Shielding insulation breakdown test method and device for cable

Abstract

The invention discloses a shielding insulation breakdown test method and device for a cable, and the method comprises the following steps: preparing a first electrode and a sample which comprises an insulating layer and a first shielding layer, a second shielding layer is attached to the surface, making contact with the side, away from the first shielding layer, of the first electrode. A sample is clamped and located between the first electrode and the second electrode, and the oil bath pan is heated to a preset temperature; according to a preset breakdown point matrix, the first electrode and the second electrode are controlled to move to the corresponding breakdown points for breakdown tests, the thickness values and breakdown voltages of the corresponding breakdown points are detected and recorded, and the breakdown tests of all the breakdown points are completed in sequence; and calculating the breakdown field strength of each breakdown point according to the thickness value and the breakdown voltage, storing each breakdown field strength and generating a test report. The breakdown field strength data obtained by the method can better reflect the insulation performance of the actual cable, and the authenticity of insulation performance evaluation is improved.

Description

Technical Field

[0001] This invention relates to the field of cable shielding insulation breakdown testing technology, and in particular to a method and apparatus for cable shielding insulation breakdown testing. Background Technology

[0002] With the development of ultra-high voltage power transmission technology, the insulation performance of cables with voltage levels of 110kV and above has become the core guarantee for power grid safety. The breakdown field strength of the cable insulation layer (such as cross-linked polyethylene XLPE) is a key parameter for designing insulation thickness and needs to be accurately measured through breakdown tests.

[0003] The ball-electrode test method used in common cable insulation breakdown tests is a classic test method for evaluating the ability of insulation materials to withstand electric fields. It mainly uses two spherical electrodes to create a uniform electric field environment, thereby measuring the breakdown voltage and breakdown characteristics of the insulation material. It is mainly for testing the performance of pure insulation materials. However, actual cables are produced using a three-layer co-extrusion process of shielding-insulation-shielding. The interface state and electric field distribution characteristics between the shielding layer (semi-conductive layer) and the insulation layer have a significant impact on the insulation performance. Existing test schemes do not consider the synergistic effect between the shielding layer and the insulation layer, resulting in test results that cannot truly reflect the insulation performance of the cable in actual operation. Summary of the Invention

[0004] The technical problem that this invention aims to solve is that existing testing schemes only target the performance of pure insulating materials and do not consider the synergistic effect of the shielding layer and the insulation layer, resulting in test results that cannot truly reflect the insulation performance of the cable in actual operation.

[0005] To address the aforementioned technical problems, this invention provides a method for testing the breakdown of shielding insulation for cables, comprising the following steps: A first electrode and a sample are prepared. The sample includes an insulating layer and a first shielding layer disposed on one side of the insulating layer. A second shielding layer is attached to the surface of the first electrode that contacts the side of the insulating layer that is away from the first shielding layer. The sample is clamped and positioned between the first electrode and the second electrode, and the oil bath is heated to a preset temperature. According to the preset breakdown point matrix, the first electrode and the second electrode are controlled to move to the corresponding breakdown point to carry out the breakdown test, and the thickness value and breakdown voltage of the corresponding breakdown point are detected and recorded, and the breakdown test of all the breakdown points is completed in sequence. The breakdown field strength at each breakdown point is calculated based on the thickness value and the breakdown voltage, and each breakdown field strength is stored and a test report is generated.

[0006] Furthermore, the first electrode is prepared using a mold, which includes a pressure seat, a limiting plate, a guide rod, a barrier ring, and a base with a cavity. The limiting plate and the base are connected through the guide rod. One end of the pressure seat is used to connect to the ball electrode, and the other end passes through the limiting plate and is connected to an external hydraulic drive device to drive the ball electrode to move up and down. The barrier ring is used to be placed on the base and fits against the surface of the ball electrode to seal the cavity. The cavity is used to hold the shielding material.

[0007] Furthermore, the fabrication of the first electrode includes the following steps: Install the ball electrode at one end of the pressure seat, and add a preset amount of shielding material into the cavity; The ball electrode is pressed down a first distance at a preset speed, so that a preset gap is formed between the ball electrode and the shielding material; Adjust the barrier ring to seal the cavity, and heat the cavity to a first preset temperature under no-pressure conditions so that the shielding material is completely melted to a molten state; The temperature of the cavity is raised to a second preset temperature, and the ball electrode is pressed onto the shielding material with a pressure of 5-20kN, so that the shielding material is cross-linked and cured on the surface of the ball electrode; After the cavity cools to room temperature, the pressure is released, the barrier ring is removed, and the ball electrode is disassembled. At this time, the shielding material is attached to the surface of the ball electrode to form the first electrode.

[0008] Further, heating the cavity to a first preset temperature under no-pressure conditions to completely melt the shielding material to a molten state includes the following steps: The cavity is heated to 120-150°C under no-pressure conditions; Then keep it at that temperature for 10-15 minutes to allow the shielding material to completely melt to a molten state.

[0009] Further, raising the temperature of the cavity to a second preset temperature, and pressing the ball electrode onto the shielding material with a pressure of 5-20 kN, so that the shielding material crosslinks and solidifies on the surface of the ball electrode, includes the following steps: The ball electrode is pressed onto the shielding material with a pressure of 5-20kN, while the temperature of the cavity is raised to 180-200℃. Keep warm for 20-60 minutes to allow the shielding material to crosslink and solidify on the surface of the ball electrode.

[0010] Furthermore, according to a preset breakdown point matrix, the first electrode and the second electrode are controlled to move to the corresponding breakdown point to conduct a breakdown test, and the thickness value and breakdown voltage of the corresponding breakdown point are detected and recorded before the following steps are taken: According to the preset breakdown point matrix, the first electrode and the second electrode are controlled to move to the corresponding breakdown point; Obtain the thickness value of each of the breakdown points, and extract the maximum and minimum values ​​to calculate the difference; If the difference between the maximum and minimum values ​​is less than 0.05 mm, a subsequent breakdown test is performed; otherwise, the sample is replaced or the breakdown point matrix is ​​reset.

[0011] The present invention also provides a cable shielding insulation breakdown test device, which performs shielding insulation breakdown tests using the cable shielding insulation breakdown test method described above. The cable shielding insulation breakdown test device includes a control unit, a robotic arm, an oil bath, a sample clamp, a moving device, a first electrode, a second electrode, a temperature measuring device, and a housing. The sample clamp and the second electrode are located inside the oil bath. The sample clamp is used to hold the sample, and the second electrode is located below the sample clamp. The moving device is connected to the second electrode to drive the second electrode to move inside the oil bath. The first electrode is suspended above the sample clamp by the robotic arm and moves inside the oil bath by the robotic arm. The temperature measuring device is located inside the oil bath and is used to measure the temperature of the medium surrounding the sample. The outer shell covers the outer periphery of the oil bath and the robotic arm. The control unit is electrically connected to the robotic arm, the moving device, the first electrode, the second electrode, and the temperature measuring device.

[0012] Furthermore, the sample fixture includes a fixed base, a telescopic rod, a clamping frame for clamping the sample, and a clamp. The fixed base is installed at each of the four corners of the inner wall of the oil bath. Each fixed base is connected to a telescopic rod. The end of the telescopic rod away from the fixed base is connected to the corresponding clamp. The four clamps are clamped at the four corners of the clamping frame, and multiple temperature measuring devices are installed in the corresponding clamps.

[0013] Furthermore, the moving device includes a fixed guide rod, a first slider, a second slider, a first driving member, a second driving member, a mounting base, a first connecting rod, and a second connecting rod, and the fixed guide rod is respectively installed on the four side walls of the oil bath. The second electrode is mounted on the mounting base, the first connecting rod and the second connecting rod are inserted into the mounting base, and the first connecting rod and the second connecting rod are arranged perpendicularly. The two ends of the first connecting rod are movably mounted to the corresponding fixed guide rod through the corresponding first slider, and the two ends of the second connecting rod are movably mounted to the corresponding fixed guide rod through the corresponding second slider. The first driving member is connected to a first slider to drive the mounting base to reciprocate along a first direction, and the second driving member is connected to a second slider to drive the mounting base to reciprocate along a second direction, wherein the first direction and the second direction are perpendicular to each other.

[0014] Furthermore, the robotic arm is equipped with a displacement sensor, which is used to detect the displacement distance of the first electrode.

[0015] The cable shielding insulation breakdown test method and apparatus of this invention, compared with the prior art, have the following advantages: This invention, through the construction of a three-layer structure sample consisting of shielding, insulation, and shielding, replicates the physical structure of cables during manufacturing and operation, more closely approximating real-world conditions. The resulting breakdown field strength data better reflects the actual insulation performance of the cable, improving the accuracy of cable insulation performance evaluation. This solves the problem that traditional tests only test pure insulation materials, neglecting the interface effect between the shielding and insulation layers, which leads to test results that cannot accurately reflect the actual insulation performance of the cable during operation. Attached Figure Description

[0016] The present application will be further described in detail below with reference to the accompanying drawings and preferred embodiments. However, those skilled in the art will appreciate that these drawings are drawn only for the purpose of explaining the preferred embodiments and therefore should not be construed as limiting the scope of the present application. Furthermore, unless specifically indicated, the drawings are intended only to conceptually represent the composition or structure of the described objects and may contain exaggerated representations, and the drawings are not necessarily drawn to scale.

[0017] Figure 1 This is a flowchart of the cable shielding insulation breakdown test method provided in the embodiments of the present invention; Figure 2 This is a schematic diagram of the structure of the first electrode provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the mold provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the cable shielding insulation breakdown test device provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the cable shielding insulation breakdown test device provided in this embodiment of the invention, excluding the outer shell and oil bath. In the diagram, 1. First electrode; 11. Second shielding layer; 12. Ball electrode; 2. Second electrode; 3. Oil bath; 4. Mold; 41. Pressure seat; 42. Limiting plate; 43. Guide rod; 44. Barrier ring; 441. Annular barrier block; 442. Connecting block; 45. Base; 451. Cavity; 452. Arc plate; 453. Fixing block; 5. Control unit; 51. Control terminal; 52. Power supply terminal; 53. Automatic control center; 6. Robotic arm; 7. Sample clamp; 71. Fixed seat; 72. Telescopic rod; 73. Clamping frame; 74. Clamp; 8. Moving device; 81. Fixed guide rod; 82. First slider; 83. Second slider; 84. Mounting seat; 85. First connecting rod; 86. Second connecting rod; 9. Temperature measuring device; 10. Outer shell. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0019] like Figure 1 , Figure 2 and Figure 5 As shown, the present invention provides a method for testing the breakdown of shielding insulation for cables, comprising the following steps: S110. Prepare a first electrode 1 and a sample. The sample includes an insulating layer and a first shielding layer disposed on one side of the insulating layer. A second shielding layer 11 is attached to the surface of the first electrode 1 that contacts the side of the insulating layer away from the first shielding layer. In this step, the sample is made into a square sheet of the required thickness using conventional manufacturing methods. The prepared sample is used to simulate the conductor shielding layer-insulation layer structure in the cable. The side of the first electrode 1 that contacts the insulation layer is attached with a second shielding layer 11 so that when the first electrode 1 contacts the sample, a shielding-insulation-shielding structure is formed to simulate the inner shielding-main insulation-outer shielding structure in the actual cable.

[0020] S120. Clamp the sample, with the sample located between the first electrode 1 and the second electrode 2, and heat the oil bath 3 to a preset temperature to simulate the thermal environment during cable operation. S130. According to the preset breakdown point matrix, control the first electrode 1 and the second electrode 2 to move to the corresponding breakdown point to carry out the breakdown test, and detect and record the thickness value and breakdown voltage of the corresponding breakdown point, and complete the breakdown test of all breakdown points in sequence. Understandably, the breakdown point matrix is ​​a pre-defined two-dimensional coordinate list representing multiple locations on the sample surface where breakdown testing is required. For example, a 3×3 grid may contain 9 breakdown points. The number of breakdown points is not specifically limited and can be set according to actual needs. This step involves testing multiple breakdown points on the sample surface according to the pre-defined breakdown point matrix. A voltage is applied to each breakdown point until the sample breaks down, indicating insulation failure at that point, and the corresponding data is recorded.

[0021] S140. Calculate the breakdown field strength at each breakdown point based on the thickness value and breakdown voltage, store each breakdown field strength and generate a test report.

[0022] This step uses the formula: Breakdown field strength = Breakdown voltage / Thickness value to calculate the breakdown field strength (in kV / mm) at each breakdown point, stores all relevant data, and automatically generates a test report to reflect its insulation performance for production design purposes.

[0023] Based on the above steps, this embodiment constructs a three-layer structure sample of shield-insulation-shield, which restores the physical structure of the cable during manufacturing and operation, and is closer to the real working conditions. The resulting breakdown field strength data can better reflect the insulation performance of the actual cable, improve the authenticity of the cable insulation performance evaluation, and solve the problem that traditional tests only test pure insulation materials and ignore the interface effect between the shielding layer and the insulation layer, which leads to the test results not being able to truly reflect the insulation performance of the cable in actual operation.

[0024] like Figure 3 As shown, the first electrode 1 is prepared using a mold 4. The mold 4 includes a pressure seat 41, a limiting plate 42, a guide rod 43, a barrier ring 44, and a base 45. The base 45 serves as the base of the mold 4 and has a cavity 451 for placing the shielding material. The limiting plate 42 and the base 45 are connected by the guide rod 43 to form a frame. One end of the pressure seat 41 is used to connect to the ball electrode 12, and the other end passes through the limiting plate 42 and is connected to an external hydraulic drive device. Under the action of the hydraulic drive device, the pressure seat 41 can provide a controllable pressure of 0-50kN to transmit external driving force to the ball electrode 12. While driving the ball electrode 12 to move up and down, it can also be used to contact and press the shielding material, thereby pressurizing and crosslinking the shielding material in the cavity 451. The barrier ring 44 is placed on the base 45 and fits against the surface of the ball electrode 12 to seal the cavity 451, forming a sealed molding space to prevent the shielding material in the cavity 451 from leaking.

[0025] Based on the above structure, the mold 4 in this embodiment serves as a pressurizable electrode forming device. Through a combination of mechanical structure and hydraulic drive, it melts the shielding material and performs pressurized cross-linking with the ball electrode 12 to prepare a first electrode 1 with a second shielding layer 11 on its surface. Understandably, the shielding material is a semi-conductive material used to improve the electric field distribution, such as a vinyl copolymer material with added semi-conductive carbon black; the ball electrode 12 is a metal sphere of the same material as the second electrode 2 used in the shielding insulation breakdown test, such as brass; the bottom of the ball electrode 12 is connected to the pressure seat 41 via threads for easy assembly and disassembly.

[0026] In some embodiments, the limiting plate 42 can be a metal block, which can be adjusted in height by setting a corresponding locking position on the guide rod 43, or it can be driven by an external driving device to move along the height direction of the guide rod 43, and the position of the electrode descent can be controlled by a preset height requirement, and the thickness of the second shielding layer 11 can be controlled in conjunction with the cavity 451, with the adjustment range preferably being 0.1-2mm.

[0027] Furthermore, the barrier ring 44 is made of a high-temperature resistant insulating material, such as polytetrafluoroethylene (PTFE). It consists of four quarter-ring barrier blocks 441 and four connecting blocks 442. After the ball electrode 12 is lowered, the size of the barrier ring 44 can be adjusted through the connecting blocks 442 to make it fit tightly against the surface of the ball electrode 12. Understandably, the connecting blocks 442 are hollow structures, with both ends of the ring barrier blocks 441 located within these hollow structures. They are locked and fixed by bolts connected to the threaded holes at the ends of the ring barrier blocks 441, or by snap-fit ​​connections. When the size of the barrier ring 44 needs to be adjusted, the two ends of the ring barrier blocks 441 are pulled out of or inserted into the hollow structure to match the diameter of the ball electrode 12. Understandably, since the range of diameter variation is small, the curvature change caused by the radius is negligible here.

[0028] Similarly, cavity 451 is a hemispherical groove structure composed of four arc-shaped plates 452 and four fixing blocks 453. By pulling out the four fixing blocks 453, the cavity 451 can be enlarged while the arc-shaped plates 452 hidden inside are pulled out, thereby adjusting the internal size of cavity 451 and thus the thickness of the shielding material. The inner wall of cavity 451 is polished to prevent material adhesion. Since the thickness variation range of the shielding material is small, only on the order of mm, the change in spherical curvature caused by the radius is negligible here. In actual operation, the height of the limiting plate 42 and the internal size of cavity 451 are adjusted by determining the thickness of the second shielding layer 11.

[0029] Further, the preparation of the first electrode 1 includes the following steps: S111, Install the ball electrode 12 at one end of the pressure seat 41, and add a preset amount of shielding material into the cavity 451; The spherical electrode 12 in this step is the core conductor for the subsequent formation of the first electrode 1. The shielding material is used to cover the surface of the spherical electrode 12, which plays a role in homogenizing the electric field and providing insulation shielding. By setting a preset amount of shielding material, the coating thickness is ensured to be controllable, avoiding excessive or insufficient coating. During the sample preparation process, the center of the spherical electrode 12 after it descends coincides with the center of the barrier ring 44 and the center of the hemispherical groove of the cavity 451.

[0030] S112, the ball electrode 12 is pressed down a first distance at a preset speed, so that a preset gap is formed between the ball electrode 12 and the shielding material; In this step, the ball electrode 12 is slowly pressed down to near the surface of the shielding material, so that a preset distance gap is maintained between the ball electrode 12 and the shielding material, so that the shielding material can flow and fill after it forms a molten state, preventing the generation of bubbles or voids and ensuring that the final coating layer thickness is uniform.

[0031] S113. Adjust the barrier ring 44 to seal the cavity 451, and heat the cavity 451 to the first preset temperature under no pressure so that the shielding material is completely melted to a molten state. In this embodiment, the pressureless state means that the ball electrode 12 does not apply pressure to the shielding material so that the shielding material can melt to a molten state; in addition, the first preset temperature is usually slightly higher than the melting point or softening point of the shielding material so that it becomes a melt with good fluidity, such as the first preset temperature being 5°C higher than the melting point or softening point of the shielding material.

[0032] It should be noted that the side of the barrier ring 44 facing the cavity 451 has an inverted triangular structure. During pressurization, the shielding material is compressed against this inverted triangular structure, which allows the barrier ring 44 to fit more closely to the ball electrode 12, creating a sealed high-pressure environment. In addition, a flexible sealing layer is embedded in the wall of the barrier ring 44. This flexible sealing layer is made of fluororubber and can adaptively fill the gap between the ball electrode 12 and the cavity 451 as the shielding material flows during pressurization, preventing the shielding material from overflowing and causing deviations in the thickness of the second shielding layer 11.

[0033] S114. The temperature of the cavity 451 is raised to the second preset temperature, and the ball electrode 12 is pressed onto the shielding material with a pressure of 5-20kN so that the shielding material is cross-linked and cured on the surface of the ball electrode 12. This step promotes the cross-linking reaction by heating and applies pressure to ensure that the shielding material adheres tightly to the surface of the ball electrode 12, thereby eliminating the interfacial gaps between the two and improving the adhesion of the shielding material, ultimately forming a strong second shielding layer 11. The pressure range of 5–20 kN can both compact the material and prevent damage to the ball electrode 12.

[0034] S115. After the cavity 451 cools to room temperature, the pressure is released, the barrier ring 44 is pulled out and the ball electrode 12 is disassembled. At this time, the shielding material is attached to the surface of the ball electrode 12 to form the first electrode 1.

[0035] This step stabilizes the cross-linked structure through cooling, followed by depressurization and disassembly of the ball electrode 12. At this point, the shielding material has firmly adhered to the ball electrode 12 to form the second shielding layer 11.

[0036] This embodiment achieves the coating and molding of shielding material on the surface of ball electrode 12 by controlling temperature, pressure and material phase change, so as to obtain a first electrode 1 with a second shielding layer 11 on the surface. When the first electrode 1 comes into contact with the sample, a shielding-insulation-shielding structure is formed to simulate the inner shielding-main insulation-outer shielding structure in the actual cable.

[0037] Further, heating the cavity 451 to a first preset temperature under pressureless conditions to completely melt the shielding material to a molten state includes the following steps: S1131. Heat the cavity 451 to 120-150℃ under no-pressure conditions; This step uses a heating device to raise the temperature of the entire cavity 451 to the range of 120℃-150℃. At this temperature, the material begins to flow and exhibits good wettability. Simultaneously, the upper temperature limit is controlled below 150℃ to prevent the organic shielding material from degrading or volatilizing due to overheating. Excessive temperature can easily lead to material aging. Understandably, the specific temperature can be adjusted according to the characteristics of the shielding material.

[0038] S1132, then keep warm for 10-15 minutes to allow the shielding material to completely melt to a molten state.

[0039] The shielding material may be thick and the internal heating may be delayed. After reaching the target temperature, this step should maintain the temperature for 10 to 15 minutes. The holding time ensures that the heat is fully conducted to the central area to achieve overall melting, so that the shielding material forms a melt with good fluidity. The surface tension of the material in the molten state allows it to spread naturally, preparing for the cross-linking reaction and helping to uniformly coat the ball electrode 12 in the subsequent process. If the holding time is too long, the material may age or cross-link prematurely, affecting the final performance.

[0040] Further, raising the temperature of the cavity 451 to a second preset temperature, and pressing the ball electrode 12 onto the shielding material with a pressure of 5-20 kN, so that the shielding material crosslinks and solidifies on the surface of the ball electrode 12, includes the following steps: S1141, the ball electrode 12 is pressed onto the shielding material with a pressure of 5-20kN, and at the same time the temperature of the cavity 451 is raised to 180-200℃; With the shielding material already in a molten state, an axial pressure of 5-20 kN is simultaneously applied (pressed downwards through the ball electrode 12) to force the molten shielding material to more tightly wrap the surface of the ball electrode 12, eliminating interfacial gaps or micropores and improving adhesion and interfacial bonding strength. The cavity 451 is then further heated to 180°C to 200°C, at which temperature the material transforms from a flowable melt into a non-melting solid. It should be noted that this pressure and heating step is performed simultaneously, not sequentially.

[0041] Understandably, if the pressure is too low, the shielding material may not be properly coated, which could lead to voids or delamination; if the pressure is too high, the ball electrode 12 or the equipment may be damaged.

[0042] S1142, keep warm for 20-60 minutes to allow the shielding material to crosslink and solidify on the surface of the ball electrode 12.

[0043] Since the cross-linking reaction requires sufficient time to achieve a high conversion rate, maintain this state for 20 to 60 minutes at a constant temperature of 180℃-200℃ and pressure to ensure the cross-linking reaction is fully completed. Insufficient time will result in under-cured material with low mechanical strength. The specific time can be adjusted according to the material; thinner samples can use a shorter time, while thicker samples require a longer time.

[0044] This application employs a pressureless melting method followed by a 120-150℃ heat treatment to transform the shielding material into a molten state. Subsequently, a cross-linking and curing process involving 5-20kN pressure and 180-200℃ heat treatment is used to firmly attach the shielding material to the surface of the ball electrode 12, forming the first ball electrode 12 with an electrode-shielding layer structure. This achieves precise control of the shielding layer thickness (e.g., 0.1-2mm), laying the foundation for simulating the actual structure of a cable.

[0045] Furthermore, according to the preset breakdown point matrix, the first electrode 1 and the second electrode 2 are controlled to move to the corresponding breakdown points to conduct a breakdown test, and the thickness value and breakdown voltage of the corresponding breakdown points are detected and recorded. This process also includes: S131. According to the preset breakdown point matrix, control the first electrode 1 and the second electrode 2 to move to the corresponding breakdown point; This step automatically controls the first electrode 1 and the second electrode 2 to move to the designated breakdown point, thereby achieving automated multi-point testing, avoiding human error, and improving testing efficiency and coverage.

[0046] S132. Obtain the thickness value of each breakdown point, and extract the maximum and minimum values ​​to calculate the difference. At each breakdown point, the actual thickness of the sample at that breakdown point is calculated by controlling the moving distance of the first electrode 1, and a set of thickness data is obtained. Then, the maximum and minimum thicknesses in this set of data are found, and their difference, i.e. the thickness fluctuation range, is calculated to evaluate the thickness uniformity of the sample in the test area.

[0047] Understandably, the breakdown voltage of a material is closely related to its thickness; generally, the thicker the material, the more difficult it is to break down. If the thickness difference is too large, the breakdown voltage at different points will be incomparable, affecting the experimental conclusions. The thickness value can be obtained by measuring it with a displacement sensor. There are no particular limitations on the measurement method here, as long as it can achieve the measurement of the thickness value at the breakdown point.

[0048] S133. If the difference between the maximum and minimum values ​​is less than 0.05 mm, then proceed with the subsequent breakdown test; otherwise, replace the sample or reset the breakdown point matrix.

[0049] This step involves setting a thickness tolerance threshold. If the difference between the maximum and minimum values ​​does not exceed the thickness tolerance threshold, the sample is considered to meet the requirements and the breakdown test can continue. Otherwise, the sample is considered unqualified or the current test point selection is unreasonable, and a new sample or the test point position needs to be adjusted (e.g., avoiding edges or defect areas).

[0050] This embodiment uses the above steps to perform a self-testing procedure for the breakdown point thickness, ensuring that only samples that meet the thickness uniformity requirements enter the formal testing stage. This improves the reliability of the test data and avoids errors during sample preparation that could lead to significant thickness non-uniformity in a particular insulating material sample, resulting in obvious differences in the thickness of each breakdown point. For example, some points may have a thickness of 0.1-0.2 mm, while others may have a thickness of 0.2-0.3 mm, which could affect the test results.

[0051] like Figure 4 and Figure 5 As shown, the present invention also provides a cable shielding insulation breakdown test device, which performs shielding insulation breakdown tests using the cable shielding insulation breakdown test method described above. This cable shielding insulation breakdown test device includes a control unit 5, a robotic arm 6, an oil bath 3, a sample clamp 7, a moving device 8, a first electrode 1, a second electrode 2, a temperature measuring device 9, and a housing 10. The oil bath 3 provides a constant-temperature, insulating, and stable liquid environment, such as transformer oil, to simulate the high-temperature environment that cables may encounter in actual operation. Transformer oil itself has high dielectric strength, which prevents premature discharge of the first electrode 1 and the second electrode 2 in non-sample areas and facilitates uniform heat transfer, ensuring uniform heating of the sample. The temperature measuring device 9 is located inside the oil bath 3 and is used to measure the temperature of the medium surrounding the sample (i.e., the transformer oil), ensuring that the test is conducted under the temperature conditions specified in the standard.

[0052] In this embodiment, the sample clamp 7 and the second electrode 2 are located inside the oil bath 3. The sample clamp 7 is used to hold the sample, ensuring its stable position during the test and avoiding test errors caused by movement. The second electrode 2 is located below the sample clamp 7, and the moving device 8 is connected to the second electrode 2 to drive the second electrode 2 to move within the oil bath 3. The first electrode 1 is suspended above the sample clamp 7 by a robotic arm 6, which moves within the oil bath 3, causing the first electrode 1 to move up and down or horizontally within the oil bath 3. This ensures that the first electrode 1 can accurately align with the breakdown point and safely contact or remove the sample before and after the test. High voltage is applied to both sides of the sample by the first electrode 1 and the second electrode 2 to form an electric field. Together, they constitute a test circuit. When the voltage rises to a certain value, if the sample insulation fails, breakdown occurs, and the current increases sharply. This embodiment adjusts the distance or relative position between the first electrode 1 and the second electrode 2 to accommodate samples of different thicknesses and achieves coordinated alignment of high and low voltage electrodes, ensuring the positional accuracy (±0.01mm) for multi-point testing. The first electrode 1 is detachably mounted on the robotic arm 6, and the second electrode 2 is detachably mounted on the moving device 8. The metal rods connected to the first electrode 1 on the robotic arm 6 and the first electrode 1 on the moving device 8 are used to conduct electricity and provide voltage. The metal rod on the high-voltage side is connected to the high-voltage power supply, and the metal rod on the low-voltage side is directly grounded. The fault current is quickly discharged through the low-impedance path, which can clamp the potential of the outer casing 10 to zero and avoid the risk of electric shock to personnel.

[0053] The outer casing 10 is installed around the oil bath 3 and the robotic arm 6, serving as a safety protection and environmental isolation layer. The casing can be made of an insulating and transparent material to allow observation of the test process and timely detection and handling of any emergencies. The control unit 5 is electrically connected to the robotic arm 6, the moving device 8, the first electrode 1, the second electrode 2, and the temperature measuring device 9 to set test parameters such as voltage, temperature, and electrode movement speed, and to collect data such as the voltage, temperature, and breakdown point thickness at the moment of breakdown.

[0054] This device uses automated control to conduct high-voltage breakdown tests on samples under simulated actual working conditions, thereby evaluating the quality and reliability of cable insulation materials and providing data support for cable design and production process improvement.

[0055] Furthermore, the sample fixture 7 includes a fixed base 71, a telescopic rod 72, a clamping frame 73 for clamping the sample, and a clamp 74. Fixed bases 71 are installed at the four corners of the inner wall of the oil bath 3 as support starting points, forming a symmetrical support structure. Each fixed base 71 is connected to a telescopic rod 72. The end of the telescopic rod 72 away from the fixed base 71 is connected to the corresponding clamp 74. The four clamps 74 are clamped at the four corners of the clamping frame 73 to ensure that the clamping frame 73 is centered and stable. The clamping frame 73 is divided into upper and lower layers. During the test, the sample is clamped and fixed between the two layers. Multiple temperature measuring devices 9 are installed on the corresponding clamps 74 to monitor the oil temperature around the sample in real time. The data is synchronized to the control unit 5 to ensure temperature uniformity and test accuracy. The number of temperature measuring devices 9 is preferably four, and the temperature measuring devices 9 are temperature sensors with an accuracy of ±0.1℃.

[0056] Understandably, the clamping frame 73 of the corresponding specification can be selected according to the size of the sample, and the clamping of different specifications of clamping frames 73 can be achieved by extending and retracting the telescopic rod 72. In some embodiments, the size of the clamping frame 73 can be adjusted according to the different specifications of the sample. The clamping frame 73 is made of insulating elastic material, such as polyimide, polyphenylene sulfide (PPS), fluororubber, perfluoroether rubber, phenyl silicone rubber, borosilicate rubber, silicone nitride rubber, etc.; or in other embodiments, the clamping frame 73 can be a telescopic structure, that is, the four corners of the clamping frame 73 are respectively connected by four hollow rods to form a rectangular frame, the two ends of the four corners are respectively connected to the corresponding hollow rods, and the ends of the corners are telescopically installed in the corresponding hollow rods. As the telescopic rod 72 extends and retracts, it drives the corners to stretch, thereby realizing the adjustment of the size of the clamping frame 73 to adapt to samples of different sizes and achieve stable clamping of samples of different specifications.

[0057] It can also be understood that the fixed base 71 can be equipped with a control center, which is connected to the control unit 5 through a connecting line to control the extension and retraction of the corresponding telescopic rods 72, thereby adjusting the size of the clamping frame 73 to fit the size of the sample.

[0058] Further, the moving device 8 includes a fixed guide rod 81, a first slider 82, a second slider 83, a first driving member, a second driving member, a mounting base 84, a first connecting rod 85, and a second connecting rod 86. A fixed guide rod 81 is installed on each of the four side walls of the oil bath 3, serving as the movement track for the first slider 82 and the second slider 83. The second electrode 2 is mounted on the mounting base 84. The first connecting rod 85 and the second connecting rod 86 are inserted into the mounting base 84, and are perpendicular to each other. The two ends of the first connecting rod 85 are movably mounted to the corresponding fixed guide rod 81 via the corresponding first slider 82, and the two ends of the second connecting rod 86 are movably mounted to the corresponding fixed guide rod 81 via the corresponding second slider 83. The first driving member is connected to a first slider 82 to drive the mounting base 84 to reciprocate along a first direction, and the second driving member is connected to a second slider 83 to drive the mounting base 84 to reciprocate along a second direction. The first and second directions are perpendicular to each other.

[0059] The moving device 8 in this embodiment is an orthogonal biaxial sliding mechanism. By controlling the first and second driving components, the second electrode 2 inside the oil bath 3 is moved along a preset path in two vertical directions within the horizontal plane to the corresponding breakdown point for testing. It is understood that the first and second driving components in this embodiment can be cylinders.

[0060] Furthermore, the robotic arm 6 is equipped with a displacement sensor, which is used to detect the displacement distance of the first electrode 1. The robotic arm 6 is equipped with a high-precision displacement sensor with a resolution of 0.001 mm. The robotic arm 6 moves the first electrode 1 to the preset breakdown point in three-dimensional space, and automatically measures the sample thickness by measuring the displacement change of the first electrode 1. When there is no sample between the first electrode 1 and the second electrode 2 and they are in close contact, the displacement sensor value is set to 0. When a sample is added, the change in height of the robotic arm 6 is the change in the displacement sensor reading, which is the sample thickness.

[0061] It should be noted that the control unit 5 of this application includes a control terminal 51, a power supply 52, and an automatic control center 53. The control terminal 51 consists of a computer used for visualizing real-time data such as voltage, sample thickness, and temperature. It also issues relevant commands to the automatic control center, collects test data, calculates it, records and saves it for easy retrieval. The power supply 52 mainly provides high-voltage power, and can provide DC or AC high voltage as needed for the test. The automatic control center 53 controls the robotic arm 6, the moving device 8, and the sample clamp 7. After the sample dimensions are input into the control terminal 51, the automatic control center 53 receives the command from the control terminal 51 and controls the extension and retraction of the sample clamp 7 to make it the appropriate size for the sample. After the control terminal 51 determines the number and location of the breakdown points, the automatic control center 53 receives the command from the control terminal 51 and controls the robotic arm 6 and the moving device 8 to move the first electrode 1 and the second electrode 2 to the pre-set breakdown point positions, measure the thickness, and perform a breakdown test.

[0062] In summary, the embodiments of the present invention provide a method and apparatus for testing the shielded insulation breakdown of cables. By constructing a three-layer structure sample of shield-insulation-shield, it restores the physical structure of the cable during manufacturing and operation, which is closer to the actual working conditions. The breakdown field strength data obtained can better reflect the insulation performance of the actual cable, improve the authenticity of the cable insulation performance evaluation, and solve the problem that traditional tests only test pure insulation materials and ignore the interface effect between the shielding layer and the insulation layer, resulting in test results that cannot truly reflect the insulation performance of the cable in actual operation.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method of shielded insulation breakdown test for a cable, characterized by, The method comprises the following steps: Preparation of the first electrode and the sample, the sample comprising an insulating layer and a first shielding layer arranged on one side of the insulating layer, the surface of the first electrode in contact with the side of the insulating layer away from the first shielding layer being attached with a second shielding layer; Clamping the sample between the first electrode and the second electrode, and heating the oil bath to a preset temperature; According to the preset breakdown point matrix, controlling the first electrode and the second electrode to move to the corresponding breakdown point for breakdown test, and detecting and recording the thickness value and breakdown voltage of the corresponding breakdown point, and sequentially completing the breakdown test of all the breakdown points; According to the thickness value and the breakdown voltage, calculating the breakdown field strength of each breakdown point, storing each breakdown field strength and generating a test report.

2. The shielded insulation breakdown test method for electric cables according to claim 1, characterized by, The first electrode is prepared by using a mold, the mold comprising a pressure seat, a limiting plate, a guide rod, a blocking ring and a base with a cavity, the limiting plate and the base being connected by the guide rod, one end of the pressure seat being used for connecting with a ball electrode, the other end penetrating through the limiting plate and being connected with a hydraulic driving device outside to drive the ball electrode to move up and down, the blocking ring being used for being placed on the base and being attached with the surface of the ball electrode to close the cavity, and the cavity being used for placing shielding material.

3. The shielded insulation breakdown test method for electric cables according to claim 2, characterized by, The preparation of the first electrode comprises the following steps: The ball electrode is installed on one end of the pressure seat, and a preset amount of shielding material is added into the cavity; The ball electrode is pressed down by a first distance at a preset speed, so that a preset interval is formed between the ball electrode and the shielding material; The blocking ring is adjusted to close the cavity, and the cavity is warmed up to a first preset temperature under a pressure-free state, so that the shielding material is completely melted to a molten state; The temperature of the cavity is increased to a second preset temperature, and the ball electrode is pressed on the shielding material at a pressure of 5-20 kN, so that the shielding material is cross-linked and solidified on the surface of the ball electrode; After the cavity is cooled to room temperature, the pressure is released, the blocking ring is extracted, and the ball electrode is disassembled, at which time the shielding material is attached to the surface of the ball electrode to form the first electrode.

4. The shielded insulation breakdown test method for a power cable according to claim 3, characterized by, Warming up the cavity to a first preset temperature under a pressure-free state, so that the shielding material is completely melted to a molten state, comprises the following steps: Warming up the cavity to 120-150℃ under a pressure-free state; Then, keeping warm for 10-15 min, so that the shielding material is completely melted to a molten state.

5. The shielded insulation breakdown test method for a power cable according to claim 3, characterized by, Increasing the temperature of the cavity to a second preset temperature, and pressing the ball electrode on the shielding material at a pressure of 5-20 kN, so that the shielding material is cross-linked and solidified on the surface of the ball electrode, comprises the following steps: Pressing the ball electrode on the shielding material at a pressure of 5-20 kN, and at the same time, increasing the temperature of the cavity to 180-200℃; Keeping warm for 20-60 min, so that the shielding material is cross-linked and solidified on the surface of the ball electrode.

6. The shielded insulation breakdown test method for electric cables according to claim 1, characterized by, Before the step of according to the preset breakdown point matrix, controlling the first electrode and the second electrode to move to the corresponding breakdown point for breakdown test, and detecting and recording the thickness value and breakdown voltage of the corresponding breakdown point, and sequentially completing the breakdown test of all the breakdown points, further comprises the following steps: According to a preset breakdown point matrix, the first electrode and the second electrode are moved to a corresponding breakdown point; Thickness values of each breakdown point are obtained, and a difference between a maximum value and a minimum value is calculated; If the difference between the maximum value and the minimum value is less than 0.05 mm, subsequent breakdown tests are performed; otherwise, the sample is replaced or the breakdown point matrix is reset.

7. A shielded insulation breakdown test device for a cable, which is subjected to a shielded insulation breakdown test by the shielded insulation breakdown test method for a cable as claimed in any one of claims 1 to 6, characterized by The cable shielding insulation breakdown test device comprises a control unit, a mechanical arm, an oil bath pot, a sample clamp, a moving device, a first electrode, a second electrode, a temperature measuring device, and a shell; The sample clamp and the second electrode are located in the oil bath pot, the sample clamp is used for clamping a sample, the second electrode is located below the sample clamp, the moving device is connected with the second electrode to drive the second electrode to move in the oil bath pot, the first electrode is suspended above the sample clamp by the mechanical arm and moves in the oil bath pot by the mechanical arm, the temperature measuring device is located in the oil bath pot and is used for measuring the temperature of a medium around the sample, the shell is arranged on the outer circumferential side of the oil bath pot and the mechanical arm, and the control unit is electrically connected with the mechanical arm, the moving device, the first electrode, the second electrode, and the temperature measuring device respectively.

8. The shielded insulation breakdown test device for electric cables according to claim 7, characterized by The sample clamp comprises a fixed seat, an extension rod, a clamping frame for clamping the sample, and a clamp, the fixed seat is installed on each corner of the inner wall of the oil bath pot, each fixed seat is connected with the extension rod, the extension rod is connected with the corresponding clamp at the end away from the fixed seat, the four clamps are clamped at the four corners of the clamping frame, and the temperature measuring device is installed on the corresponding clamp.

9. The shielded insulation breakdown test device for electric cables according to claim 7, characterized by The moving device comprises a fixed guide rod, a first sliding block, a second sliding block, a first driving member, a second driving member, a mounting seat, a first connecting rod, and a second connecting rod, and the fixed guide rod is installed on each side wall of the oil bath pot; The second electrode is installed on the mounting seat, the first connecting rod and the second connecting rod are inserted into the mounting seat, and the first connecting rod and the second connecting rod are arranged vertically, the two ends of the first connecting rod are movably installed on the corresponding fixed guide rod through the corresponding first sliding block, and the two ends of the second connecting rod are movably installed on the corresponding fixed guide rod through the corresponding second sliding block; The first driving member is connected with the first sliding block to drive the mounting seat to reciprocate in a first direction, the second driving member is connected with the second sliding block to drive the mounting seat to reciprocate in a second direction, and the first direction and the second direction are arranged vertically.

10. The shielded insulation breakdown test device for electric cables according to claim 7, characterized by The mechanical arm is internally loaded with a displacement sensor, and the displacement sensor is used for detecting the displacement distance of the first electrode.

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