Cable accessory insulation degradation evaluation method and system based on comprehensive degradation index

Abstract

The invention discloses a cable accessory insulation degradation evaluation method and system based on a comprehensive degradation index. The method comprises the following steps: measuring the surface potential attenuation rate, the carbonyl index, the dielectric loss increment and the glass-transition temperature deviation of the insulation of a to-be-evaluated cable accessory; determining an objective weighting value of each index by adopting an entropy weight method; determining a subjective weighting value of each index by adopting an analytic hierarchy process; performing weighted averaging on the objective weighting value and the subjective weighting value of each index to obtain a comprehensive weight; establishing a comprehensive degradation index calculation formula according to the comprehensive weight, and calculating a comprehensive degradation index of cable accessory insulation by using the comprehensive degradation index calculation formula; and evaluating the degradation state of the cable accessory insulation based on the comprehensive degradation index. According to the method, multi-dimensional parameters are comprehensively considered, the comprehensive degradation index of the insulation of the cable accessory is calculated through a simple and efficient operation method, and then the degradation degree of the insulation of the cable accessory is effectively evaluated.

Description

Technical Field

[0001] The present invention relates to an insulation detection technology for power equipment, and in particular to a cable accessory insulation degradation assessment method and system based on a comprehensive degradation index. Background Art

[0002] With rapid economic development and growing electricity demand, high-voltage cables, as key equipment in power transmission systems, are crucial for their safe and stable operation. The composite interface between cables and accessories, as well as areas where electric field stress concentrations occur, are weak links in power transmission systems. Insulation degradation directly impacts the overall performance and service life of the cables. Over long-term operation, cable accessories are subject to the combined effects of electric, thermal, mechanical, and environmental factors, making them susceptible to insulation degradation. This in turn becomes a potential vulnerability to electrical breakdown, jeopardizing the safe operation of the cables.

[0003] Currently, methods for detecting and evaluating insulation degradation in cable accessories primarily rely on the measurement of single parameters, such as partial discharge and dielectric loss factor. While these methods can reflect the insulation status of cable accessories to a certain extent, due to the complexity and multi-factor influence of insulation degradation, a single parameter is often unable to comprehensively and accurately assess the degree of insulation degradation. For example, while partial discharge can reflect local defects in cable accessories, its measurement results are susceptible to environmental interference and cannot fully reflect the overall aging of the insulation material. While dielectric loss factor can reflect the polarization and leakage losses of the insulation material, its low sensitivity to early degradation makes it difficult to provide early warning. Therefore, there is an urgent need for a cable accessory insulation degradation assessment method and system that can comprehensively consider multi-dimensional parameters to provide a basis for maintenance personnel to evaluate the service performance of cable accessory insulation and ensure the safe and reliable operation of the power system. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a cable accessory insulation degradation assessment method and system based on a comprehensive degradation index, which comprehensively considers multi-dimensional parameters, calculates the comprehensive degradation index of the cable accessory insulation through a simple and efficient operation method, and then effectively evaluates the degree of degradation of the cable accessory insulation.

[0005] Technical solution: The present invention provides a cable accessory insulation degradation assessment method based on a comprehensive degradation index, comprising:

[0006] Measure the surface potential decay rate, carbonyl index, dielectric loss increment and glass transition temperature shift of the insulation of the cable accessories to be evaluated;

[0007] If the surface potential decay rate is greater than a preset threshold, the entropy weight method is used to determine the objective weight value of each indicator, and the hierarchical analysis method is used to determine the subjective weight value of each indicator; the objective weight value and subjective weight value of each indicator are weighted averaged to obtain the comprehensive weight;

[0008] An expression for the comprehensive degradation index is established based on the comprehensive weight to calculate the comprehensive degradation index of cable accessory insulation. The expression for the comprehensive degradation index includes the mathematical relationship between the comprehensive degradation index and the surface potential decay rate, carbonyl index, dielectric loss increment, and glass transition temperature shift;

[0009] Evaluate the deterioration state of cable accessory insulation based on the comprehensive deterioration index.

[0010] Furthermore, a surface potential test system is used to measure a number of insulating samples to obtain a number of surface potential decay rates.

[0011] Furthermore, several insulating samples were measured using Fourier transform infrared spectroscopy to obtain several carbonyl indices.

[0012] Furthermore, dielectric spectrum tests are performed on a number of insulation samples to obtain a number of dielectric loss increments.

[0013] Furthermore, several glass transition temperature shifts were obtained by measuring several insulating samples using differential scanning calorimetry.

[0014] Furthermore, the plurality of insulation samples are obtained by cutting out an insulation sample with the same thickness from each cable terminal or connector.

[0015] Furthermore, the entropy weight method is used to determine the objective weight value of each indicator, including:

[0016] Normalize each parameter to eliminate the dimension effect:

[0017]

[0018] Where, X min and X max The minimum and maximum values ​​of the data measured within the preset time period;

[0019] Calculate the entropy value of each parameter based on the normalized parameters:

[0020]

[0021] Where, E j represents the entropy value of the jth parameter; n is the number of samples; p ij is the normalized value of the jth parameter of the i-th sample.

[0022] According to the entropy value E of the jth parameter j Calculate the objective weight value w of each parameter je :

[0023]

[0024] The hierarchical analysis method is used to determine the subjective weight value of each indicator, including:

[0025] The importance of each parameter is compared pairwise and a judgment matrix is ​​constructed;

[0026] The weight of each parameter is calculated by the eigenvector method;

[0027] Calculate the consistency index and random consistency ratio to ensure the consistency of the judgment matrix:

[0028]

[0029] Where, CI is the consistency index; CR is the random consistency ratio; λ max is the maximum eigenvalue of the judgment matrix; n is the number of samples; RI is the random consistency index; if CR < 0.1, the judgment matrix is ​​considered to have acceptable consistency.

[0030] Furthermore, the calculation formula of the comprehensive weight is as follows:

[0031] w j =αw je +(1-α)w ja

[0032] Where α is the weight coefficient of the entropy weight method; w ja is the objective weight value of each parameter.

[0033] Furthermore, the expression of the comprehensive degradation index is as follows:

[0034] CDI=w1v n +w2CI n +w3Δtanδ n +w4ΔTg n

[0035] Where CDI is the comprehensive degradation index; w1, w2, w3, and w4 are the comprehensive weight coefficients of surface potential decay rate, carbonyl index, dielectric loss increment, and glass transition temperature shift, respectively; v n is the normalized value of the surface potential decay rate; CI n is the normalized value of the carbonyl index; Δtanδ n is the normalized value of dielectric loss increment; ΔTg n is the normalized value of the glass transition temperature offset.

[0036] Based on the same inventive concept, the present invention provides a cable accessory insulation degradation assessment system based on a comprehensive degradation index, comprising:

[0037] Test data acquisition module, used to measure the surface potential decay rate, carbonyl index, dielectric loss increment and glass transition temperature shift of the cable accessory insulation to be evaluated;

[0038] The intelligent diagnosis module is used to determine the objective weight value of each indicator using the entropy weight method and the subjective weight value of each indicator using the hierarchical analysis method when the surface potential decay rate is greater than a preset threshold; the objective weight value and the subjective weight value of each indicator are weighted averaged to obtain the comprehensive weight;

[0039] The intelligent diagnosis module is further used to establish an expression for a comprehensive degradation index based on the comprehensive weight, which is used to calculate the comprehensive degradation index of the cable accessory insulation. The expression for the comprehensive degradation index includes a mathematical relationship between the comprehensive degradation index and the surface potential decay rate, the carbonyl index, the dielectric loss increment, and the glass transition temperature offset.

[0040] The intelligent diagnosis module is also used to evaluate the degradation state of the cable accessory insulation based on the comprehensive degradation index.

[0041] Beneficial effects: Compared with the existing technology, the significant technical effects of the present invention are as follows: (1) Comprehensive evaluation of multi-dimensional parameters to improve the comprehensiveness and accuracy of the evaluation: By measuring parameters of four different dimensions, namely surface potential decay rate (electrical properties), carbonyl index (chemical aging), dielectric loss increment (dielectric properties) and glass transition temperature offset (thermal properties), a comprehensive degradation index is constructed. This overcomes the problems of one-sidedness and sensitivity to environmental interference caused by traditional methods relying on a single parameter (such as partial discharge or dielectric loss factor). It comprehensively reflects the degree of degradation of cable accessory insulation in electrical, chemical, dielectric and thermal properties, significantly improves the comprehensiveness and accuracy of the evaluation results, and provides a reliable basis for early degradation warning; (2) A weight allocation method combining subjective and objective factors to enhance the scientific nature of weights: The entropy weight method (objective weighting based on data discreteness) is combined with the hierarchical analysis method (subjective weighting based on expert experience) to obtain a comprehensive weight by weighted average. This solves the problem that a single weighting method is easily affected by data distribution or subjective judgment bias, resulting in unreasonable weight allocation. Balance objective data and expert experience, improve the scientificity and rationality of weight allocation, and ensure the objectivity and credibility of comprehensive degradation index calculation; (3) Modular system design to improve operational efficiency and practicality: Design four functional modules: experimental data collection, comprehensive weight calculation, comprehensive degradation index calculation, and degradation status assessment, to achieve full process automation. It overcomes the problem that traditional assessment methods rely on manual operation, the process is complex and inefficient, and it is difficult to meet the needs of rapid on-site detection. Simplify the operation process, improve assessment efficiency, reduce human errors, facilitate promotion and use in power systems, and provide real-time support for maintenance plan formulation; (4) Clear degradation level classification to guide operation and maintenance decisions: Based on the comprehensive degradation index, three thresholds are set: mild aging (≤0.325), moderate aging (0.325-0.6275), and severe aging (>0.6275), and the corresponding operation and maintenance measures are matched. It solves the problem that the existing method lacks quantitative grading standards and is difficult to accurately guide operation and maintenance strategies. It provides an intuitive basis for judging the degradation level, helping operation and maintenance personnel to quickly formulate targeted measures (such as emergency maintenance, enhanced monitoring or routine maintenance) to improve the safety and economy of the power system; (5) Compatibility and scalability: normalization processing eliminates dimensional differences and supports the integrated analysis of multiple types of data; the modular design of the system facilitates the addition of new evaluation parameters or optimization algorithms. It adapts to the introduction of different types of cable accessories and new degradation indicators, reserves expansion space for future technology upgrades, and enhances the long-term applicability of the method; (6) The present invention measures the surface potential decay rate, carbonyl index, dielectric loss increment and glass transition temperature offset of the cable accessory insulation, calculates the comprehensive degradation index, and can systematically evaluate the insulation degradation degree of the cable accessory. The evaluation results can provide a reference for the line maintenance plan. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1A schematic flow chart of a method for evaluating insulation degradation of cable accessories based on a comprehensive degradation index disclosed in an embodiment of the present invention;

[0043] Figure 2 This is a structural schematic diagram of a cable accessory insulation degradation assessment system based on a comprehensive degradation index disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is described in detail below in conjunction with specific implementation methods and the accompanying drawings.

[0045] Example 1

[0046] like Figure 1 As shown, the cable accessory insulation degradation assessment method based on the comprehensive degradation index of the present invention includes the following steps:

[0047] S1. Measure the surface potential decay rate, carbonyl index, dielectric loss increment and glass transition temperature shift of the insulation of the cable accessories to be evaluated.

[0048] The surface potential decay rate is a key parameter that characterizes the speed at which surface charge dissipates in insulating materials. Insulation degradation in cable accessories often first appears at the interface between the semiconducting layer and the insulating layer. The mobility of surface charge directly reflects changes in the interface state. In this example, a surface potential decay rate was measured on several insulation samples using a surface potential test system to obtain several values.

[0049] During long-term operation, the insulation material of cable accessories will generate carbonyl compounds due to oxidation reactions. The carbonyl index directly reflects the degree of oxidation of the material. Chemical aging can cause the electrical and mechanical properties of the insulation material to deteriorate, and changes in the carbonyl index can indirectly reflect the deterioration trend of the insulation performance. In this embodiment, the carbonyl index is obtained by measuring several insulation samples using Fourier transform infrared spectroscopy (FTIR).

[0050] Dielectric loss increment is a key parameter characterizing the dielectric properties of insulation materials. During operation, insulation materials in cable accessories can experience increases in polarization loss and leakage loss due to electrical and thermal aging. Dielectric loss increment directly reflects changes in the material's dielectric properties. Increased dielectric loss is often accompanied by increased partial discharge activity, and changes in dielectric loss increment can indirectly reflect the severity of partial discharge. In this example, dielectric spectrum testing was performed on several insulation samples to obtain several dielectric loss increments.

[0051] Glass transition temperature shift is a key parameter for characterizing the thermal properties of insulating materials. During operation, the insulating material of a cable accessory can experience a decrease in molecular segment mobility due to thermal aging. This shift directly reflects the degree of thermal aging. Thermal aging can cause a decrease in the mechanical properties of the insulating material (such as elastic modulus and elongation at break). Changes in the glass transition temperature shift indirectly reflect the deterioration trend of these mechanical properties. In this example, differential scanning calorimetry (DSC) was used to measure several insulating samples and obtain several glass transition temperature shifts.

[0052] It is worth noting that several insulation samples are obtained by cutting out an insulation sample of the same thickness from each cable terminal or joint.

[0053] S2. If the surface potential decay rate is greater than a preset threshold, the entropy weight method is used to determine the objective weight value of each indicator; the hierarchical analysis method is used to determine the subjective weight value of each indicator; the objective weight value and subjective weight value of each indicator are weighted averaged to obtain the comprehensive weight.

[0054] The specific implementation process of step S2 is as follows:

[0055] S2.1. If the surface potential decay rate is greater than a preset threshold, it is determined that there is a risk of degradation and the process proceeds to step S2.2; otherwise, the process proceeds to the normal monitoring mode.

[0056] S2.2. Use the entropy weight method to determine the objective weight value of each indicator, as follows:

[0057] Normalize each parameter to eliminate the dimension effect:

[0058]

[0059] Where, X min and X max is the minimum and maximum values ​​of the data measured within the preset time period. In this embodiment, X min and X max It is the minimum and maximum value of the data measured in the last 30 days.

[0060] Calculate the entropy value of each parameter based on the normalized parameters:

[0061]

[0062] Where, E j represents the entropy value of the jth parameter; n is the number of samples; p ij is the normalized value of the jth parameter of the i-th sample.

[0063] According to the entropy value E of the jth parameter jCalculate the objective weight value w of each parameter je :

[0064]

[0065] S2.3. Use the analytic hierarchy process to determine the subjective weighting value of each indicator, which specifically includes the following steps:

[0066] S2.3.1. Compare the importance of each parameter pairwise and construct a judgment matrix using the 1-9 scaling method shown in Table 1;

[0067] Table 1

[0068]

[0069] S2.3.2. Calculate the weights of each parameter using the eigenvector method, specifically including the following steps:

[0070] S2.3.2.1. Calculate the geometric mean of each row of the judgment matrix:

[0071]

[0072] Where M j is the geometric mean, a jk is the value in the jth row and kth column of the matrix.

[0073] S2.3.2.2. Normalize the geometric mean to obtain the weight vector:

[0074]

[0075] Where W j is the weight value.

[0076] S2.3.3. Calculate the consistency index and random consistency ratio to ensure the consistency of the judgment matrix:

[0077]

[0078] Where CI is the consistency index, CR is the random consistency ratio, λ max is the maximum eigenvalue of the judgment matrix; n is the number of samples; RI is the random consistency index; if CR < 0.1, the judgment matrix is ​​considered to have acceptable consistency.

[0079] S2.4. Take the weighted average of the objective weighting value and subjective weighting value of each indicator to obtain the comprehensive weight.

[0080] The calculation formula for the comprehensive weight is as follows:

[0081] w j =αw je+(1-α)w ja

[0082] Where α is the weight coefficient of the entropy weight method, usually 0.5; w ja is the objective weight value of each parameter.

[0083] S3. An expression for the comprehensive degradation index is established based on the comprehensive weight, which is used to calculate the comprehensive degradation index of the cable accessory insulation. The expression for the comprehensive degradation index includes the mathematical relationship between the comprehensive degradation index and the surface potential decay rate, the carbonyl index, the dielectric loss increment and the glass transition temperature offset.

[0084] In this embodiment, the comprehensive degradation index CDI is expressed as follows:

[0085] CDI=w1v n +w2CI n +w3Δtanδ n +w4ΔTg n

[0086] Where CDI is the comprehensive degradation index; w1, w2, w3, and w4 are the comprehensive weight coefficients of surface potential decay rate, carbonyl index, dielectric loss increment, and glass transition temperature shift, respectively; v n is the normalized value of the surface potential decay rate; CI n is the normalized value of the carbonyl index; Δtanδ n is the normalized value of dielectric loss increment; ΔTg n is the normalized value of the glass transition temperature offset.

[0087] S4. Evaluate the degradation status of cable accessory insulation based on the comprehensive degradation index.

[0088] If CDI≤0.325, the outer sheath of the tested cable is considered to be slightly aged;

[0089] If 0.325<CDI≤0.6275, the outer sheath of the tested cable is considered to be moderately aged;

[0090] If CDI>0.6275, the outer sheath of the tested cable is considered to be severely aged;

[0091] If the evaluation result is severe aging, measures need to be taken as soon as possible; if the evaluation result is moderate aging, monitoring needs to be strengthened and measures need to be taken if necessary; if the evaluation result is mild aging, normal maintenance inspections are carried out.

[0092] The technical effect of the cable accessory insulation degradation assessment method based on the comprehensive degradation index of the present invention is verified through a specific embodiment below.

[0093] The cable accessory insulation degradation assessment method based on the comprehensive degradation index of the present invention comprises the following steps:

[0094] S1. Measure the surface potential decay rate, carbonyl index, dielectric loss increment and glass transition temperature shift of the insulation of the cable accessories to be evaluated.

[0095] The specific process of measuring the surface potential decay rate of accessory insulation is to cut the 110kV cable accessory to be evaluated with a slicer to obtain 5 sheet samples with a thickness of 1mm and a length and width of 25*25mm. The surface of the sample is cleaned with anhydrous ethanol to remove stains and impurities on the surface of the sample; then it is placed in a vacuum drying oven at 70℃ for 8h and taken out. The surface potential decay test is performed using a surface potential test system to calculate the surface potential decay rate v i (i=1, 2, 3, 4, 5). The surface potential decay rate is calculated as follows:

[0096] v=ΔU / t

[0097] Where ΔU represents the potential change, and t represents the time it takes for the measured potential to drop from 90% to 10%.

[0098] The specific process of measuring the carbonyl index of cable accessories is to cut the 110kV cable accessories to be evaluated with a slicer to obtain 5 sheet samples with a thickness of 0.5mm and a length and width of 20*20mm. The surface of the sample is cleaned with anhydrous ethanol to remove stains and impurities on the surface of the sample; then it is placed in a vacuum drying oven at 70℃ for 8 hours, and the sample is scanned using a Fourier transform infrared spectrometer to calculate the carbonyl index Cl i (i=1, 2, 3, 4, 5). The carbonyl index is calculated as follows:

[0099] Cl=A1720 / A2010

[0100] Wherein, A1720 represents the carbonyl peak (1720cm -1 ), A2010 is the absorbance of the reference peak (2010 cm-1).

[0101] The specific process for measuring the dielectric loss increment of cable accessories is to cut the 110kV cable accessories to be evaluated with a slicer to obtain five sheet samples with a thickness of 1mm and a length and width of 20*10mm. The sample surface is cleaned with anhydrous ethanol to remove stains and impurities on the sample surface; then, the sample is placed in a vacuum drying oven at 70℃ for 8 hours and then taken out to measure the dielectric loss increment Δtanδ of the cable accessories using an impedance analyzer. i (i=1, 2, 3, 4, 5).

[0102] The specific process of measuring the glass transition temperature shift of cable accessories is to cut the 110kV cable accessories to be evaluated with a slicer to obtain 5 particle samples with a mass of 5mg, and use a differential scanning calorimeter to measure the glass transition temperature shift ΔTg of the cable accessories. i (i=1, 2, 3, 4, 5).

[0103] S2. If the surface potential decay rate is greater than a preset threshold, the objective weight value of each indicator is determined by the entropy weight method, and the subjective weight value of each indicator is determined by the hierarchical analysis method; the objective weight value and the subjective weight value of each indicator are weighted averaged to obtain the comprehensive weight;

[0104] The specific implementation process of step S2 is as follows:

[0105] S2.1. If the surface potential decay rate is greater than a preset threshold, it is determined that there is a risk of degradation and the process proceeds to step S2.2; otherwise, the process proceeds to the normal monitoring mode.

[0106] S2.2. Use the entropy weight method to determine the objective weight value of each indicator, as follows:

[0107] Normalize each parameter to eliminate the dimension effect:

[0108]

[0109] Where, X min and X max is the minimum and maximum values ​​of the data measured within the preset time period. In this embodiment, X min and X max It is the minimum and maximum value of the data measured in the last 30 days.

[0110] Calculate the entropy value of each parameter based on the normalized parameters:

[0111]

[0112] Where, E j represents the entropy value of the jth parameter; n is the number of samples; p ij is the normalized value of the jth parameter of the i-th sample.

[0113] According to the entropy value E of the jth parameter j Calculate the objective weight value w of each parameter je :

[0114]

[0115] S2.3. Use the analytic hierarchy process to determine the subjective weighting value of each indicator, which specifically includes the following steps:

[0116] S2.3.1. Compare the importance of each parameter pairwise and construct a judgment matrix using the 1-9 scaling method shown in Table 1;

[0117] Table 1

[0118]

[0119]

[0120] S2.3.2. Calculate the weights of each parameter using the eigenvector method, specifically including the following steps:

[0121] S2.3.2.1. Calculate the geometric mean of each row of the judgment matrix:

[0122]

[0123] Where M j is the geometric mean, a jk is the value in the jth row and kth column of the matrix.

[0124] S2.3.2.2. Normalize the geometric mean to obtain the weight vector:

[0125]

[0126] Where W j is the weight value.

[0127] S2.3.3. Calculate the consistency index and random consistency ratio to ensure the consistency of the judgment matrix:

[0128]

[0129] Where CI is the consistency index, CR is the random consistency ratio, λ max is the maximum eigenvalue of the judgment matrix; n is the number of samples; RI is the random consistency index; if CR < 0.1, the judgment matrix is ​​considered to have acceptable consistency.

[0130] S2.4. Take the weighted average of the objective weighting value and subjective weighting value of each indicator to obtain the comprehensive weight.

[0131] The calculation formula for the comprehensive weight is as follows:

[0132] w j =αw je +(1-α)w ja

[0133] Where α is the weight coefficient of the entropy weight method, which is usually 0.5.

[0134] S3. Establish a comprehensive degradation index calculation formula based on the comprehensive weight, and use the comprehensive degradation index calculation formula to calculate the comprehensive degradation index of the cable accessory insulation.

[0135] In this embodiment, the comprehensive degradation index CDI is expressed as follows:

[0136] CDI=w1v n +w2CI n +w3Δtanδ n +w4ΔTg n

[0137] Where CDI is the comprehensive degradation index; w1, w2, w3, and w4 are the comprehensive weight coefficients of surface potential decay rate, carbonyl index, dielectric loss increment, and glass transition temperature shift, respectively; v n is the normalized value of the surface potential decay rate; CI n is the normalized value of the carbonyl index; Δtanδ n is the normalized value of dielectric loss increment; ΔTg n is the normalized value of the glass transition temperature offset.

[0138] S4. Evaluate the degradation status of cable accessory insulation based on the comprehensive degradation index.

[0139] If CDI≤0.325, the outer sheath of the tested cable is considered to be slightly aged;

[0140] If 0.325<CDI≤0.6275, the outer sheath of the tested cable is considered to be moderately aged;

[0141] If CDI>0.6275, the outer sheath of the tested cable is considered to be severely aged;

[0142] If the evaluation result is severe aging, measures need to be taken as soon as possible; if the evaluation result is moderate aging, monitoring needs to be strengthened and measures need to be taken if necessary; if the evaluation result is mild aging, normal maintenance inspections are carried out.

[0143] Example 2

[0144] like Figure 2 As shown, the cable accessory insulation degradation assessment system based on the comprehensive degradation index of the present invention includes:

[0145] Test data acquisition module, used to measure the surface potential decay rate, carbonyl index, dielectric loss increment and glass transition temperature shift of the cable accessory insulation to be evaluated;

[0146] The intelligent diagnosis module is used to determine the objective weight value of each indicator using the entropy weight method and the subjective weight value of each indicator using the hierarchical analysis method when the surface potential decay rate is greater than a preset threshold; the objective weight value and the subjective weight value of each indicator are weighted averaged to obtain the comprehensive weight;

[0147] The intelligent diagnosis module is further used to establish an expression for a comprehensive degradation index based on the comprehensive weight, which is used to calculate the comprehensive degradation index of the cable accessory insulation. The expression for the comprehensive degradation index includes a mathematical relationship between the comprehensive degradation index and the surface potential decay rate, the carbonyl index, the dielectric loss increment, and the glass transition temperature offset.

[0148] The degradation state assessment module is used to assess the degradation state of the insulation of cable accessories based on the comprehensive degradation index.

[0149] In an optional embodiment, a cable accessory insulation degradation assessment method based on a comprehensive degradation index includes: a) measuring the surface potential decay rate, carbonyl index, dielectric loss increment and glass transition temperature offset of the cable accessory insulation to be assessed; b) using an entropy weight method to determine the objective weight value of each indicator; using a hierarchical analysis method to determine the subjective weight value of each indicator; taking a weighted average of the objective weight value and the subjective weight value of each indicator to obtain a comprehensive weight; c) establishing a comprehensive degradation index calculation formula based on the comprehensive weight, and using the comprehensive degradation index calculation formula to calculate the comprehensive degradation index of the cable accessory insulation; d) assessing the degradation state of the cable accessory insulation based on the comprehensive degradation index.

[0150] In this embodiment, the intelligent diagnosis module implements rapid screening and in-depth assessment based on a two-layer diagnostic architecture, determines indicator weights, and calculates a comprehensive degradation index. The intelligent diagnosis module includes a rapid screening layer and a in-depth detection layer.

[0151] In the rapid screening layer, the surface potential decay rate is input. If the surface potential decay rate is greater than the preset threshold, it is determined that there is a degradation risk and the deep detection layer is triggered; otherwise, the system enters the conventional monitoring mode.

[0152] The deep detection layer is used to determine the objective weight value of each indicator using the entropy weight method and the subjective weight value of each indicator using the hierarchical analysis method; the objective weight value and subjective weight value of each indicator are weighted averaged to obtain the comprehensive weight;

[0153] The depth detection layer is used to establish an expression for the comprehensive degradation index based on the comprehensive weight, and is used to calculate the comprehensive degradation index of the cable accessory insulation. The expression for the comprehensive degradation index includes the mathematical relationship between the comprehensive degradation index and the surface potential decay rate, carbonyl index, dielectric loss increment, and glass transition temperature offset;

[0154] A deep detection layer for evaluating the degradation state of cable accessory insulation based on a comprehensive degradation index.

Claims

1. A cable accessory insulation degradation assessment method based on a comprehensive degradation index, characterized in that: include: Measure the surface potential decay rate, carbonyl index, dielectric loss increment and glass transition temperature shift of the insulation of the cable accessories to be evaluated; If the surface potential decay rate is greater than a preset threshold, the entropy weight method is used to determine the objective weight value of each indicator, and the hierarchical analysis method is used to determine the subjective weight value of each indicator; the objective weight value and subjective weight value of each indicator are weighted averaged to obtain the comprehensive weight; An expression for the comprehensive degradation index is established based on the comprehensive weight to calculate the comprehensive degradation index of cable accessory insulation. The expression for the comprehensive degradation index includes the mathematical relationship between the comprehensive degradation index and the surface potential decay rate, carbonyl index, dielectric loss increment, and glass transition temperature shift; Evaluate the deterioration state of cable accessory insulation based on the comprehensive deterioration index.

2. The cable accessory insulation degradation assessment method based on the comprehensive degradation index according to claim 1 is characterized in that: A surface potential test system is used to measure several insulating samples to obtain several surface potential decay rates.

3. The cable accessory insulation degradation assessment method based on comprehensive degradation index according to claim 1, characterized in that: Several carbonyl indices were obtained by measuring several insulating samples using Fourier transform infrared spectroscopy.

4. The cable accessory insulation degradation assessment method based on comprehensive degradation index according to claim 1, characterized in that: Dielectric spectrum testing is performed on several insulation samples to obtain several dielectric loss increments.

5. The cable accessory insulation degradation assessment method based on comprehensive degradation index according to claim 1, characterized in that: Several glass transition temperature shifts were obtained by measuring several insulating samples using differential scanning calorimetry.

6. The cable accessory insulation degradation assessment method based on a comprehensive degradation index according to any one of claims 2 to 5, characterized in that: The plurality of insulation samples are obtained by cutting out an insulation sample with the same thickness from each cable terminal or joint.

7. The cable accessory insulation degradation assessment method based on comprehensive degradation index according to claim 1, characterized in that: The entropy weight method is used to determine the objective weight value of each indicator, including: Normalize each parameter to eliminate the dimension effect: Where, X min and X max The minimum and maximum values ​​of the data measured within the preset time period; Calculate the entropy value of each parameter based on the normalized parameters: Where, E j represents the entropy value of the jth parameter; n is the number of samples; p ij is the normalized value of the jth parameter of the i-th sample. According to the entropy value E of the jth parameter j Calculate the objective weight value w of each parameter je : The hierarchical analysis method is used to determine the subjective weight value of each indicator, including: The importance of each parameter is compared pairwise and a judgment matrix is ​​constructed; The weight of each parameter is calculated by the eigenvector method; Calculate the consistency index and random consistency ratio to ensure the consistency of the judgment matrix: Where, CI is the consistency index; CR is the random consistency ratio; λ max is the maximum eigenvalue of the judgment matrix; n is the number of samples; RI is the random consistency index; if CR < 0.1, the judgment matrix is ​​considered to have acceptable consistency.

8. The cable accessory insulation degradation assessment method based on comprehensive degradation index according to claim 7, characterized in that: The calculation formula of the comprehensive weight is as follows: w j =αw je +(1-a)w ja Where α is the weight coefficient of the entropy weight method; w ja is the objective weight value of each parameter.

9. The cable accessory insulation degradation assessment method based on comprehensive degradation index according to claim 1, characterized in that: The expression of the comprehensive degradation index is as follows: CDI=w1v n +w2CI n +w3Δtanδ n +w4ΔTg n Where CDI is the comprehensive degradation index; w1, w2, w3, and w4 are the comprehensive weight coefficients of surface potential decay rate, carbonyl index, dielectric loss increment, and glass transition temperature shift, respectively; v n is the normalized value of the surface potential decay rate; CI n is the normalized value of the carbonyl index; Δtanδ n is the normalized value of dielectric loss increment; ΔTg n is the normalized value of the glass transition temperature offset.

10. A cable accessories insulation degradation assessment system based on a comprehensive degradation index, characterized in that: include: Test data acquisition module, used to measure the surface potential decay rate, carbonyl index, dielectric loss increment and glass transition temperature shift of the cable accessory insulation to be evaluated; The intelligent diagnosis module is used to determine the objective weight value of each indicator using the entropy weight method and the subjective weight value of each indicator using the hierarchical analysis method when the surface potential decay rate is greater than a preset threshold; the objective weight value and the subjective weight value of each indicator are weighted averaged to obtain the comprehensive weight; The intelligent diagnosis module is further used to establish an expression for a comprehensive degradation index based on the comprehensive weight, which is used to calculate the comprehensive degradation index of the cable accessory insulation. The expression for the comprehensive degradation index includes a mathematical relationship between the comprehensive degradation index and the surface potential decay rate, the carbonyl index, the dielectric loss increment, and the glass transition temperature offset. The intelligent diagnosis module is also used to evaluate the degradation state of the cable accessory insulation based on the comprehensive degradation index.

Images