Glycerol pressure resistance test method and system for the insulation performance of enameled wire

Abstract

The application discloses a glycerol voltage resistance test method and system for the insulation performance of an enameled wire and relates to the technical field of enameled wire insulation performance testing, which comprises the following steps: making a conductive liquid contact with the enameled wire to be tested, so that the conductive liquid naturally forms a ring-shaped coated liquid microzone on the surface of the enameled wire to be tested; and combining a glycerol-salt water mixed conductive liquid with a three-phase contact line stable boundary principle to realize the construction of a local insulation test microzone that can move along the axial direction on the surface of the continuous enameled wire, thereby achieving the point-by-point quantitative characterization of the insulation state of each position along the length direction of the whole wire, converting the evaluation object from the whole wire to the local microzone, obtaining the insulation performance distribution information along the length direction, clearly exposing the isolated defects such as micro-holes, pinholes and uneven insulation layers and their spatial positions that are originally covered by the overall average value, and improving the detection capability and positioning accuracy of the local insulation defects of the enameled wire.

Description

Technical Field

[0001] This invention relates to the field of enameled wire insulation performance testing technology, and in particular to a glycerol withstand voltage test method and system for enameled wire insulation performance. Background Technology

[0002] Enameled wire is the core insulating conductor used in electrical equipment such as electromagnetic coils, transformers, relays, and motors to achieve electromagnetic conversion. The integrity and reliability of its insulation layer directly determine the electrical life and safety threshold of the end product.

[0003] Existing standard testing methods typically employ two enameled wires to form a sample structure in contact and apply voltage to obtain the breakdown voltage result. The results obtained by this type of method mainly reflect the comprehensive withstand voltage level of the enamel film on both sides of the contact area. However, during the winding, insertion, and other processing, a single enameled wire may exhibit local insulation abnormalities due to local scratches, indentations, eccentricity, or micropore defects. Based solely on the above test results, it is difficult to reflect the true withstand voltage state of the insulating enamel film at a local location of a single enameled wire, and it is also difficult to identify weak insulation areas along the length of the wire.

[0004] Therefore, existing technologies still have shortcomings. They cannot construct locally insulating test micro-regions with controllable boundaries and movable point-by-point along the axial direction on the surface of continuous enameled wire without physical segmentation, and obtain information on the distribution of insulation performance along the length direction accordingly. Summary of the Invention

[0005] In a first aspect, the present invention provides a method for testing the glycerol withstand voltage of enameled wire insulation performance, comprising: S1. Bring the conductive liquid into contact with the enameled wire to be tested, so that the conductive liquid naturally forms a ring-shaped liquid micro-region on the surface of the enameled wire to be tested. The conductive liquid is a mixture of glycerol and saturated saline solution, wherein the glycerol and saturated saline solution are mixed in a weight ratio of 85:15, and the saturated saline solution is a saturated solution at room temperature. The length of the liquid micro-region along the axial direction of the enameled wire to be tested is defined by the stable position of the gas-liquid-solid three-phase contact line formed by it together with air and the surface of the enameled wire; S2. Control the wetting state of the conductive liquid and / or the relative position between the enameled wire under test and the conductive liquid, so that the three-phase contact wire is stabilized on the surface of the enameled wire under test, thereby forming a local test micro-area with controllable boundary conditions. S3. Remove the enamel film from one end of the enameled wire to be tested to expose the conductor, and connect the conductor to one end of the high-voltage test circuit. Connect the other end of the high-voltage test circuit to the counter electrode placed in the conductive liquid, so that a test circuit is formed between the conductor, the insulation layer of the enameled wire to be tested, the conductive liquid and the counter electrode. A test voltage is applied to the corresponding region of the local test micro-region to obtain the insulation response parameters of the local test micro-region. S4. Change the relative position between the enameled wire under test and the conductive liquid, so that the local test micro-area moves along the axis of the enameled wire under test, and repeat the insulation response test on the local area at different axial positions. S5. Based on the insulation response parameters of multiple local test micro-areas, obtain the local insulation performance distribution information of the enameled wire under test along the length direction, and identify local insulation weak areas, micropore defect areas and / or conductor surface abnormal areas accordingly.

[0006] Preferably, in S2, the boundary of the local test micro-region is kept stable by adjusting the conductive liquid ratio, temperature, immersion depth of the enameled wire to be tested, relative moving speed, and residence time.

[0007] Preferably, in S2, the boundary stability of the three-phase contact line is controlled by at least one of the following parameters: conductivity, viscosity, liquid level height, and surface tension of the conductive liquid.

[0008] Preferably, in S3, the insulation response parameter includes at least one of the following: Local breakdown voltage, local breakdown time, and local Vt characteristic parameters.

[0009] Preferably, in S3, a boost breakdown test mode is adopted, and the voltage is uniformly increased at a rate of 500V / second until insulation breakdown occurs, and the breakdown voltage value is recorded as the local breakdown voltage of the local test micro-region.

[0010] Preferably, in S3, a constant voltage holding test mode is adopted, a set voltage is applied to the local test micro-area and held, and the time required from the start of voltage application to insulation breakdown is recorded to obtain local Vt characteristic parameters; The set voltage is 4kV to 4.4kV.

[0011] Preferably, before applying the test voltage, a prestressing treatment is also included on the enameled wire to be tested; The prestressing treatment includes at least one of the following: Mechanical bending, tension loading, heat treatment, and heat cycling.

[0012] The present invention also provides a glycerol withstand voltage testing system for the insulation performance of enameled wire, comprising: Conductive liquid containment module, used to contain conductive liquid; The sample carrier module is used to carry the enameled wire to be tested; The high-voltage test module is used to apply a test voltage to the local test micro-area corresponding to the enameled wire under test; One end of the high-voltage test module is electrically connected to the exposed conductor of the enameled wire to be tested, and the other end is electrically connected to the counter electrode placed in a conductive liquid. The counter electrode module includes a counter electrode that comes into contact with the conductive liquid and is used to form a test circuit. The relative displacement control module is used to change the relative position between the enameled wire under test and the conductive liquid, so that the local liquid-covered micro-area naturally formed by the conductive liquid on the surface of the enameled wire under test moves along the axial direction of the enameled wire under test. The data acquisition and analysis module is used to collect insulation response parameters of multiple local test micro-regions and generate local insulation performance distribution information of the enameled wire under test.

[0013] Preferably, the relative displacement control module is used to adjust the immersion depth, moving speed, and dwell time of the enameled wire under test.

[0014] Preferably, the acquisition and analysis module is used to output the local breakdown voltage distribution, local breakdown time distribution, and local anomaly location determination results.

[0015] The beneficial effects of this invention are: This invention combines a glycerol-salt water mixture with the principle of stable boundary of three-phase contact wires to transform the lumped response of traditional whole-section immersion test into a local micro-area insulation test that can move along the axis. It realizes point-by-point scanning and spatial resolution of the insulation state at different positions on the surface of continuous enameled wire, thereby elevating the whole-section fuzzy evaluation to the level of micro-area quantitative evaluation. Unlike the two-wire contact breakdown voltage test, this invention forms a test circuit between a conductive liquid and the outer surface of a single enameled wire under test, thus changing the test object from the combined withstand voltage of the two-sided enamel film to the withstand voltage of the single-sided enamel film insulation. Because the conductive liquid forms a ring-shaped coating on the enameled wire under test in the local test area, it is easier to contact the fine bumps, scratches or local weak points on the surface of the enamel film, thus improving the ability to expose local insulation abnormalities. The testing method provided by this invention effectively solves the inherent limitation of the whole-section glycerol withstand voltage method in being unable to locate local defects, and makes isolated weak areas such as micropores, pinholes, and uneven insulation layers that were originally covered by "overall qualified" visible, thereby improving the detection capability and spatial resolution accuracy of local insulation defects in enameled wires. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0017] Figure 1 This is a flowchart of the glycerol withstand voltage test method for the insulation performance of enameled wire in Example 1; Figure 2 This is a flowchart of the testing system for the insulation performance of enameled wire in Example 1; Figure 3 This is a diagram showing the partial test circuit configuration in Example 1; Figure 4 This is a schematic diagram of the two-level scanning strategy in Example 1. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] It should be noted that the local test micro-region in this invention refers to the local annular coating area formed by the conductive liquid on the surface of a single enameled wire under test. During the test, the high-voltage test circuit is closed through the conductor of the enameled wire under test, the insulation layer corresponding to the local test micro-region, the conductive liquid, and the counter electrode. Therefore, the insulation response parameters obtained by this invention reflect the withstand voltage state of the insulating varnish film of a single enameled wire under test at this local location, rather than the comprehensive withstand voltage result of the varnish film on both sides under the condition of contact between two enameled wires.

[0020] Example 1 Reference Figures 1 to 4 This is the first embodiment of the present invention, which provides a glycerol withstand voltage test method for the insulation performance of enameled wire, used to illustrate the specific implementation in the initial screening of local insulation distribution in continuous wires, including the following steps: A conductive liquid formed by glycerol and saturated saline solution can naturally form a local liquid micro-region with controllable boundaries on the surface of a continuous enameled wire (the enameled wire under test). After applying a test voltage to the corresponding region of the local liquid micro-region, the local insulation response parameters distributed along the length of the enameled wire under test can be obtained, thereby realizing the transformation from fuzzy evaluation of the whole section to quantitative evaluation of the local micro-region. This embodiment can also be used for verification testing during the motor manufacturing design stage. By conducting destructive sampling of samples, it can be confirmed whether there are any abnormalities in the winding equipment, wiring equipment, or the enameled wire used. In this embodiment, a batch of high-insulation enameled wire used for winding of small high-frequency transformers was selected as the test object. The batch of wire was judged to be qualified in the routine whole section withstand voltage sampling inspection. However, in the subsequent customer winding and finished product withstand voltage process, a low proportion of failures occurred, the location of which was not fixed and it was difficult to reproduce. To determine whether this type of failure originates from local micropore defects, weak local insulation areas, or conductor surface abnormalities on the surface of the continuous wire, this embodiment does not physically cut the wire. Instead, a local liquid micro-region formed by the conductive liquid itself and stably defined by its boundary is constructed on the continuous sample line. A withstand voltage test is performed on the local insulation area corresponding to the local liquid micro-region, and the local insulation performance distribution information along the length direction is obtained accordingly.

[0021] In this embodiment, six enameled wires from the same production batch were selected as samples. Each sample was 280 mm long, with a nominal conductor diameter of 0.18 mm. The actual measured outer diameter was 0.246 mm to 0.252 mm. Remove 8mm of the varnish from one end of each sample to expose the conductor for connection to the high-voltage test circuit. The conductive liquid is a mixture of glycerol and saturated saline solution, wherein the glycerol and saturated saline solution are mixed in a weight ratio of 85:15, and the concentration of the saturated saline solution is 28%. In the specific preparation, first add 28g of salt to 72g of deionized water and stir at room temperature to form saturated salt water. Then weigh 567g of glycerin and mix it with 100g of the above saturated salt water. After stirring evenly, let it stand for 30 minutes to remove visible bubbles before use. The testing apparatus includes a high-pressure tester, a micro-liquid supply tank, a relative displacement platform, a counter electrode, and a microscopic imaging unit. The high voltage tester has an output range of 0 to 10 kV, is set to AC mode, has a leakage current protection threshold of 2 mA, and an adjustable boost rate. The top of the micro-liquid supply tank is provided with an annular opening so that the enameled wire to be tested can pass through the opening along the axis and come into contact with the conductive liquid; The relative displacement platform is used to control the immersion depth, pull-up speed, and axial scanning position of the enameled wire under test relative to the conductive liquid. The electrode uses a 0.3mm diameter platinum wire, which is inserted into a local liquid micro-region during testing but does not contact the surface of the enameled wire. It should be noted that, in order to ensure that the aforementioned counter electrode does not contact the enameled wire surface, the tip of the counter electrode is slowly inserted into the local liquid micro-region under the guidance of a micro-imaging unit, so that the radial distance between the tip of the counter electrode and the enameled wire surface is maintained at 0.5mm to 0.8mm. The magnification of the micro-imaging unit is set to 200x to clearly distinguish the relative position of the counter electrode and the enameled wire surface, ensuring that the two do not contact each other; the micro-imaging unit is used to observe the boundary of the liquid micro-region and measure its axial length. The test environment was controlled at 23±1℃ and relative humidity at 45%±5%. In this embodiment, the local liquid micro-regions are formed as follows: First, fix the enameled wire to be tested vertically on the displacement platform so that its center line passes through the annular opening at the top of the micro-supply tank; The aforementioned conductive liquid is pre-added to the liquid supply tank so that the liquid level is 0.4 mm below the upper edge of the annular opening; Control the enameled wire to be tested to move downwards, immerse its end in the conductive liquid to a certain depth, maintain the preset dwell time, and then pull the enameled wire to be tested upwards at a set speed. During this process, the conductive liquid does not form a continuous, unbounded wetting on the enameled wire under test. Instead, it retains a ring-shaped liquid micro-region on its surface that is closed circumferentially and has a limited length along the axial direction. The upper and lower boundaries of this liquid micro-region are defined by the stable position of the gas-liquid-solid three-phase contact line. After the local liquid micro-region is formed, the liquid supply tank is moved down by 2mm to remove it from the direct mechanical constraint of the liquid micro-region. This ensures that the local boundary in subsequent tests comes from the wetting behavior of the conductive liquid itself and the pinning behavior of the contact line, rather than from mechanical clamping, mask blocking or physical segmentation.

[0022] To enable those skilled in the art to implement the present invention, this embodiment first screens parameters for the formation and boundary stability of local liquid micro-regions. After the liquid micro-regions are formed, they are left to stand for 3 seconds, and images are continuously acquired through a microscopic imaging unit to measure the axial length of the liquid micro-regions and the amount of boundary drift in a short time. In this embodiment, the axial length of the liquid micro-region is defined as the distance between the upper and lower three-phase contact lines along the axial direction of the enameled wire under test in the microscopic image. If the boundary position drift within 5 seconds after the formation of the liquid micro-region is no greater than 0.08 mm, and the change in the axial length of the micro-region is no more than 0.10 mm, then the boundary of the local liquid micro-region is determined to be stable and can proceed to the pressure resistance test. The results of liquid micro-region formation and boundary stability screening under different parameter conditions are shown in Table 1.

[0023] Table 1: Screening Results of Liquid Microregion Formation and Boundary Stability

[0024] As shown in Table 1, when the weight ratio of glycerol to saturated saline is 85:15, the liquid temperature is about 23°C, the immersion depth is 1.5 mm, the lifting speed is 0.8 mm / s, and the residence time is 1.0 s, the axial length of the liquid micro-region is about 2.14 mm, and the boundary drift within 5 s is only 0.05 mm. This balances boundary stability and local test window size, making it a suitable preferred formation condition for the subsequent local pressure resistance test in this embodiment. In contrast, when the temperature rises to around 30°C, although the liquid conductivity increases, the liquid viscosity decreases significantly, and the boundary drift increases markedly. When the glycerol ratio decreases to 82 / 18, the liquid fluidity increases, and although local liquid micro-regions can be formed, the boundary retention ability decreases. When the glycerol ratio increases to 88 / 12, although the boundary is stable, the length of the liquid micro-region is too short, which is not conducive to the repeated establishment of subsequent local test windows. Therefore, in this embodiment, the conditions in Group A of Table 1 are finally selected as the formation window for subsequent local scanning tests.

[0025] After determining the preferred formation conditions for local liquid microregions, a local test loop is constructed, specifically: Connect the stripped end of the enameled wire to the output end of the high voltage tester, insert the counter electrode into the local liquid micro-region, and connect it to the other end of the high voltage tester, thereby forming a high voltage test circuit of conductor-enameled wire insulation layer-local liquid micro-region-counter electrode. Since the counter electrode is coupled only to the conductive region corresponding to the local liquid micro-region, and the axial boundary of the local liquid micro-region is defined by the three-phase contact line, the applied voltage acts on the local insulation region of the single enameled wire under test at the corresponding position of the liquid micro-region, rather than on the entire sample wire; in other words, what is measured in this embodiment is the withstand voltage response of the enamel film at this local position of the single enameled wire under test, rather than the combined result of the enamel films on both sides under the condition of contact between two enameled wires.

[0026] In this embodiment, a localized boost breakdown mode is used for initial screening of the sample line. The high-voltage tester is set to AC mode, with a leakage current threshold of 2mA, and the voltage is increased uniformly at a rate of 500V / s until a localized insulation area breaks down. The corresponding voltage value is recorded as the localized breakdown voltage at that location. To balance testing efficiency and location resolution, this embodiment employs a two-stage scanning strategy: First, a local liquid micro-region is formed every 10 mm along the length of the sample line and a first-level scan is performed to obtain the overall distribution of the local breakdown voltage. If the local breakdown voltage at a certain location is more than 0.45kV lower than the median value of the local breakdown voltage in the first-level scan of that sample line, it is identified as a suspected abnormal area, and a second-level fine scan is performed near that location to determine the lowest point and the range of the abnormal area. Secondary fine scanning is preferably performed near suspected abnormal areas with a step size of 1 mm. The significance of adopting this two-stage strategy is that the first-stage scanning is used to quickly establish the local breakdown voltage profile of the entire sample line, and the second-stage fine scanning is used to restore the spatial distribution details of the low-value area, thereby further locating the overall "low value" as a specific local anomaly area.

[0027] In this embodiment, a sample line is selected as a representative sample line, and its effective test area is scanned in the first stage. The suspected abnormal areas identified in the first stage scan are then scanned in the second stage. Meanwhile, another control sample line from the same batch was used to conduct an overall pressure test using the traditional whole-section immersion glycerin pressure resistance method as a comparative example. The results of the partial scanning and the comparison with the whole-section immersion method are shown in Table 2.

[0028] Table 2: Comparison of results between local scanning voltage boosting breakdown and full-section immersion method

[0029] As shown in Table 2, the median local breakdown voltage of the first-stage scan of the sample line is approximately 4.69 kV. In contrast, the first-stage scan results at 110 mm, 120 mm, and 200 mm are significantly lower, thus requiring a second-stage fine scan. After the fine scan, a first local anomaly zone was identified near 112 mm, with a minimum value of 3.98 kV; a second local anomaly zone was identified near 200 mm, with a minimum value of 4.14 kV. In contrast, the traditional whole-section immersion glycerol withstand voltage method only measured a single overall value of 4.07 kV. This single overall value only indicates the presence of a priority failure location in the whole sample line, but it cannot answer whether the sample line has only one anomaly zone, whether there are multiple separate local weak zones, where each anomaly zone is located, or what the differences in severity between the anomaly zones are.

[0030] It should be noted that the 4.07kV measured by the full immersion method reflects the breakdown voltage of the weakest point in the entire wire section, rather than the overall insulation level of the wire. In this embodiment, through local micro-area scanning, the median local breakdown voltage of the sample wire is obtained as 4.69kV. This median value represents the basic insulation level of the entire wire section after excluding isolated defects, which is information that cannot be obtained by traditional methods. The difference between the median value and the lowest value (0.71kV) further quantifies the microscopic non-uniformity of the wire insulation strength. Conversely, this embodiment transforms the overall withstand voltage problem of the entire sample wire section into a series of independent withstand voltage problems at local locations through local test windows formed by local liquid micro-areas, thereby enabling the identification of multiple separate local anomaly areas along the length direction.

[0031] Further analysis of Table 2 reveals that the degradation levels of the first and second abnormal zones are not the same. The lowest value in the first abnormal zone is 3.98 kV, and it is pointed to by two primary scanning points at 110 mm and 120 mm. In the secondary fine scan, the lowest point is located near 112 mm, indicating that this abnormal zone has a certain axial span. The lowest value in the second abnormal zone is 4.14 kV, located near 200 mm, and its overall low value is weaker than that of the first abnormal zone. This shows that the method of the present invention can not only locate the abnormal position, but also distinguish the relative severity between different abnormal zones. Compared with the traditional whole-segment immersion method, the present invention no longer obtains a fuzzy overall result dominated by the "first failure position" in the whole-segment sample line, but a distributed result that can reflect the differences in insulation status in different local areas.

[0032] From the perspective of the test object itself, the traditional whole-span immersion method applies long-scale distributed electrical stress, and the resulting breakdown voltage is essentially close to the minimum response in the local insulation strength distribution of the whole-span sample wire. In this embodiment, the local liquid micro-region formed by the conductive liquid on the surface of the enameled wire under test has its axial boundary defined by the three-phase contact wire, so that the test voltage is limited to the local insulation area corresponding to the liquid micro-region. By changing the relative position between the enameled wire under test and the conductive liquid, this local test window can be moved along the axial direction of the enameled wire under test, thereby realizing point-by-point scanning of the local insulation performance of the continuous wire. Because this invention does not rely on cutting, masking, or mechanical obstruction to define the test window, but relies on the local liquid micro-region formed by the conductive liquid itself on the surface of the enameled wire under test to define the area of ​​electrical stress, its test object changes from "whole-span insulation state" to "local micro-region insulation state", which is also the fundamental reason why this invention can achieve local quantitative evaluation.

[0033] The results of this embodiment also demonstrate that the method has clear engineering feasibility. The conductive liquid ratio, temperature, immersion depth, pull-up speed, and residence time required for the formation of the liquid micro-region can all be directly controlled; the stability of the liquid micro-region boundary has clear criteria; the local test circuit is clearly constructed; and the first-level scanning and second-level fine scanning strategies also have clear execution logic. With the above conditions, those skilled in the art can not only reproduce the formation process of the local liquid micro-region described in this embodiment, but also repeatedly establish local test windows on the surface of similar continuous enameled wire samples, thereby obtaining the local insulation performance distribution along the length direction.

[0034] In summary, this embodiment fully demonstrates that: a conductive liquid formed by mixing glycerol and saturated saline solution can naturally form a locally controlled liquid micro-region on the surface of a continuous enameled wire under specific physical properties and operating parameters; by using this locally controlled liquid micro-region as a local test window and performing a boost breakdown scan, the local breakdown voltage results distributed along the length direction can be obtained; compared with the traditional whole-section immersion glycerol withstand voltage method, this embodiment can identify multiple independent local insulation weak areas and micropore defect areas, thereby realizing the technical transformation from whole-section fuzzy evaluation to local micro-region quantitative evaluation; thus, it can be seen that the present invention not only has clear technical effects, but also has an implementable and feasible engineering basis.

[0035] It should be noted that the physical mechanism of the formation and stabilization of local liquid micro-regions in this embodiment is as follows: When the enameled wire to be tested is pulled out of the glycerol-saline mixture (conductive liquid), the liquid is simultaneously subjected to gravity, viscosity, and the solid-liquid interface force of the enameled wire surface on the liquid. The high viscosity of glycerol (approximately 685 mPa·s at room temperature) causes significant viscous resistance in the liquid film during the lifting process, inhibiting continuous retraction and full coverage of the liquid film. This is a prerequisite for the liquid film to not form a continuous coverage but only remain locally. The addition of saline solution adjusts the solid-liquid interfacial tension between the mixture and the insulation layer of the enameled wire (usually a polymer material such as polyurethane, polyester, or polyesterimide), allowing the liquid to form an appropriate contact angle on the surface of the enameled wire, enabling the three-phase contact wire to be pinned at the microscopic unevenness of the enameled wire surface. After the lifting action stops, the pinning effect and the liquid viscosity force work together to keep the position of the upper and lower three-phase contact line stable for several seconds, thus forming a local liquid micro-region with controllable axial length, whose boundary is defined by the position of the gas-liquid-solid three-phase contact line. The effects of parameters such as temperature, immersion depth, and pull-out speed on boundary stability reflected in Tables 1 and 2 are essentially achieved by changing the balance between the aforementioned viscous forces and interfacial forces.

[0036] Example 2 This embodiment is used to further illustrate that the local liquid micro-regions naturally formed by the conductive liquid on the surface of the enameled wire under test in this invention are not accidental droplet residue areas, but rather local test micro-regions with repeatable boundaries, predictable axial lengths, and reproducible test results can be obtained by controlling the state of the conductive liquid and the relative motion parameters between the enameled wire under test and the conductive liquid. All sample types, conductive liquid compositions, conductive liquid preparation methods, basic test equipment, overall process of local liquid micro-region formation, microscopic imaging observation methods, and high-voltage test circuit connection relationships that are the same as in Example 1 will not be repeated in this embodiment, and can be referred to Example 1.

[0037] This embodiment further explains under what parameter conditions the liquid micro-region can maintain boundary stability during the test, thereby ensuring the comparability of subsequent local breakdown voltage, local leakage current and local Vt parameters.

[0038] If the boundary of the local liquid micro-region cannot be stably maintained, even if the nominal test position is the same, the local insulation area actually subjected to electrical stress will still drift, resulting in large dispersion of the measurement results and weakening the quantitative significance of local scanning. Therefore, the stability of the three-phase contact line boundary is one of the basic conditions for the present invention to transform the whole-section fuzzy withstand voltage evaluation into local micro-region quantitative evaluation.

[0039] In this embodiment, the same batch of high-insulation enameled wire as in Example 1 was selected, and 12 additional sample wires with a length of 220mm were cut as parameter control test sample wires; wherein, one end of each sample wire was stripped of the enamel film and the conductor was exposed in the manner of Example 1.

[0040] During the experiment, the method of Example 1 was still used to form a ring-shaped local liquid micro-region, and the axial length and upper and lower boundary positions of the liquid micro-region were recorded using a microscopic imaging unit.

[0041] To quantify boundary stability, the following evaluation metrics are used in this embodiment: First, the axial length Lm of the liquid micro-region; Secondly, the maximum drift ΔL of the contact line position of the upper and lower three phases within 5 seconds after the formation of the liquid micro-region; Third, the standard deviation (SD) of the length of 10 consecutive liquid micro-regions formed under the same set of parameters; Fourth, the success rate of forming a system that meets the criterion of "contact line drift not exceeding 0.08mm within 5 seconds"; The above indicators can be used to evaluate the instantaneous stability, repeatability, and feasibility of the process window of the liquid microregion.

[0042] To determine a suitable parameter window for implementation, this embodiment focuses on investigating the effects of conductive liquid temperature, immersion depth of the enameled wire under test, pulling speed, residence time, and liquid level on the boundary stability of the local liquid micro-region. In order to reduce the coupling interference between variables, only one control factor was changed in each group of experiments, while the remaining parameters remained at the preferred formation conditions corresponding to Example 1. The boundary stability results of the local liquid micro-region under different parameter conditions are shown in Table 3.

[0043] Table 3: Effects of different control parameters on the boundary stability of local liquid microregions

[0044] It should be noted that, in addition to the temperature, immersion depth, lifting speed, residence time, and liquid level directly listed in the table above, the surface tension of the conductive liquid is also an important parameter affecting the stability of the three-phase contact line boundary. In the glycerol-saline solution mixture used in this invention, the surface tension is mainly determined by the ratio of glycerol to water. The addition of salt further fine-tunes the gas-liquid and solid-liquid interface states. When the glycerol weight ratio is 85%, the surface tension of the mixture at 23°C is approximately 63 mN / m to 67 mN / m. If the glycerol ratio is reduced to 82%, the surface tension will decrease. As the water content increases, the surface tension of the mixture decreases, the liquid tends to spread more on the surface of the enameled wire, the three-phase contact line is less likely to pin, and the boundary drift increases, as shown in the boundary drift of group D (82 / 18) in Table 1, which reaches 0.16 mm. If the glycerol ratio increases to 88%, the surface tension is too high, the droplet contraction tendency increases, and the axial length of the micro-region is shortened to 1.68 mm (group E in Table 1), which is not conducive to the establishment of a local test window. Therefore, controlling the surface tension of the mixture within the above range is one of the important conditions for balancing the micro-region length and boundary stability.

[0045] It should be noted that the repeated operating points are set in Table 3 to verify the repeatability of the boundary stability of local liquid micro-regions under the same formation conditions, thereby confirming the feasibility of this parameter window.

[0046] As shown in Table 3, when the temperature is between 22.8℃ and 26.4℃, the axial length of the liquid micro-region remains between 2.01mm and 2.12mm, the maximum drift within 5s is controlled within 0.09mm, the standard deviation of the repeatability length is not higher than 0.10mm, and the formation success rate is not lower than 90%. This indicates that the viscosity, surface tension, and wetting state of the conductive liquid are still within a range conducive to the stable pinning of the three-phase contact line. When the temperature rises to 29.7℃, the length of the liquid micro-region shortens to 1.92mm, the maximum drift within 5s increases to 0.16mm, and the formation success rate drops to 60%, indicating that the boundary retention ability is significantly weakened after the liquid viscosity decreases. Therefore, in this invention, the temperature of the conductive liquid not only affects its conductivity but also directly affects the formation quality of the liquid micro-region as a local test boundary.

[0047] As shown in Table 3, when the immersion depth is 1.0 mm, the liquid micro-region length is only 1.54 mm. Although the boundary drift is still within an acceptable range, the local test window is too narrow, which is not conducive to the repeated establishment of the subsequent local electric field window. When the immersion depth increases to 1.5 mm, the liquid micro-region length increases to about 2.15 mm, while the maximum drift decreases to 0.04 mm, showing a better balance. When the immersion depth is further increased to 2.1 mm, the liquid micro-region length increases to 2.63 mm, but the maximum drift increases to 0.12 mm, indicating that when the liquid retention is too large, gravity and liquid retraction will weaken the boundary stability. Therefore, the immersion depth should be controlled within a range that balances the micro-region length and boundary stability, rather than being arbitrarily increased.

[0048] As shown in Table 3, when the lifting speed is 0.5 mm / s or 0.8 mm / s, the length of the liquid micro-region is approximately 2.26 mm and 2.14 mm, respectively, and the boundary drift is no greater than 0.05 mm. This indicates that a low to medium lifting speed is beneficial for the liquid to form a smooth, continuous, and clearly defined coating area on the surface of the enameled wire to be tested. When the lifting speed is increased to 1.4 mm / s, the length of the liquid micro-region decreases to 1.98 mm, the boundary drift increases to 0.13 mm, and the success rate decreases to 70%. This shows that an excessively fast lifting speed will cause stronger dynamic retraction when the liquid leaves the liquid surface, making it difficult to stabilize the initial position of the three-phase contact line, thereby weakening the repeatability of the local test micro-region.

[0049] As shown in Table 3, when the residence time is shortened to 0.4 s, the liquid micro-region length decreases to 1.71 mm, and the boundary drift increases to 0.10 mm, indicating that the wetting of the liquid and the enameled wire surface is not sufficient. When the residence time is extended to 1.6 s, the liquid micro-region length increases to 2.31 mm, and the boundary drift can still be controlled at 0.06 mm, indicating that moderate residence is beneficial for the formation of a stable pinning state of the three-phase contact line. The best performance is achieved when the liquid level is 0.4 mm from the upper edge of the opening. When the liquid level is too high or too low, the micro-region length and drift both deteriorate significantly, indicating that the liquid level height can further affect the boundary formation quality by changing the initial meniscus shape and the liquid supply.

[0050] To further verify the influence of boundary stability on the repeatability of local insulation response, this embodiment selects the test conditions with stable boundary conditions and the test conditions with unstable boundary conditions in Table 3 for comparison. When a local liquid micro-region is formed under boundary stability conditions, 10 local voltage boost tests are performed continuously near the same local region. The measured local breakdown voltage is concentrated between 4.58kV and 4.71kV, with an average value of about 4.64kV and a standard deviation of about 0.05kV. Under boundary instability conditions, the distribution of local breakdown voltage measured 10 times expanded to 4.31kV to 4.79kV, with an average value of approximately 4.56kV and a standard deviation of approximately 0.16kV. This indicates that when the three-phase contact line boundary remains stable, the local electrical stress window corresponding to the same area has good repeatability, and the obtained local insulation response parameters can be used for quantitative comparison. Conversely, when the boundary drift is large, even if the nominal test position is the same, the actual pressure area will still shift, resulting in a significant increase in the dispersion of local breakdown results.

[0051] Based on Table 3 and the above repeatability comparison results, this embodiment provides a preferred control window suitable for practical implementation. When implementing this invention, those skilled in the art can control the conductive liquid temperature to 22°C to 26°C, the immersion depth to 1.3mm to 1.7mm, the lifting speed to 0.5mm / s to 0.9mm / s, the residence time to 0.8s to 1.3s, and the liquid level distance from the upper edge of the opening to 0.3mm to 0.5mm, forming a local liquid micro-region with an axial length of approximately 1.9mm to 2.3mm and a maximum boundary drift of no more than 0.08mm within 5s.

[0052] In summary, this embodiment fully discloses and verifies that by adjusting parameters such as the temperature of the conductive liquid, immersion depth, pulling speed, residence time, and liquid level, the local liquid micro-region formed on the surface of the enameled wire by the glycerol / saturated saline solution can be stably controlled. This local liquid micro-region exhibits quantifiable and predictable control laws in terms of axial length, boundary drift, and consistency of repeated formation. Under stable boundary conditions, the insulation response parameters of the same local region show good repeatability, thus supporting the quantitative evaluation of the local insulation performance distribution of continuous sample lines. Therefore, this embodiment provides a stable and feasible boundary condition basis for subsequently obtaining local insulation response parameters using local boost breakdown mode and local Vt mode.

[0053] Example 3 This embodiment is used to further illustrate that, under the boundary stability conditions determined in Embodiment 2, by adopting the local boost breakdown test mode, a local breakdown voltage distribution with spatial resolution can be obtained on the surface of the continuous enameled wire, and the local insulation weak area, micropore defect area and conductor surface abnormal area can be identified accordingly. For all sample types, conductive liquid compositions, conductive liquid preparation methods, local liquid micro-region formation methods, high-voltage test circuit connection methods that are the same as in Example 1, as well as the preferred formation conditions and boundary stability control windows of the local liquid micro-regions that are the same as in Example 2, this embodiment will not repeat them. Please refer to Examples 1 and 2 respectively. Table 2 in Example 1 has already given the basic results of local scanning voltage boosting breakdown and the comparative results with the whole-segment immersion method. Table 3 in Example 2 has already given the parameter conditions required to ensure the stability of the local test window. Therefore, this embodiment further illustrates the ability of the local voltage boosting breakdown mode to identify local anomalies of different types of sample lines.

[0054] In this embodiment, four enameled wire samples from the same production batch were selected as test objects and numbered W1, W2, W3 and W4 respectively. Each sample was 260mm long and was stripped and electrically connected in accordance with the method of Example 1. Local liquid micro-regions were formed according to the preferred boundary control conditions determined in Example 2.

[0055] During testing, the effective scanning area is 240mm in the middle of the sample line. First, a first-level scan is performed with a step size of 10mm. When the local breakdown voltage at a certain test position is more than 0.40kV lower than the median value of the local breakdown voltage at the first-level scan of the sample line, a second-level fine scan is performed with that position as the center and a step size of 1mm within a range of ±4mm.

[0056] The purpose of using the above scanning method is, on the one hand, to quickly obtain the local breakdown voltage distribution profile of the entire sample line with a large step size, and on the other hand, to perform high-resolution rescanning on the local low-value areas to confirm whether they are independent abnormal areas and to determine the axial range of the abnormal areas.

[0057] The local voltage boost breakdown test still adopts the same voltage boosting rule as in Example 1, that is, the high voltage tester is set to AC mode, the leakage current protection threshold is set to 2mA, and the voltage is continuously and uniformly boosted at a rate of 500V / s until the insulation area corresponding to the local liquid micro-region breaks down, and the voltage value at that time is recorded as the local breakdown voltage at that test location. The voltage ramp rate is consistent with the existing glycerol breakdown voltage test conditions. In order to verify whether the local low value area corresponds to the actual surface anomaly, after the local scan is completed, the detected abnormal area is located and marked, and then re-examined using an 80x to 200x stereomicroscope.

[0058] Table 2 in Example 1 shows that, within the same sample line, multiple independent low-value regions can be identified through primary screening and secondary fine scanning. The first abnormal region is concentrated around 111mm to 113mm, with a minimum value of 3.98kV. The second abnormal region is concentrated around 199mm to 201mm, with a minimum value of approximately 4.14kV. In contrast, the corresponding whole-segment immersion method only yields a single overall value of 4.07kV. This result demonstrates that the localized breakdown mode of the present invention can transform the "overall result dominated by the first failure location of the entire sample line" into "multiple distinguishable localized breakdown voltage data along the length direction." Furthermore, this example demonstrates, through comparison between different sample lines, that this mode can not only identify localized anomalies but also distinguish the differences in anomaly modes between different sample lines. Specifically: When sample line W1 was tested using the whole-section immersion glycerol withstand voltage method, its overall breakdown voltage was 4.62kV. When scanned using the local boost breakdown mode of this invention, its median local breakdown voltage was 4.71kV, and the lowest value was 4.53kV, with a difference of only 0.18kV between the median and the lowest value. Furthermore, no independent abnormal areas were detected in either the first-stage scan or the second-stage rescan. Microscopic examination of W1 also revealed no obvious surface abnormalities. This indicates that the local insulation distribution along the length of W1 is relatively uniform, and the local breakdown voltage only exhibits normal fluctuations, without any weak points sufficient to form independent low-value valleys.

[0059] In contrast, when the entire immersion method was used to test sample W2, its overall breakdown voltage was 4.21kV. Judging from the overall value alone, it can only be determined that its overall withstand voltage level is lower than that of W1, but the specific source of the low value cannot be determined. After adopting the local voltage boosting breakdown mode of the present invention, the median local breakdown voltage of W2 was 4.68kV, while the lowest value dropped to 3.97kV. The difference between the median and the lowest value reached 0.71kV, and an independent abnormal area was detected in the range of 112mm to 115mm. When the area was microscopically examined, micropore-like defects were visible on the surface of the varnish film. This result indicates that the insulation of W2 did not decrease generally throughout the entire sample line, but rather there was a significant weak point in the insulation in a local area, which dominated the overall breakdown result of the entire immersion method.

[0060] Sample W3 also exhibited a low overall breakdown voltage, with a full-length immersion breakdown voltage of 4.11 kV. Based solely on the overall value, W3 and W2 might be classified as the same type of "low-voltage sample". However, using the local boost breakdown mode of this invention, the median local breakdown voltage of W3 was 4.64 kV, and the lowest was 3.88 kV, with a difference of 0.76 kV between the median and the lowest. Two separate and independent anomalous areas were detected in the ranges of 86 mm to 89 mm and 193 mm to 196 mm, respectively. Microscopic examination showed that one of them corresponded to a fine scratch, and the other to a local roughness protrusion. Therefore, the failure risk of W3 stems from the coexistence of multiple local anomalous areas, rather than a single weak point, information that the full-length immersion method cannot provide.

[0061] The overall immersion breakdown voltage of sample line W4 is 4.48kV, only 0.14kV lower than that of W1. Judging solely from the overall value, W4 might be considered a sample line that is "slightly low but still close to normal". However, the local boost breakdown mode of this invention shows that the median local breakdown voltage of W4 is 4.69kV, and the lowest value is 4.18kV, with a difference of 0.51kV between the median and the lowest value. An independent abnormal area was detected in the range of 151mm to 153mm. Microscopic examination showed that there was local unevenness of the paint film at this location, accompanied by slight indentation. This indicates that although the overall breakdown value of W4 is not extremely low, a clear local weak area has been formed inside. If this local weak area happens to be at the stress concentration point during subsequent winding, hot pressing, or bending, it may still become the source of terminal failure. Therefore, the local boost breakdown mode described in this invention can not only identify obviously defective samples, but also reveal those samples whose overall value is close to normal but have local risk points.

[0062] As can be seen from the comparison of the different sample lines, the difference between the median value and the minimum value can be used as a characterizing parameter to reflect the uniformity of local insulation distribution. When the difference is small, for example, W1 is only 0.18kV, it indicates that the local breakdown voltage distribution along the length direction is relatively flat, and there are no obvious outlier low-value points. When the difference increases to more than 0.5kV, such as W2, W3 and W4 being 0.71kV, 0.76kV and 0.51kV respectively, it indicates that there are obvious low-value valleys in the local breakdown voltage distribution, corresponding to at least one independent local anomaly area. At the same time, this invention does not use a fixed value of the difference as the only judgment threshold, but combines the median value of the first-level scan, the low-value valley morphology obtained from the second-level fine scan and the microscopic verification results to comprehensively identify local anomalies. The key significance of this processing method is that this invention no longer focuses on a single overall breakdown value, but on the distribution morphology and low-value valley structure of the local breakdown voltage along the length direction of the sample line.

[0063] It should be noted that the microscopic verification results are used to assist in the verification of local low-value areas, while the determination of local abnormal areas is based on the distribution results obtained from local boost breakdown scanning.

[0064] This embodiment also illustrates that, within the boundary stability window given in Embodiment 2, a boost rate of 500V / s is suitable as a uniform test condition for the local boost breakdown mode. On the one hand, this boost rate enables the local insulation area to enter the breakdown judgment state in a short time, ensuring scanning efficiency. On the other hand, its boost process is relatively stable, making the local breakdown voltage results between different test points more comparable. If the boost rate is too low, the single-point test time will be too long, which is not conducive to multi-point scanning on the same continuous sample line. If the boost rate is too high, the local insulation response will not be fully established before breakdown, which may weaken the resolution between different local locations. Therefore, in this embodiment, by using the boundary stability condition determined in Embodiment 2 in conjunction with the 500V / s uniform boost rule, a local breakdown voltage distribution with spatial resolution can be obtained within the actual operable test time.

[0065] In summary, this embodiment fully demonstrates that, under the boundary stability conditions determined in Embodiment 2, by adopting the local boost breakdown test mode, a local breakdown voltage distribution with spatial resolution can be obtained on the surface of a continuous enameled wire. Compared with the full immersion method, this mode can not only identify local insulation weak areas, but also distinguish between the "single local anomaly dominating" and the "multiple local anomalies coexisting" of the sample lines, and can reveal those sample lines where the overall breakdown value is not extremely abnormal but there are already local risk points. Therefore, the localized voltage boosting breakdown mode described in this invention can transform the single overall result of the traditional whole-section withstand voltage method into locally distinguishable insulation distribution data along the length direction, thereby providing a more informative testing method for anomaly screening, defect location, and reliability evaluation of high-insulation enameled wires.

[0066] Example 4 This embodiment is used to further illustrate that, under the boundary stability conditions determined in Embodiment 2, the constant voltage holding test mode can obtain the local breakdown time at different axial positions of the continuous enameled wire, thereby forming a local Vt characteristic distribution, and distinguishing between normal areas and local insulation weak areas accordingly. All sample types, conductive liquid compositions, conductive liquid preparation methods, local liquid micro-region formation methods, high-voltage test circuit connection methods that are the same as in Embodiment 1, as well as the preferred local liquid micro-region formation conditions and boundary stability control windows that are the same as in Embodiment 2, will not be repeated in this embodiment, and will be referred to in Embodiments 1 and 2 respectively. As illustrated in Example 3, under the local voltage boost breakdown mode, different axial positions can exhibit significantly different local breakdown voltage distributions. This example further illustrates that, by using a constant voltage holding method, different local positions can also exhibit significantly different breakdown time distributions, thereby enabling quantitative differentiation of the local insulation lifetime reserves of the same continuous sample line. In this embodiment, two adjacent sample lines cut from the same continuous wire are selected as a group of test samples. The first sample line is used for local anomaly location according to the local voltage boost breakdown method described in Example 3, and the second sample line is used for local Vt test at the same axial coordinate position. To improve the comparability of the two sample lines in axial position, the two sample lines are cut from the same continuous wire in adjacent sections, and their overall distribution trend is confirmed to be consistent through local preliminary screening before testing. The purpose of this method is to avoid performing voltage boost breakdown test first and then constant voltage holding test on the same sample line, thereby preventing the previous breakdown from affecting the subsequent life test, while maintaining the continuity of process state and axial defect distribution by means of adjacent sample lines.

[0067] According to the method of Example 3, a first local abnormal area was identified in the range of 112mm to 115mm on the first sample line, and a second local abnormal area was identified in the range of 199mm to 201mm. At the same time, no independent abnormal areas were detected at the positions of 60mm and 140mm, which can be used as reference positions for local normal areas. Based on this, four axial positions of 60mm, 140mm, 112mm and 200mm were selected as constant pressure holding test points on the second adjacent sample line, of which 60mm and 140mm are used as normal reference points, and 112mm and 200mm correspond to the first and second local abnormal areas, respectively.

[0068] This embodiment uses a constant pressure holding test mode to obtain local Vt characteristic parameters; Before testing, a local liquid micro-region was formed at the target location according to the preferred boundary control conditions described in Example 2, and its boundary was confirmed to meet the stability criterion. Subsequently, the high-voltage tester was preset with a target voltage value. After the local liquid micro-region was formed and stabilized, the stripped conductor of the enameled wire to be tested was connected to the high-voltage output terminal. The electrode was inserted into the local liquid micro-region and connected to the other end of the circuit. Timing was started at the same time as the high-voltage output was started, until local insulation breakdown occurred. The time elapsed from the start of applying the set voltage to the occurrence of breakdown was recorded as the local breakdown time of the local location under the set voltage. If no breakdown occurs after the preset maximum observation time, the test is stopped and the result is recorded as "no breakdown". However, in order to facilitate comparison with the broken-down sample, this embodiment prefers to conduct the test within a voltage window that allows each position to break down within a reasonable time.

[0069] Preliminary tests show that the 4.0kV to 4.4kV range can distinguish between normal and abnormal regions within a reasonable time. Therefore, this example selects this range as the example voltage window for demonstration.

[0070] To ensure comparability of local Vt results across different locations, this embodiment, based on the local boost breakdown results obtained in Example 3, selects three set voltages of 4.0kV, 4.2kV, and 4.4kV as test conditions. The reason for choosing this voltage range is as follows: Firstly, this range is located near the breakdown window of the normal and abnormal regions reflected by the local boost breakdown results. It will not cause all normal regions to fail in a short time, nor will it cause all abnormal regions to exhibit extremely long lifespans, thus facilitating the formation of comparable time differences. Secondly, this range corresponds to the preferred local constant voltage holding test voltage window of the present invention, which facilitates the explanation of the actual application of the local Vt mode of the present invention; For each local location, three adjacent undamaged micro-regions were repeatedly tested at each set voltage. The data listed in Table 4 are the average values ​​of the three tests.

[0071] Table 4: Local Vt Test Results

[0072] Table 4 shows that different local locations exhibit significantly different breakdown time distributions under the same set voltage. Taking 4.0kV as an example, the average breakdown times at the 60mm and 140mm locations in the normal reference zone are 712s and 688s, respectively, both showing relatively long withstand times. However, the average breakdown time at the 112mm location in the first local anomaly zone is only 12.6s, far lower than that in the normal reference zone. The average breakdown time at the 200mm location in the second local anomaly zone is 86s, significantly lower than that in the normal reference zone, but still significantly higher than that at the 112mm location. This result indicates that under the same constant voltage conditions, there are significant differences in lifetime reserves at different local locations, and the severity of different anomalies can be further distinguished. This suggests that the local Vt mode can not only determine whether a local anomaly exists, but also reflect the differences in withstand time between different local anomaly zones under the same voltage.

[0073] When the set voltage is increased to 4.2kV, the average breakdown time in the normal reference area decreases to 264s and 301s, while it decreases to 3.8s at the 112mm position and 14.7s at the 200mm position. It can be seen that as the set voltage increases, the breakdown time at each position decreases, but the decrease is more significant in the abnormal area. The breakdown time at the 112mm position is close to the instantaneous failure range. This result indicates that the local Vt characteristics are highly sensitive to differences in local insulation conditions. In particular, when the set voltage is close to or slightly higher than the local breakdown voltage exhibited by a certain local area in the boost test, the breakdown time at that position will be shortened sharply, thus forming a low-life point that is significantly different from the surrounding normal area.

[0074] When the set voltage was further increased to 4.4kV, the average breakdown times in the normal reference region were 67s and 74s, respectively. Although still significantly higher than in the abnormal region, these times showed a substantial decrease. The average breakdown times at the 112mm and 200mm positions were further shortened to 0.9s and 2.4s, respectively. This result further illustrates that the local Vt mode and the local boost breakdown mode in Example 3 are not independent of each other, but rather mutually corroborate each other in a physical sense: the lower the local boost breakdown voltage, the shorter the breakdown time is usually observed in the constant voltage holding mode. For example, at the 112mm position... For example, it exhibited the lowest local boost breakdown voltage in Example 3, and the shortest local breakdown time in this example, indicating that this location is indeed the weakest local insulation area in the entire sample wire; while the 200mm location is also an abnormal area, its degradation is weaker than that of the 112mm location, regardless of whether it is in the local boost breakdown mode or the local Vt mode; this consistency of "local breakdown voltage - local breakdown time" further proves that the local liquid micro-area test window established by the present invention can truly reflect the differences in different local insulation areas of the continuous wire, rather than being caused by random test errors.

[0075] To further illustrate the difference between the local Vt mode of the present invention and the traditional whole-segment immersion Vt method, this embodiment uses the whole-segment immersion glycerol constant pressure maintenance method to test the control sample line of the same batch as the above sample line. At 4.0 kV, the average breakdown time measured by the full immersion method is approximately 10.9 s; At 4.2kV, the average breakdown time is approximately 2.9s; At 4.4kV, the average breakdown time is approximately 0.8s; It can be seen that the results obtained by the whole-segment immersion method are closest to the data of the 112mm local anomaly area in this embodiment, while they differ significantly from the normal reference area and the second local anomaly area. This indicates that the time value obtained by the whole-segment immersion Vt test is essentially still dominated by the weakest local area that fails first in the whole sample line, reflecting the "first failure time" of the whole sample line, rather than the insulation lifetime distribution of each local area. In contrast, the local Vt mode of the present invention can distinguish the lifetime reserves of different local areas in the whole sample line point by point, thereby transforming the traditional overall weakest point evaluation into a local lifetime distribution evaluation along the length direction.

[0076] This embodiment also demonstrates that the local Vt mode is particularly significant for distinguishing sample lines with "similar overall values ​​but different local states"; in embodiment 3, the overall immersion breakdown voltages of W2 and W3 are both low, but it is impossible to determine whether they are caused by a single local anomaly or multiple local anomalies; the local Vt method of this embodiment can further verify: If a certain line has only a single strong anomaly region, it will show a significantly shorter lifespan than the surrounding area near the corresponding anomaly point, while other locations can still maintain a longer breakdown time. If a certain line has multiple independent abnormal regions, multiple lifetime troughs will appear at multiple axial positions. In other words, the local Vt mode provides another dimension of time domain verification for the local boost breakdown results in Example 3, so that the "local abnormal region" not only has low value characteristics in voltage threshold, but also short-time failure characteristics in lifetime domain; When the two are combined, localized weak insulation areas can be identified more reliably.

[0077] For FIW type enameled wires that require high reliability, knowing only the overall withstand voltage level of the entire sample wire is not enough to support a reliability judgment, because local weak areas may fail first under subsequent winding, hot pressing, welding or operating electrical stress. This embodiment demonstrates through local Vt testing that even if the difference in boost breakdown voltage at different local locations on the same sample line is not extremely large, as long as there are significantly different breakdown times in constant voltage holding mode, it is sufficient to indicate that there are significant differences in the lifetime reserves at these local locations. Therefore, the local Vt test of this invention is not only applicable to defect screening, but also to the classification of local insulation status, thereby providing more granular data for production release, risk identification, and process traceability.

[0078] In summary, this embodiment fully discloses and verifies that: under the boundary stability conditions determined in Embodiment 2, using the constant voltage holding test mode, local breakdown times at different axial positions can be obtained on the surface of continuous enameled wire, thereby forming a local Vt characteristic distribution; compared with the whole-segment immersion Vt method, the local Vt mode of the present invention can distinguish between the normal reference area, the weaker abnormal area, and the weakest abnormal area, revealing the local lifetime differences masked by the whole-segment method; the local boost breakdown results and the local Vt results have good consistency, indicating that the local liquid micro-area test window established by the present invention can truly reflect the local insulation state of the continuous wire; therefore, this embodiment further proves that the present invention can not only realize the measurement of local breakdown voltage distribution, but also realize the measurement of local lifetime distribution, thereby providing an implementable and feasible technical path for the local reliability evaluation of high-insulation enameled wire.

[0079] Example 5 This embodiment is used to further illustrate that, under the boundary stability conditions determined in Embodiment 2, after applying prestress treatment to the enameled wire to be tested, the local voltage boost breakdown mode described in Embodiment 3 and the local Vt mode described in Embodiment 4 are used for testing. This can reveal latent insulation weak areas that are not easily exposed under normal conditions but will evolve into local failure sources under subsequent winding, heating or thermal cycling conditions, thereby realizing the evaluation of the local reliability reserve of continuous enameled wire. All sample types, conductive liquid compositions, conductive liquid preparation methods, local liquid micro-region formation methods, high-voltage test circuit connection methods that are the same as in Example 1, as well as the preferred local liquid micro-region formation conditions and boundary stability control windows that are the same as in Example 2, will not be repeated. Please refer to Example 1 and Example 2 respectively. The local boost breakdown scanning method that is the same as in Example 3 and the local Vt test method that is the same as in Example 4 will not be repeated, and will be referred to Example 3 and Example 4 respectively.

[0080] The purpose of this embodiment is not to prove again that the present invention can identify already formed local abnormal regions, but to further illustrate: For some latent weak areas that have acceptable overall withstand voltage values ​​in the initial state and only show slight low value fluctuations in local scans, but may deteriorate rapidly during actual use due to winding bending, tension loading, thermosetting and operating thermal cycling, this invention can reveal them in advance before leaving the factory or during the process verification stage through a combination of "prestressing treatment and local micro-area testing". Therefore, what is verified in this embodiment is not simply the ability to detect local defects, but the sensitivity of local insulation state to evolution under typical pre-service stress.

[0081] In this embodiment, three adjacent sample lines cut from the same continuous wire are selected and numbered R0, R1, and R2, each with a length of 300 mm. R0 serves as the reference sample line without prestress, and local voltage boosting breakdown scanning and local Vt testing are performed directly according to the methods in Embodiments 3 and 4. R1 is used to apply combined mechanical bending and tension prestress before local testing. R2 is used to apply thermal cycling prestress before local testing. The reason for using adjacent sample lines instead of the same sample line for "before and after prestressing" comparison is that local voltage boosting breakdown testing is itself a local destructive test. If the full-length scan is completed on the same sample line before prestressing, the local damage formed in the previous test will interfere with the subsequent results. Therefore, this embodiment selects adjacent sections of the same continuous wire as grouped sample lines to ensure that the three have the highest possible consistency in the original process state and local defect distribution trend, while avoiding the influence of the previous breakdown on the subsequent evaluation.

[0082] It should be noted that the comparison of the coaxial positions of the adjacent templates is mainly used to illustrate the evolution trend of the local insulation state under prestress, rather than requiring that different templates correspond one-to-one in terms of micro-defect morphology.

[0083] The combined mechanical bending and tensile prestress of R1 is applied as follows: First, bend the sample line around a ceramic cylinder with a diameter of 6mm to form a single 180° bend, then restore it to a near-straight state. Repeat this process 5 times. Then apply a constant tension of 6N at both ends of the sample line and hold for 60s; The reason for using this prestressed combination is that it can better simulate the typical mechanical loads of enameled wire in automatic winding and tension control stations. The thermal cycling prestress of R2 is applied as follows: The sample line was placed in a constant temperature circulating chamber and thermally circulated between 25℃ and 155℃. The heating time was 15 minutes, the high temperature was held for 20 minutes, and the temperature was lowered to 25℃ and held for 15 minutes to complete one cycle. A total of 8 cycles were performed. The reason for using this thermal cycling condition is that it can better simulate the temperature alternation process experienced by high-insulation enameled wire under winding curing and subsequent thermal shock conditions. After the prestress is applied, R1 and R2 are subjected to the same local pressure boost breakdown scan and local Vt test as R0.

[0084] In this embodiment, the local scanning positions are uniformly set to six axial positions: 40mm, 82mm, 113mm, 151mm, 198mm, and 228mm. The selection criteria for these locations are as follows: The 40mm and 228mm areas were used as reference normal zones, which were located in areas where no obvious abnormalities were found in the preliminary screening of the aforementioned transects. 82mm, 113mm, 151mm and 198mm cover the locations that showed different degrees of low value fluctuations or abnormal signs in the previous embodiments, and are used to observe whether these locations deteriorate further under prestressing. At each location, the local boost breakdown voltage was first measured according to the method of Example 3, and then the local breakdown time was measured under a constant voltage holding condition of 4.2 kV according to the method of Example 4. The reason for selecting 4.2kV as the local Vt comparison voltage is that this voltage has been proven in Example 4 to effectively widen the life difference between the normal area and the abnormal area, while not causing the normal area to show instantaneous failure or not fail for a very long time. It is suitable as a unified evaluation condition for the comparison before and after prestressing. The results of the local boost breakdown voltage and local breakdown time at 4.2kV for R0, R1 and R2 at each test location are shown in Table 5.

[0085] Table 5: Comparison of Local Insulation Distribution Before and After Prestressing

[0086] As shown in Table 5, in the reference line R0 without prestress, the 40mm and 228mm positions exhibit typical normal reference zones, with local step-up breakdown voltages of 4.72kV and 4.69kV, respectively, and local breakdown times of 286s and 274s under a constant voltage of 4.2kV, respectively, indicating that these positions have good local insulation reserves. The 113mm and 198mm positions, however, show local abnormal zones. The local step-up breakdown voltage at 113mm is 4.27kV, with a breakdown time of only 19.4s at 4.2kV; the local step-up breakdown voltage at 198mm is 4.36kV, with a breakdown time of 31.7s. This indicates that, without prestress, these two positions constitute the main local weak points in the entire reference line. In contrast, the 82mm and 151mm locations only exhibit slight low-value fluctuations in R0, with localized breakdown voltages still reaching 4.55kV and 4.61kV respectively, and breakdown times of 118s and 143s. Although these are lower than the normal reference range, they have not yet reached the level of a significantly abnormal region. If only the results under the unstressed state are considered, these two locations might be classified as "normal fluctuation range" and not attract special attention. However, after applying combined mechanical bending and tensile prestress, R1 showed significant deterioration at both 82mm and 151mm positions. Specifically: The localized boost breakdown voltage at the 82mm position decreased from 4.55kV in R0 to 4.21kV, while the localized breakdown time at 4.2kV dropped sharply from 118s to 27.9s; the localized boost breakdown voltage at the 151mm position decreased from 4.61kV to 4.32kV, and the breakdown time decreased from 143s to 41.5s; at the same time, the already weak 113mm and 198mm positions deteriorated further, with the localized boost breakdown voltage at the 113mm position dropping to 3.94kV and the breakdown time shortening to 4. The localized breakdown voltage at the 198mm position dropped to 4.08kV, and the breakdown time was shortened to 9.8s. This shows that mechanical bending and tension loading not only exacerbated the insulation degradation of the original abnormal area, but also transformed the 82mm and 151mm positions, which originally showed only slight fluctuations under no prestress conditions, into newly identifiable abnormal areas. This indicates that these two positions already had latent local insulation weaknesses in the initial state, which were not fully exposed when no external mechanical stress was applied, but deteriorated rapidly under simulated winding stress.

[0087] Similarly, after applying thermal cycling prestress, R2 also showed significant degradation at the 82mm and 151mm positions; the local boost breakdown voltage at the 82mm position decreased to 4.29kV, and the local breakdown time at 4.2kV shortened to 39.8s; the local boost breakdown voltage at the 151mm position decreased to 4.37kV, and the breakdown time shortened to 56.2s. Although its degradation was slightly less severe than that at the corresponding position of R1, it still significantly deviated from the slight fluctuation zone level in R0, indicating that thermal cycling can also reduce the potential for degradation. The weak areas became apparent; meanwhile, the two original abnormal areas at 113mm and 198mm continued to deteriorate after thermal cycling. The local breakdown voltage at the 113mm location decreased to 4.02kV and the breakdown time decreased to 6.7s; the local breakdown voltage at the 198mm location decreased to 4.11kV and the breakdown time decreased to 11.4s. Compared with R1, the decrease at these two locations in R2 was slightly slower, but the overall trend was the same, indicating that the original abnormal areas were sensitive not only to mechanical stress but also to thermal cycling stress.

[0088] It is worth noting that although the 40mm and 228mm normal reference areas also showed slight decreases in R1 and R2, the decreases in both local breakdown voltage and local breakdown time were significantly smaller than those at the 82mm, 113mm, 151mm, and 198mm locations. For example, the breakdown time at the 40mm location was 286s in R0, 251s in R1, and 236s in R2; at the 228mm location, it was 274s in R0, 221s in R1, and 208s in R2, still significantly higher than the levels in the abnormal areas and newly manifested abnormal areas. This indicates that the prestress does not act uniformly across the entire sample line, but rather preferentially causes significant deterioration at locations where latent defects or local structural weaknesses already exist. Therefore, this invention, through the combined method of "prestress treatment and local micro-area testing," can identify latent local risk points that were originally hidden in the overall average state in advance, rather than simply causing a synchronous decrease in insulation performance at all locations.

[0089] The results in Table 5 also show that the local step-up breakdown voltage and the local Vt result maintain good consistency before and after prestressing. Taking the 82mm position as an example, in R0, the local step-up breakdown voltage at this position is still 4.55kV, corresponding to a breakdown time of 118s, showing only slight low-value fluctuations. In R1, the local step-up breakdown voltage drops to 4.21kV, and the local breakdown time drops to 27.9s simultaneously. In R2, the local step-up breakdown voltage drops to 4.29kV, and the local breakdown time drops to 39.8s simultaneously. Similarly, the 151mm position also shows the same trend. This indicates that the local step-up breakdown voltage and local Vt lifetime measured by this invention are not two isolated indicators, but rather jointly reflect the withstand capability of the local insulation area in both the voltage and time domains. Because of this dual consistency, this invention can more reliably determine whether a certain local location is a "normal fluctuation" or a "latent weak area".

[0090] To further illustrate the difference between the present invention and the traditional whole-section prestressed pressure resistance evaluation method, this embodiment uses the whole-section immersion glycerol pressure resistance method to test the control sample lines of the same batch as R0, R1 and R2. The results show that without prestress, the overall breakdown voltage of the entire submerged section is approximately 4.23 kV; after applying combined mechanical bending and tension prestress, the overall breakdown voltage drops to approximately 3.98 kV; after applying thermal cycling prestress, the overall breakdown voltage drops to approximately 4.05 kV. Although these overall results reflect the overall decrease in the withstand voltage level of the test line after prestressing, they still cannot reveal whether the overall value decrease is due to the deterioration of the original anomalous area or the activation of new latent anomalous areas; nor can they indicate which specific locations have changed from "slightly fluctuating areas" to "clearly anomalous areas". In contrast, the present invention, through the local test results shown in Table 5, can clearly indicate that the 82 mm and 151 mm locations have changed from the original slightly low-value fluctuation areas to newly manifested anomalous areas under prestressing, while the 113 mm and 198 mm locations have further evolved from the original anomalous areas to significant anomalous areas. This ability to distinguish the local state evolution process is not possessed by the traditional whole-section prestressed withstand voltage evaluation method.

[0091] For enameled wires with high insulation requirements, actual failures are often not determined by the most obvious single defect at the time of manufacture, but by latent local weak points that are not prominent in the initial inspection but deteriorate rapidly after winding, heat curing, or thermal cycling. If only a full-length withstand voltage test without prestress is used, locations like 82mm and 151mm may not be identified. However, these locations may become the real sources of failure when the product enters the customer's process. This embodiment demonstrates that by applying controllable prestress to the sample wire and then conducting local micro-area testing, this invention can reveal these latent risk points in advance, thereby further improving material screening from "static qualification judgment" to "pre-service risk prediction".

[0092] It should be noted that when a sample is subjected to significant tension or elongation strain before testing, microcracks may appear in the paint film due to stress, resulting in an abnormally low local breakdown voltage. Therefore, when an abnormally low value is found in the test results, the abnormality caused by stress-induced microcracks can be distinguished from that caused by paint film eccentricity, mechanical damage, etc., by combining the sample's stress history, retest results, and visual inspection.

[0093] Prestressing treatment can bring latent local insulation weaknesses to light, and its mechanism is as follows: During the manufacturing process, the insulation layer of enameled wire may have tiny structural discontinuities, such as incompletely cured local areas, submicron-sized bubbles, and weak points in the adhesion between the enamel base and the copper conductor. These minute defects have limited impact on insulation performance when not subjected to external force, exhibiting only slight low-value fluctuations in localized breakdown tests. However, when mechanical bending and tension are applied, localized stress concentration occurs within the varnish film. At the location of the minute defects, microcracks propagate or the interface between the varnish base and the conductor debonds due to stress concentration, resulting in a significant decrease in the localized breakdown voltage and breakdown time at that location. When a thermal cycle is applied, the difference in the coefficient of thermal expansion between the varnish film and the copper conductor (copper is approximately 17 × 10⁻⁶) will cause a thermal expansion. -6 / ℃, polyurethane coating film approximately 30×10 -6 / ℃~60×10 -6 The repeated expansion and contraction stresses generated by the prestressing method (at / ℃) cause minute defects to gradually expand over multiple cycles, leading to localized insulation degradation. These two prestressing methods simulate typical operating conditions of enameled wires in practical applications, such as winding bending, tension loading, impregnation curing, and thermal shock during operation. Therefore, the method of this invention can not only detect existing obvious defects but also expose potential weak areas that may evolve into failure sources in subsequent processes or operations.

[0094] In summary, this embodiment fully discloses and verifies that: under the boundary stability conditions determined in Embodiment 2, after applying prestress treatments such as mechanical bending, tension loading, or thermal cycling to the enameled wire under test, and then conducting tests using the local voltage boost breakdown mode and the local Vt mode, latent local insulation weak areas that are not easily exposed under the unstressed state can be revealed; the prestressing effect not only exacerbates the deterioration of the original abnormal area, but also transforms the location that originally only showed slight low-value fluctuations into a clear abnormal area; the consistent trend of local voltage boost breakdown voltage and local breakdown time before and after prestressing indicates that the local liquid micro-area test window established by this invention can truly reflect the evolution process of the local insulation state of continuous wires under typical pre-service stress; therefore, this embodiment further proves that this invention can not only implement static local defect screening, but also implement local reliability reserve evaluation for actual application conditions.

[0095] Example 6 This embodiment is used to further illustrate the specific structure, connection relationship and operation process of a local micro-area testing system for the insulation performance of enameled wire used to implement the aforementioned glycerol withstand voltage test method.

[0096] The same conductive liquid composition, conductive liquid preparation method, type of enameled wire to be tested, formation mechanism of local liquid micro-regions as in Example 1, and the same local liquid micro-region boundary stability control principle as in Example 2 will not be repeated. Please refer to Example 1 and Example 2 respectively. The local boost breakdown test mode that is the same as in Example 3 and the local Vt test mode that is the same as in Example 4 will not be repeated. Please refer to Example 3 and Example 4 respectively. For any prestressed treatment application scenario that is the same as in Example 5, Example 5 can also be referred to.

[0097] The purpose of this embodiment is to illustrate that the present invention is not limited to the manual step-by-step operation of forming, moving, applying voltage to and judging the local liquid micro-region, but can achieve quantitative evaluation of the local insulation performance of continuous sample lines through a well-structured and modularly divided testing system. This system can not only stably form a local test micro-region with a boundary naturally defined by conductive liquid, but also control the movement of the local test micro-region along the axial direction of the enameled wire under test, and automatically collect the local breakdown voltage, local breakdown time and abnormal location judgment results, thereby enabling the present invention to be implemented in an engineering manner.

[0098] The testing system described in this embodiment includes a conductive liquid containment module, a sample carrying module, a high-voltage testing module, a counter electrode module, a relative displacement control module, and an acquisition and analysis module.

[0099] Among them, the conductive liquid containment module is used to contain conductive liquid and provide the liquid supply environment required for the formation of local liquid micro-regions in the enameled wire under test; The sample carrier module is used to clamp and position the enameled wire to be tested, so that it comes into contact with the conductive liquid along a predetermined path; The high-voltage test module is used to apply test voltage to the local insulation area corresponding to the local test micro-area; The counter electrode in the counter electrode module is in contact with the conductive liquid and is used to form a test circuit together with the high voltage test module. The relative displacement control module is used to drive a controllable relative displacement between the enameled wire under test and the conductive liquid, thereby forming and moving a local liquid micro-region on the surface of the enameled wire under test. The acquisition and analysis module is used to receive the voltage, current and time signals output by the high voltage test module, and generate the results of local breakdown voltage distribution, local breakdown time distribution and local anomaly location determination.

[0100] The above modules can be coordinated by a single controller or implemented in a distributed manner by multiple functional units, as long as they can complete the formation of local liquid micro-regions, relative displacement control, local pressure application, and signal acquisition and analysis.

[0101] In this embodiment, the conductive liquid containing module includes a liquid storage cavity and a local liquid supply structure located on its upper part. The liquid storage cavity is used to hold the glycerol and saturated saline solution described in Example 1. The local liquid supply structure is preferably configured as the top area of ​​the liquid supply tank with an annular opening, through which the enameled wire to be tested can pass. The function of this structure is not to mechanically segment the enameled wire to be tested, but to provide initial liquid boundary conditions for the conductive liquid to form a local liquid micro-region with an annular coating on the surface of the enameled wire to be tested during the relative contact, immersion, residence and lifting of the enameled wire to be tested and the conductive liquid. After the local liquid micro-region is formed, the conductive liquid containing module is freed from the direct mechanical constraint of the micro-region. The axial boundaries of the micro-region are defined by the stable position of the gas-liquid-solid three-phase contact line, thereby ensuring that the locality of the test window originates from the liquid itself, rather than the solid segmentation component.

[0102] The sample carrying module includes clamps for fixing both ends of the enameled wire under test and guides for maintaining the linearity of the enameled wire under test. Preferably, the sample carrying module arranges the enameled wire under test vertically so that the relative displacement control module can control the immersion and lifting of the enameled wire under test relative to the conductive liquid containing module. After the enamel film is removed from one end of the enameled wire under test, the conductor is exposed, and this conductor end is connected to the output end of the high-voltage test module through a wire. The sample carrying module is not only used to maintain the stability of the sample wire, but also to ensure that the axial coordinate of the enameled wire under test corresponds one-to-one with the movement coordinate of the relative displacement control module during continuous scanning, so that the acquisition and analysis module can correlate the local insulation response parameters obtained from each test with the specific test location.

[0103] The high-voltage test module can be implemented using a programmable withstand voltage tester or an equivalent high-voltage output device, and it has at least two working modes. The first mode is a boost breakdown test mode, which is used to uniformly boost the voltage at 500V / s as described in Example 3 until the local insulation area breaks down, and record the local breakdown voltage. The second mode is a constant voltage holding test mode, which is used to apply a preset voltage to the local test micro-area as described in Example 4 and hold it, and record the time elapsed from the start of voltage application to the occurrence of local insulation breakdown, thereby obtaining the local Vt characteristic parameters. The local insulation area is the insulating varnish film area at the corresponding position of the single enameled wire under test in the local test micro-area. The high-voltage test module detects the withstand voltage state at this local position through the circuit formed by the conductor, insulating layer, conductive liquid and counter electrode. Preferably, the high-voltage test module also has leakage current threshold detection, abnormal conduction protection and automatic power-off function at the end of the test, so as to ensure that the power supply is cut off in time after the local breakdown occurs and reduce the impact on adjacent areas.

[0104] The counter electrode module includes a counter electrode body and its supporting structure that are in direct contact with the conductive liquid. The counter electrode is preferably made of a thin metal wire or rod and is positioned in the region adjacent to the local liquid micro-region, but does not directly contact the surface of the enameled wire under test. When the high-voltage test module applies a voltage to the exposed conductor end of the enameled wire under test, the electric field path passes sequentially through the conductor, the insulation layer of the enameled wire under test, the local liquid micro-region, and the counter electrode, thereby forming a local test circuit. Since the counter electrode is only coupled to the local conductive region formed by the local liquid micro-region, the voltage applied by the high-voltage test module is limited to the local insulation region corresponding to the liquid micro-region, and will not extend to the distributed pressure-bearing region of the entire sample wire.

[0105] The relative displacement control module is the key module for realizing the local scanning function in this embodiment. This module can be implemented by a linear motor, a stepper motor slide, or a servo displacement platform. It is at least configured to control the immersion depth, lifting speed, dwell time, and axial scanning step distance of the enameled wire under test. Preferably, the relative displacement control module first drives the enameled wire under test to move down relative to the conductive liquid receiving module to a set immersion depth, maintains a set dwell time to promote sufficient wetting of the conductive liquid and the surface of the enameled wire under test, and then moves the enameled wire under test up at a set lifting speed, so that the conductive liquid retains a local liquid micro-region with stable boundary on the surface of the enameled wire under test. Subsequently, the relative displacement control module continues to drive the enameled wire under test to move along the axial direction by a preset step distance, so as to repeatedly form local liquid micro-regions at different axial positions and carry out the test. Through this process, the system can move the local test window point by point along a continuous sample line without physically cutting the enameled wire under test, thereby obtaining the local insulation performance distribution.

[0106] The data acquisition and analysis module is connected to the high-voltage testing module and the relative displacement control module via signals. It receives voltage, current, time, and displacement information from each test location and converts it into local insulation response parameters corresponding to the axial coordinate. Specifically: In the boost breakdown test mode, the acquisition and analysis module records the local breakdown voltage at each location and forms a local breakdown voltage distribution along the length direction; In constant voltage holding test mode, the acquisition and analysis module records the local breakdown time at each location under the set voltage and forms a local breakdown time distribution or local Vt characteristic distribution. When comparing test results at different locations, the data acquisition and analysis module can also determine local abnormal locations based on local median values, minimum values, time troughs, and location clustering. Preferably, the acquisition and analysis module can output at least the following three types of results: First, the local breakdown voltage distribution; Second, the local breakdown time distribution; Third, the results of determining the location of local anomalies; If necessary, these results can be superimposed and compared with the results before and after prestressing in Example 5 to assess whether latent weak areas become apparent under mechanical stress or thermal cycling conditions.

[0107] In this embodiment, the system's operation flow is as follows: First, the glycerol / saturated saline solution described in Example 1 is contained in a conductive liquid containing module; Then, the sample carrying module fixes the enameled wire to be tested, and the relative displacement control module moves the enameled wire to be tested to the starting test position. Next, the relative displacement control module controls the immersion depth, lifting speed and dwell time according to the preferred process window described in Example 2, forming a local liquid micro-region on the surface of the enameled wire to be tested; Subsequently, under the instruction of the acquisition and analysis module, the high-voltage test module enters either the boost breakdown mode or the constant-voltage holding mode to complete the local test at that location. After the test is completed, the relative displacement control module moves the enameled wire under test to the next test position and repeats the above micro-area formation and pressure application actions until the local scan of the entire test wire is completed. In some implementations, in the constant voltage holding test mode, the relative displacement control module can also cooperate with the continuous wire feeding mechanism to make the enameled wire under test continuously pass through the conductive liquid containing module under a preset reference voltage, so as to continuously screen the withstand voltage of a longer wire. Finally, the data acquisition and analysis module integrates the data from all test locations into a local insulation performance distribution map or a list of abnormal locations.

[0108] To verify the engineering feasibility of the system, this embodiment uses the test locations and test modes verified in Embodiments 3 and 4 as examples. Sample lines from the same batch are loaded into the system, and local boost breakdown scanning and local Vt scanning are performed respectively. The test results show that the system can repeatedly form locally liquid micro-regions with stable boundaries during continuous scanning. The results of the local breakdown voltage and local breakdown time distribution at each test location are in good agreement with the results obtained by step-by-step method in Embodiments 3 and 4. For sample lines with significant abnormal areas, the acquisition and analysis module can automatically output local low-value valleys near the abnormal coordinates and provide the abnormal location determination results. For sample lines in Embodiment 5 where local abnormalities are aggravated or newly manifested after prestressing treatment, the system can also output the low voltage and short life characteristics at the corresponding locations. This shows that the method of the present invention can not only be implemented through manual point-by-point testing in the laboratory, but can be implemented in a system device with clear module structure and action logic.

[0109] Compared with traditional full-segment immersion withstand voltage equipment, the fundamental difference of the system described in this embodiment is that traditional equipment is usually only responsible for immersing the entire sample line into the conductive medium and applying the overall voltage. Its output result is dominated by the weakest point that fails first in the entire sample line, so only a single overall value can be obtained. The system described in this embodiment, through the cooperation of the conductive liquid containment module and the relative displacement control module, constructs a local liquid micro-region on the surface of the enameled wire to be tested that can move along the axial direction, thereby transforming the test object from the "overall insulation state of the entire sample wire" to the "spatial resolution state of the local insulation region".

[0110] Because the logic for forming and moving this local test window is implemented at the system level, this invention can truly support the creativity embodied in the aforementioned method embodiments on the device, that is, using the conductive liquid itself to form and define the local test boundary, rather than relying on physical segmentation, mechanical shielding or insulation to define the test area.

[0111] In summary, this embodiment fully discloses and verifies that a system for implementing the aforementioned glycerol withstand voltage test method may include a conductive liquid containment module, a sample carrying module, a high-voltage test module, a counter electrode module, a relative displacement control module, and an acquisition and analysis module. This system can form a local liquid micro-region on the surface of a continuous enameled wire under test, with a boundary naturally defined by the conductive liquid, and control the axial movement of this local liquid micro-region. The high-voltage test module can apply a boost breakdown test voltage or a constant voltage holding test voltage to the corresponding region of this local micro-region. The acquisition and analysis module can output the local breakdown voltage distribution, local breakdown time distribution, and local anomaly location determination results. Therefore, this embodiment further demonstrates that the present invention is not only implementable in terms of method, but also has a clear engineering implementation path at the system device level, and can be used for screening the local insulation performance, locating defects, and evaluating the reliability of continuous enameled wires.

[0112] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for testing the glycerol withstand voltage of enameled wire insulation performance, characterized in that, include: S1. Bring the conductive liquid into contact with the enameled wire to be tested, so that the conductive liquid naturally forms a ring-shaped liquid micro-region on the surface of the enameled wire to be tested. The conductive liquid is a mixture of glycerol and saturated saline solution, wherein the glycerol and saturated saline solution are mixed in a weight ratio of 85:15, and the saturated saline solution is a saturated solution at room temperature. The length of the liquid micro-region along the axial direction of the enameled wire to be tested is defined by the stable position of the gas-liquid-solid three-phase contact line formed by it together with air and the surface of the enameled wire; S2. Controlling the wetting state of the conductive liquid and the relative position between the enameled wire under test and the conductive liquid refers to adjusting the ratio of the conductive liquid, the temperature, the immersion depth of the enameled wire under test, the relative moving speed, and the dwell time to stabilize the three-phase contact wire on the surface of the enameled wire under test, thereby forming a local test micro-area with stable axial boundary. S3. Remove the enamel film from one end of the enameled wire to be tested to expose the conductor, and connect the conductor to one end of the high-voltage test circuit. Connect the other end of the high-voltage test circuit to the counter electrode placed in the conductive liquid, so that a test circuit is formed between the conductor, the insulation layer of the enameled wire to be tested, the conductive liquid and the counter electrode. During the test, the counter electrode is guided by the microscopic imaging unit to be inserted into the local liquid micro-region, but does not contact the surface of the enameled wire. A test voltage is applied to the corresponding region of the local test micro-region to obtain the insulation response parameters of the local test micro-region. S4. Change the axial relative position between the enameled wire to be tested and the conductive liquid, and repeatedly form the local test micro-region at different axial positions of the enameled wire to be tested, and perform insulation response tests on the local insulation areas corresponding to each local test micro-region. S5. Based on the insulation response parameters of multiple local test micro-regions formed at different axial positions, obtain the local insulation performance distribution information of the enameled wire under test along the length direction, and identify local insulation weak areas, micropore defect areas and / or conductor surface abnormal areas accordingly.

2. The glycerol withstand voltage test method for the insulation performance of enameled wire as described in claim 1, characterized in that, In S2, the boundary stability of the three-phase contact line is controlled by at least one of the following parameters: conductivity, viscosity, liquid level, and surface tension of the conductive liquid.

3. The glycerol withstand voltage test method for the insulation performance of enameled wire as described in claim 1, characterized in that, In S3, the insulation response parameter includes at least one of the following: Local breakdown voltage, local breakdown time, and local Vt characteristic parameters.

4. The glycerol withstand voltage test method for the insulation performance of enameled wire as described in claim 3, characterized in that, In S3, a boost breakdown test mode is adopted, and the voltage is uniformly increased at a rate of 500V / second until insulation breakdown occurs, and the breakdown voltage value is recorded as the local breakdown voltage of the local test micro-region.

5. The glycerol withstand voltage test method for the insulation performance of enameled wire as described in claim 3, characterized in that, In S3, a constant voltage holding test mode is adopted, a set voltage is applied to the local test micro-area and held, and the time required from the start of voltage application to the occurrence of insulation breakdown is recorded to obtain the local Vt characteristic parameters; The set voltage is 4kV to 4.4kV.

6. A glycerol withstand voltage test system for enameled wire insulation performance, used to implement the glycerol withstand voltage test method for enameled wire insulation performance according to any one of claims 1 to 5, characterized in that, include: Conductive liquid containment module, used to contain conductive liquid; The sample carrier module is used to carry the enameled wire to be tested; The high-voltage test module is used to apply a test voltage to the local test micro-area corresponding to the enameled wire under test; One end of the high-voltage test module is electrically connected to the exposed conductor of the enameled wire to be tested, and the other end is electrically connected to the counter electrode placed in a conductive liquid. The counter electrode module includes a counter electrode that comes into contact with the conductive liquid and is used to form a test circuit. The relative displacement control module is used to change the relative position between the enameled wire under test and the conductive liquid, so that the local liquid-covered micro-area naturally formed by the conductive liquid on the surface of the enameled wire under test moves along the axial direction of the enameled wire under test. The data acquisition and analysis module is used to collect insulation response parameters of multiple local test micro-regions and generate local insulation performance distribution information of the enameled wire under test.

7. The glycerol withstand voltage test system for the insulation performance of enameled wire as described in claim 6, characterized in that, The relative displacement control module is used to adjust the immersion depth, moving speed, and dwell time of the enameled wire under test.

8. The glycerol withstand voltage test system for the insulation performance of enameled wire as described in claim 6, characterized in that, The acquisition and analysis module is used to output the local breakdown voltage distribution, local breakdown time distribution, and local anomaly location determination results.

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