Construction and Test Method of Load Spectrum for Accelerated Degradation Test of Ceramic Insulators on Overhead Contact Line Bracket

Abstract

This invention discloses a method for constructing and testing the accelerated degradation test load spectrum of contact network cantilever porcelain insulators. The method includes constructing a composite load spectrum and conducting accelerated degradation tests based on the composite load spectrum. By constructing a composite load spectrum that can simulate the coupled effects of dynamic temperature cycling and static mechanical bending loads under actual working conditions, accelerated degradation tests are conducted based on the composite load spectrum to obtain performance degradation data of the contact network cantilever porcelain insulators under the coupled effects of temperature and mechanical loads. This enables prediction of the lifespan and reliability assessment of the contact network cantilever porcelain insulators. The load spectrum obtained by this method can realistically simulate the lifespan of contact network cantilever porcelain insulators under various load environments, helping railway operators determine the optimal insulator maintenance and replacement cycle, thereby improving safety and reliability. Furthermore, the performance degradation data of contact network cantilever porcelain insulators under the combined effects of temperature and mechanical loads obtained through accelerated degradation tests provides a reference for porcelain insulator structure optimization and material selection.

Description

Technical Field

[0001] This invention relates to the field of electrified railway technology, specifically to the construction and testing method of the load spectrum for accelerated degradation test of porcelain insulators on catenary cantilever arms. Background Technology

[0002] High-speed railways are a vital infrastructure for national economic and social development. The high-speed overhead contact system has transitioned from large-scale design and construction to operation and maintenance, with some sections now entering the later stages of service. This means the contact system is subjected to greater dynamic impacts, more frequent arc erosion, and higher mechanical stress. Failure of any component can lead to widespread and prolonged operational disruptions with extremely serious consequences. Therefore, developing scientific and efficient plans for maintenance and replacement cycles is crucial for ensuring railway power supply security and improving operational efficiency.

[0003] The overhead contact system is the "lifeline" of electrified railways, and its construction and maintenance costs are enormous. How to scientifically plan maintenance and replacement cycles, avoiding waste caused by "premature replacement" and safety accidents caused by "late replacement," is key to optimizing the asset's life-cycle cost. Accelerated degradation testing, which accurately predicts the remaining lifespan of overhead contact system components, is crucial for selecting the timing of batch replacements. Accelerated degradation testing of the contact system cantilever porcelain insulators simulates actual environmental conditions in the laboratory, accelerating the aging process of the insulators and obtaining performance degradation data in a shorter time. Accelerated degradation testing needs to maintain the original failure mechanisms and modes of the contact system cantilever porcelain insulators; therefore, it is essential to construct a working load spectrum that matches actual operating conditions. How to construct this working load spectrum is crucial for accelerated degradation testing.

[0004] While existing accelerated degradation test methods for insulators play an important role in assessing insulator life and performance, they still have some shortcomings and limitations: (1) Existing accelerated degradation tests usually simulate the aging process of insulators by using artificial light sources, high temperature and high humidity, etc., but these simulation conditions are significantly different from the natural environment.

[0005] (2) The actual aging process of insulators is the result of the combined effect of multiple factors, such as electric field, mechanical stress, environmental pollution, ultraviolet radiation, etc. However, existing test methods can only simulate a single or a few factors, which is difficult to reflect the real aging situation under the combined effect of multiple factors.

[0006] (3) In existing accelerated degradation tests of insulators, the temperature, humidity and other conditions are set to be quite harsh, which is quite different from the mild changes in the natural environment. Such harsh conditions may cause atypical aging phenomena in insulator materials, such as rapid decline in material performance or structural damage, thus failing to accurately reflect the true state of the insulator in long-term operation.

[0007] (4) Existing accelerated degradation tests for insulators have certain defects and limitations in terms of technical simulation, cost control, data reliability, and practical application. These shortcomings not only affect the accuracy and reliability of the test results, but also limit their application in insulator life assessment and fault prediction. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, this invention proposes a method for constructing and testing load spectra of contact network cantilever porcelain insulators under the combined effects of temperature cycling and mechanical loading, mainly including a method for constructing working load spectra and an accelerated degradation test scheme. This method constructs temperature load spectra and bending load spectra based on the actual operating conditions of contact network cantilever porcelain insulators, making the load spectra more closely resemble the actual operating conditions of contact network cantilever porcelain insulators. A temperature-bending force superimposed loading spectrum is constructed, and an accelerated degradation test method is proposed, enabling the test load spectra to reflect the stress superposition effect of contact network cantilever porcelain insulators under complex environments.

[0009] The objective of this invention can be achieved through the following technical solutions: An accelerated degradation test load spectrum construction and test method for contact wire cantilever porcelain insulators includes the construction of a composite load spectrum and an accelerated degradation test based on the composite load spectrum. By constructing a composite load spectrum that can simulate the coupling effect of dynamic temperature cycling and static mechanical bending load in actual working conditions, and conducting an accelerated degradation test based on the composite load spectrum, the performance degradation data of contact wire cantilever porcelain insulators under the coupling effect of temperature and mechanical loads are obtained, thereby realizing the life prediction and reliability assessment of contact wire cantilever porcelain insulators. The composite load spectrum construction is based on real working condition data, which associates and superimposes dynamic temperature load with static or quasi-static bending mechanical load, specifically including temperature load spectrum construction, bending mechanical load spectrum construction and composite load spectrum synthesis. The temperature load spectrum is constructed based on the measured environmental temperature data of the installation location of the ceramic insulator of the catenary arm. After data preprocessing, cyclic counting statistics, probability distribution fitting and load level division, a one-dimensional temperature load time history for laboratory loading is formed. The bending mechanical load spectrum is constructed by establishing a finite element model of the cantilever system, analyzing and calculating the working bending stress of the contact wire cantilever porcelain insulator under various actual loads such as self-weight, conductor tension and wind load, and determining the typical bending load applied in the test accordingly. The composite load spectrum synthesis superimposes the temperature load time history, which reflects the actual temperature fluctuation law, with the bending load, which characterizes the long-term mechanical stress level, to generate a temperature-bending force composite load spectrum for accelerated degradation testing. Accelerated degradation test based on composite load spectrum: The actual service stress state of the contact wire bracket porcelain insulator is reproduced in the laboratory using the synthesized composite load spectrum. The test includes test preparation and grouping, composite stress accelerated test and performance degradation assessment. The test preparation and grouping involved dividing the contact network cantilever porcelain insulator samples, including both in-service samples and new non-in-service products, into multiple test groups to study performance degradation under different stress levels and initial conditions. The composite stress accelerated test places each group of specimens in the test equipment and applies a specified temperature cycle and bending static load simultaneously according to the synthesized composite load spectrum. The performance degradation assessment involves sampling and performing bending failure load tests after a predetermined cumulative load application time or number of cycles. By analyzing the attenuation data of the failure load, a performance degradation model for the contact wire cantilever porcelain insulator is established for life prediction.

[0010] Furthermore, the specific method for constructing the temperature load spectrum includes: S21: Preprocess the measured temperature data, including compression of adjacent equal-value data, extraction of peak and valley values, and removal of invalid range values; S22: For the preprocessed temperature data, the four-point rainflow counting method is used for statistical analysis. The mean and range values ​​of the temperature load cycle are fitted using normal distribution and Weibull distribution respectively. The mean and range of the temperature load cycle are proved to be independent of each other through calculation. S23: Divide the average temperature load cycle into 8 equal parts using the equal interval method, and divide the range into 8 levels using the Conover ratio coefficient unequal interval method, and calculate the number of cycles corresponding to the average temperature load cycle and range value of each level. S24: The two-dimensional temperature load spectrum is transformed into a one-dimensional load spectrum of temperature load cycles using the variable mean method.

[0011] Furthermore, the specific method for constructing the bending mechanical load spectrum includes: S31: Based on the drawings, establish a scaled three-dimensional finite element model of the cantilever device; S32: Analyze and calculate the bending load of the contact wire cantilever porcelain insulator. The bending load of the contact wire cantilever porcelain insulator includes the self-weight load of the cantilever device, the self-weight load of the contact suspension, the horizontal load borne by the suspension point positioning clamp, the vertical load borne by the suspension point positioning clamp, and the accidental load borne by the insulator. S33: Apply the bending load of the contact wire cantilever porcelain insulator to the solid three-dimensional model of the cantilever device, and solve the working bending load of the contact wire cantilever porcelain insulator through finite element analysis. The bending load of the flat cantilever porcelain insulator is about 637.32N, and the bending load of the inclined cantilever porcelain insulator is about 314.85N. If we assume that the safety factor is not less than 3, the working bending load of the contact wire cantilever porcelain insulator can be considered as 2000N.

[0012] Furthermore, in the composite stress accelerated test, the applied bending static load is a constant load achieved by weights, with a value in the range of 1kN to 3kN; the applied temperature cyclic load has a high temperature range between +40℃ and +65℃ and a low temperature range between -25℃ and -5℃, with the heating and cooling rates controlled at 1℃ / min, and the holding time for both high and low temperatures is 3 hours.

[0013] Furthermore, in the test preparation and grouping, the required test equipment includes a temperature cycling test platform for porcelain insulators of the contact wire cantilever arm and a bending and torsion testing machine. The temperature cycling test platform for porcelain insulators of the contact wire cantilever arm has the functions of bending static load loading and temperature cycling control; the bending and torsion testing machine is used to measure the maximum bending failure load of the porcelain insulator. The required test samples include contact network cantilever porcelain insulators that have been in service for a specific number of years and new contact network cantilever porcelain insulators that have not yet been in service. The required test groups are to divide the in-service samples into several groups with the same number of samples and number them, and to apply different levels of composite stress to accelerate degradation. The new products that have not yet been in service are used as a control group to obtain initial performance data, and to study the complete performance degradation process by taking samples from this group after different cumulative cycles.

[0014] Furthermore, in the performance degradation assessment, a fixed-interval sampling strategy is adopted for the in-service sample group, that is, when the cumulative temperature cycle count reaches 6, 12, 18 and 24, a single sample is taken out sequentially for bending failure load test.

[0015] Furthermore, in the performance degradation assessment, for the non-service new product control group, a replacement continuous sampling strategy is adopted, the specific steps of which include: S71: Before the test begins, take some new samples for initial bending failure load test; S72: Put the remaining new product samples into the composite stress test; S73: At predetermined cumulative cycle number nodes, samples that have undergone partial cycle tests are taken out sequentially for destructive testing, and new replacement samples are simultaneously introduced to continue the test. S74: At the final cumulative cycle count node, all samples still in the test are removed for destructive testing, thus obtaining a continuous performance degradation data chain from the initial state to the final state. Furthermore, the cumulative test cycle count nodes include 9, 18, 27, 36, and 42 cycles. Specifically, after accumulating 9, 18, 27, and 36 temperature cycles, one of the tested specimens is taken out sequentially for a bending load failure test, and a new replacement specimen is simultaneously added to continue the test. After accumulating 42 temperature cycles, all remaining specimens in the test platform are taken out together for a bending load failure test.

[0016] Furthermore, the constructed composite load spectrum and the obtained performance degradation data can be directly used to guide the safety maintenance, life assessment, and replacement cycle formulation of contact network cantilever porcelain insulators in the rail transit field.

[0017] Compared with the prior art, the present invention has the following technical effects: (1) Based on the actual operating conditions of the contact wire cantilever porcelain insulator, temperature load spectrum and bending mechanical load spectrum were constructed respectively, making the load spectrum closer to the actual operating conditions of the contact wire cantilever porcelain insulator in actual use. Compared with the traditional method, this construction method based on actual operating conditions can more accurately reflect the working state of the contact wire cantilever porcelain insulator and more realistically reflect the performance changes of the contact wire cantilever porcelain insulator under the combined action of temperature change and mechanical stress.

[0018] (2) By measuring the ambient temperature and various bending loads of the contact wire canopy porcelain insulator during operation, the extreme environments that the contact wire canopy porcelain insulator may face in actual operation can be simulated. Traditional tests are mostly conducted under ideal conditions, which makes it difficult to reflect the performance changes of the insulator under complex working conditions.

[0019] (3) By constructing a temperature-bending force superimposed loading spectrum, the test load spectrum can reflect the stress superposition effect of the contact wire bracket porcelain insulator under complex environment. This method overcomes the problem of traditional methods ignoring random factors, helps to more comprehensively simulate the multi-condition environment of the contact wire bracket porcelain insulator, and improves the reliability of test results. Attached Figure Description

[0020] Figure 1 Data was collected for the highest and lowest temperatures throughout the year; Figure 2 This is a diagram illustrating the compression of adjacent equal-value data. Figure 3This is a schematic diagram of peak and valley extraction. Figure 4 A diagram illustrating the removal of invalid range values; Figure 5 This is the preprocessed temperature data; Figure 6 To fit a histogram of the cyclic mean to a normal distribution curve; Figure 7 The histogram of the cyclic range values ​​is fitted to the Weibull distribution curve; Figure 8 This is the extrapolated temperature load cycle mean-range value matrix; Figure 9 The one-dimensional temperature working load for the brace porcelain insulator; Figure 10 A scaled three-dimensional finite element model of the wrist arm device; Figure 11 Simulation diagram of a porcelain insulator under load on a cantilever arm; Figure 12 This is the temperature-bending force composite load spectrum. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the invention, any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art to all other embodiments obtained without creative effort should be included within the protection scope of the present invention.

[0022] An accelerated degradation test load spectrum construction and test method for contact wire cantilever porcelain insulators includes the construction of a composite load spectrum and an accelerated degradation test based on the composite load spectrum. By constructing a composite load spectrum that can simulate the coupling effect of dynamic temperature cycling and static mechanical bending load in actual working conditions, and conducting an accelerated degradation test based on the composite load spectrum, the performance degradation data of contact wire cantilever porcelain insulators under the coupling effect of temperature and mechanical loads are obtained, thereby realizing the life prediction and reliability assessment of contact wire cantilever porcelain insulators. The composite load spectrum construction is based on real working condition data, which associates and superimposes dynamic temperature load with static or quasi-static bending mechanical load, specifically including temperature load spectrum construction, bending mechanical load spectrum construction and composite load spectrum synthesis. The specific methods for constructing the temperature load spectrum include: S21: Based on meteorological observation data, the regional temperature variation characteristics were analyzed. The dataset contains dual-temporal records of daily maximum and minimum temperatures, with a total of 730 valid observation samples. The annual temperature load variation curve is shown below. Figure 1 As shown. From Figure 1 It can be seen that: ① The daily temperature range shows a typical fluctuation range of 5-10℃; ② The extreme temperature values ​​reached 36.7℃ (2023-07-26) and 5.8℃ (2023-01-30), respectively; ③ The temperature environmental load is a random variable with significant seasonal characteristics.

[0023] The measured temperature data is preprocessed, including the following: Figure 2 The adjacent equal-value data compression shown is as follows: Figure 3 Peak and valley value extraction as shown and as Figure 4 The invalid range values ​​are removed as shown; after preprocessing, the temperature data is as follows: Figure 5 As shown.

[0024] S22: For the preprocessed temperature data, the four-point rainflow counting method is used for statistical analysis. The mean and range of the temperature load cycle are fitted by the normal distribution (probability density function as shown in Equation 1) and the Weibull distribution (probability density function as shown in Equation 2), respectively. The mean and range of the temperature load cycle are proved to be independent of each other through calculation. (1) In equation (1), The mean of a normal distribution is . is the standard deviation of the normal distribution.

[0025] (2) In equation (2), Let be the shape parameter of the Weibull distribution. is the scale parameter of the Weibull distribution.

[0026] The parameters of the fitted distribution function are shown in Table 1, and the fitted distribution function curve is shown in Table 1. Figure 6 and 7 As shown.

[0027] Table 1. Fitted Distribution Characteristics of Mean and Range Values ​​of Temperature Cycles

[0028] The KS test was used to verify the good fit of the above distribution, and the test results are shown in Table 2. The p-value is much larger than the significance level, so the hypothesis is reasonable, and the test statistic is also small.

[0029] Table 2. KS test results for normal and Weibull distributions

[0030] S23: Calculate the given extrapolated cumulative frequency using the probability density method. Maximum value of temperature load cycle mean and the maximum value of the range As in equation (3): (3) Since the mean and range of the temperature load cycles are independent of each other, equation (3) can be transformed into: (4) (5) Furthermore, it can be written as: (6) (7) Based on the Conover principle, the mean and range of the two-dimensional temperature load spectrum can be divided into eight levels. Since the mean follows a normal distribution, equal-interval grading is suitable for its symmetry and facilitates the description of central concentration and symmetrical extrema; therefore, the mean is graded using equal intervals. The range values ​​follow a Weibull distribution, and unequal-interval grading is suitable for its right skewness and long-tail characteristics, ensuring fine division and data balance in the critical tail region; therefore, the range values ​​are graded using the Conover ratio coefficient unequal-interval method.

[0031] Specifically, the equal-interval grading method divides the interval between the maximum and minimum mean values ​​of the temperature load cycles into 7 equal parts, as shown in equation (8): (8) In the formula, (9) (10) In equation (10), The first one obtained by the rainflow meter method The number of cycles to achieve the average temperature load cycle; The first one obtained by the rainflow meter method Level of average temperature load cycle; The load cycle mean is at level 7. The center of fluctuation of the temperature load mean is determined. The minimum average temperature was 22.42℃. The temperature is 8.00℃. It is 4.12℃.

[0032] The Conover ratio coefficient unequal interval method for grading determines the temperature load cycle range value level for each level according to equation (11), i.e. (11) In equation (11), .

[0033] Therefore, based on the equal interval grading method and the Conover ratio coefficient unequal interval method, eight temperature load levels were obtained as shown in Table 3.

[0034] Table 3 Classification of mean and range values ​​of temperature load cycles

[0035] The number of cycles corresponding to the average and range values ​​of each temperature load cycle is calculated using equation (12). ,Right now: (12) In equation (12), This represents the cumulative number of cycles over 15 years, or 1447.5 times. It is expressed as the joint probability density function of mean and range values, defined by equation (3); , Indicates the upper and lower limits of integration. , , , , , , , , This represents the mean of each level. The range values ​​for each level are shown in Table 3. The temperature load spectrum, extrapolated from the cumulative frequency of 15-year temperature load cycles, is shown in Table 4. The corresponding mean-range value matrix of the temperature load cycles is as follows: Figure 8 As shown.

[0036] Table 4 Two-dimensional load spectrum of 8×8 temperature load cycles (mean-range values)

[0037] S24: As shown in equation (13), the two-dimensional temperature load spectrum in Table 4 is transformed into a one-dimensional load spectrum of temperature load cycle using the variable mean method, as shown in Table 5.

[0038] (13) In equation (13), Represented as the first The average value corresponding to the range of values; Indicates the first Grade mean; express Level range value, first The number of cycles corresponding to the average value. If the duration of both high and low temperatures is set to 3 hours, the corresponding temperature loads in Table 5 are as follows: Figure 9 As shown.

[0039] Table 5. One-dimensional load spectrum of temperature load cycle mean-range values

[0040] The specific methods for constructing the bending mechanical load spectrum include: S31: According to the drawings, such as Figure 10 As shown, a scaled-down three-dimensional finite element model of the cantilever arm device was established. The cantilever arm base spacing is 1150mm, the horizontal cantilever arm length is 3200mm, the inclined cantilever arm length is 2000mm, the cantilever arm support length is 800mm, and the positioning tube length is 2450mm. The three-dimensional model was started from the low-voltage side of the insulator, simplifying non-critical components and features that have little impact on the overall stress analysis of the insulator, such as threads, washers, and cotter pins. The material performance parameters of each component of the cantilever arm device are shown in Table 6, and the weights of each piece of equipment in the contact suspension are shown in Table 7.

[0041] Table 6. Main material properties of various components of the cantilever arm device

[0042] Table 7 Unit weight of contact suspension equipment

[0043] S32: Analyze and calculate the bending load of the contact wire cantilever porcelain insulator. The bending load of the contact wire cantilever porcelain insulator includes the self-weight load of the cantilever device, the self-weight load of the contact suspension, the horizontal load borne by the suspension point positioning clamp, the vertical load borne by the suspension point positioning clamp, and the accidental load borne by the insulator. The self-weight load of the cantilever device is automatically calculated by establishing a proportional three-dimensional model of the cantilever support device and based on the structural and material parameters using finite element components.

[0044] The self-weight load of the contact suspension is determined by the self-weight of the contact wire, catenary cable, and droppers. Equation (14) can be used for calculation: (14) In equation (14), For the unit weight of the load-bearing cable, ; The span is 50m; The tension of the catenary is 1.2 kN. Therefore, the sag of the catenary is 0.15 m.

[0045] The average length of the suspension string is: (15) In equation (15), If the structural height is 0.85m, then .

[0046] The horizontal load at the suspension point is caused by the horizontal component of the tension at the suspension point, resulting from the zigzag arrangement of the contact wires. The horizontal component of the tension in the straight section is: (16) In equation (16), Indicates the contact wire tension; and These represent the spans between two adjacent spans of the suspension point j; This represents the pull-out value at suspension point j; and These represent the pull-out values ​​of adjacent suspension points. Assuming a pull-out value of 250mm, a span of 50m, and a contact wire tension of 14kN, the horizontal load borne by the suspension point is 280N.

[0047] Vertical load borne by the suspension point positioning clamp Loaded by the positioner's own weight Positioning clamp self-weight load The horizontal load of the positioning clamp is determined by the position.

[0048] S33: As Figure 11 As shown, the bending load of the contact wire cantilever porcelain insulator is applied to the solid three-dimensional model of the cantilever device. The working bending load of the contact wire cantilever porcelain insulator is solved by finite element analysis. It can be obtained that the bending load of the flat cantilever porcelain insulator is about 637.32N and the bending load of the inclined cantilever porcelain insulator is about 314.85N. If it is assumed that the safety factor is not less than 3, the working bending load of the cantilever porcelain insulator can be considered as 2000N.

[0049] Will Figure 9 The obtained temperature load and bending load are superimposed to generate a temperature-bending force composite load spectrum for accelerated degradation testing, such as... Figure 12 As shown; the accelerated degradation test based on composite load spectrum uses the synthesized composite load spectrum to reproduce the actual service stress state of the contact wire bracket porcelain insulator in the laboratory, specifically including test preparation and grouping, composite stress accelerated test and performance degradation assessment.

[0050] To verify the rationality of the temperature load spectrum and bending mechanical load spectrum of the contact wire cantilever porcelain insulator constructed in this invention, and to ensure the accuracy of the superimposed load spectrum in simulating the actual working conditions and life prediction of the porcelain insulator, a systematic experimental design and verification were conducted. The temperature load spectrum and bending load spectrum were superimposed using a test chamber and a bending-torsion testing machine to simulate the actual working state of the contact wire cantilever porcelain insulator under complex conditions. The parameters of this superimposed loading spectrum were adjusted based on experimental data to ensure that the stress changes of the contact wire cantilever porcelain insulator under multiple loads conform to the actual situation.

[0051] The accelerated degradation test scheme for the ceramic insulator of the overhead contact line bracket in this invention includes: (1) Purpose of the experiment This experiment accelerated the aging of QBN2-25P rod-shaped contact wire bracket porcelain insulators under different static loads and temperature cycling conditions to evaluate the degradation effect of temperature cycling-mechanical static load on their mechanical strength. The study investigated the attenuation law of the insulator's bending failure load under temperature cycling and mechanical static load conditions to predict its long-term service life in harsh environments.

[0052] (2) Test equipment 1) Temperature cycling test platform for contact wire cantilever porcelain insulators, with functions of bending static load loading and temperature cycling control.

[0053] 2) Bending and torsion testing machine, used to measure the maximum bending failure load of porcelain insulators on the contact wire bracket.

[0054] (3) Test samples and grouping 1) Test samples: 20 QBN2-25P rod-shaped porcelain insulators that have been in service for 20 years; 12 QBN2-25P rod-shaped porcelain insulators that have not been in service.

[0055] 2) Experimental grouping: Twenty QBN2-25P rod-shaped porcelain insulators that had been in service for 20 years were randomly divided into 5 groups of 4 in each group, and were numbered as follows: I-1, I-2, I-3, I-4; II-1, II-2, II-3, II-4; III-1, III-2, III-3, III-4; IV-1, IV-2, IV-3, IV-4; V-1, V-2, V-3, V-4.

[0056] Twelve unused QBN2-25P rod-shaped porcelain insulators were designated as Group 6, numbered VI-1, VI-2, VI-3, VI-4, VI-5, VI-6, VI-7, VI-8, VI-9, VI-10, VI-11, and VI-12.

[0057] The loading test parameters for all groups are shown in Table 8.

[0058] Table 8 Loading Test Parameters

[0059] (4) Test Procedure Test procedure for conditions I-V: 1) Sample preparation: Visual inspection and numbering of 20 QBN2-25P rod-shaped contact wire cantilever porcelain insulator samples that have been in service for 20 years; 2) Apply static load: Install 4 samples in the porcelain insulator bending load-temperature cycling test platform, fix one end and bear static load on the other end, and apply the set bending force (the preset bending force is applied by suspending weights). 3) Temperature Cycling: Start the temperature program: Increase the temperature from room temperature to the set maximum temperature (e.g., +65℃) at a rate of 1℃ / min, and hold for 3 hours; then decrease the temperature to the set minimum temperature (e.g., -25℃) at a rate of 1℃ / min, and hold for 3 hours. Begin the next cycle immediately after completing one cycle. 4) Sampling Destructive Testing: After every 6 temperature cycles (cumulative cycles of 6, 12, 18, and 24), one specimen is removed (a total of 4 specimens are taken within 24 cycles). A bending failure test is performed on the removed specimens, and the failure load value (in kN) is recorded. 5) Repeat the test: Repeat steps 1-4 to complete the temperature cycling test for operating conditions I-V.

[0060] Operating Condition VI Test Procedure: 1) Sample preparation: Visual inspection and numbering of 12 non-service QBN2-25P rod-shaped porcelain insulator samples; 2) Initial bending failure load test: Select 3 specimens, numbered VI-1, VI-2, and VI-3, and conduct bending failure load tests. Record the bending failure load before temperature cycling. 3) Apply static load: Install 5 samples (numbered VI-4, VI-5, VI-6, VI-7, VI-8) in the temperature cycling test platform, fix one end and bear static load on the other end, and apply a set bending force of 2 kN (the preset bending force is applied by suspending weights). 4) Temperature Cycling: Start the temperature program: Increase the temperature from room temperature to the set maximum temperature (+50℃) at 1℃ / min, hold for 3 hours; then decrease the temperature to the set minimum temperature (e.g., -20℃) at 1℃ / min, hold for 3 hours. Begin the next cycle immediately after completing one cycle. 5) Sampling failure test: After a total of 9 temperature cycles (75h), take out sample VI-4 and conduct a bending failure load test. Record the magnitude of the bending failure load and put sample VI-9 into the temperature cycling test platform. After a total of 18 temperature cycles (150h), sample VI-5 was removed and subjected to a bending failure load test. The magnitude of the bending failure load was recorded, and sample VI-10 was placed into the temperature cycling test platform. After a total of 27 temperature cycles (225h) were completed, sample VI-6 was removed and subjected to a bending failure load test. The magnitude of the bending failure load was recorded, and sample VI-11 was placed into the temperature cycling test platform. After a total of 36 temperature cycles (300h) were completed, sample VI-7 was removed and subjected to a bending failure load test. The magnitude of the bending failure load was recorded, and sample VI-12 was placed into the temperature cycling test platform. After a total of 42 temperature cycles (350h), the tubes numbered VI-8, VI-9, VI-10, VI-11, and VI-12 were removed and subjected to bending failure load tests. The magnitude of the bending failure load was recorded.

[0061] The composite load spectrum and performance degradation data constructed in this invention can be directly used to guide the safety maintenance, life assessment, and replacement cycle determination of contact wire cantilever porcelain insulators in the rail transit field. The application areas of this invention are mainly focused on occasions requiring accurate simulation and evaluation of the lifespan of contact wire cantilever porcelain insulators, particularly in rail transit and power transmission. In high-speed railway and subway systems, it can be used to evaluate and test the lifespan of contact wire cantilever porcelain insulators. By using this experimental load spectrum, the lifespan of contact wire cantilever porcelain insulators under various load environments can be simulated more realistically, helping railway operators determine the optimal maintenance and replacement cycle for contact wire cantilever porcelain insulators, thereby improving the safety and reliability of the railway system. Through accelerated degradation testing, performance degradation data of contact wire cantilever porcelain insulators under the combined effects of temperature and mechanical loads can be obtained, providing a reference for the structural optimization and material selection of contact wire cantilever porcelain insulators.

Claims

1. A method for constructing and testing the load spectrum of accelerated degradation test for porcelain insulators on overhead contact wire brackets, characterized in that... The method includes the construction of a composite load spectrum and an accelerated degradation test based on the composite load spectrum. By constructing a composite load spectrum that can simulate the coupling effect of dynamic temperature cycling and static mechanical bending load in actual working conditions, and conducting an accelerated degradation test based on the composite load spectrum, the performance degradation data of the contact wire cantilever porcelain insulator under the coupling effect of temperature and mechanical load are obtained, thereby realizing the life prediction and reliability assessment of the contact wire cantilever porcelain insulator. The composite load spectrum construction is based on real working condition data, which associates and superimposes dynamic temperature load with static or quasi-static bending mechanical load, specifically including temperature load spectrum construction, bending mechanical load spectrum construction and composite load spectrum synthesis. The temperature load spectrum is constructed based on the measured environmental temperature data of the installation location of the ceramic insulator of the catenary arm. After data preprocessing, cyclic counting statistics, probability distribution fitting and load level division, a one-dimensional temperature load time history for laboratory loading is formed. The bending mechanical load spectrum is constructed by establishing a finite element model of the cantilever system, analyzing and calculating the working bending stress of the contact wire cantilever porcelain insulator under various actual loads such as self-weight, conductor tension and wind load, and determining the typical bending load applied in the test accordingly. The composite load spectrum synthesis superimposes the temperature load time history, which reflects the actual temperature fluctuation law, with the bending load, which characterizes the long-term mechanical stress level, to generate a temperature-bending force composite load spectrum for accelerated degradation testing. Accelerated degradation test based on composite load spectrum: The actual service stress state of the contact wire bracket porcelain insulator is reproduced in the laboratory using the synthesized composite load spectrum. The test includes test preparation and grouping, composite stress accelerated test and performance degradation assessment. The test preparation and grouping involved dividing the contact network cantilever porcelain insulator samples, including both in-service samples and new non-in-service products, into multiple test groups to study performance degradation under different stress levels and initial conditions. The composite stress accelerated test places each group of specimens in the test equipment and applies a specified temperature cycle and bending static load simultaneously according to the synthesized composite load spectrum. The performance degradation assessment involves sampling and performing bending failure load tests after a predetermined cumulative load application time or number of cycles. By analyzing the attenuation data of the failure load, a performance degradation model for the contact wire cantilever porcelain insulator is established for life prediction.

2. The method for constructing and testing the accelerated degradation test load spectrum of the contact wire bracket porcelain insulator according to claim 1, characterized in that, The specific methods for constructing the temperature load spectrum include: First, the measured temperature data is preprocessed by isobaric data compression and peak-valley value extraction; Secondly, the rainflow counting method was used to perform cyclic statistics to obtain the mean and amplitude of the temperature load cycle; and the probability distribution was used to fit the cycle mean and amplitude respectively, and their independence was verified. Then, the design load level is obtained by extrapolation based on the probability density method, and the mean and amplitude are classified by equal interval and Conover unequal interval methods. Finally, the two-dimensional load spectrum is transformed into a one-dimensional temperature load spectrum using the variable mean method.

3. The method for constructing and testing the accelerated degradation test load spectrum of the contact wire bracket porcelain insulator according to claim 2, characterized in that, The specific methods for constructing the bending mechanical load spectrum include: First, a three-dimensional finite element model of the wrist arm device is established; Secondly, calculate and load the self-weight load, contact suspension load, horizontal load, vertical load and accidental load borne by the ceramic insulator of the contact wire cantilever arm; Finally, the working bending load of the contact wire cantilever porcelain insulator was solved by finite element analysis, and the bending load value of the test load was determined after considering the safety factor.

4. The method for constructing and testing the accelerated degradation test load spectrum of the contact wire bracket porcelain insulator according to claim 3, characterized in that, In the composite stress accelerated test, the applied bending static load is a constant load achieved by weights, with a value in the range of 1kN to 3kN; the applied temperature cyclic load has a high temperature range between +40℃ and +65℃ and a low temperature range between -25℃ and -5℃, with the heating and cooling rates controlled at 1℃ / min, and the holding time for both high and low temperatures is 3 hours.

5. The method for constructing and testing the accelerated degradation test load spectrum of the contact wire bracket porcelain insulator according to claim 4, characterized in that, In the test preparation and grouping, the required test equipment includes a temperature cycling test platform for contact wire cantilever porcelain insulators and a bending and torsion tester. The temperature cycling test platform for contact wire cantilever porcelain insulators has the functions of bending static load loading and temperature cycling control. The bending and torsion tester is used to measure the maximum bending failure load of the contact wire cantilever porcelain insulators. The required test samples include contact network cantilever porcelain insulators that have been in service for a specific number of years and new contact network cantilever porcelain insulators that have not yet been in service. The required test groups are to divide the in-service samples into several groups with the same number of samples and number them, and to apply different levels of composite stress to accelerate degradation. The new products that have not yet been in service are used as a control group to obtain initial performance data, and to study the complete performance degradation process by taking samples from this group after different cumulative cycles.

6. The method for constructing and testing the accelerated degradation test load spectrum of the contact wire bracket porcelain insulator according to claim 5, characterized in that, In the performance degradation assessment, a fixed interval sampling strategy is adopted for the service sample group, that is, when the cumulative temperature cycle count reaches 6, 12, 18 and 24, a single sample is taken out in sequence for bending failure load test.

7. The method for constructing and testing the accelerated degradation test load spectrum of the contact wire bracket porcelain insulator according to claim 6, characterized in that, In the performance degradation assessment, for the control group of new products that have not yet entered service, a replacement sampling strategy is adopted, that is, some samples are taken at different cumulative test cycle nodes for bending failure load testing, and additional samples can be added to continue the test, thereby obtaining performance degradation data covering a wider time range.

8. The method for constructing and testing the accelerated degradation test load spectrum of the contact wire bracket porcelain insulator according to claim 7, characterized in that, The cumulative test cycle count nodes include 9, 18, 27, 36, and 42 cycles. Specifically, after accumulating 9, 18, 27, and 36 temperature cycles, a test specimen is taken out sequentially for bending load failure testing, and a new replacement specimen is simultaneously added to continue the test. After accumulating 42 temperature cycles, all remaining specimens in the test platform are taken out together for bending load failure testing.

9. The method for constructing and testing the accelerated degradation test load spectrum of the contact wire bracket porcelain insulator according to claim 8, characterized in that, The constructed composite load spectrum and the obtained performance degradation data can be used to guide the safety maintenance, life assessment and replacement cycle formulation of contact network cantilever porcelain insulators in the rail transit field.

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