Insulation condition prediction method for non-uniformly aged oiled paper capacitive bushing

Abstract

The invention relates to the technical field of fault diagnosis of oiled paper capacitive bushings, in particular to a method for predicting the insulation condition of a non-uniformly aged oiled paper capacitive bushing. Comprising the following steps: acquiring the outer radius of a sleeve conducting 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 axial length of each layer of aluminum foil and the complex relative dielectric constant of insulating oil; dividing each layer of insulation paper interval into a plurality of insulation paper units with the same length along the axial direction; predicting a non-uniform aging state distribution condition and respectively setting a polymerization degree of each insulation paper unit; obtaining a complex relative dielectric constant of each insulation paper unit; and obtaining a mathematical expression of the enhanced X model for predicting the insulation condition of the oiled paper capacitive bushing in the non-uniform aging state. According to the method, the non-uniform aging effect of the insulation paper in the radial direction and the axial direction is considered, the prediction method of the enhanced X model is more reasonable, and the insulation condition prediction of the oiled paper capacitive bushing is more accurate.

Description

Technical Field

[0001] The invention relates to the technical field of oil-paper capacitor bushing fault diagnosis, and in particular to a method for predicting the insulation condition of an unevenly aged oil-paper capacitor bushing. Background Art

[0002] Oil-paper capacitor bushing is an important power equipment that connects power transformer windings and power system lines. Its interior is mainly composed of insulating paper and insulating oil. The performance of insulating paper determines the operating safety, stability and service life of the oil-paper capacitor bushing. Therefore, accurate status assessment of insulating paper can effectively avoid operating accidents of oil-paper capacitor bushings.

[0003] When working with power for a long time, an unevenly distributed temperature field will be generated inside the oil-paper capacitor bushing, which will lead to unequal aging degrees of the insulation paper in different parts of the oil-paper capacitor bushing, that is, the insulation paper has undergone uneven aging. In recent years, frequency domain dielectric spectroscopy has been widely used to detect the aging state of oil-immersed insulation paper. Its principle is to apply sinusoidal alternating current of different frequencies on both sides of the oil-immersed insulation paper in sequence through a frequency domain dielectric response tester, and then the complex relative dielectric constant of the oil-immersed insulation paper at each frequency can be obtained. The complex relative dielectric constant has a quantitative relationship with the aging degree (polymerization degree) of the oil-immersed insulation paper, so the aging degree (polymerization degree) of the oil-immersed insulation paper can be evaluated by measuring the complex relative dielectric constant.

[0004] The traditional X-model describes the quantitative relationship between the complex relative dielectric constants of the insulating paper, insulating oil and composite insulating oil-paper in the oil-paper capacitor bushing, and can be used to predict the FDS curve of the oil-paper capacitor bushing under uniform aging. However, the traditional X-model assumes that the aging state of the insulating paper in the oil-paper capacitor bushing along the axial and radial directions is consistent. In fact, the internal temperature distribution of the oil-paper capacitor bushing in operation is uneven. The temperature at the bottom and inside of the oil-paper capacitor bushing is much higher than other parts, and the uneven temperature field will cause the insulating paper to age unevenly in the axial and radial directions. Therefore, the accuracy of the traditional X-model cannot be guaranteed, and the uneven aging in the axial and radial directions is not taken into account, which needs to be further improved.

[0005] In addition, some scholars have proposed a modified X model that takes into account uneven aging for the uneven aging of oil-paper capacitor bushings. This model can realize the FDS curve prediction under radial uneven aging. However, this model assumes that the axial lengths of each layer of insulating paper in the oil-paper capacitor bushing are equal, and also assumes that the axial lengths of each layer of aluminum foil are equal, which is inconsistent with the actual situation of the oil-paper capacitor bushing. Therefore, the accuracy of the prediction needs to be studied; moreover, the modified X model does not consider the uneven aging of the insulating paper of the oil-paper capacitor bushing in the axial direction, so its applicability is limited. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for predicting the insulation condition of an unevenly aged oil-paper capacitor bushing, which takes into account the uneven aging of the insulating paper of the oil-paper capacitor bushing in the radial and axial directions. The insulation condition prediction model is more accurate, which helps to improve the safety and stability of the power system operation.

[0007] In order to solve the above technical problems, the present invention provides a method for predicting the insulation condition of an unevenly aged oil-paper capacitor bushing, comprising the following steps:

[0008] S11, obtaining basic parameters of the oil-paper capacitor bushing, wherein the basic parameters include: the outer radius of the conductive rod of the oil-paper capacitor bushing, 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 axial length of each layer of aluminum foil, and the complex relative dielectric constant of the insulating oil;

[0009] S12, dividing the insulating paper intervals, wherein the insulating paper intervals are the insulating paper in the area where the lengths of the aluminum foil and the insulating paper of the same layer overlap, and dividing the insulating paper intervals of each layer into a plurality of insulating paper units of equal length along the axial direction;

[0010] S13, constructing a non-uniform aging state prediction model for multiple layers of the insulating paper, and setting the polymerization degree of each insulating paper unit respectively;

[0011] S14, obtaining the complex relative dielectric constant of each of the insulating paper units;

[0012] S15, the mathematical expression of the enhanced X-model for predicting the insulation condition of oil-paper capacitor bushing under non-uniform aging state is obtained:

[0013]

[0014] In the formula, is the complex relative dielectric constant of the oil-paper capacitor bushing, ε' rtot yes The real part of rtot yes The imaginary part, L i is the axial length of the i-th layer of aluminum foil, r i is the outer radius of the i-th layer of insulating paper, f(i) is the number of insulating paper units divided by the i-th layer of insulating paper, N is the total number of insulating paper layers, is the complex relative dielectric constant of the kth insulating paper unit of the i-th insulating paper layer, is the complex relative dielectric constant of the insulating oil, and X is the thickness ratio of each layer of insulating paper to the corresponding layer of insulating oil paper composited with insulating oil and insulating paper.

[0015] Preferably, the method for obtaining the complex relative dielectric constant of the insulating oil in step S11 is: pouring the insulating oil into a three-electrode measurement container, keeping a distance of 2 mm between the upper and lower electrode plates, and measuring the complex relative dielectric constant of the insulating oil using an instrument.

[0016] Preferably, in step S11, the number of layers of insulating paper and aluminum foil is equal, and the length of the insulating paper in the same layer is greater than or equal to the length of the aluminum foil.

[0017] Preferably, the function expression for dividing the insulating paper intervals in step S12 is:

[0018]

[0019] Where, T top is the measured temperature at the top of the oil-paper capacitor bushing, T down is the measured bottom temperature of the oil-paper capacitor bushing, ΔT is the temperature interval, L1 is the axial length of the first layer of aluminum foil, L i is the axial length of the i-th layer of aluminum foil, and [] is a function of rounding to a positive integer.

[0020] Preferably, in step S12, the temperature distribution inside the oil-paper capacitor bushing is uneven, and the aging state of the insulating paper along the axial direction and radial direction is uneven.

[0021] Preferably, in step S13, two or more insulating paper units with different degrees of polymerization are radially arranged between the multiple layers of insulating paper.

[0022] Preferably, in the step S13, at least two insulating paper units with different degrees of polymerization are provided in the axial direction between each layer of the insulating paper.

[0023] Preferably, the degree of polymerization of the insulating paper unit in step S13 is set in a range from 0 to 1500.

[0024] Preferably, the method for obtaining the complex relative dielectric constant of each insulating paper unit in step S14 is: making insulating paper according to the degree of polymerization set in step S13, using an instrument to measure the complex relative dielectric constant of the made insulating paper, as the complex relative dielectric constant of the insulating paper unit with the corresponding degree of polymerization.

[0025] Compared with the existing technology, the present invention has the following beneficial effects:

[0026] The invention predicts the insulation condition of the oil-paper capacitor bushing under the non-uniform aging state by constructing an enhanced X-model, takes into account the influence of the non-uniform aging effect of the insulating paper of the oil-paper capacitor bushing in radial and axial directions on the complex relative dielectric constant characteristics, and is more comprehensive than the prediction method of the prior art, so that the insulation condition prediction of the oil-paper capacitor bushing is more accurate, and can provide a reference model basis for the subsequent non-uniform aging state evaluation of the insulating paper of the oil-paper capacitor bushing, which is helpful to timely discover the potential risks of the oil-paper capacitor bushing insulation system, thereby improving the safety and stability of the power system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a flow chart of a method for predicting the insulation condition of an unevenly aged oil-paper capacitor bushing.

[0028] Figure 2 FIG. 4 is a schematic diagram of the structure of the enhanced X model according to an embodiment of the present invention.

[0029] Figure 3 This is a schematic diagram of the distribution structure of the degree of polymerization of insulating paper units including three sets of prediction models No. 1, No. 2 and No. 3 according to an embodiment of the present invention.

[0030] Figure 4 This is a coordinate diagram of the complex relative dielectric constant curve of the oil-paper capacitor bushing corresponding to the prediction model No. 1 of the verification test of the enhanced X model of the embodiment of the present invention.

[0031] Figure 5 It is a coordinate diagram of the complex relative dielectric constant curve of the oil-paper capacitor bushing corresponding to the prediction model No. 2 of the verification test of the enhanced X model of the embodiment of the present invention.

[0032] Figure 6 This is a coordinate diagram of the complex relative dielectric constant curve of the oil-paper capacitor bushing corresponding to the prediction model No. 3 of the verification test of the enhanced X model of the embodiment of the present invention.

[0033] Figure 7 This is a diagram showing the error analysis results of the complex relative dielectric constant of the oil-paper capacitor bushing corresponding to prediction model No. 1 of the verification test of the enhanced X model of an embodiment of the present invention.

[0034] Figure 8 This is a diagram showing the error analysis results of the complex relative dielectric constant of the oil-paper capacitor bushing corresponding to the prediction model No. 2 of the verification test of the enhanced X model of an embodiment of the present invention.

[0035] Fig. 9 This is a diagram showing the error analysis results of the complex relative dielectric constant of the oil-paper capacitor bushing corresponding to prediction model No. 3 of the verification test of the enhanced X model of an embodiment of the present invention. DETAILED DESCRIPTION

[0036] 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.

[0037] Frequency Domain Spectroscopy (FDS) is a new insulation detection method. The method is: applying a variable frequency AC voltage signal to the insulating material, and testing the change law of the complex capacitance, complex relative dielectric constant, and dielectric loss factor of the insulating material with frequency. The insulation condition of the insulating material is evaluated by analyzing the change law of the complex capacitance, complex relative dielectric constant, and dielectric loss factor. FDS measurement of the insulation state of oil-paper capacitor bushing is to extend the conventional power frequency dielectric loss and capacitance measurement of the above method to low-frequency and high-frequency bands, such as 0.1mHz to 1kHz, so as to reflect the polarization and loss conditions in a wider frequency domain.

[0038] like Figure 1 As shown, this embodiment discloses a method for predicting the insulation condition of an unevenly aged oil-paper capacitor bushing, comprising the following steps:

[0039] S11, obtaining basic parameters of the oil-paper capacitor bushing, including the outer radius of the conductive rod of the oil-paper capacitor bushing, 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 axial length of each layer of aluminum foil, and the complex relative dielectric constant of the insulating oil.

[0040] It is worth noting that the thickness of each layer of aluminum foil is negligible; if the number of layers of insulating paper and aluminum foil is equal, the thickness of each layer of insulating paper and each layer of aluminum foil is uniform, and the length of the insulating paper in the same layer is greater than or equal to the length of the aluminum foil.

[0041] Specifically, the method for determining the complex relative dielectric constant of the insulating oil is as follows: pour the insulating oil into a three-electrode measuring container, keep 2 mm between the upper and lower electrode plates, and use an instrument to measure the complex relative dielectric constant of the insulating oil; when performing a frequency domain dielectric spectrum test on the insulating oil, pour the insulating oil into the three-electrode measuring container, use a dielectric response tester to connect the signal output end to the upper copper electrode plate, and connect the signal receiving end to the lower copper electrode plate, and the complex relative dielectric constant of the insulating oil can be measured.

[0042] S12, dividing the insulation paper intervals, the insulation paper intervals are the insulation paper in the area where the length of the aluminum foil and the insulation paper of the same layer overlap, and dividing each layer of insulation paper intervals into a plurality of insulation paper units of equal length along the axial direction. Figure 2, since the thickness of each layer of insulating paper is much smaller than the length of the same layer of aluminum foil, the electric field at the edge of the insulating paper can be ignored, that is, the insulating paper that exceeds the length of the aluminum foil will not affect the complex relative dielectric constant of the oil-paper capacitor bushing, so the insulating paper that exceeds the length of the aluminum foil does not need to be considered. The function expression for dividing the insulating paper interval is:

[0043]

[0044] Where f(i) is the number of units divided by the i-th layer of insulation paper, T top is the measured temperature at the top of the oil-paper capacitor bushing, T down is the measured bottom temperature of the oil-paper capacitor bushing, ΔT is the temperature interval, L1 is the axial length of the first layer of aluminum foil, L i is the axial length of the i-th layer of aluminum foil, and [] is a function of rounding to a positive integer.

[0045] Furthermore, the temperature distribution inside the oil-paper capacitor bushing is uneven, and the aging state of the insulating paper in the axial and radial directions is uneven. When working with power for a long time, an unevenly distributed temperature field will be generated inside the oil-paper capacitor bushing, resulting in uneven aging of the insulating paper in different parts of the oil-paper capacitor bushing. The ΔT of each layer is the same, and the value of ΔT is less than the temperature difference between the top and bottom of the end screen of the oil-paper capacitor bushing. The smaller the value of ΔT, the more insulating paper units are divided.

[0046] S13, construct a prediction model for the uneven aging state of multiple layers of insulation paper, and set the degree of polymerization of each insulation paper unit respectively. When constructing the prediction model, the temperature field in the oil-paper capacitor bushing can be analyzed to predict the uneven aging distribution of each layer of insulation paper, and then the degree of polymerization of each insulation paper unit can be set respectively; it can be understood that in order to fully consider the uneven aging state of the insulation paper along the axial and radial directions, and the setting of the degree of polymerization of each insulation paper unit is irrelevant, so the multiple layers of insulation paper are provided with more than two insulation paper units with different degrees of polymerization along the radial direction, and each layer of insulation paper is provided with more than two insulation paper units with different degrees of polymerization along the axial direction.

[0047] It is worth noting that when testing the polymerization degree of insulation paper in the laboratory, it is known that the polymerization degree of unaged insulation paper is about 1200, and the polymerization degree of insulation paper at the end of aging is between 200 and 250. Therefore, the polymerization degree setting range of the insulation paper unit is between 0 and 1500.

[0048] S14, obtaining the complex relative dielectric constant of each insulating paper unit. Specifically, the method for obtaining the complex relative dielectric constant of each insulating paper unit is: making insulating paper according to the degree of polymerization set in step S13, using an instrument to measure the complex relative dielectric constant of the made insulating paper, as the complex relative dielectric constant of the insulating paper unit corresponding to the degree of polymerization.

[0049] According to the polymerization degree set in step S13, insulating paper with various polymerization degrees can be produced through accelerated thermal aging experiments. During the production process, a viscometer is used to measure the polymerization degree of the insulating paper to ensure that the production of insulating paper with various polymerization degrees is completed accurately, and a dielectric response tester is used to measure the complex relative dielectric constant corresponding to the insulating paper with various polymerization degrees. The complex relative dielectric constant of insulating paper and insulating paper unit with the same polymerization degree is the same; in addition, insulating paper with different polymerization degrees can be produced through accelerated thermal aging experiments, and a dielectric response tester is used to measure the FDS data of the insulating paper and draw a coordinate curve diagram of the polymerization degree and the complex relative dielectric constant of insulating paper with different aging degrees, so that when the prediction model is adjusted later, the complex relative dielectric constant corresponding to the polymerization degree of the insulating paper unit can be quickly obtained according to the coordinate curve diagram.

[0050] S15, the mathematical expression of the enhanced X-model for predicting the insulation condition of oil-paper capacitor bushing under non-uniform aging state is obtained:

[0051]

[0052] In the formula, is the complex relative dielectric constant of the oil-paper capacitor bushing, ε' rtot yes The real part of rtot yes The imaginary part, L i is the axial length of the i-th layer of aluminum foil, r i is the outer radius of the i-th layer of insulating paper, f(i) is the number of insulating paper units divided by the i-th layer of insulating paper, N is the total number of insulating paper layers, is the complex relative dielectric constant of the kth insulating paper unit of the i-th insulating paper layer, is the complex relative dielectric constant of the insulating oil, X is the thickness ratio of each layer of insulating paper to the corresponding layer of insulating oil paper composited with insulating oil and insulating paper, and the value range of X is between 0.9 and 1.

[0053] like Figure 3As shown, in this embodiment, the enhanced X-model is used to predict the insulation condition of the oil-paper capacitor bushing under the non-uniform aging state, and three groups of prediction models, No. 1, No. 2, and No. 3, are respectively constructed for experimental verification, and the basic parameters of the three groups of prediction models are determined according to step S11, and the insulation paper interval division is completed according to step S12. The temperature interval ΔT in the three groups of prediction models is set to be one quarter of the temperature difference between the top and the bottom of the oil-paper capacitor bushing, so that the first layer of insulation paper is divided into four insulation paper units of equal length along the axial direction; according to step S13, the polymerization degree distribution order of the insulation paper units in the three groups of prediction models is respectively set.

[0054] Insulating paper is manufactured according to each polymerization degree set above through accelerated thermal aging experiment, and insulating paper units corresponding to the set polymerization degree are further manufactured, and the complex relative dielectric constant of each insulating paper unit is determined according to the polymerization degree of the insulating paper and the complex relative dielectric constant coordinate curve diagram, and the complex relative dielectric constant calculation of the oil-paper capacitor bushing corresponding to the three groups of prediction models is completed respectively according to the mathematical expression of the enhanced X model in step S15;

[0055] In addition, the corresponding oil-paper capacitor bushing physical test structures were built according to the distribution order of the degree of polymerization of the insulating paper units in the three sets of prediction models, and the complex relative dielectric constant measurements of the three sets of physical test structures were completed using FDS equipment.

[0056] Finally, through data analysis of three sets of prediction models and corresponding physical test structures, the reliability verification test of the enhanced X-model was completed, thereby realizing the prediction of the insulation condition of the oil-paper capacitor bushing under uneven aging conditions.

[0057] Calculated value of real part of complex relative dielectric constant ε′ of the whole insulation of oil-paper capacitor bushing calaulated and the measured value ε′ measured , imaginary part calculation value ε″ calaulated and the measured value ε″ measured Comparison Figure 4-6 As shown, Figure 4 Corresponding to prediction model No. 1, Figure 5 Corresponding to prediction model No. 2, Figure 6 Corresponding to prediction model No. 3.

[0058] Furthermore, the relative error analysis between the calculated and measured values ​​of the complex relative dielectric constant of the oil-paper capacitor bushing corresponding to the three sets of prediction models was performed. The relative error of the real part of the complex relative dielectric constant is RE′, and the relative error of the imaginary part is RE″. The error analysis results are shown in Table 1. Figure 7-9 shown.

[0059] Table 1. Relative error analysis results

[0060]

[0061]

[0062] The magnitude of the above error values ​​indicates that the error between the calculated data and the measured data is very small, almost approaching zero, which indicates that the calculated data, that is, the addition of the X model, is acceptable and its effectiveness has been further verified.

[0063] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A method for predicting the insulation condition of an unevenly aged oil-paper capacitor bushing, characterized in that: The following steps are involved: S11, obtaining basic parameters of the oil-paper capacitor bushing, wherein the basic parameters include: the outer radius of the conductive rod of the oil-paper capacitor bushing, 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 axial length of each layer of aluminum foil, and the complex relative dielectric constant of the insulating oil; S12, dividing the insulating paper intervals, wherein the insulating paper intervals are the insulating paper in the area where the lengths of the aluminum foil and the insulating paper of the same layer overlap, and dividing the insulating paper intervals of each layer into a plurality of insulating paper units of equal length along the axial direction; S13, constructing a non-uniform aging state prediction model for multiple layers of the insulating paper, and setting the polymerization degree of each insulating paper unit respectively; S14, obtaining the complex relative dielectric constant of each of the insulating paper units; S15, the mathematical expression of the enhanced X-model for predicting the insulation condition of oil-paper capacitor bushing under non-uniform aging state is obtained: In the formula, is the complex relative dielectric constant of the oil-paper capacitor bushing, ε'rtot is The real part of ε"rtot is The imaginary part, L i is the axial length of the i-th layer of aluminum foil, r i is the outer radius of the i-th layer of insulating paper, f(i) is the number of insulating paper units divided by the i-th layer of insulating paper, N is the total number of insulating paper layers, is the complex relative dielectric constant of the kth insulating paper unit of the i-th insulating paper layer, is the complex relative dielectric constant of the insulating oil, and X is the thickness ratio of each layer of insulating paper to the corresponding layer of insulating oil paper composited with insulating oil and insulating paper.

2. The insulation condition prediction method of unevenly aged oil-paper capacitor bushing according to claim 1 is characterized in that: The method for obtaining the complex relative dielectric constant of the insulating oil in step S11 is: pour the insulating oil into a three-electrode measurement container, keep 2 mm between the upper and lower electrode plates, and use an instrument to measure the complex relative dielectric constant of the insulating oil.

3. The insulation condition prediction method of unevenly aged oil-paper capacitor bushing according to claim 1 is characterized in that: In step S11, the number of layers of the insulating paper and the aluminum foil is equal, and the length of the insulating paper in the same layer is greater than or equal to the length of the aluminum foil.

4. The insulation condition prediction method of unevenly aged oil-paper capacitor bushing according to claim 3 is characterized in that: The function expression for dividing the insulating paper into intervals in step S12 is: Where, T top is the measured temperature at the top of the oil-paper capacitor bushing, T down is the measured bottom temperature of the oil-paper capacitor bushing, ΔT is the temperature interval, L1 is the axial length of the first layer of aluminum foil, L i is the axial length of the i-th layer of aluminum foil, and [] is a function of rounding to a positive integer.

5. The insulation condition prediction method of unevenly aged oil-paper capacitor bushing according to claim 3 is characterized in that: In step S12, the temperature distribution inside the oil-paper capacitor bushing is uneven, and the aging state of the insulating paper in the axial and radial directions is uneven.

6. The insulation condition prediction method of unevenly aged oil-paper capacitor bushing according to claim 1 is characterized in that: In the step S13, two or more insulating paper units with different polymerization degrees are arranged radially between the multiple layers of insulating paper.

7. The insulation condition prediction method of unevenly aged oil-paper capacitor bushing according to claim 6 is characterized in that: In the step S13, at least two insulating paper units with different degrees of polymerization are arranged in the axial direction between each layer of the insulating paper.

8. The insulation condition prediction method of unevenly aged oil-paper capacitor bushing according to claim 6 is characterized in that: The degree of polymerization of the insulating paper unit in step S13 is set in a range between 0 and 1500.

9. The insulation condition prediction method of unevenly aged oil-paper capacitor bushing according to claim 6 is characterized in that: The method for obtaining the complex relative dielectric constant of each insulating paper unit in step S14 is: making insulating paper according to the polymerization degree set in step S13, using an instrument to measure the complex relative dielectric constant of the made insulating paper, as the complex relative dielectric constant of the insulating paper unit with the corresponding polymerization degree.

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