Identification method and system for damping quantification of transformer bushing

Abstract

The invention provides a transformer bushing damping quantification identification method and system, and the method comprises the steps: testing a frequency domain dielectric spectrum curve of a to-be-tested transformer bushing, and generating a corresponding hybrid polarization circuit model according to the frequency domain dielectric spectrum curve; fitting parameters of the hybrid circuit model through the hybrid polarization circuit model, determining a characteristic value representing the equivalent water content according to a fitting result, and determining the equivalent water content according to the characteristic value representing the equivalent water content; and extracting a non-uniform index diagnosis characteristic quantity through the frequency domain dielectric spectrum curve of the transformer bushing, and determining a final transformer bushing damp quantification result according to the non-uniform index diagnosis characteristic quantity and the equivalent water content. According to the method, a hybrid circuit model is used as a frequency domain dielectric spectrum equivalent circuit model, and parameter identification is carried out on a test result of the transformer oil-paper bushing; and a quantitative analysis method for the damping degree and uniformity of the insulating medium is provided based on model parameters and dielectric spectrum curve characteristic values.

Description

Technical Field

[0001] The invention relates to the technical field of identification of the moisture content of a transformer bushing, and in particular to an identification method and system for the moisture content of a transformer bushing. Background Art

[0002] As one of the main equipment in power plants and substations, power transformers are expensive and indispensable core equipment. As one of the key equipment in the outlet device of power transformers, the safe and reliable operation of high-voltage bushings needs to be guaranteed. Oil-paper insulated bushings are the main bushing type used in electrical engineering at present, with a usage ratio of about 93%, and are widely used in voltage levels of 110kV and above. However, transformer oil-paper bushings are easily affected by the external environment during use, especially the intrusion of moisture and water, which poses a serious threat to their insulation performance and long-term reliability. Therefore, studying the insulation moisture problem of transformer oil-paper bushings is of great significance to improving the operating safety, reliability and extending the service life of transformers.

[0003] Traditional insulation testing methods for oil-paper capacitor bushings include insulation resistance, power frequency dielectric loss, power frequency capacitance, partial discharge test, oil sample analysis, etc. However, these traditional methods have limitations. For example, the measurement of insulation resistance will be affected by leakage current and temperature; power frequency dielectric loss and power frequency capacitance cannot detect local insulation degradation; partial discharge measurement is easily disturbed by the electromagnetic environment of the project site, resulting in unreliable measurement results; oil sample analysis is complicated to operate and easily causes the equipment to get damp. Frequency domain dielectric spectroscopy technology has become a key technology for studying the insulation status of oil-paper capacitor bushings in recent years due to its non-destructive measurement, rich information carrying, and strong anti-interference ability.

[0004] In terms of dielectric spectrum diagnosis, existing studies have found that with the increase of water content, the real part of complex capacitance will increase significantly at low frequency. Therefore, it is proposed to use the real part ratio of complex capacitance as the characteristic value to diagnose the moisture of oil-paper capacitor bushings. This characteristic value can eliminate the influence of bushing structure on dielectric spectrum. In view of the problem that it is difficult to distinguish the two deterioration effects of aging and moisture on oil-paper bushings, existing studies have divided the degree of bushing insulation degradation into 25 intervals, and carried out comprehensive diagnosis through multiple characteristic values ​​to achieve the distinction of insulation degradation status. For the circuit model of frequency domain dielectric spectrum, a study proposed a method for evaluating the moisture content of oil-paper insulation based on a hybrid polarization circuit model. By extracting the insulation resistance, average series polarization branch time constant and average interface polarization branch time constant from the circuit model parameters as characteristic parameters, a method for evaluating the moisture content of transformer oil-paper insulation system through the value of each characteristic parameter and the relationship between each characteristic parameter and moisture content was proposed.

[0005] The above-mentioned studies on frequency domain dielectric spectroscopy have proposed relevant methods for moisture diagnosis, but no clear quantitative evaluation method for moisture has been obtained. In addition, the moisture state of oil-paper insulation is often studied based on overall moisture, ignoring the uneven distribution of moisture in the insulation of actual equipment. The uneven moisture distribution can cause accelerated degradation of local areas of the insulation material, which seriously endangers the normal operation of the oil-paper insulation bushing. Therefore, it is of great significance to study the quantitative evaluation method of the overall moisture state and moisture content distribution of the oil-paper capacitor bushing. Summary of the invention

[0006] The purpose of the present invention is to provide a method and system for quantitatively identifying moisture content of transformer bushings, so as to solve the technical problem of quantitatively analyzing the moisture content and uniformity of insulating media.

[0007] On the one hand, a method for quantitatively identifying moisture in a transformer bushing is provided, comprising:

[0008] Testing a frequency domain dielectric spectrum curve of a transformer bushing to be tested, and generating a corresponding hybrid polarization circuit model according to the frequency domain dielectric spectrum curve;

[0009] Fitting the hybrid circuit model parameters through the hybrid polarization circuit model, determining the characteristic value characterizing the equivalent water content according to the fitting result, and determining the equivalent water content according to the characteristic value characterizing the equivalent water content;

[0010] The non-uniformity index diagnostic feature is extracted from the frequency domain dielectric spectrum curve of the transformer bushing, and the final quantitative result of the transformer bushing moisture is determined based on the non-uniformity index diagnostic feature and the equivalent water content.

[0011] Preferably, the hybrid polarization circuit model includes:

[0012]

[0013] Among them, C' and C" are the real and imaginary parts of the complex capacitance, R g , C g is the geometric equivalent branch resistance and capacitance, R i , C i is the resistance and capacitance of each RC series branch, i is the serial number of each RC series branch, R h(2k-1) , R h(2k) , C h(2k-1) and C h(2k) are the resistance and capacitance of each interface polarization branch, k is the serial number of the polarization branch, tanδ is the dielectric loss tangent, N is the upper limit of the serial number of the polarization branch, and n is the upper limit of the serial number of the RC series branch.

[0014] Preferably, the hybrid polarization circuit model further includes:

[0015]

[0016] Among them, τ i is the time constant of the RC series branch, τ hk is the time constant of the polarization branch.

[0017] Preferably, the method further comprises fitting the hybrid circuit model parameters according to the following formula:

[0018]

[0019] Among them, C' 测量 、C" 测量 is the complex capacitance measured by frequency domain dielectric spectroscopy, C' 拟合 、C" 拟合 is the complex capacitance fitted by the hybrid circuit model, and y is the circuit model parameter to be fitted.

[0020] Preferably, determining the characteristic value characterizing the equivalent water content according to the fitting result comprises:

[0021] The hybrid circuit model is used for parameter identification, and the accuracy of the fitting results is evaluated using goodness of fit;

[0022] Extract the insulation resistance of the hybrid circuit model parameter as the first eigenvalue for evaluating the equivalent moisture content of the bushing, and calculate the RC series branch parameter as the second eigenvalue of the equivalent moisture content;

[0023] If the first characteristic value and the second characteristic value are greater than the preset evaluation threshold, the second characteristic value is used as the evaluation result; if the first characteristic value or the second characteristic value is not greater than the preset evaluation threshold, the first characteristic value is used as the equivalent water content.

[0024] Preferably, the method further comprises calculating the goodness of fit according to the following formula:

[0025]

[0026] Among them, y i are the original values ​​of the circuit model parameters, is the fitting value of the circuit model parameters, is the average of the original values, R 2 is the goodness of fit.

[0027] Preferably, the method further comprises calculating the RC series branch parameters according to the following formula:

[0028]

[0029] Among them, D x To characterize the equivalent water content using RC series branch parameters.

[0030] Preferably, the extraction of the non-uniformity index diagnostic feature comprises extracting the dielectric loss tangent at 10 -3 Hz~10 -1 The integral value of Hz is equal to 10 1 Hz~10 3 The ratio of the integrated values ​​of Hz.

[0031] Preferably, the final quantitative result of the transformer bushing moisture exposure is determined by performing three-dimensional nonlinear surface fitting on the unevenness index, the evaluation result and the unevenness according to the following formula:

[0032] R x (Mc avg ,n)=a+b*Mc avg +c*n+d*Mc avg 2 +e*Mc avg *n

[0033] +f*n 2 +g*Mc avg 2 *n+h*Mc avg *n 2 +i*n 3

[0034] Among them, R x Represents the diagnostic characteristic of unevenness index, Mc avg represents the equivalent water content, n represents the unevenness index, and a, b, c, d, e, f, g, h, and i are surface fitting parameters.

[0035] On the other hand, a system for identifying the amount of moisture on a transformer bushing is provided, which is used to implement the method for identifying the amount of moisture on a transformer bushing, and comprises:

[0036] A model generation module, used to test the frequency domain dielectric spectrum curve of the transformer bushing to be tested, and generate a corresponding hybrid polarization circuit model according to the frequency domain dielectric spectrum curve;

[0037] A fitting module, used for fitting the hybrid circuit model parameters through the hybrid polarization circuit model, determining the characteristic value characterizing the equivalent water content according to the fitting result, and determining the equivalent water content according to the characteristic value characterizing the equivalent water content;

[0038] The quantification module is used to extract the non-uniformity index diagnostic feature quantity through the frequency domain dielectric spectrum curve of the transformer bushing, and determine the final transformer bushing moisture quantification result based on the non-uniformity index diagnostic feature quantity and the equivalent water content.

[0039] In summary, the implementation of the embodiments of the present invention has the following beneficial effects:

[0040] The invention provides a method and system for quantitatively identifying moisture in transformer bushings. The method and system use a hybrid circuit model as a frequency domain dielectric spectrum equivalent circuit model, and perform parameter identification on the test results of the transformer oil-paper bushing by combining a genetic algorithm with a weighted least squares fitting algorithm. The method also proposes a quantitative analysis method for the moisture degree and uniformity of the insulating medium based on the model parameters and the characteristic values ​​of the dielectric spectrum curve. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying creative labor, other drawings obtained based on these drawings still belong to the scope of the present invention.

[0042] Figure 1 The main flow diagram of a method for identifying the moisture content of a transformer bushing according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0044] like Figure 1 FIG. 1 is a schematic diagram of an embodiment of a method for identifying the moisture content of a transformer bushing provided by the present invention. In this embodiment, the method comprises the following steps:

[0045] Step S1, testing the frequency domain dielectric spectrum curve of the transformer bushing to be tested, and generating a corresponding hybrid polarization circuit model according to the frequency domain dielectric spectrum curve; understandably, the frequency domain dielectric spectrum curve of the product to be tested is tested first. According to the frequency domain dielectric spectrum curve obtained by the test, an interface polarization equivalent branch is introduced on the basis of the extended Debye model to simulate the interface polarization process, so as to form a hybrid polarization circuit model.

[0046] In one embodiment, the hybrid polarization circuit model includes:

[0047]

[0048] Among them, C' and C" are the real and imaginary parts of the complex capacitance, R g , C g is the geometric equivalent branch resistance and capacitance, R i , C i is the resistance and capacitance of each RC series branch, i is the serial number of each RC series branch, R h(2k-1) , R h(2k) , Ch(2k-1) and C h(2k) are the resistance and capacitance of each interface polarization branch, k is the serial number of the polarization branch, tanδ is the dielectric loss tangent, N is the upper limit of the serial number of the polarization branch, and n is the upper limit of the serial number of the RC series branch.

[0049] The hybrid polarization circuit model also includes:

[0050]

[0051] Among them, τ i is the time constant of the RC series branch, τ hk is the time constant of the polarization branch.

[0052] Step S2, fitting the hybrid circuit model parameters through the hybrid polarization circuit model, determining the characteristic value characterizing the equivalent moisture content according to the fitting result, and determining the equivalent moisture content according to the characteristic value characterizing the equivalent moisture content; it can be understood that the frequency domain dielectric spectrum parameters are associated with the hybrid circuit model based on the above formula, and the hybrid circuit model parameters can be fitted by solving the multivariate nonlinear equation. Fit the hybrid circuit model parameters and extract the characteristic quantity that can characterize the insulation state.

[0053] In one embodiment, the branch structure of the hybrid circuit model should be determined before solving the hybrid circuit model. Six polarization branches and two interface polarization branches are used to achieve both accurate fitting results and minimize the complexity of calculation. The weighted least squares method is used to fit the objective function, and multi-objective optimization can be converted to single-objective optimization; the hybrid circuit model parameters are fitted according to the following formula:

[0054]

[0055] Among them, C' 测量 、C" 测量 is the complex capacitance measured by frequency domain dielectric spectroscopy, C' 拟合 、C" 拟合 is the complex capacitance fitted by the hybrid circuit model, and y is the circuit model parameter to be fitted.

[0056] In one embodiment, determining the characteristic value characterizing the equivalent water content according to the fitting result includes:

[0057] First, the hybrid circuit model is parameter identified, and the accuracy of the fitting result is evaluated by the goodness of fit; understandably, the hybrid circuit model is parameter identified by a genetic algorithm, and the accuracy of the fitting result is evaluated by the goodness of fit. Among them, the goodness of fit is calculated according to the following formula,

[0058]

[0059] Among them, y i are the original values ​​of the circuit model parameters, is the fitting value of the circuit model parameters, is the average of the original values, R 2 is the goodness of fit.

[0060] Secondly, the insulation resistance of the hybrid circuit model parameter is extracted as the first eigenvalue for evaluating the equivalent moisture content of the bushing, and the RC series branch parameter is calculated as the second eigenvalue of the equivalent moisture content; it can be understood that after the parameter identification is completed, the insulation resistance R of the hybrid circuit model parameter is extracted. g As the equivalent water content M of the casing c％ There is a certain fluctuation in parameter extraction using the hybrid circuit model, and small fluctuations at high water content have little effect on the insulation resistance R g Another characteristic value representing the equivalent moisture content is proposed (RC series branch parameter representing the equivalent moisture content). Among them, the RC series branch parameter is calculated according to the following formula:

[0061]

[0062] Among them, D x To characterize the equivalent water content using RC series branch parameters.

[0063] Again, if the first eigenvalue and the second eigenvalue are greater than the preset evaluation threshold, the second eigenvalue is used as the evaluation result; if the first eigenvalue or the second eigenvalue is not greater than the preset evaluation threshold, the first eigenvalue is used as the equivalent moisture content. It can be understood that the equivalent moisture content is evaluated by a segmented evaluation method. When the moisture evaluation results of the two evaluation functions are greater than the threshold, D is used. x The evaluation result of the function; otherwise, R g The evaluation result of the function completes the equivalent moisture content evaluation.

[0064] Step S3, extracting the non-uniformity index diagnostic feature quantity through the frequency domain dielectric spectrum curve of the transformer bushing, and determining the final transformer bushing moisture quantification result according to the non-uniformity index diagnostic feature quantity and the equivalent water content. It can be understood that the non-uniformity index diagnostic feature quantity is extracted based on the analysis of the frequency domain dielectric spectrum curve characteristics and circuit model parameters in different states. Finally, the quantitative analysis of the degree of moisture and uniformity of the transformer bushing oil-paper insulation is realized according to the equivalent water content evaluation function and the non-uniformity index evaluation function.

[0065] In one embodiment, the extraction of the non-uniformity index diagnostic feature comprises extracting the dielectric loss tangent between 10 -3 Hz~10-1 The integral value of Hz is equal to 10 1 Hz~10 3 The ratio of the integral value of Hz. Among them, the characteristic quantity R for evaluating the unevenness index x , whose expression is:

[0066]

[0067] The final quantitative result of the moisture exposure of the transformer bushing is determined by performing three-dimensional nonlinear surface fitting on the unevenness index, the evaluation result and the unevenness according to the following formula:

[0068] R x (Mc avg ,n)=a+b*Mc avg +c*n+d*Mc avg 2 +e*Mc avg *n

[0069] +f*n 2 +g*Mc avg 2 *n+h*Mc avg *n 2 +i*n 3

[0070] Among them, R x Represents the diagnostic characteristic of unevenness index, Mc avg represents the equivalent water content, n represents the unevenness index, and a, b, c, d, e, f, g, h, and i are the surface fitting parameters. Considering R x It is also related to the equivalent water content and the heterogeneity index. x Perform three-dimensional nonlinear surface fitting with equivalent water content and unevenness, and the fitting formula is as above.

[0071] The embodiment of the present invention further provides a system for identifying the amount of moisture on a transformer bushing, which is used to implement the method for identifying the amount of moisture on a transformer bushing, and comprises:

[0072] A model generation module, used to test the frequency domain dielectric spectrum curve of the transformer bushing to be tested, and generate a corresponding hybrid polarization circuit model according to the frequency domain dielectric spectrum curve;

[0073] A fitting module, used for fitting the hybrid circuit model parameters through the hybrid polarization circuit model, determining the characteristic value characterizing the equivalent water content according to the fitting result, and determining the equivalent water content according to the characteristic value characterizing the equivalent water content;

[0074] The quantification module is used to extract the non-uniformity index diagnostic feature quantity through the frequency domain dielectric spectrum curve of the transformer bushing, and determine the final transformer bushing moisture quantification result based on the non-uniformity index diagnostic feature quantity and the equivalent water content.

[0075] It should be noted that the system described in the above embodiment corresponds to the method described in the above embodiment. Therefore, the undetailed parts of the system described in the above embodiment can be obtained by referring to the contents of the method described in the above embodiment, and will not be repeated here.

[0076] In summary, the implementation of the embodiments of the present invention has the following beneficial effects:

[0077] The invention provides a method and system for quantitatively identifying moisture in transformer bushings. The method and system use a hybrid circuit model as a frequency domain dielectric spectrum equivalent circuit model, and perform parameter identification on the test results of the transformer oil-paper bushing by combining a genetic algorithm with a weighted least squares fitting algorithm. The method also proposes a quantitative analysis method for the moisture degree and uniformity of the insulating medium based on the model parameters and the characteristic values ​​of the dielectric spectrum curve.

[0078] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for quantitatively identifying the moisture content of a transformer bushing, characterized in that: include: Testing a frequency domain dielectric spectrum curve of a transformer bushing to be tested, and generating a corresponding hybrid polarization circuit model according to the frequency domain dielectric spectrum curve; Fitting the hybrid circuit model parameters through the hybrid polarization circuit model, determining the characteristic value characterizing the equivalent water content according to the fitting result, and determining the equivalent water content according to the characteristic value characterizing the equivalent water content; The non-uniformity index diagnostic feature is extracted from the frequency domain dielectric spectrum curve of the transformer bushing, and the final quantitative result of the transformer bushing moisture is determined based on the non-uniformity index diagnostic feature and the equivalent water content.

2. The method according to claim 1, characterized in that The hybrid polarization circuit model includes: Among them, C' and C" are the real and imaginary parts of the complex capacitance, R g , C g is the geometric equivalent branch resistance and capacitance, R i , C i is the resistance and capacitance of each RC series branch, i is the serial number of each RC series branch, R h(2k-1) , R h(2k) , C h(2k-1) and C h(2k) are the resistance and capacitance of each interface polarization branch, k is the serial number of the polarization branch, tanδ is the dielectric loss tangent, N is the upper limit of the serial number of the polarization branch, and n is the upper limit of the serial number of the RC series branch.

3. The method according to claim 2, characterized in that The hybrid polarization circuit model also includes: Among them, τ i is the time constant of the RC series branch, τ hk is the time constant of the polarization branch.

4. The method according to claim 3, characterized in that It also includes fitting the hybrid circuit model parameters according to the following formula: Among them, C' 测量 、C" 测量 is the complex capacitance measured by frequency domain dielectric spectroscopy, C' 拟合 、C" 拟合 is the complex capacitance fitted by the hybrid circuit model, and y is the circuit model parameter to be fitted.

5. The method according to claim 4, characterized in that The characteristic value characterizing the equivalent water content determined according to the fitting result includes: The hybrid circuit model is used for parameter identification, and the accuracy of the fitting results is evaluated using goodness of fit; Extract the insulation resistance of the hybrid circuit model parameter as the first eigenvalue for evaluating the equivalent moisture content of the bushing, and calculate the RC series branch parameter as the second eigenvalue of the equivalent moisture content; If the first eigenvalue and the second eigenvalue are greater than a preset evaluation threshold, the second eigenvalue is used as the evaluation result; If the first characteristic value or the second characteristic value is not greater than a preset evaluation threshold, the first characteristic value is taken as the equivalent water content.

6. The method according to claim 5, characterized in that It also includes calculating the goodness of fit according to the following formula, Among them, y i are the original values ​​of the circuit model parameters, is the fitting value of the circuit model parameters, is the average of the original values, R 2 is the goodness of fit.

7. The method according to claim 6, characterized in that It also includes calculating the RC series branch parameters according to the following formula: Among them, D x To characterize the equivalent water content using RC series branch parameters.

8. The method according to claim 1, characterized in that The extraction of the non-uniformity index diagnostic feature quantity includes extracting the dielectric loss tangent in the frequency domain dielectric spectrum curve of the transformer bushing within 10 -3 Hz~10 -1 The integral value of Hz is equal to 10 1 Hz~10 3 The ratio of the integrated values ​​of Hz.

9. The method according to claim 1, characterized in that The final quantitative result of the moisture exposure of the transformer bushing is determined by performing three-dimensional nonlinear surface fitting on the unevenness index, the evaluation result and the unevenness according to the following formula: R x (Mc avg ,n)=a+b*Mc avg +c*n+d*Mc avg 2 +e*Mc avg *n+f*n 2 +g*Mc avg 2 *n+h*Mc avg *n 2 +i*n 3 Among them, R x Represents the diagnostic characteristic of unevenness index, Mc avg represents the equivalent water content, n represents the unevenness index, and a, b, c, d, e, f, g, h, and i are surface fitting parameters.

10. A system for identifying the moisture content of transformer bushings, used to implement the method according to any one of claims 1 to 9, characterized in that: include: A model generation module, used to test the frequency domain dielectric spectrum curve of the transformer bushing to be tested, and generate a corresponding hybrid polarization circuit model according to the frequency domain dielectric spectrum curve; A fitting module, used for fitting the hybrid circuit model parameters through the hybrid polarization circuit model, determining the characteristic value characterizing the equivalent water content according to the fitting result, and determining the equivalent water content according to the characteristic value characterizing the equivalent water content; The quantification module is used to extract the non-uniformity index diagnostic feature quantity through the frequency domain dielectric spectrum curve of the transformer bushing, and determine the final transformer bushing moisture quantification result based on the non-uniformity index diagnostic feature quantity and the equivalent water content.

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