A method and system for evaluating the early aging state of polypropylene cable insulation

Abstract

The present invention discloses a method and system for evaluating the early aging state of polypropylene cable insulation. The method includes the following steps: obtaining polypropylene cable insulation samples with different aging times, processing the insulation samples to obtain a number of insulation specimens; statistically calculating the rubber phase size of the insulation specimens to obtain the average rubber phase size; calculating a size-time change function based on the average rubber phase sizes with different aging times, obtaining the rubber phase size of the cable insulation to be evaluated, and evaluating the aging state of the cable insulation to be evaluated based on the rubber phase size of the cable insulation to be evaluated and the size-time change function. The present invention is an accurate, simple method suitable for evaluating the early aging state of polypropylene, and can effectively solve the technical problem that the existing detection methods cannot accurately evaluate the early aging state of polypropylene aging.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoplastic insulation material detection, and particularly relates to a method and system for evaluating the early aging state of polypropylene cable insulation. Background Art

[0002] During the operation of a cable, due to different temperature resistance grades, the normal operating temperatures are also different. For a cross-linked polyethylene cable, the temperature of the cable insulation under normal operating conditions will reach 90°C, while the expected long-term operating temperature of a polypropylene cable is higher than that of cross-linked polyethylene, and is expected to reach 110°C, which results in a more severe thermal environment for the polypropylene cable. Under the long-term action of heat, the cable insulation material will age, leading to a decline in material properties. In addition, the loose rubber phase in polypropylene insulation is more sensitive to heat than the dense polypropylene matrix, and self-polymerization, coarsening, etc. will occur in the rubber phase at the initial stage of aging. Currently, there are many methods for detecting the aging degree of polypropylene cable insulation materials, such as testing their elongation at break, breakdown field strength, dielectric loss tangent, etc.

[0003] However, in the early stage of thermal aging of polypropylene cable insulation, the changes in the above macroscopic properties are not obvious. Instead, due to the post-crystallization effect in the initial stage of aging, the electrical properties will increase, which cannot be used as a reliable method for detecting the aging degree of polypropylene cable insulation. If a characteristic that monotonically changes with the aging time of polypropylene cable insulation can be targeted, it will be beneficial to accurately judge the aging condition of polypropylene cable insulation materials and provide a reference for the operation and maintenance of polypropylene insulated cables. Summary of the Invention

[0004] The present invention aims to solve the deficiencies of the prior art and provides the following solutions:

[0005] A method for evaluating the early aging state of polypropylene cable insulation includes the following steps:

[0006] Obtain polypropylene cable insulation samples with different aging times, process the insulation samples to obtain a number of insulation specimens;

[0007] Perform statistical calculation on the rubber phase size of the insulation specimens to obtain the average rubber phase size;

[0008] Calculate the size-time change function based on the average rubber phase size at different aging times, obtain the rubber phase size of the cable insulation to be evaluated, and evaluate the aging state of the cable insulation to be evaluated based on the rubber phase size of the cable insulation to be evaluated and the size-time change function.

[0009] Preferably, the processing method includes:

[0010] Process the insulation sample into a strip-shaped specimen with a thickness greater than 0.2 mm;

[0011] Cool the strip-shaped specimen in liquid nitrogen to the glass state to obtain a glassy specimen;

[0012] Quench-break the glassy specimen to obtain an initial insulating specimen with a cross-section having undulations not exceeding 100 μm;

[0013] Place the initial insulating specimen in xylene at 60 °C and etch for 12 hours to remove the rubber phase;

[0014] Spray gold on the cross-section of the initial insulating specimen from which the rubber phase has been removed to obtain the insulating specimen.

[0015] Preferably, the method of statistical calculation includes:

[0016] Obtain a cross-sectional image of the insulating specimen after spraying gold;

[0017] Use the image method to select no less than 50 typical rubber-phase holes in the cross-sectional image for size statistics, and calculate the average size of the rubber phase.

[0018] Preferably, the size-time variation function is:

[0019]

[0020] Wherein, is the average size of the rubber phase when the aging time of the polypropylene cable insulation is t, is the average size of the rubber phase of the unaged polypropylene cable insulation, and K is the aging evaluation characteristic constant.

[0021] The present invention also provides a system for evaluating the early aging state of polypropylene cable insulation. The evaluation system applies the above evaluation method and includes: a sample processing module, a statistical calculation module, and an evaluation module;

[0022] The sample processing module is used to obtain polypropylene cable insulation samples with different aging times, process the insulation samples to obtain a number of insulating specimens;

[0023] The statistical calculation module is used to perform statistical calculations on the rubber phase size of the insulating specimens to obtain the average size of the rubber phase;

[0024] The evaluation module calculates the size-time variation function based on the average size of the rubber phase at different aging times, obtains the size of the rubber phase of the cable insulation to be evaluated, and evaluates the aging state of the cable insulation to be evaluated based on the size of the rubber phase of the cable insulation to be evaluated and the size-time variation function.

[0025] Preferably, the working process of the sample processing module includes:

[0026] Process the insulation sample into a strip-shaped specimen with a thickness greater than 0.2 mm;

[0027] Put the strip-shaped specimen into liquid nitrogen and cool it to the glassy state to obtain a glassy specimen;

[0028] Quench and break the glassy specimen to obtain an initial insulation specimen with a cross-section having undulations not exceeding 100 μm;

[0029] Place the initial insulation specimen in xylene at 60 °C and etch it for 12 hours to remove the rubber phase;

[0030] Spray gold on the cross-section of the initial insulation specimen after removing the rubber phase to obtain the insulation specimen.

[0031] Preferably, the working process of the statistical calculation module includes:

[0032] Obtain the cross-sectional image of the insulation specimen after spraying gold;

[0033] Use the image method to select no less than 50 typical rubber phase holes in the cross-sectional image for size statistics, and calculate the average size of the rubber phase.

[0034] Preferably, the size-time variation function is:

[0035]

[0036] Wherein, is the average size of the rubber phase when the aging time of the polypropylene cable insulation is t, is the average size of the rubber phase of the unaged polypropylene cable insulation, and K is the aging evaluation characteristic constant.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] The method for evaluating the early aging state of the polypropylene cable insulation of the present invention processes the polypropylene cable insulation with different aging times according to a preset scheme, statistically calculates the size of the rubber phase, and fits a reference curve for the evolution of the rubber phase size based on the evolution law of the rubber phase size of the polypropylene cable insulation, so as to evaluate the early aging state of other polypropylene cable insulations. According to the corresponding time between the rubber phase size of the aged polypropylene and the reference curve for the evolution of the rubber phase size, the early aging state of the polypropylene can be effectively obtained. Therefore, the present invention is an accurate, simple and applicable method for evaluating the early aging state of polypropylene, and can effectively solve the technical problem that the existing detection methods cannot accurately evaluate the early aging state of polypropylene. Description of the Drawings

[0039] To more clearly illustrate the technical solution of the present invention, the following briefly introduces the attached drawings required in the embodiments. Obviously, the attached drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other attached drawings can also be obtained based on these attached drawings.

[0040] Figure 1 Schematic diagram of the method flow of the embodiment of the present invention;

[0041] Figure 2 Cross-sectional pictures of the target specimen and the specimen to be tested of the polypropylene cable insulation in the embodiment of the present invention;

[0042] Figure 3 Reference curve of the rubber phase size evolution obtained by fitting the rubber phase size evolution law of the polypropylene cable insulation in the embodiment of the present invention, and the prediction results of the specimen to be tested. Specific implementation manners

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the attached drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0044] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the attached drawings and specific implementation manners.

[0045] In actual working conditions, the aging of polypropylene cable insulation is mainly divided into two stages: the early stable stage and the later rapid deterioration stage. First, the aging condition in the later rapid deterioration stage of aging can be obtained through traditional test methods such as elongation at break, breakdown field strength, and dielectric loss tangent. However, when the aging condition of polypropylene cable insulation can be significantly evaluated by traditional test methods, the polypropylene cable insulation is already in the later stage of aging, which poses a great threat to the power system. Second, the performance change in the early stage of aging is not obvious, and it is difficult to use traditional methods to evaluate the aging state. Moreover, the size of the rubber phase in polypropylene cable insulation will monotonically increase under the action of heat, and the method for obtaining the size of the rubber phase is relatively easy. Therefore, the early aging state of polypropylene cable insulation can be judged according to the change of its rubber phase size.

[0046] Embodiment 1

[0047] In the first embodiment, as Figure 1 shown, a method for evaluating the early aging state of polypropylene cable insulation includes the following steps:

[0048] S1. Obtain polypropylene cable insulation samples with different aging times, process the insulation samples to obtain a number of insulation specimens.

[0049] The processing method includes: processing the insulation sample into a strip specimen with a thickness greater than 0.2 mm; placing the strip specimen in liquid nitrogen and cooling it to the glassy state to obtain a glassy specimen; quenching and breaking the glassy specimen to obtain an initial insulation specimen with a cross-section having undulations not exceeding 100 μm. Place the initial insulation specimen in xylene at 60 °C and etch it for 12 hours to remove the rubber phase; sputter gold on the cross-section of the initial insulation specimen after removing the rubber phase to obtain an insulation specimen.

[0050] In this embodiment, prepare a number of polypropylene cable insulation materials, take one of the polypropylene cable insulations as the unaged target specimen, that is, the unaged polypropylene cable insulation sample. Then take out a number of polypropylene cable insulations for thermal aging treatment for different times to obtain aged polypropylene cable insulation samples. The aging time of the polypropylene cable insulation can be controlled and the time gradient can be adjusted. At least two aged polypropylene cable insulations are set, and the aging times of each aged polypropylene cable insulation are distributed according to a preset time gradient, which is convenient for subsequent aging state evaluation.

[0051] After that, process the obtained unaged polypropylene cable insulation sample and aged polypropylene cable insulation sample. Process the sample into a strip specimen with a thickness greater than 0.2 mm, and fully cool it to the glassy state in liquid nitrogen and then quench and break it to obtain a polypropylene cable insulation specimen with a cross-section. After the polypropylene cable insulation is quenched and broken in liquid nitrogen, place the specimen in xylene at 60 °C and etch it for 12 hours to remove the rubber phase, and perform sputter gold treatment on the cross-section of the polypropylene cable insulation.

[0052] S2. Statistically calculate the rubber phase size of the insulation specimen to obtain the average rubber phase size.

[0053] The statistical calculation method includes: obtaining the cross-sectional image of the insulation specimen after sputter gold; using the image method to select no less than 50 typical rubber phase holes in the cross-sectional image for size statistics and calculate the average size.

[0054] Specifically, when statistically calculating the rubber phase size of the unaged polypropylene cable insulation, no less than 50 typical rubber phase holes conforming to the normal distribution need to be selected for statistics by the image method; when statistically calculating the rubber phase size of the aged polypropylene cable insulation, no less than 50 typical rubber phase holes conforming to the normal distribution need to be selected for statistics by the image method; calculate the statistical results to obtain the average size.

[0055] S3. Calculate the size-time variation function based on the average size of the rubber phase at different aging times, obtain the size of the rubber phase of the cable insulation to be evaluated, and evaluate the aging state of the cable insulation to be evaluated based on the size of the rubber phase of the cable insulation to be evaluated and the size-time variation function.

[0056] The size-time variation function is:

[0057]

[0058] Wherein, is the average size of the rubber phase when the aging time of the polypropylene cable insulation is t, is the average size of the rubber phase of the unaged polypropylene cable insulation, and K is the aging evaluation characteristic constant.

[0059] Example 2

[0060] In this example, taking a typical polypropylene cable insulation material: 10kV polypropylene insulated cable as an example, the aging state is evaluated by the evolution law of the rubber phase size: The model of the electron microscope used in this example is Hitachi S2700, and the specific steps are as follows:

[0061] 1) Specimen preparation. Prepare several unaged polypropylene insulated cables, cut the cables into circular sections to obtain cable main insulation slices with a thickness of 0.5 mm. Perform high-temperature thermal aging experiments on the selected specimens at a temperature of 135°C, and the experimental durations are 0 days, 12 days, and 24 days respectively, for a total of three target specimens.

[0062] 2) Specimen pretreatment. Cut the target specimens into strips with a width of 10 mm and a length of 40 mm, soak them in liquid nitrogen for 15 minutes to fully vitrify the specimen system, then quench the specimens, etch the specimens with the cross-section in 60°C xylene for 12 hours to completely remove the rubber phase, and perform sputtering on the cross-section of the etched specimens.

[0063] 3) Rubber phase size statistics. Place the cross-section of the pretreated target specimens under an electron microscope for observation, with a magnification of 2000 times and an acceleration voltage of 2 kV. Refer to Figure 2 , which is a typical cross-section pattern selected for this example, and use the image method to statistically analyze the diameters of no less than 50 typical rubber phase holes that conform to the normal distribution to obtain the average rubber phase size of the target specimens.

[0064] 4) Drawing of the reference curve for the evolution of the rubber phase size. Refer to Figure 3 , which is the reference curve for the evolution of the rubber phase size drawn according to the aging days and the average rubber phase size of the target specimens in this example. The fitting result of the reference curve for the evolution of the rubber phase size is:

[0065]

[0066] 5) Evaluation of the thermal aging state of the polypropylene sample to be tested. Also refer to Figure 2 , and the cross-section pattern of the polypropylene sample to be tested is in the red frame. Also refer to Figure 3 , and the red circle is the polypropylene cable insulation sample thermally aged for 36 days in this embodiment, which is used to verify the accuracy of the method. According to the reference formula and curve of the rubber phase size evolution, the corresponding aging days can be deduced as: 35.44 days, which corresponds well to the actual thermal aging days of 36 days.

[0067] Example Three

[0068] In this embodiment, a system for evaluating the early aging state of polypropylene cable insulation includes: a sample processing module, a statistical calculation module, and an evaluation module.

[0069] The sample processing module is used to obtain polypropylene cable insulation samples with different aging times, process the insulation samples to obtain a number of insulation specimens. The working process of the sample processing module includes: processing the insulation sample into a strip specimen with a thickness greater than 0.2 mm; cooling the strip specimen in liquid nitrogen to the glassy state to obtain a glassy specimen; quenching the glassy specimen to obtain an initial insulation specimen with a cross-section having a fluctuation not exceeding 100 μm; placing the initial insulation specimen in xylene at 60 °C for etching for 12 hours to remove the rubber phase; spraying gold on the cross-section of the initial insulation specimen after removing the rubber phase to obtain an insulation specimen.

[0070] The statistical calculation module is used to statistically calculate the rubber phase size of the insulation specimen to obtain the average rubber phase size. The working process of the statistical calculation module includes: obtaining the cross-section image of the insulation specimen after spraying gold; using the image method to select no less than 50 typical rubber phase holes in the cross-section image for size statistics and calculating the average size.

[0071] The evaluation module calculates the size-time variation function based on the average rubber phase size at different aging times, obtains the rubber phase size of the cable insulation to be evaluated, and evaluates the aging state of the cable insulation to be evaluated based on the rubber phase size of the cable insulation to be evaluated and the size-time variation function. The size-time variation function is:

[0072]

[0073] Wherein, is the average rubber phase size when the aging time of the polypropylene cable insulation is t, is the average rubber phase size of the unaged polypropylene cable insulation, and K is the aging evaluation characteristic constant.

[0074] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the spirit of the design of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for evaluating the early aging state of polypropylene cable insulation, characterized in that It includes the following steps: Obtain polypropylene cable insulation samples with different aging times, process the insulation samples to obtain a number of insulation specimens; Perform statistical calculation on the rubber phase size of the insulation specimens to obtain the average rubber phase size; Calculate the size-time change function based on the average rubber phase size at different aging times, obtain the rubber phase size of the cable insulation to be evaluated, and evaluate the aging state of the cable insulation to be evaluated based on the rubber phase size of the cable insulation to be evaluated and the size-time change function; The method of the processing includes: Process the insulation sample into a strip specimen with a thickness greater than 0.2 mm; Put the strip specimen into liquid nitrogen and cool it to the glassy state to obtain a glassy specimen; Quench the glassy specimen to obtain an initial insulation specimen with a cross-section having a fluctuation not exceeding 100 μm; Place the initial insulation specimen in xylene at 60 °C and etch it for 12 hours to remove the rubber phase; Spray gold on the cross-section of the initial insulation specimen after removing the rubber phase to obtain the insulation specimen; The method of the statistical calculation includes: Obtain the cross-sectional image of the insulation specimen after spraying gold; Use the image method to select no less than 50 typical rubber phase holes in the cross-sectional image for size statistics, and calculate the average rubber phase size.

2. The method for evaluating the early aging state of polypropylene cable insulation according to claim 1, wherein The size-time change function is: Among them, is the average size of the rubber phase when the aging time of the polypropylene cable insulation is t, is the average size of the rubber phase of the unaged polypropylene cable insulation, and K is the aging evaluation characteristic constant.

3. A polypropylene cable insulation early aging state evaluation system, wherein the evaluation system applies the evaluation method described in any one of claims 1-2, and is characterized in that It includes: A sample processing module, a statistical calculation module, and an evaluation module; The sample processing module is used to obtain polypropylene cable insulation samples with different aging times, process the insulation samples to obtain a number of insulation specimens; The statistical calculation module is used to perform statistical calculation on the rubber phase size of the insulation specimens to obtain the average rubber phase size; The evaluation module calculates the size-time change function based on the average rubber phase size at different aging times, obtains the rubber phase size of the cable insulation to be evaluated, and evaluates the aging state of the cable insulation to be evaluated based on the rubber phase size of the cable insulation to be evaluated and the size-time change function; The working process of the sample processing module includes: Process the insulation sample into a strip specimen with a thickness greater than 0.2 mm; Put the strip specimen into liquid nitrogen and cool it to the glassy state to obtain a glassy specimen; Quench the glassy specimen to obtain an initial insulation specimen with a cross-section having a fluctuation not exceeding 100 μm; Place the initial insulation specimen in xylene at 60 °C and etch it for 12 hours to remove the rubber phase; Spray gold on the cross-section of the initial insulation specimen after removing the rubber phase to obtain the insulation specimen; The working process of the statistical calculation module includes: Obtain the cross-sectional image of the insulation specimen after spraying gold; Use the image method to select no less than 50 typical rubber phase holes in the cross-sectional image for size statistics, and calculate the average rubber phase size.

4. The polypropylene cable insulation early aging state evaluation system according to claim 3, characterized in that The size-time change function is: Wherein, is the average size of the rubber phase when the aging time of the polypropylene cable insulation is t, is the average size of the rubber phase of the unaged polypropylene cable insulation, and K is the aging evaluation characteristic constant.

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