Method for evaluating non-uniform aging state of transformer in combination with alternating current conductivity

Abstract

The invention discloses a method for evaluating a non-uniform aging state of a transformer in combination with alternating current conductivity, which belongs to the technical field of oil-paper insulation life evaluation, and directly reflects the change of potential barrier height required to be overcome during ion transition in a medium in combination with alternating current conductivity. By constructing a database of alternating current conductivity of insulating paperboards with different polymerization degrees changing along with frequency, a database of alternating current conductivity of oil changing along with frequency and an oil viscosity database, the information amount of insulating medium degradation is enriched, and the non-uniform aging state of the transformer can be evaluated more accurately; performing grid division on the main insulation structure of the transformer; the overall alternating current conductivity expression of the main insulation structure of the transformer is obtained by using the relation between the resistance and the conductivity, physical model construction more conforming to reality is carried out on the transformer, the relation between the local structure and the overall structure of the transformer is effectively represented, and therefore the non-uniform aging state is quantitatively analyzed.

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 the power system, the long-term stable operation of oil-immersed power equipment and its components is of vital importance. Due to the differences in ambient temperature and load conditions in different regions, the insulation in some power equipment deteriorates, which will threaten the long-term reliability of the equipment and the service life of the insulation. Therefore, it is extremely important to accurately evaluate the insulation status of the above power equipment.

[0003] For oil-paper insulation equipment, the operation and maintenance departments of power systems in various countries will carry out regular maintenance plans, such as partial discharge, power frequency withstand voltage, power frequency dielectric loss, insulation resistance, dissolved gas analysis in oil, infrared imaging temperature, winding DC resistance test, etc. The characteristic parameter changes extracted from the above multiple methods reflect the operating status of the equipment. The above methods are more accurate in the evaluation results when there are problems such as concentrated insulation defects or latent faults that have developed in the equipment, but they still cannot be quantitatively analyzed for problems such as non-uniform insulation aging. They can only be qualitatively compared based on factory parameter values ​​or current test values ​​between three phases of power equipment, such as power frequency dielectric loss and insulation resistance.

[0004] Therefore, a new technical solution is urgently needed in the prior art to solve this problem. Summary of the invention

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

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: 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 the AC conductivity of insulating paperboards with different polymerization degrees that varies with frequency; construct a database of the AC conductivity of oils with different aging days that varies with frequency and an oil viscosity database;

[0009] S3. Meshing the main insulation structure of the transformer; using the relationship between resistance and conductivity to obtain the overall AC conductivity expression of the main insulation structure of the transformer; the overall AC conductivity expression is used to reflect the relationship between the local AC conductivity of the transformer and the overall AC conductivity, 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. According to the AC conductivity expression of S3, a coupling equation group is constructed at different frequency points;

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

[0012] S6, taking the measured value of the transformer AC conductivity at each frequency point in S5 as the output result of the equation in S4 for inversion; and obtaining 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 by 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, according to the AC conductivity optimal matrix of each frequency point of S7 and the database of S2, respectively calculate and obtain the AC conductivity curve of the transformer as a whole; compare it with the curve of the AC conductivity of the transformer measured with the frequency of S5, and select the frequency point and AC conductivity matrix corresponding to the curve with the best fitting degree;

[0015] S9. According to 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, the dual translation method of frequency-temperature translation and conductivity translation is used to effectively expand the low-frequency band of AC conductivity, and the traditional AC conductivity formula of a single relaxation time is corrected to obtain the frequency-related mathematical model shape correction parameter α; based on the corrected AC conductivity, a database of the AC conductivity of insulating cardboard with different polymerization degrees changing with frequency, a database of the AC conductivity of oil with different aging days changing with frequency, 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 comprises the following steps:

[0018] S801, according to the AC conductivity values ​​in the optimal matrix at each frequency point and the field test temperature, and by comparing the different AC conductivities at the same frequency point in the database of the AC conductivity of the insulating paperboard changing with the frequency in S2, a curve of the AC conductivity of the insulating paperboard changing with the frequency corresponding to each AC conductivity value in the matrix can be determined;

[0019] S802, the aging days of the transformer oil can be determined according to the oil viscosity database in S2; an AC conductivity curve of the transformer oil can be determined according to the database of AC conductivity of oils with different aging days varying with frequency;

[0020] S803. Substitute the curve of the AC conductivity of the insulating paperboard corresponding to each AC conductivity value in the matrix S801 with the 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, and a transformer overall AC conductivity curve can be calculated.

[0021] Compared with the relaxation behavior characterized by the complex dielectric constant and loss factor at different test temperatures, the conductivity behavior can show more information about the degradation of the insulating medium. For the AC conductivity curve of oil-paper insulation, the change in its slope is directly related to the moisture migration characteristics and material degradation characteristics in the oil-paper insulation material; at the same time, the AC conductivity contains two parts: relaxation activation energy and conductivity activation energy. Compared with the complex dielectric constant and loss factor, the change in conductivity activation energy is closely related to its internal moisture content and aging degree, and can directly indicate the change in the potential barrier height that needs to be overcome when the ions in the medium transition. Therefore, the present application invents a method for evaluating the uneven aging state of a transformer in combination with 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 height of the potential barrier that needs to be overcome when ions in the medium transition; by constructing a database of the AC conductivity of insulating paperboards with different polymerization degrees that changes with frequency, as well as a database of the AC conductivity of oil that changes with frequency and an oil viscosity database, the amount of information on the degradation of the insulating medium is enriched, and the uneven aging state of the transformer can be more accurately evaluated;

[0024] 2. Grid the main insulation structure of the transformer; use the relationship between resistance and conductivity to obtain the AC conductivity expression of the main insulation structure of the transformer as a whole, so as to build a more realistic physical model of the transformer and effectively characterize the relationship between its local structure and overall structure;

[0025] 3. Construct a coupling equation group at different frequency points; invert and screen to obtain the optimal AC conductivity matrix at the frequency point, and then obtain the AC conductivity curve of the transformer as a whole based on the optimal matrix. Compare with the measured curve to select the frequency point and AC conductivity matrix corresponding to the curve with the best fitting degree, and convert it into a matrix composed of the local polymerization degree of the transformer at the frequency point and the oil viscosity, so as to quantitatively analyze 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, and the traditional AC conductivity formula with a single relaxation time is corrected by the shape correction parameter α, making it more suitable for the actual working conditions of the oil-paper insulation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a flowchart of a method for evaluating the uneven aging state of a transformer in combination with AC conductivity.

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

[0029] Figure 3 It is an equivalent XY model diagram of the physical model of the transformer 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 It 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 It 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 of 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 bringing the data filtered by the characteristic equation f into the physical model in an embodiment of the 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 implementation of the present invention in conjunction with the accompanying drawings.

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

[0036] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with the preferred embodiments. It should be understood by those skilled in the art. The content described in detail below is illustrative rather than restrictive, and the user may make various changes to the following parameters without departing from the inventive mechanism and scope set forth in the claims. In order to avoid confusing the essence of the present invention, known methods and processes are not described in detail.

[0037] By the attached Figures 1 to 7 As shown: A method for evaluating the uneven aging state of a transformer in combination with AC conductivity comprises 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 the AC conductivity of insulating paperboards with different polymerization degrees that varies with frequency; construct a database of the AC conductivity of oils with different aging days that varies with frequency and an oil viscosity database;

[0040] S3. Mesh the main insulation structure of the transformer; obtain the overall AC conductivity expression of the 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 of the transformer and the overall AC conductivity, 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 radial oil gap side area in the nth layer of paper tube to the oil gap plus the side area of ​​the support bar; m is the width of the support bar; 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] Among them, r2 is the inner diameter of the first layer of paper tube, L is the axial height, n1 is the ratio of the axial height of the first layer of paper tube to the total height, and γ0 is the AC conductivity of the transformer oil. When the AC conductivity value of the transformer oil at a certain frequency point at a certain temperature is known, its aging degree can be known, and its viscosity can be known from the corresponding oil viscosity database.

[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. 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 that is 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 that is 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 paper tube support strips in the nth layer in both axial and radial directions, γ nn It is the AC conductivity of the paper tube and the struts of 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 the axial and radial directions, p 11 is the denominator of the composite resistance formula for the first layer in both the 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 composite resistance formula 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 composite resistance formula 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 radial 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 by measuring the transformer at a certain frequency.

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

[0076] S6, taking the measured value of the transformer AC conductivity at each frequency point in S5 as the output result of the equation in S4 for inversion; and obtaining the AC conductivity matrix set at the frequency point according to the inversion result;

[0077] The specific inversion process can be implemented 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 database of the AC conductivity of oil with different aging days and the values ​​in the database of the AC conductivity of insulating paperboard with different polymerization degrees that varies with frequency in S2.

[0080] When the value of tends to 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 by 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, according to the AC conductivity optimal matrix of each frequency point of S7 and the database of S2, respectively calculate and obtain the AC conductivity curve of the transformer as a whole; compare it with the curve of the AC conductivity of the transformer measured with the frequency of S5, and select the frequency point and AC conductivity matrix corresponding to the curve with the best fitting degree;

[0083] S9. According to 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] In S2, the 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 of a single relaxation time is modified to obtain the frequency-related mathematical model shape correction parameter α; when there is a set of dispersed relaxation times in the medium, it is different from 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 related to frequency. When the shape parameters change, the shapes of these models also change;

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

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

[0087]

[0088] Wherein, f(T2) is the frequency required to be shifted to T1 temperature, unit: Hz; f(T1) is the test frequency, unit: Hz; T1 is the temperature required to be shifted, unit: K; T2 is the test temperature, unit: K.

[0089]

[0090] Wherein, σ(T1) is the conductivity at temperature T1, unit: S / m; σ(T2) is the conductivity at temperature T2, unit: S / m; ΔE(σ) is the 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 of insulating paperboards with different polymerization degrees, a database of AC conductivity variation with frequency of oils with different aging days, and an oil viscosity database are constructed.

[0098] 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, and the traditional AC conductivity with a single relaxation time is corrected. According to the corrected AC conductivity, a curve library of the measured transformer AC conductivity changing with frequency is constructed, and 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 is all the AC conductivity data that does not contain 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 in the inversion result. 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 of S7 and the database of S2 includes the following steps:

[0103] S801, according to the AC conductivity values ​​in the optimal matrix at each frequency point and the field test temperature, and by comparing the different AC conductivities at the same frequency point in the database of the AC conductivity of the insulating paperboard changing with the frequency in S2, a curve of the AC conductivity of the insulating paperboard changing with the frequency corresponding to each AC conductivity value in the matrix can be determined;

[0104] S802, the aging days of the transformer oil can be determined according to the oil viscosity database in S2; an AC conductivity curve of the transformer oil can be determined according to the database of AC conductivity of oils with different aging days varying with frequency;

[0105] S803. Substitute the curve of the AC conductivity of the insulating paperboard corresponding to each AC conductivity value in the matrix S801 with the 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, and a transformer overall AC conductivity curve can be calculated.

[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 matrix at each frequency point is obtained as follows: 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; compared with the curve of the measured transformer AC conductivity changing with frequency in S5, the frequency point and AC conductivity matrix corresponding to the curve with the best fitting degree are selected;

[0123] The curve with the best calculation fit is the result of inversion at a frequency of 1 Hz, with a calculation fit of 95.7%. According to the relationship between the degree of polymerization, oil viscosity and AC conductivity in the S2 database, the AC conductivity matrix of the result of inversion at 1 Hz is converted into the local degree of polymerization and oil viscosity of the transformer at this 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 transformer is DP=637, and the viscosity of the transformer oil is 39.75 mm 2 / s.

[0125] Obviously, the above described embodiments are only some embodiments of the present invention, not all 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.

[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 can be understood that in order to implement the above functions, the network device includes a hardware structure and / or software module corresponding to 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 in this article,

[0127] The present application can be implemented in the form of hardware or a combination of hardware and computer software. Whether a function is performed in the form of hardware or computer software driving hardware depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present 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, 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, which is stored in a memory and includes several instructions for 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, disk or optical disk and other media that can store program codes.

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 the AC conductivity of insulating paperboards with different polymerization degrees that varies with frequency; construct a database of the AC conductivity of oils with different aging days that varies with frequency and an oil viscosity database; S3. Meshing the main insulation structure of the transformer; using the relationship between resistance and conductivity to obtain the overall AC conductivity expression of the main insulation structure of the transformer; the overall AC conductivity expression is used to reflect the relationship between the local AC conductivity of the transformer and the overall AC conductivity, 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. According to the AC conductivity expression of S3, a coupling equation group is constructed at different frequency points; S5. Perform AC conductivity and DC conductivity tests at different temperatures on the actual transformer; construct a curve library of AC conductivity of the measured transformer changing with frequency; S6, taking the measured value of the transformer AC conductivity at each frequency point in S5 as the output result of the equation in S4 for inversion; and obtaining 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 by 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, according to the AC conductivity optimal matrix of each frequency point of S7 and the database of S2, respectively calculate and obtain the AC conductivity curve of the transformer as a whole; compare it with the curve of the AC conductivity of the transformer measured with the frequency of S5, and select the frequency point and AC conductivity matrix corresponding to the curve with the best fitting degree; S9. According to 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. According to claim 1, a method for evaluating the uneven aging state of a transformer in combination with AC conductivity is characterized in that: In S2, the 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 corrected to obtain the frequency-related mathematical model shape correction parameter α; based on the corrected AC conductivity, a database of the AC conductivity of insulating cardboard with different polymerization degrees changing with frequency, a database of the AC conductivity of oil with different aging days changing with frequency, and an oil viscosity database are constructed.

3. According to claim 1, a method for evaluating the uneven aging state of a transformer in combination with AC conductivity is 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, and the traditional single relaxation time AC conductivity is corrected. According to the corrected AC conductivity, a curve library of 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 is all the AC conductivity data that does not contain 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 in the inversion result. 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 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 according to the AC conductivity optimal matrix of each frequency point in S7 and the database in S2 comprises the following steps: S801, according to the AC conductivity values ​​in the optimal matrix at each frequency point and the field test temperature, and by comparing the different AC conductivities at the same frequency point in the database of the AC conductivity of the insulating paperboard changing with the frequency in S2, a curve of the AC conductivity of the insulating paperboard changing with the frequency corresponding to each AC conductivity value in the matrix can be determined; S802, the aging days of the transformer oil can be determined according to the oil viscosity database in S2; an AC conductivity curve of the transformer oil can be determined according to the database of AC conductivity of oils with different aging days varying with frequency; S803. Substitute the curve of the AC conductivity of the insulating paperboard corresponding to each AC conductivity value in the matrix S801 with the 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, and a transformer overall AC conductivity curve can be calculated.

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