Simulation method for non-uniformly damped oiled paper capacitive bushing

Abstract

The invention discloses a simulation method for a non-uniformly damped oiled paper capacitive bushing. The method comprises the following steps: S1, building a finite element model containing a conducting rod, insulating paper, insulating oil and an aluminum foil, and carrying out grid division; s2, dividing the insulation paper into a plurality of intervals in the axial direction, and setting the water content of each interval; s3, preparing insulation paper samples and insulation oil samples with different water contents in a laboratory, and respectively measuring complex relative dielectric constants of the insulation paper samples and the insulation oil samples; s4, assigning the calculated relative dielectric constant and conductivity of the insulation paper sample and the insulation oil sample to a corresponding material of the finite element model; and S5, carrying out frequency domain dielectric spectrum simulation calculation on the model to obtain a finite element model complex relative dielectric constant curve of the bushing with non-uniform damping in the axial direction and the radial direction. According to the model, axial and radial non-uniform damp and the influence of insulating oil and aluminum foil are considered, and the simulation calculation precision is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of fault diagnosis of electric power equipment, and in particular relates to a simulation method for an oil-paper capacitor bushing that is unevenly dampened. Background Art

[0002] Oil-paper capacitor bushing is one of the important power equipment in the power system. Its function is to realize the connection between the power transformer winding and the external high-voltage busbar, and provide insulation and mechanical support. The insulation performance of oil-paper capacitor bushing is mainly provided by the internal insulation paper. Once the insulation paper is damp, the insulation performance will be seriously reduced. Therefore, accurate moisture status assessment of the insulation paper can avoid fire and explosion accidents of the bushing.

[0003] Due to improper operation during manual maintenance and the gradual aging of sealing components, external moisture will gradually invade the inside of the bushing and diffuse in the insulation paper, resulting in unequal moisture content in the insulation paper at various parts of the bushing. Due to the influence of gravity, moisture will gradually settle to the bottom, resulting in uneven moisture in the bushing insulation paper. Frequency domain dielectric spectroscopy has been widely used to evaluate the moisture state of bushing insulation paper. Its principle is to evaluate the moisture state of bushing insulation paper by testing parameters such as complex capacitance and complex relative dielectric constant of insulation paper at different frequencies, and establishing a quantitative relationship between the parameters and the moisture content of insulation paper.

[0004] In the patent document with application number "CN202110563278X", a capacitive bushing insulation simulation modeling method based on finite element considering uneven degradation state is proposed. The model can realize the frequency domain dielectric spectrum prediction under axial uneven moisture and radial uneven aging, but the model ignores the radial uneven moisture, aluminum foil structure and oil gap structure of the bushing, which limits the prediction accuracy of the real uneven moisture capacitive bushing insulation failure. The model has great limitations.

[0005] Therefore, the present invention proposes a simulation method for an oil-paper capacitor bushing with uneven moisture absorption to solve the above technical problems. Summary of the invention

[0006] The purpose of the present invention is to provide a simulation method for an oil-paper capacitor bushing with uneven moisture, so as to solve the problems in the prior art that the finite element simulation modeling method for the oil-paper capacitor bushing with uneven moisture only considers the axial uneven moisture, does not consider the radial uneven moisture of the insulating paper and does not consider the influence of the oil gap and the aluminum foil, and has low insulation fault prediction accuracy and insufficient applicability of the model.

[0007] To achieve the above object, the present invention provides a simulation method for an oil-paper capacitor bushing with uneven moisture. The technical solution of the present invention comprises the following steps:

[0008] Step S1, determining the parameters of the oil-paper capacitor bushing, building a finite element model of the oil-paper capacitor bushing, the model including a conductive rod, insulating paper, insulating oil and aluminum foil; meshing the finite element model;

[0009] Step S2, dividing each layer of insulating paper in the finite element model into a plurality of intervals in the axial direction; setting the moisture content of each interval;

[0010] Step S3, preparing a plurality of insulating paper samples with different moisture contents in the laboratory, and measuring their complex relative dielectric constants respectively; measuring the complex relative dielectric constant of the insulating oil sample;

[0011] Step S4, according to the measured complex relative dielectric constants of the insulating paper sample and the insulating oil sample, respectively calculate their relative dielectric constants and electrical conductivity, input the relative dielectric constants and electrical conductivity of the insulating paper sample and the insulating oil sample into the material properties of the corresponding parts of the finite element model, and assign values ​​to the properties of the materials of each part of the finite element model;

[0012] Step S5, performing frequency domain dielectric spectrum simulation calculation on the finite element model to obtain a complex relative dielectric constant curve of the finite element model of the oil-paper capacitor bushing that is unevenly damped in the axial and radial directions.

[0013] Preferably, in the above-mentioned simulation method for unevenly damped oil-paper capacitor bushing, in step S2, the division calculation function for axially dividing each layer of insulating paper in the finite element model into multiple intervals is:

[0014] f(N)=[L N / ΔL] (1)

[0015] Where, L N It represents the axial length of the Nth layer of insulating paper, and ΔL is the length gradient.

[0016] Preferably, in the above-mentioned simulation method for the oil-paper capacitor bushing with uneven moisture, in the step S1, the specific process of building the finite element model is:

[0017] (1) In the COMSOL Multiphysics AC / DC module, set the conductive rod to a cylindrical structure;

[0018] (2) Building a three-layer hollow cylindrical insulating paper structure around the conductive rod;

[0019] (3) After each layer of insulating paper is built, a layer of oil gap and aluminum foil is built on the periphery. The axial length of the oil gap and aluminum foil is equal to that of each layer of insulating paper. Repeat three times.

[0020] Preferably, in the above-mentioned simulation method for unevenly damped oil-paper capacitor bushing, in step S1, the meshing process is specifically: tetrahedral meshing is performed on the finite element model, wherein the insulating paper and the conductive rod use refined meshes, and the aluminum foil and the oil gap use ultra-fine meshes.

[0021] Preferably, in the above-mentioned simulation method for unevenly damped oil-paper capacitor bushing, in step S4, the relative dielectric constant calculation formula of the insulating paper sample and the insulating oil sample is:

[0022] ε r =ε′ r (2)

[0023] In the formula, ε′ r is the real part of the complex relative permittivity;

[0024] The conductivity calculation formula of insulating paper samples and insulating oil samples is:

[0025] σ=ε″ r ε0ω (3)

[0026] In the formula, ε″ r is the imaginary part of the complex relative permittivity, ε0 ​​is the permittivity of vacuum, and ω is the angular frequency.

[0027] Preferably, in the above-mentioned simulation method of the oil-paper capacitor bushing with uneven moisture, in step S5, boundary conditions are set in COMSOL Multiphysics software, the conductive rod of the finite element model is set as the signal input segment, and an AC voltage signal is input, the outermost aluminum foil is set to the ground potential, and a grounding point is added.

[0028] Preferably, in the above-mentioned simulation method for the oil-paper capacitor bushing with uneven moisture, in the step S5, the relative dielectric constant and conductivity of the aluminum foil and the conductive rod in the finite element model are provided by COMSOL Multiphysics software, the oil gap thickness of each layer of insulating oil is set, the finite element model of the oil-paper capacitor bushing with uneven moisture in the axial and radial directions is globally calculated, the model is subjected to frequency domain analysis at different frequencies, the complex relative dielectric constant of the model at different frequency points is obtained, and then the complex relative dielectric constant curve of the finite element model of the oil-paper capacitor bushing with uneven moisture in the axial and radial directions is obtained through data fitting.

[0029] Compared with the existing technology, the present invention has the following beneficial effects:

[0030] The present invention builds a finite element model of an oil-paper capacitor bushing in a COMSOL Multiphysics AC / DC module. The finite element model includes a conductive rod, insulating paper, aluminum foil and an oil gap. A plurality of intervals are divided in the axial direction of each layer of insulating paper. The moisture content of each interval of each layer of insulating paper is set according to the uneven moisture distribution. Insulating paper samples with multiple moisture contents are prepared in a laboratory, and the complex relative dielectric constant of each insulating paper sample is measured respectively. The complex relative dielectric constant of the insulating oil sample is also measured at the same time. The relative dielectric constant and conductivity of the insulating paper sample and the insulating oil sample are calculated according to the measured complex relative dielectric constants of the insulating paper sample and the insulating oil sample respectively, and these values ​​are input into the material properties corresponding to the finite element model. The COMSOL Multiphysics software is used for simulation calculation to obtain the complex relative dielectric constant data curve of the oil-paper capacitor bushing with uneven moisture in the axial direction and radial direction. The model fully considers the uneven moisture in the axial direction and radial direction of the oil-paper capacitor bushing, and considers the influence of the aluminum foil and the oil gap at the same time, thereby improving the frequency domain dielectric spectrum simulation prediction accuracy of the uneven moisture of the oil-paper capacitor bushing. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a finite element model diagram of the oil-paper capacitor bushing with uneven moisture in the axial direction and radial direction of the present invention.

[0032] Figure 2 It is a mesh division diagram of the finite element model of the present invention.

[0033] Figure 3 It is a moisture setting diagram of each interval of each layer of insulation paper of the finite element model of the present invention.

[0034] Figure 4 This is a sample diagram of an oil-paper capacitor bushing that is unevenly damped and prepared in a laboratory according to the present invention.

[0035] Figure 5 It is a dielectric response test diagram of the insulating oil sample of the oil-paper capacitor bushing prepared in the laboratory of the present invention.

[0036] Figure 6 is a complex relative dielectric constant curve of the insulating oil sample of the present invention.

[0037] Figure 7 It is a complex relative dielectric constant curve diagram of the uniformly damp insulating paper of the present invention.

[0038] Figure 8 It is a complex relative dielectric constant curve diagram obtained by simulation calculation of No. 1, No. 2 and No. 3 finite element models of the present invention.

[0039] Fig. 9 It is a complex relative dielectric constant curve diagram of different oil gap thicknesses of the No. 1 finite element model of the present invention.

[0040] Fig.10 It is a complex relative dielectric constant curve diagram of different oil gap thicknesses of the No. 2 finite element model of the present invention.

[0041] Fig.11 It is a complex relative dielectric constant curve diagram of different oil gap thicknesses of the No. 3 finite element model of the present invention.

[0042] Fig.12 Graph showing the relative errors of the real and imaginary parts of the complex relative permittivity of the finite element model of the present invention and the casing sample. DETAILED DESCRIPTION

[0043] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the invention is not limited by the specific implementation modes.

[0044] The simulation method of the oil-paper capacitor bushing with uneven moisture absorption specifically comprises the following steps:

[0045] Step S1, determine the parameters of the oil-paper capacitor bushing, the parameters include the length and outer radius of the conductive rod, the number of layers of insulating paper, the thickness of each layer of insulating paper, the axial length of each layer of insulating paper, the thickness and axial length of each layer of aluminum foil and the thickness of the oil gap. Build a finite element model of the oil-paper capacitor bushing, the model includes a conductive rod, insulating paper, insulating oil and aluminum foil, the constructed finite element model of the oil-paper capacitor bushing is as follows Figure 1 As shown, the specific process is:

[0046] (1) In the COMSOL Multiphysics AC / DC module, set the conductive rod to a cylindrical structure;

[0047] (2) Building a three-layer hollow cylindrical insulating paper structure around the conductive rod;

[0048] (3) After each layer of insulating paper is built, a layer of oil gap and aluminum foil is built on the periphery. The axial length of the oil gap and aluminum foil is equal to that of each layer of insulating paper. Repeat three times.

[0049] The finite element model is meshed as follows: Figure 2 As shown, the tetrahedral mesh method is selected, in which the insulating paper and the conductive rod use a refined mesh, and the aluminum foil and the oil gap use an ultra-fine mesh.

[0050] Step S2: Divide each layer of insulating paper in the finite element model into multiple intervals in the axial direction, and set the moisture content of each interval, wherein the division calculation function is:

[0051] f(N)=[L N / ΔL] (1)

[0052] Where, L NIt represents the axial length of the Nth layer of insulating paper, and ΔL is the length gradient.

[0053] Through the division calculation function, the axial interval division of each layer of insulation paper in the finite element model and the moisture control accuracy of each interval of each layer of insulation paper in the preparation of unevenly damped oil-paper capacitor bushings are realized, thereby improving the simulation calculation accuracy of the finite element model.

[0054] Step S3, prepare 15 insulating paper samples with different moisture contents in the laboratory, wherein each insulating paper sample is uniformly damped, and the moisture content of each insulating paper sample corresponds to the moisture content of an interval in the insulating paper in the finite element model. During this period, the moisture content of the insulating paper sample is measured using a Karl Fischer moisture tester to ensure that the moisture content of each insulating paper sample is consistent with the moisture content set for each interval of the insulating paper in the finite element model, and then a dielectric response tester is used to measure the complex relative dielectric constant data of each insulating paper sample in different frequency domains, as shown in Tables 1 and 2, and the complex relative dielectric constant data of the insulating paper samples with different moisture contents in different frequency domains are fitted into a curve graph, as shown in Tables 1 and 2. Figure 7 shown.

[0055] Table 1 Real part of complex relative permittivity ε′ of insulating paper samples with different moisture contents paper data

[0056]

[0057] Table 2 Imaginary part of complex relative dielectric constant ε″ of insulating paper samples with different moisture contents paper data

[0058]

[0059] The complex relative dielectric constant of the insulating oil sample is measured. The specific process is as follows: first, pour the insulating oil sample into Figure 5 In the three-electrode measuring container shown in the figure, the upper electrode plate of the container is connected to the output end of the dielectric tester, and the lower electrode plate is connected to the input end of the dielectric tester. The distance between the upper and lower electrode plates is kept at 2 mm. Then the complex relative dielectric constant of the insulating oil sample is measured and fitted into a curve as shown in Figure 6 shown.

[0060] Among them, the relative dielectric constant calculation formula of the insulating paper sample and the insulating oil sample is:

[0061] ε r =ε′ r (2)

[0062] In the formula, ε′ r is the real part of the complex relative permittivity;

[0063] The conductivity calculation formula of insulating paper samples and insulating oil samples is:

[0064] σ=ε″ r ε0ω (3)

[0065] In the formula, ε″ r is the imaginary part of the complex relative permittivity, ε0 ​​is the permittivity of vacuum, and ω is the angular frequency.

[0066] Step S4, according to the measured complex relative dielectric constants of the insulating paper sample and the insulating oil sample, respectively calculate their relative dielectric constants and conductivity, input the relative dielectric constants and conductivity of the insulating paper sample and the insulating oil sample into the material properties of the corresponding parts of the finite element model, and obtain three finite element models with different moisture contents, which are respectively recorded as No. 1, No. 2 and No. 3 finite element models of oil-paper capacitor bushing with axial and radial uneven moisture.

[0067] Step S5, the finite element model is subjected to frequency domain dielectric spectrum simulation calculation, and the complex relative dielectric constant curve of the finite element model of the oil-paper capacitor bushing with uneven damping in the axial and radial directions is obtained. The specific process is as follows: first, the boundary conditions are set in the COMSOL Multiphysics software, the conductive rod of the finite element model is set as the signal input segment, and the AC voltage signal is input, the outermost aluminum foil is set as the ground potential, and the grounding point is added to obtain a test signal consistent with the actual frequency domain dielectric response test. The relative dielectric constant and conductivity of the aluminum foil and the conductive rod in the finite element model are provided by the COMSOL Multiphysics software, and then the oil gap thickness of each layer of insulating oil is set, and the finite element model of the oil-paper capacitor bushing with uneven damping in the axial and radial directions is globally calculated, and the model is subjected to frequency domain analysis at different frequencies to obtain the complex relative dielectric constant of the model at different frequency points, and then the complex relative dielectric constant curve of the finite element model of the oil-paper capacitor bushing with uneven damping in the axial and radial directions is obtained through data fitting.

[0068] Figure 8 is a complex relative dielectric constant curve obtained by simulation calculation of the finite element model of the oil-paper capacitor bushings No. 1, No. 2 and No. 3 of the present invention that are unevenly damp in the axial and radial directions, wherein ε′ total represents the real part of the complex relative permittivity of the bushing model, ε″ total Represents the imaginary part of the complex relative dielectric constant of the bushing model. Three different oil gaps were set in the finite element model of the oil-paper capacitor bushing with axial and radial uneven moisture, No. 1, No. 2 and No. 3, respectively, and the finite element model was simulated and calculated to obtain the complex relative dielectric constant curves of the finite element model of the oil-paper capacitor bushing with axial and radial uneven moisture with different oil gaps.

[0069] Fig. 9 The complex relative dielectric constant curves of different oil gap thicknesses of the finite element model of the oil-paper capacitor bushing with uneven axial and radial moisture absorption of the present invention are shown, Fig.10The complex relative dielectric constant curves of different oil gap thicknesses of the finite element model of the oil-paper capacitor bushing with uneven axial and radial moisture absorption of the present invention are shown, Fig.11 It is a complex relative dielectric constant curve of different oil gap thicknesses of the finite element model of the oil-paper capacitor type bushing with uneven moisture in the axial direction and radial direction of the present invention.

[0070] like Figure 4 As shown, in order to verify the accuracy of the simulation calculation of the finite element model of the present invention, this embodiment prepared three axially and radially unevenly damp oil-paper capacitor bushing samples that were consistent with the finite element model in size, material, and moisture conditions in the laboratory, and were recorded as No. 1, No. 2, and No. 3 axially and radially unevenly damp oil-paper capacitor bushing samples.

[0071] The present invention measures the complex relative dielectric constant data of the oil-paper capacitor bushing samples No. 1, No. 2 and No. 3 which are unevenly damped in the axial direction and radial direction, and then performs error calculation and analysis on the complex relative dielectric constant data of the finite element model and the corresponding unevenly damped oil-paper capacitor bushing samples, and obtains an error curve diagram as shown in FIG. Fig.12 As shown, the error calculation formula is:

[0072]

[0073] Where, MRE' Real Represents the error between the measured and simulated values ​​of the real part of the complex relative permittivity, ε' total (Mea) represents the real part of the measurement value, ε' total (Sim) represents the real part simulation value, MREI ” mag is the error between the measured and simulated values ​​of the imaginary part of the complex relative permittivity, ε” total (Mea) represents the imaginary part of the measurement, ε” total (Sim) represents the imaginary part simulation value.

[0074] The results show that the simulation value of the finite element model of the oil-paper capacitor bushing with axial and radial uneven moisture constructed by the present invention and the measured value of the oil-paper capacitor bushing samples with axial and radial uneven moisture prepared in the laboratory are highly consistent, and the average errors of the real and imaginary parts of the simulation value and the measured value of the complex relative dielectric constant are 9.29% and 10.21% respectively, which proves that the proposed bushing finite element model is accurate and can realize the accurate prediction of the frequency domain dielectric spectrum of the bushing under the state of uneven moisture.

[0075] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and illustration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is apparent that many changes and variations are possible in light of the above teachings. The exemplary embodiments are selected and described for the purpose of explaining the specific principles of the present invention and its practical application, thereby enabling those skilled in the art to implement and utilize various exemplary embodiments of the present invention and various selections and variations. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A simulation method for an oil-paper capacitor bushing with uneven moisture, characterized in that: The steps include: Step S1, determining the parameters of the oil-paper capacitor bushing, building a finite element model of the oil-paper capacitor bushing, the model including a conductive rod, insulating paper, insulating oil and aluminum foil; meshing the finite element model; Step S2, dividing each layer of insulating paper in the finite element model into a plurality of intervals in the axial direction; Set the moisture content in each interval; Step S3, preparing a plurality of insulating paper samples with different moisture contents in the laboratory, and measuring their complex relative dielectric constants respectively; measuring the complex relative dielectric constant of the insulating oil sample; Step S4, according to the measured complex relative dielectric constants of the insulating paper sample and the insulating oil sample, respectively calculate their relative dielectric constants and electrical conductivity, input the relative dielectric constants and electrical conductivity of the insulating paper sample and the insulating oil sample into the material properties of the corresponding parts of the finite element model, and assign values ​​to the properties of the materials of each part of the finite element model; Step S5, performing frequency domain dielectric spectrum simulation calculation on the finite element model to obtain a complex relative dielectric constant curve of the finite element model of the oil-paper capacitor bushing that is unevenly damped in the axial and radial directions.

2. The method for simulating unevenly damped oil-paper capacitor bushing according to claim 1, characterized in that: In step S2, the division calculation function for dividing each layer of insulating paper in the finite element model into multiple intervals in the axial direction is: f(N)=[L N / ΔL] (1) Where, L N It represents the axial length of the Nth layer of insulating paper, and ΔL is the length gradient.

3. The method for simulating unevenly damped oil-paper capacitor bushing according to claim 1, characterized in that: In step S1, the specific process of building the finite element model is as follows: (1) In the COMSOL Multiphysics AC / DC module, set the conductive rod to a cylindrical structure; (2) Building a three-layer hollow cylindrical insulating paper structure around the conductive rod; (3) After each layer of insulating paper is built, a layer of oil gap and aluminum foil is built on the periphery. The axial length of the oil gap and aluminum foil is equal to that of each layer of insulating paper. Repeat three times.

4. The method for simulating unevenly damped oil-paper capacitor bushing according to claim 3, characterized in that: In the step S1, the meshing process is specifically as follows: tetrahedral meshing is performed on the finite element model, wherein the insulating paper and the conductive rods are divided into fine meshes, and the aluminum foil and the oil gap are divided into ultra-fine meshes.

5. The method for simulating unevenly damped oil-paper capacitor bushing according to claim 1, characterized in that: In step S4, the relative dielectric constant calculation formula of the insulating paper sample and the insulating oil sample is: e r =e′ r (2) In the formula, ε′ r is the real part of the complex relative permittivity; The conductivity calculation formula of insulating paper samples and insulating oil samples is: σ=ε″ r 00:00 (3) In the formula, ε″ r is the imaginary part of the complex relative permittivity, ε0 ​​is the permittivity of vacuum, and ω is the angular frequency.

6. The method for simulating unevenly damped oil-paper capacitor bushing according to claim 1, characterized in that: In step S5, boundary conditions are set in COMSOL Multiphysics software, the conductive rod of the finite element model is set as a signal input segment, an AC voltage signal is input, the outermost aluminum foil is set as a ground potential, and a grounding point is added.

7. The method for simulating unevenly damped oil-paper capacitor bushing according to claim 1, characterized in that: In the step S5, the relative dielectric constant and conductivity of the aluminum foil and the conductive rod in the finite element model are provided by COMSOL Multiphysics software, the oil gap thickness of each layer of insulating oil is set, a global calculation is performed on the finite element model of the oil-paper capacitor bushing with uneven moisture in the axial and radial directions, the model is subjected to frequency domain analysis at different frequencies to obtain the complex relative dielectric constant of the model at different frequency points, and then the complex relative dielectric constant curve of the finite element model of the oil-paper capacitor bushing with uneven moisture in the axial and radial directions is obtained through data fitting.

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