A method for evaluating the uneven aging state of transformers by combining AC conductivity

Abstract

The present invention discloses a method for evaluating the uneven aging state of a transformer in combination with AC conductivity, belonging to the technical field of oil-paper insulation life assessment. The method, in combination with AC conductivity, directly reflects the change in the height of the potential barrier that needs to be overcome during ion transitions in the medium. By constructing a database showing the AC conductivity of insulating paperboards with different degrees of polymerization varying with frequency, as well as a database showing the AC conductivity of oil varying with frequency and an oil viscosity database, the amount of information on insulation medium degradation is enriched, and the uneven aging state of the transformer can be more accurately assessed. The main insulation structure of the transformer is gridded, and an expression for the overall AC conductivity of the main insulation structure of the transformer is obtained by utilizing the relationship between resistance and conductivity, thereby achieving a more realistic physical model construction of the transformer, effectively characterizing the relationship between its local structure and overall structure, and thereby quantitatively analyzing the uneven aging state.

Description

Technical Field

[0001] The invention belongs to the technical field of oil-paper insulation life assessment, and in particular relates to a method for assessing the uneven aging state of a transformer in combination with AC conductivity. Background Art

[0002] As key equipment in power systems, oil-immersed power equipment and its components are crucial for long-term stable operation. Differences in ambient temperature and load conditions across regions can cause insulation degradation in some power equipment, threatening the long-term reliability and service life of the equipment. Therefore, accurately evaluating the insulation condition of these equipment is crucial.

[0003] For oil-paper insulated equipment, power system operations and maintenance departments in all countries implement regular maintenance programs, using methods such as partial discharge, power frequency withstand voltage, power frequency dielectric loss, insulation resistance, dissolved gas analysis in oil, infrared imaging temperature, and winding DC resistance testing. Changes in characteristic parameters extracted from these various methods reflect the equipment's operating status. These methods provide relatively accurate assessment results for issues such as concentrated insulation defects or latent faults within the equipment. However, they are unable to provide quantitative analysis for issues such as uneven insulation aging. Instead, qualitative comparisons can be made based on factory parameter values ​​or current three-phase test values ​​for power equipment, such as power frequency dielectric loss and insulation resistance.

[0004] Therefore, a new technical solution is urgently needed in the existing technology to solve this problem. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention provides a method for evaluating the uneven aging state of a transformer in combination with AC conductivity, which is used to solve the problem that uneven insulation aging cannot be quantitatively analyzed.

[0006] To achieve the above object, the present invention adopts a technical solution: a method for evaluating the uneven aging state of a transformer in combination with AC conductivity, comprising the following steps:

[0007] S1. Perform AC conductivity and DC conductivity tests on insulating paperboard samples with different polymerization degrees at different temperatures; perform AC conductivity, DC conductivity and oil viscosity tests on insulating oil samples with different aging days at different temperatures;

[0008] S2. Construct a database of AC conductivity changes with frequency for insulating paperboards with different degrees of polymerization; construct a database of AC conductivity changes with frequency for oils with different aging days, and a database of oil viscosity;

[0009] S3. Meshing the main insulation structure of the transformer; obtaining an AC conductivity expression for the entire main insulation structure of the transformer using the relationship between resistance and conductivity; the overall AC conductivity expression is used to reflect the relationship between the local AC conductivity and the overall AC conductivity of the transformer, and the overall AC conductivity expression corresponds to a matrix composed of local AC conductivities; the local AC conductivity is the AC conductivity of each block obtained after meshing the main insulation structure of the transformer;

[0010] S4. Based on the AC conductivity expression in S3, a coupled equation group is constructed at different frequency points;

[0011] S5. Perform AC conductivity and DC conductivity tests on actual transformers at different temperatures; construct a curve library showing the AC conductivity of the measured transformer changing with frequency;

[0012] S6. Invert the measured AC conductivity value of the transformer at each frequency point in S5 as the output result of the equation in S4; obtain the AC conductivity matrix set at the frequency point according to the inversion result;

[0013] S7, screening the AC conductivity matrix set of each frequency point using the characteristic equation f, and obtaining the AC conductivity matrix corresponding to the maximum f value as the optimal AC conductivity matrix of each frequency point;

[0014] S8. Calculate the AC conductivity curve of the transformer as a whole based on the optimal AC conductivity matrix at each frequency point in S7 and the database in S2; compare it with the curve of the measured transformer AC conductivity varying with frequency in S5, and select the frequency point and AC conductivity matrix corresponding to the curve with the best fit;

[0015] S9. Based on the relationship between the degree of polymerization, oil viscosity and AC conductivity in the database of S2, the AC conductivity matrix selected in S8 is converted into a matrix composed of the local degree of polymerization of the transformer and the oil viscosity at the frequency point.

[0016] In the preferred S2, a dual translation method of frequency-temperature translation and conductivity translation is used to effectively expand the low-frequency band of AC conductivity. The traditional AC conductivity formula with a single relaxation time is modified to obtain a frequency-dependent mathematical model shape correction parameter α. Based on the modified AC conductivity, a database of the AC conductivity variation with frequency of insulating cardboards with different polymerization degrees, a database of the AC conductivity variation with frequency of oils with different aging days, and an oil viscosity database are constructed.

[0017] Preferably, the specific method of calculating and obtaining the AC conductivity curve of the entire transformer according to the AC conductivity optimal matrix of each frequency point in S7 and the database in S2 includes the following steps:

[0018] S801. Based on the AC conductivity values ​​in the optimal matrix at each frequency point and the field test temperature, and comparing the different AC conductivities at the same frequency point in the database of AC conductivity variation of insulating paperboard as a function of frequency (S2), a curve of AC conductivity variation of insulating paperboard as a function of frequency corresponding to each AC conductivity value in the matrix can be determined.

[0019] S802, determining the aging days of the transformer oil based on the oil viscosity database in S2; determining an AC conductivity curve of the transformer oil based on the database of AC conductivity changes of oils with different aging days as a function of frequency;

[0020] S803. Substitute the curve of the AC conductivity of the insulating paperboard corresponding to each AC conductivity value in the matrix S801 as a function of frequency and the AC conductivity curve of the transformer oil in S802 into the AC conductivity expression of the main insulation structure as a whole in S3 to obtain an AC conductivity curve for the entire transformer.

[0021] Compared to relaxation behavior characterized by complex permittivity and dissipation factor at different test temperatures, conductivity behavior provides a richer picture of insulation degradation. For oil-paper insulation, the slope of the AC conductivity curve is directly related to the moisture migration and degradation characteristics within the insulation. Furthermore, AC conductivity includes both relaxation activation energy and conductivity activation energy. Compared to the complex permittivity and dissipation factor, changes in conductivity activation energy are closely related to the internal moisture content and degree of aging, directly indicating changes in the potential barrier height required for ion transitions within the dielectric. Therefore, this application proposes a method for assessing the uneven aging of transformers using AC conductivity.

[0022] Through the above design scheme, the present invention can bring the following beneficial effects:

[0023] 1. Combined with AC conductivity, it directly reflects the change in the potential barrier height that needs to be overcome when ions transition within the medium. By constructing a database of the AC conductivity variation with frequency for insulating paperboards of different polymerization degrees, as well as a database of the AC conductivity variation with frequency for oil and a database of oil viscosity, the amount of information on insulation medium degradation is enriched, enabling a more accurate assessment of the uneven aging state of transformers.

[0024] 2. Mesh the transformer's main insulation structure. Utilizing the relationship between resistance and conductivity, we derive the AC conductivity expression for the transformer's main insulation structure as a whole. This allows for a more realistic physical model of the transformer and effectively characterizes the relationship between its local and overall structures.

[0025] 3. Construct a coupled equation system at different frequency points; invert and screen to obtain the optimal AC conductivity matrix at that frequency point. Then, based on the optimal matrix, obtain the AC conductivity curve of the entire transformer. Compare it with the measured curve and select the frequency point and AC conductivity matrix corresponding to the curve with the best fit. Convert it into a matrix composed of the local polymerization degree of the transformer and the oil viscosity at that frequency point, thereby quantitatively analyzing the uneven aging state.

[0026] 4. The dual translation method of frequency-temperature translation and conductance translation is used to effectively expand the low-frequency band of AC conductivity. The shape correction parameter α is used to correct the traditional AC conductivity formula with a single relaxation time, making it more suitable for the actual working conditions of the oil-paper insulation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flowchart of a method for evaluating the uneven aging state of a transformer by combining AC conductivity according to the present invention.

[0028] Figure 2 Schematic diagram of a transformer physical model in an embodiment of a method for evaluating the uneven aging state of a transformer in combination with AC conductivity according to the present invention.

[0029] Figure 3 This is an equivalent XY model diagram of a transformer physical model in an embodiment of a method for evaluating the uneven aging state of a transformer in combination with AC conductivity of the present invention.

[0030] Figure 4 This is an equivalent circuit diagram of a transformer physical model in an embodiment of a method for evaluating the uneven aging state of a transformer in combination with AC conductivity of the present invention.

[0031] Figure 5 This is a schematic diagram of a dual translation method of frequency-temperature translation and conductivity translation in an example of a method for evaluating the uneven aging state of a transformer in combination with AC conductivity according to the present invention.

[0032] Figure 6 This is a comparison diagram of calculation results before and after correction of the AC conductivity calculation model in an embodiment of a method for evaluating the uneven aging state of a transformer in combination with AC conductivity of the present invention.

[0033] Figure 7 This is a comparison chart of the AC conductivity calculated by substituting the data filtered by the characteristic equation f into the physical model in an embodiment of a method for evaluating the uneven aging state of a transformer in combination with AC conductivity of the present invention and the AC conductivity actually measured by the transformer. DETAILED DESCRIPTION

[0034] The following is a detailed description of the specific embodiments of the present invention with reference to the accompanying drawings.

[0035] It should be noted that the terms "front and back, up and down, left and right" mentioned in the text are merely simplified expressions for intuitively describing positional relationships based on the accompanying drawings, and are not limitations on the technical solution.

[0036] To more clearly illustrate the present invention, the present invention is further described below with reference to preferred embodiments. Those skilled in the art will appreciate that the detailed description below is illustrative and non-restrictive, and that the user may make various changes to the following parameters without departing from the mechanism and scope of the invention as set forth in the claims. To avoid obscuring the essence of the present invention, well-known methods and processes are not described in detail.

[0037] By the attached Figures 1 to 7 A method for evaluating the uneven aging state of a transformer by combining AC conductivity is shown, comprising the following steps:

[0038] S1. Perform AC conductivity and DC conductivity tests on insulating paperboard samples with different polymerization degrees at different temperatures; perform AC conductivity, DC conductivity and oil viscosity tests on insulating oil samples with different aging days at different temperatures;

[0039] S2. Construct a database of AC conductivity changes with frequency for insulating paperboards with different degrees of polymerization; construct a database of AC conductivity changes with frequency for oils with different aging days, and a database of oil viscosity;

[0040] S3. Mesh the main insulation structure of the transformer; use the relationship between resistance and conductivity to obtain an AC conductivity expression for the entire main insulation structure of the transformer; the overall AC conductivity expression is used to reflect the relationship between the local AC conductivity and the overall AC conductivity of the transformer, and the overall AC conductivity expression corresponds to a matrix composed of local AC conductivities; the local AC conductivity is the AC conductivity of each block obtained after meshing the main insulation structure of the transformer; the specific construction steps are as follows:

[0041] The ratio of the radial first layer low-voltage winding oil gap side area to the oil gap plus the support bar side area is as follows:

[0042]

[0043] Among them, Y1 is the ratio of the radial side area of ​​the oil gap in the first layer of paper tube to the side area of ​​the oil gap plus the support bar; m is the width of the support bar; r1 is the inner diameter of the first layer of oil gap.

[0044]

[0045] Among them, Y n is the ratio of the oil gap side area in the radial nth layer of paper tube to the oil gap plus the support side area; m is the support width; r 2n-1is the inner diameter of the nth layer of oil gap.

[0046] The resistance of the oil gap in the paper tube with the first layer in both axial and radial directions is:

[0047]

[0048] Where r2 is the inner diameter of the first paper tube, L is the axial height, n1 is the ratio of the axial height of the first paper tube to the total height, and γ0 is the AC conductivity of the transformer oil. Knowing the AC conductivity of the transformer oil at a certain frequency and temperature can reveal its aging degree. The corresponding oil viscosity database can also reveal its viscosity.

[0049] The resistance of the inner support strip of the paper tube with the first layer in both axial and radial directions:

[0050]

[0051] Among them, γ 11 The AC conductivity of the paper tube and the stay with the first layer in both axial and radial directions is the resistance of the paper tube with the first layer in both axial and radial directions:

[0052]

[0053] Among them, r3 is the inner diameter of the second oil gap.

[0054] The composite resistance of the first layer in both axial and radial directions is:

[0055]

[0056] Among them, α1 is the numerator of the resistance formula of the oil gap in the paper tube with the first layer in both axial and radial directions, and β1 is the numerator of the resistance formula of the support strip in the paper tube with the first layer in both axial and radial directions.

[0057] The composite resistances of the nth axial layer and the nth radial layer are:

[0058]

[0059] Among them, the first n in nn is the axial nth layer, the second n is the radial nth layer, α n is the numerator of the resistance formula of the oil gap in the paper tube of the nth layer in both axial and radial directions, β n is the numerator of the resistance formula of the inner support strip of the paper tube with the nth layer in both axial and radial directions, γ nn The AC conductivity of the paper tube and struts in the nth layer in both axial and radial directions.

[0060] The resistance of the first paper tube is:

[0061]

[0062] Among them, R11 is the composite resistance of the first layer in both axial and radial directions, R 21 is the composite resistance of the second axial layer and the first radial layer, R n1 is the composite resistance of the nth axial layer and the first radial layer, q 11 is the molecular part of the composite resistance formula for the first layer in both axial and radial directions, p 11 is the denominator of the composite resistance formula for the first layer in both axial and radial directions, q 21 is the molecular part of the composite resistance formula of the second axial layer and the first radial layer, p 21 is the denominator of the composite resistance formula of the second axial layer and the first radial layer, q 31 is the molecular part of the composite resistance formula of the third axial layer and the first radial layer, q n1 is the molecular part of the formula for the composite resistance of the nth axial layer and the first radial layer, p n1 It is the denominator of the formula for the composite resistance of the nth axial layer and the first radial layer.

[0063] The resistance of the nth paper tube is:

[0064]

[0065] Among them, R 1n is the composite resistance of the first axial layer and the nth radial layer, R 2n is the composite resistance of the second axial layer and the nth radial layer, R nn is the composite resistance of the nth axial layer and the nth radial layer, q 1n is the molecular part of the composite resistance formula of the first axial layer and the nth radial layer, p 1n is the denominator of the composite resistance formula of the first axial layer and the nth radial layer, q 2n is the molecular part of the composite resistance formula of the second axial layer and the nth radial layer, p 2n is the denominator of the composite resistance formula of the second axial layer and the nth radial layer, q 3n is the molecular part of the composite resistance formula of the third axial layer and the nth radial layer, q nn is the molecular part of the formula for the composite resistance of the nth axial layer and the nth radial layer, p n1 It is the denominator of the formula for the composite resistance of the nth axial layer and the nth radial layer.

[0066] The overall resistance is:

[0067]

[0068] Among them, k is the number of paper tubes.

[0069] The overall AC conductivity can be obtained:

[0070]

[0071] S4. According to the AC conductivity expression of S3, a coupling equation group is constructed at different frequency points; the coupling equation group is a multi-parameter coupling equation group, and the parameters include the AC conductivity of the oil, the composite AC conductivity of the first axial layer and the first radial layer, the composite AC conductivity of the first axial layer and the second radial layer, the composite AC conductivity of the first axial layer and the third axial layer, ..., the composite AC conductivity of the first axial layer and the Nth radial layer, the composite AC conductivity of the second axial layer and the first radial layer, the composite AC conductivity of the second axial layer and the second radial layer, the composite AC conductivity of the second axial layer and the third radial layer, ..., the composite AC conductivity of the Mth axial layer and the Nth radial layer.

[0072] The multi-parameter coupled equations are:

[0073]

[0074] Among them, γ n It indicates the value of the AC conductivity test curve obtained from the actual measurement of the transformer at a certain frequency.

[0075] S5. Perform AC conductivity and DC conductivity tests on actual transformers at different temperatures; construct a curve library showing the AC conductivity of the measured transformer changing with frequency;

[0076] S6. Invert the measured AC conductivity value of the transformer at each frequency point in S5 as the output result of the equation in S4; obtain the AC conductivity matrix set at the frequency point according to the inversion result;

[0077] The specific inversion process can be done as follows: the constructed physical model can be written as

[0078]

[0079] The particle swarm algorithm is used to iteratively optimize the minimum value of the above formula, and the input and output values ​​are defined as the values ​​in the database of AC conductivity of oil with different aging days and frequency changes in S2 and the values ​​in the database of AC conductivity of insulating cardboard with different polymerization degrees and frequency changes.

[0080] When the value of approaches 0, the iteration stops when the fitness value requirement is met. The output result is the AC conductivity matrix set at this frequency point.

[0081] S7, screening the AC conductivity matrix set of each frequency point using the characteristic equation f, and obtaining the AC conductivity matrix corresponding to the maximum f value as the optimal AC conductivity matrix of each frequency point;

[0082] S8. Calculate the AC conductivity curve of the transformer as a whole based on the optimal AC conductivity matrix at each frequency point in S7 and the database in S2; compare it with the curve of the measured transformer AC conductivity varying with frequency in S5, and select the frequency point and AC conductivity matrix corresponding to the curve with the best fit;

[0083] S9. Based on the relationship between the degree of polymerization, oil viscosity and AC conductivity in the database of S2, the AC conductivity matrix selected in S8 is converted into a matrix composed of the local degree of polymerization of the transformer and the oil viscosity at the frequency point.

[0084] Furthermore, in S2, a dual translation method of frequency-temperature translation and conductivity translation was used to effectively expand the low-frequency range of AC conductivity. The traditional AC conductivity formula for a single relaxation time was modified to obtain a frequency-dependent mathematical model shape correction parameter α. When a set of dispersed relaxation times exists in the medium, there is a difference compared to the traditional Debye model theoretical analysis. According to the Cole-Cole model, Davidson-Cole model, Havriliak-Negami model, and Dissado-Hill model analysis, the shape parameter α is all related to frequency. Changing the shape parameter also changes the shape of these models.

[0085] The traditional AC conductivity formula for a single relaxation time is: γ=ωε0ε″

[0086] The AC conductivity correction method is to effectively expand the low-frequency band of AC conductivity using a double translation method.

[0087]

[0088] Where f(T2) is the frequency to be shifted to T1, in Hz; f(T1) is the test frequency, in Hz; T1 is the temperature to be shifted, in K; and T2 is the test temperature, in K.

[0089]

[0090] Wherein, σ(T1) is the electrical conductivity at temperature T1, unit: S / m; σ(T2) is the electrical conductivity at temperature T2, unit: S / m; ΔE(σ) is the electrical conductivity activation energy of the oil-impregnated paperboard, unit: eV.

[0091] The frequency-dependent shape parameter α is calculated using the equivalent relationship between low-frequency AC conductivity and DC conductivity:

[0092] γ 直 =γ 低

[0093] ωε0ε″=γ 直

[0094] ω a ε0ε″=γ 低

[0095]

[0096] The corrected AC conductivity formula is γ=ω α ε0ε″.

[0097] According to the corrected AC conductivity, a database of AC conductivity variation with frequency for insulating paperboards with different polymerization degrees, a database of AC conductivity variation with frequency for oils with different aging days, and an oil viscosity database are constructed.

[0098] Furthermore, in S5, the dual translation method of frequency-temperature translation and conductance translation is used to effectively expand the low-frequency band of AC conductivity. The traditional AC conductivity with a single relaxation time is corrected. Based on the corrected AC conductivity, a curve library of the measured transformer AC conductivity changing with frequency is constructed. The correction method is the same as above.

[0099] The expression of the characteristic equation f in S7 is further:

[0100]

[0101] Among them, γ m All AC conductivity data that do not include γ0 in the inversion results, γ min is the minimum value of the AC conductivity data that does not include γ0 in the inversion result, and γ is the minimum value of the AC conductivity data that does not include γ0 and γ min All AC conductivity data of ; γ0 is the AC conductivity of oil.

[0102] Further, the specific method of calculating and obtaining the AC conductivity curve of the entire transformer according to the AC conductivity optimal matrix of each frequency point in S7 and the database in S2 includes the following steps:

[0103] S801. Based on the AC conductivity values ​​in the optimal matrix at each frequency point and the field test temperature, and comparing the different AC conductivities at the same frequency point in the database of AC conductivity variation of insulating paperboard as a function of frequency (S2), a curve of AC conductivity variation of insulating paperboard as a function of frequency corresponding to each AC conductivity value in the matrix can be determined.

[0104] S802, determining the aging days of the transformer oil based on the oil viscosity database in S2; determining an AC conductivity curve of the transformer oil based on the database of AC conductivity changes of oils with different aging days as a function of frequency;

[0105] S803. Substitute the curve of the AC conductivity of the insulating paperboard corresponding to each AC conductivity value in the matrix S801 as a function of frequency and the AC conductivity curve of the transformer oil in S802 into the AC conductivity expression of the main insulation structure as a whole in S3 to obtain an AC conductivity curve for the entire transformer.

[0106] In the specific implementation, the main insulation structure of the transformer is a paper tube-oil gap-strut structure; the specific division method of the main insulation structure of the transformer is radial three-division and axial division from top to bottom at a ratio of 1:1:8; the actual structure of the transformer is: height 7.05m, width 5.45m, body hanging weight 128500kg, transformer oil weight 34200kg, high-voltage side rated voltage 242kV, low-voltage side rated voltage 15.75kV, the insulating oil sample is 45# cycloalkyl transformer mineral insulating oil; the oil gap strut width is 50mm, the main insulating paperboard width is 20mm; the selected frequency points are: 0.001Hz, 1Hz, 50Hz and 1000Hz.

[0107] Each aging degree in the AC conductivity database has a corresponding shape parameter at the test temperature; the results of the partial shape parameter α are:

[0108] Table 4 Shape parameters α

[0109]

[0110] The multi-parameter coupled equations are:

[0111]

[0112] Where n1 is 0.1 and n2 is 0.1.

[0113] After inversion and screening, the optimal AC conductivity matrices at each frequency point are: 0.001Hz:

[0114]

[0115] 1Hz:

[0116]

[0117] 50Hz:

[0118]

[0119] 1000Hz:

[0120]

[0121] The fourth row in the matrix contains the AC conductivity of the oil;

[0122] The data at each frequency point is brought into the database of S2 to calculate the AC conductivity curve of the transformer as a whole. This is compared with the curve of the measured transformer AC conductivity varying with frequency in S5, and the frequency point and AC conductivity matrix corresponding to the curve with the best fit are selected.

[0123] The best fitting curve is the one inverted at 1 Hz, with a calculated fitting degree of 95.7%. Based on the relationship between degree of polymerization, oil viscosity, and AC conductivity in the S2 database, the AC conductivity matrix of the inverted result at 1 Hz is converted to the transformer's local degree of polymerization and oil viscosity at that frequency point.

[0124] The local polymerization degrees of the transformer are DP=1002, DP=962, DP=983, DP=872, DP=839, DP=861, DP=670, DP=637, and DP=664. The polymerization degree of the most seriously aged part of the transformer is DP=637, and the viscosity of the transformer oil is 39.75mm 2 / s.

[0125] Obviously, the embodiments described above are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0126] The above mainly introduces the solution of the embodiment of the present application from the perspective of the execution process of the method side. It is understandable that in order to implement the above functions, the network device includes hardware structures and / or software modules corresponding to the execution of each function. Those skilled in the art should easily realize that, in combination with the units and algorithm steps of each example described in the embodiment provided herein,

[0127] This application can be implemented in hardware or a combination of hardware and computer software. Whether a function is implemented in hardware or by computer software driving hardware depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0128] If the above-mentioned integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable memory. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a memory and includes several instructions for enabling a computer device (which can be a personal computer, server or TRP, etc.) to execute all or part of the steps of the various embodiments of the present application. The aforementioned memory includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk and other media that can store program code.

Claims

1. A method for evaluating the uneven aging state of a transformer in combination with AC conductivity, characterized in that: The steps include: S1. Perform AC conductivity and DC conductivity tests on insulating paperboard samples with different polymerization degrees at different temperatures; perform AC conductivity, DC conductivity and oil viscosity tests on insulating oil samples with different aging days at different temperatures; S2. Construct a database of AC conductivity changes with frequency for insulating paperboards with different degrees of polymerization; construct a database of AC conductivity changes with frequency for oils with different aging days, and a database of oil viscosity; S3. Meshing the main insulation structure of the transformer; obtaining an AC conductivity expression for the entire main insulation structure of the transformer using the relationship between resistance and conductivity; the overall AC conductivity expression is used to reflect the relationship between the local AC conductivity and the overall AC conductivity of the transformer, and the overall AC conductivity expression corresponds to a matrix composed of local AC conductivities; the local AC conductivity is the AC conductivity of each block obtained after meshing the main insulation structure of the transformer; S4. Based on the AC conductivity expression in S3, a coupled equation group is constructed at different frequency points; S5. Perform AC conductivity and DC conductivity tests on actual transformers at different temperatures; construct a curve library showing the AC conductivity of the measured transformer changing with frequency; S6. Invert the measured AC conductivity value of the transformer at each frequency point in S5 as the output result of the equation in S4; obtain the AC conductivity matrix set at the frequency point according to the inversion result; S7, screening the AC conductivity matrix set of each frequency point using the characteristic equation f, and obtaining the AC conductivity matrix corresponding to the maximum f value as the optimal AC conductivity matrix of each frequency point; S8. Calculate the AC conductivity curve of the transformer as a whole based on the optimal AC conductivity matrix at each frequency point in S7 and the database in S2; compare it with the curve of the measured transformer AC conductivity varying with frequency in S5, and select the frequency point and AC conductivity matrix corresponding to the curve with the best fit; S9. Based on the relationship between the degree of polymerization, oil viscosity and AC conductivity in the database of S2, the AC conductivity matrix selected in S8 is converted into a matrix composed of the local degree of polymerization of the transformer and the oil viscosity at the frequency point.

2. The method for evaluating the uneven aging state of a transformer in combination with AC conductivity according to claim 1, characterized in that: In S2, a dual translation method of frequency-temperature translation and conductivity translation is used to effectively expand the low-frequency band of AC conductivity. The traditional AC conductivity formula with a single relaxation time is modified to obtain the frequency-dependent mathematical model shape correction parameter α. Based on the corrected AC conductivity, a database of the AC conductivity variation with frequency of insulating cardboard with different polymerization degrees, a database of the AC conductivity variation with frequency of oil with different aging days, and an oil viscosity database are constructed.

3. The method for evaluating the uneven aging state of a transformer in combination with AC conductivity according to claim 1, characterized in that: The main insulation structure of the transformer S3 is a paper tube-oil gap-strut structure.

4. The method for evaluating the uneven aging state of a transformer in combination with AC conductivity according to claim 1, characterized in that: In S5, the dual translation method of frequency-temperature translation and conductance translation is used to effectively expand the low-frequency band of AC conductivity. The traditional AC conductivity with a single relaxation time is corrected. Based on the corrected AC conductivity, a curve library of the measured transformer AC conductivity changing with frequency is constructed.

5. The method for evaluating the uneven aging state of a transformer in combination with AC conductivity according to claim 1, characterized in that: The expression of the characteristic equation f in S7 is: Among them, γ m All AC conductivity data that do not include γ0 in the inversion results, γ min is the minimum value of the AC conductivity data that does not include γ0 in the inversion result, and γ is the minimum value of the AC conductivity data that does not include γ0 and γ min All AC conductivity data of ; γ0 is the AC conductivity of oil.

6. The method for evaluating the uneven aging state of a transformer in combination with AC conductivity according to claim 1, characterized in that: The specific division method of the grid division of the main insulation structure of the transformer described in S3 is to divide it into three equal parts radially and to divide it into three equal parts axially from top to bottom in a ratio of 1:1:

8.

7. The method for evaluating the uneven aging state of a transformer in combination with AC conductivity according to claim 1, characterized in that: The specific method of calculating the AC conductivity curve of the transformer as a whole based on the AC conductivity optimal matrix of each frequency point in S7 and the database in S2 includes the following steps: S801. Based on the AC conductivity values ​​in the optimal matrix at each frequency point and the field test temperature, and comparing the different AC conductivities at the same frequency point in the database of AC conductivity variation of insulating paperboard as a function of frequency (S2), a curve of AC conductivity variation of insulating paperboard as a function of frequency corresponding to each AC conductivity value in the matrix can be determined. S802, determining the aging days of the transformer oil based on the oil viscosity database in S2; determining an AC conductivity curve of the transformer oil based on the database of AC conductivity changes of oils with different aging days as a function of frequency; S803. Substitute the curve of the AC conductivity of the insulating paperboard corresponding to each AC conductivity value in the matrix S801 as a function of frequency and the AC conductivity curve of the transformer oil in S802 into the AC conductivity expression of the main insulation structure as a whole in S3 to obtain an AC conductivity curve for the entire transformer.

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