This represents the grid movement speed.

4. The simulation method for oil flow velocity during internal arc faults in ultra-high voltage converter transformers according to claim 1, characterized in that, The arc energy of an ultra-high voltage converter transformer during an internal arc fault is calculated using the following formula: In the formula, W arc It is the energy of the electric arc; t 0 represents the fault initiation time; t It is time; u arc It is the arc voltage; i arc It is electric arc current.

5. The simulation method for oil flow velocity during internal arc faults in ultra-high voltage converter transformers according to claim 3, characterized in that, Arc voltage is calculated using the following formula: In the formula, E The electric field strength of the arc column, l arc This is the length of the electric arc.

6. The simulation method for oil flow velocity during internal arc faults in ultra-high voltage converter transformers according to claim 1, characterized in that, internal pressure of the bubble Calculated using the following formula: In the formula, It is the specific heat ratio of methane gas; V b It is the volume of the gas bubbles. U b It is the internal energy of gas bubbles.

7. The method for simulating oil flow velocity during internal arc faults in ultra-high voltage converter transformers according to claim 6, characterized in that, Internal energy of gas bubbles U b Calculated using the following formula: In the formula, Q It is the energy injected into the gas bubbles; W b The expansion of the bubbles does work. U 0 is the initial internal energy of the bubble.

8. The simulation method for oil flow velocity during internal arc faults in ultra-high voltage converter transformers according to claim 1, characterized in that, The Navier-Stokes equations are: In the formula, f For mass force; p For pressure; The fluid's kinematic viscosity coefficient. u For fluid velocity vector; k - The turbulence model is: In the formula, k It is turbulent kinetic energy. u i fluid velocity vector u The i One component; x i and x j Spatial coordinates; It is the turbulent dissipation rate; For turbulent dynamic viscosity; G b and G k These represent the turbulent kinetic energy generated by buoyancy and the average velocity gradient, respectively. Y M This represents the contribution of wave expansion to the total dissipation rate in compressible turbulence. S k This is the first source term; It is the first Prandtl number for turbulence.

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