Numerical simulation method and device for transformer arc fault explosion based on gas inflow

Abstract

The present application relates to a kind of transformer arc fault explosion numerical simulation method and equipment based on gas inflow, which comprises the following steps: obtaining the fault position of transformer, fault energy and fault duration;Simplify and establish the fluid-solid coupling finite element model of transformer containing insulating oil considering strain rate effect;The mass inflow rate and boundary flow velocity of gas are calculated based on the fault energy and fault duration;Based on the mass inflow rate and boundary flow velocity, gas is injected into the fault position by inflow boundary to realize the simulation of transformer arc fault explosion process.Compared with prior art, the present application has the advantages of improving simulation accuracy, etc.

Description

Technical Field

[0001] This invention relates to the field of transformer safety application technology, and in particular to a numerical simulation method and device for transformer arc fault explosion based on gas inflow. Background Technology

[0002] Large power transformers are crucial equipment in ultra-high voltage power transmission projects, and the main type of large power transformer used is the oil-immersed transformer. These large transformers are enormous, filled with hundreds of tons of flammable insulating oil. This oil is in direct contact with high-voltage components; if an arcing fault occurs, the insulating oil will instantly vaporize, causing the transformer to explode, leading to a reduction or even paralysis of the power grid in the area.

[0003] Research on disaster mitigation for transformer arc fault explosions has gradually become a key focus in the industry. From 2002 to 2004, Electricité de France (France) and CEPEL (Brazil) conducted 62 arc fault tests on oil-immersed transformers, obtaining data on the internal pressure time history, acceleration response of the transformer tank, and total gas production in the insulating oil under different energy levels for different transformer models. However, these tests are expensive and difficult to implement, limiting their scale and resulting in limited experimental data that cannot yield universally applicable conclusions. Therefore, numerical experiments have become an important research method.

[0004] Scholars have proposed various numerical simulation methods for arc faults in oil-immersed transformers, which can be divided into methods that generate loads through a one-time energy release and methods that consider the energy release process to generate loads. Typical methods for generating loads through a one-time energy release include the TNT equivalent method and the instantaneous gas injection method. The TNT equivalent method converts the arc energy into TNT equivalent based on energy conservation and uses the explosive simulation method in LS-DYNA to analyze the oil pressure distribution and tank response characteristics inside the transformer under arc fault conditions. The instantaneous gas injection method is based on the simplified five equations describing the hydrodynamic behavior of compressible two-phase flow. A bubble is generated at the fault location, and the total amount of gas corresponding to the arc fault energy is injected at once to simulate the dynamic load of the arc fault; this is referred to as the instantaneous gas injection method below. Considering the relationship between arc power and bubble pressure, some scholars have proposed a multi-field coupling model for oil-immersed transformers. Based on the COMSOL Multiphysics software platform, they have established the relationship between arc power and the pressure difference between the two-phase interfaces for load application, and provided data on transient leakage flux of windings, dynamic electrodynamics, tank deformation, and oil pressure.

[0005] Comparison with experimental data revealed that the load application method considering the relationship between arc power and bubble pressure exhibited poor verification of pressure time-history characteristics compared to experimental data. The TNT equivalent method and the instantaneous gas injection method both resulted in excessively high peak loads and excessively rapid pressure increases, and failed to reflect the impact of continuous gas generation on the load, making them unsuitable for the need for accurate structural response analysis. A key factor limiting the effectiveness of numerical experiments was the poor reproduction of the gas generation process in insulating oil caused by arc faults in numerical simulations. Summary of the Invention

[0006] The purpose of this invention is to provide a numerical simulation method and device for transformer arc fault explosion based on gas inflow, which improves simulation accuracy.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A numerical simulation method for transformer arc fault explosion based on gas inflow includes the following steps:

[0009] Obtain the fault location, fault energy, and fault duration of the transformer;

[0010] A simplified and established fluid-structure interaction finite element model of a transformer containing insulating oil, considering strain rate effects, wherein the fault location of the transformer is located inside the fluid-structure interaction finite element model;

[0011] The mass inflow rate and boundary velocity of the gas are calculated based on the fault energy and fault duration.

[0012] Based on the mass inflow rate and boundary velocity, gas is injected into the fault location through the inflow boundary to simulate the transformer arc fault explosion process.

[0013] Furthermore, the simplified fluid-structure interaction finite element model of the transformer includes the transformer housing, riser base, and core.

[0014] Furthermore, the transformer housing, riser base, and core are constructed using Lagrange shell units.

[0015] Furthermore, the Johnson-Cook model was used to establish the fluid-structure interaction finite element model of the transformer.

[0016] Furthermore, the Cowper-Symonds model was used to establish the fluid-structure interaction finite element model of the transformer.

[0017] Furthermore, the expression for calculating the mass inflow rate is as follows:

[0018]

[0019] in, Let Q be the mass inflow rate, Q be the amount of gas produced per unit arc energy, and E be the mass flow rate. f Let ρ be the energy of the arc fault, t be the gas density, and t be the energy of the arc fault. f For the duration of the electric arc.

[0020] Furthermore, the expression for calculating the boundary flow velocity is:

[0021]

[0022] in, For the boundary flow velocity, Let ρ be the mass inflow rate, ρ be the gas density, and A be the gas injection area.

[0023] Furthermore, the fault energy is obtained through an internal fault arc energy model, the model expression of which is:

[0024]

[0025] In the formula, W arc The fault energy is Δt, the arcing time is u. arc i is the voltage drop across the arc. arc This is the arc current.

[0026] Furthermore, the inflow boundary is applied at the insulating oil unit at the fault location.

[0027] The present invention also provides an electronic device comprising: one or more processors; a memory; and one or more programs stored in the memory, said one or more programs including instructions for executing the numerical simulation method for transformer arc fault explosion based on gas inflow as described above.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) By considering the gas generation process of transformer insulating oil caused by arc fault and the deformation and displacement of solid structure caused by shock wave and insulating oil itself on solid structure, the flow field boundary will change, thus changing the properties of insulating oil flow field. Therefore, this invention establishes a transformer fluid-structure coupling finite element model containing insulating oil, and injects gas into the fault location inside the model through the obtained mass inflow rate and boundary velocity to apply load, thereby improving the simulation accuracy of this invention.

[0030] (2) The present invention effectively restores the process of gas generation in insulating oil caused by arc fault, making the characteristics of the generated explosive load more consistent with the actual situation.

[0031] (3) In the process of constructing the finite element model, the present invention takes into account the material properties of the transformer structure and uses the Johnson-Cook model or the Cowper-Symonds model to consider the strain rate and strengthening effect of the steel, thereby making the simulation process closer to the real situation and improving the simulation accuracy.

[0032] (4) This invention improves the simulation analysis capabilities of transformer pressure limit analysis and explosion response analysis in the technical field, which require high response accuracy, and reduces the casualties and economic losses caused by such accidents. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the method flow of the present invention;

[0034] Figure 2 This is the fluid-structure interaction finite element model established in this invention;

[0035] Figure 3 This is a perspective view of the fluid-structure interaction finite element model established in this invention, where (a) is the left view and (b) is the front view;

[0036] Figure 4 This is a comparison and verification diagram of the pressure time history of the present invention and the experiment;

[0037] Figure 5 This is a comparison chart of the pressure time history of the present invention and two other simulation methods;

[0038] Figure 6 This is a schematic diagram of the bubble development process in numerical simulation as implemented by the present invention. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0040] This embodiment provides a numerical simulation method for transformer arc fault explosion based on gas inflow, such as... Figure 1 As shown, the method includes the following steps:

[0041] Step 1: Obtain the fault location, fault energy, and fault duration of the transformer.

[0042] This embodiment uses a 500kV oil-immersed transformer from a certain company as a basis for calculation.

[0043] The location of the transformer fault can be determined by inspecting the transformer.

[0044] The internal fault arc energy model is used to obtain the fault energy, and the model expression is as follows:

[0045]

[0046] In the formula, W arc The fault energy is represented by Δt, and the arcing time is represented by u. arc i is the voltage drop across the arc. arc This is the arc current.

[0047] The duration of the fault is determined based on parameters such as the transformer's protection action time, fault clearing time, and arc extinction time.

[0048] Step 2: Simplify and establish a fluid-structure interaction finite element model of the transformer that includes insulating oil.

[0049] This step involves simplifying the transformer model based on the analysis requirements and establishing a fluid-structure interaction finite element model of the transformer, including the insulating oil, on the software platform.

[0050] (1) Establishing the transformer geometric model. The main components of a transformer include the tank, core, coils, tap changer, riser, bushings, oil conservator, and cooling system. The numerical model is simplified to include the transformer tank and riser, two important components requiring response analysis, as well as the core, a component that affects the propagation of pressure waves inside the tank. The tank, riser, and core are all built using Lagrange shell elements, as shown in the model below. Figure 2 , Figure 3 As shown in Figure (3), (a) is the left view of the model and (b) is the front view of the model. The sphere in the figure is the location where the bubble is generated.

[0051] (2) Assigning structural material properties. Since the transformer structure is composed of steel, a bifolded linear material property model can be used. The strain rate and strengthening effect of the steel should be considered through models such as the Johnson-Cook model or the Cowper-Symonds model.

[0052] (3) Consider fluid-structure interaction. When the shock wave and the insulating oil itself act on the solid structure, the deformation and displacement of the solid structure will cause changes in the flow field boundary, thus altering the properties of the insulating oil flow field. Therefore, this design needs to consider the fluid-structure interaction between the insulating oil and the enclosure to ensure the accuracy of the calculation results.

[0053] Step 3: Calculate the gas mass inflow rate and boundary velocity based on the fault energy and fault duration.

[0054] Due to insufficient research on the time-history characteristics of gas generation in insulating oil caused by arc faults, this is simplified to uniform gas generation. Based on relevant research, the gas generation rate Q per unit arc energy is 85 ml / kJ, therefore the mass inflow rate... The boundary flow velocity is obtained from equation (1). It can be obtained from equation (2).

[0055]

[0056]

[0057] Among them, E f Let ρ be the energy of the arc fault, t be the gas density, and t be the energy of the arc fault. f When the electric arc is held, A is the gas injection area.

[0058] Step 4: Based on the mass inflow rate and boundary velocity, inject gas into the fault location through the inflow boundary to simulate the gas generation process of transformer arc fault and the propagation of explosion shock wave.

[0059] An inflow boundary is applied at the insulating oil unit at the preset fault location. Gas is injected through the inflow boundary using the calculated mass inflow rate and boundary velocity, thus achieving gas inflow to apply load. This effectively recreates the gas generation process and explosion shock wave propagation of the transformer arc fault. The fault energy and duration used in this embodiment are the same as in the experiment. The original experiment only stated that the measuring point was near the fault location, without giving the exact location of the measuring point, and only provided the pressure curve with a pressure relief device. Therefore, it is not possible to accurately compare the pressure time history of the experiment and the calculation example. In this calculation example, the pressure at the measuring point near the fault location is compared with the experimental results. Figure 4 As shown. In the first pressure peak portion, unaffected by structural geometry and pressure relief devices, the uniform injection method and the experiment demonstrated good results in terms of pressure rise rate, pressure fall rate, and peak pressure, and the subsequent time history trends also showed good agreement. For comparison, pressure-time history curves at the same measuring point from both the TNT equivalent method and the instantaneous injection method are presented as follows. Figure 5 As shown. A high-energy example illustrates the bubble development process, such as... Figure 6 As shown.

[0060] Based on the above method for describing the arc fault explosion load, we can further analyze the transformer response characteristics, failure features, ability to withstand arc faults, and the effectiveness of explosion-proof design.

[0061] Example 2

[0062] This embodiment provides an electronic device, including: one or more processors; a memory; and one or more programs stored in the memory, the one or more programs including instructions for executing the numerical simulation method for transformer arc fault explosion based on gas inflow as described in Embodiment 1.

[0063] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0064] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0065] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0066] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0067] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0068] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A numerical simulation method for transformer arc fault explosion based on gas inflow, characterized in that, Includes the following steps: Obtain the fault location, fault energy, and fault duration of the transformer; A simplified and established fluid-structure interaction (FSI) finite element model of a transformer including insulating oil is constructed, considering strain rate effects. The fault location of the transformer is located inside the FSI finite element model. The simplified FSI finite element model of the transformer includes the transformer tank and riser base that require response analysis, as well as the iron core that affects the propagation of pressure waves inside the tank. The transformer tank, riser base, and iron core are constructed using Lagrange shell elements. The mass inflow rate and boundary velocity of the gas are calculated based on the fault energy and fault duration. Based on the mass inflow rate and boundary velocity, gas is injected into the fault location through the inflow boundary to simulate the transformer arc fault explosion process.

2. The numerical simulation method for transformer arc fault explosion based on gas inflow according to claim 1, characterized in that, The Johnson-Cook model was used to establish the fluid-structure interaction finite element model of the transformer.

3. The numerical simulation method for transformer arc fault explosion based on gas inflow according to claim 1, characterized in that, The Cowper-Symonds model was used to establish the fluid-structure interaction finite element model of the transformer.

4. The numerical simulation method for transformer arc fault explosion based on gas inflow according to claim 1, characterized in that, The formula for calculating the mass inflow rate is: in, For quality inflow rate, Q The amount of gas produced per unit of electric arc energy. E f For arc fault energy, ρ For gas density, t f For the duration of the electric arc.

5. The numerical simulation method for transformer arc fault explosion based on gas inflow according to claim 1, characterized in that, The expression for calculating the boundary flow velocity is: in, For the boundary flow velocity, For quality inflow rate, ρ For gas density, A This represents the area where the gas is injected.

6. The numerical simulation method for transformer arc fault explosion based on gas inflow according to claim 1, characterized in that, The fault energy is obtained through an internal fault arc energy model, the model expression of which is: In the formula, For fault energy, For arc burning time, The voltage drop across the arc, This is the arc current.

7. The numerical simulation method for transformer arc fault explosion based on gas inflow according to claim 1, characterized in that, The inflow boundary is applied at the insulating oil unit at the fault location.

8. An electronic device, characterized in that, include: One or more processors; Memory; and One or more programs stored in a memory, the one or more programs including instructions for executing the numerical simulation method for transformer arc fault explosion based on gas inflow as described in any one of claims 1-7.

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