Method for evaluating insulation damp state of valve-side dry-type bushing

Abstract

The invention relates to a valve side dry-type bushing insulation damp state evaluation method, and belongs to the technical field of power equipment performance evaluation. The method comprises the following steps: S1, carrying out high-voltage impedance spectroscopy test on dry-type bushing samples with different moisture contents to obtain a function expression of frequency and moisture so as to obtain a frequency domain impedance spectrum of the valve-side dry-type bushing; s2, converting the frequency domain impedance spectrum into a multi-time-scale relaxation dynamic spectrum of a time domain by using an improved inverse Laplace transformation algorithm and combining a regularization technology and a machine learning algorithm; s3, extracting multi-time scale relaxation dynamics behavior spectrum characteristics strongly related to the moisture content; and S4, establishing a nonlinear mapping relationship with the moisture content characteristic parameters, and constructing a moisture content evaluation model. According to the method, the applicability and robustness of evaluation are remarkably improved, and technical support is provided for guaranteeing safe and stable operation of the valve side dry type casing pipe.

Description

Technical Field

[0001] The present invention belongs to the technical field of performance evaluation of electric power equipment and relates to a method for evaluating the moisture status of dry-type bushing insulation on a valve side under different voltage levels. Background Art

[0002] Valve-side dry-type bushings are a key piece of electrical equipment in HVDC transmission systems. Their primary function is to connect transformers and converters, providing electrical insulation and mechanical support. Due to their harsh operating environment and long-term operation under high voltage stress, the overall insulation performance of valve-side dry-type bushings is directly related to equipment reliability and the safety and stability of the overall HVDC transmission system. The primary insulation system of dry-type bushings utilizes solid insulating materials such as epoxy resin and fiberglass composites. However, moisture is one of the most critical factors that can lead to reduced insulation strength, discharge, accelerated insulation degradation, and even explosion. Therefore, accurately estimating the internal moisture content of valve-side dry-type bushings is crucial for improving equipment reliability and overall power system safety.

[0003] Frequency domain dielectric spectroscopy has been widely used as a non-destructive testing technology to evaluate the insulation status of high-voltage power equipment. In particular, frequency domain dielectric spectroscopy has outstanding advantages in realizing the diagnosis and evaluation of the moisture content of valve-side dry bushings. Based on this, the dry bushing moisture status evaluation methods are mainly divided into: (1) Qualitative comparison of frequency domain dielectric spectrum curves: Some researchers tested the frequency domain dielectric spectrum curves of dry bushings with different moisture contents, and achieved qualitative analysis of the moisture status of dry bushing insulation by comparing the curves such as the real part of capacitance and the dielectric loss tangent value. (2) Mathematical calculation of frequency domain dielectric spectrum curves: Some researchers performed mathematical calculations such as integration, differentiation and summation on the frequency domain dielectric spectrum curves of dry bushings with different moisture contents to obtain quantitative characteristic parameters, and achieved the dry bushing insulation moisture content evaluation by constructing the correlation between characteristic parameters and moisture content. (3) Frequency domain dielectric spectrum curve fitting based on empirical equations and equivalent circuit models: Some scholars use the Cole-Cole equation, Cole-Davidson equation, Havriliak-Negami equation and the "resistance-capacitance" equivalent circuit model to fit the frequency domain dielectric spectrum curves of the tested dry bushings with different moisture contents. By constructing the correlation between the model parameters obtained by fitting and the moisture content, the quantitative estimation of the moisture status of the dry bushing insulation is achieved.

[0004] The above methods are mostly based on complex dielectric constant, complex capacitance or dielectric loss tangent value for analysis. However, these methods have the following challenges in engineering applications: (1) Geometric capacitance dependence: The calculation of the complex dielectric constant requires the determination of the geometric capacitance of the dry bushing. However, the insulation structure of the valve-side dry bushing is complex, and the geometric capacitance is difficult to obtain accurately, which limits the application of the complex dielectric constant. (2) Geometric size influence: The complex capacitance and dielectric loss tangent value are strongly dependent on the geometric size of the high-voltage power equipment. The high-voltage valve-side dry bushing has a larger geometric size, which causes a significant change in the characteristic parameters and affects the evaluation accuracy. (3) Insufficient applicability and robustness: The existing methods are difficult to extend to valve-side dry bushings of different voltage levels and structural forms, which limits their universality and engineering practicality.

[0005] Furthermore, there is currently a lack of systematic research on the underlying dynamic mechanisms of solid insulation materials for dry bushings under varying moisture levels. Under the influence of an applied variable-frequency field, polar particles in solid polymer insulation undergo multi-scale migration and relaxation, which is strongly correlated with their moisture state. However, existing techniques have not yet considered the impact of the intrinsic dynamic properties of solid insulation materials on moisture content assessment. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a method for evaluating the moisture status of valve-side dry bushing insulation. Starting from the physical mechanism of multi-time-scale relaxation dynamics behavior of the underlying insulating material, a new multi-time-scale relaxation dynamics spectrum is proposed. Through the optimized inverse Laplace transform, the accurate inversion analysis of the moisture dynamics behavior of the valve-side dry bushing insulation is realized, which makes up for the limitations of the traditional method of only considering the complex dielectric constant, complex capacitance and dielectric loss tangent value, and provides an efficient and feasible technical method support for accurately estimating the moisture content of valve-side dry bushings of different voltage levels.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for evaluating the moisture status of a valve-side dry-type bushing insulation comprises the following steps:

[0009] S1: Perform high-voltage impedance spectroscopy tests on dry bushing samples with different moisture contents to obtain a functional expression of frequency and moisture, thereby obtaining the frequency domain impedance spectrum of the valve-side dry bushing;

[0010] S2: Using an improved inverse Laplace transform algorithm combined with regularization techniques and machine learning algorithms, the frequency domain impedance spectrum is converted into a multi-time-scale relaxation dynamics spectrum in the time domain;

[0011] S3: Extract the multi-time-scale relaxation dynamics behavior spectral features that are strongly correlated with the water content;

[0012] S4: Establish a nonlinear mapping relationship with the moisture content characteristic parameters and construct a moisture content assessment model.

[0013] Furthermore, in step S1, the frequency domain impedance spectrum of the valve side dry bushing is expressed as:

[0014] Z(f,W)=R(f,W)+jX(f,W)

[0015] where Z(f,W), R(f,W), and X(f,W) are the complex impedance, real impedance, and imaginary impedance, respectively.

[0016] The function expression of frequency f and moisture W is:

[0017] R(f,W)=R0+α1W+α2f m +α3Wf n

[0018]

[0019] Where R(f, W) and X(f, W) are the real and imaginary impedance parts, respectively; R0, α1, α2, α3, m, and n are the coefficients of the real impedance part; C0, β1, β2, β3, p, and q are the coefficients of the imaginary impedance part.

[0020] Furthermore, in step S2, the frequency domain impedance spectrum is converted into a multi-time-scale relaxation dynamics spectrum g(τ,W) in the time domain, which is expressed as:

[0021]

[0022] Where τ is the multi-scale relaxation time of polar particles inside the insulating material, λ is the regularization parameter, f is the frequency, and ||·|| 2 is the norm budget operator.

[0023] Furthermore, in step S3, multi-time-scale relaxation dynamics behavior spectrum characteristics that are strongly correlated with moisture content are extracted. Specifically, by analyzing the multi-time-scale relaxation dynamics spectrum, characteristic parameters significantly correlated with moisture content are screened, including relaxation intensity, average relaxation time, and time constant distribution width. Characteristic parameters significantly correlated with moisture content are screened using methods such as principal component analysis and Pearson correlation coefficient.

[0024] The expression of relaxation strength P1(W) is:

[0025] The expression of the average relaxation time P2(W) is:

[0026] The expression of the time constant distribution width P3(W) is:

[0027] Furthermore, in step S4, a data-driven algorithm (such as a neural network or a support vector machine) is combined with the multi-time-scale relaxation dynamics behavior spectrum characteristics to establish a nonlinear mapping relationship between moisture content and relaxation intensity, average relaxation time and time constant distribution width, and construct a moisture content assessment model W 估计 ; and use cross-validation method to optimize model parameters;

[0028]

[0029] Among them, W 估计 is the moisture content evaluation value, b0, b1, b2, b3 are polynomial coefficients, P1(W) is the relaxation strength, is the average relaxation time, P3(W) is the time constant distribution width, and τ is the multi-scale relaxation motion time of polar particles inside the insulating material.

[0030] The beneficial effects of the present invention are as follows: by revealing the intrinsic relationship between moisture state and the underlying dynamic properties of solid insulating materials, the present invention establishes a new moisture state assessment technology. Specifically, based on the physical mechanism of the multi-time-scale relaxation dynamic behavior of the underlying insulating material, a new multi-time-scale relaxation dynamic spectrum is proposed. Through the optimized inverse Laplace transform, the precise inversion analysis of the moisture dynamic behavior of the valve-side dry bushing insulation is achieved, which makes up for the limitations of the traditional method that only considers the complex dielectric constant, complex capacitance and dielectric loss tangent. The present invention first obtains the high-voltage impedance spectrum of the valve-side dry bushing insulation under different moisture contents; based on the optimized inverse Laplace transform, an analytical model for the quantitative relationship of moisture state is established, achieving the precise inversion analysis of the physical mechanism of the multi-time-scale relaxation dynamic behavior of the valve-side dry bushing insulation; based on the obtained moisture state-sensitive multi-time-scale relaxation dynamic spectrum, multi-time-scale characteristic parameters strongly correlated with the moisture state are extracted, including relaxation peak intensity, width and relaxation time distribution characteristics; finally, the strong correlation between the relaxation peak intensity, width and relaxation time distribution characteristics and the moisture state is analyzed, significantly improving the sensitivity and robustness of the assessment technology. This method can effectively and accurately assess the insulation moisture status of valve-side dry bushings at different voltage levels, ensuring the safe and reliable operation of valve-side dry bushings. This method overcomes the dependence of traditional assessment techniques on the geometric capacitance and dimensions of valve-side dry bushings, significantly improving the applicability and robustness of the assessment.

[0031] The present invention is applicable to analysis and evaluation of moisture content of valve-side dry bushing insulation at different voltage levels, and is particularly applicable to the field of moisture status analysis of epoxy resin-impregnated valve-side bushing insulation.

[0032] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0034] Figure 1 A flow chart of the method for evaluating the moisture status of the valve-side dry-type bushing insulation provided in this embodiment;

[0035] Figure 2 An example diagram of the multi-time-scale relaxation dynamics spectrum of the valve-side dry casing under different moisture content conditions. DETAILED DESCRIPTION

[0036] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0037] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0038] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0039] This embodiment provides a method for evaluating the moisture state of valve-side dry bushing insulation by inverting the multi-time-scale relaxation dynamics behavior of the bottom layer of solid insulation material under different moisture contents. The technical process is as follows: Figure 1 As shown, it mainly includes the following five steps:

[0040] Step 1: Test the high voltage impedance of casing with different water contents.

[0041] First, high-voltage impedance spectroscopy tests were performed on dry-type bushing samples with varying moisture contents to obtain basic data. The complex impedance data (real and imaginary components) were recorded using a high-precision impedance analyzer. The test frequency range (from 1 MHz to 1 kHz) was determined, and at least seven frequency points were set per decade to ensure comprehensive coverage of the insulation material's frequency response characteristics. The insulation impedance expression for the valve-side dry-type bushing test is shown in Equation (1), as a function of frequency f and moisture content W.

[0042] Z(f,W)=R(f,W)+jX(f,W) (1)

[0043] where Z(f, W), R(f, W), and X(f, W) are the complex impedance, real impedance, and imaginary impedance, respectively, and are functions of the applied electric field frequency and the moisture content inside the insulating material.

[0044] R(f,W)=R0+α1W+α2f m +α3Wf n (2)

[0045] Among them, R0, α1, α2, α3, m, and n are all coefficients of the real part of impedance, which are related to moisture content and frequency and need to be obtained by fitting the measured data.

[0046]

[0047] Among them, C0, β1, β2, β3, p, and q are all coefficients of the imaginary part of impedance, which are related to moisture content and frequency and need to be obtained by fitting the measured data.

[0048] Step 2: Construct a new multi-time-scale relaxation dynamics spectrum.

[0049] An improved inverse Laplace transform algorithm (i.e., an improved ILT algorithm) is introduced to convert the measured frequency-domain impedance spectrum (Equation (1)) into a multi-time-scale relaxation dynamics spectrum g(τ, W) in the time domain (Equation (4)). Regularized optimization techniques and machine learning algorithms are used to improve the resolution of the spectrum g(τ, W), ensuring that weak dynamic behaviors in insulating materials can be distinguished, including strong relaxation dynamics mechanisms related to moisture content, such as dipole motion and ion migration. This new underlying physical mechanism spectrum introduces multi-time-scale characteristic parameters based on traditional analysis, which can more comprehensively and accurately reflect the moisture effect in solid insulating materials.

[0050] Among them, the introduction of the regularization parameter λ ensures the stability and rationality of the inversion results of the underlying physical mechanism. This step realizes the precise conversion of impedance frequency domain data to multi-scale dynamic behavior in the time scale domain.

[0051]

[0052] Here, τ is the multi-scale relaxation time of polar particles inside the insulating material.

[0053] Step 3: Extract the spectral characteristics of multi-time-scale relaxation dynamics behavior that is strongly correlated with the moisture content.

[0054] By analyzing the multi-time-scale relaxation dynamics spectrum, characteristic parameters that can significantly reflect the moisture content are extracted, including the relaxation intensity P1(W) (Equation (5)), the average relaxation time P2(W) (Equation (6)), and the time constant distribution width P3(W) (Equation (7)). These characteristics can accurately reflect the multi-scale migration and dynamic characteristics of polar water particles. Characteristic parameters that are significantly correlated with moisture content are screened using methods such as principal component analysis and the Pearson correlation coefficient. The robustness of the characteristic parameters is verified in samples with different moisture contents to ensure their universality and engineering applicability.

[0055]

[0056] Step 4: Build an accurate quantitative evaluation model.

[0057] By combining data-driven algorithms (such as neural networks or support vector machines) with multi-time-scale relaxation dynamics spectra, a nonlinear mapping relationship between moisture content and relaxation intensity, average relaxation time and time constant distribution width is established. The moisture content assessment model W 估计 As shown in formula (8), the model parameters are optimized using the cross-validation method to ensure that it can accurately analyze the intrinsic physical relationship between the kinetic characteristic parameters and water migration and polarization behavior.

[0058]

[0059] Step 5: Case analysis and application guidance

[0060] Verification test:

[0061] This experiment uses five groups of samples as examples, namely reference sample, moisture 1, moisture 2, moisture 3, and moisture 4 (the moisture content is ranked as moisture 1 < moisture 2 < moisture 3 < moisture 4). After obtaining the high-voltage impedance spectrum results, based on equations (4) to (8), the multi-time-scale relaxation dynamics spectrum of the valve-side dry casing is obtained as follows: Figure 2 As shown in the figure, the multi-time-scale relaxation dynamics spectrum of the valve-side dry bushing shows significant changes with increasing moisture content. The relaxation peak intensity P1 and width P3 increase with increasing moisture content, and a new relaxation time distribution, P2, emerges at high moisture content. This case analysis demonstrates that the proposed method can effectively diagnose the moisture content of valve-side dry bushing insulation based on the underlying physical mechanism.

[0062] The method of the present invention can be applied to actual power grid projects, has a clear physical mechanism, is applicable to dry-type bushings of different voltage levels, has excellent versatility and robustness, and can provide effective technical support for insulation status monitoring and safe operation of valve-side dry-type bushings.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for evaluating the moisture status of valve-side dry bushing insulation, characterized in that: The method specifically comprises the following steps: S1: Perform high-voltage impedance spectroscopy tests on dry bushing samples with different moisture contents to obtain a functional expression of frequency and moisture, thereby obtaining the frequency domain impedance spectrum of the valve-side dry bushing; S2: Using an improved inverse Laplace transform algorithm combined with regularization techniques and machine learning algorithms, the frequency domain impedance spectrum is converted into a multi-time-scale relaxation dynamics spectrum in the time domain; S3: Extract the multi-time-scale relaxation dynamics behavior spectral features that are strongly correlated with the water content; S4: Establish a nonlinear mapping relationship with the moisture content characteristic parameters and construct a moisture content assessment model.

2. The method for evaluating the moisture status of the valve-side dry bushing insulation according to claim 1, characterized in that: In step S1, the frequency domain impedance spectrum of the valve side dry bushing is expressed as: Z(f,W)=R(f,W)+jX(f,W) where Z(f,W), R(f,W), and X(f,W) are the complex impedance, real impedance, and imaginary impedance, respectively.

3. The method for evaluating the insulation moisture status of a valve-side dry-type bushing according to claim 1 or 2, characterized in that: In step S1, the function expression of frequency f and moisture W is: R(f,W)=R0+α1W+α2f m +α3Wf n Where R(f, W) and X(f, W) are the real and imaginary impedance parts, respectively; R0, α1, α2, α3, m, and n are the coefficients of the real impedance part; C0, β1, β2, β3, p, and q are the coefficients of the imaginary impedance part.

4. The method for evaluating the moisture status of the valve-side dry bushing insulation according to claim 2, characterized in that: In step S2, the frequency domain impedance spectrum is converted into a multi-time-scale relaxation dynamics spectrum g(τ,W) in the time domain, which is expressed as: Where τ is the multi-scale relaxation time of polar particles inside the insulating material, λ is the regularization parameter, and f is the frequency.

5. The method for evaluating the insulation moisture status of a valve-side dry-type bushing according to claim 4, characterized in that: In step S3, the multi-time-scale relaxation dynamics behavior spectrum characteristics that are strongly correlated with the moisture content are extracted. Specifically, by analyzing the multi-time-scale relaxation dynamics spectrum, characteristic parameters that are significantly correlated with the moisture content are screened, including relaxation intensity, average relaxation time and time constant distribution width.

6. The method for evaluating the moisture status of the valve-side dry bushing insulation according to claim 5, characterized in that: In step S3, characteristic parameters significantly correlated with moisture content are screened through principal component analysis and Pearson correlation coefficient.

7. The method for evaluating the moisture status of the valve-side dry bushing insulation according to claim 5, characterized in that: In step S3, the expression of relaxation intensity P1(W) is:

8. The method for evaluating the moisture status of the valve-side dry bushing insulation according to claim 5, characterized in that: In step S3, the expression of the average relaxation time P2(W) is:

9. The method for evaluating the moisture status of the valve-side dry bushing insulation according to claim 8, characterized in that: In step S3, the expression of the time constant distribution width P3(W) is:

10. The method for evaluating the insulation moisture status of a valve-side dry-type bushing according to claim 1, characterized in that: In step S4, a data-driven algorithm is combined with the multi-time-scale relaxation dynamics behavior spectrum characteristics to establish a nonlinear mapping relationship between moisture content and relaxation intensity, average relaxation time and time constant distribution width, and construct a moisture content assessment model W 估计 ; Among them, W 估计 is the moisture content evaluation value, b0, b1, b2, b3 are polynomial coefficients, P1(W) is the relaxation strength, is the average relaxation time, P3(W) is the time constant distribution width, and τ is the multi-scale relaxation motion time of polar particles inside the insulating material.

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