Numerical simulation method for frequency domain dielectric properties of multilayer composite insulating material under temperature gradient

Abstract

The invention discloses a numerical simulation method for frequency domain dielectric properties of a multi-layer composite insulating material under a temperature gradient. The method comprises the following steps: determining the volume fraction of an impregnated material in the multi-layer composite insulating material; determining dielectric parameters of the impregnated material based on the volume fraction of the impregnated material and the frequency domain dielectric parameters of the impregnated material and the multi-layer composite insulating material; and performing finite element simulation on the frequency domain dielectric characteristic numerical value of the multilayer composite insulating material according to the dielectric parameters of the impregnated material and the impregnated material. According to the invention, the limitation of experimental conditions for directly measuring the dielectric property of the single-layer impregnated material is overcome, and the dielectric behavior of the material can be simulated and predicted more accurately.

Description

Technical Field

[0001] The present invention relates to the technical field of dielectric property simulation, and more specifically to a frequency domain dielectric property numerical simulation method for a multilayer composite insulating material under a temperature gradient. Background Art

[0002] The multi-layer composite insulating material is usually prepared by an impregnation process, and the structure includes an impregnated material and a multi-layer impregnated material. Due to the interaction between the impregnated material and the impregnated material, as well as the physical and chemical changes that may occur during the impregnation process, the dielectric properties of the impregnated material change;

[0003] At present, multilayer composite insulation materials actually work under different temperature gradients. In the study of the dielectric properties of multilayer composite insulation materials, there are no experimental conditions for directly measuring the dielectric properties of the impregnated materials. For example, in the dry-type ultra-high voltage converter transformer bushing, the bushing body adopts a composite insulation composed of gas and epoxy composite insulation materials, wherein the solid inner insulation material is a composite material of epoxy and impregnated paper. Since it is impossible to obtain a single layer of impregnated insulation paper layer by experimental means such as peeling or separate preparation, it is impossible to directly measure the dielectric properties of the single layer of impregnated insulation paper layer material, resulting in the inability to perform accurate numerical simulation of the frequency domain dielectric properties of the multilayer composite insulation material.

[0004] However, establishing an accurate simulation and calculation model of the dielectric properties of multilayer composite materials is an indispensable part in the research and development of new insulating materials, optimizing the design of electrical equipment, and improving the reliability and safety of insulation systems.

[0005] Therefore, the present application provides a method for numerical simulation of the frequency domain dielectric properties of a multilayer composite insulating material. Summary of the invention

[0006] In view of this, in order to overcome the current technical bottleneck, the present invention provides a numerical simulation method for the frequency domain dielectric properties of multilayer composite insulation materials under temperature gradient.

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

[0008] A method for numerically simulating frequency domain dielectric properties of a multilayer composite insulation material under a temperature gradient, comprising the following steps:

[0009] Determine the volume fraction of impregnated material in multi-layer composite insulation materials;

[0010] Determine the dielectric parameters of the impregnated material based on the volume fraction of the impregnated material and the frequency domain dielectric parameters of the impregnated material and the multilayer composite insulating material;

[0011] Finite element simulation of the frequency domain dielectric properties of multilayer composite insulation materials is carried out based on the dielectric parameters of the impregnating material and the impregnated material.

[0012] Preferably, determining the volume fraction of the impregnated material in the multilayer composite insulating material comprises:

[0013] Obtain a multi-layer composite insulation material sample and divide it into equal parts to obtain a plurality of thin strips;

[0014] According to the PPI value of the image of each thin strip cross section, the area of ​​each pixel is determined;

[0015] Based on the pixel area, the volume and volume fraction of the impregnated material are determined by calculating the area of ​​the impregnated material in each thin strip.

[0016] Preferably, the dielectric parameter of the impregnated material includes the real part of the complex dielectric constant, and the determining step includes:

[0017] Based on the structure of the multi-layer composite insulating material, it is equivalent to a capacitor series circuit, wherein each layer of the impregnated material or the impregnated material is equivalent to a capacitor;

[0018] Determine the equivalent capacitance value based on the real part of the complex dielectric constant corresponding to each capacitor; the formula is as follows:

[0019]

[0020] Among them, A i is the equivalent capacitance plate area of ​​the i-th layer of insulating material, d i is the thickness of the equivalent capacitor plate of the i-th insulating material, ε i is the real part of the complex dielectric constant of the equivalent capacitance of the i-th layer of insulating material;

[0021] The relationship between each capacitance value and the total capacitance of the capacitor series circuit is obtained, and simplified in combination with the volume fraction of the impregnated material to obtain the real part of the complex dielectric constant of the impregnated material.

[0022] Preferably, the dielectric parameter of the impregnated material comprises the real part of the complex AC conductivity, and the determining step comprises:

[0023] Based on the structure of multi-layer composite insulation materials, it is equivalent to an RC series-parallel circuit, where the capacitance represents the polarization of the insulation material and the resistance represents the loss;

[0024] The resistance value of each layer of material is determined according to the real part of the complex conductivity of each layer of material, and the voltage division ratio of each layer is determined according to the real part of the dielectric constant of each layer; wherein,

[0025]

[0026] In the formula, σ i ' is the real part of the complex conductivity of the i-th layer material, A i is the cross-sectional area of ​​the equivalent resistance of the i-th layer of material, d iis the average thickness of the i-th layer of material;

[0027]

[0028] Where E1 and E2 represent the electric field strength on the first and second layers of insulating materials, respectively; d represents the average thickness of the material; ε1' and ε'2 represent the real part of the dielectric constant of the first and second layers of insulating materials, respectively;

[0029] Substitute the resistance value and the voltage divider ratio into the active power equation of the capacitor series circuit;

[0030] By simplifying the volume fraction of the impregnated material, the dielectric parameters of the impregnated material include the real part of the complex AC conductivity.

[0031] Preferably, the dielectric parameters of the impregnated material include the imaginary part of the complex dielectric constant and the imaginary part of the complex AC conductivity; the determining step includes:

[0032] The current density of multilayer composite insulation materials in an alternating electric field is determined according to Maxwell's equations; the formula is expressed as:

[0033] j * =σ * ·E *

[0034] σ * is the complex AC conductivity, E * is the alternating electric field strength;

[0035] According to the equivalent relationship between the derivative of current density and electric displacement with respect to time t, the real part σ'(ω) and imaginary part σ"(ω) of complex AC conductivity are obtained; the expression is:

[0036] σ'(ω)=ωε0ε”(ω)

[0037] σ”(ω)=ωε0ε'(ω)

[0038] In the formula, ε * (ω) is the complex dielectric constant, ω is the angular velocity of the AC voltage, and ε0 is the vacuum dielectric constant;

[0039] The imaginary part of the complex dielectric constant and the imaginary part of the complex conductivity of the impregnated material are determined according to the real part and the imaginary part of the complex AC conductivity.

[0040] Preferably, when the multi-layer composite insulating material is a three-layer structure of impregnating material / impregnated material / impregnated material, the calculation formula for each dielectric parameter of the impregnated material is:

[0041]

[0042] σ”2(ω)=ωε0ε2'(ω)

[0043] Wherein, a is the volume fraction of the impregnated material in the multilayer composite insulation material, ε0′ is the real part of the dielectric constant of the multilayer composite insulation material, ε1′ is the real part of the dielectric constant of the impregnated material, σ0′ is the real part of the complex AC conductivity of the three-layer composite material, σ1′ is the real part of the complex AC conductivity of the impregnated material, ω is the angular velocity of the AC voltage, ε0 is the vacuum dielectric constant, σ2′(ω) and σ″2(ω) are the real and imaginary parts of the complex AC conductivity of the impregnated material when the angular velocity is ω, respectively, and ε2′(ω) and ε2″(ω) are the real and imaginary parts of the complex dielectric constant of the impregnated material when the angular velocity is ω, respectively.

[0044] Preferably, the finite element simulation of the frequency domain dielectric properties of the multilayer composite insulation material includes:

[0045] A two-dimensional simulation model is constructed according to the volume fraction of the impregnated material and the structure of the multi-layer composite insulation material;

[0046] Calculate the temperature field of the simulation model to obtain the internal temperature distribution of the model;

[0047] Linearly interpolating the dielectric parameters of the impregnating material and the impregnated material within a preset temperature range, and coupling the temperature distribution with the dielectric parameters at the corresponding temperature;

[0048] Finite element simulation is performed on the coupled model to obtain the numerical values ​​of the frequency domain dielectric properties of the multilayer composite insulation material.

[0049] Preferably, the finite element simulation includes:

[0050]

[0051]

[0052] In the formula, σ * represents the equivalent complex AC conductivity of the multilayer composite insulation material, ε * represents the complex dielectric constant of the multilayer composite insulation material, J * represents the average current density of the simulation model, E * represents the average electric field strength of the simulation model, D * represents the average electric displacement of the simulation model, and ε0 is the dielectric constant of vacuum.

[0053] Preferably, the average electric field strength calculation formula of the simulation model is:

[0054]

[0055] Where d represents the total thickness of the multi-layer composite insulation material, U * Represents the effective AC voltage of the simulation model.

[0056] Preferably, the linear interpolation formula is:

[0057]

[0058] In the formula, θ a and θ c Respectively, in T a and T c Dielectric parameters at temperature, T a represents the temperature at time a, T c represents the temperature at time c, T b represents the temperature at time b to be interpolated, θ b is the interpolated T b Dielectric parameters at temperature.

[0059] The numerical simulation method for the frequency domain dielectric characteristics of multilayer composite insulation materials under temperature gradient provided by the present invention can more accurately simulate and predict the dielectric behavior of materials; compared with the prior art, it has the following effects:

[0060] 1) Use image processing technology (PPI value analysis) to accurately obtain the volume fraction of the impregnated material, providing reliable data support for the subsequent calculation of dielectric parameters;

[0061] 2) Based on the equivalent circuit model and volume fraction, the real and imaginary parts of the complex dielectric constant and complex AC conductivity of the impregnated material are fully determined;

[0062] 3) By using finite element simulation technology, combined with temperature field calculation and linear interpolation of dielectric parameters, the numerical simulation of the frequency domain dielectric properties of multilayer composite insulation materials at different temperatures is realized. This not only improves the accuracy and practicality of the simulation, but also makes the simulation results more in line with actual application conditions because the influence of temperature gradient on the dielectric properties of the material is fully considered.

[0063] The simulation method provided in this application plays an important supporting role in the research and development of new insulating materials, the optimal design of electrical equipment, and improving the reliability and safety of insulation systems. It overcomes the experimental condition limitations of directly measuring the dielectric properties of a single layer of impregnated materials, making it possible to study complex multilayer composite materials, thereby promoting technological progress in the field of insulating materials, especially in the design and application of high-voltage electrical equipment.

[0064] In addition, this method combines electromagnetic theory with practical engineering applications, providing a comprehensive analytical framework for studying the dielectric properties of multilayer composite insulation materials. This combination of theory and practice not only helps to promote theoretical research in related fields, but also helps to guide practical engineering applications and improve the performance and safety of electrical equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] 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.

[0066] Figure 1 It is a flow chart of the numerical simulation method of the frequency domain dielectric characteristics of multilayer composite insulation materials under temperature gradient;

[0067] Figure 2 It is a schematic diagram of the structure of a three-layer composite insulation material;

[0068] Figure 3 It is an equivalent RC series-parallel circuit;

[0069] Figure 4 It is an equivalent capacitor series circuit;

[0070] Figure 5 Figures for epoxy resin specimens and epoxy composite specimens;

[0071] Figure 6 This is the dielectric property diagram of epoxy resin;

[0072] Figure 7 This is the dielectric property diagram of epoxy composite material;

[0073] Figure 8 This is the dielectric property diagram of epoxy impregnated paper;

[0074] Fig. 9 This is a two-dimensional simulation model diagram of a 9-layer epoxy impregnated paper composite insulation material;

[0075] Fig.10 This is a diagram of the comprehensive dielectric properties of 9 layers of materials. DETAILED DESCRIPTION

[0076] 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.

[0077] To solve the problems in the prior art, the present invention discloses a method for numerically simulating the frequency domain dielectric properties of a multilayer composite insulating material under a temperature gradient, the steps are as follows: Figure 1 ,include:

[0078] Determine the volume fraction of impregnated material in multi-layer composite insulation materials;

[0079] Determine the dielectric parameters of the impregnated material based on the volume fraction of the impregnated material and the frequency domain dielectric parameters of the impregnated material and the multilayer composite insulating material;

[0080] Finite element simulation of the frequency domain dielectric properties of multilayer composite insulation materials is carried out based on the dielectric parameters of the impregnating material and the impregnated material.

[0081] The following is an explanation through specific embodiments.

[0082] Embodiment 1

[0083] First, the volume fraction of the impregnated material in the multi-layer composite insulating material is determined. Since the volume of the impregnated material in the three-layer composite insulating material cannot be directly obtained, this embodiment designs the following acquisition steps:

[0084] Obtain a multi-layer composite insulation material sample and divide it into equal parts to obtain a plurality of thin strips;

[0085] According to the PPI value of the image of each thin strip cross section, the area of ​​each pixel is determined;

[0086] Based on the pixel area, the volume and volume fraction of the impregnated material are determined by calculating the area of ​​the impregnated material in each thin strip.

[0087] In a specific embodiment, a composite insulating material sample is prepared according to the composition of the composite insulating material, and the geometric dimensions of the prepared sample are measured. The dimensions of the composite insulating material sample are a0×b0×d0 (length×width×thickness);

[0088] Divide the composite material sample n into thin strips of width m, where n is as large as possible. Use an optical microscope to take a picture of the cross section of each composite material thin strip. Import the image taken by the microscope into the image processing program, denoise the image and binarize the image. Divide the pixels according to the good light transmittance of the impregnated material, that is, the white pixels are the impregnated material, and the black pixels are the impregnated material after impregnation. Traverse each pixel in the binary image, count the number of white pixels as z1, the number of black pixels as z2, and the image PPI value as u, then the area of ​​each pixel in the image is:

[0089]

[0090] Then the total area of ​​black pixels in the i-th thin strip sample, that is, the area of ​​the impregnated material in the i-th thin strip sample, is:

[0091] S i =S s × 2i , i=1,2,3,...,n

[0092] where z 2i is the number of black pixels in the cross-sectional image of the i-th strip.

[0093] The cross-sectional images of n thin strip samples are statistically analyzed, and the area of ​​the impregnated material in each thin strip is calculated to be S1, S2, S3, ..., S n .

[0094] Volume of impregnated material V = (S1 + S2 + S3 + ... + S n )×m

[0095] The volume of the composite material is V0 = a0 × b0 × d0

[0096] The volume fraction of the composite material occupied by the impregnated material is

[0097] Embodiment 2

[0098] Determine the dielectric parameters of the impregnated material; mainly including: the real part of the complex dielectric constant ε′, the imaginary part of the complex dielectric constant ε″, the real part of the complex AC conductivity σ′, and the imaginary part of the complex AC conductivity σ″;

[0099] Most of the multi-layer composite insulation materials that are widely used at present are prepared by the impregnation process. Common impregnating materials include resin materials such as epoxy resin, phenolic resin and polyester resin, as well as silicone rubber and polytetrafluoroethylene. The raw materials of the impregnated materials are mostly insulating paper, cardboard, glass fiber and synthetic fiber.

[0100] Moreover, all of them present a layered structure of "impregnating material / impregnated material / impregnating material".

[0101] Therefore, in this embodiment, a three-layer structure is selected as the basic repeating unit in the multi-layer composite structure, and a brief schematic diagram is shown as follows: Figure 2 At the same time, a sample of impregnated material is prepared, with the size of a1×b1×d1 (length×width×thickness).

[0102] In one embodiment, the real part of the complex dielectric constant of the impregnated material is determined,

[0103] In this embodiment, the real part of the complex dielectric constant of the three-layer composite insulating material is ε0′, the imaginary part is ε0″, the real part of the complex AC conductivity is σ0′, and the imaginary part is σ0″; the real part of the complex dielectric constant of the impregnated material is ε1′, the imaginary part is ε1″, the real part of the complex AC conductivity is σ1′, and the imaginary part is σ1″; the real part of the complex dielectric constant of the impregnated material is ε2′, the imaginary part is ε2″, the real part of the complex AC conductivity is σ2′, and the imaginary part is σ2″.

[0104] The steps include:

[0105] (1) Based on the structure of the multi-layer composite insulating material, it is equivalent to a capacitor series circuit, wherein each layer of the impregnated material or the impregnated material is equivalent to a capacitor;

[0106] According to the structure of the multilayer composite material under an optical microscope, the present invention uses an RC series-parallel circuit model to equalize the multilayer composite insulating material, wherein the capacitance is used to characterize the polarization of the insulating material, and the resistance is used to characterize the loss; Figure 3 As shown;

[0107] The real part of the complex dielectric constant is used to characterize the polarization ability of the insulating material in the AC electric field or the ability to store electric energy under the action of the electric field, reflecting the capacitive properties of the dielectric. The capacitive reactance of the equivalent capacitance of the insulating material under AC voltage is much smaller than the equivalent resistance, so the equivalent impedance of each parallel unit is mainly determined by the capacitance, and the influence of the resistance can be ignored. Therefore, the circuit is simplified to a circuit consisting of three capacitors in series, such as Figure 4 shown.

[0108] (2) Determine the equivalent capacitance value based on the real part of the complex dielectric constant corresponding to each capacitor; the equivalent capacitance of any layer of insulating material under a sinusoidal AC voltage can be expressed as:

[0109]

[0110] Among them, A i is the equivalent capacitance plate area of ​​the i-th layer of insulating material, d i is the thickness of the equivalent capacitor plate of the i-th insulating material, ε i is the real part of the complex dielectric constant of the equivalent capacitance of the i-th layer of insulating material; in the three-layer composite insulating material specimen, the equivalent capacitance plate areas of each layer of insulating material are approximately equal A1=A2=A3=A, and d1 and d3 represent the average thickness of the left and right impregnated material layers respectively; d2 represents the average thickness of the middle impregnated material layer, and d0 is the total thickness of the composite material specimen.

[0111] (3) Obtain the relationship between each capacitance value and the total capacitance of the capacitor series circuit, simplify it based on the volume fraction of the impregnated material, and obtain the real part of the complex dielectric constant of the impregnated material.

[0112] When three capacitors are connected in series, the total capacitance of the series circuit is:

[0113]

[0114] Substituting into the equivalent capacitance expression, we get:

[0115]

[0116] ε0′ is the real part of the complex dielectric constant of the three-layer composite insulating material, ε1′ and ε3′ are the real parts of the complex dielectric constants of the left and right two layers of impregnated materials, and ε1′=ε3′, ε2′ is the real part of the complex dielectric constant of the middle impregnated material, and the transformation yields:

[0117]

[0118] In the above formula, ε1'=ε3',

[0119] And d1+d3=(1-a)·d0, d2=a·d0;

[0120] After substituting, the formula can be simplified to:

[0121]

[0122] Where a is the volume fraction of the impregnated material in the composite material, ε0′ is the real part of the dielectric constant of the composite material, ε1′ is the real part of the dielectric constant of the impregnated material, and the real part of the complex dielectric constant ε′2 of the impregnated material is calculated as:

[0123]

[0124] In one embodiment, determining the real part of the complex AC conductivity of the impregnated material comprises:

[0125] (1) Based on the structure of the multilayer composite insulation material, it is equivalent to an RC series-parallel circuit, where the capacitance represents the polarization of the insulation material and the resistance represents the loss;

[0126] (2) Determine the resistance value of each layer of material according to the real part of the complex conductivity of each layer of material, and determine the voltage division ratio of each layer according to the real part of the dielectric constant of each layer; wherein,

[0127]

[0128] In the formula, σ i ' is the real part of the complex conductivity of the i-th layer material, A i is the cross-sectional area of ​​the equivalent resistance of the i-th layer of material. The cross-sectional areas of the equivalent resistance of each layer of insulating material are approximately equal. A1 = A2 = A3 = A, d i is the average thickness of the i-th layer of material, d0 is the total thickness of the three layers of insulating material, and the average thickness of the impregnated material is d2 = ad0;

[0129] The voltage division of the insulating material is mainly determined by its equivalent capacitive reactance. The electric field strength E on the series insulating material i The real part of its dielectric constant ε i 'Inversely proportional, E i , i=1,2,3 means the i-th layer of the three-layer composite material is subjected to the electric field, so:

[0130]

[0131] And U i =d i ·E i ,i=1,2,3

[0132] By combining:

[0133]

[0134] (3) Substitute the resistance value and the voltage divider ratio into the active power equation of the capacitor series circuit;

[0135] At the same time, since the left side (first layer material) and the right side (third layer material) are the same material, we have:

[0136] ε1′=ε3′

[0137] and

[0138] U1+U2+U3=U0

[0139] d1+d2+d3=d0

[0140] get:

[0141]

[0142] U1 is the voltage borne by the first layer of insulating material on the left, U2 is the voltage borne by the middle layer of insulating material, and U0 is the voltage borne by the entire composite material. Where σ0' is the real part of the complex AC conductivity of the three-layer composite material, σ1' is the real part of the complex AC conductivity of the impregnated material, σ2' is the real part of the complex AC conductivity of the impregnated material, and a is the volume fraction of the impregnated material in the composite material;

[0143] (4) Using the volume fraction of the impregnated material to simplify, the dielectric parameters of the impregnated material include the real part of the complex AC conductivity, expressed as:

[0144]

[0145] In one embodiment, determining the imaginary part of the complex dielectric constant and the imaginary part of the complex AC conductivity of the impregnated material comprises:

[0146] (1) According to Maxwell's equations, the current density of the multilayer composite insulation material in the alternating electric field is determined; the formula is expressed as:

[0147] j * =σ * ·E *

[0148] σ *is the complex AC conductivity, E * is the alternating electric field strength;

[0149] (2) According to the equivalent relationship between the derivative of current density and electric displacement with respect to time t,

[0150]

[0151] ε * (ω) is the complex dielectric constant, ω is the angular velocity of the AC voltage, ε0 is the vacuum dielectric constant, and i is the imaginary unit; where σ * (ω)=σ'(ω)-iσ”(ω)=iωε0ε * (ω)

[0152] The expressions of the real part σ'(ω) and the imaginary part σ”(ω) of the complex AC conductivity are obtained as follows:

[0153] σ'(ω)=ωε0ε”(ω)

[0154] σ”(ω)=ωε0ε'(ω)

[0155] In the formula, ε * (ω) is the complex dielectric constant, ω is the angular velocity of the AC voltage, and ε0 is the vacuum dielectric constant;

[0156] (3) According to the real and imaginary parts of the complex AC conductivity, the imaginary part of the complex dielectric constant and the imaginary part of the complex conductivity of the impregnated material are determined; the expression is:

[0157]

[0158] σ”2(ω)=ωε0ε2'(ω)

[0159] Embodiment 3

[0160] In this embodiment, finite element simulation is performed on the frequency domain dielectric property value of the multilayer composite insulation material, including:

[0161] S1. Construct an N-layer two-dimensional simulation model according to the volume fraction of the impregnated material and the microstructure of the multi-layer composite insulation material;

[0162] S2, calculate the temperature field of the simulation model to obtain the temperature distribution inside the model;

[0163] In this embodiment, the entire model is meshed using finite element software, and T is set on the left and right sides. min ' and T max 'Boundary conditions, where T min ≤T min '<T max '≤T max, calculate the temperature field of the simulation model and obtain the temperature distribution inside the model;

[0164] S3, linearly interpolating the dielectric parameters of the impregnating material and the impregnated material within a preset temperature range, and coupling the temperature distribution with the dielectric parameters at the corresponding temperature;

[0165] This embodiment uses a linear interpolation method to approximately obtain T min ~T max The dielectric parameters of a single-layer insulating material at any temperature within the range of ℃, taking the real part of the complex dielectric constant ε1′ as an example, when the frequency is f1, T a At this temperature, the real part of the complex dielectric constant of the single-layer insulating material is measured to be ε′ a ,T c At this temperature, the real part of the complex dielectric constant of the single-layer insulating material is measured to be ε c ′,T min ≤T a <T b <T c ≤T max , T a , T c is the experimental condition T min ~T max Two adjacent test temperatures within the range of ℃,

[0166] T can be approximated by linear interpolation. b The real part of the complex dielectric constant of the single-layer insulating material at temperature, where:

[0167]

[0168] Similarly, the imaginary part of the complex dielectric constant ε of the single-layer insulating material can be calculated: b ″, real part of complex AC conductivity σ b ′, imaginary part of complex AC conductivity σ b ″.

[0169] According to the above steps, the dielectric parameters of the impregnating material and the impregnated material at any temperature can be obtained.

[0170] Furthermore, the temperature of each finite element is coupled to the dielectric parameters obtained at the corresponding temperature.

[0171] S4. Perform finite element simulation on the coupled model to obtain the frequency domain dielectric property values ​​of the multilayer composite insulation material.

[0172] In this embodiment, one side of the simulation model is connected to the AC power supply, and the other side is grounded. The effective value of the applied AC voltage is V, the initial phase angle is θ, and the frequency is f. min ~f maxHz sinusoidal alternating current. The temperature and dielectric parameters are coupled as the input data of the simulation model, and the average current density J of the entire model is calculated by finite element software. * , average electric displacement D * And the average electric field strength E * , then the equivalent complex AC conductivity σ of the entire composite material can be obtained * and the complex dielectric constant ε * , the specific formula is as follows:

[0173]

[0174] In the formula, σ * represents the equivalent complex AC conductivity of the multilayer composite insulation material, ε * represents the complex dielectric constant of multilayer composite insulation materials, J * represents the average current density of the simulation model, E * represents the average electric field strength of the simulation model, D * represents the average electric displacement of the simulation model, and ε0 is the dielectric constant of vacuum.

[0175] The calculation formula for the average electric field strength of the simulation model is:

[0176]

[0177] Where d represents the total thickness of the multi-layer composite insulation material, U * Represents the effective AC voltage of the simulation model.

[0178] In a specific embodiment, taking the epoxy composite material used for the glue-impregnated paper dry-type bushing as an example, the impregnating material used is epoxy resin, and the impregnated material is insulating crepe paper. After the impregnation treatment, the epoxy composite material is obtained, and the epoxy impregnated paper is between the two epoxy resin layers.

[0179] 1. Prepare epoxy resin samples and epoxy composite material samples, and measure the sizes of the two samples. The size of the epoxy resin sample is 100mm×100mm×0.24mm, and the size of the epoxy composite material sample is 100mm×100mm×0.43mm.

[0180] 2. Pass the comprehensive testing system of insulation materials, 10 -3 ~10 3 In the Hz frequency range, the frequency domain dielectric properties of epoxy resin samples and epoxy composite samples were measured at 25℃, 40℃, 60℃, 80℃, 100℃, and 120℃. The main measurement parameters are the real part of the complex dielectric constant ε′, the imaginary part of the complex dielectric constant ε″, the real part of the complex AC conductivity σ′, and the imaginary part of the complex AC conductivity σ″ of epoxy resin and epoxy composite materials.

[0181] Epoxy resin specimens and epoxy composite specimens such as Figure 5 The dielectric properties of epoxy resin are shown in Figure 6 As shown; the dielectric properties of epoxy composite materials are shown Figure 7 shown.

[0182] 3. Divide the epoxy composite material sample 43 into thin strips with a width of 1 mm. Use a polarizing microscope to take pictures of the cross section of each epoxy composite material thin strip. Import all cross-sectional images into graphics processing software, perform denoising on the images and binarize the images, wherein the transmittance of epoxy resin is higher, that is, white pixels are epoxy resin, and black pixels are epoxy composite materials. The volume fraction of epoxy composite materials occupied by epoxy impregnated paper is calculated to be a=41% by step 3 in the invention content.

[0183] 4. Calculate the real part of the complex dielectric constant and the real part of the complex AC conductivity of the epoxy impregnated paper according to the steps described in Example 2; as well as the imaginary part of the complex dielectric constant and the imaginary part of the complex conductivity. The calculated dielectric properties of the epoxy impregnated paper are as follows: Figure 8 shown.

[0184] 7. The dielectric parameters of epoxy resin and epoxy impregnated paper at any temperature in the range of 25℃-120℃ are approximately obtained by interpolation method. The following table shows the real part of the dielectric constant at some temperatures in the range of 25℃-40℃ calculated by interpolation method;

[0185]

[0186]

[0187] 8. Establish a two-dimensional simulation model of 9-layer epoxy impregnated paper composite insulation material Fig. 9 As shown in the figure, the thermal field is calculated first to obtain the temperature distribution inside the 9-layer model, and then the dielectric parameters at each temperature are coupled with the thermal field, the electric field boundary conditions are set, and the full domain is calculated to obtain the dielectric properties of the entire material. The comprehensive dielectric properties of the 9-layer material are shown in Fig.10 shown.

[0188] 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.

[0189] 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 numerical simulation method for frequency domain dielectric properties of multilayer composite insulation materials under temperature gradient, characterized in that: Determine the volume fraction of impregnated material in multi-layer composite insulation materials; Determine the dielectric parameters of the impregnated material based on the volume fraction of the impregnated material and the frequency domain dielectric parameters of the impregnated material and the multilayer composite insulating material; Finite element simulation of the frequency domain dielectric properties of multilayer composite insulation materials is carried out based on the dielectric parameters of the impregnating material and the impregnated material.

2. The dielectric properties numerical simulation method according to claim 1, characterized in that: Determining the volume fraction of the impregnated material in the multi-layer composite insulation material comprises: Obtain a multi-layer composite insulation material sample and divide it into equal parts to obtain a plurality of thin strips; According to the PPI value of the image of each thin strip cross section, the area of ​​each pixel is determined; Based on the pixel area, the volume and volume fraction of the impregnated material are determined by calculating the area of ​​the impregnated material in each thin strip.

3. The dielectric property numerical simulation method according to claim 1, characterized in that: The dielectric parameters of the impregnated material include the real part of the complex dielectric constant, and the determination steps include: Based on the structure of the multi-layer composite insulating material, it is equivalent to a capacitor series circuit, wherein each layer of the impregnated material or the impregnated material is equivalent to a capacitor; Determine the equivalent capacitance value according to the real part of the complex dielectric constant corresponding to each capacitor; The relationship between each capacitance value and the total capacitance of the capacitor series circuit is obtained, and simplified in combination with the volume fraction of the impregnated material to obtain the real part of the complex dielectric constant of the impregnated material.

4. The dielectric property numerical simulation method according to claim 1, characterized in that: The dielectric parameters of the impregnated material include the real part of the complex AC conductivity, and the determination steps include: Based on the structure of multi-layer composite insulation materials, it is equivalent to an RC series-parallel circuit, where the capacitance represents the polarization of the insulation material and the resistance represents the loss; Determine the resistance value of each layer of material according to the real part of the complex conductivity of the material, and determine the voltage division ratio of each layer according to the real part of the dielectric constant of each layer; Substitute the resistance value and the voltage divider ratio into the active power equation of the capacitor series circuit; By simplifying the volume fraction of the impregnated material, the dielectric parameters of the impregnated material include the real part of the complex AC conductivity.

5. The dielectric property numerical simulation method according to claim 1, characterized in that: The dielectric parameters of the impregnated material include the imaginary part of the complex dielectric constant and the imaginary part of the complex AC conductivity; the determination steps include: Determine the current density of multilayer composite insulation materials in an alternating electric field based on Maxwell equations; Based on the derivative equivalence of current density and electric displacement with respect to time t, the real and imaginary parts of complex AC conductivity are obtained; The imaginary part of the complex dielectric constant and the imaginary part of the complex conductivity of the impregnated material are determined according to the real part and the imaginary part of the complex AC conductivity.

6. The dielectric property numerical simulation method according to claim 1, characterized in that: When the multi-layer composite insulating material is a three-layer structure of impregnating material / impregnated material / impregnated material, the calculation formula for each dielectric parameter of the impregnated material is: σ”2(ω)=ωε0ε2'(ω) Wherein, a is the volume fraction of the impregnated material in the multilayer composite insulation material, ε0' is the real part of the dielectric constant of the multilayer composite insulation material, ε1' is the real part of the dielectric constant of the impregnated material, σ0' is the real part of the complex AC conductivity of the three-layer composite material, σ1' is the real part of the complex AC conductivity of the impregnated material, ω is the angular velocity of the AC voltage, ε0 is the vacuum dielectric constant, σ′2(ω) and σ′2(ω) are the real and imaginary parts of the complex AC conductivity of the impregnated material when the angular velocity is ω, respectively, and ε′2(ω) and ε′2(ω) are the real and imaginary parts of the complex dielectric constant of the impregnated material when the angular velocity is ω, respectively.

7. The dielectric property numerical simulation method according to claim 1, characterized in that: Finite element simulation of the frequency domain dielectric properties of multilayer composite insulation materials, including: A two-dimensional simulation model is constructed according to the volume fraction of the impregnated material and the structure of the multi-layer composite insulation material; Calculate the temperature field of the simulation model to obtain the internal temperature distribution of the model; Linearly interpolating the dielectric parameters of the impregnating material and the impregnated material within a preset temperature range, and coupling the temperature distribution with the dielectric parameters at the corresponding temperature; Finite element simulation is performed on the coupled model to obtain the numerical values ​​of the frequency domain dielectric properties of the multilayer composite insulation material.

8. The dielectric property numerical simulation method according to claim 1 or 7, characterized in that: Finite element simulation, including: In the formula, σ * represents the equivalent complex AC conductivity of the multilayer composite insulation material, ε * represents the complex dielectric constant of the multilayer composite insulation material, J * represents the average current density of the simulation model, E * represents the average electric field strength of the simulation model, D * represents the average electric displacement of the simulation model, and ε0 is the dielectric constant of vacuum.

9. The dielectric property numerical simulation method according to claim 8, characterized in that: The calculation formula for the average electric field strength of the simulation model is: Where d represents the total thickness of the multi-layer composite insulation material, U * Represents the effective AC voltage of the simulation model.

10. The dielectric property numerical simulation method according to claim 7, characterized in that: The linear interpolation formula is: In the formula, θ a and θ c Respectively, in T a and T c Dielectric parameters at temperature, T a represents the temperature at time a, T c represents the temperature at time c, T b represents the temperature at time b to be interpolated, θ b is the interpolated T b Dielectric parameters at temperature.

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