Dynamic test method for thermoelectric synergy stress of aramid fiber-synthetic ester insulating material

Abstract

The invention discloses a dynamic test method for thermoelectric synergy stress of an aramid fiber-synthetic ester insulating material, and belongs to the technical field of electrical insulating material testing. The method sequentially comprises the steps of sample preparation, baseline measurement, steady state judgment, low-field scanning, middle-field reciprocating circulation, short-time high-field pulse sensitive detection, long-time high-temperature constant-field aging and recovery comparison. In a wide temperature and wide electric field range, a system applies and couples multi-mode electric stress and thermal stress such as low-field, middle-field and high-field pulses and constant-field aging, and it is ensured that a sample reaches a steady state before testing in each stage strictly according to temperature difference and parameter change rate criteria. According to the method, the evolution law of the dielectric property of the material under the complex electric-thermal synergistic effect can be comprehensively and dynamically represented, early damage caused by transient impact and accumulated degradation under cyclic stress can be sensitively recognized, and reversible and irreversible changes in the aging process can be quantitatively distinguished; therefore, a more accurate experimental basis closer to an actual operation condition is provided for reliability evaluation and life prediction of the material.

Description

Technical Field

[0001] This invention belongs to the field of electrical insulation material testing technology, and particularly relates to a dynamic testing method for thermoelectric synergistic stress of aramid-synthetic ester insulation materials. Background Technology

[0002] With the continuous development of high-voltage, high-capacity, and high-reliability electrical equipment, power transformers, high-temperature motors, power electronic equipment, and electrical systems for new energy applications are placing increasingly stringent demands on the comprehensive performance of insulating materials under high electric field strength, high operating temperature, and long-term service conditions. In actual operation, insulating materials often simultaneously experience the coupling effects of electrical and thermal stresses, and the evolution of their dielectric properties directly affects the safety, reliability, and service life of the equipment. Especially under harsh conditions of high temperature, high field, and long-term operation, a series of complex processes occur within the insulating material, including polarization, carrier migration, interfacial charge accumulation, and changes in chemical structure. These processes are coupled and dynamically evolve, potentially leading to irreversible degradation of material performance and even serious faults such as partial discharge or insulation breakdown.

[0003] Aramid fiber reinforced insulation materials are widely used in high-temperature electrical insulation fields due to their excellent heat resistance, mechanical strength, and electrical insulation properties. In recent years, with the increasing application of synthetic ester insulating media in high-temperature and environmentally friendly electrical equipment, aramid-synthetic ester composite insulation systems have gradually become an important development direction for high-temperature insulation systems. In actual operation, these composite insulation materials are immersed in synthetic ester media for extended periods and simultaneously withstand high operating temperatures and electric field strengths. Their dielectric constant, loss factor, conductivity, and other dielectric parameters dynamically change over time, and may even experience irreversible degradation, leading to risks of partial discharge, insulation breakdown, and other failures. Therefore, accurately characterizing the dielectric performance evolution behavior of these materials under thermo-electric synergistic stress is of significant engineering importance for assessing their long-term operational reliability and optimizing material formulations and insulation structure design.

[0004] However, existing methods for testing the dielectric properties of insulating materials mostly focus on static or quasi-static tests under single stress conditions. For example, measuring the dielectric constant and loss factor at room temperature or a single temperature, or conducting short-term tests under low electric field strength. While some studies have introduced heating conditions or increased electric field strength, they typically employ only a simple combination of constant temperature and constant electric field, with short test times. Furthermore, they often fail to consider the complex operating conditions experienced by the material in actual operation, such as electric field fluctuations, temperature cycling, and transient overvoltages. Therefore, they cannot accurately reflect the performance evolution of the material under long-term high-temperature, high-field operating conditions. In addition, existing testing methods mostly focus on measuring steady-state parameters, lacking a systematic characterization of the dynamic changes in dielectric properties under the combined effects of electrothermal and electrical forces. In actual operation, insulating materials not only experience prolonged steady-state electrothermal stress but may also suffer from transient high-electric field impacts or fluctuations. Existing methods often struggle to capture the impact of such transient stresses on dielectric properties, resulting in insufficient ability to identify early material degradation or potential failure risks.

[0005] On the other hand, when conducting dielectric property tests over a wide temperature and electric field range, issues such as uneven internal temperature distribution and measurements being started before parameters reach thermal steady state are common due to factors such as material thermal conductivity, electrode contact effects, and environmental control precision. These problems easily introduce significant testing errors, leading to poor comparability between test results from different laboratories or batches, making it difficult to establish unified and reliable evaluation standards. This is especially true for composite insulating materials like aramid-synthetic esters, whose dielectric properties are highly sensitive to the coupling response of temperature and electric field. If temperature and field are not strictly controlled during testing, or if a stable state is not reached, the obtained data often fails to accurately reflect the intrinsic characteristics of the material, thus affecting the accurate judgment of material performance and lifetime assessment.

[0006] Therefore, there is an urgent need in this field for a dynamic testing method for the thermo-electric synergistic stress of aramid-synthetic ester insulating materials. This method should be able to systematically, dynamically, and repeatably test and evaluate the dielectric properties of the material under long-term high-temperature operation and transient electrical stress conditions within a wide electric field strength and temperature range. This would allow for a more realistic characterization of the dielectric property evolution of such materials under actual service conditions, thus providing a reliable basis for material selection, structural design, and life assessment. Currently, there are no publicly reported systematic testing schemes that simultaneously cover multiple testing stages, including low-field scanning, mid-field cycling, short-duration high-field pulse, long-duration high-temperature aging, and recovery comparison, and possess a clear steady-state determination mechanism. This is precisely the technical problem that this invention aims to solve. Summary of the Invention

[0007] In view of the fact that existing testing methods for insulating materials are mostly limited to single stress conditions, static or quasi-static tests, which are difficult to truly reflect the dynamic evolution behavior of materials under long-term high temperature and high field and transient electrothermal synergistic stress, and have problems such as unstable test conditions, poor data comparability, and insensitivity to early failure precursors, this invention proposes a dynamic testing method for thermoelectric synergistic stress of aramid-synthetic ester insulating materials.

[0008] To achieve the above objectives, the present invention provides a method for dynamic testing of thermo-electric synergistic stress in aramid-synthetic ester insulating materials, comprising the following steps in sequence: (1) Sample preparation steps: Prepare aramid-synthetic ester insulating material samples, clean, dry and equilibrate the samples, and measure and record the effective thickness and effective electrode area of ​​the samples; (2) Baseline measurement steps: Under the predetermined baseline temperature conditions, the dielectric properties of the sample are tested without an external electric field to obtain the initial dielectric constant, dielectric loss factor and conductivity as baseline data; (3) Steady-state determination step: After applying the target temperature and / or target electric field strength, monitor the temperature and dielectric properties of the sample at different locations. When the temperature difference at different locations of the sample is not greater than the preset threshold, and the rate of change of the dielectric properties of the sample within a continuous preset time is less than the preset threshold, the sample is determined to have reached a steady state. (4) Low-field scanning test procedure: Under the condition that the sample reaches steady state, apply a low-intensity electric field to the sample at the target temperature, starting from zero and gradually increasing. After the sample reaches steady state again under each electric field intensity, collect the corresponding dielectric constant, dielectric loss factor and conductivity. (5) Mid-field reciprocating cycle test procedure: At the target temperature, apply at least one reciprocating electric field cycle to the sample, gradually increasing the electric field strength from zero to a medium electric field strength and then falling back to zero electric field, and collect dielectric performance parameters during the cycle or at the cycle node. (6) Short-time high-field pulse sensitive detection steps: The sample is placed under constant temperature and constant background electric field conditions and reaches a steady state. At least one short-time high electric field pulse is applied to the sample, and the dielectric properties are measured at different time points before and after the pulse is applied. (7) Long-term high temperature constant field aging test steps: Under high temperature conditions higher than the baseline temperature, a constant electric field is applied to the sample and the aging time is continued for a preset time. Dielectric performance parameters are collected at multiple aging time nodes. (8) Recovery comparison step: After completing the long-term high temperature constant field aging test, the sample is placed under low temperature conditions and / or no electric field conditions below the aging temperature for recovery treatment. Then, its dielectric performance parameters are measured again and compared with the baseline data and the data after aging.

[0009] Furthermore, the electric field strength applied in steps (4), (5), (6), and (7) is continuously adjustable in the range of 0 kV / mm to 25 kV / mm, with an adjustment accuracy of no more than 0.1 kV / mm.

[0010] Furthermore, the baseline temperature, target temperature, and high-temperature conditions range from 20°C to 190°C, and the sample temperature fluctuation is controlled to be no greater than ±0.5°C during the test.

[0011] Furthermore, in the steady-state determination step (3), the preset threshold includes: the temperature difference between different positions of the sample is not greater than 0.5℃, and the rate of change of the dielectric performance parameter to be tested within 10 consecutive minutes is less than 0.1%; the dielectric performance parameter to be tested is the dielectric constant or the dielectric loss factor.

[0012] Furthermore, in the low-field scanning test step (4), the upper limit of the low-intensity electric field is no higher than 5 kV / mm.

[0013] Furthermore, in the medium field reciprocating cycle test step (5), the medium electric field strength is not higher than 15 kV / mm, and the number of reciprocating electric field cycles is not less than 5.

[0014] Furthermore, in the short-time high-field pulse sensitive detection step (6), the peak electric field intensity of the short-time high-field pulse does not exceed 90% of the short-time allowable electric field intensity of the material under the corresponding temperature conditions, and the pulse duration is in the range of milliseconds to seconds.

[0015] Furthermore, in the long-term high-temperature constant field aging test step (7), the preset aging time is not less than 24 hours.

[0016] Furthermore, the dielectric performance parameters collected in each step include at least one or more of the following: dielectric constant, dielectric loss factor, and conductivity.

[0017] The present invention also provides an application of the test method described above in evaluating the performance stability and failure risk of aramid-synthetic ester insulating materials. By comparing the dielectric performance parameters obtained by the baseline measurement step (2), the short-time high-field pulse sensitive detection step (6), the long-time high-temperature constant-field aging test step (7), and the recovery comparison step (8), the performance evolution trend, damage reversibility, and potential failure risk of the material under the action of thermo-electric synergistic stress are determined.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects: This method fundamentally solves the industry problem of large fluctuations and poor comparability of dielectric test data under wide temperature ranges and wide field strengths by introducing a rigorous "steady-state determination" step. This step ensures that each measurement is performed under conditions where the sample has a uniform internal temperature and a sufficiently stable dielectric response, thereby greatly improving the repeatability and reliability of the test results and establishing a unified and reliable benchmark for performance comparison between different batches of materials or under different test conditions.

[0019] This method innovatively integrates "short-time high-field pulse-sensitive detection" and "mid-field reciprocating cycle testing" into the traditional steady-state testing process. This design enables the method not only to characterize the long-term performance evolution of materials under constant stress, but also to sensitively capture early latent damage caused by unavoidable transient overvoltage impacts and alternating electric field cycles in actual operation. In particular, the transient surge and residual effect of dielectric parameters induced by the pulse step provide a key technical means for identifying precursory signs of material breakdown, achieving early warning of potential failure risks.

[0020] This invention, through a systematic combination of "long-term high-temperature constant-field aging test" and subsequent "recovery comparison step," enables an in-depth analysis of the aging mechanism of materials. It not only quantifies the rate of performance degradation over time to predict service life, but also effectively distinguishes between reversible damage and irreversible deterioration during the aging process. This distinction is crucial for accurately assessing the true aging state of materials, determining the repairability of damage, and understanding the physicochemical nature of failure.

[0021] In summary, this method constructs a comprehensive technical system for evaluating the performance evolution of insulating materials under complex operating conditions through multi-stress coupling and multi-scale dynamic test sequences. The obtained data more realistically reflects the actual service behavior of the materials, significantly improving the accuracy and predictability of the evaluation. Therefore, it provides extremely important and reliable experimental evidence and technical support for the research and development improvement of high-performance insulating materials such as aramid-synthetic esters, as well as the reliability design and life assessment of equipment insulation systems. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] All raw materials used in this invention are not particularly restricted in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0024] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of analytical grade or purity commonly used in the field of chemical synthesis.

[0025] The essence of this invention lies in constructing a multi-scale, multi-stress coupled progressive test sequence to simulate the entire life cycle of insulating materials, from initial commissioning to long-term aging and even transient overvoltage. Its core process sequentially includes: sample preparation and baseline establishment, steady-state determination, low-field scanning, mid-field reciprocating cycling, short-term high-field pulse-sensitive detection, long-term high-temperature constant-field aging, and recovery comparison. Each step is interconnected, with the results of the previous stage serving as the foundation and reference for the next.

[0026] The electric field strength test range is typically 0–25 kV / mm, with continuous adjustability. The adjustment accuracy is recommended to be no greater than 0.1 kV / mm to ensure accurate capture of subtle changes in dielectric properties with increasing field strength. The temperature test range is typically 20℃–190℃, with sample temperature fluctuations controlled to be no greater than ±0.5℃ during testing to ensure thermal stability. Steady-state determination is crucial for data comparability. The conditions are: the temperature difference ΔT between different locations on the sample (e.g., surface and center) ≤ 0.5℃, and the rate of change of key dielectric properties (e.g., dielectric constant ε′ or dielectric loss factor tanδ) within 10 consecutive minutes is less than 0.1%. Formal data acquisition under this condition is only permitted after these conditions are met. The dielectric properties of interest include at least one or more of the following: dielectric constant (ε′), dielectric loss factor (tanδ), and conductivity (σ). Simultaneous monitoring is preferred for correlation analysis.

[0027] The following examples all use aramid fiber-reinforced composite insulating sheets impregnated with synthetic ester insulating oil as the test objects. Samples were uniformly cut, with a measured thickness d of 0.20 mm (tolerance ±0.01 mm). Electrodes were prepared using vacuum silver deposition, with an effective electrode area A of 1.0 cm². 2 Unless otherwise specified, dielectric spectrum measurements are recorded and discussed using 1 kHz as the representative frequency (in actual testing, multiple frequency points from 0.01 Hz to 1 MHz are recorded simultaneously). Conductivity σ is calculated using the formula σ = 2πfε0ε′′, and is corroborated by low-frequency DC conductivity.

[0028] Example 1 This embodiment aims to fully demonstrate the standard operating procedure of the method of the present invention and the comprehensive data obtained.

[0029] 1. Sample Preparation and Baseline Measurement: After equilibration for 24 hours at 23±2℃ and 50±5% relative humidity, baseline measurements were performed at 20℃ without an external electric field. The following values ​​were obtained at 1 kHz: ε′0 = 3.20, tanδ0 = 0.0020, σ0 = 1.0×10⁻⁶. -12 S / m.

[0030] 2. Low-field scanning test: At 20℃, the electric field was increased from 0 kV / mm to 5 kV / mm in steps of 0.5 kV / mm. Measurements were taken at each field strength point only after the steady-state condition was met. The results (1 kHz) show that when E = 5 kV / mm, ε′ = 3.22, tanδ = 0.0023, and σ = 1.2 × 10⁻⁶. -12 S / m indicates that the material response is gradual at low fields, primarily exhibiting reversible polarization.

[0031] 3. Cyclic Field Test: The sample was heated to 120.0℃ and brought to steady state. A triangular wave electric field was applied, cycling from 0 to 15 kV / mm to 0, for a total of 10 cycles. The parameters at the peak (15 kV / mm) and trough (0 kV / mm) of each cycle were recorded. At the first peak: ε′=3.40, tanδ=0.0080; at the tenth peak: ε′=3.52, tanδ=0.0125. After the cycle ended and the sample was kept in a field-free environment for 30 minutes, tanδ remained at 0.0065, significantly higher than the baseline value of 0.0020. This step successfully revealed the irreversible cumulative increase in dielectric loss under thermo-electric cyclic stress, which cannot be detected by traditional single-cycle tests.

[0032] 4. Short-duration high-field pulse sensitivity detection: Another set of samples was stabilized for 60 minutes at 150.0℃ and a constant background electric field of 10 kV / mm. Then, a single short-duration high-voltage pulse was applied: peak field strength Epulse = 22 kV / mm, pulse width tp = 100 ms. The transient changes in dielectric parameters before and after the pulse were monitored. Before the pulse: tanδ = 0.015. One second after the pulse: tanδ jumps instantaneously to 0.028, σ increases from 8.3 × 10⁻⁶. -10 S / m surged to 2.1 × 10 -9 S / m. 300 seconds after the pulse, tanδ recovered to 0.017, but was still higher than the level before the pulse. This step shows that short-term overvoltage impacts can cause transient charge injection and possible structural disturbances inside the material, leaving "sequelae," providing a direct basis for assessing the material's impact resistance and early damage warning.

[0033] 5. Long-term high-temperature constant-field aging test: Three parallel samples were subjected to accelerated aging under constant electric fields of 10, 15, and 20 kV / mm at 170℃. Dielectric parameters were measured periodically. A tanδ value reaching 0.1 was used as one of the failure criteria. The results are shown in Table 1.

[0034] Table 1. Variation of tanδ (1 kHz) during long-term aging under different field intensities

[0035] Data shows that, at the same temperature, the aging lifespan decreases sharply as the field strength increases.

[0036] Recovery comparison procedure: Take the sample aged at 170℃ and 15 kV / mm for 168 hours (tanδ=0.055), place it in an annealing environment at 80℃ without an electric field for 48 hours, and then cool it to 23℃ for measurement again. After recovery: ε′=3.60 (6.5% decrease compared to the aged state), tanδ=0.010 (82% decrease), σ=2.5×10 -10 S / m (decreased by 75%). This step clearly distinguishes between the reversible part of aging damage (such as the dissipation of space charge and relaxation of dipole orientation) and the irreversible part (such as chemical structure degradation). ε′ did not fully recover to the initial 3.20, indicating the presence of irreversible structural changes.

[0037] Through the complete process of Example 1, the method of the present invention systematically provides a complete set of data from initial performance, nonlinear response, cyclic cumulative effect, transient impact resistance to long-term aging life and damage reversibility evaluation, comprehensively characterizing the dynamic evolution characteristics of materials under thermo-electric synergistic stress.

[0038] Example 2 To illustrate that the method of the present invention can be used to identify the performance differences of different material systems, two aramid reinforcements were selected: aramid insulating paper (Nomex® type) and aramid plain weave fabric. Both were impregnated with the same synthetic ester and prepared into insulating boards.

[0039] According to the standard procedure of this invention, the two materials were subjected to a mid-field reciprocating cyclic test at 120°C (0→12 kV / mm→0, 10 cycles).

[0040] Results Comparison: The tanδ increase (relative to the first cycle) of the aramid paper-based material at the peak of the 10th cycle was 40%, while that of the aramid cloth-based material was as high as 95%. After a 30-minute recovery period following the cycle, the irreversible tanδ increase of the aramid paper-based material was 150% of the baseline value, while that of the aramid cloth-based material was as high as 320%.

[0041] Technical Results: This method sensitively reveals that, despite similar static properties, aramid-reinforced materials exhibit more significant performance degradation and greater irreversible damage under cyclic electro-thermal stress. This provides crucial evidence for "evaluating materials under dynamic stress," avoiding the risks associated with material selection based solely on static parameters.

[0042] Example 3 The transient behavior of the material was investigated as it approached the upper limit of its heat resistance rating. The sample was placed at 185°C (close to the upper limit of 190°C for common aramid materials), and the background electric field was set to 8 kV / mm.

[0043] After stabilization, a single pulse with a peak field strength of 18 kV / mm (85% of the estimated short-time withstand strength at this temperature) and a pulse width of 500 ms is applied.

[0044] Results: After the pulse, tanδ spiked from 0.022 to 0.065 within 10 seconds and only recovered to 0.048 within the following 30 minutes, exhibiting a severe and irreversible jump. Simultaneously, the dielectric constant decreased by approximately 3% at a high frequency of 1 MHz.

[0045] Technical Effect Description: Near the high-temperature limit, the material's resistance to overvoltage surges decreases sharply, and the damage becomes increasingly irreversible. The method of this invention, through a combination of "high-temperature steady-state testing + pulse detection," can effectively calibrate the safe operating window boundary of the material, providing quantitative data for equipment overvoltage protection design.

[0046] Comparative Example 1: Traditional aging process omitting the short-time high-field pulse step This comparative simulation is a common traditional testing method, which only involves long-term aging monitoring under constant temperature and field conditions.

[0047] Procedure: The sample was subjected to a long-term aging test for 500 hours at 150℃ and 10 kV / mm, and the dielectric parameters were measured periodically.

[0048] Results: During the entire 500-hour aging process, tanδ increased slowly and steadily from 0.015 to 0.032, and no steep jumps or early abrupt changes as seen after the pulse in Example 1 were observed.

[0049] Comparative Analysis: Compared with step 4 of Example 1 and Example 3, the traditional method completely fails to capture the early latent damage that may be caused by transient overvoltages. In actual operating conditions, equipment may experience multiple overvoltages that do not lead to immediate breakdown; these accumulated latent damages will accelerate the aging process. The method in Comparative Example 1, due to the lack of a pulse-sensitive detection step, will significantly overestimate the material's lifespan in real-world complex power grid environments and underestimate its failure risk.

[0050] Comparative Example 2: "Rapid Test" without Strictly Implementing Steady-State Criteria This comparative demonstration ignores the impact of steady-state determination on the repeatability and accuracy of test results.

[0051] Steps: Perform a mid-field cycle test at 120°C (same as step 3 in Example 1), but cancel the steady-state determination wait. That is, whenever the temperature or electric field setpoint is reached, the measurement and the next cycle will begin immediately.

[0052] Results: The measured data fluctuated greatly. For example, under the same 12 kV / mm field strength, the tanδ values ​​of three consecutive rapid measurements were 0.0075, 0.0092, and 0.0068, respectively, with a dispersion exceeding ±15%. The performance change trend after the final cycle was chaotic, making it impossible to draw the clear conclusion of irreversible accumulation as in Example 1.

[0053] Comparative Analysis: Compared to the stringent steady-state determination in Example 1, Comparative Example 2 demonstrates that in thermo-electric synergistic testing, the internal temperature gradient and polarization relaxation process of the material lead to transient instability of the parameters. If a steady-state condition is not reached, the data will be severely distorted, losing comparability and reliability, rendering the entire dynamic test meaningless. The steady-state determination step of this invention is an essential technical feature for ensuring the scientific validity of the method and the quality of the data.

[0054] Comparative Example 3: A simplified evaluation method involving only low-field and room temperature testing This comparative example represents an oversimplified method for material screening.

[0055] Procedure: Perform low-field scanning tests at 0-5 kV / mm only at two temperature points: 20℃ and 90℃.

[0056] Results: At 90℃ and 5 kV / mm, tanδ is only 0.0045, and the conclusion is that "the material has good high-temperature and low-field performance".

[0057] Comparative Analysis: Compared with Examples 1 (steps 3, 4, and 5) and Example 2, this simplified method completely omits the significant degradation behavior of materials under medium-to-high electric fields, cyclic stress, and long-term high-temperature aging (e.g., tanδ can reach above 0.1). Materials that pass the evaluation using this method, if directly used in medium-to-high voltage and high-temperature equipment, may pose significant safety hazards. This indicates that relying solely on low-field or single field strength-temperature point tests is insufficient for a comprehensive evaluation of insulating materials, especially those used in harsh operating conditions.

[0058] Comparative Example 4: Test sequence shuffled – long-term aging first, then pulse and cycle testing. This comparative study explores the impact of changing the order of the testing process.

[0059] Procedure: For brand-new samples, without low-field scanning and mid-field cycling, directly perform long-term high-temperature constant-field aging (170℃, 15 kV / mm, 168 hours) as described in Example 1. After aging, perform short-term high-field pulse (150℃, 10 kV / mm background, 22 kV / mm pulse) and mid-field reciprocating cycle (120℃) tests.

[0060] Results: The aged sample was severely degraded (tanδ=0.055), and subsequent pulse application caused it to break down directly, making it impossible to obtain effective pulse response data. When the remaining unbroken samples were subjected to mid-cycle cycling, the performance curves were chaotic, and the initial state was far from the "baseline," making it impossible to clearly observe the cumulative effect of cycling.

[0061] Comparative Analysis: Compared to the standard sequence in Example 1, the disordered sequence disrupts the progressive observation logic from "healthy state" to "damaged state" in the testing process. Pulse and cyclic testing are used to detect the sensitivity and evolution of materials from healthy to failed states. However, if performed after the material has severely aged, the testing's significance is greatly diminished, and it can easily damage the sample. The present invention's sequence of "from weak to strong, from steady state to transient, and from short-term to long-term" conforms to the objective laws of material damage evolution and ensures the system obtains effective information.

[0062] Comparative Example 5: The traditional "step stress method" is used to replace the dynamic cycle and pulse test of this invention. The step stress method is a traditional aging test method that involves keeping the temperature constant and gradually increasing the electric field until breakdown occurs.

[0063] Procedure: Apply a constant electric field at 120℃, and increase the field strength by 2 kV / mm every 24 hours. The initial field strength is 10 kV / mm. Record the tanδ at each field strength level until the sample breaks down.

[0064] Results: The sample broke down when the electric field strength increased to 18 kV / mm, with a total time of 96 hours. The tanδ of the last stable point before breakdown (16 kV / mm, 24 hours) was 0.035.

[0065] Comparative Analysis: Comparison with the results of medium-field cycling and long-term constant-field aging in Example 1. The step stress method only yields a breakdown field strength and a monotonic performance-field strength curve, but completely fails to provide the following information: (a) the cumulative effect of electric field cycling fluctuations on performance (as in the cycle test of Example 1); (b) long-term lifetime data at a certain subcritical field strength (e.g., 15 kV / mm) (as in the long-term aging of Example 1); (c) the response to transient overvoltage impacts (as in the pulse test of Example 1). The step stress method focuses on finding the "strength limit," while the method of this invention focuses on revealing the "evolution process and failure mechanism under a given stress," the latter being more important for reliability design and lifetime prediction.

[0066] The method provided by this invention can provide a scientific, comprehensive, and reliable testing and evaluation tool for the research, selection, quality control, and life assessment of aramid-synthetic ester and other similar composite insulating materials and equipment insulation systems.

[0067] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for dynamic testing of thermo-electric synergistic stress in aramid-synthetic ester insulating materials, characterized in that, The steps are performed in the following order: (1) Sample preparation steps: Prepare aramid-synthetic ester insulating material samples, clean, dry and equilibrate the samples, and measure and record the effective thickness and effective electrode area of ​​the samples; (2) Baseline measurement steps: Under the predetermined baseline temperature conditions, the dielectric properties of the sample are tested without an external electric field to obtain the initial dielectric constant, dielectric loss factor and conductivity as baseline data; (3) Steady-state determination step: After applying the target temperature and / or target electric field strength, monitor the temperature and dielectric properties of the sample at different locations. When the temperature difference at different locations of the sample is not greater than the preset threshold, and the rate of change of the dielectric properties of the sample within a continuous preset time is less than the preset threshold, the sample is determined to have reached a steady state. (4) Low-field scanning test procedure: Under the condition that the sample reaches steady state, apply a low-intensity electric field to the sample at the target temperature, starting from zero and gradually increasing. After the sample reaches steady state again under each electric field intensity, collect the corresponding dielectric constant, dielectric loss factor and conductivity. (5) Mid-field reciprocating cycle test procedure: At the target temperature, apply at least one reciprocating electric field cycle to the sample, gradually increasing the electric field strength from zero to a medium electric field strength and then falling back to zero electric field, and collect dielectric performance parameters during the cycle or at the cycle node. (6) Short-time high-field pulse sensitive detection steps: The sample is placed under constant temperature and constant background electric field conditions and reaches a steady state. At least one short-time high electric field pulse is applied to the sample, and the dielectric properties are measured at different time points before and after the pulse is applied. (7) Long-term high temperature constant field aging test steps: Under high temperature conditions higher than the baseline temperature, a constant electric field is applied to the sample and the aging time is continued for a preset time. Dielectric performance parameters are collected at multiple aging time nodes. (8) Recovery comparison step: After completing the long-term high temperature constant field aging test, the sample is placed under low temperature conditions and / or no electric field conditions below the aging temperature for recovery treatment. Then, its dielectric performance parameters are measured again and compared with the baseline data and the data after aging.

2. The method according to claim 1, characterized in that, The electric field strength applied in steps (4), (5), (6), and (7) is continuously adjustable in the range of 0 kV / mm to 25 kV / mm, with an adjustment accuracy of no more than 0.1 kV / mm.

3. The method according to claim 1, characterized in that, The baseline temperature, target temperature, and high-temperature conditions are within the range of 20°C to 190°C, and the sample temperature fluctuation is controlled to be no greater than ±0.5°C during the test.

4. The method according to claim 1, characterized in that, In the steady-state determination step (3), the preset threshold includes: the temperature difference between different positions of the sample is not greater than 0.5℃, and the rate of change of the dielectric performance parameter to be tested within 10 consecutive minutes is less than 0.1%; the dielectric performance parameter to be tested is the dielectric constant or the dielectric loss factor.

5. The method according to claim 1, characterized in that, In the low-field scanning test step (4), the upper limit of the low-intensity electric field is no higher than 5 kV / mm.

6. The method according to claim 1, characterized in that, In the medium-field reciprocating cycle test step (5), the medium electric field strength is not higher than 15 kV / mm, and the number of reciprocating electric field cycles is not less than 5.

7. The method according to claim 1, characterized in that, In the short-time high-field pulse sensitive detection step (6), the peak electric field intensity of the short-time high-field pulse does not exceed 90% of the short-time allowable electric field intensity of the material under the corresponding temperature conditions, and the pulse duration is in the range of milliseconds to seconds.

8. The method according to claim 1, characterized in that, In the long-term high-temperature constant field aging test step (7), the preset aging time is not less than 24 hours.

9. The method according to any one of claims 1 to 8, characterized in that, The dielectric performance parameters collected in each step include at least one or more of the following: dielectric constant, dielectric loss factor, and conductivity.

10. The application of the test method as described in any one of claims 1 to 9 in evaluating the performance stability and failure risk of aramid-synthetic ester insulating materials, characterized in that, By comparing the dielectric properties obtained from the baseline measurement step (2), the short-time high-field pulse sensitive detection step (6), the long-time high-temperature constant-field aging test step (7), and the recovery comparison step (8), the performance evolution trend, damage reversibility, and potential failure risk of the material under the combined action of thermo-electric stress are determined.

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