A method for simulating partial discharge of oil-paper insulation under cuprous sulfide deposition

Abstract

The present application belongs to the technical field of transformer oil sulfur corrosion protection, and relates to a method for simulating partial discharge of oil-paper insulation under cuprous sulfide deposition, which comprises the following steps: establishing a geometric model of partial discharge of oil-paper insulation by using finite element simulation software COMSOL Multiphysics, and designing cuprous sulfide deposition points; setting physical fields and boundary conditions based on the geometric model, and establishing a fluid dynamics model of transformer oil and a bipolar carrier transport model of insulation paper; performing grid division on the model, and setting initial parameters, solver parameters and voltage excitation; performing transient calculation on the model, and solving the electric field distribution and charge distribution in the partial discharge process of the model. The present application uses the fluid dynamics model and the bipolar carrier model to predict and calculate the severity of partial discharge when cuprous sulfide is deposited at different positions of oil-paper insulation, thereby providing a reference for the influence of cuprous sulfide deposition on the partial discharge characteristics in oil-immersed transformers, and reducing the safety accidents caused by the insulation deterioration of transformers due to cuprous sulfide deposition.

Description

Technical Field

[0001] This invention relates to a method for simulating partial discharge in oil-paper insulation under cuprous sulfide deposition. Background Technology

[0002] Oil-immersed transformers are the most commonly used transformers in power transmission and distribution equipment. They contain a large amount of mineral insulating oil, and the aging of this oil poses a significant threat to the safe and stable operation of the transformer. Transformer insulating oil contains trace impurities, one of which is corrosive sulfur. Sulfur can corrode the copper in the transformer, exposing the oil-paper insulation to sulfur corrosion. Research has found that corrosive sulfur in transformer oil reacts with copper conductors to form cuprous sulfide deposits. These deposits lead to a decline in the performance of the transformer's oil-paper insulation and are suspected to be a cause of numerous transformer accidents both domestically and internationally, especially converter transformer accidents. Oil-paper insulation is highly susceptible to partial discharge under the combined effects of electrical, thermal, and mechanical forces, leading to a decrease in its insulation performance and even power outages. The cuprous sulfide deposits formed under the action of corrosive sulfur have been shown to exacerbate partial discharge, causing further insulation deterioration and hindering the long-term stable operation of the transformer.

[0003] Current research mainly focuses on the partial discharge characteristics of oil-paper insulation under different electric field environments, lacking relevant studies on the influence of cuprous sulfide deposition on these characteristics. Cuprous sulfide deposition exhibits strong dispersion, randomness, and a significant polarity effect, easily inducing partial discharge and posing a significant threat to insulation. As a factor influencing partial discharge, the impact of cuprous sulfide deposition on the space charge characteristics of insulating oil-paper requires further investigation, particularly the effects of different deposition locations, amounts, and penetration levels on space charge characteristics and spatial electric field distribution. This invention utilizes COMSOL simulation to simulate the transient partial discharge of cuprous sulfide deposition at different locations, obtaining data on space charge density, electric field intensity distribution, and temperature distribution during the partial discharge process. This is of great significance for the study of sulfur corrosion in oil-immersed transformers and for reducing the probability of transformer accidents. Summary of the Invention

[0004] The purpose of this invention is to provide a method for simulating partial discharge of oil-paper insulation under cuprous sulfide deposition. By simulating the partial discharge process of oil-paper insulation under cuprous sulfide deposition, the method calculates key data such as space charge distribution and electric field intensity distribution under transient conditions. This simulation model provides a reference for the impact of cuprous sulfide on the partial discharge characteristics of oil-immersed transformers in power grid systems, thereby reducing safety accidents caused by transformer insulation degradation due to cuprous sulfide deposition.

[0005] To achieve the above objectives, the present invention employs the following technical solution: a method for simulating partial discharge of oil-paper insulation under cuprous sulfide deposition, comprising the following steps:

[0006] Step 1: Establish a partial discharge geometric model of oil-paper insulation based on the finite element simulation software COMSOL Multiphysics, and set the deposition points of cuprous sulfide;

[0007] Step 2: Based on the geometric model, set the materials, physical fields and boundary conditions. Use the fluid dynamics model and the bipolar load cell transport model to describe the charge transport process of insulating oil and insulating paper respectively. Use the Ohm model to describe the charge transport characteristics of the oil-paper interface and the oil-cuprous sulfide deposition interface.

[0008] Step 3: Mesh the model and set the initial parameters, solver parameters, and voltage excitation;

[0009] Step 4: Perform transient calculations on the model to solve for the electric field distribution and charge distribution during the partial discharge process;

[0010] The partial discharge geometric model of the oil-paper insulation described in S1 is a needle-plate discharge geometry, wherein insulating paper is placed on the surface of the plate electrode, the cavity is filled with transformer oil, and cuprous sulfide deposits of different sizes and quantities are placed on the surface of the insulating paper, in the core of the insulating paper, and in the depression.

[0011] The fluid dynamics model in oil and the bipolar load sub-model in insulating paper described in S2 are as follows:

[0012] First, a fluid dynamics model in the oil is established: the current continuity equation and Poisson's equation are used to describe the generation, migration and dissipation of electrons and positive and negative ions in the oil, and the heat conduction equation is used to describe the temperature change in the oil.

[0013]

[0014]

[0015]

[0016]

[0017]

[0018] In the formula: ρ p ρ n and ρ e These represent the charge densities of positive ions, negative ions, and electrons in transformer oil, respectively; G I G D and G T These represent the rate of change in charge density caused by field ionization of oil molecules, dissociation of ion pairs in oil, and collisional ionization in oil, respectively; Rpe and R pn These are the recombination rates of positive ions and electrons, and positive ions and negative ions, respectively. τ is the electric field strength; a The time it takes for electrons to be adsorbed by molecules;

[0019]

[0020] Let be the field-induced ionization density generation rate. Field-related ionization refers to the ionization of neutral molecules into free positive ions and free electrons under the influence of an extremely strong electric field, where ... It is the ionization energy of the liquid phase;

[0021] Based on the hydrodynamic model in oil, a bipolar charge carrier transport model in paper is established: the charge density of each type of charge carrier is calculated using the continuity equation and Poisson equation of four types of particles: free electrons, trapped electrons, free holes and trapped holes.

[0022]

[0023]

[0024]

[0025]

[0026]

[0027] In the formula: ρ eμ ρ hμ ρ et and ρ ht These represent the charge densities of free electrons, free holes, trapped electrons, and trapped holes in the insulating paper, respectively; μ eμ and μ hμ S0, S1, S2, and S3 are the mobilities of free electrons and free holes, respectively; S0, S1, S2, and S3 are the recombination rates of trapped holes and trapped electrons, free holes and trapped electrons, respectively; B e B h D e and D h These are, respectively, electron trapping rate, hole trapping rate, electron detrapping rate, and hole trapping rate; N et0 and N ht0 These represent the maximum electron trap density and the maximum hole trap density.

[0028] The Ohm model is used to describe the charge transfer process between the oil paper interface.

[0029]

[0030] In the formula: ρ s σ is the interfacial charge density; μ0 is the charge mobility in the oil; σ p The paper conductivity;

[0031] The boundary conditions between cuprous sulfide deposition and transformer oil are as follows:

[0032]

[0033]

[0034] In the formula: σ s (t) represents the charge density at the interface between cuprous sulfide and transformer oil; and E represents the longitudinal and transverse electric field strengths on the surface of cuprous sulfide, respectively. ⊥oil and E oil (t) represents the longitudinal and transverse electric field strengths on the transformer oil surface, respectively;

[0035] S3 performs mesh generation on the model and sets initial parameters, boundary conditions, and voltage excitation;

[0036] Obtain the dielectric constant, microparticle mobility, oil mass density, oil thermal conductivity, oil electrical conductivity, oil specific heat capacity, microparticle recombination rate, and collision coefficient of the insulating oil and insulating paper in the oil-paper insulation model;

[0037] Based on the geometric model established in step S1, the model is meshed, voltage excitation is added to the surface of the needle electrode, and the surface of the plate electrode is grounded.

[0038] S4 performs transient calculations on the model to solve for the electric field distribution and charge distribution during the partial discharge process.

[0039] The changes in space charge distribution and electric field intensity distribution over time in the partial discharge model of oil-paper insulation under cuprous sulfide deposition were obtained. The results were post-processed to calculate the changes in the average and maximum values ​​of charge density and electric field intensity over time in the partial discharge model, and the positions of the maximum values ​​of charge density and electric field intensity were marked.

[0040] Compared to existing technologies, the advantages of this invention are as follows: This invention simulates the partial discharge process of oil-paper insulation under cuprous sulfide deposition, and calculates key data such as space charge density, electric field intensity distribution, and temperature distribution of the oil-paper insulation under transient conditions. This simulation model provides a reference for the mechanism of partial discharge caused by cuprous sulfide deposition in oil-immersed transformers in power grid systems, thereby reducing safety accidents caused by insulation degradation due to partial discharge. Attached Figure Description

[0041] Figure 1This is the overall flowchart of the present invention.

[0042] Figure 2 A geometric model for partial discharge in oil-paper insulation.

[0043] Figure 3 This is a partial square-sized view of the geometric model of cuprous sulfide deposited on the surface of insulating paper.

[0044] Figure 4 This is a magnified view of a partial geometric model of cuprous sulfide deposited in the recesses of insulating paper.

[0045] Figure 5 This is a magnified view of a partial geometric model of cuprous sulfide deposited in insulating paper.

[0046] Figure 6 This is a mesh partitioning diagram.

[0047] Figure 7 This is a diagram showing the voltage excitation applied to the needle electrode.

[0048] Figure 8 The average charge density of cuprous sulfide deposited on the surface of insulating paper varies with time.

[0049] Figure 9 The value of the electric field strength varies with time when cuprous sulfide is deposited on the surface of insulating paper. Detailed Implementation

[0050] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0051] Figure 1 This invention relates to a method for simulating partial discharge in oil-paper insulation under cuprous sulfide deposition, the steps of which are as follows:

[0052] Step S1: Establish a partial discharge geometric model of oil-paper insulation based on the finite element simulation software COMSOL Multiphysics, and set the deposition sites of cuprous sulfide;

[0053] Based on the needle-plate discharge geometric model in step 1, the surfaces, middle, and recesses of the insulating paper are identified as copper sulfide deposition sites.

[0054] Step S2: Based on the geometric model, set the materials, physical fields and boundary conditions. Use the fluid dynamics model and the bipolar load cell transport model to describe the charge transport process of insulating oil and insulating paper, respectively. Use the Ohm model to describe the charge transport characteristics of the oil-paper interface and the oil-cuprous sulfide deposition interface.

[0055] Step S3: Mesh the model, set the initial parameters, solver parameters and voltage excitation;

[0056] Obtain the dielectric constant, microparticle mobility, oil mass density, oil thermal conductivity, oil electrical conductivity, oil specific heat capacity, microparticle recombination rate, collision coefficient, and voltage excitation function of the insulating oil and insulating paper in the oil-paper insulation model.

[0057] Step S4: Perform transient calculations on the model to solve for the electric field distribution and charge distribution during the partial discharge process;

[0058] For each cuprous sulfide deposition site, the distance between the cuprous sulfide and the needle tip and the amount of cuprous sulfide deposition were varied to simulate the partial discharge process under cuprous sulfide deposition.

[0059] The geometric model in step S1 is as follows: Figure 2 As shown in (a), to save computational resources, sampling is as follows Figure 2 (b) Simulation calculations were performed using the two-dimensional axisymmetric model shown. The setting of cuprous sulfide deposition on the surface of the insulating paper is as follows: Figure 3 As shown, the geometric model of cuprous sulfide deposited in the insulating paper core is as follows: Figure 4 As shown, the geometric model of cuprous sulfide deposited in the recesses of insulating paper is as follows: Figure 5 As shown.

[0060] The fluid dynamics model in the oil described in step S2 uses the current continuity equation and Poisson's equation to describe the generation, migration and dissipation of electrons and positive and negative ions in the oil, and the heat conduction equation to describe the temperature change in the oil.

[0061]

[0062]

[0063]

[0064]

[0065]

[0066] In the formula: ρ p ρ n and ρ e These represent the charge densities of positive ions, negative ions, and electrons in transformer oil, respectively; G I G D and G T These represent the rate of change in charge density caused by field ionization of oil molecules, dissociation of ion pairs in oil, and collisional ionization in oil, respectively; R pe and R pn These are the recombination rates of positive ions and electrons, and positive ions and negative ions, respectively. τ is the electric field strength; a The time it takes for electrons to be adsorbed by molecules;

[0067]

[0068] Let be the field-induced ionization density generation rate. Field-related ionization refers to the ionization of neutral molecules into free positive ions and free electrons under the influence of an extremely strong electric field, where ... It is the liquid phase ionization energy.

[0069] Based on the hydrodynamic model in oil, a bipolar charge carrier transport model in paper is established: the charge density of each type of charge carrier is calculated using the continuity equation and Poisson equation of four types of particles: free electrons, trapped electrons, free holes and trapped holes.

[0070]

[0071]

[0072]

[0073]

[0074]

[0075] In the formula: ρ eμ ρ hμ ρ et and ρ ht These represent the charge densities of free electrons, free holes, trapped electrons, and trapped holes in the insulating paper, respectively; μ eμ and μ hμ S0, S1, S2, and S3 are the mobilities of free electrons and free holes, respectively; S0, S1, S2, and S3 are the recombination rates of trapped holes and trapped electrons, free holes and trapped electrons, respectively; B e B h D e and D h These are, respectively, electron trapping rate, hole trapping rate, electron detrapping rate, and hole trapping rate; N et0 and N ht0 These represent the maximum electron trap density and the maximum hole trap density.

[0076] The Ohm model is used to describe the charge transfer process between the oil paper interface.

[0077]

[0078] In the formula: ρ s σ is the interfacial charge density; μ0 is the charge mobility in the oil; σ p The paper conductivity;

[0079] The boundary conditions between cuprous sulfide deposition and transformer oil are as follows:

[0080]

[0081]

[0082] Where: σ s (t) represents the charge density at the interface between cuprous sulfide and transformer oil; and E represents the longitudinal and transverse electric field strengths on the surface of cuprous sulfide, respectively. ⊥oil and E oil (t) represents the longitudinal and transverse electric field strengths on the surface of the transformer oil, respectively.

[0083] Based on the partial discharge mathematical model established above, for example... Figure 3 (b) The partial discharge under the set cuprous sulfide deposition was simulated and calculated.

[0084] The specific parameters in the mathematical model in step two are shown in Table 1:

[0085] Table 1

[0086]

[0087]

[0088] The mesh is generated according to step S3, and the mesh division is as follows: Figure 6 As shown.

[0089] The voltage excitation of the needle electrode is set to simulate lightning impulse voltage, and the voltage waveform is as follows: Figure 7 As shown, the peak voltage U = 200kV and the simulation time t = 640ns.

[0090] According to model calculations, cuprous sulfide deposited on the surface, such as... Figure 3 (b) Change in average electric field intensity (e.g.) Figure 8 ) and changes in average charge density (e.g. Figure 9 ).

Claims

1. A method for simulating partial discharge in oil-paper insulation under cuprous sulfide deposition, characterized in that, The steps are as follows: Step S1: Establish a partial discharge geometric model of oil-paper insulation based on finite element simulation software, and set the deposition sites of cuprous sulfide; The partial discharge geometric model of the oil-paper insulation is a needle-plate discharge, wherein insulating paper is placed on the surface of the plate electrode, the cavity is filled with transformer oil, and cuprous sulfide deposition is set on the surface of the insulating paper, in the insulating paper, and in the depression. Step S2: Based on the geometric model, set the materials, physical fields and boundary conditions, and describe the charge transport process of insulating oil and insulating paper using the fluid dynamics model and the bipolar load cell transport model, respectively; The boundary conditions of the two models are combined using the Ohm model to describe the charge transfer process between the oil and paper interfaces, and the relationship is shown in Equation (1). (1) In the formula: ρ s For the interface charge density, μ 0 The charge mobility in oil, The paper conductivity; The boundary conditions between cuprous sulfide deposition and transformer oil are shown in equations (2) and (3); (2) (3) In the formula: This represents the charge density at the interface between cuprous sulfide and transformer oil. and These represent the longitudinal and transverse electric field intensities on the surface of cuprous sulfide, respectively. and These represent the longitudinal and transverse electric field strengths on the surface of the transformer oil, respectively. Step S3: Mesh the model, set the initial parameters, solver parameters and voltage excitation; During mesh generation, the mesh is refined in the tip discharge region and sparse in the outer region. The voltage excitation is a simulated lightning impulse voltage. Step S4: Perform transient calculations on the model to solve for the electric field distribution and charge distribution during the partial discharge process.

2. The method for simulating partial discharge of oil-paper insulation under cuprous sulfide deposition according to claim 1, characterized in that, The oil fluid dynamics model in step S2 includes: The generation, migration and dissipation of electrons and positive and negative ions in the oil are described by the current continuity equation and Poisson equation, and the temperature change in the oil is described by the heat conduction equation. The relationship is shown in equations (4) to (8). (4) (5) (6) (7) (8) In the formula: ρ p , ρ n and ρ e These represent the charge densities of positive ions, negative ions, and electrons in transformer oil, respectively. G I , G D and G T These represent the rate of change in charge density caused by field ionization of oil molecules, dissociation of ion pairs in oil, and collisional ionization in oil, respectively. R pe and R pn These represent the recombination rates of positive ions and electrons, and positive ions and negative ions, respectively. For electric field strength, τ a This represents the time it takes for electrons to be adsorbed by molecules. μ p , μ n and μ e These represent the mobilities of positive ions, negative ions, and electrons, respectively. q The amount of electron charge. ε 0 The vacuum permittivity, ε r Let be the relative permittivity of oil. ρ l The mass density of the oil, c v The specific heat capacity of oil, k T The value represents the thermal conductivity of oil.

3. The method for simulating partial discharge of oil-paper insulation under cuprous sulfide deposition according to claim 1, characterized in that, The bipolar payload subtransmission model in step S2 includes: The charge density of each type of charge is calculated using the continuity equation and Poisson equation for four types of particles: free electrons, trapped electrons, free holes, and trapped holes. (9) (10) (11) (12) (13) In the formula: , , and These represent the charge densities of free electrons, free holes, trapped electrons, and trapped holes in the insulating paper, respectively. and These are the mobilities of free electrons and free holes, respectively. , , and These are, respectively, the recombination rate of trapped holes and trapped electrons, the recombination rate of trapped holes and free electrons, and the recombination rate of free electrons and free holes. , , and These are, respectively, electron trapping rate, hole trapping rate, electron detrapping rate, and hole detrapping rate. and These represent the maximum electron trap density and the maximum hole trap density. ε 0 The vacuum permittivity, ε r is the relative permittivity of the insulating paper.

Images