A method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths

Abstract

The present invention discloses a method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths, including: constructing a one-dimensional simulation model according to the actual structure of a target epoxy resin composite insulating material; constructing a spatial charge dissipation characteristics model of randomly distributed trap densities at different depths according to the constructed one-dimensional simulation model; simulating the spatial charge dissipation characteristics model of randomly distributed trap densities at different depths to obtain the spatial charge distribution of the target epoxy resin composite insulating material after decompression. The method predicts the spatial charge dissipation process of epoxy resin composite insulating materials based on the random distribution of energy of trap densities at different depths, thereby providing assistance for subsequent research on the influence of the internal electrical distribution and behavioral characteristics of epoxy composite materials after decompression on the insulating properties of epoxy composite materials.

Description

Technical Field

[0001] The invention relates to the technical field of insulation status evaluation of power equipment, and more particularly to a method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths. Background Art

[0002] Energy issues are a major strategic issue related to the overall economic and social development. my country's energy resources and productivity development are inversely distributed: the northwest and southwest regions have rich energy reserves but low load, while the eastern region has a developed economy, high energy consumption, but very scarce resources. As China's industrialization and urbanization process continues to accelerate, electricity demand continues to grow, and the demand for energy and electricity will continue to grow for a long time.

[0003] As a key component in UHV DC transmission projects, UHV bushings are the throat of equipment such as the inlet and outlet lines of the converter station valve hall and the converter transformer. Epoxy impregnated paper DC dry bushings are increasingly used in UHV DC transmission systems, and their insulation reliability will be directly related to the safety and stability of the Northwest UHV DC transmission project. In addition to the need to withstand AC, DC, and AC / DC superimposed voltages during operation, the internal current-carrying conductors of DC dry bushings need to pass several kA of harmonic-rich commutation currents.

[0004] The accumulation, dissipation and migration of space charge will cause a series of changes in the electric field in the dielectric. Especially when the insulation is subjected to the combined effects of electricity, heat and force, the space charge effect will be more prominent, causing electric field distortion, partial discharge and even breakdown, which will eventually accelerate the aging of the insulation material and lead to insulation failure of the bushing. min ~Δ max Within the trap depth range, the trap density at different depths is uniformly distributed according to the energy. However, there are few simulation studies on trap density at different depths according to the random distribution of energy.

[0005] Therefore, how to predict the spatial charge dissipation process of epoxy resin composite insulating materials based on the random distribution of energy at different depth trap densities, so as to provide support for subsequent research on the influence of internal electrical distribution and behavioral characteristics of epoxy composite materials after decompression on the insulating properties of epoxy composite materials, is an urgent problem that technicians in this field need to solve. Summary of the invention

[0006] In view of the above problems, the present invention provides a method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths, so as to at least solve some of the technical problems mentioned in the above background technology.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths, characterized by comprising the following steps:

[0009] S1. Construct a one-dimensional simulation model according to the actual structure of the target epoxy resin composite insulation material;

[0010] S2. Based on the constructed one-dimensional simulation model, a spatial charge dissipation characteristic model with randomly distributed trap densities at different depths is constructed;

[0011] S3. Simulate the spatial charge dissipation characteristic model of randomly distributed trap densities at different depths to obtain the spatial charge distribution of the target epoxy resin composite insulating material after decompression.

[0012] Furthermore, the step S2 specifically includes:

[0013] S21. Based on the constructed one-dimensional simulation model, the relationship between charge trapping and charge detrapping, charge transport, and the relationship between charge recombination and electric field is combined to establish the relationship between the electric field and the charge dissipation characteristics of the internal space of the medium;

[0014] S22, add physical fields to simulate charge trapping, charge detrapping, charge injection, charge extraction and charge recombination inside the medium;

[0015] S23. Add the physical parameters of the target epoxy resin composite insulating material, add boundary conditions in the physical field based on the bipolar carrier transport model, hopping conductivity model and Schottky's law, and combine the current space charge dissipation model to obtain the space charge dissipation characteristic model with random distribution of trap density at different depths.

[0016] Furthermore, the space charge dissipation characteristics inside the medium include: trap density, carrier density, current density and carrier mobility.

[0017] Furthermore, the physical field includes an electrostatic field and a dilute species transfer field.

[0018] Furthermore, in step S21, a mutually coupled equation group consisting of a current continuity equation, a conduction equation, and a Poisson equation for electrostatic field is used to describe the relationship between charge trapping and charge detrapping, charge transport, and the relationship between charge recombination and the electric field, which is expressed as:

[0019]

[0020] Where x represents the position of the one-dimensional simulation model; j c(e) (x, t) represents the electron current density at position x in the conduction band and valence band at time t; j c(h) (x, t) represents the hole current density at position x in the conduction band and valence band at time t; q free(e)(x, t) represents the electron carrier density at position x at time t; q free(h) (x, t) represents the hole carrier density at position x at time t; μ 0(e) Represents the carrier mobility of electrons in dielectrics; μ 0(h) represents the carrier mobility of holes in the dielectric; q trap(e) represents the capture density of electrons; q trap(h) represents the capture density of holes; S e represents the electron charge capture-capture-recombination coefficient; S h represents the charge capture-trapping-recombination coefficient of holes; E(x,t) represents the electric field intensity at position x at time t before decompression; q net represents the net charge density; ε0 represents the vacuum dielectric constant, ε r represents the relative dielectric constant;

[0021] Furthermore, the electron charge capture-recruitment coefficient S e Including parameters of free electrons and free electrons, as well as parameters of free electrons and captured electrons; the charge capture-capture-recombination coefficient S of holes h Including parameters of free electrons and free holes, as well as parameters of free electrons and captured holes; specifically expressed as:

[0022]

[0023] Among them, S eμ Represents the parameters of free electrons and free electrons, S et Represents the parameters of free electrons and trapped electrons; S hμ Represents the parameters of free electrons and free holes, S ht represents the parameters of free electrons and trapped holes; P tr(e) represents the capture coefficient of free electrons; P de(e) represents the capture coefficient of free holes; q trap(e) represents the capture density of electrons; q trap(h) represents the hole capture density; N T(e) Represents the electron trap density concentration; N T(e) represents the hole trap density concentration; R eμ,ht represents the trap recombination coefficient between free electrons and trapped holes; R et,hμ represents the trap recombination coefficient between trapped electrons and free holes; R eμ,hμ represents the recombination coefficient between free electrons and free holes; q e Indicates the amount of charge.

[0024] Furthermore, in step S23, the boundary conditions include: injection of electrons and holes, extraction of electrons and holes, and carrier mobility; specifically, they are expressed as:

[0025] (1) For the injection of electrons and holes, the bipolar carrier transport model assumes that the carriers are injected from the electrodes according to the Schottky law; it can be expressed as:

[0026]

[0027] Among them, j in(e) represents the cathode injection current density; j in(h) represents the anode injection current density; N C represents the state density of the conduction band; N V represents the state density of the valence band; q e represents the charge, q e =1.6×10 -19 C; μ C represents the carrier mobility in the conduction band; μ V represents the carrier mobility in the valence band; k represents the Boltzmann constant; T represents the thermodynamic temperature; ω e represents the electron injection barrier; ω h represents the hole injection barrier; ψ represents the parameter that changes with the electric field; E(x,t) represents the electric field intensity at position x at time t; f represents the reduction electric field;

[0028] (2) The extraction of electrons and holes complies with Schottky's law, which is expressed as:

[0029]

[0030] Among them, j ex (e) represents the cathode extraction current density; j ex (h) represents the anode injection current density; ω -e represents the electron extraction barrier; ω -h represents the hole extraction barrier;

[0031] (3) Charge migration in shallow traps is considered to be a jumping process. Based on the jumping conductivity model, the carrier mobility is expressed as:

[0032]

[0033] Where μ represents the carrier mobility; d represents the distance between shallow traps; v represents the detrapping frequency; ω μ represents the jump barrier height, which is consistent with the shallow trap depth; E d (x, t) represents the electric field strength at position x at time t after the pressure is removed.

[0034] Furthermore, the spatial charge dissipation characteristic model of the randomly distributed trap densities at different depths is expressed as:

[0035]

[0036] Among them, E d represents the electric field intensity after depressurization; x represents the position of the one-dimensional simulation model; t represents the time t; x1 represents the cathode position; x2 represents the anode position; q e represents the charge; N(t) represents the trap density; k represents the Boltzmann constant; T represents the thermodynamic temperature; v represents the frequency required for detrapping; ε0 represents the vacuum dielectric constant; ε r Represents the relative dielectric constant; Y min =exp(-Δ max / kT), Y max =exp(-Δ min / kT), Δ max Indicates the deepest trap depth in the one-dimensional simulation model; Δ min represents the shallowest trap depth in the one-dimensional simulation model; E1(·) represents the integral including the exponential function.

[0037] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method for predicting the spatial charge dissipation characteristics of randomly distributed trap densities at different depths, including the following beneficial effects: the present invention is based on the random distribution of energy at trap densities at different depths, thereby realizing the prediction of the spatial charge dissipation process of epoxy resin composite insulating materials, thereby providing assistance for subsequent research on the influence of the internal electrical distribution and behavioral characteristics of epoxy composite materials after decompression on the insulating properties of epoxy composite materials.

[0038] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention.

[0039] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0041] Figure 1 A schematic flow chart of a method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths provided by an embodiment of the present invention.

[0042] Figure 2 A schematic diagram of a one-dimensional simulation model provided by an embodiment of the present invention.

[0043] Figure 3 A schematic diagram of a simulation process provided by an embodiment of the present invention.

[0044] Figure 4 A schematic diagram of spatial charge density distribution when the field strength is 40 kV / mm based on different pressurization times provided in an embodiment of the present invention.

[0045] Figure 5 A schematic diagram of spatial charge density distribution when the field strength is 60 kV / mm based on different pressurization times provided in an embodiment of the present invention.

[0046] Figure 6 A schematic diagram of spatial charge density distribution when the field strength is 80 kV / mm based on different pressurization times provided in an embodiment of the present invention.

[0047] Figure 7 A schematic diagram of spatial charge density distribution when the field strength is 40 kV / mm after depressurization provided in an embodiment of the present invention.

[0048] Figure 8 A schematic diagram of spatial charge density distribution when the field strength is 60 kV / mm after depressurization provided in an embodiment of the present invention.

[0049] Fig. 9 A schematic diagram of the spatial charge density distribution when the field strength is 80 kV / mm after depressurization provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0050] 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 only 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 are within the scope of protection of the present invention.

[0051] The embodiment of the present invention discloses a method for predicting the spatial charge dissipation characteristics of randomly distributed trap densities at different depths, see Figure 1 As shown, the following steps are included:

[0052] S1. Construct a one-dimensional simulation model according to the actual structure of the target epoxy resin composite insulation material;

[0053] S2. Based on the constructed one-dimensional simulation model, a spatial charge dissipation characteristic model with randomly distributed trap densities at different depths is constructed;

[0054] S3. Simulate the spatial charge dissipation characteristic model of randomly distributed trap densities at different depths to obtain the spatial charge distribution of the target epoxy resin composite insulating material after decompression.

[0055] Next, each of the above steps will be described respectively.

[0056] In the above step S1, the one-dimensional simulation model is a mathematical model used to simulate and analyze the performance of epoxy resin composite insulation materials; it is based on the one-dimensional space assumption, simplifies the performance of the material in all directions, and describes the behavior of the material through mathematical equations; the thickness of the one-dimensional model is 250μm. In practice, in order to avoid signal attenuation and sound wave scattering when measuring samples using the PEA method, the sample thickness is generally less than 300μm. In the embodiment of the present invention, 250μm is used as the thickness of the one-dimensional geometric model of the epoxy composite material; in the COMSOL simulation software, select the geometric node, create a line segment with a length of 250μm, and set 5 points at 20μm, 40μm, 60μm, 190μm, and 200μm respectively, and set probes at these 5 positions to measure the charge distribution and characteristics during the pressurization and depressurization process, such as Figure 2 shown.

[0057] In the above step S2, it specifically includes:

[0058] S21. Based on the constructed one-dimensional simulation model, the relationship between the electric field and the charge dissipation characteristics of the internal space of the medium is established by combining the relationship between charge trapping and charge detrapping, charge transport, and the relationship between charge recombination and the electric field; the charge dissipation characteristics of the internal space of the medium include: trap density, carrier density, current density and carrier mobility;

[0059] This step is implemented based on the bipolar carrier transport model. Specifically, a set of mutually coupled equations consisting of the current continuity equation, the conduction equation, and the electrostatic field Poisson equation is used to describe the relationship between charge trapping and charge detrapping, charge transport, and the relationship between charge recombination and the electric field, which can be expressed as:

[0060]

[0061] Where x represents the position of the one-dimensional simulation model; j c(e) (x, t) represents the electron current density at position x in the conduction band and valence band at time t; j c(h) (x, t) represents the hole current density at position x in the conduction band and valence band at time t; q free(e) (x, t) represents the electron carrier density at position x at time t; q free(h) (x, t) represents the hole carrier density at position x at time t; μ 0(e) Represents the carrier mobility of electrons in dielectrics; μ0(h) represents the carrier mobility of holes in the dielectric; q trap(e) represents the capture density of electrons; q trap(h) represents the capture density of holes; S e represents the electron charge capture-capture-recombination coefficient; S h represents the charge capture-trapping-recombination coefficient of holes; E(x,t) represents the electric field intensity at position x at time t before decompression; q net represents the net charge density; ε0 represents the vacuum dielectric constant, ε r represents the relative dielectric constant;

[0062] The first and second terms in the above formula (1) are current continuity equations, which are used to describe the relationship between charge trapping and charge detrapping; the third and fourth terms are conduction equations, which are used to describe charge transport; the fifth term is the electrostatic field Poisson equation, which is used to describe the relationship between charge recombination and electric field;

[0063] The electron charge capture-recapture-recombination coefficient S in the above formula (1) is e Including parameters of free electrons and free electrons, as well as parameters of free electrons and captured electrons; the charge capture-capture-recombination coefficient S of holes h Including parameters of free electrons and free holes, as well as parameters of free electrons and captured holes; specifically expressed as:

[0064]

[0065] Among them, S eμ Represents the parameters of free electrons and free electrons, S et Represents the parameters of free electrons and trapped electrons; S hμ Represents the parameters of free electrons and free holes, S ht represents the parameters of free electrons and trapped holes; P tr(e) represents the capture coefficient of free electrons; P de(e) represents the capture coefficient of free holes; q trap(e) represents the capture density of electrons; q trap(h) represents the hole capture density; N T(e) Represents the electron trap density concentration; N T(e) represents the hole trap density concentration; R eμ,ht represents the trap recombination coefficient between free electrons and trapped holes; R et,hμ represents the trap recombination coefficient between trapped electrons and free holes; R eμ,hμ represents the recombination coefficient between free electrons and free holes; q e Indicates the amount of charge.

[0066] S22, adding a physical field, which includes an electrostatic field and a dilute material transfer field, for simulating charge trapping, charge detrapping, charge injection, charge extraction, and charge recombination inside the medium;

[0067] S23, adding physical parameters of the target epoxy resin composite insulating material, adding boundary conditions in the physical field based on the bipolar carrier transport model, the hopping conductivity model and the Schottky law, and combining the current space charge dissipation model to obtain a space charge dissipation characteristic model with random distribution of trap densities at different depths;

[0068] In step S23, the boundary conditions in the pressurized model include: injection of electrons and holes, and extraction of electrons and holes; specifically, they are expressed as:

[0069] (1) For the injection of electrons and holes, the bipolar carrier transport model assumes that the carriers are injected from the electrodes according to the Schottky law; it can be expressed as:

[0070]

[0071] Among them, j in(e) represents the cathode injection current density; j in(h) represents the anode injection current density; N C represents the state density of the conduction band; N V represents the state density of the valence band; q e represents the charge, q e =1.6×10 -19 C; μ C represents the carrier mobility in the conduction band; μ V represents the carrier mobility in the valence band; k represents the Boltzmann constant; T represents the thermodynamic temperature; ω e represents the electron injection barrier; ω h represents the hole injection barrier; ψ represents the parameter that changes with the electric field; E(x,t) represents the electric field intensity at position x at time t; f represents the reduction electric field;

[0072] The above reduction electric field f and the parameter ψ that varies with the electric field are expressed as:

[0073] f=q e Er c / kT (4)

[0074] ψ(f)=f -1 +f -1 / 2 -f -1 (1+2f 1 / 2 ) 1 / 2 (5)

[0075] Among them, r c represents the Coulomb radius;

[0076] (2) The extraction of electrons and holes complies with Schottky's law, which is expressed as:

[0077]

[0078] Among them, j ex (e) represents the cathode extraction current density; j ex (h) represents the anode injection current density; ω -e represents the electron extraction barrier; ω -h represents the hole extraction barrier.

[0079] (3) Charge migration in shallow traps is considered to be a jumping process. Based on the jumping conductivity model, the carrier mobility is expressed as:

[0080]

[0081] Where μ represents the carrier mobility; d represents the distance between shallow traps; ω μ represents the jump barrier height, which is consistent with the shallow trap depth; E d (x, t) represents the electric field strength at position x at time t after the pressure is removed.

[0082] The above formulas (1) to (7) are bipolar carrier transport model formulas, which are simulated pressurization processes in the method provided in the embodiment of the present invention.

[0083] In step S23, the current space charge dissipation model theory is as follows:

[0084] Assume that the dissipation of space charge in the sample (i.e., one-dimensional simulation model) is mainly determined by the detrapping process of charge excited by thermal energy; Assume that each trap is filled with monovalent charge, and the charge amount is q e =1.6×10 -19 C; After the space charge is trapped, some holes and electrons neutralize each other, some holes enter the valence band, and some electrons enter the conduction band. The trapped charges will not be captured by the trap again; the charge trapping process is only related to the depth of the trap it enters, but has nothing to do with the depth of other traps; the deepest trap depth in the sample is Δ max , the shallowest trap depth is Δ min , in Δ min ~Δ max Within the trap depth range, the trap density at different depths is randomly distributed and obeys uniform distribution; if the number of traps with a trap depth of Δ per unit volume of the sample that is still filled with charges at time t after decompression is N(t), then according to the above assumptions:

[0085] Under uniform distribution, the probability density function of trap density at different depths is expressed as:

[0086]

[0087] The probability that a trap of depth Δ is filled with charge at time t is:

[0088] p(Δ,t)=p0e -υt (9)

[0089] Where v represents the escape rate; p0 represents the probability of the trap being initially filled; e represents the exponential function;

[0090] Since the trap depth is in the range [Δ min ,Δ max ] are randomly distributed in the sample, and the sum is taken at each depth, then the trap density N(t) in the sample is:

[0091]

[0092] According to the space charge dissipation model, the space charge density in the sample at time t is:

[0093] ρ(t)=q e N(t)kT[E1(νtY min )-E1(νtY max )](11)

[0094] Where E1(·) represents an integral including an exponential function, and x' is used to represent the independent variable in the brackets of E1(·); its form is as follows

[0095]

[0096] E1(x') can be expanded to obtain:

[0097] E1(x')=-ln(x')-0.57721x'<1(13)

[0098] E1(x')~e -x ' / x'x'>1(14)

[0099] Combining the Poisson equation of the electrostatic field (i.e., the fifth formula in formula (1)) with formula (11) yields the effect of the accumulation of residual charge on the distribution of electric field intensity when the charge at a certain point dissipates after decompression:

[0100]

[0101] Where ρ(x,t) represents the electric field intensity function and charge density function at position x at time t in the Poisson equation of the electrostatic field;

[0102] Integrating both sides of formula (15) with respect to x gives the electric field intensity at position x at time t after decompression:

[0103]

[0104] Among them, E d represents the electric field intensity after depressurization; x represents the position of the one-dimensional simulation model; t represents the time t; x1 represents the cathode position; x2 represents the anode position; q e represents the charge; N(t) represents the trap density; k represents the Boltzmann constant; T represents the thermodynamic temperature; v represents the frequency required for detrapping; ε0 represents the vacuum dielectric constant; ε r Represents the relative dielectric constant; Y min =exp(-Δ max / kT), Y max =exp(-Δ min / kT), Δ max Indicates the deepest trap depth in the one-dimensional simulation model; Δ min represents the shallowest trap depth in the one-dimensional simulation model; E1(·) represents the integral including the exponential function.

[0105] Combining the bipolar carrier model formulas (1)-(7) with the space charge dissipation model (8)-(16) can obtain the space charge dissipation model with random distribution of trap density at different depths after depressurization.

[0106] In the above step S3, the spatial charge dissipation characteristic model of randomly distributed trap densities at different depths is simulated to obtain the spatial charge distribution of the target epoxy resin composite insulating material after decompression; Figure 3 As shown, specifically including:

[0107] First, a one-dimensional geometric model of epoxy composite material is created, and its parameters such as applied voltage and trap barrier are set. A random function f(Δ) is created and made to obey uniform distribution. The random function is used to describe the probability of trap filling in the sample. The trap density N(t) inside the sample is obtained by combining the random function f(Δ). The spatial charge density ρ(t) at time t is obtained by substituting it into the spatial charge dissipation model. Secondly, given the initial charge distribution, the electric field strength E at position x inside the material at time t can be calculated using formula (16): d (x, t), and the carrier mobility is calculated by the PDE equation. Then, the current density of each unit layer is calculated based on the calculation results of the conduction equation in the PED square and the Schottky extraction process, including the cathode and anode injection current density after depressurization, and the cathode and anode extraction current density after depressurization; the current continuity equation in the PDE equation is used to obtain the carrier density, and thus the spatial charge distribution in each unit layer at the new moment is obtained;

[0108] The PDE equation is shown below:

[0109]

[0110] Formula (17) can be used to obtain the boundary conditions for the change of free charge caused by the conduction current inside the sample, the transport of free charge in the medium, and the influence of charge accumulation on the distribution of electric field intensity;

[0111] The charge migration in shallow traps is considered to be a jumping process. Therefore, the carrier mobility inside the sample after decompression can be expressed by the following formula:

[0112]

[0113] The carrier mobility inside the sample after decompression can be obtained by formula (18), where μ r It represents the carrier mobility inside the sample after decompression.

[0114] For the injection and extraction of electrons and holes, the space charge dissipation model assumes that the carriers are in accordance with Schottky's law at the electrode, and the formula is as follows:

[0115]

[0116] Among them, j rin(e) represents the cathode injection current density after depressurization; j rin(h) represents the anode injection current density after depressurization; j rex(e) represents the cathode extraction current density after depressurization; j rex(h) It indicates the anode extraction current density after depressurization.

[0117] The boundary conditions for charge injection and extraction after decompression can be obtained from formulas (19) and (20), which is the simulated decompression process in the method provided in the embodiment of the present invention.

[0118] COMSOL Multiphysics simulation software was used. Since the complete decompression process consists of two parts, pressurization and decompression, two nodes were selected to simulate the complete process when adding research nodes. The initial conditions during decompression are complex, and the results of the pressurization process are used as the initial values ​​of the decompression process, which is consistent with the experimental process. According to the spatial charge dissipation model, it is assumed that the charge injection stops at 10s during decompression. Therefore, 10s after the start of decompression, the Schottky injection node stops running and the Schottky extraction node continues to run. The initial physical parameters are shown in Table 1:

[0119] Table 1 Simulation initial physical parameters

[0120]

[0121]

[0122] The spatial charge density at different pressurization times is as follows Figures 4 to 6 shown.

[0123] When the field strength is 40kV / mm, see Figure 4 As shown in the figure, the same polarity charge injection began within a few minutes of pressurization. When the pressurization lasted for 180 minutes, the same polarity charge injected into the sample continued to increase slowly. After pressurization for 1440 minutes, positive polarity charge began to appear in the area near the lower electrode of the sample, and this phenomenon became more obvious after pressurization for 48 hours; due to the induction effect of the accumulation of positive charge in this area, the charge peak at the lower electrode of the sample increased significantly. While the positive charge appearing near the lower electrode of the sample partially covered up the original negative charge signal in this area, the amount of positive charge injection near the upper electrode of the sample continued to increase slowly.

[0124] When the field strength is 60kV / mm, see Figure 5 As shown in the figure, the spatial charge injection phenomenon in the epoxy sample is similar to that under the field strength of 40kV / mm, and there is obvious injection of charges of the same polarity within a few minutes of pressurization. Within 180 minutes of pressurization, the charges of the same polarity injected into the epoxy sample continued to increase, and the charge peak at the corresponding underground electrode continued to decrease. When the pressurization lasted for 1440 minutes, there was obvious accumulation of positive polarity charges in the area near the lower electrode in the sample, and the induced charge increased the charge peak of the lower electrode; when the pressurization lasted for 2880 minutes, more positive charges accumulated near the lower electrode of the sample, and the increase in the charge peak of the lower electrode was more obvious.

[0125] When the field strength is 80kV / mm, see Figure 6 As shown in the figure, the sample was injected with charges of the same polarity within a few minutes of pressurization. However, at 60 minutes of pressurization, positive charges began to accumulate in the area near the lower electrode of the sample; at 180 minutes of pressurization, this positive charge accumulation phenomenon was more obvious. At 1440 minutes of pressurization, the positive charges in the area near the lower electrode of the sample began to be covered by the injected negative charges. At 2880 minutes of pressurization, the negative charges injected by the lower electrode covered the positive charges in this area more obviously. The amount of positive charges injected near the upper electrode has been slowly and continuously increasing throughout the pressurization process.

[0126] The cloud diagram of the space charge density distribution after decompression is as follows Figures 7 to 9 shown.

[0127] When the field strength exceeds 40kV / mm, Figure 7 As shown in the figure, the spatial charge distribution measured in the epoxy material during decompression is similar, and the residual charges in the areas near the upper and lower electrodes are all positive charges; the distribution range of positive charges in the area near the upper electrode is wider than that near the lower electrode; most of the residual charges in the sample are significantly dissipated after decompression for 2×105s. When the field strength is 40kV / mm, the positive charges near the upper electrode and the negative charges in the middle of the sample dissipate faster, while the positive charges near the lower electrode dissipate slower.

[0128] When the field strength exceeds 60kV / mm, Figure 8 As shown, the positive charge dissipation rates near the upper and lower electrodes are similar.

[0129] When the field strength is 80kV / mm, Fig. 9 As shown in Figure 2, the lower electrode has a positive charge at about 2.5×105s. The simulation results are similar to the experimental results and can simulate the more general internal space charge dissipation characteristics of the sample after decompression.

[0130] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0131] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths, characterized in that: The steps include: S1. Construct a one-dimensional simulation model according to the actual structure of the target epoxy resin composite insulation material; S2. Based on the constructed one-dimensional simulation model, a spatial charge dissipation characteristic model with randomly distributed trap densities at different depths is constructed; S3. Simulate the spatial charge dissipation characteristic model of randomly distributed trap densities at different depths to obtain the spatial charge distribution of the target epoxy resin composite insulating material after decompression; The step S2 specifically includes: S21. Based on the constructed one-dimensional simulation model, the relationship between charge trapping and charge detrapping, charge transport, and the relationship between charge recombination and electric field is combined to establish the relationship between the electric field and the charge dissipation characteristics of the internal space of the medium; S22, add physical fields to simulate charge trapping, charge detrapping, charge injection, charge extraction and charge recombination inside the medium; S23, adding physical parameters of the target epoxy resin composite insulating material, adding boundary conditions in the physical field based on the bipolar carrier transport model, the hopping conductivity model and the Schottky law, and combining the current space charge dissipation model to obtain a space charge dissipation characteristic model with random distribution of trap densities at different depths; The spatial charge dissipation characteristic model of the randomly distributed trap density at different depths is expressed as: Among them, E d represents the electric field intensity after depressurization; x represents the position of the one-dimensional simulation model; t represents the time t; x1 represents the cathode position; x2 represents the anode position; q e represents the charge; N(t) represents the trap density; k represents the Boltzmann constant; T represents the thermodynamic temperature; v represents the frequency required for detrapping; ε0 represents the vacuum dielectric constant; ε r Represents the relative dielectric constant; Y min =exp(-Δ max / kT), Y max =exp(-Δ min / kT), Δ max Indicates the deepest trap depth in the one-dimensional simulation model; Δ min represents the shallowest trap depth in the one-dimensional simulation model; E1(·) represents the integral including the exponential function.

2. The method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths according to claim 1, characterized in that: The space charge dissipation characteristics inside the medium include: trap density, carrier density, current density and carrier mobility.

3. The method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths according to claim 1, characterized in that: The physical field includes an electrostatic field and a dilute species transfer field.

4. The method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths according to claim 1, characterized in that: In step S21, a mutually coupled equation group consisting of a current continuity equation, a conduction equation, and a Poisson equation for electrostatic field is used to describe the relationship between charge trapping and charge detrapping, charge transport, and the relationship between charge recombination and the electric field, which is expressed as: Where x represents the position of the one-dimensional simulation model; j c(e) (x, t) represents the electron current density at position x in the conduction band and valence band at time t; j c(h) (x, t) represents the hole current density at position x in the conduction band and valence band at time t; q free(e) (x, t) represents the electron carrier density at position x at time t; q free(h) (x, t) represents the hole carrier density at position x at time t; μ 0(e) Represents the carrier mobility of electrons in dielectrics; μ 0(h) represents the carrier mobility of holes in the dielectric; q trap(e) represents the capture density of electrons; q trap(h) represents the capture density of holes; S e represents the electron charge capture-capture-recombination coefficient; S h represents the charge capture-trapping-recombination coefficient of holes; E(x,t) represents the electric field intensity at position x at time t before decompression; q net represents the net charge density; ε0 represents the vacuum dielectric constant, ε r represents the relative dielectric constant; Electron charge capture-recruitment coefficient S e Including parameters of free electrons and free electrons, as well as parameters of free electrons and captured electrons; the charge capture-capture-recombination coefficient S of holes h Including parameters of free electrons and free holes, as well as parameters of free electrons and captured holes; specifically expressed as: Among them, S eμ Represents the parameters of free electrons and free electrons, S et Represents the parameters of free electrons and trapped electrons; S hμ Represents the parameters of free electrons and free holes, S ht represents the parameters of free electrons and trapped holes; P tr(e) represents the capture coefficient of free electrons; P de(e) represents the capture coefficient of free holes; q trap(e) represents the capture density of electrons; q trap(h) represents the hole capture density; N T(e) Represents the electron trap density concentration; N T(h) represents the hole trap density concentration; R eμ,ht represents the trap recombination coefficient between free electrons and trapped holes; R et,hμ represents the trap recombination coefficient between trapped electrons and free holes; R eμ,hμ represents the recombination coefficient between free electrons and free holes; q e Indicates the amount of charge.

5. The method for predicting spatial charge dissipation characteristics of randomly distributed trap densities at different depths according to claim 1, characterized in that: In step S23, the boundary conditions include: injection of electrons and holes, extraction of electrons and holes, and carrier mobility; specifically, they are expressed as: (1) For the injection of electrons and holes, the bipolar carrier transport model assumes that the carriers are injected from the electrodes according to the Schottky law; it can be expressed as: Among them, j in(e) represents the cathode injection current density; j in(h) represents the anode injection current density; N C represents the state density of the conduction band; N V represents the state density of the valence band; μ C represents the carrier mobility in the conduction band; μ V represents the carrier mobility in the valence band; k represents the Boltzmann constant; T represents the thermodynamic temperature; ω e represents the electron injection barrier; ω h represents the hole injection barrier; ψ represents the parameter that changes with the electric field; E(x,t) represents the electric field intensity at position x at time t; f represents the reduction electric field; (2) The extraction of electrons and holes complies with Schottky's law, which is expressed as: Among them, j ex (e) represents the cathode extraction current density; j ex (h) represents the anode injection current density; ω -e represents the electron extraction barrier; ω -h represents the hole extraction barrier; (3) Charge migration in shallow traps is considered to be a jumping process. Based on the jumping conductivity model, the carrier mobility is expressed as: Where μ represents the carrier mobility; d represents the distance between shallow traps; v represents the detrapping frequency; ω μ represents the jumping barrier height, which is consistent with the shallow trap depth; E d (x, t) represents the electric field intensity at position x at time t after the pressure is removed.

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