A test device and method for mechanical stress aging of the interturn insulation of a reactor

Abstract

A kind of test device and method for mechanical stress aging of reactor interturn insulation, belong to the technical field of aging test of electrical insulation material, it includes the inside frame with accommodating space;Spring assembly is located at the bottom of accommodating space, and with the bottom wall of frame is abutted;Jack lower end with spring assembly is abutted, and upper end is through connecting portion with pressure sensor is abutted;Two clamping parts are oppositely arranged, and the aging sample is clamped between two clamping parts, the clamping part below with pressure sensor is abutted, the clamping part above with the top wall of frame is abutted;Jack, connecting portion, pressure sensor, clamping part and aging sample in frame constitute the force transmission structure with spring assembly longitudinal jacking, and spring assembly is applied to the elastic force on aging sample by the force transmission structure.Solve the technical problems of unstable stress loading, high cost and difficult to simulate actual interturn stress condition in prior art, realize the precise simulation of aging process of insulation material.

Description

Technical Field

[0001] This invention relates to a test apparatus and method for mechanical stress aging of inter-turn insulation in reactors, belonging to the field of electrical insulation material aging test technology. Background Technology

[0002] Dry-type air-core reactors, as important reactive power compensation devices in power systems, have advantages such as good linearity, low loss, and simple maintenance, and are widely used in substations, converter stations, and flexible DC transmission systems. They operate outdoors for extended periods, enduring complex combined electro-thermal-mechanical effects. Among these, the inter-turn insulation is the weakest link in a dry-type air-core reactor, and its performance directly determines the overall service life of the reactor.

[0003] In actual operation, the inter-turn insulation of dry-type air-core reactors not only bears the electrical stress under the operating voltage but is also subjected to the electromagnetic force generated by alternating current over a long period. This periodically changing electromagnetic force subjects the inter-turn insulation layer to continuous mechanical vibration and stress, leading to microscopic damage, interface delamination, and even macroscopic cracking of the insulation material—the so-called "mechanical stress aging." Studies have shown that under the combined effects of electrical, thermal, and mechanical stress, mechanical stress accelerates the aging process of the insulation material and significantly reduces the lifespan of the inter-turn insulation. Therefore, conducting research on the aging characteristics of inter-turn insulation under continuous mechanical stress is of great significance for accurately assessing the insulation condition of reactors and formulating reasonable operation and maintenance strategies.

[0004] Currently, aging tests for the inter-turn insulation of dry-type air-core reactors mainly focus on accelerated aging tests under single electrical or thermal stress. For example, high-frequency high-voltage voltage is used to simulate inter-turn overvoltage conditions, or a high-temperature oven is used to simulate the thermal aging process. Furthermore, these methods primarily utilize structural specimens. However, these test methods generally ignore or simplify the continuous effects of mechanical stress. The few studies involving mechanical stress often employ impact loads or short-term vibrations, which cannot realistically simulate the long-term, continuous, and dynamic electromagnetic forces and other internal stresses experienced by the reactor during operation. In addition, existing multi-stress aging test platforms capable of simultaneously applying electrical, thermal, and mechanical stresses are complex in structure, expensive, and difficult to use in the laboratory.

[0005] Therefore, there is an urgent need to propose a test device and method for mechanical stress aging of inter-turn insulation in reactors. The device should be simple in structure, easy to operate, and able to quantitatively and continuously apply adjustable mechanical stress to the inter-turn insulation samples of dry-type air-core reactors to obtain a better stress correspondence during the actual operation of the reactor. The quantification of stress in sheet-like insulation samples provides a prerequisite for subsequent dielectric property testing of insulation materials. It also provides a reliable test platform for in-depth research on the aging mechanism of inter-turn insulation under the combined action of multiple stresses, thereby solving the above-mentioned technical problems. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing testing methods, which neglect or simplify the continuous effects of mechanical stress and fail to realistically simulate the long-term, dynamic mechanical stress borne by the inter-turn insulation of reactors. Furthermore, existing multi-stress coupled aging test platforms suffer from complex structures and high costs. A brief overview of this invention is provided below to offer a basic understanding of certain aspects of the invention. It should be understood that this overview is not an exhaustive summary of the invention. It is not intended to identify key or essential parts of the invention, nor is it intended to limit the scope of the invention.

[0007] The technical solution of this invention:

[0008] Option 1: A test device for mechanical stress aging of inter-turn insulation of reactors, comprising a frame, a clamping part, a pressure sensor, a connecting part, a jack and a spring assembly, wherein the frame is a rigid frame and has an internal accommodating space;

[0009] The spring assembly is located at the bottom of the receiving space and abuts against the bottom wall of the frame; the jack is located above the spring assembly, with its lower end abutting against the spring assembly and its upper end abutting against the pressure sensor through the connecting part; the two clamping parts are arranged vertically opposite each other, and the sample to be aged is clamped between the two clamping parts, with the lower clamping part abutting against the pressure sensor and the upper clamping part abutting against the top wall of the frame;

[0010] The jack, connecting part, pressure sensor, clamping part and the sample to be aged are arranged in the frame to form a force transmission structure that is longitudinally pressed against the spring assembly. The spring assembly applies elastic force to the sample to be aged through this force transmission structure.

[0011] Preferably, the clamping part is a smooth metal disc, the upper and lower surfaces of which are polished smooth and the edges are free of burrs.

[0012] Preferably, the connecting part is a metal cap, which is embedded in the upper end of the jack, and the metal cap has a groove that matches the head of the jack.

[0013] Preferably, the spring assembly includes a spring base, a spring assembly, and a spring assembly cover, wherein the spring assembly is limited and fixed between the spring base and the spring assembly cover; the spring base abuts against the bottom wall of the frame, and the spring assembly cover abuts against the lower end of the jack.

[0014] Preferably, the spring assembly consists of multiple mold springs.

[0015] Preferably, the spring base is a disc structure, with a first annular groove machined on the side facing the spring assembly, and multiple limiting posts spaced apart in the annular groove; the spring assembly cover is a disc structure, with a second annular groove, identical to that of the spring base, machined on the side facing the spring assembly; the number of mold springs in the spring assembly is the same as the number of limiting posts, with one end of each mold spring sleeved on the limiting post of the spring base, and the other end embedded in the second annular groove of the spring assembly cover.

[0016] Preferably, the pressure sensor is a large-range pressure sensor used to monitor and display the mechanical stress value applied to the sample in real time.

[0017] Option 2 - A test method for mechanical stress aging of reactor inter-turn insulation, based on the aforementioned test device for mechanical stress aging of reactor inter-turn insulation, includes the following steps:

[0018] Step 1: Clamp the sample to be aged between the two clamping parts, align the geometric center of the sample to be aged with the center of the clamping parts, and place the whole sample inside the frame, so that the spring assembly, jack, connecting part, pressure sensor, clamping part and sample to be aged form a longitudinal clamping structure from the bottom wall to the top wall within the frame.

[0019] Step 2: Slowly adjust the jack to rise, and push the clamping part and the sample to be aged at the bottom to move upward through the connecting part and pressure sensor until the clamping part at the top presses against the top wall of the frame. Further adjust the jack to compress the spring assembly, and the mechanical stress value is obtained in real time by the pressure sensor.

[0020] Step 3: When the pressure sensor reading reaches the preset target stress value, stop adjusting the jack and lock it, so that the elastic potential energy of the spring assembly is converted into a continuous and stable mechanical stress applied to the sample to be aged.

[0021] Step 4: Place the assembled and locked frame in the designated aging test environment to carry out a pure mechanical stress aging test or a multi-stress coupling aging test on the insulation material. During the test, monitor the pressure sensor values ​​regularly, and adjust the pressure by using a jack when stress decay occurs.

[0022] Preferably, before step one, a calibration step is included, that is, the stress and extension of the spring assembly are calibrated in advance using a pressure sensor to obtain the corresponding relationship curve between the spring extension and the output stress, which provides a basis for stress adjustment in step three.

[0023] Preferably, in step one, two sheet materials of the same material or size as the sample to be aged are taken, and the centers of the two clamping parts are aligned with their geometric centers and glued firmly; then, multiple samples to be aged are stacked and aligned between the two sheet materials to form a multi-layer sample stack, so that the compressive stress is evenly distributed on each layer of sample to be aged.

[0024] The present invention has the following beneficial effects:

[0025] 1. The present invention utilizes the elastic potential energy of the spring to be converted into continuous mechanical stress applied to the sample to be aged by compressing the spring assembly with a jack, overcoming the problem that existing technologies cannot simulate long-term continuous stress by only using impact loads or short-term vibrations; at the same time, the stress value is monitored in real time by a pressure sensor, and combined with the fine adjustment and self-locking function of the jack, the precise quantitative control and long-term stable maintenance of mechanical stress are achieved, providing a reliable experimental means for the study of mechanical stress aging of insulating materials;

[0026] 2. The present invention uses a rigid frame welded from channel steel as the main stress-bearing body and a mechanical jack and spring assembly as the stress application source. The overall structure is simple and the parts are easy to obtain and process. Compared with the existing electro-thermal-mechanical multi-stress coupling aging test platform, it significantly reduces manufacturing costs and operational complexity, making it easy to promote and use in the laboratory.

[0027] 3. The spring assembly, jack, connecting part, pressure sensor, clamping part and the sample to be aged in this invention form a longitudinal clamping force transmission structure from the bottom wall to the top wall inside the frame, which ensures that the mechanical stress is uniformly and vertically transmitted to the surface of the sample to be aged in the vertical direction, avoids test errors caused by off-center loading or stress deviation, and truly simulates the contact stress borne by the inter-turn insulation of the dry air reactor in actual operation.

[0028] 4. The present invention uses a small-diameter, smooth-polished metal disc as the clamping part, which reduces the contact area while ensuring uniform force. It can apply a large pressure equivalent to the actual contact stress between the reactor turns in a local area on the sample surface, and avoids stress concentration caused by irregular protrusions on the surface, making the aging test conditions closer to the actual working conditions.

[0029] 5. The present invention effectively solves the problem of slippage and disengagement during stress loading caused by unevenness of the jack head by embedding a metal cap with a matching groove at the upper end of the jack as a connecting part, thus ensuring stable stress transmission between the jack and the pressure sensor.

[0030] 6. The spring base of the present invention achieves uniform arrangement and limiting fixation of multiple mold springs through annular grooves and limiting posts. The spring assembly cover cooperates with the top of the spring through the same annular grooves to ensure that each spring is subjected to uniform force and without deviation during the compression process, providing stable elastic force output.

[0031] 7. The test method of the present invention obtains the corresponding curve of spring extension and output stress through stress and extension calibration steps, providing a calibration basis for stress adjustment in the test; the use of multi-layer sample stacking method combined with center alignment operation ensures that the compressive stress is evenly distributed on each layer of sample, which improves the standardization of the test and the repeatability of the results. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of a test device for mechanical stress aging of reactor inter-turn insulation as described in Example 1; Figure 2 This is a schematic diagram of the framework described in Embodiment 1; Figure 3 This is a schematic diagram of the U-shaped channel steel described in Example 1; Figure 4 This is a top view of the mold spring described in Example 1; Figure 5 This is a top view of the spring base described in Embodiment 1; Figure 6 This is a schematic diagram of the spring base described in Embodiment 1; Figure 7 This is a bottom view of the top cover of the spring assembly described in Embodiment 1; Figure 8 This is a schematic diagram of the structure of the upper cover of the spring assembly described in Embodiment 1; Figure 9 This is a schematic diagram of the clamping part described in Embodiment 1; Figure 10 This is a front view of the connecting part described in Embodiment 1; Figure 11 This is a bottom view of the connecting part described in Embodiment 1; Figure 12 This is a schematic diagram of the fit between the clamping part and the sample to be aged as described in Example 1; Figure 13 This is a flowchart of a test method for mechanical stress aging of reactor inter-turn insulation, as described in Example 2.

[0033] In the figure, 0-sample to be aged, 1-frame, 2-clamping part, 3-pressure sensor, 4-connecting part, 5-jack, 6-spring assembly, 61-spring base, 62-spring group, 63-spring group cover, 611-first annular groove, 612-limiting post, 631-second annular groove. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0035] The connections mentioned in this invention are divided into fixed connections and detachable connections. Fixed connections (i.e., non-detachable connections) include, but are not limited to, conventional fixed connection methods such as folded connections, riveted connections, adhesive connections, and welded connections. Detachable connections include, but are not limited to, conventional disassembly methods such as threaded connections, snap-fit ​​connections, pin connections, and hinged connections. When a specific connection method is not explicitly defined, it is assumed that at least one existing connection method can always be found to achieve the function, and those skilled in the art can choose according to their needs. For example, a welded connection can be chosen for fixed connections, and a hinged connection can be chosen for detachable connections.

[0036] Example 1: Combination Figures 1-13 This embodiment describes a test device for mechanical stress aging of inter-turn insulation of a reactor, comprising a frame 1, a clamping part 2, a pressure sensor 3, a connecting part 4, a jack 5, and a spring assembly 6.

[0037] The frame 1 is a rigid frame with internal accommodating space. Specifically, frame 1 uses No. 8 U-shaped channel steel as the base material. Two 400mm long and two 900mm long No. 8 U-shaped channel steels are cut and welded together to form a closed U-shaped rigid frame. During welding, the openings of the U-shaped channel steels face outwards, forming an accommodating cavity inside frame 1 with a height of 400mm and a width of not less than 800mm. Beveling welding is used at the weld joints to enhance the overall structural strength of the frame, ensuring that frame 1 can withstand internal expansion stresses of up to tons without deformation or damage during stress loading tests. All metal parts are treated with rust prevention, and welded parts are guaranteed to have no incomplete welds or missing welds.

[0038] The spring assembly 6 is disposed at the bottom of the receiving space and abuts against the bottom wall of the frame 1.

[0039] Specifically, the spring assembly 6 includes a spring base 61, a spring group 62, and a spring group cover 63. The spring group 62 is fixed between the spring base 61 and the spring group cover 63. The spring base 61 abuts against the bottom wall of the frame 1, and the spring group cover 63 abuts against the lower end of the jack 5.

[0040] The spring assembly 62 consists of multiple mold springs. In this embodiment, the mold springs are red mold springs with an outer diameter of 30mm, an inner diameter of 15mm, and a length of 80mm. These springs can provide huge elastic force in a very small compression space and have stable performance. The ultimate load-bearing capacity is 144kg / spring.

[0041] The spring base 61 is a disc structure, with a first annular groove 611 machined on the side facing the spring assembly 62, and multiple limiting posts 612 are spaced apart in the annular groove; specifically, the spring base 61 is a metal disc with a radius of 65mm and a thickness of 20mm, the width of the first annular groove 611 is 30mm and the depth is 10mm, and a cylinder with a diameter of 7.5mm is left in the groove every 60° as a limiting post 612.

[0042] The upper cover 63 of the spring assembly is a disc structure, and its side facing the spring assembly 62 has a second annular groove 631 identical to that of the spring base 61. Specifically, the upper cover 63 of the spring assembly is a metal disc with a radius of 65 mm and a thickness of 20 mm, and the second annular groove 631 has a width of 30 mm and a depth of 10 mm. The number of mold springs in the spring assembly 62 is the same as the number of limiting posts 612. In this embodiment, the spring assembly 62 consists of 6 mold springs. One end of each mold spring is sleeved on the limiting post 612 of the spring base 61, and the other end is embedded in the second annular groove 631 of the upper cover 63 of the spring assembly, ensuring that the spring is subjected to uniform force and without deviation during compression.

[0043] The jack 5 is positioned above the spring assembly 6, with its lower end abutting against the spring assembly 6 and its upper end abutting against the pressure sensor 3 via the connecting part 4. Specifically, the jack 5 consists of three mechanical jacks capable of bearing a load of 1 ton or more. The jack 5 is small in size, easy to adjust, and adaptable to the internal installation space of the frame 1, allowing for precise height adjustment and providing stable compression power to the spring assembly 62. The jack 5 has a self-locking function, preventing stress attenuation caused by the spring assembly 62 rebounding after the position is locked.

[0044] The connecting part 4 is a metal cap, which is embedded in the upper end of the jack 5. The metal cap has a groove that matches the head of the jack. Specifically, the base material of the metal cap is an iron block with a length and width of 80mm and a thickness of 30mm. A groove with a width of 35mm and a depth of 20mm is milled in the middle of the iron block. The groove size is precisely matched with the head of the jack, ensuring stable stress transmission between the jack 5 and the pressure sensor 3, and effectively solving the problem of slippage and disengagement during stress loading caused by unevenness of the jack head.

[0045] Two clamping parts 2 are arranged vertically opposite each other, and the sample 0 to be aged is clamped between the two clamping parts 2. The clamping part 2 is a smooth metal disc, the upper and lower surfaces of which are polished smooth and the edges are free of burrs. Specifically, the thickness of the smooth metal disc is 5mm to avoid deformation of the insulating sample due to excessive thickness; the diameter is 25mm, which, while adapting to the test electrode, achieves localized high pressure on the sample by reducing the contact area; both surfaces of the disc are finely polished to ensure a smooth surface without bumps or rough lines, and the edges are chamfered to prevent uneven stress on the sample due to irregular protrusions.

[0046] The lower clamping part 2 abuts against the pressure sensor 3, and the upper clamping part 2 abuts against the top wall of the frame 1. The jack 5, connecting part 4, pressure sensor 3, clamping part 2 and the sample 0 to be aged form a force transmission structure within the frame 1 that is longitudinally pressed against the spring assembly 6. The spring assembly 6 applies elastic force to the sample 0 to be aged through this force transmission structure.

[0047] The pressure sensor 3 is a large-range pressure sensor used to monitor and display the mechanical stress value applied to the sample in real time. It is compatible with the ton-level stress loading range of this device. The sensor output end is seamlessly connected to the clamping part to ensure lossless stress transmission.

[0048] The overall assembly process of this device is as follows: Place the finished frame 1 on a horizontal and sturdy test platform, and adjust the frame 1 to a horizontal state to ensure that there is no off-center load during subsequent stress loading; place the spring base 61 at the bottom center of the cavity inside the frame 1, so that the spring base 61 fits snugly against the bottom of the frame 1 without looseness; evenly arrange the 6 mold springs between the first annular groove 611 and the limiting post 612 of the spring base 61, ensuring that each spring is placed vertically without tilting or compression; fasten the spring assembly cover 63 to the top of the 6 springs, so that the top of the springs is embedded in the second annular groove 631, thereby fixing the spring assembly 62 as a whole; place the jack 5 at the center of the spring assembly cover 63, and insert the metal cap into the jack. At the upper end of 5, ensure that the groove of the metal cap fits precisely with the head of the jack; fix the pressure sensor 3 at the center of the top of the metal cap, with the force-bearing surface of the sensor completely in contact with the surface of the metal cap, and the output end of the sensor facing upwards, connecting it to the data display device to ensure that the sensor can collect stress data normally; place the clamping part 2 at the center of the top of the pressure sensor 3, aligning the center of the clamping part 2 with the center of the sensor to ensure uniform stress transmission; place the sample 0 to be aged on the top of the clamping part 2, aligning the geometric center of the sample with the center of the clamping part 2; place the clamping part 2 at the center of the top of the sample 0 to be aged, making the two clamping parts 2 symmetrical, clamping the sample 0 to be aged in the middle, completing the assembly of the entire device.

[0049] The stress adjustment and application process of this device is as follows: Before the test, the stress-extension calibration of the spring assembly 62 is performed using a large-range pressure sensor 3. By gradually compressing the spring assembly 62, the stress values ​​of the pressure sensor 3 under different extensions are recorded, and the spring extension-stress curve is plotted to provide a calibration basis for stress adjustment in subsequent tests. For stress calculation, the local pressure of the sample required for the test is calculated using the pressure formula P=F / S, where P is the target pressure, F is the required mechanical stress, and S is the effective pressure-bearing area of ​​the clamping part, i.e., the smooth metal disc. The area S of the smooth metal disc with a diameter of 25mm is 490.87mm², g is taken as 9.8N / kg, and M is the equivalent load mass. Taking target pressures of 4, 8, and 12MPa as examples, the target stress values ​​to be monitored by the pressure sensor are calculated to be 200kg, 400kg, and 600kg, respectively.

[0050] When using this device, slowly crank the adjusting handle of jack 5 to gradually raise jack 5, pushing the metal cap and pressure sensor 3 upwards, thereby compressing the spring assembly 62. Maintain a constant speed during adjustment to avoid impact on the spring assembly 62 due to rapid compression. Simultaneously, observe the digital display data of pressure sensor 3 in real time and record the extension / retraction of the spring assembly 62. When the monitored value of pressure sensor 3 reaches the target stress value, and the extension / retraction of the spring assembly 62 matches the calibration curve, stop adjusting jack 5. Use the self-locking function of jack 5 to lock the position, preventing the spring assembly 62 from rebounding and causing stress attenuation. After locking jack 5, let it stand for 5-10 minutes, then recheck the monitored value of pressure sensor 3. If there are slight fluctuations, make minor adjustments using jack 5 to stabilize the stress value within the allowable error range of the target value, ensuring that the sample 0 to be aged withstands continuous and stable mechanical stress.

[0051] This embodiment also includes a matching test electrode, which is a brass cylindrical electrode with a diameter of 25mm and a height of 25mm. The electrode edge is machined with a rounded chamfer with a radius of 3mm. By increasing the radius of curvature of the electrode edge, the electric field is dispersed and concentrated, so that an approximately uniform electric field is formed at the contact area between the electrode and the sheet sample. The actual contact area of ​​the electrode is smaller than the mechanical stress pressure area of ​​the sample, which is suitable for electrical performance testing after mechanical stress aging.

[0052] Example 2: Combination Figures 1-13 This embodiment describes a test method for mechanical stress aging of reactor inter-turn insulation. It is based on the test apparatus for mechanical stress aging of reactor inter-turn insulation described in Example 1. This embodiment provides a quantitative test method based on the aforementioned test apparatus. Through precise mechanical calculations, spring calibration, and a life assessment model, it achieves a systematic study of the aging characteristics of inter-turn insulation materials under continuous mechanical stress. The method includes the following steps performed sequentially:

[0053] Before step one, the calibration process must be performed first:

[0054] Electrode and clamping part matching selection: Select the appropriate metal disc diameter of clamping part 2 according to the electrode size required for the test, determine the required aging pressure, and calculate the force that jack 5 needs to provide, as follows:

[0055] In this embodiment, the electrode diameter is 25mm, therefore the clamping part 2 is a smooth metal disc with a diameter of 25mm, and its effective pressure-bearing area S is:

[0056] ; in, D The diameter of the smooth metal disc.

[0057] Target stress calculation and spring strength verification: The ultimate strength of each mold spring is verified to determine the target pressure required for aging. P Calculate the required positive force F for jack 5 according to the pressure formula:

[0058] ;

[0059] Where: g is the gravitational acceleration, taken as 9.8; M is the number of kilograms required for the jack 5 to be determined.

[0060] If the requirements are not met, replace the mold spring with one that has higher mechanical strength or a longer mold spring; if the requirements are met, proceed to step one.

[0061] Based on the above formula, taking target pressures of 4MPa, 8MPa, and 12MPa as examples, the target stress values ​​that the pressure sensor needs to monitor are approximately 200kgf, 400kgf, and 600kgf, respectively, with the gravitational acceleration g taken as 9.8N / kg. The ultimate strength of each mold spring in spring assembly 62 is checked: the ultimate load-bearing capacity of a single red mold spring is 144kg. In this embodiment, spring assembly 62 consists of 6 springs connected in parallel, with a total ultimate load-bearing capacity of 864kg, meeting the maximum force requirement of 600kgf. If the check does not meet the requirements, mold springs with higher mechanical strength need to be replaced, as shown in Table 1.

[0062] Using a large-range pressure sensor 3 in conjunction with a jack 5, the spring assembly 62 is gradually compressed. The stress values ​​of the pressure sensor 3 under different compression amounts are recorded, and a curve showing the relationship between the spring extension ΔL and the output stress F is plotted. Calibration in this embodiment yields spring assembly compression amounts of 5.24 mm, 8.46 mm, and 11.55 mm corresponding to 4 MPa, 8 MPa, and 12 MPa, respectively.

[0063] Spring assembly stress-extension calibration: Using a large-range pressure sensor 3 in conjunction with a jack 5, the spring assembly 62 is gradually compressed, and the stress values ​​of the pressure sensor 3 are recorded at different compression levels. A curve showing the relationship between the spring extension ΔL and the output stress F is plotted. The calibration results in spring assembly compression values ​​of 5.24 mm, 8.46 mm, and 11.55 mm at 4 MPa, 8 MPa, and 12 MPa, respectively, in this embodiment.

[0064] Table 1. Spring compression corresponding to each pressure required for the test.

[0065]

[0066] Sample pretreatment: Taking the polyester film commonly used for inter-turn insulation of dry-type air-core reactors as an example, the polyester film is cut into square samples with a side length of 150mm and a thickness of 0.5mm. The sample surface is checked and ensured to be free of damage, wrinkles and impurities to ensure the reliability of the test results.

[0067] Step 1: Assemble the test sample and the device in sequence. Clamp the test sample 0 between the two clamping parts 2, aligning the geometric center of the test sample 0 with the center of the clamping parts 2. Place the entire assembly inside the frame 1, ensuring that the spring assembly 6, jack 5, connecting part 4, pressure sensor 3, clamping parts 2, and test sample 0 form a longitudinal clamping structure from the bottom wall to the top wall within the frame 1. When multiple test samples need to be stacked, take two sheets of material or size identical to the test sample 0, align the centers of the two clamping parts 2 with their geometric centers, and firmly adhere them. Then, stack multiple test samples 0 between the two sheets, forming a multi-layered test sample stack. Ensure that all test samples have identical material, thickness, and size, so that the compressive stress is evenly distributed on each layer of test sample 0. During multi-test stacking tests, the number of test sample layers should not be excessive to ensure that the compressive stress can be evenly transmitted to each layer, and that the total height of the test samples is suitable for the internal space of the frame 1.

[0068] Step Two: Adjust the screw of jack 5 to apply positive pressure to the material. Slowly raise jack 5, using the connecting part 4 and pressure sensor 3 to push the lower clamping part 2 and the sample 0 to be aged upwards until the upper clamping part 2 presses against the top wall of frame 1. Further adjust jack 5 to compress spring assembly 6, and the pressure sensor 3 will acquire the mechanical stress value in real time. Maintain a constant speed during adjustment to avoid impact on spring assembly 62 due to rapid compression.

[0069] Step 3: When the pressure sensor 3 reaches the preset target stress value, and the extension / retraction of the spring assembly 62 matches the calibration curve, stop adjusting the jack 5 and lock it. Utilize the self-locking function of the jack 5 to lock the position, preventing the spring assembly 62 from rebounding and causing stress attenuation. This allows the elastic potential energy of the spring assembly 6 to be converted into continuous and stable mechanical stress applied to the sample 0 to be aged. After locking the jack 5, let it stand for 5–10 minutes, then recheck the pressure sensor 3's monitoring value. If there are slight fluctuations, make minor adjustments using the jack 5 to stabilize the stress value within the allowable error range of the target value.

[0070] Step 4: Place the assembled and locked frame 1 in the designated aging test environment to conduct a pure mechanical stress aging test or a multi-stress coupled aging test on the insulation material. For example, place the entire device in a high-temperature oven to conduct a thermo-mechanical coupled aging test, or combine it with electrical performance testing equipment to conduct an electro-thermal-mechanical multi-coupled stress aging test. During the test, monitor the value of the pressure sensor 3 regularly. If stress attenuation occurs, adjust the pressure promptly using the jack 5.

[0071] Step 5: Conduct a withstand voltage test using an exponentially decaying oscillating voltage conforming to GB / T1094.6-2011 standard, with a peak value of 21kV and a frequency of 50kHz. Record the cumulative number of times the sample withstands the voltage N(t) until breakdown. At least 12 parallel samples should be tested for each group of samples. After removing the maximum and minimum values, the average value should be taken to ensure the statistical validity of the data.

[0072] Based on the tolerance data obtained under different aging cycles t, the exponential decay model in continuous damage mechanics is used to fit the data, and a life prediction equation under this stress level is established. The exponential decay model is as follows:

[0073] ;

[0074] Where: t is the aging time. This represents the initial number of tolerance cycles. This is the decay rate constant; it is related to the stress level. For the ultimate tolerance number of cycles, the relationship between the fitting parameter k and the applied stress σ is as follows:

[0075] ;

[0076] Where: A is the intrinsic aging rate constant of the material under stress-free conditions, which is related to thermo-oxidative degradation, and is the fitted value in this embodiment. B is the stress sensitivity coefficient, reflecting the accelerating effect of stress on the aging rate. The fitted value in this embodiment is... .

[0077] Combining the above two equations, a complete mechanical stress aging life prediction model is obtained:

[0078] ;

[0079] Using this model, it is only necessary to calculate the initial tolerance number obtained from the experiment. Limit tolerance times By substituting the target stress value σ, the remaining withstand cycles corresponding to any aging time t under that stress level can be predicted. Taking the 12MPa stress level in this embodiment as an example, the model fitting results show that the coefficient of confirmation R² reaches 0.9908, verifying the effectiveness of the model in describing the mechanical stress aging process, as shown in the lifetime fitting results in Table 2. This model can provide a quantitative theoretical basis for the assessment of the remaining lifetime of the inter-turn insulation of dry-type air-core reactors.

[0080] Table 2 Lifetime Fitting Results

[0081]

[0082] During the test, the test platform must remain stable, and collisions or vibrations to the device are strictly prohibited to prevent the jacks from unlocking or components from shifting. Precision components such as metal discs and pressure sensors should be cleaned promptly after use and protected against rust and scratches to ensure the accuracy of subsequent tests. During assembly and adjustment, all components must be aligned centrally to prevent uneven loading, which could lead to excessive localized stress on the frame and deformation, or localized stress concentration on the sample causing test errors. When adjusting the jacks, apply moderate force to avoid over-compressing the spring assembly beyond its ultimate load-bearing capacity, which could result in permanent deformation or damage to the springs.

[0083] After aging is completed, the sample to be aged is removed for subsequent performance testing.

[0084] It should be noted that in the above embodiments, as long as the technical solutions are not contradictory, they can be permuted and combined. Those skilled in the art can exhaust all possibilities based on the mathematical knowledge of permutation and combination. Therefore, the present invention will not describe the technical solutions after permutation and combination one by one, but it should be understood that the technical solutions after permutation and combination have been disclosed by the present invention.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A test apparatus for mechanical stress aging of inter-turn insulation in reactors, characterized in that: It includes a frame (1), a clamping part (2), a pressure sensor (3), a connecting part (4), a jack (5), and a spring assembly (6). The frame (1) is a rigid frame with an internal accommodating space. The spring assembly (6) is located at the bottom of the accommodating space and abuts against the bottom wall of the frame (1); the jack (5) is located above the spring assembly (6), with its lower end abutting against the spring assembly (6) and its upper end abutting against the pressure sensor (3) through the connecting part (4); the two clamping parts (2) are arranged opposite each other, and the sample to be aged (0) is clamped between the two clamping parts (2), with the lower clamping part (2) abutting against the pressure sensor (3) and the upper clamping part (2) abutting against the top wall of the frame (1); The jack (5), connecting part (4), pressure sensor (3), clamping part (2) and the sample to be aged (0) form a force transmission structure in the frame (1) that is longitudinally pressed against the spring assembly (6). The spring assembly (6) applies elastic force to the sample to be aged (0) through the force transmission structure.

2. The test apparatus for mechanical stress aging of inter-turn insulation of reactors according to claim 1, characterized in that: The clamping part (2) is a smooth metal disc, the upper and lower surfaces of which are polished smooth and the edges are free of burrs.

3. The test apparatus for mechanical stress aging of reactor inter-turn insulation according to claim 2, characterized in that: The connecting part (4) is a metal cap, which is fitted into the upper end of the jack (5) and has a groove on the metal cap that is compatible with the head of the jack.

4. The test apparatus for mechanical stress aging of inter-turn insulation of reactors according to claim 3, characterized in that: The spring assembly (6) includes a spring base (61), a spring assembly (62), and a spring assembly cover (63). The spring assembly (62) is fixed between the spring base (61) and the spring assembly cover (63). The spring base (61) abuts against the bottom wall of the frame (1), and the spring assembly cover (63) abuts against the lower end of the jack (5).

5. The test apparatus for mechanical stress aging of inter-turn insulation of reactors according to claim 4, characterized in that: The spring assembly (62) consists of multiple mold springs.

6. The test apparatus for mechanical stress aging of inter-turn insulation of reactors according to claim 5, characterized in that: The spring base (61) is a disc structure, with a first annular groove (611) machined on the side facing the spring assembly (62), and multiple limiting posts (612) are spaced apart in the annular groove; the spring assembly cover (63) is a disc structure, with a second annular groove (631) the same as that of the spring base (61) machined on the side facing the spring assembly (62); the number of mold springs in the spring assembly (62) is the same as the number of limiting posts (612), one end of each mold spring is sleeved on the limiting post (612) of the spring base (61), and the other end is embedded in the second annular groove (631) of the spring assembly cover (63).

7. The test apparatus for mechanical stress aging of reactor inter-turn insulation according to claim 6, characterized in that: The pressure sensor (3) is a large-range pressure sensor used to monitor and display the mechanical stress value applied to the sample in real time.

8. A test method for mechanical stress aging of inter-turn insulation of a reactor, implemented using the test apparatus for mechanical stress aging of inter-turn insulation of a reactor as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Clamp the sample (0) to be aged between the two clamping parts (2), align the geometric center of the sample (0) to be aged with the center of the clamping part (2), and place the whole sample inside the frame (1), so that the spring assembly (6), jack (5), connecting part (4), pressure sensor (3), clamping part (2) and sample (0) to be aged form a longitudinal clamping structure from the bottom wall to the top wall in the frame (1); Step 2: Slowly adjust the jack (5) to rise, and push the clamping part (2) and the sample to be aged (0) located below through the connecting part (4) and pressure sensor (3) to move upward until the clamping part (2) located above presses against the top wall of the frame (1). Further adjust the jack (5) to compress the spring assembly (6), and the mechanical stress value is obtained in real time by the pressure sensor (3). Step 3: When the monitoring value of the pressure sensor (3) reaches the preset target stress value, stop adjusting the jack (5) and lock it, so that the elastic potential energy of the spring assembly (6) is converted into a continuous and stable mechanical stress applied to the sample (0) to be aged. Step 4: Place the assembled and locked frame (1) in the designated aging test environment and carry out a pure mechanical stress aging test or a multi-stress coupling aging test on the insulation material. During the test, monitor the value of the pressure sensor (3) regularly. When stress decay occurs, adjust the pressure by using a jack (5).

9. A test method for mechanical stress aging of inter-turn insulation of a reactor according to claim 8, characterized in that: Before step one, there is also a calibration step, that is, the stress and extension amount of the spring assembly (6) are calibrated in advance using the pressure sensor (3) to obtain the corresponding relationship curve between the spring extension amount and the output stress, which provides a basis for stress adjustment in step three. In step one, two sheet materials of the same material or size as the sample to be aged (0) are taken, and the centers of the two clamping parts (2) are aligned with their geometric centers and glued firmly. Then, multiple samples to be aged (0) are stacked and aligned between the two sheet materials to form a multi-layer sample stack, so that the compressive stress is evenly distributed on each layer of sample to be aged (0).

10. A test method for mechanical stress aging of inter-turn insulation of a reactor according to claim 8, characterized in that: It also includes step five: Samples were removed after a set aging period, and an exponentially decaying oscillating voltage was applied until breakdown. The number of withstand cycles N(t) was recorded, and the data was fitted based on an exponential decay model to evaluate the remaining life of the inter-turn insulation. The exponential decay model is as follows: ； Where: t is the aging time. This represents the initial number of tolerance cycles. This is the decay rate constant; it is related to the stress level. For the ultimate tolerance number of cycles, the relationship between the fitting parameter k and the applied stress σ is as follows: ； Where: A is the intrinsic aging rate constant of the material under no stress, and B is the stress sensitivity coefficient.

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