Power cable insulation cross-linked network uniformity evaluation method and system based on thermal shrinkage characteristic

Abstract

The invention discloses a thermal shrinkage characteristic-based power cable insulation crosslinking network uniformity evaluation method and system, and belongs to the technical field of cable insulation performance evaluation. The evaluation method comprises the following steps: establishing a calculation function of a cable insulation cross-linked network non-uniformity degree index; acquiring characteristic parameters of a stretching stage and a displacement evolution curve of displacement of a sample moving end relative to a fixed end in a shrinkage stage which are sequentially performed in the thermal shrinkage process, and acquiring characteristic parameters of the shrinkage stage through the displacement evolution curve of displacement of the sample moving end relative to the fixed end in the shrinkage stage; the non-uniformity degree in the whole shrinkage process, the relative bending degree when the maximum inflection point is reached in the shrinkage process and the stable shrinkage rate are obtained based on the characteristic parameters of the stretching stage and the characteristic parameters of the shrinkage stage, so that the non-uniformity degree indexes of the cross-linked network at different stretching temperatures and shrinkage temperatures are obtained; and evaluating the uniformity of the cable insulation cross-linked network. The method is used for solving the problems that an existing testing method cannot efficiently and conveniently test and characterize the uniformity of a cable insulation cross-linked network and cannot quantify the non-uniformity of the cross-linked network to achieve comparison.

Description

Technical Field

[0001] The present invention belongs to the technical field of cable insulation performance evaluation, and in particular relates to a method and system for evaluating the uniformity of a power cable insulation cross-linking network based on thermal shrinkage characteristics. Background Art

[0002] With the advancement of urbanization and offshore wind power construction, the demand and usage of land cables and submarine cables are constantly increasing. High-voltage power cables are developing rapidly, which puts higher requirements on the safety and reliability of cable insulation. The capacity of offshore wind power grid-connected power has increased year by year, which has promoted the development of submarine cables towards higher voltages (such as ±525kV DC) and longer distances (single cable >20km). The insulation layer of such high-voltage, large-capacity cables has been subjected to high field strength, high operating temperature and complex mechanical stress for a long time. Its safe service life directly depends on the quality of the insulation cross-linking network structure. Accurately evaluating the performance of cable insulation is an important topic in the field of electrical engineering, and the cross-linking network structure of cable insulation is the key to affecting its macroscopic electrical, thermal and mechanical properties. Therefore, it is particularly important to accurately evaluate the cross-linking network structure and its uniformity.

[0003] Currently, cross-linked network structures are generally characterized using thermal extension methods and gel content testing. The thermal extension method evaluates cross-link density by measuring the elongation under load at high temperature. The gel content method assesses the degree of cross-linking by measuring the mass percentage of residual gel after dissolution.

[0004] Thermal extension methods are time-consuming and fail to capture the real-time evolution of the cross-linked network during thermal contraction. Gel content testing is an irreversible process, preventing repeated testing of the same sample. Furthermore, the procedure is complex and requires xylene, a chemical reagent, which carries certain risks. Furthermore, significant local variations in gel content can result in statistically insignificant results.

[0005] Crosslink density and degree of crosslinking only reflect the structure of the crosslinked network. However, there is no efficient and convenient method for testing the uniformity of the crosslinked network. Using samples from multiple locations and comparing thermal extension and gel content testing to determine the uniformity of the crosslinked network is labor-intensive, inefficient, and lacks precision, making it difficult to determine uniformity within a small area. Summary of the Invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method and system for evaluating the uniformity of the power cable insulation cross-linking network based on thermal shrinkage characteristics, which is used to solve the problem that the existing testing methods cannot efficiently and conveniently test and characterize the uniformity of the cable insulation cross-linking network, and cannot quantify the unevenness of the cross-linking network and then achieve comparison.

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

[0008] In one aspect, the present invention provides a method for evaluating the uniformity of a cross-linked network of power cable insulation based on thermal shrinkage characteristics, comprising the following steps:

[0009] Establish a calculation function for the cross-linking network unevenness index of cable insulation;

[0010] Collect characteristic parameters of the stretching stage and the displacement evolution curve of the sample moving end relative to the fixed end during the contraction stage during the thermal contraction process, and obtain the characteristic parameters of the contraction stage through the displacement evolution curve of the sample moving end relative to the fixed end during the contraction stage;

[0011] Based on the characteristic parameters of the stretching stage and the characteristic parameters of the contraction stage, the unevenness of the entire contraction process, the relative bending degree when the contraction process reaches the maximum inflection point, and the stable contraction rate are obtained;

[0012] Based on the unevenness during the entire shrinkage process, the relative bending degree at the maximum inflection point during the shrinkage process, and the stable shrinkage rate, the cross-linking network unevenness index at different stretching temperatures and shrinkage temperatures is obtained to evaluate the uniformity of the cable insulation cross-linking network.

[0013] In one embodiment, the characteristic parameters of the stretching stage include the straight-line distance L0 between the fixed end and the movable end of the sample before stretching, and the straight-line distance L1 between the fixed end and the movable end of the sample after stretching is completed and cooled;

[0014] The characteristic parameters of the contraction stage include the straight-line distance L2 between the fixed end and the movable end of the sample when the contraction process reaches stability, and the displacement of the movable end relative to the fixed end in the x, y, and z directions in three-dimensional space during the contraction process.

[0015] In one embodiment, the process of obtaining the degree of unevenness during the entire shrinkage process, the relative degree of bending at the maximum inflection point during the shrinkage process, and the stable shrinkage rate based on the characteristic parameters of the stretching stage and the characteristic parameters of the shrinkage stage is as follows:

[0016] According to the displacement l in the x direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process x1 , during the contraction process, the displacement l in the z direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value z1 And the total displacement in the y direction during the entire contraction process l ym , obtain the unevenness α during the entire shrinkage process;

[0017] According to the displacement l in the x, y, and z directions at the start time t0 during the contraction processx0 , l y0 , l z0 And the displacement l in the x, y, and z directions at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process x1 , l y1 , l z1 , obtain the relative bending degree β when reaching the maximum inflection point during the contraction process;

[0018] The stable shrinkage rate θ is obtained based on the straight-line distance L0 between the fixed end and the moving end of the sample before stretching, the straight-line distance L1 between the fixed end and the moving end of the sample after stretching and cooling, and the straight-line distance L2 between the fixed end and the moving end of the sample when the shrinkage process reaches stability.

[0019] In one embodiment, the calculation formula for the degree of unevenness during the entire shrinkage process is as follows:

[0020]

[0021] Where: α represents the degree of unevenness during the entire shrinkage process; l x1 Indicates the displacement in the x-direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process; l z1 It represents the displacement in the z direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process; l ym is the total displacement in the y direction during the entire contraction process.

[0022] In one embodiment, the calculation formula for the relative bending degree when the maximum inflection point is reached during the contraction process is as follows:

[0023]

[0024] Where: β represents the relative bending degree when the maximum inflection point is reached during the contraction process; l x0 , l y0 , l z0 are the displacements in the x, y, and z directions at the start time t0 during the contraction process; l x1 , l y1 , l z1 They are the displacements in the x, y, and z directions at time t1 when the distance between the position of the mobile end in the xz plane and the starting time t0 reaches the maximum value during the contraction process.

[0025] In one embodiment, the calculation formula of the stable shrinkage rate is as follows:

[0026]

[0027] Where: θ represents the stable shrinkage rate; L0 represents the straight-line distance between the fixed end and the moving end of the sample before stretching; L1 represents the straight-line distance between the fixed end and the moving end of the sample after stretching and cooling; L2 is the straight-line distance between the fixed end and the moving end of the sample when the shrinkage process reaches stability.

[0028] In one embodiment, the calculation function of the cross-linking network non-uniformity index of the cable insulation is as follows:

[0029]

[0030] Where: ρ represents the cross-linking network heterogeneity index; α represents the heterogeneity during the entire shrinkage process; β represents the relative bending degree when the shrinkage process reaches the maximum inflection point; θ represents the stable shrinkage rate;

[0031] ω α is the weight coefficient of the unevenness α during the entire shrinkage process, ranging from 0.40 to 0.95; ω β is the weight coefficient of the relative bending degree β when the maximum inflection point is reached during the contraction process, and its value range is 0.10~0.55; ω θ is the weight coefficient for stabilizing the shrinkage rate θ, and its value range is 0.25~0.70.

[0032] In one embodiment, after obtaining the cross-linking network heterogeneity index at different stretching temperatures and shrinking temperatures, a condition judgment step is further included. The condition judgment step is as follows:

[0033] Obtaining the maximum allowable value of the cross-linking network heterogeneity index at the preset stretching temperature and shrinking temperature, and comparing it with the cross-linking network heterogeneity index at different stretching temperatures and shrinking temperatures;

[0034] When the cross-linking network non-uniformity index at different stretching temperatures and shrinking temperatures is less than the maximum allowable value of the cross-linking network non-uniformity index at the preset stretching temperature and shrinking temperature, it is judged that the conditions are met and can be used to evaluate the uniformity of the cable insulation cross-linking network.

[0035] In one embodiment, the value of the cross-linking network non-uniformity index ρ is inversely proportional to the uniformity of the cable insulation cross-linking network.

[0036] Another aspect of the present invention provides a system for evaluating the uniformity of a power cable insulation cross-linking network based on thermal shrinkage characteristics, comprising:

[0037] A cross-linking network unevenness index function establishment module is used to establish a calculation function for the cross-linking network unevenness index of cable insulation;

[0038] A feature acquisition module is used to collect the characteristic parameters of the stretching stage and the displacement evolution curve of the sample moving end relative to the fixed end during the shrinkage stage, and obtain the characteristic parameters of the shrinkage stage through the displacement evolution curve of the sample moving end relative to the fixed end during the shrinkage stage;

[0039] A parameter acquisition module is used to obtain the unevenness of the entire shrinkage process, the relative bending degree when reaching the maximum inflection point during the shrinkage process, and the stable shrinkage rate based on the characteristic parameters of the stretching stage and the characteristic parameters of the shrinkage stage;

[0040] The evaluation module is used to obtain the cross-linking network unevenness index at different stretching temperatures and shrinkage temperatures based on the unevenness during the entire shrinkage process, the relative bending degree when the shrinkage process reaches the maximum inflection point, and the stable shrinkage rate, so as to evaluate the uniformity of the cable insulation cross-linking network.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention provides a method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics. The evaluation method obtains a cross-linked network unevenness index based on characteristic parameters of the stretching stage and characteristic parameters of the shrinkage stage, and then judges the uniformity of the cable insulation cross-linked network. The method directly quantifies the uniformity of the cross-linked network by anisotropic displacement during thermal shrinkage, breaking through the limitation of traditional methods that only evaluate the overall density. The cross-linked network unevenness index of the present invention is based on the analysis of relevant parameters extracted during thermal shrinkage, and analyzes the reasons for the differences in the uniformity of the cross-linked network of power cable insulation from multiple angles according to the unevenness during the entire shrinkage process, the relative bending degree when the maximum inflection point is reached during the shrinkage process, and the stable shrinkage rate. Among them, the stable shrinkage rate reflects the uniformity of the cross-linked network from the perspective of the degree of cross-linking, while the unevenness during the entire shrinkage process reflects the uniformity of the cross-linked network from the overall unevenness during the shrinkage process, and the relative bending degree when the maximum inflection point is reached during the shrinkage process reflects the uniformity of the cross-linked network from the unevenness during the shrinkage process. The three are combined to evaluate the uniformity of the cross-linked network of power cable insulation from multiple dimensions.

[0043] Furthermore, the proposed thermal shrinkage-based testing and evaluation method allows for repeated testing of the same sample, analyzing the uniformity of the cross-linked network from the overall thermal shrinkage process. This method is both time-efficient and highly accurate. This method incorporates the displacement evolution curve of the mobile terminal during the shrinkage process to extract submillimeter deformation data, significantly improving accuracy. Compared to standard thermal shrinkage testing methods, this method offers improved accuracy and can detect localized nonuniformities as small as 0.1 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1Schematic diagram of a slicing method in an embodiment of the present invention;

[0045] Figure 2 This is a diagram of a heat shrinkage experiment scheme in an embodiment of the present invention;

[0046] Figure 3 This is a diagram of an experimental device in an embodiment of the present invention;

[0047] Figure 4 The displacement evolution curve of the moving end of the sample during the shrinkage process at a stretching temperature of 90°C and a shrinkage temperature of 120°C in an embodiment of the present invention;

[0048] Figure 5 This is a displacement evolution curve of the moving end of the sample during the shrinkage process at a stretching temperature of 110° C. and a shrinkage temperature of 120° C. in an embodiment of the present invention. DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0050] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0051] In one aspect, the present invention provides a method for evaluating the uniformity of a cross-linked network of power cable insulation based on thermal shrinkage characteristics, comprising the following steps:

[0052] Establish a calculation function for the cross-linking network unevenness index of cable insulation;

[0053] Collect characteristic parameters of the stretching stage and the displacement evolution curve of the sample moving end relative to the fixed end during the contraction stage during the thermal contraction process, and obtain the characteristic parameters of the contraction stage through the displacement evolution curve of the sample moving end relative to the fixed end during the contraction stage;

[0054] Based on the characteristic parameters of the stretching stage and the characteristic parameters of the contraction stage, the unevenness of the entire contraction process, the relative bending degree when the contraction process reaches the maximum inflection point, and the stable contraction rate are obtained;

[0055] The calculation function of the cross-linking network unevenness index of the cable insulation is used to obtain the cross-linking network unevenness index at different stretching temperatures and shrinkage temperatures by combining the unevenness during the entire shrinkage process, the relative bending degree when the shrinkage process reaches the maximum inflection point, and the stable shrinkage rate.

[0056] The uniformity of the cable insulation cross-linking network is evaluated using the cross-linking network heterogeneity index at different stretching and shrinking temperatures.

[0057] Among them, the value of the cross-linking network unevenness index ρ is inversely proportional to the uniformity of the cable insulation cross-linking network.

[0058] The displacement evolution curve of the sample moving end relative to the fixed end is a trajectory of changes in the displacement of the sample moving end relative to the fixed end in all directions during the contraction process.

[0059] The characteristic stages of the cable insulation mentioned above include a stretching stage and a contraction stage;

[0060] The characteristic parameters of the stretching stage include the straight-line distance L0 between the fixed end and the moving end of the sample before stretching, and the straight-line distance L1 between the fixed end and the moving end of the sample after stretching and cooling;

[0061] The characteristic parameters of the contraction stage include the straight-line distance L2 between the fixed end and the mobile end of the sample when the contraction process reaches stability and the displacement of the mobile end relative to the fixed end in each direction (x, y, z direction) in three-dimensional space during the contraction process; wherein, the displacement of the mobile end relative to the fixed end in each direction (x, y, z direction) in three-dimensional space during the contraction process includes the displacement l in the x, y, z directions at the start time t0 of the contraction process. x0 , l y0 , l z0 And the displacement l in the x, y, and z directions at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process x1 , l y1 , l z1 , the total displacement in the y direction during the entire contraction process l ym .

[0062] The degree of unevenness in the entire shrinkage process, the relative bending degree at the maximum inflection point during the shrinkage process, and the process of stabilizing the shrinkage rate are obtained based on the characteristic parameters of the stretching stage and the characteristic parameters of the shrinkage stage, as follows:

[0063] According to the displacement l in the x direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process x1 , during the contraction process, the displacement l in the z direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value z1 And the total displacement in the y direction during the entire contraction process l ym , obtain the unevenness α during the entire shrinkage process;

[0064] According to the displacement l in the x, y, and z directions at the start time t0 during the contraction process x0 , l y0 , l z0 And the displacement l in the x, y, and z directions at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process x1 , l y1 , l z1 , obtain the relative bending degree β when reaching the maximum inflection point during the contraction process;

[0065] The stable shrinkage rate θ is obtained based on the straight-line distance L0 between the fixed end and the moving end of the sample before stretching, the straight-line distance L1 between the fixed end and the moving end of the sample after stretching and cooling, and the straight-line distance L2 between the fixed end and the moving end of the sample when the shrinkage process reaches stability.

[0066] The calculation formula for the unevenness during the entire shrinkage process is as follows:

[0067]

[0068] The calculation formula for the relative bending degree when the maximum inflection point is reached during the contraction process is as follows:

[0069]

[0070] The calculation formula for the stable shrinkage rate is as follows:

[0071]

[0072] Among them, the calculation function of the cross-linking network unevenness index of cable insulation is as follows:

[0073]

[0074] Where: α represents the degree of unevenness during the entire shrinkage process; lx1 Indicates the displacement in the x-direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process; l z1 It represents the displacement in the z direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process; l ym is the total displacement in the y direction during the entire contraction process;

[0075] β represents the relative bending degree when the maximum inflection point is reached during the contraction process; l x0 , l y0 , l z0 are the displacements in the x, y, and z directions at the start time t0 during the contraction process; l x1 , l y1 , l z1 are the displacements in the x, y, and z directions at time t1 when the distance between the position of the mobile end in the xz plane and the starting time t0 reaches the maximum value during the contraction process;

[0076] θ represents the stable shrinkage rate, and its value reflects the degree of crosslinking. A larger value indicates a higher degree of crosslinking. L0 represents the straight-line distance between the fixed end and the moving end of the sample before stretching. L1 represents the straight-line distance between the fixed end and the moving end of the sample after stretching and cooling. L2 represents the straight-line distance between the fixed end and the moving end of the sample when the shrinkage process reaches stability.

[0077] ρ represents the cross-linking network heterogeneity index, and the larger the value, the worse the homogeneity; ω α is the weight coefficient of the unevenness α during the entire shrinkage process, ranging from 0.40 to 0.95; ω β is the weight coefficient of the relative bending degree β when the maximum inflection point is reached during the contraction process, and its value range is 0.10~0.55; ω θ is the weight coefficient for stabilizing the shrinkage rate θ, and its value range is 0.25~0.70.

[0078] When using the unevenness index to evaluate the uniformity of the cross-linking network of the power cable insulation, it should be determined whether the cable insulation meets the condition of "whether the cross-linking network unevenness index of the cable insulation is less than the maximum allowable value of the cross-linking network unevenness index at the preset temperature" at the preset temperature; when the cable insulation meets the above conditions at the preset temperature, the smaller the cross-linking network unevenness index of the cable insulation, the better the uniformity of the cable insulation.

[0079] Therefore, after obtaining the cross-linking network heterogeneity index at different stretching temperatures and shrinking temperatures, a condition judgment step is also included. The condition judgment step is as follows:

[0080] S01: obtaining a maximum allowable value of a cross-linking network non-uniformity index at a preset stretching temperature and shrinking temperature, and comparing the maximum allowable value of a cross-linking network non-uniformity index with values at different stretching temperatures and shrinking temperatures;

[0081] S02: When the cross-linking network non-uniformity index at different stretching temperatures and shrinking temperatures is less than the maximum allowable value of the cross-linking network non-uniformity index at the preset stretching temperature and shrinking temperature, it is judged that the conditions are met and can be used to evaluate the uniformity of the cable insulation cross-linking network.

[0082] The calculation formula for the maximum allowable value of the cross-linking network heterogeneity index at the preset stretching temperature and shrinkage temperature is as follows:

[0083]

[0084] Among them, ρ m Indicates the maximum allowable value of the cross-linking network heterogeneity index at the preset stretching temperature and shrinking temperature; T1 and T2 are the temperatures during stretching and shrinking, respectively, in °C.

[0085] The experimental process of the above heat shrinkage process is as follows:

[0086] Preprocessing, such as Figure 1 As shown, the insulation layer of the power cable is sliced to obtain sheet samples, which are then cut into dumbbell-shaped samples. The internal stress caused by the slicing is then eliminated by high-temperature heat treatment to obtain samples for thermal shrinkage characteristics testing.

[0087] A sample for thermal shrinkage characteristic testing is axially stretched in a high temperature environment to obtain a sample with a certain tensile elongation, and characteristic parameters of the stretching stage can be obtained based on the sample with a certain tensile elongation;

[0088] The sample after the stretching stage is placed in another high-temperature environment, one end of the sample (fixed end) is fixed, and the position change of the other end of the sample (moving end) is tested and recorded. This is the shrinkage process of the sample (shrinkage stage), which is used to obtain the displacement evolution curve of the sample moving end relative to the fixed end during the shrinkage stage.

[0089] The displacement evolution curve of the sample with a certain tensile elongation during the above-mentioned thermal shrinkage process and the displacement of the moving end of the sample relative to the fixed end during the shrinkage stage is used to extract the characteristic parameters of each characteristic stage. The degree of unevenness in the entire shrinkage process, the relative bending degree when reaching the maximum inflection point during the shrinkage process, and the stable shrinkage rate can be obtained, and then the unevenness index of the cross-linked network can be obtained, and finally the uniformity of the cross-linked network of the sample molecular chain can be judged.

[0090] The sample sections in the above experiments can be sliced in various directions, including circumferential, radial, and axial cutting. The selected areas can also be the inner layer, outer layer, or middle layer. The thickness of the sheet sample is 0.2 to 2.0 mm, and the width of the thin neck section of the dumbbell-shaped sample is 0.5 to 5 mm.

[0091] The temperature required for high-temperature heat treatment to eliminate internal stress is 110-150°C, and the time required to eliminate internal stress is 1 minute to 24 hours. The stretching rate should be kept between 5-20mm / min to avoid being too fast to cause molecular chain breakage. The strain caused by stretching should not be too short, resulting in an insignificant thermal shrinkage process, nor too long, resulting in molecular chain breakage. During the stretching process, the sample is stretched to a strain of 200-400%. After stretching to the required strain, the strain should be maintained constant and the sample should be cooled to room temperature.

[0092] The high-temperature environment required for recording the shrinkage process needs to be suitable for recording the deformation process of the sample. A transparent container is used as the cavity, silicone oil is used as the heating medium, and cameras are placed on the front and side outside the cavity to record the deformation process of the sample during the shrinkage process.

[0093] Preferably, if conditions permit, the experiment can be combined with artificial intelligence algorithms to identify and record the displacement, automatically analyze the relevant parameters of the unevenness, and compare the unevenness.

[0094] The present invention is described in further detail below with reference to the accompanying drawings:

[0095] See also Figure 1 This is a schematic diagram of the slicing method in an embodiment of the present invention, which mainly includes three directions: circular cutting, radial cutting or axial cutting. Circular cutting and axial cutting can be classified according to different thickness positions.

[0096] Figure 2 This is a diagram of the thermal shrinkage experiment scheme in an embodiment of the present invention, which is divided into two experiments: the stretching stage and the shrinkage stage. The stretching experiment is mainly a preparatory experiment, in which the sample needs to be stretched to a certain strain at high temperature, and then the strain is maintained to allow it to cool; the shrinkage experiment ensures that no external force is applied to the sample. In a high-temperature environment, it will shrink, and the displacement change of the moving end mark relative to the fixed end mark during the shrinkage process is recorded with the assistance of camera.

[0097] Figure 3 This is a diagram of the experimental device in an embodiment of the present invention, which mainly includes a transparent heat-insulating box with silicone oil added inside to provide a high-temperature environment, three rulers and a cover plate for fixing the sample on the top, and several cameras for recording, and the number of cameras can preferably be 2.

[0098] The evaluation method of the present invention is based on the thermal shrinkage characteristics test method. The specific experimental test steps are as follows:

[0099] Step 1, Slicing: See Figure 1 First, the insulation layer of the power cable sample is sliced, and sheet samples with a thickness of 0.2 to 2.0 mm are cut along the circular cutting, radial cutting or axial cutting direction of the insulation layer of the power cable sample, and cut into dumbbell shapes (thin neck section width 0.5 to 5 mm) to standardize the test area.

[0100] The sliced samples are then heat treated by placing them in an environment of 110-150°C for 1 minute to 24 hours to eliminate stress within the slices and ensure the stability of the initial state of the molecular chains.

[0101] Step 2, thermal shrinkage test: see Figure 2 The thermal shrinkage test method mainly includes two steps: stretching stage and shrinkage stage:

[0102] In the tensile test, both ends of the sample are fixed on the tensile equipment, and then the ambient temperature is heated to the required temperature, and the sample is stretched. After stretching to the required strain, the strain is maintained and the sample is cooled to room temperature to obtain a stretched sample.

[0103] In the contraction experiment, see Figure 2 and Figure 3 The sample after the above stretching treatment is placed in the required high temperature environment, a transparent container is used as the cavity, silicone oil is used as the heating medium, and cameras are placed on the front and side outside the cavity to record the deformation process of the sample during thermal shrinkage.

[0104] The interior of the experimental device includes a ruler, which includes an x-axis ruler, a y-axis ruler, and a z-axis ruler. The x-axis ruler, the y-axis ruler, and the z-axis ruler are presented in the form of a spatial rectangular coordinate system for measuring the displacement of the moving end of the sample in three directions during the contraction process. Preferably, the origin of the spatial rectangular coordinate system is at the center of the cover plate, and the fixed end of the sample is fixed at the intersection of the three rulers, that is, the origin.

[0105] The experimental device also includes at least one acquisition device, one acquisition device is arranged on the front of the experimental device, facing the plane formed by the x-axis scale and the y-axis scale, and the other acquisition device is arranged on the side of the experimental device, facing the plane formed by the y-axis scale and the z-axis scale. The above-mentioned acquisition devices can be selected as cameras.

[0106] Furthermore, when comparing the performance of different sliced samples, it is necessary to control the stretching rate, strain, stretching temperature and shrinkage temperature in step 2 to be the same to ensure that the difference in the degree of unevenness is only caused by the difference in internal structure.

[0107] The present invention provides a method for evaluating the uniformity of a power cable insulation cross-linking network based on thermal shrinkage characteristics, comprising the following steps:

[0108] Step 1: Collect characteristic parameters of thermal shrinkage process: see Figure 2 , record the straight-line distance L0 between the fixed end and the moving end of the sample before stretching, the straight-line distance L1 between the fixed end and the moving end of the sample after stretching and cooling, the straight-line distance L2 between the fixed end and the moving end of the sample when the shrinkage process reaches stability, and the displacement l in the x, y, and z directions at the starting time t0 during the shrinkage process. x0 , l y0 , l z0 During the contraction process, the displacement of the mobile end position in the xz plane and the starting time t0 reaches the maximum at time t1 in the x, y, and z directions. x1 , l y1 , l z1 , the total displacement in the y direction during the entire contraction process is l ym .

[0109] Step 2: Establish a calculation function for the cross-linking network unevenness index of cable insulation.

[0110] Step 3: Calculate the heterogeneity index of different slice samples at different stretching temperatures and shrinkage temperatures using the cross-linking network heterogeneity index calculation function.

[0111] Step 4: Evaluate the unevenness of the cable insulation cross-linking network using the unevenness index.

[0112] This method can be further combined with artificial intelligence algorithms (such as convolutional neural networks) to realize automatic analysis of displacement data and unevenness prediction, and promote the intelligent development of cable insulation quality assessment.

[0113] Example

[0114] This embodiment provides a method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics. The specific steps are as follows:

[0115] Step 1: First, select different insulation layer slices of three power cable samples and name them D1, D2 and D3 respectively; take two groups of samples and record the straight-line distance L0 between the fixed end and the moving end of each sample before stretching.

[0116] Step 2: Stretch the two groups of samples to 300% strain at high temperatures of 90°C and 110°C, respectively, at the same stretching rate of 20 mm / min, and then cool them to room temperature while maintaining the strain. Record the straight-line distance L1 between the fixed end and the moving end of each sample after stretching and cooling.

[0117] At 120°C, the sample was placed in a shrinkage experimental device, and a camera was used to record its shrinkage process in the x and y directions (only one camera was used in this embodiment), and a displacement evolution curve of the sample's moving end relative to the fixed end during the shrinkage stage was recorded.

[0118] Step 3: Analyze the image data and draw the displacement evolution path of the mobile terminal marker during the contraction process. Figure 4 , and from it we get L2,l x0 , l y0 , l z0 , l x1 , l y1 , l z1 , l ym .

[0119] Take l z , l z0 , l z1 =0, weight coefficient ω α :0.5,ω β :0.15,ω θ :0.35, and the data of α, β, θ, ρ, etc. are calculated, as shown in Tables 1 and 2 below.

[0120] Figure 4 and Figure 5 This is the displacement evolution curve of the moving end of the sample during the contraction process in the embodiment of the present invention, which is used to extract and calculate the relevant parameters required for the degree of unevenness.

[0121] Step 4: Based on the characteristic parameters of the stretching stage and the characteristic parameters of the contraction stage of the two groups of samples, the unevenness α during the entire contraction process, the relative bending degree β when reaching the maximum inflection point during the contraction process, and the stable contraction rate θ are obtained. The specific results are shown in Tables 1 and 2.

[0122] Step 5: Obtain the cross-linking network heterogeneity index ρ of the two groups of samples at different stretching temperatures and shrinkage temperatures. The specific results are shown in Tables 1 and 2.

[0123] Table 1

[0124]

[0125] Table 2

[0126]

[0127] Step 6: Obtain the maximum allowable value of the cross-linking network unevenness index at the preset temperature, and compare to determine whether the cable insulation meets the condition of "whether the cross-linking network unevenness index of the cable insulation is less than the maximum allowable value of the cross-linking network unevenness index at the preset temperature" at the preset temperature.

[0128] Comparing the maximum allowable value of the cross-linking network heterogeneity index at the preset stretching temperature and shrinkage temperature with the cross-linking network heterogeneity index at different stretching temperatures and shrinkage temperatures, the cross-linking network heterogeneity index at different stretching temperatures and shrinkage temperatures is less than the maximum allowable value of the cross-linking network heterogeneity index at the preset stretching temperature and shrinkage temperature, and the conditions are met.

[0129] Referring to the cross-linked network uniformity evaluation method and standard given above in the present invention:

[0130] The maximum allowable values of the cross-linking network heterogeneity index at the preset stretching temperature and shrinkage temperature are 0.7 and 0.6, respectively.

[0131] Step seven: Use the cross-linking network non-uniformity index at different stretching temperatures and shrinkage temperatures to evaluate the uniformity of the cable insulation cross-linking network.

[0132] A comparative analysis of the cross-linking network heterogeneity index at different stretching and shrinking temperatures reveals that sample D2 exhibits significantly lower heterogeneity than samples D1 and D3 at both 90°C and 110°C, indicating the best cross-linking network uniformity. Taking into account the heterogeneity index of samples D1 and D3 at both temperatures, D1 exhibits slightly higher cross-linking network uniformity than D3.

[0133] In one embodiment, a system for evaluating the uniformity of a power cable insulation cross-linking network based on thermal shrinkage characteristics is provided, comprising: a cross-linking network non-uniformity index function establishment module, a feature acquisition module, a parameter acquisition module, and an evaluation module;

[0134] A cross-linking network unevenness index function establishment module is used to establish a calculation function for the cross-linking network unevenness index of cable insulation;

[0135] A feature acquisition module is used to collect the characteristic parameters of the stretching stage and the displacement evolution curve of the sample moving end relative to the fixed end during the shrinkage stage, and obtain the characteristic parameters of the shrinkage stage through the displacement evolution curve of the sample moving end relative to the fixed end during the shrinkage stage;

[0136] A parameter acquisition module is used to obtain the unevenness of the entire shrinkage process, the relative bending degree when reaching the maximum inflection point during the shrinkage process, and the stable shrinkage rate based on the characteristic parameters of the stretching stage and the characteristic parameters of the shrinkage stage;

[0137] The evaluation module is used to obtain the cross-linking network unevenness index at different stretching temperatures and shrinkage temperatures based on the unevenness during the entire shrinkage process, the relative bending degree when the shrinkage process reaches the maximum inflection point, and the stable shrinkage rate, so as to evaluate the uniformity of the cable insulation cross-linking network.

[0138] It can be seen from the above scheme that the method of the present invention is simple to operate. By recording and measuring the shrinkage rate, bending degree and other characteristics of the sample during the shrinkage process and calculating the unevenness index, it can break through the limitation of the traditional method of only evaluating the overall density, improve the detection accuracy, and can conveniently and efficiently evaluate the uniformity of the cross-linked network of power cable insulation, which can provide technical support for cable insulation status evaluation and cable insulation material research and development.

[0139] The above content is only for explaining the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics, characterized in that: The following steps are involved: Establish a calculation function for the cross-linking network unevenness index of cable insulation; Collect characteristic parameters of the stretching stage and the displacement evolution curve of the sample moving end relative to the fixed end during the contraction stage during the thermal contraction process, and obtain the characteristic parameters of the contraction stage through the displacement evolution curve of the sample moving end relative to the fixed end during the contraction stage; Based on the characteristic parameters of the stretching stage and the characteristic parameters of the contraction stage, the unevenness of the entire contraction process, the relative bending degree when the contraction process reaches the maximum inflection point, and the stable contraction rate are obtained; Based on the unevenness during the entire shrinkage process, the relative bending degree at the maximum inflection point during the shrinkage process, and the stable shrinkage rate, the cross-linking network unevenness index at different stretching temperatures and shrinkage temperatures is obtained to evaluate the uniformity of the cable insulation cross-linking network.

2. The method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics according to claim 1, characterized in that: The characteristic parameters of the stretching stage include the straight-line distance L0 between the fixed end and the moving end of the sample before stretching, and the straight-line distance L1 between the fixed end and the moving end of the sample after stretching and cooling; The characteristic parameters of the contraction stage include the straight-line distance L2 between the fixed end and the movable end of the sample when the contraction process reaches stability, and the displacement of the movable end relative to the fixed end in the x, y, and z directions in three-dimensional space during the contraction process.

3. The method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics according to claim 2, characterized in that: The process of obtaining the unevenness of the entire shrinkage process, the relative bending degree when reaching the maximum inflection point during the shrinkage process, and the stable shrinkage rate based on the characteristic parameters of the stretching stage and the characteristic parameters of the shrinkage stage is as follows: According to the displacement l in the x direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process x1 , during the contraction process, the displacement l in the z direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value z1 And the total displacement in the y direction during the entire contraction process l ym , obtain the unevenness α during the entire shrinkage process; According to the displacement l in the x, y, and z directions at the start time t0 during the contraction process x0 , l y0 , l z0 And the displacement l in the x, y, and z directions at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process x1 , l y1 , l z1 , obtain the relative bending degree β when reaching the maximum inflection point during the contraction process; The stable shrinkage rate θ is obtained based on the straight-line distance L0 between the fixed end and the moving end of the sample before stretching, the straight-line distance L1 between the fixed end and the moving end of the sample after stretching and cooling, and the straight-line distance L2 between the fixed end and the moving end of the sample when the shrinkage process reaches stability.

4. The method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics according to claim 3, characterized in that: The calculation formula for the unevenness during the entire shrinkage process is as follows: Where: α represents the degree of unevenness during the entire shrinkage process; l x1 Indicates the displacement in the x-direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process; l z1 It represents the displacement in the z direction at time t1 when the distance between the moving end position in the xz plane and the starting time t0 reaches the maximum value during the contraction process; l ym is the total displacement in the y direction during the entire contraction process.

5. The method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics according to claim 3, characterized in that: The calculation formula for the relative bending degree when the maximum inflection point is reached during the contraction process is as follows: Where: β represents the relative bending degree when the maximum inflection point is reached during the contraction process; l x0 , l y0 , l z0 are the displacements in the x, y, and z directions at the start time t0 during the contraction process; l x1 , l y1 , l z1 They are the displacements in the x, y, and z directions at time t1 when the distance between the position of the mobile end in the xz plane and the starting time t0 reaches the maximum value during the contraction process.

6. The method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics according to claim 3, characterized in that: The calculation formula of the stable shrinkage rate is as follows: Where: θ represents the stable shrinkage rate; L0 represents the straight-line distance between the fixed end and the moving end of the sample before stretching; L1 represents the straight-line distance between the fixed end and the moving end of the sample after stretching and cooling; L2 is the straight-line distance between the fixed end and the moving end of the sample when the shrinkage process reaches stability.

7. The method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics according to claim 1, characterized in that: The calculation function of the cross-linking network unevenness index of the cable insulation is as follows: Where: ρ represents the cross-linking network heterogeneity index; α represents the heterogeneity during the entire shrinkage process; β represents the relative bending degree when the maximum inflection point is reached during the shrinkage process; θ represents the stable shrinkage rate; ω α is the weight coefficient of the unevenness α during the entire shrinkage process, ranging from 0.40 to 0.95; ω β is the weight coefficient of the relative bending degree β when the maximum inflection point is reached during the contraction process, and its value range is 0.10~0.55; ω θ is the weight coefficient for stabilizing the shrinkage rate θ, and its value range is 0.25~0.

70.

8. The method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics according to claim 3, characterized in that: After obtaining the cross-linking network heterogeneity index at different stretching temperatures and shrinking temperatures, a condition judgment step is also included. The condition judgment step is as follows: Obtaining the maximum allowable value of the cross-linking network heterogeneity index at the preset stretching temperature and shrinking temperature, and comparing it with the cross-linking network heterogeneity index at different stretching temperatures and shrinking temperatures; When the cross-linking network non-uniformity index at different stretching temperatures and shrinking temperatures is less than the maximum allowable value of the cross-linking network non-uniformity index at the preset stretching temperature and shrinking temperature, it is judged that the conditions are met and can be used to evaluate the uniformity of the cable insulation cross-linking network.

9. The method for evaluating the uniformity of the cross-linked network of power cable insulation based on thermal shrinkage characteristics according to claim 3, characterized in that: The value of the cross-linking network non-uniformity index ρ is inversely proportional to the uniformity of the cable insulation cross-linking network.

10. A power cable insulation cross-linking network uniformity evaluation system based on thermal shrinkage characteristics, characterized in that: include: A cross-linking network unevenness index function establishment module is used to establish a calculation function for the cross-linking network unevenness index of cable insulation; A feature acquisition module is used to collect the characteristic parameters of the stretching stage and the displacement evolution curve of the sample moving end relative to the fixed end during the shrinkage stage, and obtain the characteristic parameters of the shrinkage stage through the displacement evolution curve of the sample moving end relative to the fixed end during the shrinkage stage; A parameter acquisition module is used to obtain the unevenness of the entire shrinkage process, the relative bending degree when reaching the maximum inflection point during the shrinkage process, and the stable shrinkage rate based on the characteristic parameters of the stretching stage and the characteristic parameters of the shrinkage stage; The evaluation module is used to obtain the cross-linking network unevenness index at different stretching temperatures and shrinkage temperatures based on the unevenness during the entire shrinkage process, the relative bending degree when the shrinkage process reaches the maximum inflection point, and the stable shrinkage rate, so as to evaluate the uniformity of the cable insulation cross-linking network.

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