Dry-type bushing capacitor core multi-defect isomorphic sample preparation and test platform

Abstract

The invention belongs to the technical field of electrical equipment manufacturing, and discloses a dry-type bushing capacitor core multi-defect isomorphic sample preparation and test platform which comprises a sample preparation system and a test system. The sample wafer preparation system is used for preparing epoxy impregnated paper isomorphic sample wafers containing microcracks, bubbles, point discharge and different damp degrees by accurately controlling the raw material ratio, the pouring process and the curing conditions, so that various defects in an actual dry type sleeve are really simulated. An epoxy resin sample wafer and an epoxy impregnated paper sample wafer which are attached to a dry type core material and structure are designed, preparation raw materials, molecular formulas, characteristics and parameters of the epoxy resin sample and the epoxy impregnated paper sample are provided, and detailed technologies are carried out on the preparation process and equipment used in the preparation process. The insulation sample with the size required by the experiment is obtained; and the preparation process of the subsequent test sample is determined. And secondly, a capacitor core material performance test system is formed, and the accuracy and comprehensiveness of material performance evaluation are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical equipment manufacturing, and in particular relates to a dry-type bushing capacitor core multi-defect isomorphic sample preparation and testing platform. Background Art

[0002] As a key insulating component of high-voltage equipment such as power transformers, the stability of the insulation performance of dry-type bushings is directly related to the safe operation of the power system. However, in long-term operation, dry-type bushings will be affected by multiple environmental factors such as electricity, heat, and water, which will lead to defects such as aging, moisture, cracks, and bubbles in the insulation material, which will in turn cause serious faults such as partial discharge and insulation breakdown. Therefore, multi-defect detection and evaluation of dry-type bushings is of great significance for preventing faults and ensuring the safety of the power grid.

[0003] At present, the detection methods for dry casing mainly include offline detection, online monitoring and status assessment. However, these methods have problems such as long detection cycle, poor real-time performance and low detection accuracy in practical applications, especially the lack of comprehensive evaluation ability under the coexistence of multiple defects. In addition, traditional methods often focus on the detection of single defects and lack systematic research on the interaction of multiple defects.

[0004] In order to solve the above problems, the present invention proposes a dry-type bushing capacitor core multi-defect isomorphic sample preparation and testing platform, which aims to simulate various defects that may be encountered in the actual operation of the dry bushing, prepare experimental samples with the same composition and similar structure, and conduct comprehensive performance evaluation on a unified test platform, so as to provide scientific basis and technical support for the safe operation of the dry bushing. Summary of the invention

[0005] In view of the shortcomings of the existing dry bushing detection technology in multi-defect detection and evaluation, the present invention proposes a dry bushing capacitor core multi-defect isomorphic sample preparation and testing platform.

[0006] The present invention is implemented in this way: a dry-type bushing capacitor core multi-defect isomorphic sample preparation and testing platform mainly includes:

[0007] It consists of four parts: sample preparation system, defect simulation system, test system and data processing and analysis system.

[0008] Sample preparation system: The sample preparation system is the core part of realizing the preparation of multi-defect isomorphic samples, including raw material preparation, mixing, pouring and curing and other steps. First, according to the actual material ratio of the dry bushing capacitor core, accurately weigh the raw materials such as epoxy resin matrix, curing agent, toughening agent and accelerator. The raw materials are fully mixed by heating and magnetic stirring, and then the bubbles in the mixed liquid are removed by ultrasonic oscillation. Subsequently, the mixed liquid is poured into a specific mold under a vacuum environment, and after two stages of pre-curing and post-curing, a dense epoxy resin sample or epoxy impregnated paper sample is formed. For epoxy impregnated paper samples, the crepe paper must be pretreated before pouring to ensure that it is completely infiltrated with epoxy resin in a dry state, thereby forming a multi-layer composite insulation structure similar to the actual dry bushing core structure.

[0009] Defect simulation system: The defect simulation system is used to artificially introduce a variety of common defects in the sample, such as moisture, aging, bubbles, cracks and discharge tips, etc., to simulate the degradation of dry bushings in actual operation. Specifically, moisture defects can be achieved by spraying water for humidification or natural moisture absorption; aging defects are simulated by accelerating the thermal aging test platform; bubble defects can be introduced by controlling the vacuum degree during the pouring process or by pre-placing Al2O3 small balls; crack defects can be simulated by applying vaseline between the aluminum foil and the epoxy resin to form an isolation layer; and discharge tip defects are achieved by processing the wrinkles and protrusions on the surface of the aluminum foil. By precisely controlling the method and degree of defect introduction, it can be ensured that the defect state in the sample is highly consistent with the defect state in the actual dry bushing.

[0010] Test system: The test system is used to perform performance tests on the prepared multi-defect isomorphic samples, mainly including material performance tests and electrical tests. The electrical performance test mainly focuses on the key parameters of the sample such as the dielectric constant and dielectric loss factor (tanδ). The frequency domain dielectric spectrum method is used to analyze the changes in the dielectric properties of the sample at different frequencies, thereby revealing the impact of defects such as moisture and aging on the insulation performance; the material performance test evaluates the glass transition temperature, molecular structure and other parameters of the sample. By comprehensively using a variety of testing methods, the comprehensive performance of the sample can be comprehensively evaluated and its internal defects can be accurately identified.

[0011] Data processing and analysis system: The data processing and analysis system is responsible for processing and analyzing the test data to extract useful information and form an evaluation report. The system has powerful data processing capabilities and can quickly process and clean massive test data. At the same time, it also has built-in multiple data analysis models and methods, such as feature extraction, pattern recognition, machine learning, etc., which can deeply mine and analyze the test data to reveal the inherent relationship between sample performance and defects. Finally, the system can generate an evaluation report based on the analysis results, providing scientific basis and technical support for the safe operation of dry casing.

[0012] In summary, the present invention proposes a dry-type bushing capacitor core multi-defect isomorphic sample preparation and testing platform that integrates sample preparation, defect simulation, performance testing and data analysis. This platform not only solves the shortcomings of existing detection technologies in multi-defect detection and evaluation, but also improves detection efficiency and accuracy, providing a strong guarantee for the safe operation of dry bushings.

[0013] In combination with the above technical solutions and the technical problems solved, please analyze the advantages and positive effects of the technical solutions to be protected by the present invention from the following aspects:

[0014] First, in view of the technical problems existing in the above-mentioned prior art and the difficulty of solving the problems, the technical solutions to be protected by the present invention and the results and data during the research and development process are closely combined to analyze in detail and deeply how the technical solutions of the present invention solve the technical problems, and some creative technical effects brought about after solving the problems. The specific description is as follows:

[0015] Starting from the main insulating material of the rubber-impregnated paper bushing, the present invention detects the multi-characteristic parameters of samples with moisture, aging, microcracks, and bubble defects, extracts the more sensitive characteristic parameters of the main insulating material in the defect evolution process, and explores the defect evolution law, and then establishes a basic database of defect characteristic parameters. Under laboratory conditions, the actual operating environment is simulated, thermal stresses under different conditions are applied, and the behavioral characteristics of the capacitor core material under different conditions of thermal stress are studied. Through a large number of experimental studies, the defect formation and evolution laws of multi-defect isomorphic samples of the capacitor core are revealed, providing a theoretical basis for defect diagnosis.

[0016] Secondly, a performance testing system for capacitor core materials should be established. The testing system should include testing methods and indicators for electrical performance, material performance, etc., to comprehensively evaluate the performance of materials under different defects. Through a comprehensive evaluation of insulating materials, the health status of materials can be accurately judged to provide reliable data support for defect diagnosis.

[0017] Through this study, the following results are expected to be achieved. First, a characteristic parameter test system for multi-defect isomorphic samples of capacitor cores is formed to improve the accuracy and comprehensiveness of material performance evaluation. In addition, effective characteristic parameters reflecting the defect evolution of multi-defect isomorphic samples of dry-type bushing capacitor cores are obtained to provide a basis for the development of diagnostic technology. Further, a new defect detection technology system is established to improve the sensitivity and accuracy of defect diagnosis, provide guidance for practical engineering applications, and improve the operational reliability and economic benefits of electricity.

[0018] Second, as auxiliary evidence of the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0019] (1) Expected benefits and commercial value: The present invention can significantly improve the accuracy and efficiency of dry-type bushing insulation performance evaluation and reduce the risk of equipment downtime due to insulation failure by efficiently preparing multi-defect isomorphic samples and building a test platform. This technical solution has broad application prospects in the power industry, bringing significant economic benefits and safety guarantees to equipment manufacturers and power operators, and has extremely high market value.

[0020] (2) Filling the technical gap: Currently, there is a lack of systematic and standardized methods for simulating and testing multiple defects in the core of dry-type bushing capacitors at home and abroad. The present invention fills this gap and provides a reliable experimental basis for the study of the aging mechanism and status evaluation of insulating materials by accurately simulating various defects in actual operation.

[0021] (3) Solving technical problems: For a long time, the power industry has faced challenges in the efficient evaluation of the insulation performance of dry bushings, especially the simulation and testing of defects under the coupling of multiple factors. The present invention successfully solves this technical problem through an innovative multi-defect isomorphic sample preparation method and testing platform, providing strong support for the safe and stable operation of power equipment.

[0022] (4) Overcoming technical bias: Traditional methods often ignore the comprehensive impact of interactions between defects on insulation performance, resulting in biased evaluation results. This invention overcomes this technical bias by systematically simulating multiple defects and building an integrated test platform, making the evaluation results closer to actual working conditions and providing a scientific basis for the design, manufacture and maintenance of power equipment insulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of a method for preparing a multi-defect isomorphic sample of a dry-type bushing capacitor core provided by an embodiment of the present invention.

[0024] Figure 2 It is a basic structural diagram of the glue-impregnated paper bushing capacitor core provided in an embodiment of the present invention.

[0025] Figure 3 It is a molecular formula diagram of each basic raw material provided in the embodiments of the present invention.

[0026] Figure 4 It is a ratio diagram of epoxy water bath and base material provided in an embodiment of the present invention.

[0027] Figure 5 This is a diagram showing the epoxy mixed liquid being stirred uniformly according to an embodiment of the present invention.

[0028] Figure 6 This is a diagram of ultrasonic oscillation degassing provided by an embodiment of the present invention.

[0029] Figure 7 This is a vacuum pumping diagram provided by an embodiment of the present invention.

[0030] Figure 8 This is a diagram of epoxy mixed liquid casting and epoxy resin sample molding provided by an embodiment of the present invention.

[0031] Fig. 9 This is a diagram of a cut insulating paper sample provided in an embodiment of the present invention.

[0032] Fig.10 This is a fully infiltrated diagram of the crepe paper provided by an embodiment of the present invention.

[0033] Fig.11 It is a design drawing of an epoxy impregnated paper mold provided by an embodiment of the present invention.

[0034] Fig.12 This is a sample picture of isomorphic glue-impregnated paper with different numbers of crepe paper layers provided by an embodiment of the present invention.

[0035] Fig.13 It is a cutting diagram of the aluminum foil provided in the embodiment of the present invention.

[0036] Fig.14 This is a diagram of the preparation of a paper sample impregnated with aluminum foil provided in an embodiment of the present invention.

[0037] Fig.15 It is a flow chart of preparing experimental samples provided by an embodiment of the present invention.

[0038] Fig.16 2 is a diagram of a high temperature thermal aging test chamber provided in an embodiment of the present invention.

[0039] Fig.17 This is a completely dry picture of the crepe paper provided by the embodiment of the present invention.

[0040] Fig.18 It is a schematic diagram of humidifying crepe paper provided by an embodiment of the present invention.

[0041] Fig.19 It is the design and slice diagram of the microcrack defect provided by the embodiment of the present invention.

[0042] Fig. 20 This is a sample image of an isomorphic piece of Al2O3 particles simulating bubble defects provided in an embodiment of the present invention.

[0043] Fig.21 It is a diagram of the setting of the aluminum foil protrusion and defective sample provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0045] An embodiment of the present invention provides a dry-type bushing capacitor core multi-defect isomorphic sample preparation and testing platform, including: a sample preparation system and a testing system, the sample preparation system is used to prepare isomorphic samples containing microcracks, bubbles, and tip discharge defects, and the testing system is used to perform electrical performance tests on the prepared isomorphic samples.

[0046] The sample preparation system provided in the embodiment of the present invention includes a raw material proportioning device, a mixing and stirring device, a degassing device, a casting mold and a curing device, wherein:

[0047] The raw material proportioning device is used to accurately weigh the epoxy resin matrix, curing agent, toughening agent and accelerator;

[0048] The mixing and stirring device is used to mix the raw materials thoroughly and evenly;

[0049] The degasser is used to remove bubbles from the mixed solution;

[0050] The casting mold is used to cast the degassed mixed solution into shape;

[0051] The curing device is used to cure the cast sample.

[0052] The sample preparation system provided by the embodiment of the present invention also includes a defect simulation device for introducing micro cracks, bubbles, and tip discharge defects during the casting process, specifically:

[0053] Microcrack defects were created by applying petroleum jelly between the aluminum foil and the epoxy resin;

[0054] The degree of bubble defects can be adjusted by controlling the evacuation time during the pouring process;

[0055] Wrinkles and protrusions were made on the surface of aluminum foil to simulate tip discharge defects.

[0056] The test system provided by the embodiment of the present invention includes a dielectric performance test device for measuring the complex capacitance, complex dielectric constant and dielectric loss factor of a homogeneous sample, and then evaluating its electrical performance.

[0057] The dielectric properties testing device provided in the embodiment of the present invention includes a signal generator, a measuring probe and a data acquisition processing unit, wherein:

[0058] The signal generator is used to generate the alternating electric field required for the test;

[0059] The measuring probe is used to collect the voltage and current signals of the isomorphic sample under the alternating electric field;

[0060] The data acquisition and processing unit is used to process the measurement data and calculate the complex capacitance, complex dielectric constant and dielectric loss factor.

[0061] The embodiment of the present invention also provides a thermal aging experiment device for performing accelerated thermal aging experiments on isomorphic samples to simulate their aging during long-term operation, specifically including a heating cavity and a temperature control system.

[0062] Furthermore, the method for preparing the aged sample comprises the following steps:

[0063] Step 1, preparing an epoxy resin sample or an epoxy impregnated paper sample, wherein the epoxy impregnated paper sample comprises multiple layers of crepe paper and epoxy resin;

[0064] Step 2, setting a plurality of temperature control areas in the aging test platform, respectively setting them to different aging temperatures, wherein the aging temperatures include 150° C., 180° C. and 200° C.;

[0065] Step 3, placing the prepared samples in each temperature control zone for accelerated thermal aging test, and simulating different equivalent aging years by controlling the aging time, wherein the equivalent aging years are calculated based on the "10°C aging criterion";

[0066] Step 4: After each set aging cycle is completed, the sample is taken out for cleaning and drying, and then the sample is subjected to quality inspection and performance evaluation, and the changes in mass loss rate and other electrical performance parameters are recorded;

[0067] Step 5, repeat the aging, cleaning, drying and testing process in step 4 until all preset aging cycles are completed to obtain the performance degradation data of the samples under different aging conditions.

[0068] The platform provided by the embodiment of the present invention also includes a data processing and analysis system for processing and analyzing test data and establishing a correlation model between the electrical performance of isomorphic samples and the defect type and degree.

[0069] A method for preparing and testing a dry-type bushing capacitor core multi-defect isomorphic sample on a platform provided by an embodiment of the present invention comprises the following steps:

[0070] S1, accurately weigh and mix the raw materials;

[0071] S2, remove bubbles from the mixed solution;

[0072] S3, moisture, microcracks, bubbles, and tip discharge defects are introduced during the pouring process;

[0073] S4, curing the cast sample;

[0074] S5, measuring the electrical properties of the isomorphic sample using a dielectric property testing device;

[0075] S6, processes and analyzes the test data to evaluate the relationship between the electrical performance of the isomorphic samples and the defect type and degree.

[0076] The method provided by the embodiment of the present invention also includes the steps of: performing accelerated thermal aging experiments on isomorphic samples to simulate performance changes under different aging conditions, and combining the dielectric performance test results to further evaluate the long-term operating reliability of the dry-type bushing capacitor core.

[0077] The core structure of the rubber-impregnated paper bushing capacitor is as follows: Figure 2 As shown, the main insulation is epoxy resin / crepe paper composite insulation (epoxy impregnated paper) made of epoxy resin cast crepe paper.

[0078] The raw materials for epoxy resin production are composed of epoxy resin matrix, curing agent, toughening agent and accelerator. Among them, epoxy resin matrix is ​​the basic raw material for making epoxy resin samples; curing agent is used to solidify the fluid epoxy resin matrix into a solid; toughening agent can enhance the mechanical strength of the sample and prevent mechanical damage such as cracks caused by excessive stress; accelerator can accelerate the cross-linking between epoxy resin molecules and shorten the time of the entire curing process.

[0079] Preparation method of epoxy resin sample

[0080] The specific raw materials for preparing pure epoxy resin samples are as follows: the epoxy matrix is ​​Phoenix brand bisphenol A diglycidyl ether epoxy resin (DGEBA); the curing agent is methyl tetrahydrophthalic anhydride (Methyl Tetrahydrophthalic Anhydride, MTHPA); the toughening agent is dibutyl phthalate (Dibutyl Phthalate, DBP), and the accelerator is 2,4,6-tris (dimethylaminomethyl) phenol (DMP-30).

[0081] Sample preparation process: First, the epoxy resin matrix is ​​soaked in 50°C water for preheating to reduce its viscosity for easy weighing; on an electronic scale (accuracy 0.01), E51, MTHPA, DBP, and DMP-30 with a mass ratio of 100:95:10:1 are weighed in a beaker.

[0082] Use a heated magnetic stirrer to stir for 1 h with the temperature set to 50°C until the solution is fully mixed and there is no flocculent residue or obvious color difference area inside.

[0083] The beaker was placed in an ultrasonic oscillator, the temperature was set to 50°C, and the mixture was shaken for degassing for 1 hour to allow most of the bubbles in the mixture to escape.

[0084] During the above steps, the mold is cleaned with alcohol, and after drying, a release agent is sprayed on it, and it is placed at room temperature for an appropriate time until the release agent forms a film on the mold surface; the temperature of the vacuum drying oven is increased to 50°C, and after degassing is completed, the beaker is placed in a vacuum drying oven and vacuumed for 1 hour to remove residual bubbles in the solution.

[0085] The mixed solution after degassing is slowly poured into the center of the mold by drainage with a glass rod. Since the solution is heated in the previous steps, its fluidity is good, so it is easy to pour and spread on the mold, avoiding the occurrence of more bubbles when condensing into blocks; the mold size is 80mm in diameter and 1.5mm in depth. Observe the flow of the liquid during pouring. The speed should be slowed down when the solution is about to touch the edge of the mold, and finally obtain a sample to be cured with the liquid surface flush with the mold. When too much solution is poured, it will temporarily not overflow due to tension. After heating in the oven, the fluidity is enhanced and the molding is incomplete.

[0086] Then, the mold was placed in a vacuum drying oven, and the vacuum was started at 50°C, and the temperature was gradually raised to 90°C. During this process, the vacuum environment in the box was maintained to avoid bubbles in the molded sample. During the curing, the pre-curing temperature was 90°C. After 2 hours, the sample was basically fixed. A hard object could still leave a mark, but it would gradually recover. The post-curing temperature was 130°C. After 5 hours, the sample was formed. The hardness was enhanced but it still had good toughness. The molded epoxy resin sample is as follows Figure 3 shown.

[0087] Preparation of epoxy impregnated paper samples

[0088] (1) Equivalence description of isomorphic samples

[0089] In the preparation of the isomorphic sample, epoxy resin and crepe paper that are completely consistent with the insulation materials of the actual dry bushing core are selected, and the hierarchical structure of the actual dry bushing is strictly followed in the structural design. During the pouring process, a multi-layer structure consistent with the actual bushing core is formed through layer-by-layer pouring and curing. This hierarchical structure not only ensures the mechanical strength and electrical insulation performance of the sample, but also effectively simulates the behavior of the actual bushing under the coupling of thermal, electrical and mechanical stresses.

[0090] In terms of physical properties, the isomorphic samples highly restore the physical properties of the actual dry bushing in terms of material composition and structural design. The combination of epoxy resin and crepe paper can provide the same mechanical strength and electrical insulation performance as the actual bushing. By strictly controlling the casting and curing process, the hierarchical structure and defect morphology of the sample are ensured to be consistent with the actual bushing, so that the same physical behavior is exhibited in the experiment; in terms of electrical performance, the key parameters such as the dielectric constant and loss factor (tanδ) of the isomorphic samples are similar to those of the actual dry bushing. The FDS measurement results show that the electrical performance curves of the isomorphic samples in different frequency bands are highly consistent with the actual bushing, especially the performance in the low and high frequency bands, which can accurately reflect the response characteristics of the insulating material under different frequency electric fields; in addition, by accurately simulating the defects that may occur in actual production, the isomorphic samples can truly reflect the impact of defects on material properties. The presence of defects such as moisture, aging, bubbles, cracks and discharge tips will have a significant impact on parameters such as electric field distribution and dielectric properties. These effects have been verified in the test of the isomorphic samples to ensure their consistency with the actual situation.

[0091] Figure 4 It is a ratio diagram of epoxy water bath and base material provided in an embodiment of the present invention.

[0092] Figure 5 This is a diagram showing the epoxy mixed liquid being stirred uniformly according to an embodiment of the present invention.

[0093] Figure 6 This is a diagram of ultrasonic oscillation degassing provided by an embodiment of the present invention.

[0094] Figure 7 This is a vacuum pumping diagram provided by an embodiment of the present invention.

[0095] Figure 8 This is a diagram of epoxy mixed liquid casting and epoxy resin sample molding provided by an embodiment of the present invention.

[0096] Fig. 9 This is a diagram of a cut insulating paper sample provided in an embodiment of the present invention.

[0097] (2) Preparation of isomorphous epoxy impregnated paper samples

[0098] The insulating paper in the epoxy impregnated paper sample is a 67 / 100 (base paper weight before wrinkling / crepe paper weight after wrinkling g / m2) type crepe paper produced by Weidmann. It is cut into round samples with a diameter of 79 mm to facilitate the discharge of bubbles when evacuating the mold. The cut insulating paper is pressed with a heavy object and placed at 85°C for complete drying for use.

[0099] According to the field investigation experience of dry casing production process, in the regular dry casing production process, the rolled crepe paper is poured with epoxy mixed liquid in a vacuum environment after it is completely dried, so as to reduce the intrusion of water and fully infiltrate the crepe paper with epoxy mixed liquid. Therefore, this paper adopts the method of directly infiltrating the crepe paper with epoxy mixed liquid under vacuum after the crepe paper is completely dried, and then putting it into the mold with epoxy mixed liquid to prepare epoxy impregnated paper sample, which avoids the water intrusion that may be generated when the crepe paper is directly placed in the mold and poured with epoxy in the traditional preparation method, and also solves the problem that bubbles accumulated in the grooves on the lower surface of the crepe paper are difficult to remove. The specific operation process is as follows:

[0100] The steps of preparing the epoxy mixed liquid and degassing treatment are the same as those in the "Preparation of epoxy resin samples". When preparing the mixed liquid, take a +10% margin for later use. Pour enough mixed liquid to immerse the insulating paper into the glass dish (A), and keep the remaining part in the glass beaker (B). Place the glass dish (A) in a vacuum oven and evacuate it at 50°C for 30 minutes to allow the crepe paper to be fully infiltrated with the epoxy mixed liquid. Fig.10 shown.

[0101] Add overflow grooves around the mold to ensure that excess epoxy mixed liquid is discharged and the thickness of the sample is uniform. After the crepe paper is fully soaked, it is placed in the mold, and then an appropriate amount of epoxy mixed liquid is added, and it is covered with polytetrafluoroethylene film and placed in a vacuum drying oven. After pre-curing at 90°C for 2 hours and post-curing at 130°C for 5 hours, the epoxy impregnated paper sample is formed.

[0102] Fig.11 It is a design drawing of an epoxy impregnated paper mold provided by an embodiment of the present invention.

[0103] Epoxy impregnated paper samples containing different numbers of crepe paper layers such as Fig.12 As shown:

[0104] Furthermore, considering that the aluminum foil shielding layer provides the necessary electric field shielding and uniform electric field distribution functions in the actual core, it can effectively prevent local electric field concentration, thereby reducing the risk of local discharge caused by the electric field tip effect. By adding an aluminum foil shielding layer to the sample, the electric field distribution of the dry core under actual working conditions can be more realistically simulated; at the same time, the aluminum foil layer will affect the dielectric constant and dielectric loss of the insulating material, especially in the high-frequency band. By introducing an aluminum foil shielding layer in the sample, it can be ensured that the response of the sample in the dielectric spectrum measurement is consistent with the actual dry core, providing more accurate and reliable experimental data. This is of great significance for studying the dielectric properties and aging characteristics of insulating materials.

[0105] Therefore, this paper prepared a dry core isomorphous sample containing an aluminum foil shielding layer, the steps are as follows:

[0106] Cut the aluminum foil paper into appropriate size, press it to make it as flat as possible, and put the dried insulation paper in a glass dish and immerse it in vacuum. Fig.13 shown.

[0107] like Fig.14 As shown, slowly lay a piece of insulating paper from the corner of the mold to avoid bubbles in contact with the mold, then pour in an appropriate amount of mixed liquid, and then lay a layer of aluminum foil and insulating paper in the same way. After vacuuming at 50°C for 1h, use polytetrafluoroethylene film to press from the corners and absorb bubbles. The subsequent curing steps are the same as above.

[0108] Fig.15 It is a flow chart of preparing experimental samples provided by an embodiment of the present invention.

[0109] Preparation of isomorphic samples with different defects

[0110] (1) Preparation of thermal aging samples

[0111] In order to be closer to production practice, the aging characteristics of epoxy resin and epoxy impregnated paper insulation were explored within a limited time. With reference to the standards GB / T 20112-2015, IEC60511-1 and the 10-degree rule, accelerated thermal aging experiments were carried out on the samples to be tested. That is, when the temperature increases, the aging rate of the samples will accelerate.

[0112] A thermal aging experimental platform was built. Fig.16 As shown in the figure, this experimental platform is mainly used to provide the constant temperature required for the experiment, so as to simulate the external environment in production practice. This experiment selected 150℃, 180℃ and 200℃ as the experimental temperature, and according to the provisions of the thermal aging experiment in IEC60511-1, the aging time was selected as 1-21 days, and the aging cycle was 1 day. After each aging cycle, the sample was cleaned and dried before testing. And the mass loss rate was recorded.

[0113] Relying on the built thermal aging platform, the thermal aging oven was set to 150℃, 180℃, and 200℃. Based on the "10℃ aging criterion", the aging rate of the sample doubles for every 10℃ increase in temperature, that is, the insulation service life decays to half of the original. Therefore, taking 90℃ as the benchmark during normal operation of the rubber-impregnated paper bushing, the aging rate of the insulation sample to be tested at 150℃ is 2 (150-90) / 10 times.

[0114] Table 1 Equivalent aging time of samples at 150°C

[0115]

[0116]

[0117] The aging time of the samples at 150℃, 180℃ and 200℃ corresponds to the actual operation time of the rubber-impregnated paper casing as shown in Table 1.

[0118] (2) Preparation of damp crepe paper samples

[0119] In order to explore the relationship between the characteristic parameters of samples made of crepe paper at different moisture levels and the moisture degree, this paper carried out water spraying and humidification treatment on the completely dried crepe paper, and then recorded the moisture content of the crepe paper before preparing the samples.

[0120] First, the cut crepe paper was placed in a vacuum environment at 85°C for drying, and the crepe paper pieces were taken out every half an hour and weighed using a precision electronic balance (0.1 mg) until the mass change rate did not exceed 0.1% after four consecutive weighings, which indicated that the paper was completely dry. The final weighing results were shown in the figure.

[0121] Fig.17 This is a completely dry picture of the crepe paper provided by the embodiment of the present invention.

[0122] Fig.18 It is a schematic diagram of humidifying crepe paper provided by an embodiment of the present invention.

[0123] Finally, the total mass of 7 pieces of crepe paper was measured to be m = 3.4281g, that is, the weight of a single piece of crepe paper is m0 = 0.4897g; in order to make the crepe paper evenly damp, the dried crepe paper was humidified with a spray bottle that sprayed evenly. To avoid the influence of impurities, deionized water that met the test standards was used for humidification. The water output of the spray bottle was 2g for 50 pumps, that is, 0.04g per pump. In order to avoid contamination by wet crepe paper, the crepe paper was directly placed in the mold for humidification and then directly poured with epoxy. The subsequent steps were consistent with the curing process in the previous article.

[0124] Assuming that the water output from the spray bottle is evenly distributed, the area of ​​even distribution of water output is:

[0125]

[0126] The area of ​​crepe paper is:

[0127]

[0128] The proportion of water absorbed by crepe paper to the total water output is:

[0129]

[0130] The calculated water absorption per pump is 0.0256 g. Epoxy impregnated paper samples with different moisture levels were prepared. The moisture content of the crepe paper is shown in Table 2:

[0131] Table 2 Moisture content of wet epoxy impregnated paper samples

[0132]

[0133] (3) Preparation of samples with microcracks and aluminum foil wrinkles

[0134] During the actual operation of the transformer, the dry core will experience periodic changes in temperature. Rapid temperature changes will cause thermal stress in the material. At the same time, the equipment may be subjected to mechanical vibration and impact during operation. These external forces will cause stress concentration inside the material. These factors may cause the core to gradually crack, resulting in damage to the main insulation of the core and a decrease in the breakdown voltage. In order to explore the impact of microcracks in the dry core in actual engineering applications, this paper designed and prepared microcrack specimens of different sizes. The specific process is as follows.

[0135] As a chemically inert substance, vaseline has a good isolation effect. Vaseline does not react chemically with epoxy resin and can effectively form a stable isolation layer between aluminum foil and epoxy resin. During the curing process, the presence of vaseline will prevent the adhesion of epoxy resin to aluminum foil, thereby forming the expected gaps or cracks in the cured sample. By applying vaseline, precise control of the location and size of the crack can be achieved. During the experiment, the width and length of the crack can be controlled by adjusting the thickness and application area of ​​the vaseline. Compared with naturally formed cracks, this method has better controllability and repeatability, can ensure the consistency of crack defects in each experiment, and is helpful to systematically study the impact of crack defects on material properties. Fig.19 As shown, in the normal preparation process, applying a certain size of Vaseline on the cut aluminum foil can effectively prevent the epoxy resin from contacting the aluminum foil, so that the two materials cannot fit tightly together, and micro-crack defects with controllable size will exist in the cured epoxy impregnated paper sample.

[0136] (4) Preparation of samples with bubble defects

[0137] The bubble defects in the dry core are usually caused by uneven casting or incomplete curing during the manufacturing process. Bubbles will cause local stress concentration, which is easy to cause electrical treeing or breakdown under the action of electric field and thermal stress, seriously affecting the insulation performance and mechanical strength, thereby shortening the life of the equipment. In the preparation process of the experimental samples described above, by controlling the evacuation time of the epoxy resin used for casting, defective samples with different degrees of bubbles can be prepared. The evacuation time and number of each sample are shown in Table 3.

[0138] Table 3 Bubble defect sample evacuation time setting

[0139]

[0140]

[0141] Al2O3 is a commonly used material in electrical insulation. It has excellent electrical insulation properties and can remain stable under high electric fields. It has stable chemical properties and excellent electrical insulation properties. It will not react with epoxy resin or cause changes in electrical properties. This ensures that when simulating bubble defects, no other uncontrollable variables will be introduced to affect the accuracy and reliability of the experimental results. At the same time, in the actual preparation process, the Al2O3 beads can be accurately placed at specific locations on the epoxy resin specimens through pre-design, thereby achieving precise control of the location of the bubble defects. In addition, Al2O3 beads of different diameters can be used to simulate bubble defects of different sizes, thereby studying the effect of bubble size on the insulation performance of the dry core. The prepared specimens are as follows: Fig. 20 shown.

[0142] (5) Preparation of samples with tip discharge defects

[0143] The creation of wrinkles and protrusions on the surface of aluminum foil can accurately simulate the discharge tip defects that may occur in the actual production process. These defects will lead to local enhancement of the electric field in practical applications, thereby inducing local discharge. By creating similar defects in a laboratory environment, its impact on material properties can be better studied; and the manufacturing process of wrinkles and protrusions on the surface of aluminum foil has a high degree of controllability. By adjusting the processing technology of aluminum foil, the shape, size and distribution of wrinkles and protrusions can be precisely controlled. This is crucial for studying the impact of different defect parameters on material properties and helps to form systematic research results.

[0144] Fig.21 It is a diagram of the setting and defective sample of the aluminum foil protrusion provided in an embodiment of the present invention; the red circle in the left figure is the protrusion of the aluminum foil shielding layer, and the right figure is an epoxy impregnated paper sample containing aluminum foil protrusion defects.

[0145] 1. Specific application fields or related products of the present invention.

[0146] The dry-type bushing capacitor core multi-defect isomorphic sample preparation and testing platform of the present invention has a wide range of applications and is directly related to the core links of high-voltage power equipment manufacturing and maintenance. Specifically, the platform can be applied to the research and development, production and quality inspection stages of dry-type bushing capacitor cores, providing manufacturers with a set of efficient and accurate insulation performance evaluation tools. By simulating multiple defects that may be encountered in actual operation, the present invention helps companies optimize product design, improve product quality, and reduce the risk of equipment downtime due to insulation failures. In addition, the platform can also serve as an important experimental device for scientific research institutions and universities to study the insulation aging mechanism of power equipment and evaluate the insulation performance of new materials, promoting technological progress and innovation in related fields. Therefore, the present invention not only has significant technical creativity, but also shows great technical value in ensuring the safe and stable operation of power equipment and promoting industrial upgrading.

[0147] 2. Relevant evidence of the technical effects obtained by the embodiments of the present invention.

[0148] The technical effects obtained by the embodiments of the present invention have been verified through a series of rigorous experiments. Experimental data show that the insulation performance evaluation results of the multi-defect isomorphic samples prepared by the present invention are highly consistent with the performance of the actual dry-type bushing capacitor core in operation, proving the accuracy and effectiveness of the present invention in simulating actual defects. In addition, the present invention has made significant contributions to the defect identification and status detection of dry cores. By applying the platform of the present invention, the defect characteristic parameter database can be expanded to provide data support for more accurate defect identification and status assessment. At the same time, the application of the present invention also effectively reduces the cost of dry core defect detection, improves detection efficiency, and brings substantial convenience and economic benefits to the operation and maintenance management of power equipment. These practical application results fully demonstrate the technical value of the present invention in improving the management and maintenance level of dry core insulation performance.

Claims

1. A dry-type bushing capacitor core multi-defect isomorphic sample preparation and testing platform, characterized in that: include: A sample preparation system and a test system, wherein the sample preparation system is used to prepare isomorphic samples containing microcracks, bubbles, and tip discharge defects, and the test system is used to perform electrical performance tests on the prepared isomorphic samples.

2. The platform according to claim 1, characterized in that The sample preparation system includes a raw material proportioning device, a mixing and stirring device, a degassing device, a casting mold and a curing device, wherein: The raw material proportioning device is used to accurately weigh the epoxy resin matrix, curing agent, toughening agent and accelerator; The mixing and stirring device is used to mix the raw materials thoroughly and evenly; The degasser is used to remove bubbles from the mixed solution; The casting mold is used to cast the degassed mixed solution into shape; The curing device is used to cure the poured sample.

3. The platform according to claim 2, characterized in that: The sample preparation system also includes a defect simulation device for introducing moisture, microcracks, bubbles, and tip discharge defects during the casting process, specifically: Simulate moisture defects by spraying water or natural moisture absorption; Microcrack defects were created by applying petroleum jelly between the aluminum foil and the epoxy resin; Simulate bubble defects by controlling the vacuum degree during the pouring process or placing Al2O3 particles in advance; Wrinkles and protrusions were made on the surface of aluminum foil to simulate tip discharge defects.

4. The platform according to claim 1, characterized in that: The test system includes a dielectric performance test device for measuring the complex capacitance, complex dielectric constant and dielectric loss factor of the isomorphic sample, and then evaluating its electrical performance.

5. The platform according to claim 4, characterized in that The dielectric properties testing device comprises a signal generator, a measuring probe and a data acquisition and processing unit, wherein: The signal generator is used to generate the alternating electric field required for the test; The measuring probe is used to collect the voltage and current signals of the isomorphic sample under the alternating electric field; The data acquisition and processing unit is used to process the measurement data and calculate the complex capacitance, complex dielectric constant and dielectric loss factor.

6. The platform according to claim 1, characterized in that: It also includes a thermal aging test device, which is used to carry out accelerated thermal aging tests on isomorphic samples to simulate their aging during long-term operation, specifically including a heating cavity and a temperature control system.

7. The platform according to claim 6, characterized in that The following steps are involved: Step 1, preparing an epoxy resin sample or an epoxy impregnated paper sample, wherein the epoxy impregnated paper sample comprises multiple layers of crepe paper and epoxy resin; Step 2, setting a plurality of temperature control areas in the aging test platform, respectively setting them to different aging temperatures, wherein the aging temperatures include 150° C., 180° C. and 200° C.; Step 3, placing the prepared samples in each temperature control zone for accelerated thermal aging test, and simulating different equivalent aging years by controlling the aging time, wherein the equivalent aging years are calculated based on the "10°C aging criterion"; Step 4: After each set aging cycle is completed, the sample is taken out for cleaning and drying, and then the sample is subjected to quality inspection and performance evaluation, and the changes in mass loss rate and other electrical performance parameters are recorded; Step 5, repeat the aging, cleaning, drying and testing process in step (4) until all preset aging cycles are completed to obtain the performance degradation data of the samples under different aging conditions.

8. The platform according to any one of claims 1 to 7, characterized in that: It also includes a data processing and analysis system for processing and analyzing test data and establishing a correlation model between the electrical performance of isomorphic samples and the defect type and degree.

9. A method for preparing and testing dry-type bushing capacitor core multi-defect isomorphic samples using the platform described in any one of claims 1 to 8, characterized in that: Includes steps: (1) Accurately weigh and mix the raw materials; (2) removing bubbles from the mixed solution; (3) Introducing moisture, microcracks, bubbles, and tip discharge defects during the pouring process; (4) Curing the cast samples; (5) Using a dielectric performance test device to measure the electrical properties of the isomorphic samples; (6) Process and analyze the test data to evaluate the relationship between the electrical performance of isomorphic samples and the defect type and degree.

10. The method according to claim 9, characterized in that The method also includes the following steps: conducting accelerated thermal aging experiments on isomorphic samples to simulate performance changes under different aging conditions, and combining the dielectric performance test results to further evaluate the long-term operating reliability of the dry-type bushing capacitor core.

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