Space charge numerical calculation method and system for oil paper insulation structure of converter transformer

Abstract

The invention relates to a space charge numerical calculation method and system of a converter transformer oil paper insulation structure. According to the method, firstly, key parameters of the oil paper insulation structure of the converter transformer are obtained, and a two-dimensional finite element simulation calculation domain is established according to the key parameters; defining constraint conditions in a two-dimensional finite element policy calculation domain, and establishing a liquid medium dynamic drift diffusion model as a space charge calculation model according to a Poisson equation and a carrier transport equation; and finally, under a constraint condition, performing non-uniform mesh generation on the model, solving a space charge calculation model, and outputting a space charge numerical value of the space charge calculation model. Compared with the prior art, the method has the advantages that the space charge distribution condition at the insulating oil paper interface can be accurately restored in the operation process of the converter transformer when the polarity of an electric field is reversed under the microscopic view angle of charge transport characteristics of different voltage waveforms, and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of insulation performance of electrical equipment, and in particular to a method and system for numerically calculating space charge of an oil-paper insulation structure of a converter transformer. Background Art

[0002] With the continuous progress and development of UHV DC transmission technology, the requirements of power systems are becoming more and more complex and demanding. In UHV DC transmission systems, converter transformers not only undertake the important function of power conversion, but also play an important role in isolating current and voltage and ensuring the stability and reliability of power transmission. Therefore, the insulation system of the converter transformer directly affects the safe operation of the entire power system. The converter transformer works under high voltage and high current conditions for a long time, and its insulation system must have high reliability and durability. Any insulation failure may cause serious system accidents or shutdowns, bringing great risks to power supply and equipment safety. In addition, the operating environment of the converter transformer is more complex than that of ordinary transformers, including operating environments of various voltage conditions such as AC and DC. Especially under DC voltage, it is more likely to cause charge accumulation. When the electric field reverses its polarity due to changes in the working environment, the sudden electric field is superimposed on the space charge, which greatly reduces the insulation performance of the oil-paper interface and is more likely to cause surface flashover, causing irreparable damage to the equipment. Therefore, how to prevent system failures caused by deterioration or damage of insulating materials has become one of the core issues that the power industry needs to solve urgently.

[0003] In the insulation system of converter transformers, insulating materials such as transformer oil and insulating paper are widely used and are the main insulating media. Due to their excellent electrical properties, high voltage resistance and good thermal stability, they can effectively suppress the accumulation of space charge in the electric field under high voltage and high current environments, thereby improving the insulation performance of the transformer. The accumulation of space charge is a key factor affecting the electrical strength of oil-paper insulation materials, and is also the main cause of aging, performance degradation and eventual flashover breakdown of insulation materials. Space charge accumulates inside or at the interface of oil-paper insulation during the operation of the transformer. These accumulated space charges will change the electric field distribution, leading to the strengthening of the local electric field, thereby greatly increasing the risk of local breakdown of the insulating material. The presence of space charge may not only lead to insulation failure of the transformer, but also affect the stability and safety of the entire power system.

[0004] Therefore, it is crucial to deeply understand the distribution and accumulation mechanism of space charge in transformer oil-paper insulation materials for the insulation structure design of converter transformers. Existing research mainly focuses on observing the electrical properties of oil-paper insulation materials through experiments. However, since experiments are usually conducted over a long time scale, it is difficult to fully and accurately reveal the distribution characteristics and evolution process of space charge in oil-paper insulation. Especially in a short time of micro-nanoseconds, the electric field distribution and the dynamic changes of space charge are difficult to directly observe and measure. This makes the traditional experimental method face certain limitations and cannot provide sufficient theoretical basis and data support. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a method and system for numerical calculation of space charge of oil-paper insulation structure of converter transformer.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] According to one aspect of the present invention, a method for numerically calculating space charge of an oil-paper insulation structure of a converter transformer is provided, the method comprising the following steps:

[0008] S1. Obtain key parameters of the oil-paper insulation structure of the converter transformer, and establish its two-dimensional finite element simulation calculation domain according to the key parameters;

[0009] S2. In the two-dimensional finite element method calculation domain, define the constraint conditions, and establish the liquid medium dynamic drift diffusion model as the space charge calculation model according to the Poisson equation and the carrier transport equation;

[0010] S3. Under the constraint conditions, the model is non-uniformly meshed, and the space charge calculation model is solved to output its space charge value.

[0011] As a preferred technical solution, the key parameters in S1 include geometric parameters, electrostatic numbers and operating condition parameters; among them, the geometric parameters include the length, width, thickness and height of the oil-paper insulation interface of the insulating structure; the electrostatic parameters include dielectric constant and carrier transport parameters; the operating condition parameters include operating temperature, applied voltage polarity, voltage waveform and voltage amplitude.

[0012] As a preferred technical solution, the liquid medium dynamic drift diffusion model in S2 includes the dynamic behaviors of electrons and positive and negative ions. When the model is numerically calculated, the behavior process of each charge is processed.

[0013] As a preferred technical solution, the behavior process of each charge is processed, specifically, the combined, generated, diffused and drifted processes of the charge are processed simultaneously using a coupled drift-diffusion equation group.

[0014] As a preferred technical solution, the coupled drift diffusion equation group includes the yield equations of three carriers: electrons, positive ions and negative ions, the equations for coupling the electric field and space charge of the three carriers through Gauss's law, the field-mass ionization process equations of electrons and positive ions in the liquid space, and the recombination equation of positive ions and electrons. The specific formula is:

[0015]

[0016] In the formula, ρ e is electron; p is a positive ion; n is a negative ion; rp , ε0, ε ro is the dielectric constant; μ e , μ n , μ n are the mobility of electrons, positive ions, and negative ions, respectively; G is the generation rate; E is the electric field strength; q is the electron charge; R pe , R pn Represent the recombination rates of positive ions and electrons, positive ions and negative ions, respectively, satisfying Langevin's law; m * is the effective mass; n0 is the equilibrium carrier concentration; a is the structural parameter; τ a is the time when electrons are adsorbed by molecules to become negative ions; G1 is the charge generation source term of strong field ionization, ρ e / T a It is the process of electrons adsorbing on neutral molecules to form negative ions.

[0017] As a preferred technical solution, the constraints in S2 are interface conditions and boundary conditions, specifically including the oil-paper insulation interface, the conductivity of oil and paper, and the boundary voltage conditions.

[0018] As a preferred technical solution, the network segmentation in S3 specifically uses triangular units and performs adaptive meshing through a nonlinear algorithm and a generalized α-time domain method.

[0019] As a preferred technical solution, the specific process of solving the space charge calculation model in S3 is:

[0020] S31, setting initial charge distribution, temperature, and electric field;

[0021] S32, discretizing the time by the difference method, and gradually advancing the change of the charge distribution according to the discretized time;

[0022] S33. Discretize the spatial domain using the finite element method or the finite difference method to solve for the electric field, the concentrations of electrons and holes;

[0023] S34, return to step S31, continuously iterate and solve the Poisson equation and the carrier transport equation until the solution converges, and output it.

[0024] As a preferred technical solution, the space charge values ​​in S3 include electric field, space charge density, and corresponding voltage and current characteristics.

[0025] According to another aspect of the present invention, a system for numerical calculation of space charge of oil-paper insulation structure of converter transformer is provided, the system works by applying the above-mentioned method for numerical calculation of space charge of oil-paper insulation structure of converter transformer, the system comprises a calculation domain establishment module, a model establishment module and a model solving module;

[0026] Among them, the calculation domain establishment module is used to obtain the key parameters of the oil-paper insulation structure of the converter transformer, and establish its two-dimensional finite element simulation calculation domain based on the key parameters; the model establishment module is used to define constraints in the two-dimensional finite element simulation domain, and establish a liquid medium dynamic drift diffusion model as a space charge calculation model based on the Poisson equation and the liquid medium drift diffusion equation; the model solving module is used to perform non-uniform grid division on the model under constraints, solve the space charge calculation model, and output its space charge value.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. In the present invention, the key parameters of the oil-paper insulation structure of the converter transformer are first obtained, and its two-dimensional finite element simulation calculation domain is established according to the key parameters; then, in the two-dimensional finite element simulation calculation domain, the constraint conditions are defined, and the liquid medium dynamic drift diffusion model is established as the space charge calculation model according to the Poisson equation and the carrier transport equation; finally, under the constraint conditions, the model is non-uniformly meshed, and the space charge calculation model is solved to output its space charge value. This enables it to accurately restore the space charge distribution at the insulation oil-paper interface when the polarity of the electric field is reversed during the operation of the converter transformer under the microscopic perspective of the charge transport characteristics of different voltage waveforms.

[0029] 2. In the present invention, the model is non-uniformly meshed, specifically using triangular units, and adaptively meshed by nonlinear algorithms and generalized α time domain methods. While reducing computing resources, the dynamic propagation processes such as the drift and diffusion of electrons and positive and negative charges are accurately simulated, which is helpful for analyzing the insulation failure mechanism caused by the space charge effect at the oil-paper insulation interface and deepening the theoretical understanding of the flashover along the liquid-solid interface.

[0030] 3. The key parameters in the present invention include geometric parameters, electrostatic numbers and operating condition parameters; wherein, the geometric parameters include the length, width, thickness of the insulation structure and the height of the oil-paper insulation interface; the electrostatic parameters include the dielectric constant and the carrier transport parameters; the operating condition parameters include the operating temperature, the polarity of the applied voltage, the voltage waveform and the voltage amplitude. By constructing a numerical calculation model of the space charge of the oil-paper insulation structure of the converter transformer with key parameters, and simulating the distribution and evolution of the space charge of the oil-paper insulation interface at the micro-nanosecond time scale under the influence of factors such as the degree of aging of different insulation materials, voltage polarity reversal, and the thickness of the insulation paper material based on the finite element method, it is helpful to analyze the insulation failure mechanism of the converter transformer under long-term operating temperature, which is of great significance to the optimization of the insulation structure of the oil-filled equipment and provides a basis for industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the steps of a method for numerically calculating space charge of an oil-paper insulation structure of a converter transformer in the present invention;

[0032] Figure 2a Schematic diagram of the geometric model of the insulating oil paper of the oil-paper insulation structure of the converter transformer in the embodiment;

[0033] Figure 2b A schematic diagram of grid division of the insulating oil paper of the oil-paper insulation structure of the converter transformer in the embodiment;

[0034] Figure 3 is the polarity reversal voltage waveform in the embodiment;

[0035] Figure 4a Schematic diagram of the change of space charge value in the oil-paper insulation structure when the time is 40ms in the embodiment;

[0036] Figure 4b Schematic diagram of the change of space charge value in the oil-paper insulation structure when the time is 340ms in the embodiment;

[0037] Figure 4c Schematic diagram of the change of space charge value in the oil-paper insulation structure when the time is 380ms in the embodiment;

[0038] Figure 4d Schematic diagram of the change of space charge value in the oil-paper insulation structure when the time is 420ms in the embodiment;

[0039] Figure 4e Schematic diagram of the change of space charge value in the oil-paper insulation structure when the time is 720ms in the embodiment;

[0040] Figure 5 It is a schematic diagram of the numerical change of the charge distribution along the axial direction of the oil-paper insulation structure in the embodiment. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0042] With the continuous progress and development of UHV DC transmission technology, the requirements of power systems are becoming more and more complex and stringent, especially for the insulation system of the core equipment, the converter transformer, which has higher safety and stability requirements. In the UHV DC transmission system, the converter transformer not only undertakes the important function of power conversion, but also plays an important role in isolating current and voltage and ensuring the stability and reliability of power transmission. Therefore, the insulation system of the converter transformer directly affects the safe operation of the entire power system. Since the converter transformer works under high voltage and high current conditions for a long time, its insulation system must have a high degree of reliability and durability. Any insulation failure may cause serious system accidents or shutdowns, posing great risks to power supply and equipment safety. Therefore, how to prevent system failures caused by deterioration or damage of insulation materials has become one of the core issues that the power industry needs to solve urgently.

[0043] In addition, the operating environment of the converter transformer is more complex than that of an ordinary transformer, including operating environments with various voltage conditions such as AC and DC. Especially under DC voltage, charge accumulation is more likely to occur. When the electric field reverses polarity due to changes in the working environment, the sudden change in the electric field is superimposed on the space charge, which greatly reduces the insulation performance of the oil-paper interface and makes surface flashover more likely to occur, causing irreparable damage to the equipment.

[0044] In the insulation system of converter transformers, insulating materials such as transformer oil and insulating paper are widely used and are the main insulating media. Due to their excellent electrical properties, high voltage resistance and good thermal stability, they can effectively suppress the accumulation of space charge in the electric field under high voltage and high current environments, thereby improving the insulation performance of the transformer. The accumulation of space charge is a key factor affecting the electrical strength of oil-paper insulation materials, and is also the main cause of aging, performance degradation and eventual flashover breakdown of insulation materials. Space charge accumulates inside or at the interface of oil-paper insulation during the operation of the transformer. These accumulated space charges will change the electric field distribution, leading to the strengthening of the local electric field, thereby greatly increasing the risk of local breakdown of the insulating material. The presence of space charge may not only lead to insulation failure of the transformer, but also affect the stability and safety of the entire power system.

[0045] Therefore, it is crucial to deeply understand the distribution and accumulation mechanism of space charge in transformer oil-paper insulation materials for the insulation structure design of converter transformers. The accumulation of space charge is closely related to factors such as electric field distribution, electrical conductivity of oil-paper materials, and temperature distribution. Existing research mainly focuses on observing the electrical properties of oil-paper insulation materials through experiments, but because experiments are usually conducted over a long time scale, it is difficult to fully and accurately reveal the distribution characteristics and evolution process of space charge in oil-paper insulation. Especially in short time scales at the micro-nanosecond level, the electric field distribution and the dynamic changes of space charge are difficult to directly observe and measure. This makes traditional experimental methods face certain limitations and cannot provide sufficient theoretical basis and data support.

[0046] In order to solve this problem, computer simulation and finite element analysis technology have become an effective means to study the spatial charge distribution of oil-paper insulation. Through simulation, the distribution of spatial charge in the oil-paper insulation structure can be accurately calculated at the micro-nanosecond scale, and the influence of changes in environmental factors such as electric field and temperature on the accumulation of spatial charge can be simulated. Finite element simulation can provide researchers with more detailed electric field distribution, spatial charge accumulation and its influence mechanism on insulation performance, thereby providing theoretical support for the insulation design of converter transformers. It can not only reveal the accumulation law of spatial charge under different working conditions, but also effectively predict possible insulation failure locations and discharge characteristics, providing a scientific basis for subsequent insulation structure optimization.

[0047] Example 1

[0048] Reference Figure 1 , a numerical calculation method for space charge of oil-paper insulation structure of converter transformer, the method comprising a simulation system;

[0049] S1: Model parameter input: Load the two-dimensional geometric parameters of the oil-paper insulation structure of the converter transformer, and establish a two-dimensional finite element simulation calculation domain based on the actual engineering operating conditions of the equipment and the electrostatic parameters and physical parameters of the oil-paper insulation material.

[0050] S2: Setting of interface and boundary conditions: Setting appropriate boundary and interface conditions, including oil-paper insulation interface, conductivity of oil and paper, boundary voltage conditions, etc., to ensure the accuracy and rationality of calculation. In the calculation process, the heterogeneity of the oil-paper composite medium and the difference in electrical properties of each layer of medium are considered.

[0051] S3: Finite element meshing: According to the two-dimensional geometric parameters and material properties of the model input, the Delaunay triangulation algorithm is used to non-uniformly divide the two-dimensional area to meet the calculation requirements of the results.

[0052] S4: Numerical solution and iterative calculation: Numerical solution is performed on the established mathematical model, and the electric field, space charge density, and corresponding voltage and current characteristics are gradually solved through iterative methods.

[0053] In this embodiment, the key parameters include geometric parameters, electrostatic parameters and operating condition parameters; wherein the geometric parameters include the length, width, thickness and height of the oil-paper insulation interface of the insulating structure; the electrostatic parameters include the dielectric constant and the carrier transport parameters; the operating condition parameters include the operating temperature, the applied voltage polarity, the voltage waveform and the voltage amplitude.

[0054] In this embodiment, the liquid medium dynamic drift diffusion model includes the drift diffusion behaviors of electrons, negative charges and positive charges. When the model is numerically calculated, the behavior process of each charge is processed.

[0055] In this embodiment, the behavior process of each charge is processed, specifically, the combined, generated, diffused and drifted processes of the charge are processed simultaneously using a coupled drift-diffusion equation group. The constraints are interface conditions and boundary conditions, specifically including the oil-paper insulation interface, the conductivity of the oil and paper, and the boundary voltage conditions. The network partitioning is specifically to use triangular units, and to perform adaptive meshing through nonlinear algorithms and generalized α time domain methods. The specific process of solving the spatial charge calculation model is: setting the initial charge distribution, temperature, and electric field; then discretizing the time by the difference method, and gradually advancing the change of the charge distribution according to the discretized time; then using the finite element method or the finite difference method, discretizing the space domain to solve the concentration of the electric field, electrons, positive and negative charges; then returning to the step, continuously iterating and solving the Poisson equation and the carrier transport equation until the solution converges and outputs it. The spatial charge values ​​include the electric field, spatial charge density, and the corresponding voltage and current characteristics.

[0056] In this embodiment, the movement behavior of the charges in the insulating oil can be accurately described by means of simulation, which provides important data support and theoretical basis for the numerical calculation of space charges.

[0057] In this embodiment, the key geometric parameters include the length and thickness of the insulating paperboard, the height of the oil-paper insulation interface; the electrostatic parameters and physical parameters of the oil-paper insulation material, including the dielectric constant, the carrier transport parameters, etc.; the operating condition parameters include the operating temperature, the polarity of the applied voltage, the voltage waveform, the voltage amplitude, etc.; the geometric model of the oil-paper insulation structure of the converter transformer is shown in FIG2, and the grid division of the oil-paper insulation structure of the converter transformer is shown in FIG. Figure 3 shown.

[0058] In this embodiment, the transport of electrons, positive charges, and negative charges follows similar drift-diffusion equations, and because of their mutual influence, they usually need to be considered simultaneously. The charge recombination, generation, diffusion, and drift processes must be processed simultaneously during numerical calculations, and a common processing method is to use a coupled drift-diffusion equation group.

[0059] In this embodiment, the coupled drift diffusion equations include the yield equations of three types of carriers: electrons, positive ions, and negative ions; the equations for coupling the electric field with the space charge through Gauss's law for the three types of carriers; the field-mass ionization process equations for electrons and positive ions in the liquid space; and the recombination equations for positive ions and electrons. e 、Positive ion ρ p 、Negative ion ρ n The three charges are the charge sources of the space charge. The three carriers couple the electric field with the space charge through Gauss's law. The continuity equation represents the yield of the three carriers. The movement of the carriers is the key to the generation of streamers, which explains the generation and capture mechanism of the charge. G(E) represents the field-mass ionization process of electrons and positive ions in the liquid space. R pe and R pn Represent the recombination process of positive ions and electrons, and the recombination process of positive ions and negative ions, respectively. e / T a It refers to the process of electrons being adsorbed on neutral molecules to form negative ions.

[0060] The coupled drift diffusion equation group includes the yield equations of three carriers: electrons, positive ions and negative ions, the equations for coupling the electric field with the space charge by the three carriers through Gauss's law, the field-mass ionization process equations of electrons and positive ions in the liquid space, and the recombination equation of positive ions and electrons. The specific formula is:

[0061]

[0062]

[0063] In the formula, ρ e is electron; p is a positive ion; n is a negative ion; rp , ε0, ε ro is the dielectric constant; μ e , μ n , μ n are the mobility of electrons, positive ions, and negative ions, respectively; G is the generation rate; E is the electric field strength; q is the electron charge; R pe , R pn Represent the recombination rates of positive ions and electrons, positive ions and negative ions, respectively, satisfying Langevin's law; m *is the effective mass; n0 is the equilibrium carrier concentration; a is the structural parameter; τ a is the time when electrons are adsorbed by molecules to become negative ions; G1 is the charge generation source term of strong field ionization, ρ e / T a It is the process of electrons adsorbing on neutral molecules to form negative ions.

[0064] In this embodiment, the total conduction current in the liquid medium is:

[0065]

[0066] In this embodiment, the solid medium is considered as a fixed conductivity region. The total conduction current J in the solid medium s :

[0067]

[0068] Among them, the electric field distribution is calculated by Poisson's equation and Laplace's equation:

[0069]

[0070] Where E is the electric field strength, is the electric potential, ρ is the space charge density, and ε is the relative dielectric constant.

[0071] In this embodiment, the model is iteratively calculated and solved according to the constraint equations and non-uniform meshing defined in the model, and the output result is returned.

[0072] In this embodiment, the numerical solution of the bipolar charge transport model includes the following steps:

[0073] Initialization: setting initial conditions, including charge distribution, temperature, electric field, etc.;

[0074] Time stepping: Discretize time through the difference method and gradually advance the change of charge distribution;

[0075] Spatial discretization: Use the finite element method or finite difference method to discretize the spatial domain and solve for the electric field, electron and hole concentrations;

[0076] Iterative solution: Iteratively solves the Poisson equation, continuity equation and drift-diffusion equations until convergence;

[0077] In this embodiment, the data output module is used to manage the calculation results returned by the model solution, including the electric field value and space charge development at each moment, and convert the simulation data into a visual form that is easy to analyze.

[0078] In this embodiment, if Figure 3 Figure 4 Figure 5As shown, Figure 5 In the figure, the blue, green, red, cyan, and purple lines represent the numerical changes of the charge distribution along the axial direction of the oil-paper insulation structure at 40ms, 340ms, 380ms, 420ms, and 720ms, respectively. The model solving and data output module is used to establish a model building module that meets the actual size using COMSOL Multiphysics software, which is used to build a two-dimensional geometric model of the oil-paper insulation structure and construct a finite element simulation model based on the electrostatic field and coefficient form partial differential equations.

[0079] In this embodiment, the network is divided using triangular elements and adaptively meshed by a nonlinear algorithm and a generalized α-time domain method;

[0080] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for numerically calculating the space charge of an oil-paper insulation structure of a converter transformer, characterized in that: The method comprises the following steps: S1. Obtain key parameters of the oil-paper insulation structure of the converter transformer, and establish its two-dimensional finite element simulation calculation domain according to the key parameters; S2. In the two-dimensional finite element simulation calculation domain, define the constraint conditions, and establish the liquid medium dynamic drift diffusion model as the space charge calculation model according to the Poisson equation and the carrier transport equation; S3. Under the constraint conditions, the space charge calculation model is non-uniformly meshed, and the space charge calculation model is solved to output its space charge value.

2. The method for numerically calculating the space charge of the oil-paper insulation structure of a converter transformer according to claim 1 is characterized in that: The key parameters in S1 include geometric parameters, electrostatic parameters and operating condition parameters; wherein the geometric parameters include the length, width, thickness and height of the oil-paper insulation interface of the insulation structure; the electrostatic parameters include the dielectric constant and the carrier transport parameters; the operating condition parameters include the operating temperature, the applied voltage polarity, the voltage waveform and the voltage amplitude.

3. The method for numerically calculating space charge of oil-paper insulation structure of converter transformer according to claim 1 is characterized in that: The liquid medium dynamic drift diffusion model transport model in S2 includes the transport behaviors of electrons, i.e., negative charges, and holes, i.e., positive charges. When the model is numerically calculated, the behavior process of each charge is processed.

4. The method for numerically calculating space charge of oil-paper insulation structure of converter transformer according to claim 3 is characterized in that: The processing of the behavior process of each charge is specifically to use a coupled drift-diffusion equation group to simultaneously process the recombination, generation, diffusion and drift processes of the charges.

5. The method for numerically calculating space charge of oil-paper insulation structure of converter transformer according to claim 4 is characterized in that: The coupled drift diffusion equation group includes the yield equations of three types of carriers: electrons, positive ions and negative ions, the equations for coupling the electric field with the space charge by the three types of carriers through Gauss's law, the field-mass ionization process equations of electrons and positive ions in the liquid space, and the recombination equation of positive ions and electrons. The specific formula is: In the formula, ρ e is electron; p is a positive ion; n is a negative ion; rp , ε0, ε ro is the dielectric constant; μ e , μ n , μ n are the mobility of electrons, positive ions, and negative ions, respectively; G is the generation rate; E is the electric field strength; q is the electron charge; R pe , R pn Represent the recombination rates of positive ions and electrons, positive ions and negative ions, respectively, satisfying Langevin's law; m * is the effective mass; n0 is the equilibrium carrier concentration; a is the structural parameter; τ a is the time when electrons are adsorbed by molecules to become negative ions; G1 is the charge generation source term of strong field ionization, ρ e / T a It is the process of electrons adsorbing on neutral molecules to form negative ions.

6. The method for numerically calculating space charge of oil-paper insulation structure of converter transformer according to claim 1, characterized in that: The constraints in S2 are interface conditions and boundary conditions, specifically including oil-paper insulation interface, conductivity of oil and paper, and boundary voltage conditions.

7. The method for numerically calculating space charge of oil-paper insulation structure of converter transformer according to claim 1, characterized in that: The network segmentation in S3 is specifically to use triangular units, and to perform adaptive meshing through a nonlinear algorithm and a generalized α time domain method.

8. The method for numerically calculating space charge of oil-paper insulation structure of converter transformer according to claim 1, characterized in that: The specific process of solving the space charge calculation model in S3 is: S31, setting initial charge distribution, temperature, and electric field; S32, discretizing the time by the difference method, and gradually advancing the change of the charge distribution according to the discretized time; S33. Discretize the spatial domain using the finite element method or the finite difference method to solve for the electric field, the concentrations of electrons and holes; S34, return to step S31, continuously iterate and solve the Poisson equation and the liquid medium drift-diffusion equation until the solution converges, and output it.

9. The method for numerically calculating space charge of oil-paper insulation structure of converter transformer according to claim 1, characterized in that: The space charge values ​​in S3 include electric field, space charge density, and corresponding voltage and current characteristics.

10. A space charge numerical calculation system for oil-paper insulation structure of converter transformer, characterized in that: The system applies the space charge numerical calculation method of the oil-paper insulation structure of the converter transformer as described in claims 1-9, and the system includes a calculation domain establishment module, a model establishment module and a model solution module; The calculation domain establishment module is used to obtain key parameters of the oil-paper insulation structure of the converter transformer and establish its two-dimensional finite element simulation calculation domain according to the key parameters; The model building module is used to define constraint conditions in a two-dimensional finite element method calculation domain, and to establish a liquid medium dynamic drift diffusion model as a space charge calculation model based on the Poisson equation and the carrier transport equation; The model solving module is used to perform non-uniform grid division on the model under constraint conditions, solve the space charge calculation model, and output its space charge value.

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