A method and system for predicting the breakdown field strength of XLPE cable insulation

Abstract

The application belongs to the technical field of high voltage and insulation, and relates to a method and system for predicting the breakdown field strength of XLPE cable insulation, the method comprising the following steps: step S1: a sampling, weighing, shredding and bagging step; step S2: an extraction, weighing and gel content calculation step; step S3: a step of constructing an evaluation model; and step S4: a step of predicting the breakdown field strength; the technical scheme of the application is based on a small amount of breakdown data and gel content, a model is constructed to quickly evaluate the breakdown field strength of XLPE insulation of different processes, the breakdown field strength of XLPE cable insulation under various preparation processes can be accurately evaluated, the test method is simple, the operation is convenient, the universality is strong, the test cost of the breakdown field strength of XLPE sample insulation can be greatly reduced, the scientific research efficiency is improved, the time cost of optimizing the preparation process of cable manufacturers can be reduced, and a scientific and effective analysis means is provided for the analysis of XLPE materials and the production of cables.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high voltage and insulation, and particularly relates to a method and system for predicting the breakdown field strength of XLPE cable insulation. BACKGROUND

[0002] With the rapid development of urbanization and economy in China, the demand for electricity continues to grow, and power cables have become a key equipment for urban underground energy channels and long-distance power transmission. Cross-linked polyethylene (XLPE) is widely used as a cable insulation material due to its excellent electrical, thermal and mechanical properties. In recent years, with the progress of materials and power transmission technology, XLPE insulated high-voltage cables have played a core role in important projects such as cross-sea power transmission and power grid interconnection.

[0003] Currently, cable manufacturing is developing towards large size and high voltage grade, but there is still a lack of relatively mature preparation process in this field, and the influence of cable vulcanization temperature and time on its insulation performance is not clear enough. Currently, the evaluation of cable insulation performance mainly relies on traditional methods such as withstand voltage test and type test, and the breakdown field strength needs to be obtained through slicing and multiple destructive tests, which is a cumbersome and costly process, seriously restricting the development of high-end cable manufacturing technology. This is the deficiency of the prior art.

[0004] Therefore, the application provides a method and system for predicting the breakdown field strength of XLPE cable insulation, which can accurately evaluate the insulation performance of the cable, avoid the cumbersome electrical performance test, and provide the variation law of the breakdown field strength, to solve the above-mentioned defects existing in the prior art, which is very necessary. SUMMARY

[0005] The purpose of the application is to provide a method and system for predicting the breakdown field strength of XLPE cable insulation to solve the above technical problems in view of the defects of the prior art.

[0006] To achieve the above purpose, the application provides the following technical scheme:

[0007] A method for predicting the breakdown field strength of XLPE cable insulation, comprising the following steps:

[0008] Step S1, sampling, weighing and cutting and bagging, in which:

[0009] XLPE cable samples under different process parameters are weighed, cut and placed in a mesh bag.

[0010] Step S2, extraction, weighing and gel content calculation, in which:

[0011] The net bag is placed in a flask containing the extraction solution, heated to boiling until the extraction is complete, then washed several times, dried and weighed, and the gel content of different samples is calculated.

[0012] Step S3, the step of constructing an evaluation model, in which:

[0013] The model of the complex nonlinear relationship between the gel content and the breakdown field strength is established by comprehensively considering the positive enhancement effect of the gel content on the breakdown field strength and the negative weakening effect caused by potential defects.

[0014] Step S4, the step of predicting the breakdown field strength, in which:

[0015] According to the gel content and a small part of the breakdown field strength of the sample to be evaluated, the model obtained in step S3 is used to obtain the breakdown field strength of the sample to be evaluated.

[0016] As preferred, in step 1, XLPE cable samples under different process parameters are weighed, and then cut into small pieces and placed in a net bag for weighing, including:

[0017] The XLPE cable samples under different process parameters (such as different vulcanization temperatures and times) are weighed, and the mass of each selected sample should be kept basically the same. Then, each sample is cut into small pieces using clean scissors or a slicing machine to significantly increase its contact area with the extraction solvent, ensuring the sufficiency and uniformity of the extraction reaction. Next, the cut samples are quantitatively loaded into a net bag made of iron wire. Finally, a device with an accuracy of 0.1 mg or higher is used to weigh the sample-loaded net bag, and the initial total mass is recorded, which will be used for the accurate calculation of the gel content of the subsequent samples.

[0018] As preferred, in step 2, the net bag is placed in a flask containing the extraction solution, heated to boiling until the extraction is complete, then washed several times, dried and weighed, and the gel content of different samples is calculated, including:

[0019] The iron wire net bag containing the sample is placed in a round-bottom flask, and a sufficient amount of organic solvent (such as m-xylene, p-xylene, etc.) that can effectively dissolve non-crosslinked polyethylene is added. A reflux condenser is installed, and the solvent is continuously heated to boiling at the boiling point temperature, and the extraction is kept constant for a long enough time (such as more than 12 hours), until the mass of the net bag no longer changes significantly, ensuring that the soluble components are completely extracted, i.e., the extraction is considered complete.

[0020] After the extraction is complete, the net bag is removed and washed several times with a volatile solvent that is miscible with the extractant to thoroughly remove the residual extractant and dissolved substances. Then, the washed net bag is placed in a vacuum drying oven at a temperature lower than the melting point of XLPE (such as 80°C) for sufficient drying until the mass is constant to remove all volatile components.

[0021] Subsequently, the total mass of the dried mesh bag and the extracted sample is weighed using a device with an accuracy of 0.1 mg or higher, and the gel content of different samples can be calculated , which is calculated as follows:

[0022]

[0023] wherein, is the weight of the mesh bag, is the total weight of the sample and the mesh bag, is the total mass of the extracted and dried sample and the mesh bag.

[0024] As a preferred, the step S3 comprehensively considers the positive enhancement effect of the gel content on the breakdown field strength and the negative weakening effect caused by potential defects, and establishes a model of complex nonlinear relationship between the gel content and the breakdown field strength , i.e. a sample breakdown field strength prediction model, including:

[0025] The theoretical basis of the sample breakdown field strength prediction model lies in considering two competing microscopic mechanisms at the same time: one is the positive enhancement effect of the crosslinking degree improvement represented by the increase of the gel content on the insulation strength, and the other is the negative weakening effect of the micro defects possibly introduced in the preparation process on the insulation performance. Therefore, the overall framework of the sample breakdown field strength prediction model is established as the sum of a basic strength and two regulation terms, which is as follows:

[0026]

[0027] wherein, is the basic breakdown field strength, is the maximum increase of the breakdown field strength, is the influence proportion of the gel content on the increase of the breakdown field strength, which is between 0 and 1, is the defect influence strength.

[0028] In the sample breakdown field strength prediction model, it is divided into three parts: the basic breakdown field strength term , the enhancement effect term , and the defect weakening term .

[0029] The enhancement effect term part, the gel content of the sample under different process parameters exists in the growth area, which has a positive influence on the increase of the breakdown field strength, and the relationship between its influence proportion and the gel content can be expressed as:

[0030]

[0031] wherein, is the rate of gel content enhancement, is the impact ratio of the enhancement effect. Based on the equation above, the impact ratio is as follows:

[0032]

[0033] where, is the gel content enhancement starting point, i.e., from this point the strength increases significantly. This function indicates that when the gel content exceeds a certain starting point , the breakdown field strength begins to increase significantly, and the growth rate is controlled by the parameter ; as continues to increase, the gain effect eventually tends to saturation.

[0034] The defect weakening term part, for samples under different process parameters, the defect density about gel content approximately follows a unimodal distribution, then the defect density can be expressed as:

[0035]

[0036] where, is the peak density of defects, is the standard deviation, is the gel content at which the defects of the sample are most concentrated. Breakdown is a random failure event, which is closely related to defects. Under the small perturbation approximation, the breakdown strength decrement is proportional to the defect density, so the defect impact strength of the sample is:

[0037]

[0038] Combining into a constant , for the convenience of writing, define , so

[0039]

[0040] where, is the defect amplitude, is the gel content at which the defects are most concentrated, is the defect width.

[0041] Finally, the complete breakdown field strength prediction model is expressed as follows:

[0042]

[0043] As preferred, the step 4 of obtaining the breakdown field strength of the sample to be evaluated according to the gel content and a small part of the breakdown field strength of the sample to be evaluated using the model obtained in step S3, comprises:

[0044] First, representative partial samples are selected to conduct traditional breakdown field strength tests to obtain their real experimental values. Subsequently, these known breakdown field strength data and their corresponding gel content data are input into the prediction model established in step S3, and a nonlinear regression fitting algorithm is used to accurately calibrate the key unknown parameters 、 and in the model. After obtaining the calibrated model, it can be applied to predict the breakdown field strength of samples prepared under other processes. Only the gel content of the sample to be evaluated needs to be measured and input into the above model to directly calculate the predicted breakdown field strength.

[0045] In addition, the present application also provides a system for predicting the breakdown field strength of XLPE cable insulation, comprising:

[0046] A sampling, weighing, and shredding and bagging module, in which:

[0047] XLPE cable samples under different process parameters are weighed, shredded, and placed in mesh bags for weighing.

[0048] An extraction, weighing, and gel content calculation module, in which:

[0049] The mesh bags are placed in flasks containing extraction solution, heated to boiling until extraction is complete, then washed multiple times, dried and weighed, and the gel content of different samples is calculated.

[0050] A model evaluation module, in which:

[0051] A model of the complex nonlinear relationship between gel content and breakdown field strength is established by considering the positive enhancing effect of gel content on breakdown field strength and the negative weakening effect of potential defects.

[0052] A breakdown field strength prediction module, in which:

[0053] The breakdown field strength of the sample to be evaluated is obtained using the model obtained in the model evaluation module according to the gel content and a small amount of breakdown field strength of the sample to be evaluated.

[0054] As a preferred, in the sampling, weighing, and shredding and bagging module:

[0055] XLPE cable samples under different process parameters (such as different vulcanization temperature, vulcanization time) are weighed, and the mass of each sample selected should be kept basically consistent. Then, each sample is cut into small pieces using clean scissors or a slicing machine to significantly increase its contact area with the extraction solvent, ensuring the sufficiency and uniformity of the extraction reaction. Next, the cut sample is quantitatively loaded into a mesh bag made of iron wire. Finally, the mesh bag containing the sample is weighed using a device with an accuracy of 0.1 mg or higher, and the initial total mass is recorded, which will be used for the subsequent accurate calculation of the gel content.

[0056] As preferred, in the extraction weighing and gel content calculation module:

[0057] The iron wire mesh bag containing the sample is placed in a round-bottom flask, and a sufficient amount of organic solvent (such as m-xylene, p-xylene, etc.) that can effectively dissolve non-crosslinked polyethylene is added. A reflux condenser is installed, and the boiling is continuously heated at the boiling point temperature of the solvent, keeping the temperature constant for a long enough time (such as more than 12 hours) to ensure that the soluble components are completely extracted, i.e., the extraction is considered complete.

[0058] After the extraction is complete, the mesh bag is removed and washed several times with a volatile solvent that is miscible with the extractant to thoroughly remove residual extractant and dissolved substances. Then, the washed mesh bag is placed in a vacuum drying oven and dried at a certain temperature (such as 80°C) below the melting point of XLPE until the mass is constant to remove all volatile components.

[0059] Then, the total mass of the dried mesh bag and the extracted sample is weighed using a device with an accuracy of 0.1 mg or higher, and the gel content of different samples can be calculated , which is calculated as follows:

[0060]

[0061] wherein, is the weight of the mesh bag, is the total weight of the sample and the mesh bag, is the total mass of the extracted and dried sample and the mesh bag.

[0062] As preferred, in the construction evaluation model module:

[0063] The theoretical basis of the sample breakdown field strength prediction model lies in considering two competing micro-mechanisms simultaneously: one is the positive enhancement of the crosslinking degree represented by the increase of the gel content on the insulation strength, and the other is the negative weakening effect of the micro-defects possibly introduced in the preparation process on the insulation performance. Therefore, the overall framework of the sample breakdown field strength prediction model is established as the sum of one basic strength and two regulation terms, which is as follows:

[0064]

[0065] where, is the base breakdown field strength, is the maximum breakdown field strength enhancement, is the impact ratio of gel content on breakdown field strength enhancement, which is between 0 and 1, is the defect impact strength.

[0066] In the breakdown field strength prediction model of the sample, it is divided into three parts: the base breakdown field strength term , the enhancement effect term , and the defect weakening term .

[0067] The enhancement effect term part, the gel content of the sample under different process parameters exists in the growth area, which has a positive effect on the increase of the breakdown field strength, and the relationship between its impact ratio and the gel content can be expressed as:

[0068]

[0069] where, is the rate of gel content enhancement, is the impact ratio of enhancement effect. Based on the equation, the impact ratio can be obtained as follows:

[0070]

[0071] where, is the starting point of gel content enhancement, that is, the strength increases significantly from this point. This function shows that when the gel content exceeds a certain starting point , the breakdown field strength begins to increase significantly, and the growth rate is controlled by the parameter ; as continues to increase, the gain effect eventually tends to saturation.

[0072] The defect weakening term part, the defect density of the sample under different process parameters approximately follows a unimodal distribution about the gel content , so the defect density can be expressed as:

[0073]

[0074] where, is the peak density of defects, is the standard deviation, The gel content is the most concentrated place of defects of the sample. The breakdown is a random failure event, which is closely related to defects. In the small perturbation approximation, the breakdown strength reduction is proportional to the defect density, and the defect impact strength of the sample is:

[0075]

[0076] The is combined into a constant is defined for the convenience of writing , so

[0077]

[0078] Wherein, is the defect amplitude, is the gel content of the most concentrated place of defects, is the defect width.

[0079] Finally, the complete breakdown field strength prediction model is as follows:

[0080]

[0081] As preferred, in the prediction breakdown field strength module:

[0082] First, a representative part of the sample is selected for traditional breakdown field strength test to obtain its true experimental value. Then, the known breakdown field strength data and its corresponding gel content data are introduced into the prediction model established by the evaluation model module, and the nonlinear regression fitting algorithm is used to accurately calibrate the key unknown parameters 、 and in the model. After obtaining the calibrated model, it can be applied to predict the breakdown field strength of the sample under other preparation processes. Only the gel content of the sample to be evaluated needs to be measured and introduced into the above model, and the predicted breakdown field strength can be directly calculated.

[0083] The beneficial effects of the present application are that by obtaining the gel content of XLPE under different preparation process parameters, combined with the established XLPE cable breakdown field strength prediction method, the breakdown field strength of XLPE cable with non-insulation degradation can be evaluated. Moreover, the test method of the present application is simple, does not need a large number of electrical tests, is convenient to operate, and has strong universality. The method can greatly reduce the test process of researchers on the breakdown of XLPE samples, improve the product research and development efficiency, and provide a scientific and effective evaluation method for the research and development of high-end cables.

[0084] Therefore, compared with the prior art, the present application has outstanding substantial characteristics and significant progress, and the beneficial effects of its implementation are also obvious. Attached Figure Description

[0085] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0086] Figure 1 This is a flowchart of a method for predicting the insulation breakdown field strength of XLPE cables.

[0087] Figure 2 This is a block diagram illustrating the principle of a system for predicting the insulation breakdown field strength of XLPE cables.

[0088] Figure 3 These are the actual values, confidence intervals, and prediction results of samples under different preparation processes.

[0089] The module includes: 1-Sampling, weighing, cutting, and bagging module; 2-Extraction, weighing, and gel content calculation module; 3-Evaluation model construction module; and 4-Breakthrough field strength prediction module. Detailed Implementation

[0090] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments are explanations of the present invention, but the present invention is not limited to the following implementation methods.

[0091] Example 1:

[0092] like Figure 1 As shown in the figure, this embodiment provides a method for predicting the insulation breakdown field strength of XLPE cables, which includes the following steps:

[0093] Step S1, the sampling, weighing, cutting, and bagging process, in which:

[0094] Weigh XLPE cable samples under different process parameters, cut them into pieces, and place them in a mesh bag for weighing.

[0095] Step S2, the extraction weighing and gel content calculation step, in which:

[0096] The mesh bag was placed in a flask containing the extraction solution and heated to boiling until extraction was complete. After that, the sample was washed several times, dried, weighed, and the gel content of different samples was calculated.

[0097] Step S3, the step of constructing the evaluation model, in which:

[0098] A model of the complex nonlinear relationship between the gel content and the breakdown field strength is established by comprehensively considering the positive enhancement effect of the gel content on the breakdown field strength and the negative weakening effect caused by potential defects.

[0099] Step S4, a step of predicting the breakdown field strength, in which:

[0100] According to the gel content and a small part of the breakdown field strength of the sample to be evaluated, the model obtained in step S3 is used to obtain the breakdown field strength of the sample to be evaluated.

[0101] In step 1, XLPE cable samples under different process parameters are weighed, and then cut into pieces and placed in a mesh bag for weighing, including:

[0102] XLPE cable samples under different process parameters (such as different vulcanization temperatures and times) are weighed, and the mass of each sample selected should be kept basically the same. Then, each sample is cut into small pieces using clean scissors or a slicing machine to significantly increase its contact area with the extraction solvent, ensuring the sufficiency and uniformity of the extraction reaction. Next, the cut samples are quantitatively loaded into mesh bags made of iron wire. Finally, a device with an accuracy of 0.1 mg or higher is used to weigh the mesh bag containing the samples, and the initial total mass is recorded, which will be used for subsequent accurate calculation of the gel content.

[0103] In step 2, the mesh bag is placed in a flask containing an extraction solution, heated to boiling until the extraction is complete, then washed multiple times, dried and weighed, and the gel content of different samples is calculated, including:

[0104] The iron wire mesh bag containing the sample is placed in a round-bottom flask, and an adequate amount of organic solvent (such as m-xylene, p-xylene, etc.) that can effectively dissolve non-crosslinked polyethylene is added. Install a reflux condenser and continue to heat and boil at the boiling point of the solvent, maintain constant temperature extraction for a long enough time (such as more than 12 hours), until the mass of the mesh bag no longer changes significantly, ensuring that the soluble components are completely extracted, i.e. the extraction is considered complete.

[0105] After the extraction is complete, the mesh bag is removed and washed multiple times with a volatile solvent that is miscible with the extractant to thoroughly remove residual extractant and dissolved substances. Then, the washed mesh bag is placed in a vacuum drying oven at a temperature lower than the melting point of XLPE (such as 80°C) for sufficient drying until the mass is constant to remove all volatile components.

[0106] Then, the total mass of the dried mesh bag and the extracted sample is weighed using a device with an accuracy of 0.1 mg or higher, and then the gel content of different samples can be calculated , the calculation method is as follows:

[0107]

[0108] wherein, is the weight of the net bag, is the total weight of the sample and the net bag, is the total mass of the sample and the net bag after extraction and drying.

[0109] The step S3 comprehensively considers the positive enhancement effect of the gel content on the breakdown field strength and the negative weakening effect caused by potential defects, to establish a model of the complex nonlinear relationship between the gel content and the breakdown field strength , i.e., a sample breakdown field strength prediction model, including:

[0110] The theoretical basis of the sample breakdown field strength prediction model lies in considering two kinds of competing micro-mechanisms at the same time: one is the positive enhancement effect of the crosslinking degree improvement represented by the increase of the gel content on the insulation strength, and the other is the negative weakening effect of the micro-defects possibly introduced in the preparation process on the insulation performance. Therefore, the overall framework of the sample breakdown field strength prediction model is established as the sum of a basic strength and two regulating terms, which has the following form:

[0111]

[0112] wherein, is the basic breakdown field strength, is the maximum increase of the breakdown field strength, is the influence proportion of the gel content on the increase of the breakdown field strength, which is between 0 and 1, is the defect influence strength.

[0113] In the sample breakdown field strength prediction model, there are three parts: the basic breakdown field strength term , the enhancement effect term , and the defect weakening term .

[0114] The enhancement effect term part, the gel content of the sample under different process parameters exists in the growth area, which has a positive influence on the increase of the breakdown field strength, and the relationship between its influence proportion and the gel content can be expressed as:

[0115]

[0116] wherein, is the rate of the gel content enhancement, is the influence proportion of the enhancement effect. Based on the equation, the influence proportion can be obtained as follows:

[0117]

[0118] wherein, is the starting point of the gel content enhancement, i.e. the strength increases significantly from this point. This function indicates that when the gel content exceeds a certain starting point , the breakdown field strength begins to increase significantly, and the growth rate is controlled by the parameter ; as the gel content continues to increase, the gain effect eventually tends to saturation.

[0119] The defect weakening term part, for samples under different process parameters, the defect density about the gel content approximately follows a unimodal distribution, then the defect density can be expressed as:

[0120]

[0121] where, is the peak density of defects, is the standard deviation, is the gel content at which the defects of the sample are most concentrated. Breakdown is a random failure event, which is closely related to defects. Under the small perturbation approximation, the breakdown strength decrement is proportional to the defect density, then the defect-affected strength of the sample is:

[0122]

[0123] combining into a constant , for the convenience of writing, define , then

[0124]

[0125] where, is the defect amplitude, is the gel content at which the defects are most concentrated, is the defect width.

[0126] Finally, the complete breakdown field strength prediction model is expressed as follows:

[0127]

[0128] The step 4, according to the gel content and a small part of the breakdown field strength of the sample to be evaluated, uses the model obtained in step S3 to obtain the breakdown field strength of the sample to be evaluated, including:

[0129] First, select a representative part of the sample for traditional breakdown field strength testing to obtain its true experimental value. Then, these known breakdown field strength data and their corresponding gel content data are input into the prediction model established in step S3, and a nonlinear regression fitting algorithm is used to fit the key unknown parameters , and The calibrated model can be applied to predict the breakdown field strength of samples prepared under other processes. Only the gel content of the sample to be evaluated needs to be determined and substituted into the above model, and the predicted breakdown field strength can be directly calculated.

[0130] Example 2:

[0131] As shown in Figure 2 , the system for predicting the breakdown field strength of XLPE cable insulation provided in this embodiment comprises:

[0132] A sampling, weighing and shredding and bagging module 1, in which:

[0133] XLPE cable samples under different process parameters are weighed and shredded and placed in mesh bags for weighing.

[0134] An extraction, weighing and gel content calculation module 2, in which:

[0135] The mesh bags are placed in flasks containing extraction solution, heated to boiling until extraction is complete, then washed multiple times, dried and weighed, and the gel content of different samples is calculated.

[0136] A model building and evaluation module 3, in which:

[0137] A model of the complex nonlinear relationship between gel content and breakdown field strength is established, taking into account the positive enhancing effect of gel content on breakdown field strength and the negative weakening effect of potential defects.

[0138] A breakdown field strength prediction module 4, in which:

[0139] The breakdown field strength of the sample to be evaluated is obtained using the model obtained in the model building and evaluation module, based on the gel content and a small amount of breakdown field strength of the sample to be evaluated.

[0140] In the sampling, weighing and shredding and bagging module 1:

[0141] XLPE cable samples under different process parameters (such as different vulcanization temperatures and times) are weighed, and the mass of each sample selected should be kept essentially the same. Then, each sample is cut into small pieces using clean scissors or a slicing machine to significantly increase its contact area with the extraction solvent, ensuring the completeness and uniformity of the extraction reaction. Next, the shredded sample is quantitatively placed in a mesh bag made of iron wire. Finally, a device with an accuracy of 0.1 mg or higher is used to weigh the mesh bag containing the sample, and the initial total mass is recorded, which will be used for the accurate calculation of the gel content.

[0142] In the extraction, weighing and gel content calculation module 2:

[0143] Place the wire mesh bag containing the sample into a round bottom flask, add enough amount of organic solvent (e.g. m-xylene, p-xylene, etc.) that can effectively dissolve the non-crosslinked polyethylene. Install a reflux condenser, continue to heat under boiling point of the solvent, keep constant temperature extraction for a long enough time (e.g. 12 hours or more), until the mass of the bag no longer changes significantly, ensuring that the soluble components are completely extracted, i.e. the extraction is considered complete.

[0144] After the extraction is complete, remove the bag, and use a volatile solvent that is miscible with the extractant to wash the bag multiple times to thoroughly remove the residual extractant and dissolved materials. Then, place the washed bag into a vacuum drying oven, and dry at a temperature lower than the melting point of XLPE (e.g. 80°C) until the mass is constant, to remove all volatile components.

[0145] Then, use a device with an accuracy of 0.1 mg or higher to weigh the total mass of the dried bag and the extracted sample, and then the gel content of different samples can be calculated , in the following way:

[0146]

[0147] wherein, is the weight of the bag, is the total weight of the sample and the bag, is the total mass of the sample and the bag after extraction and drying.

[0148] In the construction evaluation model module 3:

[0149] The theoretical basis of the sample breakdown field strength prediction model is to consider two competing microscopic mechanisms at the same time: one is the positive enhancement effect of the increase of crosslinking degree represented by the gel content on the insulation strength, and the other is the negative weakening effect of the micro-defects possibly introduced in the preparation process on the insulation performance. Therefore, the overall framework of the sample breakdown field strength prediction model is established as the sum of a basic strength and two regulation terms, which is as follows:

[0150]

[0151] wherein, is the basic breakdown field strength, is the maximum increase of the breakdown field strength, is the influence ratio of the gel content on the breakdown field strength increase, which is between 0 and 1, is the defect influence strength.

[0152] In the sample breakdown field strength prediction model, there are three parts: the basic breakdown field strength term , the enhancement effect term , and the defect weakening term .

[0153] The enhancement effect part, the gel content of the sample under different process parameters exists in the growth area, which has a positive effect on the increase of breakdown field strength, and the relationship between the influence proportion and the gel content can be expressed as:

[0154]

[0155] wherein, is the rate of gel content enhancement, is the influence proportion of enhancement effect. Based on the above equation, the influence proportion is obtained as follows:

[0156]

[0157] wherein, is the starting point of gel content enhancement, that is, the strength significantly increases from this point. This function shows that when the gel content exceeds a certain starting point , the breakdown field strength begins to increase significantly, and the growth rate is controlled by the parameter ; as continues to increase, the gain effect eventually tends to saturation.

[0158] The defect weakening part, the defect density of the sample under different process parameters approximately follows a unimodal distribution about the gel content , then the defect density can be expressed as:

[0159]

[0160] wherein, is the peak density of defects, is the standard deviation, is the gel content at which the defects of the sample are most concentrated. Breakdown is a random failure event, which is closely related to defects. Under the small perturbation approximation, the breakdown strength decrement is proportional to the defect density, then the defect influence strength of the sample is:

[0161]

[0162] Combining into a constant , for the convenience of writing, define , then

[0163]

[0164] wherein, is the defect amplitude, is the gel content at which the defects are most concentrated, is the defect width.

[0165] Finally, the complete breakdown field prediction model is expressed as follows:

[0166]

[0167] In the prediction breakdown field module 4:

[0168] First, a representative part of the sample is selected for the traditional breakdown field test to obtain the true experimental value. Then, these known breakdown field data and their corresponding gel content data are introduced into the prediction model established by the evaluation model module 3, and the nonlinear regression fitting algorithm is used to accurately calibrate the key unknown parameters 、 and in the model. After obtaining the calibrated model, it can be applied to predict the breakdown field of the sample under other preparation processes. Only the gel content of the sample to be evaluated needs to be measured and introduced into the above model to directly calculate its predicted breakdown field.

[0169] Example 3:

[0170] This embodiment provides further details of the content of the present application.

[0171] Step S1, select XLPE samples under different process parameters, which are 160 ℃ hot pressing for 15 min (160-0.25), 30 min (160-0.5), 1 h (160-1), 2 h (160-2), 4 h (160-4) and 180 ℃ hot pressing for 4 h (180-4) samples, respectively. 0.3 g of sample is cut and placed in a wire mesh woven bag, and weighed.

[0172] Step S2, place the bag in a flask containing dimethylbenzene extraction solution, heat to boiling for 12 h, then wash with alcohol several times, dry and weigh. The gel content of different samples is calculated using the following formula:

[0173]

[0174] The calculation results are shown in Table 1:

[0175] Table 1 Gel content of XLPE samples under different preparation process parameters

[0176]

[0177] Step S3, combine the process type and bring the gel content into the following formula to ensure the highest fitting degree of the regression model:

[0178]

[0179] Results can be obtained is 0.1362, is 36.7891%. Based on and The physical meaning, the average and standard deviation of the three measured points with the highest gel content are calculated. Then is 63.1031%, is 13.8574.

[0180] Step S4, the first three samples are selected for breakdown test, and the characteristic breakdown field strength is obtained. The test results are as follows: the 160-0.25 sample is 338.59 kV / mm, the 160-0.5 sample is 413.77 kV / mm, and the 160-1 sample is 404.32 kV / mm. The above characteristic breakdown field strength is brought into the following formula:

[0181]

[0182] obtained is 189.60 kV / mm, is 231.06 kV / mm, is 28.47 kV / mm. Combined with the known parameters, the breakdown field strength prediction model in the following formula can be obtained:

[0183]

[0184] Based on the above formula, the breakdown field strength of the sample under different gel contents can be predicted, and the results are shown in Table 2 and Figure 2 .

[0185] Table 2: Predicted breakdown field strength of samples under different gel contents and errors

[0186]

[0187] It can be seen from Table 2 and Figure 3 that the predicted breakdown field strength of the sample is close to the true value, and is much smaller than the confidence interval value of the true value. This result shows the accuracy of the prediction result of the present application.

[0188] In the specification, each embodiment is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts of each embodiment can be referred to each other. For the method disclosed in the embodiment, since it corresponds to the system disclosed in the embodiment, the description is relatively simple, and the related parts can be referred to the method part.

[0189] Those skilled in the art will further appreciate that the functionality of the various examples described herein can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the

[0190] In several embodiments of the present application, it should be understood that the disclosed system, system and method can be implemented in other ways. For example, the above-described system embodiments are merely illustrative, for example, the division of the units is only a logical function division, and actual implementation can have another division, for example, multiple units or components can be combined or integrated into another system, or some features can be omitted or not executed. In addition, the coupling or direct coupling or communication connection between the displayed or discussed units can be indirect coupling or communication connection through some interfaces, systems or units, which can be electrical, mechanical or other forms.

[0191] The units described as separate components can or can not be physically separated, and the components displayed as units can or can not be physical units, that is, they can be located in one place, or they can be distributed on multiple network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiment.

[0192] In addition, the functional modules in each embodiment of the present application can be integrated in one processing unit, or each module can be physically present separately, or two or more modules can be integrated in one unit.

[0193] Similarly, the processing units in each embodiment of the present application can be integrated in one functional module, or each processing unit can be physically present, or two or more processing units can be integrated in one functional module.

[0194] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein can be directly implemented by hardware, software modules executed by a processor, or a combination of the two. The software modules can be placed in random access memory (RAM), memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium known in the art.

[0195] Finally, it needs to be explained that in this text, relational terms such as first and second and the like can merely be used to distinguish one entity or action from another, without necessarily requiring or implying any actual such relationship or order between or among the entities or actions. Also, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0196] The above disclosed are only the preferred embodiments of the present application, but the present application is not limited thereto, any non-creative changes and several improvements and refinements made by any person skilled in the art without departing from the principles of the present application should fall within the protection scope of the present application.

Claims

1. A method for predicting the insulation breakdown field strength of XLPE cables, characterized in that, Includes the following steps: Step S1, the sampling, weighing, cutting, and bagging process, in which: Weigh XLPE cable samples under different process parameters, cut them into pieces, place them in a mesh bag, and weigh them. Step S2, the extraction weighing and gel content calculation step, in which: Place the mesh bag in a flask containing the extraction solution, heat to boiling until extraction is complete, then wash repeatedly, dry and weigh, and calculate the gel content of different samples. Step S3, the step of constructing the evaluation model, in which: A model was established to demonstrate the complex nonlinear relationship between gel content and breakdown field strength. Step S4, the step of predicting the breakdown field strength, in which: Based on the gel content and a small portion of the breakdown field strength of the sample to be evaluated, the breakdown field strength of the sample to be evaluated is obtained using the model obtained in step S3. In step S3, the positive enhancing effect of gel content on breakdown field strength and the negative weakening effect caused by potential defects are comprehensively considered to establish the gel content... With penetration field strength The model for the complex nonlinear relationship between them, i.e., the sample breakdown field strength prediction model, includes: The theoretical basis of the sample breakdown field strength prediction model lies in simultaneously considering two competing microscopic mechanisms: one is the positive enhancing effect of increased crosslinking degree represented by increased gel content on insulation strength, and the other is the negative weakening effect of microscopic defects that may be introduced during the preparation process on insulation performance. Therefore, the overall framework of the sample breakdown field strength prediction model is established as the sum of a basic strength and two control terms, in the following form: in, It is the basic penetration field strength. This represents the largest increase in field strength. This represents the percentage effect of gel content on the increase in breakdown field strength, with a value between 0 and 1. It is the intensity of the defect's impact; The sample breakdown field strength prediction model consists of three parts: the basic breakdown field strength term. Enhancement effect term Defects and Weakening Items ; Regarding the enhancement effect, the gel content of the samples under different process parameters exhibits an increasing region, which has a positive impact on the increase of the breakdown field strength. The relationship between the influence ratio and the gel content can be expressed as follows: in, It is the rate at which the gel content increases. This is the proportion of the enhancement effect; based on the above equation, the proportion of influence can be obtained. as follows: in, This is the starting point for increased gel content, meaning the strength increases significantly from this point; this function indicates that when the gel content... Exceeding a specific starting point Afterwards, the breakdown field strength began to increase significantly, and its growth rate changed from the parameter Control; with As the gain continues to increase, it eventually reaches saturation. In the defect reduction term, the defect density of samples under different process parameters is related to the gel content. If it approximately follows a unimodal distribution, then the defect density... It can be represented as: in, It is the peak density of defects. It is the standard deviation. This represents the gel content at the location where defects are most concentrated in the sample; breakdown is a random failure event closely related to defects. Under the small perturbation approximation, the reduction in breakdown strength is proportional to the defect density. Therefore, the defect influence strength of the sample is: Will Combined into constants Defined for ease of writing ,then in, It is the defect amplitude. It is the gel content at the location where defects are most concentrated. It is the defect width; Finally, the complete breakdown field strength prediction model is expressed as follows: 。 2. The method for predicting the insulation breakdown field strength of an XLPE cable according to claim 1, characterized in that, In step 1, XLPE cable samples under different process parameters are weighed, cut into pieces, placed in mesh bags, and weighed, including: Weigh XLPE cable samples under different process parameters, ensuring that the mass of each sample is basically consistent. Then, use clean scissors or a slicer to cut each sample into small pieces. Next, quantitatively pack the shredded samples into a wire mesh bag. Finally, weigh the mesh bag containing the samples using an instrument with an accuracy of 0.1 mg or higher, and record its initial total mass.

3. The method for predicting the insulation breakdown field strength of an XLPE cable according to claim 1, characterized in that, In step 2, the mesh bag is placed in a flask containing the extraction solution, heated to boiling until extraction is complete, then washed multiple times, dried, weighed, and the gel content of different samples is calculated, including: Place the wire mesh bag containing the sample in a round-bottom flask, add a sufficient amount of organic solvent that can effectively dissolve non-crosslinked polyethylene, install a reflux condenser, and continuously heat to boiling at the solvent's boiling point temperature. Maintain a constant temperature for extraction for a sufficient time until the mass of the mesh bag no longer changes significantly, ensuring that the soluble components are completely extracted. This completes the extraction process. After extraction, the mesh bag is removed and washed multiple times with a highly volatile solvent that is miscible with the extractant to thoroughly remove any residual extractant and dissolved substances. Then, the washed mesh bag is placed in a vacuum drying oven and dried thoroughly at a temperature below the melting point of XLPE until the mass is constant and all volatile components are removed. Subsequently, the total mass of the dried mesh bag and the extracted sample was weighed using a device with an accuracy of 0.1 mg or higher, and the gel content of different samples could then be calculated. The calculation method is as follows: in, For the weight of the mesh bag, This is the total weight of the sample and the mesh bag. This represents the total mass of the sample and mesh bag after extraction and drying.

4. A method for predicting the insulation breakdown field strength of an XLPE cable according to claim 1 or 3, characterized in that, In step 4, based on the gel content and a small portion of the breakdown field strength of the sample to be evaluated, the breakdown field strength of the sample to be evaluated is obtained using the model obtained in step S3, including: First, a representative sample was selected for conventional breakdown field strength testing to obtain its true experimental values. Then, these known breakdown field strength data, along with their corresponding gel content data, were substituted into the prediction model established in step S3. A nonlinear regression fitting algorithm was then used to adjust the key unknown parameters in the model. , and Accurate calibration is performed; once the calibrated model is obtained, it can be applied to predict the breakdown field strength of samples prepared using other methods; only the gel content of the sample to be evaluated needs to be measured. By substituting this into the above model, the predicted breakdown field strength can be directly calculated.

5. A system for predicting the breakdown field strength of XLPE cable insulation, characterized in that, include: The sampling, weighing, shearing, and bagging module includes: Weigh XLPE cable samples under different process parameters, cut them into pieces, place them in a mesh bag, and weigh them. The extraction weighing and gel content calculation module contains: Place the mesh bag in a flask containing the extraction solution, heat to boiling until extraction is complete, then wash repeatedly, dry and weigh, and calculate the gel content of different samples. The module for building the evaluation model includes: Taking into account both the positive enhancing effect of gel content on breakdown field strength and the negative weakening effect caused by potential defects, a model is established to establish a complex nonlinear relationship between gel content and breakdown field strength. The module for predicting breakdown field strength includes: Based on the gel content and a small portion of the breakdown field strength of the sample to be evaluated, the breakdown field strength of the sample to be evaluated is obtained using the model obtained in the evaluation model construction module. In the module for constructing the evaluation model: The theoretical basis of the sample breakdown field strength prediction model lies in simultaneously considering two competing microscopic mechanisms: one is the positive enhancing effect of increased crosslinking degree represented by increased gel content on insulation strength, and the other is the negative weakening effect of microscopic defects that may be introduced during the preparation process on insulation performance. Therefore, the overall framework of the sample breakdown field strength prediction model is established as the sum of a basic strength and two control terms, in the following form: in, It is the basic penetration field strength. This represents the largest increase in field strength. This represents the percentage effect of gel content on the increase in breakdown field strength, with a value between 0 and 1. It is the intensity of the defect's impact; The sample breakdown field strength prediction model consists of three parts: the basic breakdown field strength term. Enhancement effect term Defects and Weakening Items ; Regarding the enhancement effect, the gel content of the samples under different process parameters exhibits an increasing region, which has a positive impact on the increase of the breakdown field strength. The relationship between the influence ratio and the gel content can be expressed as follows: in, It is the rate at which the gel content increases. This is the proportion of the enhancement effect; based on the above equation, the proportion of influence can be obtained. as follows: in, This is the starting point for increased gel content, meaning the strength increases significantly from this point; this function indicates that when the gel content... Exceeding a specific starting point Afterwards, the breakdown field strength began to increase significantly, and its growth rate changed from the parameter Control; with As the gain continues to increase, it eventually reaches saturation. In the defect reduction term, the defect density of samples under different process parameters is related to the gel content. If it approximately follows a unimodal distribution, then the defect density... It can be represented as: in, It is the peak density of defects. It is the standard deviation. This represents the gel content at the location where defects are most concentrated in the sample; breakdown is a random failure event closely related to defects. Under the small perturbation approximation, the reduction in breakdown strength is proportional to the defect density. Therefore, the defect influence strength of the sample is: Will Combined into constants Defined for ease of writing ,then in, It is the defect amplitude. It is the gel content at the location where defects are most concentrated. It is the defect width; Finally, the complete breakdown field strength prediction model is expressed as follows: 。 6. The system for predicting the insulation breakdown field strength of an XLPE cable according to claim 5, characterized in that, In the sampling, weighing, cutting, and bagging module: Weigh XLPE cable samples with different process parameters, ensuring that the mass of each sample is basically consistent. Then, use clean scissors or a slicer to cut each sample into small pieces. Next, quantitatively pack the shredded samples into a wire mesh bag. Finally, weigh the mesh bag containing the samples using a device with an accuracy of 0.1 mg or higher, and record its initial total mass. This data will be used for the accurate calculation of the gel content in the subsequent process.

7. The system for predicting the insulation breakdown field strength of XLPE cables according to claim 5, characterized in that, In the extraction weighing and gel content calculation module: Place the wire mesh bag containing the sample in a round-bottom flask, add a sufficient amount of organic solvent that can effectively dissolve non-crosslinked polyethylene, install a reflux condenser, and continuously heat to boiling at the solvent's boiling point temperature. Maintain a constant temperature for extraction for a sufficient time until the mass of the mesh bag no longer changes significantly, ensuring that the soluble components are completely extracted. This completes the extraction process. After extraction, the mesh bag is removed and washed multiple times with a highly volatile solvent that is miscible with the extractant to thoroughly remove any residual extractant and dissolved substances. Then, the washed mesh bag is placed in a vacuum drying oven and dried thoroughly at a temperature below the melting point of XLPE until the mass is constant to remove all volatile components. Subsequently, the total mass of the dried mesh bag and the extracted sample is weighed using a device with an accuracy of 0.1 mg or higher, and then the gel content of different samples can be calculated. The calculation method is as follows: in, For the weight of the mesh bag, This is the total weight of the sample and the mesh bag. This represents the total mass of the sample and mesh bag after extraction and drying.

8. A system for predicting the insulation breakdown field strength of an XLPE cable according to claim 5, characterized in that, In the predicted breakdown field strength module: First, a representative sample was selected for traditional breakdown field strength testing to obtain its true experimental values. Then, these known breakdown field strength data, along with their corresponding gel content data, were substituted into the prediction model established by the evaluation model module. A nonlinear regression fitting algorithm was then used to adjust the key unknown parameters in the model. , and Accurate calibration is performed; once the calibrated model is obtained, it can be applied to predict the breakdown field strength of samples prepared using other methods; only the gel content of the sample to be evaluated needs to be measured. By substituting this into the above model, the predicted breakdown field strength can be directly calculated.

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